High fat diet consumption and social instability stress impair stress adaptation and maternal care in C57Bl/6 dams

Poor maternal diet and psychosocial stress represent two environmental factors that can significantly impact maternal health during pregnancy. While various mouse models have been developed to study the relationship between maternal and offspring health and behaviour, few incorporate multiple sources of stress that mirror the complexity of human experiences. Maternal high-fat diet (HF) models in rodents are well-established, whereas use of psychosocial stress interventions in female mice are still emerging. The social instability stress (SIS) paradigm, serves as a chronic and unpredictable form of social stress. To evaluate the combined effects of a poor maternal diet and intermittent social stress on maternal health and behaviour, we developed a novel maternal stress model using adult female C57Bl/6 mice. We observed that all HF+ mice demonstrated rapid weight gain, elevated fasting blood glucose levels and impaired glucose tolerance independent of the presence (+) or absence (-) of SIS. Behavioural testing output revealed anxiety-like behaviours remained similar across all groups prior to pregnancy. However, integrated anxiety z-scores revealed a mixed anxious profile amongst HF+/SIS+ females prior to pregnancy. HF+/SIS+ females also did not show reduced plasma ACTH and corticosterone levels that were observed in our other HF+ and HF- stress groups after SIS exposure. Further, HF+/SIS+ females demonstrated significant postpartum maternal neglect, resulting in fewer numbers of live offspring. These findings suggest that prolonged maternal HF diet consumption, coupled with previous exposure to SIS, places a significant burden on the maternal stress response system, resulting in reduced parental investment and negative postpartum behaviour towards offspring.

Parenting in a changing environment: A long-term study of prolactin, parental effort and reproductive success in common eiders

Parental care is regulated by multiple endocrine mechanisms. Among these hormones, prolactin (PRL) is involved in the expression of parental behaviors. Despite the consensus that PRL mediates variation in parental effort with age and body condition, its role in the adjustment of parental effort to fluctuating environmental conditions, including changing predation pressure, still awaits further investigation. To shed light on this knowledge gap, we relied on a long-term monitoring of female common eiders Somateria mollissima (n = 1277 breeding attempts, 2012-2022) incubating under fluctuating predation risk to investigate the link between baseline PRL levels and female minimum age, body condition, clutch size, environmental parameters (predation pressure, climate, nest microhabitat) and hatching success. We predicted that PRL would be higher in older females, those in better condition or incubating larger clutches. We also predicted that females would reduce parental effort when nesting under challenging environmental conditions (high predation pressure or poor climatic conditions), translated into reduced baseline PRL levels. We also explored how variation in PRL levels, female characteristics and environmental parameters were related to hatching success. Following our predictions, PRL levels were positively associated with body condition and female age (before showing a senescent decline in the oldest breeders). However, we did not observe any population-level or individual-level reduction in PRL levels in response to increasing predation pressure. Population-level baseline PRL levels instead increased over the study period, coincident with rising predation threat, but also increasing female body condition and age. While we did not provide evidence for a direct association between baseline PRL levels and predation risk, our results support the idea that elevated baseline PRL levels promote hatching success under internal constraints (in young, inexperienced, breeders or those incubating a large clutch) or constraining environmental conditions (during years of high predation pressure or poor climatic and foraging conditions). Finally, the low repeatability of baseline PRL levels and high interannual variability highlight considerable within-individual flexibility in baseline PRL levels. Further research should explore flexibility in parental effort to changing environmental conditions, focusing on both baseline and stress-induced PRL levels.

Infants' cortisol reactivity and infant-mother cortisol synchrony in urban Chinese families: The role of maternal control strategy

Maternal control strategy refers to a mother's practices used to impel, inhibit, guide, or shape their children's behaviors during mother-child interaction. The present study examined control strategies used by Chinese urban mothers and how they associated with infants' cortisol trajectory and infant-mother cortisol synchrony during a separation task. Participants were 115 infant-mother dyads. Maternal control strategy was assessed during mother-infant free-play when the infants were 6 months (T1) and 1 year (T2) old. Salivary cortisol samples were collected from both infants and mothers during a stress-inducing task at T2. The results indicated that mothers most frequently adopted the moderate power control strategy, at both T1 and T2. T1 maternal low control strategy significantly predicted infants' cortisol response curve, namely infants of mothers who predominantly adopted a low power control strategy had a more dynamic reactivity and recovery in their cortisol response to the separation task. Positive cortisol synchrony was observed between mothers and infants during the separation stress condition. In addition, T2 maternal high power control strategy accounted for inter-individual variations in infant-mother cortisol synchrony, such that mothers who predominantly adopted a high power control strategy exhibited a heightened level of cortisol synchrony with their infants. Our findings suggest that targeted training in maternal control strategies could help mothers calibrate their infants' adrenocortical regulation.

