This work is funded by the Canadian Institutes of Health Research, Grant/Award Number: 14392.

<ol>
	<li>Condamine, S., Lavoie, R., Verdier, D., Kolta, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+rhythmogenic+domains+defined+by+astrocytic+networks+in+the+trigeminal+main+sensory+nucleus.">Functional rhythmogenic domains defined by astrocytic networks in the trigeminal main sensory nucleus.</a> Glia. 66 (2), 311-326 (2018).</li><li>Verkhratsky, A., Orkand, R. K., Kettenmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glial+calcium:+homeostasis+and+signaling+function.">Glial calcium: homeostasis and signaling function.</a> Physiological Review. 78 (1), 99-141 (1998).</li><li>Christensen, R. K., Petersen, A. V., Perrier, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+do+glial+cells+contribute+to+motor+control?.">How do glial cells contribute to motor control?.</a> Current Pharmaceutical Design. 19 (24), 4385-4399 (2013).</li><li>Verkhratsky, A., Steinhauser, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+channels+in+glial+cells.">Ion channels in glial cells.</a> Brain Research Review. 32 (2-3), 380-412 (2000).</li><li>Harada, K., Kamiya, T., Tsuboi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gliotransmitter+Release+from+Astrocytes:+Functional,+Developmental,+and+Pathological+Implications+in+the+Brain.">Gliotransmitter Release from Astrocytes: Functional, Developmental, and Pathological Implications in the Brain.</a> Frontiers Neuroscience. 9, 499 (2015).</li><li>Montero, T. D., Orellana, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemichannels:+new+pathways+for+gliotransmitter+release.">Hemichannels: new pathways for gliotransmitter release.</a> Neuroscience. 286, 45-59 (2015).</li><li>Araque, 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=Gliotransmitters+travel+in+time+and+space.">Gliotransmitters travel in time and space.</a> Neuron. 81 (4), 728-739 (2014).</li><li>Augustin, V., 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=Functional+anisotropic+panglial+networks+in+the+lateral+superior+olive.">Functional anisotropic panglial networks in the lateral superior olive.</a> Glia. 64 (11), 1892-1911 (2016).</li><li>Houades, V., Koulakoff, A., Ezan, P., Seif, I., Giaume, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gap+junction-mediated+astrocytic+networks+in+the+mouse+barrel+cortex.">Gap junction-mediated astrocytic networks in the mouse barrel cortex.</a> Journal of Neuroscience. 28 (20), 5207-5217 (2008).</li><li>Roux, L., Benchenane, K., Rothstein, J. D., Bonvento, G., Giaume, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasticity+of+astroglial+networks+in+olfactory+glomeruli.">Plasticity of astroglial networks in olfactory glomeruli.</a> Proceedings of the National Academy of Science of the United State of America. 108 (45), 18442-18446 (2011).</li><li>Morquette, P., 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=An+astrocyte-dependent+mechanism+for+neuronal+rhythmogenesis.">An astrocyte-dependent mechanism for neuronal rhythmogenesis.</a> Nature Neuroscience. 18 (6), 844-854 (2015).</li><li>Brocard, F., Verdier, D., Arsenault, I., Lund, J. P., Kolta, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emergence+of+intrinsic+bursting+in+trigeminal+sensory+neurons+parallels+the+acquisition+of+mastication+in+weanling+rats.">Emergence of intrinsic bursting in trigeminal sensory neurons parallels the acquisition of mastication in weanling rats.</a> Journal of Neurophysiology. 96 (5), 2410-2424 (2006).</li><li>Anders, S., 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=Spatial+properties+of+astrocyte+gap+junction+coupling+in+the+rat+hippocampus.">Spatial properties of astrocyte gap junction coupling in the rat hippocampus.</a> Philosophical Transactions of the Royal Society of London. Series B, Biological Science. 369 (1654), (2014).</li><li>Houades, V., 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=Shapes+of+astrocyte+networks+in+the+juvenile+brain.">Shapes of astrocyte networks in the juvenile brain.</a> Neuron Glia Biology. 2 (1), 3-14 (2006).</li><li>Rouach, N., Koulakoff, A., Abudara, V., Willecke, K., Giaume, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Astroglial+metabolic+networks+sustain+hippocampal+synaptic+transmission.">Astroglial metabolic networks sustain hippocampal synaptic transmission.</a> Science. 322 (5907), 1551-1555 (2008).</li><li>Claus, L., 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=Barreloid+Borders+and+Neuronal+Activity+Shape+Panglial+Gap+Junction-Coupled+Networks+in+the+Mouse+Thalamus.">Barreloid Borders and Neuronal Activity Shape Panglial Gap Junction-Coupled Networks in the Mouse Thalamus.</a> Cerebral Cortex. 28 (1), 213-222 (2018).</li><li>Cameron, M. 