The Effects of Cocaine Self-Administration on Dendritic Spine Density in the Rat Hippocampus Are Dependent on Genetic Backgroun

Chronic exposure to cocaine induces modif icat ions to neurons in the brain regions involved in addict ion. Hence, we evaluated cocaine-induced changes in the hippocampal CAÍ field in Fischer 344 (F344) and Lewis (LEW) rats, 2 strains that have been widely used to study genetic predisposit ion to drug addict ion, by combining intracellular Lucifer yel low injection wi th confocal microscopy reconstruct ion of labeled neurons. Specifically, we examined the effects of cocaine se l f -admin is t rat ion on the structure, size, and branching complexi ty of the apical dendrites of CAÍ pyramidal neurons. In addi t ion, we quanti f ied spine density in the collaterals of the apical dendrit ic arbors of these neurons. We found differences between these strains in several morphological parameters. For example, CAÍ apical dendrites were more branched and complex in LEW than in F344 rats, while the spine density in the collateral dendrites of the apical dendrit ic arbors was greater in F344 rats. Interestingly, cocaine sel f -adminis t rat ion in LEW rats augmented the spine density, an effect that was not observed in the F344 strain. These results reveal signif icant structural differences in CAÍ pyramidal cells between these strains and indicate that cocaine sel f -adminis t rat ion has a dist inct effect on neuron morphology in the hippocampus of rats wi th dif ferent genetic backgrounds.