Plasticity of the parental brain: a case for neurogenesis

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.

Highlights regarding prolactin in the dentate gyrus and hippocampus

Prolactin (PRL) is a pituitary hormone that has been typically related to lactogenesis in mammals. However, it has been described over 300 roles in the organism of vertebrae and its relationship with the central nervous system (CNS) is yet to be clarified. Mainly secreted by the pituitary gland, the source of prolactin in the CNS remains unclear, where some experiments suggest active transport via an unknown carrier or, on the contrary, PRL being synthesized on the brain. So far, it seems to be involved with neurogenesis, neuroprotection, maternal behavior and cognitive processes in the hippocampus and dentate gyrus, among other regions.

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.

Decoding signaling pathways involved in prolactin-induced neuroprotection: A review

It has been well recognized that prolactin (PRL), a pleiotropic hormone, has many functions in the brain, such as maternal behavior, neurogenesis, and neuronal plasticity, among others. Recently, it has been reported to have a significant role in neuroprotection against excitotoxicity. Glutamate excitotoxicity is a common alteration in many neurological and neurodegenerative diseases, leading to neuronal death. In this sense, several efforts have been made to decrease the progression of these pathologies. Despite various reports of PRL's neuroprotective effect against excitotoxicity, the signaling pathways that underlie this mechanism remain unclear. This review aims to describe the most recent and relevant studies on the molecular signaling pathways, particularly, PI3K/AKT, NF-κB, and JAK2/STAT5, which are currently under investigation and might be implicated in the molecular mechanisms that explain the PRL effects against excitotoxicity and neuroprotection. Remarkable neuroprotective effects of PRL might be useful in the treatment of some neurological diseases.

Brain orchestration of pregnancy and maternal behavior in mice: A longitudinal morphometric study

Reproduction induces changes within the brain to prepare for gestation and motherhood. However, the dynamic of these central changes and their relationships with the development of maternal behavior remain poorly understood. Here, we describe a longitudinal morphometric neuroimaging study in female mice between pre-gestation and weaning, using new magnetic resonance imaging (MRI) resources comprising a high-resolution brain template, its associated tissue priors (60-µm isotropic resolution) and a corresponding mouse brain atlas (1320 regions of interest). Using these tools, we observed transient hypertrophies not only within key regions controlling gestation and maternal behavior (medial preoptic area, bed nucleus of the stria terminalis), but also in the amygdala, caudate nucleus and hippocampus. Additionally, unlike females exhibiting lower levels of maternal care, highly maternal females developed transient hypertrophies in somatosensory, entorhinal and retrosplenial cortices among other regions. Therefore, coordinated and transient brain modifications associated with maternal performance occurred during gestation and lactation.

The behavioral neuroendocrinology of maternal behavior: Past accomplishments and future directions

Research on the neuroendocrine-endocrine-neural regulation of maternal behavior has made significant progress the past 50 years. In this mini-review progress during this period has been divided into five stages. These stages consist of advances in the identification of endocrine factors that mediate maternal care, the characterization of the neural basis of maternal behavior with reference to endocrine actions, the impact of developmental and experiential states on maternal care, the dynamic neuroplastic maternal brain, and genes and motherhood. A final section concludes with a discussion of future directions in the field of the neurobiology/neuroendocrinology of motherhood.

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.

Differential effects of oxytocin on olfactory, hippocampal and hypothalamic neurogenesis in adult sheep

New neurons are continuously added in the dentate gyrus of the hippocampus, the olfactory bulb and the hypothalamus of mammalian brain. In sheep, while the control of adult neurogenesis by the social environment or the photoperiod has been the subject of several studies, its regulation by intrinsic factors, like hormones or neurotransmitters is less documented. We addressed this question by investigating the effects of central oxytocin administration on hippocampal, olfactory and hypothalamic neurogenesis. Endogenous markers, Ki67, Sox2 and DCX were used to assess cell proliferation, progenitor cells density and cell survival respectively in non-gestant ewes receiving a steroid treatment followed by intracerebroventricular injections of either oxytocin or saline. The results showed that oxytocin treatment significantly decreases the density of neuroblasts in the olfactory bulb, increases the density of neuroblasts in the ventromedian nucleus of the hypothalamus while no change is observed in both ventral and dorsal dentate gyrus. In addition, no change in the density of progenitor cells is found in the three neurogenic niches. These findings show for the first time that in females, oxytocin can regulate adult neurogenesis by acting on neuroblasts but not on progenitor cells and that this regulation is region specific.

High social motivation induces deficits in maternal behaviour but not plasticity of the subventricular zone in Japanese quail (Coturnix japonica)

Maternal behaviour develops differently depending on the characteristics of an individual, such as age or emotional reactivity. Social motivation, defined as the propensity to establish social contact, has received little attention in relation to maternal behaviour in birds. In addition, the transition to motherhood is a time of plasticity in the brain of the new mother in mammals. However, it remains to be determined how maternal brain plasticity is affected in avian species. The present study investigated how a the social motivation of a mother alters maternal behaviour and brain plasticity of the Japanese quail (Coturnix japonica). Adult females from lines selected for high and low social motivation were exposed to chicks for 11 days. After maternal care testing, and at matched time points in controls, the brains of females were perfused for assessment of doublecortin-immunoreactive staining, a marker of neurogenesis, in the subventricular zone (SVZ), a neurogenic niche. The results obtained showed that high socially motivated female quail spent significantly less time performing maternal behaviour when exposed to chicks compared to low socially motivated females. Moreover, the warming of chicks by high socially motivated females involved less covering postures and mothers were more rejecting of chicks. Interestingly, the plasticity indicators in the SVZ did not differ between low and high socially motivated females and were not associated with differences in maternal caregiving when using doublecortin-immunoreactive staining. Thus, high social motivation in this avian species does not favour maternal behaviour and this level of motivation to the mother is not related to changes in neuroplasticity in the SVZ of the female quail.

