Postnatal expression of nerve growth factor receptors in the rat testis

Because nerve growth factor beta (NGF beta) and its corresponding receptors have been implicated in the paracrine regulation of spermatogenesis, we examined the postnatal developmental expression of the low- and high-affinity NGF receptors in the rat testis, and localized their expression to specific testicular cell types. The neurotropin receptors consist of a low-affinity p75 nerve growth factor receptor (LNGFR) and a family of high-affinity tyrosine receptor kinases (trk). Both the p75 LNGFR gene product and the trk receptor gene product were detected in immature rat testes, with maximal expression in 10- and 20-day-old rats. Expression of the testicular p75 LNGFR and the trk receptor progressively declined in older animals so that they were barely detectable in 90-day-old adult rats. The 75-kDa LNGFR was detected in membrane fractions of Sertoli cells, whereas the p75 LNGFR was not detected by Western blot in membrane fractions of round spermatids and primary spermatocytes. Interestingly, microsomal fractions of peritubular myoid cells were immunoreactive for a 65-kDa band on Western blots with the p75 LNGFR monoclonal antibody. Immunoblot analysis of the trk receptor in cell lysates of isolated cell types was inconclusive. Excess NGF beta and round spermatid protein, which is known to contain a NGF-like protein, were both capable of displacing the binding of 125I-NGF beta from the surface of Sertoli cells.