Reinstatement of ethanol and sucrose seeking by the neurosteroid allopregnanolone in C57BL/6 mice.
BACKGROUND
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.


OBJECTIVE
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.


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.


RESULTS
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.


CONCLUSIONS
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.
Finn
Deborah A
DA
VAMC Research (R&D-49), Department of Veterans Affairs Medical Center, Portland, OR 97239, USA. finnd@ohsu.edu
Mark
Gregory P
GP
Fretwell
Andrea M
AM
Gililland-Kaufman
Katherine R
KR
Strong
Moriah N
MN
Ford
Matthew M
MM