Neuronal STAT5 signaling is required for maintaining lactation but not for postpartum maternal behaviors in mice

Prolactin-induced neuroprotection against excitotoxicity is mediated via PI3K/AKT and GSK3β/NF-κB in primary cultures of hippocampal neurons

Prolactin (PRL) is a polypeptide hormone that has been reported to play a significant role in neuroprotection against neuronal excitotoxicity produced by glutamate (Glu) or kainic acid (KA) in both, in vitro and in vivo models. However, the molecular mechanisms involved in PRL's neuroprotective effects in the hippocampus have not been completely elucidated. The aim of the present study was to assess the signaling pathways involved in PRL neuroprotection against excitotoxicity. Primary rat hippocampal neuronal cell cultures were used to assess PRL-induced signaling pathway activation. The effects of PRL on neuronal viability, as well as its effects on activation of key regulatory pathways, phosphoinositide 3-kinases/Protein Kinase B (PI3K/AKT) and glycogen synthase kinase 3β / nuclear factor kappa B (GSK3β/NF-κB), were evaluated under conditions of Glutamate-induced excitotoxicity. Additionally, the effect on downstream regulated genes such as Bcl-2 and Nrf2, was assessed. Here, we show that the PI3K/AKT signaling pathway is activated by PRL treatment during excitotoxicity, promoting neuronal survival through upregulation of active AKT and GSK3β/NF-κB, resulting in induction of Bcl-2 and Nrf2 gene expression. Inhibition of the PI3K/AKT signaling pathway abrogated the protective effect of PRL against Glu-induced neuronal death. Overall, results indicate that the neuroprotective actions of PRL are mediated in part, by the activation of the AKT pathway and survival genes. Our data support the idea that PRL could be useful as a potential neuroprotective agent in different neurological and neurodegenerative diseases.

The brain as a source and a target of prolactin in mammals

Prolactin is a polypeptide hormone associated with an extensive variety of biological functions. Among the roles of prolactin in vertebrates, some were preserved throughout evolution. This is the case of its function in the brain, where prolactin receptors, are expressed in different structures of the central nervous system. In the brain, prolactin actions are principally associated with reproduction and parental behavior, and involves the modulation of adult neurogenesis, neuroprotection, and neuroplasticity, especially during pregnancy, thereby preparing the brain to parenthood. Prolactin is mainly produced by specialized cells in the anterior pituitary gland. However, during vertebrate evolution many other extrapituitary tissues do also produce prolactin, like the immune system, endothelial cells, reproductive structures and in several regions of the brain. This review summarizes the relevance of prolactin for brain function, the sources of prolactin in the central nervous system, as well as its local production and secretion. A highlight on the impact of prolactin in human neurological diseases is also provided.

Growth hormone receptor contributes to the activation of STAT5 in the hypothalamus of pregnant mice

Growth hormone (GH) receptor (GHR) signaling induces the phosphorylation of the signal transducer and activator of transcription 5 (pSTAT5) in the cells of several tissues including in the hypothalamus. During pregnancy, several STAT5-recruiting hormones (e.g., prolactin, GH and placental lactogens) are highly secreted. However, the precise contribution of GHR signaling to the surge of pSTAT5 immunoreactive neurons that occurs in the hypothalamus of pregnant mice is currently unknown. Thus, the objective of the present study was to determine whether GHR expression in neurons is required for inducing pSTAT5 expression in several hypothalamic nuclei during pregnancy. Initially, we demonstrated that late pregnant C57BL/6 mice (gestational day 14 to 18) exhibited increased pulsatile GH secretion compared to virgin females. Next, we confirmed that neuron-specific GHR ablation robustly reduces hypothalamic Ghr mRNA levels and prevents GH-induced pSTAT5 in the arcuate, paraventricular and ventromedial hypothalamic nuclei. Subsequently, the number of pSTAT5 immunoreactive cells was determined in the hypothalamus of late pregnant mice. Although neuron-specific GHR ablation did not affect the number of pSTAT5 immunoreactive cells in the paraventricular nucleus of the hypothalamus, reduced pSTAT5 expression was observed in the arcuate and ventromedial nuclei of pregnant neuron-specific GHR knockouts, compared to control pregnant mice. In summary, a subset of hypothalamic neurons requires GHR signaling to express pSTAT5 during pregnancy. These findings contribute to the understanding of the endocrine factors that affect the activation of transcription factors in the brain during pregnancy.

