Quantitative trait locus analyses of sleep-times induced by sedative-hypnotics in LSXSS recombinant inbred strains of mice

Alcohol Sensitivity as an Endophenotype of Alcohol Use Disorder: Exploring Its Translational Utility between Rodents and Humans

Alcohol use disorder (AUD) is a complex, chronic, relapsing disorder with multiple interacting genetic and environmental influences. Numerous studies have verified the influence of genetics on AUD, yet the underlying biological pathways remain unknown. One strategy to interrogate complex diseases is the use of endophenotypes, which deconstruct current diagnostic categories into component traits that may be more amenable to genetic research. In this review, we explore how an endophenotype such as sensitivity to alcohol can be used in conjunction with rodent models to provide mechanistic insights into AUD. We evaluate three alcohol sensitivity endophenotypes (stimulation, intoxication, and aversion) for their translatability across human and rodent research by examining the underlying neurobiology and its relationship to consumption and AUD. We show examples in which results gleaned from rodents are successfully integrated with information from human studies to gain insight in the genetic underpinnings of AUD and AUD-related endophenotypes. Finally, we identify areas for future translational research that could greatly expand our knowledge of the biological and molecular aspects of the transition to AUD with the broad hope of finding better ways to treat this devastating disorder.

Antipsoriatic Effects of Wannachawee Recipe on Imiquimod-Induced Psoriasis-Like Dermatitis in BALB/c Mice

Psoriasis is a common immune-mediated chronic inflammatory skin disease characterized by thick and erythema raised plaques with adherent silvery scales. T-cells are activated via the IL-23/Th17 axis which is involved in psoriasis pathogenesis. Conventional treatments of psoriasis have adverse events that influence patients' adherence. Wannachawee Recipe (WCR) is Thai traditional medicine that is known to be effective for psoriasis patients; however, preclinical evidence is still lacking. This study investigated the therapeutic potential of WCR on antiproliferant activity using imiquimod- (IMQ-) induced psoriasis-like dermatitis in a mouse model. Psoriasis-like dermatitis was induced on the shaved dorsal skin and right ear pinna of BALB/c mice by topical application of IMQ for 15 consecutive days after which WCR was administered to the mice by oral gavage for 10 days. Phenotypical observations, histopathological examinations, and ELISA of skin and blood samples were conducted. WCR significantly ameliorated development of IMQ-induced psoriasis-like dermatitis and reduced levels of Th17 cytokines (IL-17A, IL-22, and IL-23) in both serum and dorsal skin. Histopathological findings showed a decrease in epidermal thickness and inflammatory T-cell infiltration in the WCR-treated groups. The WCR has pharmacological actions which regulate Th17 related cytokines suggesting that it is a potential alternative therapeutic strategy for psoriasis.

Transcriptome analysis of Inbred Long Sleep and Inbred Short Sleep mice

Many studies have utilized the Inbred Long Sleep and Inbred Short Sleep mouse strains to model the genetic influence on initial sensitivity to ethanol. The mechanisms underlying this divergent phenotype are still not completely understood. In this study, we attempt to identify genes that are differentially expressed between these two strains and to identify baseline networks of co-expressed genes, which may provide insight regarding their phenotypic differences. We examined the whole brain and striatal transcriptomes of both strains, using next generation RNA sequencing techniques. Many genes were differentially expressed between strains, including several in chromosomal regions previously shown to influence initial sensitivity to ethanol. These results are in concordance with a similar sample of striatal transcriptomes measured using microarrays. In addition to the higher dynamic range, RNA-Seq is not hindered by high background noise or polymorphisms in probesets as with microarray technology, and we are able to analyze exome sequence of abundant genes. Furthermore, utilizing Weighted Gene Co-expression Network Analysis, we identified several modules of co-expressed genes corresponding to strain differences. Several candidate genes were identified, including protein phosphatase 1 regulatory unit 1b (Ppp1r1b), prodynorphin (Pdyn), proenkephalin (Penk), ras association (RalGDS/AF-6) domain family member 2 (Rassf2), myosin 1d (Myo1d) and transthyretin (Ttr). In addition, we propose a role for potassium channel activity as well as map kinase signaling in the observed phenotypic differences between the two strains.

