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 surgery supplies such as sterile cotton swaps, disinfectant, sterile phosphate buffered saline (PBS, pH 7.4), and H2O2 on a sterile surgical drape.</li>
	<li>Pull glass micropipettes for injections (Figure 1A, inset) using a 3 mm wide box filament on a horizontal microelectrode puller according to the manufacturer&#39;s instructions. 
	Note: For deep injections, the electrode taper should be sufficiently long to reach the ventral most coordinates (approx. 5 mm; for coordinates, see 1.10).</li>
	<li>Premix 1 &#181;l of virus solution and&#160;0.2 &#181;l of 0.1% fast green solution in sterile PBS (for better visibility of solution in the glass pipette). Fill glass pipettes with mixture of virus solution and fast green using a microliter pipette with a fine tip (Figure 1A, inset). 
	Note: Work with recombinant Adeno-associated viral vectors (rAAV) is considered biosafety level 1 (BSL 1) work and needs to be performed in a BSL 1 laboratory. rAAVs used in this study (Figure 1C) were: 1)&#160;mPFC: rAAV-hSyn-ChR2(H134R)-eYFP (serotype 2/9) 16; 2) MGm/PIN: rAAV-CAGh-ChR2(H134R)-mCherry (serotype 2/9) 23; 3) mpITC/BLA: rAAV-EF1a-DIOhChR2(H134R)-YFP (serotype 2/1) 23</li>
	<li>Anesthetize a mouse using a small animal anesthesia machine (Isoflurane: 3% in oxygen for induction). 
	Note: Mice used in this study were 4 - 7 weeks old and of the following strains and genotypes: C57Bl6/J wild type (experiment in Figures 2A and 3A-D); GAD67-GFP 24 (experiment in Figures 2B and 3E-H); Tac2-Cre 25 (experiment in Figures 2C and 3I-J).</li>
	<li>Shave head between ears and eyes. Apply disinfectant (providone-iodine based) to shaved head using cotton swabs.</li>
	<li>Apply an eye ointment to prevent drying of eyes during anesthesia. Subcutaneously inject mouse with analgesic (meloxicam-based, 0.1 ml of 5 mg/ml solution).</li>
	<li>Place mouse in stereotactic frame (Figure 1A) and maintain anesthesia via a gas anesthesia mask (Isoflurane: 2% in oxygen for maintenance). Check anesthesia depth using limb withdrawal reflex before continuing. 
	Note: Maintain sterile conditions as well as possible during the entire surgical procedure; wear disposable facemask, surgical gown, and gloves.</li>
	<li>Make skin incision on top of the head using scissors. Gently pull skin to the side using blunt forceps, fix with clamps to expose skull surface, and clean skull with H2O2.</li>
	<li>Mark injection sites on skull using a fine tip permanent marker and drill holes for both hemispheres (Figure 1B). Coordinates for injections in this study are (from Bregma (mm)): mPFC: anterior 1.9, lateral &#177; 0.3, ventral 2.1; MGm/PIN: posterior 3.0, lateral &#177; 1.8, ventral 3.8; mpITC/BLA: posterior 1.45, lateral &#177; 3.35, and ventral 4.75.</li>
	<li>Mount filled glass pipette onto stereotactic frame connected to a pressure injection device and bring the pipette to Bregma position.</li>
	<li>Break off the tip of the glass pipette using fine straight-tip forceps. Do this gently to prevent aerosol generation of virus solution. Make sure the pipette tip is open by applying a few pressure pulses and observing extrusion of drops of virus solution.</li>
	<li>Go to the desired injection coordinates and inject half of the pipette content (~0.5 &#181;l) using the following settings on the pressure injection device: Pressure: 20 psi, average pulse length: 30 ms, average number of pulses: 50.</li>
	<li>Leave pipette in place for ~1 min before slowly (1 mm/min) retracting it. 
	Note: Make sure pipette is not blocked before repeating procedure with same pipette on other hemisphere. In case of blocked tip, clean or break off tip and zero pipette position at Bregma again.</li>
	<li>Clean skull with PBS (pH 7.4), remove clamps, gently pull the skin together, and suture the incision with individual button suture (3 - 4 knots). Apply disinfectant (providone-iodine based) around the wound.</li>
	<li>Stop the anesthesia and do not leave mouse unattended until it is fully awake. Keep single housed or return to company of other animals only when fully recovered. Postoperatively, continue to monitor the health status, and administer analgesic if necessary. Follow procedures according to rules put forward by the local Animal Care and Use Committee.</li>
</ol>
2. Preparation of Acute Slices
<ol>
	<li>Prepare ACSF, cutting solution, tools (scissors, scalpel, forceps, spatula, Pasteur pipette), and agar blocks. 
	Note: 1 L&#160;of artificial cerebro-spinal fluid (ACSF) is required per experiment, and is prepared by dissolving chemicals in double-distilled H2O as previously published 16,23. Cutting solution is prepared by supplementing 200 ml of ACSF with 0.87 ml of 2 M MgSO4 stock solution.</li>
	<li>Oxygenate ACSF and cutting solution throughout the experiment with 95% O2 and 5% CO2.</li>
	<li>Deeply anesthetize mouse using a small animal anesthesia machine using isoflurane (3% in oxygen). Check anesthesia depth using limb withdrawal reflex before continuing.</li>
	<li>Decapitate mouse using large scissors and immediately chill head in ice-cold cutting solution.</li>
	<li>Open skull by a single midline incision from caudal to rostral and gently push pieces of skull to the sides using forceps. Rapidly remove brain by gently lifting it out of the skull using a small rounded spatula. Cut off cerebellum with scalpel. Place brain in ice-cold cutting solution.</li>
	<li>For mPFC injection sites: cut off anterior part of the brain (containing mPFC) using a scalpel and put in ice-cold cutting solution until slicing.</li>
	<li>Remove excess cutting solution with a filter paper and glue the posterior part of the brain onto the vibratome stage.</li>
	<li>For tilted amygdala slices, glue the brain on an agar block (4%) cut at a 35&#176; angle (Figure 1D, middle). For coronal amygdala slices, MGm/PIN injection sites and mPFC injection sites, glue the brain directly on stage (Figure 1D, left and right). Place an additional agar block behind brain for stability while slicing.</li>