With a little help from her friends (and family) part II: Non-maternal caregiving behavior and physiology in mammals

The diversity of competing frameworks for explaining the evolution of non-maternal care in mammals (Part I, this issue) reflects the vast range of behaviors and associated outcomes these theories attempt to subsume. Caretaking comprises a wide variety of behavioral domains, and is mediated by an equally large range of physiological systems. In Part II, we provide an overview of how non-maternal care in mammals is expressed, the ways in which it is regulated, and the many effects such care has on both recipients and caretakers. We also discuss the two primary ways in which closer integration of ultimate and proximate levels of explanation can be useful when addressing questions about non-maternal caretaking. Specifically, proximate mechanisms provide important functional clues, and are key to testing theory concerning evolutionary tradeoffs. Finally, we highlight a number of methodological and publication biases that currently shape the literature, which provide opportunities for knowledge advancement in this domain going forward. In this conclusion to our two-part introduction, we provide a broad survey of the behavior and physiology that the contributions to this special issue represent.

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.

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.

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.

Down-regulation of fatty acid binding protein 7 (Fabp7) is a hallmark of the postpartum brain

Fatty acid binding protein 7 (Fabp7) is a versatile protein that is linked to glial differentiation and proliferation, neurogenesis, and multiple mental health disorders. Recent microarray studies identified a robust decrease in Fabp7 expression in key brain regions of the postpartum rodents. Given its diverse functions, Fabp7 could play a critical role in sculpting the maternal brain and promoting the maternal phenotype. The present study aimed at investigating the expression profile of Fabp7 across the postpartum CNS. Quantitative real-time PCR (qPCR) analysis showed that Fabp7 mRNA was consistently down-regulated across the postpartum brain. Of the 9 maternal care-related regions tested, seven exhibited significant decreases in Fabp7 in postpartum (relative to virgin) females, including medial prefrontal cortex (mPFC), nucleus accumbens (NA), lateral septum (LS), bed nucleus of stria terminalis dorsal (BnSTd), paraventricular nucleus (PVN), lateral hypothalamus (LH), and basolateral and central amygdala (BLA/CeA). For both ventral tegmental area (VTA) and medial preoptic area (MPOA) levels of Fabp7 were lower in mothers, but levels of changes did not reach significance. Confocal microscopy revealed that protein expression of Fabp7 in the LS paralleled mRNA findings. Specifically, the caudal LS exhibited a significant reduction in Fabp7 immunoreactivity, while decreases in medial LS were just above significance. Double fluorescent immunolabeling confirmed the astrocytic phenotype of Fabp7-expressing cells. Collectively, this research demonstrates a broad and marked reduction in Fabp7 expression in the postpartum brain, suggesting that down-regulation of Fabp7 may serve as a hallmark of the postpartum brain and contribute to the maternal phenotype.

Changes in behavior and brain immediate early gene expression in male threespined sticklebacks as they become fathers

Motherhood is a period of intense behavioral and brain activity. However, we know less about the neural and molecular mechanisms associated with the demands of fatherhood. Here, we report the results of two experiments designed to track changes in behavior and brain activation associated with fatherhood in male threespined stickleback fish (Gasterosteus aculeatus), a species in which fathers are the sole providers of parental care. In experiment 1, we tested whether males' behavioral reactions to different social stimuli depends on parental status, i.e. whether they were providing parental care. Parental males visited their nest more in response to social stimuli compared to nonparental males. Rates of courtship behavior were high in non-parental males but low in parental males. In experiment 2, we used a quantitative in situ hybridization method to compare the expression of an immediate early gene (Egr-1) across the breeding cycle - from establishing a territory to caring for offspring. Egr-1 expression peaked when the activities associated with fatherhood were greatest (when they were providing care to fry), and then returned to baseline levels once offspring were independent. The medial dorsal telencephalon (basolateral amygdala), lateral part of dorsal telencephalon (hippocampus) and anterior tuberal nucleus (ventral medial hypothalamus) exhibited high levels of Egr-1 expression during the breeding cycle. These results help to define the neural circuitry associated with fatherhood in fishes, and are consistent with the hypothesis that fatherhood - like motherhood - is a period of intense behavioral and neural activity.

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.

Nongenomic Actions of 17-β Estradiol Restore Respiratory Neuroplasticity in Young Ovariectomized Female Rats

Gonadal steroids modulate CNS plasticity, including phrenic long-term facilitation (pLTF), a form of spinal respiratory neuroplasticity resulting in increased phrenic nerve motor output following exposure to acute intermittent hypoxia (aIH; three 5 min episodes, 10.5% O₂). Despite the importance of respiratory system neuroplasticity, and its dependence on estrogen in males, little is known about pLTF expression or mechanisms of estrogen signaling in females. Here, we tested the hypotheses that (1) pLTF expression in young, gonadally intact female rats would be expressed during estrous cycle stages in which 17β-estradiol (E2) is naturally high (e.g., proestrus vs estrus), (2) pLTF would be absent in ovariectomized (OVX) rats and in physiological conditions in which serum progesterone, but not E2, is elevated (e.g., lactating rats, 3-10 d postpartum), and (3) acute E2 administration would be sufficient to restore pLTF in OVX rats. Recordings of phrenic nerve activity in female Sprague Dawley rats (3-4 months) revealed a direct correlation between serum E2 levels and pLTF expression in cycling female rats. pLTF was abolished with OVX, but was re-established by acute E2 replacement (3 h, intraperitoneal). To identify underlying E2 signaling mechanisms, we intrathecally applied BSA-conjugated E2 over the spinal phrenic motor nucleus and found that pLTF expression was restored within 15 min, suggesting nongenomic E2 effects at membrane estrogen receptors. These data are the first to investigate the role of ovarian E2 in young cycling females, and to identify a role for nongenomic estrogen signaling in any form of respiratory system neuroplasticity.SIGNIFICANCE STATEMENT Exposure to acute intermittent hypoxia induces phrenic long-term facilitation (pLTF), a form of spinal respiratory motor plasticity that improves breathing in models of spinal cord injury. Although pathways leading to pLTF are well studied in males and estradiol (E2) is known to be required, it has seldom been investigated in females, and underlying mechanisms of E2 signaling are unknown in either sex. We found that while ovariectomy abolished pLTF, it could be restored by acute systemic E2, or by intraspinal application of the membrane-impermeable E2 (BSA-conjugated E2; 15 min). The ability of nongenomic estrogen signaling within the cervical spinal cord to recover respiratory neuroplasticity in disorders of respiratory insufficiency suggests that membrane estrogen receptors may represent novel therapeutic targets to restore breathing in both sexes.

