Incubation of nicotine seeking is associated with enhanced protein kinase A‐regulated signaling of dopamine‐ and cAMP‐regulated phosphoprotein of 32 kDa in the insular cortex

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Abstract
A recent clinical study demonstrated that damage to the insular cortex can disrupt tobacco addiction. The neurobiological mechanisms for this effect are not yet understood. In this study we used an animal model of nicotine addiction to examine the possibility that changes in insular cortex levels of dopamine (DA)‐ and cAMP‐regulated phosphoprotein of 32 kDa (DARPP‐32), a phosphoprotein enriched in DA neurons containing DA D1 receptors, may be associated with changes in vulnerability to nicotine addiction. Once rats acquired self‐administration, they were given unlimited access to nicotine (0.01 mg/kg/infusion) for 23 h/day for a total of 10 days. Each infusion was paired with a visual cue (stimulus light) and auditory cue (sound of pump). Nicotine seeking, as assessed under a cue‐induced reinstatement paradigm, and markers of DARPP‐32 signaling, as assessed using western blot analysis, were examined in separate groups of rats at two different abstinent intervals: 1 and 7 days. Consistent with findings with other drugs of abuse, rats in the 7‐day abstinence group took longer to extinguish and responded at higher levels during reinstatement testing as compared with rats in the 1‐day reinstatement group. Relative to saline controls, rats in the 7‐day but not the 1‐day abstinence group had higher levels of DARPP‐32 phosphorylated at the protein kinase A site in the insular cortex. These results demonstrate incubation of drug seeking following extended access to nicotine self‐administration and suggest that enhanced protein kinase A signaling in the insular cortex via phosphorylation of DARPP‐32 at Thr34 is associated with this effect.