EXPRESSION OF GABA IN THE FETAL, POSTNATAL, AND ADULT HUMAN RETINAS -AN IMMUNOHISTOCHEMICAL STUDY

The expression of GABA in the human fetal (12-25 weeks of gestation), postnatal (five-month-old), and adult (35-year-old) retinas was invest igated by immunohistochemistry. GABA expression was seen as early as 1 2 weeks in the undifferentiated cells of the inner neuroblast zone; a few optic nerve fiber layer axons were clearly labeled, suggesting tha t some of the stained cell bodies were prospective ganglion cells, oth ers could be displaced amacrine cells. From 16-17 to 24-25 weeks, inte nse labeling was found in the amacrine, displaced amacrine, and some g anglion cells. During this time period, horizontal cells (identified b y calbindin immunohistochemistry), undergoing migration (periphery) an d differentiation (center), expressed GABA prominently. In the postnat al retina, some horizontal cells were moderately labeled, but very wea kly in a few cells, in the adult. The Muller cells developed immunorea ctivity first weakly at 12 weeks and then moderately from 16-17 weeks onward. The staining was also evident in the postnatal and adult retin as, showing labeled processes of these glial cells. Virtually no axons in the adult optic nerve and nerve fiber layer were stained; the stai ning was restricted to a few, large ganglion cells and displaced amacr ine cells. Some amacrines were also labeled. The possibility that GABA might play a role in horizontal cell differentiation and maturation i s highlighted. Other evidences suggest that GABA might play a role in metabolism during retinal development.