EFFECTS OF COPULATION ON APOMORPHINE-INDUCED ERECTION IN RATS

By testing the effects of antecedent copulation on subsequent apomorph ine-induced penile erection we sought to test an implicit assumption i n the research on drug-induced ''spontaneous'' erection-namely, that t his research provides information relevant to the regulation of erecti on in copula. In experiment 1, male rats were observed after being inj ected SC with 0, 15, 30, 60, or 120 mu g/kg apomorphine (APO); 60 mu g /kg yielded the maximum probability of erection and yawning. In experi ment 2, males were injected with 60 mu g/kg APO after no exposure to f emales, after three intromissions, or after copulation to sexual satie ty. There was no significant effect of three intromissions, but sexual ly sated males displayed no erections, the first evidence that copulat ion affects drug-induced erections. In experiment 3, males had one eja culation, three intromissions, or no exposure to females immediately b efore injection with APO (60 mu g/kg, SC) or ascorbic acid vehicle. AP O induced both erection and yawning, but neither behavior was reliably affected by copulation in APO-treated males. Among vehicle-treated ma les, those having three intromissions or one ejaculation before the te st had shorter erection latencies and more erections than males not ex posed to females. Thus, a relatively small amount of copulation result ed in a level of erectile response similar to that of APO-treated male s. Optimal doses of APO may be no more effective in promoting erection in male rats than are the natural neurochemical sequelae to copulatio n.