The influence of human activity patterns on personal PM exposure: a comparative analysis of filter-based and continuous particle measurements

Particulate matter (PM) exposure data from the U.S. Environmental Protection Agency (EPA)-sponsored 1998 Baltimore and 1999 Fresno PM exposure studies were analyzed to identify important microenvironments and activities that may lead to increased particle exposure for select elderly (>65 years old) subjects. Integrated 24-hr filter-based PM2.5 or PM10 mass measurements [using Personal Environmental Monitors (PEMs)] included personal measurements, indoor and outdoor residential measurements, and measurements at a central indoor site and a community monitoring site. A subset of the participants in each study wore passive nephelometers that continuously measured (1-min averaging time) particles ranging in size from 0.1 to approximately 10 microm. Significant activities and locations were identified by a statistical mixed model (p < 0.01) for each study population based on the measured PM2.5 or PM10 mass and time activity data. Elevated PM concentrations were associated with traveling (car or bus), commercial locations (store, office, mall, etc.), restaurants, and working. The modeled results were compared to continuous PM concentrations determined by the nephelometers while participants were in these locations. Overall, the nephelometer data agreed within 6% of the modeled PM2.5 results for the Baltimore participants and within approximately 20% for the Fresno participants (variability was due to zero drift associated with the nephelometer). The nephelometer did not agree as well with the PM10 mass measurements, most likely because the nephelometer optimally responds to fine particles (0.3-2 microm). Approximately one-half (54 +/- 31%; mean +/- standard deviation from both studies) of the average daily PM2.5 exposure occurred inside residences, where the participants spent an average of 83 +/- 10% of their time. These data also showed that a significant portion of PM2.5 exposure occurred in locations where participants spent only 4-13% of their time.

Genetic control of the mouse cerebellum: identification of quantitative trait loci modulating size and architecture

To discover genes influencing cerebellum development, we conducted a complex trait analysis of variation in the size of the adult mouse cerebellum. We analyzed two sets of recombinant inbred BXD strains and an F2 intercross of the common inbred strains, C57BL/6J and DBA/2J. We measured cerebellar size as the weight or volume of fixed or histologically processed tissue. Among BXD recombinant inbred strains, the cerebellum averages 52 mg (12.4% of the brain) and ranges 18 mg in size. In F2 mice, the cerebellum averages 62 mg (12.9% of the brain) and ranges approximately 20 mg in size. Five quantitative trait loci (QTLs) that significantly control variation in cerebellar size were mapped to chromosomes 1 (Cbs1a), 8 (Cbs8a), 14 (Cbs14a), and 19 (Cbs19a, Cbs19b). In combination, these QTLs can shift cerebellar size an appreciable 35% of the observed range. To assess regional genetic control of the cerebellum, we also measured the volume of the cell-rich, internal granule layer (IGL) in a set of BXD strains. The IGL ranges from 34 to 43% of total cerebellar volume. The QTL Cbs8a is significantly linked to variation in IGL volume and is suggestively linked to variation in the number of cerebellar folia. The QTLs we have discovered are among the first loci shown to modulate the size and architecture of the adult mouse cerebellum.

Identification of quantitative trait loci controlling activation of TRBV4 CD8+ T cells during murine gamma-herpesvirus-induced infectious mononucleosis

The murine gamma-herpesvirus, MHV-68, shares important biological and genetic features with the human gamma-herpesvirus, Epstein-Barr virus. Following intranasal infection, mice develop an infectious mononucleosis-like syndrome accompanied by increased numbers of activated CD8+ T cells in the blood. A consistent feature of the CD8+ T-cell activation is a marked increase in the frequency of cells expressing a TRBV4+ T-cell receptor. Previous studies suggested that the magnitude of TRBV4 expansion varied significantly among mouse strains, and was influenced by both MHC and non-MHC genes. Detailed analysis of strains with high (C57BL/6) or low (DBA/2) TRBV4 CD8+ T-cell expansion showed that differences in the degree of expansion were not a consequence of variation in genetic susceptibility to the viral infection. Rather, the magnitude of the TRBV4 CD8+ T-cell expansion correlated with differences in expression of the unidentified stimulatory ligand on activated, latently infected B cells. In the present study, analysis of TRBV4 expansion in C57BL/6, DBA/2, B6D2 F1 mice, BXD recombinant inbred strains, and the progeny of C57BL/6xDBA/2 F1 hybrids backcrossed to C57BL/6 demonstrated strong cumulative dominance of the low DBA/2 trait and moderately high heritability (h2 approximately 0.5). Two quantitative trait loci (QTLs) strongly associated with variance in TRBV4 expansion were identified using simple and composite mapping procedures. The first QTL is located on Chromosome (Chr) 17, near or proximal to H2. The second QTL is located on Chr 6 in a region spanning the Tcrb and Cd8a loci.

