Natural variation in early parental care correlates with social behaviors in adolescent prairie voles (Microtus ochrogaster)

Multiple behavioral mechanisms shape development in a highly social cichlid fish

Early-life social experiences shape adult phenotype, yet the underlying behavioral mechanisms remain poorly understood. We manipulated early-life social experience in the highly social African cichlid fish Astatotilapia burtoni to investigate the effects on behavior and stress axis function in juveniles. Juveniles experienced different numbers of social partners in stable pairs (1 partner), stable groups (6 fish; 5 partners), and socialized pairs (a novel fish was exchanged every 5 days; 5 partners). Treatments also differed in group size (groups vs. pairs) and stability (stable vs. socialized). We then measured individual behavior and water-borne cortisol to identify effects of early-life experience. We found treatment differences in behavior across all assays: open field exploration, social cue investigation, dominant behavior, and subordinate behavior. Treatment did not affect cortisol. Principal components (PC) analysis revealed robust co-variation of behavior across contexts, including with cortisol, to form behavioral syndromes sensitive to early-life social experience. PC1 (25.1 %) differed by social partner number: juveniles with more partners (groups and socialized pairs) were more exploratory during the social cue investigation, spent less time in the territory, and were more interactive as dominants. PC5 (8.5 %) differed by stability: socialized pairs were more dominant, spent less time in and around the territory, were more socially investigative, and had lower cortisol than stable groups or pairs. Observations of the home tanks provided insights into the social experiences that may underlie these effects. These results contribute to our understanding of how early-life social experiences are accrued and exert strong, lasting effects on phenotype.

Chd8 haploinsufficiency impacts rearing experience in C57BL/6 mice

Mutations in CHD8 are one of the highest genetic risk factors for autism spectrum disorder. Studies in mice that investigate underlying mechanisms have shown Chd8 haploinsufficient mice display some trait disruptions that mimic clinical phenotypes, although inconsistencies have been reported in some traits across different models on the same strain background. One source of variation across studies may be the impact of Chd8 haploinsufficiency on maternal-offspring interactions. While differences in maternal care as a function of Chd8 genotype have not been studied directly, a previous study showed that pup survival was reduced when reared by Chd8 heterozygous dams compared with wild-type (WT) dams, suggesting altered maternal care as a function of Chd8 genotype. Through systematic observation of the C57BL/6 strain, we first determined the impact of Chd8 haploinsufficiency in the offspring on WT maternal care frequencies across preweaning development. We next determined the impact of maternal Chd8 haploinsufficiency on pup care. Compared with litters with all WT offspring, WT dams exhibited less frequent maternal behaviors toward litters consisting of offspring with mixed Chd8 genotypes, particularly during postnatal week 1. Dam Chd8 haploinsufficiency decreased litter survival and increased active maternal care also during postnatal week 1. Determining the impact of Chd8 haploinsufficiency on early life experiences provides an important foundation for interpreting offspring outcomes and determining mechanisms that underlie heterogeneous phenotypes.

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.

Oxytocin: A developmental journey

The neuropeptide hormone oxytocin is involved in many processes in our bodies, linking our social lives to our internal states. I started out my career studying primate families, an interest that expanded into the role of oxytocin in family-oriented behaviors such as pair bonding and parenting in prairie voles, humans, and other primates. Starting as a post-doc with Dr. C. Sue Carter, I also became interested in the role of oxytocin during development and the way that we manipulate oxytocin clinically. During that post-doc and then as a faculty member at the University of California, Davis, I have worked on a number of these questions.

Father's care uniquely influences male neurodevelopment

Mammalian infants depend on parental care for survival, with numerous consequences for their behavioral development. We investigated the epigenetic and neurodevelopmental mechanisms mediating the impact of early biparental care on development of alloparenting behavior, or caring for offspring that are not one's own. We find that receiving high parental care early in life leads to slower epigenetic aging of both sexes and widespread male-specific differential expression of genes related to synaptic transmission and autism in the nucleus accumbens. Examination of parental care composition indicates that high-care fathers promote a male-specific increase in excitatory synapses and increases in pup retrieval behavior as juveniles. Interestingly, females raised by high-care fathers have the opposite behavioral response and display fewer pup retrievals. These results support the concept that neurodevelopmental trajectories are programmed by different features of early-life parental care and reveal that male neurodevelopmental processes are uniquely sensitive to care by fathers.

The Neurobiology of Love and Pair Bonding from Human and Animal Perspectives

Love is a powerful emotional experience that is rooted in ancient neurobiological processes shared with other species that pair bond. Considerable insights have been gained into the neural mechanisms driving the evolutionary antecedents of love by studies in animal models of pair bonding, particularly in monogamous species such as prairie voles (Microtus ochrogaster). Here, we provide an overview of the roles of oxytocin, dopamine, and vasopressin in regulating neural circuits responsible for generating bonds in animals and humans alike. We begin with the evolutionary origins of bonding in mother-infant relationships and then examine the neurobiological underpinnings of each stage of bonding. Oxytocin and dopamine interact to link the neural representation of partner stimuli with the social reward of courtship and mating to create a nurturing bond between individuals. Vasopressin facilitates mate-guarding behaviors, potentially related to the human experience of jealousy. We further discuss the psychological and physiological stress following partner separation and their adaptive function, as well as evidence of the positive health outcomes associated with being pair-bonded based on both animal and human studies.

Oxytocin receptor is not required for social attachment in prairie voles

Prairie voles are among a small group of mammals that display long-term social attachment between mating partners. Many pharmacological studies show that signaling via the oxytocin receptor (Oxtr) is critical for the display of social monogamy in these animals. We used CRISPR mutagenesis to generate three different Oxtr-null mutant prairie vole lines. Oxtr mutants displayed social attachment such that males and females showed a behavioral preference for their mating partners over a stranger of the opposite sex, even when assayed using different experimental setups. Mothers lacking Oxtr delivered viable pups, and parents displayed care for their young and raised them to the weanling stage. Together, our studies unexpectedly reveal that social attachment, parturition, and parental behavior can occur in the absence of Oxtr signaling in prairie voles.

Behavioral trajectories of aging prairie voles (Microtus ochrogaster): Adapting behavior to social context wanes with advanced age

Several studies using mice have examined the effects of aging on cognitive tasks, as well as sensory and motor functions. However, few studies have examined the influence of aging on social behavior. Prairie voles (Microtus ochrogaster) are a socially monogamous and biparental rodent that live in small family groups and are now among the most popular rodent models for studies examining social behavior. Although the social behavioral trajectories of early-life development in prairie voles have been well-studied, how social behavior may change throughout adulthood remains unknown. Here we examined behavior in virgin male and female prairie voles in four different age groups: postnatal day (PND) 60–80, 140–160, 220–240, and 300–320. All animals underwent testing in a novel object task, a dominance test, a resident-intruder test, and several iterations of social approach and social interaction tests with varying types of social stimuli (i.e., novel same-sex conspecific, novel opposite-sex conspecific, familiar same-sex sibling/cagemate, small group of novel same-sex conspecifics). We found that age influenced neophobia and dominance, but not social approach behavior. Further, we found that young adult, but not older adult, prairie voles adapt prosocial and aggressive behavior relative to social context, and that selective aggression occurs in relation to age even in the absence of a pair bond. Our results suggest that prairie voles calibrate social phenotype in a context-dependent manner in young adulthood and stop adjusting behavior to social context in advanced age, demonstrating that social behavior is plastic not only throughout early development, but also well into adulthood. Together, this study provides insight into age-related changes in social behavior in prairie voles and shows that prairie voles may be a viable model for studying the cognitive and physiological benefits of social relationships and social engagement in advanced age.

