Decreased experimental anxiety and voluntary ethanol consumption in rats following central but not basolateral amygdala lesions

A long-debated ‘tension reduction' hypothesis postulates anti-anxiety effects to be important for ethanol reward, and states that elevated anxiety levels might predispose for ethanol consumption and addiction. Human data are contradictory, possibly due to heterogeneity of patient samples. In rats, baseline levels of experimental anxiety have been reported to correlate with voluntary ethanol consumption. Here, we addressed the possibility that mechanisms underlying experimental anxiety might be causally related to regulation of voluntary ethanol intake. Rats were bilaterally lesioned in central amygdala using microinjections of ibotenic acid. This resulted in a robust release of punished drinking in a modified Vogel conflict test, an effect typically seen with anxiety reducing drugs. This effect was specific, as unpunished drinking was unaffected by the lesion. On the elevated plus-maze, central amygdala lesions did not affect behaviour under baseline conditions, but attenuated the anxiogenic effect of restraint stress. Measures of locomotor activity were not affected. Voluntary ethanol consumption was examined in a two-bottle, free choice paradigm. Ethanol intake was markedly decreased in the lesion group. Total fluid intake was not affected. Basolateral amygdala lesions, which did not affect conflict behaviour, also left ethanol intake unaffected. These results are consistent with previous reports of an important role for central amygdala in anxiety related behaviours, and suggest that cell bodies located in central amygdala might be important in this context. Further, our results support a relation between experimental anxiety and voluntary ethanol consumption.