Effects of chronic social stress during lactation on maternal behavior and growth in rats

The Lateral Habenula Is Necessary for Maternal Behavior in the Naturally Parturient Primiparous Mouse Dam

Mammalian parenting is an unusually demanding commitment. How has the reward system been co-opted to ensure parental care? Previous work has implicated the lateral habenula (LHb), an epithalamic nucleus, as a potential intersection of parenting behavior and reward. Here, we examine the role of the LHb in the maternal behavior of naturally parturient primiparous mouse dams. We show that kainic acid lesions of the LHb induced a severe maternal neglect phenotype in dams toward their biological pups. Next, we demonstrate that chronic chemogenetic inactivation of the LHb using inhibitory DREADDs impaired acquisition and performance of various maternal behaviors, such as pup retrieval and nesting. We present a random intercept model suggesting LHb inactivation prevents the acquisition of pup retrieval, a novel maternal behavior in primiparous mouse dams, and decreases nest building performance, an already-established behavior, in primiparous mouse dams. Lastly, we examine the spatial histology of kainic acid-treated dams with a random intercept model, which suggests the role of LHb in maternal behavior may be preferentially localized at the posterior aspect of this structure. Together, these findings serve to establish the LHb as required for maternal behavior in the mouse dam, thereby complementing previous findings implicating the LHb in parental behavior using pup-sensitized virgin female mice.

Stress and parental behaviors

In nearly all mammalian species, newborn pups are weak and vulnerable, relying heavily on care and protection from parents for survival. Thus, developmentally hardwired neural circuits are in place to ensure the timely expression of parental behaviors. Furthermore, several neurochemical systems, including estrogen, oxytocin, and dopamine, facilitate the emergence and expression of parental behaviors. However, stress can adversely affect these systems, impairing parental behaviors. In this review, we will summarize our current knowledge regarding the impact of stress on pup-directed behavior circuits that lead to infant neglect, abuse, and, in extreme cases, killing. We will discuss various stressors that influence parental behaviors at different life stages and how stress induces changes in the neurochemical systems that support parental care, ultimately leading to its poor performance.

Wheel Running During Pregnancy Alleviates Anxiety-and Depression-Like Behaviors During the Postpartum Period in Mice: The Roles of NLRP3 Neuroinflammasome Activation, Prolactin, and the Prolactin Receptor in the Hippocampus

Despite the increase in the prevalence of postpartum depression among maternal disorder, its treatment outcomes remain suboptimal. Studies have shown that exercise can reduce postpartum depressive episodes in the mother, but the effects of exercise during pregnancy on maternal behavior and the potential mechanisms involved remain poorly understood. From the second day of pregnancy to the day of birth, dams exercised for 1 h a day by running on a controlled wheel. The maternal behaviors of the dams were assessed on postpartum day 2 to postpartum day 8. Chronic restraint stress was applied from postpartum day 2 to day 12. Blood was collected on postpartum days 3 and 8, then subjected to ELISA to determine the serum concentration of prolactin. The weight of each dam and the food intake were recorded. Anxiety- and depression-like behavioral tests were conducted, and hippocampal neuroinflammation and prolactin receptor levels were measured. The dams exhibited elevated levels of anxiety and depression, decreased serum prolactin levels, decreased prolactin receptor expression, and activation of NLRP3-mediated neuroinflammation in the hippocampus following the induction of postpartum chronic restraint stress, which were reversed with controlled wheel running during pregnancy. Overall, the findings of this study revealed that the preventive effects of exercise during pregnancy on postpartum anxiety-and depression-like behaviors were accompanied by increased serum prolactin levels, hippocampal prolactin receptor expression and hippocampal NLRP3-mediated neuroinflammation.

Bridging Neurobiological Insights and Clinical Biomarkers in Postpartum Depression: A Narrative Review

Postpartum depression (PPD) affects 174 million women worldwide and is characterized by profound sadness, anxiety, irritability, and debilitating fatigue, which disrupt maternal caregiving and the mother-infant relationship. Limited pharmacological interventions are currently available. Our understanding of the neurobiological pathophysiology of PPD remains incomplete, potentially hindering the development of novel treatment strategies. Recent hypotheses suggest that PPD is driven by a complex interplay of hormonal changes, neurotransmitter imbalances, inflammation, genetic factors, psychosocial stressors, and hypothalamic-pituitary-adrenal (HPA) axis dysregulation. This narrative review examines recent clinical studies on PPD within the past 15 years, emphasizing advancements in neuroimaging findings and blood biomarker detection. Additionally, we summarize recent laboratory work using animal models to mimic PPD, focusing on hormone withdrawal, HPA axis dysfunction, and perinatal stress theories. We also revisit neurobiological results from several brain regions associated with negative emotions, such as the amygdala, prefrontal cortex, hippocampus, and striatum. These insights aim to improve our understanding of PPD's neurobiological mechanisms, guiding future research for better early detection, prevention, and personalized treatment strategies for women affected by PPD and their families.

Perinatal Tetrahydrocannabinol Compromises Maternal Care and Increases Litter Attrition in the Long-Evans Rat

The marijuana legalization trend in the U.S. will likely lead to increased use by younger adults during gestation and postpartum. The current study examined the hypothesis that delta-9-tetrahydrocannabinol (THC) would disrupt voluntary maternal care behaviors and negatively impact offspring development. Rat dams were gavaged with 0, 2, 5, or 10 mg/kg THC from the 1st day of gestation through the 21st postnatal day. Somatic growth and developmental milestones were measured in the offspring, and maternal pup retrieval tests were conducted on postnatal days 1, 3, and 5. THC did not affect body growth but produced transient delays in the righting reflex and eye opening in offspring. However, there was significant pup mortality due to impaired maternal care. Dams in all THC groups took significantly longer to retrieve their pups to the nest and often failed to retrieve any pups. Serum levels of THC and metabolites measured at this time were comparable to those in breastfeeding women who are chronic users. Benchmark doses associated with a 10% reduction of pup retrieval or increased pup mortality were 0.383 (BMDL 0.228) and 0.794 (BMDL 0.442) mg/kg THC, respectively. The current findings indicate that maternal care is an important and heretofore overlooked index of THC behavioral toxicity and should be included in future assessments of THC's health risks.

