Odor of specific alcohol solutions selectively alters locomotor activity of alcohol-drinking P rats

Evidence exists that the olfactory property of alcohol affects cerebral processes to influence the pattern of alcohol drinking in an experimental animal. In this study, the level of activity was quantified in the genetically selected alcohol-preferring P rats during exposure to the odor of 4 concentrations of alcohol. A Mini-Mitter transmitter was implanted intraperitoneally in each animal to record individual locomotor activity continuously, in terms of counts per unit time. In the first experiment, each rat was exposed between 1730 and 1930 h to the odor of 5%, 15%, 30%, or 60% alcohol placed in 2 petri dishes flanking both sides of each cage. The control condition was identical, except that the petri dishes were empty. In the second experiment, each rat was offered water and its individually preferred solution of alcohol in the drinking tubes during 1730 to 1930 h on alternate days of exposure to the odor of alcohol. During the odor condition alone, the 30% concentration of alcohol increased the activity counts significantly from the control level of 228.8 +/- 23.9 to 303.5 +/- 28.1 over the first 30 min of the 2-h test period. Plots of activity every 30 min for each alcohol solution, calculated as percent of control, also showed that the odor of 30% alcohol evoked significantly greater activity during the first and fourth intervals, in contrast to the exposure to 5%, 15%, and 60% alcohol, which failed to shift activity beyond the control level. When the P rats were exposed to 30% alcohol 24 h after 2 h of alcohol drinking, their profile of activity was concordant with that prior to alcohol drinking. These results demonstrate that the odor of a specific concentration of alcohol (i.e., 30%) selectively enhances the activity of the P rat. This could reflect an association of the sensory quality of alcohol with an anticipation of drinking. Finally, these experiments provide the first quantitative evidence that an olfactory cue associated with the unique odor of a specific solution of alcohol may determine the nature of the drinking response.