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=Prolonged+Incubation+of+Acute+Neuronal+Tissue+for+Electrophysiology+and+Calcium-imaging.">Prolonged Incubation of Acute Neuronal Tissue for Electrophysiology and Calcium-imaging.</a> Journal of Visualized Experiments. (120), (2017).</li><li>Kafitz, K. W., Meier, S. D., Stephan, J., Rose, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developmental+profile+and+properties+of+sulforhodamine+101--Labeled+glial+cells+in+acute+brain+slices+of+rat+hippocampus.">Developmental profile and properties of sulforhodamine 101--Labeled glial cells in acute brain slices of rat hippocampus.</a> Journal of Neuroscience Methods. 169 (1), 84-92 (2008).</li><li>Neher, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correction+for+liquid+junction+potentials+in+patch+clamp+experiments.">Correction for liquid junction potentials in patch clamp experiments.</a> Methods in Enzymology. , 123-131 (1992).</li><li>Giaume, C., Leybaert, L., Naus, C. C., Saez, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connexin+and+pannexin+hemichannels+in+brain+glial+cells:+properties,+pharmacology,+and+roles.">Connexin and pannexin hemichannels in brain glial cells: properties, pharmacology, and roles.</a> Frontiers in Pharmacology. 4, 88 (2013).</li><li>Torres, 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=Extracellular+Ca(2)(+)+acts+as+a+mediator+of+communication+from+neurons+to+glia.">Extracellular Ca(2)(+) acts as a mediator of communication from neurons to glia.</a> Science Signaling. 5 (208), ra8 (2012).</li><li>Ye, Z. C., Wyeth, M. S., Baltan-Tekkok, S., Ransom, B. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+hemichannels+in+astrocytes:+a+novel+mechanism+of+glutamate+release.">Functional hemichannels in astrocytes: a novel mechanism of glutamate release.</a> Journal of Neuroscience. 23 (9), 3588-3596 (2003).</li><li>Ma, B., 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=Gap+junction+coupling+confers+isopotentiality+on+astrocyte+syncytium.">Gap junction coupling confers isopotentiality on astrocyte syncytium.</a> Glia. 64 (2), 214-226 (2016).</li><li>Meme, W., Vandecasteele, M., Giaume, C., Venance, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+coupling+between+hippocampal+astrocytes+in+rat+brain+slices.">Electrical coupling between hippocampal astrocytes in rat brain slices.</a> Neuroscience Research. 63 (4), 236-243 (2009).</li><li>Ransom, B. R., Kettenmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+coupling,+without+dye+coupling,+between+mammalian+astrocytes+and+oligodendrocytes+in+cell+culture.">Electrical coupling, without dye coupling, between mammalian astrocytes and oligodendrocytes in cell culture.</a> Glia. 3 (4), 258-266 (1990).</li><li>Audesirk, G., Audesirk, T., Bowsher, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Variability+and+frequent+failure+of+lucifer+yellow+to+pass+between+two+electrically+coupled+neurons+in+Lymnaea+stagnalis.">Variability and frequent failure of lucifer yellow to pass between two electrically coupled neurons in Lymnaea stagnalis.</a> Journal of Neurobiology. 13 (4), 369-375 (1982).</li><li>Ewadinger, N., Syed, N., Lukowiak, K., Bulloch, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+Tracer+Coupling+between+Pairs+of+Identified+Neurones+of+the+Mollusc+Lymnaea+Stagnalis.">Differential Tracer Coupling between Pairs of Identified Neurones of the Mollusc Lymnaea Stagnalis.</a> Journal of Experimental Biology. 192 (1), 291-297 (1994).</li><li>Griemsmann, S., 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=Characterization+of+Panglial+Gap+Junction+Networks+in+the+Thalamus,+Neocortex,+and+Hippocampus+Reveals+a+Unique+Population+of+Glial+Cells.">Characterization of Panglial Gap Junction Networks in the Thalamus, Neocortex, and Hippocampus Reveals a Unique Population of Glial Cells.</a> Cerebral Cortex. 25 (10), 3420-3433 (2015).</li><li>Kuwajima, T., 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=ClearT:+a+detergent-+and+solvent-free+clearing+method+for+neuronal+and+non-neuronal+tissue.">ClearT: a detergent- and solvent-free clearing method for neuronal and non-neuronal tissue.</a> Development. 140 (6), 1364-1368 (2013).</li><li>Gourine, A. V., 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=Astrocytes+control+breathing+through+pH-dependent+release+of+ATP.">Astrocytes control breathing through pH-dependent release of ATP.</a> Science. 329 (5991), 571-575 (2010).</li><li>Forsberg, D., Ringstedt, T., Herlenius, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Astrocytes+release+prostaglandin+E2+to+modify+respiratory+network+activity.">Astrocytes release prostaglandin E2 to modify respiratory network activity.</a> eLife. 6, (2017).</li></ol>

