We thank Cora H&#252;bner and Andrea Gall for help in acquiring some of the representative results. This work was supported by the Werner Reichardt Centre for Integrative Neuroscience (CIN) at the University of Tuebingen, an Excellence Initiative funded by the Deutsche Forschungsgemeinschaft (DFG) within the framework of the Excellence Initiative (EXC 307), and by funds from the Charitable Hertie Foundation.

Ethics statement: All experimental procedures were in accordance with the EU directive on use of animals in research and were approved by the local Animal Care and Use Committee (Regierungspr&#228;sidium Tuebingen, state of Baden-W&#252;rttemberg, Germany) responsible for the University of T&#252;bingen.&#160;
1. Stereotactic Injection Procedure
<ol>
	<li>Prepare sterile tools (scissors, scalpel, clamps, drill, needles, suture material) using a sterilizer. Arrange sterile tools and other required solutions and s...

<ol>
	<li>Nagel, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Channelrhodopsin-2,+a+directly+light-gated+cation-selective+membrane+channel.">Channelrhodopsin-2, a directly light-gated cation-selective membrane channel.</a> Proc Natl Acad Sci U S A. 100 (24), 13940-13945 (2003).</li><li>Boyden, E. S., Zhang, F., Bamberg, E., Nagel, G., Deisseroth, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Millisecond-timescale,+genetically+targeted+optical+control+of+neural+activity.">Millisecond-timescale, genetically targeted optical control of neural activity.</a> Nat Neurosci. 8 (9), 1263-1268 (2005).</li><li>Tye, K. M., Deisseroth, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optogenetic+investigation+of+neural+circuits+underlying+brain+disease+in+animal+models.">Optogenetic investigation of neural circuits underlying brain disease in animal models.</a> Nat Rev Neurosci. 13 (4), 251-266 (2012).</li><li>Yizhar, O., Fenno, L. E., Davidson, T. J., Mogri, M., Deisseroth, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optogenetics+in+neural+systems.">Optogenetics in neural systems.</a> Neuron. 71 (1), 9-34 (2011).</li><li>Petreanu, L., Huber, D., Sobczyk, A., Svoboda, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Channelrhodopsin-2-assisted+circuit+mapping+of+long-range+callosal+projections.">Channelrhodopsin-2-assisted circuit mapping of long-range callosal projections.</a> Nat Neurosci. 10 (5), 663-668 (2007).</li><li>Cetin, A., Komai, S., Eliava, M., Seeburg, P. H., Osten, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stereotaxic+gene+delivery+in+the+rodent+brain.">Stereotaxic gene delivery in the rodent brain.</a> Nat Protoc. 1 (6), 3166-3173 (2006).</li><li>Huang, Z. J., Zeng, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+approaches+to+neural+circuits+in+the+mouse.">Genetic approaches to neural circuits in the mouse.</a> Annu Rev Neurosci. 36, 183-215 (2013).</li><li>LeDoux, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emotion+circuits+in+the+brain.">Emotion circuits in the brain.</a> Annu Rev Neurosci. 23, 155-184 (2000).</li><li>Pape, H. C., Pare, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plastic+synaptic+networks+of+the+amygdala+for+the+acquisition,+expression,+and+extinction+of+conditioned+fear.">Plastic synaptic networks of the amygdala for the acquisition, expression, and extinction of conditioned fear.</a> Physiol Rev. 90 (2), 419-463 (2010).</li><li>Myers, K. M., Davis, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+fear+extinction.">Mechanisms of fear extinction.</a> Mol Psychiatry. 12 (2), 120-150 (2007).</li><li>Quirk, G. J., Mueller, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+mechanisms+of+extinction+learning+and+retrieval.">Neural mechanisms of extinction learning and retrieval.</a> Neuropsychopharmacology. 33 (1), 56-72 (2008).</li><li>Vidal-Gonzalez, I., Vidal-Gonzalez, B., Rauch, S. L., Quirk, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microstimulation+reveals+opposing+influences+of+prelimbic+and+infralimbic+cortex+on+the+expression+of+conditioned+fear.">Microstimulation reveals opposing influences of prelimbic and infralimbic cortex on the expression of conditioned fear.</a> Learn Mem. 13 (6), 728-733 (2006).</li><li>Sierra-Mercado, D., Padilla-Coreano, N., Quirk, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissociable+roles+of+prelimbic+and+infralimbic+cortices,+ventral+hippocampus,+and+basolateral+amygdala+in+the+expression+and+extinction+of+conditioned+fear.">Dissociable roles of prelimbic and infralimbic cortices, ventral hippocampus, and basolateral amygdala in the expression and extinction of conditioned fear.</a> Neuropsychopharmacology. 36 (2), 529-538 (2011).</li><li>Cho, J. H., Deisseroth, K., Bolshakov, V. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synaptic+encoding+of+fear+extinction+in+mPFC-amygdala+circuits.">Synaptic encoding of fear extinction in mPFC-amygdala circuits.</a> Neuron. 80 (6), 1491-1507 (2013).</li><li>Arruda-Carvalho, M., Clem, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathway-Selective+Adjustment+of+Prefrontal-Amygdala+Transmission+during+Fear+Encoding.">Pathway-Selective Adjustment of Prefrontal-Amygdala Transmission during Fear Encoding.</a> J Neurosci. 34 (47), 15601-15609 (2014).</li><li>Hubner, C., Bosch, D., Gall, A., Luthi, A., Ehrlich, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ex+vivo+dissection+of+optogenetically+activated+mPFC+and+hippocampal+inputs+to+neurons+in+the+basolateral+amygdala:+implications+for+fear+and+emotional+memory.">Ex vivo dissection of optogenetically activated mPFC and hippocampal inputs to neurons in the basolateral amygdala: implications for fear and emotional memory.</a> Front Behav Neurosci. 8, 64 (2014).</li><li>Strobel, C., Marek, R., Gooch, H. M., Sullivan, R. K., Sah, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prefrontal+and+Auditory+Input+to+Intercalated+Neurons+of+the+Amygdala.">Prefrontal and Auditory Input to Intercalated Neurons of the Amygdala.</a> Cell Rep. 10 (9), 1435-1442 (2015).</li><li>Sigurdsson, T., Doyere, V., Cain, C. K., LeDoux, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+potentiation+in+the+amygdala:+a+cellular+mechanism+of+fear+learning.">Long-term potentiation in the amygdala: a cellular mechanism of fear learning.</a> Neuropharmacology. 52 (1), 215-227 (2007).</li><li>Ehrlich, I., Humeau, Y., Grenier, F., Ciocchi, S., Herry, C., Luthi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amygdala+inhibitory+circuits+and+the+control+of+fear+memory.">Amygdala inhibitory circuits and the control of fear memory.</a> Neuron. 62 (6), 757-771 (2009).</li><li>Millhouse, O. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+intercalated+cells+of+the+amygdala.">The intercalated cells of the amygdala.</a> J Comp Neurol. 247 (2), 246-271 (1986).</li><li>Busti, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Different+fear+states+engage+distinct+networks+within+the+intercalated+cell+clusters+of+the+amygdala.">Different fear states engage distinct networks within the intercalated cell clusters of the amygdala.