Name: optogenetic entrainment of hippocampal theta oscillations in behaving mice
Uploaded: 2018-06-29T13:30:00
Description: Watch this Scientific Journal Video about Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice at JoVE.com

We would like to thank Maria Gorbati for expert help with data analysis and Jennifer Kupferman for comments on the manuscript. This work was supported by Deutsche Forschungsgemeinschaft (DFG; Exc 257 NeuroCure, TK and AP; Priority Program 1665, 1799/1-1(2), Heisenberg Programme, 1799/2-1, AP), the German-Israeli Foundation for Scientific Research and Development (GIF; I-1326-421.13/2015, TK) and the Human Frontier Science Program (HFSP; RGY0076/2012, TK).

PV-Cre knock-in male mice59, 10-25 weeks old, were used. Mice were housed under standard conditions in the animal facility and kept on a 12 h light/dark cycle. All procedures were performed in accordance with national and international guidelines, and were approved by the local health authorities&#160;(Landesamt f&#252;r Natur, Umwelt und Verbraucherschutz, Nordrhein-Westfalen).
1. Viral Injection
<ol>
	<li>During the whole procedure, follow biological safety guidelin...

Here we presented a widely accessible methodology to entrain and elicit hippocampal theta oscillations in the behaving animal. This approach can be useful for studies of theta rhythm&#39;s functions in information processing and behavior. Critical aspects of this method include: (1) choice of the opsin and targeting of ChR2 to axons of MS cells in the hippocampus, (2) robust optical and electrical features of implanted optic fiber-wire array assemblies to ensure continuous stimulation and LFP recording in behaving mice, ...

Neuronal activity in mammals is coordinated by network oscillations, which assist information transfer within and between brain regions1,2,3,4. Brain rhythms include oscillations ranging from very slow (&#60; 0.8 Hz) up to ultrafast (&#62; 200 Hz) frequencies. A large body of evidence supports involvement of network oscillations in diverse brain functions, including cognition5,6,7,8,9,10, innate behaviors11,12 as well as neuropsychiatric disorders such as Parkinson&#39;s disease and epilepsy13,14,15. Selective and temporally precise methods for experimental manipulation of network oscillations are therefore essential for the development of physiologically plausible models of synchronization and for establishing causal links with behavior.
Network synchronization is mediated by diverse biological substrates and processes, ranging from molecular identity of ion channels and their kinetics to neuromodulation of excitability and network connectivity. The biological design of rhythm generators16 has been revealed for many brain rhythms, distinct aspects of which (e.g., frequency, amplitude) are often brought about by dynamics of distinct cell types and networks. For instance, inhibitory interneurons targeting the somata of principal cells are the most important players across frequency bands and brain regions17,18, including theta19,20, gamma20,21, and ripple (140-200 Hz)22 oscillations. In turn, phase synchronization of distant cells is ensured by robust feed-forward signaling of pyramidal cells, which resets the firing of interneurons. A crucial parameter of oscillations, the size of the synchronized neuronal population, is closely related to the measured LFP oscillation&#39;s amplitude and, at least for fast oscillations, depends on the excitatory drive onto interneurons2. In contrast, slower oscillations, like delta and theta rhythms, are generated by long-range reentrant loops, formed by cortico-thalamic23,24 and hippocampal-medial septal projections25,26,27, respectively. Oscillations in such circuits are brought about by interactions of signal propagation delays, excitable responses, and their frequency preference in participating cells28,29,30,31,32. Inhibitory projections from GABAergic parvalbumin (PV)-positive cells of the medial septum (MS) to interneurons in the hippocampus25,33, parahippocampal regions and entorhinal cortex26 are essential for the generation of theta oscillations in the medial temporal lobe. Thus, physiological mechanisms of network oscillations and neuronal synchronization can be manipulated using optogenetics with a real-time precision.
Cell type-specific optogenetic manipulations have been applied for studies of the hippocampal and cortical oscillations in vitro34,35,36,37,38 and in vivo30,39,40,41,42,43,44,45, including functional investigations of gamma5,12,36,46,47,48,49,50,51,52 and ripple oscillations40,53,54 and sleep spindles55,56. Recently we expressed a Cre-dependent ChR2 virus in the MS, a key region for the generation of the hippocampal theta rhythm, of PV-Cre mice. Using this preparation, features of the hippocampal theta oscillations (frequency and temporal stability) were controlled by optogenetic stimulation of inhibitory projections of the MS in the hippocampus11. Furthermore, theta-frequency optogenetic stimulation of inhibitory septo-hippocampal projections evoked theta rhythm during awake immobility. The optogenetically entrained theta rhythm displayed properties of spontaneous theta oscillations in the mouse at LFP and neuronal activity levels.
Key features of this protocol include: (1) utilization of an inhibitory pathway that is physiologically critical for spontaneous theta oscillations while avoiding unspecific effects on hippocampal excitability; (2) axonal, i.e., projection-specific stimulation to minimize a direct influence on non-hippocampal MS efferents; (3) local theta-rhythmic light stimulation, ensuring a minimal direct interference with theta-rhythmic septo-hippocampal dynamics and a global bilateral entrainment of theta oscillations; (4) parametric control of theta oscillations frequency and regularity; and (5) quantification of entrainment fidelity with high temporal resolution using LFP to enable quantitative causality analysis in behaving animals. Since this preparation essentially capitalizes on a well-known role of the septo-hippocampal disinhibition in theta generation25,30, it enables robust control over several parameters of theta oscillations in behaving mice. Studies where other less investigated pathways and cell types of the septo-hippocampal circuitry were manipulated38,39,47,49,50,51,52,53,54,55,56,57,58 reveal further mechanisms of the theta rhythm.

