Activity of brainstem neurons

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DESCRIPTION (provided by applicant): With the introduction of high potency "crack" and "freebase", cocaine abuse increased dramatically in the 1980's and 1990's, and is the leading drug of abuse. Epidemiological data have implicated cocaine as a contributing factor to myocardial infarction, stroke, thrombosis, hypertension and arrhythmias in users on the basis of temporal relationship between drug use and event onset. Clinical and animal studies suggest that the central sympathetic nervous system plays a critical role in cocaine-induced cardiovascular abnormality. The hypothesis central to this proposal is that cocaine interacts with sigma-1 receptors located in neurons of the rostral ventrolateral medulla (RVLM), leading to a potentiation of glutamatergic responses, thereby an augmented sympathetic nerve activity in cocaine users. There is evidence that the central action of cocaine is mediated through sigma-1 receptors. The goal of this project is to define the central cardiovascular action of cocaine on RVLM neurons of the rat, with particular reference to sigma-1 receptors. First, immunohisto- chemical studies will examine the expression of sigma-1 receptors and their relationship to subtypes of glutamate receptors in a population of bulbospinally projecting RVLM neurons. Second, the effect of cocaine, which will be microinjected into the RVLM area, on blood pressure, heart rate and greater splanchnic nerve activity will be assessed in urethane-anesthetized rats. In addition, the effect of cocaine on the pressor response will be monitored before and after pretreatment with sigma-1 receptor antagonists or dopamine and norepinephrine uptake inhibitors. Third, intracellular Ca2+ concentrations in dissociated, retrogradely labeled RVLM neurons in response to glutamate and cocaine before and after treatment of sigma-1 receptor antagonists will be measured by means of the Fura 2 method. Fourth, whole-cell patch recordings will be made from retrogradely labeled RVLM neurons in the coronal medullary slice and the effect of cocaine on the electrical activity and synaptic transmission of single neurons will be studied. Collectively, these studies are designed to provide a mechanistic approach to the understanding of the central action of cocaine relative to cardiovascular activity. Cocaine abuse is a risk factor to a variety of cardiovascular disorders. To be able to identify the receptor and transmitters that respond to cocaine will be a major step toward a better understanding of the mechanisms involved in cocaine-induced cardiac disorders. More importantly, the knowledge gained would permit a rational approach to the design of novel therapeutic agents, for example, sigma-1 receptor or subtypes of glutamate receptor antagonists, for the management of cocaine-induced cardiovascular dysfunction.