Postnatal expression of polysialic acid-neural cell adhesion molecule in the hypothalamus of the male rhesus monkey (Macaca mulatta).

Puberty in primates is triggered by a gonad-independent reinitiation of a pulsatile mode of GnRH release. The purpose of the present study was to begin to examine the hypothesis that this neuroendocrine event is the result of structural or plastic changes within the neural network governing the activity of GnRH neurons. Specifically, we sought to determine whether polysialic acid neural cell adhesion molecule (PSA-NCAM), a plasma membrane-associated glycoprotein that has previously been proposed to be a marker for postnatal neuronal plasticity, was expressed within GnRH neuron containing areas of the rhesus monkey hypothalamus. The study employed male monkeys that were castrated prepubertally. Immunocytochemistry of hypothalamic tissue from four animals of pubertal age employing a monoclonal antibody (12F8) specific for PSA-NCAM revealed the presence of PSA-NCAM immunoreactivity within the region of the arcuate nucleus and median eminence of the medial basal hypothalamus (MBH) and in the region of the organum vasculosum of the lamina terminalis of the rostral hypothalamus, two areas in the monkey brain where GnRH neurons are concentrated. As expected, immunostaining for total NCAM using a polyclonal rabbit antibody to mouse total NCAM was uniformly distributed throughout hypothalamic sections containing the MBH. Double staining showed that some, though not all, GnRH cell bodies of the MBH were located within the PSA-NCAM-immunopositive region of the arcuate nucleus and the median eminence. The pattern of PSA-NCAM immunoreactivity in the MBH of three prepubertal monkeys was similar to that seen for the older animals. Western analysis of a membrane extract from the MBH of a monkey of pubertal age, employing antibody 12F8, identified a broad band of staining at the expected molecular weight for this adhesion molecule. A similar, but less intense, immunoreactive band was observed for the preoptic area. In contrast, an immunoblot of a membrane extract of cerebral cortex was only faintly positive for PSA-NCAM. Taken together, the foregoing findings are consistent with the notion that structural changes within the MBH may underlie the pubertal reinitiation of pulsatile GnRH release. Moreover, the presence of PSA-NCAM in the MBH of prepubertal monkeys suggests that the role, if any, of this molecule in the onset of sexual maturation in primates is permissive in nature.