Identification of neuronal input to the arcuate nucleus (ARH) activated during lactation: implications in the activation of neuropeptide Y neurons

Calcitonin Gene-Related Peptide-Induced Phosphorylation of STAT3 in Arcuate Neurons Is a Link in the Metabolic Benefits of Portal Glucose

INTRODUCTION

Intestinal gluconeogenesis (IGN) exerts metabolic benefits in energy homeostasis via the neural sensing of portal glucose.

OBJECTIVE

The aim of this work was to determine central mechanisms involved in the effects of IGN on the control of energy homeostasis.

METHODS

We investigated the effects of glucose infusion into the portal vein, at a rate that mimics IGN, in conscious wild-type, leptin-deficient Ob/Ob and calcitonin gene-related peptide (CGRP)-deficient mice.

RESULTS

We report that portal glucose infusion decreases food intake and plasma glucose and induces in the hypothalamic arcuate nucleus (ARC) the phosphorylation of STAT3, the classic intracellular messenger of leptin signaling. This notably takes place in POMC-expressing neurons. STAT3 phosphorylation does not require leptin, since portal glucose effects are observed in leptin-deficient Ob/Ob mice. We hypothesized that the portal glucose effects could require CGRP, a neuromediator previously suggested to suppress hunger. In line with this hypothesis, neither the metabolic benefits nor the phosphorylation of STAT3 in the ARC take place upon portal glucose infusion in CGRP-deficient mice. Moreover, intracerebroventricular injection of CGRP activates hypothalamic phosphorylation of STAT3 in mice, and CGRP does the same in hypothalamic cells. Finally, no metabolic benefit of dietary fibers (known to depend on the induction of IGN), takes place in CGRP-deficient mice.

CONCLUSIONS

CGRP-induced phosphorylation of STAT3 in the ARC is part of the neural chain determining the hunger-modulating and glucose-lowering effects of IGN/portal glucose.

Neural Activation Patterns Associated with Maternal Mouthbrooding and Energetic State in an African Cichlid Fish

Parental care is widespread in the animal kingdom, but for many species, provisioning energetic resources must be balanced with trade-offs between self-promoting and offspring-promoting behaviors. However, little is known about the neural mechanisms underlying these motivational decisions. Mouthbrooding is an extreme form of parental care most common in fishes that provides an ideal opportunity to examine which brain regions are involved in parenting and energetics. The African cichlid fish Astatotilapia burtoni is a maternal mouthbrooder in which females hold developing young inside their mouths for 2 weeks. This brood care makes feeding impossible, so females undergo obligatory starvation. We used immunohistochemistry for the neural activation marker pS6 to examine which brain regions were involved in processing salient information in mouthbrooding, starved, and fed females. We identified brain regions more associated with maternal brood care (TPp, Dc-4/-5), and others reflective of energetic state (Dl-v, NLTi). Most nuclei examined, however, were involved in both maternal care and energetic status. Placement of each of the 16 examined nuclei into these functional categories was supported by node by node comparisons, co-activity networks, hierarchical clustering, and discriminant function analysis. These results reveal which brain regions are involved in parental care and food intake in a species where provisioning is skewed towards the offspring when parental feeding is not possible. This study provides support for both distinct and shared circuitry involved in regulation of maternal care, food intake, and energy balance, and helps put the extreme parental case of mouthbrooding into a comparative and evolutionary context.

Synaptic proteome changes in the hypothalamus of mother rats

To establish synaptic proteome changes associated with motherhood, we isolated synaptosome fractions from the hypothalamus of mother rats and non-maternal control females at the 11th postpartum day. Proteomic analysis by two-dimensional differential gel electrophoresis combined with mass spectrometric protein identification established 26 significant proteins, 7 increasing and 19 decreasing protein levels in the dams. The altered proteins are mainly involved in energy homeostasis, protein folding, and metabolic processes suggesting the involvement of these cellular processes in maternal adaptations. The decrease in a significantly altered protein, complement component 1q subcomponent-binding protein (C1qbp) was validated with Western blotting. Furthermore, immunohistochemistry showed its presence in hypothalamic fibers and terminals in agreement with its presence in synaptosomes. We also found the expression of C1qbp in different hypothalamic nuclei including the preoptic area and the paraventricular hypothalamic nucleus at the protein and at the mRNA level using immunohistochemistry and in situ hybridization histochemistry, respectively. Bioinformatical network analysis revealed that cytokines, growth factors, and protein kinases are common regulators, which indicates a complex regulation of the proteome change in mothers. The results suggest that maternal responsiveness is associated with synaptic proteins level changes in the hypothalamus, and that growth factors and cytokines may govern these alterations.

BIOLOGICAL SIGNIFICANCE

The period of motherhood is accompanied with several behavioral, neuroendocrine, emotional and metabolic adaptations in the brain. Although it is established that various hypothalamic networks participate in the maternal adaptations of the rodent brain, our knowledge on the molecular background of these alterations remains seriously limited. In the present study, we first determined that the functional alterations of the maternal brain can be detected at the level of the synaptic proteome in the hypothalamus. Independent confirmation of synaptic localization, and also the established decrease in the level of C1qbp protein suggest the validity of the data. Common regulators of altered proteins belonging to the growth factor and cytokine family suggest that the synaptic adaptation is governed by these extracellular signals and future studies should focus on their specific roles. Our study was also the first to describe the expression pattern of C1qbp in the hypothalamus, a protein potentially involved in mitochondrial and neuroimmunological regulations of synaptic plasticity. Its presence in the preoptic area responsible for maternal behaviors and also in the paraventricular hypothalamic and arcuate nuclei regulating hormonal levels suggests that the same proteins may be involved in different aspects of maternal adaptations. The conclusions of the present work contribute to establishing the molecular alterations that determine different maternal adaptations in the brain. Since maternal changes are models of neuronal plasticity in all social interactions, the reported results can affect a wide field of molecular and behavioral neuroscience.

Plasticity in gastrointestinal morphology and enzyme activity in lactating striped hamsters (Cricetulus barabensis)

In small mammals marked phenotypic plasticity of digestive physiology has been shown to make it easier to cope with the energetically stressful periods, such as lactation. It has been proposed that the capacity of the gut to digest and absorb food is not the factor limiting to sustained energy intake (SusEI) during peak lactation. In this study, plasticity in energy intake and gastrointestinal morphology was examined in striped hamsters at different stages of reproduction and raising litters of different sizes. Mechanisms associated with digestive enzymes and neuroendocrine hormones underpinning the plasticity were also examined. The females significantly increased energy intake, digestibility, masses of digestive tracts and activity of stomach pepsin and maltase, sucrase and aminopeptidase of small intestine in peak lactation compared to the non-productive and post-lactating periods. Further, the females raising large litters significantly increased energy intake, digestibility, gastrointestinal mass and activity of digestive enzymes, and weaned heavier offspring compared with those nursing small and medium litters, indicating that the significant plasticity of digestive physiology increased reproductive performance. The agouti-related protein (AgRP) mRNA expression in the hypothalamus was up-regulated significantly in the females raising large litters relative to those raising small litters. Serum leptin levels, hypothalamus neuropeptide Y (NPY), or anorexigenic neuropeptides (pro-opiomelanocortin / cocaine- and amphetamine-regulated transcript, POMC / CART) mRNA expression did not differ among the females raising small, medium and large litters, indicating that leptin levels in lactation might only reflect a state of energy balance rather than being the prime driver of hyperphagia. Some hypothalamic neuropeptides, such as NPY, POMC and CART, would be involved in the limits to the SusEI during lactation.

