Characterization of the quantitative trait locus for haloperidol-induced catalepsy on distal mouse chromosome 1.

We report here the confirmation of the quantitative trait locus for haloperidol-induced catalepsy on distal chromosome (Chr) 1. We determined that this quantitative trait locus was captured in the B6.D2-Mtv7a/Ty congenic mouse strain, whose introgressed genomic interval extends from approximately 169.1 to 191.3 Mb. We then constructed a group of overlapping interval-specific congenic strains to further break up the interval and remapped the locus between 177.5 and 183.4 Mb. We next queried single nucleotide polymorphism (SNP) data sets and identified three genes with nonsynonymous coding SNPs in the quantitative trait locus. We also queried two brain gene expression data sets and found five known genes in this 5.9-Mb interval that are differentially expressed in both whole brain and striatum. Three of the candidate quantitative trait genes were differentially expressed using quantitative real-time polymerase chain reaction analyses. Overall, the current study illustrates how multiple approaches, including congenic fine mapping, SNP analysis and microarray gene expression screens, can be integrated both to reduce the quantitative trait locus interval significantly and to detect promising candidate quantitative trait genes.

New quantitative trait loci for the genetic variance in circadian period of locomotor activity between inbred strains of mice.

Provisional quantitative trait loci (QTL) for circadian locomotor period and wheel-running period have been identified in recombinant inbred (RI) mouse strains. To confirm those QTL and identify new ones, the genetic component of variance of the circadian period was partitioned among an F2 intercross of RI mouse strains (BXD19 and CXB07). First, a genomic survey using 108 SSLP markers with an average spacing of 15 cM was carried out in a population of 259 (BXD19 x CXB07)F2 animals. The genome-wide survey identified two significant QTL for period of locomotor activity measured by infrared photobeam crossings on mouse chromosomes 1 (lod score 5.66) and 14 (lod score 4.33). The QTL on distal chromosome 1 confirmed a previous report based on congenic B6.D2-Mtv7a/Ty mice. Lod scores greater than 2.0 were found on chromosomes 1, 2, 6, 12, 13, and 14. In a targeted extension study, additional genotyping was performed on these chromosomes in the full sample of 341 F2 progeny. The 6 chromosome-wide surveys identified 3 additional QTL on mouse chromosomes 6, 12, and 13. The QTL on chromosome 12 overlaps with circadian period QTL identified in several prior studies. For wheel-running period, the chromosome-wide surveys identified QTL on chromosomes 2 and 13 and one highly suggestive QTL on proximal chromosome 1. The results are compared to other published studies of QTL of circadian period.

A QTL for the genetic variance in free-running period and level of locomotor activity between inbred strains of mice.

Many genes support the manifestation of the circadian period in mice. In a multiple-gene trait all genes contributing in a minor way to this characteristic are quantitative trait loci (QTL). Screens of both the BXD and the CXB panels of recombinant inbred mice suggested that distal chromosome 1, between 90 and 100 cM, contained a QTL, Cplaq3, for a difference in the circadian period of locomotor activity between the C57BL/6J and the DBA/2J and between the BALB/cBy and the C57BL/6By progenitor strains. The mice studied were a commercially available congenic strain, B6.D2-Mtv7a/Ty, from 50 to 100 days old. This congenic strain contains a small DBA/2J genomic insert that covers the region of the provisional QTL in a 99.9% C57BL/6J background. The congenic mice had a shorter period than C57BL/6J mice, confirming that this region has a QTL for the difference in period between the C57BL/6J and the DBA/2J strains. In addition, these data suggest that this region has a QTL for the mean amount of daily activity and for the pattern of locomotor activity.

Provisional QTL for circadian period of wheel running in laboratory mice: quantitative genetics of period in RI mice.

Wheel running was monitored in B x D recombinant inbred (RI) mice under dark-dark (DD) conditions, and the mean circadian period was calculated for each strain. There were significant differences for this trait among B x D recombinant inbred strains (p < .0001) and a narrow-sense heritability of 21%. Analysis of strain means and variances indicates that at least four segregating loci contribute to the genetic variance for the free-running circadian period in this population. Correlation of the strain means for the circadian period of wheel running for each RI strain against the distribution of markers at over 1500 loci along the mouse genome identified a number of provisional quantitative trait loci (QTL). There were provisional QTL for wheel running at p < .001 on chromosome 11 and at p < .01 on chromosomes 1, 6, 9, 17, and 19. Most were in agreement with a second analysis done under similar conditions.

Provisional quantitative trait loci (QTL) for the Aschoff effect in RI mice.

Mice of the CXB recombinant inbred (RI) panel were phenotyped for period of locomotor activity in continuous dark (tau) and in continuous 10-lux light (tauLL). There were significant differences in the effect of light on period, delta tau (tauLL-tau), among CXB RI strains and their progenitors. By comparing strain means for delta tau in the CXB RI strains with typed genetic loci using a product moment correlation, it was possible to hypothesize quantitative trait loci (QTL) important to the genetic variance in the effect of constant low-level light on circadian period. Some of the candidate genes linked to statistically associated markers are neuropharmacologically interesting. Provisional QTL for delta tau were found on proximal Chromosome 8 and mid Chromosome 11 in regions near QTL identified in a similar analysis of the BXD RI panel. This provides additional evidence for the importance of loci on Chromosomes 8 and 11.

Aging lengthens TauDD in C57BL/6J, DBA/2J, and outbred SWR male mice (Mus musculus).

