Genetic variability for regional brain gangliosides in five strains of young mice

The quantitative and qualitative distributions of gangliosides were determined in the cerebrum, cerebellum, and brain stem of five inbred strains (C57BL/6J, DBA/2J, LG/J, C3H/HeJ, BALB/cJ) of mice at 21 days of age. Genetic differences were found among the strains for wet weight, absolute amount of gangliosides per region, and concentration of ganglioside (expressed on both a wet and a dry weight basis) in all three regions of the brain. The water content of the various brain regions showed the least amount of genetic variability. Coefficients of genetic determination were used to estimate the magnitude of genetic influence on these traits in each brain region. Significant differences were also found among the five strains for the distribution of certain gangliosides. The DBA strain, which is susceptible to audiogenic seizure at this age, had the highest level of the myelin-enriched ganglioside G_M1 in all brain regions. Most of the genetic variation that influences the content and distribution of gangliosides among neurologically normal mice can be considered polygenic. Several possible sources of this genetic variation that may contribute to the differences observed among the strains are discussed.This work was supported by USPHS Grant NS 11853 and by a grant from the Swebilius Fund. T. N. S. is the recipient of a USPHS postdoctoral fellowship (1F32NS0443).     

Amiloride inhibition on NaCl responses of the chorda tympani nerve in two 129 substrains of mice, 129P3/J and 129X1/SvJ

Amiloride, a sodium channel blocker, is known to suppress NaCl responses of the chorda tympani (CT) nerve in various mammalian species. In mice, the NaCl suppressing effect of amiloride is reported to differ among strains. In C57BL mice, amiloride inhibits NaCl responses to about 50% of control, whereas no such clear suppression was evident in prior studies with 129 mice. However, evidence from behavioral studies is not entirely consistent with this. Recently, it has been found that genetic backgrounds of 129 mice differ within substrains. 129X1/SvJ (formerly 129/SvJ) mice differ from the 129P3/J (formerly 129/J) strain by 25% of sequence length polymorphisms. Therefore, we examined possible substrain difference between 129P3/J and 129X1/SvJ mice in the amiloride sensitivity of electrophysiologically recorded NaCl responses. Amiloride significantly suppressed CT responses to NaCl without affecting responses to KCl both in 129P3/J and 129X1/SvJ mice. However, the magnitude of the amiloride inhibition was significantly larger (approximately 50% of control in response to 0.01-1.0 M NaCl by 100 microM amiloride) in 129X1/SvJ than in 129P3/J mice (approximately 20% of control in response to 0.03-0.3 M NaCl by 100 microM amiloride). Threshold amiloride concentration for suppression of responses to 0.3 M NaCl was 30 microM in 129P3/J mice, which was higher than that in 129X1/SvJ mice (10 microM). In 129X1/SvJ mice, the threshold amiloride concentration eliciting inhibition of NaCl responses and the magnitude of the inhibition were comparable with those in C57BL/6 mice. These results suggest that amiloride sensitivity of NaCl responses differs even among the 129 substrains, 129P3/J and 129 X1/SvJ, and the substrain difference of 129 mice in amiloride sensitivity is as large as that between two inbred strains (129P3/J and C57BL/6).     

Differences in sensitivity to the convulsant pilocarpine in substrains and sublines of C57BL/6 mice

