CONICET | Buscador de Institutos y Recursos Humanos

Behavioral sensitization is an example of experience-dependent plasticity, induced by drug or stress, which has been suggested to involve cellular adaptations in excitatory transmission in the nucleus accumbens (NAc) (Wolf, 1998; Nestler, 2005; Kalivas and O?Brien, 2008, Esparza et al., 2012). Like repeated drug administration, repeated exposure to stressors induced enduring adaptations in dendritic branching, the shape and the number of spines in NAc (Robinson & Kolb, 2004; Shen et al., 2009; Christoffel et al. 2011). GABAergic medium spiny neurons (MSNs) are the predominant cells of the NAc and reside in two functionally and anatomically distinct subregions of the NAc: core and shell. Since the stressinduced changes in the neuronal architecture within NAc and their role in the crosssensitization to cocaine are unknown, the purpose of the present study was to determine the structural changes that occur in NAc after seven daily restraint stress session (two hours) and cocaine. Three weeks after the last restraint stress, we analyzed the morphology and density of dendritic spines using DiI microinjections in fixed brain sections from rats 45 min after an acute injection of saline or cocaine (15 mg ⁄ kg i.p.). We observed an increase in the density of mushroom spines in NAc core twenty-one days after chronic restraint stress, either after saline or cocaine challenge. Meanwhile, the total density of dendritic spines in the NAc core was not modified in these animals. This finding in the morphology of dendritic spines in core reminds to that observed following chronic cocaine (Shen et al., 2009), and could be also associated to previous findings showing a key role of core in the stress-induced crosssensitization to cocaine (Garcia-keller et al., 2013).