INTERACTIONS BETWEEN 5-HYDROXYTRYPTAMINE (5-HT) AND TESTOSTERONE IN THE CONTROL OF SEXUAL AND NONSEXUAL BEHAVIOR IN MALE AND FEMALE RATS

Two 5-hydroxytryptamine(2) (5-HT2) agents, ritanserin and 1-(2,5-dimet hoxy-4-iodophenyl)-2-aminopropane HCl (DOI) (both at 0.25 mg/kg IF), w ere administered to castrated males bearing graded testosterone implan ts (empty, 2.5-, 5-, and 10-mm length) and to normal and neonatally an drogenized ovariectomized females bearing 10-mm testosterone implants. The results indicate that testosterone stimulates male sexual behavio ur and appears to have a dose-related anxiolytic effect, but no effect on other nonsexual activities. 5-HT and testosterone had opposite eff ects on male sexual behavior, with ritanserin (5-HT antagonist) enhanc ing activity in both sexes and DOI (5-HT agonist) inhibiting behaviour in males, the latter being testosterone-dependent. Independent of tes tosterone, ritanserin reduced locomotion and exploration and increased anxiety in males, while DOI increased locomotion and exploration in b oth sexes. Ritanserin had a gender-specific effect on anxiety which wa s independent of testosterone, since in castrated males it was anxioge nic whether they bore testosterone implants or not, while in females i t was anxiolytic whether the females were neonatally androgenized (250 mu g/pup testosterone proprionate [TP] on day 1) or not. These result s show that 5-HT and testosterone have opposite effects on male sexual behaviour and these may be interrelated. In adulthood, their effects on nonsexual activities are not inversely related and are independent of each other in contrast to the relationship seen in the neonatal per iod.