Extracellular concentrations of dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were examined concurrently, using in vivo microdialysis, in the nucleus accumbens and dorsal striatum of sexually active male rats during tests of locomotor activity, exposure to a novel chamber, exposure to sex odors, the presentation of a sexually receptive female, and copulation. DA increased significantly in the nucleus accumbens when the males were presented with a sexually receptive female behind a screen and increased further during copulation. Although DA also increased significantly in the dorsal striatum during copulation, the magnitude of the effect was significantly lower than that observed in the nucleus accumbens. In contrast, forced locomotion on a rotating drum, exposure to a novel chamber, and exposure to sex odors did not increase DA significantly in either region, although both DOPAC and HVA increased significantly in both regions during the locomotion test. These results indicate that novelty or locomotor activity alone cannot account for the increased extracellular DA concentrations observed in the nucleus accumbens of male rats during the presentation of a sexually receptive female behind a screen, nor can they account for the increased DA concentrations observed in both the nucleus accumbens and dorsal striatum of male rats during copulation. The preferential increase in DA transmission in the nucleus accumbens, compared with that in the striatum, suggests that anticipatory and consummatory aspects of sexual activity may belong to a class of naturally occurring events with reward values that are mediated by DA release in the nucleus accumbens.

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In vivo brain microdialysis was used to characterize the effects of some dopamine uptake inhibitors on the extracellular concentrations of dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striata of awake, freely moving rats. d-Amphetamine, GBR 12909, cocaine, nomifensine, methylphenidate, bupropion, and benztropine were administered directly to the striatum via the perfusion fluid in increasing concentrations (1-1,000 microM). All drugs increased extracellular DA in a dose-dependent manner; however, only d-amphetamine produced dose-dependent decreases in DOPAC and HVA concentrations. The shapes of the dose-response functions differed considerably between the drugs. At 100 and 1000 microM d-amphetamine had biphasic effects (an increase followed by a decrease) on dialysate DA concentrations. GBR 12909, methylphenidate, and benztropine also had biphasic effects when applied at the 1,000 microM concentration. In contrast, cocaine, nomifensine, and bupropion produced relatively monophasic increases in extracellular DA. Tetrodotoxin (TTX), which prevents action potentials by blocking voltage-dependent Na+ channels, did not prevent d-amphetamine induced increases in extracellular DA, but blocked completely the effects of cocaine, nomifensine, bupropion, and methylphenidate. While low doses (10 microM) of GBR 12909 and benztropine were highly sensitive to TTX, the toxin was only partially effective against higher doses of the compounds.(ABSTRACT TRUNCATED AT 250 WORDS)