EXTRACELLULAR SEROTONIN IN THE LATERAL HYPOTHALAMIC AREA IS INCREASEDDURING THE POSTEJACULATORY INTERVAL AND IMPAIRS COPULATION IN MALE RATS

Serotonin (5-HT) is generally inhibitory to masculine sexual behavior, It has been suggested that 5-HT released after ejaculation may promot e the sexual quiescence of the postejaculatory interval (PEI). The fol lowing experiments were conducted to test (1) whether extracellular 5- HT increases in either the anterior lateral hypothalamic area (LHA(A)) or the medial preoptic area (MPOA) of male rats after ejaculation; (2 ) whether increasing 5-HT in these sites, by microinjecting the select ive serotonin reuptake inhibitor alaproclate, could inhibit copulatory abilities; and (3) whether copulation deficits produced by alaproclat e were attributable to locomotor impairments, The effects of local app lication of alaproclate on extracellular 5-HT levels in the LHA(A) and the MPOA were also tested. Extracellular serotonin was measured in al l experiments using in vivo microdialysis. Ejaculation was correlated with enhanced 5-HT release from the LHA(A); no 5-HT increases were obs erved before ejaculation, and levels were decreased toward basal value s during a subsequent copulatory series. Elevating 5-HT in the LHA(A) by microinjecting alaproclate inhibited copulation by increasing the l atency to mount, intromit, and ejaculate, This inhibition did not resu lt from nonspecific locomotor impairments. In the MPOA, 5-HT release r emained stable throughout copulation, and microinjecting alaproclate i nto this site did not significantly alter sexual behavior. These data support the large body of evidence suggesting that 5-HT is inhibitory to masculine sexual behavior. Furthermore, the LHA(A), but not the MPO A, may be one site responsible for serotonergic inhibition of copulati on during the PEI.