Uncontrollable stress potentiates morphine's rewarding properties

Abstract

Strategies used to explore the role of stressors in drug addiction include measuring stressor's effects on drug's rewarding properties. The current investigation explored the effect of an acute stressor on morphine conditioned place preference. Twenty-four hours following either inescapable tail shock or home-cage control treatment, all subjects were conditioned with morphine (0, 1, 2, and 3 mg/kg SC) over 2 days, and later tested for conditioned place preference. Inescapably shocked subjects demonstrated a potentiated place preference compared to controls. The inescapable shock- induced potentiated place preference developed even when conditioning was delayed until 6 and 7 days following the stressor, while no longer occurring after a 14- and 15-day interval. The potentiation was not a result of reduced locomotion in the inescapably shocked subjects, as activity in inescapably shocked and home-cage control subjects was the same following 'mock' saline conditioning. Furthermore, the anxiogenic methyl-6,7-dimethoxy-4-ethyl-beta- carboline-3-carboxylate (DMCM) (0.3 mg/kg IP), which produces effects similar to those produced by inescapable shock, also potentiated morphine place preference. In addition, the potentiation in inescapably shocked subjects was dependent upon the stressor's uncontrollability, as identical escapable shock did not potentiate place preference above control subjects. Finally, the inescapable shock-induced potentiated place preference was drug specific, as amphetamine place preference was not affected.