The Prolactin Family of Hormones as Regulators of Maternal Mood and Behavior

Transition into motherhood involves profound physiological and behavioral adaptations that ensure the healthy development of offspring while maintaining maternal health. Dynamic fluctuations in key hormones during pregnancy and lactation induce these maternal adaptations by acting on neural circuits in the brain. Amongst these hormonal changes, lactogenic hormones (e.g., prolactin and its pregnancy-specific homolog, placental lactogen) are important regulators of these processes, and their receptors are located in key brain regions controlling emotional behaviors and maternal responses. With pregnancy and lactation also being associated with a marked elevation in the risk of developing mood disorders, it is important to understand how hormones are normally regulating mood and behavior during this time. It seems likely that pathological changes in mood could result from aberrant expression of these hormone-induced behavioral responses. Maternal mental health problems during pregnancy and the postpartum period represent a major barrier in developing healthy mother-infant interactions which are crucial for the child's development. In this review, we will examine the role lactogenic hormones play in driving a range of specific maternal behaviors, including motivation, protectiveness, and mother-pup interactions. Understanding how these hormones collectively act in a mother's brain to promote nurturing behaviors toward offspring will ultimately assist in treatment development and contribute to safeguarding a successful pregnancy.

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.

Tumor Necrosis Factor α and Interleukin-1β Acutely Inhibit AgRP Neurons in the Arcuate Nucleus of the Hypothalamus

Obesity-associated low-grade inflammation favors weight gain, whereas systemic infection frequently leads to anorexia. Thus, inflammatory signals can either induce positive or negative energy balance. In this study, we used whole-cell patch-clamp to investigate the acute effects of three important proinflammatory cytokines, tumor necrosis factor α (TNF-α), interleukin-6, and interleukin-1β (IL-1β) on the membrane excitability of agouti-related peptide (AgRP)- or proopiomelanocortin (POMC)-producing neurons. We found that both TNF-α and IL-1β acutely inhibited the activity of 35-42% of AgRP-producing neurons, whereas very few POMC neurons were depolarized by TNF-α. Interleukin-6 induced no acute changes in the activity of AgRP or POMC neurons. Our findings indicate that the effect of TNF-α and IL-1β, especially on the activity of AgRP-producing neurons, may contribute to inflammation-induced anorexia observed during acute inflammatory conditions.

Acute effects of prolactin on hypothalamic prolactin receptor expressing neurones in the mouse

In addition to its critical role in lactation, the anterior pituitary hormone prolactin also influences a broad range of other physiological processes. In particular, widespread expression of prolactin receptor (Prlr) in the brain has highlighted pleiotropic roles for prolactin in regulating neuronal function, including maternal behaviour, reproduction and energy balance. Research into the central actions of prolactin has predominately focused on effects on gene transcription via the canonical JAK2/STAT5; however, it is evident that prolactin can exert rapid actions to stimulate activity in specific populations of neurones. We aimed to investigate how widespread these rapid actions of prolactin are in regions of the brain with large populations of prolactin-sensitive neurones, and whether physiological state alters these responses. Using transgenic mice where the Cre-dependent calcium indicator, GCaMP6f, was conditionally expressed in cells expressing the long form of the Prlr, we monitored changes in levels of intracellular calcium ([Ca²⁺ ]_i ) in ex vivo brain slice preparations as a surrogate marker of cellular activity. Here, we surveyed hypothalamic regions implicated in the diverse physiological functions of prolactin such as the arcuate (ARC) and paraventricular nuclei of the hypothalamus (PVN), as well as the medial preoptic area (MPOA). We observed that, in the ARC of males and in both virgin and lactating females, prolactin can exert rapid actions to stimulate neuronal activity in the majority of Prlr-expressing neurones. In the PVN and MPOA, we found a smaller subset of cells that rapidly respond to prolactin. In these brain regions, the effects we detected ranged from rapid or sustained increases in [Ca²⁺ ]_i to inhibitory effects, indicating a heterogeneous nature of these Prlr-expressing populations. These results enhance our understanding of mechanisms by which prolactin acts on hypothalamic neurones and provide insights into how prolactin might influence neuronal circuits in the mouse brain.