Structural and Functional Plasticity in the Maternal Brain Circuitry

Parenting recruits a distributed network of brain structures (and neuromodulators) that coordinates caregiving responses attuned to the young's affect, needs, and developmental stage. Many of these structures and connections undergo significant structural and functional plasticity, mediated by the interplay between maternal hormones and social experience while the reciprocal relationship between the mother and her infant forms and develops. These alterations account for the remarkable behavioral plasticity of mothers. This review will examine the molecular and neurobiological modulation and plasticity through which parenting develops and adjusts in new mothers, primarily discussing recent findings in nonhuman animals. A better understanding of how parenting impacts the brain at the molecular, cellular, systems/network, and behavioral levels is likely to significantly contribute to novel strategies for treating postpartum neuropsychiatric disorders in new mothers, and critical for both the mother's physiological and mental health and the development and well-being of her young.

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

The adult brain shows remarkable neuroplasticity in response to hormones and the socioemotional modifications that they influence. In females with reproductive and maternal experience, this neuroplasticity includes the birth and death of cells in several forebrain regions involved in maternal caregiving and postpartum affective state. Such plasticity in midbrain sites critical for these behavioral and emotional processes has never been examined, though. By visualizing bromodeoxyuridine (BrdU) to label mitotic cells, NeuroD for neuronal precursors, and TUNEL to identify dying cells, we found that the midbrain dorsal raphe nucleus (DR, the source of most ascending serotoninergic projections) exhibited significant neuroplasticity in response to motherhood. Specifically, BrdU analyses revealed that DR newborn cell survival (but not proliferation) was regulated by reproductive state, such that cells born early postpartum were less likely to survive 12 days to reach the late postpartum period compared to cells born during late pregnancy that survived 12 days to reach the early postpartum period. Many of the surviving cells in the DR were NeuN immunoreactive, suggesting a neuronal phenotype. Consistent with these findings, late postpartum rats had fewer NeuroD-immunoreactive DR cells than early postpartum rats. Maternal experience contributed to the late postpartum reduction in DR newborn cell survival because removing the litter at parturition increased cell survival as well as reduced cell death. Unlike cytogenesis in the maternal hippocampus, which is reduced by circulating glucocorticoids, DR newborn cell survival was unaffected by postpartum adrenalectomy. These effects of reproductive state and motherhood on DR plasticity were associated with concurrent changes in DR levels of serotonin's precursor, 5-HTP, and its metabolite, 5-HIAA. Our results demonstrate for the first time that cytogenesis occurs in the midbrain DR of any adult mammal, that DR plasticity is influenced by female reproductive state and maternal experience, and that this plasticity is accompanied by changes in DR serotonergic function. Because serotonin is critical for postpartum caregiving behaviors and maternal affective state, plasticity in the DR may contribute to the neurochemical changes necessary for successful motherhood.

Effect of Reproductive History and Exogenous Hormone Use on Cognitive Function in Mid- and Late Life

OBJECTIVES

To investigate the association between reproductive history indicators of hormonal exposure, including reproductive period, pregnancy, and use of hormonal contraceptives, and mid- and late-life cognition in postmenopausal women.

DESIGN

Analysis of baseline data from two randomized clinical trials: the Women's Isoflavone Soy Health and the Early vs Late Intervention Trial of Estradiol.

SETTING

University academic research center.

PARTICIPANTS

Naturally menopausal women (N = 830).

MEASUREMENTS

Participants were uniformly evaluated using a cognitive battery and a structured reproductive history questionnaire. Outcomes were composite scores for verbal episodic memory, executive function, and global cognition. Reproductive variables included ages at pregnancies, menarche, and menopause; reproductive period; number of pregnancies; and use of hormones for contraception and menopausal symptoms. Multivariable linear regression was used to evaluate associations between cognitive scores (dependent variable) and reproductive factors (independent variables), adjusting for age, race and ethnicity, income, and education.

RESULTS

On multivariable modeling, age at menarche of 13 and older was inversely associated with global cognition (P = .05). Last pregnancy after age 35 was positively associated with verbal memory (P = .03). Use of hormonal contraceptives was positively associated with global cognition (P trend = .04), and verbal memory (P trend = .007). The association between hormonal contraceptive use and verbal memory and executive function was strongest for more than 10 years of use. Reproductive period was positively associated with global cognition (P = .04) and executive function (P = .04).

CONCLUSION

In this sample of healthy postmenopausal women, reproductive life events related to sex hormones, including earlier age at menarche, later age at last pregnancy, longer reproductive period, and use of oral contraceptives are positively related to aspects of cognition in later life.

Exposure to young preferentially activates adult-born neurons in the main olfactory bulb of sheep mothers

New neurons are continuously added to the main olfactory bulb (MOB) of the mammalian brain. While their function has been demonstrated in olfactory learning, it is less known in an ethological context such as mothering. We addressed this question by investigating whether in sheep mothers the adult-generated olfactory neurons contribute to the processing of odors involved in attraction to lambs and in memorization of its individual signature. Parturient ewes, after having 2 days of contact with their lamb and being separated from them for 3 h, were exposed for 2 h either to their own lamb, an unfamiliar lamb or a familiar adult sheep and then sacrificed. A control group was composed of mothers not exposed to any lambs for 5 h before sacrifice. Bromodeoxyuridine, a marker of cell division, was injected 3 months before parturition and revealed through immunocytochemistry in combination with markers of activation or neuronal maturation. The percentage of adult-born cells activated in the granular layer of the MOB was compared between the four groups. Results show that the whole population of olfactory neuroblasts and in particular the 3-month-old neuroblasts, are preferentially activated by lamb exposure and that the preferential activation is specific to olfactory neurogenesis since no activation was observed in newborn neurons of the dentate gyrus. However, neither neuroblasts nor mature neurons of the MOB differentiate between familiar and unfamiliar lamb exposure. Therefore, our data shows that adult-born neurons contribute to the processing of infantile odors which are determinant for maternal behavior.

Genetic and neuroendocrine regulation of the postpartum brain

Changes in expression of hundreds of genes occur during the production and function of the maternal brain that support a wide range of processes. In this review, we synthesize findings from four microarray studies of different maternal brain regions and identify a core group of 700 maternal genes that show significant expression changes across multiple regions. With those maternal genes, we provide new insights into reward-related pathways (maternal bonding), postpartum depression, social behaviors, mental health disorders, and nervous system plasticity/developmental events. We also integrate the new genes into well-studied maternal signaling pathways, including those for prolactin, oxytocin/vasopressin, endogenous opioids, and steroid receptors (estradiol, progesterone, cortisol). A newer transcriptional regulation model for the maternal brain is provided that incorporates recent work on maternal microRNAs. We also compare the top 700 genes with other maternal gene expression studies. Together, we highlight new genes and new directions for studies on the postpartum brain.

