Experimental Research Showing the Reduction of Naloxone-Place Aversion by Oral Zinc Administration in Rats.

Previous studies showed the attenuation of both morphine-dependence and morphine-place preference by zinc. Conditioned place preference and aversion are experimental models frequently used to test the reward-stimulating, respectively the aversive effects induced by different stimuli or substances. Addictive substances usually induce place preference (exhibit reward-stimulating properties), while their antagonists determine place-avoidance (aversion). The present study aimed to assess the effect determined by zinc sulphate oral administration (2 and 4 mg/kg/day, 14 days, prior to habituation) on the place aversion induced by two naloxone doses (1.5 and 2.5 mg/kg/administration). The results show a robust, dose-dependent reduction of the aversion determined by both naloxone doses (the aversion induced by 1.5 mg/kg naloxone was reduced with 15%-the lower zinc dose and with 24%-the higher zinc dose; the aversion induced by 2.5 mg/kg naloxone was reduced with 16%-the lower zinc dose and with 29%-the higher zinc dose). This represents a new proof of the interactions between zinc and opioidergic system and a further argument for dietary zinc supplementation in patients on opioids for cancer-related chronic pain.