Behavioral Traits are Affected by Selective Breeding for Increased Wheel-Running Behavior in Mice

Voluntary physical activity may be related to personality traits. Here, we investigated these relations in two mouse lines selectively bred for high voluntary wheel-running behavior and in one non-selected control line. Selection lines were more explorative and “information gathering” in the open-field test, either with increased upright positions or horizontal locomotion toward the middle ring. Furthermore, one of the selection lines had an increased risk-taking behavior relative to the control line in approaching a novel object placed in the center of the open field. However, anxiety behavior was increased in selection lines during the plus-maze test. Maze learning was not statistically different among lines, but routine behavior was increased in both selection lines when the maze exit after 2 days of testing was displaced. Specifically, in the displaced maze, selected mice traveled more frequently to the old, habituated exit, bypassing the new exit attached to their home cage. Although the generality of the results would need to be confirmed in future studies including all eight lines in the selection experiment, the increased routine and exploratory behavior (at least in the lines used in the present study) may be adaptive to sustain high activity levels.     

Selective Breeding for High and Low Alcohol Preference in Mice

High and low alcohol preference (HAP and LAP, respectively) mice were created by 10 generations of bidirectional selection for differences in two-bottle choice alcohol consumption. The progenitors used for selection were HS/lbg mice, which are a genetically defined, out-bred stock. During selection, mice had 24-h, daily access to 10% alcohol (v/v) and water ad libitum for 30 days and were selected based on the alcohol (g/kg) consumed per day over the entire period. Food was available ad libitum. At S10, line means for alcohol consumption differed greatly, with consumption of over 12 g/kg per day in the HAP mice and less than 2 g/kg per day in the LAP mice. Realized heritability for bidirectional selection was approximately 0.2. Female mice consumed more alcohol than male mice. There were no differences between lines in alcohol elimination rate, nor were there line differences in intake of salt or quinine solutions. However, consumption of saccharin solutions was greater in HAP mice than LAP mice, consistent with previous findings of a genetic correlation between sweet preference and alcohol drinking. Because the mouse genome is relatively well characterized, these selected lines should prove a useful tool for assessment of the genetic basis of, and phenotypes that correlate with, alcohol drinking.     

Short-Term Selective Breeding as a Tool for QTL Mapping: Ethanol Preference Drinking in Mice

Short-term selective breeding starting from an F₂ intercross of two inbred strains is a largely unexploited but potentially useful tool for quantitative trait locus (QTL) mapping. The selection lines can also serve as a valuable confirmation test of recornbinant inbred (RI) QTL results when the same two progenitor strains are used. Starting from an F₂ from a C57BL/6J (B6) × DBA/2J (D2) cross (B6D2F2), this approach was used in a population of ~72 mice per generation bidirectionally selected for two-bottle choice 10% ethanol (alcohol) preference for four generations. The high-preference line diverged significantly from the low line in the first generation with a realized heritabittty of .32. By generation 4, the preference ratios in the high line were double those seen in the low line. Regions of the genome previously implicated by BXD RI QTL analysis as containing QTLs were searched using microsatellite markers. The test for the presence of QTLs was based on the divergence of marker allele frequencies in the two oppositely selected lines significantly exceeding that expected from random (genetic) drift and allele frequency estimation error. Combining the BXD and two-way selection line results, the most probable QTL was found on chromosome 3 (near the AdhI locus; LOD ~2.9), other probable QTLs were found with LOD 2.4–2.6.     

Mediators of Increased Physical Activity and Change in Subjective Well-being: Results from the Activity Counseling Trial (ACT)

The purpose of this study was to examine whether change in satisfaction with physical function (SF), satisfaction with physical appearance (SA), and self-efficacy (SE) mediate the effects that increased physical activity has on change in subjective well-being (SWB). Participants in this investigation consisted of 854 men (n = 471) and women (n = 383) who took part in the Activity Counseling Trial (ACT). ACT was a 24-month multicenter, randomized controlled trial to evaluate the effectiveness of interventions to promote physical activity in the primary care setting. Participants were assigned to one of three treatments: standard care control, staff-assisted intervention, or staff-counseling intervention. Results revealed that, irrespective of treatment arm, change in physical activity was related to change in SBW and to change in all mediators of interest. A statistical test of mediation revealed that the influence of change in physical activity on SWB was due to change in all three mediators with change in SF making the greatest contribution to the model.     

