8-OH-DPAT INFLUENCES EXTRACELLULAR LEVELS OF SEROTONIN AND DOPAMINE IN THE MEDIAL PREOPTIC AREA OF MALE RATS

Serotonin (5-HT) is generally inhibitory to male rat sexual behavior. However, the 5-HT,, agonist 8-hydroxy-di-propylaminotetralin (8-OH-DPA T), injected either systemically or into the medial preoptic area (MPO A), facilitates ejaculation. Three experiments were conducted to test the effects of 8-OH-DPAT on 5-HT and dopamine (DA) neurotransmission i n the MPOA, a very important site for the control of male sexual behav ior. In Experiment 1, systemically injected 8-OH-DPAT (0.4 mg/kg) decr eased extracellular 5-HT levels in the MPOA as measured by in vivo mic rodialysis. In Experiment 2, 8-OH-DPAT (500 mu M) administered directl y into the MPOA via reverse dialysis increased extracellular levels of both DA and 5-HT; pretreatment with the selective 5-HT1A antagonist e nyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPP I) failed to prevent 8-OH-DPAT's stimulatory effects on DA and 5-HT le vels in the MPOA. In Experiment 3, 8-OH-DPAT (8 mu g) co-injected with 5,7-dihydroxytryptamine (5,7-DHT; 6 mu g) prevented neurotoxic deplet ion of 5-HT in the site of injection (MPOA). Because systemic and MPOA injections of 8-OH-DPAT resulted in opposite effects on extracellular 5-HT in the MPOA, yet both can facilitate ejaculation, these data sug gest that moderate changes in 5-HT in the MPOA may have relatively lit tle influence on male copulatory behavior. Instead, the facilitative e ffects of 8-OH-DPAT in the MPOA on male copulatory behavior may result , at least in part, from stimulatory effects of 8-OH-DPAT on DA transm ission. Facilitative effects of systemic injections of 8-OH-DPAT may r esult from decreased 5-HT release in several sites. (C) 1998 Elsevier Science B.V.