Regulation and neurochemical identity of melanin-concentrating hormone neurones in the preoptic area of lactating mice

Neurones expressing the melanin-concentrating hormone (MCH) can be found in the medial preoptic area (mPOA) and ventral aspects of the periventricular preoptic nucleus of rats by mid-to-late lactation and this expression disappears after weaning. The transitory expression of MCH in the preoptic area suggests a role for these neurones in the control of the end of lactation. However, the neurochemical identity of mPOA MCH neurones and the regulatory factors that control the transient MCH expression remain largely unknown, especially in the mouse. In the present study, we showed that mice also present the transitory expression of MCH in the mPOA at late lactation. mPOA MCH cells did not colocalise significantly with markers of GABAergic (VGAT), glutamatergic (VGLUT2 and VGLUT3) or dopaminergic (tyrosine hydroxylase) neurones. mPOA MCH cells also did not express Kiss1 or oxytocin. By contrast, approximately 70% and 90% of mPOA MCH neurones colocalised with oestrogen receptor α and prolactin-induced phosphorylated signal transducer and activator of transcription 5 (STAT5), respectively. Finally, we demonstrated that the number of MCH neurones in the mPOA is significantly higher in females during the first lactation, compared to mice on the second lactation or pregnant mice during the first lactation or brain-specific STAT5 knockout mice during the first lactation. In summary, our findings indicate that MCH neurones in the mPOA of lactating mice are sensitive to oestrogens and prolactin. Thus, mPOA MCH expression is possibly influenced by hormonal variations. Furthermore, the STAT5 signalling pathway is likely involved in the regulation of MCH expression in the mPOA of lactating mice.

The role of prolactin in co-ordinating fertility and metabolic adaptations during reproduction

Mammalian pregnancy and lactation is accompanied by a period of infertility that takes place in the midst of a sustained increase in food intake. Indeed, successful reproduction in females is dependent on co-ordination of the distinct systems that regulate reproduction and metabolism. Rather than arising from different mechanisms during pregnancy and lactation, we propose that elevations in lactogenic hormones (predominant among these being prolactin and the placental lactogens), are ideally placed to influence both of these systems at the appropriate time. We review the literature examining the impacts of lactogens on fertility and energy homeostasis in the virgin state, during pregnancy and lactation and potential long-term impacts of reproductive experience. Taken together, the literature indicates that duration and pattern of lactogen exposure is a vital factor in the ability of these hormones to alter reproduction and food intake. Transient increases in prolactin, as typically seen in healthy virgin females and males, are unable to exert lasting impacts. Importantly, both suppression of fertility and increased food intake are only observed following exposure to chronically-elevated levels of lactogens. Physiologically, the only time this pattern of lactogenic secretion is maintained in the healthy female is during pregnancy and lactation, when co-ordination between these regulatory systems emerges. This article is part of the special issue on 'Neuropeptides'.

