Cofilin linked to GluN2B subunits of NMDA receptors is required for behavioral sensitization by changing the dendritic spines of neurons in the caudate and putamen after repeated nicotine exposure

Abstract

Background Nicotine dependence is associated with changes in glutamatergic neurotransmission in the caudate and putamen (CPu) of the forebrain. Changes in the structure of dendritic spines in the glutamate synapses after nicotine exposure induce habitual behaviors such as smoking. The present study investigated the hypothesis that cofilin, an actin-binding protein that is linked to the GluN2B subunits of N-methyl-D-aspartate (NMDA) receptors regulates the morphology of dendritic spines in the neurons of the CPu after repeated exposure to nicotine. Results Subcutaneous injections of nicotine for seven consecutive days (0.3 mg/kg/day) decreased the phosphorylation of cofilin while increasing the formation of thin spines and filopodia in the dendrites of medium spiny neurons (MSN) in the CPu of rats. Bilateral intra-CPu infusion of the cofilin inhibitor, cytochalasin D (12.5 µg/µL/side), restored the thin spines and filopodia from mushroom types after repeated exposure to nicotine. Similar results were obtained from the bilateral intra-CPu infusion of the selective GluN2B subunit antagonist, Ro 25-6981 (4 µM/µL/side). Bilateral intra-CPu infusion of cytochalasin D that interferes with the actin-cofilin interaction attenuated the repeated nicotine-induced increase in locomotor sensitization in rats. Conclusions These findings suggest that active cofilin alters the structure of spine heads from mushroom to thin spine/filopodia by potentiating actin turnover, contributing to behavioral sensitization after nicotine exposure.