The efferents and/or afferents of the dorsal raphe nucleus (DRN) were transected by several types of cut in castrated male rats, and lordosis behavior was observed after implantation with Silastic tubes containing estradiol. Throughout the behavioral tests, low incidences of lordosis were observed in control male rate without brain surgery or with a sham operation. In contrast, all male rats with a horizontal circle cut at the ventral area of the DRN displayed lordosis, and the mean lordosis quotient (LQ) was higher than that in control rats, while rats with a horizontal cut at the dorsal area of the DRN did not. Furthermore, mean LQs in male rats with an anterior half-circle horizontal cut at the ventral area of the DRN were higher than those in control groups. A posterior half-circle cut at the ventral area had no effect. In addition, male rats with a half-dome cut located anterior to the DRN showed a high LQ score, but rats with a posterior half-dome cut did not. These results suggest that anterior and anteroventral neural fibers of the DRN are involved in the lordosis inhibiting mechanism in male rats.
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