Genetic architecture of nest building in mice LG/J × SM/J

Evolutionary rescue via niche construction: Infrequent construction can prevent post-invasion extinction

A population experiencing habitat loss can avoid extinction by undergoing genetic adaptation-a process known as evolutionary rescue. Here we analytically approximate the probability of evolutionary rescue via a niche-constructing mutation that allows carriers to convert a novel, unfavorable reproductive habitat to a favorable state at a cost to their fecundity. We analyze competition between mutants and non-niche-constructing wild types, who ultimately require the constructed habitats to reproduce. We find that over-exploitation of the constructed habitats by wild types can generate damped oscillations in population size shortly after mutant invasion, thereby decreasing the probability of rescue. Such post-invasion extinction is less probable when construction is infrequent, habitat loss is common, the reproductive environment is large, or the population's carrying capacity is small. Under these conditions, wild types are less likely to encounter the constructed habitats and, consequently, mutants are more likely to fix. These results suggest that, without a mechanism that deters wild type inheritance of the constructed habitats, a population undergoing rescue via niche construction may remain prone to short-timescale extinction despite successful mutant invasion.

Bidirectional Behavioral Selection in Mice: A Novel Pre-clinical Approach to Examining Compulsivity

Obsessive-compulsive disorder (OCD) and related disorders (OCRD) is one of the most prevalent neuropsychiatric disorders with no definitive etiology. The pathophysiological attributes of OCD are driven by a multitude of factors that involve polygenic mechanisms, gender, neurochemistry, physiological status, environmental exposures and complex interactions among these factors. Such complex intertwining of contributing factors imparts clinical heterogeneity to the disorder making it challenging for therapeutic intervention. Mouse strains selected for excessive levels of nest- building behavior exhibit a spontaneous, stable and predictable compulsive-like behavioral phenotype. These compulsive-like mice exhibit heterogeneity in expression of compulsive-like and other adjunct behaviors that might serve as a valuable animal equivalent for examining the interactions of genetics, sex and environmental factors in influencing the pathophysiology of OCD. The current review summarizes the existing findings on the compulsive-like mice that bolster their face, construct and predictive validity for studying various dimensions of compulsive and associated behaviors often reported in clinical OCD and OCRD.

Evolution of Epistatic Networks and the Genetic Basis of Innate Behaviors

Instinctive behaviors are genetically programmed behaviors that occur independent of experience. How genetic programs that give rise to the manifestation of such behaviors evolve remains an unresolved question. I propose that evolution of species-specific innate behaviors is accomplished through progressive modifications of pre-existing genetic networks composed of allelic variants. I hypothesize that changes in frequencies of one or more constituent allelic variants within the network leads to changes in gene network connectivity and the emergence of a reorganized network that can support the emergence of a novel behavioral phenotype and becomes stabilized when key allelic variants are driven to fixation.

The effect of dietary fat on behavior in mice

Purpose

Obesity is linked to cognitive dysfunction in humans and rodents, and its effects can be passed on to the next generation. However, the extent of these effects is not well understood. The purpose of this study was to determine the effect of a prenatal maternal high-fat diet and an individual high-fat diet in inbred mice.

Methods

We varied maternal diet and offspring diet to test the hypothesis that a high-fat diet would increase anxiety, reduce activity levels, and impair nest-building. First, we fed a high-fat (HF) or low-fat (LF) diet to genetically identical female Small (SM/J) mice and mated them with LF males. We cross-fostered all offspring to LF-fed SM/J nurses and weaned them onto an HF or LF diet. We weighed the mice weekly and we tested anxiety with the Open Field Test, activity levels with instantaneous scan sampling, and nest building using the Deacon Scale.

Results

Diet significantly affected weight, with HF females weighing 28.2 g (± 1.4 g SE) and LF females weighing 15.1 g (± 1.6 g SE) at 17 weeks old. The offspring's own diet had major behavioral effects. HF mice produced more fecal boli and urinations in the Open Field Test, built lower-quality nests, and had lower activity in adulthood than LF mice. The only trait that a prenatal maternal diet significantly affected was whether the offspring built their nests inside or outside of a hut.

Conclusions

Offspring diet, but not prenatal maternal diet, affected a wide range of behaviors in these mice.

The paradox of intelligence: Heritability and malleability coexist in hidden gene-environment interplay

Intelligence can have an extremely high heritability, but also be malleable; a paradox that has been the source of continuous controversy. Here we attempt to clarify the issue, and advance a frequently overlooked solution to the paradox: Intelligence is a trait with unusual properties that create a large reservoir of hidden gene-environment (GE) networks, allowing for the contribution of high genetic and environmental influences on individual differences in IQ. GE interplay is difficult to specify with current methods, and is underestimated in standard metrics of heritability (thus inflating estimates of "genetic" effects). We describe empirical evidence for GE interplay in intelligence, with malleability existing on top of heritability. The evidence covers cognitive gains consequent to adoption/immigration, changes in IQ's heritability across life span and socioeconomic status, gains in IQ over time consequent to societal development (the Flynn effect), the slowdown of age-related cognitive decline, and the gains in intelligence from early education. The GE solution has novel implications for enduring problems, including our inability to identify intelligence-related genes (also known as IQ's "missing heritability"), and the loss of initial benefits from early intervention programs (such as "Head Start"). The GE solution can be a powerful guide to future research, and may also aid policies to overcome barriers to the development of intelligence, particularly in impoverished and underprivileged populations. (PsycINFO Database Record

do Monte BG, Watanabe IM, Cunha J, Peripato AC. A link between thrifty phenotype and maternal care across two generations of intercrossed mice