	<li>Place stage in cutting chamber with ice-cold oxygenated cutting solution that is maintained at 4 &#176;C using a cooling unit. Prepare acute slices of the amygdala (320 &#181;m) using a sapphire blade. Place slices in an interface chamber supplied with oxygenated ACSF at RT.</li>
	<li>After preparation of acute amygdala slices, place the interface chamber in a waterbath at 36 &#176;C to recover slices for 35 - 45 min. Subsequently, return the interface chamber to RT. For recording from these slices, proceed with step 3.2.</li>
	<li>During commencement of step 2.10, cut slices of the injection sites as described before for acute amygdala slices (steps 2.8 - 2.9). Recovery of slices in the waterbath is not required here. Optional: To quickly estimate injection site location, observe slices on a stereoscope equipped with a fluorescent lamp and appropriate filter sets.</li>
	<li>Fix slices containing injection sites for post-hoc analysis by sandwiching them between two filter papers and submerging them in 4% paraformaldehyde (PFA) in PBS solution O/N. For analysis of injection sites proceed with step 4.1.</li>
</ol>
3. Visualization and Stimulation of Presynaptic Fibers
<ol>
	<li>Prepare patch microscope for optogenetic activation of fibers and cells:
	<ol>
		<li>Center the mounted light emitting diode (LED) onto the light delivery pathway.</li>
		<li>Measure the LED light intensity at the back focal plane and at the output of each objective with a power meter choosing the appropriate wavelength of 470 nm.</li>
		<li>Calculate the light intensity in mW/mm2 and create a calibration curve (LED intensity (%) versus light output (mW/mm2)) for each objective for values measured for 470 nm wavelength.</li>
	</ol>
	</li>
	<li>Retrieve an acute amygdala slice from the interface chamber and place in the slice chamber mounted onto the upright microscope equipped with a fluorescent lamp. Take care to position the slice such that the slice surface facing upward in the interface chamber is also facing upward in the recording chamber. Perfuse slice with fresh, oxygenated ASCF at a rate of 1 - 2 ml/min at a temperature of ~31 &#176;C.</li>
	<li>Observe presynaptic fibers in the slice using the fluorescent lamp in combination with appropriate filter sets for the specific fluorescent protein expressed. Use 5x objective to obtain an overview (Figure 1E), and 60x objective for assessment of fiber density within the target area. 
	Note: For GFP and YFP,&#160;use Filter set &#34;green&#34; (Excitation 472/20, Beamsplitter 495, Emission 490 LP) for mCherry use filter set &#34;red&#34; (Excitation 560/40, Beamsplitter 585, Emission 630/70) as specified in the materials/equipment table.</li>
	<li>Open or restrict the aperture in the microscope light pathway as desired for the experiment (Figure 2D).</li>
	<li>To obtain a patch recording, fill a patch pipette with internal solution and mount in electrode holder. Apply positive pressure to the patch pipette and slowly lower it first into the bath solution and then under visual control into the slice using the micromanipulator.
	<ol>
		<li>Approach the neuron of interest with the patch pipette from the side and top. Release positive pressure when the pipette is on the surface of the cell (dimple visible on cell surface) and obtain a &#34;gigaseal&#34; by applying negative pressure.</li>
		<li>Apply further suction to rupture the membrane patch to obtain whole-cell recording. Subsequently, stimulate labeled fibers with the connected LED using the appropriate wavelength for activating ChR (470 nm) while recording electrical responses from the cell.</li>
		<li>For synaptic stimulation start with a low LED intensity and increase until the desired synaptic current amplitude is reached. Trigger the LED by configuring digital outputs in the data acquisition software to control the timing and pulse length (examples in Figure 3). 
		Note: other software and/or TTL-generating devices can be used to trigger LED.</li>
	</ol>
	</li>
	<li>Repeat stimulation with opened or restricted aperture (step 3.4) in the microscope light pathway as desired for the next recorded cell and/or in the presence of specific drugs.</li>
	<li>After recording, fix slices for post-hoc analysis by sandwiching them between two filter papers and submerging them in 4% PFA O/N.</li>
	<li>Analyze electrophysiological data. 
	Note: Use appropriate software to visualize recorded sweep data for each individual stimulation offline. When analyzing effects of drugs, use peak detection routines to obtain time course of drug effect on synaptic current amplitudes for all individual sweeps. Determine when the drug effect reaches steady state. To prepare representative average responses for figures, use software to average &#8805;10 individual sweeps per experimental condition (c.f. Figure 3B-D, F-H, J right panel). 
	Note: several alternative software packages can be used for data analysis.</li>
</ol>
4. Post-hoc Analysis of Injection Sites
<ol>
	<li>Wash slices of injection sites (from step 2.12) and recording sites (if re-imaging is desired, from step 3.7) three times in PBS. This is done by repeatedly replacing solution with fresh PBS on a rotating shaker three times for 10 min.</li>
	<li>Prepare 2% agar-agar solution in PBS, and let it cool down to ~65 &#176;C. Place slices flat on the bottom of a small 30 mm diameter petri dish, embed slices in agar-agar and let it cool down until solid.</li>
	<li>Glue an agar block with embedded slice or slices to the stage of a vibratome and place stage in cutting chamber with PBS.</li>
	<li>Resection embedded slices to 70 &#181;m thickness. Optional: After resectioning, slices can be stained, i.e., with Neurotrace to reveal cytoarchitecture (Figure 3A, C), and/or by immunofluorescence staining for YFP or mCherry to boost the signal from the ChR fusion protein.</li>
	<li>Mount slices on slides and coverslip with mounting media. Image injection sites and, if desired, also image slices containing fibers in the projection areas using a fluorescent microscope or a confocal laser-scanning microscope (Figure 2A-C).</li>
</ol>