Increased ethanol intake and preference in cyclin D2 knockout mice

Inhibitory effects of passive ethanol exposure on brain neurogenesis have been extensively documented in animal models. In contrast, a role of brain neurogenesis in ethanol self-administration has not been addressed, as yet. The aim of this study was to assess intake of, and preference for, ethanol solutions [2-16% (v/v)] in a mouse model of adult neurogenesis deficiency based on permanent knockout (KO) of cyclin D2 (Ccnd2). Wild type (WT) and Ccnd2 KO mice did not differ in 2% and 4% ethanol intake. The KO group consumed significantly more ethanol in g/kg when offered with 8% or 16% ethanol as compared with the WT controls. The WT and KO mice did not differ in 2% ethanol preference, but the KO group showed a significantly higher preference for 4-16% ethanol. Animal and human studies have suggested that the low level of response to the sedative/hypnotic effects of alcohol is genetically associated with enhanced alcohol consumption. However, in this study, there were no between-genotype differences in ethanol-induced loss of righting reflex. Previous reports have also suggested that high ethanol intake is genetically associated with the avidity for sweets and better acceptance of bitter solutions. However, the KO and WT mice consumed similar amounts of saccharin solutions and the KOs consumed less quinine (i.e. bitter) solutions as compared with the WTs. In conclusion, these results may indicate that Ccnd2 and, possibly, brain neurogenesis are involved in central regulation of ethanol intake in mice.

No effect of prenatal alcohol exposure on activity in three inbred strains of mice

AIMS

Prenatal exposure to alcohol can have adverse effects on the developing fetus. Two of the hallmarks of children exposed to alcohol prenatally are attention deficits and hyperactivity. While hyperactivity has been observed in rats following prenatal ethanol exposure, few studies have examined these effects in mice. The present study investigated the effects of prenatal ethanol exposure on activity in mice from three inbred strains: C57BL/6 (B6), Inbred Long Sleep (ILS) and Inbred Short Sleep (ISS).

METHODS

On Days 7 through 18 of gestation, mice were intragastrically intubated twice daily with either 3.0 g/kg ethanol (E) or an isocaloric amount of maltose-dextrin (MD); non-intubated control (NIC) litters were also generated. Offspring activity was monitored at 30, 60, 90 and 150 days of age.

RESULTS

While results showed no effects of prenatal ethanol exposure on any measures of activity, we did observe differences in baseline activity among the strains. ISS mice were more active than B6 and ILS for all activity measures except stereotypy; B6 mice had higher measures of stereotypy than ILS and ISS. Younger mice were more active than older mice. The only sex effects were on measures of stereotypy, where males had higher scores.

CONCLUSIONS

Mice are an excellent organism to study genetic influences on many phenotypes. However, our study and others have shown few effects of prenatal ethanol exposure on behavior in mice. It appears as if the prenatal period in mice, corresponding to organogenesis, is not a sensitive period for producing behavioral deficits following ethanol exposure. It is likely that the first 2 weeks postnatally, corresponding to the brain growth spurt, are more sensitive for producing behavioral effects.

Mouse chromosome 7 harbors a quantitative trait locus for isoflurane minimum alveolar concentration

BACKGROUND

The minimum alveolar concentration (MAC) of isoflurane is a quantitative trait because it varies continuously in a population. The location on the genome of genes or other genetic elements controlling quantiative traits is called quantitative trait loci (QTLs). In this study we sought to detect a quantitative trait locus underlying isoflurane MAC in mice.

METHODS

To accomplish this, two inbred mouse strains differing in isoflurane MAC, the C57BL/6J and LP/J mouse strains, were bred through two generations to produce genetic recombination. These animals were genotyped for microsatellite markers. We also applied an independent, computational method for identifying QTL-regulating differences in isoflurane MAC. In this approach, the isoflurane MAC was measured in a panel of 19 inbred strains, and computationally searched for genomic intervals where the pattern of genetic variation, based on single nucleotide polymorphisms, correlated with the differences in isoflurane MAC among inbred strains.

