Neuroendocrine Control of Gonadotropin Secretion

In this chapter, I describe the similarities and differences among species in the neuroendocrine control of gonadotropin secretion. The discussion focuses on mice and rats, sheep, and primates because considerable data are available on these mammals, and information from reflex ovulators, guinea pigs, and other domestic animals is also included. I first describe species differences in ovarian cycles and review the development of current concepts for the feedback relationships between the ovary and hypothalamo–hypophysial unit underlying these cycles. I then consider species differences in the feedback control of the luteinizing hormone (LH) surge, tonic LH secretion, and follicle-stimulating hormone secretion. Next I present an overview of the anatomical areas necessary for tonic and surge secretion of LH, the sites of steroid feedback, and the roles of norepinephrine, endogenous opioid peptides, and kisspeptin. Finally, the mechanisms responsible for the physiological suppression of reproduction that occurs prior to puberty, during lactation and periods of undernutrition, in response to social stimuli stressors, and in seasonal breeders are briefly compared among mammals.