Joseph Linzey, Brigham Young University
Life Sciences
Dopamine (DA) D2 receptor expression parallels DA levels in the brain and these autoreceptors on DA neurons been shown to be modulated by long-term ethanol exposure. We have previously demonstrated that VTA GABA neurons also express D2 receptors, and that DA and D2 receptor agonists markedly enhance the excitability of VTA GABA neurons, opposite to their well-known inhibition of DA neurons. Most importantly, D2 receptor antagonists block ethanol inhibition of VTA GABA neurons and D2 receptor expression in VTA GABA neurons down-regulates with chronic ethanol. This study evaluates short-term D2 receptor adaptation in VTA GABA neurons and in DA release in the nucleus accumbens (NAc) by acute ethanol. In electrophysiology studies in anesthetized rats, periodic iontophoretic application of DA, or the D2 agonist quinpirole, markedly enhanced VTA GABA neuron firing rate, which was initially inhibited by ethanol, but resulted in latent and marked rebound excitation 30-60 min following injection. Using fast scan cyclic voltammetry (FSCV), we evoked DA signals in the core of the NAc by electrical stimulation of the medial forebrain bundle at the level of the lateral hypothalamus (60 Hz, 24 pulses). Intraperitoneal (IP) administration of ethanol (1.0-3.0 g/kg) dose-dependently decreased the amplitude of the MFB-evoked NAc DA signal. IP administration of the D2 antagonist eticlopride (1 mg/kg) markedly increased (250%) the amplitude of the evoked DA signal. When ethanol was administered after eticlopride it increased the amplitude of the DA signal an additional 42%. These findings suggest that ethanol induced decreases in evoked DA release may be due to autoreceptor feedback. Work is in progress to evaluate the short-term expression of D2 receptors in VTA GABA neurons following acute ethanol and to evaluate the effects of ethanol-induced short and long-term adaptations in VTA GABA neuron D2 expression in mediating ethanol effects on DA release in the NAc.