Comparison of VTA Dopamine Neuron Activity in Lines of Rats Selectively Bred to Prefer or Avoid Alcohol

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Abstract
Background:Studies comparing alcohol‐naïve alcohol‐preferring (P) and ‐nonpreferring (NP) rats indicate that high alcohol drinking is associated with an innate deficiency of the mesolimbic dopamine (DA) system. We previously reported that ventral tegmental area (VTA) DA neurons in alcohol‐naïve P rats burst fire more frequently than VTA DA neurons in alcohol‐naïve Wistar rats. We hypothesized that increased burst firing in P rats may represent a compensatory mechanism to maintain adequate levels of DA in terminal areas, such as the nucleus accumbens, despite the deficient mesolimbic DA system. The present study sought to extend our previous work and include NP rats and to determine whether differences in VTA DA neuron activity could be generalized to other rat lines selected for high and low alcohol preference, namely the high (HAD) and low (LAD) alcohol‐drinking rats.Methods:The extracellular activity of posterior VTA DA neurons was recorded in unanesthetized alcohol‐naïve rats from the P/NP and HAD/LAD lines. Firing frequencies, burst activity, and the number of DA neurons encountered per electrode track were compared.Results:Dopamine neurons in the posterior VTA of P rats had a greater percentage of action potentials in bursts and greater number of bursts compared with posterior VTA DA neurons in NP rats. There were no differences in VTA DA neuronal activity between both replicate lines of HAD and LAD rats.Conclusions:Burst activity of posterior VTA DA neurons distinguishes P from NP rats, but does not generalize to other lines of rats selectively bred at Indiana University for alcohol preference and nonpreference. Increased burst activity of DA neurons in the posterior VTA may be related to alcohol preference in P rats but is not necessary for high alcohol drinking.