The objective of this proposal is to understand the cellular and subcellular mechanisms by which various neuropeptides modulate the activity of brain neurons. Particularly, these studies attempt to elucidate the function and structure of brain neurons that are correlated with Alzheimer's disease. It was for this purpose that the principal investigator (P.I.) developed a unique method of culturing cholinergic neurons from the basal forebrain nuclei including the nucleus basalis as well as the noradrenergic neurons from the locus careless. Neurons in these nuclei have been shown to degenerate in Alzheimer's disease. Cultured cholinergic neurons and noradrenergic neurons were identified using immunocytochemical and histochemical methods. The P.I. plans to study the signal transduction process involved in the effects of neuropeptides on these primary cultures with particular emphasis on the mechanism by which second messengers modulate potassium channels. There are three major projects: The first project deals with the modulation of the inwardly rectifying K- channels by substance P and somatostatin in nucleus basalis and locus careless neurons. The P.I.'s previous work has demonstrated that substance P excites neurons by suppressing an inwardly rectifying K-conductance, whereas somatostatin inhibits them by inducing a similar conductance. This work will be extended at the single channel level to include a detailed analysis of the properties of these potassium channels. The second project is to identify the second messengers. The P.I. has found that two different GTP-binding proteins seem to be the second messengers for the substance P- and somatostatin-induced modulations of potassium conductance. In this project,the P.I. proposes to examine the role that arachidonic acid metabolites play in somatostatin- and substance P-induced modulation of potassium channels. The third project is to study the ionic and second messenger mechanisms involved in the effects of galanin and neurotensin on cultured nucleus basalis and locus careless neurons using the whole-cell clamp and single- channel recording. Preliminary results from the pilot study suggest that galanin inhibits locus careless neurons, whereas both galanin and neurotensin excite nucleus basalis neurons.
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