Motherhood and infant contact regulate neuroplasticity in the serotonergic midbrain dorsal raphe

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.

Beyond sex differences: short- and long-term effects of pregnancy on the brain

Growing attention has been directed to the inclusion of females in neuroscience studies, and to the importance of studying sex as a biological variable. However, how female-specific factors such as menopause and pregnancy, affect the brain remains understudied. In this review, we use pregnancy as a case in point of a female-unique experience that can alter neuroplasticity, neuroinflammation, and cognition. We examine studies in both humans and rodents indicating that pregnancy can modify neural function in the short term, as well as alter the trajectory of brain aging. Furthermore, we discuss the influence of maternal age, fetal sex, number of pregnancies, and presence of pregnancy complications on brain health outcomes. We conclude by encouraging the scientific community to prioritize researching female health by recognizing and including factors such as pregnancy history in research.

Oxytocin interactions with central dopamine and serotonin systems regulate different components of motherhood

The role of oxytocin in maternal caregiving and other postpartum behaviours has been studied for more than five decades. How oxytocin interacts with other neurochemical systems to enact these behavioural changes, however, is only slowly being elucidated. The best-studied oxytocin-neurotransmitter interaction is with the mesolimbic dopamine system, and this interaction is essential for maternal motivation and active caregiving behaviours such as retrieval of pups. Considerably less attention has been dedicated to investigating how oxytocin interacts with central serotonin to influence postpartum behaviour. Recently, it has become clear that while oxytocin-dopamine interactions regulate the motivational and pup-approach aspects of maternal caregiving behaviours, oxytocin-serotonin interactions appear to regulate nearly all other aspects including postpartum nursing, aggression, anxiety-like behaviour and stress coping strategy. Collectively, oxytocin's interactions with central dopamine and serotonin systems are thus critical for the entire suite of behavioural adaptations exhibited in the postpartum period, and these sites of interaction are potential pharmacological targets for where oxytocin could help to ameliorate deficits in maternal caregiving and poor postpartum mental health. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'.

Transcriptomics of Parental Care in the Hypothalamic-Septal Region of Female Zebra Finch Brain

(1) Background: The objective of this study was to uncover genomic causes of parental care. Since birds do not lactate and, therefore, do not show the gene expressional changes required for lactation, we investigate gene expression associated with parenting in caring and non-caring females in an avian species, the small passerine bird zebra finch (Taeniopygia guttata). Here, we compare expression patterns in the hypothalamic–septal region since, previously, we showed that this area is activated in parenting females. (2) Methods: Transcriptome sequencing was first applied in a dissected part of the zebra finch brain related to taking care of the nestlings as compared to a control group of social pairs without nestlings. (3) Results: We found genes differentially expressed between caring and non-caring females. When introducing a log2fold change threshold of 1.5, 13 annotated genes were significantly upregulated in breeding pairs, while 39 annotated genes were downregulated. Significant enrichments of dopamine and acetylcholine biosynthetic processes were identified among upregulated pathways, while pro-opiomelanocortin and thyroid hormone pathways were downregulated, suggesting the importance of these systems in parental care. Network analysis further suggested neuro-immunological changes in mothers. (4) Conclusions: The results confirm the roles of several hypothesized major pathways in parental care, whereas novel pathways are also proposed.

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.

Oxytocin receptor expression in the midbrain dorsal raphe is dynamic across female reproduction in rats

