A simple assay to study social behavior in Drosophila: measurement of social space within a group

We have established a new simple behavioral paradigm in Drosophila melanogaster to determine how genes and the environment influence the behavior of flies within a social group. Specifically, we measure social space as the distance between two flies. The majority of Canton-s flies, regardless of their gender, are within two body lengths from each other. Their social experience affects this behavior, with social isolation reducing and mating enhancing social space respectively, in both males and females. Unlike several other social behaviors in the fly, including the formation of social groups themselves (a well-described behavior), social space does not require the perception of the previously identified aggregation pheromone cis-vaccenyl acetate. Conversely, performance of the assay in darkness or mutations in the eye pigmentation gene white increased social space. Our results establish a new assay for the genetic dissection of a fundamental mode of social interaction.

Effects of short- and long-term REM sleep deprivation on sexual behavior in male rats

The influence of selective REM sleep deprivation on masculine sexual behavior has been a matter of controversy. In the present study, the sexual behavior of male rats was analyzed in subjects deprived on REM sleep by the island technique for 24 or 16 h daily during 20 days. When compared to control rats, both groups displayed changes in sexual performance since the first day. The effects were: an increase in mount, intromission and ejaculation latencies and in mount frequency as well; a decrease of ejaculation frequency and of the Hit rate. The effects became stronger as REM sleep deprivation progressed. Rats deprived of REM sleep for 24 h were extremely debilitated after 12 days and some of them died, whereas the rats REM deprived for 16 h remained healthy during the 20 days. These data indicate that REM sleep deprivation interferes with the mechanisms that regulate male sexual behavior.

Effect of acute and chronic stress on masculine sexual behavior in the rat

Masculine sexual behavior in rats can be stimulated by acutely stressing the animals. Nevertheless, little is known about the effect that different stressors could have on sexual behavior. In this work we studied the effect of different stressors applied both acutely and chronically on masculine sexual behavior. Sexually active male Wistar rats were submitted to stress by: immobilization (IMB); immersion in cold water (WIM); and electrical foot shock (EFS). These stressors were applied during 20 consecutive days and masculine sexual behavior was assessed on days 1, 4, 8, 12, 15 and 20. Motivational component, copulatory performance and copulatory potential were drastically altered by WIM. EFS produced significant alterations in almost all sexual parameters recorded but only when it was applied chronically. IMB only altered mount frequency and hit rate, although inconsistently. These results suggest that the effect of stress on sexual behavior depends on the nature and, in some conditions, on the duration of the stressor.

Muscarinic and nicotinic influences on masculine sexual behavior in rats: effects of oxotremorine, scopolamine, and nicotine

In this study, the role of cholinergic systems in the regulation of male sexual behavior was analyzed by different approaches. Both muscarinic agonists and antagonists, as well as a nicotine agonist, were administered to sexually experienced male rats. In Experiment 1, oxotremorine (OXO), a muscarinic agonist, decreased the intromission frequency and ejaculatory latency in a dose-dependent way. Moreover, an increase in ejaculatory frequency was observed. In Experiment 2, the muscarinic antagonist scopolamine (SCO) produced a dose-related impairment of sexual behavior, decreasing the percentage of sexually active males. The smaller doses of SCO delayed the initiation of sexual behavior and decreased ejaculatory frequency. In an attempt to analyze the effect of muscarinic supersensitivity on sexual behavior, in Experiment 3 a long-term blockade of muscarinic receptors (SCO for 17 days) was followed by OXO administration. Animals displayed a significant increase of mount frequency, which results in the decrease of both the hit rate and ejaculatory frequency. In Experiment 4, six doses of nicotine were acutely administered. Only the higher doses (0.4, 0.8, and 1.6 mg/kg) induced a decrease in intromission frequency, although no significant differences were found in any other parameter. These results strongly suggest that cholinergic participation in masculine sexual behavior regulation is mediated mainly through muscarinic system.