STUDIES OF EJACULATION

Report 8. Brain Monoaminergic Systems Controlling Ejaculation

Abstract

The effects of psychotropic drugs both on ejaculation, which was induced by manual stimulation fo the penis in dogs, and on the brain contents of catecholamines (CA) and serotonin (5HT) in dogs and rats were investigated.
The results obtained are as follows:
I) Effects on ejaculation in dogs.
1) Although erection was maintained after administration of 0.063mg/Kg of reserpine i. p., ejaculation was almost suppressed by the drug. When 50mg/Kg of L-dopa was administered i. p., ejaculation was recovered to the extent before the administration of reserpine. As the doses of reserpine increased to 0.125 and 0.5mg/Kg, the rate of dogs which maintained erection decreased, and ejaculation was suppressed completely. Administration of L-dopa, 50mg/Kg, i. p., also recovered ejaculation in these dogs.
2) After administration of tetrabenzaine, 100mg/Kg, i. p., erection was maintained in all dogs, but ejaculation was suppressed. Administration of L-dopa, 50mg/Kg i. p. recovered ejaculation.
3) When 50 and 25mg/Kg of L-5-hydroxytryptophan (L-5HTP) administered i. p. to 4 dogs, erection was suprressed in 3 of 4 dogs examined, and ejaculation was suppressed in all dogs. Administration of 12.5mg of 5-HTP suppressed ejaculation, although erection was maintained.
4) Administration of p-chlorophenylalanine (pCPA), 100mg/Kg once a day for 3 days did not change ejaculation. When L-5HTP 12.5mg/Kg i. p. was administered to the dogs, ejaculation was suppressed, although erection was maintained.
5) When haloperidol, 3-4mg/Kg, was administered i. v., erection was maintained but ejaculation was suppressed. In dogs, to which 5mg/Kg of haloperidol was administered, both erection and ejaculation were suppressed.
II) Effects on brain monoamine contents in rats.
1) When 50mg/Kg of tetrabenazine was administered i. p., the level of dopamine (DA) decreased in the cerebellum, pons-medulla-oblongata, hypothalamus, striatum, midbrain, hippocampus and cortex. The level of noradrenaline (NA) decreased in the cerebellum, pons-medulla-oblongata, hypothalamus, striatum, midbrain, hippocampus, and cortex. The level of 5-HT decreased in the pons-medulla-oblongata, hypothalamus, striatum, midbrain, hippocampus, and cortex.
2) When 300mg/Kg of L-dopa was administered i. p. after administration of tetrabenazine, the level of DA increased in all sites measured, compared with the rats in which tetrabenazine was administered alone. The level of NA increased significantly in the cerebellum, striatum and midbrain. The level of 5-HT did not change significantly, compared with that in the rats in which tetrabenazine was administered alone.
3) When 200mg/Kg of pCPA was administered once a day for two days, the level of DA increased in the hypothalamus and decreased in the cortex, compared with that of the controls. The level of NA increased only in the cerebellum. The level of 5-HT decreased significantly in all sites, compared with the controls.
III) Changes of brain monoamines in dogs.
Twenty-four hours after administration of reserpine, 0.063mg/Kg, the DA level was markedly decreased in the anterior hypothalamus, hippocampus and caudate. The NA level did not change in any site except for the hippocampus and caudate. The level of 5-HT decreased in the anterior hypothalamus but no change was observed in the other sites.
When L-dopa was administered to these dogs, the DA level markedly increased in the anterior and posterior hypothalamus. The DA level of the hippocampus was restored only to the control level. However, the NA and 5-HT levels did not change in any site, compared with those of the dogs in which reserpine was administered alone.
These results show that ejaculation is controlled by the dopaminergic and serotonergic systems in the brain, and that ejaculation is activated by the dopaminergic system, particularly by that in the anterior hypothalamus, and inhibited by the serotonergic system.