Alcohol intake in prairie voles is influenced by the drinking level of a peer

Abstract

Background: Peer interactions can have important effects on alcohol-drinking levels, in some cases increasing use, and in other cases preventing it. In a previous study, we have established the prairie vole as a model animal for the effects of social relationships on alcohol intake and have observed a correlation of alcohol intake between individual voles housed together as pairs. Here, we investigated this correlated drinking behavior, hypothesizing that 1 animal alters its alcohol intake to match the drinking of its partner.

Methods: Adult prairie voles were tested for baseline drinking levels with continuous access to 10% alcohol and water for 4 days. In Experiment 1, high alcohol drinkers (>9 g/kg/d) were paired with low alcohol drinkers (<5 g/kg/d) of the same sex on either side of a mesh divider for 4 days with continuous access to the same 2-bottle choice test. In Experiment 2, high drinkers were paired with high drinkers and low drinkers paired with low drinkers. In both experiments, animals were again separated following pairing, and drinking was retested in isolation. In Experiment 3, alcohol-naïve animals were tested for saccharin consumption (0.05%) first in isolation and then in high saccharin drinkers paired with low saccharin drinkers, and then in another isolation period.

Results: In Experiment 1, high drinkers paired with low drinkers significantly decreased their alcohol intake and preference from baseline drinking in isolation, and drinking levels remained significantly lower during isolation following pairing. Interestingly, there was variability between pairs in whether the high drinker decreased or the low drinker increased intake. In Experiment 2, high drinkers paired with high drinkers did not significantly change their intake level or preference, nor did low drinkers paired with low drinkers, and no changes occurred during the subsequent isolation. In Experiment 3, there was no change in saccharin intake or preference when high drinkers were paired with high drinkers or low paired with low, or in the subsequent isolation.

Conclusions: Alcohol drinking of prairie voles can be altered under social conditions, such that 1 animal changes its alcohol intake to more closely match the intake of the other animal, helping to explain previous findings of correlated alcohol drinking. The effect does not extend to saccharin, a naturally rewarding sweet substance. This behavior can be used to model the peer pressure that can often affect alcohol intake in humans.

Keywords: Microtus ochrogaster; alcohol self-administration; peer influence; prairie voles; social behavior.

Figure 1. High drinkers paired with low drinkers decrease alcohol drinking

Compared to baseline drinking in isolation, high drinkers (black bars) decrease A) preference for alcohol, and B) intake of alcohol, when paired with low drinkers (white bars), and the decrease in drinking persists during a subsequent isolation. Values indicate mean + SEM. *Statistically significant post-hoc differences (p<0.01).

Figure 2. Example of variation between pairs in intake level changes

Average alcohol intake (g/kg/day) across each four-day period is shown for individuals from two pairs. Pair 1 (open triangles) exhibits the alterations in alcohol drinking level corresponding to the group effects: the high drinker (upright triangle) decreases alcohol intake when paired with the low drinker, and the decrease persists in the subsequent isolation, while the low drinker (upside-down triangle) maintains its low drinking level. In contrast, Pair 2 (filled triangles) exhibits the opposite effect: the high drinker (upright triangle) maintains its high level of alcohol intake, even increasing when paired with the low drinker, while the low drinker (upside-down triangle) increases its intake to the level of the high drinker, and the increase persists in the subsequent isolation.

Figure 3. Matched drinkers exhibit no change in alcohol drinking

High drinkers (black bars) and low drinkers (white bars) do not alter their alcohol A) preference, or B) intake, when paired with same-level drinkers, or in a subsequent isolation. Values indicate mean + SEM.

Figure 4. Saccharin drinkers exhibit no change in drinking

High drinkers (black bars) and low drinkers (white bars) do not alter their saccharin A) preference, or B) intake, when paired with opposite-level drinkers, or in a subsequent isolation. Values indicate mean + SEM. *Statistically significant post-hoc differences (p<0.01).