Influence of photoinhibition on GABA and glutamic acid levels, and on glutamate decarboxylase activity in the testis and epididymis of the golden hamster.

Gamma-aminobutyric acid (GABA) is found in the gonads and accessory reproductive organs, and a direct effect on steroidogenesis and sperm viability and motility has been described. The golden (Syrian) hamster is a seasonal breeder, and a pattern of regression-recrudescence in their reproductive organs is observed when adult animals are exposed to less than 12.5 h daylight for an extended period of time. The purpose of this study was to investigate: (1) the presence of GABA in the testis and epididymis of golden hamsters undergoing regression and spontaneous recrudescence; (2) glutamic acid levels and glutamate decarboxylase (GAD) activity in both tissues, and (3) testicular and epididymal testosterone, dihydrotestosterone and 5 alpha-androstane-3 alpha, 17 beta-diol concentrations. Adult golden hamsters were exposed to long (LP 14L:10D) or short (SP 6L:18D) photoperiods for 9, 12, 14, 16, 18 or 22 weeks. When animals were exposed to SP for 14-16 weeks, the testis and epididymis reached maximal involution. Testicular and epididymal androgen levels showed a marked decrease (p < 0.05) during the regression period, and after 18-22 weeks, values began to recover. Between 12 and 18 weeks in SP, the testicular and epididymal content of GABA and glutamic acid was reduced significantly. The concentration of GABA in both tissues showed a sharp rise (p < 0.05), while the concentration of glutamic acid diminished during the period of maximal involution (p < 0.05). In the testis, GAD activity was increased (p < 0.001) after 14 weeks in SP, with no change in the epididymis. In conclusion, glutamic acid via GAD activity could be the main source of GABA in the testis, but not in the epididymis. Furthermore, the presence of GABA in testicular cells and its subsequent photoperiodic variations might act as an important autocrine and/or paracrine modulatory signal in gonadal processes.