Growing up in a crowd: social environment shapes the offspring's early exploratory phenotype in a colonial breeding species

In colonial breeding species, the number of adverse social interactions during early life typically varies with breeding density. Phenotypic plasticity can help deal with this social context, by allowing offspring to adjust their behaviour. Furthermore, offspring may not be unprepared since mothers can allocate resources to their embryos that may pre-adjust them to the post-hatching conditions. Thus, we hypothesize that lesser black-backed gull chicks raised in dense breeding areas, with greater exposure to intra-specific aggression, show higher levels of anxiety and lower levels of exploration compared to chicks in low-density areas, and that this is facilitated by prenatal effects. To test this, we cross-fostered clutches within and across pre-defined high- and low-breeding density areas. We measured chicks' anxiety and exploration activity in an open-field test that included a novel and a familiar object. We found that both pre- and post-natal social environment contributed nearly equally and shaped the offspring's exploratory behaviour, but not its anxiety, in an additive way. Post-natal effects could reflect a learned avoidance of intra-specific aggression, yet identifying the pathways of the prenatal effects will require further study.

Transcriptomic analysis of paternal behaviors in prairie voles

Background

The importance of fathers’ engagement in care and its critical role in the offspring’s cognitive and emotional development is now well established. Yet, little is known on the underlying neurobiology due to the lack of appropriate animal models. In the socially monogamous and bi-parental prairie vole (Microtus ochrogaster), while 60–80% of virgin males show spontaneous paternal behaviors (Paternal), others display pup-directed aggression (Attackers). Here we took advantage of this phenotypic dichotomy and used RNA-sequencing in three important brain areas to characterize gene expression associated with paternal behaviors of Paternal males and compare it to experienced Fathers and Mothers.

Results

While Paternal males displayed the same range and extent of paternal behaviors as experienced Fathers, we observed structure-specific transcriptomic differences between parental behaviors phenotypes. Using differential expression, gene set expression, as well as co-expression network analyses, we found that phenotypic differences between Paternal males and Attackers were mainly reflected by the lateral septum (LS), and to a lower extent, the nucleus accumbens (NAc), transcriptomes. In the medial preoptic area (MPOA), the profiles of gene expression mainly reflected differences between females and males regardless of their parental behaviors phenotype. Functional enrichment analyses of those gene sets associated with Paternal males or Attackers in the LS and the NAc revealed the involvement of processes related to the mitochondria, RNA translation, protein degradation processes, as well as epigenetic regulation of gene expression.

Conclusions

By leveraging the natural phenotypic differences in parental behaviors in virgin male prairie voles alongside fathers and mothers, we identified a marked structure- and phenotype-specific pattern of gene expression associated with spontaneous paternal behaviors independently from fatherhood and pair-bonding. The LS transcriptome related to the mitochondria, RNA translation, and protein degradation processes was thus highlighted as a primary candidate associated with the spontaneous display of paternal behaviors. Altogether, our observations further characterize the behavioral and transcriptomic signature of parental behaviors in the socially monogamous prairie vole and lay the groundwork to further our understanding of the molecular underpinnings of paternal behavior.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08912-y.

Multi-Level Effects Driving Cognitive and Behavioral Variability among Prairie Voles: Insights into Reproductive Decision-Making from Biological Levels of Organization

Behavioral phenotypes play an active role in maximizing fitness and shaping the evolutionary trajectory of species by offsetting the ecological and social environmental factors individuals experience. How these phenotypes evolve and how they are expressed is still a major question in ethology today. In recent years, an increased focus on the mechanisms that regulate the interactions between an individual and its environment has offered novel insights into the expression of alternative phenotypes. In this review, we explore the proximate mechanisms driving the expression of alternative reproductive phenotypes in the male prairie vole (Microtus ochrogaster) as one example of how the interaction of an individual's social context and internal milieu has the potential to alter behavior, cognition, and reproductive decision-making. Ultimately, integrating the physiological and psychological mechanisms of behavior advances understanding into how variation in behavior arises. We take a "levels of biological organization" approach, with prime focus placed on the level of the organism to discuss how cognitive processes emerge as traits, and how they can be studied as important mechanisms driving the expression of behavior.

FireMaster® 550 (FM 550) exposure during the perinatal period impacts partner preference behavior and nucleus accumbens core medium spiny neuron electrophysiology in adult male and female prairie voles, Microtus ochrogaster

One of the most widely used flame retardant (FR) mixtures in household products is Firemaster 550 (FM 550). FM 550 leaches from items such as foam-based furniture and infant products, resulting in contamination of the household environment and biota. Previous studies indicate sex-specific behavioral deficits in rodents and zebrafish in response to developmental FM 550 exposure. These deficits include impacts on social and attachment behaviors in a prosocial rodent: the prairie vole (Microtus ochrogaster). The prairie vole is a laboratory-acclimated rodent that exhibits spontaneous attachment behaviors including pair bonding. Here we extend previous work by addressing how developmental exposure to FM 550 impacts pair bonding strength via an extended-time partner preference test, as well as neuron electrophysiological properties in a region implicated in pair bond behavior, the nucleus accumbens (NAcc) core. Dams were exposed to vehicle or 1000 μg of FM 550 via subcutaneous injections throughout gestation, and female and male pups were directly exposed beginning the day after birth until weaning. Pair bond behavior of adult female and male offspring was assessed using a three hour-long partner preference test. Afterwards, acute brain slices of the NAcc core were produced and medium spiny neuron electrophysiological attributes recorded via whole cell patch-clamp. Behavioral impacts were sex-specific. Partner preference behavior was increased in exposed females but decreased in exposed males. Electrophysiological impacts were similar between sexes and specific to attributes related to input resistance. Input resistance was decreased in neurons recorded from both sexes exposed to FM 550 compared to vehicle. This study supports the hypothesis that developmental exposure to FM 550 impacts attachment behaviors and demonstrates a novel FM 550 effect on neural electrophysiology.

Transmission of paternal retrieval behavior from fathers to sons in a biparental rodent

Transmission of maternal behavior across generations occurs, but less is known about paternal behavior. In biparental species like the California mouse (Peromyscus californicus), paternal care contributes to the well-being of offspring with lasting consequences on the brain and behavior. Paternal huddling/grooming behavior can be passed on to future generations, but whether paternal retrieval, which removes young from potential harm, is transmitted independently is unclear. We manipulated paternal retrieval experience through pup displacement manipulations, then examined whether males exposed to higher levels of paternal retrieval in development altered their adult retrieval behavior with their offspring. Males exposed to heightened paternal retrievals, as compared to reduced retrievals, retrieved their offspring more often but huddled/groomed offspring less during undisturbed natural observations. No differences were observed following a pup displacement challenge. The high paternal retrieval group also exhibited more physical activity and stereotypy. Our results are consistent with the hypothesis that paternal retrieval levels are transmitted across generations and may function via mechanisms separate from huddling/grooming. One modifying factor may be anxiety because increased activity and stereotypy occurred in the high retrieval group. We speculate how the transmission of paternal retrievals may inform a protective parenting style.