Adult neurogenesis and reproductive functions in mammals

During adulthood, the mammalian brain retains the capacity to generate new cells and new neurons in particular. It is now well established that the birth of these new neurons occurs in well-described sites: the hippocampus and the subventricular zone of the lateral ventricle, as well as in other brain regions including the hypothalamus. In this review, we describe the canonical neurogenic niches and illustrate the functional relevance of adult-born neurons of each neurogenic niche in the reproductive physiology. More specifically, we highlight the effect of reproductive social stimuli on the neurogenic processes and conversely, the contributions of adult-born neurons to the reproductive physiology and behavior. We next review the recent discovery of a novel neurogenic niche located in the hypothalamus and the median eminence and the compelling evidence of the link existing between the new-born hypothalamic neurons and the regulation of metabolism. In addition, new perspectives on the possible involvement of hypothalamic neurogenesis in the control of photoperiodic reproductive physiology in seasonal mammals are discussed. Altogether, the studies highlighted in this review demonstrate the potential role of neurogenesis in reproductive function and emphasize the importance of increasing our knowledge on the regulation processes and the physiological relevance of these adult-born neurons. This constitutes a necessary step toward a potential manipulation of these plasticity mechanisms.

Social regulation of adult neurogenesis: A comparative approach

The social environment sculpts the mammalian brain throughout life. Adult neurogenesis, the birth of new neurons in the mature brain, can be up- or down-regulated by various social manipulations. These include social isolation, social conflict, social status, socio-sexual interactions, and parent/offspring interactions. However, socially-mediated changes in neuron production are often species-, sex-, and/or region-specific. In order to reconcile the variability of social effects on neurogenesis, we need to consider species-specific social adaptations and other contextual variables (e.g. age, social status, reproductive status, etc.) that shift the valence of social stimuli. Using a comparative approach to understand how adult-generated neurons in turn influence social behaviors will shed light on how adult neurogenesis contributes to survival and reproduction in diverse species.

The birth of new neurons in the maternal brain: Hormonal regulation and functional implications

The maternal brain is remarkably plastic and exhibits multifaceted neural modifications. Neurogenesis has emerged as one of the mechanisms by which the maternal brain exhibits plasticity. This review highlights what is currently known about peripartum-associated changes in adult neurogenesis and the underlying hormonal mechanisms. We also consider the functional consequences of neurogenesis in the peripartum brain and extent to which this process may play a role in maternal care, cognitive function and postpartum mood. Finally, while most work investigating the effects of parenting on adult neurogenesis has focused on mothers, a few studies have examined fathers and these results are also discussed.

Fatherhood contributes to increased hippocampal spine density and anxiety regulation in California mice

INTRODUCTION

Parenting alters the hippocampus, an area of the brain that undergoes significant experience-induced plasticity and contributes to emotional regulation. While the relationship between maternal care and hippocampal neuroplasticity has been characterized, the extent to which fatherhood alters the structure and function of the hippocampus is far less understood.

METHODS

Here, we investigated to what extent fatherhood altered anxiety regulation and dendritic morphology of the hippocampus using the highly paternal California mouse (Peromyscus californicus).

RESULTS

Fathers spent significantly more time on the open arms of the elevated plus maze, compared to non-fathers. Total distance traveled in the EPM was not changed by paternal experience, which suggests that the increased time spent on the open arms of the maze indicates decreased anxiety-like behavior. Fatherhood also increased dendritic spine density of granule cells in the dentate gyrus and basal dendrites of pyramidal cells in area CA1 of the hippocampus.

CONCLUSIONS

These findings parallel those observed in maternal rodents, suggesting that the hippocampus of fathers and mothers respond similarly to offspring.

Long-term alterations in neural and endocrine processes induced by motherhood in mammals

This article is part of a Special Issue "Parental Care". The reproductive experience of pregnancy, lactation and motherhood can significantly remodel the female's biological state, affecting endocrine, neuroendocrine, neural, and immunological processes. The brain, pituitary gland, liver, thymus, and mammary tissue are among the structures that are modified by reproductive experience. The present review that focuses on rodent research, but also includes pertinent studies in sheep and other species, identifies specific changes in these processes brought about by the biological states of pregnancy, parturition, and lactation and how the components of reproductive experience contribute to the remodeling of the maternal brain and organ systems. Findings indicate that prior parity alters key circulating hormone levels and neural receptor gene expression. Moreover, reproductive experience results in modifications in neural processes and glial support. The possible role of pregnancy-induced neurogenesis is considered in the context of neuroplasticity and behavior, and the effects of reproductive experience on maternal memory, i.e. the retention of maternal behavior, together with anxiety and learning are presented. Together, these sets of findings support the concept that the neural and biological state of the adult female is significantly and dramatically altered on a long-term basis by the experiences of parity and motherhood. Remodeling of the maternal brain and other biological systems is posited to help facilitate adaptations to environmental/ecological challenges as the female raises young and ages.

Neuroplasticity in the maternal hippocampus: Relation to cognition and effects of repeated stress

This article is part of a Special Issue "Parental Care". It is becoming clear that the female brain has an inherent plasticity that is expressed during reproduction. The changes that occur benefit the offspring, which in turn secures the survival of the mother's genetic legacy. Thus, the onset of maternal motivation involves basic mechanisms from genetic expression profiles, to hormone release, to hormone-neuron interactions, all of which fundamentally change the neural architecture - and for a period of time that extends, interestingly, beyond the reproductive life of the female. Although multiple brain areas involved in maternal responses are discussed, this review focuses primarily on plasticity in the maternal hippocampus during pregnancy, the postpartum period and well into aging as it pertains to changes in cognition. In addition, the effects of prolonged and repeated stress on these dynamic responses are considered. The maternal brain is a marvel of directed change, extending into behaviors both obvious (infant-directed) and less obvious (predation, cognition). In sum, the far-reaching effects of reproduction on the female nervous system provide an opportunity to investigate neuroplasticity and behavioral flexibility in a natural mammalian model.