Nesting Behavior of House Mice (Mus Domesticus) Selected for Increased Wheel-Running Activity

Nest building was measured in active (housed with access to running wheels) and sedentary (without wheel access) mice (Mus domesticus) from four replicate lines selected for 10 generations for high voluntary wheel-running behavior, and from four randombred control lines. Based on previous studies of mice bidirectionally selected for thermoregulatory nest building, it was hypothesized that nest building would show a negative correlated response to selection on wheel-running. Such a response could constrain the evolution of high voluntary activity because nesting has also been shown to be positively genetically correlated with successful production of weaned pups. With wheel access, selected mice of both sexes built significantly smaller nests than did control mice. Without wheel access, selected females also built significantly smaller nests than did control females, but only when body mass was excluded from the statistical model, suggesting that body mass mediated this correlated response to selection. Total distance run and mean running speed on wheels was significantly higher in selected mice than in controls, but no differences in amount of time spent running were measured, indicating a complex cause of the response of nesting to selection for voluntary wheel running.     

Defective Bone Microstructure in Hydronephrotic Mice: A Histomorphometric Study in ICR/Mlac‐hydro Mice

Chronic renal impairment can lead to bone deterioration and abnormal bone morphology, but whether hydronephrosis is associated with bone loss remains unclear. Herein, we aimed to use computer‐assisted bone histomorphometric technique to investigate microstructural bone changes in Imprinting Control Region (ICR) mice with a spontaneous mutation that was associated with bilateral nonobstructive hydronephrosis (ICR/Mlac‐hydro). The results showed that 8‐week‐old ICR/Mlac‐hydro mice manifested decreases in trabecular bone number and thickness, and an increased trabecular separation, thereby leading to a reduction in trabecular bone volume compared with the wild‐type mice. Furthermore, histomorphometric parameters related to both bone resorption and formation, that is, eroded surface, osteoclast surface, and osteoblast surface, were much lower in ICR/Mlac‐hydro mice than in the wild type. A decrease in moment of inertia was found in ICR/Mlac‐hydro mice, indicating a decrease in bone strength. In conclusion, ICR/Mlac‐hydro mice exhibited trabecular bone loss, presumably caused by marked decreases in both osteoblast and osteoclast activities, which together reflected abnormally low bone turnover. Thus, this mouse strain appeared to be a valuable model for studying the hydronephrosis‐associated bone disease. Anat Rec, 297:208–214, 2014. © 2013 Wiley Periodicals, Inc.     

A Systematic Review of Financial Incentives for Physical Activity: The Effects on Physical Activity and Related Outcomes

The aim of this review is to give an overview of the available evidence on the effects of financial incentives to stimulate physical activity. Therefore, a systematic literature search was performed for randomized trials that investigate the effects of physical–activity–related financial incentives for individuals. Twelve studies with unconditional incentives (eg, free membership sport facility) and conditional incentives (ie, rewards for reaching physical–activity goals) related to physical activity were selected. Selected outcomes were physical activity, sedentary behavior, fitness, and weight. Results show that unconditional incentives do not affect physical activity or the other selected outcomes. For rewards, some positive effects were found and especially for rewards provided for physical-activity behavior instead of attendance. In conclusion, rewards seem to have positive effects on physical activity, while unconditional incentives seem to have no effect. However, it should be kept in mind that the long-term effects of financial incentives are still unclear.     

Artificial Selection for Increased Maternal Defense Behavior in Mice

Maternal aggression is directed towards intruders by lactating females and is critical for defense of offspring. Within-family selection for increased maternal defense in outbred house mice (Mus domesticus; Hsd:ICR strain) was applied to one selected (S) line, using total duration of attacks in a 3-min test as the selection criterion. One control (C) line was maintained and both lines were propagated by 13 families in each generation. Prior to selection, heritability of maternal aggression was estimated to be 0.61 based on mother-offspring regression. Duration of attacks responded to selection with a mean realized heritability of 0.40 (corrected for within-family selection) after eight generations. At generation 5, the S and C line also differed significantly for litter size at birth and at mid-lactation (both lower in S), average individual pup mass at mid-lactation (higher in S), and pup retrieval latency (longer in S), but not for other maternal measures that we studied (e.g., dam mass). Additionally, number of entries to middle and closed plus maze compartments was significantly higher in S mice in Generation 5. This is the first study to select for high maternal defense and these mice will be made available as a tool for understanding the genetic and neural basis of maternal aggression.     