Role of sexually dimorphic oxytocin receptor-expressing neurons in the anteroventral periventricular nucleus on maternal behavior

Oxytocin is a neuropeptide produced by magnocellular neurosecretory neurons located primarily in the supraoptic nucleus and paraventricular nucleus of the hypothalamus. The long axons of these neurons project to the neurohypophysis where oxytocin is released into the general circulation in response to the physiological demands. Oxytocin plays critical roles in female reproductive physiology, specifically in uterine contraction during labor and milk ejection while nursing. Oxytocin is also called "the love hormone" due to its modulatory roles in prosocial behaviors, including social recognition, maternal behavior, and pair bonding. Oxytocin influences behaviors by binding to oxytocin receptors (OXTR) located in various parts of the brain. Previously, we discovered a group of estrogen-dependent OXTR neurons that is exclusively present in the anteroventral periventricular nucleus (AVPV) of females but not of males. The female-specific expression of OXTR in the AVPV is a rare case of neurochemically-demonstrated, all-or-none sexual dimorphism in the brain. In this review, the cellular characterization and functional significance of the sexually dimorphic OXTR neurons in the AVPV as well as the clinical implications of the research will be discussed.

Pubertal maternal presence reduces anxiety and increases adult neurogenesis in Kunming mice offspring

Puberty is a critical period of emotional development and neuroplasticity. However, most studies have focused on early development, with limited research on puberty, particularly the parental presence. In this study, four groups were established, and pubertal maternal presence (PMP) was assessed until postnatal days 21 (PD21), 28 (PD28), 35 (PD35), and 42 (PD42), respectively. The social interaction and anxiety behaviors, as well as the expression of oxytocin (OT) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON), and the number of new generated neurons and the expression of estrogen receptor alpha (ERα) in the dentate gyrus (DG) were assessed. The results suggest that there is a lot of physical contact between the mother and offspring from 21 to 42 days of age, which reduces anxiety in both female and male offspring in adulthood; for example, the PMP increased the amount of time mice spent in the center area in the open field experiment and in the bright area in the light-dark box experiment. PMP increased OT expression in the PVN and SON and the number of newly generated neurons in the DG. However, there was a sexual difference in ERα, with ERα increasing in females but decreasing in males. In conclusion, PMP reduces the anxiety of offspring in adulthood, increases OT in the PVN and SON, and adult neurogenesis; ERα in the DG may be involved in this process.

Neurobiological mechanisms underlying oxytocin-mediated parental behavior in rodents

Parental behavior is essential for mammalian offspring to survive. Because of this significance, elucidating the neurobiological mechanisms that facilitate parental behavior has received strong interest. Decades of studies utilizing pharmacology and molecular biology have revealed that in addition to its facilitatory effects on parturition and lactation, oxytocin (OT) promotes the expression of parental behavior in rodents. Recent studies have also described the modulation of sensory processing by OT and the interaction of the OT system with other brain regions associated with parental behavior. However, the precise neurobiological mechanisms underlying the facilitation of caregiving behaviors by OT remain unclear. In this Review, I summarize the findings from rats and mice with a view toward integrating past and recent progress. I then review recent advances in the understanding of the molecular, cellular, and circuit mechanisms of OT-mediated parental behavior. Based on these observations, I propose a hypothetical model that would explain the mechanisms underlying OT-mediated parental behavior. Finally, I conclude by discussing some major remaining questions and propose potential future research directions.