The authors have nothing to disclose.

A number of electrophysiological methods exist to assess functional coupling between astrocytes23,24. However, these methods do not provide information about the anatomical arrangement of astrocytic networks. A number of studies have already shown that &#34;dye- or tracer-coupling&#34;, as done here, occurs only in a fraction of coupled cells that are detected by electrophysiological methods25,26,27, suggesting that the number of cells detected with this method is underestimated. Nevertheless, this is still the best method for visualisation of coupling. Greater dye-coupling is obtained when using molecule tracers smaller than 1-1.2 KDa to permeate gap junctions20. Live visualization of coupling can be performed by monitoring diffusion of fluorescent glucose derivatives (2-NBDG) or a fluorescent marker (like some Alexa dyes or Lucifer Yellow)13, but due to its smaller size, biocytin yields better results and allows for quantification in fixed tissue. Thus, it should be noted that the number of cells detected with this method is largely underestimated. On the other hand, some of the cells may be labeled not because of their coupling, but because of the uptake of tracer that has leaked into the extracellular space. The extent of labeling resulting from leakage can be estimated in control experiments with bath applications of a gap junction blocker1. However, it can be assumed that any bias due to the method would apply to all conditions.
Finally, it should be emphasized that not all coupled cells are astrocytes. Panglial networks where astrocytes are coupled to oligodendrocytes have been described in several brain areas, including the lateral superior olive8, thalamus16, cortex, and hippocampus28. Our aim was to develop a method of comparing astrocytic networks revealed with dye-coupling under different conditions to assess the hypothesis that they form well-defined, distinctive functional domains revealed by different stimuli. Since in NVsnpr, the trigeminal brainstem nucleus in which this protocol was conducted, coupling between astrocytes is very limited under resting conditions, it was important to first develop a reliable and unbiased method to detect labeled cells. This was achieved with automated detection with ImageJFIJI. It is sometimes difficult to distinguish faintly labeled cells from background noise. Here, stack imaging and a method in ImageJFIJI are used to improve the signal, but background noise can still be too high and lead to data rejection. In future studies, clarification protocols may be used to improve the signal-to-noise ratio. A clearing protocol is an interesting method of clarification that preserves tissue morphology (no shrinkage), does not affect lipids, and is compatible with immunostaining29. Another limitation of the method described is the &#34;watershed&#34; tool used to discriminate cells that are too close to each other. Visual inspection of detected cells should be done when using this tool.
If astrocytic networks form functional domains, then they may define the boundaries of a nucleus or should at least be confined to the boundaries of a nucleus. Revealed networks may always be confined within a nucleus, more so if they are smaller in size, if the patched astrocyte is in the center (or within) the nucleus. To test if astrocytes sitting near the border of a nucleus preferably couple with other astrocytes outside the nucleus or with others within the nucleus, we needed to determine the preferential direction to which the dye spread from the patched astrocyte. Several other studies have addressed a similar issue in the barrel cortex, barreloid fields of the thalamus, olfactory glomeruli, hippocampus, and lateral superior olive, but they focused analyses mostly on the distance of diffusion of the tracer, electrophysiological characterization of different types of astrocytes in function of their localization, and spread of dye along orthogonal axes with respect to these well-defined structures8,9,10,13,14,16. Here, we used vectorial analysis to determine the dominant direction of tracer spread, which was given by the size and orientation of the normalized main vector. Small vectors indicate no clear &#34;dominant&#34; or preferential orientation. A critical step for vectorial analysis is the ability to accurately identify the patched astrocyte, which is not always possible. An interesting alternative to help locate the patched astrocyte is to add a large (non-gap junction permeant) and fixable tracer, like dextrans, to the recording solution. If it is not possible to determine the patched cell or patch location, it may be better to omit these experiments from the vector analysis.
Finally, to analyze whether properties of networks varied according to their location in the nucleus, we needed a method to express their position in a &#34;normalized&#34; nucleus. The only critical step in this procedure is the ability to clearly see the borders of the nucleus in the low magnification images (4X). A simple solution to this problem, if it occurs often, is to add a standard histological coloration to tissue processing before analysis.
Heterogeneity of astrocytes across brain regions is clearly established, and a growing body of evidence supports the concept that their specializations are particularly adapted for the function of the circuit that they are embedded in9,10,30,31. For this to be true, inter-astrocytic communication should be limited to astrocytes associated to the same circuit. Observations supporting this assumption are emerging in different brain areas but are more evident in areas with clustered representations, like sensory maps in the barrel cortex or olfactory bulb. However, most reports of overlap between neuronal and astrocytic maps are descriptive and qualitative. The methods reported here can be used to objectify&#160;these observations and develop tools to better analyze astrocytic networks according to their position in a given circuit.