Brain STAT5 Modulates Long-Term Metabolic and Epigenetic Changes Induced by Pregnancy and Lactation in Female Mice

Several metabolic and behavioral adaptations that emerge during pregnancy remain present after weaning. Thus, reproductive experience causes long-lasting metabolic programming, particularly in the brain. However, the isolate effects of pregnancy or lactation and the molecular mechanisms involved in these long-term modifications are currently unknown. In the current study, we investigated the role of brain signal transducer and activator of transcription-5 (STAT5), a key transcription factor recruited by hormones highly secreted during gestation or lactation, for the long-term adaptations induced by reproductive experience. In control mice, pregnancy followed by lactation led to increased body adiposity and reduced ambulatory activity later in life. Additionally, pregnancy+lactation induced long-term epigenetic modifications in the brain: we observed upregulation in hypothalamic expression of histone deacetylases and reduced numbers of neurons with histone H3 acetylation in the paraventricular, arcuate, and ventromedial nuclei. Remarkably, brain-specific STAT5 ablation prevented all metabolic and epigenetic changes observed in reproductively experienced control female mice. Nonetheless, brain-specific STAT5 knockout (KO) mice that had the experience of pregnancy but did not lactate showed increased body weight and reduced energy expenditure later in life, whereas pregnancy KO and pregnancy+lactation KO mice exhibited improved insulin sensitivity compared with virgin KO mice. In summary, lactation is necessary for the long-lasting metabolic effects observed in reproductively experienced female mice. In addition, epigenetic mechanisms involving histone acetylation in neuronal populations related to energy balance regulation are possibly associated with these long-term consequences. Finally, our findings highlighted the key role played by brain STAT5 signaling for the chronic metabolic and epigenetic changes induced by pregnancy and lactation.

Growth hormone/STAT5 signaling in proopiomelanocortin neurons regulates glucoprivic hyperphagia

Several hypothalamic neuronal populations are directly responsive to growth hormone (GH) and central GH action regulates glucose and energy homeostasis. However, the potential role of GH signaling in proopiomelanocortin (POMC) neurons has not been studied yet. Thus, we investigated whether POMC neurons are responsive to GH and if ablation of GH receptor (GHR) or STAT5 in POMC cells leads to metabolic imbalances. Approximately 60% of POMC neurons of the arcuate nucleus exhibited STAT5 phosphorylation after intracerebroventricular GH injection. Ablation of GHR or STAT5 in POMC cells did not affect energy or glucose homeostasis. However, glucoprivic hyperphagia was blunted in male and female GHR knockout mice, and in male POMC-specific STAT5 knockout mice. Additionally, the absence of GHR in POMC neurons decreased glycemia during prolonged food restriction in male mice. Thus, GH action in POMC neurons regulates glucoprivic hyperphagia as well as blood glucose levels during prolonged food restriction.

Removing melatonin receptor type 1 signaling leads to selective leptin resistance in the arcuate nucleus

Recent studies have highlighted the involvement of melatonin in the regulation of energy homeostasis. In this study, we report that mice lacking melatonin receptor 1 (MT1 KO) gained more weight, had a higher cumulative food intake, and were more hyperphagic after fasting compared to controls (WT). In response to a leptin injection, MT1 KO mice showed a diminished reduction in body weight and food intake. To evaluate hypothalamic leptin signaling, we tested leptin-induced phosphorylation of the signal transducer and activator of transcription 3 (STAT3). Leptin failed to induce STAT3 phosphorylation in MT1 KO mice beyond levels observed in mice injected with phosphate-buffered saline (PBS). Furthermore, STAT3 phosphorylation within the arcuate nucleus (ARH) was decreased in MT1 KO mice. Leptin receptor mRNA levels in the hypothalamus of MT1 KO were significantly reduced (about 50%) compared to WT. This study shows that: (a) MT1 deficiency causes weight gain and increased food intake; (b) a lack of MT1 signaling induces leptin resistance; (c) leptin resistance is ARH region-specific; and (d) leptin resistance is likely due to down-regulation of the leptin receptor. Our data demonstrate that MT1 signaling is an important modulator of leptin signaling.

