Ethanol-Induced Social Facilitation in Adolescent Rats: Role of Endogenous Activity at Mu Opioid Receptors

摘要: Ethanol consumption is considerably elevated during adolescence. According to the 2007 Monitoring Future National Survey, 8% of eighth graders, 19% tenth and 30% twelfth graders were reported being drunk within past 30 days, with approximately 11% 22% 25% high school seniors show binge pattern drinking (i.e., five or more drinks per occasion) in last 2 weeks (Johnston et al., 2007). Given importance interactions peers adolescence (see Spear, 2000 for references review), it not surprising that human adolescents often drink peers, heavy drinkers, problem drinkers expecting alcohol make them sociable relaxed (Brown 1987). Therefore, attractiveness ethanol seems be based, part, on its ability facilitate social (Beck Treiman, 1996; Beck al.,1993). Adolescence a developmental transition which an immature dependent youth gradually transformed into mature relatively independent adult. A similar from immaturity toward maturity can identified across different mammalian species. In humans, commonly defined as second decade life (Petersen 1996), females generally maturing rapidly than males (e.g., Buchanan 1992). conservative interval rats both sexes most breeding stock exhibit adolescent-typical neurobehavioral features range between postnatal day (P) 28 P42 (Spear, 2000), this age sometimes subdivided three phases, namely, early (around P28), mid P35), late P42) (Adriani 2002). Human other species demonstrate substantial commonalities history, age-typical behavioral predispositions, neural characteristics, changing hormonal milieu 2007, review). These across-species similarities provide sufficient face construct validity support elaboration animal models adolescence. The use model rat has demonstrated propensity intake ethanol-induced facilitation restricted adolescents. Adolescent likewise greater voluntary their adult counterparts under various circumstances (Brunell 2005; Doremus Lancaster Vetter 2007; although see also Yoshimoto Moreover, acute exposure low experimental doses (0.5 0.75 g/kg) administered intraperioneally (i.p.) been shown adolescent tested familiar, nonanxiogenic (Varlinskaya 2002, 2006). produce blood concentrations (BECs) 40 80 mg/dl—BECs are moderate humans Eckardt 1998, Ethanol-induced seen male female predominantly characterized by increase play fighting—an adolescent-characteristic form (Vanderschuren 1997). This pronounced declines period no longer evident adults Adolescents develop tolerance consequences following repeated exposure, emerging at higher these tolerant animals 2007). Although sex differences consumption, pharmacokinetics, some effects have (Blanchard Glick, 1995; Blanchard 1993; Brasser 2002; Cailhol Mormede, 2001; al, Silveri 1999; Varlinskaya 2004; Webb 2002), sufficiently powered experiments, we observed significant responsiveness among Likewise, same rats, well experiments File, 1991; Pellis Pellis, 1990; 1997; Thor Holloway, 1986), baseline activity emerged group-housed our studies 2008). Variations incidence behavior may, strain-dependent. For instance, fighting Long–Evans hooded but Sprague–Dawley (Pellis reliable testing regardless 2006), used present study explore role endogenous opioid receptors facilitation. Although multiple neurochemical brain systems implicated reinforcing current project focused systems, activation μ-opioid contributes positive stimulatory ethanol. induce release ligands (including β-endorphin) hypothalamus, nucleus accumbens, ventral tegmental area (Boyadjieva Sarkar, De Waele Gianoulakis, 1992; Olive Rasmussen 1998). The consequent interaction located mesolimbic reward system viewed central event underlying euphoric, positively (Froehlich Li, 1994; Herz, Oswald Wand, 2004). agonists (Beatty Costello, 1982; Niesink Van Ree, 1989; Vanderschuren 1995) join ethanol, alpha-2 adrenoreceptor antagonists (Siviy Baliko, 2000; Siviy 1994), indirect cannabinoid (Trezza Vanderschuren, 2008a,b), N-methyl-D-aspartate (NMDA) few pharmacological manipulations effective precipitating young animals. Together, such data hypothesis may mediated, via receptor ethanol-associated enhancement sensitivity ligands. Therefore, peer-directed investigate possible roles Specifically, Experiment 1 assessed nonselective antagonist naloxone challenged 0.5 g/kg whereas examined whether naloxone-induced blockade reflected overall shift dose–response curve pharmacokinetic factors. Finally, 3 investigated selective was attenuating