Role of mu, delta and kappa receptors upon ethanol intake and ethanol-mediated locomotors stimulation in preweanling rats.

ARIAS, C.; MOLINA, J.C.; SPEAR, N.E.

Congreso; Research society on alcoholism; 2009

The opioid system modulates ethanol intake as well as the reinforcing and activating effects of the drug in adult rodents, with the the activating effect more often seen in the mouse than the rat. Preweanling heterogeneous rats seem to be predisposed to these effects of ethanol. We recently observed that Naloxone, a non-specific opioid antagonist, attenuated ethanol-induced locomotor activation in preweanling rats. In the present study we analyzed the role of specific opioid receptors (mu, delta and kappa) in ethanol intake and ethanol-mediated locomotor stimulation. In Experiment 1 13-day-old rats received Naloxonazine (mu antagonist), Naltrindole (delta antagonist) or Nor-Binaltorphimine (Kappa antagonist) before an intragastric administration of ethanol (0 or 2.5 g/kg). In Experiment 2, on postnatal days (PD) 13 and 14, the same opioid antagonists were administered before ethanol (6%), saccharine (0.05%) or destilled water consumption. In Experiment 1 only Naloxonazine reduced ethanol-mediated locomotor stimulation. None of the opioid antagonists affected locomotor activity in water controls. In Experiment 2 Naloxonazine and Naltrindole suppressed ingestion of all the solutions employed. Nor-Binaltorphimine increased saccharin acceptance. Similar to what has been reported in adult rodents, mu-opioid receptors seem to modulate ethanol-activating effects during early ontogeny. Delta and Mu receptors regulate intake capabilities in preweanling rats, while the kappa system specifically modulates intake of some palatable flavors. The present data represent more evidence of the important role of the opioid system in regulation of ethanol effects during early ontogeny.