LXS Recombinant Inbred Strains Research Articles

Quantitative trait locus mapping of acute functional tolerance in the LXS recombinant inbred strains.

We previously reported that acute functional tolerance (AFT) to the hypnotic effects of alcohol was significantly correlated with drinking in the dark (DID) in the LXS recombinant inbred panel, but only in mice that had been pretreated with alcohol. Here, we have conducted quantitative trait locus (QTL) mapping for AFT. DNA sequencing of the progenitor ILS and ISS strains and microarray analyses were also conducted to identify candidate genes and functional correlates. LXS mice were given either saline or alcohol (5g/kg) on day 1 and then tested for loss of righting reflex AFT on day 2. QTLs were mapped using standard procedures. Two microarray analyses from brain were conducted: (i) naïve LXS mice and (ii) an alcohol treatment time course in the ILS and ISS. The full genomes of the ILS and ISS were sequenced to a depth of approximately 30×. A significant QTL for AFT in the alcohol pretreatment group was mapped to distal chromosome 4; numerous suggestive QTLs were also mapped. Preference drinking and DID have previously been mapped to the chromosome 4 locus. The credible interval of the significant chromosome 4 QTL spanned 23Mb and included 716 annotated genes of which 150 had at least 1 nonsynonymous single nucleotide polymorphism or small indel that differed between the ILS and ISS; expression of 48 of the genes was cis-regulated. Enrichment analysis indicated broad functional categories underlying AFT, including proteolysis, transcription regulation, chromatin modification, protein kinase activity, and apoptosis. The chromosome 4 QTL is a key region containing possibly pleiotropic genes for AFT and drinking behavior. Given that the region contains many viable candidates and a large number of the genes in the interval fall into 1 or more of the enriched functional categories, we postulate that many genes of varying effect size contribute to the observed QTL effect.

Genetic Studies of Acute Tolerance, Rapid Tolerance, and Drinking in the Dark in the LXS Recombinant Inbred Strains

We hypothesized that rapid tolerance (1-day tolerance) for the duration of the loss of righting reflex ("sleep time" [ST]) was mediated by an increase in acute functional tolerance (AFT). We also hypothesized that increased AFT would correspond to increased drinking. These questions were addressed using the LXS recombinant inbred mouse strain panel. Mice were given a pretreatment dose of either saline or 5g/kg alcohol on day 1. On day 2, mice were tested for ST (4.1g/kg) using a method with which it is possible to accurately assess AFT. Genetic correlation analysis was conducted among the ST-related variables and also with "drinking in the dark" (DID) which was previously measured by Saba and colleagues (2011). Saline-pretreated mice showed a continuous distribution of ST ranging from ~40minutes to over 3hours. Of the 43 strains tested, 9 showed significantly decreased ST after alcohol pretreatment, while in 3 strains, ST was significantly increased. AFT scores ranged from 0 to over 200mg% in the saline group, and in the alcohol group, 8 strains showed a significant increase in AFT and 2 strains showed significant decrease in AFT. In the saline group, AFT was significantly correlated with ST (r=-0.47), but not in the alcohol group (r=-0.22). DID was significantly correlated with only AFT in the alcohol pretreated group (r=0.64). The results suggest that AFT is an important component of the overall ST response, but that the alcohol pretreatment-induced change in AFT does not contribute to rapid ST tolerance. The significant correlation between DID and AFT in the alcohol group suggests that AFT may be a more relevant predictor of drinking behavior than the static measurement of ST. Moreover, preexposure to alcohol seems to change AFT in a way that makes it an even stronger predictor of drinking behavior.

QTL Mapping for Low‐Dose Ethanol Activation in the LXS Recombinant Inbred Strains

Most mouse quantitative trait loci (QTLs) for behavioral traits have been mapped using populations of mice derived from C57BL/6J (B6) and DBA/2J (D2). It is also important to identify QTLs for behavior in populations derived from other progenitors. We report results from QTL mapping for low-dose (ethanol) locomotor activation (LDA) using the recently developed LXS recombinant inbred (RI) strains, derived from Inbred Long Sleep (ILS) and Inbred Short Sleep (ISS) progenitors. The LXS RI panel has additional genetic variation, and greater power due to a larger number of strains, compared with other RI panels and strain crosses. Mice were tested using a 3-day protocol in which activity levels were monitored for 15 minutes each day. On day 1, baseline activity was recorded; on day 2, mice were injected with saline before testing; and on day 3, mice were injected with 1.8 g/kg ethanol and tested. Several suggestive QTLs were found, on chromosomes 2, 3, 4, 7, 8, 12, and 13; 3 of these QTLs were sex-specific. Two apparently novel LDA QTLs were identified, on chromosomes 4 and 8. The other QTLs appear to replicate previously identified LDA QTLs. These replicated QTLs will be pursued in subsequent studies designed to identify candidate genes.