Post Mortem Stability and Storage in the Cold of Brain Enzymes

Tyrosine hydroxylase (TH), glutamate‐decarboxylase (GAD) and choline acetyltransferase (CAT) were estimated in the striatum of rat brains kept at 20°C or 4°C for various periods of time up to 48 h after death. At 20°C TH and GAD activities decreased up to 4&50% of controls after 48 h; CAT activity was not affected. Maintenance of dead animals at 4°C completely (GAD and CAT) or partially (TH) prevented the decrease in enzyme activities. In a second series of experiments, TH, G A D and CAT activities were measured in striata (tissue or homogenate) stored immediately after death at different temperatures (4°C; ‐35°C; ‐70°C) for various time intervals up to 3 months. Storage of striata at 4°C induced a rapid decrease of all enzyme activities with time (GAD > CAT > TH). TH, GAD and CAT activities in striata kept at ‐35°C or ‐70°C were fairly stable. However, CAT activity was slightly decreased when the dissected striata were not homogenized; GAD activity was substantially reduced after 3 months at ‐35°C. Stability of TH, GAD and CAT activities were confirmed in homogenates of human caudate nucleus stored at ‐70°C for 1 month. If human enzymes behave similarly to the rat enzymes the following conclusions should be drawn: (1) brains should be obtained at autopsy within 8 h after death; (2) placement of dead bodies in the refrigerator should be done as soon as possible; (3) dissected brain structures (preferably as homogenates) should be stored at ‐70°C.