No evidence of a role of the ß4 subunit of the nicotinic acetylcholine receptor in alcohol-related behaviors.

BACKGROUND: Nicotinic acetylcholine receptors have gained attention in the last several years as mediators of alcohol-related behaviors. The genes that code for the α5, α3, and ß4 subunits (Chrna5, Chrna3, and Chrnb4, respectively) map adjacent to each other on human chromosome 15/mouse chromosome 9. Genetic variants in this region have been associated with alcohol phenotypes and mice that overexpress these three subunits have reduced ethanol intake. In the present experiments, we examined the role of the Chrnb4 gene in three ethanol behaviors: consumption, ataxia, and sedation. Wildtype, heterozygous, and knockout mice were tested for ethanol consumption with a 2-bottle choice procedure and the drinking-in-the-dark paradigm. Ethanol-induced ataxia was measured with the balance beam and dowel test. Finally, the sedative effects of ethanol were measured with the loss of righting reflex paradigm. RESULTS: We observed no significant genotypic effects on any of the ethanol behaviors examined, suggesting that the ß4 subunit is not involved in mediating these responses. CONCLUSIONS: While we found no evidence for the involvement of the ß4 subunit in ethanol responses, it is possible that this subunit modulates other behaviors not tested and further work should address this before completely ruling out its involvement.

Mesolimbic transcriptional response to hedonic substitution of voluntary exercise and voluntary ethanol consumption.

The mesolimbic dopaminergic pathway has been implicated in many rewarding behaviors, including the consumption of ethanol and voluntary exercise. It has become apparent that different rewarding stimuli activate this pathway, and therefore it is possible for these behaviors to influence each other, i.e. hedonic substitution. Using adult female C57BL/6J mice, we demonstrate that voluntary access to a running wheel substantially reduces the consumption and preference of ethanol. Furthermore, we examined gene expression of several genes involved in regulating the mesolimbic dopaminergic pathway, which we hypothesized to be the main pathway involved in hedonic substitution. In the striatum, we observed a reduction in mRNA expression of Drd1a due to exercise. Hippocampal Bdnf mRNA increased in response to exercise and decreased in response to ethanol. Furthermore, there was an interaction effect of exercise and ethanol on the expression of Slc18a2 in the midbrain. These data suggest an important role for this pathway, and especially for Bdnf and Slc18a2 in regulating hedonic substitution.

Alternative CHRNB4 3'-UTRs mediate the allelic effects of SNP rs1948 on gene expression.

Common genetic factors strongly contribute to both nicotine, the main addictive component of tobacco, and alcohol use. Several lines of evidence suggest nicotinic acetylcholine receptors as common sites of action for nicotine and alcohol. Specifically, rs1948, a single-nucleotide polymorphism (SNP) located in the CHRNB4 3'-untranslated region (UTR), has been associated to early age of initiation for both alcohol and tobacco use. To determine the allelic effects of rs1948 on gene expression, two rs1948-containing sequences of different lengths corresponding to the CHRNB4 3'-UTR were cloned into pGL3-promoter luciferase reporter vectors. Data obtained showed that the allelic effects of SNP rs1948 on luciferase expression are mediated by the length and species of transcripts generated. In addition, it was found that miR-3157 increased the overall luciferase expression while miR-138, a microRNA known to play a role in neuroadaptation to drug abuse, decreased luciferase expression when compared to basal conditions. These findings demonstrate the importance of SNP rs1948 on the regulation of CHRNB4 expression and provide the first evidence of CHRNB4 down-regulation by miR-138.

Three-dimensional ultrashort echo magnetic resonance imaging of orthodontic appliances in the natural dentition.

INTRODUCTION: The purpose of this study was to determine whether ultrashort echo time magnetic resonance imaging technology could be used to image teeth with orthodontic appliances in place. METHODS: High-resolution 3-T ultrashort echo time magnetic resonance imaging was performed on 60 extracted premolars with fixed ceramic orthodontic appliances (Clarity, 3M Unitek, Monrovia, Calif; Radiance, American Orthodontics, Sheboygan, Wis; and Ice, Ormco, Glendora, Calif). The teeth were collected from the orthodontic clinic at the University of Alabama at Birmingham, and the institutional review board of the University of Alabama at Birmingham approved the study. Linear measurements of tooth morphology and orthodontic bracket dimensions were acquired with calipers and compared with virtual digital magnetic resonance imaging. The spin echo and high spatial resolution multi-slice turbo spin echo were only used for visual comparison with the ultrashort echo time slices. Both the caliper and the ultrashort echo time magnetic resonance imaging measurements were highly reliable and accurate. Comparisons between the 2 methods showed no statistically significant differences in any bracket or tooth dimensions, with a P value of >0.05. In general, the differences in the values ranged from -0.01 to 0.06 mm. A visual evaluation scale was used to assess the quality of the ultrashort echo time magnetic resonance images when assessing the delineation of dental hard tissues. RESULTS: The visual evaluation scale of the images showed that enamel, dentin, pulp, and ceramic orthodontic appliances could be subjectively delineated at a high level with the ultrashort echo time magnetic resonance imaging. CONCLUSIONS: The following conclusions can be drawn from this prospective study. Ceramic orthodontic appliances, without metal components, cause no dental image distortions and are readily visible on the ultrashort echo time magnetic resonance imaging scans. The measurements comparing linear tooth measurements with virtual digital magnetic resonance images demonstrated that magnetic resonance imaging has statistically and clinically significant accuracy on external tooth and bracket measurements. Visual evaluation of the images showed that enamel, dentin, pulp, and ceramic orthodontic appliances could be subjectively delineated at a high level with ultrashort echo time magnetic resonance imaging. Metallic slots in ceramic appliances cause severe image distortions. These distortions are localized and should not affect surrounding tissues in full-volume magnetic resonance imaging.

The α6 nicotinic acetylcholine receptor subunit influences ethanol-induced sedation.

Alcohol and nicotine are often co-used and data from human and animals studies have demonstrated that common genes underlie responses to these two drugs. Recently, the genes that code for the subunits of the nicotinic acetylcholine receptors have been implicated as a common genetic mediator for alcohol and nicotine responses. The mammalian genes that code for the α6 and ß3 subunits of the nicotinic acetylcholine receptor (Chrna6 and Chrnb3, respectively) are located adjacent to each other on human and mouse chromosome 8. These subunits have gained attention as potential regulators of drug behaviors because of their expression in the striatum where they have been shown to modulate dopamine release. Human genetic studies have shown that variation in these genes is associated with alcohol phenotypes. In the current experiments, mice lacking the Chrna6 or Chrnb3 gene were tested for three ethanol behaviors: choice ethanol consumption, ataxia, and sedation. Wildtype (WT), heterozygous (HET), and knockout (KO) mice of each strain went through a standard 2-bottle choice drinking paradigm, the balance beam, and the Loss of Righting Reflex (LORR) paradigm. No genotypic effects on any of the 3 behavioral tasks were observed in Chrnb3 animals. While the Chrna6 gene did not significantly influence ethanol consumption (g/kg) or ataxia, mice lacking the α6 subunit took significantly longer to recover their righting reflex than WT animals. These data provide evidence that receptors containing this subunit modulate the sedative effects of ethanol. Further work examining other models of ethanol consumption and behavioral responses to ethanol is needed to fully characterize the role of these receptor subunits in modulating ethanol responses.