Study of endocrine disruptor effects in AVP and OT mediated behavioral and reproductive processes in female rat models

Environmental exposures may have endocrine disruptor (ED) effects, e.g., a role for halogenated hydrocarbon chlorobenzenes in increasing vasopressin (AVP), oxytocin (OT) secretion and, in association, anxiety and aggression in male rats has been shown. Our aim is to investigate whether 1,2,4-trichlorobenzenehexachlorobenzene= 1:1 (mClB) treatment of female rats also shows ED effects and reproductive biology differences, and whether AVP may have a mediator role in this? Female Wistar rats were treated (0.1; 1.0; 10.0 μg/bwkg/day) with mClB (by gastrictube) and then 30; 60; 90 days after treatment anxiety (open field test) and aggressive (resident intruder test) behaviors AVP, OT concentrations from blood plasma samples were detected by radioimmunoassay on 30; 60; 90 days. Treated female rats were mated with untreated males. Mating success, number of newborn and maternal aggression on the neonates were monitored. Results showed that AVP, OT levels; and anxiety, aggressive behaviors; and mothers' aggression towards their offspring increased significantly in relation to the duration and the dose of mClB treatment. But mating propensity and number of offspring decreased. Patterns of AVP, OT release and anxiety, aggression behaviors, and reproductive-related behaviors were correlated. Consistent with the literature, our studies confirmed the role of AVP and OT in different behavioral effects.

Postnatal rearing environment alters pup cues for caregiver-offspring interactions

Maternal behavior experienced in early life provides essential scaffolding to infant psychobiology with life-long effects on neurobiological and behavioral outcomes. However, infants are not passive recipients of caregiving. Evidence in rodents suggests that pups actively contribute to dam-pup interactions by soliciting maternal care with auditory, tactile, and hormonal cues. The limited bedding and nesting material (LBN) rearing manipulation induces changes in maternal care that have been attributed to maternal stress caused by the low-resource environment. The goal of the current study was to determine whether LBN also alters pup cues for maternal behavior, with implications for the mechanism of LBN-induced effects. Rat dams and pups were randomly assigned to LBN or Control rearing conditions on postnatal day (P) 0-6 and pups were fostered to the same or different condition on P6-13. LBN increased pup-directed maternal behaviors measured through 24 h monitoring using machine learning based automated analysis. LBN altered several pup cues known to affect maternal behavior including reducing pup core body temperature, reducing body weight, and altering pup vocalizations on P6 and P12. P6-13 LBN-exposed pups had elevated serum testosterone, which positively correlated with maternal licking and grooming. LBN reduced pup movement between nest attendance onset and the start of nursing, which was negatively related to dam nursing latency and contributed to longer nursing latency in LBN dams. P0-6 pup exposure to LBN also led to longer nest attendance bouts and shorter licking and grooming bouts on P7 and P9, suggesting lasting effects of LBN on pups. These data demonstrate that LBN changes pup behavioral and hormonal signals consistent with eliciting more maternal care, contributing to augmented pup-directed behaviors. This bidirectional interplay may be a critical mechanism involved in the lasting effects of early life environments.

Influences of quality of maternal care and environmental enrichment on associative memory function in rats with early life lead exposure

INTRODUCTION

Children in low socioeconomic status (SES) communities are at higher risk of exposure to lead (Pb) and potentially more severe adverse outcomes from Pb exposures. While the factors encompassing SES are complex, low SES households often have less enriching home environments and parent-child interactions. This study investigated the extent to which environmental/behavioral factors (quality of maternal care and richness of the postnatal environment) may modify adverse effects from Pb exposure.

METHODS

Long-Evans female rats were randomly assigned to Control (no Pb), Early Postnatal (EPN: birth through weaning), or Perinatal (PERI: 14 days pre-mating through weaning) Pb exposure groups. From postnatal days (PNDs) 2-9, maternal care behaviors were observed, and dams were classified as low or high maternal care based on amounts of licking/grooming and arched back nursing. At weaning, pups were randomly assigned to enriched or non-enriched environments. At PND 55, animals began trace fear conditioning and associative memory was tested on days 1, 2, and 10 postconditioning.

RESULTS

Control offspring showed no significant effects of maternal care or enrichment on task performance. Females with EPN-Pb exposure and males with PERI-Pb exposure living in the non-enriched environment and having an LMC mother had significant memory impairments at days 2 and 10 that were not observed in comparably housed animals with HMC mothers. Enriched animals had no deficits, regardless of maternal care status.

CONCLUSION

These results show the potential for modulatory influences of maternal care and housing environment on protecting against or reversing at least one aspect of Pb-induced cognitive/behavioral dysfunction.

