Disruption of arcuate/paraventricular nucleus connections changes body energy balance and response to acute stress

Olfactory modulation of stress-response neural circuits

Stress responses, which are crucial for survival, are evolutionally conserved throughout the animal kingdom. The most common endocrine axis among stress responses is that triggered by corticotropin-releasing hormone neurons (CRHNs) in the hypothalamus. Signals of various stressors are detected by different sensory systems and relayed through individual neural circuits that converge on hypothalamic CRHNs to initiate common stress hormone responses. To investigate the neurocircuitry mechanisms underlying stress hormone responses induced by a variety of stressors, researchers have recently developed new approaches employing retrograde transsynaptic viral tracers, providing a wealth of information about various types of neural circuits that control the activity of CRHNs in response to stress stimuli. Here, we review earlier and more recent findings on the stress neurocircuits that converge on CRHNs, focusing particularly on olfactory systems that excite or suppress the activities of CRHNs and lead to the initiation of stress responses. Because smells are arguably the most important signals that enable animals to properly cope with environmental changes and survive, unveiling the regulatory mechanisms by which smells control stress responses would provide broad insight into how stress-related environmental cues are perceived in the animal brain.

Arcuate Nucleus-Dependent Regulation of Metabolism-Pathways to Obesity and Diabetes Mellitus

The central nervous system (CNS) receives information from afferent neurons, circulating hormones, and absorbed nutrients and integrates this information to orchestrate the actions of the neuroendocrine and autonomic nervous systems in maintaining systemic metabolic homeostasis. Particularly the arcuate nucleus of the hypothalamus (ARC) is of pivotal importance for primary sensing of adiposity signals, such as leptin and insulin, and circulating nutrients, such as glucose. Importantly, energy state-sensing neurons in the ARC not only regulate feeding but at the same time control multiple physiological functions, such as glucose homeostasis, blood pressure, and innate immune responses. These findings have defined them as master regulators, which adapt integrative physiology to the energy state of the organism. The disruption of this fine-tuned control leads to an imbalance between energy intake and expenditure as well as deregulation of peripheral metabolism. Improving our understanding of the cellular, molecular, and functional basis of this regulatory principle in the CNS could set the stage for developing novel therapeutic strategies for the treatment of obesity and metabolic syndrome. In this review, we summarize novel insights with a particular emphasis on ARC neurocircuitries regulating food intake and glucose homeostasis and sensing factors that inform the brain of the organismal energy status.

Serotonin, food intake, and obesity

The role of serotonin in food intake has been studied for decades. Food intake is mainly regulated by two brain circuitries: (i) the homeostatic circuitry, which matches energy intake to energy expenditure, and (ii) the hedonic circuitry, which is involved in rewarding and motivational aspects of energy consumption. In the homeostatic circuitry, serotonergic signaling contributes to the integration of metabolic signals that convey the body's energy status and facilitates the ability to suppress food intake when homeostatic needs have been met. In the hedonic circuitry, serotonergic signaling may reduce reward-related, motivational food consumption. In contrast, peripherally acting serotonin promotes energy absorption and storage. Disturbed serotonergic signaling is associated with obesity, emphasizing the importance to understand the role of serotonergic signaling in food intake. However, unraveling the serotonin-mediated regulation of food intake is complex, as the effects of serotonergic signaling in different brain regions depend on the regional expression of serotonin receptor subtypes and downstream effects via connections to other brain regions. We therefore provide an overview of the effects of serotonergic signaling in brain regions of the homeostatic and hedonic regulatory systems on food intake. Furthermore, we discuss the disturbances in serotonergic signaling in obesity and its potential therapeutic implications.

The reuniens and rhomboid nuclei of the thalamus: A crossroads for cognition-relevant information processing?

Over the past twenty years, the reuniens and rhomboid (ReRh) nuclei, which constitute the ventral midline thalamus, have received constantly growing attention. Since our first review article about the functional contributions of ReRh nuclei (Cassel et al., 2013), numerous (>80) important papers have extended anatomical knowledge, including at a developmental level, introduced new and very original electrophysiological insights on ReRh functions, and brought novel results on cognitive and non-cognitive implications of the ReRh. The current review will cover these recent articles, more on Re than on Rh, and their contribution will be approached according to their affiliation with work before 2013. These neuroanatomical, electrophysiological or behavioral findings appear coherent and point to the ReRh nuclei as two major components of a multistructural system supporting numerous cognitive (and non-cognitive) functions. They gate the flow of information, perhaps especially from the medial prefrontal cortex to the hippocampus and back, and coordinate activity and processing across these two (and possibly other) brain regions of major cognitive relevance.

Brain mechanisms of HPA axis regulation: neurocircuitry and feedback in context Richard Kvetnansky lecture

Regulation of stress reactivity is a fundamental priority of all organisms. Stress responses are critical for survival, yet can also cause physical and psychological damage. This review provides a synopsis of brain mechanisms designed to control physiological responses to stress, focusing primarily on glucocorticoid secretion via the hypothalamo-pituitary-adrenocortical (HPA) axis. The literature provides strong support for multi-faceted control of HPA axis responses, involving both direct and indirect actions at paraventricular nucleus (PVN) corticotropin releasing hormone neurons driving the secretory cascade. The PVN is directly excited by afferents from brainstem and hypothalamic circuits, likely relaying information on homeostatic challenge. Amygdala subnuclei drive HPA axis responses indirectly via disinhibition, mediated by GABAergic relays onto PVN-projecting neurons in the hypothalamus and bed nucleus of the stria terminalis (BST). Inhibition of stressor-evoked HPA axis responses is mediated by an elaborate network of glucocorticoid receptor (GR)-containing circuits, providing a distributed negative feedback signal that inhibits PVN neurons. Prefrontal and hippocampal neurons play a major role in HPA axis inhibition, again mediated by hypothalamic and BST GABAergic relays to the PVN. The complexity of the regulatory process suggests that information on stressors is integrated across functional disparate brain circuits prior to accessing the PVN, with regions such as the BST in prime position to relay contextual information provided by these sources into appropriate HPA activation. Dysregulation of the HPA in disease is likely a product of inappropriate checks and balances between excitatory and inhibitory inputs ultimately impacting PVN output.

C1q/TNF-related Protein 4 Induces Signal Transducer and Activator of Transcription 3 Pathway and Modulates Food Intake

C1q/TNF-related protein 4 (CTRP4) has been reported to decrease food intake and regulate energy homeostasis. However, its underlying mechanism and signaling pathway remain unknown. Using an adenovirus-mediated hypothalamic CTRP4 overexpression model, we investigated the impact of CTRP4 on food intake and signal transducer and activator of transcription 3 (STAT3) signaling pathway in normal chow-fed mice. Expressions of neuropeptides including proopiomelanocortin (POMC) and neuropeptide Y (NPY) were studied in hypothalamus by Western blot and immunochemistry. STAT3 and suppressor of cytokine signaling 3 (SOCS3) were determined by Western blot. STAT3 signaling pathway was also investigated in Neuro 2A (N2a) cells after CTRP4 overexpression intervention. We found that food intake decreased significantly in mice under normal chow condition after CTRP4 overexpression. Both immunohistochemistry and Western blot demonstrated that POMC expression was significantly increased while NPY expression was significantly decreased. The changes of neuropeptides were accompanied by significant increased STAT3 phosphorylation and decreased SOCS3 levels. The same changes of neuropeptides and STAT3 signaling were also found in N2a cells after CTRP4 overexpression intervention. Collectively, our data reveals that CTRP4 induces the activation of STAT3 signaling and decreases food intake.

