Effect of estrogen and progesterone priming on the uptake and release of serotonin and noradrenaline from the ventromedial hypothalamus.

Estradiol benzoate (EB) or EB plus progesterone (P) were administered to chronic ovariectomized rats in doses which are known to induce sexual receptivity. P was injected 48 hr after EB and the animals were decapitated 54 hr after E.B. The ventromedial hypothalamus (VMH) (excluding the arcuate-median eminence region) was dissected out and used to determine 3H-noradrenaline (3H-NA) and 3H-serotonin (3H-5-HT) uptake and release induced by high potassium concentration. Animals injected with oil were used as controls. VMH from EB (10 micrograms/kg) plus P (2 mg/kg) primed animals had higher release of 3H-NE than controls; uptake and release of 3H-5-HT was also augmented in these animals. EB (100 micrograms/kg) priming alone did not induce significant variations. The increase in 3H-NA release is interpreted as evidence of incremented activity in a 3H-NA system, facilitating sexual receptivity. The change in 3H-5-HT uptake and release is discussed in respect to the existence of an inhibitory serotonergic system modulating sexual behavior.