Parenting and plasticity

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.

Preliminary report: Sleep duration during late pregnancy predicts postpartum emotional responses among parents at risk for postpartum depression

Introduction

Sleep loss is common during the perinatal period; however, few studies have assessed potential consequences of insufficient sleep for postnatal emotional responding, a key contributor to parenting behaviors with implications for parent-infant bonding and mental health. To generate hypotheses for future work assessing perinatal sleep and emotion-related outcomes, this pilot study explored whether prenatal sleep duration predicted postnatal emotional responding in a sample at risk for postpartum depression.

Methods

Participants were nine birthing parents with a prior mood disorder who were not in a current episode at enrollment. We estimated sleep with actigraphy collected for 1 week at 33 weeks' gestation and at 2 and 6 weeks postpartum. Following each week, participants completed an emotional evaluation task, rating the valence and arousal of standardized images from the International Affective Picture System. We tested whether average prenatal (33 weeks) nighttime sleep duration predicted concurrent and future responsiveness to emotional images, quantified by participants' reaction times and arousal/valence ratings.

Results

Shorter prenatal sleep duration predicted faster reaction times, both concurrently and at 2 weeks postpartum (ps ≤ .05), as well as lower arousal ratings for negative images at 2 and 6 weeks postpartum (ps ≤ .043).

Conclusions

In this small sample of birthing parents at risk for postpartum depression, shorter prenatal sleep duration predicted faster reactions to emotional stimuli and blunted arousal responses to negative images. Although preliminary, these findings justify further study of the role of prenatal sleep in postpartum emotional responses and how these factors may impact parent-infant outcomes.

The central role of the individual in the history of brains

Every species' brain, body and behavior is shaped by the contingencies of their evolutionary history; these exert pressures that change their developmental trajectories. There is, however, another set of contingencies that shape us and other animals: those that occur during a lifetime. In this perspective piece, we show how these two histories are intertwined by focusing on the individual. We suggest that organisms--their brains and behaviors--are not solely the developmental products of genes and neural circuitry but individual centers of action unfolding in time. To unpack this idea, we first emphasize the importance of variation and the central role of the individual in biology. We then go over "errors in time" that we often make when comparing development across species. Next, we reveal how an individual's development is a process rather than a product by presenting a set of case studies. These show developmental trajectories as emerging in the contexts of the "the actual now" and "the presence of the past". Our consideration reveals that individuals are slippery-they are never static; they are a set of on-going, creative activities. In light of this, it seems that taking individual development seriously is essential if we aspire to make meaningful comparisons of neural circuits and behavior within and across species.

Longitudinal Neuroanatomical Increases from Early to One-Year Postpartum

Preclinical studies have provided causal evidence that the postpartum period involves regional neuroanatomical changes in 'maternal' brain regions to support the transition to offspring caregiving. Few studies, in humans, have examined neuroanatomical changes from early to one-year postpartum with longitudinal neuroimaging data and their association with postpartum mood changes. In this study, we examined longitudinal changes in surface morphometry (cortical thickness and surface area) in regions previously implicated in the transition to parenthood. We also examined longitudinal volumetric neuroanatomical changes in three subcortical regions of the maternal brain: the hippocampus, amygdala, and ventral diencephalon. Twenty-four participants underwent longitudinal structural magnetic resonance imaging at 2-4 weeks and 1 year postpartum. Cortical thickness increased from early to one-year postpartum in the left (p = .003, Bonferroni corrected) and right (p = .02, Bonferroni corrected) superior frontal gyrus. No significant increases (or decreases) were observed in these regions for surface area. Volumetric increases, across the postpartum period, were found in the left amygdala (p = .001, Bonferroni corrected) and right ventral diencephalon (p = .01, Bonferroni corrected). An exploratory analysis of depressive symptoms found reductions in depressive symptoms from early postpartum to one-year postpartum were associated with greater cortical thickness in the superior frontal gyrus for both the left (p = .02) and right (p = .02) hemispheres. The findings expand our evidence of the neuroanatomical changes that occur across the postpartum period in humans and motivate future studies to examine how mood changes across this period are associated with cortical thickness of the superior frontal gyrus.

Effects of sensory overstimulation in postpartum rats

Research in rodents has shown that exposure to excessive early life audiovisual stimulation leads to altered anxiety-like behaviors and cognitive deficits. Since this period of stimulation typically begins prior to weaning, newborn rodents receive sensory overstimulation (SOS) as a litter within their home cage while the dam is present. However, the effects of SOS during the postpartum period remain unexplored. To this end, we adapted an SOS paradigm for use in rats and exposed rat dams and their litters from postpartum days (PD) 10-23. Maternal observations were conducted to determine whether SOS produced changes in positive and/or negative maternal behaviors. Next, we assessed changes in anxiety-like behavior and cognition by testing dams in the elevated zero maze, open field, and novel object recognition tests. To assess potential effects on HPA-axis function, levels of the stress hormone corticosterone (CORT) were measured approximately 1-week after the cessation of SOS exposure. Our results indicate increased nursing and licking in SOS dams compared to controls, although SOS dams also exhibited significant increases in pup dragging. Moreover, SOS dams exhibited reduced self-care behaviors and nest-building compared to control dams. No differences were found for anxiety-like behaviors, object recognition memory, or CORT levels. This study is the first to assess the impact of postpartum SOS exposure in rat dams. Our findings suggest an SOS-induced enhancement in positive caregiving, but limited impact in all other measures.

Effects of reproductive experience on cost-benefit decision making in female rats

Many individuals undergo mating and/or other aspects of reproductive experience at some point in their lives, and pregnancy and childbirth in particular are associated with alterations in the prevalence of several psychiatric disorders. Research in rodents shows that maternal experience affects spatial learning and other aspects of hippocampal function. In contrast, there has been little work in animal models concerning how reproductive experience affects cost-benefit decision making, despite the relevance of this aspect of cognition for psychiatric disorders. To begin to address this issue, reproductively experienced (RE) and reproductively naïve (RN) female Long-Evans rats were tested across multiple tasks that assess different forms of cost-benefit decision making. In a risky decision-making task, in which rats chose between a small, safe food reward and a large food reward accompanied by variable probabilities of punishment, RE females chose the large risky reward significantly more frequently than RN females (greater risk taking). In an intertemporal choice task, in which rats chose between a small, immediate food reward and a large food reward delivered after a variable delay period, RE females chose the large reward less frequently than RN females. Together, these results show distinct effects of reproductive experience on different forms of cost-benefit decision making in female rats, and highlight reproductive status as a variable that could influence aspects of cognition relevant for psychiatric disorders.

