Effect of histidine on morphine-induced changes in brain histamine.

Chronic morphine administration to rats resulted in a significant decrease in the hypothalamic and cerebro-cortical histamine concentrations. These low histamine values were restored to control levels when L-histidine was administered daily along with morphine treatment. Chronic treatment with L-histidine prevented the midbrain and cerebro-cortical histamine depletion in morphine-withdrawn rats, whereas in the hypothalamus the histamine level remained significantly decreased. The present data suggests that histamine may play a role in morphine dependence and withdrawal.