Environmental lighting has a selective influence on ethanol intake in rats

The effect of lighting condition on levels of absolute ethanol intake were systematically examined in the present study. Wistar rats were exposed to o ne of three lighting conditions: constant light, constant dark, and a stand ard 12/12 light/dark cycle. The animals were acclimatized to lighting condi tions for 2 weeks prior to ethanol (EtOH) acquisition with water and food a vailable ad lib. EtOH was then presented in increasing concentrations from 2% (v/v; 95% with tap water) to 10% on alternate days in free choice with w ater. Immediately following the acquisition phase, a maintenance period was initiated that began with everyday presentations of 10% EtOH solution in f ree choice with water. After 10 days, lighting conditions for the constant light and dark groups were switched to normal lighting (12/12 light/dark). EtOH and water intake were recorded for an additional 10 days. Rats exposed to constant light during EtOH acquisition and maintenance consumed less Et OH during the maintenance period than rats exposed to normal lighting condi tions. When lighting conditions were switched to a normal cycle, water cons umption increased significantly but EtOH intake did not change. Rats living in constant dark during EtOH acquisition and maintenance consumed less EtO H during the acquisition period when compared with rats living in normal li ghting conditions. Unlike animals trained under constant lighting, switchin g to normal lighting conditions had no effect on EtOH or water intake. Ther e were no differences in water consumption levels among the groups during a cquisition and maintenance, suggesting a specificity of the effects of ligh ting condition on EtOH intake. The present study, therefore, has attempted to show that an environmental variable such as lighting may exert a selecti ve influence on EtOH self-selection in rats. (C) 1999 Elsevier Science Inc.