Glial–neuronal–endothelial interactions and the neuroendocrine control of GnRH secretion

Abstract

This chapter reviews that nonneuronal cells, such as glial and endothelial cells, are dynamic signaling components with the potential to modulate the way information is generated and disseminated within the brain. It discusses that in the hypothalamus, neurons secrete gonadotropin-releasing hormone (GnRH) that offer an attractive model system to study astroglial, neuronal, and endothelial interactions, and the influence that steroid hormones may have on this process. GnRH is the neuropeptide that controls both sexual maturation and adult reproductive function. During the reproductive cycle, GnRH release into the pituitary portal vessels is modulated by dynamic alterations of the anatomical relationship that exists between GnRH nerve endings and glial cell processes in the median eminence of the hypothalamus. These plastic rearrangements and GnRH secretory activity itself appears to be modulated, at least in part, by specific cell–cell signaling molecules secreted by glial and endothelial cells. The chapter reviews that an increasing body of evidence suggests that among the different factors that may be involved, glial cells use growth factor members of the epidermal growth factor (EGF) family, acting via receptors endowed with tyrosine kinase activity to establish this modulatory control, whereas endothelial cells of the median eminence employ nitric oxide to facilitate GnRH release.