Compositional variation in early-life parenting structures alters oxytocin and vasopressin 1a receptor development in prairie voles (Microtus ochrogaster)

Paternal absence can significantly alter bio-behavioural development in many biparental species. This effect has generally been demonstrated by comparing the development of offspring reared under biparental care with those reared by a single mother. However, studies employing this design conflate two significant modifications to early-life experience: removal of father-specific qualities and the general reduction of offspring-directed care. In the socially monogamous prairie vole (Microtus ochrogaster), the experience of paternal absence without substitution during development inhibits partner preference formation in adulthood, a hallmark of social monogamy, in females and males. Employing alloparents as substitutes for fathers, our previous work demonstrated that paternal absence affects pair-bond formation in female offspring via reduced quantity of care, although it affects pair-bond formation in male offspring by means of a missing paternal quality (or qualities). Here, we present evidence that paternal absence (with and without alloparental substitution) may alter the ontogeny of neural oxytocin receptor (OXTR) and/or vasopressin 1a receptor (AVPR1a) distribution in male and female prairie voles. Compared to biparentally reared controls (BPC), male offspring reared in mother only (MON) and maternal-plus-alloparental (MPA) conditions show lower densities of OXTR in the central amygdala; and MPA males show lower densities of OXTR in the caudate putamen and nucleus accumbens. Early-life experience was not associated with differences in AVPR1a density in males. However, MON and MPA females show greater densities of AVPR1a in the medial amygdala than BPC; and MPA females show greater densities of AVPR1a in the ventromedial nucleus of the hypothalamus. We also demonstrate with corticosterone concentrations that MON and MPA offspring are not differentially susceptible to a stressor (ie, social isolation) than BPC offspring. These findings suggest that paternal absence, although likely not a salient early-life stressor, has neuroendocrine consequences for offspring, some of which may affect partner preference formation.

Familiarity and Mate Preference Assessment with the Partner Preference Test

In contrast to traditional laboratory animals, prairie voles form socially monogamous partnerships in the wild and exhibit lasting social preferences for familiar individuals-both mates and same-sex peers-in the laboratory. Decades of research into the mechanisms supporting pair bonding behavior have made prairie voles an important model organism for the study of social relationships. The partner preference test is a laboratory test of familiarity preference that takes place over an extended interval (typically 3 hr), during which test subjects can directly interact with conspecifics and often engage in resting side-by-side contact (i.e., huddling). The use of this test has enabled study of the neural pathways and mechanisms involved in promoting or impairing relationship formation. The tendency to form partner preferences is also used as a behavioral indicator of the effects of early life experiences and environmental exposures. While this test was developed to assess the extent of social preference for mates in prairie voles, it has been adapted for use in other social contexts and in multiple other species. This article provides instructions for conducting the classic partner preference test, as well as variations including same-sex "peer" partner preference tests. The effects of several protocol variations are examined, including duration of cohousing, separation interval, use of tethers versus barriers, linear versus branched apparatus configuration, and duration of the test. The roles of social variables including sex of the focal individual, sex of conspecifics, reproductive state, and use of the test in other species are then considered. Finally, sample data are provided along with discussion of scoring and statistical analysis of partner preference tests. © 2021 Wiley Periodicals LLC. Basic Protocol: Partner preference test Support Protocol: Behavioral scoring.

Raised without a father: monoparental care effects over development, sexual behavior, sexual reward, and pair bonding in prairie voles

Around 5 % of mammals are socially monogamous and both parents provide care to the pups (biparental, BP). Prairie voles are socially monogamous rodents extensively used to understand the neurobiological basis of pair bond formation and the consequences that the absence of one parent has in the offspring. Pair bonding, characterized by selective affiliation with a sexual partner, is facilitated in prairie voles by mating for 6 h or cohabitation without mating for 24 h. It was previously shown that prairie voles raised by their mother alone (monoparental, MP) show delayed pair bond formation upon reaching adulthood. In this study we evaluated the effects of BP and MP care provided on the offspring's development, ability to detect olfactory cues, preference for sexually relevant odors, display of sexual behavior, as well as the rewarding effects of mating. We also measured dopamine and serotonin concentration in the nucleus accumbens (ventral striatum) and dorsal striatum after cohabitation and mating (CM) to determine if differences in these neurotransmitters could underlie the delay in pair bond formation in MP voles. Our data showed that MP voles received less licking/grooming than BP voles, but no developmental differences between groups were found. No differences were found in the detection and discrimination of olfactory cues or preference for sexually relevant odors, as all groups innately preferred opposite sex odors. No differences were found in the display of sexual behavior. However, CM induced reinforcing properties only in BP males, followed by a preference for their sexual partner in BP but not MP males. BP males showed an increase in dopamine turnover (DOPAC/DA and HVA/DA) in the nucleus accumbens in comparison to MP voles. No differences in dopamine, serotonin or their metabolites were found in the dorsal striatum. Our results indicate that MP voles that received less licking behavior exhibit a delay in pair bond formation possibly because the sexual interaction is not rewarding enough.

Developmental Fluoxetine Exposure Alters Behavior and Neuropeptide Receptors in the Prairie Vole

Developmental exposure to selective serotonin reuptake inhibitor (SSRI) increases the risk of Autism Spectrum Disorder (ASD), however, the underlying neurobiology of this effect is not fully understood. Here we used the socially monogamous prairie vole as a translational model of developmental SSRI exposure. Paired female prairie voles (n = 20) were treated with 5 mg/kg subcutaneous fluoxetine (FLX) or saline (SAL) daily from birth of the second litter until the day of birth of the 4th litter. This design created three cohorts of FLX exposure: postnatal exposure in litter 2, both prenatal and postnatal exposure in litter 3, and prenatal exposure in litter 4. Post-weaning, subjects underwent behavioral testing to detect changes in sociality, repetitive behavior, pair-bond formation, and anxiety-like behavior. Quantitative receptor autoradiography was performed for oxytocin, vasopressin 1a, and serotonin 1a receptor density in a subset of brains. We observed increased anxiety-like behavior and reduced sociality in developmentally FLX exposed adults. FLX exposure decreased oxytocin receptor binding in the nucleus accumbens core and central amygdala, and vasopressin 1a receptor binding in the medial amygdala. FLX exposure did not affect serotonin 1A receptor binding in any areas examined. Changes to oxytocin and vasopressin receptors may underlie the behavioral changes observed and have translational implications for the mechanism of the increased risk of ASD subsequent to prenatal SSRI exposure.

Sons benefit from paternal care in African striped mice

Mammalian paternal care is rare and is often linked to enhanced fitness under particular ecological conditions. The proximate consequences of paternal care on offspring are lacking, however. Here, we tested whether levels of paternal care predict the behavioural, cognitive and physiological development of sons in the naturally paternal African striped mouse (Rhabdomys pumilio). We focused on sons raised in two treatments: biparental (both parents) or uniparental (mother alone) families. We recorded levels of interactions between pups with both parents, and later assessed the behaviour, cognition and physiology of sons at three developmental stages: juvenile, sub-adult and adult (sexual maturity). Sons from biparental families showed (a) reduced anxiety as juveniles; (b) greater exploration and social interaction at different stages; (c) better cognition; and (d) reduced corticosterone concentrations than sons from uniparental families. In contrast, sons from uniparental families showed greater levels of paternal care, although prolactin concentrations did not differ between treatments. Paternal care in striped mice enhances fitness of males. Here, we also show that sons benefit psychologically and physiologically through interactions with their fathers. However, sons also trade-off such benefits against their own paternal care behaviour, suggesting that fathers influence the development of their son's phenotype in complex ways.

