Cocaine increases actin cycling: effects in the reinstatement model of drug seeking.

Addiction to cocaine is associated with persistent changes in synaptic function. The cycling of actin between polymerized [F (for filamentous)] and depolymerized forms contributes to synaptic plasticity, and acute and withdrawal from repeated cocaine administration produced reversible and enduring elevations, respectively, in F-actin in the nucleus accumbens. Increased F-actin after 3 weeks withdrawal from repeated cocaine resulted from changes in the content or phosphorylation state of actin binding proteins (ABPs) that cosediment with F-actin. The profile of altered APBs was consistent with filopodia formation, including increased mammalian Enabled, phosphorylated (p)-cortactin, and p-vasodilator-stimulated phosphoprotein, and increased actin depolymerization [e.g., reduced LIM (Lin11/Isl-1/Mec3)-kinase and p-cofilin]. In contrast to repeated cocaine, the increase in F-actin after acute cocaine administration resulted from reduced depolymerization and actin cycling. The potential involvement of chronic cocaine-induced increases in actin cycling in cocaine addiction was examined using the reinstatement of cocaine seeking in rats previously trained to self-administer cocaine by inhibiting actin polymerization with intra-accumbens latrunculin A or by accelerating actin depolymerization with a LIM-kinase inhibitor. Disrupting actin cycling via either mechanism augmented cocaine-induced reinstatement of drug seeking but did not affect the locomotor response to acute cocaine administration. Thus, withdrawal from repeated cocaine induces a restructuring of actin-ABP complexes, which increases actin cycling and may modulate cocaine-induced reinstatement of drug seeking.