Changes in hypothalamic gene expression associated with the arrest of pulsatile gonadotropin-releasing hormone release during infancy in the agonadal male rhesus monkey (Macaca mulatta).

Abstract

This study examined whether changes in the levels of the messenger RNAs (mRNAs) encoding the gamma-aminobutyric acid (GABA) synthesizing enzymes, glutamate decarboxylase (GAD)65 and GAD67 and transforming growth factor-alpha (TGFalpha) in the hypothalamus are correlated with the arrest of pulsatile GnRH release during infancy in the agonadal male monkey. This experiment also provided the opportunity to examine changes in hypothalamic GnRH gene expression during this critical phase of primate development. Male rhesus monkeys were castrated at 1 week of age: four were killed 4-7 weeks after orchidectomy while pulsatile GnRH release was robust as reflected by high circulating LH levels, and four were killed at 12-15 months of age after establishing that pulsatile GnRH release had been arrested. GAD65, GAD67, TGFalpha, and GnRH mRNA levels were estimated using RNase protection assays employing homologous probes and the results were expressed relative to cyclophilin mRNA levels. GnRH peptide was measured by RIA. GAD65 and GAD67 mRNA levels in the hypothalamus of juveniles were significantly greater than those in neonatal monkeys. On the other hand, hypothalamic TGFalpha and GnRH mRNA (and peptide) levels in agonadal neonate and juvenile monkeys were indistinguishable. These results indicate that the molecular concomitants associated with bringing the hypothalamic GnRH pulse generator into check in agonadal neonatal males are not a mirror image of those previously reported at the time this neuronal network is reactivated at puberty when TGFalpha and GnRH gene expression increase and GAD65 and GAD67 mRNA levels remain unchanged. Thus, the neurobiological mechanism that reactivates pulsatile GnRH release at puberty is likely to involve more than a simple reversal of that underlying inhibition of the same network in late infancy.