Gestational environmental enrichment prevents chronic social stress induced anxiety- and ethanol-related behaviors in offspring

Epidemiological surveys have shown a strong relationship between maternal stress and offspring's mood disorders. Growing evidence suggested that environmental enrichment (EE) improves cognitive function in models of psychiatric and neurological disorders. However, the potential protective effects of gestational EE on social stress-elicited mood disorders in offspring have not been studied. Knowing that the undeveloped brain is more sensitive to gestational environmental stimuli, we hypothesized that initiating cognitive stimulation, during gestation, would protect against social stress-induced behavioral alterations in adulthood. Therefore, the present study aimed to investigate the effects of gestational EE on social stress-elicited anxiety- and ethanol-related behaviors in adult offspring. EE consisted of free access, of dams, to tubular devices of different shapes, colors, and sizes that were changed regularly. After birth and weaning, young adult offspring were exposed to 19 days of social stress and anxiety-like behavior was evaluated by elevated plus maze, open field, and marbles burying tests. The two-bottle choice (TBC) drinking paradigm was used to assess stress-induced ethanol intake. Results showed that gestational EE prevented social stress-elicited anxiogenic-like effects with no differences in spontaneous locomotor activity. Moreover, in the TBC paradigm, mice pre-exposed to EE consistently showed a significantly decreased consumption and preference for ethanol with no effects on tastants' intakes. Interestingly, gestational EE increased serum BDNF levels, which showed a correlation with measures of anxiety- and ethanol-related behaviors. These findings indicate that some neurodevelopmental changes associated with prenatal EE may counteract adult social stress-induced behavioral alterations through a BDNF mechanism. Therefore, we propose that gestational EE has significant protective and beneficial effects on social stress-induced cognitive impairment. It can also alleviate anxiety-like behavior and subsequent excessive alcohol consumption.

Mitochondrial might: powering the peripartum for risk and resilience

The peripartum period, characterized by dynamic hormonal shifts and physiological adaptations, has been recognized as a potentially vulnerable period for the development of mood disorders such as postpartum depression (PPD). Stress is a well-established risk factor for developing PPD and is known to modulate mitochondrial function. While primarily known for their role in energy production, mitochondria also influence processes such as stress regulation, steroid hormone synthesis, glucocorticoid response, GABA metabolism, and immune modulation - all of which are crucial for healthy pregnancy and relevant to PPD pathology. While mitochondrial function has been implicated in other psychiatric illnesses, its role in peripartum stress and mental health remains largely unexplored, especially in relation to the brain. In this review, we first provide an overview of mitochondrial involvement in processes implicated in peripartum mood disorders, underscoring their potential role in mediating pathology. We then discuss clinical and preclinical studies of mitochondria in the context of peripartum stress and mental health, emphasizing the need for better understanding of this relationship. Finally, we propose mitochondria as biological mediators of resilience to peripartum mood disorders.

Chronic Stress Decreases Lactation Performance

The ability to provision offspring with milk is a significant adaptive feature of mammals that allows for considerable maternal regulation of offspring beyond gestation, as milk provides complete nutrition for developing neonates. For mothers, lactation is a period of marked increases in energetic and nutritive demands to support milk synthesis; because of this considerable increase in demand imposed on multiple physiological systems, lactation is particularly susceptible to the effects of chronic stress. Here, we present work that explores the impact of chronic stress during lactation on maternal lactation performance (i.e., milk quality and quantity) and the expression of key milk synthesis genes in mammary tissue using a Sprague-Dawley rat model. We induced chronic stress using a well-established, ethologically relevant novel male intruder paradigm for 10 consecutive days during the postpartum period. We hypothesized that the increased energetic burden of mounting a chronic stress response during lactation would decrease lactation performance. Specifically, we predicted that chronic exposure to this social stressor would decrease either milk quality (i.e., composition of proximate components and energy density) or quantity. We also predicted that changes in proximate composition (i.e., lipid, lactose, and protein concentrations) would be associated with changes in gene expression levels of milk synthesis genes. Our results supported our hypothesis that chronic stress impairs lactation performance. Relative to the controls, chronically stressed rats had lower milk yields. We also found that milk quality was decreased; milk from chronically stressed mothers had lower lipid concentration and lower energy density, though protein and lactose concentrations were not different between treatment groups. Although there was a change in proximate composition, chronic stress did not impact mammary gland expression of key milk synthesis genes. Together, this work demonstrates that exposure to a chronic stressor impacts lactation performance, which in turn has the potential to impact offspring development via maternal effects.

Stress in the social context: a behavioural and eco-evolutionary perspective

The social environment is one of the primary sources of challenging stimuli that can induce a stress response in animals. It comprises both short-term and stable interactions among conspecifics (including unrelated individuals, mates, potential mates and kin). Social stress is of unique interest in the field of stress research because (1) the social domain is arguably the most complex and fluctuating component of an animal's environment; (2) stress is socially transmissible; and (3) stress can be buffered by social partners. Thus, social interactions can be both the cause and cure of stress. Here, we review the history of social stress research, and discuss social stressors and their effects on organisms across early life and adulthood. We also consider cross-generational effects. We discuss the physiological mechanisms underpinning social stressors and stress responses, as well as the potential adaptive value of responses to social stressors. Finally, we identify outstanding challenges in social stress research, and propose a framework for addressing these in future work.

PiE: an open-source pipeline for home cage behavioral analysis

Over the last two decades a growing number of neuroscience labs are conducting behavioral assays in rodents. The equipment used to collect this behavioral data must effectively limit environmental and experimenter disruptions, to avoid confounding behavior data. Proprietary behavior boxes are expensive, offer limited compatible sensors, and constrain analysis with closed-source hardware and software. Here, we introduce PiE, an open-source, end-to-end, user-configurable, scalable, and inexpensive behavior assay system. The PiE system includes the custom-built behavior box to hold a home cage, as well as software enabling continuous video recording and individual behavior box environmental control. To limit experimental disruptions, the PiE system allows the control and monitoring of all aspects of a behavioral experiment using a remote web browser, including real-time video feeds. To allow experiments to scale up, the PiE system provides a web interface where any number of boxes can be controlled, and video data easily synchronized to a remote location. For the scoring of behavior video data, the PiE system includes a standalone desktop application that streamlines the blinded manual scoring of large datasets with a focus on quality control and assay flexibility. The PiE system is ideal for all types of behavior assays in which video is recorded. Users are free to use individual components of this setup independently, or to use the entire pipeline from data collection to analysis. Alpha testers have included scientists without prior coding experience. An example pipeline is demonstrated with the PiE system enabling the user to record home cage maternal behavior assays, synchronize the resulting data, conduct blinded scoring, and import the data into R for data visualization and analysis.

Antagonistic circuits mediating infanticide and maternal care in female mice

In many species, including mice, female animals show markedly different pup-directed behaviours based on their reproductive state1,2. Naive wild female mice often kill pups, while lactating female mice are dedicated to pup caring3,4. The neural mechanisms that mediate infanticide and its switch to maternal behaviours during motherhood remain unclear. Here, on the basis of the hypothesis that maternal and infanticidal behaviours are supported by distinct and competing neural circuits5,6, we use the medial preoptic area (MPOA), a key site for maternal behaviours7-11, as a starting point and identify three MPOA-connected brain regions that drive differential negative pup-directed behaviours. Functional manipulation and in vivo recording reveal that oestrogen receptor α (ESR1)-expressing cells in the principal nucleus of the bed nucleus of stria terminalis (BNSTprESR1) are necessary, sufficient and naturally activated during infanticide in female mice. MPOAESR1 and BNSTprESR1 neurons form reciprocal inhibition to control the balance between positive and negative infant-directed behaviours. During motherhood, MPOAESR1 and BNSTprESR1 cells change their excitability in opposite directions, supporting a marked switch of female behaviours towards the young.

