P-chlorophenylalanine facilitates copulatory behavior in septal lesioned but not in preoptic lesioned male rats

Effects of p-chlorophenylalanine (pCPA), synthesis-inhibitor of serotonin, on copulatory behavior were examined in testosterone (T) treated castrated male rats with lesions in the lateral septum (LSL) or in the medial preoptic area (MPOL). Three weeks after the operation, all animals were chronically treated with T using silastic capsules. Behavioral tests were carried out at 10 and 20 days after the implantation of T. In half of the males in each group, 100 mg/Kg pCPA was injected daily for 4 days before each test. The other half of the group was injected with saline instead of pCPA. In saline-treated groups, the males with LSL or MPOL showed extremely lower frequencies of mount and intromission than control males without brain surgery. PCPA-treated control males showed higher copulatory activities than saline-treated control males. In contrast, even after the treatment with pCPA, severe impairment of sexual behavior was observed in males with MPOL. On the other hand, pCPA-treated LSL males displayed copulatory behavior more frequently than saline-treated LSL males. These results agreed with previous reports that both the medial preoptic area and the lateral septum play an excitatory role in regulating male sexual behavior. Conversely, the serotonergic neuronal system exerts an inhibitory influence for male sexual behavior. Furthermore, these results suggest that the inhibitory function of serotonergic neurons govern dependently on the function of the medial preoptic area, but independently on the function of the lateral septum.