Rapid postmortem increase in extracellular dopamine in the rat brain as assessed by brain microdialysis

Extracellular dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in rat nucleus accumbens were determined before and shortly following death using microdialysis. A maximal 400-fold increase in the output of DA was observed within the first 5 min of death. DA output remained elevated over the following hour at a level of approximately 70-fold above pre-death values. In contrast to that of DA, DOPAC and HVA output gradually declined. Before death the extracellular DOPAC/DA ratio was about 250; after death this ratio dropped to 0.44 at 5 min. These observations may have important implications for experiments measuring the output of (endogenous) DA and its metabolites from brain tissue in vitro: autoregulation of, e.g., transmitter release and synthesis in vitro may be seriously disrupted by the observed depletion of transmitter storage granules.