Changes in oxytocin immunoreactivity and mRNA expression in the sheep brain during pregnancy, parturition and lactation and in response to oestrogen and progesterone

The interplay of oxytocin and sex hormones

The neuropeptide oxytocin has historically been associated with reproduction and maternal behavior. However, more recent research has uncovered that oxytocin has a much wider range of roles in physiology and behavior. Despite the excitement surrounding potential therapeutical applications of intranasally administered oxytocin, the results of these intervention studies have been inconsistent. Various reasons for these mixed results have been proposed, which tend to focus on methodological issues, such as study design. While methodological issues are certainly important, emerging evidence suggests that the interaction between oxytocin and sex hormones may also account for these varied findings. To better understand the purpose and function of the interaction of oxytocin with sex hormones, with a focus on estrogens, progesterone, and testosterone, we conducted a comprehensive thematic review via four perspectives: evolutionary, developmental, mechanistic, and survival. Altogether, this synergistic approach highlights the critical function of sex hormone activity for accomplishing the diverse roles of oxytocin via the modulation of oxytocin release and oxytocin receptor activity, which is also likely to contribute to the heterogeneity of outcomes after oxytocin administration.

Oxytocin receptors in the nucleus accumbens shell are necessary for the onset of maternal behavior

In rodents, oxytocin (Oxt) contributes to the onset of maternal care by shifting the perception of pups from aversive to attractive. Both Oxt receptor knockout (Oxtr -/-) and forebrain-specific Oxtr knockout (FB/FB) dams abandon their first litters, likely due to a failure of the brain to 'switch' to a more maternal state. Whether this behavioral shift is neurochemically similar in virgin females, who can display maternal behaviors when repeatedly exposed to pups, or what neuroanatomical substrate is critical for the onset of maternal care remains unknown. To understand similarities and differences in Oxtr signaling in virgin pup-sensitized Oxtr FB/FB as opposed to post-parturient Oxtr -/- and Oxtr FB/FB dams, maternal behavior (pup-sensitized females only) and immediate early gene activation were assessed. Pup-sensitized Oxtr FB/FB females retrieved pups faster on day one of testing and had reduced c-Fos expression in the dorsal lateral septum as compared to virgin pup-sensitized Oxtr +/+ females. This differs from what was observed in post-parturient Oxtr -/- and Oxtr FB/FB dams, where increased c-Fos expression was observed in the nucleus accumbens (NAcc) shell. Based on these data, we then disrupted Oxtr signaling in the NAcc shell or the posterior paraventricular thalamus (pPVT) (control region) of female Oxtr floxed mice using a Cre recombinase expressing adeno-associated virus. Knockout of the Oxtr only in the NAcc shell prevented the onset of maternal care post-parturient females. Our data suggest that a pup-sensitized brain may differ from a post-parturient brain and that Oxtr signaling in the NAcc shell is critical to the onset of maternal behavior.

Maternal Behavior in Beef Cattle: The Physiology, Assessment and Future Directions-A Review

Bovine maternal behavior is known to be influenced by a variety of factors including hormonal mediation, breed, age, parity, host genetics and general management practices. Following centuries of varying levels of domestication processes, the behavior of the bovine cow has altered from that of her original wild ungulate ancestors, although many maternal instincts have remained unchanged. The influence of maternal behavior on calf health and performance is of interest to cow-calf beef production operations, as in most instances, the cow is solely responsible for rearing the calf until weaning. However, investigating the magnitude of this influence is challenging, in part because objective measurement of behavioral traits is difficult, particularly in extensive settings. In recent years, while a number of remote monitoring devices have been developed that afford opportunities for objective measurement of behavioral traits in livestock, characterization of physiological mechanisms that underlie superior maternal behavior, including identification of potential biomarkers remains elusive in cattle. Hormonal profiles during the periparturient period have been shown to influence behavioral patterns in both current and future generations in other mammalian species and may provide insights into the physiology of bovine maternal behavior. Therefore, the aim of this review is to describe general characteristics of bovine maternal behavior and the factors known to influence it, including hormonal drivers, through which cross-reference to other species is made. Current methods of measuring and assessing behavior that may also be applicable to most production settings have also been reviewed. At present, there is no known hormonal assay that can be used to measure and/or reliably predict bovine maternal behavior post-calving or across generations. Being able to objectively assess superior maternal behavior, whether that be through remote monitoring, hormonal profiling or indirectly through measuring calf performance will be beneficial to livestock industries in the future.

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

The Onset of Maternal Behavior in Sheep and Goats: Endocrine, Sensory, Neural, and Experiential Mechanisms

In sheep and goats, the onset of maternal behavior at parturition is characterized by a first phase called maternal responsiveness during which the mother is attracted to any newborn. In a second phase, called maternal selectivity, the mother establishes a selective bond with her young so that she only accepts it at suckling. After a description of the behavioral expression of both phases, this chapter reviews the physiological, sensory, and neural mechanisms involved. These two behavioral processes are synchronized with parturition by the vaginocervical stimulation induced by the expulsion of the newborn. Olfactory cues provided by the neonate are involved in maternal responsiveness and selectivity. Oxytocin supported by estrogens is the key factor for maternal responsiveness. The neural network involved in maternal responsiveness is mainly hypothalamic and is different from the circuitry involved in selectivity, which mainly concerns olfactory processing regions. Visual and auditory cues are necessary for offspring recognition at a distance. This multisensory recognition suggests that mothers form a mental image of their young. Maternal experience renders mothers more responsive to maternally relevant physiology and to young-related sensory inputs.

Estrogen Withdrawal Increases Postpartum Anxiety via Oxytocin Plasticity in the Paraventricular Hypothalamus and Dorsal Raphe Nucleus

BACKGROUND

Estrogen increases dramatically during pregnancy but quickly drops below prepregnancy levels at birth and remains suppressed during the postpartum period. Clinical and rodent work suggests that this postpartum drop in estrogen results in an estrogen withdrawal state that is related to changes in affect, mood, and behavior. How estrogen withdrawal affects oxytocin (OT) neurocircuitry has not been examined.

METHODS

We used a hormone-simulated pseudopregnancy followed by estrogen withdrawal in Syrian hamsters, a first for this species. Ovariectomized females were given daily injections to approximate hormone levels during gestation and then withdrawn from estrogen to simulate postpartum estrogen withdrawal. These hamsters were tested for behavioral assays of anxiety and anhedonia during estrogen withdrawal. Neuroplasticity in OT-producing neurons in the paraventricular nucleus of the hypothalamus and its efferent targets was measured.

RESULTS

Estrogen-withdrawn females had increased anxiety-like behaviors in the elevated plus maze and open field tests but did not differ from control females in sucrose preference. Furthermore, estrogen-withdrawn females had more OT-immunoreactive cells and OT messenger RNA in the paraventricular nucleus of the hypothalamus and an increase in OT receptor density in the dorsal raphe nucleus. Finally, blocking OT receptors in the dorsal raphe nucleus during estrogen withdrawal prevented the high-anxiety behavioral phenotype in estrogen-withdrawn females.

CONCLUSIONS

Estrogen withdrawal induces OT neuroplasticity in the paraventricular nucleus of the hypothalamus and dorsal raphe nucleus to increase anxiety-like behavior during the postpartum period. More broadly, these experiments suggest Syrian hamsters as a novel organism in which to model the effects of postpartum estrogen withdrawal on the brain and anxiety-like behavior.

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.

