NEUROENDOCRINOLOGY OF REPRODUCTION - OVERVIEW

This discussion began with a consideration of simplistic models of the male and female and suggested that with respect to the neural regulation of reproduction, one can consider certain factors important in intrinsic regulatory processes within one individual and others to be perhaps more important in what can be called extrinsic regulation. We have just indicated that genital stimulation, at least as defined by intromission, in some way can be monitored quantitatively by the brain of the female, resulting in an alteration in her own intrinsic regulation of pituitary-ovarian function. Moreover, it is clear that various sensory stimuli, whether they be pheromones, visual displays or perhaps ultrasonic vocalizations, may also superimpose their information on the intrinsic mechanisms for the regulation of reproduction. We have emphasized that an illustration of the brain as a simple box is much too simplistic. The brain is highly compartmentalized; the specific action of hormones is probably highly localized within specific areas of the brain which form the regulatory substrate for a particular function. At the level of the individual neuron, however, the local environment within the dendritic fields may be of paramount importance for normal neuroendocrine regulation, perhaps even more important than hormone-induced alterations in the electrical activity of 'projection' neurons. Steroid hormones may directly or indirectly modulate activity within local neuronal circuits. Finally, returning to the very beginning of this discussion, the concept of the sexual differentiation of the brain now has a morphological correlate that is easily recognized and may represent a signature of hormone action. Although the neuroendocrine control of reproduction is complex, the opportunity to explain these intricate interactions I find challenging and exciting. The reproductive process, of which neuroendocrine mechanisms form only one component, is indeed complex. However, this should not be discouraging. Additional knowledge at any level will be beneficial for the understanding of the process of reproduction and its control, and thus, for the benefit of mankind.