Influence of age and of testosterone on the response of male rats to parachlorophenylalanine.

1. Castrated male rats and male rats that had been castrated as well as adrenalectomized, showed hypersexual behaviour 24 h after treatment with parachlorophenylalanine (PCPA), as did intact rats.2. A dose of PCPA 100 mg/kg was sufficient to induce mounting behaviour; this dose lowered the cerebral 5-hydroxytryptamine (5-HT) to about 50% in 24 h and further to 40% in 72 hours.3. Groups of juvenile male rats treated chronically with PCPA 100 mg/kg or 50 mg/kg, or with testosterone propionate 1.25 mg, showed hair loss after three weeks of treatment (6 injections), because of increased social interaction.4. Groups of intact male rats 9-11 weeks old given testosterone propionate 1.25 mg subcutaneously, showed mounting behaviour 3-5 h after the injection which was indistinguishable from the behaviour seen 24 h after treatment with PCPA 100 mg/kg. The 5-HT content of the brain was not altered by testosterone.5. The number of rats which showed mounting after PCPA treatment did not change with age, but the younger rats made more mounts in the observation time than rats more than three months old.6. The age of castration (3 weeks or 4 months) did not influence the results.