AMPHETAMINE-INDUCED HYPERACTIVITY - DIFFERENCES BETWEEN RATS WITH HIGH OR LOW PREFERENCE FOR ALCOHOL

This study determined the relationship between ethanol intake and spontaneous and amphetamine-induced locomotor activity. Locomotion was studied in high-preferring (HP; >70% of total fluid intake consumed as alcohol) and low-preferring (LP; <20% of total fluid intake consumed as alcohol) male Wistar rats with free access to water and a 6% (v/v) ethanol solution for 3 weeks. Following an alcohol-free 3-week period, the animals were tested for spontaneous motor activity for 1 h. One week later, locomotion was recorded in the same activity boxes following a subcutanous injection with d-amphetamine sulfate (1 mg/kg). For determination of plasma levels of corticosterone, blood samples were taken immediately after each of the two tests for locomotor activity. There was no difference between HP and LP rats with regard to spontaneous locomotor activity. Neither were there any differences in plasma levels of corticosterone between the groups. Amphetamine stimulated locomotion in both HP and LP rats, but to a significantly greater extent in HP animals. Both groups had higher blood levels of corticosterone after the amphetamine test than after the drug-free test, but the corticosterone increase was significantly larger in the HP than in the LP rats. These data indicate that the same neural substrate (e.g., the mesocorticolimbic dopamine system) may mediate important aspects of both ethanol drinking and amphetamine responsiveness. Individual differences in the properties of this substrate may account for the finding that ethanol drinking and amphetamine responsiveness covary. A possible explanation for this association may be that prior consumption of ethanol sensitizes the neural substrate responsible for amphetamine-induced hyperactivity. Alternatively, hereditary and/or experiential factors may account for the individual variations in the responsiveness of the mesocorticolimbic DA system to ethanol and amphetamine.