MALE SEXUAL-BEHAVIOR IS ASSOCIATED WITH LHRH NEURON NUMBER IN MIDDLE-AGED RATS

LHRH administration is reported to facilitate male sexual behavior. Th e aim of the present study was to investigate whether male sexual beha vior is associated with the number of LHRH neurons in the forebrain in middle-aged rats. Male Long-Evans rats (18-19 months) were assigned t o three groups on the basis of sexual performance: (1) group MEI consi sted of rats showing complete copulatory patterns, including mounts, i ntromissions and ejaculations, (2) group MI was composed of rats showi ng mounts and intromissions, but no ejaculation and (3) group NC were non-copulators, i.e. they did not show any copulatory behavior. Young adult rats (4-5 months), displaying sexual behavior, were used as cont rols. Following the sexual behavior tests, the number of LHRH neurons in the medial septum (MS), organum vasculosum of the lamina terminalis (OVLT), preoptic area (POA) and anterior hypothalamus (AH) was determ ined by immunocytochemistry. No difference was seen in the total numbe r of LHRH neurons in these combined brain areas between group MIE and young controls. In the three middle-aged groups, the total number of L HRH neurons was greatest in group MIE, less in group MI, and lowest in group NC. In general, a similar trend was seen separately in the MS, OVLT and POA. These results suggest that changes in the number of LHRH neurons in the forebrain, in most cases, are age-related, at least in the middle-aged rats, but they also seem to be associated with male s exual performance. (C) 1997 Elsevier Science Ireland Ltd.