<table>
	<tbody>
		<tr>
			<td>PV-Cre mice</td>
			<td>The Jackson Laboratory</td>
			<td>B6;129P2-Pvalbtm1(cre)Arbr/J</td>
			<td></td>
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		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
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			<td>Surgery</td>
			<td></td>
			<td></td>
			<td></td>
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		<tr>
			<td>Stereotaxis</td>
			<td>David Kopf Instruments, Tujunga, CA, USA</td>
			<td>Model 963</td>
			<td>Ultra Precise Small Animal Stereotaxic Instrument</td>
		</tr>
		<tr>
			<td>Drill bits, 0.8 mm</td>
			<td>Bijoutil, Allschwil, Switzerland</td>
			<td>49080HM</td>
			<td></td>
		</tr>
		<tr>
			<td>0.01-1 ml syringe</td>
			<td>Braun, Melsungen, Germany</td>
			<td>9161406V</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterican cannulas</td>
			<td>Braun</td>
			<td>26 G, 0.45x25 mm BL/LB</td>
			<td></td>
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		<tr>
			<td>Fine and sharp scissors</td>
			<td>Fine Science Tools Inc., Vancouver, Canada</td>
			<td>14060-09</td>
			<td></td>
		</tr>
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			<td>Forceps</td>
			<td>Fine Science Tools Inc.</td>
			<td>11210-10</td>
			<td>Dumont AA - Epoxy Coated Forceps</td>
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			<td>Blunt stainless steel scissors</td>
			<td>Fine Science Tools Inc.</td>
			<td>14018-14</td>
			<td></td>
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			<td>Soldering station</td>
			<td>Weller Tools GmbH, Besigheim, Germany</td>
			<td>WSD 81</td>
			<td></td>
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		<tr>
			<td>Erythromycin</td>
			<td>Rotexmedica GmbH, Trittau, Germany</td>
			<td>PZN: 10823932</td>
			<td>1g Powder for Solution for Infusion</td>
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		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
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			<td>Optogenetics</td>
			<td></td>
			<td></td>
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			<td>Hamilton pump</td>
			<td>PHD Ultra, Harvard Apparatus, Holliston, MA, USA</td>
			<td>model 703008</td>
			<td>PHD Ultra Syringe Pump with push/pull mechanism</td>
		</tr>
		<tr>
			<td>Hamilton 5 &#181;L Syringe, 26 gauge</td>
			<td>PHD Ultra, Harvard Apparatus</td>
			<td>Model 75 RN SYR</td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton 5 &#181;L Plunger</td>
			<td>PHD Ultra, Harvard Apparatus</td>
			<td>Model 75 RN SYR</td>
			<td></td>
		</tr>
		<tr>
			<td>Tubing</td>
			<td>Fisher Scientific, Pittsburgh, USA</td>