Growth hormone enhances the recovery of hypoglycemia via ventromedial hypothalamic neurons

Growth hormone (GH) is secreted during hypoglycemia, and GH-responsive neurons are found in brain areas containing glucose-sensing neurons that regulate the counter-regulatory response (CRR). However, whether GH modulates the CRR to hypoglycemia via specific neuronal populations is currently unknown. Mice carrying ablation of GH receptor (GHR) either in leptin receptor (LepR)- or steroidogenic factor-1 (SF1)-expressing cells were studied. We also investigated the importance of signal transducer and activator of transcription 5 (STAT5) signaling in SF1 cells for the CRR. GHR ablation in LepR cells led to impaired capacity to recover from insulin-induced hypoglycemia and to a blunted CRR caused by 2-deoxy-d-glucose (2DG) administration. GHR inactivation in SF1 cells, which include ventromedial hypothalamic neurons, also attenuated the CRR. The reduced CRR was prevented by parasympathetic blockers. Additionally, infusion of 2DG produced an abnormal hyperactivity of parasympathetic preganglionic neurons, whereas the 2DG-induced activation of anterior bed nucleus of the stria terminalis neurons was reduced in mice without GHR in SF1 cells. Mice carrying ablation of Stat5a/b genes in SF1 cells showed no defects in the CRR. In summary, GHR expression in SF1 cells is required for a normal CRR, and these effects are largely independent of STAT5 pathway.-Furigo, I. C., de Souza, G. O., Teixeira, P. D. S., Guadagnini, D., Frazão, R., List, E. O., Kopchick, J. J., Prada, P. O., Donato, J., Jr. Growth hormone enhances the recovery of hypoglycemia via ventromedial hypothalamic neurons.

Acute effects of somatomammotropin hormones on neuronal components of the hypothalamic-pituitary-gonadal axis

Growth hormone (GH) and prolactin (PRL) are known as pleiotropic hormones. Accordingly, the distribution of their receptors comprises several organs and tissues, including the central nervous system. The appropriate secretion of both hormones is essential for sexual maturation and maintenance of reproductive functions, while defects in their secretion affect puberty onset and can cause infertility. Conversely, GH therapy at a prepubertal age may accelerate puberty. On the other hand, hyperprolactinemia is a frequent cause of infertility. While the action of PRL in some central components of the Hypothalamic-Pituitary-Gonadal (HPG) axis, such as the kisspeptin neurons, has been well documented, the possible effects of GH in the hypothalamus are still elusive. Thus, the present study was designed to investigate whether somatomammotropin hormones are able to modulate the activity of critical neuronal components of the HPG axis, including kisspeptin neurons and cells of the ventral premammillary nucleus (PMv). Our results revealed that GH effects in kisspeptin neurons of the anteroventral periventricular and rostral periventricular nuclei or in PMv neurons relies predominantly on the recruitment of the signal transducer and activator of transcription 5 (STAT5) rather than through acute changes in resting membrane potential. Importantly, kisspeptin neurons located at the arcuate nucleus were not directly responsive to GH. Additionally, our findings further identified PMv neurons as potential targets of PRL, since PRL induces the phosphorylation of STAT5 and depolarizes PMv neurons. Combined, our data provide evidence that GH and PRL may affect the HPG axis via specific hypothalamic neurons.