RESULTS AND CONCLUSIONS

Both methods of genetic analysis identified a QTL for isoflurane MAC that was located on the proximal part of mouse chromosome 7.

Mapping the contribution of beta3-containing GABAA receptors to volatile and intravenous general anesthetic actions

Background

Agents belonging to diverse chemical classes are used clinically as general anesthetics. The molecular targets mediating their actions are however still only poorly defined. Both chemical diversity and substantial differences in the clinical actions of general anesthetics suggest that general anesthetic agents may have distinct pharmacological targets. It was demonstrated previously that the immobilizing action of etomidate and propofol is completely, and the immobilizing action of isoflurane partly mediated, by β3-containing GABA_A receptors. This was determined by using the β3(N265M) mice, which carry a point mutation known to decrease the actions of general anesthetics at recombinant GABA_A receptors. In this communication, we analyzed the contribution of β3-containing GABA_A receptors to the pharmacological actions of isoflurane, etomidate and propofol by means of β3(N265M) mice.

Results

Isoflurane decreased core body temperature and heart rate to a smaller degree in β3(N265M) mice than in wild type mice, indicating a minor but significant role of β3-containing GABA_A receptors in these actions. Prolonged time intervals in the ECG and increased heart rate variability were indistinguishable between genotypes, suggesting no involvement of β3-containing GABA_A receptors. The anterograde amnesic action of propofol was indistinguishable in β3(N265M) and wild type mice, suggesting that it is independent of β3-containing GABA_A receptors. The increase of heart rate variability and prolongation of ECG intervals by etomidate and propofol were also less pronounced in β3(N265M) mice than in wild type mice, pointing to a limited involvement of β3-containing GABA_A receptors in these actions. The lack of etomidate- and propofol-induced immobilization in β3(N265M) mice was also observed in congenic 129X1/SvJ and C57BL/6J backgrounds, indicating that this phenotype is stable across different backgrounds.

Conclusion

Our results provide evidence for a defined role of β3-containing GABA_A receptors in mediating some, but not all, of the actions of general anesthetics, and confirm the multisite model of general anesthetic action. This pharmacological separation of anesthetic endpoints also suggests that subtype-selective substances with an improved side-effect profile may be developed.

Confirmation of quantitative trait loci for ethanol sensitivity and neurotensin receptor density in crosses derived from the inbred high and low alcohol sensitive selectively bred rat lines

RATIONALE

Genetically influenced alcohol sensitivity is thought to be an important risk factor for the development of alcoholism. An effective first step for identifying genes that mediate variation in alcohol sensitivity is through quantitative trait loci (QTL) mapping in model organisms.

OBJECTIVE

Fourteen provisional QTLs related to alcohol sensitivity were previously mapped in an F2 derived from the IHAS1 and ILAS1 rat lines. The objective of the current study was to confirm those QTLs in an independently derived F2 and in congenics that were bred for two of the loci.

MATERIALS AND METHODS

IHAS1 X ILAS1 F2 (n=450) were tested for alcohol-induced loss of righting reflex (LORR), blood ethanol concentration at regain of righting reflex (BECRR), sensitivity and acute tolerance on the Rotarod, and neurotensin receptor density (NTR1). Rats were genotyped at the 14 candidate loci and QTL mapping was conducted. Reciprocal congenic strains were bred for loci on chromosomes 2 and 5 and tested for LORR and BECRR.

RESULTS

Four LORR QTLs were mapped at the suggestive or significant level (chromosomes 2, 5, 12, and 13). BECRR was mapped to chromosomes 5, 12, and 13 either in the original or current experiment. Results of the congenic experiment also support QTLs for LORR and BECRR on chromosomes 2 and 5. QTLs for NTR1 density and behavior on the Rotarod were not confirmed.

CONCLUSIONS

QTL mapping in crosses derived from the IHAS1 and ILAS1 has successfully identified loci related to alcohol sensitivity. Recombinant congenics are now being bred to more finely map the confirmed QTLs.