			<td>PE 20</td>
			<td>Inner diameter 0.38 mm (.015&#34;), Outer diameter 1.09 mm (.043&#34;)</td>
		</tr>
		<tr>
			<td>Sterican cannulas</td>
			<td>Braun, Melsungen, Germany</td>
			<td>27 G, 25x0.40 mm, blunt</td>
			<td></td>
		</tr>
		<tr>
			<td>Precision drill/grinder</td>
			<td>Proxxon, Wecker, Luxemburg</td>
			<td>fbs 240/e</td>
			<td></td>
		</tr>
		<tr>
			<td>Cutting disks</td>
			<td>Proxxon</td>
			<td>NO 28812</td>
			<td></td>
		</tr>
		<tr>
			<td>Cre dependent channelrhodopsin</td>
			<td>Penn Vector Core, Philadelphia, PA, USA</td>
			<td>AV-1-18917P</td>
			<td>Contruct name: AAV2/1.CAGGS.flex.ChR2.tdTomato, titer: 1.42x1013 vg/ml</td>
		</tr>
		<tr>
			<td>Cam kinase dependent halorhodopsin</td>
			<td>Penn Vector Core</td>
			<td>AV-1-26971P</td>
			<td>Construct name: eNpHR3.0, AAV2/1.CamKIIa.eNpHR3.0-EYFP.WPRE.hGH, titer: 2.08_1012 vg/ml</td>
		</tr>
		<tr>
			<td>Multimode optic fiber</td>
			<td>ThorLabs, Dachau, Germany</td>
			<td>FG105LCA</td>
			<td>0.22 NA, Low-OH, &#216;105 &#181;m Core, 400 - 2400 nm</td>
		</tr>
		<tr>
			<td>Ceramic stick ferrule</td>
			<td>Precision Fiber Products, Milpitas, CA, USA</td>
			<td>CFLC126</td>
			<td>Ceramic LC MM Ferrule, ID 126um</td>
		</tr>
		<tr>
			<td>Polishing paper</td>
			<td>Thorlabs</td>
			<td>LF3D</td>
			<td>6&#34; x 6&#34; Diamond Lapping (Polishing) Sheet</td>
		</tr>
		<tr>
			<td>Power meter</td>
			<td>Thorlabs</td>
			<td>PM100D</td>
			<td>Compact Power and Energy Meter Console, Digital 4&#34; LCD</td>
		</tr>
		<tr>
			<td>Multimode fiber optic coupler</td>
			<td>Thorlabs</td>
			<td>FCMM50-50A-FC</td>
			<td>1x2 MM Coupler, 50:50 Split Ratio, 50 &#181;m GI Fibers, FC/PC</td>
		</tr>
		<tr>
			<td>Fiberoptic patch cord</td>
			<td>Thorlabs</td>
			<td>FG105LCA CUSTOM-MUC</td>
			<td>custom made, 3 m long, with protective tubing, Tubing: FT030, Connector 1: FC/PC, Connector 2: 1.25mm (LC) Ceramic Ferrule</td>
		</tr>
		<tr>
			<td>Sleeve</td>
			<td>Precision Fiber Products, Milpitas, CA, USA</td>
			<td>ADAL1</td>
			<td>Ceramic Split Mating Sleeve for &#216;1.25 mm (LC/PC) Ferrules</td>
		</tr>
		<tr>
			<td>473 nm DPSS laser</td>
			<td>Laserglow Technologies, Toronto, ON, Canada</td>
			<td>R471005FX</td>
			<td>LRS-0473 Series</td>
		</tr>
		<tr>
			<td>593 nm DPSS laser</td>
			<td>Laserglow Technologies</td>
			<td>R591005FX</td>
			<td>LRS-0594 Series</td>
		</tr>
		<tr>
			<td>MC_Stimulus II</td>
			<td>Multichannel Systems, Reutlingen, Germany</td>
			<td>STG 4004</td>
			<td></td>
		</tr>
		<tr>
			<td>Impedance conditioning module</td>
			<td>Neural microTargeting worldwide, Bowdoin, USA</td>