Many studies have described how the neuron-astrocyte dialogue at a sub-cellular or synaptic level can have implications in neuronal functions and synaptic transmission. It is well established that astrocytes are sensitive to surrounding neuronal activity; in fact, they have receptors for many neurotransmitters including glutamate, GABA, acetylcholine, and ATP (see previously published reviews2,3,4). In return, astrocytic processes ensheath synaptic elements and influence neuronal activity both there and at extrasynaptic sites by regulating extracellular ionic homeostasis and releasing several factors or transmitters such as glutamate, D-serine, and ATP5,6,7.
The idea that astrocytes can also modulate neuronal function at the network level has emerged, with evidence that astrocytic coupling is spatially regulated and corresponds to neuronal segmentation in areas characterized by a clear anatomical compartmentalization (like areas with sensory representations), indicating that astrocytes will couple to other astrocytes serving the same function rather than just those that are close by. In the lateral superior olive, for instance, most astrocytic networks are oriented orthogonally to the tonotopic axis8, whereas in the barrel cortex or olfactoty glomeruli, communication between astrocytes is much stronger within barrels or glomeruli and weaker between adjacent ones9,10. In both cases, the astrocytic networks are oriented towards the center of the glomerule or barrel9,10.
We recently showed that astrocytic activity modulates neuronal firing by decreasing the concentration of extracellular Ca2+ ([Ca2+]e), presumably through the release of S100&#946;, a Ca2+-binding protein11. This effect, which was demonstrated in a population of trigeminal rhythmogenic neurons in the dorsal part of the trigeminal main sensory nucleus (NVsnpr, thought to play an important role in the generation of masticatory movements), results from the fact that rhythmic firing in these neurons depends on a persistent Na+ current that is promoted by decreases of [Ca2+]e11,12. Rhythmic firing in these neurons can be elicited &#34;physiologically&#34; by stimulation of their inputs or artificial decrease of [Ca2+]e. We further showed that astrocytic coupling was required for neuronal rhythmic firing1. This raised the possibility that astrocytic networks may form circumscribed functional domains where neuronal activity can be synchronized and coordinated. To assess this hypothesis, we first needed to develop a method to rigorously document the organization of these networks within NVsnpr.
Previous studies on astrocytic networks have mostly described the extent of coupling in terms of cell number and the density and area covered. Attempts to evaluate the shape of astrocytic networks and the direction of dye-coupling were mostly performed by comparing the size of networks along two axes (x and y) in the barrel cortex9, hippocampus13,14,15, barreloid fields of the thalamus16, lateral superior olive8, olfactory glomeruli10, and cortex14. The methods described here enable unbiased counts of labeled cells in a network and an estimation of the area they cover. We also developed tools to define the preferred orientation of coupling within a network and to assess whether the preferred orientation is towards the center of the nucleus or in a different direction. In comparison to previously used methods, this protocol provides a means to describe the organization and orientation of astrocytic networks in structures like the dorsal trigeminal main sensory nucleus that do not have a known clear anatomical compartmentalization. In the above studies, the network orientation is described as a relationship to the shape of the structure itself which is already documented (e.g., the barreloid in the thalamus, barrels in the cortex, layers in the hippocampus and cortex, glomeruli in the olfactory bulb, etc.). In addition, vectorial analysis allows for comparisons of coupling orientations revealed under different conditions. To analyze whether these parameters changed according to the position of the network within the nucleus, we also developed a method to replace each network in reference to the boundaries of the nucleus. These tools can be easily adapted to other areas for investigating networks of coupled cells.

