Possible crosstalk between leptin and prolactin during pregnancy

Bioactive peptides in preterm human milk: Impact of maternal characteristics and their association to neonatal outcomes

Human milk adipokines in term babies seem partially determined by maternal factors and affect infant's development. We aimed to describe bioactive peptide concentration in very preterm human milk and associations to maternal characteristics and postnatal growth. Mothers delivering ≤32 weeks of gestation and their infant/s were recruited. At 4 weeks of lactation, an aliquot of 24-h-pooled milk was collected for exclusively breastfeeding dyads. Insulin, leptin, adiponectin, and milk fat globule epidermal growth factor-8 (MFG-E8) were measured by enzyme-linked immunoabsorbent assay in skimmed milk. One hundred mothers (28.8 ± 2.3 weeks at delivery) provided a milk sample. Milk insulin was related to gestational age, pre-pregnancy body mass index (BMI), and galactagogue treatment (final model: adjusted R2 : 0.330, p < 0.0001; adjusted β coefficients: galactagogue treatment: 0.348, p 0.001; pre-pregnancy BMI: 0.274, p 0.009; gestational age: -0.290, p 0.007). Adiponectin was higher in mothers with gestational diabetes (30.7 ± 6.5 vs. 24.8 ± 8 ng/mL, p 0.044). Leptin was associated with pre-pregnancy BMI (Spearman's ρ: 0.648, p < 0.0001) and MFG-E8 to presence of labor and multiple pregnancy (final linear regression model, R2 : 0.073, p 0.028, adjusted β coefficients: presence of labor -0.229, p 0.050; twins: -0.192, p 0.099). Milk adiponectin was associated with a greater decrease in length z-scores from birth to 28 days (Pearson's r: -0.225, p 0.032) and to discharge (Pearson's r: -0.290, p 0.003). Milk MFG-E8 was lower in milk of mothers whose babies experienced late-onset sepsis (13.3 ± 5.8 vs. 16.8 ± 6.3 μg/mL, p 0.023). Adipokines levels in preterm human milk are partially related to maternal metabolic status. Milk peptide concentration associates with early neonatal growth trajectories.

High fat diet-induced maternal obesity in mice impairs peripartum maternal behaviour

Obesity during pregnancy represents a significant health issue and can lead to increased complications during pregnancy and impairments with breastfeeding, along with long-term negative health consequences for both mother and offspring. In rodent models, diet-induced obesity (DIO) during pregnancy leads to poor outcomes for offspring. Using a DIO mouse model, consisting of feeding mice a high fat diet for 8 weeks before mating, we recapitulate the effect of high pup mortality within the first 3 days postpartum. To examine the activity of the dam around the time of birth, late pregnant control and DIO dams were recorded in their home cages and the behaviour of the dam immediately before and after birth was analysed. Prior to giving birth, DIO dams spent less time engaging in nesting behaviour, while after birth, DIO dams spent less time in the nest with their pups compared to control dams, indicating reduced pup-engagement in the early postpartum period. We have previously reported that lactogenic hormone action, mediated by the prolactin receptor, in the medial preoptic area of the hypothalamus (MPOA) is critical for the onset of normal postpartum maternal behaviour. We hypothesized that DIO dams may have lower lactogenic hormone activity during late pregnancy, which would contribute to impaired onset of normal postpartum maternal behaviour. Day 16 lactogenic activity, transport of prolactin into the brain, and plasma prolactin concentrations around birth were all similar in control and DIO dams. Moreover, endogenous pSTAT5, a marker of prolactin receptor activity, in the MPOA was unaffected by DIO. Overall, these data indicate that lactogenic activity in late pregnancy of DIO dams is not different to controls and is unlikely to play a major role in impaired onset of normal postpartum maternal behaviour.

Metabolic and feeding adjustments during pregnancy

Eating behaviours are determined by the integration of interoceptive and environmental inputs. During pregnancy, numerous physiological adaptations take place in the maternal organism to provide an adequate environment for embryonic growth. Among them, whole-body physiological remodelling directly influences eating patterns, commonly causing notable taste perception alterations, food aversions and cravings. Recurrent food cravings for and compulsive eating of highly palatable food can contribute to the development and maintenance of gestational overweight and obesity with potential adverse health consequences for the offspring. Although much is known about how maternal eating habits influence offspring health, the mechanisms that underlie changes in taste perception and food preference during pregnancy (which guide and promote feeding) are only just starting to be elucidated. Given the limited and diffuse understanding of the neurobiology of gestational eating patterns, the aim of this Review is to compile, integrate and discuss the research conducted on this topic in both experimental models and humans. This article sheds light on the mechanisms that drive changes in female feeding behaviours during distinct physiological states. Understanding these processes is crucial to improve gestational parent health and decrease the burden of metabolic and food-related diseases in future generations.

Central growth hormone action regulates neuroglial and proinflammatory markers in the hypothalamus of male mice

Growth hormone (GH) action in specific neuronal populations regulates neuroendocrine responses, metabolism, and behavior. However, the potential role of central GH action on glial function is less understood. The present study aims to determine how the hypothalamic expression of several neuroglial markers is affected by central GH action in male mice. The dwarf GH- and insulin-like growth factor-1 (IGF-1)-deficient Ghrhr^lit/lit mice showed decreased mRNA expression of Nes (Nestin), Gfap, Iba1, Adgre1 (F4/80), and Tnf (TNFα) in the hypothalamus, compared to wild-type animals. In contrast, transgenic overexpression of GH led to high serum GH and IGF-1 levels, and increased hypothalamic expression of Nes, Gfap, Adgre1, Iba1, and Rax. Hepatocyte-specific GH receptor (GHR) knockout mice, which are characterized by high serum GH levels, but reduced IGF-1 secretion, showed increased mRNA expression of Gfap, Iba1, Tnf, and Sox10, demonstrating that the increase in GH levels alters the hypothalamic expression of glial markers associated with neuroinflammation, independently of IGF-1. Conversely, brain-specific GHR knockout mice showed reduced expression of Gfap, Adgre1, and Vim (vimentin), indicating that brain GHR signaling is necessary to mediate GH-induced changes in the expression of several neuroglial markers. In conclusion, the hypothalamic mRNA levels of several neuroglial markers associated with inflammation are directly modulated by GHR signaling in male mice.