</a> J Neurosci. 31 (13), 5131-5144 (2011).</li><li>Palomares-Castillo, E., Hernandez-Perez, O. R., Perez-Carrera, D., Crespo-Ramirez, M., Fuxe, K., Perez de la Mora, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+intercalated+paracapsular+islands+as+a+module+for+integration+of+signals+regulating+anxiety+in+the+amygdala.">The intercalated paracapsular islands as a module for integration of signals regulating anxiety in the amygdala.</a> Brain Res. 1476, 211-234 (2012).</li><li>Asede, D., Bosch, D., Luthi, A., Ferraguti, F., Ehrlich, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sensory+inputs+to+intercalated+cells+provide+fear-learning+modulated+inhibition+to+the+basolateral+amygdala.">Sensory inputs to intercalated cells provide fear-learning modulated inhibition to the basolateral amygdala.</a> Neuron. 86 (2), 541-554 (2015).</li><li>Tamamaki, N., Yanagawa, Y., Tomioka, R., Miyazaki, J., Obata, K., Kaneko, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Green+fluorescent+protein+expression+and+colocalization+with+calretinin,+parvalbumin,+and+somatostatin+in+the+GAD67-GFP+knock-in+mouse.">Green fluorescent protein expression and colocalization with calretinin, parvalbumin, and somatostatin in the GAD67-GFP knock-in mouse.</a> J Comp Neurol. 467 (1), 60-79 (2003).</li><li>Mar, L., Yang, F. C., Ma, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+marking+and+characterization+of+Tac2-expressing+neurons+in+the+central+and+peripheral+nervous+system.">Genetic marking and characterization of Tac2-expressing neurons in the central and peripheral nervous system.</a> Mol Brain. 5, (2012).</li><li>Jackman, S. L., Beneduce, B. M., Drew, I. R., Regehr, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Achieving+high-frequency+optical+control+of+synaptic+transmission.">Achieving high-frequency optical control of synaptic transmission.</a> J Neurosci. 34 (22), 7704-7714 (2014).</li><li>Li, H., Penzo, M. A., Taniguchi, H., Kopec, C. D., Huang, Z. J., Li, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experience-dependent+modification+of+a+central+amygdala+fear+circuit.">Experience-dependent modification of a central amygdala fear circuit.</a> Nat Neurosci. 16 (3), 332-339 (2013).</li><li>Petreanu, L., Mao, T., Sternson, S. M., Svoboda, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+subcellular+organization+of+neocortical+excitatory+connections.">The subcellular organization of neocortical excitatory connections.</a> Nature. 457 (7233), 1142-1145 (2009).</li><li>Felix-Ortiz, A. C., Beyeler, A., Seo, C., Leppla, C. A., Wildes, C. P., Tye, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=BLA+to+vHPC+inputs+modulate+anxiety-related+behaviors.">BLA to vHPC inputs modulate anxiety-related behaviors.</a> Neuron. 79 (4), 658-664 (2013).</li><li>Chu, H. Y., Ito, W., Li, J., Morozov, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Target-specific+suppression+of+GABA+release+from+parvalbumin+interneurons+in+the+basolateral+amygdala+by+dopamine.">Target-specific suppression of GABA release from parvalbumin interneurons in the basolateral amygdala by dopamine.</a> J Neurosci. 32 (42), 14815-14820 (2012).</li><li>Zhang, Y. P., Oertner, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+induction+of+synaptic+plasticity+using+a+light-sensitive+channel.">Optical induction of synaptic plasticity using a light-sensitive channel.</a> Nat Methods. 4 (2), 139-141 (2007).</li><li>Britt, J. P., Benaliouad, F., McDevitt, R. A., Stuber, G. D., Wise, R. A., Bonci, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synaptic+and+behavioral+profile+of+multiple+glutamatergic+inputs+to+the+nucleus+accumbens.">Synaptic and behavioral profile of multiple glutamatergic inputs to the nucleus accumbens.</a> Neuron. 76 (4), 790-803 (2012).</li><li>Kohl, M. M., Shipton, O. A., Deacon, R. M., Rawlins, J. N., Deisseroth, K., Paulsen, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemisphere-specific+optogenetic+stimulation+reveals+left-right+asymmetry+of+hippocampal+plasticity.">Hemisphere-specific optogenetic stimulation reveals left-right asymmetry of hippocampal plasticity.</a> Nat Neurosci. 14 (11), 1413-1415 (2011).</li><li>Morozov, A., Sukato, D., Ito, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+suppression+of+plasticity+in+amygdala+inputs+from+temporal+association+cortex+by+the+external+capsule.">Selective suppression of plasticity in amygdala inputs from temporal association cortex by the external capsule.</a> J Neurosci. 31 (1), 339-345 (2011).</li><li>Davidson, B. L., Breakefield, X. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+vectors+for+gene+delivery+to+the+nervous+system.">Viral vectors for gene delivery to the nervous system.</a> Nat Rev Neurosci. 4 (5), 353-364 (2003).</li><li>Aschauer, D. F., Kreuz, S., Rumpel, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+transduction+efficiency,+tropism+and+axonal+transport+of+AAV+serotypes+1,+2,+5,+6,+8,+and+9+in+the+mouse+brain.">Analysis of transduction efficiency, tropism and axonal transport of AAV serotypes 1, 2, 5, 6, 8, and 9 in the mouse brain.</a> PLoS One. 8 (9), (2013).</li><li>Salegio, E. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Axonal+transport+of+adeno-associated+viral+vectors+is+serotype-dependent.">Axonal transport of adeno-associated viral vectors is serotype-dependent.</a> Gene Ther. 20 (3), 348-352 (2013).</li><li>Holehonnur, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adeno-associated+viral+serotypes+produce+differing+titers+and+differentially+transduce+neurons+within+the+rat+basal+and+lateral+amygdala.">Adeno-associated viral serotypes produce differing titers and differentially transduce neurons within the rat basal and lateral amygdala.</a> BMC Neurosci. 15, (2014).</li><li>McFarland, N. R., Lee, J. S., Hyman, B. T., McLean, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+transduction+efficiency+of+recombinant+AAV+serotypes+1,+2,+5,+and+8+in+the+rat+nigrostriatal+system.">Comparison of transduction efficiency of recombinant AAV serotypes 1, 2, 5, and 8 in the rat nigrostriatal system.</a> J Neurochem. 109 (3), 838-845 (2009).</li><li>Miyashita, T., Shao, Y. R., Chung, J., Pourzia, O., Feldman, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+channelrhodopsin-2+(ChR2)+expression+can+induce+abnormal+axonal+morphology+and+targeting+in+cerebral+cortex.">Long-term channelrhodopsin-2 (ChR2) expression can induce abnormal axonal morphology and targeting in cerebral cortex.</a> Front Neural Circuits. 7, (2013).</li></ol>

This protocol describes a method for ex&#160;vivo optogenetic investigation of neural circuits and local connectivity that can be easily implemented on most, if not all, upright slice patch-clamp recording setups by equipping them with a ~470 nm LED at the epifluorescence light port. A major advantage of optogenetic stimulation of axonal projections in slices is that it allows for specific activation and investigation of properties of connections that were not accessible with conventional electrical stimulation,...