Artificial Selection for Increased Wheel-Running Behavior in House Mice

Replicated within-family selection for increased voluntary wheel running in outbred house mice (Mus domesticus; Hsd:ICR strain) was applied with four high-selected and four control lines (10 families/line). Mice were housed individually with access to activity wheels for a period of 6 days, and selection was based on the mean number of revolutions run on days 5 and 6. Prior to selection, heritabilities of mean revolutions run per day (rev/day), average running velocity (rpm), and number of minutes during which any activity occurred (min/day) were estimated by midparent–offspring regression. Heritabilities were 0.18, 0.28, and 0.14, respectively; the estimate for min/day did not differ significantly from zero. Ten generations of selection for increased rev/day resulted in an average 75% increase in activity in the four selected lines, as compared with control lines. Realized heritability averaged 0.19 (range, 0.12–0.24 for the high-activity lines), or 0.28 when adjusted for within-family selection. Rev/day increased mainly through changes in rpm rather than min/day. These lines will be studied for correlated responses in exercise physiology capacities and will be made available to other researchers on request.     

Selective Breeding for Divergence in Novelty-seeking Traits: Heritability and Enrichment in Spontaneous Anxiety-related Behaviors

Outbred Sprague–Dawley rats can be classified as high responders (HR) or low responders (LR) based on their levels of exploratory locomotion in a novel environment. While this novelty-seeking dimension was originally related to differential vulnerability to substance abuse, behavioral, neuroendocrine and gene expression studies suggest a fundamental difference in emotional reactivity between these animals. Here, we report the first study to selectively breed rats based on this novelty-seeking dimension. Response to novelty was clearly heritable, with a >2-fold difference in behavior seen after eight generations of selection. Three tests of anxiety-like behavior consistently showed significantly greater anxiety in LR-bred rats compared to HR-bred animals, and this difference was diminished in the open field test by administration of the anxiolytic benzodiazepine drug, chlordiazepoxide. Cross-fostering revealed that responses to novelty were largely unaffected by maternal interactions, though there was an effect on anxiety-like behavior. These selected lines will enable future research on the interplay of genetic, environmental and developmental variables in controlling drug seeking behavior, stress and emotional reactivity.John H. Stead and Sarah Clinton contributed equally to this research.     

Divergent Physical Activity and Novel Alternative Responses to High Fat Feeding in Polygenic Fat and Lean Mice

We determined whether altered physical activity levels might underlie the contrasting adiposity of a divergently selected polygenic murine model of metabolic syndrome (Fat; F) and leanness (Lean; L) mice. We measured physical activity with a long term running wheel experiment and performed an additional high fat diet intervention. Further, we measured posture allocation by visual monitoring within the home cage as a non-exercise correlate of ‘normal’ physical activity. Whilst initially similar, running wheel activity of the F line declined with age, while the activity of the L line increased. Food intake was higher in the L line and increased with wheel exposure. Vertical rearing measured by video quantification in the home cage, without the stimulus of a running wheel was also significantly higher in the L line. The two lines developed novel alternate strategies to defend their body weight when exposed to high fat diets with a running wheel. F mice increased their running wheel activity, and despite unaltered food intake, still gained weight. L mice reduced their food intake and maintained activity levels without a significant change in body weight. Phenotypic selection for divergence in body fat content has co-segregated with a genetic predisposition for divergent physical activity levels and different strategies for coping with exposure to high fat diets that will facilitate the discovery of the genes underlying these important obesity related traits. Edited by Stephen Maxson.     