Prairie vole offspring only prefer mothers over fathers when mothers are a unique resource, yet fathers are the primary source of variation in parental care

In biparental species, each parent represents a semi-independent source of variable caregiving. The nature of care may differ between parents, and the type of care offspring seek is likely to change across development. We asked if caregiving differed between prairie vole (Microtus ochrogaster) mothers and fathers, and which parent pups prefer over development. We categorized parents as high- or low-contact based on daily recordings of grooming and brooding behavior. Pups were tested for their preferences between parents on postnatal days 10, 14, 18, 22, and 26. We expected individual parents would vary in the amount of care they gave, with pups preferring the parent that gives the most care and/or that most meets their needs at each developmental timepoint. Mothers spent more time in contact with pups than fathers. Mothers were consistent in the amount of care they gave, whereas fathers were variable caregivers. Pups never preferred fathers over mothers, but only demonstrated a preference for mothers before weaning. Lastly, the amount of contact did not influence pup preferences. Our data indicate that mothers are consistent sources of caregiving relative to fathers, and pups show little evidence of attachment to a specific parent beyond meeting its own immediate needs.

Effects of single parenthood on mothers' behavior, morphology, and endocrine function in the biparental California mouse

Motherhood is energetically costly for mammals and is associated with pronounced changes in mothers' physiology, morphology and behavior. In ~5% of mammals, fathers assist their mates with rearing offspring and can enhance offspring survival and development. Although these beneficial consequences of paternal care can be mediated by direct effects on offspring, they might also be mediated indirectly, through beneficial effects on mothers. We tested the hypothesis that fathers in the monogamous, biparental California mouse (Peromyscus californicus) reduce the burden of parental care on their mates, and therefore, that females rearing offspring with and without assistance from their mates will show differences in endocrinology, morphology and behavior, as well as in the survival and development of their pups. We found that pups' survival and development in the lab did not differ between those raised by a single mother and those reared by both mother and father. Single mothers spent more time in feeding behaviors than paired mothers. Both single and paired mothers had higher lean mass and/or lower fat mass and showed more anxiety-like behavior in open-field tests and tail-suspension tests, compared to non-breeding females. Single mothers had higher body-mass-corrected liver and heart masses, but lower ovarian and uterine masses, than paired mothers and/or non-breeding females. Mass of the gastrointestinal tract did not differ between single and paired mothers, but single mothers had heavier gastrointestinal tract compared to non-breeding females. Single motherhood also induced a flattened diel corticosterone rhythm and a blunted corticosterone response to stress, compared to non-breeding conditions. These findings suggest that the absence of a mate induces morphological and endocrine changes in mothers, which might result from increased energetic demands of pup care and could potentially help maintain normal survival and development of pups.

Rewritable fidelity: How repeated pairings and age influence subsequent pair-bond formation in male prairie voles

The prairie vole has proven a valuable animal model for the neurobiological study of social monogamy and pair bonding. Previous research has focused almost exclusively on virgin prairie voles forming pair-bonds for the first time - a paradigm with limited relevance to human social behavior. In the present study, we used stud males to assess the impact of repeated pair-bond formation and dissolution on the behaviors and neurobiology relevant to subsequent pair-bond formation. Stud males were tested for behavioral and neurobiological effects of repeated pair-bonding after the 1st, 5th, and 10th pairing. Aged breeder males that experienced minimal pair-bond dissolution were included to control for the effects of aging. Results showed that male prairie voles readily form new pair-bonds after repeated pair-bond dissolution. In terms of social monogamy, old age was associated with males spending less time in close social contact with unfamiliar females. There were no effects of age nor number of lifetime pairings on depressive-like behavior or paternal behavior toward pups. Within the brain, the patterns of oxytocin (OTR) and vasopressin type 1a (V1aR) receptors were largely unaffected, with the following exceptions: 1) males with only a single pairing had higher OTR densities in the paraventricular thalamus and bed nucleus of the stria terminalis; 2) there was an age-related increase in the density of OTR in the caudate putamen and an age-related decline in the density of V1aR in the cortical amygdala. The present findings have translational relevance to human social behavior in the context of aging and social experience.

Early Social Stress Promotes Inflammation and Disease Risk in Rhesus Monkeys

Early social stress has potent lifelong health effects. We examined the association of early stress in the attachment relationship (low maternal sensitivity, low MS), lower maternal social hierarchy rank, and greater frequency of group-level social conflict, with biomarkers of inflammatory stress response in plasma (IL-8, MCP-1 and CRP collected two hours after temporary separation from mothers and social groups) and risk for developing a common macaques disease outcome (infectious colitis) in 170 socially-housed rhesus monkeys. We controlled for gene-environment correlations by comparing cross-fostered subjects with infants reared by their biological mothers. Low MS predicted higher levels of pro-inflammatory cytokines and proteins at 3-4 months of age (F(3, 162) = 3.508, p = 0.002, partial eta2 = 0.061) and higher lifetime risk for developing colitis for up to twelve years of age (chi square = 5.919, p = 0.026). Lower maternal social rank (F (3, 162) = 3.789, p = 0.012, partial eta2 = 0.06) and higher rates of social conflict (F (3, 162) = 4.264, p = 0.006, partial eta2 = 0.074) each also predicted greater inflammation in infancy, but not lifetime colitis risk (both p > 0.05). The effects of low MS, lower social rank, and higher social conflict were significant in infants reared by biological mothers and cross-fostered infants, suggesting that our results did not arise from gene-environment correlations, but environmental stressors alone. We conclude that several types of early social stress confer risk for inflammation in infancy, but that stress in the mother-infant relationship may confer the longest-term risk for adverse health outcomes.

Acoustic prepulse inhibition in male and female prairie voles: Implications for models of neuropsychiatric illness

Sensory gating, the ability to suppress sensory information of irrelevant stimuli, is affected in several neuropsychiatric diseases, notably schizophrenia and autism. It is currently unclear how these deficits interact with other hallmark symptoms of these disorders, such as social withdrawal and difficulty with interpersonal relationships. The highly affiliative prairie vole (Microtus ochrogaster) may be an ideal model organism to study the neurobiology underlying social behavior. In this study, we assessed unimodal acoustic sensory gating in male and female prairie voles using the prepulse inhibition (PPI) paradigm, whereby a lower amplitude sound (prepulse) decreases the startle response to a high amplitude sound (pulse) compared to the high amplitude sound alone. Prairie voles showed evidence of PPI at all prepulse levels compared to pulse alone, with both males and females showing similar levels of inhibition. However, unlike what has been reported in other rodent species, prairie voles did not show a within-session decrease in startle response to the pulse alone, nor did they show a decrease in startle response to the pulse over multiple days, highlighting their inability to habituate to startling stimuli (short- and long-term). When contrasted with a cohort of male wildtype C57Bl/6J mice that underwent a comparable PPI protocol, individual voles showed significantly higher trial-by-trial variability as well as longer latency to startle than mice. The benefits and caveats to using prairie voles in future sensory gating experiments are discussed.