Cellular and molecular signatures of motherhood in the adult and ageing rat brain

Pregnancy is marked by robust changes, including brain changes to volume, structure, connectivity and neuroplasticity. Although some brain changes are restricted to pregnancy and the postpartum, others are long-lasting. Few studies have examined possible mechanisms of these changes or the effects of multiple pregnancies. We characterized various cellular and molecular signatures of parity (nulliparous, primiparous, biparous) in the rat hippocampus. We investigated density of neural stems cells (Sox2), microglia (Iba-1) and levels of a synaptic protein (PSD-95), cell signalling pathways, neuroinflammation, and the tryptophan-kynurenine (TRP-KYN) pathway, one week after weaning their pups from the last pregnancy (age of dam: seven months) and in middle-age (age of dam: 13 months). Parity increased PSD-95 levels in both age groups and prevented the age-related decrease in neural stem cell density observed in nulliparous rats. Biparity increased cell signalling phosphoproteins (pp70S6K, S6RP) and number of microglia in the dentate gyrus, regardless of age. Parity resulted in transient changes to the TRP-KYN system. Thus, previous parity has lasting effects on synaptic plasticity with fewer lasting effects on inflammation and cell signalling phosphoproteins in the whole hippocampus.

Association between parental behaviors and structural plasticity in the brain of male rodents

In recent decades, human fathers across the globe have shown a substantial increase in their engagement in paternal caregiving behaviors. Despite the growing interest, the precise neurobiological mechanisms underlying caregiving behaviors in males remain unclear. Neurobiological studies conducted on rodents have advanced our understanding of the molecular, cellular, and circuit-level mechanisms. Typically, sexually naïve males exhibit aggression toward offspring, while fathers display parental behaviors. This drastic behavioral plasticity may be associated with changes in connections among specific regions or cell types. Recent studies have begun to describe this structural plasticity by comparing neural connections before and after fatherhood. In this Perspective, we summarize the findings from four well-studied rodent species, namely prairie voles, California mice, laboratory rats, and laboratory mice, with a view toward integrating past and current progress. We then review recent advances in the understanding of structural plasticity for parental behaviors. Finally, we discuss remaining questions that require further exploration to gain a deeper understanding of the neural mechanisms underlying paternal behaviors in males, including their possible implications for the human brain.

The transition to motherhood: linking hormones, brain and behaviour

We are witnessing a stark increase in scientific interest in the neurobiological processes associated with pregnancy and maternity. Convergent evidence suggests that around the time of labour, first-time mothers experience a specific pattern of neuroanatomical changes that are associated with maternal behaviour. Here we provide an overview of the human neurobiological adaptations of motherhood, focusing on the interplay between pregnancy-related steroid and peptide hormones, and neuroplasticity in the brain. We discuss which brain plasticity mechanisms might underlie the structural changes detected by MRI, which hormonal systems are likely to contribute to such neuroanatomical changes and how these brain mechanisms may be linked to maternal behaviour. This Review offers an overarching framework that can serve as a roadmap for future investigations.

Polygenic scores for social science: Clarification, consensus, and controversy

In this response, I focus on clarifying my arguments, highlighting consensus, and addressing competing views about the utility of polygenic scores (PGSs) for social science. I also discuss an assortment of expansions to my arguments and suggest alternative approaches. I conclude by reiterating the need for caution and appropriate scientific skepticism.

Mating-induced prolactin surge is not required for subsequent neurogenesis in male mice

Parenting involves major behavioral transitions that are supported by coordinated neuroendocrine and physiological changes to promote the onset of novel offspring-directed behaviors. In comparison to maternal care, however, the mechanisms underlying the transition to paternal care are less understood. Male laboratory mice are predominantly infanticidal as virgins but show paternal responses 2 weeks after mating. Interestingly, males show a mating-induced surge of prolactin, which we hypothesized may be involved in initiating this behavioral transition. During pregnancy, prolactin stimulates olfactory bulb neurogenesis, which is essential for maternal behavior. Mating induces olfactory bulb neurogenesis in males, but it is unknown whether this is driven by prolactin or is important for subsequent paternal care. New olfactory neurons are generated from cells in the subventricular zone (SVZ) and take about 2 weeks to migrate to the olfactory bulb, which may account for the delayed behavioral change in mated males. We investigated whether mating increases cell proliferation at the SVZ. Males were either mated, exposed to receptive female cues, or left alone (control) and injected with Bromodeoxyuridine (BrdU, a marker of cell division). Contrary to our hypothesis, we found that mating decreased cell proliferation in the caudal lateral portion of the SVZ. Next, we tested whether prolactin itself mediates cell proliferation in the SVZ and/or new cell survival in the olfactory bulb by administering bromocriptine (prolactin inhibitor), vehicle, or bromocriptine + prolactin prior to mating. While suppressing prolactin had no effect on cell proliferation in the SVZ, administering exogenous prolactin resulted in significantly higher BrdU-labeled cells in mated but not virgin male mice. No effects of prolactin were observed on new olfactory cell survival. Taken together, prolactin may have context-dependent effects on new cell division in the SVZ, while other unknown mechanisms may be driving the effects on new olfactory cell survival following mating.

The parental umwelt: Effects of parenthood on sensory processing in rodents

An animal's umwelt, comprising its perception of the sensory environment, which is inherently subjective, can change across the lifespan in accordance with major life events. In mammals, the onset of motherhood, in particular, is associated with a neural and sensory plasticity that alters a mother's detection and use of sensory information such as infant-related sensory stimuli. Although the literature surrounding mammalian mothers is well established, very few studies have addressed the effects of parenthood on sensory plasticity in mammalian fathers. In this review, we summarize the major findings on the effects of parenthood on behavioural and neural responses to sensory stimuli from pups in rodent mothers, with a focus on the olfactory, auditory, and somatosensory systems, as well as multisensory integration. We also review the available literature on sensory plasticity in rodent fathers. Finally, we discuss the importance of sensory plasticity for effective parental care, hormonal modulation of plasticity, and an exploration of temporal, ecological, and life-history considerations of sensory plasticity associated with parenthood. The changes in processing and/or perception of sensory stimuli associated with the onset of parental care may have both transient and long-lasting effects on parental behaviour and cognition in both mothers and fathers; as such, several promising areas of study, such as on the molecular/genetic, neurochemical, and experiential underpinnings of parenthood-related sensory plasticity, as well as determinants of interspecific variation, remain potential avenues for further exploration.

Functional near-infrared spectroscopy is a useful tool for multi-perspective psychobiological study of neurophysiological correlates of parenting behaviour

The quality of the relationship between caregiver and child has long-term effects on the cognitive and socio-emotional development of children. A process involved in human parenting is the bio-behavioural synchrony that occurs between the partners in the relationship during interaction. Through interaction, bio-behavioural synchronicity allows the adaptation of the physiological systems of the parent to those of the child and promotes the positive development and modelling of the child's social brain. The role of bio-behavioural synchrony in building social bonds could be investigated using functional near-infrared spectroscopy (fNIRS). In this paper we have (a) highlighted the importance of the quality of the caregiver-child relationship for the child's cognitive and socio-emotional development, as well as the relevance of infantile stimuli in the activation of parenting behaviour; (b) discussed the tools used in the study of the neurophysiological substrates of the parental response; (c) proposed fNIRS as a particularly suitable tool for the study of parental responses; and (d) underlined the need for a multi-systemic psychobiological approach to understand the mechanisms that regulate caregiver-child interactions and their bio-behavioural synchrony. We propose to adopt a multi-system psychobiological approach to the study of parental behaviour and social interaction.

