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geno synthesis, release, and/or receptors for neurotransmitters in integrative out igrost in t copulatory patterns, and specifically sexual motivation. Testosterone increases nitric oxide synthase in the MPOA; nitric oxide increases motivation, copulatory patterns, and genital reflexes. We important for the elicitation of sexual behavior are mediated by slow genomic actions [1–5], although steroids also have rapid, nongenomic effects (reviewed in Refs. [6,7]). Among synthetic enzymes, Physiology & Behavior 83 (20 * Corresponding author. Present address: Department of Psychology,basal and female-stimulated dopamine release, which in turn facilitates copulation and genital reflexes. Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT2C receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT1A receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins. One means for this inhibition is a decrease in dopamine release in the mesolimbic tract