Intranasal Insulin: a Treatment Strategy for Addiction

Addiction to substances such as alcohol, cocaine, opioids, and methamphetamine poses a continuing clinical and public challenge globally. Despite progress in understanding substance use disorders, challenges remain in their treatment. Some of these challenges include limited ability of therapeutics to reach the brain (blood-brain barrier), adverse systemic side effects of current medications, and importantly key aspects of addiction not addressed by currently available treatments (such as cognitive impairment). Inability to sustain abstinence or seek treatment due to cognitive deficits such as poor decision-making and impulsivity is known to cause poor treatment outcomes. In this review, we provide an evidenced-based rationale for intranasal drug delivery as a viable and safe treatment modality to bypass the blood-brain barrier and target insulin to the brain to improve the treatment of addiction. Intranasal insulin with improvement of brain cell energy and glucose metabolism, stress hormone reduction, and improved monoamine transmission may be an ideal approach for treating multiple domains of addiction including memory and impulsivity. This may provide additional benefits to enhance current treatment approaches.

Central regulation of food intake in fish: an evolutionary perspective

Evidence indicates that central regulation of food intake is well conserved along the vertebrate lineage, at least between teleost fish and mammals. However, several differences arise in the comparison between both groups. In this review, we describe similarities and differences between teleost fish and mammals on an evolutionary perspective. We focussed on the existing knowledge of specific fish features conditioning food intake, anatomical homologies and analogies between both groups as well as the main signalling pathways of neuroendocrine and metabolic nature involved in the homeostatic and hedonic central regulation of food intake.

Adjunctive treatment with brexpiprazole and escitalopram reduces behavioral stress responses and increase hypothalamic NPY immunoreactivity in a rat model of PTSD-like symptoms

The study explored effects of brexpiprazole (partial D₂/5-HT_1A agonist, 5-HT_2A and α_1B/2C-adrenoceptor antagonist) in rats exposed to predator scent stress (PSS), a proposed model of PTSD-like phenotype. Brexpiprazole (3.0mg/kg, PO), escitalopram (5.0mg/kg, IP) and their combination were administered twice daily for 14 days, starting 14 days after exposure to PSS or sham-PSS, shortly after a situational stress reminder. One day after last treatment behavioral responsivity was assessed. Brexpiprazole+escitalopram-treated rats spent more time in open arms, entered open arms more often and exhibited a lower anxiety index in the elevated plus maze than vehicle-treated, PSS-exposed rats. Adjunct brexpiprazole+escitalopram treatment reduced startle amplitude, compared with vehicle-treated, PSS-exposed rats. Treatment with either drug alone did not attenuate anxiety-like behaviors following PSS exposure. Use of cut-off behavioral criteria confirmed that adjunct treatment shifted prevalence of PSS-exposed rats from extreme towards minimal behavioral responders. One day following behavioral tests, brains were prepared for immunohistochemical analysis of number of BDNF-positive cells and of NPY-positive cells/fibers. PSS exposure decreased BDNF levels in hippocampus, but this was not affected by drug treatments. PSS exposure decreased number of NPY positive cells/fibers in paraventricular and arcuate nuclei of hypothalamus. Adjunct treatment with brexpiprazole+escitalopram increased NPY in PSS- and sham-exposed rats. Treatment with brexpiprazole alone had no effects, while treatment with escitalopram alone increased NPY in the arcuate nucleus of PSS-exposed rats. In conclusion, treatment with brexpiprazole+escitalopram may be an effective intervention for the attenuation of PTSD-like stress responses, which in part may be mediated by activating NPY function.

Adolescent Alcohol Exposure-Induced Changes in Alpha-Melanocyte Stimulating Hormone and Neuropeptide Y Pathways via Histone Acetylation in the Brain During Adulthood

Background

Adolescent intermittent ethanol exposure causes long-lasting alterations in brain epigenetic mechanisms. Melanocortin and neuropeptide Y signaling interact and are affected by ethanol exposure in the brain. Here, the persistent effects of adolescent intermittent ethanol on alpha-melanocyte stimulating hormone, melanocortin 4 receptor, and neuropeptide Y expression and their regulation by histone acetylation mechanisms were investigated in adulthood.

Methods

Male rats were exposed to adolescent intermittent ethanol (2 g/kg, i.p.) or volume-matched adolescent intermittent saline from postnatal days 28 to 41 and allowed to grow to postnatal day 92. Anxiety-like behaviors were measured by the elevated plus-maze test. Brain regions from adult rats were used to examine changes in alpha-melanocyte stimulating hormone, melanocortin 4 receptor, and neuropeptide Y expression and the histone acetylation status of their promoters.

Results

Adolescent intermittent ethanol-exposed adult rats displayed anxiety-like behaviors and showed increased pro-opiomelanocortin mRNA levels in the hypothalamus and increased melanocortin 4 receptor mRNA levels in both the amygdala and hypothalamus compared with adolescent intermittent saline-exposed adult rats. The alpha-Melanocyte stimulating hormone and melanocortin 4 receptor protein levels were increased in the central and medial nucleus of the amygdala, paraventricular nucleus, and arcuate nucleus of the hypothalamus in adolescent intermittent ethanol-exposed compared with adolescent intermittent saline-exposed adult rats. Neuropeptide Y protein levels were decreased in the central and medial nucleus of the amygdala of adolescent intermittent ethanol-exposed compared with adolescent intermittent saline-exposed adult rats. Histone H3K9/14 acetylation was decreased in the neuropeptide Y promoter in the amygdala but increased in the melanocortin 4 receptor gene promoter in the amygdala and the melanocortin 4 receptor and pro-opiomelanocortin promoters in the hypothalamus of adolescent intermittent ethanol-exposed adult rats compared with controls.

Conclusions

Increased melanocortin and decreased neuropeptide Y activity due to changes in histone acetylation in emotional brain circuitry may play a role in adolescent intermittent ethanol-induced anxiety phenotypes in adulthood.

Integrating Neural Circuits Controlling Female Sexual Behavior

The hypothalamus is most often associated with innate behaviors such as is hunger, thirst and sex. While the expression of these behaviors important for survival of the individual or the species is nested within the hypothalamus, the desire (i.e., motivation) for them is centered within the mesolimbic reward circuitry. In this review, we will use female sexual behavior as a model to examine the interaction of these circuits. We will examine the evidence for a hypothalamic circuit that regulates consummatory aspects of reproductive behavior, i.e., lordosis behavior, a measure of sexual receptivity that involves estradiol membrane-initiated signaling in the arcuate nucleus (ARH), activating β-endorphin projections to the medial preoptic nucleus (MPN), which in turn modulate ventromedial hypothalamic nucleus (VMH) activity-the common output from the hypothalamus. Estradiol modulates not only a series of neuropeptides, transmitters and receptors but induces dendritic spines that are for estrogenic induction of lordosis behavior. Simultaneously, in the nucleus accumbens of the mesolimbic system, the mating experience produces long term changes in dopamine signaling and structure. Sexual experience sensitizes the response of nucleus accumbens neurons to dopamine signaling through the induction of a long lasting early immediate gene. While estrogen alone increases spines in the ARH, sexual experience increases dendritic spine density in the nucleus accumbens. These two circuits appear to converge onto the medial preoptic area where there is a reciprocal influence of motivational circuits on consummatory behavior and vice versa. While it has not been formally demonstrated in the human, such circuitry is generally highly conserved and thus, understanding the anatomy, neurochemistry and physiology can provide useful insight into the motivation for sexual behavior and other innate behaviors in humans.