Genetic dissection of age-related changes of immune function in mice

Understanding of the genetic basis of normal and abnormal development of the immune response is an enormous undertaking. The immune response, at the most minimal level, involves interactions of antigen presenting cells (APCs), T and B cells. Each of these cells produce cell surface and soluble factors (cytokines) that affect both autocrine and paracrine functions. A second level of complexity needs to consider the development of the macrophage/monocyte lineage as well as the production of the common lymphoid precursor which undergoes distinct maturation steps in the thymus and periphery to form mature T cells as well as in BM (BM) and lymphoid organs to form mature B cells. A third level of complexity involves the immune response to infectious agents including viruses and also the response to tumour antigens. In addition, there are imbalances that predispose to decreased responses (immunodeficiencies) or increased responses (autoimmunity). A fourth level of complexity involves attempts to understand the differences in the immune response that occurs at a very young age, in adults, and at a very old age. This review will focus on the use of C57BL/6 J X DBA/2 J (BXD) recombinant inbred (RI) strains of mice to map genetic loci associated with the production of lymphoid precursors in the BM, development of T cells in the thymus, and T-cell responses to stimulation in the peripheral lymphoid organs in adult and in aged mice. Strategies to improve the power and precision in which complex traits such as the age-related immune response can be mapped is limited with the current set of 35 strains of BXD mice. Strategies to increase these strains by generating recombinant intercross (RIX) strains of mice are being developed to enable this large set of lines to detect quantitative trait loci (QTLs) with a much higher consistency and statistical power. More importantly, the resolution with which these QTLs can be mapped would be greatly improved and, in many cases, adequate to carry out direct identification of candidate genes. It is likely that, given the complexity of the immune system development, the number of cells involved in an immune response, and especially the changes in the immune system with ageing, mapping hundreds of genes will be required to fully understand age-related changes in the immune response. This review outlines ongoing and future strategies that will enable the mapping and identification of these genes.

Complex trait analysis of the hippocampus: mapping and biometric analysis of two novel gene loci with specific effects on hippocampal structure in mice

Notable differences in hippocampal structure are associated with intriguing differences in development and behavioral capabilities. We explored genetic and environmental factors that modulate hippocampal size, structure, and cell number using sets of C57BL/6J (B6) and DBA/2J (D2) mice; their F1 and F2 intercrosses (n = 180); and 35 lines of BXD recombinant inbred (RI) strains. Hippocampal weights of the parental strains differ by 20%. Estimates of granule cell number also differ by approximately 20%. Hippocampal weights of RI strains range from 21 to 31 mg, and those of individual F2 mice range from 23 to 36 mg (bilateral weights). Volume and granule cell number are well correlated (r = 0.7-0.8). Significant variation is associated with differences in age and sex. The hippocampus increases in weight by 0.24 mg per month, and those of males are 0.55 mg heavier (bilateral) than those of females. Heritability of variation is approximately 50%, and half of this genetic variation is generated by two quantitative trait loci that map to chromosome 1 (Hipp1a: genome-wide p < 0.005, between 65 and 100 cM) and to chromosome 5 (Hipp5a, p < 0.05, between 15 and 40 cM). These are among the first gene loci known to produce normal variation in forebrain structure. Hipp1a and Hipp5a individually modulate hippocampal weight by 1.0-2.0 mg, an effect size greater than that generated by age or sex. The Hipp gene loci modulate neuron number in the dentate gyrus, collectively shifting the population up or down by as much as 200,000 cells. Candidate genes for the Hipp loci include Rxrg and Fgfr3.