Genetics of Physical Activity and Physical Inactivity in Humans

Emerging evidence suggests that physical activity and sedentary behavior [reflected in physical inactivity (PI)], might be two different phenotypes that may have distinct underlying physiological mechanisms. The purpose of this review is to summarize the existing literature on the genetic determinants of PA and PI phenotypes in humans, considering them as distinct behaviors. Completed in January 2011, this review includes family studies, twin studies, association studies, genome-wide linkage studies and genome-wide association scan (GWAs) reporting different physical activity/inactivity-related phenotypes. In regards to PA, familial aggregation studies resulted in heritability estimates ranging from 0 to 60 %, and twin studies yielded heritability estimates (a²) and shared environment (c²) scores for PA phenotypes ranging from 0.00 to 0.85 and 0.00 to 0.84, respectively. Unique environmental (e²) results are well dispersed from 0.12 to 0.72. Suggestive linkages were found with markers nearby different activity-related genes: EDNRB, MC4R, UCP1, FABP2, CASR, SLC9A9. Significant associations with PA phenotypes were found for Ace, Gln223ARrg, MC4R and DRD2 genes. We found one GWAs that reported novel SNPs in the PAPSS2 gene on chromosome 10q23.2 and in two intergenic regions on chromosomes 2q33.1 and 18p11.32. Heritability estimates for PI ranged from 25 to 60 % and linkage studies recorded higher LOD scores for PI versus PA. The ACE genotype was strongly associated with PI. There are potentially different genetic influences on PA versus PI phenotypes. Future studies should focus on the different genetic influences on PA and PI to improve our understanding of underlying determinants of these behaviors.     

Increased Activity and Altered Subcellular Distribution of Lysosomal Enzymes Determine Neuronal Vulnerability in Niemann-Pick Type C1-Deficient Mice

Niemann-Pick disease type C (NPC), caused by mutations in the Npc1 or Npc2 genes, is a progressive neurodegenerative disorder characterized by intracellular accumulation/redistribution of cholesterol in a number of tissues including the brain. This is accompanied by a severe loss of neurons in selected brain regions. In this study, we evaluated the role of lysosomal enzymes, cathepsins B and D, in determining neuronal vulnerability in NPC1-deficient (Npc1^−/−) mouse brains. Our results showed that Npc1^−/− mice exhibit an age-dependent degeneration of neurons in the cerebellum but not in the hippocampus. The cellular level/expression and activity of cathepsins B and D are increased more predominantly in the cerebellum than in the hippocampus of Npc1^−/− mice. In addition, the cytosolic levels of cathepsins, cytochrome c, and Bax2 are higher in the cerebellum than in the hippocampus of Npc1^−/− mice, suggesting a role for these enzymes in the degeneration of neurons. This suggestion is supported by our observation that degeneration of cultured cortical neurons treated with U18666A, which induces an NPC1-like phenotype at the cellular level, can be attenuated by inhibition of cathepsin B or D enzyme activity. These results suggest that the increased level/activity and altered subcellular distribution of cathepsins may be associated with the underlying cause of neuronal vulnerability in Npc1^−/− brains. Therefore, their inhibitors may have therapeutic potential in attenuating NPC pathology.Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral disorder caused by mutations in the Npc1 or Npc2 gene. NPC1 is a membrane protein that contains a sterol-sensing domain and resides primarily in late endosomes/lysosomes, whereas NPC2 is a soluble protein that resides primarily in lysosomes.^1,2,3,4 The loss of function of either protein results in intracellular accumulation of unesterified cholesterol and glycosphingolipids within the endosomal-lysosomal (EL) system in a number of tissues including the brain. In addition, there is evidence that homeostatic responses to exogenously supplied cholesterol and activation of cholesterol esterification are severely impaired in cells lacking functional NPC1. These defects in cholesterol accumulation/homeostasis trigger abnormal liver and spleen function as well as widespread neurological deficits including ataxia, dystonia, seizures, and dementia that eventually lead to premature death.