Neuroendocrine regulation of lactation and milk production

Prolactin (PRL) released from lactotrophs of the anterior pituitary gland in response to the suckling by the offspring is the major hormonal signal responsible for stimulation of milk synthesis in the mammary glands. PRL secretion is under chronic inhibition exerted by dopamine (DA), which is released from neurons of the arcuate nucleus of the hypothalamus into the hypophyseal portal vasculature. Suckling by the young activates ascending systems that decrease the release of DA from this system, resulting in enhanced responsiveness to one or more PRL-releasing hormones, such as thyrotropin-releasing hormone. The neuropeptide oxytocin (OT), synthesized in magnocellular neurons of the hypothalamic supraoptic, paraventricular, and several accessory nuclei, is responsible for contracting the myoepithelial cells of the mammary gland to produce milk ejection. Electrophysiological recordings demonstrate that shortly before each milk ejection, the entire neurosecretory OT population fires a synchronized burst of action potentials (the milk ejection burst), resulting in release of OT from nerve terminals in the neurohypophysis. Both of these neuroendocrine systems undergo alterations in late gestation that prepare them for the secretory demands of lactation, and that reduce their responsiveness to stimuli other than suckling, especially physical stressors. The demands of milk synthesis and release produce a condition of negative energy balance in the suckled mother, and, in laboratory rodents, are accompanied by a dramatic hyperphagia. The reduction in secretion of the adipocyte hormone, leptin, a hallmark of negative energy balance, may be an important endocrine signal to hypothalamic systems that integrate lactation-associated food intake with neuroendocrine systems.

Stress-activated afferent inputs into the anterior parvicellular part of the paraventricular nucleus of the hypothalamus: Insights into urocortin 3 neuron activation

Urocortin 3 (Ucn 3) is a member of the corticotropin-releasing factor family, which plays a major role in coordinating stress responses. Ucn 3 neurons in the anterior parvicellular part of the paraventricular nucleus of the hypothalamus (PVHap) provide prominent input into the ventromedial nucleus of the hypothalamus (VMH), a well known satiety center, where Ucn 3 acts to suppress feeding and modulate blood glucose levels. In the present study, we first determined that Ucn 3 expression in the PVHap was stimulated by acute restraint stress. We then performed retrograde tracing with fluorogold (FG) combined with immunohistochemistry for Fos as a marker for neuronal activation after restraint stress to determine the stress-activated afferent inputs into the PVHap. Substantial numbers of FG/Fos double labeled cells were found in the bed nucleus of the stria terminalis, the lateral septal nucleus, the medial amygdala, and a number of nuclei in the hypothalamus including the VMH, the arcuate nucleus, the posterior nucleus, and the ventral premammillary nucleus. In the brainstem, FG/Fos positive cells were found in the periaqueductal gray, the nucleus of the solitary tract, and the ventrolateral medulla. In conclusion, the present study showed that acute stress rapidly stimulates Ucn 3 expression in the PVHap and identified specific stress-sensitive brain areas that project to the PVHap. These areas are potentially important in mediating the stress-induced activation of Ucn 3 neurons in the PVHap.

Sexual differentiation of the brain requires perinatal kisspeptin-GnRH neuron signaling

Sex differences in brain function underlie robust differences between males and females in both normal and disease states. Although alternative mechanisms exist, sexual differentiation of the male mammalian brain is initiated predominantly by testosterone secreted by the testes during the perinatal period. Despite considerable advances in understanding how testosterone and its metabolite estradiol sexually differentiate the brain, little is known about the mechanism that generates the male-specific perinatal testosterone surge. In mice, we show that a male-specific activation of GnRH neurons occurs 0-2 h following birth and that this correlates with the male-specific surge of testosterone occurring up to 5 h after birth. The necessity of GnRH signaling for the sexually differentiating effects of the perinatal testosterone surge was demonstrated by the persistence of female-like brain characteristics in adult male, GnRH receptor knock-out mice. Kisspeptin neurons have recently been identified to be potent, direct activators of GnRH neurons. We demonstrate that a population of kisspeptin neurons appears in the preoptic area of only the male between E19 and P1. The importance of kisspeptin inputs to GnRH neurons for the process of sexual differentiation was demonstrated by the lack of a normal neonatal testosterone surge, and disordered brain sexual differentiation of male mice in which the kisspeptin receptor was deleted selectively from GnRH neurons. These observations demonstrate the necessity of perinatal GnRH signaling for driving brain sexual differentiation and indicate that kisspeptin inputs to GnRH neurons are essential for this process to occur.

Immunohistochemical mapping of neuropeptide Y in the tree shrew brain

Day-active tree shrews are promising animals as research models for a variety of human disorders. Neuropeptide Y (NPY) modulates many behaviors in vertebrates. Here we examined the distribution of NPY in the brain of tree shrews (Tupaia belangeri chinensis) using immunohistochemical techniques. The differential distribution of NPY-immunoreactive (-ir) cells and fibers were observed in the rhinencephalon, telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon of tree shrews. Most NPY-ir cells were multipolar or bipolar in shape with triangular, fusiform, and/or globular perikarya. The densest cluster of NPY-ir cells were found in the mitral cell layer of the main olfactory bulb (MOB), arcuate nucleus of the hypothalamus, and pretectal nucleus of the thalamus. The MOB presented a unique pattern of NPY immunoreactivity. Laminar distribution of NPY-ir cells was observed in the MOB, neocortex, and hippocampus. Compared to rats, the tree shrews exhibited a particularly robust and widespread distribution of NPY-ir cells in the MOB, bed nucleus of the stria terminalis, and amygdala as well as the ventral lateral geniculate nucleus and pretectal nucleus of the thalamus. By contrast, a low density of neurons were scattered in the striatum, neocortex, polymorph cell layer of the dentate gyrus, superior colliculus, inferior colliculus, and dorsal tegmental nucleus. These findings provide the first detailed mapping of NPY immunoreactivity in the tree shrew brain and demonstrate species differences in the distribution of this neuropeptide, providing an anatomical basis for the participation of the NPY system in the regulation of numerous physiological and behavioral processes.

