Foster dams rear fighters: strain-specific effects of within-strain fostering on aggressive behavior in male mice

Intergenerational transmission of maternal behavioral traits in mice: involvement of the gut microbiota

The matrilineal transmission of maternal behavior has been reported in several species. Studies, primarily on rats, have suggested the importance of postnatal experience and the involvement of epigenetic mechanisms in mediating these transmissions. This study aims to determine whether the matrilineal transmission of maternal behavior occurs in mice and whether the microbiota is involved. We first observed that early weaned (EW) female mice showed lower levels of maternal behavior, particularly licking/grooming (LG) of their own pups, than normally weaned (NW) female mice. This difference in maternal behavioral traits was also observed in the second generation, even though all mice were weaned normally. In the subsequent cross-fostering experiment, the levels of LG were influenced by the nurturing mother but not the biological mother. Finally, we transplanted the fecal microbiota from EW or NW mice into germ-free (GF) mice raising pups. The maternal behaviors that the pups exhibited toward their own offspring after growth were analyzed, and the levels of LG in GF mice colonized with microbiota from EW mice were lower than those in GF mice colonized with microbiota from NW mice. These results clearly indicate that, among maternal behavioral traits, LG is intergenerationally transmitted in mice and suggest that the vertical transmission of microbiota is involved in this process. This study demonstrates the universality of the intergenerational transmission of maternal behavioral traits and provides new insights into the role of microbiota.

Shaping the development of complex social behavior

Early life experiences can have an enduring impact on the brain and behavior, with implications for stress reactivity, cognition, and social behavior. In particular, the neural systems that contribute to the expression of social behavior are altered by early life social environments. However, paradigms that have been used to alter the social environment during development have typically focused on exposure to stress, adversity, and deprivation of species-typical social stimulation. Here, we explore whether complex social environments can shape the development of complex social behavior. We describe lab-based paradigms for studying early life social complexity in rodents that are generally focused on enriching the social and sensory experiences of the neonatal and juvenile periods of development. The impact of these experiences on social behavior and neuroplasticity is highlighted. Finally, we discuss the degree to which our current approaches for studying social behavior outcomes give insight into "complex" social behavior and how social complexity can be better integrated into lab-based methodologies.

Fostered offspring develop hyper-reactive endocrine stress responses in a plural-breeding rodent, Octodon degus

Long-term parental separation can lead to altered behavioral and physical development in human children. Rodent models are popular for studying parent-child separation, and several studies have found that maternal separation leads to chronic changes in the endocrine stress response. However, while human children are generally raised by multiple caregivers, most rodent studies utilize solitary breeding species. Therefore, we used degus (Octodon degus) as a model for studying human parental separation, as these rodents practice plural breeding and communal care. In this study, we cross-fostered degu litters at different ages (post-natal day [PND] 2, 8, and 14) to test the hypotheses that fostering affects offspring stress hormone levels in both the short- and long-term and that these impacts differ depending on the age at which offspring are fostered. We found that fostering had long-term effects, as fostered offspring had higher stress-induced cortisol levels and weaker cortisol negative feedback than non-fostered offspring at weaning age (PND28). We also found that the timing of fostering mattered, as degus fostered at PND8 had higher baseline cortisol levels the day after fostering, while degus fostered at PND2 had higher stress-induced cortisol levels at weaning. These data suggest that long-term cross-fostering has enduring impacts on the endocrine stress response in degus, therefore making them a useful model organism for investigating impacts of parental separation in humans.

Bisphenol S (BPS) Alters Maternal Behavior and Brain in Mice Exposed During Pregnancy/Lactation and Their Daughters

Estrogenic endocrine disrupting chemicals have been shown to disrupt maternal behavior in rodents. We investigated the effects of an emerging xenoestrogen, bisphenol S (BPS), on maternal behavior and brain in CD-1 mice exposed during pregnancy and lactation (F0 generation) and in female offspring exposed during gestation and perinatal development (F1 generation). We observed different effects in F0 and F1 dams for a number of components of maternal behavior, including time on the nest, time spent on nest building, latency to retrieve pups, and latency to retrieve the entire litter. We also characterized expression of estrogen receptor α in the medial preoptic area (MPOA) and quantified tyrosine hydroxylase immunoreactive cells in the ventral tegmental area, 2 brain regions critical for maternal care. BPS-treated females in the F0 generation had a statistically significant increase in estrogen receptor α expression in the caudal subregion of the central MPOA in a dose-dependent manner. In contrast, there were no statistically significant effects of BPS on the MPOA in F1 dams or the ventral tegmental area in either generation. This work demonstrates that BPS affects maternal behavior and brain with outcomes depending on generation, dose, and postpartum period. Many studies examining effects of endocrine disrupting chemicals view the mother as a means by which offspring can be exposed during critical periods of development. Here, we demonstrate that pregnancy and lactation are vulnerable periods for the mother. We also show that developmental BPS exposure alters maternal behavior later in adulthood. Both findings have potential public health implications.

