Brain Research Bulletin, Vol. 20, pp. 323-331. c Pergamon Press plc, 1988.Printed in the U.S.A. 0361-9230/88 $3.00 + .OO Regulation of Male Rat Copulatory Behavior by Preoptic Incertohypothalamic Dopamine Neurons’ DANIEL BITRAN, ELAINE M. HULL,’ GREGORY M. HOLMES AND KEITH J. LOOKINGLAND* zyxwvutsrqponmlkjihgfedcbaZY Department of Psychology State University of New York at Buffalo, Amherst, NY 14260 and *Department of Pharmacology and Toxicology M ichigan State University, East Lansing, M I 48824 Received 11 June 1987 BITRAN, D., E. M. HULL, G. M. HOLMES AND K. J. LOOKINGLAND. Regularion of male rat copulatory behavior by preoptic incertohypothalamic dopamine neurons. BRAIN RES BULL 20(3) 323-331, 1988.-The role of dopaminergic terminals in the medial preoptic area (MPO) in the regulation of male rat copulatory behavior was investigated. A 6-hydroxydopamine (6OHDA) injection into the MPO of animals pretreated with desipramine resulted in a small (23%) depletion of DA, and no impairment of copulatory activity. Further depletion of catecholamines with alpha-methyl p-tyrosine (AMPT) produced several deficits in the copulatory behavior of 6-OHDA-treated males, at a dose of AMPT that did not adversely affect copulation prior to 6-OHDA administration. The dose-related effects of intracranial apomotphine (APO) injections were also altered by 6-OHDA injections into the MPO. The inhibition previously found with 0.2 pg of APO into the lateral ventricle of normal males was abolished by 6-OHDA treatment. A facilitation of copulatory behavior was observed following the injection of 0.2 pg of APO into the MPO of 6-OHDA-treated animals, whereas this treatment did not affect the copulatory behavior of intact animals. Finally, inhibitory effects observed following an injection of 0.1 pg of APO into the MPO of normal males were blocked by 6-OHDA administration. The relative roles of presynaptic autoreceptors and postsynaptic DA receptors in the MPO in mediating the dose-related effects of APO on copulatory behavior are discussed. Sexual behavior Incertohypothalamic Dopamine Medial preoptic area Autoreceptors 6Hydroxydopamine Apomorphine Alpha-methyl p-tyrosine CLINICAL observations have long suggested that do- paminergic drugs have a facilitative effect on sexual re- sponses of men. For example, I-DOPA treatment has been reported to increase libido of Parkinson’s disease patients [6,11], and to increase the incidence and degree of penile erection in sexually impotent men [7]. Similarly, apomor- phine (APO), a dopamine (DA) receptor agonist, was re- ported to induce penile erection in alcoholics [45,46]. These clinical findings were based on self-report measures. How- ever, more convincing evidence of a dopaminergic influence in sexual responses is found in recent reports that systemic administration of APO induced penile erection in normal [34] and impotent men [35], as measured by strain gauges at- tached to the penis. Dopaminergic facilitation of sexual function in male rats has also been reported (for more detail see review in [9]). Briefly, the systemic administration of DA agonists reduced the number of intromissions prior to ejaculation, and de- creased ejaculation latency [ 12, 24, 40, 511. A central neural site of action was suggested since these effects were not affected by domperidone [24], a DA antagonist which does not cross the blood brain barrier, but were blocked by halo- peridol, a centrally acting DA antagonist [24, 40, 511. Recently, a controversy has arisen concerning the mech- anism mediating the effects of DA on sexual behavior. The reduction in intromission frequency and ejaculation latency which results from the systemic administration of DA agonists occurs in the same dose range which produces se- dation and hypoactivity. The inhibitory effects of low doses of DA agonists on locomotor behavior have been attributed to the preferential activation of presynaptic autoreceptors [22,23], which when stimulated decrease synthesis and re- ‘This research was based on a dissertation submitted to the State University of New York at Buffalo in partial fulftiment of the requirements for the Ph.D. degree, and has appeared in abstract form [8]. ZRequests for reprints should be addressed to Dr. Elaine M. Hull, State University of New York at Buffalo, Amherst, NY 14260. 323