HIPPOCAMPAL INTERNEURONS--IN CULTURE AND IN SLICES

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DESCRIPTION: Regulation of neurotransmitter release into the synaptic cleft is a primary means of achieving synaptic plasticity in the central nervous system. Since influx of calcium through voltage-dependent channels is necessary for neurotransmitter release, modulation of the activity of these channels by neurotransmitters is likely to be a common mechanism of regulating synaptic strength. The projects in the PI's laboratory exploit the well-characterized circuitry of the hippocampus to investigate the function and identity of the calcium channels controlling release in specific inhibitory synapses, and also the modulation of these channels by neurotransmitters. The hippocampus is involved in both memory formation and epileptic seizures. The inhibitory circuitry of the hippocampus, in particular, is extremely important in the control of seizure formation. The experiments outlined in this proposal will provide a solid foundation for future studies on the nature of synaptic transmission. The first specific aim is to optimize the culturing and whole cell recording conditions for hippocampal inhibitory interneurons, in order to obtain comparable excitability in culture as is seen in age-matched hippocampal slices. Tissue will be obtained from animals of various ages and allowed to remain in culture for various times. These experiments are a prerequisite for all the future experiments featured in this proposal. The second specific aim is to determine the feasibility of identifying inhibitory interneurons in culture based on electrophysiological parameters using whole cell patch clamp recording in the current clamp mode. These studies will be performed in parallel with identical experiments in age-matched hippocampal slices. The results from these experiments will validate the use of cultured hippocampal cells for studies on interneuron behavior and function. The third specific aim is to provide the first thorough characterization of the voltage dependent calcium channels in the presynaptic cells of 3 different inhibitory synapses in the hippocampus using whole cell voltage clamp recording in dissociated cells. The data obtained in these experiments will provide a foundation for future studies on neurotransmitter release and modulation of calcium channels. The vertical cells of the stratum oriens/alveus, the basket cells in the stratum pyramidale, and stellate cells in the stratum lacunosum/moleculare will be studied. The vertical and basket cells mediate both feedforward and recurrent inhibition primarily by activation of GABAA receptors. The stellate cells mediate feedforward inhibition by activation of GABAB receptors. Future studies in the PI's laboratory will be aimed at understanding how neurotransmitters regulate specific synapses by modulation of distinct calcium channel types providing insight into some of the mechanisms of synaptic plasticity. In addition, these studies will provide a better foundation for pharmaceutical therapies in diseases such a epilepsy and neurodegeneration where the use of neuromodulators is being actively pursued. Moreover, this information will also provide insights into the cellular pathology of various human neuronal disorders in which synaptic function is altered.