Scaled quantum mechanical force field for alanyl-alanine peptide in solution

We have obtained ab initio scale factors and assigned frequencies for the alanine-alanine peptide in water. Calculations were performed on the isolated acidic and basic Ala-Ala structures, two one-water basic Ala-Ala supermolecules, and one two-water acidic and one two-water basic Ala-Ala supermolecules. Force constants were scaled using the experimentally determined Raman and Fourier transform infrared vibrational frequencies of four isotopic species of Ala-Ala in water at pH 13 and pH 1. Most of the 4-31G scale factors were transferable from smaller molecules. All but one scale factor were directly transferable between the pH 1 and pH 13 species for coordinates unchanged by protonation in both the isolated and two-water supermolecule structures. Scale factors for nonpolar coordinates were transferable between all Ala-Ala species with only a few small changes. Good agreement was obtained between the calculated and experimental frequencies for all isotopic species and structures.

Covalently bound ionene polyelectrolyte-silica gel stationary phases for HPLC

Micelle-mimetic ionene-based stationary phases for high-performance liquid chromatography (HPLC) are prepared by attaching [3,16]- and [3,22]-ionenes to aminopropyl silica through a carbon-nitrogen bond. These [x,y]-ionenes are polyelectrolytic molecules consisting of dimethylammonium charge centers interconnected by alternating alkyl chain segments containing x and y methylene groups, some of which can form aggregate species whose properties mimic those of conventional surfactant micelles. These ionene-bonded stationary phases were characterized using different recommended HPLC test mixtures. Test solute chromatographic behavior on the ionene phases was found to be similar to that of intermediate oligomeric or polymeric C-18 and/or phenyl phases, depending upon the specific test mixture employed. In addition, the phases exhibit significant solute shape recognition ability. The ionene stationary phases were successfully employed for the separation of the components of the recommended ASTM reversed-phase test mixture, as well as for ortho-, meta- and para-disubstituted benzenes and other positional or geometric isomeric compounds. The ionene materials allow for chromatographic separations under either reversed-phase or ion-exchange conditions. The retention mechanism on these multimodal phases can occur by hydrophobic partitioning or electrostatic interactions, depending upon the characteristics of the components of the analyte mixture (neutral or anionic). The effects of alteration of the percent organic modifier, flow rate and temperature of the mobile phase on chromatographic retention and efficiency on these phases were briefly examined.

Anxiety-related behaviors in the elevated zero-maze are affected by genetic factors and retinal degeneration

Anxiety levels were tested in an elevated zero-maze for 8 inbred strains of mice that are used widely in biomedical and behavioral research. Strain differences were observed for activity, latency to enter an open quadrant, open time, and defecation, demonstrating that genetic factors mediate anxiety in this paradigm. Three of the strains have the rdl mutation that causes retinal degeneration and were less anxious in the maze. To discern whether visual acuity is a source of difference on the maze, anxiety levels were tested in a congenic strain in which the rdl allele has been replaced with the wild-type allele. The congenic strain, with normal vision, had higher levels of anxiety. This study provides baseline data for the selection and use of any of these strains in pharmacological challenges in the maze, and provides a starting point for the identification of strains that may have appropriate backgrounds for targeted mutation studies.

The relationships between personal PM exposures for elderly populations and indoor and outdoor concentrations for three retirement center scenarios

Personal exposures, indoor and outdoor concentrations, and questionnaire data were collected in three retirement center settings, supporting broader particulate matter (PM)--health studies of elderly populations. The studies varied geographically and temporally, with populations studied in Baltimore, MD in the summer of 1998, and Fresno, CA in the winter and spring of 1999. The sequential nature of the studies and the relatively rapid review of the mass concentration data after each segment provided the opportunity to modify the experimental designs, including the information collected from activity diary and baseline questionnaires and influencing factors (e.g., heating, ventilation, and air-conditioning (HVAC) system operation, door and window openings, air exchange rate) measurements. This paper highlights both PM2.5 and PM10 personal exposure data and interrelationships across the three retirement center settings, and identifies the most probable influencing factors. The current limited availability of questionnaire results, and chemical speciation data beyond mass concentration for these studies, provided only limited capability to estimate personal exposures from models and apportion the personal exposure collections to their sources. The mean personal PM2.5 exposures for the elderly in three retirement centers were found to be consistently higher than the paired apartment concentrations by 50% to 68%, even though different facility types and geographic locations were represented. Mean personal-to-outdoor ratios were found to 0.70, 0.82, and 1.10, and appeared to be influenced by the time doors and windows were open and aggressive particle removal by the HVAC systems. Essentially identical computed mean PM2.5 personal clouds of 3 micrograms/m3 were determined for two of the studies. The proposed significant contributing factors to these personal clouds were resuspended particles from carpeting, collection of body dander and clothing fibers, personal proximity to open doors and windows, and elevated PM levels in nonapartment indoor microenvironments.

