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Network Oscillations in organotypic slice cultures.
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Poster. Rhythmic network activity at theta frequencies is a hallmark of a functioning hippocampus. In organotypic hippocampal slice cultures, low quantities of the metabotropic receptor agonists methacholine (~20 nM) or DHPG (~100 nM) are able to activate the network and induce theta oscillations. Similar activity is also induced in the CA3 region during transient oxygen-glucose deprivation (OGD). In whole-cell voltageclamp recordings, we find that the activity induced by OGD depends on the network as it is blocked by TTX, by the glutamatergic antagonist NBQX, or by the GABAergic antagonist picrotoxin. Preventing NMDA receptor activation with CPP did not, however, prevent the network activity. Selectively blocking AMPA receptors with either SYM2206 or GYKI52466 led to a profound alteration in the OGD-induced activity marked by frequent repetitive giant depolarizing currents. The gap junction blocker mefloquine reduced rhythmicity as did the GluR6 antagonist UBP302. These data, together with the observation that the activity is dominated by inhibitory events, suggest that the interneuron network is important for the generation of these oscillations. Bulk-loading with Ca2+ indicators and high speed Ca2+ imaging with a CCD camera revealed rhythmic fluctuations in the neuropil in response to 100 nM DHPG, presumably reflecting action potentialinduced calcium signals in labeled axons and terminals. In addition, two classes of Ca2+ signal were resolved in single cells. Slow wave-like responses occurred in some cells, presumably astrocytes, whereas in other cells that are presumably neurons, much faster spike-like events were observed whose peaks corresponded with the peaks in the neuropil signal. Based on their location in the slice, many of these cells are likely to be interneurons. Further work is aimed at identifying the cell types and their roles in generating and synchronizing the network activity.
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