In rodents, the cholinomimetic convulsant pilocarpine is widely used to induce status epilepticus (SE), followed by hippocampal damage and spontaneous recurrent seizures, resembling temporal lobe epilepsy. This model has initially been described in rats, but is increasingly used in mice, including the C57BL/6 (B6) inbred strain. In the present study, we compared the effects of pilocarpine in three B6 substrains (B6JOla, B6NHsd and B6NCrl) that were previously reported to differ in several behavioral and genetic aspects. In B6JOla and B6NHsd, only a small percentage of mice developed SE independently of whether pilocarpine was administered at high bolus doses or with a ramping up dosing protocol, but mortality was high. The reverse was true in B6NCrl, in which a high percentage of mice developed SE, but mortality was much lower compared to the other substrains. However, in subsequent experiments with B6NCrl mice, striking differences in SE induction and mortality were found in sublines of this substrain coming from different barrier rooms of the same vendor. In B6NCrl from Barrier #8, administration of pilocarpine resulted in a high percentage of mice developing SE, but mortality was low, whereas the opposite was found in B6NCrl mice from four other barriers of the same vendor. The analysis of F1 mice from a cross of female Barrier 8 pilocarpine‐susceptible mice with resistant male mice from another barrier (#9) revealed that F1 male mice were significantly more sensitive to pilocarpine than the resistant parental male mice whereas female F1 mice were not significantly different from resistant Barrier 9 females. These observations strongly indicate X‐chromosome linked genetic variation as the cause of the observed phenotypic alterations. To our knowledge, this is the first report which demonstrates that not only the specific B6 substrain but also sublines derived from the same substrain may markedly differ in their response to convulsants such as pilocarpine. As the described differences have a genetic basis, they offer a unique opportunity to identify the genes and pathways involved and contribute to a better understanding of the underlying molecular mechanisms of seizure susceptibility.     

Genetic modifiers of the Kv beta2-null phenotype in mice

Shaker-type potassium (K+) channels are composed of pore-forming alpha subunits associated with cytoplasmic beta subunits. Kv beta2 is the predominant Kv beta subunit in the mammalian nervous system, but its functions in vivo are not clear. Kv beta2-null mice have been previously characterized in our laboratory as having reduced lifespans, cold swim-induced tremors and occasional seizures, but no apparent defect in Kv alpha-subunit trafficking. To test whether strain differences might influence the severity of this phenotype, we analyzed Kv beta2-null mice in different strain backgrounds: 129/SvEv (129), C57BL/6J (B6) and two mixed B6/129 backgrounds. We found that strain differences significantly affected survival, body weight and thermoregulation in Kv beta2-null mice. B6 nulls had a more severe phenotype than 129 nulls in these measures; this dramatic difference did not reflect alterations in seizure thresholds but may relate to strain differences we observed in cerebellar Kv1.2 expression. To specifically test whether Kv beta1 is a genetic modifier of the Kv beta2-null phenotype, we generated Kv beta1.1-deficient mice by gene targeting and bred them to Kv beta2-null mice. Kv beta1.1/Kv beta2 double knockouts had significantly increased mortality compared with either single knockout but still maintained surface expression of Kv1.2, indicating that trafficking of this alpha subunit does not require either Kv beta subunit. Our results suggest that genetic differences between 129/SvEv and C57Bl/6J are key determinants of the severity of defects seen in Kv beta2-null mice and that Kv beta1.1 is a specific although not strain-dependent modifier.     

Distribution of the C1473G polymorphism in tryptophan hydroxylase 2 gene in laboratory and wild mice

The neurotransmitter serotonin is implicated in the regulation of various forms of behavior, including aggression, sexual behavior and stress response. The rate of brain serotonin synthesis is determined by the activity of neuronal‐specific enzyme tryptophan hydroxylase 2. The missense C1473G substitution in mouse tryptophan hydroxylase 2 gene has been shown to lower the enzyme activity and brain serotonin level. Here, the C1473G polymorphism was investigated in 84 common laboratory inbred strains, 39 inbred and semi‐inbred strains derived from wild ancestors (mostly from Eurasia) and in 75 wild mice trapped in different locations in Russia and Armenia. Among all the classical inbred strains studied, only substrains of BALB/c, A and DBA, as well as the IITES/Nga and NZW/NSlc strains were homozygous for the 1473G allele. In contrast to laboratory strains, the 1473G allele was not present in any of the samples from wild and wild‐derived mice, although the wild mice varied substantially in the C1477T neutral substitution closely linked to the C1473G polymorphism. According to these results, the frequency of the 1473G allele in natural populations does not exceed 0.5%, and the C1473G polymorphism is in fact a rare mutation that is possibly eliminated by the forces of natural selection.     