Prefrontal cortex neurons in adult rats exposed to early life stress fail to appropriately signal the consequences of motivated actions

Early life stress (ELS) can set the stage for susceptibility to cognitive and emotional dysfunction in adulthood by disrupting typical neural development. The prefrontal cortex (PFC) continues to mature during early life, making this region particularly vulnerable to disruption for animals who experience ELS. Despite this, the effects of ELS experience on in vivo PFC function in awake and behaving adult animals are currently poorly understood. To assess this, we employed an instrumental conflict task to assess how hungry adult rats, either ELS (wet bedding) or unstressed Controls, were able to flexibly alter their motivation for food reward seeking (lever presses) in situations that were either threatening or safe. During this task, in vivo electrophysiological recordings (both single unit and local field potentials [LFPs]) were made in the rats' ventral-medial PFC (vmPFC). We found that ELS rats were less motivated to lever press for rewards than Controls in the threat situations during repeated extinction sessions. In recordings taken during this suppression task, Control vmPFC neurons displayed reliable differences between motivated actions, such as between rewarded and unrewarded presses, but ELS neurons failed to differentiate these action-outcome differences. We also found differences in task-related LFP activity between groups; in particular, prior ELS experience appears to induce abnormal changes in low-frequency oscillations during shock-associated threat stimuli prior to presses, as well as diminished higher-frequency oscillations following rewarded presses. Collectively, we demonstrate that ELS experience produces persistent impairment in motivational regulation that is associated with significant changes in in vivo PFC signals. Specifically, ELS-experienced adults fail to appropriately update motivated action strategies under threat conditions, and likewise fail to appropriately monitor and update action/outcome relationships in motivated behavior. These ELS-related changes may therefore lay the foundation for heightened susceptibility to mental-health disorders in adults such as substance abuse and post-traumatic stress disorder.

Urocortin-3 neurons in the perifornical area are critical mediators of chronic stress on female infant-directed behavior

Infant avoidance and aggression are promoted by activation of the Urocortin-3 expressing neurons of the perifornical area of hypothalamus (PeFA^Ucn3) in male and female mice. PeFA^Ucn3 neurons have been implicated in stress, and stress is known to reduce maternal behavior. We asked how chronic restraint stress (CRS) affects infant-directed behavior in virgin and lactating females and what role PeFA^Ucn3 neurons play in this process. Here we show that infant-directed behavior increases activity in the PeFA^Ucn3 neurons in virgin and lactating females. Chemogenetic inhibition of PeFA^Ucn3 neurons facilitates pup retrieval in virgin females. CRS reduces pup retrieval in virgin females and increases activity of PeFA^Ucn3 neurons, while CRS does not affect maternal behavior in lactating females. Inhibition of PeFA^Ucn3 neurons blocks stress-induced deficits in pup-directed behavior in virgin females. Together, these data illustrate the critical role for PeFA^Ucn3 neuronal activity in mediating the impact of chronic stress on female infant-directed behavior.

Locus Coeruleus-Noradrenergic Neurons Regulate Stress Coping During Subchronic Exposure to Social Threats: A Characteristic Feature in Postpartum Female Mice

Stress-coping strategies have been implicated in depression. The control of stress coping may improve the symptom and higher prevalence of depression during the postpartum period in women. However, the neuronal mechanisms underlying stress coping remain to be fully elucidated in postpartum women. In this study, we examined how locus coeruleus-noradrenergic (LC-NA) neurons, which have been associated with both stress coping and depression, regulate changes in coping style induced by subchronic exposure to unfamiliar male mice as a social threat in postpartum female mice. In contrast to virgin females, dams exposed to unfamiliar males daily for four consecutive days showed reduced immobility duration in the forced swim test, indicating that exposure to unfamiliar males decreased passive stress coping in dams. Exposure to unfamiliar males also decreased sucrose palatability in the sucrose preference test and suppressed the crouching behavior in the maternal care test but did not affect anxiety-like behavior in the hole-board test in dams. In fiber photometry analyses, LC-NA neurons showed differential activity between dams and virgin females in response to unfamiliar males. Chemogenetic inhibition of LC-NA neurons during exposure to unfamiliar males prevented the social threat-induced decrease in immobility duration in the forced swim test in dams. Furthermore, inhibition or activation of LC-NA neurons exacerbated crouching behavior in dams. These results indicate that LC-NA neurons regulate the social threat-induced decrease in passive stress coping and relieve social threat-induced inhibition of maternal care in postpartum female mice.

Prenatal maternal stress and offspring aggressive behavior: Intergenerational and transgenerational inheritance

Even though studies have shown that prenatal maternal stress is associated with increased reactivity of the HPA axis, the association between prenatal maternal stress and fetal glucocorticoid exposure is complex and most likely dependent on unidentified and poorly understood variables including nature and timing of prenatal insults. The precise mechanisms in which prenatal maternal stress influence neuroendocrine signaling between the maternal-placental-fetal interface are still unclear. The aim of this review article is to bring comprehensive basic concepts about prenatal maternal stress and mechanisms of transmission of maternal stress to the fetus. This review covers recent studies showing associations between maternal stress and alterations in offspring aggressive behavior, as well as the possible pathways for the “transmission” of maternal stress to the fetus: (1) maternal-fetal HPA axis dysregulation; (2) intrauterine environment disruption due to variations in uterine artery flow; (3) epigenetic modifications of genes implicated in aggressive behavior. Here, we present evidence for the phenomenon of intergenerational and transgenerational transmission, to better understands the mechanism(s) of transmission from parent to offspring. We discuss studies showing associations between maternal stress and alterations in offspring taking note of neuroendocrine, brain architecture and epigenetic changes that may suggest risk for aggressive behavior. We highlight animal and human studies that focus on intergenerational transmission following exposure to stress from a biological mechanistic point of view, and maternal stress-induced epigenetic modifications that have potential to impact on aggressive behavior in later generations.

Species differences in the effect of oxytocin on maternal behavior: A model incorporating the potential for allomaternal contributions

Oxytocin has historically been linked to processes involved with maternal behavior. However, the relative importance of oxytocin for maternal behavior widely varies among mammalian species, from indispensable to apparently nonessential. This review proposes a new model in which the relative importance of oxytocin for mothering across species is explained by an evolutionary pressure which we term "allomaternal potential", or the degree to which other conspecifics are capable and likely to assist with caregiving. It is notable that in animals where allomaternal potential is high (i.e., many quality helpers are available), oxytocin is decoupled from mothering. However, in animals where allomaternal potential is low (i.e., conspecifics refuse to, or do not provide, quality help), oxytocin is crucial for mothering. We posit that this relationship is a form of kin selection, whereby oxytocin is a signal that leads mothers to preferentially dispense resources to their own young when quality helpers are unlikely.

