A Causative Factor of Copulatory Disorder in Rats Following Social Stress

Abstract

We investigated the causative role of testosterone in copulatory disorder and the expression of c-fos messenger (m)RNA in the medial preoptic area in rats after social stress. To generate copulatory disorder rats in the experimental defeated group were attacked by residents for 10 minutes daily for 7 consecutive days (social stress). We then investigated the effect of repeat defeat on the frequency of mounting behavior and plasma testosterone levels. The effects of testosterone replacement and/or apomorphine (100 microg./kg. subcutaneously), a dopamine receptor agonist, on the frequency of mounting behavior were also studied. After experiencing social stress the brain area within the medial preoptic area was removed for analysis of c-fos and androgen receptor mRNA expression. Real-time reverse transcription-polymerase chain reaction was done to analyze gene expression. Rats in the defeated group showed a reduced frequency of mounting behavior and a decrease in plasma testosterone levels compared with values in control rats (p <0.01). After testosterone replacement the frequency of mounting behavior became significantly higher than that of socially stressed rat (p <0.05) but did not achieve control levels. The frequency of mounting behavior by socially stressed rats after apomorphine treatment was significantly higher than that of vehicle treated rats (p <0.05) but the frequency produced by the combination of testosterone replacement and apomorphine injection did not achieve control levels. After the social stress experience c-fos mRNA expression was significantly increased compared with that in control rats (p <0.05). The expression of androgen receptor mRNA was not affected by social stress. Testosterone replacement significantly reduced the expression of c-fos mRNA in the medial preoptic area (p <0.05). Our results indicate that a reduction in plasma testosterone may have a causative role in copulatory disorder induced by social stress. Changes in c-fos mRNA expression in the medial preoptic area correlated with copulatory disorder and, thus, they are suitable for monitoring that disorder.