Adaptive Modifications of Maternal Hypothalamic-Pituitary-Adrenal Axis Activity during Lactation and Salsolinol as a New Player in this Phenomenon

Both basal and stress-induced secretory activities of the hypothalamic-pituitary-adrenal (HPA) axis are distinctly modified in lactating females. On the one hand, it aims to meet the physiological demands of the mother, and on the other hand, the appropriate and stable plasma cortisol level is one of the essential factors for the proper offspring development. Specific adaptations of HPA axis activity to lactation have been extensively studied in several animal species and humans, providing interesting data on the HPA axis plasticity mechanism. However, most of the data related to this phenomenon are derived from studies in rats. The purpose of this review is to highlight these adaptations, with a particular emphasis on stress reaction and differences that occur between species. Existing data on breastfeeding women are also included in several aspects. Finally, data from the experiments in sheep are presented, indicating a new regulatory factor of the HPA axis-salsolinol-which typical role was revealed in lactation. It is suggested that this dopamine derivative is involved in both maintaining basal and suppressing stress-induced HPA axis activities in lactating dams.

Effects of nest-deprivation on hypothalamic mesotocin in incubating native Thai hens (Gallus domesticus)

Avian mesotocin (MT) is homologous to oxytocin in mammals. Native Thai chickens (Gallus domesticus) strongly express maternal behaviors including incubation and rearing. However, the role of MT during incubation behavior has never been studied. The objective of this study was to determine the physiological function(s) of the MTergic system in incubation behavior in native Thai chickens. The brains were collected from incubating (INC) and nest-deprived (ND) hens at different time points (days 3, 6, 8, 10, 14, 18, and 21; n=6). Immunohistochemistry technique was used to compare the numbers of MT-immunoreactive (-ir) neurons between the INC and ND hens within the Nucleus supraopticus, pars ventralis (SOv), Nucleus preopticus medialis (POM), and Nucleus paraventricularis magnocellularis (PVN). The results revealed that the numbers of MT-ir neurons within the SOv, POM, and PVN remained high during the incubating stage. The number of MT-ir neurons in the SOv was lower than that of the POM and PVN. Disruption of incubation behavior by nest deprivation caused the numbers of MT-ir neurons within the SOv, POM, and PVN to decrease throughout the observation periods. For the first time, this study demonstrates that the MTergic system within the SOv, POM, and PVN may be involved with incubation behavior. In addition, these results further suggest that the MTergic neurons in these nuclei are not only regulated by rearing behavior but also might have a role in the initiation and maintenance of incubation behavior in this tropical species.

Mood, Food, and Fertility: Adaptations of the Maternal Brain

Successfully rearing young places multiple demands on the mammalian female. These are met by a wide array of alterations in maternal physiology and behavior that are coordinated with the needs of the developing young, and include adaptations in neuroendocrine systems not directly involved in maternal behavior or lactation. In this article, attenuations in the behavioral and neuroendocrine responses to stressors, the alterations in metabolic pathways facilitating both increased food intake and conservation of energy, and the changes in fertility that occur postpartum are described. The mechanisms underlying these processes as well as the factors that contribute to them and the relative contributions of these stimuli at different times postpartum are also reviewed. The induction and maintenance of the adaptations observed in the postpartum maternal brain are dependent on mother-young interaction and, in most cases, on suckling stimulation and its consequences for the hormonal profile of the mother. The peptide hormone prolactin acting on receptors within the brain makes a major contribution to changes in metabolic pathways, suppression of fertility and the attenuation of the neuroendocrine response to stress during lactation. Oxytocin is also released, both into the circulation and in some hypothalamic nuclei, in response to suckling stimulation and this hormone has been implicated in the decrease in anxiety behavior seen in the early postpartum period. The relative importance of these hormones changes across lactation and it is becoming increasingly clear that many of the adaptations to motherhood reviewed here reflect the outcome of multiple influences. © 2016 American Physiological Society. Compr Physiol 6:1493-1518, 2016.

Oxytocin: parallel processing in the social brain?

Early studies attempting to disentangle the network complexity of the brain exploited the accessibility of sensory receptive fields to reveal circuits made up of synapses connected both in series and in parallel. More recently, extension of this organisational principle beyond the sensory systems has been made possible by the advent of modern molecular, viral and optogenetic approaches. Here, evidence supporting parallel processing of social behaviours mediated by oxytocin is reviewed. Understanding oxytocinergic signalling from this perspective has significant implications for the design of oxytocin-based therapeutic interventions aimed at disorders such as autism, where disrupted social function is a core clinical feature. Moreover, identification of opportunities for novel technology development will require a better appreciation of the complexity of the circuit-level organisation of the social brain.

The role of reproductive hormones in postpartum depression

Despite decades of research aimed at identifying the causes of postpartum depression (PPD), PPD remains common, and the causes are poorly understood. Many have attributed the onset of PPD to the rapid perinatal change in reproductive hormones. Although a number of human and nonhuman animal studies support the role of reproductive hormones in PPD, several studies have failed to detect an association between hormone concentrations and PPD. The purpose of this review is to examine the hypothesis that fluctuations in reproductive hormone levels during pregnancy and the postpartum period trigger PPD in susceptible women. We discuss and integrate the literature on animal models of PPD and human studies of reproductive hormones and PPD. We also discuss alternative biological models of PPD to demonstrate the potential for multiple PPD phenotypes and to describe the complex interplay of changing reproductive hormones and alterations in thyroid function, immune function, hypothalamic-pituitary-adrenal (HPA) axis function, lactogenic hormones, and genetic expression that may contribute to affective dysfunction. There are 3 primary lines of inquiry that have addressed the role of reproductive hormones in PPD: nonhuman animal studies, correlational studies of postpartum hormone levels and mood symptoms, and hormone manipulation studies. Reproductive hormones influence virtually every biological system implicated in PPD, and a subgroup of women seem to be particularly sensitive to the effects of perinatal changes in hormone levels. We propose that these women constitute a "hormone-sensitive" PPD phenotype, which should be studied independent of other PPD phenotypes to identify underlying pathophysiology and develop novel treatment targets.

Emotion and mood adaptations in the peripartum female:complementary contributions of GABA and oxytocin

Peripartum hormones and sensory cues from young modify the maternal brain in ways that can render females either at risk for, or resilient to, elevated anxiety and depression. The neurochemical systems underlying these aspects of maternal emotional and mood states include the inhibitory neurotransmitter GABA and the neuropeptide oxytocin (OXT). Data from laboratory rodents indicate that increased activity at the GABA(A) receptor contributes to the postpartum suppression of anxiety-related behaviour that is mediated by physical contact with offspring, whereas dysregulation in GABAergic signalling results in deficits in maternal care, as well as anxiety- and depression-like behaviours during the postpartum period. Similarly, activation of the brain OXT system accompanied by increased OXT release within numerous brain sites in response to reproductive stimuli also reduces postpartum anxiety- and depression-like behaviours. Studies of peripartum women are consistent with these findings in rodents. Given the similar consequences of elevated central GABA and OXT activity on maternal anxiety and depression, balanced and partly reciprocal interactions between these two systems may be essential for their effects on maternal emotional and mood states, in addition to other aspects of postpartum behaviour and physiology.

The effect of maternal stress activation on the offspring during lactation in light of vasopressin

Although it is obvious that preconceptional effects as well as stressors during pregnancy profoundly influence the progeny, the lactation period seems to be at least as important. Here we summarize how maternal stressors during the lactation period affect the offspring. As vasopressin is one of the crucial components both for stress adaptation and social behavior, special emphasis was given to this neuropeptide. We can conclude that stressing the mother does not have the same acute effect on the hypothalamo-pituitary-adrenocortical axis (as the main target of stress adaptation) of the pups as stressing the pups, but later endocrine and behavioral consequences can be similar. Vasopressin plays a role in acute and later consequences of perinatal stressor applied either to the mother or to the offspring, thereby contributing to transmitting the mothers' stress to the progeny. This mother-infant interaction does not necessarily mean a direct transmission of molecules, but rather is the result of programming the brain development through changes in maternal behavior. Thus, there is a time lag between maternal stress and stress-related changes in the offspring. The interactions are bidirectional as not only stress in the dam but also stress in the progeny has an effect on nursing.

