Studies of instrumental behavior with sexual reinforcement in male rats (Rattus norvegicus): II. Effects of preoptic area lesions, castration, and testosterone.

We studied effects of lesions to the medial preoptic area (POA), castration, and testosterone replacement on instrumental and unconditioned sexual behavior in male rats. We achieved instrumental measures of sexual motivation by training males to work for an estrous female, presented in an operant chamber under a second-order schedule of reinforcement. POA lesions abolished mounts, intromissions, and ejaculation but did not disrupt instrumental responses, investigation of the female, or abortive mounting attempts. Castration abolished attempts to copulate and also caused a marked decrease in instrumental responses. Testosterone resulted in the prompt reinstatement of instrumental responses and more gradual recovery of unconditioned sexual behavior. We discuss these results in terms of the motivational and performance effects of these neuroendocrine manipulations.