			<td>ICM</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Electrophysiology</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tungsten wires</td>
			<td>California Fine Wire Company, Grover Beach, CA, USA</td>
			<td>CFW0010954</td>
			<td>40 &#181;m, 99.95%</td>
		</tr>
		<tr>
			<td>Capillary tubing</td>
			<td>Optronics</td>
			<td>1068150020</td>
			<td>ID: 100.4 &#181;m</td>
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			<td>Omnetics nanoconnector</td>
			<td>Omnetics Connector Corporation, Minneapolis, USA</td>
			<td>A79038-001</td>
			<td></td>
		</tr>
		<tr>
			<td>Screws</td>
			<td>Bilaney, D&#252;sseldorf, Germany</td>
			<td>00-96x1/16</td>
			<td>stainless-steel</td>
		</tr>
		<tr>
			<td>Silicone probe</td>
			<td>NeuroNexus Technologies, Ann Arbor, MI, USA</td>
			<td>B32</td>
			<td></td>
		</tr>
		<tr>
			<td>Headstage</td>
			<td>Neuralynx, Bozeman, Montana USA</td>
			<td>HS-8</td>
			<td>miniature headstage unity gain preamplifiers</td>
		</tr>
		<tr>
			<td>Silver conductive paint</td>
			<td>Conrad electronics, Germany</td>
			<td>530042</td>
			<td></td>
		</tr>
		<tr>
			<td>Liquid flux</td>
			<td>Felder GMBH L&#246;ttechnik, Oberhausen, Germany</td>
			<td>L&#246;t&#246;l ST</td>
			<td>DIN EN 29454.1, 3.2.2.A (F-SW 11)</td>
		</tr>
		<tr>
			<td>LED</td>
			<td>Neuralynx</td>
			<td>HS-LED-Red-omni-10V</td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>Mathworks, Natick, MA, USA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MC_Stimulus software</td>
			<td>Multichannel, Systems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Neurophysiological Data Manager</td>
			<td></td>
			<td></td>
			<td>NDManager, http://neurosuite.sourceforge.net</td>
		</tr>
		<tr>
			<td>Klusters</td>
			<td></td>
			<td></td>
			<td>http://neurosuite.sourceforge.net, Hazan et al., 2006</td>
		</tr>
		<tr>
			<td>Software of the recording system</td>
			<td>Neuralynx</td>
			<td>Cheetah</td>
			<td>https://neuralynx.com/software/cheetah</td>
		</tr>
		<tr>
			<td>Multi-channel data analysis software</td>
			<td>Cambridge Electronic Design Limited, Cambridge, GB</td>
			<td>Spike2</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Targeting of ChR2 to GABAergic cells in the MS as described in section 1 is illustrated in Figure 2A. Optogenetic stimulation of axons of MS GABAergic cells in the dorsal hippocampus via an optic fiber which is implanted above the CA1 area entrains theta oscillations at the frequency of the stimulus in the ipsilateral (Figure 2B) as well as contralateral hemisphere (Figure 2C). Theta oscillations cou...

