We thank Colin Symons and James Wright for technical assistance. This work was supported by seed funding grant (WSU) to Y.B. and the innovation office at Western Sydney University. M.C. is supported by ARC fellowship (DECRA).

The protocol below describes the preparation of C57BL/6 and C3H/He (retinally degenerate) mouse neuronal tissue, but similar techniques can be applied to other species. All animals were healthy and handled with standard conditions of temperature, humidity, 12 h light/dark cycle, free access to food and water, and without any intended stress stimuli. All experiments were approved and performed in accordance with Western Sydney University Animal Care and Ethics committee and according to the animal use and care guidelines (Animal Research Authority #A9452, #A10396 and #A8967).
1. Brain Slice Preparation
<ol>
	<li>Anesthetize the animal by inhalation of isoflurane (5%) and decapitate using a rodent guillotine. Remove the brain quickly, as described previously9 and place it into ice-cold physiological solution (aCSF) containing (in mM): 125 NaCl, 2.5 KCl, 1 MgCl2, 1.25 NaH2PO4, 2 CaCl2, 25 NaHCO3, 25 dextrose, and saturated with carbogen (95% O2/5% CO2 mixture; 310 mOsm; pH 7.4).</li>
	<li>Cut brain slices, in the region of interest, 300 &#181;m thick with a vibrating microtome.</li>
	<li>Transfer slices to a custom built incubation system that closely monitors and controls pH levels (pH 7.2 - 7.4), carbogen flow, and temperature as previously described10,11.</li>
	<li>Set initial chamber temperature to 35 &#176;C for 15 - 30 min, and then slowly reduce to 15 - 16 &#176;C as shown in Figure 1C. Then incubate slices in the incubation system until needed, either for electrophysiology or imaging. 
	NOTE: If slices are to be used for calcium-imaging, follow steps below before cooling tissue below RT.</li>
</ol>
2. Retinal Wholemount Preparation and Inner Limiting Membrane Removal
<ol>
	<li>Prepare retinal wholemounts under either normal laboratory lighting conditions or dim red/infra-red light.</li>
	<li>Euthanize animal by cervical dislocation and immediately enucleate eyes. Make a small cut along the ora serrata, and place in either Ames media, or aCSF containing (mM): 125 NaCl, 25 NaHCO3, 3 KCl, 2 CaCl2, 1 MgCl2, 10 glucose, 0.5 L-glutamine, and saturate with carbogen (95% O2/5% CO2 mixture; ~300 mOsm; pH 7.4), at RT.</li>
	<li>Immediately remove the cornea, lens and vitreous by cutting along the ora serrata with small scissors and removing the lens and vitreous with forceps. Place tissue in the incubation system at RT. 
	NOTE: Retinal tissue can be maintained in the eye-cup, after slow temperature reduction to 15 - 16 &#176;C, for &#62;24 h in the incubation system until needed.</li>
	<li>To remove the ILM, transfer the eye-cup containing the retina to a small glass jar containing 30 U/mL papain, 1 mM L-cystine, 0.5 mM EDTA and 0.005% DNase in Earl&#39;s-Balanced&#160;Salt Solution (BSS) at 37 &#176;C for 20 min. Apply 95% O2/5% CO2 to the solution through the lid but do not bubble. If using tissue from young animals (&#60;6 weeks), dilute the solution to half-strength.
	<ol>
		<li>Stop enzymatic digestion, by placing the tissue in an ovomucoid (10 mg/mL) and BSA (10 mg/mL) solution for 10 min in Earl&#39;s BSS. Wash tissue thoroughly with aCSF before transfer to the incubation system and reduce temperature to 15 - 16 &#176;C.</li>
	</ol>
	</li>
	<li>Maintain retinal tissue in the eye-cup until needed. For transfer to the microscope, isolate the retina from the eye-cup and cut into 4 pieces with a razorblade. If the entire retina is required, make four small cuts in the periphery of the retina to allow it to lie flat. 
	NOTE: For imaging experiments, load with calcium-dyes before transfer to the incubation system, see below.</li>
</ol>
3. Maintaining Tissue in the Incubator
<ol>
	<li>Place tissue in the main chamber containing probes for pH and temperature measurements (Figure&#160;1A, B).</li>
	<li>Circulate aCSF through a second chamber (UVC chamber, built as previously described12) isolated from the main chamber and exposed to 1.1 W UVC light (254 nm, 5W/2P sterilizer UV lamp) in order to eradiate bacteria floating in the solution (Figure 1A). Control UVC light timing via a programmable timer using a random feature that turns ON at times varying between 15 and 26 min every 15 - 30 min to avoid excessive heating of the aCSF.</li>
	<li>Set the flow rate in the UVC chamber to 12 mL/min as previously reported12. Cover the UVC chamber with aluminum foil to prevent UVC illumination outside the chamber, which can damage neuronal tissue. 
	NOTE: For dark-adapted retinal tissue, apply a custom-made cover to the main chamber to exclude light.</li>
	<li>Use a peristaltic pump to circulate the solution (aCSF) through the two chambers and a Peltier thermoelectric cold plate cooler to either cool or heat the main chamber to the desired temperatures in the range of 0 - 50 &#176;C. For optimal tissue incubation, use 15 - 16 &#176;C for long-term viability.</li>
</ol>
4. Calcium Dye Loading
<ol>
	<li>Select calcium dyes based on the preference of the individual researcher. Here we use Fura-2AM, Fluo-8AM or Fluo-4AM. However, this method can be applied to other dyes as well: dissolve calcium dyes in DMSO to a 1 mM solution and 1% block copolymers (e.g., pluronic acid-127) to a final volume of 50 &#181;L and sonicate for 10 min.</li>