Precise tools for visualization and concurrent activation of specific connections between brain areas and specific types of neurons are becoming more important in understanding the functional connectivity underlying healthy brain function and disease states. Ideally, this entails physiological investigation of precise synaptic properties with which identified neurons communicate. This is particularly true for connections between brain areas that cannot be preserved in a single acute brain slice. In the past, this has been largely achieved in separate experiments. On the one hand, neural tracers injected in vivo have been employed combined with subsequent light or electron microscopic analysis of pre- and postsynaptic partners. On the other hand, when fiber tracts from the region of origin are preserved and accessible in the slice preparation, electrical stimulation has been used to assess synaptic communication mechanisms with cells in the target region.
With the advent of optogenetics, the targeted expression of light-gated cation-channels, such as Channelrhodopsins (ChRs) fused to fluorescent proteins, now enables activation of neurons and their axonal trajectories while allowing for their visualization and post-hoc anatomical analysis 1-4. Because ChR-expressing axons can be stimulated even when severed from parent somata 5, it is possible in brain slices to:&#160;1) assess inputs from brain regions that were not accessible with conventional electrical stimulation, because fiber tracts are not separable or the specific trajectory is not known;&#160;2) unequivocally identify the region of origin for specific inputs that were postulated but incompletely understood; and 3) investigate the functional connectivity between defined cell types, both locally and in long-range projections. Because of a number of advantages, this optogenetic mapping of circuits in brain slices has become widely used in the last years, and a variety of viral vectors for expression of fluorescently-tagged ChRs are readily available from commercial suppliers. Some key advantages of optogenetic activation over conventional electrical stimulation are no damage to the tissue due to placement of stimulation electrodes, specificity of fiber stimulation because electrical stimulation may also recruit fibers of passage or other nearby cells, and an equally rapid and temporally precise stimulation. In addition, stereotactic injection of viral vectors can easily be targeted to specific brain areas 6 and conditional or cell-type specific expression can be achieved using Cre-dependent expression and/or specific promoters 7. Here, this technique is applied for mapping of long-range and local circuits in the fear system.
The amygdala is a key region for acquisition and expression of fear, and storage of fear and emotional memories 8,9. Apart from the amygdala, the medial prefrontal cortex (mPFC) and hippocampus (HC), structures that are reciprocally connected to the amygdala, are implicated in aspects of acquisition, consolidation and retrieval of fear and extinction memories 10,11. Activity in subdivisions of the mPFC appears to play a double role in controlling both&#160;high and low fear states 12,13. This could in part be mediated by direct connections from mPFC to the amygdala that would control amygdala activity and output. Therefore, in the last years, several studies started in ex vivo slice experiments to investigate synaptic interactions between mPFC afferents and specific target cells in the amygdala 14-17.
During fear learning, sensory information about conditioned and unconditioned stimuli reaches the amygdala via projections from specific thalamic and cortical regions. Plasticity of these inputs to neurons in the lateral part (LA) of the basolateral amygdala (BLA) is an important mechanism underlying fear conditioning 9,18. Increasing evidence suggests that parallel plastic processes in the amygdala involve inhibitory elements to control fear memory 19. A group of clustered inhibitory neurons are the GABAergic medial paracapsular intercalated cells (mpITCs), but their precise connectivity and function is incompletely understood 20-22. Here, optogenetic circuit mapping is used to assess afferent and efferent connectivity of these cells and their impact on target neurons in the amygdala, demonstrating that mpITCs receive direct sensory input from thalamic and cortical relay stations&#160;23. Specific expression of ChR in mpITCs or BLA neurons allows&#160;mapping of local interactions, revealing that mpITCs inhibit, but are also mutually activated by, BLA principal neurons, placing them in novel feed-forward and feedback inhibitory circuits that effectively control BLA activity 23.