A pilot randomised controlled trial on the effectiveness of infant massage on the acceptance, commitment and awareness of influence in parents of babies with Down syndrome

BACKGROUND

The emotional state of parents of babies with Down syndrome affects their babies' development and their parent-child bonding. The aim for this study was to conduct a pilot randomised controlled evaluation of the effect of infant massage on parents of babies with Down syndrome.

METHODS

This pilot study compared two groups (intervention and control), each with 16 parents of babies with Down syndrome. Indices of acceptance, engagement and awareness of influence were measured at two different time points (pre-test and after 5 weeks) using the 'This Is My Baby' Interview. The allocation of families to each group was randomised. The experimental group performed infant massage, applied by the parents, for 5 weeks, every day for at least 10 min. The massage protocol was based on the methodology created by Vimala McClure. Parents in the control group received the intervention after completion of the study.

RESULTS

The indices of acceptance, commitment and awareness of influence improved in the experimental group and in the control group. The 2 × 2 mixed-model analysis of variance indicates a statistically significant group-by-time interaction for all indices (P < 0.001), which was significantly higher in the experimental group than in the control group.

CONCLUSIONS

The application of infant massage, by parents to their babies, improves the rates of acceptance, commitment and awareness of influence of parents of babies with Down syndrome in the short term.

Neural responses to pup calls and pup odors in California mouse fathers and virgin males

The onset of mammalian maternal care is associated with plasticity in neural processing of infant-related sensory stimuli; however, little is known about sensory plasticity associated with fatherhood. We quantified behavioral and neural responses of virgin males and new fathers to olfactory and auditory stimuli from young, unfamiliar pups in the biparental California mouse (Peromyscus californicus). Each male was exposed for 10minutes to one of four combinations of a chemosensory stimulus (pup-scented or unscented cotton [control]) and an auditory stimulus (pup vocalizations or white noise [control]). Behavior did not differ between fathers and virgins during exposure to sensory stimuli or during the following hour; however, males in both groups were more active both during and after exposure to pup-related stimuli compared to control stimuli. Fathers had lower expression of Fos in the main olfactory bulbs (MOB) but higher expression in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis medial division, ventral part (STMV) compared to virgins. Lastly, males had higher Fos expression in MPOA when exposed to pup odor compared to control stimuli, and when exposed to pup odor and pup calls compared to pup calls only or control stimuli. These findings suggest that the onset of fatherhood alters activity of MOB, MPOA and STMV and that pup odors and vocalizations have additive or synergistic effects on males' behavior and MPOA activation.

Narrative coherence across the transition to parenthood: Primiparous parents' representations of their child in relation to parental sensitivity

Narrative coherence reflects parents' ability to provide a believable, clear, relevant, and internally consistent story about their child. Parents demonstrating more narrative coherence have been theorized to show higher parental sensitivity, but this has not been examined in a normative sample, nor across the transition to parenthood, and only once in fathers. The aim of this study was to examine stability and change in narrative coherence across the transition to parenthood in mothers and fathers, as well as the relation between pre- and postnatal narrative coherence and postnatal parental sensitivity. The sample consisted of 105 primiparous expecting parents. Narrative coherence was measured at 36-weeks pregnancy and when the child was 4 months old, using the Five Minute Speech Sample procedure. Parental sensitivity was observed in three episodes. Results demonstrated that narrative coherence was moderately stable (correlations) across the transition to parenthood in fathers only. Both mothers' and fathers' narrative coherence improved over time. Furthermore, mothers and fathers were overall equally coherent, and maternal and paternal narrative coherence were positively interrelated during pregnancy only. Lastly, our findings showed weak evidence for the theorized link between narrative coherence and parental sensitivity: only postnatal narrative coherence predicted paternal sensitivity, only during free play. Our findings give new insight in the development of narrative coherence across the transition to parenthood, and how it relates to actual parenting. More research is needed to confirm our findings and further explore this topic.

Effects of pairing on color change and central gene expression in lined seahorses

Social monogamy is a reproductive strategy characterized by pair living and defense of a common territory. Pair bonding, sometimes displayed by monogamous species, is an affective construct that includes preference for a specific partner, distress upon separation, and the ability of the partner to buffer against stress. Many seahorse species show a monogamous social structure in the wild, but their pair bond has not been well studied. We examined the gene expression of lined seahorses (Hippocampus erectus) during and after the process of pairing in the laboratory as well as color change (luminance), a potential form of social communication and behavioral synchrony between pair mates. When a seahorse of either sex was interacting with its pair mate, their changes in luminance ("brightness") were correlated and larger than when interacting with an opposite-sex stranger. At the conclusion of testing, subjects were euthanized, RNA was extracted from whole brains and analyzed via RNA sequencing. Changes in gene expression in paired males versus those that were unpaired included processes governing metabolic activity, hormones and cilia. Perhaps most interesting is the overlap in gene expression change induced by pairing in both male seahorses and male prairie voles, including components of hormone systems regulating reproduction. Because of our limited sample size, we consider our results and interpretations to be preliminary, and prompts for further exploration. Future studies will expand upon these findings and investigate the neuroendocrine and genetic basis of these behaviors.

Ganoderma Lucidum Triterpenoids Improve Maternal Separation-Induced Anxiety- and Depression-like Behaviors in Mice by Mitigating Inflammation in the Periphery and Brain

Although early life stress (ELS) can increase susceptibility to adulthood psychiatric disorders and produce a greater inflammatory response in a stressful event, targeted preventive and therapeutic drugs still remain scarce. Ganoderma lucidum triterpenoids (GLTs) can exert anti-inflammatory effects in the periphery and central nervous systems. This study employed a combined model of “childhood maternal separation + adulthood sub-stress” to explore whether GLTs may alleviate anxiety- and depression-like behaviors in male and female mice by mitigating inflammation. Male and female pups were separated from their mothers for four hours per day from postnatal day 1 (PND 1) to PND 21; starting from PND 56, GLTs were administered intraperitoneally once daily for three weeks and followed by three days of sub-stress. Results showed that maternal separation increased the anxiety- and depression-like behaviors in both male and female mice, which disappeared after the preemptive GLTs treatment (40 mg/kg) before adulthood sub-stress. Maternal separation up-regulated the pro-inflammatory markers in the periphery and brain, and activated microglia in the prefrontal cortex and hippocampus. All the abnormalities were reversed by GLTs administration, with no adverse effects on immune organ indices, liver, and renal function. Our findings suggest that GLTs can be a promising candidate in treating ELS-induced psychiatric disorders.