Watch this Scientific Journal Video about Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice at JoVE.com

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

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 ...

This method can help answer key questions in the neurophysiology field, such as causal role of theta oscillation in special navigation and associated behaviors. The main advantage of this technique is that it enables a real-time control over the frequency and regularity of hippocampal theta oscillations in behaving mice. Demonstrating the procedure will be Dr.Franziska Bender, a former grad student in my laboratory.Begin with the fully anesthetized mouse secured in the stereotaxic frame. Drill a hole above the medial septum. Submerge the tip of the injection needle in a droplet of virus on a piece of paraffin film and carefully draw up the virus at about 500 nanoliters per minute while observing the level of the fluid.To prevent air from entering the injection needle, stop withdrawal before the virus is entirely taken up. Clean the needle with a paper tissue. Check that the virus and oil are separated by an air bubble and mark the level of the virus on the tube.Position the needle above the craniotomy and slowly insert it into the brain at the first injection point. Inject 450 nanoliters of the virus at a rate of 100 to 150 nanoliters per minute. Following the injection, wait for 10 minutes.After 10 minutes carefully move the needle up 0.1 millimeters and wait another five minutes. Use a micro stripper to strip 125 micrometers of cladding from a multi-mode optic fiber while the fiber is still attached to the fiber spool. Then, use a diamond knife to cut the fiber to a length of approximately two to three centimeters.Insert the optic fiber into a zirconia ceramic stick ferrule with an internal diameter of 126 microns. Approximately 0.5 to one millimeter of the fiber should protrude from the convex side of the ferrule. Using a needle, apply one drop of epoxy glue to both ends of the ferrule, but not onto the sides of the ferrule.After drying use diamond lapping fiber polishing film with three micron grits to polish the convex side of the ferrule. To prepare the tungsten wire array, first glue several 100 micron silica tube guides to the sticky side of a piece of tape. Then use forceps to thread formvar insulated 45 micron tungsten wires through the guide tubes.Next use a scalpel to strip the insulation from both ends of six enamel insulated fine copper binding wires of approximately five millimeters long. Then strip the insulation from both ends of a grounding wire of approximately two to three centimeters long. Solder each stripped wire to the nanoconnector pins.Connect each bonding wire to one tungsten wire using one drop of silver conductive paint. After drying, apply a small amount of cement to cover the copper wires. Avoid applying cement to the upper part of the nanoconnector.After allowing the cement to dry for at least 30 minutes, use blunt stainless steel scissors to cut the tungsten wires at a five to 20 degree angle. Begin by drilling four holes of 0.8 mm diameter in the clean skull of the anesthetized animal. drill two holes rostral to the coronal suture, and two above the cerebellum.Next, place stainless steel bone screws for grounding and stabilization of the implant. Position the ground screw connected to a copper wire above the cerebellum. Cover the ground screw completely with cement to prevent muscle artifacts during the electrophysiological recordings.Build a cment ring connecting all screws. Perform a craniotomy above the implantation site, then apply approximately one microliter of sterile saline on the surface of the brain tissue. Use the stereotax to slowly lower the wire array into the craniotomy.Then apply approximately five microliters of warm liquid wax above the implantation site to protect the brain tissue. Apply cement around the wire array and cover the skull with cement. Apply one drop of flux to the pre soldered ground wire or the pre soldered wire connected to the ground screw, and fuse the wires using a soldering machine.Lastly, cover the entire ground wire with cement. Check the light output from the patch cord. If the transmission rate of the implanted fiber was 50%ensure that the light output at the tip of the patch cord is 20 milliwatts.Connect the head stage preamplifier to the implanted connector, and connect the fiber optic patch cord to the implanted hippocampal fiber for optogenetic stimulation. Record the baseline behavior for a duration appropriate for the parameters being measured. Open the software to control the stimulus generator.Click file, open, and select the protocol file of choice. Click download and start to initiate the light stimulation. Observe control of the theta rhythm by the light pulses.Hippocampal local field potential during spontaneous theta oscillations is seen here. Note the gamma envelopes, an indicator of physiological theta rhythm. Hippocampal local field potential at seven hertz during optogenetic entrainment is seen here.Blue stripes indicate the time windows of light application. Note the phase reset by the light pulse indicated here by an arrow. Hippocampal local field potential at 10 hertz reflects optogenetic entrainment.Note phase-locked gamma envelopes and the phase reversal between stratham orians and stratum radiatum is also maintained during entrainment. Once mastered, this technique can be done in four hours of experiment time, plus six weeks for viral expression. While attempting this procedure, it's essential to remember to ensure efficient viral transduction.Properly connect optic fiber implant to the patch cord, and obtain good quality of spontaneous local field potential theta oscillations.