Animal models of postpartum depression revisited

Postpartum depression (PPD) is a heterogeneous mood disorder and the most frequent psychiatric complication of the postnatal period. Given its potential long-lasting repercussions on the well-being of the mother and the infants, it should be a priority in public health. In spite of efforts devoted to clinical investigation and preclinical studies, the underlying neurobiological mechanisms of this disorder remain unknown in detail. Much of the progress in the area has been made from animal models, especially rodent models. The aim of this mini-review is to update the current rodent models in PPD research and their main contributions to the field. Animal models are critical tools to advance understanding of the pathophysiological basis of this disorder and to help the development of new therapeutic strategies. Here, we group PPD models into 2 main categories (Models based on hormone manipulations, Models based on stress exposure), each of which includes different paradigms that reflect risk factors or physiological conditions associated with this disease. Finally, we provide an overview of emerging models that provide new perspectives on the study of possible pathophysiological factors related to PPD, to contribute to tackling potential therapeutic targets.

Maternal separation: Does it hold the potential to model consequences of postpartum depression?

The postpartum period is a sensitive time where women are especially vulnerable to develop postpartum depression (PPD), with 10%-15% of women affected. This review investigates whether the maternal separation (MS) paradigm in rodents holds the potential to help to understand mothers suffering from PPD. MS is a well-established stress model to investigate effects on infants, whereas effects on the dam are often overlooked. The database PubMed was searched for studies investigating effects of daily MS within the first weeks after parturition on dams in rats and mice and compared to findings in PPD mothers. MS was categorized as brief MS (5-45 min) with or without handling of pups and long MS (3-4 h and longer). MS alters maternal care, depressive-like behavior, anxiety, and aggression; leads to alterations in neuronal gene expression; and affects hormone and neurotransmitter levels similar to observations in PPD patients. Even though there are disparities between human and rodent mothers, with some results differing in directionality, as well as the reason for separation (self-induced in PPD, externally induced in MS), the overall effects found on neurobiological, hormonal, and behavioral levels mostly coincide. Thus, the MS paradigm can add relevant knowledge to existing PPD animal models, further advancing the study of PPD.

Postpartum maternal exposure to predator odor alters offspring antipredator behavior, basal HPA axis activity and immunoglobulin levels in adult Brandt's voles

Predation risk can program offspring behavior, physiology, and fitness through maternal effect, but most studies have mainly focused on this effect during pregnancy; little is known about the effect of postpartum predation risk on offspring's phenotype. Here, we compared the antipredator behaviors of adult offspring (approximately 90 days old) produced by female Brandt's voles (Lasiopodomys brandtii) exposed to one of three treatments: cat odor (CO), rabbit odor (RO), and distilled water (DW) for 60 min daily from postpartum day 1-18. Basal levels of plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT), hypothalamic corticotrophin releasing hormone (CRH), as well as spleen immunoglobulins (IgA, IgM, and IgG) were also measured. Our data showed that the offspring of CO-exposed mothers displayed less head-out behavior to acute 15-min CO exposure, and female offspring showed more freezing behavior. CO offspring showed significantly lower basal ACTH and CORT levels than the RO and DW offspring. Additionally, female but not male CO offspring had higher hypothalamic CRH expression and spleen IgG levels than controls, showing a sex-specific effect. These findings demonstrate that postpartum maternal predator risk exposure promotes a passive-avoidant response to these cues in adult offspring, showing a cross-generational maternal effect of postpartum predation risk. Further, these changes may be associated with alterations in the hypothalamic-pituitary-adrenal axis and immune function.

Postpartum scarcity-adversity disrupts maternal behavior and induces a hypodopaminergic state in the rat dam and adult female offspring

Postpartum adversity is among the strongest predictors for the emergence of postpartum depression (PPD) in humans and a translational risk factor employed in rodent models. Parental care is disturbed under conditions of environmental adversity, including low resource environments, and in PPD. Nonetheless, the neural changes associated with these adversity-induced maladaptive behavioral states remain poorly understood. Postpartum scarcity-adversity can be modeled in rats by providing the dam with limited bedding and nesting (LBN) materials, which mimics the effects of a stressful low resource environment in potentiating maltreatment/neglect in humans. Indeed, LBN exposure from postpartum days (PD) 2-9 increased adverse maternal behaviors, impaired pup retrieval, and increased passive stress coping responses. Since mesolimbic dopamine (DA) activity is an important mechanism for motivated maternal behavior and is implicated in PPD, we assessed the impact of postpartum scarcity-adversity on in vivo electrophysiological properties of ventral tegmental area (VTA) DA neurons at two timepoints. We found reduced numbers of active VTA DA neurons in LBN dams at PD 9-10 but not PD-21, suggesting a transient impact on VTA population activity in LBN dams. Finally, we assessed the impact of early life scarcity-adversity on VTA DA function by conducting VTA recordings in adult female offspring and found a long-lasting attenuation in DA activity. These findings highlight a link between adversity-induced deficits in DA function and disrupted maternal behavior, suggesting the VTA/mesolimbic DA system as a potential mechanism by which postpartum scarcity-adversity drives aberrant maternal behavior, and early postnatal programming of adult VTA function in the offspring.

Changes in maternal fecal corticosterone metabolites across lactation and in response to chronic stress

Maternal exposure to stressors during lactation has previously been demonstrated to impact various aspects of milk synthesis and to have long-term physiological effects on offspring. Much of the current literature investigating the effects of stress during lactation has used acute stressors, and the studies investigating the effects of chronic stressors largely focus on neurological changes. Further, temporal variation in glucocorticoids across lactation in response to stressors has rarely been assessed. The present work uses a novel male intruder paradigm to model the effects of chronic stress on maternal fecal corticosterone metabolites (FCMs) in Sprague-Dawley rats across lactation. FCM levels were elevated in chronically-stressed mothers relative to the control group. Further, FCMs in the stress group were time-dependent either due to repeated exposure to the stressor or lactation stage. Together, this work demonstrates the efficacy of this established paradigm in increasing circulating glucocorticoids in lactating rats. These results highlight the need for repeated temporal sampling, as glucocorticoid levels in response to a chronic stressor may change across lactation.

Ethologically relevant repeated acute social stress induces maternal neglect in the lactating female mouse

Psychosocial stress is a top predictor of peripartum mood disorders in human mothers. In the present study, we developed a novel paradigm testing the effects of direct and vicarious social stress on maternal and mood-related behaviors in B6 mice. Using a novel housing paradigm, we examined the extent to which postpartum dams withdrew from litters following psychosocial stress. Repeated acute direct social stress involved exposing dams to a virgin male mouse for 7 min/day on postpartum days 5-7 during a brief (15-min) mother-pup separation. To remove the effects of direct stress, the vicarious social stress dams were housed in the same vivarium as direct social stressed dams, but without direct exposure to intruders. Control dams were given mock intruder exposure and housed in a separate vivarium room containing breeding mice. All dams experienced pup separation, and maternal care was investigated upon reunion. Direct and vicarious social stress induced significant deficits in maternal care and increased maternal anxiety relative to controls. Although vicarious stress effects were more likely to occur on days when there was acute stress exposure, direct stress sustained maternal deficits 24 h after the final stressor. Together, these data suggest psychosocial stress induces aberrant maternal phenotypes in mice.

