GABAA AND GABAC (GABAA0r) RECEPTORS AFFECT OCULAR GROWTH AND FORM-DEPRIVATION MYOPIA

Roles of c-aminobutyric acid (GABA) antagonists on the chick model of form-deprivation myopia (FDM) were investigated. Bicuculline (GABAA) or TPMPA (GABAA0r) was injected intravitreally (1 or 10mg=mL) into the right eyes of chicks with or without 10 FDM for 13 days. The contralateral eyes served as the control. The eye weight (EW), equatorial diameter (ED), ocular length (OL), axial length (AL), and refraction (RFN) were measured. Histological sections of the retina and sclera were measured, and changes in tissue thickness were compared. The EW, ED, OL, and AL of the FDM eyes went up by 13.1 2.0% (n 1⁄4 24, p < 0.001), 18.7 2.0% (n 1⁄4 24, p < 0.001), 15 7.2 1.9% (n 1⁄4 24, p < 0.001) and 5.1 1.5% (n 1⁄4 11, p < 0.05), respectively. Bicuculline and TPMPA significantly reversed these changes (p < 0.05) but not the OL at either concentration used. The RFN measurements confirmed this (n 1⁄4 2–8, p < 0.01). The drugs have no effect on the retinal thickness but significantly reduced the thickness of cartilaginous scleral layer of chicks with or without FDM (n 1⁄4 9–120, p < 0.05). Bicuculline 20 and TPMPA reduced form-deprived as well as normal ocular growth. GABAergic-mediated mechanism may directly influence the growth, shape, and refractive state of the developing eye.