Nuclear Factor κB Signaling Regulates Neuronal Morphology and Cocaine Reward

Abstract

Although chronic cocaine-induced changes in dendritic spines on nucleus accumbens (NAc) neurons have been correlated with behavioral sensitization, the molecular pathways governing these structural changes, and their resulting behavioral effects, are poorly understood. The transcription factor, nuclear factor B (NFB), is rapidly activated by diverse stimuli and regulates expression of many genes known to maintain cell structure. Therefore, we evaluated the role of NFB in regulating cocaine-induced dendritic spine changes on medium spiny neurons of the NAc and the rewarding effects of cocaine. We show that chronic cocaine induces NFB-dependent transcription in the NAc of NFB-Lac transgenic mice. This induction of NFB activity is accompanied by increased expression of several NFB genes, the promoters of which show chromatin modifications after chronic cocaine exposure consistent with their transcriptional activation. To study the functional significance of this induction, we used viral-mediated gene transfer to express either a constitutively active or dominant-negative mutant of Inhibitor of B kinase (IKKca or IKKdn), which normally activates NFB signaling, in the NAc. We found that activation of NFB by IKKca increases the number of dendritic spines on NAc neurons, whereas inhibition of NFB by IKKdn decreases basal dendritic spine number and blocks the increase in dendritic spines after chronic cocaine. Moreover, inhibition of NFB blocks the rewarding effects of cocaine and the ability of previous cocaine exposure to increase an animal's preference for cocaine. Together, these studies establish a direct role for NFB pathways in the NAc to regulate structural and behavioral plasticity to cocaine.

Neuronal Allocation to a Hippocampal Engram

“…Wild-type full-length CREB (provided by Dr Satoshi Kida, Tokyo University of Agriculture), hM4Di (a Gi-DREADD, provided by Dr Bryan Roth, University of North Carolina) and iC++ (an engineered chloride-conducting channelrhodopsin, provided by Dr Karl Deisseroth, Stanford University) cDNAs were subcloned into an HSV vector backbone that co-expresses green fluorescent protein (GFP) as a fluorescent reporter, HSV-p1005 (Russo et al, 2009). …”

Effects of Inhibitor of κB Kinase Activity in the Nucleus Accumbens on Emotional Behavior

“…Thirty-threegauge syringe needles (Hamilton , Reno, Nevada) were used to bilaterally infuse 0.5 ml of HSV (1.5 Â 10 8 infectious units/ml) expressing GFP, or IkKca and IkKdn mutants to activate or inhibit NFkB signaling, respectively, into the NAc (bregma coordinates: anteroposterior, 1.5 mm; mediolateral, 1.6 mm; dorsoventral, 4.4 mm; angle 101; see Figure 1a for degree of infection just before behavior and after behavioral testing) at a rate of 0.1 ml/min. All of these viral vectors have been tested and validated in vivo and in vitro (Christoffel et al, 2011a;LaPlant et al, 2009;Russo et al, 2009). …”

“…Viral vectors were constructed as previously described (Russo et al, 2009). Briefly, for the IkKdn, using the coding sequence of the b form, lysine 44 was substituted with methionine (Mercurio et al, 1997) and subcloned into the bicistronic p1005 + HSV plasmid.…”

“…IkKca expression increases levels of phospho-p65 and in vivo overexpression in the NAc of NFkB-LacZ reporter mice increases b-gal expression. Additionally, overexpression of HSV-IkKdn in NAc of the NFkB-LacZ reporter mice results in a 50% reduction in b-gal expression (Russo et al, 2009 …”

“…More recently, IkK and NFkB activity has been implicated as an important regulator of synaptic signaling and neuronal morphology both in vitro and in vivo (Christoffel et al, 2011a, b;Kaltschmidt et al, 1993;Meffert et al, 2003;O'Mahony et al, 2006;Russo et al, 2009). The IkK signaling pathway is activated by extracellular cytokines (such as interleukin 1 beta (IL-1b) and IL-6), infectious agents, glutamate, and neurotrophins (Israel, 2010;O'Neill and Kaltschmidt, 1997;Schölzke et al, 2003).…”