The overall objective of this project is to describe the acute effects of ethanol on the electrophysiological properties of single neurons in the mammalian brain and to examine the basic ionic mechanisms which mediate these effects on neuronal membranes. The ultimate goal of such studies is to elucidate how ethanol alters information processing by central neurons in order to understand how brain function changes during human ethanol usage. The proposed studies will examine the ionic and second messenger mechanisms which mediate the effects of ethanol on two important groups of catecholamine neurons: the noradrenergic neurons of the locus coeruleus (LC) nucleus and the dopaminergic neurons of the ventral tegmental area (VTA). The LC is the largest noradrenergic nucleus in the brain and is involved in regulation of arousal level, vigilance and selective attention. Acute ethanol effects on 1? neurons may underlie ethanol's sedative effects and impairment of selective attention. Disruption in the activity of LC neurons may also be an important component of the alcohol withdrawal syndrome. Dopaminergic neurons of the VTA appear to be important in mediating the rewarding effects of ethanol and therefore may be of crucial importance in the control of voluntary ethanol intake and abuse. The techniques to be used are intracellular current clamp and single-electrode voltage clamp recording with sharp microelectrodes in brain slices, and whole cell recording from acutely dissociated neurons, both from adult rats. Ethanol will be applied in known concentrations (10-200 mM) in the bath. We have now identified specific membrane currents which are enhanced by ethanol, in concentrations within the behaviorally active range, namely A-current in LC neurons and h-current in VTA neurons.
Specific Aims l and 3 are directed at examining the mechanisms by which ethanol enhances these currents and whether its action is mediated through the adenylate cyclase pathway or by changes in extracellular potassium or intracellular calcium concentration. Whether these actions of ethanol mediate its effects on spontaneous firing in LC and VTA neurons will be examined.
Specific Aims 2 and 4 explore other possible mechanisms underlying ethanol's effects on firing rate of LC and VTA neurons, namely, an action on the cAMP-dependent pacemaker current in LC neurons and an ethanol-induced reduction in specific K+ currents (IA, delayed rectifier, SK, or BK) which mediate the spike after hyperpolarization in VTA neurons. A model based on the data will be formulated to explain how the effects of ethanol on identified membrane currents result in its very different effects on the input-output function of VTA and LC neurons. Information about the mechanisms of acute ethanol action is a necessary prerequisite to understanding the mechanisms underlying the rewarding effects of ethanol, as well as how ethanol tolerance and physical dependence develop. This, in turn, should permit the rational development of better therapeutic regimens for treatment of habitual ethanol usage and the ethanol withdrawal syndrome.
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