Small-conductance Ca(2+)-activated K(+) (KCa2) channels control neuronal excitability and synaptic plasticity, and have been implicated in substance abuse. However, it is unknown if genes that encode KCa2 channels (KCNN1-3) influence alcohol and drug addiction. In the present study, an integrative functional genomics approach shows that genetic datasets for alcohol, nicotine, and illicit drugs contain the family of KCNN genes. Alcohol preference and dependence QTLs contain KCNN2 and KCNN3, and Kcnn3 transcript levels in the nucleus accumbens (NAc) of genetically diverse BXD strains of mice predicted voluntary alcohol consumption. Transcript levels of Kcnn3 in the NAc negatively correlated with alcohol intake levels in BXD strains, and alcohol dependence enhanced the strength of this association. Microinjections of the KCa2 channel inhibitor apamin into the NAc increased alcohol intake in control C57BL/6J mice, while spontaneous seizures developed in alcohol-dependent mice following apamin injection. Consistent with this finding, alcohol dependence enhanced the intrinsic excitability of medium spiny neurons in the NAc core and reduced the function and protein expression of KCa2 channels in the NAc. Altogether, these data implicate the family of KCNN genes in alcohol, nicotine, and drug addiction, and identify KCNN3 as a mediator of voluntary and excessive alcohol consumption. KCa2.3 channels represent a promising novel target in the pharmacogenetic treatment of alcohol and drug addiction.

Alcohol use disorders (AUDs) are a major public health issue and produce enormous societal and economic burdens. Current FDA-approved pharmacotherapies for treating AUDs suffer from deleterious side effects and are only effective in a subset of individuals. It is therefore essential to find improved medications for the management of AUDs. Emerging evidence suggests that anticonvulsants are a promising class of drugs for treating individuals with AUDs. In these studies, we used integrative functional genomics to demonstrate that genes that encode Kv7 channels (i.e., Kcnq2/3) are related to alcohol (ethanol) consumption, preference, and acceptance in rodents. We then tested the ability of the FDA-approved anticonvulsant retigabine, a Kv7 channel opener, to reduce voluntary ethanol consumption of Wistar rats in a two-bottle choice intermittent alcohol access paradigm. Systemic administration and microinjections of retigabine into the nucleus accumbens significantly reduced alcohol drinking, and retigabine was more effective at reducing intake in high versus low drinking populations of Wistar rats. Prolonged voluntary drinking increased the sensitivity to the pro-convulsant effects of pharmacological blockade of Kv7 channels and altered surface trafficking and SUMOylation patterns of Kv7.2 channels in the nucleus accumbens. These data implicate Kcnq2/3 in the regulation of ethanol drinking and demonstrate that long-term drinking produces neuroadaptations in Kv7 channels. In addition, these results have identified retigabine as a potential pharmacotherapy for treating AUDs and Kv7 channels as a novel therapeutic target for reducing heavy drinking.

Alcohol use disorders (AUDs) are associated with functional and morphological changes in subfields of the prefrontal cortex. Clinical and preclinical evidence indicates that the orbitofrontal cortex (OFC) is critical for controlling impulsive behaviors, representing the value of a predicted outcome, and reversing learned associations. Individuals with AUDs often demonstrate deficits in OFC-dependent tasks and rodent models of alcohol exposure show that OFC-dependent behaviors are impaired by chronic alcohol exposure. To explore the mechanisms that underlie these impairments, we examined dendritic spine density and morphology, and NMDA-type glutamate receptor expression in the lateral OFC of C57BL/6J mice following chronic intermittent ethanol (CIE) exposure. Western blot analysis demonstrated that NMDA receptors were not altered immediately following CIE exposure or after 7 days of withdrawal. Morphological analysis of basal dendrites of layer II/III pyramidal neurons revealed that dendritic spine density was also not affected immediately after CIE exposure. However, the total density of dendritic spines was significantly increased after a 7 day withdrawal from CIE exposure. The effect of withdrawal on spine density was mediated by an increase in the density of long, thin spines with no change in either stubby or mushroom spines. These data suggest that morphological neuroadaptations in lateral OFC neurons develop during alcohol withdrawal and occur in the absence of changes in the expression of NMDA-type glutamate receptors. The enhanced spine density that follows alcohol withdrawal may contribute to the impairments in OFC-dependent behaviors observed in CIE treated mice.

Repeated exposure to ethanol followed by withdrawal leads to alterations in glutamatergic signaling and impaired synaptic plasticity in the nucleus accumbens (NAc) in both clinical and preclinical models of ethanol exposure. Homer2 is a member of a family of postsynaptic density (PSD) scaffolding proteins that functions in part to cluster N-methyl-D-aspartate (NMDA) signaling complexes in the PSD, and has been shown to be critically important for plasticity in multiple models of drug and alcohol abuse. Here we used Homer2 knockout (KO) mice and a chronic intermittent intraperitoneal (IP) ethanol injection model to investigate a potential role for the protein in ethanol-induced adaptations in dendritic spine morphology and PSD protein expression. While deletion of Homer2 was associated with increased density of long spines on medium spiny neurons of the NAc core of saline treated mice, ethanol exposure had no effect on dendritic spine morphology in either wild-type (WT) or Homer2 KO mice. Western blot analysis of tissue samples from the NAc enriched for PSD proteins revealed a main effect of ethanol treatment on the expression of GluN2B, but there was no effect of genotype or treatment on the expression other glutamate receptor subunits or PSD95. These data indicate that the global deletion of Homer2 leads to aberrant regulation of dendritic spine morphology in the NAc core that is associated with an increased density of long, thin spines. Unexpectedly, intermittent IP ethanol did not affect spine morphology in either WT or KO mice. Together these data implicate Homer2 in the formation of long, thin spines and further supports its role in neuronal structure.

No abstract