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Mixed depressant and stimulant actions of morphine and their relationship to brain acetylcholine

1976; Elsevier BV; Volume: 18; Issue: 4 Linguagem: Inglês

10.1016/0024-3205(76)90213-7

1879-0631

Edward F. Domino, Michael R. Vasco, Ann Wilson,

Behavioral Health and Interventions

This study examines the effects of the opioid receptor antagonist, naloxone, and the agonist, morphine, on voluntary wheel-running activity (WR) in rats. Male Sprague–Dawley rats were given 1-h access to a running wheel under non-deprived conditions. Naloxone injections (1.0, 0.5, or 0.25 mg/kg, ip), administered immediately before access to running wheels, dose-dependently suppressed WR. In another experiment, subjects were given 6-h access to running wheels under nondeprived conditions for 5 consecutive days. Morphine injections (2.0 mg/kg, sc) were found to increase WR after an initial suppression. These data demonstrate that naloxone inhibits WR, while morphine both suppresses and enhances WR depending on time and dose. These are in agreement with data on other behaviors that indicate that endogenous opioid systems play a major role in the mediation of motivational behaviors.