Central oxytocin receptor (OTR) expression is extremely sensitive to circulating steroid hormones and OTRs influence many of the neurobehavioural adaptations associated with female reproduction (e.g., postpartum caregiving, aggression, cognition, affective responses). Changes in central OTR expression across female reproduction have often been studied, but almost all of such research has focused on the forebrain, ignoring hormone-sensitive midbrain sites such as the serotonergic dorsal raphe (DR) that are also critical for postpartum behaviours. To investigate the effects of female reproductive state on OTRs in the DR, we first used autoradiography to examine OTR binding across four female reproductive states in laboratory rats: dioestrous virgin, pregnancy day 10, the day of parturition and postpartum day 7. OTR binding in the rostral DR (but not other DR subregions) was approximately 250% higher in parturient rats compared to dioestrous virgins and dropped back down to virgin levels by postpartum day 7. Given the chemical heterogeneity of the DR, we then examined OTR expression in the three most abundant neuronal phenotypes of the DR (i.e., serotonin, GABA and dopamine) in dioestrous virgins and recently parturient females. Using dual-label immunohistochemistry and in situ hybridisation, we found that twice as many dopaminergic cells in the parturient rostral DR contained OTR immunoreactivity compared to that found in virgins. On the other hand, mothers had fewer rostral DR GABAergic cells expressing OTRs than did virgins. OTR expression in serotonin cells did not differ between the two groups. Overall, these results suggest that the rostral subregion of the midbrain DR is uniquely sensitive to oxytocin around the time of parturition, with subpopulations of cells that become more sensitive (i.e., dopamine), less sensitive (i.e., GABA) and show no change (i.e., serotonin) to this neuropeptide. This dynamic OTR signalling in the female DR may help drive the numerous behavioural changes across female reproduction that are necessary for successful motherhood.

Perinatal depression: Heterogeneity of disease and in animal models

Perinatal depression (PND) can have either an antepartum or postpartum onset. Although the greatest risk factor for PND is previous depression history,de novoPND occurs with the majority of cases occurring in the postpartum. Timing of depression can impact etiology, prognosis, and response to treatment. Thus, it is crucial to study the impact of the heterogeneity of PND for better health outcomes. In this review, we outline the differences between antepartum and postpartum depression onset of PND. We discuss maternal physiological changes that differ between pregnancy and postpartum and how these may differentially impact depression susceptibility. We highlight changes in the maternal steroid and peptide hormone levels, immune signalling, serotonergic tone, metabolic factors, brain morphology, and the gut microbiome. Finally, we argue that studying the heterogeneity of PND in clinical and preclinical models can lead to improved knowledge of disease etiopathology and treatment outcomes.

Postpartum environmental challenges alter maternal responsiveness and offspring development

Because many threats exist in an animal's natural habitat, it is important to understand the impact of environmental challenges on maternal-offspring interactions and outcomes. In the current study, a rodent model incorporating the presence of restricted resources and an environmental threat (e.g. predator-related odors and sounds) was investigated. Specifically, pregnant females were assigned to one of four treatments: standard resources, without threat (SR; n = 7); standard resources plus threat (SR-T; n = 8); restricted resources, without threat (RR; n = 7); and restricted resources plus threat (RR-T; n = 6). Maternal rats were moved into the assigned conditions on postnatal day 2 and remained until pups were weaned. Following a standard pup retrieval task on postnatal days 2 and 6, maternal rats were exposed to a retrieval challenge task on postnatal day 8 in which each rat had to traverse a novel barrier to retrieve pups. For neurobiological measures of stress/resilience responsiveness, fecal samples were collected for detection of corticosterone and DHEA metabolites; additionally, immunohistochemistry was conducted on the maternal brains to indicate the presence of Neuropeptide Y (NPY) and Brain Derived Neurotrophic Factor (BDNF) immunoreactivity in the hippocampus, amygdala and hypothalamus. Pup development measures, including body weight and tail length, were also collected. Results suggest that maternal rats with restricted resources exhibited diminished maternal responsiveness that resulted in altered pup development measures; further, restricted resource rats exhibited endocrine markers of compromised emotional resilience (lower DHEA) and decreased neural markers of neuroplasticity (BDNF) and emotional resilience (NPY). Interestingly, predator threat affected various aspects of maternal-pup interactions but had no effect on neurobiological variables, suggesting that restricted resources had a more negative impact on maternal-related outcomes than the presence of predator threat.

