INFLUENCE OF PHOTOINHIBITION ON GABA AND GLUTAMIC-ACID LEVELS, AND ONGLUTAMATE-DECARBOXYLASE ACTIVITY IN THE TESTIS AND EPIDIDYMIS OF THE GOLDEN-HAMSTER

Gamma-aminobutyric acid (GABA) is found in the gonads and accessory re productive organs, and a direct effect on steroidogenesis and sperm vi ability and motility has been described. The golden (Syrian) hamster i s a seasonal breeder, and a pattern of regression-recrudescence in the ir reproductive organs is observed when adult animals are exposed to l ess than 12.5 h daylight for an extended period of time. The purpose o f this study was to investigate: (1) the presence of GABA in the testi s and epididymis of golden hamsters undergoing regression and spontane ous recrudescence; (2) glutamic acid levels and glutamate decarboxylas e (GAD) activity in both tissues, and (3) testicular and epididymal te stosterone, dihydrotestosterone and 5 alpha-androstane-3 alpha, 17 bet a-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 an d epididymis reached maximal involution. Testicular and epididymal and rogen levels showed a marked decrease (p<0.05) during the regression p eriod, and after 18-22 weeks, values began to recover. Between 12 and 18 weeks in SP, the testicular and epididymal content of GABA and glut amic acid was reduced significantly. The concentration of GABA in both tissues showed a sharp rise (p<0.05), while the concentration of glut amic 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 vi a GAD activity could be the main source of GABA in the testis, but not in the epididymis. Furthermore, the presence of GABA in testicular ce lls and its subsequent photoperiodic variations might act as an import ant autocrine and/or paracrine modulatory signal in gonadal processes.