Thalamic neuropeptide mediating the effects of nursing on lactation and maternal motivation

Nursing has important physiological and psychological consequences on mothers during the postpartum period. Tuberoinfundibular peptide of 39 residues (TIP39) may contribute to its effects on prolactin release and maternal motivation. Since TIP39-containing fibers and the receptor for TIP39, the parathyroid hormone 2 receptor (PTH2 receptor) are abundant in the arcuate nucleus and the medial preoptic area, we antagonized TIP39 action locally to reveal its actions. Mediobasal hypothalamic injection of a virus encoding an antagonist of the PTH2 receptor markedly decreased basal serum prolactin levels and the suckling-induced prolactin release. In contrast, injecting this virus into the preoptic area had no effect on prolactin levels, but did dampen maternal motivation, judged by reduced time in a pup-associated cage during a place preference test. In support of an effect of TIP39 on maternal motivation, we observed that TIP39 containing fibers and terminals had the same distribution within the preoptic area as neurons expressing Fos in response to suckling. Furthermore, TIP39 terminals closely apposed the plasma membrane of 82% of Fos-ir neurons. Retrograde tracer injected into the arcuate nucleus and the medial preoptic area labeled TIP39 neurons in the posterior intralaminar complex of the thalamus (PIL), indicating that these cells but not other groups of TIP39 neurons project to these hypothalamic regions. We also found that TIP39 mRNA levels in the PIL markedly increased around parturition and remained elevated throughout the lactation period, demonstrating the availability of the peptide in postpartum mothers. Furthermore, suckling, but not pup exposure without physical contact, increased Fos expression by PIL TIP39 neurons. These results indicate that suckling activates TIP39 neurons in the PIL that affect prolactin release and maternal motivation via projections to the arcuate nucleus and the preoptic area, respectively.

Paralemniscal TIP39 is induced in rat dams and may participate in maternal functions

The paralemniscal area, situated between the pontine reticular formation and the lateral lemniscus in the pontomesencephalic tegmentum contains some tuberoinfundibular peptide of 39 residues (TIP39)-expressing neurons. In the present study, we measured a 4 times increase in the level of TIP39 mRNA in the paralemniscal area of lactating mothers as opposed to nulliparous females and mothers deprived of pups using real-time RT-PCR. In situ hybridization histochemistry and immunolabeling demonstrated that the induction of TIP39 in mothers takes place within the medial paralemniscal nucleus, a cytoarchitectonically distinct part of the paralemniscal area, and that the increase in TIP39 mRNA levels translates into elevated peptide levels in dams. The paralemniscal area has been implicated in maternal control as well as in pain perception. To establish the function of induced TIP39, we investigated the activation of TIP39 neurons in response to pup exposure as maternal, and formalin injection as noxious stimulus. Both stimuli elicited c-fos expression in the paralemniscal area. Subsequent double labeling demonstrated that 95% of neurons expressing Fos in response to pup exposure also contained TIP39 immunoreactivity and 91% of TIP39 neurons showed c-fos activation by pup exposure. In contrast, formalin-induced Fos does not co-localize with TIP39. Instead, most formalin-activated neurons are situated medial to the TIP39 cell group. Our data indicate that paralemniscal neurons may be involved in the processing of maternal and nociceptive information. However, two different groups of paralemniscal neurons participate in the two functions. In particular, TIP39 neurons may participate in the control of maternal functions.

Hunger states switch a flip-flop memory circuit via a synaptic AMPK-dependent positive feedback loop

Synaptic plasticity in response to changes in physiologic state is coordinated by hormonal signals across multiple neuronal cell types. Here, we combine cell-type-specific electrophysiological, pharmacological, and optogenetic techniques to dissect neural circuits and molecular pathways controlling synaptic plasticity onto AGRP neurons, a population that regulates feeding. We find that food deprivation elevates excitatory synaptic input, which is mediated by a presynaptic positive feedback loop involving AMP-activated protein kinase. Potentiation of glutamate release was triggered by the orexigenic hormone ghrelin and exhibited hysteresis, persisting for hours after ghrelin removal. Persistent activity was reversed by the anorexigenic hormone leptin, and optogenetic photostimulation demonstrated involvement of opioid release from POMC neurons. Based on these experiments, we propose a memory storage device for physiological state constructed from bistable synapses that are flipped between two sustained activity states by transient exposure to hormones signaling energy levels.

Identification of urocortin 3 afferent projection to the ventromedial nucleus of the hypothalamus in rat brain

Urocortin 3 (Ucn 3) is a corticotrophin-releasing factor related neuropeptide highly expressed in the brain. Ucn 3 nerve fibers heavily innervate the hypothalamic ventromedial nucleus (VMH), and Ucn 3 injection into the VMH suppresses feeding. Currently, the origin of the Ucn 3 afferent input into the VMH is unknown. In the present study, anatomical tracing shows that the major Ucn 3 afferent input to the VMH resides in the anterior parvicellular part of the paraventricular nucleus of the hypothalamus (PVHap) and the adjacent posterior part of the bed nucleus of stria terminalis (pBNST). VMH also receives moderate Ucn 3 input from the medial amygdala. Ucn 3 neurons located immediately caudal to the PVHap/pBNST in the rostral perifornical hypothalamic area (rPFH) provide only minimal input. The paucity of rPFH-VMH Ucn 3 projection is consistent with the finding that only Ucn 3 neurons in the rPFH co-expressed enkephalin (Enk), and Ucn 3/Enk double-labeled nerve fibers and terminals were observed predominately in the lateral septum (LS), whereas only a few double-labeled fibers were found in other brain areas including the VMH. Furthermore, retrograde tracing demonstrates that Ucn 3 neurons in the rPFH project to the LS. In conclusion, the present study determines that the major Ucn 3 afferent into the VMH originates from the PVHap/pBNST. Moreover, anatomical heterogeneity is observed in the hypothalamic Ucn 3 neuron population as the rostral part (PVHap/pBNST) of the population projects to the VMH and the caudal part (rPFH) co-localizes with Enk and provides major afferent input to the LS.

