Male rats that receive an injection of lithium chloride (LiCl) after each pairing with an estrous female gradually decrease their copulatory behaviors. In the present experiments we demonstrated that a 6.0 mEq/kg (0.3 M, 20 ml/kg) dose of LiCl injected after trials spaced twice weekly at 3-4-day intervals induced more rapid acquisition of copulation-illness associations than a 3.0 mEq/kg (0.15 M, 20 ml/kg) dose. Contingent 0.3 M saline or noncontingent 0.3 M LiCl injections did not affect copulatory behaviors. The location of the male rat (home cage or test chamber) during a portion of the aversive state induced by LiCl did not influence rate of acquisition. Copulation-illness associations, once established, were retained over a 60-day interval. Comparable decrements in copulatory behaviors were evident when LiCl was injected at 1-, 5-, or 15-min intervals after pairings with estrous females when the males were detained in the test chambers during the delay intervals; decrements were not observed when the interval was increased to 30 or 60 min. An electric shock analog to the aversive state induced by LiCl did not induce decrements in copulatory behaviors. It was suggested that odor-illness associations may, in part, account for the decrements in copulatory behaviors in this paradigm.

Prior research has demonstrated that both yohimbine, an alpha2-adrenergic antagonist, and naloxone, an opiate antagonist, facilitate components of copulatory behaviors in nonstressed male rats. In the present experiments, we demonstrate that these drugs differentially affect copulatory behaviors when the behavioral testing situation contained an aversive element. Male rats received an injection of lithium chloride (0.3 M, 20 ml/kg, ip) immediately after each encounter with an estrous female. Consequently, male copulatory behaviors gradually declined during successive test sessions. These male rats also received ip injections of either yohimbine (2 mg/kg/ml), naloxone (4 mg/kg/ml), or isotonic saline 20 min prior to each copulation test. Yohimbine-treated rats were more likely to copulate than control rats during both acquisition and extinction of lithium chloride-induced associative inhibition of copulatory behavior. Conversely, naloxone-treated rats were less likely to copulate than control rats during both acquisition and extinction. These data are consistent with the hypothesis that yohimbine increases sexual motivation in the male rat and limit the generality of the excitatory effects of naloxone on copulatory behaviors.

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