	<li>Add solution to aCSF to a final concentration of 10 &#181;M, 0.01% block copolymers for brain slices, and 20 &#181;M (retina), 0.02% block copolymers for the retina. In retinae (papain treated) and brain slices from young animals, load to the bath for 45 min at 37 &#176;C (Fura-2 AM) or at RT (Fluo-4 AM; Fluo-8 AM).
	<ol>
		<li>For adult animals, (&#62;12 weeks) pipette the dyes (50 &#181;L) directly onto the brain slices, and maintain for 75 min to allow better penetration of the dye into the deep layers.</li>
		<li>To ensure adequate oxygenation of the submerged slice during dye incubation, prepare a glass loading chamber with a closed lid (circular jar of diameter 2.5 cm, 3.5 cm height) with calcium dyes diluted in 2.5 mL of aCSF. Oxygenate continuously with 95% O2/5% CO2. Do not bubble.</li>
	</ol>
	</li>
	<li>Following dye loading, wash the tissue with aCSF and transfer to the incubation system, slowly reduce the temperature to 15 - 16 &#176;C until experimental use.</li>
</ol>
5. Electrophysiological Recordings and Imaging
<ol>
	<li>Place tissue in a submerged recording chamber under a microscope, and perfuse with oxygenated aCSF at a flow rate of 4 - 5 mL/min either at RT (~22 &#176;C) or physiological temperature (~35 &#176;C). Hold the tissue in place by using a custom made &#39;&#39;harp&#39;&#39;, made of nylon or gold threads stretched and glued across a U-shaped piece of gold or platinum wire.</li>
	<li>For electrophysiology:
	<ol>
		<li>Prepare recording pipettes from 1.5 mm (1.19 mm ID) borosilicate glass using a micropipette puller to achieve a final resistance of 5-6 M&#937;.</li>
		<li>Fill the pipette with 3 - 4 &#181;L of internal solution as previously described13 and visualize cells under infrared Differential Interference Contrast (IR-DIC) using a CCD camera. The intracellular solution should be carefully tailored to each experiment to achieve experimental outcomes.</li>
		<li>Position pipette, while maintaining positive pressure applied through a suction port on the pipette holder, on the membrane of a cell using a micromanipulator. Since the ILM has been removed from the retina, no prior membrane scraping is required. Once the pipette is on the cell, apply gentle negative pressure to the pipette to achieve a gigaohm seal. Then rupture the cell membrane with a brief amount of negative pressure.</li>
		<li>Make whole-cell current- or voltage-clamp recordings using standard techniques as appropriate.</li>
	</ol>
	</li>
	<li>Calcium-imaging:
	<ol>
		<li>For ratiometric imaging of Fura-2, use an ultra-high speed wavelength switcher to provide excitation wavelengths of 340 nm and 380 nm. Pass emitted light from individual cells through an emission filter of 510 &#177;20 nm, and capture with a high sensitivity, high-speed digital camera.</li>
		<li>For a single excitation wavelength of Fluo-4, filter excitation light through a 460 - 490 nm band pass filter and emitted light through a 515 - 550 nm band pass filter. For the fastest and most sensitive recording use a high speed digital camera such. Acquire images as required.</li>
		<li>Measure alterations in fluorescence as a function of time either at a single wavelength (Fluo-4) or using the wavelength ratio method (Fura-2), as previously described8,14.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Colbert, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+cortical+brain+slices+for+electrophysiological+recording.">Preparation of cortical brain slices for electrophysiological recording.</a> Meth mol biol. 337, 117-125 (2006).</li><li>Gibb, A., Edwards, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patch+clamp+recording+from+cells+in+sliced+tissues.">Patch clamp recording from cells in sliced tissues.</a> Microelect Techniq. , 255-274 (1994).</li><li>Kantevari, S., Buskila, Y., Ellis-Davies, G. C. 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C., Perez De Sevilla Muller, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunohistochemical+and+Calcium+Imaging+Methods+in+Wholemount+Rat+Retina.">Immunohistochemical and Calcium Imaging Methods in Wholemount Rat Retina.</a> J Vis Exp. (92), e51396 (2014).</li><li>Kulkarni, M., 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=Imaging+Ca2++dynamics+in+cone+photoreceptor+axon+terminals+of+the+mouse+retina.">Imaging Ca2+ dynamics in cone photoreceptor axon terminals of the mouse retina.</a> J Vis Exp. (99), e52588 (2015).</li><li>Velte, T. J., Masland, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Action+potentials+in+the+dendrites+of+retinal+ganglion+cells.">Action potentials in the dendrites of retinal ganglion cells.</a> J neurophysiol. 81 (3), 1412-1417 (1999).</li><li>Cameron, M., 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=Calcium+imaging+of+AM+dyes+following+prolonged+incubation+in+acute+neuronal+tissue.">Calcium imaging of AM dyes following prolonged incubation in acute neuronal tissue.</a> PLoS ONE. 11 (5), (2016).</li><li>Buskila, Y., Morley, J. 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Yossi Buskila and Paul Breen declare that they are co-owners of PAYO Scientific Pty Ltd, a company specialized in building incubation systems for acute neural tissue. All other authors report no financial interests or potential conflicts of interest related to the current study.