Socially unstable conditions experienced during development prime female Octodon degus to shape the phenotype of their own offspring

Because residents and immigrants from group living species may experience fitness costs associated with permanent changes in group membership, we examined the hypothesis that females experiencing socially unstable or socially stable conditions during development compensate these costs by shaping the phenotype of their own offspring differently. Groups of adult females experiencing either socially stable or unstable conditions in the early social environment were assigned to either socially stable or unstable conditions in the social environment as adults. We quantified affiliative and agonistic interactions among the females during pregnancy and lactation of the focal female, maternal and allomaternal care, hypothalamic-anterior pituitary-adrenal axis (HPA) acute stress response, and early offspring growth. Social instability during breeding enhanced agonistic interactions among adult females, and offspring that experienced socially unstable conditions exhibited enhanced offspring care, regardless of adult environments. Neither social behavior, offspring care, acute stress physiology, nor early growth was influenced by early or adult social stability conditions. These findings imply that socially unstable conditions prime developing females to shape the phenotype of their offspring to prevent negative effects of socially unstable environments.

T3 is linked to stress-associated reduction of prolactin in lactating women

The relationship between stress responses and lactation is bidirectional. Breastfeeding confers many benefits to maternal health, including attenuated hypothalamic-pituitary-adrenal axis responsiveness to stress. However, increased stress burden can impair lactation. The mechanisms that underlie these relationships are poorly understood. The present study aimed to compare breastfeeding habits, as well as subjective and objective measures of stress, in employed and non-employed lactating women and assess the relationships between these measures and prolactin (PRL), thyroid hormones (thyroid-stimulating hormone, triiodothyronine [T3] and thyroxine), vasopressin and cortisol levels. A dexamethasone suppression test was also administered to determine the sensitivity of the hypothalamic-pituitary-adrenal axis to negative-feedback. We report that lactating employed women had lower breastfeeding rates and lower PRL than lactating non-employed women. They also had a significantly higher stress burden, indicated by elevations in blood pressure and evening cortisol, relative to lactating non-employed women. In regression analyses that controlled for feeding modality and breastfeeding duration, we found these factors differentially affected PRL in the two groups and there were significant differences in PRL across groups that were not accounted for by these factors. A mediation regression analysis suggested that group differences in PRL were best explained by differences in T3 and income levels, rather than breastfeeding duration or other variables. Our data fit a speculative model in which elevated maternal stress increases cortisol, which suppresses T3, leading to decreased PRL. The decreases in PRL are associated with higher rates of bottlefeeding, which may further contribute to decreased PRL.

Maternal glucocorticoids have minimal effects on HPA axis activity and behavior of juvenile wild North American red squirrels

As a response to environmental cues, maternal glucocorticoids (GCs) may trigger adaptive developmental plasticity in the physiology and behavior of offspring. In North American red squirrels (Tamiasciurus hudsonicus), mothers exhibit increased GCs when conspecific density is elevated, and selection favors more aggressive and perhaps more active mothers under these conditions. We tested the hypothesis that elevated maternal GCs cause shifts in offspring behavior that may prepare them for high-density conditions. We experimentally elevated maternal GCs during gestation or early lactation. We measured two behavioral traits (activity and aggression) in weaned offspring using standardized behavioral assays. Because maternal GCs may influence offspring hypothalamic-pituitary-adrenal (HPA) axis dynamics, which may in turn affect behavior, we also measured the impact of our treatments on offspring HPA axis dynamics (adrenal reactivity and negative feedback), and the association between offspring HPA axis dynamics and behavior. Increased maternal GCs during lactation, but not gestation, slightly elevated activity levels in offspring. Offspring aggression and adrenal reactivity did not differ between treatment groups. Male, but not female, offspring from mothers treated with GCs during pregnancy exhibited stronger negative feedback compared with those from control mothers, but there were no differences in negative feedback between lactation treatment groups. Offspring with higher adrenal reactivity from mothers treated during pregnancy (both controls and GC-treated) exhibited lower aggression and activity. These results suggest that maternal GCs during gestation or early lactation alone may not be a sufficient cue to produce substantial changes in behavioral and physiological stress responses in offspring in natural populations.

Decoupling the effects of food and density on life-history plasticity of wild animals using field experiments: Insights from the steward who sits in the shadow of its tail, the North American red squirrel

Long-term studies of wild animals provide the opportunity to investigate how phenotypic plasticity is used to cope with environmental fluctuations and how the relationships between phenotypes and fitness can be dependent upon the ecological context. Many previous studies have only investigated life-history plasticity in response to changes in temperature, yet wild animals often experience multiple environmental fluctuations simultaneously. This requires field experiments to decouple which ecological factor induces plasticity in fitness-relevant traits to better understand their population-level responses to those environmental fluctuations. For the past 32 years, we have conducted a long-term integrative study of individually marked North American red squirrels Tamiasciurus hudsonicus Erxleben in the Yukon, Canada. We have used multi-year field experiments to examine the physiological and life-history responses of individual red squirrels to fluctuations in food abundance and conspecific density. Our long-term observational study and field experiments show that squirrels can anticipate increases in food availability and density, thereby decoupling the usual pattern where animals respond to, rather than anticipate, an ecological change. As in many other study systems, ecological factors that can induce plasticity (such as food and density) covary. However, our field experiments that manipulate food availability and social cues of density (frequency of territorial vocalizations) indicate that increases in social (acoustic) cues of density in the absence of additional food can induce similar life-history plasticity, as does experimental food supplementation. Changes in the levels of metabolic hormones (glucocorticoids) in response to variation in food and density are one mechanism that seems to induce this adaptive life-history plasticity. Although we have not yet investigated the energetic response of squirrels to elevated density or its association with life-history plasticity, energetics research in red squirrels has overturned several standard pillars of knowledge in physiological ecology. We show how a tractable model species combined with integrative studies can reveal how animals cope with resource fluctuations through life-history plasticity.

Early detection of parenting stress in mothers of preterm infants during their first-year home

Background

Maternal stress following the birth of an infant is well acknowledged. It is particularly so when infants are born prematurely as their mothers cannot fully take on their parenting role until their infant(s) is discharged from neonatal intensive care units (NICUs). In this exploratory study, we examined whether these mothers’ parenting stress would lessen during their first-year reunification with their infant(s) as they settle into motherhood at home.