Social Interactions and Indirect Genetic Effects on Complex Juvenile and Adult Traits

Most animal species are social in one form or another, yet many studies in rodent model systems use either individually housed animals or ignore potential confounds caused by group housing. While such social interaction effects on developmental and behavioral traits are well established, the genetic basis of social interactions has not been researched in as much detail. Specifically, the effects of genetic variation in social partners on the phenotype of a focal individual have mostly been studied at the phenotypic level. Such indirect genetic effects (IGEs), where the genotype of one individual influences the phenotype of a second individual, can have important evolutionary and medically relevant consequences. In this chapter, we give a brief outline of social interaction effects, and how systems genetics approaches using recombinant inbred populations can be used to investigate indirect genetic effects specifically, including maternal genetic effects. We discuss experimental designs for the study of IGEs and show how indirect genetic loci can be identified that underlie social interaction effects, their mechanisms, and consequences for trait variation in focal individuals.

Cross-fostering: Elucidating the effects of gene×environment interactions on phenotypic development

Cross-fostering of litters from soon after birth until weaning is a valuable tool to study the ways in which gene×environment interactions program the development of neural, physiological and behavioral characteristics of mammalian species. In laboratory mice and rats, the primary focus of this review, cross-fostering of litters between mothers of different strains or treatment groups (intraspecific) or between mothers of different species (interspecific) has been conducted over the past 9 decades. Areas of particular interest have included maternal effects on emotionality, social preferences, responses to stressful stimulation, nutrition and growth, blood pressure regulation, and epigenetic effects on brain development and behavior. Results from these areas of research highlight the critical role of the postnatal maternal environment in programming the development of offspring phenotypic characteristics. In addition, experimental paradigms that have included cross-fostering have permitted investigators to tease apart prenatal versus postnatal effects of various treatments on offspring development and behavior.

Sexually-dimorphic alterations in cannabinoid receptor density depend upon prenatal/early postnatal history

Recent research has demonstrated that the endogenous cannabinoid system is central to the brain's response to stress. As part of an ongoing collaboration, we sought to examine the effects of prenatal and early postnatal rearing and housing conditions on developing endocannabinoid systems. We compare brain cannabinoid receptors (CBR) in offspring of either prenatal vehicle intubated or non-treated dams (Experiment 1) or in rats derived from a vendor and shipped at weaning to a collaborating lab (Experiment 2). From postnatal day (PND) 23, all rats were either housed in isolated conditions or enriched conditions with 3 rats/cage and a variety of stimulus objects changed twice a week. All rats underwent 5days of handling as controls for a behavior study and all rats were sacrificed at approximately PND48-50 within 2hours of the last behavioral test. All brains were processed together for CB1 receptor binding using ³H CP55,940 in prefrontal cortex, striatum, amygdala and hippocampus. Conditions in the two labs were as similar as possible since the two studies were intentionally designed to be comparable and contemporary. Results show that 1) comparing offspring of non-treated dams to offspring of dams receiving daily vehicle intubations, males show decreased CB1 binding in most brain regions while females only showed alterations in the hippocampus and these were increases in the offspring of the vehicle-intubated dams. 2) When comparing offspring of non-treated dams in NY with those derived from a vendor, shipped and maintained in the collaborating lab, this latter group showed reduced CB1 binding in prefrontal cortex in males and increased binding in all four brain regions in females. Therefore, overall, both prenatal handling (intubations) and being vendor-derived, shipped and maintained in a collaborating facility reduced CB1 receptors in males and increased them in females in key limbic brain regions. Effects of environmental enrichment or isolation were minor with only the prefrontal cortex showing an increase in binding in the isolated animals that were offspring of the vehicle-intubated dams. These results support the ideas that prenatal/early postnatal conditions produce different effects in males and females and override the effects of enrichment/isolation on cannabinoid receptors. Behavioral responses to cannabinoid challenges would therefore be expected to vary depending on sex, prenatal/early postnatal history and postweaning conditions of the rats. Since exogenous cannabinoids act through the CBR, the present data may provide a molecular basis for discrepant behavioral effects reported across various labs in the literature as well as sex differences seen following stress and/or manipulation of the cannabinoid system.