<table>
	<tbody>
		<tr>
			<td>NaCl</td>
			<td>Fisher Chemicals</td>
			<td>S671-3</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Fisher Chemicals</td>
			<td>P217-500</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Fisher Chemicals</td>
			<td>P285-500</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Fisher Chemicals</td>
			<td>M65-500</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Fisher Chemicals</td>
			<td>S233-500</td>
			<td></td>
		</tr>
		<tr>
			<td>C6H12O6 Dextrose anhydrous</td>
			<td>Fisher Chemicals</td>
			<td>D16-500</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2 dihydrated</td>
			<td>Sigma</td>
			<td>C70-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma</td>
			<td>S9378</td>
			<td></td>
		</tr>
		<tr>
			<td>D-gluconic acid potassium salt</td>
			<td>Sigma</td>
			<td>G45001</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2 anhydrous</td>
			<td>Sigma</td>
			<td>M8266</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma</td>
			<td>H3375</td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Sigma</td>
			<td>E4378</td>
			<td></td>
		</tr>
		<tr>
			<td>ATPTris Salt</td>
			<td>Sigma</td>
			<td>A9062</td>
			<td></td>
		</tr>
		<tr>
			<td>GTPTris Salt</td>
			<td>Sigma</td>
			<td>G9002</td>
			<td></td>
		</tr>
		<tr>
			<td>Biocytin</td>
			<td>Sigma</td>
			<td>B4261</td>
			<td></td>
		</tr>
		<tr>
			<td>Carbenoxolone disodium salt</td>
			<td>Sigma</td>
			<td>C4790</td>
			<td></td>
		</tr>
		<tr>
			<td>avidin-biotin complex : ABC kit</td>
			<td>Vestor laboratories</td>
			<td>PK-4000</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptavidine-alexa 594</td>
			<td>Molecular Probes</td>
			<td>S11227</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton</td>
			<td>Fisher Chemicals</td>
			<td>BP151-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>Fisher Chemicals</td>
			<td>X5-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Aqueous mounting medium 1 : Fluoromount-G</td>
			<td>SouthernBiotech</td>
			<td>0100-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Toluen-based synthetic resin mounting medium : Permount</td>
			<td>Fisher Chemicals</td>
			<td>SP15-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Slide Drying Bench</td>
			<td>Fisherbrand</td>
			<td>11-474-470</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibratome</td>
			<td>Leica</td>
			<td>VT 1000S</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope cover glass</td>
			<td>Fisherbrand</td>
			<td>12-544A</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slide ColorFrost</td>
			<td>Fisherbrand</td>
			<td>12-550-413</td>
			<td></td>
		</tr>
		<tr>
			<td>PFA</td>
			<td>Fisherchemicals</td>
			<td>04042-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus FluoView FV 1000 Confocal microscope</td>
			<td>Olympus</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>40X water-immersion lens</td>
			<td>Olympus</td>
			<td>LUMPLFLN40XW</td>
			<td></td>
		</tr>
		<tr>
			<td>20X water-immersion lens</td>
			<td>Olympus</td>
			<td>XLUMPLFL20XW</td>
			<td></td>
		</tr>
		<tr>
			<td>4X water-immersion lens</td>
			<td>Olympus</td>
			<td>XLFLUOR4X/340</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Sutter Instrument</td>
			<td>P97</td>
			<td></td>
		</tr>
		<tr>
			<td>Micromanipulator</td>
			<td>Sutter Instrument</td>
			<td>MP 225</td>
			<td></td>
		</tr>
		<tr>
			<td>Camera CCD</td>
			<td>Sony</td>
			<td>CX-ST50</td>
			<td></td>
		</tr>
		<tr>
			<td>Black and white monitor</td>
			<td>Sony</td>
			<td>SSM-125</td>
			<td></td>
		</tr>
		<tr>
			<td>Digidata</td>
			<td>Molecular devices</td>
			<td>1322A</td>
			<td></td>
		</tr>
		<tr>
			<td>Patch Clamp amplifier</td>
			<td>Axon instrument</td>
			<td>Mulitclamp 700A</td>
			<td></td>
		</tr>
		<tr>
			<td>Electrophysiology acquisition software</td>
			<td>Molecular devices</td>
			<td>pClamp 8</td>
			<td></td>
		</tr>
		<tr>
			<td>Electrophysiology analysis software</td>
			<td>Molecular devices</td>
			<td>Clampfit 8</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaging analysis software</td>
			<td>ImageJFIJI</td>
			<td>Open source software. FIJI version including plug in package.</td>
			<td></td>
		</tr>
		<tr>
			<td>Vector image editor</td>
			<td>Adobe</td>
			<td>Illustrator CS4</td>
			<td></td>
		</tr>
		<tr>
			<td>Spreadsheet application</td>
			<td>Microsoft Office</td>
			<td>Excel 2010</td>
			<td></td>
		</tr>
	</tbody>
</table>

analyzing the size, shape, and directionality of networks of coupled astrocytes

It has become increasingly clear that astrocytes modulate neuronal function not only at the synaptic and single-cell levels, but also at the network level. Astrocytes are strongly connected to each other through gap junctions and coupling through these junctions is dynamic and highly regulated. An emerging concept is that astrocytic functions are specialized and adapted to the functions of the neuronal circuit with which they are associated. Therefore, methods to measure various parameters of astrocytic networks are needed to better describe the rules governing their communication and coupling and to further understand their functions.
Here, using the image analysis software (e.g., ImageJFIJI), we describe a method to analyze confocal images of astrocytic networks revealed by dye-coupling. These methods allow for 1) an automated and unbiased detection of labeled cells, 2) calculation of the size of the network, 3) computation of the preferential orientation of dye spread within the network, and 4) repositioning of the network within the area of interest.
This analysis can be used to characterize astrocytic networks of a particular area, compare networks of different areas associated to different functions, or compare networks obtained under different conditions that have different effects on coupling. These observations may lead to important functional considerations. For instance, we analyze the astrocytic networks of a trigeminal nucleus, where we have previously shown that astrocytic coupling is essential for the ability of neurons to switch their firing patterns from tonic to rhythmic bursting1. By measuring the size, confinement, and preferential orientation of astrocytic networks in this nucleus, we can build hypotheses about functional domains that they circumscribe. Several studies suggest that several other brain areas, including the barrel cortex, lateral superior olive, olfactory glomeruli, and sensory nuclei in the thalamus and visual cortex, to name a few, may benefit from a similar analysis.

Watch this Scientific Journal Video about Analyzing the Size, Shape, and Directionality of Networks of Coupled Astrocytes at JoVE.com

Analyzing the Size, Shape, and Directionality of Networks of Coupled Astrocytes

Here we present a protocol to assess the organization of astrocytic networks. The described method minimizes bias to provide descriptive measures of these networks such as cell count, size, area, and position within a nucleus. Anisotropy is assessed with a vectorial analysis.