Methods

Two groups of mothers with infants born between 24- and 33-week gestational age were recruited. A group of 25 mothers were monitored at their infants’ 1-month corrected age (CA) and a second group of 24 mothers were monitored at their infants’ 12-month CA. Subjects completed the long form Parental Stress Index (PSI) ranking how stressful they perceive the individual subscales in the Child and Parent Domains of the self-reported questionnaire (PSI-3; Abidin; PAR Inc). The PSI theorizes that the stress mothers perceive is a resultant of their respective characteristics, interactions with their infant(s), family, and environment. Statistical analyses include descriptive statistics, χ² square analysis, and independent t-test.

Results

There was no significant difference in the levels of perceived stress in the PSI subscales between the two groups of mothers at 1- and 12-month CA. Scores for the majority of respondents fell within the 15th to 80th percentile (% ile) distribution of Abidin’s normative population, with some mothers falling below the 15th % ile.

Discussion/conclusion

The data collected suggest that: 1. the perceived stress experienced by mothers during their first-year reunited with their preterm infants is within the normal range observed in Abidin’s normative population. 2. As the PSI is a self-reported survey, care providers need to be aware that some mothers may downplay their stress responses. 3. With the ability to monitor individual participants, the PSI can be readily offered to mothers at their infants’ first year routine clinical visits to assist in the early identification of parenting issues that may threaten the development of a healthy mother-infant dyad. Early appropriate guidance and social support would help “at-risk” mothers develop more constructive parenting routines.

Gestational dioxin exposure suppresses prolactin-stimulated nursing in lactating dam rats to impair development of postnatal offspring

A number of epidemiological studies have implicated environmental chemicals including dioxins in the induction of negative effects on child development. To clarify the underlying mechanisms, almost all toxicologists have concentrated on effects on the offspring themselves. We examined an alternative hypothesis that gestational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a highly-toxic dioxin, targets factors related to maternal childcare to disturb offspring development. Oral administration of TCDD (1 µg/kg) to pregnant rats on gestational day 15 suppressed maternal licking behavior, a nursing behavior, and mammary gland maturation during the lactational stage, as well as the body weight and short-term memory of postnatal offspring. In support of these findings, maternal production of prolactin, a pituitary hormone essential for nursing including milk production, was decreased during the same period. Intracerebroventricular infusion of prolactin to dioxin-exposed dams restored or tended to restore many of the above defects observed both in mothers and offspring. The TCDD-dependent defects in maternal nursing behaviors can be due to a direct action on aryl hydrocarbon receptor (AHR) of lactating dams, because they did not emerge in AHR-knockout dams or control dams with TCDD-exposed offspring. Further examinations revealed that TCDD induces transforming growth factor β1 expression, which suppresses prolactin-producing cell proliferation, in a nursing period-specific manner. In agreement with this, the number of prolactin-positive cells in nursing dams was decreased by TCDD. These results provide novel evidence that gestational dioxin exposure attenuates prolactin-stimulated nursing in lactating dams to impair offspring development, and that immaturity of prolactin-producing cells can contribute to them.

Adaptations in reward-related behaviors and mesolimbic dopamine function during motherhood and the postpartum period

Initiation and maintenance of maternal behavior is driven by a complex interaction between the physiology of parturition and offspring stimulation, causing functional changes in maternal brain and behavior. Maternal behaviors are among the most robust and rewarding motivated behaviors. Mesolimbic dopamine (DA) system alterations during pregnancy and the postpartum enable enhanced reward-related responses to offspring stimuli. Here, we review behavioral evidence demonstrating postpartum rodents exhibit a bias towards pups and pup-related stimuli in reward-related tasks. Next, we provide an overview of normative adaptations in the mesolimbic DA system induced by parturition and the postpartum, which likely mediate shifts in offspring valence. We also discuss a causal link between dopaminergic dysfunction and disrupted maternal behaviors, which are recapitulated in postpartum depression (PPD) and relevant rodent models. In sum, mesolimbic DA system activation drives infant-seeking behavior and strengthens the mother-infant bond, potentially representing a therapeutic target for reward-related deficits in PPD.

Environmental enrichment decreases chronic psychosocial stress-impaired extinction and reinstatement of ethanol conditioned place preference in C57BL/6 male mice

RATIONALE

During the last few decades, alcohol use disorders (AUD) have reached an epidemic prevalence, yet social influences on alcoholism have not been fully addressed. Several factors can modulate alcohol intake. On one hand, stress can reinforce ethanol-induced behaviors and be an important component in AUD and alcoholism. On the other hand, environmental enrichment (EE) has a neuroprotective role and prevents the development of excessive ethanol intake in rodents. However, studies showing the role of EE in chronic psychosocial stress-impaired ethanol-conditioned rewards are nonexistent.

AIM

The purpose of the current study is to explore the potential protective role of EE on extinction and reinstatement of ethanol-conditioned place preference (EtOH-CPP) following chronic psychosocial stress.

METHODS

In the first experiment and after the EtOH-CPP test, the mice were subjected to 15 days of chronic stress, then housed in a standard (SE) or enriched environment (EE) while EtOH-CPP extinction was achieved by repeated exposure to the CPP chambers without ethanol injection. In the second experiment and after the EtOH-CPP test, extinction was achieved as described above. Mice were then exposed to chronic stress for 2 weeks before being housed in a SE or EE. EtOH-CPP reinstatement was induced by a single exposure to the conditioning chambers.

RESULTS

As expected, stress exposure increased anxiety-like behavior and reduced weight gain. More importantly, we found that EE significantly shortened chronic stress-delayed extinction and decreased the reinstatement of EtOH-CPP.

CONCLUSION

These results support the hypothesis that EE reduces the impact of alcohol-associated environmental stimuli, and hence it may be a general intervention for reducing cue-elicited craving and relapse in humans.

Maternal glucocorticoids promote offspring growth without inducing oxidative stress or shortening telomeres in wild red squirrels

Elevations in glucocorticoid (GC) levels in breeding females may induce adaptive shifts in offspring life histories. Offspring produced by mothers with elevated GCs may be better prepared to face harsh environments, where a faster pace of life is beneficial. We examined how experimentally elevated GCs in pregnant or lactating North American red squirrels (Tamiasciurus hudsonicus) affected offspring postnatal growth, structural size and oxidative stress levels (two antioxidants and oxidative protein damage) in three different tissues (blood, heart and liver) and liver telomere lengths. We predicted that offspring from mothers treated with GCs would grow faster but would also have higher levels of oxidative stress and shorter telomeres, which may predict reduced longevity. Offspring from mothers treated with GCs during pregnancy were 8.3% lighter around birth but grew (in body mass) 17.0% faster than those from controls, whereas offspring from mothers treated with GCs during lactation grew 34.8% slower than those from controls and did not differ in body mass around birth. Treating mothers with GCs during pregnancy or lactation did not alter the oxidative stress levels or telomere lengths of their offspring. Fast-growing offspring from any of the treatment groups did not have higher oxidative stress levels or shorter telomere lengths, indicating that offspring that grew faster early in life did not exhibit oxidative costs after this period of growth. Our results indicate that elevations in maternal GCs may induce plasticity in offspring growth without long-term oxidative costs to the offspring that might result in a shortened lifespan.