Maternal effects are causal influences from mother to offspring beyond genetic information, and have lifelong consequences for multiple traits. Previously, we reported that mice whose mothers did not nurse properly had low birth weight followed by rapid fat accumulation and disturbed development of some organs. That pattern resembles metabolic syndromes known collectively as the thrifty phenotype, which is believed to be an adaptation to a stressful environment which prepares offspring for reduced nutrient supply. The potential link between maternal care, stress reactivity, and the thrifty phenotype, however, has been poorly explored in the human and animal literature: only a couple of studies even mention (much less, test) these concepts under a cohesive framework. Here, we explored this link using mice of the parental inbred strains SM/J and LG/J–who differ dramatically in their maternal care–and the intercrossed generations F1 and F2. We measured individual differences in 15 phenotypes and used structural equation modeling to test our hypotheses. We found a remarkable relationship between thrifty phenotype and lower quality of maternal behaviors, including nest building, pup retrieval, grooming/licking, and nursing. To our knowledge, this is the first study to show, in any mammal, a clear connection between the natural variation in thrifty phenotype and maternal care. Both traits in the mother also had a substantial effect on survival rate in the F3 offspring. To our surprise, however, stress reactivity seemed to play no role in our models. Furthermore, the strain of maternal grandmother, but not of paternal grandmother, affected the variation of maternal care in F2 mice, and this effect was mediated by thrifty phenotype in F2. Since F1 animals were all genetically identical, this finding suggests that maternal effects pass down both maternal care and thrifty phenotype in these mice across generations via epigenetic transmission.

Mice Lacking GPR88 Show Motor Deficit, Improved Spatial Learning, and Low Anxiety Reversed by Delta Opioid Antagonist

BACKGROUND

GPR88 is an orphan G protein coupled receptor highly enriched in the striatum, and previous studies have focused on GPR88 function in striatal physiology. The receptor is also expressed in other brain areas, and here we examined whether GPR88 function extends beyond striatal-mediated responses.

METHODS

We created Gpr88 knockout mice and examined both striatal and extrastriatal regions at molecular and cellular levels. We also tested striatum-, hippocampus-, and amygdala-dependent behaviors in Gpr88(-/-) mice using extensive behavioral testing.

RESULTS

We found increased G protein coupling for delta opioid receptor (DOR) and mu opioid, but not other Gi/o coupled receptors, in the striatum of Gpr88 knockout mice. We also found modifications in gene transcription, dopamine and serotonin contents, and dendritic morphology inside and outside the striatum. Behavioral testing confirmed striatal deficits (hyperactivity, stereotypies, motor impairment in rotarod). In addition, mutant mice performed better in spatial tasks dependent on hippocampus (Y-maze, novel object recognition, dual solution cross-maze) and also showed markedly reduced levels of anxiety (elevated plus maze, marble burying, novelty suppressed feeding). Strikingly, chronic blockade of DOR using naltrindole partially improved motor coordination and normalized spatial navigation and anxiety of Gpr88(-/-) mice.

CONCLUSIONS

We demonstrate that GPR88 is implicated in a large repertoire of behavioral responses that engage motor activity, spatial learning, and emotional processing. Our data also reveal functional antagonism between GPR88 and DOR activities in vivo. The therapeutic potential of GPR88 therefore extends to cognitive and anxiety disorders, possibly in interaction with other receptor systems.

Brain serotonin determines maternal behavior and offspring survival

Maternal care is an indispensable component of offspring survival and development in all mammals and necessary for reproductive success. Although brain areas regulating maternal behaviors are innervated by serotonergic afferents, very little is known about the role of this neurotransmitter in these behaviors. To evaluate the contribution of serotonin to maternal care, we used mice with a null mutation in the gene for tryptophan hydroxylase-2 (TPH2), which results in a genetic depletion of brain serotonin, and tested them in a wide range of maternal behavior paradigms. We found that litters born to and reared by TPH2(-/-) mothers showed decreased survival, lower weaning weights and increased cannibalization. In addition, TPH2(-/-) mothers performed poorly in pup retrieval, huddling, nest construction and high-arched back nursing. Aggression in TPH2(-/-) dams was not triggered by lactation and was steadily high. Survival and weaning weight deficits of TPH2(-/-) pups were rescued by cross-fostering and in litters of mixed genotype (TPH2(-/-) and TPH2(-/+) ). However, the maternal behaviors of TPH2(-/-) dams did not improve when rearing either TPH2(+/+) pups or mixed-genotype litters. In addition, TPH2(-/-) pups significantly worsened the behavior of TPH2(+/+) dams with respect to cannibalism, weaning weight and latency to attack. Olfactory and auditory functions of TPH2(-/-) females or anxiety-like behaviors did not account for these maternal alterations as they were equal to their TPH2(+/+) counterparts. These findings illustrate a profound influence of brain serotonin on virtually all elements of maternal behavior and establish that TPH2(-/-) pups can engender maladaptive mothering in dams of both genotypes.