Genetic dissection of the olfactory bulbs of mice: QTLs on four chromosomes modulate bulb size

Olfaction is influenced by a complex mix of environmental and genetic factors that modulate the production, migration, and maturation of cells in the olfactory bulbs. In this study we analyzed effects of sex, age, body weight, and brain weight on olfactory bulb size in sexually mature mice. We then used regression corrected values (residuals) to map quantitative trait loci (QTLs) that selectively modulate bulb weight. This biometric analysis has relied on an F2 intercross between C57BL/6J (B6) and DBA/2J (D2) inbred strains and a large sample of 35 BXD recombinant inbred (RI) strains. Bilateral bulb weight in adult mice ranges from 10 to 30 mg. Half of this remarkable variation can be predicted from differences in brain weight, sex, body weight, and age. A 100-mg difference in brain weight is associated with a 4.4-mg difference in bulb weight. Bulbs gain in weight by 0.2 mg/week--a 1% increase that continues until at least 300 days of age. Males tend to have slightly larger bulbs than females. By combining data from both related crosses (F2 and RI) we identified four QTLs with selective effects on bulb size (genomewide p < .05). Bulb4a is located on chromosome 4 (Chr 4) and Bulb6a is located on Chr 6. Alleles inherited from B6 at both of these loci increase bulb weight by 0.5-1.0 mg. Bulb11a is located on proximal Chr 11 and Bulb17a is located on the proximal part of Chr 17. In contrast to the first two QTLs, B6 alleles at these two loci decrease bulb weight by 0.5-1.0 mg. Collectively, the four loci account for 20% of the phenotypic variance in bulb weight.

The genetic structure of recombinant inbred mice: high-resolution consensus maps for complex trait analysis

BACKGROUND

Recombinant inbred (RI) strains of mice are an important resource used to map and analyze complex traits. They have proved particularly effective in multidisciplinary genetic studies. Widespread use of RI strains has been hampered by their modest numbers and by the difficulty of combining results derived from different RI sets.

RESULTS

We have increased the density of typed microsatellite markers two- to five-fold in each of several major RI sets that share C57BL/6 as a parental strain (AXB, BXA, BXD, BXH and CXB). A common set of 490 markers was genotyped in just over 100 RI strains. Genotypes of around 1,100 additional microsatellites in one or more RI sets were generated, collected and checked for errors. Consensus RI maps that integrate genotypes of approximately 1,600 microsatellite loci were assembled. The genomes of individual strains typically incorporate 45-55 recombination breakpoints. The collected RI set - termed the BXN set - contains approximately 5,000 breakpoints. The distribution of recombinations approximates a Poisson distribution and distances between breakpoints average about 0.5 centimorgans (cM). Locations of most breakpoints have been defined with a precision of < 2 cM. Genotypes deviate from Hardy-Weinberg equilibrium in only a small number of intervals.

CONCLUSIONS

Consensus maps derived from RI strains conform almost exactly to theoretical expectation and are close to the length predicted by the Haldane-Waddington equation (x3.6 for a 2-3 cM interval between markers). Non-syntenic associations between different chromosomes introduce predictable distortions in quantitative trait locus (QTL) datasets that can be partly corrected using two-locus correlation matrices.