Pregnancy and estrogen enhance neural progenitor-cell proliferation in the vomeronasal sensory epithelium

Background

The hormonal state during the estrus cycle or pregnancy produces alterations on female olfactory perception that are accompanied by specific maternal behaviors, but it is unclear how sex hormones act on the olfactory system to enable these sensory changes.

Results

Herein, we show that the production of neuronal progenitors is stimulated in the vomeronasal organ (VNO) epithelium of female mice during a late phase of pregnancy. Using a wide range of molecular markers that cover the whole VNO cell maturation process in combination with Ca²⁺ imaging in early postmitotic neurons, we show that newly generated VNO cells adopt morphological and functional properties of mature sensory neurons. A fraction of these newly generated cells project their axons to the olfactory forebrain, extend dendrites that contact the VNO lumen, and can detect peptides and urinary proteins shown to contain pheromone activity. High-throughput RNA-sequencing reveals concomitant differences in gene expression in the VNO transcriptomes of pregnant females. These include relative increases in expression of 20 vomeronasal receptors, of which 17 belong to the V1R subfamily, and may therefore be considered as candidate receptors for mediating maternal behaviors. We identify the expression of several hormone receptors in the VNO of which estrogen receptor α (Esr1) is directly localized to neural progenitors. Administration of sustained high levels of estrogen, but not progesterone, is sufficient to stimulate vomeronasal progenitor cell proliferation in the VNO epithelium.

Conclusions

Peripheral olfactory neurogenesis driven by estrogen may contribute to modulate sensory perception and adaptive VNO-dependent behaviors during pregnancy and early motherhood.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0211-8) contains supplementary material, which is available to authorized users.

MicroRNA expression is altered in lateral septum across reproductive stages

MicroRNAs (miRNAs) inhibit RNA targets and may contribute to postpartum central nervous system (CNS) gene expression changes, although this has never been tested. In the present study, we directly evaluated miRNA levels using RNA sequencing during reproduction in female mice in the lateral septum (LS). We found the reliable and robust changes of miRNAs away from the virgin stage at the three other stages, namely pregnant, day 1 postpartum, and day 8 postpartum. For a given miRNA that was significantly different from the virgin condition in more than one group, the direction of change was always the same. Overall, we identified 32 upregulated miRNAs and 25 downregulated miRNAs that were consistently different from the virgin state. 'Arm switching' occurs for miR-433-3 and miR-7b. Unexpectedly, a third of upregulated miRNAs (relative to virgin) were highly localized within the 12qF1 region of chromosome 12 that includes the Dlk1-Dio3 gene cluster implicated in stem cell and neuronal differentiation. Over 1500 genes were targeted by multiple upregulated miRNAs with about 100 genes targeted by five or more miRNAs. Over 1000 genes were targeted by multiple downregulated miRNAs with about 50 genes targeted by five or more miRNAs. Half of the target genes were regulated by up and downregulated miRNAs, indicating homeostatic regulation. Transcriptional regulation was the most enriched pathway for genes linked to up or down regulated miRNAs. Other enriched pathways included protein kinase activity (e.g., MAP kinase), CNS development, axon guidance, neurotrophin signaling, neuron development/differentiation, and neurogenesis. Previously published postpartum LS gene expression changes were enrichment for LS miRNA targets, as expected. Surprisingly, postpartum gene expression changes from other regions were also enriched against LS miRNA targets, suggesting a core group of miRNAs may act across the CNS during reproduction. Together, we directly examine miRNAs and find significant alterations in the postpartum brain.

Chemical olfactory signals and parenthood in mammals

This article is part of a Special Issue "Chemosignals and Reproduction". In mammalian species, odor cues emitted by the newborn are essential to establish maternal behavior at parturition and coordinate early mother-infant interactions. Offspring odors become potent attractive stimuli at parturition promoting the contact with the young to ensure that normal maternal care develops. In some species odors provide a basis for individual recognition of the offspring and highly specialized neural mechanisms for learning the infant signals have evolved. Both the main and the accessory olfactory systems are involved in the onset of maternal care, but only the former contributes to individual odor discrimination of the young. Electrophysiological and neurochemical changes occur in the main olfactory bulb leading to a coding of the olfactory signature of the familiar young. Olfactory neurogenesis could also contribute to motherhood and associated learning. Parturition and interactions with the young influence neurogenesis and some evidence indicates a functional link between olfactory neurogenesis and maternal behavior. Although a simple compound has been found which regulates anogenital licking in the rat, studies identifying the chemical nature of these odors are lacking. Neonatal body odors seem to be particularly salient to human mothers who are able to identify their infant's odors. Recent studies have revealed some neural processing of these cues confirming the importance of mother-young chemical communication in our own species.

Comparison of steady state development and reduction of menopausal symptoms after oral or transdermal delivery of 17-β-estradiol in young healthy symptomatic menopausal women

OBJECTIVE

There is a renewed interest in the delivery of estradiol (E2) for the reduction of menopausal symptoms in young symptomatic menopausal women. This paper compares experimentally and theoretically obtained E2 plasma values by oral and transdermal delivery and compares them with relevant menopausal symptoms.

STUDY DESIGN

Two independent previously published studies were compared, which each contained 42 young symptomatic menopausal women. Experimentally obtained plasma values at days 1, 7 and 21 were compared with a theoretical model, taken from the literature, for describing plasma values for an oral immediate release formulation, consecutively for 21 days. Menopausal symptoms were determined in the steady state for oral and transdermal delivery with the Kuppermann index, previously not reported. In the case of oral delivery, estradiol was compared with estradiol valerate.

RESULTS

Previously published results for transdermal delivery of E2 showed that the matrix system establishes a steady state condition with the application of the first patch. Excellent agreement between theoretically predicted and experimentally obtained E2 plasma values for oral delivery in menopausal women was obtained. Circadian E2 plasma levels were observed continuously for transdermal delivery, were seen in oral delivery during first application and disappeared when steady state was achieved. Application of the prodrug E2-valerate delayed the maximum plasma peak from 1 pm to 4 pm, similar to the transdermal matrix patch. Investigating menopausal symptoms determined with the Kuppermann index did not reveal differences between oral or transdermal "E2 kinetic (hot flushes) relationship". This relationship was similar to symptomatic women suffering from hot flushes in untreated menopausal women or premenopausal women. Different menopausal symptoms required different E2 plasma levels: the average E2 levels higher than 23 pg/mL in plasma did abolish insomnia in 50% of postmenopausal women, with 28 pg/mL is needed to suppress 50% of dysthymia; however, rather high levels of 41 pg/mL are needed to suppress 50% of hot flushes, suggesting a rather complex mechanism beyond an E2 receptor mediated process.