Infant sensorimotor decoupling from 4 to 9 months of age: Individual differences and contingencies with maternal actions

Triadic interactions, wherein infants coordinate attention between caregivers and objects of shared focus, are believed to facilitate infant learning, and emerge around 9-12 months of age (Carpenter et al., 1998). Sensorimotor decoupling, wherein infants look at one percept while manipulating another, or use each hand for different actions, was hypothesized (de Barbaro et al., 2016) to contribute to triadic skills by allowing infants to smoothly shift attention between objects and social partners. We explored the development of Hand-Hand (H-H) and Gaze-Hand (G-H) decoupling in 38 infants at 4, 6, and 9 months. We also tested contingencies between maternal behaviors and infant decoupling: i.e., whether decoupling events followed maternal object-directed actions. Both overall and contingent infant decoupling increased from 4 to 9 months. Decoupling rates (both G-H and H-H) predicted variance in infants' fine and gross motor scores. Contingent G-H decoupling at 6 months predicted BSID-III communication scores at 18 months. Thus the development of infant sensorimotor skills, including decoupling, allows infants to smoothly shift attention and participate in triadic interactions.

Prolactin modulates changes in parental care behaviour in response to perceived paternity in bluegill sunfish (Lepomis macrochirus)

Prolactin is a hormone conserved across all vertebrates and is renowned for its role in reproduction and parental care. Previous studies on prolactin in fish have primarily relied on administration of mammalian prolactin and have suggested that increases in prolactin lead to greater parental care. However, the influence of endogenous prolactin on fish parental care remains unknown. Here, we measure circulating concentrations of endogenous prolactin during parental care in a fish and link these concentrations to parental care behaviour. We provide evidence that male bluegill sunfish with higher circulating concentrations of prolactin provide more parental care to their offspring. Furthermore, we show that nesting males with experimentally reduced perceived paternity have lower circulating prolactin concentrations and perform fewer parental behaviours, facilitating an adaptive investment in offspring in response to paternity cues. Our findings not only confirm the role of endogenous prolactin in modulating parental care behaviour in a fish but also provide a mechanism underlying the adaptive changes in parental care made in response to perceived paternity.

Facing infant cuteness: How nurturing care motivation and oxytocin system gene methylation are associated with responses to baby schema features

Baby schema features are a specific set of physical features-including chubby cheeks, large, low-set eyes, and a large, round head-that have evolutionary adaptive value in their ability to trigger nurturant care. In this study among nulliparous women (N = 81; M age = 23.60, SD = 0.44), we examined how sensitivity to these baby schema features differs based on individual variations in nurturant care motivation and oxytocin system gene methylation. We integrated subjective ratings with measures of facial expressions and electroencephalography (EEG) in response to infant faces that were manipulated to contain more or less pronounced baby schema features. Linear mixed effects analyses demonstrated that infants with more pronounced baby schema features were rated as cuter and participants indicated greater motivation to take care of them. Furthermore, infants with more pronounced baby schema features elicited stronger smiling responses and enhanced P2 and LPP amplitudes compared to infants with less pronounced baby schema features. Importantly, individual differences significantly predicted baby schema effects. Specifically, women with low OXTR methylation and high nurturance motivation showed enhanced differentiation in automatic neurophysiological responses to infants with high and low levels of baby schema features. These findings highlight the importance of considering individual differences in continued research to further understand the complexities of sensitivity to child cues, including facial features, which will improve our understanding of the intricate neurobiological system that forms the basis of caregiving behavior.

Examining the implications of contextual stress and maternal sensitivity for infants' cortisol responses to the still face paradigm

Infants' hypothalamic-pituitary-adrenocortical (HPA) axis responses to acute stressors are theorized to be shaped by parents' sensitive responsiveness to infants' cues. The strength and direction of the association between maternal sensitivity and infants' HPA responses may depend on the context in which maternal sensitivity is observed and on broader environmental sources of stress and support. In this preregistered study, we used data from 105 mothers and their 7-month-old infants to examine whether two empirically identified forms of contextual stress-poor maternal psychosocial wellbeing and family socioeconomic hardship-moderate the association between maternal sensitivity and infants' cortisol responses to the Still-Face Paradigm (SFP). Results indicated that maternal sensitivity during the free play and family socioeconomic hardship interacted to predict infants' cortisol responses to the SFP. Specifically, maternal sensitivity during this non-distressing interaction was negatively associated with cortisol responses only among infants whose mothers were experiencing relatively high socioeconomic hardship. Exploratory analyses revealed that poor maternal psychosocial wellbeing was positively associated with overall infant cortisol production during the SFP. Altogether, these findings suggest that experiences within early parent-infant attachment relationships and sources of contextual stress work together to shape infant HPA axis activity.

