No abstract

Hedonic substitution, where wheel running reduces voluntary ethanol consumption has been observed in prior studies. Here we replicate and expand on previous work showing that mice decrease voluntary ethanol consumption and preference when given access to a running wheel. While earlier work has been limited mainly to behavioral studies, here we assess the underlying molecular mechanisms that may account for this interaction. From four groups of female C57BL/6J mice (control, access to two-bottle choice ethanol, access to a running wheel, and access to both two-bottle choice ethanol and a running wheel), mRNA-sequencing of the striatum identified differential gene expression. Many genes in ethanol preference quantitative trait loci were differentially expressed due to running. Furthermore, we conducted Weighted Gene Co-expression Network Analysis and identified gene networks corresponding to each effect behavioral group. Candidate genes for mediating the behavioral interaction between ethanol consumption and wheel running include multiple potassium channel genes, Oprm1, Prkcg, Stxbp1, Crhr1, Gabra3, Slc6a13, Stx1b, Pomc, Rassf5, Polr2a, and Camta2. After observing an overlap of many genes and functional groups previously identified in studies of initial sensitivity to ethanol, we hypothesized that wheel running may induce a change in sensitivity, thereby affecting ethanol consumption. A behavioral study examining Loss of Righting Reflex to ethanol following exercise trended toward supporting this hypothesis. These data provide a rich resource for future studies that may better characterize the observed transcriptional changes in gene networks in response to ethanol consumption and wheel running.

Neuroadaptive changes that occur in the development of ethanol tolerance may be the result of alterations in gene expression. We have shown that PKCγ wild-type mice develop tolerance to the sedative-hypnotic effects of ethanol after chronic ethanol treatment; whereas, mutant mice do not, making these genotypes a suitable model for identifying changes in gene expression related to tolerance development. Using a two-stage process, several genes were initially identified using microarray analyses of cerebellar tissue from ethanol-treated PKCγ mutant and wild-type mice. Subsequent confirmation of a subset of these genes using qRT-PCR was done to verify gene expression changes. A total of 109 genes from different functional classifications were identified in these groups on the microarrays. Eight genes were selected for verification: three, Twik-1, Plp, and Adk2, were chosen as genes related to tolerance; another three, Hsp70.2, Bdnf, and Th, were chosen as genes related to resistance to tolerance; and two genes, JunB and Nur77, were selected as candidate genes sensitive to chronic ethanol. The results from the verification experiments indicated that Twik-1, which codes for a potassium channel, was associated with tolerance and appeared to be dependent on the presence of PKCγ. No genes were confirmed to be related to resistance to tolerance; however, expression of two of these, Hsp70.2 and Th, were found to be sensitive to chronic ethanol and were added to the transcription factors, JunB and Nur77, confirmed by qRT-PCR, as a subset of genes that respond to chronic ethanol.

Protein kinase C γ (PKCγ) null mutant mice demonstrate increased behavioral impulsivity and ethanol consumption. Pharmacological studies have shown that 5-HT 2A/C receptors modulate impulsivity and ethanol consumption in rodents and that PKC can regulate 5-HT 2A/C receptors. To determine whether PKCγ plays a selective role in 5-HT 2A/C receptor regulation, biochemical and behavioral experiments were performed in PKCγ mutant and wild-type mice. DOI-stimulated phosphoinositol hydrolysis and [ 125 I]-DOI saturation binding in the PFC, and quantitative autoradiography of [ 125 I]-DOI binding sites in 15 brain regions were analyzed. DOI-induced head twitch responses (HTR) were measured in naïve mice after an acute 2.5 mg/kg injection of DOI. Results indicated that DOI-induced HTR was significantly greater in mutant mice compared to wildtype mice. Results of the phosphoinositol hydrolysis, membrane binding, and autoradiography experiments indicated that in mutant mice, increased HTR was associated with increased 5-HT 2A/C receptor function in the PFC, but not increased receptor number or affinity suggesting that PKCγ regulates receptor function but not receptor number. These data support a role for 5-HT 2A/C receptors in the PFC in mediating some of the behavioral differences observed between PKCγ mutant and wild-type mice.