CENTRAL NICOTINIC CHANNEL KINETICS AND SYNAPTIC FUNCTION

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The objectives of this proposal are to investigate the interaction between the neurotransmitter, acetylcholine (ACh), and central nicotinic cholinergic receptor (nAChR) channels, in order to understand the function of nicotinic synaptic transmission in the central nervous system (CNS). Despite strong neurochemical evidence that certain cholinergic pathways project to brain regions rich in nAChRS, little information regarding the participation of nAChRs in synaptic transmission has been obtained using conventional physiological techniques. In the absence of being able to examine central nicotinic synapses directly, a different strategy will be required. The overall experimental design of this proposal is based on the general principal that transmitters, such as ACh, are rapidly released and cleared from the synaptic cleft. Using rapid perfusion techniques, pulses of ACh will be applied to nAChRs in small cells and outside-out patches. Thus, nAChRs will be rapidly activated by ACh in a manner that is analogous to synaptic stimulation. This approach will provide a powerful means of studying the behavior of nAChR channels with respect to the properties of a real synaptic response. The experiments will specifically include, evaluation of the rapid binding of ACh to nAChRs, the activation and opening of nAChR channels, the duration of the nicotinic synaptic response and the return of the nAChRs to their resting state. In addition to these studies, primary cultures of central cholinergic neurons will be developed so that activation of nAChRs at pre- and post-synaptic sites can be examined directly. Synaptic transmission is the primary means through which neurons communicate and the output of a neuron is determined largely by integrating the varied incoming synaptic signals it receives. The particular features of a synaptic response, determined by the interaction between receptor and transmitter, will control the influence that signal will have on the overall properties of the neuron. Therefore, a knowledge of the fundamental characteristics of the synaptic activation of nAChRs by ACh would be invaluable in the understanding of both the normal function of the cholinergic system in synaptic transmission and plasticity, and the full implications of cholinergic neuronal loss in certain degenerative diseases.