<table>
	<tbody>
		<tr>
			<td colspan="4">Surgery</td>
		</tr>
		<tr>
			<td>Stereotactic frame</td>
			<td>Stoelting, USA</td>
			<td>51670</td>
			<td rowspan="2">can be replaced by other stereotactic frame for mice</td>
		</tr>
		<tr>
			<td>Steretoxic frame mouse adaptor</td>
			<td>Stoelting, USA</td>
			<td>51625</td>
		</tr>
		<tr>
			<td>Gas anesthesia mask for mice</td>
			<td>Stoelting, USA</td>
			<td>50264</td>
			<td>no longer available, replaced by item no. 51609M</td>
		</tr>
		<tr>
			<td>Pressure injection device, Toohey Spritzer</td>
			<td>Toohey Company, USA</td>
			<td>T25-2-900</td>
			<td>other pressure injection devices (e.g. Picospritzer) can be used</td>
		</tr>
		<tr>
			<td>Kwik Fill glass capillaries</td>
			<td>World Precision Instruments, Germany</td>
			<td>1B150F-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Anesthesia machine, IsoFlo</td>
			<td>Eickemeyer, Germany</td>
			<td>213261</td>
			<td></td>
		</tr>
		<tr>
			<td>DC Temperature Controler and heating pad</td>
			<td>FHC, USA</td>
			<td>40-90-8D</td>
			<td></td>
		</tr>
		<tr>
			<td>Horizontal Micropipette Puller Model P-1000</td>
			<td>Sutter Instruments, USA</td>
			<td>P-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical tool sterilizer, Sterilizator 75</td>
			<td>Melag, Germany</td>
			<td>08754200</td>
			<td></td>
		</tr>
		<tr>
			<td>rAAV-hSyn-ChR2(H134R)-eYFP (serotype 2/9)</td>
			<td>Penn Vector Core, USA</td>
			<td>AV-9-26973P</td>
			<td></td>
		</tr>
		<tr>
			<td>rAAV-CAGh-ChR2(H134R)-mCherry (serotype 2/9)&#160;</td>
			<td>Penn Vector Core, USA</td>
			<td>AV-9-20938M</td>
			<td></td>
		</tr>
		<tr>
			<td>rAAV-EF1a-DIOhChR2(H134R)-YFP (serotype 2/1)&#160;</td>
			<td>Penn Vector Core, USA</td>
			<td>AV-1-20298P</td>
			<td></td>
		</tr>
		<tr>
			<td>fast green</td>
			<td>Roth, Germany</td>
			<td>0301.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane Anesthetic, Isofuran CP (1ml/ml)</td>
			<td>CP Pharma, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Antiseptic, Betadine (providone-iodine)</td>
			<td>Purdure Products, USA</td>
			<td>BSOL32</td>
			<td>can be replaced by other disinfectant</td>
		</tr>
		<tr>
			<td>Analgesic, Metacam Solution (5mg/ml meloxicam)</td>
			<td>Boehringer Ingelheim, Germany</td>
			<td></td>
			<td>can be replaced by other analgesics</td>
		</tr>
		<tr>
			<td>Bepanthen eye ointment</td>
			<td>Bayer, Germany</td>
			<td>0191</td>
			<td>can be replaced by other eye ointment</td>
		</tr>
		<tr>
			<td>Drill NM3000 (SNKG1341 and SNIH1681)</td>
			<td>Nouvag, Switzerland</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sutranox Suture Needle</td>
			<td>Fine Science Tools, Germany</td>
			<td>12050-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Braided Silk Suture</td>
			<td>Fine Science Tools, Germany</td>
			<td>18020-60</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Recordings, light stimulation, and analysis</td>
		</tr>
		<tr>
			<td>artificial cerebrospinal fluid (ACSF)</td>
			<td>for composition see references #16 and #23</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>internal patch solutions</td>
			<td>for composition see references #16 and #23</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MagnesiumSulfate Heptahydrate</td>
			<td>Roth, Germany</td>
			<td>P027.1</td>
			<td>prepare 2M stock solution in purified water</td>
		</tr>
		<tr>
			<td>Slicer, Microm HM650V</td>
			<td>Fisher Scientific, Germany</td>
			<td>920120</td>
			<td></td>
		</tr>
		<tr>
			<td>Cooling unit for tissue slicer, CU65</td>
			<td>Fisher Scientific, Germany</td>
			<td>770180</td>
			<td></td>
		</tr>
		<tr>
			<td>Sapphire blade</td>
			<td>Delaware Diamond Knives</td>
			<td></td>
			<td>custom order, inquire with company</td>
		</tr>
		<tr>
			<td>Stereoscope, SZX2-RFA16</td>
			<td>Olympus, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Xcite fluorescent lamp (XI120Q-1492)</td>
			<td>Lumen Dynamics Group, Canada</td>
			<td>2012-12699</td>
			<td></td>
		</tr>
		<tr>
			<td>Patch microscope, BX51WI</td>
			<td>Olympus, Japan</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Multiclamp 700B patch amplifier&#160;</td>
			<td>Molecular Devices, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Digitdata 1440A</td>
			<td>Molecular Devices, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PClamp software, Version 10</td>
			<td>Molecular Devices, USA</td>
			<td></td>
			<td>used to control data acquisition and stimulation</td>
		</tr>
		<tr>
			<td>Bath temperature controler, TC05</td>
			<td>Luigs &#38; Neumann, Germany</td>
			<td>200-100 500 0145</td>
			<td></td>
		</tr>
		<tr>
			<td>Three axis micromanipulator Mini 25</td>
			<td>Luigs &#38; Neumann, Germany</td>
			<td>210-100 000 0010</td>
			<td></td>
		</tr>
		<tr>
			<td>Micromanipulator controller SM7</td>
			<td>Luigs &#38; Neumann, Germany</td>
			<td>200-100 900 7311</td>
			<td></td>
		</tr>
		<tr>
			<td>glass capillaries for patch pipettes</td>
			<td>World Precision Instruments, Germany</td>
			<td>GB150F-8P</td>
			<td></td>
		</tr>
		<tr>
			<td>Cellulose nitrate filterpaper for interface chamber&#160;</td>
			<td>Satorius Stedim Biotech, Germany</td>
			<td>13006--50----ACN</td>
			<td></td>
		</tr>
		<tr>
			<td>LED unit, CoolLED pE</td>
			<td>CoolLED, UK</td>
			<td>244-1400</td>
			<td rowspan="4">CoolLED or USL 70/470 and appropriate adapters are two alternative choices for LED stimulation</td>
		</tr>
		<tr>
			<td>CoolLED 100 Dual Adapt</td>
			<td>CoolLED, UK</td>
			<td>pE-ADAPTOR-50E</td>
		</tr>
		<tr>
			<td>LED unit, USL 70/470</td>
			<td>Rapp Optoelectronic</td>
			<td>L70-000</td>
		</tr>
		<tr>
			<td>Dual port adapter</td>
			<td>Rapp Optoelectronic</td>
			<td>inquire with company</td>
		</tr>
		<tr>
			<td>Filter set red (excitation)</td>
			<td>AHF, Germany</td>
			<td>F49-560</td>
			<td rowspan="3">Filters can be bought as set F46-008</td>
		</tr>
		<tr>
			<td>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (beamsplitter)</td>
			<td>AHF, Germany</td>
			<td>F48-585</td>
		</tr>
		<tr>
			<td>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (emission)</td>
			<td>AHF, Germany</td>
			<td>F47-630</td>
		</tr>
		<tr>
			<td>Filter set green (excitation)</td>
			<td>AHF, Germany</td>
			<td>F39-472</td>
			<td rowspan="3">Alternatives: filterset F36-149 or F46-002 (with bandpass emission)</td>
		</tr>
		<tr>
			<td>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (beamsplitter)</td>
			<td>AHF, Germany</td>
			<td>F43-495W</td>
		</tr>
		<tr>
			<td>&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; (emission)</td>
			<td>AHF, Germany</td>
			<td>F76-490</td>
		</tr>
		<tr>
			<td>LaserCheck, handheld power meter</td>
			<td>Coherent, USA</td>
			<td><a>1098293</a></td>
			<td></td>
		</tr>
		<tr>
			<td>IgorPro Software, Version 6</td>
			<td>Wavemetrics, USA</td>
			<td></td>
			<td rowspan="2">for electrophysiology data analysis, other alternative software packages can also be used&#160;</td>
		</tr>
		<tr>
			<td>Neuromatic suite of macros for IgorPro</td>
			<td><a href="http://www.neuromatic.thinkrandom.com/">http://www.neuromatic.thinkrandom.com</a></td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td colspan="4">Post hoc analysis of injections and projections</td>
		</tr>
		<tr>
			<td>Paraformaldehyde powder (PFA)</td>
			<td>Roth, Germany</td>
			<td>0335.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Neurotrace 435/455 blue fluorescent Nissl stain</td>
			<td>Invitrogen</td>
			<td>N-21479</td>
			<td></td>
		</tr>
		<tr>
			<td>agar-agar for embedding and resectioning</td>
			<td>Roth, Germany</td>
			<td>5210.3</td>
			<td></td>
		</tr>
		<tr>
			<td>30 x 10 mm petri dishes for embedding</td>
			<td>SPL Life Sciences</td>
			<td></td>
			<td>alternatives can be used</td>
		</tr>
		<tr>
			<td>Slides, Super Frost</td>
			<td>R. Langenbrinck, Germany</td>
			<td>61303802</td>
			<td>alternatives can be used</td>
		</tr>
		<tr>
			<td>cover slips</td>
			<td>R. Langenbrinck, Germany</td>
			<td>3000302</td>
			<td>alternatives can be used</td>
		</tr>
		<tr>
			<td>Vecta Shield mounting medium</td>
			<td>Vector Laboratories, USA</td>
			<td>H-1000</td>
			<td>alternative mounting media can be used</td>
		</tr>
		<tr>
			<td>cellulose nitrate filter for flattening slices for fixation</td>
			<td>Satorius Stedim Biotech, Germany</td>
			<td>11406--25------N</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal Laser Scanning Microscope LSM 710</td>
			<td>Zeiss, Germany</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

