Limited access to ethanol increases the number of spontaneously active dopamine neurons in the posterior ventral tegmental area of nondependent P rats

Microdialysis experiments in alcohol-preferring (P) rats have shown that chronic ethanol exposure increases extracellular levels of dopamine (DA) in the nucleus accumbens. Because DA neuronal activity contributes to the regulation of DA overflow in terminal regions, we hypothesized that posterior ventral tegmental area (VTA) DA neuronal activity (firing frequency, burst activity, and/or the number of spontaneously active DA neurons) would be increased in P rats consuming ethanol compared with P rats consuming only water. In vivo electrophysiological techniques were used to evaluate the activity of single DA neurons in the posterior VTA. Our findings show that voluntary ethanol intake by nondependent P rats significantly increased the number of spontaneously active DA neurons in the posterior VTA compared with P rats that consumed only water. Firing frequency and burst activity did not differ between the two groups. These results suggest that adaptive changes occur in the mesolimbic DA system of nondependent P rats to increase the excitability of posterior VTA DA neurons and enhance DA release from nerve terminals in the nucleus accumbens.