The effects of 4-imidazolyl-3-amino-2-butanone (McN-A-1293), a specific histidine decarboxylase inhibitor, on the expression of morphine tolerance and physical dependence in mice

McN-A-1293, a specific histidine decarboxylase inhibitor administered intracisternally in the 'withdrawal' phase, significantly suppressed the expression of morphine tolerance. Severity of withdrawal, assessed by percentage body weight loss, was significantly enhanced although incidence of jumping was unaltered. The opposite effects of this compound on morphine tolerance and withdrawal suggest that tolerance and physical dependence are based on different underlying mechanisms.