The effect of aging on the free-running period (TauDD) of a circadian rhythm for wheel-running activity was observed in two inbred strains (DBA/ 2J and C57BL/6J) and one outbred strain (Tac: (SW)fBR) of laboratory mice (Mus musculus). TauDD in the DBA and C57 mice was monitored at approximately age 100 days and age 300 days. TauDD in the outbred strain was monitored at approximately age 100 days and age 600 days. TauDD increased with age in all three strains. Most studies of age effects in rodent species have shown a shortening of TauDD with age, with th exception of the C57BL inbred mice. These results show that the lengthening of TauDD with age in laboratory mice is not limited to the C57BL strain and may be a general characteristic of this species, in contrast to other rodent species examined.

Genomic DNA from mice: a comparison of recovery methods and tissue sources.

Our aim is to identify an extraction method and the source of mouse tissue(s) that could allow a high-resolution genomic scan from a living mouse. We compared and optimized two methods for yield, purity of DNA, and their use in the polymerase chain reaction (PCR) of DNA extracted from different mouse tissues. In addition to whole blood, tissue samples from the brain, liver, testis, and tail were included in this study. The Rapid Method (RM) is preferable for the whole blood samples and testis and brain tissue samples because it is quicker, less toxic, and more cost-effective than the proteinase K method (PM). For liver the PM produced higher yields of DNA with less degradation than the RM. For tail tip, the PM produced a higher yield of DNA, but the RM resulted in a higher yield of PCR product. From a living mouse, a tail snip generated a sufficient amount of DNA for several hundred PCRs but not a complete genomic scan. We suggest that the RM can be used to extract genomic DNA for a complete genomic scan which requires either testicular tissues or repeated blood samples from the suborbital sinus over several months without sacrificing the animal.

Hypothetical quantitative trait loci (QTL) for circadian period of locomotor activity in CXB recombinant inbred strains of mice.

The locomotor activity of male mice (Mus musculus) of 13 CXB (BALB/cBy x C57BL/6J) recombinant inbred (RI) strains and their progenitor strains was monitored for 4 to 6 weeks by infrared photoelectric beams under constant dark. The circadian period (tau) of locomotor activity was calculated and used in quantitative trait locus (QTL) analysis of strains' means. Results were compared with potential QTL found in a previous study of the BXD RI series. The mean tau of 13 CXB RI mouse strains (three to six animals per strain) in constant dark had a unimodal distribution suggesting polygenic inheritance. A number of potential QTL were found for this trait. There were two associations at p < .001. H23 on chromosome 3 and Pmv16 on chromosome 16. A region of chromosome 1 was associated with tau in both CXB and BXD RI series. There was also a conjunction with a locus determined from QTL analysis of the previously reported tau of wheel running activity in seven CXB RI strains (Schwartz and Zimmerman, 1990).

Quantitative trait loci (QTL) for circadian rhythms of locomotor activity in mice.

The locomotor activity of male mice (Mus musculus) was monitored by infrared photo-electric beams under three lighting regimens: LD (12 h of light and 12 h of dark), DD (constant dark), and LL (constant broad-spectrum light, 10 lux). Circadian period of locomotor activity (tau) was compared among 3 inbred strains of mice, C57BL/6J (B6), BALB/c (C), and DBA/2J (D2), and 26 recombinant inbred strains B x D (B6 x D2). The tau under both continuous low-intensity light and continuous darkness varied significantly among strains. Under DD the mean tau was 23.8 h for B6, 23.7 h for D2, and 23.6 h for C. Under LL the mean tau was 25.1 h for B6, 23.9 h for D2, and 25.5 h for C. Frequency histograms of the mean tau of 26 B x D RI mouse strains (three to seven animals per strain) in either DD or LL and the difference between them, delta tau, had distributions which appeared unimodal, suggesting polygenic inheritances. The narrow-sense heritability determined using 26 strains of B x D RI mice was about 55% for tau and about 38% for both tau in LL and delta tau. An estimated four loci contribute to the variance of tau in constant darkness and five to the variance of tau in constant low-intensity light among the strains studied. Quantitative trait locus (QTL) analysis identified several potential genetic loci associated with tau in constant darkness, tau in constant low-intensity light, and delta tau. The associations of highest probability for each of these traits were the D1Nds4 locus (p < .001) on mouse chromosome 1, the D5Ncvs52 locus (p < .05) on mouse chromosome 5, and the Pmv12 locus (p < .01) at 70 cM on mouse chromosome 5, respectively. A QTL identified for tau was associated (p < .05) with the D2NDS1 marker at 45 cM on chromosome 2 near the Ea 6 marker at 46 cM associated (p < .05) with that reported for the period of wheel running activity in seven C x B RI strains (Schwartz, W.J., and Zimmerman, P., J. Neurosci. 10:3685 1990).

Activity-wheel stress and serotonergic hypersensitivity in rats.

Adult male Wistar rats were subjected to activity wheel stress: unlimited access to an activity wheel for up to twelve days and food for 30 to 60 min each day. Each treated rat was paired with a control, the latter being housed in home cages and given sufficient food to maintain a weight similar to the stressed partner. All rats were previously trained on a variable interval schedule for milk reinforcement. When the activity of the stressed rat increased rapidly then decreased suddenly, the pair was decapitated for biochemical analysis. Levels of the serotonin metabolite, 5-hydroxyindoleacetic acid, decreased by 50%, and the Bmax for ketanserin binding increased by 19% in frontal cortical homogenates from the stressed rats when compared to controls. These data support the concept that stress increases the sensitivity of central serotonin receptors.