TESTICULAR GAMMA-AMINOBUTYRIC-ACID AND CIRCULATING ANDROGENS IN SYRIAN AND DJUNGARIAN HAMSTERS DURING SEXUAL DEVELOPMENT

Several factors, besides luteinizing hormone (LH), participate in the modulation of testicular function. A number of neurotransmitters are r eported to be involved in this process, including a stimulatory action of gamma-aminobutyric acid (GABA) on steroidogenesis in the rat testi s. The purpose of this study was to investigate the testicular pattern of GABA and glutamic acid, one of its main precursors, during sexual maturation in two seasonally breeding species: Syrian (golden) and Dju ngarian hamsters. Plasma androgen levels were also measured. The anima ls were maintained under long-day photoperiod (16:8, L:D) and were kil led at 23, 30, 36, 46, 60, and 90 days of age. A different pattern of developmental changes in body and testicular weight was observed in th ese two species. GABA was present in the testes at all ages studied. G ABA concentration and content showed a sharp elevation in the prepuber tal period in golden as well as Djungarian hamsters. However, glutamic acid concentrations remained nearly constant during development in bo th species. Glutamic acid content increased gradually with age in the golden hamster, while a marked peak at 36 days of age was detected in the Djungarian hamster. Plasma testosterone and dihydrotestosterone le vels were maximal at pubertal age in both species. The plasma levels o f 5 alpha-androstane-3 alpha,17 beta-diol increased significantly at 3 0 days of age in the golden hamster white in Djungarian hamsters this steroid remained unchanged. These results suggest that glutamic acid m ay serve as a precursor for GABA biosynthesis in the testis. In additi on, changes in testicular GABA and plasma androgen levels might reflec t a modulatory effect of this neurotransmitter in the acquisition of s teroidogenic capability during development.