Projections of arcuate nucleus and rostral periventricular kisspeptin neurons in the adult female mouse brain

The important role of kisspeptin neurons in the regulation of GnRH neuron activity is now well accepted. However, the ways in which kisspeptin neurons located in the arcuate nucleus (ARN) and rostral periventricular area of the third ventricle (RP3V) control GnRH neurons are poorly understood. The present study used anterograde and retrograde tracing techniques to establish the neuronal projection patterns of kisspeptin cell populations in the female mouse brain. Anterograde tracing studies revealed that kisspeptin neurons in the ARN innervated a wide number of hypothalamic and associated limbic region nuclei, whereas RP3V kisspeptin neurons projected to a smaller number of mostly medially located hypothalamic nuclei. Retrograde tracing confirmed a major projection of RP3V kisspeptin neurons to the ARN and showed that kisspeptin neurons located in the rostral half of the ARN projected to the rostral preoptic area. Peripheral administration of Fluorogold was found to label the majority of GnRH neurons but no kisspeptin neurons. Together, these studies highlight the complexity of the brain kisspeptin neuronal system and indicate that both ARN and RP3V kisspeptin neurons participate in a variety of limbic functions. In relation to the GnRH neuronal network, these investigations demonstrate that, alongside the RP3V kisspeptin cells, rostral ARN kisspeptin neurons may also project to GnRH neuron cell bodies. However, no kisspeptin neurons innervate GnRH nerve terminals in the external layer of the median eminence. These studies provide a neuroanatomical framework for the further elucidation of the functions of the ARN and RP3V kisspeptin neuron populations.

Limits to sustained energy intake. XIII. Recent progress and future perspectives

Several theories have been proposed to explain limits on the maximum rate at which animals can ingest and expend energy. These limits are likely to be intrinsic to the animal, and potentially include the capacity of the alimentary tract to assimilate energy – the ‘central limitation’ hypothesis. Experimental evidence from lactating mice exposed to different ambient temperatures allows us to reject this and similar ideas. Two alternative ideas have been proposed. The ‘peripheral limitation’ hypothesis suggests that the maximal sustained energy intake reflects the summed demands of individual tissues, which have their own intrinsic limitations on capacity. In contrast, the ‘heat dissipation limit’ (HDL) theory suggests that animals are constrained by the maximal capacity to dissipate body heat. Abundant evidence in domesticated livestock supports the HDL theory, but data from smaller mammals are less conclusive. Here, we develop a novel framework showing how the HDL and peripheral limitations are likely to be important in all animals, but to different extents. The HDL theory makes a number of predictions – in particular that there is no fixed limit on sustained energy expenditure as a multiple of basal metabolic rate, but rather that the maximum sustained scope is positively correlated with the capacity to dissipate heat.

Beyond Leptin: Emerging Candidates for the Integration of Metabolic and Reproductive Function during Negative Energy Balance

Reproductive status is tightly coupled to metabolic state in females, and ovarian cycling in mammals is halted when energy output exceeds energy input, a metabolic condition known as negative energy balance. This inhibition of reproductive function during negative energy balance occurs due to suppression of gonadotropin-releasing hormone (GnRH) release in the hypothalamus. The GnRH secretagogue kisspeptin is also inhibited during negative energy balance, indicating that inhibition of reproductive neuroendocrine circuits may occur upstream of GnRH itself. Understanding the metabolic signals responsible for the inhibition of reproductive pathways has been a compelling research focus for many years. A predominant theory in the field is that the status of energy balance is conveyed to reproductive neuroendocrine circuits via the adipocyte hormone leptin. Leptin is stimulatory for GnRH release and lower levels of leptin during negative energy balance are believed to result in decreased stimulatory drive for GnRH cells. However, recent evidence found that restoring leptin to physiological levels did not restore GnRH function in three different models of negative energy balance. This suggests that although leptin may be an important permissive signal for reproductive function as indicated by many years of research, factors other than leptin must critically contribute to negative energy balance-induced reproductive inhibition. This review will focus on emerging candidates for the integration of metabolic status and reproductive function during negative energy balance.

Characterisation of arcuate nucleus kisspeptin/neurokinin B neuronal projections and regulation during lactation in the rat

Lactation results in negative energy balance in the rat leading to decreased gonadotrophin-releasing hormone (GnRH) release and anoestrus. Inhibited GnRH release may be a result of decreased stimulatory tone from neuropeptides critical for GnRH neuronal activity, such as kisspeptin (Kiss1) and neurokinin B (NKB). The present study aimed to identify neuronal projections from the colocalised population of Kiss1/NKB cells in the arcuate nucleus (ARH) using double-label immunohistochemistry to determine where this population may directly regulate GnRH neuronal activity. Additionally, the present study further examined lactation-induced changes in the Kiss1 system that could play a role in decreased GnRH release. The colocalised ARH Kiss1/NKB fibres projected primarily to the internal zone of the median eminence (ME) where they were in close proximity to GnRH fibres; however, few Kiss1/NKB fibres from the ARH were seen at the level of GnRH neurones in the preoptic area (POA). Arcuate Kiss1/NKB peptide levels were decreased during lactation consistent with previous mRNA data. Surprisingly, anteroventral periventricular (AVPV) Kiss1 peptide levels were increased, whereas Kiss1 mRNA levels were decreased during lactation, suggesting active inhibition of peptide release. These findings indicate ARH Kiss1/NKB and AVPV Kiss1 appear to be inhibited during lactation, which may contribute to decreased GnRH release and subsequent reproductive dysfunction. Furthermore, the absence of a strong ARH Kiss1/NKB projection to the POA suggests regulation of GnRH by this population occurs primarily at the ME level via local projections.

The neuroendocrine basis of lactation-induced suppression of GnRH: role of kisspeptin and leptin

Lactation is an important physiological model of the integration of energy balance and reproduction, as it involves activation of potent appetitive neuropeptide systems coupled to a profound inhibition of pulsatile GnRH/LH secretion. There are multiple systems that contribute to the chronic hyperphagia of lactation: 1) suppression of the metabolic hormones, leptin and insulin, 2) activation of hypothalamic orexigenic neuropeptide systems NPY, AGRP, orexin (OX) and melanin concentrating hormone (MCH), 3) special induction of NPY expression in the dorsomedial hypothalamus, and 4) suppression of anorexigenic systems POMC and CART. These changes ensure adequate energy intake to meet the metabolic needs of milk production. There is significant overlap in all of the systems that regulate food intake with the regulation of GnRH, suggesting there could be several redundant factors acting to suppress GnRH/LH during lactation. In addition to an overall increase in inhibitory tone acting directly on GnRH cell bodies that is brought about by increases in orexigenic systems, there are also effects at the ARH to disrupt Kiss1/neurokinin B/dynorphin neuronal function through inhibition of Kiss1 and NKB. These changes could lead to an increase in inhibitory auto-regulation of the Kiss1 neurons and a possible disruption of pulsatile GnRH release. While the low levels of leptin and insulin contribute to the changes in ARH appetitive systems, they do not appear to contribute to the suppression of ARH Kiss1 or NKB. The inhibition of Kiss1 may be the key factor in the suppression of GnRH during lactation, although the mechanisms responsible for its inhibition are unknown.

A direct neuronal connection between the subparafascicular and ventrolateral arcuate nuclei in non-lactating female rats. Could this pathway play a role in the suckling-induced prolactin release?