小鼠的遗传学研究

自20世纪初,小鼠的遗传学研究从宠物农场进入哈佛大学的实验室只有短短一百年的历史;但是,由于小鼠基因组与人类基因组高度同源、小鼠基因组改造手段非常成熟以及小鼠近交系、突变系和工具小鼠品系种类繁多,小鼠遗传学已成为发育生物学、功能基因组学和疾病机理研究的核心研究领域,小鼠也成为最重要的模式生物之一。近年来,随着小鼠基因组序列测序的完成,不同小鼠近交系品系特异的微卫星标记或单核苷酸多态性不断被发现,小鼠生理生化表型分析手段和数据也越来越完善,这些前期工作导致了目前大规模的基因剔除计划、基因突变计划及构建和分析重组近交系计划的实施。这些计划可能构成未来10￣20年中生命科学和医学研究领域的最重要的内容之一。     

Response,use and habituation to a mouse house in C57BL/6J and BALB/c mice

Animal welfare depends on the possibility to express species-specific behaviours and canbe strongly compromised in socially and environmentally deprived conditions. Nestingmaterials and refuges are very important resources to express these behaviours and shouldbe considered as housing supplementation items. We evaluated the effects of one item ofhousing supplementation in standard settings in laboratory mice. C57BL/6JOlaHsd (B6) andBALB/cOlaHsd (BALB) young male and female mice, upon arrival, were housed in groups offour in standard laboratory cages and after 10 days of acclimatization, a red transparentplastic triangular-shaped Mouse House™ was introduced into half of the home cages. Animalswith or without a mouse house were observed in various contexts for more than one month.Body weight gain and food intake, home cage behaviours, emotionality and response tostandard cage changing procedures were evaluated. The presence of a mouse house in thehome cage did not interfere with main developmental and behavioural parameters oremotionality of BALB and B6 male and female mice compared with controls. Both strainshabituated to the mouse house in about a week, but made use of it differently, with BALBmice using the house more than the B6 strain. Our results suggest that mice habituated tothe mouse house rather quickly without disrupting their home cage activities. Scientistscan thus be encouraged to use mouse houses, also in view of the implementation of the EUDirective (2010/63/EU).     

Characterization of the parallel rod floor apparatus to test motor incoordination in mice

Impairment of motor coordination, or ataxia, is a prominent effect of alcohol ingestion in humans. To date, many models have been created to examine this phenomenon in animals. Evidence suggests that the tasks thought to measure this behavior in mice actually measure different components of this complex trait. We have characterized the parallel rod floor apparatus to quantify ethanol-induced motor incoordination. Using genetically heterogeneous mice, we evaluated the influence of rod diameter and inter-rod distance on dose-related ethanol-induced motor incoordination to select parameters that optimized testing procedures. We then used the DBA/2J and C57BL/6J inbred strains of mice to examine the effect of 2 g/kg of ethanol, by serially testing mice on two floor types, separated by 1 week. Finally, we tested eight inbred strains of mice on four floor types to examine patterns of strain sensitivity to 2 g/kg of intraperitoneal ethanol and determined the test parameters that maximized strain effect size. Motor incoordination varied depending on the floor type and strain. When data from strain 129S1/SvlmJ were removed from the analyses because of their extreme behavior, the greatest strain effect size was observed on one floor type during the first 10 min of testing after 2 g/kg of intraperitoneal ethanol. These findings suggest that the parallel rod floor apparatus provides a useful means for examining ethanol-induced motor incoordination in mice but that specific testing procedures are important for optimizing detection of motor incoordination and genetic influences.     