Maternal care affects EEG properties of spike-wave seizures (including pre- and post ictal periods) in adult WAG/Rij rats with genetic predisposition to absence epilepsy

WAG/Rij rats have a genetic predisposition to absence epilepsy and develop spontaneous spike-wave discharges in EEG during late ontogenesis (SWD, EEG manifestation of absence epilepsy). Changes in an environment during early postnatal ontogenesis can influence the genetically predetermined absence epilepsy. Here we examined the effect of maternal environment during weaning period on the EEG manifestation of absence epilepsy in adulthood. Experiments were performed in the offspring of WAG/Rij and Wistar rats. The newborn pups were fostered to dams of the same (in-fostering) or another strain (cross-fostering). Age-matched control WAG/Rij and Wistar rats were reared by their biological mothers. Absence seizures were uncommon in Wistar and were not aggravated in both in- and cross-fostered groups. In WAG/Rij rats, fewer SWD were found in the cross-fostered as compared to the in-fostered group. The cross-fostered WAG/Rij rats showed higher percentage of short-lasting SWD with duration <2s. The mean frequency of EEG at the beginning of SWD in the cross-fostered WAG/Rij rats was lower than in control (8.82 vs 9.25Hz), but it was higher in a period of 1.5s before and after SWD. It was concluded that a healthier maternal environment is able to alleviate genetically predetermined absence seizures in adulthood through changes in EEG rhythmic activity.

Aggression in non-human vertebrates: Genetic mechanisms and molecular pathways

Aggression is an adaptive behavioral trait that is important for the establishment of social hierarchies and competition for mating partners, food, and territories. While a certain level of aggression can be beneficial for the survival of an individual or species, abnormal aggression levels can be detrimental. Abnormal aggression is commonly found in human patients with psychiatric disorders. The predisposition to aggression is influenced by a combination of environmental and genetic factors and a large number of genes have been associated with aggression in both human and animal studies. In this review, we compare and contrast aggression studies in zebrafish and mouse. We present gene ontology and pathway analyses of genes linked to aggression and discuss the molecular pathways that underpin agonistic behavior in these species. © 2015 Wiley Periodicals, Inc.

Immune deficiency influences juvenile social behavior and maternal behavior

Mice with severe combined immunodeficiency (SCID) lack functional T and B lymphocytes, and have impaired cognitive abilities. We assessed social behaviors in male SCID and C57BL/6 (B6) juvenile mice. In a social preference task, SCID mice spent more time than B6 mice investigating a novel adult male mouse. In a social recognition task, SCID mice habituated to a novel ovariectomized mouse, but failed to show dishabituation when presented with an unfamiliar individual. We hypothesized that partial immune restoration could normalize behaviors. SCID pups (postnatal Day 7) received either saline or splenocytes from normal donors. Splenocyte-replaced SCID mice spent less time interacting with a novel mouse than saline-injected SCID or B6 control mice. Again, control SCID mice failed to dishabituate to a novel mouse, but splenocyte-replaced SCID mice showed dishabituation. In both of these studies, B6 and SCID pairs were used to produce offspring that remained with their dams until weaning. There are no studies of maternal behavior in SCID dams; therefore to investigate the potential role for this factor, we quantified maternal behavior in SCID and B6 dams; several significant differences were found. To control for differences in maternal care, we mated heterozygous SCIDs to produce offspring. These homozygous SCID and wild-type offspring reared by dams of the same genotypes displayed similar responses to a novel mouse; however, in the social recognition task, SCID males did not display dishabituation to a novel mouse. Taken together, our data indicate that Gene × Environment interactions influence social interactions in immune deficient mice.

Neural growth hormone: regional regulation by estradiol and/or sex chromosome complement in male and female mice

BACKGROUND

Sex differences in pituitary growth hormone (GH) are well documented and coordinate maturation and growth. GH and its receptor are also produced in the brain where they may impact cognitive function and synaptic plasticity, and estradiol produces Gh sex differences in rat hippocampus. In mice, circulating estradiol increases Gh mRNA in female but not in male medial preoptic area (mPOA); therefore, additional factors regulate sexually dimorphic Gh expression in the brain. Thus, we hypothesized that sex chromosomes interact with estradiol to promote sex differences in GH. Here, we assessed the contributions of both estradiol and sex chromosome complement on Gh mRNA levels in three large brain regions: the hippocampus, hypothalamus, and cerebellum.