Maternal metabolic adaptations are necessary for normal offspring growth and brain development

Several metabolic adaptations emerge during pregnancy and continue through lactation, including increases in food intake and body weight, as well as insulin and leptin resistance. These maternal adaptations are thought to play a role in offspring viability and success. Using a model of attenuated maternal metabolic adaptations induced by ablation of the Socs3 gene in leptin receptor expressing cells (SOCS3 KO mice), our study aimed to investigate whether maternal metabolic changes are required for normal offspring development, and if their absence causes metabolic imbalances in adulthood. The litters were subjected to a cross‐fostering experimental design to distinguish the prenatal and postnatal effects caused by maternal metabolic adaptations. Males either born or raised by SOCS3 KO mice showed reduced body weight until 8 weeks of life. Both adult males and females born or raised by SOCS3 KO mice also had lower body adiposity. Despite that, no significant changes in energy expenditure, glucose tolerance or insulin resistance were observed. However, males either born or raised by SOCS3 KO mice showed reduced brain mass in adulthood. Furthermore, animals born from SOCS3 KO mice also had lower proopiomelanocortin fiber density in the paraventricular nucleus of the hypothalamus. In conclusion, these findings indicate that the commonly observed metabolic changes in pregnancy and lactation are necessary for normal offspring growth and brain development.

Brain STAT5 signaling modulates learning and memory formation

The signal transducer and activator of transcription 5 (STAT5) is a transcription factor recruited by numerous cytokines. STAT5 is important for several physiological functions, including body and tissue growth, mammary gland development, immune system and lipid metabolism. However, the role of STAT5 signaling for brain functions is still poorly investigated, especially regarding cognitive aspects. Therefore, the objective of the present study was to investigate whether brain STAT5 signaling modulates learning and memory formation. For this purpose, brain-specific STAT5 knockout (STAT5 KO) mice were studied in well-established memory tests. Initially, we confirmed a robust reduction in STAT5a and STAT5b mRNA levels in different brain structures of STAT5 KO mice. STAT5 KO mice showed no significant alterations in metabolism, growth, somatotropic axis and spontaneous locomotor activity. In contrast, brain-specific STAT5 ablation impaired learning and memory formation in the novel object recognition, Barnes maze and contextual fear conditioning tests. To unravel possible mechanisms that might underlie the memory deficits of STAT5 KO mice, we assessed neurogenesis in the hippocampus, but no significant differences were observed between groups. On the other hand, reduced insulin-like growth factor-1 (IGF-1) mRNA expression was found in the hippocampus and hypothalamus of STAT5 KO mice. These findings collectively indicate that brain STAT5 signaling is required to attain normal learning and memory. Therefore, STAT5 is an important downstream cellular mechanism shared by several cytokines to regulate cognitive functions.

STAT5 signaling in kisspeptin cells regulates the timing of puberty

Previous studies have shown that kisspeptin neurons are important mediators of prolactin's effects on reproduction. However, the cellular mechanisms recruited by prolactin to affect kisspeptin neurons remain unknown. Using whole-cell patch-clamp recordings of brain slices from kisspeptin reporter mice, we observed that 20% of kisspeptin neurons in the anteroventral periventricular nucleus was indirectly depolarized by prolactin via an unknown population of prolactin responsive neurons. This effect required the phosphatidylinositol 3-kinase signaling pathway. No effects on the activity of arcuate kisspeptin neurons were observed, despite a high percentage (70%) of arcuate neurons expressing prolactin-induced STAT5 phosphorylation. To determine whether STAT5 expression in kisspeptin cells regulates reproduction, mice carrying Stat5a/b inactivation specifically in kisspeptin cells were generated. These mutants exhibited an early onset of estrous cyclicity, indicating that STAT5 transcription factors exert an inhibitory effect on the timing of puberty.