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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>

The authors declare that they have no competing financial interests.

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 ...

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

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JoVE Journal

Neuroscience

15.8K Views.  University of Tuebingen. Optogenetic approaches are widely used to manipulate neural activity and assess the consequences for brain function. Here, a technique is outlined that 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.

Video: Ex Vivo Optogenetic Dissection of Fear Circuits in Brain Slices

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

The cerebral cortex directs higher cognitive functions. This six layered structure is generated in an inside-first, outside-last manner, in which the first born neurons remain closer to the ventricle while the last born neurons migrate past the first born neurons towards the surface of the brain1. In addition to neuronal migration2, a key process for normal cortical function is the regulation of neuronal morphogenesis3. While neuronal morphogenesis can be studied in vitro in primary cultures, there is much to be learned from how these processes are regulated in tissue environments.
We describe techniques to analyze neuronal migration and/or morphogenesis in organotypic slices of the cerebral cortex4,6. A pSilencer modified vector is used which contains both a U6 promoter that drives the double stranded hairpin RNA and a separate expression cassette that encodes GFP protein driven by a CMV promoter7-9. Our approach allows for the rapid assessment of defects in neurite outgrowth upon specific knockdown of candidate genes and has been successfully used in a screen for regulators of neurite outgrowth8. Because only a subset of cells will express the RNAi constructs, the organotypic slices allow for a mosaic analysis of the potential phenotypes. Moreover, because this analysis is done in a near approximation of the in vivo environment, it provides a low cost and rapid alternative to the generation of transgenic or knockout animals for genes of unknown cortical function. Finally, in comparison with in vivo electroporation technology, the success of ex vivo electroporation experiments is not dependant upon proficient surgery skill development and can be performed with a shorter training time and skill.

