Identification of ethanol analgesia quantitative trait loci and candidate genes in BXD recombinant inbred mouse lines

Abstract

Alcohol consumption produces acute analgesic effects, and people experiencing pain conditions may drink alcohol to alleviate discomfort. However, tolerance to the analgesic properties of alcohol could prompt escalating consumption and dependence. Both nociception and alcohol-induced analgesia are under significant genetic control. Understanding the genetic architecture of these processes could inform better treatment options for people with pain conditions. This study aims to identify quantitative trait loci (QTL) driving variation in ethanol-induced analgesia across BXD recombinant inbred mouse lines. Male and female mice from 62 BXD strains received ethanol or saline oral gavage for five days and were tested for hot plate (HP) latency at baseline, Day 1 and Day 5. QTL mapping of HP phenotypes identified a significant provisional QTL on chromosome 17 for Day 1 HP latency in mice receiving ethanol. An additional highly suggestive QTL was present on chromosome 9 for the difference in pre- and post-ethanol thermal nociception. Candidate genes within QTL support intervals were provisionally identified using HP phenotypic correlations to transcriptomic database, expression QTL analysis and other bioinformatics inquiries. The combined behavioural and bioinformatic analyses yielded strong ethanol analgesia candidate genes, specifically Myo6. Thus, the results of this genetic study of ethanol-induced analgesia in BXD mouse strains may contribute significantly to our understanding of the molecular basis for individual variation in the analgesic response to acute ethanol.

Keywords: BXD; analgesia; ethanol; genetics.

FIGURE 1

Mean hot plate latencies in BXD mice. A) Mean hot plate latency (+/− 1 SE) in seconds at each timepoint for vehicle‐ and ethanol‐receiving mice. Acute ethanol significantly increases hot plate latency in BXD mice. B) A scatterplot depicts BXD strain mean baseline and Day 1 hot plate latencies in seconds on the x and y‐axes, respectively. Regression lines for each treatment were set to an intercept at the origin, and the dashed diagonal (slope = 1) represents a hypothetical perfect correlation between Baseline and Day 1 latency.

FIGURE 2

Correlograms for locomotor activity and hot plate latency phenotypes in ethanol‐receiving mice (2A) and saline‐receiving mice (2B). Asterisks denote a significant uncorrected p‐value < .05 for the correlation.

FIGURE 3

QTL analysis for Day 1 post‐ethanol hot plate latency. A) The genome scan of square root‐transformed Day 1 post‐ethanol hot plate latency yields a significant QTL peak with a LOD score >4 on Chr 17. B) Highlight of Chr 17 showing ethanol‐specific QTL and single nucleotide polymorphism (SNP) count. C) Mice with DBA2/J alleles at the peak locus of Pehlq1 exhibit increased post‐ethanol latency compared with mice with C57BL6/J alleles (Welch two‐sample t‐test, p < .001).

FIGURE 4

Chromosome 9 QTL for difference between pre‐ and post‐treatment hot plate latency. A) A full‐genome scan reveals a highly suggestive ethanol‐specific QTL (p < .10) on Chr 9 for the difference in pre‐ and post‐treatment thermal nociception. B) No QTL was observed at this locus when performing a genome scan for the difference phenotype in saline‐receiving mice (dashed grey line). C) Mice with DBA2/J alleles at the peak locus of Etadq1 exhibited a decreased difference phenotype compared with mice with C57BL6/J alleles (Welch two‐sample t‐test, p < .001).