It has become increasingly clear that astrocytes modulate neuronal function not only at the synaptic and single-cell levels, but also at the network ...

analyzing-size-shape-directionality-networks-coupled

Nanyang Technological University

Research

JoVE Journal

Neuroscience

8.7K Views.  Université de Montréal. Here we present a protocol to assess the organization of astrocytic networks. The described method minimizes bias to provide descriptive measures of these networks such as cell count, size, area, and position within a nucleus. Anisotropy is assessed with a vectorial analysis.

Video: Analyzing the Size, Shape, and Directionality of Networks of Coupled Astrocytes

Isolation and Culture of Mouse Cortical Astrocytes

Astrocytes are an abundant cell type in the mammalian brain, yet much remains to be learned about their molecular and functional characteristics. In vitro astrocyte cell culture systems can be used to study the biological functions of these glial cells in detail. This video protocol shows how to obtain pure astrocytes by isolation and culture of mixed cortical cells of mouse pups. The method is based on the absence of viable neurons and the separation of astrocytes, oligodendrocytes and microglia, the three main glial cell populations of the central nervous system, in culture. Representative images during the first days of culture demonstrate the presence of a mixed cell population and indicate the timepoint, when astrocytes become confluent and should be separated from microglia and oligodendrocytes. Moreover, we demonstrate purity and astrocytic morphology of cultured astrocytes using immunocytochemical stainings for well established and newly described astrocyte markers. This culture system can be easily used to obtain pure mouse astrocytes and astrocyte-conditioned medium for studying various aspects of astrocyte biology.

Astrocytes have been recognized to be versatile cells participating in fundamental biological processes that are essential for normal brain development and function, and central nervous system repair. Here we present a rapid procedure to obtain pure mouse astrocyte cultures to study the biology of this major class of central nervous system cells.

Astrocytes  are an abundant cell type in the mammalian brain, yet much remains to be  learned about their molecular and functional characteristics. In ...

Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of the dendritic tree, which eventually leads to neuronal output of action potentials at the axon. The influence of diverse spatial and temporal parameters of specific synaptic input on neuronal output is currently under investigation, e.g. the distance-dependent attenuation of dendritic inputs, the location-dependent interaction of spatially segregated inputs, the influence of GABAergig inhibition on excitatory integration, linear and non-linear integration modes, and many more.
With fast micro-iontophoresis of glutamate and GABA it is possible to precisely investigate the spatial and temporal integration of glutamatergic excitation and GABAergic inhibition. Critical technical requirements are either a triggered fluorescent lamp, light-emitting diode (LED), or a two-photon scanning microscope to visualize dendritic branches without introducing significant photo-damage of the tissue. Furthermore, it is very important to have a micro-iontophoresis amplifier that allows for fast capacitance compensation of high resistance pipettes. Another crucial point is that no transmitter is involuntarily released by the pipette during the experiment.
Once established, this technique will give reliable and reproducible signals with a high neurotransmitter and location specificity. Compared to glutamate and GABA uncaging, fast iontophoresis allows using both transmitters at the same time but at very distant locations without limitation to the field of view. There are also advantages compared to focal electrical stimulation of axons: with micro-iontophoresis the location of the input site is definitely known and it is sure that only the neurotransmitter of interest is released. However it has to be considered that with micro-iontophoresis only the postsynapse is activated and presynaptic aspects of neurotransmitter release are not resolved. In this article we demonstrate how to set up micro-iontophoresis in brain slice experiments.

In this article we introduce fast micro-iontophoresis of neurotransmitters as a technique to investigate integration of postsynaptic signals with high spatial and temporal precision.

One of the fundamental interests in neuroscience is to understand the integration of excitatory and inhibitory inputs along the very complex structure of ...

A Procedure for Implanting Organized Arrays of Microwires for Single-unit Recordings in Awake, Behaving Animals

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell level. The technique allows experimenters to examine temporally and regionally specific firing patterns in order to correlate recorded action potentials with ongoing behavior. Moreover, single-unit recordings can be combined with a plethora of other techniques in order to produce comprehensive explanations of neural function. In this article, we describe the anesthesia and preparation for microwire implantation. Subsequently, we enumerate the necessary equipment and surgical steps to accurately insert a microwire array into a target structure. Lastly, we briefly describe the equipment used to record from each individual electrode in the array. The fixed microwire arrays described are well-suited for chronic implantation and allow for longitudinal recordings of neural data in almost any behavioral preparation. We discuss tracing electrode tracks to triangulate microwire positions as well as ways to combine microwire implantation with immunohistochemical techniques in order to increase the anatomical specificity of recorded results.

Implanting organized arrays of microwires for use in single-unit electrophysiological recordings presents a number of technical challenges.&#160;Methods for performing this technique and the equipment necessary are described.&#160;Also, the beneficial use of organized microwire arrays to record from distinct neural subregions with high spatial selectivity is discussed.

In vivo electrophysiological recordings in the awake, behaving animal provide a powerful method for understanding neural signaling at the single-cell ...

Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory Sensory Neuron (OSN) is a bipolar cell with a single dendrite and a single unbranched axon. An OSN expresses only one Olfactory Receptor (OR) gene, OSNs expressing a given type of OR converge their axons to a few sets of invariant glomeruli in the Olfactory Bulb (OB). A remarkable feature of OSN projection is that the expressed ORs play instructive roles in axonal projection. ORs regulate the expression of multiple axon-sorting molecules and generate the combinatorial molecular code of axon-sorting molecules at the OSN axon termini. Thus, to understand the molecular mechanisms of OR-specific axon guidance mechanisms, it is vital to characterize their expression profiles at the OSN axon termini within the same glomerulus. The aim of this article was to introduce methods for collecting as many glomeruli as possible on a single OB section and for performing immunostaining using multiple antibodies. This would allow the comparison and analysis of the expression patterns of axon-sorting molecules without staining variation between OB sections.

Olfactory sensory neurons express a wide variety of axon-sorting molecules to establish proper neural circuitry. This protocol describes an immunohistochemical staining method to visualize combinatorial expressions of axon-sorting molecules at the axon termini of olfactory sensory neurons.

The mouse olfactory system is often used to study mechanisms of neural circuit formation&#12288;because of its simple anatomical structure. An Olfactory ...

Chronic Transcranial Electrical Stimulation and Intracortical Recording in Rats

Transcranial electrical stimulation (TES) is a powerful and relatively simple approach to diffusely influence brain activity either randomly or in a closed-loop event-triggered manner. Although many studies are focusing on the possible benefits and side-effects of TES in healthy and pathologic brains, there are still many fundamental open questions regarding the mechanism of action of the stimulation. Therefore, there is a clear need for a robust and reproducible method to test the acute and the chronic effects of TES in rodents. TES can be combined with regular behavioral, electrophysiological, and imaging techniques to investigate neuronal networks in vivo. The implantation of transcranial stimulation electrodes does not impose extra constraints on the experimental design while it offers a versatile, flexible tool to manipulate brain activity. Here we provide a detailed, step-by-step protocol to fabricate and implant transcranial stimulation electrodes to influence brain activity in a temporally constrained manner for months.

This detailed protocol describes transcranial stimulation electrode placement on the temporal bone in order to investigate the short- and long-term effects of transcranial electrical stimulation in freely moving rats.

Transcranial electrical stimulation (TES) is a powerful and relatively simple approach to diffusely influence brain activity either randomly or in a ...

Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls body functions and internal organ rhythms when animals are exposed to emotional challenges and changes in their living environments. In general experiments, signals from different organs, such as the brain and the heart, are recorded by independent recording systems that require multiple recording devices and different procedures for processing the data files. This study describes a new method that can simultaneously monitor electrical biosignals, including tens of local field potentials in multiple brain regions, electrocardiograms that represent the cardiac rhythm, electromyograms that represent awake/sleep-related muscle contraction, and breathing signals, in a freely moving rat. The recording configuration of this method is based on a conventional micro-drive array for cortical local field potential recordings in which tens of electrodes are accommodated, and the signals obtained from these electrodes are integrated into a single electrical board mounted on the animal's head. Here, this recording system was improved so that signals from the peripheral organs are also transferred to an electrical interface board. In a single surgery, electrodes are first separately implanted into the appropriate body parts and the target brain areas. The open ends of all of these electrodes are then soldered to individual channels of the electrical board above the animal's head so that all of the signals can be integrated into the single electrical board. Connecting this board to a recording device allows for the collection of all of the signals into a single device, which reduces experimental costs and simplifies data processing, because all data can be handled in the same data file. This technique will aid the understanding of the neurophysiological correlates of the associations between central and peripheral organs.

This study introduces a method for the simultaneous recording of local field potentials in the brain, electrocardiograms, electromyograms, and breathing signals of a freely moving rat. This technique, which reduces experimental costs and simplifies data analysis, will contribute to the understanding of the interactions between the brain and peripheral organs.

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls ...

Three-Dimensional Shape Modeling and Analysis of Brain Structures

Statistical shape analysis of brain structures has been used to investigate the association between their structural changes and pathological processes. We have developed a software package for accurate and robust shape modeling and group-wise analysis. Here, we introduce an pipeline for the shape analysis, from individual 3D shape modeling to quantitative group shape analysis. We also describe the pre-processing and segmentation steps using open software packages. This practical guide would help researchers save time and effort in 3D shape analysis on brain structures.

We introduce a semi-automatic protocol for shape analysis on brain structures, including image segmentation using open software, and further group-wise shape analysis using an automated modeling package. Here, we demonstrate each step of the 3D shape analysis protocol with hippocampal segmentation from brain MR images.

Statistical shape analysis of brain structures has been used to investigate the association between their structural changes and pathological processes. ...