CONCLUSION

There is a difference in the steady state between oral and transdermal E2 delivery. Steady state condition is achieved in the first application of a matrix patch, whereas with the application of a tablet the steady state is achieved in transdermal delivery within 12-14 days. Our reported calculated missed intake of a E2 tablet shows that E2 plasma levels drop for 4 days consecutively. Our conducted study has several limitations: firstly, no cross-over was conducted, but a rather cumbersome mathematical modeling; secondly, healthy women with no accompanying severe diseases were included in this study. The higher the oral dose, the higher the E2 steady state levels, but the time to achieve steady state levels is independent from the E2 dose.

Addiction and reward-related genes show altered expression in the postpartum nucleus accumbens

Motherhood involves a switch in natural rewards, whereby offspring become highly rewarding. Nucleus accumbens (NAC) is a key CNS region for natural rewards and addictions, but to date no study has evaluated on a large scale the events in NAC that underlie the maternal change in natural rewards. In this study we utilized microarray and bioinformatics approaches to evaluate postpartum NAC gene expression changes in mice. Modular Single-set Enrichment Test (MSET) indicated that postpartum (relative to virgin) NAC gene expression profile was significantly enriched for genes related to addiction and reward in five of five independently curated databases (e.g., Malacards, Phenopedia). Over 100 addiction/reward related genes were identified and these included: Per1, Per2, Arc, Homer2, Creb1, Grm3, Fosb, Gabrb3, Adra2a, Ntrk2, Cry1, Penk, Cartpt, Adcy1, Npy1r, Htr1a, Drd1a, Gria1, and Pdyn. ToppCluster analysis found maternal NAC expression profile to be significantly enriched for genes related to the drug action of nicotine, ketamine, and dronabinol. Pathway analysis indicated postpartum NAC as enriched for RNA processing, CNS development/differentiation, and transcriptional regulation. Weighted Gene Coexpression Network Analysis (WGCNA) identified possible networks for transcription factors, including Nr1d1, Per2, Fosb, Egr1, and Nr4a1. The postpartum state involves increased risk for mental health disorders and MSET analysis indicated postpartum NAC to be enriched for genes related to depression, bipolar disorder (BPD), and schizophrenia. Mental health related genes included: Fabp7, Grm3, Penk, and Nr1d1. We confirmed via quantitative PCR Nr1d1, Per2, Grm3, Penk, Drd1a, and Pdyn. This study indicates for the first time that postpartum NAC involves large scale gene expression alterations linked to addiction and reward. Because the postpartum state also involves decreased response to drugs, the findings could provide insights into how to mitigate addictions.

Functional significance of hormonal changes in mammalian fathers

In the 5-10% of mammals in which both parents routinely provide infant care, fathers as well as mothers undergo systematic endocrine changes as they transition into parenthood. Although fatherhood-associated changes in such hormones and neuropeptides as prolactin, testosterone, glucocorticoids, vasopressin and oxytocin have been characterised in only a small number of biparental rodents and primates, they appear to be more variable than corresponding changes in mothers, and experimental studies typically have not provided strong or consistent evidence that these endocrine shifts play causal roles in the activation of paternal care. Consequently, their functional significance remains unclear. We propose that endocrine changes in mammalian fathers may enable males to meet the species-specific demands of fatherhood by influencing diverse aspects of their behaviour and physiology, similar to many effects of hormones and neuropeptides in mothers. We review the evidence for such effects, focusing on recent studies investigating whether mammalian fathers in biparental species undergo systematic changes in (i) energetics and body composition; (ii) neural plasticity, cognition and sensory physiology; and (iii) stress responsiveness and emotionality, all of which may be mediated by endocrine changes. The few published studies, based on a small number of rodent and primate species, suggest that hormonal and neuropeptide alterations in mammalian fathers might mediate shifts in paternal energy balance, body composition and neural plasticity, although they do not appear to have major effects on stress responsiveness or emotionality. Further research is needed on a wider variety of biparental mammals, under more naturalistic conditions, to more fully determine the functional significance of hormone and neuropeptide profiles of mammalian fatherhood and to clarify how fatherhood may trade off with (or perhaps enhance) aspects of organismal function in biparental mammals.

Hippocampal plasticity during the peripartum period: influence of sex steroids, stress and ageing

The peripartum period is accompanied by dramatic changes in hormones and a host of new behaviours in response to experience with offspring. Both maternal experience and maternal hormones can have a significant impact upon the brain and behaviour. This review outlines recent studies demonstrating modifications in hippocampal plasticity across the peripartum period, as well as the putative hormonal mechanisms underlying these changes and their modulation by stress. In addition, the impact of reproductive experience upon the ageing hippocampus is discussed. Finally, we consider how these changes in hippocampal structure may play a role in postpartum cognitive function and mood disorders, as well as age-related cognitive decline.

Using animal models to study post-partum psychiatric disorders

The post-partum period represents a time during which all maternal organisms undergo substantial plasticity in a wide variety of systems in order to ensure the well-being of the offspring. Although this time is generally associated with increased calmness and decreased stress responses, for a substantial subset of mothers, this period represents a time of particular risk for the onset of psychiatric disorders. Thus, post-partum anxiety, depression and, to a lesser extent, psychosis may develop, and not only affect the well-being of the mother but also place at risk the long-term health of the infant. Although the risk factors for these disorders, as well as normal peripartum-associated adaptations, are well known, the underlying aetiology of post-partum psychiatric disorders remains poorly understood. However, there have been a number of attempts to model these disorders in basic research, which aim to reveal their underlying mechanisms. In the following review, we first discuss known peripartum adaptations and then describe post-partum mood and anxiety disorders, including their risk factors, prevalence and symptoms. Thereafter, we discuss the animal models that have been designed in order to study them and what they have revealed about their aetiology to date. Overall, these studies show that it is feasible to study such complex disorders in animal models, but that more needs to be done in order to increase our knowledge of these severe and debilitating mood and anxiety disorders.