Dopamine receptor agonists mechanism of actions on glucose lowering and their connections with prolactin actions

Robust experiment evidence suggests that prolactin can enhance beta-cell proliferation and increase insulin secretion and sensitivity. Apart from acting as an endocrine hormone, it also function as an adipokine and act on adipocytes to modulate adipogenesis, lipid metabolism and inflammation. Several cross-sectional epidemiologic studies consistently showed that circulating prolactin levels positive correlated with increased insulin sensitivity, lower glucose and lipid levels, and lower prevalence of T2D and metabolic syndrome. Bromocriptine, a dopamine receptor agonist used to treat prolactinoma, is approved by Food and Drug Administration for treatment in type 2 diabetes mellitus since 2009. Prolactin lowering suppress insulin secretion and decrease insulin sensitivity, therefore dopamine receptor agonists which act at the pituitary to lower serum prolactin levels are expected to impair glucose tolerance. Making it more complicating, studies exploring the glucose-lowering mechanism of bromocriptine and cabergoline have resulted in contradictory results; while some demonstrated actions independently on prolactin status, others showed glucose lowering partly explained by prolactin level. Previous studies showed that a moderate increase in central intraventricular prolactin levels stimulates hypothalamic dopamine with a decreased serum prolactin level and improved glucose metabolism. Additionally, sharp wave-ripples from the hippocampus modulates peripheral glucose level within 10 minutes, providing evidence for a mechanistic link between hypothalamus and blood glucose control. Central insulin in the mesolimbic system have been shown to suppress dopamine levels thus comprising a feedback control loop. Central dopamine and prolactin levels plays a key role in the glucose homeostasis control, and their dysregulation could lead to the pathognomonic central insulin resistance depicted in the “ominous octet”. This review aims to provide an in-depth discussion on the glucose-lowering mechanism of dopamine receptor agonists and on the diverse prolactin and dopamine actions on metabolism targets.

SOCS3 Ablation in Leptin Receptor-Expressing Cells Causes Autonomic and Cardiac Dysfunctions in Middle-Aged Mice despite Improving Energy and Glucose Metabolism

Leptin resistance is a hallmark of obesity. Treatments aiming to improve leptin sensitivity are considered a promising therapeutical approach against obesity. However, leptin receptor (LepR) signaling also modulates several neurovegetative aspects, such as the cardiovascular system and hepatic gluconeogenesis. Thus, we investigated the long-term consequences of increased leptin sensitivity, considering the potential beneficial and deleterious effects. To generate a mouse model with increased leptin sensitivity, the suppressor of cytokine signaling 3 (SOCS3) was ablated in LepR-expressing cells (LepR^∆SOCS3 mice). LepR^∆SOCS3 mice displayed reduced food intake, body adiposity and weight gain, as well as improved glucose tolerance and insulin sensitivity, and were protected against aging-induced leptin resistance. Surprisingly, a very high mortality rate was observed in aging LepR^∆SOCS3 mice. LepR^∆SOCS3 mice showed cardiomyocyte hypertrophy, increased myocardial fibrosis and reduced cardiovascular capacity. LepR^∆SOCS3 mice exhibited impaired post-ischemic cardiac functional recovery and middle-aged LepR^∆SOCS3 mice showed substantial arhythmic events during the post-ischemic reperfusion period. Finally, LepR^∆SOCS3 mice exhibited fasting-induced hypoglycemia and impaired counterregulatory response to glucopenia associated with reduced gluconeogenesis. In conclusion, although increased sensitivity to leptin improved the energy and glucose homeostasis of aging LepR^∆SOCS3 mice, major autonomic/neurovegetative dysfunctions compromised the health and longevity of these animals. Consequently, these potentially negative aspects need to be considered in the therapies that increase leptin sensitivity chronically.

Characterization of the metabolic differences between male and female C57BL/6 mice

AIMS

The present study aims to compare the responses between male and female C57BL/6 mice to multiple metabolic challenges to understand the importance of sex in the control of energy homeostasis.

MAIN METHODS

Male and female C57BL/6 mice were subjected to nutritional and hormonal challenges, such as food restriction and refeeding, diet-induced obesity, feeding response to ghrelin and leptin, ghrelin-induced growth hormone secretion, and central responsiveness to ghrelin and leptin. The hypothalamic expression of transcripts that control energy homeostasis was also evaluated.

KEY FINDINGS

Male mice lost more weight and lean body mass in response to food restriction, compared to females. During refeeding, males accumulated more body fat and exhibited lower energy expenditure and glycemia, as compared to females. Additionally, female mice exhibited a higher protection against diet-induced obesity and related metabolic imbalances in comparison to males. Low dose ghrelin injection elicited higher food intake and growth hormone secretion in male mice, whereas the acute anorexigenic effect of leptin was more robust in females. However, the sex differences in the feeding responses to ghrelin and leptin were not explained by variations in the central responsiveness to these hormones nor by differences in the fiber density from arcuate nucleus neurons. Female, but not male, mice exhibited compensatory increases in hypothalamic Pomc mRNA levels in response to diet-induced obesity.

SIGNIFICANCE

Our findings revealed several sexually differentiated responses to metabolic challenges in C57BL/6 mice, highlighting the importance of taking into account sex differences in metabolic studies.

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.

Leptin Receptor Expression in GABAergic Cells is Not Sufficient to Normalize Metabolism and Reproduction in Mice

Previous studies indicate that leptin receptor (LepR) expression in GABAergic neurons is necessary for the biological effects of leptin. However, it is not clear whether LepR expression only in GABAergic neurons is sufficient to prevent the metabolic and neuroendocrine imbalances caused by LepR deficiency. In the present study, we produced mice that express the LepR exclusively in GABAergic cells (LepRVGAT mice) and compared them with wild-type (LepR+/+) and LepR-deficient (LepRNull/Null) mice. Although LepRVGAT mice showed a pronounced reduction in body weight and fat mass, as compared with LepRNull/Null mice, male and female LepRVGAT mice exhibited an obese phenotype relative to LepR+/+ mice. Food intake was normalized in LepRVGAT mice; however, LepRVGAT mice still exhibited lower energy expenditure in both sexes and reduced ambulatory activity in the females, compared with LepR+/+ mice. The acute anorexigenic effect of leptin and hedonic feeding were normalized in LepRVGAT mice despite the hyperleptinemia they present. Although LepRVGAT mice showed improved glucose homeostasis compared with LepRNull/Null mice, both male and female LepRVGAT mice exhibited insulin resistance. In contrast, LepR expression only in GABAergic cells was sufficient to normalize the density of agouti-related peptide (AgRP) and α-MSH immunoreactive fibers in the paraventricular nucleus of the hypothalamus. However, LepRVGAT mice exhibited reproductive dysfunctions, including subfertility in males and alterations in the estrous cycle of females. Taken together, our findings indicate that LepR expression in GABAergic cells, although critical to the physiology of leptin, is insufficient to normalize several metabolic aspects and the reproductive function in mice.

Circadian rhythm in hypothalamic leptin receptor (Ob-Rb) mRNA expressions and cerebrospinal fluid and circulating glucose and leptin levels in lactating rats

In lactating animals, the food consumption increases several-fold for milk supply to the pups. The present study was conducted to clarify the relationship between the hyperphagia during lactation and hypothalamic leptin receptor (Ob-Rb) mRNA expression, cerebrospinal fluid (CSF) and circulating leptin and glucose levels. Food intakes significantly higher in lactation than in non-lactation at all time points (3 points: light phase, 4 points: dark phase) of the day. However, the expression of the hypothalamic Ob-Rb mRNA showed similar circadian rhythms in both the non-lactation and lactation, with only slight differences between the two groups. CSF leptin and glucose levels were constant throughout the day in both non-lactation and lactation, and there was almost no difference between the two groups at each time point. Circulating leptin and glucose levels showed circadian rhythms only in the non-lactating period, and were lower in lactation than in non-lactation, especially in the dark phase. In conclusion, the present study provides evidence that Ob-Rb mRNA expression fluctuates in the lactation period as well as in the non-lactation period, suggesting that the expression profile of whole hypothalamic Ob-Rb may not contribute to the difference in food consumption between lactation and non-lactation, and that chronic decrease in blood glucose levels may be associated with the increase in food consumption during lactation.