The neuronal pathways, through which prolactin secretion is regulated during lactation, have still not been fully explored. Studies indicate that the suckling stimulus travels through the spinal cord, the brain stem, and then reaches the hypothalamus. The focus of this present experiment is to further explore the neuronal connections between the brain stem and the arcuate nucleus that may be involved in suckling-induced prolactin release. Ante- and retrograde tracing techniques were used. To chemically characterize the explored neurons neuropeptide immunohistochemistry was applied. Previous studies have indicated that the peripeduncular nucleus is a relay of the suckling stimulus in the midbrain, conveying the information to the hypothalamus. In our experiments, we have found an additional cell group in the subparafascicular parvocellular nucleus located just behind the posterior thalamus that projects to the arcuate neurons. The injection of the retrograde tracer into the ventrolateral part of the arcuate nucleus labeled cells in the lateral subdivision of the subparafascicular parvocellular nucleus. Anterograde tracing from the subparafascicular parvocellular nucleus resulted in fiber labeling in the arcuate nucleus in close apposition with dynorphin immunopositive neurons. Double labeling revealed that a subpopulations of the subparafascicular parvocellular neurons projecting to the arcuate nucleus contained tuberoinfundibular peptide of 39 residues or calcitonin gene-related peptide. The presented findings suggest that the ascending fibers from the subparafascicular parvocellular nucleus might be in the pathway involved in the suckling-induced prolactin release.

Activating mu-opioid receptors in the lateral parabrachial nucleus increases c-Fos expression in forebrain areas associated with caloric regulation, reward and cognition

The pontine parabrachial nucleus (PBN) has been implicated in the modulation of ingestion and contains high levels of mu-opioid receptors (MOPRs). In previous work, stimulating MOPRs by infusing the highly selective MOPR agonist [d-Ala2, N-Me-Phe4, Gly5-ol]enkephalin (DAMGO) into the lateral parabrachial region (LPBN) increased food intake. The highly selective MOPR antagonist d-Phe-Cys-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) prevented the hyperphagic action of DAMGO. The present experiments aimed to analyze both the pattern of neural activation and the underlying cellular processes associated with MOPR activation in the LPBN. Male Sprague-Dawley rats received a unilateral microinfusion of a nearly maximal hyperphagic dose of DAMGO into the LPBN. We then determined the level of c-Fos immunoreactivity in regions throughout the brain. MOPR activation in the LPBN increased c-Fos in the LPBN and in the nucleus accumbens, hypothalamic arcuate nucleus, paraventricular nucleus of the thalamus and hippocampus. Pretreatment with CTAP prevented the increase in c-Fos translation in each of these areas. CTAP also prevented the coupling of MOPRs to their G-proteins which was measured by [(35)S] guanosine 5'-O-[gamma-thio]triphosphate ([(35)S]GTPgammaS) autoradiography. Together, these data strongly suggest that increasing the coupling of MOPRs to their G-proteins in the LPBN disinhibits parabrachial neurons which subsequently leads to excitation of neurons in regions associated with caloric regulation, ingestive reward and cognitive processes in feeding.

The medial paralemniscal nucleus and its afferent neuronal connections in rat

Previously, we described a cell group expressing tuberoinfundibular peptide of 39 residues (TIP39) in the lateral pontomesencephalic tegmentum, and referred to it as the medial paralemniscal nucleus (MPL). To identify this nucleus further in rat, we have now characterized the MPL cytoarchitectonically on coronal, sagittal, and horizontal serial sections. Neurons in the MPL have a columnar arrangement distinct from adjacent areas. The MPL is bordered by the intermediate nucleus of the lateral lemniscus nucleus laterally, the oral pontine reticular formation medially, and the rubrospinal tract ventrally, whereas the A7 noradrenergic cell group is located immediately mediocaudal to the MPL. TIP39-immunoreactive neurons are distributed throughout the cytoarchitectonically defined MPL and constitute 75% of its neurons as assessed by double labeling of TIP39 with a fluorescent Nissl dye or NeuN. Furthermore, we investigated the neuronal inputs to the MPL by using the retrograde tracer cholera toxin B subunit. The MPL has afferent neuronal connections distinct from adjacent brain regions including major inputs from the auditory cortex, medial part of the medial geniculate body, superior colliculus, external and dorsal cortices of the inferior colliculus, periolivary area, lateral preoptic area, hypothalamic ventromedial nucleus, lateral and dorsal hypothalamic areas, subparafascicular and posterior intralaminar thalamic nuclei, periaqueductal gray, and cuneiform nucleus. In addition, injection of the anterograde tracer biotinylated dextran amine into the auditory cortex and the hypothalamic ventromedial nucleus confirmed projections from these areas to the distinct MPL. The afferent neuronal connections of the MPL suggest its involvement in auditory and reproductive functions.

Kisspeptin-GPR54 signaling is essential for preovulatory gonadotropin-releasing hormone neuron activation and the luteinizing hormone surge

Kisspeptin and its receptor GPR54 have recently been identified as key signaling partners in the neural control of fertility in animal models and humans. The gonadotropin-releasing hormone (GnRH) neurons represent the final output neurons of the neural network controlling fertility and are suspected to be the primary locus of kisspeptin-GPR54 signaling. Using mouse models, the present study addressed whether kisspeptin and GPR54 have a key role in the activation of GnRH neurons to generate the luteinizing hormone (LH) surge responsible for ovulation. Dual-label immunocytochemistry experiments showed that 40-60% of kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) expressed estrogen receptor alpha and progesterone receptors. Using an ovariectomized, gonadal steroid-replacement regimen, which reliably generates an LH surge, approximately 30% of RP3V kisspeptin neurons were found to express c-FOS in surging mice compared with 0% in nonsurging controls. A strong correlation was found between the percentage of c-FOS-positive kisspeptin neurons and the percentage of c-FOS-positive GnRH neurons. To evaluate whether kisspeptin and/or GPR54 were essential for GnRH neuron activation and the LH surge, Gpr54- and Kiss1-null mice were examined. Whereas wild-type littermates all exhibited LH surges and c-FOS in approximately 50% of their GnRH neurons, none of the mutant mice from either line showed an LH surge or any GnRH neurons with c-FOS. These observations provide the first evidence that kisspeptin-GPR54 signaling is essential for GnRH neuron activation that initiates ovulation. This broadens considerably the potential roles and therapeutic possibilities for kisspeptin and GPR54 in fertility regulation.

