Plasma concentrations of testosterone in adult male rats following acquisition of copulation-illness associations

Abstract

<p>Prior research has demonstrated that testosterone is necessary for the expression of copulatory behaviors in adult male rats. Further, stimuli paired with copulatory experiences elevate circulating levels of testosterone. The purpose of the present experiment was to assess testosterone levels in adult male rats whose copulatory behaviors had been associatively inhibited. Each male rat was exposed to an inaccessible estrous female for seven min and was then given an opportunity to copulate. Two groups received an injection of either lithium chloride (LiCl; 0.3 M, 20 ml/kg, ip; n = 9) or saline (0.3 M, 20 ml/kg, ip; n = 8) immediately after each of 12 such pairings spaced at 3-4 day intervals. A third group (n = 8) received a noncontingent injection of LiCl 24 hr after each pairing. On the thirteenth trial male rats were returned to their home cages after seven min of exposure to an inaccessible female. Blood was collected by decapitation 38 min later. Testosterone levels were measured using radioimmunoassay techniques. Male copulatory behaviors of rats that received contingent administration of LiCl gradually declined during successive test sessions while rats that received noncontingent LiCl or saline remained vigorous copulators. Mean levels of plasma testosterone were comparable for rats that received either contingent or noncontingent LiCl, and were significantly lower than that of rats receiving saline. Thus, the gradual decline in copulatory behaviors in rats that received LiCl immediately after each pairing with an estrous female cannot be attributed to inadequate levels of circulating testosterone. Male rats that received LiCl 24 hr after each pairing with an estrous female had comparable levels of testosterone, yet copulated during all test sessions.</p>