Transcriptional regulatory dynamics drive coordinated metabolic and neural response to social challenge in mice

Agonistic encounters are powerful effectors of future behavior, and the ability to learn from this type of social challenge is an essential adaptive trait. We recently identified a conserved transcriptional program defining the response to social challenge across animal species, highly enriched in transcription factor (TF), energy metabolism, and developmental signaling genes. To understand the trajectory of this program and to uncover the most important regulatory influences controlling this response, we integrated gene expression data with the chromatin landscape in the hypothalamus, frontal cortex, and amygdala of socially challenged mice over time. The expression data revealed a complex spatiotemporal patterning of events starting with neural signaling molecules in the frontal cortex and ending in the modulation of developmental factors in the amygdala and hypothalamus, underpinned by a systems-wide shift in expression of energy metabolism-related genes. The transcriptional signals were correlated with significant shifts in chromatin accessibility and a network of challenge-associated TFs. Among these, the conserved metabolic and developmental regulator ESRRA was highlighted for an especially early and important regulatory role. Cell-type deconvolution analysis attributed the differential metabolic and developmental signals in this social context primarily to oligodendrocytes and neurons, respectively, and we show that ESRRA is expressed in both cell types. Localizing ESRRA binding sites in cortical chromatin, we show that this nuclear receptor binds both differentially expressed energy-related and neurodevelopmental TF genes. These data link metabolic and neurodevelopmental signaling to social challenge, and identify key regulatory drivers of this process with unprecedented tissue and temporal resolution.

Brain STAT5 signaling and behavioral control

Several growth factors and cytokines recruit the signal transducer and activator of transcription 5 (STAT5) signaling pathway to control cell proliferation, differentiation and apoptosis. Nonetheless, the importance of this transcription factor for brain functions is still poorly understood. Because some STAT5-inducing hormones, such as prolactin and leptin, act in the brain to regulate the expression of motivated behaviors, this signaling pathway is likely involved in behavioral modulation. Therefore, the objective of the present review was to summarize and discuss the available data regarding the possible role of central STAT5 signaling in the regulation of brain functions, especially on behavioral control. We discussed studies that investigated the importance of STAT5 signaling in the regulation of maternal and feeding behaviors. Additionally, we highlighted other behaviors that could be potentially affected by STAT5 signaling. This knowledge may help to understand how motivated behaviors are regulated at the cellular level.

Interactions between prolactin and kisspeptin to control reproduction

Prolactin is best known for its effects of stimulating mammary gland development and lactogenesis. However, prolactin is a pleiotropic hormone that is able to affect several physiological functions, including fertility. Prolactin receptors (PRLRs) are widely expressed in several tissues, including several brain regions and reproductive tract organs. Upon activation, PRLRs may exert prolactin's functions through several signaling pathways, although the recruitment of the signal transducer and activator of transcription 5 causes most of the known effects of prolactin. Pathological hyperprolactinemia is mainly due to the presence of a prolactinoma or pharmacological effects induced by drugs that interact with the dopamine system. Notably, hyperprolactinemia is a frequent cause of reproductive dysfunction and may lead to infertility in males and females. Recently, several studies have indicated that prolactin may modulate the reproductive axis by acting on specific populations of hypothalamic neurons that express the Kiss1 gene. The Kiss1 gene encodes neuropeptides known as kisspeptins, which are powerful activators of gonadotropin-releasing hormone neurons. In the present review, we will summarize the current knowledge about prolactin's actions on reproduction. Among other aspects, we will discuss whether the interaction between prolactin and the Kiss1-expressing neurons can affect reproduction and how kisspeptins may become a novel therapeutic approach to treat prolactin-induced infertility.

Changes in Leptin Signaling by SOCS3 Modulate Fasting-Induced Hyperphagia and Weight Regain in Mice