This article describes an incubation method to extend the viability of acute neuronal tissue for imaging and electrophysiological experiments, thereby reducing the animal numbers needed to complete experimental goals. Two main processes govern the deterioration of neuronal tissue over time: i) increased bacteria levels, and the accompanying increase in bacterial endotoxin released, and ii) excitotoxicity which follows the traumatic slicing procedure10. As acute neuronal tissue is environmentally d...

Electrophysiology and functional imaging (calcium, voltage sensitive dyes) are two of the most commonly used experimental techniques in neuroscience. Brain slice preparations and retinal wholemount, which will be examined here, provide a means of examining electrophysiological properties and synaptic connectivity without contamination from anesthetics or muscle relaxants. Brain slices and retinal wholemount maintain their structural integrity, unlike cultures or cell homogenates, allowing the study of specific circuits and brain networks1. Recordings from isolated tissue have advantages over in vivo recordings as movements associated with the heartbeat and respiration are eliminated. Moreover, direct visualization allows specific classes of cells to be targeted, and local application of pharmacological tools 2,3.
Patch-clamp recordings and calcium dye-loading in retinal wholemount is complicated by the existence of the Inner Limiting Membrane (ILM), which covers the Retinal Ganglion Cell (RGC) layer and prevents direct access to the cells. Typically, this membrane is scraped away with a glass pipette to allow direct application of a patch pipette and formation of a gigaohm seal on a single cell. In addition, bath-applied calcium&#160;dyes do not cross the ILM and must either be injected beneath this membrane4, retrogradely transported following injection at the optic nerve5 or electroporated through the tissue6. Furthermore, when utilizing a rodent model of retinitis pigmentosa, the rd/rd mouse, the ILM is thicker and more impenetrable. Here, we use a technique to remove the ILM with enzymatic digestion7, to allow both ubiquitous calcium&#160;dye-loading, and direct access to retinal ganglion cells for patch-clamp recordings8.
Successful recordings from either brain slices or retinal wholemount depend on dissection and incubation of viable neuronal tissue. Typically, tissue is extracted on the morning of the experiment and incubated in artificial cerebrospinal fluid (aCSF) until it is used for recordings. Usually, tissue remains viable for 6 - 8 h, with significant degradation following this time window. However, both brain slices and wholemount retinae preparations usually produce more tissue than can be recorded from within this short time period. Consequently, tissue is often discarded at the end of the day and the dissection is completed again on subsequent days. This means another animal is utilized and ~2 h of setup and dissection/staining repeated. The following protocol describes a method for extending the life of neuronal tissue for more than 24 h, meaning fewer animals are utilized, and more experimental time is available. Tissue viability was assessed through recording electrophysiological properties and calcium dynamics, and these properties were indistinguishable between &#60;4 h and &#62;24 h postdissection.
These results indicate that not only are single cell properties intact and functional after prolonged incubation, but network activity, as assessed by calcium-imaging and electrophysiological recordings, is unchanged &#62;24 h postdissection. Moreover, we show that calcium dyes can remain in cells for prolonged periods without causing any detrimental effects. Application of this protocol demonstrates that the functional activity of neurons in acute neuronal tissue can be maintained for long periods, once the external environment is highly regulated. Moreover, as tissue viability varies greatly between laboratories due to different incubation protocols, this method establishes a gold standard for the ideal parameters that should be applied to reduce variability in the health of acute neuronal tissue.