Neurobiology of maternal mental illness

This chapter provides an overview of current research discoveries beginning to uncover the neurobiology of maternal mental illness. Results are described according to standard diagnostic categories (specifically, perinatal depression, perinatal anxiety and OCD, postpartum psychosis and bipolar disorder, and trauma and posttraumatic stress disorder), yet we aim to put this approach in context with the introduction of a classification model for psychiatric research, the research domain criteria, gaining traction in basic and clinical translational fields. We first review a new area of study, the neuroplasticity of the pregnant and postpartum brain, as work here has relevance for understanding the pathophysiology of mental disorders and may provide clues to changes in brain functioning that are related to compromised parenting in the context of postpartum depression. We next provide background information on neuroendocrine and immune changes during pregnancy and, to a lesser extent, the postpartum period, as alterations in these systems are significantly implicated in underlying neurobiology of mental illness for peripartum women. Our discussion of the major mental illnesses for pregnant and postpartum women includes neuroendocrine changes, neuroinflammation, and neurotransmitter alterations, as well as circuit dysfunction. Overall, remarkable progress has been made in identifying variations in neurobiology (and related systems) involved in maternal mental illness; yet, it is clear that, as classified with standard diagnostic systems, these are heterogeneous disorders and there is individual variability in the alterations in neurobiology for the same illness.

Sex Differences in Vulnerability and Resilience to Stress Across the Life Span

Susceptibility and resilience to stress depend on 1) the timing of the exposure with respect to development, 2) the time across the life span at which effects are measured, and 3) the behavioral or biological phenotype under consideration. This translational review examines preclinical stress models that provide clues to causal mechanisms and their relationship to the more complex phenomenon of stress-related psychiatric and cognitive disorders in humans. We examine how genetic sex and epigenetic regulation of hormones contribute to the proximal and distal effects of stress at different epochs of life. Stress during the prenatal period and early postnatal life puts male offspring at risk of developing diseases involving socialization, such as autism spectrum disorder, and attention and cognition, such as attention-deficit/hyperactivity disorder. While female offspring show resilience to some of the proximal effects of prenatal and early postnatal stress, there is evidence that risk associated with developmental insults is unmasked in female offspring following periods of hormonal activation and flux, including puberty, pregnancy, and perimenopause. Likewise, stress exposures during puberty have stronger proximal effects on girls, including an increased risk of developing mood-related and stress-related illnesses, such as depression, anxiety, and posttraumatic stress disorder. Hormonal changes during menopause and andropause impact the processes of memory and emotion in women and men, though women are preferentially at risk for dementia, and childhood adversity further impacts estradiol effects on neural function. We propose that studies to determine mechanisms for stress risk and resilience across the life span must consider the nature and timing of stress exposures as well as the sex of the organism under investigation.

Maternal social environment affects offspring cognition through behavioural and immune pathways in rats

The social environment of lactation is a key etiological factor for the occurrence of postpartum disorders affecting women and their children. Postpartum depression and anxiety disorders are highly prevalent in new mothers and negatively affect offspring's cognitive development through mechanisms which are still unclear. Here, using a rat model, we manipulated the maternal social environment during lactation and explored the pathways through which social isolation (vs. the opportunity for limited social interaction with another lactating female, from 1 day before parturition to postpartum day 16) and chronic social conflict (daily exposure to a male intruder from postpartum day 2 to day 16) affect offspring learning and memory, measured at 40 to 60 days of age. We specifically explored the consequences of these social treatments on two main hypothesized mediators likely to affect offspring neurophysiological development: the quality of maternal care and maternal inflammation factors (brain-derived neurotrophic factor, granulocyte-macrophage colony-stimulating factor, intercellular adhesion molecule 1, tissue inhibitor of metalloproteinases 1 and vascular endothelial growth factor) likely to influence offspring development through lactation. Maternal rats which had the opportunity to interact with another lactating female spent more time with their pups which, in turn, displayed improved working and reference memory. Social stress affected maternal plasma levels of cytokines that were associated with cognitive deficits in their offspring. However, females subjected to social stress were protected from these stress-induced immune changes and associated offspring cognitive impairment by increased social affiliation. These results underscore the effects of social interaction for new mothers and their offspring and can be used to inform the development of clinical preventative measures and interventions.

The maternal reward system in postpartum depression

The experience of motherhood is most often emotionally positive and rewarding, but for many new mothers suffering from postpartum depression (PPD), this is not the case. Preclinical and clinical research has sought to uncover brain changes underlying PPD in order to gain a better understanding of how this disorder develops. This review focuses on the mesolimbic dopamine system, particularly the ventral tegmental area-nucleus accumbens pathway which has been implicated in the regulation of critical functions disrupted in PPD including mood, motivation, and mothering. Specifically, we discuss normative changes in the mesolimbic system during motherhood in both rodents and humans and how these are impacted in PPD. We also consider modulation of mesolimbic dopamine by the hypothalamic neuropeptide oxytocin and how oxytocin-dopamine interactions regulate mood and mothering during the postpartum period. In addition to providing an overview of reward mechanisms in PPD, our goal is to highlight open questions which warrant further research.

Cross-Generational Transmission of Early Life Stress Effects on HPA Regulators and Bdnf Are Mediated by Sex, Lineage, and Upbringing

Early life stress (ELS) is a potent developmental disruptor and increases the risk for psychopathology. Various forms of ELS have been studied in both humans and rodents, and have been implicated in altered DNA methylation, gene transcription, stress hormone levels, and behavior. Although recent studies have focused on stress-induced epigenetic changes, the extent to which ELS alters HPA axis function and stress responsivity across generations, whether these effects are sex-specific, and how lineage interacts with upbringing to impact these effects, remain unclear. To address these points, two generations of rodents were utilized, with the first generation subjected to ELS via maternal separation, and the second to a balanced cross-fostering paradigm. We hypothesized that ELS would disrupt normative development in both generations, manifesting as altered methylation and expression of genes associated with stress signaling pathways (Nr3c1, Nr3c2, and Bdnf), blunted corticosterone (CORT), and anxiety-like behaviors. Additionally, we expected deficits in the second generation to be modulated by caretaking environment and for the pattern of results to differ between the sexes. Results suggest that direct exposure to ELS leads to sex-specific effects on gene regulation and HPA functioning in adulthood, with maternal separation leading to increases in Bdnf methylation in both sexes, decreases in Bdnf expression in females, and decreases in Nr3c1 methylation in males, as well as blunted CORT and less anxiety-like behavior in females. These alterations converged with caretaking to impart perturbations upon the subsequent generation. Across sex, ELS lineage led to decreased methylation of Nr3c1, and increased methylation of Bdnf. In fostered animals, upbringing by a previously stressed mother interacted with offspring lineage to impact methylation of Nr3c1 and Bdnf. Upbringing was also implicated in altered anxiety-like behavior in males, and baseline CORT levels in females. Such effects may correspond with observed alterations in maternal behavior across groups. In conclusion, ELS conferred enduring sex-specific alterations, both first-hand and trans-generationally via lineage and upbringing. Importantly, lineage of cross-fostered pups was sufficient to normalize or disturb maternal behavior of foster-dams, an observation requiring further elucidation. These results have implications for multi-generational effects of ELS in humans and may motivate early interventions.

