Reinstatement of ethanol and sucrose seeking by the neurosteroid allopregnanolone in C57BL/6 mice
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Recent work in our laboratory documented that the “sipper” method of operant ethanol self-administration produced high ethanol intake and blood ethanol concentrations as well as the typical extinction “burst” in responding under nonreinforced conditions in male C57BL/6 mice. However, the neurochemical basis for reinstatement of responding following extinction has not been examined in mice with this model.
Based on findings that the GABAergic neurosteroid allopregnanolone (ALLO) significantly increased the consummatory phase of ethanol self-administration, the present study determined the effect of ALLO on the reinstatement of extinguished ethanol-seeking behavior and compared this effect to the reinstatement of responding for sucrose reward.
Materials and methods
Separate groups of male C57BL/6 mice were trained to lever press for access to a 10% ethanol (10E) or a 5% sucrose (5S) solution. A single response requirement of 16 presses (RR16) on an active lever resulted in 30 min of continuous access to the 10E or 5S solution. After the animals responded on the RR16 schedule for 14 weeks, mice were exposed to 30 min extinction sessions where responding had no scheduled consequence. Once responding stabilized below the preextinction baseline, mice received an intraperitoneal injection of ALLO (0, 3.2, 5.6, 10, or 17 mg/kg) 15 min prior to the extinction session in a within-subjects design.
ALLO produced a dose-dependent increase in responding under nonreinforced conditions in both the 10E and 5S groups. Additional work documented the ability of a conditioned cue light or a compound cue (light+lever retraction) to reinstate nonreinforced responding on the previously active lever.
These findings definitively show that conditioned cues and priming with ALLO are potent stimuli for reinstating both ethanol- and sucrose-seeking behavior in C57BL/6 mice.
KeywordsOperant self-administration GABA Conditioned cues Alcohol Relapse Reward
All experiments performed complied with current National Institute of Health guidelines for the proper care and use of animals in research. No author has a conflict of interest with the funding institute that sponsored the research. These studies were supported in part by a VA Merit Review grant (DAF) from the Department of Veterans Affairs and NIH grant AA012439 (DAF) from the National Institute on Alcohol Abuse and Alcoholism (NIAAA). MMF is supported by a KO1 award from NIAAA (AA016849). GPM is supported by NIH grant DA 014639 from the National Institute on Drug Abuse and the Methamphetamine Abuse Research Center grant P50 DA018165.
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