<table border="0" cellpadding="0" cellspacing="0" width="831">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Sodium Chloride</td>
			<td style="width:159px;">Sigma Aldrich VETEC</td>
			<td style="width:135px;">V800372</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Potassium chloride</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">P9333</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:315px;">N-Methyl-D-glucamine</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">M2004&#160;</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">D-glucose</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">G5767</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Sodium bicarbonate</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">S6014</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Sodium phosphate monobasic</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">S2554</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;width:315px;">Magnesium chloride</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">M9272&#160;</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="31">
			<td height="31" style="height:31px;width:315px;">Calcium chloride&#160;</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">223506</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Papain Dissociation System</td>
			<td style="width:159px;">Worthington&#160;</td>
			<td style="width:135px;">LK003150</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Dimethyl sulfoxide anhydrous</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:135px;">276855</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:315px;">Pluronic F-127 Low UV absorbance*</td>
			<td style="width:159px;">Life technologies</td>
			<td style="width:135px;">P-6867</td>
			<td style="width:225px;">20% solution in DMSO&#160;</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:315px;"></td>
			<td style="width:159px;"></td>
			<td style="width:135px;"></td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Fura-2 AM&#160;&#160;</td>
			<td style="width:159px;">Anaspec</td>
			<td style="width:135px;">84017</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Fluo-4 AM&#160;&#160;</td>
			<td style="width:159px;">Life Technologies</td>
			<td style="width:135px;">F23917</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Fluo-8 AM</td>
			<td style="width:159px;">Abcam</td>
			<td style="width:135px;">Ab142773</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="60">
			<td height="60" style="height:60px;width:315px;">Vibrating blade microtome&#160;</td>
			<td style="width:159px;">Leica Biosystem</td>
			<td style="width:135px;">VT1200 S</td>
			<td style="width:225px;">Equiped with Leica&#8217;s Vibrocheck&#8482; measurement device&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Antivibration table</td>
			<td style="width:159px;">Kinetic Systems Vibraplane&#160;</td>
			<td style="width:135px;">Vibraplane 9100/9200&#160;</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Fixed Stage Upright Microscope</td>
			<td style="width:159px;">Olympus</td>
			<td style="width:135px;">BX51WI&#160;</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Microscope Objective</td>
			<td style="width:159px;">Olympus</td>
			<td style="width:135px;">XLUMPlanFLN 20x/1.00w</td>
			<td style="width:225px;">20X&#160;</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Microscope Objective</td>
			<td style="width:159px;">Olympus</td>
			<td style="width:135px;">LUMPlanFLN 60x/1.00w</td>
			<td style="width:225px;">60X</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">CCD Camera</td>
			<td style="width:159px;">Andor</td>
			<td style="width:135px;">Ixon +</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">High speed wavelength switcher</td>
			<td style="width:159px;">Sutter instrument</td>
			<td style="width:135px;">Lambda DG-4&#160;</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Patch clamp amplifier</td>
			<td style="width:159px;">Molecular Devices</td>
			<td style="width:135px;">MultiClamp 700B</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Data acquisition system</td>
			<td style="width:159px;">Molecular Devices</td>
			<td style="width:135px;">Digidata 1440A</td>
			<td style="width:225px;">Axon Digidata&#174; System</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Borosilicate glass capillaries</td>
			<td style="width:159px;">Sutter Instrument Co</td>
			<td style="width:135px;">BF150-86-10</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Microelectrode puller</td>
			<td style="width:159px;">Sutter Instrument Co</td>
			<td style="width:135px;">P-97</td>
			<td style="width:225px;">Flaming/Brown type micropipette puller</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:315px;">Recording/perfusion chamber</td>
			<td style="width:159px;">Warner Instruments</td>
			<td style="width:135px;">RC-40LP</td>
			<td style="width:225px;">Low Profile Open Bath Chambers</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Software</td>
			<td style="width:159px;">Molecular Devices</td>
			<td style="width:135px;">pClamp 10.2</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Andor iQ Live Cell Imaging Software</td>
			<td style="width:159px;">Andor</td>
			<td style="width:135px;">Andor iQ3</td>
			<td style="width:225px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:315px;">Braincubator</td>
			<td style="width:159px;">Payo Scientific</td>
			<td style="width:135px;">BR26021976</td>
			<td style="width:225px;">www.braincubator.com.au</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Peltier-Thermoelectric Cold Plate Cooler</td>
			<td>TE Technology</td>
			<td>CP-121</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Temperature Controller</td>
			<td>TE Technology</td>
			<td>TC-36-25 RS232</td>
			<td></td>
		</tr>
	</tbody>
</table>

prolonged incubation of acute neuronal tissue for electrophysiology and calcium-imaging

