TAURINE, GLUTAMATE AND GABA MODULATE THE OUTGROWTH FROM GOLDFISH RETINAL EXPLANTS AND ITS CONCENTRATIONS ARE AFFECTED BY THE CRUSH OF THE OPTIC-NERVE

The amino acid taurine plays an important trophic role during developm ent and regeneration of the central nervous system. Other amino acid s ystems, such as those for glutamate and gamma-aminobutyric acid (GABA) , are modified during the same physiological and pathological processe s. After crushing the optic nerve, goldfish retinal explants were plat ed in the absence and in the presence of different amino acids and ami no acid receptor agonists. The length and the density of the neurites were measured at 5 days in culture. Taurine increased the length and t he density of neurites. Glutamate and glycine increased them at low co ncentration, but were inhibitors at higher concentration. The combinat ion of N-methyl-D-aspartate (NMDA) and glycine produced a greater inhi bitory effect than NMDA alone. NMDA or pha-amino-3-hydroxy-5-methyl-4- isoxazole-propionic acid (AMPA) added simultaneously with taurine impa ired the stimulatory effect of the latter. GABA stimulated the emissio n of neurites in a concentration dependent manner. Hypotaurine also el evated the length of neurites, but cysteinesulfinic acid did not produ ce a significant effect. The concentrations of taurine, glutamate and GABA were determined by HPLC with fluorescent detection in the retina of goldfish at various days post-crushing the optic nerve. The levels of taurine were significantly increased at 48 h after the crush, and w ere elevated up to 20 days. Glutamate level decreased after the lesion of the optic nerve and was still low at 20 days. GABA concentration w as not significantly different from the control. The interaction of th ese amino acids during the regenerative period, especially the balance between taurine and glutamate, may be a determinant in restoring visi on after the crush.