Neuroactive Steroids and GABAergic Involvement in the Neuroendocrine Dysfunction Associated With Major Depressive Disorder and Postpartum Depression

Stress and previous adverse life events are well-established risk factors for depression. Further, neuroendocrine disruptions are associated with both major depressive disorder (MDD) and postpartum depression (PPD). However, the mechanisms whereby stress contributes to the underlying neurobiology of depression remains poorly understood. The hypothalamic-pituitary-adrenal (HPA) axis, which mediates the body's neuroendocrine response to stress, is tightly controlled by GABAergic signaling and there is accumulating evidence that GABAergic dysfunction contributes to the impact of stress on depression. GABAergic signaling plays a critical role in the neurobiological effects of stress, not only by tightly controlling the activity of the HPA axis, but also mediating stress effects in stress-related brain regions. Deficits in neuroactive steroids and neurosteroids, some of which are positive allosteric modulators of GABA_A receptors (GABA_ARs), such as allopregnanolone and THDOC, have also been implicated in MDD and PPD, further supporting a role for GABAergic signaling in depression. Alterations in neurosteroid levels and GABAergic signaling are implicated as potential contributing factors to neuroendocrine dysfunction and vulnerability to MDD and PPD. Further, potential novel treatment strategies targeting these proposed underlying neurobiological mechanisms are discussed. The evidence summarized in the current review supports the notion that MDD and PPD are stress-related psychiatric disorders involving neurosteroids and GABAergic dysfunction.

Alteration in oxytocin levels induced by early social environment affects maternal behavior and estrogen receptor alpha in mandarin voles (Microtus mandarinus)

Many studies have shown that the early social environment exerts long-term effects on the brain and also the parental behavior of adults. Oxytocin (OXT) is one of the most important neurotransmitters that regulate social behavior; howerve, whether the early social environment affects parental behavior via OXT remains unclear. Using socially monogamous adult mandarin voles (Microtus mandarinus), the present study found that 1) both paternal deprivation and early social deprivation significantly decreased OXT expression in both the paraventricular hypothalamic nucleus (PVN) and the supraoptic nucleus (SON) of F2 generation offspring; 2) systemic neonatal OXT injection in naïve animals promoted maternal but not paternal behavior in adult F2 offspring; 3) systemic neonatal OXT injection significantly increased ERα expression in both the medial preoptic area (MPOA) and the ventro medial hypothalamic nucleus (VMH) in female but not in male mandarin voles; 4) systemic neonatal administration of an OXT antagonist significantly reduced ERα expression in the bed nucleus of the stria terminalis (BNST), VMH, and the arcuate hypothalamic nucleus (Arc) in females and in all examined brain regions in males. In summary, the obtained data demonstrate that the early social environment could affect OXT level, which in turn leads to long-term effects on ERα expression in relevant brain regions, consequently affecting maternal behavior but not paternal behavior.

Maternal care modulates transgenerational effects of endocrine-disrupting chemicals on offspring pup vocalizations and adult behaviors

Endocrine-disrupting chemicals (EDCs) can act upon a developing organism to change its endocrine health and behavior in adulthood. Beyond actions on the exposed individuals, transgenerational effects of several EDCs have been reported. This study assessed the combinatorial impact of EDC-altered maternal care and transgenerational inheritance on F3 male and female offspring. Pregnant rats were exposed to EDCs with different modes of action: the weakly estrogenic polychlorinated biphenyl (PCB) mixture Aroclor 1221, the anti-androgenic fungicide vinclozolin (VIN), or the vehicle (6% dimethylsulfoxide in sesame oil; VEH) during embryonic development. The F1 male and female offspring were bred through the paternal- or maternal-lineage with untreated partners to generate F2 offspring. This process was repeated through both maternal and paternal lineages to create the F3 generation. Maternal care of F2 dams towards their F3 offspring was altered in a lineage-dependent manner, particularly in PCB paternal-lineage animals. When F3 pups were recorded for ultrasonic vocalizations (USVs) following separation from the mother, the rate of neonatal USVs in F3 offspring were decreased in PCB paternal-lineage pups. In adulthood, anxiety-like behaviors of the F3 rats were tested, with only small effects of EDCs detected. These interactions of maternal behaviors and EDC effects across generations, especially via the paternal lineage, has implications for health and environmental responses in wildlife and humans.

Pathophysiological mechanisms implicated in postpartum depression

This review aims to summarize the diverse proposed pathophysiological mechanisms contributing to postpartum depression, highlighting both clinical and basic science research findings. The risk factors for developing postpartum depression are discussed, which may provide insight into potential neurobiological underpinnings. The evidence supporting a role for neuroendocrine changes, neuroinflammation, neurotransmitter alterations, circuit dysfunction, and the involvement of genetics and epigenetics in the pathophysiology of postpartum depression are discussed. This review integrates clinical and preclinical findings and highlights the diversity in the patient population, in which numerous pathophysiological changes may contribute to this disorder. Finally, we attempt to integrate these findings to understand how diverse neurobiological changes may contribute to a common pathological phenotype. This review is meant to serve as a comprehensive resource reviewing the proposed pathophysiological mechanisms underlying postpartum depression.

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.

Early life social stress and resting state functional connectivity in postpartum rat anterior cingulate circuits

INTRODUCTION

Continued development and refinement of resting state functional connectivity (RSFC) fMRI techniques in both animal and clinical studies has enhanced our comprehension of the adverse effects of stress on psychiatric health. The objective of the current study was to assess both maternal behavior and resting state functional connectivity (RSFC) changes in these animals when they were dams caring for their own young. It was hypothesized that ECSS exposed dams would express depressed maternal care and exhibit similar (same networks), yet different specific changes in RSFC (different individual nuclei) than reported when they were adult females.

METHODS

We have developed an ethologically relevant transgenerational model of the role of chronic social stress (CSS) in the etiology of postpartum depression and anxiety. Initial fMRI investigation of the CSS model indicates that early life exposure to CSS (ECSS) induces long term changes in functional connectivity in adult nulliparous female F1 offspring.

RESULTS

ECSS in F1 dams resulted in depressed maternal care specifically during early lactation, consistent with previous CSS studies, and induced changes in functional connectivity in regions associated with sensory processing, maternal and emotional responsiveness, memory, and the reward pathway, with robust changes in anterior cingulate circuits.

LIMITATIONS

The sample sizes for the fMRI groups were low, limiting statistical power.

CONCLUSION

This behavioral and functional neuroanatomical foundation can now be used to enhance our understanding of the neural etiology of early life stress associated disorders and test preventative measures and treatments for stress related disorders.