Genetic Mapping of a Possible New Alcohol Dehydrogenase Sequence to Mouse Chromosome 3 at the Adh-1/Adh-3 Complex

Southern blot analysis of mouse genomic DNA reveals two Eco RI fragments which faintly hybridize to mouse Adh-1 cDNA and are not part of the Adh-1 gene. These fragments were isolated from agarose gels, cloned, and characterized. Sequence analysis of the 2.1-kb Eco RI fragment suggests that it is likely a pseudogene since it does not contain a long open reading frame. However, the 2.0-kb Eco RI fragment contains a coding sequence with a long open reading frame which corresponds to exon 6 of the mouse Adh-1 gene. Comparison of the coding sequence with other known ADHs suggests that the sequence has diverged sufficiently from any currently known class of ADH to be a possible distinct class. Further confirmation awaits analysis of currently available genomic clones. Using these sequences as probe, restriction fragment length polymorphisms were identified for each sequence between C57Bl/6J and DBA/2J inbred mouse strains. The strain distribution pattern for these allelic differences was determined among the B × D recombinant inbred strains. This analysis revealed that the 2.1-kb Eco RI sequence is located on chromosome 3 but at a distance from the Adh-1/Adh-3 complex as previously reported. However, the new polymorphism identified in the 2.0-kb Eco RI fragment enabled this sequence to be mapped at the Adh-1/Adh-3 complex.     

Genetic variation in dopamine‐related gene expression influences motor skill learning in mice

Several neurodevelopmental disorders with a strong genetic basis, including attention‐deficit/hyperactivity disorder, autism spectrum disorders and developmental coordination disorder, involve deficits in fine motor skills. This phenotype may depend on heritable variation in components of the dopamine (DA) system, which is known to play a critical role in motor skill learning. In this study, we took advantage of two inbred strains of mice (BALB/c and C57BL/6) that differ markedly in the number of midbrain DA neurons in order to investigate the influence of such naturally occurring genetic variation on the acquisition and performance of fine motor skills. Gene expression analysis of midbrain, frontal cortex and striatum showed significant differences in the expression of presynaptic and postsynaptic dopaminergic (DAergic) markers (e.g. tyrosine hydroxylase, DA transporter, DA D4 receptor, DA D5 receptor and DARPP‐32) between these two strains. BALB/c mice had lower learning rate and performance scores in a complex skilled reaching task when compared with C57BL/6 mice. A negative correlation was found between the motor learning rate and level of DARPP‐32 mRNA expression in the frontal cortex contralateral to the trained forelimb. The rate of motor learning was also negatively correlated with the levels of DARPP‐32 and DA D1 receptor mRNAs in the striatum. Our results suggest that genetically driven variation in frontostriatal DAergic neurotransmission is a major contributor to individual differences in motor skill learning. Moreover, these findings implicate the D1R/cAMP/DARPP‐32 signaling pathway in those neurodevelopmental disorders that are associated with fine motor skill deficits.     

Genetic map of AFLP markers in the rat (Rattus norvegicus) derived from the H x B/Ipcv and B x H/Cub sets of recombinant inbred strains

The amplified fragment length polymorphism (AFLP) technique has been used to enhance marker density in a large set of recombinant inbred strains (H × B and B × H) derived from a spontaneously hypertensive rat (SHR/OlaIpcv) and a Brown-Norway (BN.lx/Cub) inbred strain. Thirteen different primer combinations were tested and a total of 191 polymorphic bands were detected. From these polymorphic bands 89 AFLP markers could be assigned to specific chromosomes. Several of these AFLP markers were mapped to regions with low marker density, thus filling up gaps in the existing genetic map of these recombinant inbred strains. These results substantiate the value of the AFLP technology in increasing marker density in genetic maps.     

Genetic dissection of quantitative trait locus for ethanol sensitivity in long- and short-sleep mice

