Although testosterone is essential to spermatogenesis in primates, factors controlling spermatogonial proliferation are still unclear. Protein gene product (PGP) 9.5 is not only one of the markers of the nervous system, but also a common protein which is present in neurons and spermatogonia. To investigate the behavior of PGP 9.5 in primate spermatogenesis, two adult male Japanese macaques were studied during the breeding season using PGP 9.5 immunohistochemical methods, and also combined with proliferating cell nuclear antigen. (PCNA). During the 10 stages of the epithelial cycle the PGP 9.5 immunopositive cell number per 1 mm of basal lamina of the seminiferous tubules were compared using the NIH Image computer program. At each epithelial stage the PGP 9.5 positive ratios in the three types of spermatogonia were examined. PGP 9.5 was found only in the spermatogonia. Compared with the number of PGP 9.5 immunopositive spermatogonia/mm of basal lamina of the seminiferous tubule in each epithelial stage, there was a significant difference between the numbers in. stage I to VI and those in stage VII to X. The number of PGP 9.5 positive cells in stage VII decreased abruptly. The value gradually decreased from stage VII to X and finally the value in stage X was about 40% that of stage I. The PGP 9.5 positive ratio of type Ap spermatogonia was significantly decreased at stage VII and VIII, which coincided with the decrease of total positive cells during the latter half of the epithelial stage, while positive ratios of type Ad and B spermatogonia were consistent during the epithelial cycle; type Ad was over 90%, while type B was almost zero. Dual immunohistochemistry of PGP 9.5 and PCNA revealed that spermatogonia expressed either PGP 9.5 or PCNA. The total of both were only 15 out of 2620 (0.5%). The present study suggests that PGP 9.5 is one of the factors that closely relate to the proliferation of spermatogonia in Japanese macaques (Macaca fuscata).