ex vivo optogenetic dissection of fear circuits in brain slices

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated proteins and subsequent manipulation of neural activity by light. Channelrhodopsins (ChRs) are light-gated cation-channels and when fused to a fluorescent protein their expression allows for visualization and concurrent activation of specific cell types and their axonal projections in defined areas of the brain. Via stereotactic injection of viral vectors, ChR fusion proteins can be constitutively or conditionally expressed in specific cells of a defined brain region, and their axonal projections can subsequently be studied anatomically and functionally via ex vivo optogenetic activation in brain slices. This is of particular importance when aiming to understand synaptic properties of connections that could not be addressed with conventional electrical stimulation approaches, or in identifying novel afferent and efferent connectivity that was previously poorly understood. Here, a few examples illustrate how this technique can be applied to investigate these questions to elucidating fear-related circuits in the amygdala. The amygdala is a key region for acquisition and expression of fear, and storage of fear and emotional memories. Many lines of evidence suggest that the medial prefrontal cortex (mPFC) participates in different aspects of fear acquisition and extinction, but its precise connectivity with the amygdala is just starting to be understood. First, it is shown how ex vivo optogenetic activation can be used to study aspects of synaptic communication between mPFC afferents and target cells in the basolateral amygdala (BLA). Furthermore, it is illustrated how this ex vivo optogenetic approach can be applied to assess novel connectivity patterns using a group of GABAergic neurons in the amygdala, the paracapsular intercalated cell cluster (mpITC), as an example.

This section shows the workflow of an ex&#160;vivo optogenetic approach and representative results from different experimental strategies to investigate the physiological properties of sensory and modulatory long-range projections to BLA and mpITC neurons as well as properties of local connectivity between mpITC and BLA.
After stereotactic injection of the selected viral vector at the desired coordinates into the mouse ...

Watch this Scientific Journal Video about Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices at JoVE.com

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are widely used to manipulate neural activity and assess the consequences for brain function. Here, a technique is outlined that&#160;upon in vivo expression of the optical activator Channelrhodopsin, allows for ex vivo analysis of synaptic properties of specific long range and local neural connections in fear-related circuits.

Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Optogenetic approaches are now widely used to study the function of neural populations and circuits by combining targeted expression of light-activated ...

The overall goal of this experiment is to investigate functional and synaptic properties of neural projections and micro-circuits using ex-vivo optogenetics. This includes expression of channel rhodopsin and its activation in specific projections combined with patch-clamp recordings. This method can help answer key questions about synaptic properties of local and long-range connectivity within and between brain areas.This is illustrated here investigating the neural circuits that support fear behavior. The main advantage of this technique is that it allows to study circuits and synapses that are not amenable with conventional electrical stimulation techniques. Generally, people new to this method will have to overcome the challenge of performing all the required steps in an optimal way.This includes the stereotactic targeting of viral injections, identifying the optimal expression time for channel rhodpsin, the preparation of good quality brain slices, and stable light activation and recordings. Before beginning this part of the procedure, a recombinant adeno-associated viral vector engineered to express channel rhodopsin fused to a fluorescent protein was introduced into the medial pre-frontal cortex by stereotactic surgery. Prepare the vibratome by fitting a sapphire blade and setting it to cut at 320 micron thickness.After sacrifice according to approved methods and removal of the brain, use a scalpel to cut off the cerebellum, then isolate the anterior portion of the brain containing the medial pre-frontal cortex. Place the anterior portion of the brain in ice-cold cutting solution until slicing. Fill the cutting chamber with ice-cold cutting solution maintained at 4 degrees Celsius using a cooling unit.Oxygenate the solution. Blot the brain dry with filter paper. Glue the four per cent agar block that that has been cut at a 35 degree angle to the vibratome stage, and glue the posterior part of the brain tissue onto this block.Glue two additional agar blocks in front of and behind the brain block for stability while slicing. Place the stage with tissue attached in the cutting chamber and ensure it is submerged. Begin cutting the acute slices.Cut each slice in half and transfer to an interface chamber supplied with oxygenated ACSF at room temperature. After cutting the acute amygdala slices, place the interface chamber in a water bath at 36 degrees Celsius and allow the slices to recover for 35 to 45 minutes. Fix a subset of the slices containing the injection site for post-hoc analysis by sandwiching them between two pieces of filter paper and submerging them in four per cent paraformaldehyde in PBS overnight.Here, a recombinant adeno-associated viral vector engineered to express channel rhodopsin fused to a fluorescent protein was introduced into the medial division of the medial geniculate nucleus and adjacent posterior intra-laminar nucleus by stereotactic surgery. After obtaining the brain, use a scalpel to remove the cerebellum and anterior part of the brain and then cool the middle portion of the brain in ice-cold cutting solution as before. Blot the brain with filter paper and then glue it to the vibratome stage.Again, fix an additional agar block behind the brain for stability while slicing. After fitting the stage into the cutting chamber filled with four degree Celsius cutting solution, cut 320 micron coronal sections through the amygdala, cut them in half, and collect the sections in the interface chamber as before. Under a stereomicroscope using fluorescent illumination check the injection site.To prepare the patch microscope for optogenetic activation of fibers and cells, center the mounted light-emitting diode or LED onto the light delivery pathway. Use a power meter to measure the LED light intensity at the back focal plane and at the output of each objective at a wavelength of 470 nanometers. Use a spreadsheet to calculate the light intesity in milliwatts per millimeter squared and create a calibration curve for each objective.Next, retrieve an acute amygdala slice from the interface chamber and place it in the slice chamber mounted onto the microscope. Position the slice so that the slice surface facing upward in the interface chamber is also facing upward in the recording chamber. Perfuse the slice with fresh, oxygenated ACSF at a rate of one to two milliliters per minute.The temperature should be approximately 31 degrees Celsius. Turn on the fluorescent lamp and select the appropriate filter set for the specific fluoresent protein expressed. Use the 5x objective to obtain an overview.And the 60x objective for assessment of fiber density within the target area. Next, open or restrict the aperture in the microscope light pathway as necessary for the experiment. To obtain a patch recording, fill a patch pipette with internal solution and mount it in the electrode holder.Apply positive pressure to the patch pipette and slowly lower it into the bath solution. Then, under visual control use the micromanipulator to lower the patch pippette into the slice. Approach the neuron of interest with the patch pipette from the side and top.Release the positive pressure when the pipette reaches the surface of the cell as indicated by a dimple visible on the cell surface. Apply negative pressure to obtain a gigaseal. Apply further suction to rupture the membrane patch and obtain the whole cell recording.Next, stimulate the labeled fibers with a connected LED by activating channel rhodopsin with 470 nanometer wavelength light while recording electrical responses from the cell. For synaptic stimulation, use the digital outputs of the data-acquisition software to trigger the LED. Adjust the LED stimulation intensity manually.Repeat the stimulation with an opened or restricted aperture as necessary for the next recorded cell or in the presence of specific test substances. After recording, fix slices for post-hoc analysis by sandwiching them between two filter papers and submerging them in four percent paraformaldehyde overnight. Fibers from the medial pre-frontal cortex were stimulated using optogenetic paired pulse stimulation while excitatory post-synaptic currents were recorded from basolateral amygdala principal neuron and an interneuron.These representative traces show the paired pulse facilitation and paired pulse depression elicited from the stimulation. The following two images demonstrate feed-forward inhibition elicited by optogenetic activation of fibers from the medial prefrontal cortex. This first image shows a representative excitatory postsynaptic current at 70 millivolts and inhibitory postsynaptic current at zero millivolts in a basolateral amygdala principal neuron.The inhibitory postsynaptic current has a longer synaptic latency compared to the excitatory postsynaptic current indicating disynaptic and monosynaptic input, respectively. This image shows that the light evoked by phasic excitatory and inhibitory postsynaptic current sequence at 50 millivolt is blocked by the AMPA kainate antagonist, CNQX, further supporting the disynaptic nature of the inhibitory postsynaptic current. This image shows the effects of a subsequent block of the excitatory and inhibitory postsynaptic current sequence at 50 millivolts by the chloride channel-blocker, picrotoxin, and picrotoxin plus CNQX.The inhibitory postsynaptic current is blocked by picrotoxin and the remaining excitatory postsynaptic current by CNQX. Once mastered, the preparation of brain slices and the recording of light-evoked responses can be done within several hours to a full day. Prerequisites are good injection sites and sufficient expression of channel rhodopsin in cells and projections to be studied.Following this procedure, other methods like anatomical studies of labeled axons and synapses can be performed at the light and electron microscopic level. This allows to correlate functional with anatomical and molecular properties of activated synapses. After watching this video, you should have good understanding of all the required steps for analysis of light-activated fibers and brain slices.This includes channel rhodopsin expression, evaluation and activation of labeled fibers, as well as recording and analysis of the synaptic responses.