^5,6,7,8,9 Interestingly, BALB/cNctr-Npc^N/N mice, which do not express NPC1 protein because of a spontaneous deletion/insertion mutation in the Npc1 gene, have been shown to recapitulate pathological features associated with NPC disease. These Npc1^−/− mice are asymptomatic at birth but gradually develop tremor and ataxia, dying prematurely at ∼3 months.^10,11,12,13 As in the human disease, Npc1^−/− mice show accumulation of unesterified cholesterol in the EL system and exhibit activation of microglia and astrocytes as well as degradation of the myelin sheath throughout the central nervous system. Progressive loss of neurons is particularly evident in the prefrontal cortex, thalamus, brainstem, and cerebellum but not in the hippocampal formation.^{13,14,15,16,17,18} However, at present, very little is known about the underlying mechanisms associated with the vulnerability of select populations of neurons in Npc1^−/− mice.A number of earlier studies have shown that the EL system, the major site of cholesterol accumulation in NPC pathology, consists of two dynamic interrelated cellular pathways: the endocytic pathway and the lysosomal system. Under normal conditions, the EL system serves as an important site for intracellular protein turnover and proteolytic processing of certain proteins mediated by lysosomal hydrolases termed cathepsins.^19,20,21 After their synthesis in the endoplasmic reticulum, cathepsins bind to the insulin-like growth factor-II (IGF-II)/mannose 6-phosphate (M6P) receptor on the trans face of the Golgi complex and are transported in vesicles to the EL system.^22,23,24 The importance of lysosomal enzymes in the proper functioning of the EL system is underscored by the fact that altered synthesis, sorting, or targeting of lysosomal enzymes is the molecular basis of more than 40 inherited disorders associated with extensive neurodegeneration, mental retardation and often progressive cognitive decline.^19,25,26,27There is evidence that increased endosome volumes and/or levels of cathepsins, such as cathepsins B and D, can mediate cell death by inducing lysosomal destabilization and enzyme leakage into cell cytosol, as is observed during oxidative stress²⁸ and experimental brain ischemia in primates.²⁹ Conversely, a number of recent studies have shown that lysosomal enzyme expression/levels can be up-regulated in the absence of cell death as a compensatory mechanism to repair damage/injury.^30,31,32,33 Thus, it seems that lysosomal enzymes are not only involved in the degeneration of neurons but also in the protection of neurons against toxicity in a variety of experimental as well as pathological paradigms. Although the EL system, the major site of cholesterol accumulation in NPC1-deficient cells, has been suggested to play a critical role in the development of NPC pathology,^6,7,8 very little is known about the significance of lysosomal cathepsins in determining neuronal vulnerability associated with the disease. To address this issue, we measured age-related changes in the levels, distribution, and activity of cathepsins B and D in the hippocampus and cerebellum of Npc1^−/− and age-matched control mice. In parallel, we evaluated the levels and distribution of the IGF-II/M6P receptor in Npc1^−/− and control mice to establish whether factors regulating cathepsin bioavailability can also influence the development of pathological changes. In addition, using cultured mouse cortical neurons we determined the significance of cathepsins B and D in the degeneration of neurons after accumulation of cholesterol. Our results reveal that alterations in the levels/activity as well as subcellular distribution of the lysosomal enzymes may be one of the underlying mechanisms associated with the selective neuronal vulnerability observed in NPC pathology.     