QTL analysis and genomewide mutagenesis in mice: complementary genetic approaches to the dissection of complex traits

Quantitative genetics and quantitative trait locus (QTL) mapping have undergone a revolution in the last decade. Progress in the next decade promises to be at least as rapid, and strategies for fine-mapping QTLs and identifying underlying genes will be radically revised. In this Commentary we address several key issues: first, we revisit a perennial challenge--how to identify individual genes and allelic variants underlying QTLs. We compare current practice and procedures in QTL analysis with novel methods and resources that are just now being introduced. We argue that there is no one standard of proof for showing QTL = gene; rather, evidence from several sources must be carefully assembled until there is only one reasonable conclusion. Second, we compare QTL analysis with whole-genome mutagenesis in mice and point out some of the strengths and weakness of both of these phenotype-driven methods. Finally, we explore the advantages and disadvantages of naturally occurring vs mutagen-induced polymorphisms. We argue that these two complementary genetic methods have much to offer in efforts to highlight genes and pathways most likely to influence the susceptibility and progression of common diseases in human populations.

The 1999 Fresno particulate matter exposure studies: comparison of community, outdoor, and residential PM mass measurements

Two collaborative studies have been conducted by the U.S. Environmental Protection Agency (EPA) National Exposure Research Laboratory (NERL) and National Health and Environmental Effects Research Laboratory to determine personal exposures and physiological responses to particulate matter (PM) of elderly persons living in a retirement facility in Fresno, CA. Measurements of PM and other criteria air pollutants were made inside selected individual residences within the retirement facility and at a central outdoor site on the premises. In addition, personal PM exposure monitoring was conducted for a subset of the participants, and ambient PM monitoring data were available for comparison from the NERL PM research monitoring platform in central Fresno. Both a winter (February 1-28, 1999) and a spring (April 19-May 16, 1999) study were completed so that seasonal effects could be evaluated. During the spring study, a more robust personal exposure component was added, as well as a more detailed evaluation of physical factors, such as air-exchange rate, that are known to influence the penetration of particles into the indoor environment. In this paper, comparisons are made among measured personal PM exposures and PM mass concentrations measured at the NERL Fresno Platform site, outside on the premises of the retirement facility, and inside selected residential apartments at the facility during the two 28-day study periods. The arithmetic daily mean personal PM2.5 exposure during the winter study period was 13.3 micrograms/m3, compared with 9.7, 20.5, and 21.7 micrograms/m3 for daily mean overall apartment, outdoor, and ambient (i.e., platform) concentrations, respectively. The daily mean personal PM2.5 exposure during the spring study period was 11.1 micrograms/m3, compared with 8.0, 10.1, and 8.6 micrograms/m3 for the daily mean apartment, outdoor, and ambient concentrations, respectively.

Use of a continuous nephelometer to measure personal exposure to particles during the U.S. Environmental Protection Agency Baltimore and Fresno Panel studies

In population exposure studies, personal exposure to PM is typically measured as a 12- to 24-hr integrated mass concentration. To better understand short-term variation in personal PM exposure, continuous (1-min averaging time) nephelometers were worn by 15 participants as part of two U.S. Environmental Protection Agency (EPA) longitudinal PM exposure studies conducted in Baltimore County, MD, and Fresno, CA. Participants also wore inertial impactor samplers (24-hr integrated filter samples) and recorded their daily activities in 15-min intervals. In Baltimore, the nephelometers correlated well (R2 = 0.66) with the PM2.5 impactors. Time-series plots of personal nephelometer data showed each participant's PM exposure to consist of a series of peaks of relatively short duration. Activities corresponding to a significant instrument response included cooking, outdoor activities, transportation, laundry, cleaning, shopping, gardening, moving between microenvironments, and removing/putting on the instrument. On average, 63-66% of the daily PM exposure occurred indoors at home (about 2/3 of which occurred during waking hours), primarily due to the large amount of time spent in that location (an average of 72-77%). Although not a reference method for measuring mass concentration, the nephelometer did help identify PM sources and the relative contribution of those sources to an individual's personal exposure.