Mesotocin and maternal care of chicks in native Thai hens (Gallus domesticus)

Oxytocin (OT) is known to induce and regulate maternal behaviors in mammals via the supraoptic nucleus and paraventricular nucleus (PVN), whereas the function of mesotocin (MT; the avian homolog of OT) is poorly understood in birds. To elucidate the association of MT and the regulation of maternal behaviors in birds, we studied changes in the number of MT-immunoreactive (ir) neurons in native Thai chickens using immunohistochemistry. We observed that MT-ir neurons and fibers appeared in discrete regions located close to the third ventricle from the level of the preoptic area through the anterior hypothalamus with an abundance observed in the nucleus supraopticus, pars ventralis (SOv), nucleus preopticus medialis (POM), and PVN. The number of MT-ir neurons was low in the SOv, POM, and PVN of non-laying hens, but it increased gradually when the hens entered the laying stage, and peaked in incubating and rearing hens. We compared the number of MT-ir neurons in the SOv, POM, and PVN of native Thai hens rearing chicks (R) with that of non-rearing chicks (NR). The number of MT-ir neurons was high in the R hens, but low in the NR hens in these nuclei. For the first time, these results indicate that the association between the MT neurons and the presence of chicks might, in part, play a role in the neuroendocrine reorganization to establish and maintain maternal behaviors in native Thai chickens. MTergic activity is likely related to the contribution of rearing behavior in this equatorial precocial species.

Glutamic acid decarboxylase 65 and 67 expression in the lateral septum is up-regulated in association with the postpartum period in mice

The postpartum period in mammals undergoes a variety of physiological adaptations, including metabolic, behavioral and neuroendocrine alterations. GABA signaling has been strongly linked to various emotional states, stress responses and offspring protection. However, whether GABA signaling may change in the lateral septum (LS), a core brain region for regulating behavioral, emotional and stress responses in postpartum mice has not previously been examined. In this study, we tested whether the expression of two isoforms of glutamic acid decarboxylase (GAD), GAD65 (GAD2) and GAD67 (GAD1), the rate-limiting enzyme for GABA synthesis, exhibits altered expression in postpartum mice relative to nonmaternal, virgin mice. Using microdissected septal tissue from virgin and age-matched postpartum females, quantitative real-time PCR and Western blotting were carried out to assess GAD mRNA and protein expression, respectively. We found both protein and mRNA expression of GAD67 in the whole septum was up-regulated in postpartum mice. By contrast, no significant difference in the whole septum was observed in GAD65 expression. We then conducted a finer level of analysis using smaller microdissections and found GAD67 to be significantly increased in rostral LS, but not in caudal LS or medial septum (MS). Further, GAD65 mRNA expression in rostral LS, but not in caudal LS or MS was also significantly elevated in postpartum mice. These findings suggest that an increased GABA production in rostral LS of the postpartum mice via elevated GAD65 and GAD67 expression may contribute to multiple alterations in behavioral and emotional states, and responses to stress that occur during the postpartum period. Given that rostral LS contains GABA neurons that are projection neurons or local interneurons, it still needs to be determined whether the function of elevated GABA is for local or distant action or both.

Gene expression changes in the septum: possible implications for microRNAs in sculpting the maternal brain

The transition from the non-maternal to the maternal state is characterized by a variety of CNS alterations that support the care of offspring. The septum (including lateral and medial portions) is a brain region previously linked to various emotional and motivational processes, including maternal care. In this study, we used microarrays (PLIER algorithm) to examine gene expression changes in the septum of postpartum mice and employed gene set enrichment analysis (GSEA) to identify possible regulators of altered gene expression. Genes of interest identified as differentially regulated with microarray analysis were validated with quantitative real-time PCR. We found that fatty acid binding protein 7 (Fabp7) and galanin (Gal) were downregulated, whereas insulin-like growth factor binding protein 3 (Igfbp3) was upregulated in postpartum mice compared to virgin females. These genes were previously found to be differentially regulated in other brain regions during lactation. We also identified altered expression of novel genes not previously linked to maternal behavior, but that could play a role in postpartum processes, including glutamate-ammonia ligase (Glul) and somatostatin receptor 1 (Sstr1) (both upregulated in postpartum). Genes implicated in metabolism, cell differentiation, or proliferation also exhibited altered expression. Unexpectedly, enrichment analysis revealed a high number of microRNAs, transcription factors, or conserved binding sites (177 with corrected P-value <0.05) that were significantly linked to maternal upregulated genes, while none were linked to downregulated genes. MicroRNAs have been linked to placenta and mammary gland development, but this is the first indication they may also play a key role in sculpting the maternal brain. Together, this study provides new insights into genes (along with possible mechanisms for their regulation) that are involved in septum-mediated adaptations during the postpartum period.

Effect of oxytocin, prolactin-releasing peptide, or corticotropin-releasing hormone on feeding behavior in steers

As a preliminary step to elucidate the involvement of central neurotransmitters in the dip in voluntary feed intake during the perinatal period in cows, we investigated the effect of intracerebroventricular (ICV) administration of oxytocin, prolactin-releasing peptide (PrRP), or corticotropin-releasing hormone (CRH), the central functions of all of which undergo drastic changes during the perinatal period, on feed intake in steers. Thirty minutes before the onset of feeding, the treatment solution was injected into the third ventricle through an implanted cannula, and feeding-related behaviors were observed for 1 h after the onset of feeding. Neither ICV oxytocin (5 and 50 μg) nor PrRP (2 and 20 nmol) reduced feed intake (n=6). Twenty nanomoles of bovine CRH noticeably inhibited feeding behavior compared with vehicle treatment (n=5, p<0.05). Fifty micrograms of oxytocin reduced latency to the first water access after feeding onset (p<0.1), which may be because of the stimulation of arginine vasopressin V1b receptor by the high dose of oxytocin. We conclude that CRH inhibits feeding behavior by its central action in this species, although this could also be an indirect effect due to the increased expression of abnormal behaviors caused by CRH. Central administration of neither oxytocin nor PrRP reduced feed intake in steers. Although the effects of sex steroids need to be examined, it appears that increased activity of oxytocin, and possibly PrRP, during the perinatal period does not contribute to the dip in voluntary feed intake in this species. On the other hand, it makes sense that suppressed central CRH activity during the perinatal period should act in the direction of maintaining or even increasing food intake to aid a steady supply of energy to the fetus or offspring. We thus speculate that CRH is not a prime candidate involved in the dip in voluntary feed intake during the perinatal period in cows.

Maternal neglect: oxytocin, dopamine and the neurobiology of attachment

Maternal neglect, including physical and emotional neglect, is a pervasive public health challenge with serious long-term effects on child health and development. I provide an overview of the neurobiological basis of maternal caregiving, aiming to better understand how to prevent and respond to maternal neglect. Drawing from both animal and human studies, key biological systems are identified that contribute to maternal caregiving behaviour, focusing on the oxytocinergic and dopaminergic systems. Mesocorticolimbic and nigrostriatal dopamine pathways contribute to the processing of infant-related sensory cues leading to a behavioural response. Oxytocin may activate the dopaminergic reward pathways in response to social cues. Human neuroimaging studies are summarised that demonstrate parallels between animal and human maternal caregiving responses in the brain. By comparing different patterns of human adult attachment, we gain a clearer understanding of how differences in maternal brain and endocrine responses may contribute to maternal neglect. For example, in insecure/dismissing attachment, which may be associated with emotional neglect, we see reduced activation of the mesocorticolimbic dopamine reward system in response to infant face cues, as well as decreased peripheral oxytocin response to mother-infant contact. We are currently testing whether the administration of intranasal oxytocin, as part of a randomised placebo controlled trial, may reverse some of these neurological differences, and potentially augment psychosocial and behavioural interventions for maternal neglect.

Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr-/-) and a conditional Oxtr knockout (OxtrFB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum OxtrFB/FB females toward their own pups and maternal behavior of virgin Oxtr-/- females toward foster pups and compared knockouts of both lines to wildtype (Oxtr+/+) littermates. We found that both Oxtr-/- and OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed.

Roles of α- and β-estrogen receptors in mouse social recognition memory: effects of gender and the estrous cycle

Establishing clear effects of gender and natural hormonal changes during female ovarian cycles on cognitive function has often proved difficult. Here we have investigated such effects on the formation and long-term (24 h) maintenance of social recognition memory in mice together with the respective involvement of α- and β-estrogen receptors using α- and β-estrogen receptor knockout mice and wildtype controls. Results in wildtype animals showed that while females successfully formed a memory in the context of a habituation/dishabituation paradigm at all stages of their ovarian cycle, only when learning occurred during proestrus (when estrogen levels are highest) was it retained after 24 h. In α-receptor knockout mice (which showed no ovarian cycles) both formation and maintenance of this social recognition memory were impaired, whereas β-receptor knockouts showed no significant deficits and exhibited the same proestrus-dependent retention of memory at 24 h. To investigate possible sex differences, male α- and β-estrogen receptor knockout mice were also tested and showed similar effects to females excepting that α-receptor knockouts had normal memory formation and only exhibited a 24 h retention deficit. This indicates a greater dependence in females on α-receptor expression for memory formation in this task. Since non-specific motivational and attentional aspects of the task were unaffected, our findings suggest a general α-receptor dependent facilitation of memory formation by estrogen as well as an enhanced long-term retention during proestrus. Results are discussed in terms of the differential roles of the two estrogen receptors, the neural substrates involved and putative interactions with oxytocin.

The impact of neonatal bisphenol-A exposure on sexually dimorphic hypothalamic nuclei in the female rat

Now under intense scrutiny, due to its endocrine disrupting properties, the potential threat the plastics component bisphenol-A (BPA) poses to human health remains unclear. Found in a multitude of polycarbonate plastics, food and beverage containers, and medical equipment, BPA is thought to bind to estrogen receptors (ERs), thereby interfering with estrogen-dependent processes. Our lab has previously shown that exposure to BPA (50mg/kg bw or 50μg/kg bw) during the neonatal critical period is associated with advancement of puberty, early reproductive senescence and ovarian malformations in female Long Evans rats. Here, using neural tissue obtained from the same animals, we explored the impact of neonatal BPA exposure on the development of sexually dimorphic hypothalamic regions critical for female reproductive physiology and behavior. Endpoints included quantification of oxytocin-immunoreactive neurons (OT-ir) in the paraventricular nucleus (PVN), serotonin (5-HT-ir) fiber density in the ventrolateral subdivision of the ventromedial nucleus (VMNvl) as well as ERα-ir neuron number in the medial preoptic area (MPOA), the VMNvl, and the arcuate nucleus (ARC). Both doses of BPA increased the number of OT-ir neurons within the PVN, but no significant effects were seen on 5-HT-ir fiber density or ERα-ir neuron number in any of the areas analyzed. In addition to hypothalamic development, we also assessed female sex behavior and body weight. No effect of BPA on sexual receptivity or proceptive behavior in females was observed. Females treated with BPA, however, weighed significantly more than control females by postnatal day 99. This effect of BPA on weight is critical because alterations in metabolism, are frequently associated with reproductive dysfunction. Collectively, the results of this and our prior study indicate that the impact of neonatal BPA exposure within the female rat hypothalamus is region specific and support the hypothesis that developmental BPA exposure may adversely affect reproductive development in females.

Resetting the dynamic range of hypothalamic-pituitary-adrenal axis stress responses through pregnancy

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in the neuroendocrine response to stress. Dynamic changes in HPA axis regulation and hence HPA responsivity occur over the lifetime of an animal. This article focuses on two extremes of the spectrum. The first occurs naturally during pregnancy when stress responses are dampened. The second, at the opposite end of the scale, occurs in offspring of mothers who were exposed to stress during pregnancy and display exaggerated HPA axis stress responses. Reduced glucocorticoid output in response to stress in pregnancy may have important consequences for conserving energy supply to the foetus(es), in modulating immune system adaptations and in protecting against adverse foetal programming by glucocorticoids. Understanding the mechanisms underpinning this adaptation in pregnancy may provide insights for manipulating HPA axis responsiveness in later life, particularly in the context of resetting HPA axis hyperactivity associated with prenatal stress exposure, which may underlie several major pathologies, including cardiovascular disease, diabetes mellitus type 2, obesity, cognitive decline and mood disorders.

Patterns of fos-like immunoreactivity in the brains of parent ring doves (Streptopelia risoria) given tactile and nontactile exposure to their young

Neuronal activation was examined by fos immunohistochemistry in ring doves (Streptopelia risoria) reunited with their young after overnight separation. In an initial study, squab-exposed parents showed more fos immunoreactivity (ir) in the preoptic area (POA) and lateral hypothalamus (LH) than squab-deprived parents. In a 2nd study, parents allowed free access to young and those separated from young by a wire mesh partition showed more fos-ir in the POA, LH, and lateral septum than box-exposed controls. Contact with young also increased fos-ir in the medial preoptic nucleus and bed nucleus of the stria terminalis, but noncontact exposure did not. Conversely, nontactile squab exposure stimulated more fos-ir in the POA than did free access to young, which suggests POA involvement in appetitive aspects of parenting.

Individual variation in the expression of maternal behaviour: a review of the neuroendocrine mechanisms in the sheep

Individual variation in the expression of maternal behaviour can affect offspring development and survival. Ewes showing a poorer quality of maternal behaviour (low levels of licking and grooming, infrequent low-pitched bleating, inconsistent udder acceptance) at parturition and throughout lactation (large ewe-lamb distance, low vigilance) form a weaker bond with their lambs, and have higher lamb mortality, than ewes which show high levels of grooming and low-pitched bleating, close ewe-lamb distances and high levels of vigilance. Using two models of variation in maternal behaviour in the sheep (differences between ewes of two breeds, and differences between primiparous and multiparous ewes), the neuroendocrine mechanisms that underpin these differences are explored. In both cases, significant variation in oestrogen priming is observed, with breed differences in circulating concentrations of oestrogen in late gestation, and parity effects on receptor density but not circulating concentrations. The consequences of these differences for central oxytocin release and binding are discussed. In addition, preliminary data suggest that opioid modulation, in both breed and parity models, may also play a role in mediating individual variation in maternal behaviour in the sheep.

