Laminar distribution of GABA (γ-aminobutyric acid) in the dorsal lateral geniculate nucleus, Area 17 and Area 18 of the visual cortex, and the superior colliculus of the cat

Abstract

The laminar distribution of γ-aminobutyric acid (GABA) was studied in certain structures of the visual system of the adult cat. A microassay method to measure GABA (10 −12 mol) was established using enzymatic cycling of NADP-NADPH. In the dorsal lateral geniculate nucleus, GABA concentration was highest in lamina A (average concentration 23 mmol/kg dry weight) and lowest in lamina C. In the visual cortex (Areas 17 and 18), the concentration of GABA was 10–12 mmol/kg dry weight in layers I–IV and 5–8 mmol/kg dry weight in layers V and VI. No significant difference was found in the GABA distribution in Areas 17 and 18. In the superior colliculus, the highest level of GABA was found in the upper part of the superficial gray layer (40 mmol/kg dry weight), whereas the deep layers contained GABA at a concentration of 23–28 mmol/kg dry weight. The results of the GABA distribution measurements revealed an orderly, layer-specific disposition of the neurotransmitter in the cat visual system. GABA may play an important role in the function of the visual system.