Pregnancy Promotes Maternal Hippocampal Neurogenesis in Guinea Pigs

Adult neurogenesis in the hippocampal dentate gyrus (DG) modulates cognition and behavior in mammals, while motherhood is associated with cognitive and behavioral changes essential for the care of the young. In mice and rats, hippocampal neurogenesis is reported to be reduced or unchanged during pregnancy, with few data available from other species. In guinea pigs, pregnancy lasts ~9 weeks; we set to explore if hippocampal neurogenesis is altered in these animals, relative to gestational stages. Time-pregnant primigravidas (3-5 months old) and age-matched nonpregnant females were examined, with neurogenic potential evaluated via immunolabeling of Ki67, Sp8, doublecortin (DCX), and neuron-specific nuclear antigen (NeuN) combined with bromodeoxyuridine (BrdU) birth-dating. Relative to control, subgranular Ki67, Sp8, and DCX-immunoreactive (+) cells tended to increase from early gestation to postpartum and peaked at the late gestational stage. In BrdU pulse-chasing experiments in nonpregnant females surviving for different time points (2-120 days), BrdU+ cells in the DG colocalized with DCX partially from 2 to 42 days (most frequently at 14-30 days) and with NeuN increasingly from 14 to 120 days. In pregnant females that received BrdU at early, middle, and late gestational stages and survived for 42 days, the density of BrdU+ cells in the DG was mostly high in the late gestational group. The rates of BrdU/DCX and BrdU/NeuN colocalization were similar among these groups and comparable to those among the corresponding control group. Together, the findings suggest that pregnancy promotes maternal hippocampal neurogenesis in guinea pigs, at least among primigravidas.

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.

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.

The dynamic serotonin system of the maternal brain

Many pregnant and postpartum women worldwide suffer from high anxiety and/or depression, which can have detrimental effects on maternal and infant well-being. The first-line pharmacotherapies for prepartum and postpartum affective disorders continue to be the selective serotonin reuptake inhibitors (SSRIs), despite the lack of large well-controlled studies demonstrating their efficacy in reproducing women and the potential for fetal/neonatal exposure to the drugs. Prepartum or postpartum use of SSRIs or other drugs that modulate the brain's serotonin system is also troubling because very little is known about the typical, let alone the atypical, changes that occur in the female central serotonin system across reproduction. We do know from a handful of studies of women and female laboratory rodents that numerous aspects of the central serotonin system are naturally dynamic across reproduction and are also affected by pregnancy stress (a major predisposing factor for maternal psychopathology). Thus, it should not be assumed that the maternal central serotonin system being targeted by SSRIs is identical to non-parous females or males. More information about the normative and stress-derailed changes in the maternal central serotonin system is essential for understanding how serotonin is involved in the etiology of, and the best use of SSRIs for potentially treating, affective disorders in the pregnant and postpartum populations.

Semiotic Regulation in the Construction of Maternal Bond: From Body Experience to the Semiotic Field

The objective of this paper is to analyze how the maternal bond in first-time pregnant women emerges from bodily experiences in the pre-semiotic level and leads to the emergence of the semiotic field. The bond as a sign field is internally structured and enables the regulation of connections with other signs outside the field. As a result of the dialogue between biological and sociocultural imperatives, sociocultural meanings are turned into personal meanings and presented by women through behavior. This study is based on longitudinally-collected interview data consisting of six interviews with women from the time they were pregnant until their child turned one year old. During this period, three ruptures as turning points in the formation of the bond were identified. Based on idiographic analyses, it was concluded that body signals caused by the development of the fetus are coded by women into signs of various kinds, which define the status of mother and create the foundation for the mother-child relationship which continues throughout the lifespan.

Sex differences in depression: Insights from clinical and preclinical studies

Depression represents a global mental health concern, and disproportionally affects women as they are twice more likely to be diagnosed than men. In this review, we provide a summary of evidence to support the notion that differences in depression between men and women span multiple facets of the disease, including epidemiology, symptomology, treatment, and pathophysiology. Through a lens of biological sex, we overview depression-related transcriptional patterns, changes in neuroanatomy and neuroplasticity, and immune signatures. We acknowledge the unique physiological and behavioral demands of pregnancy and motherhood by devoting special attention to depression occurring in the peripartum period. Specifically, we discuss issues surrounding the presentation, time course, treatment, and neurobiology of peripartum depression. We write this review with the intention of highlighting the encouraging advancements in our understanding of sex differences in depression, while underscoring the gaps that remain. A more systematic consideration of biological sex as a variable in depression research will be critical in the discovery and development of pharmacotherapies that are efficacious for both men and women.