Perinatal protein malnutrition alters maternal behavior and leads to maladaptive stress response, neurodevelopmental delay and disruption on DNA methylation machinery in female mice offspring

Deficiencies in maternal nutrition have long-term consequences affecting brain development of the progeny and its behavior. In the present work, female mice were exposed to a normal-protein or a low-protein diet during gestation and lactation. We analyzed behavioral and molecular consequences of malnutrition in dams and how it affects female offspring at weaning. We have observed that a low-protein diet during pregnancy and lactation leads to anxiety-like behavior and anhedonia in dams. Protein malnutrition during the perinatal period delays physical and neurological development of female pups. Glucocorticoid levels increased in the plasma of malnourished female offspring but not in dams when compared to the control group. Interestingly, the expression of glucocorticoid receptor (GR) was reduced in hippocampus and amygdala on both malnourished dams and female pups. In addition, malnourished pups exhibited a significant increase in the expression of Dnmt3b, Gadd45b, and Fkbp5 and a reduction in Bdnf VI variant mRNA in hippocampus. In contrast, a reduction on Dnmt3b has been observed on the amygdala of weaned mice. No changes have been observed on global methylation levels (5-methylcytosine) in hippocampal genomic DNA neither in dams nor female offspring. In conclusion, deregulated behaviors observed in malnourished dams might be mediated by a low expression of GR in brain regions associated with emotive behaviors. Additionally, low-protein diet differentially deregulates the expression of genes involved in DNA methylation/demethylation machinery in female offspring but not in dams, providing an insight into regional- and age-specific mechanisms due to protein malnutrition.

Social transmission of inflammation in mice

The ability to detect and respond to sickness in others promotes survival. Here we show that mouse dams respond to immune challenged pups by mirroring their inflammatory response. Dams with pups subjected to immune challenge displayed a marked induction of inflammatory mediators in both the brain and the periphery, accompanied by an increase in maternal behaviors and corticosterone levels. This social transmission of inflammation did not require physical contact, and it contributed to the stress hormone response in the dams. In adult dyads, interaction with an immune challenged cagemate did not elicit robust inflammatory signaling but induced an increased responsiveness to a subsequent immune challenge. The identification of social transmission of inflammation, or inflammatory responsiveness, may open new avenues for research on social behavior, just like the description of similar phenomena such as observational fear and transmitted pain has done.

Paternal absence and increased caregiving independently and interactively shape the development of male prairie voles at subadult and adult life stages

The influence of maternal caregiving is a powerful force on offspring development. The absence of a father during early life in biparental species also has profound implications for offspring development, although it is far less studied than maternal influences. Moreover, we have limited understanding of the interactive forces that maternal and paternal caregiving impart on offspring. We investigated if behaviorally upregulating maternal care compensates for paternal absence on prairie vole (Microtus ochrogaster) pup development. We used an established handling manipulation to increase levels of caregiving in father-absent and biparental families, and later measured male offspring behavioral outcomes at sub-adulthood and adulthood. Male offspring raised without fathers were more prosocial (or possibly less socially anxious) than those raised biparentally. Defensive behavior and responses to contextual novelty were also influenced by the absence of fathers, but only in adulthood. Offensive aggression and movement in the open field test changed as a function of life-stage but not parental exposure. Notably, adult pair bonding was not impacted by our manipulations. Boosting parental care produced males that moved more in the open field test. Parental handling also increased oxytocin immunoreactive cells within the supraoptic nucleus of the hypothalamus (SON), and in the paraventricular nucleus (PVN) of biparentally-reared males. We found no differences in vasopressinergic cell groups. We conclude that male prairie voles are contextually sensitive to the absence of fathers and caregiving intensity. Our study highlights the importance of considering the ways early experiences synergistically shape offspring behavioral and neural phenotypes across the lifespan.