Acute neuronal tissue preparations, brain slices and retinal wholemount, can usually only be maintained for 6 - 8 h following dissection. This limits the experimental time, and increases the number of animals that are utilized per study. This limitation specifically impacts protocols such as calcium imaging that require prolonged pre-incubation with bath-applied dyes. Exponential bacterial growth within 3 - 4 h after slicing is tightly correlated with a decrease in tissue health. This study describes a method for&#160;limiting the proliferation of bacteria in acute preparations to maintain viable neuronal tissue for prolonged periods of time (&#62;24 h) without the need for antibiotics, sterile procedures, or tissue culture media containing growth factors. By cycling the extracellular fluid through UV irradiation and keeping the tissue in a custom holding chamber at 15 - 16 &#176;C, the tissue shows no difference in electrophysiological properties, or calcium signaling through intracellular calcium dyes at &#62;24 h postdissection. These methods will not only extend experimental time for those using acute neuronal tissue, but will reduce the number of animals required to complete experimental goals, and will set a gold standard for acute neuronal tissue incubation.

Tight regulation of the bacterial load and temperature of the aCSF during incubation is essential to maintain neuronal tissue viability. This can be optimized through irradiation with UVC light and maintaining the temperature of the aCSF at 15 - 16 &#176;C (Figure 1). Furthermore, the aCSF parameters stamp (APS; Figure 1C) provides the experimenter with a record of the environmental conditions (pH and temp.), thus offering a gold standard for parameters w...

Watch this Scientific Journal Video about Prolonged Incubation of Acute Neuronal Tissue for Electrophysiology and Calcium-imaging at JoVE.com

Prolonged Incubation of Acute Neuronal Tissue for Electrophysiology and Calcium-imaging

Once removed from the body, neuronal tissue is greatly affected by environmental conditions, leading to eventual degradation of the tissue after 6 - 8 h. Using a unique incubation method, which closely monitors and regulates the extracellular environment of the tissue, tissue viability can be significantly extended for &#62;24 h.

Acute neuronal tissue preparations, brain slices and retinal wholemount, can usually only be maintained for 6 - 8 h following dissection. This limits the ...

prolonged-incubation-acute-neuronal-tissue-for-electrophysiology

Research

JoVE Journal

Neuroscience

11.8K Views.  Western Sydney University. Once removed from the body, neuronal tissue is greatly affected by environmental conditions, leading to eventual degradation of the tissue after 6 - 8 h. Using a unique incubation method, which closely monitors and regulates the extracellular environment of the tissue, tissue viability can be significantly extended for >24 h.

Video: Prolonged Incubation of Acute Neuronal Tissue for Electrophysiology and Calcium-imaging

Cryopreservation of Cortical Tissue Blocks for the Generation of Highly Enriched Neuronal Cultures

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. For this protocol the freezing medium used is 10% dimethyl sulfoxide (DMSO) diluted in Hank's Buffered Salt Solution (HBSS). Blocks of cortical tissue are transferred to cryovials containing the freezing medium and slowly frozen at -1&deg;C/min in a rate-controlled freezing container. Post-thaw processing and dissociation of frozen tissue blocks consistently produced neuronal-enriched cultures which exhibited rapid neuritic growth during the first 5 days in culture and significant expansion of the neuronal network within 10 days. Immunocytochemical staining with the astrocytic marker glial fibrillary acidic protein (GFAP) and the neuronal marker beta-tubulin class III, revealed high numbers of neurons and astrocytes in the cultures. Generation of neural precursor cell cultures after tissue block dissociation resulted in rapidly expanding neurospheres, which produced large numbers of neurons and astrocytes under differentiating conditions. This simple cryopreservation protocol allows for the rapid, efficient, and inexpensive preservation of cortical brain tissue blocks, which grants increased flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

Here, we describe a method for efficient cryopreservation and thawing of cortical brain tissue blocks to generate highly enriched neuronal cultures. This simple protocol provides flexibility for later generation of neuronal, astrocyte, and neuronal precursor cell cultures.