Relaxin-3/RXFP3 signalling in mouse hypothalamus: no effect of RXFP3 activation on corticosterone, despite reduced presynaptic excitatory input onto paraventricular CRH neurons in vitro

Relaxin-3/RXFP3 signalling is proposed to be involved in the neuromodulatory control of arousal- and stress-related neural circuits. Furthermore, previous studies in rats have led to the proposal that relaxin-3/RXFP3 signalling is associated with activation of the hypothalamic-pituitary-adrenal axis, but direct evidence for RXFP3-related actions on the activity of hypothalamic corticotropin-releasing hormone (CRH) neurons is lacking. In this study, we investigated characteristics of the relaxin-3/RXFP3 system in mouse hypothalamus. Administration of an RXFP3 agonist (RXFP3-A2) intra-cerebroventricularly or directly into the paraventricular nucleus of hypothalamus (PVN) of C57BL/6J mice did not alter corticosterone levels. Similarly, there were no differences between serum corticosterone levels in Rxfp3 knockout (C57BL/6J^RXFP3TM1) and wild-type mice at baseline and after stress, despite detection of the predicted stress-induced increases in serum corticosterone. We examined the nature of the relaxin-3 innervation of PVN in wild-type mice and in Crh-IRES-Cre;Ai14 mice that co-express the tdTomato fluorophore in CRH neurons, identifying abundant relaxin-3 fibres in the peri-PVN region, but only sparse fibres associated with densely packed CRH neurons. In whole-cell voltage-clamp recordings of tdTomato-positive CRH neurons in these mice, we observed a reduction in sEPSC frequency following local application of RXFP3-A2, consistent with an activation of RXFP3 on presynaptic glutamatergic afferents in the PVN region. These studies clarify the relationship between relaxin-3/RXFP3 inputs and CRH neurons in mouse PVN, with implications for the interpretation of current and previous in vivo studies and future investigations of this stress-related signalling network in normal and transgenic mice, under normal and pathological conditions.

Polyunsaturated fatty acid receptors, GPR40 and GPR120, are expressed in the hypothalamus and control energy homeostasis and inflammation

BACKGROUND

The consumption of large amounts of dietary fats is one of the most important environmental factors contributing to the development of obesity and metabolic disorders. GPR120 and GPR40 are polyunsaturated fatty acid receptors that exert a number of systemic effects that are beneficial for metabolic and inflammatory diseases. Here, we evaluate the expression and potential role of hypothalamic GPR120 and GPR40 as targets for the treatment of obesity.

METHODS

Male Swiss (6-weeks old), were fed with a high fat diet (HFD, 60% of kcal from fat) for 4 weeks. Next, mice underwent stereotaxic surgery to place an indwelling cannula into the right lateral ventricle. intracerebroventricular (icv)-cannulated mice were treated twice a day for 6 days with 2.0 μL saline or GPR40 and GPR120 agonists: GW9508, TUG1197, or TUG905 (2.0 μL, 1.0 mM). Food intake and body mass were measured during the treatment period. At the end of the experiment, the hypothalamus was collected for real-time PCR analysis.

RESULTS

We show that both receptors are expressed in the hypothalamus; GPR120 is primarily present in microglia, whereas GPR40 is expressed in neurons. Upon intracerebroventricular treatment, GW9508, a non-specific agonist for both receptors, reduced energy efficiency and the expression of inflammatory genes in the hypothalamus. Reducing GPR120 hypothalamic expression using a lentivirus-based approach resulted in the loss of the anti-inflammatory effect of GW9508 and increased energy efficiency. Intracerebroventricular treatment with the GPR120- and GPR40-specific agonists TUG1197 and TUG905, respectively, resulted in milder effects than those produced by GW9508.

CONCLUSIONS

GPR120 and GPR40 act in concert in the hypothalamus to reduce energy efficiency and regulate the inflammation associated with obesity. The combined activation of both receptors in the hypothalamus results in better metabolic outcomes than the isolated activation of either receptor alone.

Thalamic dopaminergic neurons projects to the paraventricular nucleus-rostral ventrolateral medulla/C1 neural circuit

Paraventricular nuclei (PVN) projections to the rostral ventrolateral medulla (RVLM)/C1 catecholaminergic neuron group constitute the pre-autonomic sympathetic center involved in the neural control of systemic cardiovascular function. However, the role of extra-hypothalamic and thalamic dopaminergic (DA) inputs in this circuit remains underexplored. Using retrograde neuroanatomical tracing and high contrast confocal imaging methods, we investigated the projections and morphology of the discrete thalamic DA neuron groups in the dorsal hypothalamic area and their contribution to the PVN-RVLM neural circuit. We found that DA neuron subgroups in the Zona Incerta (Zi; 60%) and Reuniens thalamic nuclei (Re; 40%) were labeled comparably to the PVN (85%) after a retrograde tracer was injected into the RVLM/C1 (P < 0.01 mean ± SEM). The Re/Zi DA neuron subgroups were characterized by angulated cell bodies, superiomedial and inferiomedial projections reaching the contralateral Re/Zi and ipsilateral PVN DA neurons respectively. Ultimately, we deduced that the DA projections of the Re/Zi to the PVN contribute to the PVN-RVLM/C1 neural circuit. As a result of these connections, the Re/Zi DA neuron groups may regulate preautonomic sympathetic events associated with the PVN-RVLM pathway. Anat Rec, 300:1307-1314, 2017. © 2016 Wiley Periodicals, Inc.

Contribution of adaptive thermogenesis to the hypothalamic regulation of energy balance

Obesity and its related disorders are among the most pervasive diseases in contemporary societies, and there is an urgent need for new therapies and preventive approaches. Given (i) our poor social capacity to correct unhealthy habits, and (ii) our evolutionarily genetic predisposition to store excess energy as fat, the current environment of caloric surplus makes the treatment of obesity extremely difficult. During the last few decades, an increasing number of methodological approaches have increased our knowledge of the neuroanatomical basis of the control of energy balance. Compelling evidence underlines the role of the hypothalamus as a homeostatic integrator of metabolic information and its ability to adjust energy balance. A greater understanding of the neural basis of the hypothalamic regulation of energy balance might indeed pave the way for new therapeutic targets. In this regard, it has been shown that several important peripheral signals, such as leptin, thyroid hormones, oestrogens and bone morphogenetic protein 8B, converge on common energy sensors, such as AMP-activated protein kinase to modulate sympathetic tone on brown adipose tissue. This knowledge may open new ways to counteract the chronic imbalance underlying obesity. Here, we review the current state of the art on the role of hypothalamus in the regulation of energy balance with particular focus on thermogenesis.