Structure of the cone photoreceptor mosaic in the retinal periphery of adult humans: analysis as a function of age, sex, and hemifield

We have analyzed variation in the structure of the human photoreceptor mosaic as a function of age, sex, and retinal location using the nearest neighbor and density recovery profile methods. In contrast to most previous work, we have focused our analysis on the mid- and far-peripheral human retina. Video-enhanced differential interference contrast optics was used to characterize differences in the nasal and temporal periphery of unstained wholemounts from 12 males and 12 females ranging in age from 15- to 83-years-old. At sites matched for cone density (approximately 5,000 cones/mm2), the mosaic is far more orderly in the temporal than in the nasal periphery. This is true at all ages and in both sexes. Despite their increased local order, regularity ratios of adjacent temporal fields tend to be much more variable than are those of adjacent nasal fields. These marked nasal-temporal differences are eliminated when eccentricity is held constant and cone density is allowed to vary. There is a mild, statistically significant age-related decline in the regularity of the cone mosaic, but only in the nasal periphery. There are no significant differences in the precision of the cone mosaic between sexes. The equivalence of the regularity of the mosaic at matched eccentricities, but not at matched cone densities, suggests that the irregularity of the mosaic is secondary to developmental gradients and, more generally, to reduced selection for high acuity vision in the retinal periphery.

Multiple modes of cell division control in Arabidopsis flower development

Control of the pattern of cell divisions is central to plant development. Several different types of control exist: examples include control of overall cell number in floral meristems, control of relative cell numbers in floral whorls, and control of the relative spacing of the cell divisions that establish floral organs. Mutations that change each of these levels of control are described: mutations in the SUPERMAN gene affect relative amounts of cell division in adjacent floral whorls; mutations in the CLAVATA genes affect overall meristematic cell number; and mutations in PERIANTHIA affect the spacing of floral organs.

Extrinsic modulation of retinal ganglion cell projections: analysis of the albino mutation in pigmentation mosaic mice

Tyrosinase is a key enzyme involved in the synthesis of melanin in the retinal pigment epithelium (RPE). Mice that are homozygous for the albino allele at the tyrosinase locus have fewer retinal ganglion cells with uncrossed projections at the optic chiasm. To determine the site of the albino gene action we studied the projections of retinal ganglion cells in two types of pigmentation mosaic mice. First, we generated mosaic mice that contain a translocated allele of the wild-type tyrosinase on one X chromosome but that also have the lacZ reporter transgene on the opposite X chromosome. In these lacZ/tyrosinase mice, which are homozygous for the albino allele on chromosome 7, X-inactivation ensures that tyrosinase cannot be functional within 50% of the retinal ganglion cells and that these individual cells can be identified by their expression of the lacZ reporter gene product, beta-galactosidase. The proportion of uncrossed retinal ganglion cells expressing beta-galactosidase was found to be identical to the proportion that did not express it, indicating that the albino mutation associated with axonal behavior at the optic chiasm must affect ganglion cells in a cell-extrinsic manner. Second, to determine whether the RPE is the source of the extrinsic signal, we generated aggregation chimeras between pigmented and albino mice. In these mosaic mice, the extent of the uncrossed projection corresponded with the amount of pigmented cells within the RPE, but did not correspond with the genotypes of neural retinal cells. These studies demonstrate that the albino mutation acts indirectly upon retinal ganglion cells, which in turn respond by making axonal guidance errors at the optic chiasm.

Asymmetric connections, duplicate layers, and a vertically inverted map in the primary visual system

The achiasmatic mutation is a remarkable and rare visual system mutation carried in a line of black sheepdogs. In affected animals, the optic chiasm is missing, and each retina projects entirely to the ipsilateral hemisphere. As a result of this navigational error, maps of visual space in the lateral geniculate nucleus (LGN) have a unique structure with mirror reversals of field position across the A-A1 border. Animals also have a persistent and severe congenital nystagmus. In this report we analyze a novel variant of the achiasmatic mutation, one in which retinal axons from only one eye successfully cross midline and in which the great majority of fibers from both eyes terminate in a single lateral geniculate nucleus. The dominant optic tract contains four times as many axons as the other tract. The hyperinnervated LGN has a lamination pattern consisting of duplicate and partly interwoven layers. A multiunit mapping study of visual cortex (primarily area 17 along the marginal gyrus) shows that receptive field topography and orientation selectivity are normal. The size of central binocular visual space is nearly normal and is flanked by monocular domains in the periphery. However, there is an inexplicable vertical inversion in the orientation of the cortical representation: superior fields are located rostrally, and inferior fields are located caudally. Despite a host of drastic abnormalities at all level of the visual system, from retina to cortex, this animal was behaviorally indistinguishable from normal dogs and did not have any detectable oculomotor abnormalities.