A Microarray Analysis of Potential Genes Underlying the Neurosensitivity of Mice to Propofol

Establishing the mechanism of action of general anesthetics at the molecular level is difficult because of the multiple targets with which these drugs are associated. Inbred short sleep (ISS) and long sleep (ILS) mice are differentially sensitive in response to ethanol and other sedative hypnotics and contain a single quantitative trait locus (Lorp1) that accounts for the genetic variance of loss-of-righting reflex in response to propofol (LORP). In this study, we used high-density oligonucleotide microarrays to identify global gene expression and candidate genes differentially expressed within the Lorp1 region that may give insight into the molecular mechanism underlying LORP. Microarray analysis was performed using Affymetrix MG-U74Av2 Genechips and a selection of differentially expressed genes was confirmed by semiquantitative reverse transcription-polymerase chain reaction. Global expression in the brains of ILS and ISS mice revealed 3423 genes that were significantly expressed, of which 139 (4%) were differentially expressed. Analysis of genes located within the Lorp1 region showed that 26 genes were significantly expressed and that just 2 genes (7%) were differentially expressed. These genes encoded for the proteins AWP1 (associated with protein kinase 1) and "BTB (POZ) domain containing 1," whose functions are largely uncharacterized. Genes differentially expressed outside Lorp1 included seven genes with previously characterized neuronal functions and thus stand out as additional candidate genes that may be involved in mediating the neurosensitivity differences between ISS and ILS.

Quantitative trait loci mapping for ethanol sensitivity and neurotensin receptor density in an F2 intercross derived from inbred high and low alcohol sensitivity selectively bred rat lines

BACKGROUND

Genetic variance in initial sensitivity to ethanol has been implicated as a risk factor for the development of alcoholism. Identification of the genes that confer differential initial sensitivity is an important goal for the development of new treatment strategies and for a comprehensive understanding of the mechanism of ethanol's action. Quantitative trait loci (QTL) mapping for initial sensitivity and other ethanol-related behavioral traits in model organisms has become an important first step for the ultimate identification of genes that contribute to variation in ethanol responses.

METHODS

An F(2) intercross was made from the Inbred High and Low Alcohol Sensitivity rat lines (IHAS and ILAS). The F(2) rats were tested for duration of the loss of righting reflex test (LORR); blood ethanol concentration at regain of righting reflex (BECrrr); BEC at the first time to reach criterion on the rotarod after 1.6 g/kg of ethanol (BEC1); acute functional tolerance on the rotarod (AFT); and high-affinity neurotensin receptor (NTR1) density in the nucleus accumbens (NAc), caudate putamen (CP), and ventral midbrain (VMB). A full genome scan with an average marker spacing of 16.8 cM for interval QTL mapping was conducted on the F(2) rats (N = 363).

RESULTS

Seven significant or suggestive QTL were detected for LORR, one for BECrrr, three for BEC1, two for NTR1 binding in the CP, and one for binding in the NAc, but none were mapped for AFT or NTR1 binding density in the VMB. Effect size of the seven LORR QTL, the trait for which the parental strains were selected, ranged from 3 to 4%, with all accounting for approximately 22% of the total phenotypic variation. One of the LORR QTL on chromosome 2 (approximately 87 cM) was significant, and a second QTL on chromosome 5 (approximately 37 cM) was suggestive for both LORR and BECrrr.

CONCLUSIONS

The results indicate that segregating populations derived from the IHAS and ILAS strains can be used for mapping ethanol sensitivity QTL. The chromosome 2 LORR QTL may confer variation in ethanol metabolism, whereas the chromosome 5 LORR/BECrrr QTL likely mediates central nervous system ethanol sensitivity. The small number or absence of QTL for BEC1, AFT, and NTR1 receptor density suggests that genetic variation for these traits is minimal in the IHAS/ILAS strains and/or the effect size of QTL for these traits is too small to be mapped efficiently in this sample of F(2) rats. The ultimate identification of genes underlying these alcohol sensitivity QTL will contribute to our understanding of the actions of alcohol in the central nervous system if not to a deeper understanding of the genetic risk factors for alcoholism.