Genetic and physiological determinants of maternal behavior and lamb survival: Implications for low-input sheep management1,2

The relatively intensive supervision afforded many ewes at lambing time is a barrier to the development of low-input sheep management systems. However, in some flocks, reduction in this level of supervision may initially affect lamb mortality and animal welfare. In this review, possibilities for optimizing behavioral interaction between the ewe and lamb are considered, with the goal of improving lamb survival without the need for high levels of human supervision. At birth, ewes show specific behavioral patterns (e.g., licking or grooming, low-pitched bleats, udder acceptance) that facilitate the transition of the lamb from pre- to postnatal life and that accompany the formation of an exclusive olfactory memory for the lamb. The lamb also performs a specific sequence of behaviors directed toward standing, finding the udder, and sucking. The successful accomplishment of these behavior patterns is vital for the formation of a strong attachment between both partners, and for lamb survival. The expression of maternal behavior in the ewe is affected by her previous maternal experience, by nutrition in pregnancy, by breed, by temperament, and, to some extent, by the behavior of her lamb. The maternal care expressed by a ewe at parturition is indicative of her behavior throughout that lactation and in successive pregnancies, suggesting an underlying basis to maternal care intrinsic to that ewe. Studies with Scottish Blackface and Suffolk ewes show that ewes expressing high levels of maternal care have elevated plasma estradiol in late gestation compared with ewes with poorer maternal care, and that circulating estradiol concentration is correlated with maternal behaviors. Although the genetic basis of maternal behaviors has still to be fully determined, there are possibilities of improving maternal behavior by selection, and a better understanding of the neuroendocrine processes underlying individual differences in maternal behavior may help in developing selection strategies. In addition, selection on lamb behaviors, which show some genetic basis, may also be a route to improve lamb survival. Because behavior of both the ewe and lamb is affected by environmental factors, appropriate management, through pregnancy and at parturition, will enhance the expression of maternal behavior and lamb vigor, and so contribute to improving lamb survival.

Parity effects on maternal behaviour are not related to circulating oestradiol concentrations in two breeds of sheep

Primiparous females of many species, including the sheep, do not show as competent maternal behaviour as multiparous mothers. In this study we investigated whether circulating concentrations of oestradiol might be related to this response, since breed differences in oestradiol concentrations have been shown to correlate with maternal behaviours. Oestradiol concentrations were measured in plasma collected at 2-weekly intervals from primiparous and multiparous ewes of two breeds (Scottish Blackface and Suffolk) throughout gestation, and maternal behaviour was recorded at parturition. Circulating oestradiol concentrations, and the ratio of oestradiol to progesterone concentration (O:P ratio) were higher in late pregnancy in Blackface ewes, but there were no significant effects of ewe parity. However, there was a significant interaction between breed and parity as O:P ratio was lower in primiparous Suffolk ewes compared to multiparous. This relationship was not seen in Blackface ewes. Blackface ewes of both parities groomed their lambs more frequently and made more low-pitched vocalisations than Suffolk ewes. Primiparous ewes were more likely to move as the lamb attempted to suck, and to show withdrawal or aggression towards the lamb. Primiparous Suffolk ewes also made more high pitched bleats than other classes of ewe. The data support previous studies which show an effect of breed on circulating oestradiol and O:P ratio but suggest that parity effects on maternal behaviour may be mediated by sensitivity to circulating concentration of oestradiol rather than variations in the plasma concentrations of this hormone.

Mother-infant bonding and the evolution of mammalian social relationships

A wide variety of maternal, social and sexual bonding strategies have been described across mammalian species, including humans. Many of the neural and hormonal mechanisms that underpin the formation and maintenance of these bonds demonstrate a considerable degree of evolutionary conservation across a representative range of these species. However, there is also a considerable degree of diversity in both the way these mechanisms are activated and in the behavioural responses that result. In the majority of small-brained mammals (including rodents), the formation of a maternal or partner preference bond requires individual recognition by olfactory cues, activation of neural mechanisms concerned with social reward by these cues and gender-specific hormonal priming for behavioural output. With the evolutionary increase of neocortex seen in monkeys and apes, there has been a corresponding increase in the complexity of social relationships and bonding strategies together with a significant redundancy in hormonal priming for motivated behaviour. Olfactory recognition and olfactory inputs to areas of the brain concerned with social reward are downregulated and recognition is based on integration of multimodal sensory cues requiring an expanded neocortex, particularly the association cortex. This emancipation from olfactory and hormonal determinants of bonding has been succeeded by the increased importance of social learning that is necessitated by living in a complex social world and, especially in humans, a world that is dominated by cultural inheritance.

Maternal responsiveness and maternal selectivity in domestic sheep and goats: The two facets of maternal attachment

Sheep and goats rapidly establish an exclusive relationship with their neonate following contact with it during a sensitive period of maternal responsiveness induced by the physiological events occurring at parturition. The data concerning the sensory, physiological, and neurobiological factors involved in the activation of both maternal responsiveness and the establishment of selective nursing indicates that these processes are activated simultaneously by the combined action of two main factors, the prepartum rise in circulating estrogen and the vaginocervical stimulation (VCS) caused by fetus expulsion. On the one hand, these two factors act on a neural network including the main olfactory system (MOB), the medial preoptic area (MPOA), and the paraventricular nucleus of the hypothalamus (PVN) to induce maternal responsiveness towards any neonate. The intracerebral release of oxytocin (OT) from the PVN, and the triggering of olfactory attraction for amniotic fluid (AF) are key elements in this process. On the other hand, VCS at birth also sets the MOB ready to memorize the individual odor of the neonate, through the release of peptides and neurotransmitters (noradrenaline and acetylcholine). In addition to the MOB, the network involved in recognition mainly includes the medial and cortical amygdala. Across consolidation processes, reorganization occurs in the network engaged in lamb recognition. Whether this memorization may be potentiated by other sensory cues is not known. The identification of the chemosensory compounds involved in the attraction for AF and in the recognition of the neonate is important for understanding the mechanisms of maternal attachment.

Neurochemical bases of plasticity in the magnocellular oxytocin system during gestation

The central and systemic release of oxytocin (OT) has been well documented during parturition and lactation. In preparation for the demands of these events, the magnocellular hypothalamic neurons of the central OT system undergo a variety of biochemical, molecular, electrophysiological, and anatomical adaptations during gestation. However, the mechanisms responsible for these changes have not been well established. A number of neurochemical mediators have been implicated in contributing to the plasticity in the OT magnocellular system during gestation, including ovarian hormones, as well as central neurotransmitters, such as glutamate, gamma-amino butyric acid (GABA), and central neurosteroids, e.g., allopregnanolone. In addition, several lines of evidence suggest that central OT release and subsequent OT receptor stimulation may contribute to adaptations of the OT system during gestation, and may be necessary for its subsequent functioning during lactation. Here, we review evidence for involvement of the neurochemical systems implicated in contributing to adaptations that occur in the OT system during the course of gestation.

Estradiol receptor-alpha expression in hypothalamic and limbic regions of ewes is influenced by physiological state and maternal experience

The influence of estrus, pregnancy, parturition, and maternal experience on the expression of estrogen receptor-alpha (ERalpha) was investigated in hypothalamic and limbic regions of the sheep brain, using immunocytochemistry. Four days before parturition, previous maternal experience was associated with a higher density of ERalpha-labeled neurons in the paraventricular and supraoptic nuclei, the medial preoptic area, and the medial amygdala, but not in the mediobasal hypothalamus. Furthermore, an interaction was found between physiological state and experience in the peripartum period as the effect of experience existing 4 days prepartum was not found at parturition, when densities were lowest both in primiparous and in multiparous ewes. An additional effect of physiological state was also observed between parturition and estrus, densities being significantly lower at parturition than at estrus in the SON, PVN, and MPOA, but not in the medial amygdala. These results indicate that in sheep ERalpha expression is influenced by previous physiological and/or maternal experience at specific times of the reproductive cycle. They are also congruent with the higher ability of multiparous than nulliparous ewes to show maternal behavior several days prepartum.