In this study, we outline a standardized protocol for the successful cryopreservation and thawing of cortical brain tissue blocks to generate highly ...

Preparation of Acute Subventricular Zone Slices for Calcium Imaging

The subventricular zone (SVZ) is one of the two neurogenic zones in the postnatal brain. The SVZ contains densely packed cells, including neural progenitor cells with astrocytic features (called SVZ astrocytes), neuroblasts, and intermediate progenitor cells. Neuroblasts born in the SVZ tangentially migrate a great distance to the olfactory bulb, where they differentiate into interneurons. Intercellular signaling through adhesion molecules and diffusible signals play important roles in controlling neurogenesis. Many of these signals trigger intercellular calcium activity that transmits information inside and between cells. Calcium activity is thus reflective of the activity of extracellular signals and is an optimal way to understand functional intercellular signaling among SVZ cells.
Calcium activity has been studied in many other regions and cell types, including mature astrocytes and neurons. However, the traditional method to load cells with calcium indicator dye (i.e. bath loading) was not efficient at loading all SVZ cell types. Indeed, the cellular density in the SVZ precludes dye diffusion inside the tissue. In addition, preparing sagittal slices will better preserve the three-dimensional arrangement of SVZ cells, particularly the stream of neuroblast migration on the rostral-caudal axis.
Here, we describe methods to prepare sagittal sections containing the SVZ, the loading of SVZ cells with calcium indicator dye, and the acquisition of calcium activity with time-lapse movies. We used Fluo-4 AM dye for loading SVZ astrocytes using pressure application inside the tissue. Calcium activity was recorded using a scanning confocal microscope allowing a precise resolution for distinguishing individual cells. Our approach is applicable to other neurogenic zones including the adult hippocampal subgranular zone and embryonic neurogenic zones. In addition, other types of dyes can be applied using the described method.

A method to load subventricular zone (SVZ) cells with calcium indicator dyes for recording calcium activity is described. The postnatal SVZ contains tightly packed cells including neural progenitor cells and neuroblasts. Rather than using bath loading we injected the dye by pressure inside the tissue allowing better dye diffusion.

The subventricular zone (SVZ) is one of the two neurogenic zones in the postnatal brain. The SVZ contains densely packed cells, including neural ...

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 ...

In vivo Neuronal Calcium Imaging in C. elegans

The nematode worm C. elegans is an ideal model organism for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, well-characterized nervous system allows identification and fluorescence imaging of any neuron within the intact animal. Simple immobilization techniques with minimal impact on the animal's physiology allow extended time-lapse imaging. The development of genetically-encoded calcium sensitive fluorophores such as cameleon 1 and GCaMP 2 allow in vivo imaging of neuronal calcium relating both cell physiology and neuronal activity. Numerous transgenic strains expressing these fluorophores in specific neurons are readily available or can be constructed using well-established techniques. Here, we describe detailed procedures for measuring calcium dynamics within a single neuron in vivo using both GCaMP and cameleon. We discuss advantages and disadvantages of both as well as various methods of sample preparation (animal immobilization) and image analysis. Finally, we present results from two experiments: 1) Using GCaMP to measure the sensory response of a specific neuron to an external electrical field and 2) Using cameleon to measure the physiological calcium response of a neuron to traumatic laser damage. Calcium imaging techniques such as these are used extensively in C. elegans and have been extended to measurements in freely moving animals, multiple neurons simultaneously and comparison across genetic backgrounds. C. elegans presents a robust and flexible system for in vivo neuronal imaging with advantages over other model systems in technical simplicity and cost.

In vivo Neuronal Calcium Imaging in C. elegans

With its small transparent body, well-documented neuroanatomy and a host of amenable genetic techniques and reagents, C. elegans makes an ideal model organism for in vivo neuronal imaging using relatively simple, low-cost techniques. Here we describe single neuron imaging within intact adult animals using genetically encoded fluorescent calcium indicators.

The nematode worm C. elegans is an ideal model organism  for relatively simple, low cost neuronal imaging in vivo. Its small transparent body and simple, ...