Maternal and paternal origin differentially affect prosocial behavior and neural mechanisms in prairie voles

This study tested the hypotheses that maternal and paternal effects differentially influence expression of their offspring's adult behavior and underlying neural mechanisms. We predicted that maternal influences would be greater than paternal influences on male offspring. We tested these hypotheses by cross-breeding two phenotypically-, behaviorally- and neuroanatomically-distinct populations of prairie voles (Microtus ochrogaster) from Illinois, which are highly prosocial, and Kansas, which are significantly less prosocial. Females from each population were crossed with males from the other population. F₁ crosses were tested as adults to determine the effect of parentage on the expression of prosocial behavior and aggression, using a same-sex dyadic encounter and a heterosexual partner preference test, and for the expression of oxytocin (OT) and arginine vasopressin (AVP) in the paraventricular nucleus of the hypothalamus (PVN). As predicted, all significant differences in males, behavioral, OT and AVP immunoreactivity, were associated exclusively with maternal influences. There was a significant effect of treatment in the OT immunoreactivity of females. The effect of treatment in females' OT was associated with an interaction of population and sex, while same-sex social interactions differences were associated with population. Finally, in females, paternity influenced heterosexual bonds, with females with Illinois sires forming a partner preference. The results indicate that maternal influences dominate in male offspring, suggesting a parent-of-origin effect, while paternal effects are limited to selected prosocial behavioral expression in daughters.

Consequences of prenatal exposure to valproic acid in the socially monogamous prairie voles

Environmental risk factors contribute to autism spectrum disorders (ASD) etiology. In particular, prenatal exposure to the highly teratogenic anticonvulsant valproic acid (VPA) significantly increases ASD prevalence. Although significant discoveries on the embryopathology of VPA have been reported, its effects on the ability to form enduring social attachment—characteristic of ASD but uncommonly displayed by rats and mice—remains unknown. We aimed to examine the effects of prenatal VPA exposure in the social, monogamous prairie voles (Microtus ochrogaster). Compared to prenatal vehicle-exposed controls, prenatal VPA-exposed prairie voles had lower body weight throughout postnatal development, engaged in fewer social affiliative behaviors in a familial context, exhibited less social interactions with novel conspecifics, and showed enhanced anxiety-like behavior. Along these behavioral deficits, prenatal VPA exposure downregulated prefrontal cortex vasopressin receptor (V1aR) and methyl CpG-binding protein 2 (MeCP2) mRNA expression, but did not alter spine density in adults. Remarkably, adult social bonding behaviors, such as partner preference formation and selective aggression, were not disrupted by prenatal VPA exposure. Collectively, these studies suggest that, in this animal model, VPA alters only certain behavioral domains such as sex-naive anxiety and affiliative behaviors, but does not alter other domains such as social bonding with opposite sex individuals.

Early nurture epigenetically tunes the oxytocin receptor

Mammalian sociality is regulated in part by the neuropeptide oxytocin. In prairie voles, subtle variation in early life experience changes oxytocin receptor-mediated social behaviors. We report that low levels of early care in voles leads to de novo DNA methylation at specific regulatory sites in the oxytocin receptor gene (Oxtr), impacting gene expression and protein distribution in the nucleus accumbens. DNA methylation state of the blood predicts expression in the brain indicating the utility of the blood as a biomarker for the transcription state of the brain. These experience-sensitive CpG sites are conserved in humans, are related to gene expression in the brain, and have been associated with psychiatric disorders and individual differences in neural response to social stimuli. These results identify a mechanism by which early care regulates later displays of typical prairie vole social behavior and suggest the potential for nurture driven epigenetic tuning of OXTR in humans.

Prenatal stress enhances postnatal plasticity: The role of microbiota

Separate fields of inquiry indicate (a) that prenatal stress is associated with heightened behavioral and physiological reactivity and (b) that these postnatal phenotypes are themselves associated with increased susceptibility to both positive and negative environmental influences. Collectively, this work supports Pluess and Belsky's (Psychopathology, 2011, 23, 29) claim that prenatal stress fosters, promotes or "programs" postnatal developmental plasticity. Herein, we review animal and human evidence consistent with this hypothesis before advancing the novel idea that infant intestinal microbiota may be one candidate mechanism for instantiating developmental plasticity as a result of prenatal stress. We then review research indicating that prenatal stress predicts differences in infant intestinal microbiota; that infant intestinal microbiota is associated with behavioral and physiological reactivity phenotypes; and, thus, that prenatal stress may influence infant intestinal microbiota in a way that results in heightened physiological and behavioral reactivity and, thereby, postnatal developmental plasticity. Finally, we offer ideas for testing this claim and consider implications for intervention and use of probiotics during early infancy.

The Monogamy Paradox: What Do Love and Sex Have to Do With It?

Genetic monogamy is rare-at least at the level of a species-and monogamy can exist in the absence of sexual fidelity. Rather than focusing on mating exclusivity, it has become common to use the term "social monogamy" to describe a cluster of social features, including the capacity for selective and lasting social bonds, central to what humans call "love." Socially monogamous mammals often exhibit selective aggression toward strangers and form extended families. These features of social monogamy in mammals are supported by patterns of hormonal function originating in the neurobiology of maternity, including oxytocin, as well as a more primitive vasopressin pathway. Another key feature of social monogamy is reduced sexual dimorphism. Processes associated with sexual differentiation offer clues to the mysteries surrounding the evolution of monogamy. Although there is consistency in the necessary ingredients, it is likely that there is no single recipe for social monogamy. As reviewed here, genes for steroids and peptides and their receptors are variable and are subject to epigenetic regulation across the lifespan permitting individual, gender and species variations and providing substrates for evolution. Reduced sensitivity to gonadal androgens, and a concurrent increased reliance on vasopressin (for selective defense) and oxytocin (for selective affiliation) may have offered pathways to the emergence of social monogamy.

Prenatal programming of postnatal plasticity revisited-And extended

Two sets of evidence reviewed herein, one indicating that prenatal stress is associated with elevated behavioral and physiological dysregulation and the other that such phenotypic functioning is itself associated with heightened susceptibility to positive and negative environmental influences postnatally, raises the intriguing hypothesis first advanced by Pluess and Belsky (2011) that prenatal stress fosters, promotes, or "programs" postnatal developmental plasticity. Here we review further evidence consistent with this proposition, including new experimental research systematically manipulating both prenatal stress and postnatal rearing. Collectively this work would seem to explain why prenatal stress has so consistently been linked to problematic development: stresses encountered prenatally are likely to continue postnatally, thereby adversely affecting the development of children programmed (by prenatal stress) to be especially susceptible to environmental effects. Less investigated are the potential benefits prenatal stress may promote, due to increased plasticity, when the postnatal environment proves to be favorable. Future directions of research pertaining to potential mechanisms instantiating postnatal plasticity and moderators of such prenatal-programming effects are outlined.