ex-vivo-optogenetic-dissection-of-fear-circuits-in-brain-slices

Research

JoVE Journal

Neuroscience

15.4K ビュー.  University of Tuebingen. The overall goal of this experiment is to investigate functional and synaptic properties of neural projections and micro-circuits using ex-vivo optogenetics. This includes expression of channel rhodopsin and its activation in specific projections combined with patch-clamp recordings. This method can help answer key questions about synaptic properties of local and long-range connectivity within and between brain areas.This is illustrated here investigating the neural circuits that suppo...

ビデオ: Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Functional Neuroimaging Using Ultrasonic Blood-brain Barrier Disruption and Manganese-enhanced MRI

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains technically challenging. One approach, Activation-Induced Manganese-enhanced MRI (AIM MRI), has been used successfully to map neuronal activity in rodents 1-5. In AIM MRI, Mn2+ acts a calcium analog and accumulates in depolarized neurons 6,7. Because Mn2+ shortens the T1 tissue property, regions of elevated neuronal activity will enhance in MRI. Furthermore, Mn2+ clears slowly from the activated regions; therefore, stimulation can be performed outside the magnet prior to imaging, enabling greater experimental flexibility. However, because Mn2+ does not readily cross the blood-brain barrier (BBB), the need to open the BBB has limited the use of AIM MRI, especially in mice.
One tool for opening the BBB is ultrasound. Though potentially damaging, if ultrasound is administered in combination with gas-filled microbubbles (i.e., ultrasound contrast agents), the acoustic pressure required for BBB opening is considerably lower. This combination of ultrasound and microbubbles can be used to reliably open the BBB without causing tissue damage 8-11.
Here, a method is presented for performing AIM MRI by using microbubbles and ultrasound to open the BBB. After an intravenous injection of perflutren microbubbles, an unfocused pulsed ultrasound beam is applied to the shaved mouse head for 3 minutes. For simplicity, we refer to this technique of BBB Opening with Microbubbles and UltraSound as BOMUS 12. Using BOMUS to open the BBB throughout both cerebral hemispheres, manganese is administered to the whole mouse brain. After experimental stimulation of the lightly sedated mice, AIM MRI is used to map the neuronal response.
To demonstrate this approach, herein BOMUS and AIM MRI are used to map unilateral mechanical stimulation of the vibrissae in lightly sedated mice 13. Because BOMUS can open the BBB throughout both hemispheres, the unstimulated side of the brain is used to control for nonspecific background stimulation. The resultant 3D activation map agrees well with published representations of the vibrissae regions of the barrel field cortex 14. The ultrasonic opening of the BBB is fast, noninvasive, and reversible; and thus this approach is suitable for high-throughput and/or longitudinal studies in awake mice.

A technique is described for broadly opening the blood-brain barrier in the mouse using microbubbles and ultrasound. Using this technique, manganese can be administered to the mouse brain. Because manganese is an MRI contrast agent that accumulates in depolarized neurons, this approach enables imaging of neuronal activity.

Although mice are the dominant model system for studying the genetic and molecular underpinnings of neuroscience, functional neuroimaging in mice remains ...

In vivo Optogenetic Stimulation of the Rodent Central Nervous System

The ability to probe defined neural circuits in awake, freely-moving animals with cell-type specificity, spatial precision, and high temporal resolution has been a long sought tool for neuroscientists in the systems-level search for the neural circuitry governing complex behavioral states. Optogenetics is a cutting-edge tool that is revolutionizing the field of neuroscience and represents one of the first systematic approaches to enable causal testing regarding the relation between neural signaling events and behavior. By combining optical and genetic approaches, neural signaling can be bi-directionally controlled through expression of light-sensitive ion channels (opsins) in mammalian cells. The current protocol describes delivery of specific wavelengths of light to opsin-expressing cells in deep brain structures of awake, freely-moving rodents for neural circuit modulation. Theoretical principles of light transmission as an experimental consideration are discussed in the context of performing in vivo optogenetic stimulation. The protocol details the design and construction of both simple and complex laser configurations and describes tethering strategies to permit simultaneous stimulation of multiple animals for high-throughput behavioral testing.