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There was no difference in CSF leptin levels between lactating and non-lactating rats.

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Hypothalamic Ob-Rb mRNA expressions showed different circadian rhythms between non-lactation and lactation.

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Chronic decrease in blood glucose levels may be associated with the elevation of food consumption in lactating rats.

LPS-induced SOCS3 antagonizes the JAK2-STAT5 pathway and inhibits β-casein synthesis in bovine mammary epithelial cells

Bovine mammary epithelial cells (BMECs) are essential for lactation in the dairy cow mammary gland, and are often used as a cellular model to study changes in inflammatory responses and lactation functions with exogenous stimuli. Prolactin (PRL) promotes milk protein synthesis by continuously activating the Janus kinase 2 and signal transducer and activator of transcription 5 (JAK2-STAT5) pathway. Lipopolysaccharides (LPS) activates inflammatory responses in cells and inhibits casein synthesis, but the exact mechanism is still unclear. Suppressor of cytokine signaling-3 (SOCS3) is a negative regulator of the JAK-STATs signaling pathway, and regulates a variety of inflammatory responses by inhibiting STAT3. Previous studies also suggested that SOCS3 plays a role in the development and involution of bovine mammary glands. The purpose of this study was to investigate whether LPS activated SOCS3, and whether SOCS3 resisted the regulation of casein synthesis by PRL in a JAK2-STAT5-dependent manner. We treated in vitro BMECs with 125 ng/mL PRL, 10 μg/mL LPS, SOCS3 siRNA (silencing), a SOCS3-GFP adenovirus overexpression vector, or combinations, to determine β-casein expression. We demonstrated that PRL up-regulated phospho-JAK2, phsopho-STAT5 and β-casein expression, whereas LPS caused the opposite effects, and activated SOCS3. SOCS3 overexpression interrupted the JAK2-STAT5 pathway in BMECs. With SOCS3 was silenced, LPS could not activate the JAK2-STAT5 pathway, and no inhibition of β-casein expression was observed. In conclusion, we showed that LPS activated SOCS3 in BMECs, antagonized the JAK2-STAT5 pathway via SOCS3 regulation, and ultimately reduced β-casein expression in these cells.

Fasting reduces the number of TRH immunoreactive neurons in the hypothalamic paraventricular nucleus of male rats, but not in mice

During fasting or weight loss, the fall in leptin levels leads to suppression of thyrotropin-releasing hormone (TRH) expression in the paraventricular nucleus of the hypothalamus (PVH) and, consequently, inhibition of the hypothalamic-pituitary-thyroid (HPT) axis. However, differently than rats, just few PVH^TRH neurons express the leptin receptor in mice. In the present study, male adult rats and mice were submitted to 48 -h fasting to evaluate the consequences on proTRH peptide expression at the PVH level. Additionally, the proTRH peptide expression was also assessed in the brains of leptin-deficient (Lep^ob/ob) mice. We observed that approximately 50 % of PVH^TRH neurons of leptin-injected rats exhibited phosphorylation of the signal transducer and activator of transcription 3 (pSTAT3), a marker of leptin receptor activation. In contrast, very few PVH^TRH neurons of leptin-injected mice exhibited pSTAT3. Rats submitted to 48 -h fasting showed a significant reduction in the number of PVH^TRH immunoreactive neurons, as compared to fed rats. On the other hand, no changes in the number of PVH^TRH immunoreactive neurons were observed between fasted and fed mice. Next, the number of TRH immunoreactive cells was determined in the PVH, dorsomedial nucleus of the hypothalamus and nucleus raphe pallidus of Lep^ob/ob and wild-type mice and no significant differences were observed, despite reduced plasma T4 levels in Lep^ob/ob mice. Taken together, these findings provide additional evidence of the important species-specific differences in the mechanisms used by fasting and/or leptin to regulate the HPT axis.

Distribution of growth hormone-responsive cells in the brain of rats and mice

A growth hormone (GH) injection is able to induce the phosphorylated form of the signal transducer and activator of transcription 5 (pSTAT5) in a large number of cells throughout the mouse brain. The present study had the objective to map the distribution of GH-responsive cells in the brain of rats that received an intracerebroventricular injection of GH and compare it to the pattern found in mice. We observed that rats and mice exhibited a similar distribution of GH-induced pSTAT5 in the majority of areas of the telencephalon, hypothalamus and brainstem. However, rats exhibited a higher density of GH-responsive cells than mice in the horizontal limb of the diagonal band of Broca (HDB), supraoptic and suprachiasmatic nuclei, whereas mice displayed more GH-responsive cells than rats in the hippocampus, lateral hypothalamic area and dorsal motor nucleus of the vagus (DMX). Since both HDB and DMX contain acetylcholine-producing neurons, pSTAT5 was co-localized with choline acetyltransferase in GH-injected animals. We found that 50.0 ± 4.5% of cholinergic neurons in the rat HDB coexpressed GH-induced pSTAT5, whereas very few co-localizations were observed in the mouse HDB. In contrast, rats displayed fewer cholinergic neurons responsive to GH in the DMX at the level of the area postrema. In summary, pSTAT5 can be used as a marker of GH-responsive cells in the rat brain. Although rats and mice exhibit a relatively similar distribution of GH-responsive neurons, some species-specific differences exist, as exemplified for the responsiveness to GH in distinct populations of cholinergic neurons.

Prolactin receptor-mediated activation of pSTAT5 in the pregnant mouse brain

Pregnancy represents a period of remarkable adaptive physiology throughout the body, with many of these important adaptations mediated by changes in gene transcription in the brain. A marked activation of the transcription factor signal transducer and activator of transcription 5 (STAT5) has been described in the brain during pregnancy and likely drives some of these changes. We aimed to investigate the physiological mechanism causing this increase in phosphorylated STAT5 (pSTAT5) during pregnancy. In various tissues, STAT5 is known to be activated by a number of different cytokines, including erythropoietin, growth hormone and prolactin. Because the lactogenic hormones that act through the prolactin receptor (PRLR), prolactin and its closely-related placental analogue placental lactogen, are significantly increased during pregnancy, we hypothesised that this receptor was primarily responsible for the pregnancy-induced increase in pSTAT5 in the brain. By examining temporal changes in plasma prolactin levels and the pattern of pSTAT5 immunoreactivity in the hypothalamus during early pregnancy, we found that the level of pSTAT5 was sensitive to circulating levels of endogenous prolactin. Using a transgenic model to conditionally delete PRLRs from forebrain neurones (Prlr^lox/lox /CamK-Cre), we assessed the relative contribution of the PRLR to the up-regulation of pSTAT5 in the brain of pregnant mice. In the absence of PRLRs on most forebrain neurones, a significant reduction in pSTAT5 was observed throughout the hypothalamus and amygdala in late pregnancy, confirming that PRLR is key in mediating this response. The exception to this was the hypothalamic paraventricular nucleus, where only 17% of pSTAT5 immunoreactivity during pregnancy was in PRLR-expressing cells. Taken together, these data indicate that, although there are region-specific mechanisms involved, lactogenic activity through the PRLR is the primary signal activating STAT5 in the brain during pregnancy.

