Abstract
A simple and sensitive microradiometrical assay method for L-glutamic acid decarboxylase (GAD: EC 4.1.1.15) has been designed. Cerebral tissue was frozen and sectioned at 300 μ thickness, after which the slice was further dissected into rectangular blocks (750 750 μ). The GAD activity was assayed microradio-metrically. The incubation vessel held a volume of approximately 500 μl and the incubation mixture was 90 μl. The 14CO2 evolved from L-[l-14C]-glutamic acid was absorbed with a filter paper immersed in 100 μl of hyamine base. GAD activity in neuronal tissues containing less than 5-10 μg of protein was easily and accurately detected by this method. The assay was found to be linear at 5-500 μg of protein concentration in various CNS preparations. Utilizing this microradiometric assay method, it was found that in the rat hypothalamus, the distribution pattern of GAD activity was essentially the same as that of GABA.