In vivo Optogenetic Stimulation of the Rodent Central Nervous System

Optogenetics has become a powerful tool for use in behavioral neuroscience experiments. This protocol offers a step-by-step guide to the design and set-up of laser systems, and provides a full protocol for carrying out multiple and simultaneous in vivo optogenetic stimulations compatible with most rodent behavioral testing paradigms.

The ability to probe defined neural circuits in awake, freely-moving animals with cell-type specificity, spatial precision, and high temporal resolution ...

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise from extra-retinal sources. Ex vivo ERG provides an efficient method to dissect the function of retinal cells directly from an intact isolated retina of animals or donor eyes. In addition, ex vivo ERG can be used to test the efficacy and safety of potential therapeutic agents on retina tissue from animals or humans. We show here how commercially available in vivo ERG systems can be used to conduct ex vivo ERG recordings from isolated mouse retinas. We combine the light stimulation, electronic and heating units of a standard in vivo system with custom-designed specimen holder, gravity-controlled perfusion system and electromagnetic noise shielding to record low-noise ex vivo ERG signals simultaneously from two retinas with the acquisition software included in commercial in vivo systems. Further, we demonstrate how to use this method in combination with pharmacological treatments that remove specific ERG components in order to dissect the function of certain retinal cell types.

Simultaneous ex vivo Functional Testing of Two Retinas by in vivo Electroretinogram System

Ex vivo ERG can be used to record electrical activity of retinal cells directly from isolated intact retinas of animals or humans. We demonstrate here how common in vivo ERG systems can be adapted for ex vivo ERG recordings in order to dissect the electrical activity of retinal cells.

An In vivo electroretinogram (ERG) signal is composed of several overlapping components originating from different retinal cell types, as well as noise ...

Preparing Fresh Retinal Slices from Adult Zebrafish for Ex Vivo Imaging Experiments

The retina is a complex tissue that initiates and integrates the first steps of vision. Dysfunction of retinal cells is a hallmark of many blinding diseases, and future therapies hinge on fundamental understandings about how different retinal cells function normally. Gaining such information with biochemical methods has proven difficult because contributions of particular cell types are diminished in the retinal cell milieu. Live retinal imaging can provide a view of numerous biological processes on a subcellular level, thanks to a growing number of genetically encoded fluorescent biosensors. However, this technique has thus far been limited to tadpoles and zebrafish larvae, the outermost retinal layers of isolated retinas, or lower resolution imaging of retinas in live animals. Here we present a method for generating live ex vivo retinal slices from adult zebrafish for live imaging via confocal microscopy. This preparation yields transverse slices with all retinal layers and most cell types visible for performing confocal imaging experiments using perfusion. Transgenic zebrafish expressing fluorescent proteins or biosensors in specific retinal cell types or organelles are used to extract single-cell information from an intact retina. Additionally, retinal slices can be loaded with fluorescent indicator dyes, adding to the method&#39;s versatility. This protocol was developed for imaging Ca2+ within zebrafish cone photoreceptors, but with proper markers it could be adapted to measure Ca2+ or metabolites in M&#252;ller cells, bipolar and horizontal cells, microglia, amacrine cells, or retinal ganglion cells. The retinal pigment epithelium is removed from slices so this method is not suitable for studying that cell type. With practice, it is possible to generate serial slices from one animal for multiple experiments. This adaptable technique provides a powerful tool for answering many questions about retinal cell biology, Ca2+, and energy homeostasis.

Preparing Fresh Retinal Slices from Adult Zebrafish for Ex Vivo Imaging Experiments

Imaging retinal tissue can provide single-cell information that cannot be gathered from traditional biochemical methods. This protocol describes preparation of retinal slices from zebrafish for confocal imaging. Fluorescent genetically encoded sensors or indicator dyes allow visualization of numerous biological processes in distinct retinal cell types.

The retina is a complex tissue that initiates and integrates the first steps of vision. Dysfunction of retinal cells is a hallmark of many blinding ...

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

Extensive data on relationships of neural network oscillations to behavior and organization of neuronal discharge across brain regions call for new tools to selectively manipulate brain rhythms. Here we describe an approach combining projection-specific optogenetics with extracellular electrophysiology for high-fidelity control of hippocampal theta oscillations (5-10 Hz) in behaving mice. The specificity of the optogenetic entrainment is achieved by targeting channelrhodopsin-2 (ChR2) to the GABAergic population of medial septal cells, crucially involved in the generation of hippocampal theta oscillations, and a local synchronized activation of a subset of inhibitory septal afferents in the hippocampus. The efficacy of the optogenetic rhythm control is verified by a simultaneous monitoring of the local field potential (LFP) across lamina of the CA1 area and/or of neuronal discharge. Using this readily implementable preparation we show efficacy of various optogenetic stimulation protocols for induction of theta oscillations and for the manipulation of their frequency and regularity. Finally, a combination of the theta rhythm control with projection-specific inhibition addresses the readout of particular aspects of the hippocampal synchronization by efferent regions.

We describe the use of optogenetics and electrophysiological recordings for selective manipulations of hippocampal theta oscillations (5-10 Hz) in behaving mice. The efficacy of the rhythm entrainment is monitored using local field potential. A combination of opto- and pharmacogenetic inhibition addresses the efferent readout of hippocampal synchronization.

Extensive data on relationships of neural network oscillations to behavior and organization of neuronal discharge across brain regions call for new tools ...

An Alternative Approach to Study Primary Events in Neurodegeneration Using Ex Vivo Rat Brain Slices

Despite&#160;numerous studies that attempt to develop reliable animal models&#160;which reflecting the primary processes underlying neurodegeneration, very few have been widely accepted. Here, we propose&#160;a new procedure&#160;adapted from the well-known ex vivo brain slice technique, which offers a closer in vivo-like scenario than in vitro preparations, for investigating the early events triggering cell degeneration, as observed in Alzheimer&#39;s disease (AD). This variation consists of simple and easily reproducible steps, which enable preservation of the anatomical cytoarchitecture of the selected brain region and its local functionality in a physiological milieu. Different anatomical areas can be obtained from the same brain, providing the opportunity to perform multiple experiments with the treatments in question in a site-, dose-, and time-dependent manner. Potential limitations&#160;which could affect the outcomes related to this methodology are related to the conservation of the tissue, i.e., the maintenance of its anatomical integrity during the slicing and incubation steps and the section thickness, which can influence the biochemical and immunohistochemical analysis. This approach can be employed for different purposes, such as exploring molecular mechanisms involved in physiological or pathological conditions, drug screening, or dose-response assays. Finally, this protocol could also reduce the number of animals employed in behavioral studies. The application reported here has been recently described and tested for the first time on ex vivo rat brain slices containing the basal forebrain (BF), which is one of the cerebral regions primarily affected in AD. Specifically, it has been demonstrated that the administration of a toxic peptide derived from the C-terminus of acetylcholinesterase (AChE) could prompt an AD-like profile, triggering, along the antero-posterior axis of the BF, a differential expression of proteins altered in AD, such as the alpha7 nicotinic receptor (&#945;7-nAChR), phosphorylated Tau (p-Tau), and amyloid beta (A&#946;).