Experience-Regulated Neuronal Signaling in Maternal Behavior

Maternal behavior is shaped and challenged by the changing developmental needs of offspring and a broad range of environmental factors, with evidence indicating that the maternal brain exhibits a high degree of plasticity. This plasticity is displayed within cellular and molecular systems, including both intra- and intercellular signaling processes as well as transcriptional profiles. This experience-associated plasticity may have significant overlap with the mechanisms controlling memory processes, in particular those that are activity-dependent. While a significant body of work has identified various molecules and intracellular processes regulating maternal care, the role of activity- and experience-dependent processes remains unclear. We discuss recent progress in studying activity-dependent changes occurring at the synapse, in the nucleus, and during the transport between these two structures in relation to maternal behavior. Several pre- and postsynaptic molecules as well as transcription factors have been found to be critical in these processes. This role reflects the principal importance of the molecular and cellular mechanisms of memory formation to maternal and other behavioral adaptations.

Less can be more: Fine tuning the maternal brain

PAWLUSKI, J.L., Hoekzema, E., Leuner, B., and Lonstein, J.S. Less can be more: Fine tuning the maternal brain. NEUROSCI BIOBEHAV REV (129) XXX-XXX, 2022. Plasticity in the female brain across the lifespan has recently become a growing field of scientific inquiry. This has led to the understanding that the transition to motherhood is marked by some of the most significant changes in brain plasticity in the adult female brain. Perhaps unexpectedly, plasticity occurring in the maternal brain often involves a decrease in brain volume, neurogenesis and glial cell density that presumably optimizes caregiving and other postpartum behaviors. This review summarizes what we know of the 'fine-tuning' of the female brain that accompanies motherhood and highlights the implications of these changes for maternal neurobehavioral health. The first part of the review summarizes structural and functional brain changes in humans during pregnancy and postpartum period with the remainder of the review focusing on neural and glial plasticity during the peripartum period in animal models. The aim of this review is to provide a clear understanding of when 'less is more' in maternal brain plasticity and where future research can focus to improve our understanding of the unique brain plasticity occurring during matrescence.

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.

Long-term association of pregnancy and maternal brain structure: the Rotterdam Study

The peripartum period is the highest risk interval for the onset or exacerbation of psychiatric illness in women’s lives. Notably, pregnancy and childbirth have been associated with short-term structural and functional changes in the maternal human brain. Yet the long-term effects of pregnancy on maternal brain structure remain unknown. We investigated a large population-based cohort to examine the association between parity and brain structure. In total, 2,835 women (mean age 65.2 years; all free from dementia, stroke, and cortical brain infarcts) from the Rotterdam Study underwent magnetic resonance imaging (1.5 T) between 2005 and 2015. Associations of parity with global and lobar brain tissue volumes, white matter microstructure, and markers of vascular brain disease were examined using regression models. We found that parity was associated with a larger global gray matter volume (β = 0.14, 95% CI = 0.09–0.19), a finding that persisted following adjustment for sociodemographic factors. A non-significant dose-dependent relationship was observed between a higher number of childbirths and larger gray matter volume. The gray matter volume association with parity was globally proportional across lobes. No associations were found regarding white matter volume or integrity, nor with markers of cerebral small vessel disease. The current findings suggest that pregnancy and childbirth are associated with robust long-term changes in brain structure involving a larger global gray matter volume that persists for decades. Future studies are warranted to further investigate the mechanism and physiological relevance of these differences in brain morphology.

Recent Neuroscience Advances in Human Parenting

The transition to parenthood entails brain adaptations to the demands of caring for a newborn. This chapter reviews recent neuroscience findings on human parenting, focusing on neuroimaging studies. First, we describe the brain circuits underlying human maternal behavior, which comprise ancient subcortical circuits and more sophisticated cortical regions. Then, we present the short-term and long-term functional and structural brain adaptations that characterize the transition to motherhood, discuss the long-term effects of parenthood on the brain, and propose several underlying neural mechanisms. We also review neuroimaging findings in biological fathers and alloparents (such as other relatives or adoptive parents), who engage in parenting without directly experiencing pregnancy or childbirth. Finally, we describe perinatal mental illnesses and discuss the neural responses associated with such disorders. To date, studies indicate that parenthood is a period of enhanced brain plasticity within brain areas critical for cognitive and social processing and that both parenting experience and gestational-related factors can prime such plasticity.

Hormones and neuroplasticity: A lifetime of adaptive responses

Major life transitions often co-occur with significant fluctuations in hormones that modulate the central nervous system. These hormones enact neuroplastic mechanisms that prepare an organism to respond to novel environmental conditions and/or previously unencountered cognitive, emotional, and/or behavioral demands. In this review, we will explore several examples of how hormones mediate neuroplastic changes in order to produce adaptive responses, particularly during transitions in life stages. First, we will explore hormonal influences on social recognition in both males and females as they transition to sexual maturity. Next, we will probe the role of hormones in mediating the transitions to motherhood and fatherhood, respectively. Finally, we will survey the long-term impact of reproductive experience on neuroplasticity in females, including potential protective effects and risk factors associated with reproductive experience in mid-life and beyond. Ultimately, a more complete understanding of how hormones influence neuroplasticity throughout the lifespan, beyond development, is necessary for understanding how individuals respond to life changes in adaptive ways.

Grandparents caring for grandchildren in rural China: consequences for emotional and cognitive health in later life

In rural China, where families serve as critical safety-nets for their vulnerable members, grandparents play an essential role caring for the offspring of their migrant children. Evidence is mixed as to whether caring for grandchildren provides health benefits or incurs health risks. In this article, we used six waves of data from a study in rural China to examine the impact of caregiving for grandchildren on grandparents' emotional and cognitive health. Further, we examined financial transfers from adult children as a resource that potentially moderates the impact of high intensity caregiving on these outcomes. Data derived from six waves (2001-2015) of the Longitudinal Study of Older Adults in Anhui Province, China. We constructed 2,835 person-interval observations derived from 1,067 grandparents to examine lagged change in depressive symptoms and cognitive ability. Results show that caregiving frequency is not by itself harmful or beneficial to the emotional and cognitive health of grandparents, but it does appear to be harmful in the context of custodial care that is less economically supported by adult children. These results are discussed in terms of their relevance to intergenerational reciprocity in a filial culture, time-for-money exchange expectations, and the need for financial resources among caregiving grandparents in rural China.

Involvement of the dopamine system in paternal behavior induced by repeated pup exposure in virgin male ICR mice

Like mothers, fathers play a vital role in the development of the brain and behavior of offspring in mammals with biparental care. Unlike mothers, fathers do not experience the physiological processes of pregnancy, parturition, or lactation before their first contact with offspring. Whether pup exposure can induce the onset of paternal behavior and the underlying neural mechanisms remains unclear. By using Slc:ICR male mice exhibiting maternal-like parental care, the present study found that repeated exposure to pups for six days significantly increased the total duration of paternal behavior and shortened the latency to retrieve and care for pups. Repeated pup exposure increased c-Fos-positive neurons and the levels of dopamine- and TH-positive neurons in the nucleus accumbens (NAc). In addition, inhibition of dopamine projections from the ventral tegmental area to the NAc using chemogenetic methods reduced paternal care induced by repeated pup exposure. In conclusion, paternal behavior in virgin male ICR mice can be initiated by repeated pup exposure via sensitization, and the dopamine system may be involved in this process.