Metabolic functions of prolactin: Physiological and pathological aspects

Prolactin is named after its vital role of promoting milk production during lactation, although it has been implicated in multiple functions within the body, including metabolism and energy homeostasis. Prolactin has been hypothesised to play a key role in driving many of the adaptations of the maternal body to allow the mother to meet the physiological demands of both pregnancy and lactation, including the high energetic demands of the growing foetus followed by milk production to support the offspring after birth. Prolactin receptors are found in many tissues involved in metabolism and food intake, such as the pancreas, liver, hypothalamus, small intestine and adipose tissue. We review the literature examining the effects of prolactin in these various tissues and how they relate to changes in function in physiological states of high prolactin, such as pregnancy and lactation, and in pathological states of hyperprolactinaemia in the adult. In many cases, whether prolactin promotes healthy metabolism or leads to dysregulation of metabolic functions is highly dependent on the situation. Overall, although prolactin may not play a major role in regulating metabolism and body weight outside of pregnancy and lactation, it definitely has the ability to contribute to metabolic function.

Pregnancy-induced adaptation of central sensitivity to leptin and insulin

Pregnancy is a time of increased food intake and fat deposition in the mother, and adaptations of glucose homeostasis to meet the energy demands of the growing fetus. As part of these adaptations, leptin and insulin concentrations increase in the maternal circulation during pregnancy. Central effects of leptin and insulin, however, are counterproductive to pregnancy, as increased action of these hormones in the brain lead to suppression of food intake. To prevent this, it is well documented that pregnancy induces a state of leptin- and insulin-insensitivity in the brain, particularly the hypothalamus, in a range of species. While the mechanisms underlying leptin- or insulin-insensitivity during pregnancy vary between species, there is evidence of reduced transport into the brain, impaired activation of intracellular signalling pathways, including reduced leptin receptor expression, and attenuated activation of downstream neuronal pathways, especially for leptin insensitivity. Pregnancy-induced changes in prolactin, growth hormone and leptin are discussed in terms of their role in mediating this reduced response to leptin and insulin.

Neurochemical phenotype of growth hormone-responsive cells in the mouse paraventricular nucleus of the hypothalamus

Multiple neuroendocrine, autonomic and behavioral responses are regulated by the paraventricular nucleus of the hypothalamus (PVH). Previous studies have shown that PVH neurons express the growth hormone (GH) receptor (GHR), although the role of GH signaling on PVH neurons is still unknown. Given the great heterogeneity of cell types located in the PVH, we performed a detailed analysis of the neurochemical identity of GH-responsive cells to understand the possible physiological importance of GH action on PVH neurons. GH-responsive cells were detected via the phosphorylated form of the signal transducer and activator of transcription-5 (pSTAT5) in adult male mice that received an intraperitoneal GH injection. Approximately 51% of GH-responsive cells in the PVH co-localized with the vesicular glutamate transporter 2. Rare co-localizations between pSTAT5 and vesicular GABA transporter or vasopressin were observed, whereas approximately 20% and 38% of oxytocin and tyrosine hydroxylase (TH) cells, respectively, were responsive to GH in the PVH. Approximately 55%, 35% and 63% of somatostatin, thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) neurons expressed GH-induced pSTAT5, respectively. Additionally, 8%, 49% and 75% of neuroendocrine TH, TRH and CRH neurons, and 67%, 32% and 74% of nonneuroendocrine TH, TRH and CRH neurons were responsive to GH in the PVH of Fluoro-Gold-injected mice. Our findings suggest that GH action on PVH neurons is involved in the regulation of the thyroid, somatotropic and adrenal endocrine axes, possibly influencing homeostatic and stress responses.

Differences between rats and mice in the leptin action on the paraventricular nucleus of the hypothalamus: Implications for the regulation of the hypothalamic-pituitary-thyroid axis

Previous studies indicate that leptin regulates the hypothalamic-pituitary-thyroid (HPT) axis via direct and indirect mechanisms. The indirect mechanism involves leptin action in pro-opiomelanocortin (POMC)- and agouti-related peptide (AgRP)-expressing neurones. These cells innervate the paraventricular nucleus of the hypothalamus (PVH) where they modulate hypophysiotrophic thyrotrophin-releasing hormone (TRH)-producing neurones. The direct mechanism involves the expression of leptin receptor (LepR) in a subpopulation of PVH TRH neurones. However, to our knowledge, the existence of LepR in PVH TRH neurones of mice has not been clearly confirmed. Therefore, we investigated possible species-specific differences between rats and mice with respect to the mechanisms recruited by leptin to regulate the HPT axis. We observed that an acute leptin injection induced phosphorylated signal transducer and activator of transcription 3 (pSTAT3), a marker of leptin-responsive cells, in 46.2 ± 8.0% of PVH proTRH immunoreactive neurones in rats. By contrast, an insignificant number of proTRH positive neurones in the mouse PVH co-expressed leptin-induced pSTAT3 or LepR. Similarly, central leptin injection increased the percentage of PVH proTRH neurones containing cAMP response element-binding protein phosphorylation in rats, but not in mice. We investigated the innervation of AgRP and POMC axons in the PVH and observed that rats exhibited a denser POMC innervation in the PVH compared to mice, whereas rats and mice showed similar density of AgRP axons in the PVH. In conclusion, rats and mice exhibit important species-specific differences in the direct and indirect mechanisms used by leptin to regulate the HPT axis.

Postnatal Overnutrition Induces Changes in Synaptic Transmission to Leptin Receptor-Expressing Neurons in the Arcuate Nucleus of Female Mice

The adipocyte-derived hormone leptin is a potent neurotrophic factor that contributes to the neural plasticity and development of feeding circuitry, particularly in the arcuate nucleus of the hypothalamus (ARH). Postnatal overnutrition affects leptin secretion and sensitivity, but whether postnatal overnutrition produces changes in the development of the synaptic transmission to ARH neurons is currently unknown. We evaluated the excitatory and inhibitory currents to ARH leptin receptor (LepR)-expressing neurons in prepubertal, pubertal and adult female mice. The effects of postnatal overnutrition in the expression of genes that code ion channels subunits in the ARH were also evaluated. We observed that the transition from prepubertal to pubertal stage is characterized by a rise in both excitatory and inhibitory transmission to ARH LepR-expressing neurons in control mice. Postnatal overnutrition induces a further increase in the excitatory synaptic transmission in pubertal and adult animals, whereas the amplitude of inhibitory currents to ARH LepR-expressing cells was reduced. Postnatal overnutrition also contributes to the modulation of gene expression of N-methyl-D-aspartate, GABA_B and ATP-sensitive potassium channel subunits in ARH. In summary, the synaptic transmission to ARH cells is profoundly influenced by postnatal overnutrition. Thus, increased adiposity during early postnatal period induces long-lasting effects on ARH cellular excitability.