Medial prefrontal cortex: genes linked to bipolar disorder and schizophrenia have altered expression in the highly social maternal phenotype

The transition to motherhood involves CNS changes that modify sociability and affective state. However, these changes also put females at risk for post-partum depression and psychosis, which impairs parenting abilities and adversely affects children. Thus, changes in expression and interactions in a core subset of genes may be critical for emergence of a healthy maternal phenotype, but inappropriate changes of the same genes could put women at risk for post-partum disorders. This study evaluated microarray gene expression changes in medial prefrontal cortex (mPFC), a region implicated in both maternal behavior and psychiatric disorders. Post-partum mice were compared to virgin controls housed with females and isolated for identical durations. Using the Modular Single-set Enrichment Test (MSET), we found that the genetic landscape of maternal mPFC bears statistical similarity to gene databases associated with schizophrenia (5 of 5 sets) and bipolar disorder (BPD, 3 of 3 sets). In contrast to previous studies of maternal lateral septum (LS) and medial preoptic area (MPOA), enrichment of autism and depression-linked genes was not significant (2 of 9 sets, 0 of 4 sets). Among genes linked to multiple disorders were fatty acid binding protein 7 (Fabp7), glutamate metabotropic receptor 3 (Grm3), platelet derived growth factor, beta polypeptide (Pdgfrb), and nuclear receptor subfamily 1, group D, member 1 (Nr1d1). RT-qPCR confirmed these gene changes as well as FMS-like tyrosine kinase 1 (Flt1) and proenkephalin (Penk). Systems-level methods revealed involvement of developmental gene networks in establishing the maternal phenotype and indirectly suggested a role for numerous microRNAs and transcription factors in mediating expression changes. Together, this study suggests that a subset of genes involved in shaping the healthy maternal brain may also be dysregulated in mental health disorders and put females at risk for post-partum psychosis with aspects of schizophrenia and BPD.

Interactions with the young down-regulate adult olfactory neurogenesis and enhance the maturation of olfactory neuroblasts in sheep mothers

New neurons are continuously added in the dentate gyrus (DG) and the olfactory bulb of mammalian brain. While numerous environmental factors controlling survival of newborn neurons have been extensively studied, regulation by social interactions is less documented. We addressed this question by investigating the influence of parturition and interactions with the young on neurogenesis in sheep mothers. Using Bromodeoxyuridine, a marker of cell division, in combination with markers of neuronal maturation, the percentage of neuroblasts and new mature neurons in the olfactory bulb and the DG was compared between groups of parturient ewes which could interact or not with their lamb, and virgins. In addition, a morphological analysis was performed by measuring the dendritic arbor of neuroblasts in both structures. We showed that the postpartum period was associated with a decrease in olfactory and hippocampal adult neurogenesis. In the olfactory bulb, the suppressive effect on neuroblasts was dependent on interactions with the young whereas in the DG the decrease in new mature neurons was associated with parturition. In addition, dendritic length and number of nodes of neuroblasts were significantly enhanced by interactions with the lamb in the olfactory bulb but not in the DG. Because interactions with the young involved learning of the olfactory signature of the lamb, we hypothesize that this learning is associated with a down-regulation in olfactory neurogenesis and an enhancement of olfactory neuroblast maturation. Our assumption is that fewer new neurons decrease cell competition in the olfactory bulb and enhance maturation of those new neurons selected to participate in the learning of the young odor.

Proteomic Analysis of Pig (Sus scrofa) Olfactory Soluble Proteome Reveals O-Linked-N-Acetylglucosaminylation of Secreted Odorant-Binding Proteins

The diversity of olfactory binding proteins (OBPs) is a key point to understand their role in molecular olfaction. Since only few different sequences were characterized in each mammalian species, they have been considered as passive carriers of odors and pheromones. We have explored the soluble proteome of pig nasal mucus, taking benefit of the powerful tools of proteomics. Combining two-dimensional electrophoresis, mass spectrometry, and western-blot with specific antibodies, our analyses revealed for the first time that the pig nasal mucus is mainly composed of secreted OBP isoforms, some of them being potentially modified by O-GlcNAcylation. An ortholog gene of the glycosyltransferase responsible of the O-GlcNAc linking on extracellular proteins in Drosophila and Mouse (EOGT) was amplified from tissues of pigs of different ages and sex. The sequence was used in a phylogenetic analysis, which evidenced conservation of EOGT in insect and mammalian models studied in molecular olfaction. Extracellular O-GlcNAcylation of secreted OBPs could finely modulate their binding specificities to odors and pheromones. This constitutes a new mechanism for extracellular signaling by OBPs, suggesting that they act as the first step of odor discrimination.

Mothers' amygdala response to positive or negative infant affect is modulated by personal relevance

Understanding, prioritizing and responding to infant affective cues is a key component of motherhood, with long-term implications for infant socio-emotional development. This important task includes identifying unique characteristics of one's own infant, as they relate to differences in affect valence—happy or sad—while monitoring one's own level of arousal. The amygdala has traditionally been understood to respond to affective valence; in the present study, we examined the potential effect of personal relevance on amygdala response, by testing whether mothers' amygdala response to happy and sad infant face cues would be modulated by infant identity. We used functional MRI to measure amygdala activation in 39 first-time mothers, while they viewed happy, neutral and sad infant faces of both their own and a matched unknown infant. Emotional arousal to each face was rated using the Self-Assessment Manikin Scales. Mixed-effects linear regression models were used to examine significant predictors of amygdala response. Overall, both arousal ratings and amygdala activation were greater when mothers viewed their own infant's face compared with unknown infant faces. Sad faces were rated as more arousing than happy faces, regardless of infant identity. However, within the amygdala, a highly significant interaction effect was noted between infant identity and valence. For own-infant faces, amygdala activation was greater for happy than sad faces, whereas the opposite trend was seen for unknown-infant faces. Our findings suggest that the amygdala response to positive or negative valenced cues is modulated by personal relevance. Positive facial expressions from one's own infant may play a particularly important role in eliciting maternal responses and strengthening the mother-infant bond.