Not all "caregivers" are created equal: Liking, caring and facial expression responses to the baby schema as a function of parenthood and testosterone

The baby schema elicits care from potential caregivers. However, much of the research on the baby schema is based on self-report only. To address this issue, we explored the effects of baby schema and child age on facial expressions (EMG) and eye-blink startle, in addition to self-reported liking and caring for 43 men and 48 women (39 parents). Further, basal testosterone was assessed. All groups responded with liking and caring to high baby schema, but only women also responded with more positive facial expressions. Caring and smiling towards infants compared to first graders depended on parenthood and testosterone levels. Basal testosterone levels were negatively associated with overall responsiveness to children in women and fathers, but positively in non-fathers. Whereas the baby schema overall lead to positive affect and caring, the scope of these responses and the processes underlying them depended on gender, parenthood and hormonal status.

Beneficial intergenerational effects of exercise on brain and cognition: a multilevel meta-analysis of mean and variance

Physical exercise not only helps to improve physical health but can also enhance brain development and cognition. Recent reports on parental (both maternal and paternal) effects raise the possibility that parental exercise may provide benefits to offspring through intergenerational inheritance. However, the general magnitude and consistency of parental exercise effects on offspring is still controversial. Additionally, empirical research has long overlooked an important aspect of exercise: its effects on variability in neurodevelopmental and cognitive traits. Here, we compiled data from 52 studies involving 4786 rodents (412 effect sizes) to quantify the intergenerational transmission of exercise effects on brain and cognition. Using a multilevel meta-analytic approach, we found that, overall, parental exercise showed a tendency for increasing their offspring's brain structure by 12.7% (albeit statistically non-significant) probably via significantly facilitating neurogenesis (16.5%). Such changes in neural anatomy go in hand with a significant 20.8% improvement in neurobehaviour (improved learning and memory, and reduced anxiety). Moreover, we found parental exercise significantly reduces inter-individual differences (i.e. reduced variance in the treatment group) in progeny's neurobehaviour by 10.2% (coefficient of variation ratio, lnCVR), suggesting the existence of an individual by intervention interaction. The positive effects of exercise are modulated by several covariates (i.e. moderators), such as the exercised parent's sex, offspring's sex, and age, mode of exercise, and exercise timing. In particular, parental forced exercise is more efficient than voluntary exercise at significantly improving offspring neurobehaviour (26.0%) and reducing its variability (14.2%). We observed larger effects when parental exercise started before pregnancy. However, exercising only during pregnancy also had positive effects. Mechanistically, exercise significantly upregulated brain-derived neurotrophic factor (BDNF) by 28.9%, vascular endothelial growth factor (VEGF) by 35.8%, and significantly decreased hippocampal DNA methylation by 3.5%, suggesting that brain growth factor cascades and epigenetic modifications can moderate the transmission of parental exercise effects. Collectively, by coupling mean with variance effects, our analyses draw a more integrated picture of the benefits that parental exercise has on offspring: not only does it improve offspring brain development and cognitive performance, but it also reduces inter-individual differences in cognition-related traits. We advocate that meta-analysis of variation together with the mean of a trait provides novel insights for old controversies as well as emerging new questions, opening up a new era for generating variance-based hypotheses.

Social Behavior as a Transdiagnostic Marker of Resilience

The recent shift from psychopathology to resilience and from diagnosis to functioning requires the construction of transdiagnostic markers of adaptation. This review describes a model of resilience that is based on the neurobiology of affiliation and the initial condition of mammals that mature in the context of the mother's body and social behavior. The model proposes three tenets of resilience-plasticity, sociality, and meaning-and argues that coordinated social behavior stands at the core sustaining resilience. Two lines in the maturation of coordinated social behavior are charted, across animal evolution and throughout human development, culminating in the mature human reciprocity of empathy, mutuality, and perspective-taking. Cumulative evidence across ages and clinical conditions and based on our behavioral coding system demonstrates that social reciprocity, defined by plasticity at the individual, dyadic, and group levels, denotes resilience, whereas the two poles of disengagement/avoidance and intrusion/rigidity characterize specific psychopathologies, each with a distinct behavioral signature. Attention to developmentally sensitive markers and to the dimension of meaning in human sociality may open new, behavior-based pathways to resilience.

How stress can influence brain adaptations to motherhood

Research shows that a woman's brain and body undergo drastic changes to support her transition to parenthood during the perinatal period. The presence of this plasticity suggests that mothers' brains may be changed by their experiences. Exposure to severe stress may disrupt adaptive changes in the maternal brain and further impact the neural circuits of stress regulation and maternal motivation. Emerging literature of human mothers provides evidence that stressful experience, whether from the past or present environment, is associated with altered responses to infant cues in brain circuits that support maternal motivation, emotion regulation, and empathy. Interventions that reduce stress levels in mothers may reverse the negative impact of stress exposure on the maternal brain. Finally, outstanding questions regarding the timing, chronicity, types, and severity of stress exposure, as well as study design to identify the causal impact of stress, and the role of race/ethnicity are discussed.

Sex-biased impact of endocrine disrupting chemicals on behavioral development and vulnerability to disease: Of mice and children

Sex is a fundamental biological characteristic that influences many aspects of an organism's phenotype, including neurobiological functions and behavior as a result of species-specific evolutionary pressures. Sex differences have strong implications for vulnerability to disease and susceptibility to environmental perturbations. Endocrine disrupting chemicals (EDCs) have the potential to interfere with sex hormones functioning and influence development in a sex specific manner. Here we present an updated descriptive review of findings from animal models and human studies regarding the current evidence for altered sex-differences in behavioral development in response to early exposure to EDCs, with a focus on bisphenol A and phthalates. Overall, we show that animal and human studies have a good degree of consistency and that there is strong evidence demonstrating that EDCs exposure during critical periods of development affect sex differences in emotional and cognitive behaviors. Results are more heterogeneous when social, sexual and parental behaviors are considered. In order to pinpoint sex differences in environmentally-driven disease vulnerabilities, researchers need to consider sex-biased developmental effects of EDCs.