Bardoxolone methyl prevents obesity and hypothalamic dysfunction

High-fat (HF) diet-induced obesity is associated with hypothalamic leptin resistance and low grade chronic inflammation, which largely impairs the neuroregulation of negative energy balance. Neuroregulation of negative energy balance is largely controlled by the mediobasal and paraventricular nuclei regions of the hypothalamus via leptin signal transduction. Recently, a derivative of oleanolic acid, bardoxolone methyl (BM), has been shown to have anti-inflammatory effects. We tested the hypothesis that BM would prevent HF diet-induced obesity, hypothalamic leptin resistance, and inflammation in mice fed a HF diet. Oral administration of BM via drinking water (10 mg/kg daily) for 21 weeks significantly prevented an increase in body weight, energy intake, hyperleptinemia, and peripheral fat accumulation in mice fed a HF diet. Furthermore, BM treatment prevented HF diet-induced decreases in the anorexigenic effects of peripheral leptin administration. In the mediobasal and paraventricular nuclei regions of the hypothalamus, BM administration prevented HF diet-induced impairments of the downstream protein kinase b (Akt) pathway of hypothalamic leptin signalling. BM treatment also prevented an increase in inflammatory cytokines, tumour necrosis factor alpha (TNFα) and interleukin 6 (IL-6) in these two hypothalamic regions. These results identify a potential novel neuropharmacological application for BM in preventing HF diet-induced obesity, hypothalamic leptin resistance, and inflammation.

Hypothalamic inflammation and food intake regulation during chronic illness

Anorexia is a common symptom in chronic illness. It contributes to malnutrition and strongly affects survival and quality of life. A common denominator of many chronic diseases is an elevated inflammatory status, which is considered to play a pivotal role in the failure of food-intake regulating systems in the hypothalamus. In this review, we summarize findings on the role of hypothalamic inflammation on food intake regulation involving hypothalamic neuropeptide Y (NPY) and pro-opiomelanocortin (POMC). Furthermore, we outline the role of serotonin in the inability of these peptide based food-intake regulating systems to respond and adapt to changes in energy metabolism during chronic disease.

Neuronal Regulation of Energy Homeostasis: Beyond the Hypothalamus and Feeding

The essential role of the brain in maintaining energy homeostasis has motivated the drive to define the neural circuitry that integrates external and internal stimuli to enact appropriate and consequential metabolic and behavioral responses. The hypothalamus has received significant attention in this regard given its ability to influence feeding behavior, yet organisms rely on a much broader diversity and distribution of neuronal networks to regulate both energy intake and expenditure. Because energy balance is a fundamental determinant of survival and success of an organism, it is not surprising that emerging data connect circuits controlling feeding and energy balance with higher brain functions and degenerative processes. In this review, we will highlight both classically defined and emerging aspects of brain control of energy homeostasis.

Anorexia in human and experimental animal models: physiological aspects related to neuropeptides

Anorexia, a loss of appetite for food, can be caused by various physiological and pathophysiological conditions. In this review, firstly, clinical aspects of anorexia nervosa are summarized in brief. Secondly, hypothalamic neuropeptides responsible for feeding regulation in each hypothalamic nucleus are discussed. Finally, three different types of anorexigenic animal models; dehydration-induced anorexia, cisplatin-induced anorexia and cancer anorexia-cachexia, are introduced. In conclusion, hypothalamic neuropeptides may give us novel insight to understand and find effective therapeutics strategy essential for various kinds of anorexia.

Participation of the central melanocortin system in metabolic regulation and energy homeostasis

Obesity and metabolic disorders, such as type 2 diabetes and hypertension, have attracted considerable attention as life-threatening diseases not only in developed countries but also worldwide. Additionally, the rate of obesity in young people all over the world is rapidly increasing. Accumulated evidence suggests that the central nervous system may participate in the development of and/or protection from obesity. For example, in the brain, the hypothalamic melanocortin system senses and integrates central and peripheral metabolic signals and controls the degree of energy expenditure and feeding behavior, in concert with metabolic status, to regulate whole-body energy homeostasis. Currently, researchers are studying the mechanisms by which peripheral metabolic molecules control feeding behavior and energy balance through the central melanocortin system. Accordingly, recent studies have revealed that some inflammatory molecules and transcription factors participate in feeding behavior and energy balance by controlling the central melanocortin pathway, and have thus become new candidates as therapeutic targets to fight metabolic diseases such as obesity and diabetes.

The anorectic actions of the TGFβ cytokine MIC-1/GDF15 require an intact brainstem area postrema and nucleus of the solitary tract

Macrophage inhibitory cytokine-1 (MIC-1/GDF15) modulates food intake and body weight under physiological and pathological conditions by acting on the hypothalamus and brainstem. When overexpressed in disease, such as in advanced cancer, elevated serum MIC-1/GDF15 levels lead to an anorexia/cachexia syndrome. To gain a better understanding of its actions in the brainstem we studied MIC-1/GDF15 induced neuronal activation identified by induction of Fos protein. Intraperitoneal injection of human MIC-1/GDF15 in mice activated brainstem neurons in the area postrema (AP) and the medial (m) portion of the nucleus of the solitary tract (NTS), which did not stain with tyrosine hydroxylase (TH). To determine the importance of these brainstem nuclei in the anorexigenic effect of MIC-1/GDF15, we ablated the AP alone or the AP and the NTS. The latter combined lesion completely reversed the anorexigenic effects of MIC-1/GDF15. Altogether, this study identified neurons in the AP and/or NTS, as being critical for the regulation of food intake and body weight by MIC-1/GDF15.

Temporal and concentration-dependent effects of oestradiol on neural pathways mediating sexual receptivity

The acceptance of oestradiol signalling through receptors found in the cell membrane, as well as, the nucleus, has provided for a re-examination of the timing and location of the actions of oestradiol on neural circuits mediating sexual receptivity (lordosis). Oestradiol membrane signalling involves the transactivation of metabotrophic glutamate receptors (mGluRs) that transduce steroid information through protein kinase C signalling cascades producing rapid activation of lordosis-regulating circuits. It has been known for some time that oestradiol initially produces an inhibition of the medial preoptic nucleus. We have demonstrated that underlying this inhibition is oestradiol acting in the arcuate nucleus to induce β-endorphin release, which inhibits the medial preoptic nucleus through a μ-opioid receptor mechanism. This transient inhibition is relieved by either subsequent progesterone treatment or longer exposure to higher doses of oestradiol to facilitate lordosis behaviour. We review recent findings about oestradiol membrane signalling inducing dendritic spine formation in the arcuate nucleus that is critical for oestradiol induction of sexual receptivity. Moreover, we discuss the evidence that, in addition to oestrogen receptor α, several other putative membrane oestrogen receptors facilitate lordosis behaviour through regulation of the arcuate nucleus. These include the GRP30 and the STX activated Gq-mER. Finally, we report on the importance of GABA acting at GABAB receptors for oestradiol membrane signalling that regulates lordosis circuit activation and sexual receptivity.

Estradiol signaling in the regulation of reproduction and energy balance

Our knowledge of membrane estrogenic signaling mechanisms and their interactions that regulate physiology and behavior has grown rapidly over the past three decades. The discovery of novel membrane estrogen receptors and their signaling mechanisms has started to reveal the complex timing and interactions of these various signaling mechanisms with classical genomic steroid actions within the nervous system to regulate physiology and behavior. The activation of the various estrogenic signaling mechanisms is site specific and differs across the estrous cycle acting through both classical genomic mechanisms and rapid membrane-initiated signaling to coordinate reproductive behavior and physiology. This review focuses on our current understanding of estrogenic signaling mechanisms to promote: (1) sexual receptivity within the arcuate nucleus of the hypothalamus, (2) estrogen positive feedback that stimulates de novo neuroprogesterone synthesis to trigger the luteinizing hormone surge important for ovulation and estrous cyclicity, and (3) alterations in energy balance.