Limited Bedding and Nesting as a Model for Early-Life Adversity in Mice

Early-life adversity (ELA), such as abuse, neglect, lack of resources, and an unpredictable home environment, is a known risk factor for developing neuropsychiatric disorders such as depression. Animal models for ELA have been used to study the impact of chronic stress on brain development, and typically rely on manipulating the quality and/or quantity of maternal care, as this is the major source of early-life experiences in mammals, including humans. Here, a detailed protocol for employing the Limited Bedding and Nesting (LBN) model in mice is provided. This model mimics a low-resource environment, which provokes fragmented and unpredictable patterns of maternal care during a critical developmental window (postnatal days 2-9) by limiting the amount of nesting materials given to the dam to build a nest for her pups and separating the mice from the bedding via a mesh platform in the cage. Representative data are provided to illustrate the changes in maternal behavior, as well as the diminished pup weights and long-term changes in basal corticosterone levels, that result from the LBN model. As adults, offspring reared in the LBN environment have been shown to exhibit an aberrant stress response, cognitive deficits, and anhedonia-like behavior. Therefore, this model is an important tool to define how the maturation of stress-sensitive brain circuits is altered by ELA and results in long-term behavioral changes that confer vulnerability to mental disorders.

Neuropeptides affecting social behavior in mammals: Oxytocin

Oxytocin (OXT), a neuropeptide consisting of only nine amino acids, is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Although OXT is best known for its role in lactation and parturition, recent research has shown that it also has a significant impact on social behaviors in mammals. However, a comprehensive review of this topic is still lacking. In this paper, we systematically reviewed the effects of OXT on social behavior in mammals. These effects of OXT from the perspective of five key behavioral dimensions were summarized: parental behavior, anxiety, aggression, attachment, and empathy. To date, researchers have agreed that OXT plays a positive regulatory role in a wide range of social behaviors, but there have been controversially reported results. In this review, we have provided a detailed panorama of the role of OXT in social behavior and, for the first time, delved into the underlying regulatory mechanisms, which may help better understand the multifaceted role of OXT. Levels of OXT in previous human studies were also summarized to provide insights for diagnosis of mental disorders.

Maternal probiotic Lactocaseibacillus rhamnosus HN001 treatment alters postpartum anxiety, cortical monoamines, and the gut microbiome

Peripartum mood and anxiety disorders (PMADs) affect 15-20% of peripartum women and are well known to disrupt infant caregiving. A recent study in humans reported that anxiety and depressive symptoms were alleviated by peripartum treatment with the probiotic, Lactocaseibacillus rhamnosus HN001. The current study determined the effects of chronic Lactocaseibacillus rhamnosus HN001 (HN001) treatment on postpartum affective and caregiving behaviors in a laboratory rodent model. Female rats were given probiotic overnight in their drinking water, or untreated water, from the first day of pregnancy through postpartum day 10. To determine whether the HN001 effects were influenced by a background of stress, half the females underwent chronic variable pregnancy stress and the other half remained undisturbed. The results revealed that, even without pregnancy stress, HN001 reduced postpartum anxiety-related behavior, increased variability in behavioral fragmentation when dams interacted with pups, increased time away from pups, and decreased prefrontal cortex norepinephrine (NE), dopamine (DA) and serotonin (5-HT). Probiotic plus stress consistently reduced the latency to float in the forced swim test, increased DA and 5-HT turnovers in the prefrontal cortex, increased hippocampal NE, and reduced hypothalamic DA. Fecal microbe alpha and beta diversities were lower postpartum than prepartum, which was prevented by the probiotic treatment and/or stress. Across the entire sample lower postpartum anxiety behavior was associated with lower fecal Bacteroides dorei. This study reveals novel information about how L. rhamnosus HN001 influences postpartum behavior and microbiota-gut-brain physiology in female laboratory rats, with implications for probiotic supplement use by pregnant and postpartum women.