Prepartum plasma estradiol and postpartum cortisol, but not oxytocin, are associated with interindividual and breed differences in the expression of maternal behaviour in sheep

Consistent, individual differences in the expression of maternal behaviour have been described in several species including the sheep. The neuroendocrine mechanisms underlying the onset of maternal behaviour in the sheep have been described, although the relationship between hormonal events and individual differences in behaviour has yet to be determined. In this study, we examined whether the individual differences in plasma estradiol, progesterone, oxytocin and cortisol concentrations were related to observed individual and breed differences in maternal behaviours in two breeds of sheep (Scottish Blackface and Suffolk) known to differ in maternal behavioural expression. Maternal estradiol concentration increased rapidly before parturition and was higher in Blackface ewes than Suffolk ewes. Plasma progesterone declined before parturition and was higher in Suffolk than Blackface ewes. Prepartum estradiol, but not progesterone, was related to individual differences in maternal grooming of the lamb. Plasma oxytocin did not differ between breeds in late gestation. There was a tendency for oxytocin to be higher in Blackface than Suffolk ewes immediately after birth. However, there were no significant relationships between prepartum or postpartum oxytocin and any maternal behaviours. Plasma cortisol was higher in Blackface than Suffolk ewes in the last days of pregnancy but rose in both breeds over the last 24 h before parturition and did not differ at delivery. Cortisol peripartum was negatively related to individual differences in maternal affiliative behaviours. These data suggest that estradiol, and potentially cortisol, may mediate individual differences in maternal behaviour in sheep.

Changes in cerebrospinal fluid neurochemistry during pregnancy

BACKGROUND

Little is known about changes in brain function that may occur during pregnancy. Studies in rodents and sheep suggest that several brain neurotransmitter and neurohormonal systems known to modulate anxiety may be altered during pregnancy.

METHODS

Cerebrospinal fluid (CSF) and plasma samples were obtained from 21 women (during weeks 38-39 of pregnancy) who were undergoing elective cesarean section and from 22 healthy nonpregnant women.

RESULTS

The CSF levels of g-aminobutyric acid (GABA) and 3-methoxy-4-hydroxyphenylglycolwere reduced in pregnant women. There were no changes in CSF glutamate, 5-hydroxyindoleactic acid, and homovanillic acid. There was a large increase in CSF prolactin in pregnant women and also a trend toward an elevation in CSF oxytocin. Levels of prolactin, but not oxytocin, in CSF and plasma were correlated in pregnant women.

CONCLUSIONS

These results suggest that pregnancy alters regulation of brain GABA, norepinephrine, and prolactin, which may play a role in changes in vulnerability to anxiety and depression during pregnancy and postpartum. Prolactin circulating in the bloodstream seems to be the major source of CSF prolactin during pregnancy.

Immunolocalization of estrogen receptor beta in the hypothalamic paraventricular nucleus of female mice during pregnancy, lactation and postnatal development

Previous studies have shown that estrogen receptor beta (ERbeta) is the predominant estrogen receptor in the hypothalamic paraventricular nucleus (PVN) of mouse, mediating estrogen regulation of the neuroendocrine activities of the PVN, but the exact roles that ERbeta plays in the PVN remain unclear. In this study, we used immunocytochemistry to investigate the expression of ERbeta in the maternal PVN of mice during pregnancy (pregnant days 8, 10, 12, 15 and 18), lactation (postpartum days 1, 4 and 8) as well as in the PVN of the females from postnatal days 1, 3, 5, 7, 9, 15, 30 and 70. We found out that ERbeta was predominantly localized in the magnocellular divisions of PVN. In the pregnant female brain, generally, the ERbeta was lower than that of the postnatal development, the lowest level was found at gestational days 10-12; then from gestational day 18 to postpartum day 1, it increased to higher levels, followed by a decrease from postpartum day 4. During the postnatal development, the highest level of ERbeta was found at early postnatal days (before postnatal day 15), thereafter, it decreased to a lower level. The above results indicate that circulating sex steroids may differentially regulate the expression of ERbeta in the PVN of mice. It also suggests that this receptor may play important roles in the regulation of parturition and in the development, food intake and body weight increases of the newborns by acting on the neuropeptides, which were also detected in the PVN.

Brain mechanisms underlying emotional alterations in the peripartum period in rats

In the period before and after parturition, i.e., in pregnancy and lactation, a variety of neuroendocrine alterations occur that are accompanied by marked behavioral changes, including emotional responsiveness to external challenging situations. On the one hand, activation of neuroendocrine systems (oxytocin, prolactin) ensures reproduction-related physiological processes, but in a synergistic manner also ensures accompanying behaviors necessary for the survival of the offspring. On the other hand, there is a dramatic reduction in the responsiveness of neuroendocrine systems to stimuli not relevant for reproduction, such as the hypothalamo-pituitary-adrenal (HPA) axis responses to physical or emotional stimuli in both pregnant and lactating rats. With CRH being the main regulator of the HPA axis, downregulation of the brain CRH system may result in various behavioral, in particular emotional, adaptations of the maternal organisms, including changes in anxiety-related behavior. In support of this, the lactating rat becomes less emotionally responsive to novel situations, demonstrating reduced anxiety, and shows a higher degree of aggressive behavior in the test for agonistic behavior as well as in the maternal defense test. These changes in emotionality are independent of the innate (pre-lactation) level of anxiety and are seen in both rats bred for high as well as low levels of anxiety. Both brain oxytocin and prolactin, highly activated at this time, play a significant role in these behavioral and possibly also neuroendocrine adaptations in the peripartum period.

Characterization of social behaviors and oxytocinergic neurons in the S-100 beta overexpressing mouse model of Down Syndrome

S-100 beta, a gene triplicated in Down Syndrome (DS), is thought to play a role in development of the brain in general, and in the serotonergic neuronal system in particular. We have been studying an animal model of DS, based on overexpression of this gene. In the current study, we report on the social behaviors of these animals, both in same-strain and mixed-strain pairings. In addition, as the neuropeptide oxytocin is often thought to be involved in social behaviors, we have looked at oxytocin-containing cells. In non-social behaviors, such as grooming and line-crossing, the S-100 beta animals were more active than the CD-1 control animals and showed significantly less social sniffing. In mixed-strain studies, these differences became more pronounced, with the CD-1 animals showing significantly greater levels of sniffing and anogenital sniffing. As well, the CD-1 animals showed more rearing and an increase in line crossings, suggesting a heightened level of vigilance or awareness of novelty. The S-100 beta animals, conversely, did not appear to respond to the novelty of the CD-1 animals. In mixed pair studies, the S-100 beta animals more frequently took submissive postures, while the CD-1 animals more frequently took dominant postures, and showed a significant increase in biting the S-100 beta partner. The S-100 beta animals showed less rearing, perhaps a further indication that they were inhibited by the CD-1 animals. Analysis of oxytocin-containing neurons showed comparable levels in the supraoptic and paraventricular nuclei of the hypothalamus, but significantly reduced numbers of cells in the bed nucleus of the stria terminalis of the S-100 beta animals. These results are discussed in terms of oxytocin contributions to socialization and fear responding and the significance of these findings to DS.