Interval-specific congenic strains (ISCS) allow fine mapping of a quantitative trait locus (QTL), narrowing its confidence interval by an order of magnitude or more. In earlier work, we mapped four QTL specifying differential ethanol sensitivity, assessed by loss of righting reflex because of ethanol (LORE), in the inbred long-sleep (ILS) and inbred short-sleep (ISS) strains, accounting for approximately 50% of the genetic variance for this trait. Subsequently, we generated reciprocal congenic strains in which each full QTL interval from ILS was bred onto the ISS background and vice versa. An earlier paper reported construction and results of the ISCS on the ISS background; here, we describe this process and report results on the ILS background. We developed multiple ISCS for each Lore QTL in which the QTL interval was broken into a number of smaller intervals. For each of the four QTL regions (chromosomes 1, 2, 11 and 15), we were successful in reducing the intervals significantly. Multiple, positive strains were overlapped to generate a single, reduced interval. Subsequently, this reduced region was overlaid on previous reductions from the ISS background congenics, resulting in substantial reductions in all QTL regions by approximately 75% from the initial mapping study. Genes with sequence or expression polymorphisms in the reduced intervals are potential candidates; evidence for these is presented. Genetic background effects can be important in detection of single QTL; combining this information with the generation of congenics on both backgrounds, as described here, is a powerful approach for fine mapping QTL.     

Control of absence seizures induced by the pathways connected to SRN in corticothalamic system

The cerebral cortex, thalamus and basal ganglia together form an important network in the brain, which is closely related to several nerve diseases, such as parkinson disease, epilepsy seizure and so on. Absence seizure can be characterized by 2–4 Hz oscillatory activity, and it can be induced by abnormal interactions between the cerebral cortex and thalamus. Many experimental results have also shown that basal ganglia are a key neural structure, which closely links the corticothalamic system in the brain. Presently, we use a corticothalamic-basal ganglia model to study which pathways in corticothalamic system can induce absence seizures and how these oscillatory activities can be controlled by projections from the substantia nigra pars reticulata (SNr) to the thalamic reticular nucleus (TRN) or the specific relay nuclei (SRN) of the thalamus. By tuning the projection strength of the pathway “Excitatory pyramidal cortex-SRN”, ”SRN-Excitatory pyramidal cortex” and “SRN–TRN” respectively, different firing states including absence seizures can appear. This indicates that absence seizures can be induced by tuning the connection strength of the considered pathway. In addition, typical absence epilepsy seizure state “spike-and-slow wave discharges” can be controlled by adjusting the activation level of the SNr as the pathways SNr–SRN and SNr–TRN open independently or together. Our results emphasize the importance of basal ganglia in controlling absence seizures in the corticothalamic system, and can provide a potential idea for the clinical treatment.     

Abnormal anxiety-related behavior in serotonin transporter null mutant mice: the influence of genetic background

Serotonin transporter (5-HTT) null mutant mice provide a model system to study the role genetic variation in the 5-HTT plays in the regulation of emotion. Anxiety-like behaviors were assessed in 5-HTT null mutants with the mutation placed on either a B6 congenic or a 129S6 congenic background. Replicating previous findings, B6 congenic 5-HTT null mutants exhibited increased anxiety-like behavior and reduced exploratory locomotion on the light ↔ dark exploration and elevated plus-maze tests. In contrast, 129S6 congenic 5-HTT null mutant mice showed no phenotypic abnormalities on either test. 5-HTT null mutants on the 129S6 background showed reduced 5-HT_1A receptor binding (as measured by quantitative autoradiography) and reduced 5-HT_1A receptor function (as measured by 8-OH-DPAT-indcued hypothermia). These data confirm that the 5-HTT null mutation produced alterations in brain 5-HT function in mice on the 129S6 background, thereby discounting the possibility that the absence of an abnormal anxiety-like phenotype in these mice was due to a suppression of the mutation by 129 modifier genes. Anxiety-like behaviors in the light ↔ dark exploration and elevated plus-maze tests were significantly higher in 129S6 congenic +/+ mice as compared to B6 congenic +/+ mice. This suggests that high baseline anxiety-like behavior in the 129S6 strain might have precluded detection of the anxiety-like effects of the 5-HTT null mutation on this background. Present findings provide further evidence linking genetic variation in the 5-HTT to abnormalities in mood and anxiety. Furthermore, these data highlight the utility of conducting behavioral phenotyping of mutant mice on multiple genetic backgrounds.     