optogenetic-entrainment-hippocampal-theta-oscillations-behaving

Research

JoVE Journal

Neuroscience

Isolation and Culture of Hippocampal Neurons from Prenatal Mice

Primary cultures of rat and murine hippocampal neurons are widely used to reveal cellular mechanisms in neurobiology. By isolating and growing individual neurons, researchers are able to analyze properties related to cellular trafficking, cellular structure and individual protein localization using a variety of biochemical techniques. Results from such experiments are critical for testing theories addressing the neural basis of memory and learning. However, unambiguous results from these forms of experiments are predicated on the ability to grow neuronal cultures with minimum contamination by other brain cell types. In this protocol, we use specific media designed for neuron growth and careful dissection of embryonic hippocampal tissue to optimize growth of healthy neurons while minimizing contaminating cell types (i.e. astrocytes). Embryonic mouse hippocampal tissue can be more difficult to isolate than similar rodent tissue due to the size of the sample for dissection. We show detailed dissection techniques of hippocampus from embryonic day 19 (E19) mouse pups. Once hippocampal tissue is isolated, gentle dissociation of neuronal cells is achieved with a dilute concentration of trypsin and mechanical disruption designed to separate cells from connective tissue while providing minimum damage to individual cells. A detailed description of how to prepare pipettes to be used in the disruption is included. Optimal plating densities are provided for immuno-fluorescence protocols to maximize successful cell culture. The protocol provides a fast (approximately 2 hr) and efficient technique for the culture of neuronal cells from mouse hippocampal tissue.

We provide a protocol for the culture of highly purified hippocampal neurons from prenatal mouse brains without the use of a feeder glial cell layer.

Primary cultures of rat and murine hippocampal neurons are widely used to reveal cellular mechanisms in neurobiology. By isolating and growing individual ...

Dual Electrophysiological Recordings of Synaptically-evoked Astroglial and Neuronal Responses in Acute Hippocampal Slices

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs through activation of their ion channels and neurotransmitter receptors, and process information in part through activity-dependent release of gliotransmitters. Furthermore, astrocytes constitute the main uptake system for glutamate, contribute to potassium spatial buffering, as well as to GABA clearance. These cells therefore constantly monitor synaptic activity, and are thereby sensitive indicators for alterations in synaptically-released glutamate, GABA and extracellular potassium levels. Additionally, alterations in astroglial uptake activity or buffering capacity can have severe effects on neuronal functions, and might be overlooked when characterizing physiopathological situations or knockout mice. Dual recording of neuronal and astroglial activities is therefore an important method to study alterations in synaptic strength associated to concomitant changes in astroglial uptake and buffering capacities. Here we describe how to prepare hippocampal slices, how to identify stratum radiatum astrocytes, and how to record simultaneously neuronal and astroglial electrophysiological responses. Furthermore, we describe how to isolate pharmacologically the synaptically-evoked astroglial currents.

The preparation of acute brain slices from isolated hippocampi, as well as the simultaneous electrophysiological recordings of astrocytes and neurons in stratum radiatum during stimulation of schaffer collaterals is described. The pharmacological isolation of astroglial potassium and glutamate transporter currents is demonstrated.

Astrocytes form together with neurons tripartite synapses, where they integrate and modulate neuronal activity. Indeed, astrocytes sense neuronal inputs ...

Optogenetic Stimulation of Escape Behavior in Drosophila melanogaster

A growing number of genetically encoded tools are becoming available that allow non-invasive manipulation of the neural activity of specific neurons in Drosophila melanogaster1. Chief among these are optogenetic tools, which enable the activation or silencing of specific neurons in the intact and freely moving animal using bright light. Channelrhodopsin (ChR2) is a light-activated cation channel that, when activated by blue light, causes depolarization of neurons that express it. ChR2 has been effective for identifying neurons critical for specific behaviors, such as CO2 avoidance, proboscis extension and giant-fiber mediated startle response2-4. However, as the intense light sources used to stimulate ChR2 also stimulate photoreceptors, these optogenetic techniques have not previously been used in the visual system. Here, we combine an optogenetic approach with a mutation that impairs phototransduction to demonstrate that activation of a cluster of loom-sensitive neurons in the fly's optic lobe, Foma-1 neurons, can drive an escape behavior used to avoid collision. We used a null allele of a critical component of the phototransduction cascade, phospholipase C-&beta;, encoded by the norpA gene, to render the flies blind and also use the Gal4-UAS transcriptional activator system to drive expression of ChR2 in the Foma-1 neurons. Individual flies are placed on a small platform surrounded by blue LEDs. When the LEDs are illuminated, the flies quickly take-off into flight, in a manner similar to visually driven loom-escape behavior. We believe that this technique can be easily adapted to examine other behaviors in freely moving flies.

