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The earliest study implicating the medial preoptic area/anterior hypothalamus (MPOA/AH) in the control of masculine reproductive behavior dates back to 1941, when Brookhart and Dey (1941) reported that sexual behavior was disrupted in male guinea pigs following the placement of lesions in this part of the diencephalon. These lesions, which were located near the base of the brain between the optic chiasm and the pituitary stalk, caused no sign of testicular atrophy, thereby raising the possibility that pituitary gonadotrophin secretion and sexual behavior are controlled by different brain circuits. Further support for this hypothesis was derived from studies showing that electrical stimulation of different limbic brain regions, including the MPOA/AH, induced penile erections in squirrel monkeys (McLean & Ploog, 1962). Working with male rats, Hillarp, Olivercrona, and Silfverskiold (1954) showed that electrical stimulation of the MPOA activated mating, and Soulairac and Soulairac (1956) showed that lesions of the MPOA/AH eliminated mating behavior in male rats without producing gonadal atrophy.
Other researchers from that same period suggested that the MPOA/AH is a crucial site for the steroidal activation of masculine coital behavior. For example, Davidson (1966) and Lisk (1967) showed that implantation of testosterone propionate (TP) into the MPOA/AH restored copulation in long-term castrated male rats, suggesting that sex steroids act in MPOA/AH neurons to reverse the deficits in sexual motivation and performance that invariably occur in rats after castration. Shortly thereafter, Pfaff (1968) and Sar and Stumpf (1973) used in vivo autoradiography to show that both ^sup 3^H-testosterone and ^sup 3^H-estradiol were specifically bound, respectively, by neurons in the female and male rat's MPOA/AH. Further evidence of a crucial role of steroids in enhancing the responsiveness of MPOA/AH neurons to socially relevant pheromonal cues came from Pfaff and Pfaffman (1969) who showed that testosterone (T) augmented the electrical activity of MPOA/AH neurons following exposure to urine from an estrous female rat. Nonreproductive odors, such as amyl acetate (banana odor), had no such effect. In these classic studies, investigators pointed to the critical role of the MPOA/AH in reproductive function and inspired several lines of research that have contributed greatly to our knowledge of the role of the MPOA/AH in the control of masculine sexual behavior. The aim of the present review is to summarize these...