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SummaryThe mouse is often the model of choice for genetic analysis of neurological disorders, but the introduction of pathogenic mutations into a single inbred strain sometimes fails to yield phenotypes relevant to human disease. Interrogating genetically diverse panels of mice can identify better models of human sensitivity and resistance to candidate disease variants. We developed anin vitromethodology for modeling multiple stages of central nervous system development using a panel of genetically diverse mouse embryonic stem cell lines. Chemical knockdown of the neurodevelopmental geneDyrk1ademonstrated profound strain differences in the cellular response to the ablation of DYRK1A activity throughout developmentin vitro. Responsive strains showedin vitrodevelopmental defects consistent with those observedin vivoinDyrk1aknockout mice, and mirrored the phenotype seen in neural progenitors derived fromDYRK1Aknockout human pluripotent cells. Transcriptomic analysis of differentiated cells from sensitive and resistant cell strain backgrounds successfully identified key molecular pathways in neural development known to be associated withDyrk1ahaploinsufficiencyin vivo. Thus, comparative phenotypic analysis of differentiated cells from human and genetically diverse mouse pluripotent stem cells bearing disease mutations provides a facile route to identification of optimal mouse strains for precision disease modelingin vivo.

Exposing a male rat to an obesogenic high-fat diet (HFD) influences attractiveness to potential female mates, the subsequent interaction of female mates with infant offspring, and the development of stress-related behavioral and neural responses in offspring. To examine the stomach and fecal microbiome’s potential roles, fecal samples from 44 offspring and stomach samples from offspring and their fathers were collected and bacterial community composition was studied by 16 small subunit ribosomal RNA (16S rRNA) gene sequencing. Paternal diet (control, high-fat), maternal housing conditions (standard or semi-naturalistic housing), and maternal care (quality of nursing and other maternal behaviors) affected the within-subjects alpha-diversity of the offspring stomach and fecal microbiomes. We provide evidence from beta-diversity analyses that paternal diet and maternal behavior induced community-wide shifts to the adult offspring gut microbiome. Additionally, we show that paternal HFD significantly altered the adult offspring Firmicutes to Bacteroidetes ratio, an indicator of obesogenic potential in the gut microbiome. Additional machine-learning analyses indicated that microbial species driving these differences converged on Bifidobacterium pseudolongum. These results suggest that differences in early-life care induced by paternal diet and maternal care significantly influence the microbiota composition of offspring through the microbiota-gut-brain axis, having implications for adult stress reactivity.

Paternal preconception risk factors (e.g. stress, diet, drug use) correlate with metabolic dysfunction in offspring, which is often comorbid with depressive and anxiety-like phenotypes. Detection of these risk factors or deleterious phenotypes informs a female about prevailing ecological demands, in addition to potential adverse environment-induced phenotypes that may be disseminated to her offspring. We examined whether a F0 male rat's prior exposure to an obesogenic high-fat diet (HFD) influences a female's attraction towards a male, subsequent mother-infant interactions and the development of defensive (emotional) responses in the F1 offspring. Females displayed less interest in the HFD exposed F0 males relative to control diet-exposed F0 males. Dams that reared F1 offspring in larger, semi-naturalistic housing provided more licking and grooming and active arched-back-nursing behavior. However, some of these effects interacted with paternal experience. F0 HFD and maternal rearing environment revealed sex-dependent, between group differences in F1 offspring wean weight, juvenile social interactions and anxiety-like behavior in adolescence. Our results show for the first time in mammals that male exposure to HFD may contribute to stable behavioral variation among females in courtship, maternal care, even when the females are not directly exposed to a HFD, and anxiety-like behavior in F1 offspring. Furthermore, when offspring were exposed to a predatory threat, hypothalamic Crf gene regulation was influenced by early housing. These results, together with our previous findings, suggest that paternal experience and maternal rearing conditions can influence maternal behavior and development of defensive responses of offspring.

