Glial ensheathment of GnRH neurons in pubertal female rhesus macaques.

During the period of development, prior to full sexual maturity, gonadotropin hormone-releasing hormone (GnRH) neurons are fully capable of synthesizing and processing the GnRH decapeptide. Nonetheless, the secretion of the hormone is not adequate to stimulate adult patterns of gonadotropin release. The present study was undertaken to examine ultrastructural characteristics of the GnRH neuron and its relationship to its environment in early-midpubertal female rhesus monkey. The neurons bore all the ultrastructural immunocytochemical characteristics of those in mature animals, but quantitative morphometrics revealed that they were extensively apposed by glial processes. Such ensheathment was described earlier in ovariectomized adult animals and was found to be reversible by administration of gonadal steroids. The density of synaptic input to GnRH neurons in the pubertal animals did not differ significantly from that of adult intact or ovariectomized animals from a previous study. Chemical identification will be required to determine whether there are age or hormonal differences in the innervation of these neurons. These results provide anatomical evidence in support of indications from other studies that the ovarian steroidal milieu affects GnRH-glial relationships. Further testing will be required to determine whether the attainment of sexual maturity in the female rhesus macaque is dependent upon a reduction in glial ensheathment of GnRH neurons.