Fatherhood alters gene expression within the MPOA

Female parenting is obligate in mammals, but fathering behavior among mammals is rare. Only 3-5% of mammalian species exhibit biparental care, including humans, and mechanisms of fathering behavior remain sparsely studied. However, in species where it does exist, paternal care is often crucial to the survivorship of offspring. The present study is the first to identify new gene targets linked to the experience of fathering behavior in a biparental species using RNA sequencing. In order to determine the pattern of gene expression within the medial preoptic area that is specifically associated with fathering behavior, we identified genes in male prairie voles (Microtus ochrogaster) that experienced one of three social conditions: virgin males, pair bonded males, and males with fathering experience. A list of genes exhibiting different expression patterns in each comparison (i.e. Virgin vs Paired, Virgin vs Fathers, and Paired vs Fathers) was evaluated using the gene ontology enrichment analysis, and Kyoto Encyclopedia of Genes and Genomes pathways analysis to reveal metabolic pathways associated with specific genes. Using these tools, we generated a filtered list of genes that exhibited altered patterns of expression in voles with different amounts of social experience. Finally, we used NanoString to quantify differences in the expression of these selected genes. These genes are involved in a variety of processes, with enrichment in genes associated with immune function, metabolism, synaptic plasticity, and the remodeling of dendritic spines. The identification of these genes and processes will lead to novel insights into the biological basis of fathering behavior.

Social touch during development: Long-term effects on brain and behavior

In this paper, our goal is to explore what is known about the role of social touch during development. We first address the neural substrates of social touch and the role of tactile experience in neural development. We discuss natural variation in early exposure to social touch, followed by a discussion on experimental manipulations of social touch during development and "natural experiments", such as early institutionalization. We then consider the role of other developmental and experiential variables that predict social touch in adults. Throughout, we propose and consider new theoretical models of the role of social touch during development on later behavior and neurobiology.

The Combinatorial Creature: Cortical Phenotypes within and across Lifetimes

The neocortex is one of the most distinctive structures of the mammalian brain, yet also one of the most varied in terms of both size and organization. Multiple processes have contributed to this variability, including evolutionary mechanisms (i.e., alterations in gene sequence) that alter the size, organization, and connections of neocortex, and activity dependent mechanisms that can also modify these same features. Thus, changes to the neocortex can occur over different time-scales, including within a single generation. This combination of genetic and activity dependent mechanisms that create a given cortical phenotype allows the mammalian neocortex to rapidly and flexibly adjust to different body and environmental contexts, and in humans permits culture to impact brain construction.

Prenatal stress and enhanced developmental plasticity

Two separate lines of inquiry indicate (a) that prenatal stress is associated with heightened behavioral and physiological reactivity, and (b) that these postnatal phenotypes are associated with increased susceptibility to both positive and negative developmental experiences and environmental exposures. This research considered together raises the intriguing hypothesis first advanced by Pluess and Belsky (Dev Psychopathol 23:29-38, 2011) that prenatal-stress fosters, promotes or "programs" postnatal developmental plasticity. In this paper, we review further evidence consistent with this proposition, including a novel animal study which experimentally manipulated both prenatal stress and postnatal rearing. Directions for future work focused on mechanisms mediating the plasticity-inducing effects of prenatal stress and the moderators of such effects are outlined.

Intranasal oxytocin reduces weight gain in diet-induced obese prairie voles

Oxytocin (OT) elicits weight loss in diet-induced obese (DIO) rodents, nonhuman primates and humans by reducing food intake and increasing energy expenditure. In addition to being important in the regulation of energy balance, OT is involved in social behaviors including parent-infant bonds, friendships, and pair bonds. However, the impact of social context on susceptibility to diet-induced obesity (DIO) and feeding behavior (including food sharing) has not been investigated in a rodent model that forms strong social bonds (i.e. prairie vole). Our goals were to determine in Prairie voles (Microtus ochrogaster) whether i) social context impacts susceptibility to DIO and ii) chronic intranasal OT reverses DIO. Voles were housed in divided cages with holes in the divider and paired with a same-sex animal with either the same food [high fat diet (HFD)/HFD, [low fat diet (LFD; chow)/chow], or the opposite food (HFD/chow or chow/HFD) for 19 weeks. HFD-fed voles pair-housed with voles maintained on the HFD demonstrated increased weight relative to pair-housed voles that were both maintained on chow. The study was repeated to determine the impact of social context on DIO susceptibility and body composition when animals are maintained on purified sugar-sweetened HFD and LFD to enhance palatability. As before, we found that voles demonstrated higher weight gain on the HFD/HFD housing paradigm, in part, through increased energy intake and the weight gain was a consequence of an increase in fat mass. However, HFD-fed animals housed with LFD-fed animals (and vice versa) showed intermediate patterns of weight gain and evidence of food sharing. Of translational importance is the finding that chronic intranasal OT appeared to reduce weight gain in DIO voles through a decrease in fat mass with no reduction in lean body mass. These effects were associated with transient reductions in food intake and increased food sharing. These findings identify a role of social context in the pathogenesis of DIO and indicate that chronic intranasal OT treatment reduces weight gain and body fat mass in DIO prairie voles, in part, by reducing food intake.

Developmental trajectories and influences of environmental complexity on oxytocin receptor and vasopressin 1A receptor expression in male and female prairie voles

Nonapeptide receptors, like oxytocin receptor (OTR) and vasopressin 1a receptor (V1aR), modulate a variety of functions across taxa, and mediate phenotypic variation within and between species. Despite the popularity of studying nonapeptides in adults, developmental perspectives on properties of OTR and V1aR expression are lacking. Study of prairie voles (Microtus ochrogaster) has facilitated an understanding of mechanisms of social behavior and provides great potential to inform how early life experiences alter phenotype. We provide the first comprehensive profiling of OTR and V1aR in male and female prairie voles across postnatal development and into adulthood. Differences in receptor densities across the forebrain were region- and sex-specific. Postnatal changes in receptor expression fell into four themes: (a) constant over time, (b) increasing with age, (c) decreasing with age, or (d) peaking during late pre-weaning (postnatal day 15-21). We also examined the influence of post-weaning social and spatial enrichment (i.e., environmental complexity) on OTR and V1aR. Environmental complexity appeared to promote expression of OTR in males and females, and reduced expression of V1aR across several brain regions in males. Our results show that nonapeptide receptor profiles are plastic over development and suggest that different patterns of expression might represent functional differences in sensitivity to nonapeptide activation over a period when social environments are dynamic. Our results on environmental complexity suggest that nonapeptide sensitivity responds flexibly to different environmental contexts during development. Understanding the developmental trajectories of nonapeptide receptors provides a better understanding of the dynamic nature of social behavior and the underlying mechanisms.