Ewe-lamb bonding behaviours at birth are affected by maternal undernutrition in pregnancy

Maternal undernutrition in pregnancy results in low birth-weights and impaired postnatal survival in sheep. Largely anecdotal evidence suggests that the expression of appropriate maternal and neonate behaviours may also be disrupted by undernutrition. In the present study, we investigated the effect of a moderate (35 %) reduction in ewe nutritional intake in pregnancy on the expression of ewe-lamb bonding behaviours in primiparous Scottish Blackface ewes. Low-intake (L) ewes had significantly higher plasma progesterone than high-intake (H) ewes from mid-gestation onwards (e.g. plasma progesterone at 20 weeks (ng/ml): H 15.72, L 22.38, sed 1.80, P<0.001), and a lower oestradiol: progesterone value than H ewes at delivery (H 0.46, L 0.35, sed 0.05, P<0.05). Lamb birth-weight was reduced in the L lambs compared with H lambs (mean body weight (kg): H 3.31, L 3.00, sed 0.14, P<0.05), but the incidence of malpresentation at delivery was greater in L lambs. L ewes spent significantly less time licking their lambs than H ewes after delivery (time grooming in 2 h after birth (%): H 56.12, L 48.17, sed 2.639, P<0.01) and were more aggressive towards the lambs. Lamb behaviours were not directly affected by maternal nutritional treatment, but lamb birth-weight had a significant effect on neonatal developmental progress. Low-birth-weight lambs were slower than heavier lambs to stand and sucked less frequently. In tests of maternal attachment to the lamb, H ewes received higher scores than L ewes at both 24 h after birth (ewes receiving high scores (%): H 41.3, L 21.4, P<0.05) and at 3 d postnatal. We conclude that even a moderate level of undernutrition impairs the attachment between ewes and lambs by affecting maternal behaviours expressed at birth. In addition, the results suggest that levels of nutrition resulting in a decrease in birth weight will affect neonatal lamb behavioural progress.

Molecular approaches to aggregation behavior and social attachment

In many animal species individuals aggregate to live in groups. A range of experimental approaches in different animals, including studies of social feeding in nematodes, maternal behavior in rats and sheep, and pair-bonding in voles, are providing insights into the neural bases for these behaviors. These studies are delineating multiple neural circuits and gene networks in the brain that interact in ways that are as yet poorly understood to coordinate social behavior.

Brain preparations for maternity--adaptive changes in behavioral and neuroendocrine systems during pregnancy and lactation. An overview

Pregnancy, parturition and lactation comprise a continuum of adaptive changes necessary for the development and maintenance of the offspring. The endocrine changes that are driven by the conceptus and are essential for the maintenance of pregnancy and are involved in the preparations for motherhood are outlined. These changes include large increases in the secretion of sex steroid hormones, and the secretion of peptide hormones that are unique to pregnancy. The ability of these pregnancy hormones to alter several aspects of brain function in pregnancy is considered, and the adaptive importance of some of these changes is discussed, for example in metabolic and body fluid adjustments, and the induction of maternal behavior. The importance of sex steroids in determining the timing of the various adaptive changes in preparing for parturition and maternal behavior is emphasized, and the concept that the actions of prolactin and oxytocin, quintessential mammalian motherhood neuropeptides, can serve to coordinate a spectrum of adaptive changes is discussed. The part played by oxytocin neurons and their regulatory mechanisms is reviewed to illustrate how neural systems involved in maternity are prepared in pregnancy via changes in phenotype, synaptic organization and in the relative importance of their different inputs, to function optimally when needed. For oxytocin neurons secreting from the posterior pituitary, important in parturition and essential in lactation, these changes include mechanisms to restrain their premature activation, and adaptations to support synchronized burst firing for pulsatile oxytocin secretion in response to stimulation via afferents from the birth canal, olfactory system or suckled nipples. Within the brain, expression of oxytocin receptors permits centrally released oxytocin to facilitate the expression of maternal behavior. Changes in other neuroendocrine systems are similarly extensive, leading to lactation, suppression of ovulation, reduced stress responses and increased appetite; these changes in lactation are driven by the suckling stimulus. The possible link between these adaptations and changes in cognition and mood in pregnancy and post partum are considered, as well as the dysfunctions that lead to common problems of depression and puerperal psychoses.

Alterations in behavioral and neuroendocrine stress coping strategies in pregnant, parturient and lactating rats

In the present chapter the behavioral and neuroendocrine alterations accompanying pregnancy and lactation will be discussed. It will be shown that many are dependent on the innate level of emotionality of the rats. In late pregnancy the level of anxiety, as measured on the elevated plus-maze is increased in rats with both high and low level of innate anxiety-related behavior, whereas lactating rats display less anxiety in such tests and higher degrees of aggressive behavior in tests for agonistic behavior. There is a dramatic reduction in the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis to various physical or emotional stimuli in both pregnant and lactating rats. This appears to be due to changes throughout the HPA axis. Oxytocin has been implicated in the control of the axis at this time, but the inhibitory action of central oxytocin on ACTH or corticosterone secretion seen in virgin female rats is not evident during pregnancy and lactation. However, central oxytocin is involved in the regulation of emotionality at this time. In addition to its anxiolytic effect, prolactin, acting at brain prolactin receptors, seems to exert an inhibitory effect on HPA axis responsiveness. At the time of parturition, the HPA axis is not stimulated by parturition-related stimuli and is under strong inhibition by endogenous opioids as revealed by the application of the opioid receptor antagonist naloxone.

The neurobiology of attachment

It is difficult to think of any behavioural process that is more intrinsically important to us than attachment. Feeding, sleeping and locomotion are all necessary for survival, but humans are, as Baruch Spinoza famously noted, "a social animal" and it is our social attachments that we live for. Over the past decade, studies in a range of vertebrates, including humans, have begun to address the neural basis of attachment at a molecular, cellular and systems level. This review describes some of the important insights from this work.

Distribution of estrogen receptor beta (ERbeta) mRNA in hypothalamus, midbrain and temporal lobe of spayed macaque: continued expression with hormone replacement

This study used in situ hybridization (ISH) to examine the distribution of estrogen receptor beta (ERbeta) mRNA in hypothalamic, limbic, and midbrain regions of monkey brain and its regulation by estrogen (E) and progesterone (P). Monkey-specific ERbeta cDNAs were developed with human primers and reverse transcription and polymerase chain reaction (RT-PCR) using mRNA extracted from a rhesus monkey prostate gland. ERbeta 5' (262 bases) and 3' (205 bases) riboprobes were used in combination for ISH. Ovariectomized and hysterectomized (spayed) pigtail macaques (Macaca nemestrina; four per treatment group) were either untreated spayed-controls, treated with E (28 days), or treated with E plus P (14 days E+14 days E and P). Dense ERbeta hybridization signal was seen in the preoptic area, paraventricular nucleus, and ventromedial nucleus of the hypothalamus; the substantia nigra, caudal linear, dorsal raphe, and pontine nuclei of the midbrain; the dentate gyrus, CA1, CA2, CA3, CA4, and the prosubiculum/subiculum areas of the hippocampus. Expression in the suprachiasmatic region, supraoptic nucleus, arcuate nucleus, and amygdala was less intense. Image analysis of the dense areas showed no significant difference in the hybridization signal in individual regions of the hypothalamus, midbrain, or hippocampus between any of the treatment groups. However, P treatment decreased overall ERbeta signal in the hypothalamus and hippocampus when several different subregions were combined. The localization of ERbeta in monkey brain by ISH is in general agreement with that previously described in rodents. The presence of monkey ERbeta mRNA in brain regions that lack ERalpha should help to clarify the molecular mechanisms by which E acts in the central nervous system to influence hormone secretion, mood disorders, cognition, and neuroprotection.