Secretion and Function of Pituitary Prolactin in Evolutionary Perspective

The hypothalamo-pituitary system developed in early vertebrates. Prolactin is an ancient vertebrate hormone released from the pituitary that exerts particularly diverse functions. The purpose of the review is to take a comparative approach in the description of prolactin, its secretion from pituitary lactotrophs, and hormonal functions. Since the reproductive and osmoregulatory roles of prolactin are best established in a variety of species, these functions are the primary subjects of discussion. Different types of prolactin and prolactin receptors developed during vertebrate evolution, which will be described in this review. The signal transduction of prolactin receptors is well conserved among vertebrates enabling us to describe the whole subphylum. Then, the review focuses on the regulation of prolactin release in mammals as we have the most knowledge on this class of vertebrates. Prolactin secretion in response to different reproductive stimuli, such as estrogen-induced release, mating, pregnancy and suckling is detailed. Reproduction in birds is different from that in mammals in several aspects. Prolactin is released during incubation in avian species whose regulation and functional significance are discussed. Little information is available on prolactin in reptiles and amphibians; therefore, they are mentioned only in specific cases to explain certain evolutionary aspects. In turn, the osmoregulatory function of prolactin is well established in fish. The different types of pituitary prolactin in fish play particularly important roles in the adaptation of eutherian species to fresh water environments. To achieve this function, prolactin is released from lactotrophs in hyposmolarity, as they are directly osmosensitive in fish. In turn, the released prolactin acts on branchial epithelia, especially ionocytes of the gill to retain salt and excrete water. This review will highlight the points where comparative data give new ideas or suggest new approaches for investigation in other taxa.

Biology of heat stress; the nexus between intestinal hyperpermeability and swine reproduction

Unfavorable weather conditions are one of the largest constraints to maximizing farm animal productivity. Heat stress (HS), in particular, compromises almost every metric of profitability and this is especially apparent in the grow-finish and reproductive aspects of the swine industry. Suboptimal production during HS was traditionally thought to result from hypophagia. However, independent of inadequate nutrient consumption, HS affects a plethora of endocrine, physiological, metabolic, circulatory, and immunological variables. Whether these changes are homeorhetic strategies to survive the heat load or are pathological remains unclear, nor is it understood if they temporally occur by coincidence or if they are chronologically causal. However, mounting evidence suggest that the origin of the aforementioned changes lie at the gastrointestinal tract. Heat stress compromises intestinal barrier integrity, and increased appearance of luminal contents in circulation causes local and systemic inflammatory responses. The resulting immune activation is seemingly the epicenter to many, if not most of the negative consequences HS has on reproduction, growth, and lactation. Interestingly, thermoregulatory and production responses to HS are only marginally related. In other words, increased body temperature indices poorly predict decreases in productivity. Further, HS induced malnutrition is also a surprisingly inaccurate predictor of productivity. Thus, selecting animals with a "heat tolerant" phenotype based solely or separately on thermoregulatory capacity or production may not ultimately increase resilience. Describing the physiology and mechanisms that underpin how HS jeopardizes animal performance is critical for developing approaches to ameliorate current production issues and requisite for generating future strategies (genetic, managerial, nutritional, and pharmaceutical) aimed at optimizing animal well-being, and improving the sustainable production of high-quality protein for human consumption.

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.

Neurophysiological and cognitive changes in pregnancy

The hormonal fluctuations in pregnancy drive a wide range of adaptive changes in the maternal brain. These range from specific neurophysiological changes in the patterns of activity of individual neuronal populations, through to complete modification of circuit characteristics leading to fundamental changes in behavior. From a neurologic perspective, the key hormone changes are those of the sex steroids, estradiol and progesterone, secreted first from the ovary and then from the placenta, the adrenal glucocorticoid cortisol, as well as the anterior pituitary peptide hormone prolactin and its pregnancy-specific homolog placental lactogen. All of these hormones are markedly elevated during pregnancy and cross the blood-brain barrier to exert actions on neuronal populations through receptors expressed in specific regions. Many of the hormone-induced changes are in autonomic or homeostatic systems. For example, patterns of oxytocin and prolactin secretion are dramatically altered to support novel physiological functions. Appetite is increased and feedback responses to metabolic hormones such as leptin and insulin are suppressed to promote a positive energy balance. Fundamental physiological systems such as glucose homeostasis and thermoregulation are modified to optimize conditions for fetal development. In addition to these largely autonomic changes, there are also changes in mood, behavior, and higher processes such as cognition. This chapter summarizes the hormonal changes associated with pregnancy and reviews how these changes impact on brain function, drawing on examples from animal research, as well as available information about human pregnancy.

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.

Central growth hormone action regulates metabolism during pregnancy

The maternal organism undergoes numerous metabolic adaptations to become prepared for the demands associated with the coming offspring. These metabolic adaptations involve changes induced by several hormones that act at multiple levels, ultimately influencing energy and glucose homeostasis during pregnancy and lactation. Previous studies have shown that central growth hormone (GH) action modulates glucose and energy homeostasis. However, whether central GH action regulates metabolism during pregnancy and lactation is still unknown. In the present study, we generated mice carrying ablation of GH receptor (GHR) in agouti-related protein (AgRP)-expressing neurons, in leptin receptor (LepR)-expressing cells or in the entire brain to investigate the role played by central GH action during pregnancy and lactation. AgRP-specific GHR ablation led to minor metabolic changes during pregnancy and lactation. However, while brain-specific GHR ablation reduced food intake and body adiposity during gestation, LepR GHR knockout (KO) mice exhibited increased leptin responsiveness in the ventromedial nucleus of the hypothalamus during late pregnancy, although their offspring showed reduced growth rate. Additionally, both Brain GHR KO and LepR GHR KO mice had lower glucose tolerance and glucose-stimulated insulin secretion during pregnancy, despite presenting increased insulin sensitivity, compared with control pregnant animals. Our findings revealed that during pregnancy central GH action regulates food intake, fat retention, as well as the sensitivity to insulin and leptin in a cell-specific manner. Together, the results suggest that GH acts in concert with other "gestational hormones" to prepare the maternal organism for the metabolic demands of the offspring.