Frank Beach Award Winner: Lessons from poison frogs on ecological drivers of behavioral diversification

Variation in natural behavior is tightly linked to the ecological resources with which they co-evolved. This review discusses poison frog behavior and neuroendocrinology to illustrate how ecological factors drive diversification of behavior and its underlying neural mechanisms. Poison frogs show tremendous diversity in reproductive strategies that are tightly linked to water resources in their environment. Different species utilize particular pool sizes to rear their offspring, which has selected for sex differences in parental behavior among poison frog species. Tadpole behavior reflects the behavioral diversity of adults, where tadpoles can display social group living or violent aggression and begging behavior, which are all associated with pool size and occupancy. Using this behavioral diversity among poison frog species, we have identified core brain regions, like the hippocampus and preoptic area, as being involved in regulating different aspects of amphibian parental behavior. In contrast to core brain regions, the neuromodulators governing these behaviors seem to be more labile across species. This work exemplifies how comparative studies are a prime experimental system to study how evolution tunes neural circuits that give rise to the diversity of behaviors we observe in the natural world. Finally, this review ends on a more important form of diversity - that of our scientific community - and how community outreach, decolonization of field based science, and inclusion of groups historically excluded from conducting research are needed for the scientific enterprise to transform into something truly beneficial for all members of our society.

What is resilience: an affiliative neuroscience approach

Resilience - a key topic in clinical science and practice - still lacks a clear conceptualization that integrates its evolutionary and human-specific features, refrains from exclusive focus on fear physiology, incorporates a developmental approach, and, most importantly, is not based on the negation (i.e., absence of symptoms following trauma). Building on the initial condition of mammals, whose brain matures in the context of the mother's body and caregiving behavior, we argue that systems and processes that participate in tuning the brain to the social ecology and adapting to its hardships mark the construct of resilience. These include the oxytocin system, the affiliative brain, and biobehavioral synchrony, all characterized by great flexibility across phylogenesis and ontogenesis. Three core features of resilience are outlined: plasticity, sociality and meaning. Mechanisms of sociality by which coordinated action supports diversity, endurance and adaptation are described across animal evolution. Humans' biobehavioral synchrony matures from maternal attuned behavior in the postpartum to adult-adult relationships of empathy, perspective-taking and intimacy, and extends from the mother-child relationship to other affiliative bonds throughout life, charting a fundamental trajectory in the development of resilience. Findings from three high-risk cohorts, each tapping a distinct disruption to maternal-infant bonding (prematurity, maternal depression, and early life stress/trauma), and followed from birth to adolescence/young adulthood, demonstrate how components of the neurobiology of affiliation confer resilience and uniquely shape the social brain.

Baby cry recognition is independent of motherhood but improved by experience and exposure

Neurobiological changes affecting new mothers are known to support the development of the mother-infant relationship (the 'maternal brain'). However, which aspects of parenting are actually mother-specific and which rely on general cognitive abilities remains debated. For example, refuting earlier findings, a recent study demonstrated that fathers identify their own baby from their cries just as well as mothers. Here we show that this performance is independent not only of sex, but also of parenthood status. We found that mothers' ability to recognize their newborn from their cries increased rapidly within few days postpartum, with highly multiparous mothers performing better. However, both male and female non-parents could similarly recognize an assigned baby, even after a very short exposure. As in mothers, both the initial amount of experimental exposure to the baby's cries (learning opportunity) and prior experience of caring for infants (auditory expertise) affected participants' performance. We thus suggest that, rather than being female-specific or motherhood-dependent, the ability to recognize a baby from their cries derives from general auditory and learning skills. By being available to non-parents of both sexes, it may contribute to the caregiving flexibility required for efficient cooperative breeding in humans.

Becoming a mother entails anatomical changes in the ventral striatum of the human brain that facilitate its responsiveness to offspring cues

In mothers, offspring cues are associated with a powerful reinforcing value that motivates maternal care. Animal studies show that this is mediated by dopamine release into the nucleus accumbens, a core component of the brain's reward system located in the ventral striatum (VStr). The VStr is also known to respond to infant signals in human mothers. However, it is unknown whether pregnancy modifies the anatomy or functionality of this structure, and whether such modifications underlie its strong reactivity to offspring cues. Therefore, we analyzed structural and functional neuroimaging data from a unique pre-conception prospective cohort study involving first-time mothers investigated before and after their pregnancy as well as nulliparous control women scanned at similar time intervals. First, we delineated the anatomy of the VStr in each subject's neuroanatomical space and examined whether there are volumetric changes in this structure across sessions. Then, we tested if these changes could predict the mothers' brain responses to visual stimuli of their infants. We found decreases in the right VStr and a trend for left VStr reductions in the women who were pregnant between sessions compared to the women who were not. Furthermore, VStr volume reductions across pregnancy were associated with infant-related VStr responses in the postpartum period, with stronger volume decreases predicting stronger functional activation to offspring cues. These findings provide the first indications that the transition to motherhood renders anatomical adaptations in the VStr that promote the strong responsiveness of a mother's reward circuit to cues of her infant.

Effect of sertraline on central serotonin and hippocampal plasticity in pregnant and non-pregnant rats

One of the most frequently prescribed selective serotonin reuptake inhibitor medications (SSRIs) for peripartum mood and anxiety disorders is sertraline (Zoloft®). Sertraline can help alleviate mood and anxiety symptoms in many women but it is not known how sertraline, or SSRIs in general, affect the neurobiology of the brain particularly when pregnant. The aim of this study was to investigate how sertraline affects plasticity in the hippocampus, a brain area integral in depression and SSRI efficacy (particularly in males), during late pregnancy and whether these effects differ from the effects of sertraline in non-pregnant females. To do this pregnant and age-matched non-pregnant female Sprague-Dawley rats were used. For the last half of pregnancy (10 days), and at matched points in non-pregnant females, rats were given sertraline (2.5 mg/kg/day or 10 mg/kg/day) or vehicle (0 mg/kg/day). Brains were used to investigate effects on the serotonergic system in the hippocampus and prefrontal cortex and measures of neuroplasticity in the hippocampus. Results show that pregnant females have significantly higher serum levels of sertraline compared to non-pregnant females but that rates of serotonin turnover in the hippocampus and PFC are similar between pregnant and non-pregnant females. Sertraline increased synaptophysin density in the dentate gyrus and CA3 and was associated with a decrease in cell proliferation in the dentate gyrus of non-pregnant, but not pregnant, females. During late pregnancy the hippocampus showed significant reductions in neurogenesis and increases in synaptophysin density. This research highlights the need to consider the unique effect of reproductive state on the neuropharmacology of SSRIs.

Impact of parturition on maternal cardiovascular and neuronal integrity in a high risk cohort - a prospective cohort study

Background

To better understand the profound multisystem changes in maternal physiology triggered by parturition, in particular in the underexplored neuronal system, by deploying a panel of pre- vs post-delivery maternal serum biomarkers, most notably the neuronal cytoskeleton constituent neurofilament light chain (NfL). This promising fluid biomarker is not only increasingly applied to investigate disease progression in numerous brain diseases, particularly in proteopathies, but also in detection of traumatic brain injury or monitoring neuroaxonal injury after ischemic stroke.

Methods

The study was nested within a prospective cohort study of pregnant women at risk of developing preeclampsia at the University Hospital of Basel. Paired ante- and postpartum levels of progesterone, soluble fms-like tyrosine kinase-1 (sFlt-1), placental growth factor (PlGF), mid-regional pro-atrial natriuretic peptide (MR-proANP), copeptin (CT-proAVP), and NfL were measured in 56 women with complete clinical data.

