Effects of number of cagemates on home cage ethanol drinking during proximal cagemate drinking (PCD) procedures in male and female CD-1 mice.

The present experiment evaluated the effects of the Number of Cagemates (0 vs 1 vs 2) on home cage ethanol drinking during Proximal Cagemate Drinking (PCD) procedures in Male and Female CD-1 mice. Continuous-access home cage 2-bottle (ethanol vs. water) free-choice procedures were employed. PCD procedures eliminate the distracting effects of direct physical contact between Drinkers and their Cagemates on ethanol drinking by imposing a translucent plastic barrier strip between them. If direct physical contact distracts from drinking, then one Cagemate would drink more ethanol and more water than two Cagemates housed together on the same side of the barrier. This would be the case even if two Cagemates stimulated more ethanol drinking in the Drinker housed on the other side of the barrier, due to the social stimulation effects of additional Cagemates. Results revealed that the ethanol intake of Female Drinkers was directly related to the number of Cagemates on the other side of the barrier strip, but this social stimulation effect was not observed in Male Drinkers. For Male Cagemates and Female Cagemates, the single Cagemate provided elevated ethanol intake and elevated water intake relative to the ethanol intake and water intake of each Cagemate in the two Cagemates condition. The data revealed that direct physical contact between Cagemates reduced their ethanol intake, even while stimulating ethanol intake of the Drinker on the other side of the barrier, indicating that the effects of social stimulation on ethanol drinking are not entirely due to effects of modeling or peer pressure. The PCD procedures allow the evaluation of effects of a broad range of social factors on home cage ethanol drinking in mice.