The effect of GABA on neurotransmission in frog tectal slices

The regional distribution of gamma-aminobutyric acid (GABA) was determined in the central nervous system of the frog. The highest amount of GABA was found in the tectum (35.7 +/- 2.3 mmol/kg protein). A thin tectal slice (400-600 microns thick) preparation was developed in which the postsynaptic potential (PSP) could be elicited. The addition of GABA to the perfusion medium depressed the PSP in a dose-dependent manner in the concentration range 1-12.5 mM at 28 degrees C. Nipecotic acid, a GABA uptake inhibitor, at a concentration of 0.5 mM shifted the dose-response curve for GABA to the left. These results from the frog, a cold-blooded animal, were in good agreement with those for hippocampal slices from the guinea-pig.