Leptin and the hypothalamo-pituitary-adrenal stress axis

Leptin is a 16-kDa protein mainly produced and secreted by white adipose tissue and informing various brain centers via leptin receptor long and short forms about the amount of fat stored in the body. In this way leptin exerts a plethora of regulatory functions especially related to energy intake and metabolism, one of which is controlling the activity of the hypothalamo-pituitary-adrenal (HPA) stress axis. First, this review deals with the basic properties of leptin's structure and signaling at the organ, cell and molecule level, from lower vertebrates to humans but with emphasis on rodents because these have been investigated in most detail. Then, attention is given to the various interactions of adipose leptin with the HPA-axis, at the levels of the hypothalamus (especially the paraventricular nucleus), the anterior lobe of the pituitary gland (action on corticotropes) and the adrenal gland, where it releases corticosteroids needed for adequate stress adaptation. Also, possible local production and autocrine and paracrine actions of leptin at the hypothalamic and pituitary levels of the HPA-axis are being considered. Finally, a schematic model is presented showing the ways peripherally and centrally produced leptin may modulate, via the HPA-axis, stress adaptation in conjunction with the control of energy homeostasis.

Leptin receptors

The hormone leptin, secreted predominantly from adipose tissue, plays a crucial role in the regulation of numerous neuroendocrine functions, from energy homeostasis to reproduction. Genetic deficiency as a consequence of leptin or leptin receptor mutations, although rare in humans, leads to early onset of chronic hyperphagia and massive obesity. In most human obesity, however, leptin levels are chronically elevated. Under these conditions of persistent hyperleptinaemia, and particularly when obesity is associated with a high-fat diet, leptin resistance develops, and signalling through the leptin receptor is curtailed, fuelling further weight gain. Here, we review the role of leptin receptors in the regulation of feeding and obesity development. Leptin receptors are found in each of the major components of the CNS "feeding" circuitry-the brainstem, hypothalamus and distributed reward centres. Through these receptors, leptin exerts influences on signalling and integration within these circuits to alter feeding behaviours. Although some progress is now being made with peptide analogues, the leptin receptor has not proved to be amenable to small molecule pharmacological intervention to date. Where clinical benefit from recombinant leptin administration has been achieved, this has been under circumstances of complete endogenous leptin deficiency or relative hypoleptinaemia such as in lipodystrophy.

Protective effects of leptin during the suckling period against later obesity may be associated with changes in promoter methylation of the hypothalamic pro-opiomelanocortin gene

Leptin supplementation of neonatal rats during the suckling period protects against being overweight in adulthood and ameliorates the control of food intake. This was associated with changes in the expression of hypothalamic genes involved in the central action of leptin: pro-opiomelanocortin (Pomc), leptin receptor (Lepr) and suppressor of cytokine signalling (Socs3). The purpose of the present study was to determine the methylation status within the promoter regions of these genes and to assess whether the observed changes in the expression levels of these genes could be explained by changes in their methylation status. Male rats were treated daily with an oral physiological dose of leptin or vehicle during the suckling period. After weaning, animals were fed with a normal-fat or a high-fat (HF) diet until aged 6 months. DNA was extracted from the hypothalamus and methylation within the promoter regions of the gene panel was measured by pyrosequencing. Pomc promoter methylation increased in control animals fed the HF diet but decreased in leptin-treated animals. In addition, there was a weak negative correlation between DNA methylation and POMC mRNA levels (P = 0·075). There were no changes in the methylation status of the CpG sites studied within the promoter regions of Lepr and Socs3 in response to leptin or HF treatments. This is the first demonstration that leptin treatment during lactation may programme methylation of an appetite-related gene in the hypothalamus of animals fed HF diets, with possible implications for gene expression and protection against the development of obesity.

Plasticity of the stress response early in life: mechanisms and significance

The concept that early-life experience influences the brain long-term has been extensively studied over the past 50 years, whereas genetic factors determine the sequence and levels of expression of specific neuronal genes, this genetic program can be modified enduringly as a result of experience taking place during critical developmental periods. This programming is of major importance because it appears to govern many behavioral and physiological phenotypes and promote susceptibility or resilience to disease. An established example of the consequences of early-life experience-induced programming includes the effects of maternal care, where patterns of augmented care result in decreased neuroendocrine stress responses, improved cognition and resilience to depression in the recipients of this care. Here, we discuss the nature and mechanisms of this programming phenomenon, focusing on work from our lab that was inspired by Seymour Levine and his fundamental contributions to the field.

Multinodal regulation of the arcuate/paraventricular nucleus circuit by leptin

Melanocortin-4 receptor (MC4R) is critical for energy homeostasis, and the paraventricular nucleus of the hypothalamus (PVN) is a key site of MC4R action. Most studies suggest that leptin regulates PVN neurons indirectly, by binding to receptors in the arcuate nucleus or ventromedial hypothalamus and regulating release of products like α-melanocyte-stimulating hormone (α-MSH), neuropeptide Y (NPY), glutamate, and GABA from first-order neurons onto the MC4R PVN cells. Here, we investigate mechanisms underlying regulation of activity of these neurons under various metabolic states by using hypothalamic slices from a transgenic MC4R-GFP mouse to record directly from MC4R neurons. First, we show that in vivo leptin levels regulate the tonic firing rate of second-order MC4R PVN neurons, with fasting increasing firing frequency in a leptin-dependent manner. We also show that, although leptin inhibits these neurons directly at the postsynaptic membrane, α-MSH and NPY potently stimulate and inhibit the cells, respectively. Thus, in contrast with the conventional model of leptin action, the primary control of MC4R PVN neurons is unlikely to be mediated by leptin action on arcuate NPY/agouti-related protein and proopiomelanocortin neurons. We also show that the activity of MC4R PVN neurons is controlled by the constitutive activity of the MC4R and that expression of the receptor mRNA and α-MSH sensitivity are both stimulated by leptin. Thus, leptin acts multinodally on arcuate nucleus/PVN circuits to regulate energy homeostasis, with prominent mechanisms involving direct control of both membrane conductances and gene expression in the MC4R PVN neuron.

Differential regulation of hypothalamic neuropeptide Y hnRNA and mRNA during psychological stress and insulin-induced hypoglycemia

Many signals reflecting energy balance and stress are integrated at the hypothalamic orexigenic NPY neurons. To determine transcriptional changes of the NPY gene in response to stress, we followed the time course and compared the expression of heteronuclear (hn)- and messenger (m)RNA levels by in situ hybridization histochemistry and by real time PCR in mice following insulin-induced hypoglycemia and restraint. Hypoglycemia in fasted mice resulted in a rapid increase of NPY hnRNA that peaked at 1h, declined thereafter by 2-4h after insulin injection and run parallel to that of NPY mRNA. Throughout the time course examined, NPY expressing cells in the medial basal hypothalamus remained overwhelmingly localized to the arcuate nucleus. Following restraint NPY mRNA slightly increased, however hnRNA levels decreased up to 2h, suggesting increased stability of mature NPY mRNA. These results highlight rapid changes and differential regulation of NPY expression in response to metabolic and stress challenges.