Gating of the neuroendocrine stress responses by stressor salience in early lactating female rats is independent of infralimbic cortex activation and plasticity

In early lactation (EL), stressor salience modulates neuroendocrine stress responses, but it is unclear whether this persists throughout lactation and which neural structures are implicated. We hypothesized that this process is specific to EL and that the infralimbic (IL) medial prefrontal cortex (mPFC) might provide a critical link between assessment of threat and activation of the hypothalamo-pituitary-adrenal (HPA) axis in EL. We measured neuroendocrine responses and neuronal Fos induction to a salient (predator odor) or non-salient (tail pinch) psychogenic stressor in EL and late lactation (LL) females. We found that EL females exhibited a large response to predator stress only in the presence of pups, while responses to tail pinch were reduced independently of pup presence. In LL, HPA axis responses were independent of pup presence for both stressors and only responses to tail pinch were modestly reduced compared to virgins. Intracerebral injection of the local anesthetic bupivacaine (BUP) (0.75%; 0.5 µl/side) in the IL mPFC did not differentially affect neuroendocrine responses to predator odor in virgin and EL females, suggesting that lactation-induced changes in this structure might not regulate stressor salience for the HPA axis. However, the IL mPFC displayed morphological changes in lactation, with significant increases in dendritic spine numbers and density in EL compared to LL and virgin females. EL females also showed improved performance in the attention set-shifting task (AST), which could reflect early plasticity in the IL mPFC at a time when rapid adaptation of the maternal brain is necessary for pup survival.

Serotonin-specific lesions of the dorsal raphe disrupt maternal aggression and caregiving in postpartum rats

The behavioral modifications associated with early motherhood, which include high aggression, caring for the young, and low anxiety, are all affected by acute pharmacological manipulation of serotonin signaling. However, the effects on all these behaviors of permanently disrupting serotonin signaling from one of its primary sources, the dorsal raphe nucleus (DR), have not been examined in detail. To address this, serotonin-specific lesions centered on the dorsomedial DR (DRdm; DR subregion strongly implicated in emotional behaviors) were induced at mid-pregnancy (day 15) or early postpartum (day 2) in rats using a saporin-conjugated neurotoxin targeting the serotonin transporter (Anti-SERT-SAP). Prepartum or postpartum Anti-SERT-SAP reduced DRdm serotonin immunoreactivity by ∼40-65%, and postpartum Anti-SERT-SAP also reduced it in the ventromedial and lateral wings of the DR, as well as in the median raphe. Serotonin-immunoreactive fibers were significantly reduced in the anterior hypothalamus, but not medial preoptic area, of lesioned dams. Pre- or postpartum lesions both greatly reduced maternal aggression, but while prepartum lesions did not affect later undisturbed maternal caregiving, the larger postpartum lesions prevented the postpartum decline in kyphotic nursing and reduced pup licking. Serotonin lesions did not affect pup retrieval, but the prepartum lesions temporarily increased maternal hovering over and licking the pups observed immediately after the disruptive retrieval tests. Dams' anxiety-like behaviors and litter weight gains were unaffected by the lesions. These findings suggest that DRdm serotonin projecting to the AH is particularly critical for maternal aggression, but that more widespread disruption of midbrain raphe serotonin is necessary to greatly impair maternal caregiving. Postpartum anxiety may rely more on other neurochemical systems or different midbrain serotonergic cell populations.

Adult Neurogenesis in Sheep: Characterization and Contribution to Reproduction and Behavior

Sheep have many advantages to study neurogenesis in comparison to the well-known rodent models. Their development and life expectancy are relatively long and they possess a gyrencephalic brain. Sheep are also seasonal breeders, a characteristic that allows studying the involvement of hypothalamic neurogenesis in the control of seasonal reproduction. Sheep are also able to individually recognize their conspecifics and develop selective and lasting bonds. Adult olfactory neurogenesis could be adapted to social behavior by supporting recognition of conspecifics. The present review reveals the distinctive features of the hippocampal, olfactory, and hypothalamic neurogenesis in sheep. In particular, the organization of the subventricular zone and the dynamic of neuronal maturation differs from that of rodents. In addition, we show that various physiological conditions, such as seasonal reproduction, gestation, and lactation differently modulate these three neurogenic niches. Last, we discuss recent evidence indicating that hypothalamic neurogenesis acts as an important regulator of the seasonal control of reproduction and that olfactory neurogenesis could be involved in odor processing in the context of maternal behavior.