Methods for Study of Neuronal Morphogenesis: Ex vivo RNAi Electroporation in Embryonic Murine Cerebral Cortex

To conduct a rapid assessment of the function of genes in the development of cerebral cortex, we describe methods involving the ex vivo electroporation of plasmids co-expressing inhibitory RNA (RNAi) and GFP in murine embryonic cortex. This protocol is amenable to the study of various aspects of neurodevelopment such as neurogenesis, neuronal migration and neuronal morphogenesis including dendrite and axon outgrowth.

The cerebral cortex directs higher cognitive functions. This six layered structure is generated in an inside-first, outside-last manner, in which the ...

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 ...

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion channel, and transporter cell surface presentation on a minutes time scale.&#160;There is a broad diversity of mechanisms that control endocytic trafficking of individual proteins. Studies investigating the molecular underpinnings of trafficking have primarily relied upon surface biotinylation to quantitatively measure changes in membrane protein surface expression in response to exogenous stimuli and gene manipulation.&#160;However, this approach has been mainly limited to cultured cells, which may not faithfully reflect the physiologically relevant mechanisms at play in adult neurons.&#160;Moreover, cultured cell approaches may underestimate region-specific differences in trafficking mechanisms.&#160;Here, we describe an approach that extends cell surface biotinylation to the acute brain slice preparation.&#160;We demonstrate that this method provides a high-fidelity approach to measure rapid changes in membrane protein surface levels in adult neurons.&#160;This approach is likely to have broad utility in the field of neuronal endocytic trafficking.

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Neuronal membrane trafficking dynamically controls plasma membrane protein availability and significantly impacts neurotransmission.&#160;To date, it has been challenging to measure neuronal endocytic trafficking in adult neurons.&#160;Here, we describe a highly effective, quantitative method to measure rapid changes in surface protein expression ex vivo in acute brain slices.

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion ...

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 ...

Ex Vivo Preparations of the Intact Vomeronasal Organ and Accessory Olfactory Bulb

The mouse accessory olfactory system (AOS) is a specialized sensory pathway for detecting nonvolatile social odors, pheromones, and kairomones. The first neural circuit in the AOS pathway, called the accessory olfactory bulb (AOB), plays an important role in establishing sex-typical behaviors such as territorial aggression and mating. This small (&#60;1 mm3) circuit possesses the capacity to distinguish unique behavioral states, such as sex, strain, and stress from chemosensory cues in the secretions and excretions of conspecifics. While the compact organization of this system presents unique opportunities for recording from large portions of the circuit simultaneously, investigation of sensory processing in the AOB remains challenging, largely due to its experimentally disadvantageous location in the brain. Here, we demonstrate a multi-stage dissection that removes the intact AOB inside a single hemisphere of the anterior mouse skull, leaving connections to both the peripheral vomeronasal sensory neurons (VSNs) and local neuronal circuitry intact. The procedure exposes the AOB surface to direct visual inspection, facilitating electrophysiological and optical recordings from AOB circuit elements in the absence of anesthetics. Upon inserting a thin cannula into the vomeronasal organ (VNO), which houses the VSNs, one can directly expose the periphery to social odors and pheromones while recording downstream activity in the AOB. This procedure enables controlled inquiries into AOS information processing, which can shed light on mechanisms linking pheromone exposure to changes in behavior.

Ex Vivo Preparations of the Intact Vomeronasal Organ and Accessory Olfactory Bulb

The mouse accessory olfactory bulb (AOB) has been difficult to study in the context of sensory coding. Here, we demonstrate a dissection that produces an ex vivo preparation in which AOB neurons remain functionally connected to their peripheral inputs, facilitating research into information processing of mouse pheromones and kairomones.

The mouse accessory olfactory system (AOS) is a specialized sensory pathway for detecting nonvolatile social odors, pheromones, and kairomones. The first ...

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 ...