Longitudinal Trajectories and Inter-parental Dynamics of Prairie Vole Biparental Care

For altricial mammalian species, early life social bonds are constructed principally between offspring and their mothers, and the mother-offspring relationship sets the trajectory for offspring bio-behavioral development. In the rare subset of monogamous and biparental species, offspring experience an expanded social network which includes a father. Accordingly, in biparental species fathers also have the potential to influence trajectories of offspring development. Previous semi-natural and laboratory study of one monogamous and biparental species, the prairie vole (Microtus ochrogaster), has given insight into the role that mothers and fathers play in shaping behavioral phenotypes of offspring. Of particular interest is the influence of biparental care in the development of monogamous behavior in offspring. Here, we first briefly review that influence. We then present novel research which describes how parental investment in prairie voles changes across sequential litters of pups, and the extent to which it is coordinated between mothers and fathers. We use approximately 6 years of archival data on prairie vole parenting to investigate trajectories and inter-parent dynamics in prairie vole parenting. We use a series of latent growth models to assess the stability of parental investment across the first 4 l. Our findings suggest that prairie voles display sexually dimorphic patterns of change in parental behavior: mothers' investment declines linearly whereas fathers' pattern of change is characterized by initial decline between litters 1 and 2 with subsequent increase from litters 2 to 4. Our findings also support a conclusion that prairie vole paternal care may be better characterized as compensatory-that is, fathers may compensate for decline in maternal investment. Opposing trends in investment between mothers and fathers ultimately imply stability in offspring investment across sequential litters. These findings, combined with previous studies, generate a hypothesis that paternal compensation could play an important role in maintaining the development of monogamous behavioral phenotypes in individual offspring and across cohorts of those offspring. Understanding longitudinal and inter-individual dynamics of complex social behaviors is critical for the informed investigation of both proximate and ultimate mechanisms that may subserve these behaviors.

Mechanistic substrates of a life history transition in male prairie voles: Developmental plasticity in affiliation and aggression corresponds to nonapeptide neuronal function

Although prairie vole (Microtus ochrogaster) social behavior is well-characterized in adults, surprisingly little is known about the development of social behavior in voles. Further, the overwhelming majority of studies in prairie voles examine social behavior in a reproductive context. Here, we examine developmental plasticity in affiliation and aggression and their underlying neural correlates. Using sexually naïve males, we characterized interactions with an age-matched, novel, same-sex conspecific in four different age groups that span pre-weaning to adulthood. We found that prosocial behavior decreased and aggression increased as males matured. Additionally, pre-weaning males were more prosocial than nonsocial, whereas post-weaning males were more nonsocial than prosocial. We also examined nonapeptide neural activity in response to a novel conspecific in brain regions important for promoting sociality and aggression using the immediate early gene cFos. Assessment of developmental changes in neural activity showed that vasopressin neurons in the medial bed nucleus of the stria terminalis exhibit functional plasticity, providing a potential functional mechanism that contributes to this change in sociality as prairie voles mature. This behavioral shift corresponds to the transition from a period of allopatric cohabitation with siblings to a period of time when voles disperse and presumably attempt to establish and defend territories. Taken together our data provide a putative mechanism by which brain and behavior prepare for the opportunity to pairbond (characterized by selective affiliation with a partner and aggression toward unfamiliar conspecifics) by undergoing changes away from general affiliation and toward selective aggression, accounting for this important life history event.

Prenatal Stress as a Risk-and an Opportunity-Factor

Two separate lines of research indicate (a) that prenatal stress is associated with heightened behavioral and physiological reactivity and (b) that these postnatal phenotypes are associated with increased susceptibility to both positive and negative developmental experiences. Therefore, prenatal stress may increase sensitivity to the rearing environment. We tested this hypothesis by manipulating prenatal stress and rearing-environment quality, using a cross-fostering paradigm, in prairie voles. Results showed that prenatally stressed voles, as adults, displayed the highest behavioral and physiological reactivity when cross-fostered to low-contact (i.e., low-quality) rearing but the lowest behavioral and physiological reactivity when cross-fostered to high-contact (i.e., high-quality) rearing; non-prenatally stressed voles showed no effect of rearing condition. Additionally, while neither prenatal stress nor rearing condition affected oxytocin receptor binding, prenatally stressed voles cross-fostered to high-contact rearing showed the highest vasopressin-1a receptor binding in the amygdala. Results indicate that prenatal stress induces greater environmental sensitivity, making it both a risk and an opportunity factor.

Resting state brain networks in the prairie vole

Resting state functional magnetic resonance imaging (rsfMRI) has shown the hierarchical organization of the human brain into large-scale complex networks, referred as resting state networks. This technique has turned into a promising translational research tool after the finding of similar resting state networks in non-human primates, rodents and other animal models of great value for neuroscience. Here, we demonstrate and characterize the presence of resting states networks in Microtus ochrogaster, the prairie vole, an extraordinary animal model to study complex human-like social behavior, with potential implications for the research of normal social development, addiction and neuropsychiatric disorders. Independent component analysis of rsfMRI data from isoflurane-anestethized prairie voles resulted in cortical and subcortical networks, including primary motor and sensory networks, but also included putative salience and default mode networks. We further discuss how future research could help to close the gap between the properties of the large scale functional organization and the underlying neurobiology of several aspects of social cognition. These results contribute to the evidence of preserved resting state brain networks across species and provide the foundations to explore the use of rsfMRI in the prairie vole for basic and translational research.

Nucleus accumbens core medium spiny neuron electrophysiological properties and partner preference behavior in the adult male prairie vole, Microtus ochrogaster

Medium spiny neurons (MSNs) in the nucleus accumbens have long been implicated in the neurobiological mechanisms that underlie numerous social and motivated behaviors as studied in rodents such as rats. Recently, the prairie vole has emerged as an important model animal for studying social behaviors, particularly regarding monogamy because of its ability to form pair bonds. However, to our knowledge, no study has assessed intrinsic vole MSN electrophysiological properties or tested how these properties vary with the strength of the pair bond between partnered voles. Here we performed whole cell patch-clamp recordings of MSNs in acute brain slices of the nucleus accumbens core (NAc) of adult male voles exhibiting strong and weak preferences for their respective partnered females. We first document vole MSN electrophysiological properties and provide comparison to rat MSNs. Vole MSNs demonstrated many canonical electrophysiological attributes shared across species but exhibited notable differences in excitability compared with rat MSNs. Second, we assessed male vole partner preference behavior and tested whether MSN electrophysiological properties varied with partner preference strength. Male vole partner preference showed extensive variability. We found that decreases in miniature excitatory postsynaptic current amplitude and the slope of the evoked action potential firing rate to depolarizing current injection weakly associated with increased preference for the partnered female. This suggests that excitatory synaptic strength and neuronal excitability may be decreased in MSNs in males exhibiting stronger preference for a partnered female. Overall, these data provide extensive documentation of MSN electrophysiological characteristics and their relationship to social behavior in the prairie vole. NEW & NOTEWORTHY This research represents the first assessment of prairie vole nucleus accumbens core medium spiny neuron intrinsic electrophysiological properties and probes the relationship between cellular excitability and social behavior.