Mapping quantitative trait loci mediating sensitivity to etomidate

Long- and Short-Sleep (LS and SS) mice were selectively bred for differences in ethanol-induced loss of the righting reflex (LORR) and have been found to differ in LORR induced by various anesthetic agents. We used a two-stage mapping strategy to identify quantitative trait loci (QTLs) affecting duration of LORR caused by the general anesthetic etomidate and brain levels of etomidate (BEL) following regain of the righting reflex. Analysis of recombinant-inbred strains derived from a cross between LS and SS mice (LSXSS) yielded a heritability estimate of 0.23 for etomidate-induced LORR and identified one marker that showed suggestive linkage for a QTL, on mouse Chromosome (chr) 12. Mapping in an F(2) population derived from a cross between inbred LS and SS (ILS and ISS) revealed a significant QTL for etomidate-induced LORR on Chr 12, and two significant QTLs mediating BEL on Chrs 6 and 12. Several QTLs showing suggestive linkage for etomidate-induced LORR and BEL were also identified in the F(2) population. Brain levels of etomidate in the RI and F(2) mice suggested that differences in LORR were due to differential central nervous system sensitivity, rather than differential etomidate metabolism. Interestingly, the region on Chr 7 has also been identified as a region influencing ethanol-induced LORR, suggesting the possibility of a common genetic mechanism mediating etomidate and ethanol sensitivity. These QTL regions need to be further narrowed before the testing of candidate genes is feasible.

Harnessing the mouse to unravel the genetics of human disease

Complex traits, i.e. those with multiple genetic and environmental determinants, represent the greatest challenge for genetic analysis, largely due to the difficulty of isolating the effects of any one gene amid the noise of other genetic and environmental influences. Methods exist for detecting and mapping the Quantitative Trait Loci (QTLs) that influence complex traits. However, once mapped, gene identification commonly involves reduction of focus to single candidate genes or isolated chromosomal regions. To reach the next level in unraveling the genetics of human disease will require moving beyond the focus on one gene at a time, to explorations of pleiotropism, epistasis and environment-dependency of genetic effects. Genetic interactions and unique environmental features must be as carefully scrutinized as are single gene effects. No one genetic approach is likely to possess all the necessary features for comprehensive analysis of a complex disease. Rather, the entire arsenal of behavioral genomic and other approaches will be needed, such as random mutagenesis, QTL analyses, transgenic and knockout models, viral mediated gene transfer, pharmacological analyses, gene expression assays, antisense approaches and importantly, revitalization of classical genetic methods. In our view, classical breeding designs are currently underutilized, and will shorten the distance to the target of understanding the complex genetic and environmental interactions associated with disease. We assert that unique combinations of classical approaches with current behavioral and molecular genomic approaches will more rapidly advance the field.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Distinct roles of the Y1 and Y2 receptors on neuropeptide Y-induced sensitization to sedation

Intracranial injection of neuropeptide Y (NPY) increases the sensitivity to sodium pentobarbital and ketamin sedation and has similar properties as GABA agonists on sleep. Mice sensitive to sedation have increased levels of NPY in many brain regions and Y1(-/-) mice show a marked resistance to barbiturates. Here we characterized the role of the NPY Y receptors in anesthetic-induced sedation. We show that Y1 and Y2, but not Y5, receptors participate in the modulation of sedation. Administration of a Y1 agonist increased the sodium pentobarbital-induced sedation and Y1(-/-) mice were less sensitive to this anesthetic. However, Y2(-/-) mice display increased sensitivity, showing that Y2 modulates GABAergic induced sedation both pharmacologically and physiologically and has a functionally opposing role to the Y1 receptor. Analysis of Y1(-/-)/Y2(-/-) double mutant mice show that increased sensitivity by Y1 occurs independent of the Y2 receptor, while the decreased sensitivity mediated by Y2 depend on an intact Y1 receptor. In contrast to sodium pentobarbital, both Y1 and Y2 receptors increase the sensitivity in a collaborative fashion to NMDA antagonist-induced sedation. These data demonstrate the physiological and pharmacological impact of the Y1 and Y2 receptors on sedation.