Estrogen, predominantly via estrogen receptor α, attenuates postpartum-induced anxiety- and depression-like behaviors in female rats

Contributions from estrogen receptor (ER) subtypes (ERα and ERβ) to postpartum anxiogenic and depressive responses remain unresolved in rats. Using the elevated-plus maze (EPM) and forced swim (FS) tests, we confirmed that primiparous rats exhibited anxiogenic and depressive responses 3 weeks postpartum, improved 5 weeks postpartum (EPM), and recovered at 5 (FS) or 10 weeks postpartum (EPM) compared with diestrus nulliparous females. Immunohistochemistry suggested that these behavioral changes were temporally associated with decreased ERα but not ERβ expression in the medial amygdala (MEA). Additionally, ERα expression in the medial preoptic area (MPOA) significantly increased 10 weeks postpartum. Brain-derived neurotrophic factor (BDNF) expression was significantly elevated in the MEA 3 weeks postpartum. BDNF receptor tropomyosin-related kinase expression was significantly elevated in the MEA at 3 and 10 weeks but not at 5 weeks postpartum. The phosphorylation of ERK (pERK)-2 in the MEA, MPOA, and hippocampal CA1 region was significantly elevated 3 and 5 weeks postpartum. The effects of single daily sc injections of the ERα-selective agonist, propyl pyrazoletriol (PPT); ERβ-selective agonist, diarylpropionitrile; 17β-estradiol (E₂); and vehicle for 6 days in primiparous rats were assessed. PPT and E₂ significantly produced anxiolytic and antidepressant actions in the EPM and FS tests but PPT to a lesser degree than E₂ in the EPM test. Diarylpropionitrile affected the EPM test but was not significantly different from vehicle. BDNF expression was significantly increased 3 weeks postpartum by all treatments in the MPOA but not the CA1 and MEA. E₂ and PPT treatment significantly increased tropomyosin-related kinase and pERK1/2 expression in the MEA and MPOA and increased pERK1/2 expression in the CA1. The onset of anxiety- and depression-like behaviors in postpartum rats may be partly caused by a complex estrogen-mediated mechanism; nevertheless, changes in the ERα-related system, likely in the MEA, are predominantly involved.

The adaptive significance of adult neurogenesis: an integrative approach

Adult neurogenesis in mammals is predominantly restricted to two brain regions, the dentate gyrus (DG) of the hippocampus and the olfactory bulb (OB), suggesting that these two brain regions uniquely share functions that mediate its adaptive significance. Benefits of adult neurogenesis across these two regions appear to converge on increased neuronal and structural plasticity that subserves coding of novel, complex, and fine-grained information, usually with contextual components that include spatial positioning. By contrast, costs of adult neurogenesis appear to center on potential for dysregulation resulting in higher risk of brain cancer or psychological dysfunctions, but such costs have yet to be quantified directly. The three main hypotheses for the proximate functions and adaptive significance of adult neurogenesis, pattern separation, memory consolidation, and olfactory spatial, are not mutually exclusive and can be reconciled into a simple general model amenable to targeted experimental and comparative tests. Comparative analysis of brain region sizes across two major social-ecological groups of primates, gregarious (mainly diurnal haplorhines, visually-oriented, and in large social groups) and solitary (mainly noctural, territorial, and highly reliant on olfaction, as in most rodents) suggest that solitary species, but not gregarious species, show positive associations of population densities and home range sizes with sizes of both the hippocampus and OB, implicating their functions in social-territorial systems mediated by olfactory cues. Integrated analyses of the adaptive significance of adult neurogenesis will benefit from experimental studies motivated and structured by ecologically and socially relevant selective contexts.

Large scale expression changes of genes related to neuronal signaling and developmental processes found in lateral septum of postpartum outbred mice

Coordinated gene expression changes across the CNS are required to produce the mammalian maternal phenotype. Lateral septum (LS) is a brain region critically involved with aspects of maternal care, and we recently examined gene expression of whole septum (LS and medial septum) in selectively bred maternal mice. Here, we expand on the prior study by 1) conducting microarray analysis solely on LS in virgin and postpartum mice, 2) using outbred mice, and 3) evaluating the role of sensory input on gene expression changes. Large scale changes in genes related to neuronal signaling were identified, including four GABA_A receptor subunits. Subunits α4 and δ were downregulated in maternal LS, likely reflecting a reduction in the extrasynaptic, neurosteroid-sensitive α4/δ containing receptor subtype. Conversely, subunits ε and θ were increased in maternal LS. Fifteen K+ channel related genes showed altered expression, as did dopamine receptors Drd1a and Drd2 (both downregulated), hypocretin receptor 1 (Hcrtr1), kappa opioid receptor 1 (Oprk1), and transient receptor potential channel 4 (Trpc4). Expression of a large number of genes linked to developmental processes or cell differentiation were also altered in postpartum LS, including chemokine (C-X-C) motif ligand 12 (Cxcl12), fatty acid binding protein 7 (Fabp7), plasma membrane proteolipid (Pllp), and suppressor of cytokine signaling 2 (Socs2). Additional genes that are linked to anxiety, such as glutathione reductase (Gsr), exhibited altered expression. Pathway analysis also identified changes in genes related to cyclic nucleotide metabolism, chromatin structure, and the Ras gene family. The sensory presence of pups was found to contribute to the altered expression of a subset of genes across all categories. This study suggests that both large changes in neuronal signaling and the possible terminal differentiation of neuronal and/or glial cells play important roles in producing the maternal state.

The main but not the accessory olfactory system is involved in the processing of socially relevant chemosignals in ungulates

Ungulates like sheep and goats have, like many other mammalian species, two complementary olfactory systems. The relative role played by these two systems has long been of interest regarding the sensory control of social behavior. The study of ungulate social behavior could represent a complimentary alternative to rodent studies because they live in a more natural environment and their social behaviors depend heavily on olfaction. In addition, the relative size of the main olfactory bulb (MOB) [in comparison to the accessory olfactory bulb (AOB)] is more developed than in many other lissencephalic species like rodents. In this review, we present data showing a clear involvement of the main olfactory system in two well-characterized social situations under olfactory control in ungulates, namely maternal behavior and offspring recognition at birth and the reactivation of the gonadotropic axis of females exposed to males during the anestrous season. In conclusion, we discuss the apparent discrepancy between the absence of evidence for a role of the vomeronasal system in ungulate social behavior and the existence of a developed accessory olfactory system in these species.