Central adiponectin functions to inhibit arginine vasopressin release in conscious rats

The adipocyte-derived hormone adiponectin plays an important role in modulating energy homeostasis through peripheral tissues and the central nervous system. Several studies have reported that adiponectin exists in cerebrospinal fluid and that adiponectin receptors are expressed in the hypothalamus, including the paraventricular nucleus (PVN), which plays a key role in controlling pituitary hormone secretion. Furthermore, it has been reported that magnocellular arginine vasopressin (AVP) neurones within the PVN express adiponectin receptors. These findings suggest a central role of adiponectin in the modulation of neuroendocrinological functions. In the present study, we investigated the effect of centrally-administered adiponectin on AVP release in conscious rats. Intracerebroventricular (i.c.v.) administration of adiponectin significantly reduced the basal plasma AVP concentration in a dose-dependent manner, with a maximal effect being obtained 10 min after administration. The plasma AVP increase in response to either hyperosmolar or hypovolaemic stimulation was also significantly attenuated by an i.c.v. injection of adiponectin. Treatment with AMP-activated protein kinase (AMPK) inhibitor compound C (100 nmol, i.c.v.) partially reversed the inhibitory effects of adiponectin on AVP release. These findings suggest that central adiponectin plays an inhibitory role in the osmoregulation and baroregulation of AVP release, that the AMPK pathway is at least partly involved in the action of adiponectin, and further suggest a novel physiological or pathophysiological role for central adiponectin in water balance via inhibition of AVP release.

Messenger RNA for neuropeptide Y in the arcuate nucleus increases in parallel with plasma adrenocorticotropin during sepsis in the rat

Loss of appetite occurs in the cecal ligation and puncture (CLP) model of sepsis in conjunction with the activation of central neural stress pathways. Neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus is upregulated by several stressors and is stimulatory to feeding. To examine the response of NPY messenger RNA in the arcuate nucleus to sepsis, we used biotinylated RNA probes and a quantitative non-isotopic in situ hybridization approach in cryo-preserved sections from rats made septic by CLP. The mRNA in arcuate neurons was upregulated from the first day after CLP. By the afternoon of the third day through the morning of the fourth day, the average grey level of NPY mRNA clusters was 30% greater after CLP than after sham surgery (P<0.05), and the integrated optical density based on both the grey level and the amount of area with detectable mRNA was 60% greater after CLP than after sham surgery (P<0.03). Both the average grey level and area with detectable staining were positively correlated to plasma ACTH (r=0.953 and 0.917, respectively, n=10 and P<0.01 in each case). Thus sepsis increases the expression of the mRNA for NPY in the arcuate nucleus in proportion to the magnitude of the stress response. However, the suppression of feeding behavior in the CLP model suggests that sepsis activates additional mechanisms that negate the orexigenic contribution of the neuronal increase in NPY mRNA.

Sex-associated differences in the leptin and ghrelin systems related with the induction of hyperphagia under high-fat diet exposure in rats

Leptin and ghrelin are known to be main hormones involved in the control of food intake, with opposing effects. Here we have explored whether changes in the leptin and ghrelin system are involved in the long-term effects of high-fat (HF) diet feeding in rats and whether sex-associated differences exist. Male and female Wistar rats were fed until the age of 6 months with a normal-fat (NF) or an HF-diet. Food intake and body weight were followed. Gastric and serum levels of leptin and ghrelin, and mRNA levels of leptin (in stomach and adipose tissue), ghrelin (in stomach), and NPY, POMC, and leptin and ghrelin receptors (OB-Rb and GHS-R) (in the hypothalamus) were measured. In both males and females, total caloric intake and body weight were greater under the HF-diet feeding. In females, circulating ghrelin levels and leptin mRNA expression in the stomach were higher under HF-diet. HF-diet feeding also resulted in higher hypothalamic NPY/POMC mRNA levels, more marked in females, and in lower OB-Rb mRNA levels, more marked in males. In addition, in females, serum ghrelin levels correlated positively with hypothalamic NPY mRNA levels, and these with caloric intake. In males, hypothalamic OB-Rb mRNA levels correlated positively with POMC mRNA levels and these correlated negatively with caloric intake and with body weight. These data reflect differences between sexes in the effects of HF-diet feeding on food intake control systems, suggesting an impairment of the anorexigenic leptin-POMC system in males and an over-stimulation of the orexigenic ghrelin-NPY system in females.

Intranasal insulin attenuates the hypothalamic-pituitary-adrenal axis response to psychosocial stress

Previous studies have shown that intranasally administered insulin exerts an inhibitory influence on the basal hypothalamic-pituitary-adrenal (HPA) axis activity. To date, however, it remains unclear as to whether intranasal insulin does furthermore affect HPA axis responsiveness in situations of stress. Here, we tested whether intranasally administered insulin attenuates the HPA axis response to psychosocial stress. Fifty minutes before being exposed to the Trier Social Stress Test (TSST), 26 healthy young male participants received a single intranasal dose of human insulin (40 I.U.) or placebo in a placebo controlled, double-blind between-subject design. Plasma cortisol, saliva cortisol, heart rate, and blood pressure were measured at resting baseline and in response to the TSST. Plasma cortisol (P<.001) and saliva cortisol (P<.001) increased in response to stress, as did heart rate (P<.001) and blood pressure (P<.001). Intranasal insulin did not influence plasma or saliva cortisol, heart rate, blood pressure, blood glucose, and plasma insulin levels at baseline. However, intranasal insulin diminished the saliva cortisol (two-way ANOVA; treatment by time interaction: P=.05) and plasma cortisol (two-way ANOVA; treatment by time interaction: P=.05) response to the TSST without affecting heart rate, and blood pressure stress reactivity. Our data show that a single intranasal insulin administration effectively lowers stress-induced HPA axis responsiveness. Intranasal insulin may offer a therapeutic potential to prevent hyperactivity of the HPA system.

Distribution of the androgen receptor in the diencephalon and the pituitary gland in goats: Co-localisation with corticotrophin releasing hormone, arginine vasopressin and corticotrophs

Previously it has been shown that androgen suppresses transportation-induced increases in plasma adrenocorticotropic hormone (ACTH), possibly by suppressing the secretion of corticotrophin releasing hormone (CRH) or arginine vasopressin (AVP) from the hypothalamus, or secretion of ACTH from the pituitary gland. The aim of the present study was to examine androgen target sites in the caprine diencephalon and pituitary gland using immunohistochemical methods. The androgen receptor (AR) was expressed strongly in the bed nucleus of the stria terminalis, the medial preoptic area, the arcuate nucleus, the ventromedial hypothalamic nucleus and the suprachiasmatic nucleus in the diencephalon. Between 8% and 11% of CRH and AVP neurons in the paraventricular hypothalamic nucleus (PVN) expressed AR. In the pituitary gland, 7.1% of corticotrophs expressed AR. The results are consistent with the proposal that androgen acts directly and indirectly on CRH and/or AVP neurons in the PVN. The possibility of a direct action of androgen on the corticotrophs in the pituitary gland was also considered.

