Differential role of mu, delta and kappa opioid receptors in ethanol-mediated locomotor activation and ethanol intake in preweanling rats - PubMed (original) (raw)

Differential role of mu, delta and kappa opioid receptors in ethanol-mediated locomotor activation and ethanol intake in preweanling rats

Carlos Arias et al. Physiol Behav. 2010.

Abstract

The opioid system modulates ethanol intake and reinforcement in adult and preweanling rodents. While adult heterogeneous rats normally do not show ethanol-mediated locomotor stimulation, preweanling rats show it quite clearly. We recently observed that naloxone, a non-specific opioid antagonist, attenuated ethanol-induced locomotor activation in preweanling rats. In the present study we tested the role of specific opioid receptors (mu, delta and kappa) in ethanol-mediated locomotor stimulation and ethanol intake. In Experiment 1 13-day-old rats received naloxonazine (mu antagonist: 0, 7.5 or 15 mg/kg), naltrindole (delta antagonist: 0, 2 or 4 mg/kg) or nor-binaltorphimine (kappa antagonist: 0, 2, 4 or 8 mg/kg) before an intragastric administration of ethanol (0 or 2.5 g/kg), and subsequent locomotor activity assessment. In Experiment 2, the same opioid antagonists were administered on postnatal days 13 and 14 before consumption of ethanol (6%), saccharin (0.05%) or distilled water. 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 tested. Similar to what has been reported in adult rodents, mu-opioid receptors seem to modulate ethanol-activating effects during early ontogeny. Hence, there seems to be a partial overlap of neurochemical mechanisms involved in the rewarding and stimulating effects of ethanol in preweanling rats. Mu-receptor antagonists reduced both ethanol-induced activity and ethanol intake, but it is unclear whether the latter effect is specific to ethanol or only a reflection of an effect on consummatory behavior generally, since mu and delta receptor antagonists also suppressed ingestion of water and saccharin.

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Figures

Figure 1

Locomotor activity in preweanling rats as a function of ethanol (0 or 2.5 g/kg) and naloxonazine (0, 7.5 or 15 mg/kg, Figure 1a), naltrindole (0, 2 or 4 mg/kg, Figure 1b) or nor-binaltorphimine (0, 2, 4 or 8 mg/kg, Figure 1c) treatments. Vertical lines illustrate standard errors of the means. * Significant difference between ethanol treated group and the corresponding water control. # Significant difference between ethanol- vehicle treated group and ethanol-Naloxonazine treated group.

Figure 2

Water, saccharin or ethanol intake on postnatal days 13 and 14 as a function of ethanol naloxonazine (0 or 7.5 mg/kg, Figure 2a), naltrindole (0 or 4 mg/kg, Figure 2b) or nor-binaltorphimine (0 or 4 mg/kg, Figure 2c) treatments. Vertical lines illustrate standard errors of the means. In Experiment 2a naloxonazine significantly reduced consumption overall (water, saccharin and ethanol). In Experiment 2b naltrindole suppressed intake regardless the solution. In Experiment 3 no significant effects of nor-binaltorphimine were detected.

References

1. Arias C, Chotro MG. Increased palatability of ethanol after prenatal ethanol exposure is mediated by the opioid system. Pharmacol Biochem Behav. 2005;82(3):434–442. - PubMed
1. Arias C, Chotro MG. Ethanol-induced preferences or aversions as a function of age in preweanling rats. Behav Neurosci. 2006;120(3):710–718. - PubMed
1. Arias C, Mlewski EC, Miller S, Molina JC, Spear NE. Novelty modulates the stimulating motor effects of ethanol in preweanling rats. Pharmacol Biochem Behav. 2009;92(3):448–456. - PMC - PubMed
1. Arias C, Mlewski EC, Molina JC, Spear NE. Ethanol induces locomotor activating effects in preweanling Sprague-Dawley rats. Alcohol. 2009a;43(1):13–23. - PMC - PubMed
1. Arias C, Mlewski EC, Molina JC, Spear NE. Naloxone and baclofen attenuate ethanol’s locomotor-activating effects in preweanling Sprague-Dawley rats. Behav Neurosci. 2009b;123(1):172–180. - PubMed

Differential role of mu, delta and kappa opioid receptors in ethanol-mediated locomotor activation and ethanol intake in preweanling rats - PubMed (original) (raw)