An Alternative Approach to Study Primary Events in Neurodegeneration Using Ex Vivo Rat Brain Slices

We present a method which can&#160;provide further insights into the early events underlying neurodegeneration and based on the established ex-vivo brain technique, combining the advantages of in vivo and in vitro experiments. Moreover, it represents a unique opportunity for direct comparison of treated and untreated group in the same anatomical plane.

Despite&#160;numerous studies that attempt to develop reliable animal models&#160;which reflecting the primary processes underlying neurodegeneration, ...

Optogenetic Manipulation of Neural Circuits During Monitoring Sleep/wakefulness States in Mice

In recent years, optogenetics has been widely used in many fields of neuroscientific research. In many cases, an opsin, such as channel rhodopsin 2 (ChR2), is expressed by a virus vector in a particular type of neuronal cells in various Cre-driver mice. Activation of these opsins is triggered by application of light pulses which are delivered by laser or LED through optic cables, and the effect of activation is observed with very high time resolution. Experimenters are able to acutely stimulate neurons while monitoring behavior or another physiological outcome in mice. Optogenetics can enable useful strategies to evaluate function of neuronal circuits in the regulation of sleep/wakefulness states in mice. Here we describe a technique for examining the effect of optogenetic manipulation of neurons with a specific chemical identity during electroencephalogram (EEG) and electromyogram (EMG) monitoring to evaluate the sleep stage of mice. As an example, we describe manipulation of GABAergic neurons in the bed nucleus of the stria terminalis (BNST). Acute optogenetic excitation of these neurons triggers a rapid transition to wakefulness when applied during NREM sleep. Optogenetic manipulation along with EEG/EMG recording can be applied to decipher the neuronal circuits that regulate sleep/wakefulness states.

Here, we describe methods of optogenetic manipulation of particular types of neurons during monitoring of sleep/wakefulness states in mice, presenting our recent work on the bed nucleus of the stria terminalis as an example.

In recent years, optogenetics has been widely used in many fields of neuroscientific research. In many cases, an opsin, such as channel rhodopsin 2 ...

In Vivo Intracerebral Stereotaxic Injections for Optogenetic Stimulation of Long-Range Inputs in Mouse Brain Slices

Knowledge of cell-type specific synaptic connectivity is a crucial prerequisite for understanding brain-wide neuronal circuits. The functional investigation of long-range connections requires targeted recordings of single neurons combined with the specific stimulation of identified distant inputs. This is often difficult to achieve with conventional and electrical stimulation techniques, because axons from converging upstream brain areas may intermingle in the target region. The stereotaxic targeting of a specific brain region for virus-mediated expression of light-sensitive ion channels allows selective stimulation of axons originating from that region with light. Intracerebral stereotaxic injections can be used in well-delimited structures, such as the anterior thalamic nuclei, in addition to other subcortical or cortical areas throughout the brain.
Described here is a set of techniques for precise stereotaxic injection of viral vectors expressing channelrhodopsin in the mouse brain, followed by photostimulation of axon terminals in the brain slice preparation. These protocols are simple and widely applicable. In combination with whole-cell patch clamp recording from a postsynaptically connected neuron, photostimulation of axons allows the detection of functional synaptic connections, pharmacological characterization, and evaluation of their strength. In addition, biocytin filling of the recorded neuron can be used for post-hoc morphological identification of the postsynaptic neuron.

This protocol describes a set of methods to identify the cell-type specific functional connectivity of long-range inputs from distant brain regions using optogenetic stimulations in ex vivo brain slices.

Knowledge of cell-type specific synaptic connectivity is a crucial prerequisite for understanding brain-wide neuronal circuits. The functional ...

Assessment of Long-term Depression Induction in Adult Cerebellar Slices

Synaptic plasticity provides a mechanism for learning and memory. For cerebellar motor learning, long-term depression (LTD) of synaptic transmissions from parallel fibers (PF) to Purkinje cells (PC) is considered the basis for motor learning, and deficiencies of both LTD and motor learning are observed in various gene-manipulated animals. Common motor learning sets, such as adaptation of the optokinetic reflex (OKR), the vestibular-ocular reflex (VOR), and rotarod test were used for evaluation of motor learning ability. However, results obtained from the GluA2-carboxy terminus modified knock-in mice demonstrated normal adaptation of the VOR and the OKR, despite lacking PF-LTD. In that report, induction of LTD was only attempted using one type of stimulation protocol at room temperature. Thus, conditions to induce cerebellar LTD were explored in the same knock-in mutants using various protocols at near physiological temperature. Finally, we found stimulation protocols, by which LTD could be induced in these gene-manipulated mice. In this study, a set of protocols are proposed to evaluate LTD-induction, which will more accurately allow examination of the causal relationship between LTD and motor learning. In conclusion, experimental conditions are crucial when evaluating LTD in gene-manipulated mice.

In some gene-manipulated animals, using a single protocol may fail to induce LTD in cerebellar Purkinje cells, and there may be a discrepancy between LTD and motor learning. Multiple protocols are necessary to assess LTD-induction in gene-manipulated animals. Standard protocols are shown.

Synaptic plasticity provides a mechanism for learning and memory. For cerebellar motor learning, long-term depression (LTD) of synaptic transmissions from ...

Optogenetic Activation of Afferent Pathways in Brain Slices and Modulation of Responses by Volatile Anesthetics

Anesthetics influence consciousness in part via their actions on thalamocortical circuits. However, the extent to which volatile anesthetics affect distinct cellular and network components of these circuits remains unclear. Ex vivo brain slices provide a means by which investigators may probe discrete components of complex networks and disentangle potential mechanisms underlying the effects of volatile anesthetics on evoked responses. To isolate potential cell type- and pathway-specific drug effects in brain slices, investigators must be able to independently activate afferent fiber pathways, identify non-overlapping populations of cells, and apply volatile anesthetics to the tissue in aqueous solution. In this protocol, methods to measure optogenetically-evoked responses to two independent afferent pathways to neocortex in ex vivo brain slices are described. Extracellular responses are recorded to assay network activity and targeted whole-cell patch clamp recordings are conducted in somatostatin- and parvalbumin-positive interneurons. Delivery of physiologically relevant concentrations of isoflurane via artificial cerebral spinal fluid to modulate cellular and network responses is described.

Ex vivo brain slices can be used to study the effects of volatile anesthetics on evoked responses to afferent inputs. Optogenetics are employed to independently activate thalamocortical and corticocortical afferents to non-primary neocortex, and synaptic and network responses are modulated with isoflurane.

Anesthetics influence consciousness in part via their actions on thalamocortical circuits. However, the extent to which volatile anesthetics affect ...