Simultaneous Electrophysiological Recording and Calcium Imaging of Suprachiasmatic Nucleus Neurons

Simultaneous electrophysiological and fluorescent imaging recording methods were used to study the role of changes of membrane potential or current in regulating the intracellular calcium concentration. Changing environmental conditions, such as the light-dark cycle, can modify neuronal and neural network activity and the expression of a family of circadian clock genes within the suprachiasmatic nucleus (SCN), the location of the master circadian clock in the mammalian brain. Excitatory synaptic transmission leads to an increase in the postsynaptic Ca2+ concentration that is believed to activate the signaling pathways that shifts the rhythmic expression of circadian clock genes. Hypothalamic slices containing the SCN were patch clamped using microelectrodes filled with an internal solution containing the calcium indicator bis-fura-2. After a seal was formed between the microelectrode and the SCN neuronal membrane, the membrane was ruptured using gentle suction and the calcium probe diffused into the neuron filling both the soma and dendrites. Quantitative ratiometric measurements of the intracellular calcium concentration were recorded simultaneously with membrane potential or current. Using these methods it is possible to study the role of changes of the intracellular calcium concentration produced by synaptic activity and action potential firing of individual neurons. In this presentation we demonstrate the methods to simultaneously record electrophysiological activity along with intracellular calcium from individual SCN neurons maintained in brain slices.

Procedures are described to perform simultaneous recordings of membrane potential or current and changes of intracellular calcium concentration. Suprachiasmatic nucleus neurons are filled with the calcium indicator bis-fura-2 using a patch clamp electrode in the whole cell patch clamp configuration.

Simultaneous electrophysiological and fluorescent imaging recording methods were used to study the role of changes of membrane potential or current in ...

Real-time Electrophysiology: Using Closed-loop Protocols to Probe Neuronal Dynamics and Beyond

Experimental neuroscience is witnessing an increased interest in the development and application of novel and often complex, closed-loop protocols, where the stimulus applied depends in real-time on the response of the system. Recent applications range from the implementation of virtual reality systems for studying motor responses both in mice1 and in zebrafish2, to control of seizures following cortical stroke using optogenetics3. A key advantage of closed-loop techniques resides in the capability of probing higher dimensional properties that are not directly accessible or that depend on multiple variables, such as neuronal excitability4 and reliability, while at the same time maximizing the experimental throughput. In this contribution and in the context of cellular electrophysiology, we describe how to apply a variety of closed-loop protocols to the study of the response properties of pyramidal cortical neurons, recorded intracellularly with the patch clamp technique in acute brain slices from the somatosensory cortex of juvenile rats. As no commercially available or open source software provides all the features required for efficiently performing the experiments described here, a new software toolbox called LCG5 was developed, whose modular structure maximizes reuse of computer code and facilitates the implementation of novel experimental paradigms. Stimulation waveforms are specified using a compact meta-description and full experimental protocols are described in text-based configuration files. Additionally, LCG has a command-line interface that is suited for repetition of trials and automation of experimental protocols.

Closed-loop protocols are becoming increasingly widespread in modern day electrophysiology. We present a simple, versatile and inexpensive way to perform complex electrophysiological protocols in cortical pyramidal neurons in vitro, using a desktop computer and a digital acquisition board.

Experimental neuroscience is witnessing an increased interest in the development and application of novel and often complex, closed-loop protocols, where ...

Two-photon Calcium Imaging in Neuronal Dendrites in Brain Slices

Calcium (Ca2+) imaging is a powerful tool to investigate the spatiotemporal dynamics of intracellular Ca2+ signals in neuronal dendrites. Ca2+ fluctuations can occur through a variety of membrane and intracellular mechanisms and play a crucial role in the induction of synaptic plasticity and regulation of dendritic excitability. Hence, the ability to record different types of Ca2+ signals in dendritic branches is valuable for groups studying how dendrites integrate information. The advent of two-photon microscopy has made such studies significantly easier by solving the problems inherent to imaging in live tissue, such as light scattering and photodamage. Moreover, through combination of conventional electrophysiological techniques with two-photon Ca2+ imaging, it is possible to investigate local Ca2+ fluctuations in neuronal dendrites in parallel with recordings of synaptic activity in soma. Here, we describe how to use this method to study the dynamics of local Ca2+ transients (CaTs) in dendrites of GABAergic inhibitory interneurons. The method can be also applied to studying dendritic Ca2+ signaling in different neuronal types in acute brain slices.

We present a method combining whole-cell patch-clamp recordings and two-photon imaging to record Ca2+ transients in neuronal dendrites in acute brain slices.

Calcium (Ca2+) imaging is a powerful tool to investigate the spatiotemporal dynamics of intracellular Ca2+ signals in neuronal dendrites. Ca2+ ...

