Acute morphine treatment and morphine tolerance/dependence alter immunoreactive oxytocin levels in the mouse hippocampus.

Immunoreactive oxytocin levels were measured in the mouse hippocampal tissue (h-OXT). Acute morphine treatment increased h-OXT, which effect was reversed by naloxone. In mice rendered tolerant to and dependent on morphine h-OXT was lower than in placebo pellet-implanted control mice. In the tolerant/dependent animals naloxone resulted in precipitated withdrawal syndrome which was associated with a slight increase in h-OXT. The data indicate that h-OXT is affected by acute morphine treatment and by morphine tolerance/dependence and raises the possibility that h-OXT participates in the adaptive response of the organism towards narcotic drugs.