Neural connectivity in the mediobasal hypothalamus of the sheep brain

The ventromedial nucleus of the hypothalamus (VMN) and the arcuate nucleus (ARC) are two centres regulating energy balance and food intake, but inter-connectivity of these nuclei is not well defined in non-rodent species. In this study, we performed retrograde tracing and immunohistochemistry in the ovine brain with ewes receiving FluoroGold (FG) injections into either ARC or VMN for the mapping of retrogradely labelled cells. Strong reciprocal connections were found between the two regions. The distribution of the FG labelled neurons in other regions of the hypothalamus and brain stem was also mapped. Some of the cells projecting from ARC to VMN were immunopositive for neuropeptide Y, galanin, adrenocorticotropin (marker of pro-opiomelanocortin cells) or tyrosine hydroxylase (marker of dopaminergic cells). Melanin-concentrating hormone and orexin neurons in the lateral hypothalamic area were also found to provide input to the VMN and ARC. This observed interconnectivity between regions important for metabolic regulation and other neuroendocrine functions presumably allows coordinated functions. Input to both the ARC and VMN from other brain regions, such as brain stem cell groups, provides a further level of regulation. These data provide a substrate upon which further understanding of appetite regulation and neuroendocrine function can be derived in this species.

PreproThyrotropin-releasing hormone 178-199 affects tyrosine hydroxylase biosynthesis in hypothalamic neurons: a possible role for pituitary prolactin regulation

ProThyrotropin-releasing hormone (proTRH) is a prohormone widely distributed in many areas of the brain. After biosynthesis, proTRH is subjected to post-translational processing to generate TRH and seven non-TRH peptides. Among these non-TRH sequences, we found previously that preproTRH178-199 could regulate the secretion of prolactin in suckled rats by their pups. Dopamine (DA), the main regulator of prolactin secretion, is produced in dopaminergic tyrosine hydroxylase (TH)-positive neurons in the hypothalamic arcuate nucleus (ARC). In this study we investigated whether prolactin release during the estrous sexual cycle is regulated by preproTRH178-199 through its effect on DA neurons of the ARC. We observed that biotinylated preproTRH178-199 bound to neurons in the ARC; this was higher during proestrus than during diestrus. Binding of preproTRH178-199 to DA neurons was seen only during proestrus in the ARC. Using primary neuronal hypothalamic cultures we found that preproTRH178-199 peptide decreased TH levels in a dose-responsive manner, whereas intra-ARC administration of preproTRH178-199 induced a 20-fold increase in plasma prolactin levels. Together, these results suggest a potential role for preproTRH178-199 in regulating dopaminergic neurons involved in the inhibition of pituitary prolactin release.

Chronic fasting-induced changes of neuropeptide Y immunoreactivity in the lateral septum of intact and ovariectomized female rats

The effect of 40% food deprivation for 1 week on the immunohistochemically detectable amount of neuropeptide Y (NPY) was studied in the lateral septum (LS) of intact and ovariectomized (OVX) female rats. Animals were either fed ad libitum or 40% food-deprived. Densitometric analysis of immunostained material showed a significant decrease in NPY-immunoreactivity (NPY-IR) in OVX rats compared to the control group. Food deprivation increased the density of punctate NPY-IR profiles in both intact and OVX animals, however, the density in food-deprived OVX animals was increased compared to baseline but remained reduced compared to intact rats. Our study indicates that the lack of gonadal hormones - most likely estrogen - results in a decrease in the density of NPY-IR axonal fibers within the LS, while food deprivation induced considerable elevation in NPY density. Food restriction-induced changes in the density of NPY-containing neural elements suggest that the LS may play a crucial role in the regulation of food intake and energy balance, in concert with the relevant hypothalamic areas.

Definition of estrogen receptor pathway critical for estrogen positive feedback to gonadotropin-releasing hormone neurons and fertility

The mechanisms through which estrogen regulates gonadotropin-releasing hormone (GnRH) neurons to control mammalian ovulation are unknown. We found that estrogen positive feedback to generate the preovulatory gonadotropin surge was normal in estrogen receptor beta knockout (ERbeta) mutant mice, but absent in ERalpha mutant mice. An ERalpha-selective compound was sufficient to generate positive feedback in wild-type mice. As GnRH neurons do not express ERalpha, estrogen positive feedback upon GnRH neurons must be indirect in nature. To establish the cell type responsible, we generated a neuron-specific ERalpha mutant mouse line. These mice failed to exhibit estrogen positive feedback, demonstrating that neurons expressing ERalpha are critical. We then used a GnRH neuron-specific Pseudorabies virus (PRV) tracing approach to show that the ERalpha-expressing neurons innervating GnRH neurons are located within rostral periventricular regions of the hypothalamus. These studies demonstrate that ovulation is driven by estrogen actions upon ERalpha-expressing neuronal afferents to GnRH neurons.

Ontogeny of the projections from the anteroventral periventricular nucleus of the hypothalamus in the female rat

Neurons in the anteroventral periventricular nucleus of the hypothalamus (AVPV) mediate a variety of autonomic functions. In adults they primarily innervate neuroendocrine nuclei in the periventricular zone of the hypothalamus, including the paraventricular and arcuate nuclei (PVH, ARH). Ascending projections from the AVPV also provide inputs to the ventrolateral septum (LSv) and the principal division of the bed nuclei of the stria terminalis (BSTp). Consistent with a role in regulating preovulatory luteinizing hormone secretion, rostral projections from the AVPV contact gonadotropin-releasing hormone (GnRH) neurons surrounding the vascular organ of the lamina terminalis (OVLT). To study the development of these pathways, we placed implants of the lipophilic tracers DiI and CMDiI into the AVPV of female rats ranging in age from embryonic day 19 (E19) through adulthood. The earliest projections targeted a population of GnRH neurons, with apparent contacts from labeled fibers observed as early as E19. These connections appeared to be fully developed before birth, as similar numbers of appositions from AVPV projections onto the GnRH-immunoreactive cells were observed at all ages examined. Caudal projections were delayed relative to projections to the OVLT. Labeled AVPV fibers reached the PVH during the first postnatal week, and fibers targeting the BSTp and LSv were not observed until the second and third postnatal weeks, respectively. Labeled AVPV fibers were not seen in the ARH of animals at any age. Our results demonstrate that projections from the AVPV develop with both spatial and temporal specificity, innervating each target with a unique developmental profile.

Deoxyribonucleic acid microarray analysis of gene expression pattern in the arcuate nucleus/ventromedial nucleus of hypothalamus during lactation

Lactation is characterized by extreme hyperphagia and negative energy balance resulting from a large energy drain due to milk production and by a suppression of cyclic ovarian function. Increases in neuropeptide Y and agouti-related protein and a decrease in proopiomelanocortin expression in the arcuate nucleus of hypothalamus (ARH) may contribute to the hyperphagia to maintain energy balance and to the suppression of LH secretion associated with lactation. However, little is known about the full extent of neuroendocrine changes in the ARH that may contribute to the various adaptations occurring during lactation. To address this issue, we used Affymetrix microarray to acquire a reliable profile of the lactation-induced transcriptional changes in micropunches containing the ARH and a portion of the ventromedial nucleus of the hypothalamus. Using high stringency criteria, 12 genes were identified as being differentially regulated during lactation, and an additional 10 genes and three transcribed sequences were identified using moderate stringency criteria. Changes in neuropeptide Y, enkephalin, tyrosine hydroxylase, and dynorphin, genes previously shown to be differentially regulated during lactation, provide validation for the microarray analysis. New genes identified as being differentially expressed include those related to neurotransmission, growth factors, signal transduction, and structure remodeling. These data identify new genes in ARH/ventromedial nucleus of the hypothalamus that may play an important role in the adaptations of lactation related to hyperphagia, milk production, and the suppression of cyclic reproductive function and may contribute to elucidating a framework for integrating changes in energy intake with the regulation of reproductive function during lactation.