Ablation of a Neuronal Population Using a Two-photon Laser and Its Assessment Using Calcium Imaging and Behavioral Recording in Zebrafish Larvae

To identify the role of a subpopulation of neurons in behavior, it is essential to test the consequences of blocking its activity in living animals. Laser ablation of neurons is an effective method for this purpose when neurons are selectively labeled with fluorescent probes. In the present study, protocols for laser ablating a subpopulation of neurons using a two-photon microscope and testing of its functional and behavioral consequences are described. In this study, prey capture behavior in zebrafish larvae is used as a study model. The pretecto-hypothalamic circuit is known to underlie this visually-driven prey catching behavior. Zebrafish pretectum were laser-ablated, and neuronal activity in the inferior lobe of the hypothalamus (ILH; the target of the pretectal projection) was examined. Prey capture behavior after pretectal ablation was also tested.

Here, we present a protocol to ablate a genetically labeled subpopulation of neurons by a two-photon laser from Zebrafish larvae.

To identify the role of a subpopulation of neurons in behavior, it is essential to test the consequences of blocking its activity in living animals. Laser ...

Microinjectrode System for Combined Drug Infusion and Electrophysiology

This microinjectrode system is designed for drug infusion, electrophysiology, and delivery and retrieval of experimental probes, such as microelectrodes and nanosensors, optimized for repeated use in awake, behaving animals. The microinjectrode system can be configured for multiple purposes: (1) simple arrangement of the cannula for placement of an experimental probe that would otherwise be too fragile to penetrate the dura mater, (2) microfluidic infusion of a drug, either independently or coupled to a cannula containing an experimental probe (i.e., microelectrode, nanosensor). In this protocol we explain the step by step construction of the microinjectrode, its coupling to microfluidic components, and the protocol for use of the system in vivo. The microfluidic components of this system allow for delivery of volumes on the nanoliter scale, with minimal penetration damage. Drug infusion can be performed independently or simultaneously with experimental probes such as microelectrodes or nanosensors in an awake, behaving animal. Applications of this system range from measuring the effects of a drug on cortical electrical activity and behavior, to understanding the function of a specific region of cortex in the context of behavioral performance based on probe or nanosensor measurements. To demonstrate some of the capabilities of this system, we present an example of muscimol infusion for reversible inactivation of the frontal eye field (FEF) in rhesus macaque during a working memory task.

We present a microinjectrode system designed for electrophysiology and assisted delivery of experimental probes (i.e., nanosensors, microelectrodes), with optional drug infusion. Widely available microfluidic components are coupled to a cannula containing the probe. A step-by-step protocol for microinjectrode construction is included, with results during muscimol infusion in macaque cortex.

This microinjectrode system is designed for drug infusion, electrophysiology, and delivery and retrieval of experimental probes, such as microelectrodes ...

Culture of Brain Capillary Pericytes for Cytosolic Calcium Measurements and Calcium Imaging Studies

Pericytes are associated with endothelial cells and astrocytic endfeet in a structure known as the neurovascular unit (NVU). Brain capillary pericyte function is not fully known. Pericytes have been suggested to be involved in capillary development, regulation of endothelial barrier tightness and trancytosis activity, regulation of capillary tone and to play crucial roles in certain brain pathologies.
Pericytes are challenging to investigate in the intact brain due to the difficulties in visualizing processes in the brain parenchyma, as well as the close proximity to the other cells of the NVU. The present protocol describes a method for isolation and culture of primary bovine brain capillary pericytes and their following usage in calcium imaging studies, where effects of agonists involved in brain signaling and pathologies can be investigated. Cortical capillary fragments are allowed to attach to the bottom of culture flasks and, after 6 days, endothelial cells and pericytes have grown out from the capillary fragments. The endothelial cells are removed by gentle trypsinization and pericytes are cultured for 5 additional days before passaging.
Isolated pericytes are seeded in 96-well culture plates and loaded with the calcium indicator dye (Fura-2 acetoxymethyl (AM)) to allow for measurements of intracellular calcium levels in a plate reader setup. Alternatively, pericytes are seeded on coverslips and mounted in cell chambers. Following loading with the calcium indicator (Cal-520 AM), calcium live-imaging can be performed using confocal microscopy at an excitation wavelength of 488 nm and emission wavelength of 510-520 nm.
The method described here has been used to obtain the first intracellular calcium measurements from primary brain capillary pericytes, demonstrating that pericytes are stimulated via ATP and are able to contract in vitro.

Brain capillary pericytes are essential players in the regulation of blood-brain barrier properties and blood flow. This protocol describes how brain capillary pericytes can be isolated, cultured, characterized with respect to cell type and applied for investigations of intracellular calcium signaling with fluorescent probes.

Pericytes are associated with endothelial cells and astrocytic endfeet in a structure known as the neurovascular unit (NVU). Brain capillary pericyte ...