Skeletal development of mice lacking bone sialoprotein (BSP)--impairment of long bone growth and progressive establishment of high trabecular bone mass

Adult Ibsp-knockout mice (BSP−/−) display shorter stature, lower bone turnover and higher trabecular bone mass than wild type, the latter resulting from impaired bone resorption. Unexpectedly, BSP knockout also affects reproductive behavior, as female mice do not construct a proper "nest" for their offsprings. Multiple crossing experiments nonetheless indicated that the shorter stature and lower weight of BSP−/− mice, since birth and throughout life, as well as their shorter femur and tibia bones are independent of the genotype of the mothers, and thus reflect genetic inheritance. In BSP−/− newborns, µCT analysis revealed a delay in membranous primary ossification, with wider cranial sutures, as well as thinner femoral cortical bone and lower tissue mineral density, reflected in lower expression of bone formation markers. However, trabecular bone volume and osteoclast parameters of long bones do not differ between genotypes. Three weeks after birth, osteoclast number and surface drop in the mutants, concomitant with trabecular bone accumulation. The growth plates present a thinner hypertrophic zone in newborns with lower whole bone expression of IGF-1 and higher IHH in 6 days old BSP−/− mice. At 3 weeks the proliferating zone is thinner and the hypertrophic zone thicker in BSP−/− than in BSP+/+ mice of either sex, maybe reflecting a combination of lower chondrocyte proliferation and impaired cartilage resorption. Six days old BSP−/− mice display lower osteoblast marker expression but higher MEPE and higher osteopontin(Opn)/Runx2 ratio. Serum Opn is higher in mutants at day 6 and in adults. Thus, lack of BSP alters long bone growth and membranous/cortical primary bone formation and mineralization. Endochondral development is however normal in mutant mice and the accumulation of trabecular bone observed in adults develops progressively in the weeks following birth. Compensatory high Opn may allow normal endochondral development in BSP−/− mice, while impairing primary mineralization.

The causes of variation in learning and behavior: why individual differences matter

IN A SEMINAL PAPER WRITTEN FIVE DECADES AGO, CRONBACH DISCUSSED THE TWO HIGHLY DISTINCT APPROACHES TO SCIENTIFIC PSYCHOLOGY: experimental and correlational. Today, although these two approaches are fruitfully implemented and embraced across some fields of psychology, this synergy is largely absent from other areas, such as in the study of learning and behavior. Both Tolman and Hull, in a rare case of agreement, stated that the correlational approach held little promise for the understanding of behavior. Interestingly, this dismissal of the study of individual differences was absent in the biologically oriented branches of behavior analysis, namely, behavioral genetics and ethology. Here we propose that the distinction between "causation" and "causes of variation" (with its origins in the field of genetics) reveals the potential value of the correlational approach in understanding the full complexity of learning and behavior. Although the experimental approach can illuminate the causal variables that modulate learning, the analysis of individual differences can elucidate how much and in which way variables interact to support variations in learning in complex natural environments. For example, understanding that a past experience with a stimulus influences its "associability" provides little insight into how individual predispositions interact to modulate this influence on associability. In this "new" light, we discuss examples from studies of individual differences in animals' performance in the Morris water maze and from our own work on individual differences in general intelligence in mice. These studies illustrate that, opposed to what Underwood famously suggested, studies of individual differences can do much more to psychology than merely providing preliminary indications of cause-effect relationships.

Milk ejection in mice LG/J x SM/J

In mammals, milk provision is crucial to offspring survival and growth from birth to weaning. Milk deficiency early in life may cause death or changes in the progeny metabolism that later may lead to obesity and metabolic disorders. This study investigates milk ejection (ME) the first day after birth (D1) in F(2) females from the intercross of LG/J and SM/J inbred mice strains. The absence of milk in F(3) pups' stomach at D1 is directly associated with their survival (p < 0.001) and growth pattern (p < 0.001) in the early stages of life. Furthermore, late growth pattern is also affected by this lack of nutrients at D1 because pups that survive this absence, mostly males, are heavier at weaning (p < 0.001) which, after necropsy, is shown to be due to significant higher total fat deposition (p < 0.01). We performed QTL analysis for ME at D1 in these F(2) females. Maternal performance of ME revealed a complex genetic architecture which even though it contains only a single QTL (accounting for 8 % of the variation in ME), it is totally context-dependent on the genetic background. We discovered many regions involved in epistatic interactions that together with the single QTL explain 19 % of the genetic variation for this trait. Milk ejection is an important component of maternal care, and understanding the mechanisms modulating its variation, along with other maternal features, may help to disentangle the complexity that is the mother/offspring relationship.