With the development of modern immunocytochemical and intracellular electrophysiological techniques, the complexity of local circuitry in hippocampus has become apparent. Although the hippocampus is a relatively simple cortical structure, it is thought to participate in complex information processing tasks. The diversity of interneuron types, their transmitters, and their local circuitry must be key elements in providing the system with the means of modulating the activity of primary projection cells. In the present application, we continue our study of those interneurons and local circuitries. Further, we propose to initiate a series of studies examining the effects of various """"""""traumatic"""""""" treatments on the interneurons of hippocampus, and the consequences of damaging specific vulnerable cell populations. The studies will be carried out on parallel, but closely interacting, tracks. Morphological characterization, by light and electron n=microscopic/immunocytochemical techniques, will describe the locations, arborization patterns, and putative neurotransmitter content of specific interneuron populations in the CA1, CA3, and dentate regions of rat hippocampus. These studies will also provide guidance for in vitro slice electrophysiological investigations with will attempt to characterize interneurons on the basis of their electrophysiological properties and their synaptic inter-actions with principal cell types (using simultaneous intracellular recordings of cell pairs). Interneurons will be intracellularly labeled and examined, in turn, at the morphological level. The same morphological and electrophysiological techniques will be used to assess the effects of various treatments on hippocampal interneurons and interneuron-dependent circuitry. Ischemia, anoxia, and stimulation treatments will be delivered to intact animals, which will be examined morphologically, and from which hippocampal slices will be obtained from electrophysiological investigation. Parallel treatments will be carried out in slices while recording from suspected vulnerable interneurons. Procedures will be developed to """"""""protect"""""""" vulnerable interneurons from effects of these treatments. These studies will provide a descriptive basis for understanding interneurons and interneuron local circuitry in hippocampus, and will test a number of specific hypotheses regarding interneuron action in hippocampus.
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