Genetic influences on drug‐induced psychomotor activation in mice

A number of processes are important in the development of substance dependence including initial sensitivity to the acute pharmacological effects of drugs/alcohol. The objectives of the present study were (1) to identify quantitative trait loci (QTLs) associated with the initial sensitivity to the effects of morphine in the A/J, C57BL/6J and AXB/BXA recombinant inbred strains of mice; (2) to identify potential commonalities in the chromosomal regions associated with morphine, cocaine and ethanol sensitivity using multiple‐trait genetic analysis and (3) to determine whether there were interstrain differences in dopamine uptake and transporter binding. Initial sensitivity to morphine was determined by measuring locomotor activity in a computerized open‐field apparatus following acute morphine administration (0, 10, 20 and 40 mg/kg). Significant differences in morphine‐induced activation were observed across the panel of AXB/BXA mice. Genetic analysis found significant QTLs on chromosomes 5, 7, 11, 12, 15 and 17 close to loci previously mapped for cocaine‐related behaviours and to parameters of dopaminergic functioning (uptake and receptor binding). Comparisons of the A/J vs. C57BL/6J progenitors found no strain differences for total dopamine uptake (V_max or K_m) in freshly prepared striatal synaptosomes from naive animals, and no differences in the IC₅₀ for the inhibition of dopamine uptake by cocaine. In addition, there were no differences in dopamine transporter density (B_max or K_d) measured using ³H‐GBR 12935 binding in synaptosomal membranes or via quantitative autoradiography. Multiple‐trait analysis was conducted to examine the genetic interrelationships among morphine‐, cocaine‐ and ethanol‐induced activation in the AXB/BXA. Analysis yielded suggestive QTLs for the joint trait on chromosomes 5, 8, 13 and 15, as well as significant regions on chromosomes 11 (Pmv46, 11 cM, LOD = 7.39) and 12 (D12Mit110, 19 cM, LOD = 4.43) that may be common to all three drugs of abuse.     

Comparison of glucokinase in C3H/He and C58 mice that differ in their hepatic activity

Partially purified preparations of the hepatic glucokinase from C3H/He and C58 inbred mice have been used to explore the molecular basis for the observed twofold difference in activity between the strains. The single codominant gene that appears to regulate activity, the alleles of which are designated Gk^a and Gk^b, respectively, for the two strains, could represent a structural gene change. This now seems unlikely because the mouse enzyme, although showing small differences from rat glucokinase, appeared to be identical in the two strains with respect to thermal stability, electrophoretic mobility in agarose gels, and kinetic properties such as the apparent K _m values for MgATP^2– and glucose and the unique cooperative interaction with the latter substrate. The enzymes also reacted identically in a range of immunological tests (double-diffusion, immunoelectrophoresis, immune precipitation and immune inhibition assays) and ELISA immune inhibition assays indicated that the twofold difference in activity was due to a similar difference in antigenically active enzyme. Genetic control over the physiologically significant regulation of enzyme amount is therefore probable.This work has been supported in part by a grant from the British Diabetic Association and a Training Studentship to PAJ from the Medical Research Council (U.K.).     

Characterization of single nucleotide polymorphisms for a forward genetics approach using genetic crosses in C57BL/6 and BALB/c substrains of mice

Forward genetics is a powerful approach based on chromosomal mapping of phenotypes and has successfully led to the discovery of many mouse mutations in genes responsible for various phenotypes. Although crossing between genetically remote strains can produce F₂ and backcross mice for chromosomal mapping, the phenotypes are often affected by background effects from the partner strains in genetic crosses. Genetic crosses between substrains might be useful in genetic mapping to avoid genetic background effects. In this study, we investigated single nucleotide polymorphisms (SNPs) available for genetic mapping using substrains of C57BL/6 and BALB/c mice. In C57BL/6 mice, 114 SNP markers were developed and assigned to locations on all chromosomes for full utilization for genetic mapping using genetic crosses between the C57BL/6J and C57BL/6N substrains. Moreover, genetic differences were identified in the 114 SNP markers among the seven C57BL/6 substrains from five production breeders. In addition, 106 SNPs were detected on all chromosomes of BALB/cAJcl and BALB/cByJJcl substrains. These SNPs could be used for genotyping in BALB/cJ, BALB/cAJcl, BALB/cAnNCrlCrlj, and BALB/cCrSlc mice, and they are particularly useful for genetic mapping using crosses between BALB/cByJJcl and other BALB/c substrains. The SNPs characterized in this study can be utilized for genetic mapping to identify the causative mutations of the phenotypes induced by N-ethyl-N-nitrosourea mutagenesis and the SNPs responsible for phenotypic differences between the substrains of C57BL/6 and BALB/c mice.     