Effects of a novel uncompetitive NMDA receptor antagonist, MRZ 2/579 on ethanol self-administration and ethanol withdrawal seizures in the rat

It has been repeatedly reported that NMDA receptors may contribute to ethanol-induced discriminative stimulus effects and withdrawal syndrome. However, the role of NMDA receptors in the reinforcing properties of ethanol remains unclear. The aim of the present study was to evaluate effects of the novel low-affinity, uncompetitive NMDA receptor antagonist, 1-amino-1,3,3,5,5-pentamethyl-cyclohexane hydrochloride (MRZ 2/579), on ethanol self-administration and ethanol withdrawal-associated seizures in rats. Both an operant (lever pressing for ethanol) and non-operant two-bottle choice setups were employed to initiate ethanol self-administration. In another procedure, forced treatment with high doses (9--15 g/kg/day) was used to induce physical dependence on ethanol. MRZ 2/579 delivered chronically by osmotic minipumps (9.6 mg/day, s.c.) did not alter either operant or non-operant ethanol drinking behaviour in a maintenance phase of ethanol self-administration. In contrast, repeated daily injections of the drug (5 mg/kg, i.p.) led to a progressive decrease in operant responding for ethanol. MRZ 2/579 (0.5--7.5 mg/kg, i.p.) and another low-affinity NMDA receptor antagonist, memantine (1--10 mg/kg, i.p.) dose-dependently suppressed ethanol withdrawal seizures with efficacies comparable with that of a standard benzodiazepine derivative, diazepam. The results of the present study indicate that: (i) intermittent administration of MRZ 2/579 may lead to a gradual decrease of operant responding for ethanol; and (ii) the group of low-affinity uncompetitive NMDA receptor antagonists may be an interesting alternative to benzodiazepines in the treatment of alcohol withdrawal.

Strain distribution patterns for genetic markers in the LSXSS recombinant-inbred series

We present the strain distribution patterns (SDPs) of 118 SSLP markers and three pigmentation genes that have been characterized in 27 strains from the LSXSS RI series. This coarse map provides a resource for linkage studies of phenotypes that are heritable in the LSXSS RI series. The LSXSS recombinant inbred (RI) strains were derived from the Long-Sleep (LS) and Short-Sleep (SS) selected lines of mice that were selected for differential sensitivity to ethanol but are also differentially sensitive to a variety of other alcohols, barbiturates, sedative hypnotics, and general anesthetics. Since the parents were not inbred, two atypical factors are present in these SDPs. First, more than two alleles are frequently found in these RIs, and second, some alleles can be uniquely associated with one or the other parent while other alleles may be found in both parental lines. To validate the markers found in the parental line, we genotyped all parental mice from one generation of both the LS and SS lines, thus leading to a set of marker SDPs that are useful for further phenotypic association and identification of provisional QTLs.

Genetic models in the study of anesthetic drug action

This chapter reviews the use of genetic models in the study of anesthetic drug action. Genetic model systems provide a novel approach to understanding mechanisms of anesthetic drug action. Many models have been derived using selection processes that emphasize differential drug sensitivity, producing animal lines that differ in their CNS drug response. Studies of vertebrate (rodent) and invertebrate (Drosophila, Caenorhabditis elegans) animal model systems are covered. The review discusses studies employing lines derived from spontaneous and induced mutagenic processes, selectively bred lines, and inbred lines possessing inherent differential drug sensitivities. The primary focus of included studies is the general anesthetic drugs that are commonly used in the clinical setting. These are drugs such as the inhalational agents (halothane, enflurane, isoflurane, nitrous oxide) and the intravenous induction agents (propofol and diazepam). Rodent lines with differential sensitivity to opiates are also discussed. Finally, an approach to identifying and isolating the genes that control anesthetic sensitivity is discussed in a section on mapping quantitative trait loci (QTL) in recombinant inbred lines.