Behavioral and Morphological Responses to Cocaine Require Kalirin7

BackgroundLong-lasting increases in dendritic spine density and gene expression in the nucleus accumbens and in the ambulatory response to cocaine occur following chronic cocaine treatment. Despite numerous reports of these findings, the molecular mechanisms leading to these morphological, biochemical, and behavioral changes remain unclear.MethodsWe used mice genetically lacking Kalirin7 (Kal7KO), a Rho guanine nucleotide exchange factor that regulates dendritic spine formation and function. Both wild-type (Wt) and Kal7KO mice were given high-dose cocaine (20 mg/kg) for 4 or 8 consecutive days. Locomotor sensitization and conditioned place preference elicited by cocaine were evaluated. The nucleus accumbens core was diolistically labeled and spine density and morphology were quantified using confocal microscopy.ResultsCocaine increased Kalirin7 messenger RNA and protein expression in the nucleus accumbens of Wt mice. The Kal7KO animals showed greater locomotor sensitization to cocaine than Wt mice. In contrast, Kal7KO mice exhibited decreased place preference for cocaine, despite displaying a normal place preference for food. While Wt mice showed a robust increase in dendritic spine density after 4 and 8 days of cocaine treatment, dendritic spine density failed to increase in cocaine-exposed Kal7KO mice. Wild-type mice treated with cocaine for 8 days exhibited larger dendritic spines than cocaine-treated Kal7KO mice.ConclusionsKalirin7 is an essential determinant of dendritic spine formation following cocaine treatment. The absence of this single isoform of one of the many Rho guanine nucleotide exchange factors expressed in the nucleus accumbens results in enhanced locomotor sensitization and diminished place preference in response to cocaine.