Optogenetic Stimulation of Escape Behavior in Drosophila melanogaster

Genetically encoded optogenetic tools enable noninvasive manipulation of specific neurons in the Drosophila brain. Such tools can identify neurons whose activation is sufficient to elicit or suppress particular behaviors. Here we present a method for activating Channelrhodopsin2 that is expressed in targeted neurons in freely walking flies.

A  growing number of genetically encoded tools are becoming available that allow non-invasive  manipulation of the neural activity of specific neurons in ...

Assessment of Dendritic Arborization in the Dentate Gyrus of the Hippocampal Region in Mice

Dendritic arborization has been shown to be a reliable marker for examination of structural and functional integrity of neurons. Indeed, the complexity and extent of dendritic arborization correlates well with the synaptic plasticity in these cells. A reliable method for assessment of dendritic arborization is needed to characterize the deleterious effects of neurological disorders on these structures and to determine the effects of therapeutic interventions. However, quantification of these structures has proven to be a formidable task given their complex and dynamic nature. Fortunately, sophisticated imaging techniques can be paired with conventional staining methods to assess the state of dendritic arborization, providing a more reliable and expeditious means of assessment. Below is an example of how these imaging techniques were paired with staining methods to characterize the dendritic arborization in wild type mice. These complementary imaging methods can be used to qualitatively and quantitatively assess dendritic arborization that span a rather wide area within the hippocampal region.

We describe two methods for visualization and quantification of dendritic arborization in the hippocampus of mouse models: real-time and extended depth of field imaging. While the former method allows sophisticated topographical tracing and quantification of the extent of branching, the latter allows speedy visualization of the dendritic tree.

Dendritic arborization has been shown to be a reliable marker for examination of structural and functional integrity of neurons. Indeed, the complexity ...

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.

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.

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

Assessment of Hippocampal Dendritic Complexity in Aged Mice Using the Golgi-Cox Method

Dendritic spines are the protuberances from the neuronal dendritic shafts that contain&#160; excitatory synapses. The morphological and branching variations of the neuronal dendrites within the hippocampus are implicated in cognition and memory formation. There are several approaches to Golgi staining, all of which have been useful for determining the morphological characteristics of dendritic arbors and produce a clear background. The present Golgi-Cox method, (a slight variation of the protocol that is provided with a commercial Golgi staining kit), was designed to assess how a relatively low dose of the chemotherapeutic drug 5-flurouracil (5-Fu) would affect dendritic morphology, the number of spines, and the complexity of arborization within the hippocampus. The 5-Fu significantly modulated the dendritic complexity and decreased the spine density throughout the hippocampus in a region-specific manner. The data presented show that the Golgi staining method effectively stained the mature neurons in the CA1, the CA3, and the dentate gyrus (DG) of the hippocampus. This protocol reports the details for each step so that other researchers can reliably stain tissue throughout the brain with high quality results and minimal troubleshooting.

Here we present a Golgi-Cox protocol in extensive detail. This reliable tissue stain method allows for a high-quality assessment of the cytoarchitecture in the hippocampus, and throughout the entire brain, with minimal troubleshooting.

Dendritic spines are the protuberances from the neuronal dendritic shafts that contain&#160; excitatory synapses. The morphological and branching ...

