Sexual arousal in male mice: effects of brief periods of isolation or grouping

The effects of short periods of postpubertal social isolation on mating in male mice were examined to elucidate behavioral transitions accompanying isolation and mechanisms mediating these transitions. Experiment 1 compared sexual performance of mice isolated or grouped for periods of 1 day or 2 weeks. Isolated males showed more mounts and intromissions and shorter mount and intromission latencies than grouped males at both intervals. This result differs from findings in other studies of social isolation, where effects on behavior and physiology tend to increase with increased time in isolation. Experiment 2 examined animals isolated for intervals ranging from 1 hr to 1 week. Isolates showed more mounts and intromissions than grouped animals at all intervals exceeding 12 hr. Simple cleaning of grouped animals' cages produced similar increases in mounting and intromitting at 1- and 4-hr intervals. In neither experiment was ejaculation frequency significantly affected by the experimental manipulations. The effects on sexual arousal, reflected in differences in mounting and intromitting, may be attributable to differences between isolated and grouped mice in exposure to aggressive encounters and pheromones. Such differences may in turn affect hormonal and neurochemical systems that modulate sexual activity.Denys deCatanzaro is now at the Department of Psychology, McMaster University, Hamilton, Ontario, L8S 4K1, Canada.