Impaired hypothalamic leptin sensitivity in pseudopregnant rats treated with chronic prolactin to mimic pregnancy

Pregnancy in rodents is associated with hyperphagia, increased fat deposition, elevated leptin concentrations and insensitivity to the satiety action of leptin. To investigate the hormonal mechanisms involved in the development of this state of pregnancy-induced leptin resistance, we have used a pseudopregnancy rat model. We have previously demonstrated that pseudopregnant rats have a normal feeding response to leptin, although, if pseudopregnancy is extended using chronic i.c.v. ovine prolactin infusion along with progesterone implants, then leptin no longer suppresses food intake. The present study aimed to investigate the effect of chronically high lactogen levels, as seen in mid-pregnancy, on leptin-induced activation of hypothalamic Janus kinase/signal transducer and activator of transcription (JAK/STAT) signal transduction and mRNA expression of leptin (LepR-B) and prolactin (Prlr-L) receptors, using pseudopregnant rats chronically infused with ovine prolactin. Groups of virgin (dioestrous) and pseudopregnant rats were treated with chronic i.c.v. infusion of either prolactin (2.5 μg μL^-1  h^-1 for 5 days) or vehicle (artificial cerebrospinal fluid [aCSF]) via a minipump connected to a cannula surgically implanted into the lateral ventricle. Rats were fasted overnight and then received an i.c.v. injection of leptin (400 ng) or vehicle (aCSF) and were perfused 30 minutes later. In chronic vehicle-infused pseudopregnant rats, i.c.v. leptin increased the number of phosphorylated STAT3 positive cells in the arcuate nucleus and ventromedial nucleus (VMH) of the hypothalamus, similar to all acute-leptin treated virgin groups. This effect of leptin, however, was not observed in the pseudopregnant rats that were chronically infused with prolactin. A quantitative polymerase chain reaction analysis also showed decreased expression of LepR-B in the arcuate and VMH nuclei, as well as decreased Prlr-L in the arcuate nucleus of prolactin-infused "extended pseudopregnancy" rats. These data suggest that the attenuation of the leptin-induced suppression of food intake caused by chronically high lactogen levels in pseudopregnant rats is associated with impaired leptin-induced activation of the JAK/STAT pathway in specific hypothalamic nuclei.

Exposure to Organic Fraction Extracted from Oil Sands Process-Affected Water Has Negligible Impact on Pregnancy and Lactation of Mice

Dissolved organic compounds are major contaminants in oil sands process-affected water (OSPW), of which naphthenic acids (NAs) are one of the main persistent toxicants. In the present study, we explore the toxic effects of the organic fraction extracted from OSPW (OSPW-OF) in mice during pregnancy and lactation. Here, we report that acute oral exposure of female Balb/c mice during gestation, and subchronic exposure throughout gestation and lactation to OSPW-OF (containing naturally occurring levels of NAs found in tailings ponds), had negligible effects on their reproductive performance. Specifically, mating behavior, pregnancy success, embryonic implantation, gestation period, litter size, and offspring viability were not affected by OSPW-OF containing up to 55 mg/L NAs. OSPW-OF exposure also did not affect plasma concentrations of pregnancy-associated hormones or pro- and anti-inflammatory cytokines, and it had minimal effects on liver stress gene expression. This study presents the first comprehensive in vivo analysis of mammalian toxicity associated with OSPW-OF exposure. Overall, our results suggest that the risk of acute and subchronic toxicity to mice exposed to OSPW-OF at environmentally relevant concentrations of NAs in contaminated drinking water is likely negligible.

SOCS3 as a future target to treat metabolic disorders

The suppressors of cytokine signaling (SOCS) are a group of eight proteins responsible for preventing excessive cytokine signaling. Among this protein family, SOCS3 has received special attention. SOCS3 expression is important to control certain allergy autoimmune diseases. Furthermore, SOCS3 expression is elevated in obesity and it is involved in the inhibition of leptin and insulin signaling, two important hormones involved in the control of energy metabolism. Therefore, increased SOCS3 expression in obese individuals is associated with several metabolic disorders, including reduced energy expenditure, increased food intake and adiposity, and insulin and leptin resistance. In addition, recent studies found that SOCS3 expression regulates energy and glucose homeostasis in several metabolic conditions, such as pregnancy, caloric restriction, and refeeding. Importantly, attenuation of SOCS3 expression in most cases improves leptin and insulin sensitivity, leading to beneficial metabolic effects. This review aims to discuss the role of SOCS3 in the control of blood glucose levels as well as in energy homeostasis. The development of pharmacological compounds to inhibit SOCS3 activity and/or expression may represent a promising therapeutic approach to treat type 2 diabetes mellitus, obesity, and other metabolic imbalances.

Prolactin and human weight disturbances: A puzzling and neglected association

Weight gain at the outset of prolactinomas in many women is well documented. Yet, this symptom is absent from the clinical descriptions of the disease in textbooks and reviews. This omission is almost certainly due to the absence of a physiological explanation for the phenomenon, as prolactin is not a recognized fat promoting hormone. In this review we present the clinical evidence for a relationship between prolactin and fat accumulation and address some possible mechanisms involved. We put forward the hypothesis that prolactin is a component of a neuroendocrine program - maternal subroutine - aimed at optimizing the care of the young through the production of milk, promotion of maternal behavior and increase in the metabolic efficiency of the mother. These adaptations can enable her to face the extraordinary metabolic expenses of pregnancy and nursing, especially during times of suboptimal environmental conditions. We emphasize the uniqueness of prolactin in that it is a hormone that is tonically inhibited and which has its major effects on the regulation of an inter-individual (the mother - offspring dyad), rather than an intra-individual, system. This approach opens a window to consider the possibility of external events as regulators of this system. It also allows addressing a variety of hitherto unexplained findings reported in the literature. Examples include: association of prolactinomas with paternal deprivation and with stressful life events; pseudocyesis; acute life event-driven episodes of galactorrhea; episodes of rapid weight gain following a life event; prolactin surges (without associated cortisol surges) following some psychological stresses.

Suppression of Leptin Transport Into the Brain Contributes to Leptin Resistance During Pregnancy in the Mouse

During pregnancy, when both food intake and circulating leptin concentrations increase, the brain becomes insensitive to leptin. The mechanism by which central leptin resistance during pregnancy emerges remains poorly understood. We investigated whether structural changes in the blood-brain barrier (BBB) or changes in carrier-mediated transport of leptin into the brain might contribute to pregnancy-induced leptin resistance. Immunohistochemical evaluation of the BBB at the level of the arcuate nucleus and median eminence in virgin, pregnant, and lactating mice was undertaken by labeling for tanycytes (vimentin), tight junction protein (zona occludens-1), and a marker of fenestrated endothelial capillaries (MECA-32). There were no changes in these BBB markers between virgin, pregnant or lactating mice. Transport of iodine 125-labeled leptin from the peripheral circulation into the brain was completely suppressed during pregnancy, however (days 14 through 16), compared with virgin and lactating (days 7 through 11) mice. This was accompanied by a suppression of leptin clearance from the blood in pregnant mice. We also investigated in virgin mice whether competition with other hormones for transport might contribute to suppression of leptin transport into the brain. Although leptin was able to compete with prolactin transport into the brain, prolactin did not compete with leptin transport. These data demonstrate that suppression of the transport of leptin into the brain during pregnancy, in the absence of structural changes in the BBB, is an important contributor to the insensitivity of the hypothalamus to leptin at this time.