Visualizing and Analyzing Intracellular Transport of Organelles and Other Cargos in Astrocytes

Astrocytes are among the most abundant cell types in the adult brain, where they play key roles in a multiplicity of functions. As a central player in brain homeostasis, astrocytes supply neurons with vital metabolites and buffer extracellular water, ions, and glutamate. An integral component of the &#8220;tri-partite&#8221; synapse, astrocytes are also critical in the formation, pruning, maintenance, and modulation of synapses. To enable these highly interactive functions, astrocytes communicate among themselves and with other glial cells, neurons, the brain vasculature, and the extracellular environment through a multitude of specialized membrane proteins that include cell adhesion molecules, aquaporins, ion channels, neurotransmitter transporters, and gap junction molecules. To support this dynamic flux, astrocytes, like neurons, rely on tightly coordinated and efficient intracellular transport. Unlike neurons,&#160;where intracellular trafficking has been extensively delineated, microtubule-based transport in astrocytes has been less studied. Nonetheless, exo- and endocytic trafficking of cell membrane proteins and intracellular organelle transport orchestrates astrocytes&#8217; normal biology, and these processes are often affected in disease or in response to injury. Here we present a straightforward protocol to culture high quality murine astrocytes, to fluorescently label astrocytic proteins and organelles of interest, and to record their intracellular transport dynamics using time-lapse confocal microscopy. We also demonstrate how to extract and quantify relevant transport parameters from the acquired movies using available image analysis software (i.e., ImageJ/FIJI) plugins.

Here we describe an in vitro live-imaging method to visualize intracellular transport of organelles and trafficking of plasma membrane proteins in murine astrocytes. This protocol also presents an image analysis methodology to determine cargo transport itineraries and kinetics.

Astrocytes are among the most abundant cell types in the adult brain, where they play key roles in a multiplicity of functions. As a central player in ...

Reliable Acquisition of Electroencephalography Data during Simultaneous Electroencephalography and Functional MRI

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), EEG-fMRI, combines the complementary properties of scalp EEG (good temporal resolution) and fMRI (good spatial resolution) to measure neuronal activity during an electrographic event, through hemodynamic responses known as blood-oxygen-level-dependent (BOLD) changes. It is a non-invasive research tool that is utilized in neuroscience research and is highly beneficial to the clinical community, especially for the management of neurological diseases, provided that proper equipment and protocols are administered during data acquisition. Although recording EEG-fMRI is apparently straightforward, the correct preparation, especially in placing and securing the electrodes, is not only important for safety but is also critical in ensuring the reliability and analyzability of the EEG data obtained. This is also the most experience-demanding part of the preparation. To address these issues, a straightforward protocol that ensures data quality was developed. This article provides a step-by-step guide for acquiring reliable EEG data during EEG-fMRI using this protocol that utilizes readily available medical products. The presented protocol can be adapted to different applications of EEG-fMRI in research and clinical settings, and may be beneficial to both inexperienced and expert operators.

This article provides a straightforward protocol for acquiring good quality electroencephalography (EEG) data during simultaneous EEG and functional magnetic resonance imaging by utilizing readily available medical products.

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), EEG-fMRI, combines the complementary properties of scalp EEG ...

Stimulating and Analyzing Adult Neurogenesis in the Drosophila Central Brain

The molecular and cellular mechanisms underlying neurogenesis in response to disease or injury are not well understood. However, understanding these mechanisms is crucial for developing neural regenerative therapies. Drosophila melanogaster is a leading model for studies of neural development but historically has not been exploited to investigate adult brain regeneration. This is primarily because the adult brain exhibits very low mitotic activity. Nonetheless, penetrating traumatic brain injury (PTBI) to the adult Drosophila central brain triggers the generation of new neurons and new glia. The powerful genetic tools available in Drosophila combined with the simple but rigorous injury protocol described here now make adult Drosophila brain a robust model for neural regeneration research. Provided here are detailed instructions for (1) penetrating injuries to the adult central brain and (2) dissection, immunohistochemistry, and imaging post-injury. These protocols yield highly reproducible results and will facilitate additional studies to dissect mechanisms underlying neural regeneration.

Stimulating and Analyzing Adult Neurogenesis in the Drosophila Central Brain

This article provides detailed protocols for inflicting Penetrating Traumatic Brain Injury (PTBI) to adult Drosophila and examining the resulting neurogenesis.

The molecular and cellular mechanisms underlying neurogenesis in response to disease or injury are not well understood. However, understanding these ...

Analyzing the Size, Shape, and Directionality of Networks of Coupled Astrocytes

Summary

Explore More Videos

Chapters in this video

Isolation and Culture of Mouse Cortical Astrocytes

Fast Micro-iontophoresis of Glutamate and GABA: A Useful Tool to Investigate Synaptic Integration

A Procedure for Implanting Organized Arrays of Microwires for Single-unit Recordings in Awake, Behaving Animals

Quadruple Immunostaining of the Olfactory Bulb for Visualization of Olfactory Sensory Axon Molecular Identity Codes

Chronic Transcranial Electrical Stimulation and Intracortical Recording in Rats

Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat

Three-Dimensional Shape Modeling and Analysis of Brain Structures

Visualizing and Analyzing Intracellular Transport of Organelles and Other Cargos in Astrocytes

Reliable Acquisition of Electroencephalography Data during Simultaneous Electroencephalography and Functional MRI

Stimulating and Analyzing Adult Neurogenesis in the Drosophila Central Brain