Prolactin is associated with proximity to incubating partner rather than parental care in black-headed gulls

The peptide hormone prolactin plays an important role in the expression of parental care behaviours across bird and mammal taxa. While a great deal is known about how plasma prolactin concentrations vary across the reproductive cycle, the few studies that investigate how prolactin relates to individual-level variation in parental care have reported mixed results. We argue that, since parental care is also affected by social interactions and environmental constraints, prolactin may better reflect behaviours that are indirectly related to parenting than the absolute level of care that is eventually expressed. In this study, we tested for associations between plasma prolactin and the expression of both parental care and proximity to the partner in incubating black-headed gulls, Chroicocephalus ridibundus. Baseline prolactin levels increased with calendar date but were unrelated to incubation behaviours. However, parents who showed a weaker decrease in prolactin to an acute stressor spent more time in close proximity to their incubating partner while not on the nest themselves, suggesting that individual variation in stress-induced prolactin changes reflect differences in parents' tendency to be closely associated with their partner and the joint nesting attempt. Baseline and stress-induced levels of the stress hormone corticosterone were unrelated to both prolactin levels and parental behaviours, suggesting that this hormone is not a strong moderator of parental care in black-headed gulls. One potential explanation for the link between prolactin dynamics and partner proximity is that prolactin reflects parental motivation to provide parental care or retain contact with the breeding partner, but further work is needed to directly test this hypothesis.

Effect of high fat diet on maternal behavior, brain-derived neurotrophic factor and neural stem cell proliferation in mice expressing human placental lactogen during pregnancy

Maternal obesity is a serious health concern because it increases risks of neurological disorders, including anxiety and peripartum depression. In mice, a high fat diet (HFD) in pregnancy can negatively affect placental structure and function as well as maternal behavior reflected by impaired nest building and pup-retrieval. In humans, maternal obesity in pregnancy is associated with reduced placental lactogen (PL) gene expression, which has been linked to a higher risk of depression. PL acting predominantly through the prolactin receptor maintains energy homeostasis and is a marker of placenta villous trophoblast differentiation during pregnancy. Impaired neurogenesis and low serum levels of brain-derived neurotrophic factor (BDNF) have also been implicated in depression. Augmented neurogenesis in brain during pregnancy was reported in the subventricular zone (SVZ) of mice at gestation day 7 and linked to increased prolactin receptor signaling. Here, we used transgenic CD-1 mice that express human (h) PL during pregnancy to investigate whether the negative effects of diet on maternal behavior are mitigated in these (CD-1[hGH/PL]) mice. Specifically, we examined the effect of a HFD on nest building prepartum and pup retrieval postpartum, as well as on brain BDNF levels and neurogenesis. In contrast to wild-type CD-1[WT]mice, CD-1[hGH/PL] mice displayed significantly less anxiety-like behavior, and showed no impairment in prepartum nest building or postpartum pup-retrieval when fed a HFD. Furthermore, the HFD decreased prepartum and increased postpartum BDNF levels in CD-1[WT] but not CD-1[hGH/PL] mice. Finally, neurogenesis in the SVZ as well as phosphorylated mitogen-activated protein kinase, indicative of lactogenic signaling, appeared unaffected by pregnancy and diet at gestation day 7 in CD-1[hGH/PL] mice. These observations indicate that CD-1[hGH/PL] mice are resistant to the negative effects of HFD reported for CD-1[WT] mice, including effects on maternal behaviors and BDNF levels, and potentially, neurogenesis. This difference probably reflects a direct or indirect effect of the products of the hGH/PL transgene.

Computer vision analysis of mother-infant interaction identified efficient pup retrieval in V1b receptor knockout mice

Close contact between lactating rodent mothers and their infants is essential for effective nursing. Whether the mother's effort to retrieve the infants to their nest requires the vasopressin-signaling via V1b receptor has not been fully defined. To address this question, V1b receptor knockout (V1bKO) and control mice were analyzed in pup retrieval test. Because an exploring mother in a new test cage randomly accessed to multiple infants in changing backgrounds over time, a computer vision-based deep learning analysis was applied to continuously calculate the distances between the mother and the infants as a parameter of their relationship. In an open-field, a virgin female V1bKO mice entered fewer times into the center area and moved shorter distances than wild-type (WT). While this behavioral pattern persisted in V1bKO mother, the pup retrieval test demonstrated that total distances between a V1bKO mother and infants came closer in a shorter time than with a WT mother. Moreover, in the medial preoptic area, parts of the V1b receptor transcripts were detected in galanin- and c-fos-positive neurons following maternal stimulation by infants. This research highlights the effectiveness of deep learning analysis in evaluating the mother-infant relationship and the critical role of V1b receptor in pup retrieval during the early lactation phase.