Different Cabergoline Effect on Metabolic and Anthropometric Parameters in Female Prolactinoma Patients Versus Idiopathic Hyperprolactinemia Patients

BACKGROUND

Hyperprolactinemia can lead to weight gain, insulin resistance, abnormal glucose homeostasis and dyslipidemia. Reversibility of these changes after normalization of prolactin with dopamine agonists is still controversial and needs more clarification.

OBJECTIVE

We aimed to: 1) evaluate and compare metabolic and anthropometric profile in female with newly diagnosed prolactin-secreting adenoma versus female idiopathic hyperprolactinemic patients; 2) compare the effects of one year cabergoline therapy on the metabolic profile and anthropometric parameters (by using visceral adiposity index as index for evaluation of adipose tissue dysfunction) in females with prolactinoma to female idiopathic hyperprolactinemic patients.

PATIENTS AND METHODS

We enrolled 40 female patients with newly diagnosed prolactinoma and 40 female patients with idiopathic hyperprolactinemia, who were matched according to: age; weight; BMI; waist; and prolactin levels. We enrolled the participants in this study at the time of diagnosis before therapy and they were followed up for 12 months.

RESULTS

Cabergoline therapy had significant favorable effects on metabolic and anthropometric parameters, visceral adiposity index and in all patients (apart from HDLc in prolactinoma patients). Cabergoline therapy was significantly more effective in patient with idiopathic hyperprolactinemia than prolactinoma patients with regard to BMI, waist circumference, HDLc and visceral adiposity index despite normalization of prolactin levels in both groups.

CONCLUSION

12 months of Cabergoline treatment improved most of the anthropometric and metabolic parameters, and visceral adiposity index as a marker for adipose tissue dysfunction in both idiopathic hyperprolactinemia and prolactinoma patients. However, Cabergoline treatment was more effective in idiopathic hyperprolactinemic than prolactinoma patients.

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.

Suppression of Prolactin Secretion Partially Explains the Antidiabetic Effect of Bromocriptine in ob/ob Mice

Previous studies have shown that bromocriptine mesylate (Bromo) lowers blood glucose levels in adults with type 2 diabetes mellitus; however, the mechanism of action of the antidiabetic effects of Bromo is unclear. As a dopamine receptor agonist, Bromo can alter brain dopamine activity affecting glucose control, but it also suppresses prolactin (Prl) secretion, and Prl levels modulate glucose homeostasis. Thus, the objective of the current study was to investigate whether Bromo improves insulin sensitivity via inhibition of Prl secretion. Male and female ob/ob animals (a mouse model of obesity and insulin resistance) were treated with Bromo and/or Prl. Bromo-treated ob/ob mice exhibited lower serum Prl concentration, improved glucose and insulin tolerance, and increased insulin sensitivity in the liver and skeletal muscle compared with vehicle-treated mice. Prl replacement in Bromo-treated mice normalized serum Prl concentration without inducing hyperprolactinemia. Importantly, Prl replacement partially reversed the improvements in glucose homeostasis caused by Bromo treatment. The effects of the Prl receptor antagonist G129R-hPrl on glucose homeostasis were also investigated. We found that central G129R-hPrl infusion increased insulin tolerance of male ob/ob mice. In summary, our findings indicate that part of Bromo effects on glucose homeostasis are associated with decrease in serum Prl levels. Because G129R-hPrl treatment also improved the insulin sensitivity of ob/ob mice, pharmacological compounds that inhibit Prl signaling may represent a promising therapeutic approach to control blood glucose levels in individuals with insulin resistance.

Neuroendocrinology and Adaptive Physiology of Maternal Care

Parental care is critical for offspring survival in many species. In mammals, parental care is primarily provided through maternal care, due to obligate pregnancy and lactation constraints, although some species also show paternal and alloparental care. These behaviors are driven by specialized neural circuits that receive sensory, cortical, and hormonal input to generate a coordinated and timely change in behavior, and sustain that behavior through activation of reward pathways. Importantly, the hormonal changes associated with pregnancy and lactation also act to coordinate a broad range of physiological changes to support the mother and enable her to adapt to the demands of these states. This chapter will review the neural pathways that regulate maternal behavior, the hormonal changes that occur during pregnancy and lactation, and how these two facets merge together to promote both young-directed maternal responses (including nursing and grooming) and young-related responses (including maternal aggression and other physiological adaptions to support the development of and caring for young). We conclude by examining how experimental animal work has translated into knowledge of human parenting, particularly in regards to maternal mental health issues.

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.

SOCS3 expression in SF1 cells regulates adrenal differentiation and exercise performance

Many hormones/cytokines are secreted in response to exercise and cytokine signaling may play a pivotal role in the training adaptations. To investigate the importance of cytokine signaling during vertical ladder climbing, a resistance exercise model, we produced mice lacking SOCS3 protein exclusively in steroidogenic factor-1 (SF1) cells (SF1 Socs3 KO mice). SF1 expression is found in steroidogenic cells of the adrenal cortex and gonads, as well as in neurons of the ventromedial nucleus of the hypothalamus. Histological markers of the fetal adrenal zone (or X-zone in rodents) were still present in adult males and postpartum SF1 Socs3 KO females, suggesting a previously unrecognized effect of SOCS3 on the terminal differentiation of the adrenal gland. This change led to a distinct distribution of lipid droplets along the adrenal cortex. Under basal conditions, adult SF1 Socs3 KO mice exhibited similar adrenal weight, and plasma ACTH and corticosterone concentrations. Nonetheless, SF1 Socs3 KO mice exhibited a blunted ACTH-induced corticosterone secretion. The overall metabolic responses induced by resistance training remained unaffected in SF1 Socs3 KO mice, including changes in body adiposity, glucose tolerance and energy expenditure. However, training performance and glucose control during intense resistance exercise were impaired in SF1 Socs3 KO mice. Furthermore, a reduced counter-regulatory response to 2-deoxy-d-glucose was observed in mutant mice. These findings revealed a novel participation of SOCS3 regulating several endocrine and metabolic aspects. Therefore, cytokine signaling in SF1 cells exerts an important role to sustain training performance possibly by promoting the necessary metabolic adjustments during exercise.

