Ontogenic studies of the neural control of adenohypophyseal hormones in the rat: gonadotropins.

1. Serotonergic, dopaminergic, and opioid systems controlling luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion develop with particular characteristics in the male and female prepubertal rats. 2. Serotonergic pathways evoke a maximal release of LH and FSH in female rats from day 12 to day 20 of age, but not in males of the same age. 3. Antidopaminergic drugs increase LH and FSH levels only in the female infantile rats. This effect is absent at birth and disappears after 20 days of age. 4. Naloxone markedly increases gonadotropins in 12-day-old females. 5. On the other hand, in 12-day-old male rats some neurotropic drugs such as diazepam could enhance LH levels, the effect being absent at other ages or in female littermates. 6. A period of high sensitivity of gonadotropins to neurotropic drugs is present during the second and third weeks of life of the rat and it is related to the sexual differentiation of the brain.