Food deprivation-induced changes in body fat mobilization after neonatal monosodium glutamate treatment

The reversal of obesity is a difficult feat at best and is a growing problem as the obesity epidemic increases worldwide. Considerable focus has been made on the arcuate nucleus (Arc) in the control of body and lipid mass and food intake. To test the role of the Arc in body fat mobilization, we compared the effects of food deprivation on white adipose tissue (WAT) mass in adult Siberian hamsters by making exocytotic lesions of the Arc via neonatal subcutaneous injections of monosodium glutamate (MSG). MSG-treated hamsters had significantly increased body mass, total and individual WAT pad masses, and serum leptin concentrations compared with their vehicle-injected counterparts. MSG produced marked reductions in Arc Nissl staining, tyrosine hydroxylase-immunoreactive (ir) neurons, and neuropeptide Y (NPY)- and agouti-related protein (AgRP)-ir fibers compared with controls. MSG significantly decreased hypothalamic paraventricular nucleus (PVN) NPY- and AgRP fiber-ir compared with controls, likely because of Arc projections to this nucleus. MSG treatment also reduced area postrema (AP) tyrosine hydroxylase (TH)-ir fibers compared with controls. MSG treatment did not, however, block food deprivation-induced decreases in WAT pad mass compared with controls. Thus, despite considerable damage to the Arc and some of its projections to the PVN, as well as the AP, body fat was mobilized apparently normally, bringing into question the necessity of these structures for food deprivation-induced lipid mobilization. These data support recent evidence that chronically decerebrate rats, in which the forebrain is surgically isolated from the caudal brainstem, show normal food deprivation responses, including lipid mobilization.

Early life programming of obesity and metabolic disease

It is becoming increasingly apparent that conditions experienced in early life play an important role in the long-term health of individuals. Alterations in development due to impaired, excessive or imbalanced growth, both in utero and during critical periods of relative plasticity beyond birth, can lead to the permanent programming of physiological systems. The regulation of energy balance is one area that is receiving particular attention, as rates of obesity and associated metabolic and cardiovascular disease continue to rise. Over recent decades, much progress has been made toward understanding the way in which metabolic tissues and physiological systems develop, and the impact of early life events and nutrition on these processes. It is apparent within human populations that some individuals are better able to maintain an appropriate body weight in the face of an obesogenic environment. Animal models have been widely used for the investigation of differential susceptibility to diet-induced obesity (DIO) and impaired energy balance regulation, and are shedding light on key pathways that may be involved. Alterations in pathways mediating energy homeostasis, outlined below, are likely candidates for programming effects following disturbed growth in early life.

The intake of physiological doses of leptin during lactation in rats prevents obesity in later life

BACKGROUND

There is epidemiological evidence that perinatal nutritional factors may have long-term effects on obesity. Which nutrients or food components are involved in this programming mechanism are unknown. Breast milk contains leptin, a hormone that regulates food intake and energy expenditure, and previous studies in rats have shown that leptin orally administered during lactation exerts anorexigenic effects.

OBJECTIVE

To evaluate whether supplementation with physiological doses of oral leptin during lactation has long-term effects on body weight regulation.

DESIGN

A daily oral dose of leptin (equivalent to five times the amount of leptin ingested normally from maternal milk during the suckling period) or the vehicle was given to suckling male rats during lactation. Animals were fed after weaning with a normal fat (NF) or a high-fat (HF) diet. We followed body weight and food intake of animals until the age of 6 months, and measured the size of adipose tissue depots, the thermogenic capacity, the expression of leptin in the stomach and adipose tissues and the expression of two appetite-related peptides (neuropeptide Y (NPY) and proopiomelanocortin (POMC)), leptin receptor (OB-Rb) and suppressor of cytokine signalling 3 (SOCS-3) in the hypothalamus at the age of 6 months.

RESULTS

Leptin-treated animals had, in adulthood, lower body weight and fat content and ate fewer calories than their untreated controls. Unlike adipocitary leptin production, adult animals that were leptin-treated during lactation displayed higher gastric leptin production without changes in OB-Rb mRNA levels. In addition, in response to HF diet, leptin-treated animals (contrary to controls) showed lower hypothalamic NPY/POMC mRNA ratio. Hypothalamic OB-Rb mRNA levels decreased in control animals as an effect of HF diet feeding, but remained unchanged in leptin-treated animals; SOCS-3 mRNA levels were lower in leptin-treated animals than in their controls, both under normal or HF diet.

CONCLUSION

The animals that received leptin during lactation become more protected against fat accumulation in adult life and seem to be more sensitive to the short- and long-term regulation of food intake by leptin. Thus, leptin plays an important role in the earlier stages of neonatal life, as a component of breast milk, in the prevention of later obesity.

Hypothalamic and brainstem sources of pituitary adenylate cyclase-activating polypeptide nerve fibers innervating the hypothalamic paraventricular nucleus in the rat

The hypothalamic paraventricular nucleus (PVN) coordinates major neuroendocrine and behavioral mechanisms, particularly responses to homeostatic challenges. Parvocellular and magnocellular PVN neurons are richly innervated by pituitary adenylate cyclase-activating polypeptide (PACAP) axons. Our recent functional observations have also suggested that PACAP may be an excitatory neuropeptide at the level of the PVN. Nevertheless, the exact localization of PACAP-producing neurons that project to the PVN is not understood. The present study examined the specific contribution of various brain areas sending PACAP innervation to the rat PVN by using iontophoretic microinjections of the retrograde neuroanatomical tracer cholera toxin B subunit (CTb). Retrograde transport was evaluated from hypothalamic and brainstem sections by using multiple labeling immunofluorescence for CTb and PACAP. PACAP-containing cell groups were found to be retrogradely labeled from the PVN in the median preoptic nucleus; preoptic and lateral hypothalamic areas; arcuate, dorsomedial, ventromedial, and supramammillary nuclei; ventrolateral midbrain periaqueductal gray; rostral and midlevel ventrolateral medulla, including the C1 catecholamine cell group; nucleus of the solitary tract; and dorsal motor nucleus of vagus. Minor PACAP projections with scattered double-labeled neurons originated from the parabrachial nucleus, pericoeruleus area, and caudal regions of the nucleus of the solitary tract and ventrolateral medulla. These observations indicate a multisite origin of PACAP innervation to the PVN and provide a strong chemical neuroanatomical foundation for interaction between PACAP and its potential target neurons in the PVN, such as parvocellular CRH neurons, controlling physiologic responses to stressful challenges and other neuroendocrine or preautonomic PVN neurons.

Prenatal development of hypothalamic neuropeptide systems in the nonhuman primate

In the rodent, arcuate nucleus of the hypothalamus (ARH)-derived neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons have efferent projections throughout the hypothalamus that do not fully mature until the second and third postnatal weeks. Since this process is likely completed by birth in primates we characterized the ontogeny of NPY and melanocortin systems in the fetal Japanese macaque during the late second (G100), early third (G130) and late third trimesters (G170). NPY mRNA was expressed in the ARH, paraventricular nucleus (PVH), and dorsomedial nucleus of the hypothalamus (DMH) as early as G100. ARH-derived NPY projections to the PVH were initiated at G100 but were limited and variable; however, there was a modest increase in density and number by G130. ARH-NPY/agouti-related peptide (AgRP) fiber projections to efferent target sites were completely developed by G170, but the density continued to increase in the postnatal period. In contrast to NPY/AgRP projections, alphaMSH fibers were minimal at G100 and G130 but were moderate at G170. This study also revealed several significant species differences between rodent and the nonhuman primate (NHP). There were few NPY/catecholamine projections to the PVH and ARH prior to birth, while projections were increased in the adult. A substantial proportion of the catecholamine fibers did not coexpress NPY. In addition, cocaine and amphetamine-related transcript (CART) and alpha-melanocyte stimulating hormone (alphaMSH) were not colocalized in fibers or cell bodies. As a consequence of the prenatal development of these neuropeptide systems in the NHP, the maternal environment may critically influence these circuits. Additionally, because differences exist in the neuroanatomy of NPY and melanocortin circuitry the regulation of these systems may be different in primates than in rodents.