Results

Placental delivery significantly decreased all placental markers: progesterone 4.5-fold, PlGF 2.2-fold, and sFlt-1 1.7-fold. Copeptin and MR-proANP increased slightly (1.4- and 1.2-fold, respectively). Unexpectedly, NfL levels (median [interquartile range]) increased significantly post-partum: 49.4 (34.7–77.8) vs 27.7 (16.7–31.4) pg/ml (p < 0.0001). Antepartum NfL was the sole independent predictor of NfL peri-partum change; mode of delivery, duration of labor, clinical characteristics and other biomarkers were all unrelated. Antepartum NfL levels were themselves independently predicted only by maternal age.

Conclusions

Parturition per se increases maternal serum NfL levels, suggesting a possible impact of parturition on maternal neuronal integrity.

An IL-6 receptor antagonist attenuates postpartum anhedonia, but has no effect on anhedonia precipitated by subchronic stress in female rats

RATIONALE

Nearly 60-80% of women experience some form of sadness, anxiety, or anhedonia in the weeks following the birth of a child (Patel et al. 23(2):534-42, 2012; Degner 10: 359;j4692, 2017); however, the exact mechanisms that precipitate these changes in mood postpartum are still unknown. It is well-known that the function of the peripheral immune system is significantly altered during pregnancy in order to protect the developing fetus from being rejected by the maternal immune system (Fallon et al. 17(1):7-17, 2002), and we have recently found a dramatic change in the central immune system during and just after pregnancy in female rats (Sherer et al. 66:201-209, 2017). We observed anhedonia in Sprague-Dawley rat dams on the day of birth that is associated with an increase in interleukin (IL)-6 expression in the brain on the day of birth (Posillico and Schwarz 298(Pt B):218-28, 2016).

OBJECTIVES

The goal of the current experiments was to determine whether inhibiting the IL-6 receptor could prevent onset of this postpartum anhedonia, or anhedonia precipitated by subchronic stress in non-pregnant females.

RESULTS

Treatment with an IL-6 receptor antibody attenuated postpartum anhedonia as characterized by a decrease in sucrose preference. In contrast, this antibody had no effect on the decrease in sucrose preference induced following a week of forced swim stress in non-pregnant female rats.

CONCLUSIONS

The results of these studies suggest that the molecular mechanisms that underlie the onset of anhedonia following birth or mild stress in female rats may be distinct.

Fatherhood diminishes the hippocampal damaging action of excitotoxic lesioning in mice

Parental experience imposes neuroplasticity in the hippocampus of females and males. In lactating rat dams, the hippocampus is protected against excitotoxic damage by kainic acid lesioning, although it is still unknown whether paternity can provide such protection to male rodents. To evaluate the protective effects of fatherhood against excitotoxic lesions, we paired male mice with females and co-housed them until the day of parturition (PPD0), when we randomly assigned them to two groups: (i) the pregnancy group (males housed individually overnight and injected i.c.v. with 100 ng per 1 μL of kainic acid or vehicle on PPD1) and (ii) the sire group (males housed with the dam and pups until PPD8, when injected i.c.v. after evaluation of parental behaviour). Individually housed virgin adult male mice formed the control group. Markers of neurodegeneration (NeuN, Fluoro-Jade C) and astrogliosis (glial fibrillary acidic protein) were evaluated in fixed cerebral tissue containing the dorsal CA1, CA3 and CA4 hippocampal subfields. The CA1 subfield did not suffer damage in any of the experimental groups. The sire group exhibited less neurodegeneration and astrogliosis in the CA3 and CA4 subfields compared to their respective controls, independently of the expression of parental behaviour. Western blot analysis was conducted for prolactin (PRL), PRL receptor and related intracellular pathways. Monomeric PRL was lower in the hippocampus of sires in the first week postpartum with a parallel rise of a 48-kDa dimerised isoform compared to virgin controls. The long isoform of PRL receptor did not change, and signal transducer and activator of transcription 5 (STAT5) was not detected in the hippocampus. However, a sustained rise in pAkt, a signalling molecule that participates in cell survival, was observed in the sire group. These results indicate that the hippocampus of sires housed with the dam and pups is less sensitive to neurotoxic injury, which might not be primarily regulated by PRL-STAT5-modulated mechanisms.

Experience of Adversity during a First Lactation Modifies Prefrontal Cortex Morphology in Primiparous Female Rats: Lack of Long Term Effects on a Subsequent Lactation

Reproductive experience is associated with morphological and functional plasticity in brain areas important for cognitive and emotional responses, including the infralimbic (IL) medial prefrontal cortex (mPFC). Here we examined whether suboptimal conditions during a first lactation could modify lactation-induced morphological IL mPFC changes, leading to alterations in stress responses and attention and whether any observed effects would persist into a second lactation. Reduced availability of bedding and nesting material (LB) was used to induce unfavorable conditions in primiparous (P) mothers. In normal bedding (NB) conditions, P mothers exhibited high spine number and density on postpartum day (PPD)10, which greatly decreased 2 weeks after weaning of their pups. In contrast, P-LB mothers had a lower spine number and density on PPD10, which markedly increased after weaning. LB exposure did not modify stress responsiveness to a ferret odor on PPD5 in primiparous or in multiparous (M) females. Number of errors and trials to criterion in the attention set shifting task were not modified by a history of adversity in multiparous females, although this group tended to exhibit higher attentional abilities than M-NB females. These results suggest that adversity acutely reduces morphological plasticity in the maternal mPFC during lactation, an effect that is not associated with significant changes in stress responses and/or glucocorticoid production. Medial PFC morphological changes induced by LB subside during a subsequent lactation as does the effect of maternity itself.

Dissecting maternal care: Patterns of maternal parenting in a prospective cohort study

Parental care has a strong impact on neurodevelopment and mental health in the offspring. Although numerous animal studies have revealed that the parental brain is a highly complex system involving many brain structures and neuroendocrine systems, human maternal parenting as a multidimensional construct with cognitive, emotional, and behavioural components has not been characterised comprehensively. This unique multi-method analysis aimed to examine patterns of self-reported and observed parenting from 6 to 60 months postpartum in a cohort of 496 mothers (mean maternal age = 32 years). Self-report questionnaires assessed motivational components of mothering, parenting stress, parenting-related mood, maternal investment, maternal parenting style, mother-child relationship satisfaction, and mother-child bonding at multiple time points. Observed parenting variables included the Ainsworth Sensitivity Scales at 6 and 18 months, the Behavioral Evaluation Strategies Taxonomies at 6 months, an Etch-A-Sketch cooperation task at 48 months, and the Parent-Child Early Relationship Assessment at 60 months. To examine whether different latent constructs underlie these measures of maternal parenting, we conducted an exploratory factor analysis. Self-report measures of parenting correlated only weakly with behavioural observations. Factor analysis on a subsample (n = 197) revealed four latent factors that each explained from 7% to 11% of the variance in the data (32% total variance explained). Based on the loadings of the instruments, the factors were interpreted as: Supportive Parenting, Self-Enjoyment Parenting, Overwhelmed Parenting, and Affectionate Parenting. These factor scores showed specific associations with maternal education and depressive symptoms, as well as with child outcomes, including maternally reported internalising and externalising behavioural problems, school readiness, and child-reported symptoms of mental health. These findings parallel the complexity of the parental brain, suggesting that maternal parenting consists of multiple components, each of which is associated with different maternal characteristics and child outcomes.