Weight regain frequently follows interventions that reduce body weight, leading to a failure in long-term obesity treatment. Inhibitory proteins of the leptin signaling pathway, such as the suppressor of cytokine signaling 3 (SOCS3), have been studied in conditions that predispose animals to obesity. However, whether SOCS3 modulates postrestriction hyperphagia and weight regain remains unknown. Mice lacking SOCS3 protein specifically in leptin receptor (LepR)-expressing cells (LepR SOCS3 knockout [KO]) were generated and studied in fasting and refeeding conditions. LepR SOCS3 KO mice exhibited increased leptin sensitivity in the hypothalamus. Notably, LepR SOCS3 KO males and females showed attenuated food intake and weight regain after 48 hours of fasting. Postrestriction hyperleptinemia was also prevented in LepR SOCS3 KO mice. Next, we studied possible mechanisms and neural circuits involved in the SOCS3 effects. SOCS3 deletion did not prevent fasting- or refeeding-induced c-Fos expression in the arcuate nucleus of the hypothalamus (ARH) nor fasting-induced increased excitability of ARH LepR-expressing cells. On the other hand, SOCS3 ablation reduced the mRNA levels of hypothalamic orexigenic neuropeptides during fasting (neuropeptide Y, agouti-related protein, orexin, and melanin-concentrating hormone). In summary, our findings suggest that increased leptin sensitivity contributes to the maintenance of a reduced body weight after food deprivation. In addition, the attenuated postrestriction food intake observed in mutant mice was not explained by fasting-induced changes in the activity of ARH neurons but exclusively by a lower transcription of orexigenic neuropeptides during fasting. These results indicate a partial dissociation between the regulation of neuronal activity and gene expression in ARH LepR-expressing cells.

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.

Obesity impairs lactation performance in mice by inducing prolactin resistance

Obesity reduces breastfeeding success and lactation performance in women. However, the mechanisms involved are not entirely understood. In the present study, female C57BL/6 mice were chronically exposed to a high-fat diet to induce obesity and subsequently exhibited impaired offspring viability (only 15% survival rate), milk production (33% reduction), mammopoiesis (one-third of the glandular area compared to control animals) and postpartum maternal behaviors (higher latency to retrieving and grouping the pups). Reproductive experience attenuated these defects. Diet-induced obese mice exhibited high basal pSTAT5 levels in the mammary tissue and hypothalamus, and an acute prolactin stimulus was unable to further increase pSTAT5 levels above basal levels. In contrast, genetically obese leptin-deficient females showed normal prolactin responsiveness. Additionally, we identified the expression of leptin receptors specifically in basal/myoepithelial cells of the mouse mammary gland. Finally, high-fat diet females exhibited altered mRNA levels of ERBB4 and NRG1, suggesting that obesity may involve disturbances to mammary gland paracrine circuits that are critical in the control of luminal progenitor function and lactation. In summary, our findings indicate that high leptin levels are a possible cause of the peripheral and central prolactin resistance observed in obese mice which leads to impaired lactation performance.

Short-term hyperprolactinemia decreases allergic inflammatory response of the lungs

AIMS

Prolactin is a major immunomodulator. The present study evaluated the effects of short-term hyperprolactinemia induced by domperidone before ovalbumin antigenic challenge on the lung's allergic inflammatory response.

MAIN METHODS

To induce hyperprolactinemia, domperidone was injected in rats at a dose of 5.1mg·kg(-1) per day, i.p., for 5days from 10th to 14th day after OVA immunization. Total and differential leukocyte counts from bronchoalveolar lavage (BAL), femoral marrow lavage (FML), and blood were analyzed. The percentages of mucus and collagen production were evaluated. Levels of corticosterone and prolactin in serum, interleukin-4 (IL-4), IL-6, IL-10, tumor necrosis factor α (TNF-α) in lung explants supernatants were measured and interferon gamma (IFN-γ) in bronchiolar lavage cells suspensions (BAL) was measured.

KEY FINDINGS

The rats that were subjected to short-term hyperprolactinemia exhibited a decrease in leukocyte counts in bronchoalveolar lavage, cellularity decrease in femoral marrow lavage fluid, a lower percentage of mucus, and an increase in lung IL-4, IL-6, IL-10, TNF-α and IFN-γ expression.

SIGNIFICANCE

Hyperprolactinemia induced before antigenic challenge decreased allergic lung inflammation. These data suggest that prolactin may play a role in the pathophysiology of asthma. The present study demonstrates a prospective beneficial side effect of domperidone for asthmatic patients.