Web-Based Assessments of Physical Activity in Youth: Considerations for Design and Scale Calibration

This paper describes the design and methods involved in calibrating a Web-based self-report instrument to estimate physical activity behavior. The limitations of self-report measures are well known, but calibration methods enable the reported information to be equated to estimates obtained from objective data. This paper summarizes design considerations for effective development and calibration of physical activity self-report measures. Each of the design considerations is put into context and followed by a practical application based on our ongoing calibration research with a promising online self-report tool called the Youth Activity Profile (YAP).We first describe the overall concept of calibration and how this influences the selection of appropriate self-report tools for this population. We point out the advantages and disadvantages of different monitoring devices since the choice of the criterion measure and the strategies used to minimize error in the measure can dramatically improve the quality of the data. We summarize strategies to ensure quality control in data collection and discuss analytical considerations involved in group- vs individual-level inference. For cross-validation procedures, we describe the advantages of equivalence testing procedures that directly test and quantify agreement. Lastly, we introduce the unique challenges encountered when transitioning from paper to a Web-based tool. The Web offers considerable potential for broad adoption but an iterative calibration approach focused on continued refinement is needed to ensure that estimates are generalizable across individuals, regions, seasons and countries.     

Selective Breeding for an Infant Phenotype: Rat Pup Ultrasonic Vocalization (USV)

To examine processes underlying generational and developmental influences on anxiety, this laboratory produced two lines of (N:NIH strain) rats, selectively bred on the basis extreme rates of ultrasonic vocalization in 2 minutes of isolation at Postnatal Day 10. The research reviewed in this article focuses on: (1) establishment of the selectively bred lines; (2) defining infant behavioral and physiological phenotypes and (3) determining whether infantile USV phenotypes endure over development. The High and Low lines have diverged widely in their USV rates from each other and from the Random control line, which has maintained N:NIH strain rates overall from generation to generation. Beginning in the 11th generation, High USV pups have shown significantly higher frequencies of defecation and urination during isolation screening than the Low USV and random control line. Both lines show altered autonomic regulation of heart rates (HR) in response to stressors as juveniles and adults. These differences in HR responses in High and Low lines appear to be mediated by changes in the balance of sympathetic versus parasympathetic mechanisms. Other behavioral characteristics of the High line are consistent with an anxious/ depressive phenotype, such as vocalizations to touch in a novel environment, and performance in the Porsolt Swim, whereas Low line shows few differences in anxiety behavior. Future work will resolve the similarities and differences in the High and Low phenotypes and provide a developmental perspective to the growing body of information about affective regulation in humans and animals provided by selectively bred animal models.     

The Relatedness to Others in Physical Activity Scale: Evidence for Structural and Criterion Validity

The purpose of this study was to test the structural and criterion validity of scores derived from the Relatedness to Others in Physical Activity Scale (ROPAS). The participants (n₁ = 893; n₂ = 522) completed the ROPAS in addition to demographic questions (study 1) and well-being indicators (study 2) using cross-sectional, nonexperimental surveys. Confirmatory factor analysis (study 1) supported the tenability of a 6-item ROPAS measurement model that was invariant across gender. Higher ROPAS scores were associated with greater perceived autonomy and competence and greater well-being (study 2). Overall, these findings suggested the ROPAS displays a number of psychometric properties that render the instrument useful for investigating issues of belonging and connectedness with others in global physical activity settings.     

Increased Thymic Size and Thymocyte Interleukin 2 Production in Androgen-Resistant Mice

The functional significance of androgen receptors in thymocytes is unknown. To investigate whether such receptors might mediate androgen-induced effects on thymocyte proliferation or differentiation we examined mice bearing a known defect in the gene coding for the androgen receptor. This mutation, termed testicular feminization (Tfm/Y), renders these mice resistant to the action of androgenic hormones. Testicular feminization mice were found to have large thymuses that were an average of 2.8 times as heavy as those of their unaffected male litter mates, and contained up to 36 times as many thymocytes. Similar findings were observed when Tfm mice were compared with C57Bl/6 control mice. Thymocytes from androgen-resistant mice produced several times more interleukin 2 in culture than did thymocytes from control mice. A small but significant reduction in the population of cells bearing neither CD4 nor CD8 surface markers ('double negatives') was observed in the androgen-resistant mice. These data indicate that androgen resistance is associated in the Tfm/Y mouse with alterations in thymocyte number, phenotype, and function that may be attributable to lack of androgen action during thymic development.     

Spleen Cells from Antithymocyte Serum Pretreated Mice Do Not Induce GVHD but Exert Increased Repopulating Activity in Irradiated Semiallogeneic Recipients

Graft-versus-host disease (GVHD) due to allogeneic bone marrow transplantation can be prevented by depleting the T cells from the marrow graft in vitro . However, the elimination of the donor T cells results in a higher frequency of graft failure, secondary infections and, in case of leukaemia, relapse. We found, that, in contrast to normal spleen cells, spleen cells from A or B10 donor mice pretreated with xenogeneic antithymocyte serum (ATS) in vivo did not induce GVHD in non-irradiated (B10 x A)F₁ hybrids. Spleen cells of ATS-pretreated A donors did not cause GVHD in allogeneic CBA mice made neonataily tolerant to the A donor strain either. Furthermore, spleen cells from ATS-treated donors did not cause GVHD in irradiated F₁ hybrid recipients, moreover, they decreased the lethal effect of irradiation. The in vivo ATS pretreatment improved the repopulating capacity of spleen cells in irradiated syngeneic recipients, too. The effect of the ATS treatment does not rely solely upon the elimination of T cells, since flow cytofluorometric analysis revealed only a partial depletion of both the CD4₊ and CD8₊ T cells of the ATS-pretreated animals. These observations may also have clinical relevance.