Brain oxytocin: differential inhibition of neuroendocrine stress responses and anxiety-related behaviour in virgin, pregnant and lactating rats

The involvement of brain oxytocin in the attenuated responsiveness of the hypothalamo-pituitary-adrenal axis and the oxytocin systems to external stressors found in pregnant and lactating rats has been studied, including both neuroendocrine and behavioural aspects. Intracerebroventricular infusion of an oxytocin receptor antagonist (0.75 microg/5 microl), but not of vehicle, elevated basal corticotropin and corticosterone secretion into blood of virgin female, but not of late pregnant or lactating rats. Oxytocin antagonist treatment further elevated the stress-induced (exposure to the elevated plus-maze or forced swimming) secretion of both corticotropin and corticosterone, but only in virgin and not in pregnant or lactating rats. Thus, corticotropin and corticosterone plasma concentrations remained attenuated in antagonist-treated pregnant and lactating animals. In contrast, infusion of the oxytocin antagonist significantly elevated the stress-induced secretion of oxytocin into blood in pregnant and lactating, but not in virgin, animals, indicating an autoinhibitory influence of intracerebral oxytocin on neurohypophysial oxytocin secretion induced by non-reproduction-related stimuli. Treatment with oxytocin antagonist 10 min prior to behavioural testing on the elevated plus-maze significantly reduced the anxiety-related behaviour in both pregnant and lactating rats, without exerting similar effects in virgin female rats. The results demonstrate a tonic inhibitory effect of endogenous oxytocin on corticotropin and, consequently, corticosterone secretion in virgin female rats, an effect which is absent in the peripartum period. In contrast, an anxiolytic action of endogenous oxytocin was detectable exclusively in pregnant and lactating rats. Therefore, we conclude that the actions of intracerebral oxytocin include independent effects on the responses of the hypothalamo-pituitary-adrenal axis and oxytocin systems to stressors and the anxiety-related behaviour which are modulated by the reproductive state of the animals.

Oxytocin, motherhood and bonding

Release of the peptide hormone oxytocin in the brain has been shown to influence both maternal, sexual and social bonding behaviours although there are a number of species differences. This review summarizes findings on the distributions of oxytocin and oxytocin receptors in the brain, together with factors governing their expression, release of the peptide in the brain and its behavioural actions. A model of how oxytocin may act to alter maternal and socio-sexual behaviours is proposed which initially involves activation of oxytocin neurones in a single brain site, the paraventricular nucleus of the hypothalamus (PVN), following vaginal and cervical stimulation. This causes a co-ordinated release of the peptide in the PVN and its terminal projection regions for up to 1 h and this promotes different behavioural components, primarily through modulation of classical transmitter systems.

Previous maternal experience potentiates the effect of parturition on oxytocin receptor mRNA expression in the paraventricular nucleus

In sheep, central oxytocin release at parturition induces maternal behaviour which is thought to be mediated by changes in the expression of central oxytocin receptors. The distribution, effects of parturition, previous maternal experience and hormonal status on the distribution of an oxytocin receptor was investigated using immunocytochemistry and in situ hybridization. In ewes with no previous maternal experience, parturition induced significant increases in oxytocin receptor mRNA expression in the anterior olfactory nucleus, medial preoptic area, ventromedial hypothalamus, lateral septum, medial amygdala, bed nucleus of the stria terminalis and diagonal band of Broca. In maternally experienced ewes, parturition induced additional increases in two areas, the paraventricular nucleus and the Islands of Calleja. The changes in progesterone and oestrogen that occur during late pregnancy and parturition appear to contribute to increases in expression in the anterior olfactory nucleus, Islands of Calleja, medial preoptic area, ventromedial hypothalamus, bed nucleus of the stria terminalis and diagonal band of Broca, but not in the paraventricular nucleus, lateral septum and medial amygdala. These results demonstrate that progesterone and oestrogen priming enhance oxytocin receptor mRNA expression in a number of regions in the olfactory system, hypothalamus and limbic brain. These effects appear to be independent of maternal experience. Parturition increases oxytocin receptor mRNA expression in all the areas influenced by hormonal priming and the lateral septum, medial amygdala and paraventricular nucleus. Maternal experience also enhances expression of oxytocin receptor mRNA in the paraventricular nucleus and the Islands of Calleja. Because the paraventricular nucleus is the main source of oxytocin release in the brain, this upgrading of autoreceptors as a result of maternal experience may serve to enhance release of this peptide in projection sites regulating maternal behaviour.

Physiological correlates of maternal-offspring behaviour in sheep: a factor analysis

The onset of maternal behaviour in sheep is controlled by levels of oestrogen and progesterone in gestation and the release of oxytocin during delivery. Factor analysis was used to investigate the relationships between maternal behaviour, offspring behaviour, and maternal ovarian hormone levels during gestation in sheep. Ewes gave birth to lambs following embryo transfer between two breeds (Suffolk and Scottish Blackface), which differ in their expression of maternal behaviour. Plasma oestradiol-17beta concentration was significantly higher in Blackface ewes in the last 6 weeks of pregnancy, whereas plasma progesterone was higher in Suffolk ewes in early and mid gestation. Factor analysis revealed three factors that accounted for 50% of the total variation between variables. Factor 1 described lamb activity and had positive loadings for lamb behavioural latencies immediately postpartum, and negative loadings for sucking frequency. Factor 2 described some aspects of ewe maternal behaviour, and had positive loadings for ewe-lamb separation and lamb vocalisation, and negative loadings for ewe grooming behaviour and plasma oestradiol concentration. Factor 3 described ewe and lamb-sucking interactions, and had positive loadings for ewe moving as the lamb made sucking attempts, and negative loadings for ewe and lamb vocalisation. Factor 1 scores were significantly affected by lamb breed: Suffolk lambs received positive scores, indicating a longer latency to right and stand, whereas Blackface lambs had negative scores. Maternal progesterone concentration was significantly correlated with Factor 1 scores. Factor 2 and 3 scores were significantly affected by ewe breed. This study has shown that there are two behavioural axes to maternal behaviour in sheep, and that maternal oestradiol concentration is related to affiliative behaviours (e.g., grooming) but only weakly to ewe responsiveness to lamb-sucking attempts.

C-fos and c-jun in the paraventricular nucleus play a role in regulating peptide gene expression, oxytocin and glutamate release, and maternal behaviour

In sheep, birth leads to the induction of maternal behaviour through brain oxytocin release. Associated with these events is an upregulation of oxytocin, opioid and corticotrophin-releasing hormone (CRH) gene expression, as well as that of the immediate early gene c-fos in the paraventricular nucleus (PVN) of the hypothalamus. We investigated the role of c-fos dimerizing with c-jun in controlling the induction of maternal behaviour, altered peptide gene expression, and oxytocin and amino acid release in this region at birth. Fluorescence-labelled antisense oligodeoxyribonucleotides (ODNs) against c-fos/c-jun were infused bilaterally in the PVN, via microdialysis probes with 100 kDa cut-off membranes, and were incorporated into 50-60% of the cells. Compared with the control (scrambled) sequences, they significantly reduced basal concentration of glutamate (to 31.7% of baseline after 10 h) and prevented birth-induced release of aspartate. In addition, antisense treatment reduced the birth-induced increase in oxytocin concentration in the PVN, but not in blood. Although all the animals were fully maternal, the antisense treatment did reduce the peak expression of two components of maternal behaviour: low-pitched bleats; and lamb sniffing. Finally, in situ hybridization histochemistry revealed that the antisense treatment significantly reduced the birth-induced upregulation of c-fos, oxytocin, CRH and preproenkephalin mRNA expression in the PVN, whilst not affecting that of arginine vasopressin. These results suggest that c-fos/c-jun transcription factors play a role in the birth-induced upregulation of oxytocin, CRH and preproenkephalin gene expression, as well as on glutamate and oxytocin release in the sheep PVN.