Role of the amygdala and the organum vasculosum laminae terminalis in the control of ovarian function in the female rat

Experiments have been performed to study the role of the amygdala and of the organum vasculosum laminae terminate (OVLT) in the control of gonadotrophin secretion. Amygdala. Drugs known as antagonists or agonists of the adrenergic and of the cholinergic receptors have been implanted at the level of the basomedial area of the amygdala in long-term castrated female rats. The animals were sacrificed at different time intervals after implantation, and their serum levels of LH and FSH were measured with specific radioimmunoassays and compared to those of shamimplanted animals. The results have shown that adrenergic and cholinergic receptors involved in the control of gonadotrophin secretion are present in the amygdala. In particular, the data have shown that: (1) α-adrenergic receptors of the amygdala exert an inhibitory tone on LH and FSH secretion; (2) β-adrenergic receptors seem to exert an inhibitory influence only on LH release; (3) cholinergic receptors of the muscarinic type appear to exert an inhibitory influence on LH output; (4) cholinergic receptors of the nicotinic type seem to play a role in depressing FSH secretion. OVLT. This structure was destroyed by radiofrequency lesions in regularly cycling and in long-term castrated adult female rats. After OVLT lesion practically all cycling females (16 out of 22) entered a dioestrous status, as indicated by vaginal smears. At the moment of sacrifice (8 days after the lesion) their serum gonadotrophin levels were as low as those present in cycling animals in the phase of dioestrus. Castrated females bearing OVLT lesions had serum titres of LH and FSH as high as those of castrated controls. It is concluded that the OVLT plays a role in the control of the "cyclic" release of gonadotrophins, but is not involved in the "tonic" regulation of gonadotrophin secretion.