Effect of low doses of ethanol on spontaneous locomotor activity in UChB and UChA rats

The effects of low to moderate doses of ethanol on spontaneous locomotor activity were studied in the selectively bred high-ethanol drinking (UChB) and the low-ethanol drinking (UChA) strain of rats. Alcohol-naive rats had food and water available ad libitum, although food was removed 24 hours before and during activity testing. After an injection of c.15 M NaCl or ethanol (0.25-1.0 g/kg), spontaneous locomotor activity was monitored every 5 minutes for 20 minutes in an open field apparatus. The UChB rats exhibited increased locomotor activity after doses of 0.25 and 0.50 g/kg of ethanol, while UChA rats failed to show increased locomotor activity at any ethanol dose. Moreover, the UChA rats appeared to be more sensitive to the sedating effects of 1.0 g/kg of ethanol than the UChB rats. These differences were not the result of different brain-blood alcohol levels. Ethanol intakes by the UChB and UChA rats determined at the conclusion of activity testing averaged 5.0 ± 0.5 and 1.9 ± 0.4 g/kg/day, respectively. The data suggest that ethanol-induced locomotor stimulation may be associated with ethanol preference and that hyperactivity may be an expression of the positive reinforcing effect of ethanol in UChB rats.