Estrogen in the medial preoptic area of male rats facilitates copulatory behavior

Mating was studied in sexually experienced, gonadally intact male rats assi gned to two surgical groups matched on the basis of mean mounting frequency during behavioral screening trials conducted prior to the study. Estradiol (E-2) was delivered bilaterally into the medial preoptic area (MPO) of exp erimental males by means of hormone-coated implants, and fadrozole was give n sc (0.25 mg/kg/day) via osmotic minipumps to block E-2 formation from tes ticular testosterone throughout the brain. Control males received blank bil ateral implants in the MPO and sc fadrozole. After the completion of behavi oral testing, immunocytochemical comparisons of the brains from experimenta l and control rats were made using the H222 antiestrogen receptor (ER) anti body, whose labeling is inhibited by the presence of E-2. The histology dem onstrated that E-2 was confined exclusively to the MPO of experimental male s but was absent throughout the brains of controls. In controls, mounting d ecreased significantly by the 7th day after surgery compared with presurgic al levels and did not recover. In contrast, on all postsurgical days, the m ounting frequency of the experimental group was significantly higher than t hat of controls. Although experimental males also showed an initial, signif icant postsurgical decline in mounting frequency, it recovered completely b y the 28th postoperative day. Ejaculations declined significantly after sur gery in both groups but, unlike in controls whose performance remained low, ejaculations in experimental males partially recovered and were significan tly higher than in controls during the postoperative period. Results showed that ER-containing neurons in the MPO influence male rat copulatory behavi or. (C) 2000 Academic Press.