The neural basis of tadpole transport in poison frogs

Parental care has evolved repeatedly and independently across animals. While the ecological and evolutionary significance of parental behaviour is well recognized, underlying mechanisms remain poorly understood. We took advantage of behavioural diversity across closely related species of South American poison frogs (Family Dendrobatidae) to identify neural correlates of parental behaviour shared across sexes and species. We characterized differences in neural induction, gene expression in active neurons and activity of specific neuronal types in three species with distinct care patterns: male uniparental, female uniparental and biparental. We identified the medial pallium and preoptic area as core brain regions associated with parental care, independent of sex and species. The identification of neurons active during parental care confirms a role for neuropeptides associated with care in other vertebrates as well as identifying novel candidates. Our work is the first to explore neural and molecular mechanisms of parental care in amphibians and highlights the potential for mechanistic studies in closely related but behaviourally variable species to help build a more complete understanding of how shared principles and species-specific diversity govern parental care and other social behaviour.

The Impact of Ethologically Relevant Stressors on Adult Mammalian Neurogenesis

Adult neurogenesis—the formation and functional integration of adult-generated neurons—remains a hot neuroscience topic. Decades of research have identified numerous endogenous (such as neurotransmitters and hormones) and exogenous (such as environmental enrichment and exercise) factors that regulate the various neurogenic stages. Stress, an exogenous factor, has received a lot of attention. Despite the large number of reviews discussing the impact of stress on adult neurogenesis, no systematic review on ethologically relevant stressors exists to date. The current review details the effects of conspecifically-induced psychosocial stress (specifically looking at the lack or disruption of social interactions and confrontation) as well as non-conspecifically-induced stress on mammalian adult neurogenesis. The underlying mechanisms, as well as the possible functional role of the altered neurogenesis level, are also discussed. The reviewed data suggest that ethologically relevant stressors reduce adult neurogenesis.

The long and short term effects of motherhood on the brain

Becoming a mother is associated with dramatic changes in physiology, endocrinology, immune function, and behaviour that begins during pregnancy and persists into the postpartum. Evidence also suggests that motherhood is accompanied by long-term changes in brain function. In this review, we summarize the short (pregnancy and postpartum) and long-term (beyond the postpartum and into middle age) effects of pregnancy and motherhood on cognition, neuroplasticity, and neuroimmune signalling. We also discuss the effects of previous history of pregnancy and motherhood (parity) on brain health and disease (neurodegenerative diseases and stroke outcomes) and on efficacy of hormone and antidepressant treatments. Finally, we argue that pregnancy and motherhood are unique female experiences that need to be taken into account to better understand female brain function and aging.

More than just mothers: The neurobiological and neuroendocrine underpinnings of allomaternal caregiving

In a minority of mammalian species, mothers depend on others to help raise their offspring. New research is investigating the neuroendocrine mechanisms supporting this allomaternal behavior. Several hormones have been implicated in allomaternal caregiving; however, the role of specific hormones is variable across species, perhaps because allomothering independently evolved multiple times. Brain regions involved in maternal behavior in non-human animals, such as the medial preoptic area, are also critically involved in allomaternal behavior. Allomaternal experience modulates hormonal systems, neural plasticity, and behavioral reactivity. In humans, fatherhood-induced decreases in testosterone and increases in oxytocin may support sensitive caregiving. Fathers and mothers activate similar neural systems when exposed to child stimuli, and this can be considered a global "parental caregiving" network. Finally, early work on caregiving by non-kin (e.g., foster parents) suggests reliance on similar mechanisms as biologically-related parents. This article is part of the 'Parental Brain and Behavior' Special Issue.

Serotonin and motherhood: From molecules to mood

Emerging research points to a valuable role of the monoamine neurotransmitter, serotonin, in the display of maternal behaviors and reproduction-associated plasticity in the maternal brain. Serotonin is also implicated in the pathophysiology of numerous affective disorders and likely plays an important role in the pathophysiology of maternal mental illness. Therefore, the main goals of this review are to detail: (1) how the serotonin system of the female brain changes across pregnancy and postpartum; (2) the role of the central serotonergic system in maternal caregiving and maternal aggression; and (3) how the serotonin system and selective serotonin reuptake inhibitor medications (SSRIs) are involved in the treatment of maternal mental illness. Although there is much work to be done, studying the central serotonin system's multifaceted role in the maternal brain is vital to our understanding of the processes governing matrescence and the maintenance of motherhood.

Pregnancy and adolescence entail similar neuroanatomical adaptations: A comparative analysis of cerebral morphometric changes

Mapping the impact of pregnancy on the human brain is essential for understanding the neurobiology of maternal caregiving. Recently, we found that pregnancy leads to a long-lasting reduction in cerebral gray matter volume. However, the morphometric features behind the volumetric reductions remain unexplored. Furthermore, the similarity between these reductions and those occurring during adolescence, another hormonally similar transitional period of life, still needs to be investigated. Here, we used surface-based methods to analyze the longitudinal magnetic resonance imaging data of a group of 25 first-time mothers (before and after pregnancy) and compare them to those of a group of 25 female adolescents (during 2 years of pubertal development). For both first-time mothers and adolescent girls, a monthly rate of volumetric reductions of 0.09 mm³ was observed. In both cases, these reductions were accompanied by decreases in cortical thickness, surface area, local gyrification index, sulcal depth, and sulcal length, as well as increases in sulcal width. In fact, the changes associated with pregnancy did not differ from those that characterize the transition during adolescence in any of these measures. Our findings are consistent with the notion that the brain morphometric changes associated with pregnancy and adolescence reflect similar hormonally primed biological processes.

Adult mammalian neurogenesis and motivated behaviors

Adult neurogenesis continues to captivate the curiosity of the scientific community; and researchers seem to have a particular interest in identifying the functional implications of such plasticity. While the majority of research focuses on the association between adult neurogenesis and learning and memory (including spatial learning associated with hippocampal neurogenesis and olfactory discrimination associated with neurogenesis in the olfactory system), the following review will explore the link to motivated behaviors. In particular, goal-directed behaviors such as sociosexual, parental, aggressive, as well as depression- and anxiety-like behaviors and their reciprocal association to adult neurogenesis will be evaluated. The review will detail research in humans and other mammalian species. Furthermore, the potential mechanisms underlying these neurogenic alterations will be highlighted. Lastly, the review will conclude with a discussion on the functional significance of these newly generated cells in mediating goal-directed behaviors.