A quantitative genetic analysis of slow-wave sleep in influenza-infected CXB recombinant inbred mice

Influenza-infected C57BL/6J mice spend increased amounts of time in slow-wave sleep (SWS) during the dark phase of the circadian cycle compared to healthy mice. In contrast, infected BALB/cByJ mice show a normal or reduced time in SWS, particularly during the light phase. To identify genetic loci with linkage to these traits, we measured sleep in 13 CXB recombinant inbred (RI) strains derived from a cross between C57BL/6ByJ and BALB/cByJ mice. The probability density distribution of sleep patterns of influenza-infected CXB RI mice showed modes that correspond roughly with the parental modes during the dark phase of the circadian cycle and are intermediate or C57BL/6-like during the light phase. These patterns are consistent with the presence of a low number of major effect quantitative trait loci (QTLs). Chromosomal regions with provisional association to strain variation in influenza-induced SWS patterns were identified. In particular, a 10- to 12-cM interval on Chr 6 between D6Mit74 and D6Mit188 contains a QTL (LRS = 16.6 at 1 cM proximal to D6Mit316; genomewide p < .05) that influences the SWS response to influenza infection during the light phase. We have provisionally named this QTL Srilp1 (sleep response to influenza, light phase 1). Candidate genes for mediation of this phenotype include Ghrhr (growth hormone releasing hormone receptor), Crhr2 (corticotropin releasing hormone receptor 2), and Cd8a (an epitope on cytotoxic T lymphocytes). Several other intervals achieved suggestive probability scores that are sufficient to warrant further analysis either with additional RI strains or with F2 panels. The analysis also suggests that dark phase and light phase responses are regulated by different genetic factors.

A quantitative genetic analysis of locomotor activity in CXB recombinant inbred mice

Recent studies have identified genes that influence the length of the circadian period maintained by mice housed under constant lighting conditions. However, a less studied circadian activity variable is the amplitude of daily oscillations in locomotor activity. This parameter reflects spontaneous activity exhibited under standard lighting and housing conditions and, therefore, differs conceptually from assessments of exploratory or open-field activity, voluntary wheel-running, or circadian period during exposure to constant light or constant darkness conditions. We recently observed a greater daily amplitude of oscillation in spontaneous locomotor activity in C57BL/6 mice compared to BALB/cBy mice. To identify genetic loci with potential linkage to circadian variation in the amount of locomotor activity, we measured the spontaneous activity of 13 CXB recombinant inbred (RI) strains of mice. The probability density distributions of locomotor activity phenotypes for the 13 CXB RI strains were consistent with the presence of a low number of major quantitative trait loci affecting this trait. Regions of chromosomes 3, 8, 12, 13, and 19 showed provisional linkage to strain variation in locomotor activity. Probabilities of linkage were not sufficient for declaration of an activity-related quantitative trait locus but were sufficient to warrant further analysis either with additional RI strains or with F2 panels.

A quantitative genetic analysis of slow-wave sleep and rapid-eye movement sleep in CXB recombinant inbred mice

Various inbred strains of mice show different daily amounts of slow-wave sleep (SWS) and rapid-eye movement sleep (REMS), suggesting the possibility of genetic influences on sleep propensity. Previous work by others studying the spontaneous sleep patterns of seven strains of CXB recombinant inbred (RI) mice suggested several candidate quantitative trait loci (QTLs) associated with variation in REMS. Extending this approach, we evaluated the sleep patterns of 13 CXB RI strains and conducted linkage analyses based on 223 discrete informative loci. The probability density distribution of light phase REMS for the CXB RI strains showed deflections that correspond approximately to the parental phenotypes. This type of pattern is consistent with the presence of a low number of major effect quantitative trait loci. Regions of chromosomes 4, 16, and 17 showed provisional linkage to strain variation in REMS. The distribution of loci further suggested that dark phase and light phase REMS may be regulated by different genetic factors. Probabilities of linkage were not sufficient for declaration of a quantitative trait locus for REMS but were sufficient to warrant further analysis either with additional RI strains or with F2 panels.