Prenatal restraint stress affects early neurobehavioral response and oxidative stress in mice pups

Prenatal stress (PS), in both humans and animals, presents a potential risk to the mother and her fetus throughout gestation. PS is always associated with physiological changes that alter embryonic development and predispose the individual to lifelong health problems, including susceptibility to mental illness. This study aims to identify the harmful effects of prenatal restraint stress (PRS), commonly employed to induce stress painlessly and without any lasting debilitation during gestation. This stress is applied to pregnant Swiss albino mice from E7.5 to delivery for three hours daily. Our results show that PS affects dams' weight gain during the gestational period; moreover, the PS dams prefer passive nursing, exhibit a lower percentage of licking and grooming, and impair other maternal behaviors, including nesting and pup retrieval. Concerning the offspring, this stress induces neurobehavioral impairments, including a significant increase in the time of recovery of the young stressed pups in the surface righting reflex, the latency to avoid the cliff in the cliff avoidance test, longer latencies to accomplish the task in negative geotaxis, and a lower score in swimming development. These alterations were accompanied by increased Malondialdehyde activity (MDA) at PND17 and 21 and downregulation of AchE activity in the whole brain of pups on postnatal days 7 and 9. These findings demonstrated that PS causes deleterious neurodevelopmental impairments that can alter various behaviors later in life.

Maternal care leads to the evolution of long, slow lives

Animals, and mammals in particular, vary widely in their "pace of life," with some species living long lives and reproducing infrequently (slow life histories) and others living short lives and reproducing often (fast life histories). These species also vary in the importance of maternal care in offspring fitness: In some species, offspring are fully independent of their mothers following a brief period of nutritional input, while others display a long period of continued dependence on mothers well after nutritional dependence. Here, we hypothesize that these two axes of variation are causally related to each other, such that extended dependence of offspring on maternal presence leads to the evolution of longer lives at the expense of reproduction. We use a combination of deterministic modeling and stochastic agent-based modeling to explore how empirically observed links between maternal survival and offspring fitness are likely to shape the evolution of mortality and fertility. Each of our modeling approaches leads to the same conclusion: When maternal survival has a strong impact on the survival of offspring and grandoffspring, populations evolve longer lives with less frequent reproduction. Our results suggest that the slow life histories of humans and other primates as well as other long-lived, highly social animals such as hyenas, whales, and elephants are partially the result of the strong maternal care that these animals display. We have designed our models to be readily parameterized with demographic data that are routinely collected by long-term researchers, which will facilitate more thorough testing of our hypothesis.

The Effect of Massage on Maternal Role Adaptation in Mothers with Premature Infants

Background

Accepting and adapting the maternal role by mothers with premature infants is complicated. Active participation of mothers in neonate massage may facilitate this process.

Primary Study Objective

Determining the effect of massage on maternal role adaptation in mothers of premature infants admitted to the neonatal intensive care unit (NICU).

Methods/Design

A non-parallel quasi-experimental study with a sequential sampling method.

Setting

This study was done in the NICU of Imam Ali Hospital in Amol City, Iran.

Participants

90 mothers of premature infants hospitalized in the NICU participated in this study.

Intervention

The mothers in the intervention group after receiving two training sessions massaged their infant for 15 minutes daily from the third day of hospitalization for 5 consecutive days.

Primary Outcome Measures

A maternal role adaptation questionnaire was used. Participants completed the maternal role adaptation questionnaire 3 times: before, on the fifth day, and 14 days after the first day of intervention. The maternal role adaptation questionnaire was used to assess the maternal role adaptation. The participants of the control group also filled out the questionnaire at similar time.

Results

The mean scores of maternal adaptation were significantly different between the two control groups (5th day and 14th day) and intervention (day 5: 136.88 ± 10.062 (P = .025); day 14: 151.93 ± 6 (P < .001)). Maternal role adaptation showed an upward trend in the two groups during the 14 days of study, but this trend was significantly higher in the intervention group over time, compared to the control group.

Conclusion

Massage of premature infants facilitates the adaptation to maternal role. It is recommended, along with other nursing interventions, to empower mothers with premature neonates admitted to the NICU.