Pre and postnatal environments can have a profound impact on offspring development. This is especially true when considering the origin of neurological diseases, including epilepsy, a relatively common and chronic neurological condition, affecting 1–2% of the population. Previously, we have used maternal stress and an enhanced home cage (EHC) in an effort to identify potential factors in the early environment that may increase the risk for experiencing seizures. First, pregnant Long-Evans rats were exposed to a predator stress (PS). Then, at birth, litters were divided into standard cage (SC) and EHC groups until postnatal Day 14 (PD14) when a model of febrile convulsions was used to determine convulsion susceptibility of the various groups. Twenty-four hours later, pup brains were processed for immunohistochemical detection of corticotrophic releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus. Analysis of CRH immunoreactive (-ir) patterns revealed a buffering of CRH-ir in EHC reared offspring. Further, experiencing convulsions led to decreased CRH-ir. Our results support the concept that postnatal environmental influences affect neonatal programming and neurodevelopment of processes that could underlie seizure susceptibility, and that these effects can be modulated by EHC conditions. © 2015 Wiley Periodicals, Inc. Dev Psychobiol 57: 374–381, 2015.

The influence of early life experience and degree of parental-infant attachment on emotional development in children and adolescents has been comprehensively studied. Structural and mechanistic insight into the biological foundation and maintenance of mammalian defensive systems (metabolic, immune, nervous and behavioral) is slowly advancing through the emerging field of developmental molecular (epi)genetics. Initial evidence revealed that differential nurture early in life generates stable differences in offspring hypothalamic-pituitary-adrenal (HPA) regulation, in part, through chromatin remodeling and changes in DNA methylation of specific genes expressed in the brain, revealing physical, biochemical and molecular paths for the epidemiological concept of gene-environment interactions. Herein, a primary molecular mechanism underpinning the early developmental programming and lifelong maintenance of defensive (emotional) responses in the offspring is the alteration of chromatin domains of specific genomic regions from a condensed state (heterochromatin) to a transcriptionally accessible state (euchromatin). Conversely, DNA methylation promotes the formation of heterochromatin, which is essential for gene silencing, genomic integrity and chromosome segregation. Therefore, inter-individual differences in chromatin modifications and DNA methylation marks hold great potential for assessing the impact of both early life experience and effectiveness of intervention programs—from guided psychosocial strategies focused on changing behavior to pharmacological treatments that target chromatin remodeling and DNA methylation enzymes to dietary approaches that alter cellular pools of metabolic intermediates and methyl donors to affect nutrient bioavailability and metabolism. In this review article, we discuss the potential molecular mechanism(s) of gene regulation associated with chromatin modeling and programming of endocrine (e.g., HPA and metabolic or cardiovascular) and behavioral (e.g., fearfulness, vigilance) responses to stress, including alterations in DNA methylation and the role of DNA repair machinery. From parental history (e.g., drugs, housing, illness, nutrition, socialization) to maternal-offspring exchanges of nutrition, microbiota, antibodies and stimulation, the nature of nurture provides not only mechanistic insight into how experiences propagate from external to internal variables, but also identifies a composite therapeutic target, chromatin modeling, for gestational/prenatal stress, adolescent anxiety/depression and adult-onset neuropsychiatric disease.

As the incidence of obesity continues to grow, more children are exposed to less than optimal nutritional fetal environments. This has serious implications for the developing brain and the incidence stress-related disorders such as anxiety and depression, in addition to other neurodevelopmental disorders. Adult stress responding is programmed during developmental periods, resulting in individual variability in our responses to situations that threaten homeostasis. Under conditions of poor coping or excess exposure to stress, some individuals will be susceptible to developing stress-related mental health disorders. A poor prenatal metabolic/nutritional environment leads to altered programming of neural circuitry that supports adult stress responding, putting individuals at risk for stress-related disorders. More work is needed to manage obesity rates and to better understand the mechanisms underlying altered neural development as a result of parental diet.

Intranasal delivery of oxytocin (Oxt) has been identified as a potential therapeutic to target human conditions characterized by social deficits, yet the ability of this administrative route to deliver to the brain is unconfirmed. Oxt knockout (Oxt KO) and wildtype C57BL/6 J male mice received Oxt (12 μg total amount) either by nasal or intraperitoneal administration. Oxt concentrations were monitored for 2 h after administration in circulation via a jugular vein catheter and in the brain by two intracerebral microdialysis probes. Group sizes varied from 4 to 7 mice (n = 22 total). We document for the first time that Oxt applied to the nasal mucosa after nasal administration is delivered to the extracellular fluid in the brain. After nasal application, Oxt concentrations in circulation and in the extracellular fluid of the amygdala and, to an extent, the dorsal hippocampus, rose within the first 30 min and remained elevated for the subsequent hour. These findings were confirmed in an Oxt KO mouse line, establishing that the circulating and brain Oxt elevations derive from the administered dose. Interestingly, the pharmacokinetics of Oxt were slightly biased to the brain after nasal administration and to the periphery following intraperitoneal injection. No change in vasopressin levels was detected. These findings have stimulating implications for the interpretation of various behavioral and physiological effects described in animal and human studies after nasal administration of Oxt and provide the pharmacokinetics necessary to develop this drug delivery route for therapeutic purposes.

