The Effect of Morphine on Tyrosine Hydroxylase Activity in Rat Brain.
ARMED FORCES RADIOBIOLOGY RESEARCH INST BETHESDA MD
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The activity of rat brain tyrosine hydroxylase TH has been determined after acute or chronic treatment with morphine sulfate. In acutely treated animals there was an increase in hypothalamic TH activity 15 minutes after morphine injection followed by a decrease by 1 hour after injection. In chronically treated rats there was a decrease in TH activity within the 1st hour after the last morphine injection in both thalamus and corpus striatum. The rapidity of onset of these changes and their transient nature suggest that the morphine-induced alterations in TH activity are not due to an altered rate of enzyme synthesis. The observed changes in TH activity may be the result of a transient shift in the physical state of TH from particulate to soluble form and this is currently the subject of investigation.