METHODS

We used the four core genotypes (FCG) mice, which uncouple effects of sex chromosomes and gonadal sex. The FCG model has a deletion of the sex-determining region on the Y chromosome (Sry) and transgenic insertion of Sry on an autosome. Adult FCG mice were gonadectomized and given either a blank Silastic implant or an implant containing 17β-estradiol. Significant differences in GH protein and mRNA were attributed to estradiol replacement, gonadal sex, sex chromosome complement, and their interactions, which were assessed by ANOVA and planned comparisons.

RESULTS

Estradiol increased Gh mRNA in the cerebellum and hippocampus, regardless of sex chromosome complement or gonadal sex. In contrast, in the hypothalamus, females had higher Gh mRNA than males, and XY females had more Gh mRNA than XY males and XX females. This same pattern was observed for GH protein. Because the differences in Gh mRNA in the hypothalamus did not replicate prior studies using other mouse models and tissue from mPOA or arcuate nucleus, we examined GH protein in the arcuate, a subdivision of the hypothalamus. Like the previous reports, and in contrast to the entire hypothalamus, a sex chromosome complement effect showed that XX mice had more GH than XY in the arcuate.

CONCLUSIONS

Sex chromosome complement regulates GH in some but not all brain areas, and within the hypothalamus, sex chromosomes have cell-specific actions on GH. Thus, sex chromosome complement and estradiol both contribute to GH sex differences in the brain.

What makes a good mother? Implication of inter-, and intrastrain strain "cross fostering" for emotional changes in mouse offspring

Currently, the mouse represents the preferred model organism among mammals used for animal studies. Due to a great availability of mutant strains it represents a standard method to analyze in vivo the effects of targeted gene manipulations. While this - at least in theory - represents a valuable tool to elucidate the pathophysiology of certain human diseases, there are several caveats which need to be considered working with animals. In our study we aimed at elucidating, how a widely established breeding strategy, i.e. the use of "foster mothers" to save the survival of compromised mouse pups for ongoing experiments, per se, affects the emotional phenotype of the fostered offspring. Since it is a popular method to use outbred strains like NMRI to do this job, we sought to evaluate the potential effects of such an artificial postnatal condition and compare either offspring nurtured by their biological mothers or two different strains of foster mothers. Hence we analysed changes in maternal care and later on the emotional behaviour of male and female C57BL/6 mice reared by (i) their biological C57BL/6 mothers, (ii) C57BL/6 foster mothers and (iii) NMRI foster mothers in a behavioural test battery. In addition we assessed corticosterone levels as indicator for stress-physiological changes. Besides clear differences in maternal behaviour, our study indicates an altered emotional state (i.e. differences in anxiety and depressive-like features) in mice reared by different "categories" of mothers, which emphasizes the importance to embed such perinatal conditions in the evaluation of animal-deriving data.

Genetic mapping of escalated aggression in wild-derived mouse strain MSM/Ms: association with serotonin-related genes

The Japanese wild-derived mouse strain MSM/Ms (MSM) retains a wide range of traits related to behavioral wildness, including high levels of emotionality and avoidance of humans. In this study, we observed that MSM showed a markedly higher level of aggression than the standard laboratory strain C57BL/6J. Whereas almost all MSM males showed high frequencies of attack bites and pursuit in the resident-intruder test, only a few C57BL/6J males showed aggressive behaviors, with these behaviors observed at only a low frequency. Sexually mature MSM males in their home cages killed their littermates, or sometimes female pair-mates. To study the genetic and neurobiological mechanisms that underlie the escalated aggression observed in MSM mice, we analyzed reciprocal F1 crosses and five consomic strains of MSM (Chr 4, 13, 15, X and Y) against the background of C57BL/6J. We identified two chromosomes, Chr 4 and Chr 15, which were involved in the heightened aggression observed in MSM. These chromosomes had different effects on aggression: whereas MSM Chr 15 increased agitation and initiation of aggressive events, MSM Chr 4 induced a maladaptive level of aggressive behavior. Expression analysis of mRNAs of serotonin receptors, serotonin transporter and Tph2, an enzyme involved in serotonin synthesis in seven brain areas, indicated several differences among MSM, C57BL/6J, and their consomic strains. We found that Tph2 expression in the midbrain was increased in the Chr 4 consomic strain, as well as in MSM, and that there was a strong positive genetic correlation between aggressive behavior and Tph2 expression at the mRNA level. Therefore, it is possible that increased expression of the Tph2 gene is related to escalated aggression observed in MSM.