Limits to sustained energy intake IX: a review of hypotheses

Several lines of evidence indicate that animals in the wild may be limited in their maximal rates of energy intake by their intrinsic physiology rather than food availability. Understanding the limits to sustained energy intake is important because this defines an envelope within which animals must trade-off competing activities. In the first part of this review, we consider the initial ideas that propelled this area and experimental evidence connected with them. An early conceptual advance in this field was the idea that energy intake could be centrally limited by aspects of the digestive process, or peripherally limited at the sites of energy utilisation. A model system that has been widely employed to explore these ideas is lactation in small rodents. Initial studies in the late 1980s indicated that energy intake might be centrally limited, but work by Hammond and colleagues in the 1990s suggested that it was more likely that the limits were imposed by capacity of the mammary glands, and other works tended to support this view. This consensus, however, was undermined by studies that showed milk production was higher in mice at low temperatures, suggesting that the capacity of the mammary gland is not a limiting factor. In the second part of the review we consider some additional hypotheses that might explain these conflicting data. These include the heat dissipation limits hypothesis, the seasonal investment hypothesis and the saturated neural control hypothesis. Current evidence with respect to these hypotheses is also reviewed. The limited evidence presently available does not unambiguously support any one of them.

Co-regulation of female sexual behavior and pregnancy induction: an exploratory synthesis

This paper will review both new and old data that address the question of whether brain mechanisms involved in reproductive function act in a coordinated way to control female sexual behavior and the induction of pregnancy/pseudopregnancy (P/PSP) by vaginocervical stimulation. Although it is clear that female sexual behavior, including pacing behavior, is important for induction of P/PSP, there has been no concerted effort to examine whether or how common mechanisms may control both functions. Because initiation of P/PSP requires that the female receive vaginocervical stimulation, central mechanisms controlling P/PSP may be modulated by or interactive with those that control female sexual behavior. This paper presents a synthesis of the literature and recent data from our lab for the purpose of examining whether there are interactions between behavioral and neuroendocrine mechanisms which reciprocally influence both reproductive functions.

Properties of native P2X receptors in large multipolar neurons dissociated from rat hypothalamic arcuate nucleus

ATP, the ligand of P2X receptors, is a candidate of neurotransmitter or co-transmitter in the peripheral and the central nervous systems. Anatomical studies have revealed the wide distribution of P2X receptors in the brain. So far, P2X-mediated small synaptic responses have been recorded in some brain regions. To determine the physiological significance of postsynaptic ATP receptors in the brain, we have investigated the P2X responses in rat dissociated hypothalamic arcuate neurons by using the patch-clamp technique. ATP evoked inward currents in a concentration-dependent manner (EC(50)=42 microM) at a holding potential of -70 mV. The current-voltage relationship showed a marked inward rectification starting around -10 mV. Although neither 300 microM alphabeta-methylene-ATP nor 300 microM betagamma-methylene-ATP induced any currents, 100 microM ATPgammaS and 100 microM 2-methylthio-ATP evoked inward currents of which amplitude was about 60% of the control currents evoked by 100 microM ATP. PPADS, one of P2 receptor antagonists, inhibited the ATP-evoked currents in a time- and a concentration-dependent manners (IC(50)=19 microM at 2 min). Permeant Ca(2+) inhibited the ATP-evoked currents in the range of millimolars (IC(50)=7 mM); however, Cd(2+) (1-300 microM), a broad cation channel blocker, facilitated the currents with slow off-response. Zn(2+) in the range of 1-100 microM facilitated the currents whereas Zn(2+) at the concentrations over 100 microM inhibited the currents. These observations suggest that functional P2X receptors are expressed in the hypothalamic arcuate nucleus. The most likely subunit combinations of the P2X receptors are P2X(2)-homomultimer and P2X(2)/P2X(6)-heteromultimer.

Suckling-induced activation of neuronal input to the dorsomedial nucleus of the hypothalamus: possible candidates for mediating the activation of DMH neuropeptide Y neurons during lactation

Activation of the neuropeptide Y (NPY) neuronal system in the dorsomedial nucleus of the hypothalamus (DMH) during lactation in the rat is in part due to neural impulses arising from the suckling stimulus. However, the afferent neuronal input to the DMH that is activated during lactation and is responsible for activation of NPY neurons is currently unknown. Previously, using cFos as a marker for neuronal activation, we identified several brain areas in the lactating animals that were activated by the suckling stimulus. Thus, the objective of the present study was to determine if any of these suckling activated areas project directly to the DMH. The retrograde tracer, fluorogold (FG), was injected into the DMH on day 4 postpartum. FG-injected lactating rats were then deprived of their eight-pup litters on day 9 postpartum, and 48 h later, the pups were returned to the females to reinitiate the suckling stimulus for 90 min and induce cFos expression. The animals were then perfused and the brains were subjected to double-label immunohistochemistry to visualize both FG- and cFos-positive cells. Substantial numbers of FG/cFos double-labeled cells were found in forebrain regions, including the preoptic area, lateral septal nucleus, ventral subiculum, and supramammillary nucleus, and in brainstem regions, including the lateral parabrachial nucleus, periaqeductal gray, and ventrolateral medulla. In conclusion, these areas are potentially important candidates for mediating the activation of the NPY neuronal system in the DMH during lactation.

Expression and distribution of tuberoinfundibular peptide of 39 residues in the rat central nervous system

Tuberoinfundibular peptide of 39 residues (TIP39) has been recently purified and identified as a selective ligand for the parathyroid hormone 2 receptor. As a next step toward understanding its functions, we report the expression and distribution of TIP39 in the rat central nervous system. In situ hybridization histochemistry and immunocytochemistry revealed TIP39-containing cell bodies in three distinct areas. The major one comprises the subparafascicular area posterior through the intralaminar nucleus of the thalamus; a second is the medial paralemniscal nucleus at the pontomesencephalic junction; and a third is in the dorsal and dorsolateral hypothalamic areas, which contained a few, scattered cell bodies. We found, in contrast to the highly restricted localization of TIP39-containing cell bodies, a much more widespread localization of TIP39-containing fibers. The highest density of fibers was observed in limbic areas such as the septum, the amygdala, and the bed nucleus of the stria terminalis; in areas involved in endocrine regulation, such as the hypothalamic dorsomedial, paraventricular, periventricular, and arcuate nuclei; in auditory areas, such as the ectorhinal and temporal cortices, inferior colliculus, medial geniculate body, and some of the nuclei of the superior olivary complex; and in the dorsolateral funiculus of the spinal cord. The localization of TIP39-containing nuclei and fibers provides an anatomical basis for previously demonstrated endocrine and nociceptive effects of TIP39 and suggests additional functions for TIP39, one apparent candidate being the regulation of auditory information processing.