Hypertriglyceridemia in female rats during pregnancy induces obesity in male offspring via altering hypothalamic leptin signaling

Maternal obesity influence the child's long-term development and health. Though, the mechanism concerned in this process is still uncertain. In the present study, we explored whether overfeeding of a high-fat diet during pregnancy in female rats altered metabolic phenotypes in an F1 generation and authenticated the contribution of hypothalamic leptin signaling. Leptin responsiveness and the number of immunopositive neurons for phosphorylated signal transducer and activator transcription 3 (pSTAT3) were analyzed. Neuropeptide Y in the arcuate nucleus of the hypothalamus and in nucleus tractus solitaries was examined. Triglycerides and leptin levels were increased in the high-fat diet mother. The number of neuropeptide Y positive cell bodies and neurons was significantly increased in the high-fat diet-F1 offspring (HDF-F1) as compared to Chow-F1. Leptin administration significantly decreased the food intake and increased the pSTAT3 expression levels in neurons in the arcuate nucleus of Chow-F1. However, leptin did not show any effect on food intake and had a reduced effect on pSTAT3 expression levels in neurons in the arcuate nucleus of HDF-F1. From the present domino effect, we conclude that mothers exposed to high-fat diet during pregnancy may pass the obese phenotype to the succeeding generation via altering hypothalamic leptin signaling.

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.

The role of leptin in health and disease

Leptin is a master regulator of energy balance and body adiposity. Additionally, leptin exerts important control on glucose homeostasis, thermogenesis, autonomic nervous system and neuroendocrine axes. In metabolic diseases, such as obesity and diabetes mellitus, leptin signaling may be compromised, indicating the important role of this hormone in the etiology and pathophysiological manifestations of these conditions. In the present manuscript, we reviewed important concepts of leptin signaling, as well as about the effects of leptin on several biologic functions. We also discussed the possible therapeutic use of leptin administration and how our current obesogenic environment contributes to the development of leptin resistance. Our objective was to provide a comprehensive and state-of-the-art review about the importance of leptin to maintain the homeostasis and during pathological conditions.

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.

Central Effects of Leptin on Glucose Homeostasis are Modified during Pregnancy in the Rat

Despite increased leptin concentrations during pregnancy, fat mass and food intake are increased. The satiety response to central leptin is suppressed, indicating a state of leptin insensitivity in the hypothalamus. Although the regulation of food intake is a major function of leptin, this hormone also influences a wide range of functions within the body. These actions include the regulation of glucose homeostasis, which undergoes major adaptation in the maternal body to generate optimal conditions for foetal development and growth. The present study aimed to investigate the effects of central leptin treatment on glucose homeostasis in pregnant rats to determine whether pregnancy-induced leptin insensitivity is functionally specific, and to further investigate changes in glucose homeostasis during pregnancy. After an overnight fast, nonpregnant and day 14 pregnant rats received an i.c.v. injection of leptin (100 ng or 4 μg) or vehicle then underwent a glucose tolerance test (GTT). Further groups of nonpregnant and day 14 pregnant rats were killed 30 min after leptin (doses ranging from 40 ng-4 μg) or vehicle i.c.v. injections for western blot analysis of phospho-signal transducer and activator of transcription 3 (STAT3) and phospho-Akt in various hypothalamic nuclei. Central leptin injection prior to a GTT lead to lowered basal insulin concentrations and impaired glucose tolerance in nonpregnant female rats, whereas the same doses of leptin had no significant effect on glucose tolerance in day 14 pregnant rats, indicating that, similar to the satiety actions of leptin, the effects of leptin on glucose homeostasis are suppressed during pregnancy. Furthermore, in the arcuate nucleus and ventromedial and dorsomedial nuclei of the hypothalamus, comprising three leptin-sensitive areas, there was no evidence that leptin induced Akt phosphorylation despite significant increases in phospho-STAT3, suggesting that leptin does not act through phospho-Akt in these areas in female rats.

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.

Leptin Signaling Is Not Required for Anorexigenic Estradiol Effects in Female Mice

Estradiol and leptin are critical hormones in the regulation of body weight. The aim of this study was to determine whether this cross talk between leptin receptor (LepRb) and estrogen receptor-α (ERα) signaling is critical for estradiol's anorexigenic effects. Leprb-Cre mice were crossed with Cre-dependent Tau-green fluorescent protein (GFP) reporter, Stat3-flox or Erα-flox mice to generate female mice with GFP expression, signal transducer and activator of transcription 3 (STAT3) knockout (KO), or ERα KO, specifically in LepRb-expressing cells. The proportion of Leprb-GFP cells colocalizing ERα was high (∼80%) in the preoptic area but low (∼10%) in the mediobasal hypothalamus, suggesting that intracellular cross talk between these receptors is minimal for metabolic regulation. To test whether estradiol enhanced arcuate leptin sensitivity, ovarectomized mice received varying levels of estradiol replacement. Increasing estrogenic states did not increase the degree of leptin-induced STAT3 phosphorylation. LepRb-specific STAT3 KO mice and controls were ovarectomized and given either chronic estradiol or vehicle treatment to test whether STAT3 is required for estrogen-induced body weight suppression. Both groups of estradiol-treated mice showed an equivalent reduction in body weight and fat content compared with vehicle controls. Finally, mice lacking ERα specifically in LepRb-expressing neurons also showed no increase in body weight or impairments in metabolic function compared with controls, indicating that estradiol acts independently of leptin-responsive cells to regulate body weight. However, fecundity was impaired in in Leprb-ERα KO females. Contrary to the current dogma, we report that estradiol has minimal direct actions on LepRb cells in the mediodasal hypothalamus and that its anorexigenic effects can occur entirely independently of LepRb-STAT3 signaling in female mice.

Distribution of growth hormone-responsive cells in the mouse brain

Growth hormone (GH) exerts important biological effects primarily related to growth and metabolism. However, the role of GH signaling in the brain is still elusive. To better understand GH functions in the brain, we mapped the distribution of GH-responsive cells and identified the receptors involved in GH central effects. For this purpose, mice received an acute intraperitoneal challenge with specific ligands of the GH receptor (mouse GH), prolactin receptor (prolactin) or both receptors (human GH), and their brains were subsequently processed immunohistochemically to detect the phosphorylated form of STAT5 (pSTAT5). GH induced pSTAT5 immunoreactivity in neurons, but not in astroglial cells of numerous brain regions, including the cerebral cortex, nucleus accumbens, hippocampus, septum and amygdala. The most prominent populations of GH-responsive neurons were located in hypothalamic areas, including several preoptic divisions, and the supraoptic, paraventricular, suprachiasmatic, periventricular, arcuate, ventromedial, dorsomedial, tuberal, posterior and ventral premammillary nuclei. Interestingly, many brainstem structures also exhibited GH-responsive cells. Experiments combining immunohistochemistry for pSTAT5 and in situ hybridization for GH and prolactin receptors revealed that human GH induced pSTAT5 in most, but not all, brain regions through both prolactin and GH receptors. Additionally, males and females exhibited a similar number of GH-responsive cells in forebrain structures known to be sexually dimorphic. In summary, we found GH-responsive cells primarily distributed in brain regions implicated in neurovegetative, emotional/motivational and cognitive functions. Our findings deepen the understanding of GH signaling in the brain and suggest that central GH signaling is likely more ample and complex than formerly recognized.