Lost connections: Oxytocin and the neural, physiological, and behavioral consequences of disrupted relationships

In humans and rodent animal models, the brain oxytocin system is paramount for facilitating social bonds, from the formation and consequences of early-life parent-infant bonds to adult pair bond relationships. In social species, oxytocin also mediates the positive effects of healthy social bonds on the partners' well-being. However, new evidence suggests that the negative consequences of early neglect or partner loss may be mediated by disruptions in the oxytocin system as well. With a focus on oxytocin and its receptor, we review studies from humans and animal models, i.e. mainly from the biparental, socially monogamous prairie vole (Microtus ochrogaster), on the beneficial effects of positive social relationships both between offspring and parents and in adult partners. The abundance of social bonds and benevolent social relationships, in general, are associated with protective effects against psycho- and physiopathology not only in the developing infant, but also during adulthood. Furthermore, we discuss the negative effects on well-being, emotionality and behavior, when these bonds are diminished in quality or are disrupted, for example through parental neglect of the young or the loss of the partner in adulthood. Strikingly, in prairie voles, oxytocinergic signaling plays an important developmental role in the ability to form bonds later in life in the face of early-life neglect, while disruption of oxytocin signaling following partner loss results in the emergence of depressive-like behavior and physiology. This review demonstrates the translational value of animal models for investigating the oxytocinergic mechanisms that underlie the detrimental effects of developmental parental neglect and pair bond disruption, encouraging future translationally relevant studies on this topic that is so central to our daily lives.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Influence of Maternal Care on Behavioural Development of Domestic Dogs (Canis Familiaris) Living in a Home Environment

Simple Summary

Maternal care in dogs and its impact on the behavioural development of puppies has become the subject of growing research interest. In order to determine the effects of maternal care on the behaviour of family dog puppies, maternal care during the first three weeks after birth was observed in 12 litters of puppies reared in a home environment (72 puppies). The behavioural responses of the puppies were assessed at two months of age, in an arena and an isolation test. In both tests, the amount of maternal care was found to be positively associated with some stress behaviours and, in the arena test, also with the puppies’ interest in an unfamiliar person who was present during the test. These behaviours are similar to those observed during the separation of other young mammals from an attachment figure with which they have a high quality of bond. Amount of maternal care was also found to be negatively associated with exploration and play. The difference in results between the present study and our previous study involving laboratory dogs reared in relative social isolation suggests that the developmental trajectory of puppies is influenced by a combination of maternal behaviour and social and physical environmental enrichment.

Abstract

Maternal care has been shown to affect the development of the brain, behaviour, social skills and emotional systems of the young of many mammalian species including dogs. The aim of the present study was to determine the effects of maternal care on the behavioural responses of family dog puppies towards environmental and social stimuli. In order to do this, maternal care (licking puppy’s ano-genital area, licking the puppy, nursing and mother-puppy contact) during the first three weeks after birth was assessed in 12 litters of domestic dog puppies reared in home environments (total = 72 puppies). The behavioural responses of puppies were assessed in an arena and an isolation test, which were performed when the puppies were two-month old. Data were analysed using principal components analysis and projection to latent structures regression. A systematic relationship was found between maternal care and behaviour in both tests. In the arena test, maternal care was found to be positively associated with approach to the stranger, attention oriented to the stranger, time spent near the enclosure, yawning, whining and yelping (R²Y = 0.613, p = 8.2 × 10⁻⁹). Amount of maternal care was negatively associated with the number of squares crossed and the time spent individually playing with the rope. In the isolation test, the amount of maternal care was positively associated with standing posture, paw lifting, and howling, and it was negatively associated with yawning, lying down and nose licking (R²Y = 0.507, p = 0.000626). These results suggest that the amount of maternal care received during early life influences the pattern of behavioural responses and coping strategies of puppies at two-months of age. On the basis of these findings it could be speculated that early maternal care contributes to adaption to the environment in which family puppies are developing, with particular regard to social relationships with people.

Paternal Care in Biparental Rodents: Intra- and Inter-individual Variation

Parental care by fathers, although rare among mmmals, can be essential for the survival and normal development of offspring in biparental species. A growing body of research on biparental rodents has identified several developmental and experiential influences on paternal responsiveness. Some of these factors, such as pubertal maturation, interactions with pups, and cues from a pregnant mate, contribute to pronounced changes in paternal responsiveness across the course of the lifetime in individual males. Others, particularly intrauterine position during gestation and parental care received during postnatal development, can have long-term effects on paternal behavior and contribute to stable differences among individuals within a species. Focusing on five well-studied, biparental rodent species, we review the developmental and experiential factors that have been shown to influence paternal responsiveness, and consider their roles in generating both intra- and inter-individual variation. We also review hormones and neuropeptides that have been shown to modulate paternal care and discuss their potential contributions to behavioral differences within and between males. Finally, we discuss the possibility that vasopressinergic and possibly oxytocinergic signaling within the brain, modulated by gonadal steroid hormones, may represent the "final common pathway" mediating effects of developmental and experiential variables on intra- and inter-individual variation in paternal care.

Parenting in Animals

The study of parenting in animals has allowed us to come to a better understanding of the neural and physiological mechanisms that underlie mammalian parental behavior. The long-term effects of parenting (and parental abuse or neglect) on offspring, and the neurobiological changes that underlie those changes, have also been best studied in animal models. Our greater experimental control and ability to directly manipulate neural and hormonal systems, as well as the environment of the subjects, will ensure that animal models remain important in the study of parenting; while in the future, the great variety of parental caregiving systems displayed by animals should be more thoroughly explored. Most importantly, cross-talk between animal and human subjects research should be promoted.

The neurobiological causes and effects of alloparenting

Alloparenting, defined as care provided by individuals other than parents, is a universal behavior among humans that has shaped our evolutionary history and remains important in contemporary society. Dysfunctions in alloparenting can have serious and sometimes fatal consequences for vulnerable infants and children. In spite of the importance of alloparenting, they still have much to learn regarding the underlying neurobiological systems governing its expression. Here, they review how a lack of alloparental behavior among traditional laboratory species has led to a blind spot in our understanding of this critical facet of human social behavior and the relevant neurobiology. Based on what is known, they draw from model systems ranging from voles to meerkats to primates to describe a conserved set of neuroendocrine mechanisms supporting the expression of alloparental care. In this review we describe the neurobiological and behavioral prerequisites, ontogeny, and consequences of alloparental care. Lastly, they identified several outstanding topics in the area of alloparental care that deserve further research efforts to better advance human health and wellbeing. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 214-232, 2017.

Intergenerational transmission of sociality: the role of parents in shaping social behavior in monogamous and non-monogamous species

Social bonds are necessary for many mammals to survive and reproduce successfully. These bonds (i.e. pair-bonds, friendships, filial bonds) are characterized by different periods of development, longevity and strength. Socially monogamous species display certain behaviors not seen in many other mammals, such as adult pair-bonding and male parenting. In our studies of prairie voles (Microtus ochrogaster) and titi monkeys (Callicebus cupreus), we have examined the neurohormonal basis of these bonds. Here, we discuss the evidence from voles that aspects of adolescent and adult social behavior are shaped by early experience, including changes to sensory systems and connections, neuropeptide systems such as oxytocin and vasopressin, and alterations in stress responses. We will compare this with what is known about these processes during development and adulthood in other mammalian species, both monogamous and non-monogamous, and how our current knowledge in voles can be used to understand the development of and variation in social bonds. Humans are endlessly fascinated by the variety of social relationships and family types displayed by animal species, including our own. Social relationships can be characterized by directionality (either uni- or bi-directional), longevity, developmental epoch (infant, juvenile or adult) and strength. Research on the neurobiology of social bonds in animals has focused primarily on 'socially monogamous' species, because of their long-term, strong adult affiliative bonds. In this Review, we attempt to understand how the ability and propensity to form these bonds (or lack thereof), as well as the display of social behaviors more generally, are transmitted both genomically and non-genomically via variation in parenting in monogamous and non-monogamous species.

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.