Integration of the regulation of reproductive function and energy balance: lactation as a model

Lactation is a physiological model for studying how the hypothalamus integrates peripheral signals, such as sensory signals (suckling stimulus) and those denoting energy balance (leptin), to alter hypothalamic function regulating food intake/energy balance and reproduction. The characteristics of food intake/energy balance during lactation are extreme hyperphagia, coupled with negative energy balance. The arcuate nucleus Neuropeptide Y (ARH-NPY) system is activated by: (1) brainstem projections specifically activated by the suckling stimulus, and (2) the decrease in leptin in response to the metabolic drain of milk production. NPY neurons from the ARH make direct contact with GnRH neurons and with CRH neurons in the PVH. NPY neurons also make contact with orexin and MCH neurons in the LHA, which, in turn, make contacts with GnRH neurons. Thus, the ARH-NPY system provides a neuroanatomical framework by which to integrate changes in food intake/energy with the regulation of cyclic reproductive function.

Multiple neural systems controlling food intake and body weight

Discovery of the leptin receptor and its downstream peptidergic pathways has reconfirmed the crucial role of the hypothalamus in the regulation of food intake and energy balance. Strategically located in the midst of the mammalian neuraxis, the hypothalamus receives at least three distinct types of relevant information via direct or indirect neural connections as well as hormone receptors and substrate sensors bestowed on hypothalamic neurons. First, the medial and to a lesser extent the lateral hypothalamus receive a rich mix of information pertaining to the internal state of relative energy repletion/depletion. Second, specific hypothalamic nuclei receive information about the behavioral state, such as diurnal clock, physical activity-level, reproductive cycle, developmental stage, as well as imminent (e.g. fight and flight) and chronic (e.g. infection) stressors, that can potentially impact on short-term availability of fuels and long-term energy balance. Third, the hypothalamus, particularly its lateral aspects, receives information from areas in the forebrain involved in the acquisition, storage, and retrieval of sensory representations of the external food space and internal food experience, as well as from the executive forebrain involved in behavior selection and initiation. In addition, rich intrahypothalamic connections facilitate further distribution of incoming information to various hypothalamic nuclei. On the other hand, the hypothalamus has widespread neural projections to the same cortical areas it receives inputs, and many hypothalamic neurons are one synapse away from most endocrine systems and from both sympathetic and parasympathetic effector organs involved in the flux, storage, mobilization, and utilization of fuels. It is argued that processing within cortico-limbic areas and communication with hypothalamic areas are particularly important in human food intake control that is more and more guided by cognitive rather than metabolic aspects in the obesigenic environment of affluent societies. A distributed neural network for the control of food intake and energy balance consisting of a central processor and several parallel processing loops is hypothesized. Detailed neurochemical, anatomical, and functional analysis of reciprocal connections of the numerous peptidergic neuron populations in the hypothalamus with extrahypothalamic brain areas will be necessary to better understand what hypothalamus, forebrain, and brainstem tell each other and who is in charge under specific conditions of internal and external nutrient availability.

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

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

Hypothalamic and vagal neuropeptide circuitries regulating food intake

It has been recognized for some time that a number of different neuropeptides exert powerful effects on food intake. During the last few years, the neurocircuitry within which these peptides operate has also begun to be elucidated. Peptidergic feeding-regulatory neurones are found both in the hypothalamus and the brainstem, where they act as input stations for hormonal and gastrointestinal information, respectively. These cell populations both project to several other brain regions and interconnect extensively. The present review summarizes the neuroanatomy and connectivity of some prominent peptides involved in food intake control, including neuropeptide Y, melanocortin peptides, agouti gene-related protein, cocaine- and amphetamine-regulated transcript, orexin/hypocretin, melanin-concentrating hormone and cholecystokinin. Disturbances in the hypothalamic neuropeptide systems have been implicated in the phenotype of a genetic model of fatal hypophagia, the mouse anorexia (anx) mutation, which is also discussed.

Neural populations in the rat forebrain and brainstem activated by the suckling stimulus as demonstrated by cFos expression

During lactation in the rat, the suckling stimulus plays an important role in mediating alterations in hypothalamic neuroendocrine function associated with lactation. To provide the basis for understanding the neural circuitry that may transmit suckling-induced signals into the hypothalamus, the present study used the expression of the immediate-early gene product, cFos protein, as a marker for neuronal activation to identify neural populations in the brain of lactating female rats activated by the suckling stimulus. In addition, cFos expression induced by the exteroceptive sensory stimuli (olfactory, auditory, visual) associated with pup exposure alone was also determined. Thus, cFos patterns in response to the physical suckling stimulus, which would include exteroceptive sensory stimuli associated with pup exposure, were compared with the patterns induced in response to pup exposure alone, so that neuronal populations specifically activated by the suckling stimulus could be identified. After 90 min of suckling, several forebrain areas, including the lateral septum, medial preoptic area, periventricular preoptic area and supraoptic nucleus of hypothalamus, showed a significant increase in cFos expression, compared with non-suckled controls and pup exposure animals. In addition, in the bed nucleus of stria terminalis, the medial amygdala and several cortical areas, cFos-positive cells were found in both suckling and pup exposure animals. In the brainstem, the suckling stimulus induced a significant increase in cFos expression in the ventrolateral medulla, locus coeruleus, lateral parabrachial nucleus, lateral and ventrolateral portions of the caudal part of the periaqueductal gray, and caudal portion of the paralemniscal nucleus, compared with non-suckled controls and pup exposure animals. As expected, in several areas related with sensory input, such as reticular formation and pontine nucleus, cFos expression was found in both suckling and pup exposure animals. Moreover, when double-label immunocytochemistry was used to identify cFos- and catecholamine-positive neurons in the brainstem, it was found that catecholamine-positive neurons in the ventrolateral medulla and locus coeruleus showed a significant increase in cFos expression in response to suckling compared with non-resuckled and pup-exposure groups. Using cFos expression as a marker for neuronal activation, the present studies identified the neural populations in the brain that are activated by the suckling stimulus. By comparing the pattern of cFos expression observed in response to pup exposure alone or the suckling stimulus, the present studies differentiated the neural populations activated by the physical suckling stimulus from the populations activated by the exteroceptive sensory stimuli associated with pup exposure. These suckling-activated areas are likely candidates for playing an important role in transmitting the effects of the suckling stimulus into the hypothalamus to regulate neuroendocrine alterations associated with lactation.