Blockade of ionotropic glutamatergic transmission in the ventral tegmental area attenuates the physical signs of morphine withdrawal in rats

Abstract

The present study sought to assess whether the blockade of ionotropic glutamate receptors in the ventral tegmental area (VTA) could modulate the morphine withdrawal in male Sprague–Dawley rats. The effects of dizocilpine (MK-801) or 6,7-dinitroquinnoxaline-2,3-dione (DNQX), ionotropic glutamate receptor antagonists, microinjected unilaterally into the VTA 30 min before naloxone [2 mg/kg, intraperitoneally (i.p.)] administration on the morphine withdrawal were assessed. Morphine dependence was developed with increasing morphine injection (i.p.), and morphine withdrawal was induced by injection of naloxone (2 mg/kg, i.p.). Jumping, wet-dog shakes, writhing posture, wall clamber, weight loss and Gellert–Holtzman scale were used as the indices to evaluate the intensity of morphine withdrawal. The results showed that unilateral microinjection of MK-801 or DNQX into the VTA significantly increased the incidence of wall clamber, had no effect on weight loss, and reduced all other symptoms of morphine withdrawal. These data suggest that the ionotropic glutamate receptors in the VTA are involved in mediating naloxone-precipitated opiate withdrawal.