ACUTE AND REPEATED ACTIVATION OF MALE SEXUAL-BEHAVIOR BY TAIL PINCH -OPIOID AND DOPAMINERGIC MECHANISMS

We studied the effect of tail pinch on male sexual behavior and its ne urochemical basis. Male rats were gonadectomized and maintained on low doses of testosterone propionate (20.0 mu g/day). Tail pinch signific antly increased the percentage of males that mounted, intromitted, and ejaculated within a 30-min test, and these increases were attenuated by both pimozide (1.0 mg/kg, IP) and by naloxone (0.5, 1.0, and 2.0 mg /kg, SC). Moreover, tail pinch in the presence of an estrous female le d to significantly increased female-directed behavior 48 h later durin g a test without tail pinch. Repeated tail pinch tests led to progress ively more sexual activity, and the development of this behavioral sen sitization was prevented by naloxone. These findings suggest that tail pinch increases the salience of the incentive characteristics of the female. Furthermore, during subsequent tests, with or without tail pin ch, the increased salience of the female remains, as measured by the c ontinued increases in sexual activity. These acute and sensitized beha vioral increases might result from tail pinch-induced activation of th e midbrain dopamine system via an opioid mechanism; either preventing tail pinch-induced dopamine activation (by an opioid antagonist) or bl ocking the effects of dopamine activation (by a dopamine antagonist) a ttenuated the long-term facilitation of sexual behavior seen after pai ring the female with tail pinch.