Quantitative trait loci for electrical seizure threshold mapped in C57BLKS/J and C57BL/10SnJ mice

We mapped the quantitative trait loci (QTL) that contribute to the robust difference in maximal electroshock seizure threshold (MEST) between C57BLKS/J (BKS) and C57BL10S/J (B10S) mice. BKS, B10S, BKS × B10S F1 and BKS × B10S F2 intercross mice were tested for MEST at 8-9 weeks of age. Results of F2 testing showed that, in this cross, MEST is a continuously distributed trait determined by polygenic inheritance. Mice from the extremes of the trait distribution were genotyped using microarray technology. MEST correlated significantly with body weight and sex; however, because of the high correlation between these factors, the QTL mapping was conditioned on sex alone. A sequential series of statistical analyses was used to map QTLs including single-point, multipoint and multilocus methods. Two QTLs reached genome-wide levels of significance based upon an empirically determined permutation threshold: chromosome 6 (LOD = 6.0 at ～69 cM) and chromosome 8 (LOD = 5.7 at ～27 cM). Two additional QTLs were retained in a multilocus regression model: chromosome 3 (LOD = 2.1 at ～68 cM) and chromosome 5 (LOD = 2.7 at ～73 cM). Together the four QTLs explain one third of the total phenotypic variance in the mapping population. Lack of overlap between the major MEST QTLs mapped here in BKS and B10S mice and those mapped previously in C57BL/6J and DBA/2J mice (strains that are closely related to BKS and B10S) suggest that BKS and B10S represent a new polygenic mouse model for investigating susceptibility to seizures.     

Genetic basis for the psychostimulant effects of nicotine: a quantitative trait locus analysis in AcB/BcA recombinant congenic mice

Genetic differences in sensitivity to nicotine have been reported in both animals and humans. The present study utilized a novel methodology to map genes involved in regulating both the psychostimulant and depressant effects of nicotine in the AcB/BcA recombinant congenic strains (RCS) of mice. Locomotor activity was measured in a computerized open-field apparatus following subcutaneous administration of saline (days 1 and 2) or nicotine on day 3. The phenotypic measures obtained from this experimental design included total basal locomotor activity, as well as total nicotine activity, nicotine difference scores, nicotine percent change and nicotine regression residual scores. The results indicated that the C57BL/6J (B6) were insensitive to nicotine over the entire dose-response curve (0.1, 0.2, 0.4 and 0.8 mg/kg). However, the 0.8-mg/kg dose of nicotine produced a significant decrease in the locomotor activity in the A/J strain and a wide and continuous range of both locomotor excitation and depression among the AcB/BcA RCS. Single-locus association analysis in the AcB RCS identified quantitative trait loci (QTL) for the psychostimulant effects of nicotine on chromosomes 11, 12, 13, 14 and 17 and one QTL for nicotine-induced depression on chromosome 11. In the BcA RCS, nicotine-induced locomotor activation was associated with seven putative regions on chromosomes 2, 7, 8, 13, 14, 16 and 17. There were no overlapping QTL and no genetic correlations between saline- and nicotine-related phenotypes in the AcB/BcA RCS. A number of putative candidate genes were in proximity to regions identified with nicotine sensitivity, including the alpha2 subunit of the nicotinic acetylcholine receptor and the dopamine D3 receptor.