Tuning in the Hippocampal Theta Band In Vitro: Methodologies for Recording from the Isolated Rodent Septohippocampal Circuit

This protocol outlines the procedures for preparing and recording from the isolated whole hippocampus, of WT and transgenic mice, along with recent improvements in methodologies and applications for the study of theta oscillations. A simple characterization of the isolated hippocampal preparation is presented whereby the relationship between internal hippocampal theta oscillators is examined together with the activity of pyramidal cells, and GABAergic interneurons, of the cornu ammonis-1 (CA1) and subiculum (SUB) areas. Overall, we show that the isolated hippocampus is capable of generating intrinsic theta oscillations in vitro and that rhythmicity generated within the hippocampus can be precisely manipulated by optogenetic stimulation of parvalbumin-positive (PV) interneurons. The in vitro isolated hippocampal preparation offers a unique opportunity to use simultaneous field and intracellular patch-clamp recordings from visually-identified neurons to better understand the mechanisms underlying theta rhythm generation.

Tuning in the Hippocampal Theta Band In Vitro: Methodologies for Recording from the Isolated Rodent Septohippocampal Circuit

Here, we present a protocol for recording rhythmic neuronal network theta and gamma oscillations from an isolated whole hippocampal preparation. We describe the experimental steps from extraction of the hippocampus to details of field, unitary and whole-cell patch clamp recordings as well as optogenetic pacing of the theta rhythm.

This protocol outlines the procedures for preparing and recording from the isolated whole hippocampus, of WT and transgenic mice, along with recent ...

Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans

It has become increasingly clear that neural circuit activity in behaving animals differs substantially from that seen in anesthetized or immobilized animals. Highly sensitive, genetically encoded fluorescent reporters of Ca2+ have revolutionized the recording of cell and synaptic activity using non-invasive optical approaches in behaving animals. When combined with genetic and optogenetic techniques, the molecular mechanisms that modulate cell and circuit activity during different behavior states can be identified.
Here we describe methods for ratiometric Ca2+ imaging of single neurons in freely behaving Caenorhabditis elegans worms. We demonstrate a simple mounting technique that gently overlays worms growing on a standard Nematode Growth Media (NGM) agar block with a glass coverslip, permitting animals to be recorded at high-resolution during unrestricted movement and behavior. With this technique, we use the sensitive Ca2+ reporter GCaMP5 to record changes in intracellular Ca2+ in the serotonergic Hermaphrodite Specific Neurons (HSNs) as they drive egg-laying behavior. By co-expressing mCherry, a Ca2+-insensitive fluorescent protein, we can track the position of the HSN within ~ 1 &#181;m and correct for fluctuations in fluorescence caused by changes in focus or movement. Simultaneous, infrared brightfield imaging allows for behavior recording and animal tracking using a motorized stage. By integrating these microscopic techniques and data streams, we can record Ca2+ activity in the C. elegans egg-laying circuit as it progresses between inactive and active behavior states over tens of minutes.

Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans

This protocol describes the use of genetically encoded Ca2+ reporters to record changes in neural activity in behaving Caenorhabditis elegans worms. &#8195;

It has become increasingly clear that neural circuit activity in behaving animals differs substantially from that seen in anesthetized or immobilized ...

Recording Spatially Restricted Oscillations in the Hippocampus of Behaving Mice

The local field potential (LFP) emerges from ion movements across neural membranes. Since the voltage recorded by LFP electrodes reflects the summed electrical field of a large volume of brain tissue, extracting information about local activity is challenging. Studying neuronal microcircuits, however, requires a reliable distinction between truly local events and volume-conducted signals originating in distant brain areas. Current source density (CSD) analysis offers a solution for this problem by providing information about current sinks and sources in the vicinity of the electrodes. In brain areas with laminar cytoarchitecture such as the hippocampus, one-dimensional CSD can be obtained by estimating the second spatial derivative of the LFP. Here, we describe a method to record multilaminar LFPs using linear silicon probes implanted into the dorsal hippocampus. CSD traces are computed along individual shanks of the probe. This protocol thus describes a procedure to resolve spatially restricted neuronal network oscillations in the hippocampus of freely moving mice.

This protocol describes the recording of local field potentials with multi-shank linear silicon probes. Conversion of the signals using current source density analysis allows the reconstruction of local electrical activity in the mouse hippocampus. With this technique, spatially restricted brain oscillations can be studied in freely moving mice.

The local field potential (LFP) emerges from ion movements across neural membranes. Since the voltage recorded by LFP electrodes reflects the summed ...

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 ...