Pre and postnatal environments can have a profound impact on offspring development. This is especially true when considering the origin of neurological diseases, including epilepsy, a relatively common and chronic neurological condition, affecting 1-2% of the population. Previously, we have used maternal stress and an enhanced home cage (EHC) in an effort to identify potential factors in the early environment that may increase the risk for experiencing seizures. First, pregnant Long-Evans rats were exposed to a predator stress (PS). Then, at birth, litters were divided into standard cage (SC) and EHC groups until postnatal Day 14 (PD14) when a model of febrile convulsions was used to determine convulsion susceptibility of the various groups. Twenty-four hours later, pup brains were processed for immunohistochemical detection of corticotrophic releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus. Analysis of CRH immunoreactive (-ir) patterns revealed a buffering of CRH-ir in EHC reared offspring. Further, experiencing convulsions led to decreased CRH-ir. Our results support the concept that postnatal environmental influences affect neonatal programming and neurodevelopment of processes that could underlie seizure susceptibility, and that these effects can be modulated by EHC conditions.

Detecting past experiences with predators of a potential mate informs a female about prevailing ecological threats, in addition to stress-induced phenotypes that may be disseminated to offspring. We examined whether prior exposure of a male rat to a predator (cat) odor influences the attraction of a female toward a male, subsequent mother–infant interactions and the development of defensive (emotional) responses in the offspring. Females displayed less interest in males that had experienced predator odor. Mothers that reared young in larger, seminaturalistic housing provided more licking and grooming and active arched back-nursing behavior toward their offspring compared with dams housed in standard housing, although some effects interacted with paternal experience. Paternal predation risk and maternal rearing environment revealed sex-dependent differences in offspring wean weight, juvenile social interactions, and anxiety-like behavior in adolescence. Additionally, paternal predator experience and maternal housing independently affected variations incrfgene promoter acetylation andcrfgene expression in response to an acute stressor in offspring. Our results show for the first time in mammals that variation among males in their predator encounters may contribute to stable behavioral variation among females in preference for mates and maternal care, even when the females are not directly exposed to predator threat. Furthermore, when offspring were exposed to the same threat experienced by the father, hypothalamiccrfgene regulation was influenced by paternal olfactory experience and early housing. These results, together with our previous findings, suggest that paternal stress exposure and maternal rearing conditions can influence maternal behavior and the development of defensive responses in offspring.

Variation in response styles in the hypothalamic–pituitary–adrenal (HPA) axis are known to be predictors of short- and long-term health outcomes. The nature of HPA responses to stressors changes with developmental stage, and some components of the stress response exhibit long-term individual consistency (i.e., are trait-like) while others are transient or variable (i.e., state-like). Here we evaluated the response of marmoset monkeys (Callithrix geoffroyi) to a standardized social stressor (social separation and exposure to a novel environment) at three different stages of development: juvenile, subadult, and young adult. We monitored levels of urinary cortisol (CORT), and derived multiple measures of HPA activity: Baseline CORT, CORT reactivity, CORT Area Under the Curve (AUC), and CORT regulation. Juvenile marmosets exhibited the most dramatic stress response, had higher AUCs, and tended to show poorer regulation. While baseline CORT and CORT regulation were not consistent within an individual across age, CORT reactivity and measures of AUC were highly correlated across time; i.e., individuals with high stress reactivity and AUC as juveniles also had high measures as subadults and adults, and vice-versa. Marmoset co-twins did not exhibit similar patterns of stress reactivity. These data suggest that regardless of the source of variation in stress response styles in marmosets, individually-distinctive patterns are established by six months of age, and persist for at least a year throughout different phases of marmoset life history.