Social learning about ethanol in preweanling rats: Role of endogenous opioids

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Abstract
The role of the endogenous opioid system in social learning about ethanol was examined in three experiments using preweanling rats. Experiment 1 showed that interactions with intoxicated siblings in the home cage on postnatal Days (PD) 12, 14, and 16 results in increased voluntary intake of ethanol when subjects are tested 24 hr after the final exposure. The results also suggested that the endogenous opioid system is not involved in acquisition. Administration of naloxone during social exposure to ethanol had no effect on later ethanol intake. Experiment 2 examined the effects of receptor-selective antagonists administered prior to test. For subjects that had social exposure to ethanol, intake of ethanol was completely suppressed by either naloxone or the delta antagonist naltrindole. For ethanol-naïve subjects, intake also was completely suppressed by naloxone. However, intake was partially blocked by naltrindole or the micro antagonist beta-FNA. Experiment 3 confirmed the differential involvement of micro and delta receptors in ethanol intake through a more comprehensive dose-response analysis of beta-FNA and naltrindole. Collectively, these data reveal that learning about ethanol from intoxicated conspecifics not only affects voluntary intake of ethanol but also alters the opioidergic response to ethanol consumption.