The rise, fall, and resurrection of the ventromedial hypothalamus in the regulation of feeding behavior and body weight

Early researchers found that lesions of the ventromedial hypothalamus (VMH) resulted in hyperphagia and obesity in a variety of species including humans, which led them to designate the VMH as the brain's "satiety center." Many researchers later dismissed a role for the VMH in feeding behavior when Gold claimed that lesions restricted to the VMH did not result in overeating and that obesity was observed only with lesions or knife cuts that extended beyond the borders of the VMH and damaged or severed the ventral noradrenergic bundle (VNAB) or paraventricular nucleus (PVN). However, anatomical studies done both before and after Gold's study did not replicate his results with lesions, and in nearly every published direct comparison of VMH lesions vs. PVN or VNAB lesions, the group with VMH lesions ate substantially more food and gained twice as much weight. Several other important differences have also been found between VMH and both PVN and VNAB lesion-induced obesity. Concerns regarding (a) motivation to work for food and (b) the effects of nonirritative lesions have also been addressed and answered in many studies. Lesion studies with weanling rats and adult pair-tube-fed rats, as well as recent studies of knockout mice deficient in the orphan nuclear receptor steroidogenic factor 1, indicate that VMH lesion-induced obesity is in large part a metabolic obesity (due to autonomic nervous system disorders) independent of hyperphagia. However, there is ample evidence that the VMH also plays a primary role in feeding behavior. Neuroimaging studies in humans have shown a marked increase in activity in the area of the VMH during feeding. The VMH has a large population of glucoresponsive neurons that dynamically respond to blood glucose levels and numerous histamine, dopamine, serotonin, and GABA neurons that respond to feeding-related stimuli. Recent studies have implicated melanocortins in the VMH regulation of feeding behavior: food intake decreases when arcuate nucleus pro-opiomelanocortin (POMC) neurons activate VMH brain-derived neurotrophic factor (BDNF) neurons. Moderate hyperphagia and obesity have also been observed in female rats with damage to the efferent projections from the posterodorsal amygdala to the VMH. Hypothalamic obesity can result from damage to either the POMC or BDNF neurons. The concept of hypothalamic feeding and satiety centers is outdated and unnecessary, and progress in understanding hypothalamic mechanisms of feeding behavior will be achieved only by appreciating the different types of neural and blood-borne information received by the various nuclei, and then attempting to determine how this information is integrated to obtain a balance between energy intake and energy output.

Ventromedial arcuate nucleus communicates peripheral metabolic information to the suprachiasmatic nucleus

The arcuate nucleus (ARC) is crucial for the maintenance of energy homeostasis as an integrator of long- and short-term hunger and satiety signals. The expression of receptors for metabolic hormones, such as insulin, leptin, and ghrelin, allows ARC to sense information from the periphery and signal it to the central nervous system. The ventromedial ARC (vmARC) mainly comprises orexigenic neuropeptide agouti-related peptide and neuropeptide Y neurons, which are sensitive to circulating signals. To investigate neural connections of vmARC within the central nervous system, we injected the neuronal tracer cholera toxin B into vmARC. Due to variation of injection sites, tracer was also injected into the subependymal layer of the median eminence (seME), which showed similar projection patterns as the vmARC. We propose that the vmARC forms a complex with the seME, their reciprocal connections with viscerosensory areas in brain stem, and other circumventricular organs, suggesting the exchange of metabolic and circulating information. For the first time, the vmARC-seME was shown to have reciprocal interaction with the suprachiasmatic nucleus (SCN). Activation of vmARC neurons by systemic administration of the ghrelin mimetic GH-releasing peptide-6 combined with SCN tracing showed vmARC neurons to transmit feeding related signals to the SCN. The functionality of this pathway was demonstrated by systemic injection of GH-releasing peptide-6, which induced Fos in the vmARC and resulted in a reduction of about 40% of early daytime Fos immunoreactivity in the SCN. This observation suggests an anatomical and functional pathway for peripheral hormonal feedback to the hypothalamus, which may serve to modulate the activity of the SCN.

Changes in hypothalamic-pituitary-adrenal function, body temperature, body weight and food intake with repeated social stress exposure in rats

These present studies aimed to compare changes in hypothalamic-pituitary-adrenal (HPA) activity and body temperature in response to acute social defeat, to repeated social stress and to novel restraint after repeated stress, as well as to assess effects on metabolic parameters by measuring body weight gain and food and water intake. We found that social defeat produced a marked increase in both adrenocorticotrophic hormone and corticosterone compared to placement in a novel cage. Similarly, body temperature was also increased during social defeat and during 30 min of recovery from defeat. We then examined the effects of 6 days of repeated social stress and observed minimal HPA responses to repeated social stress compared to control rats. These neuroendocrine responses were contrasted by robust increases in body temperature during stress and during recovery from stress during 6 days of repeated stress. However, in response to novel restraint, repeatedly stressed rats displayed facilitated body temperature responses compared to controls, similar to our previous findings with HPA activity. Food intake was increased during the light period during which defeat took place, but later intake during the dark period was not affected. Repeated stress decreased body weight gain in the dark period but food intake was increased overall during the 6 days of repeated stress in the light period. As a result, repeated stress increased cumulative food intake during the light period in the stressed rats but these relatively small increases in food intake were unable to prevent the diminished total weight gain in repeatedly stressed rats. Overall, the results demonstrate that, although acute social defeat has similar effects on temperature and HPA activity, repeated exposure to social stress has divergent effects on HPA activity compared to body temperature and that dampened weight gain produced by repeated social stress cannot be fully explained by changes in food intake.

Leptin inhibits hypothalamic Npy and Agrp gene expression via a mechanism that requires phosphatidylinositol 3-OH-kinase signaling

Phosphatidylinositol 3-OH-kinase (PI3K) and STAT3 are signal transduction molecules activated by leptin in brain areas controlling food intake. To investigate their role in leptin-mediated inhibition of hypothalamic neuropeptide Y (Npy) and agouti-related peptide (Agrp) gene expression, male Sprague-Dawley rats (n = 5/group) were either fed ad libitum or subjected to a 52-h fast. At 12-h intervals, the PI3K inhibitor LY-294002 (LY, 1 nmol) or vehicle was injected intracerebroventricularly (ICV) as a pretreatment, followed 1 h later by leptin (3 microg icv) or vehicle. Fasting increased hypothalamic Npy and Agrp mRNA levels (P < 0.05), and ICV leptin administration prevented this increase. As predicted, LY pretreatment blocked this inhibitory effect of leptin, such that Npy and Agrp levels in LY-leptin-treated animals were similar to fasted controls. By comparison, leptin-mediated activation of hypothalamic STAT3 signaling, as measured by induction of both phospho-STAT3 immunohistochemistry and suppressor of cytokine signaling-3 (Socs3) mRNA, was not significantly attenuated by ICV LY pretreatment. Because NPY/AgRP neurons project to the hypothalamic paraventricular nucleus (PVN), we next investigated whether leptin activation of PVN neurons is similarly PI3K dependent. Compared with vehicle, leptin increased the number of c-Fos positive cells within the parvocellular PVN (P = 0.001), and LY pretreatment attenuated this effect by 35% (P = 0.043). We conclude that leptin requires intact PI3K signaling both to inhibit hypothalamic Npy and Agrp gene expression and activate neurons within the PVN. In addition, these data suggest that leptin activation of STAT3 is insufficient to inhibit expression of Npy or Agrp in the absence of PI3K signaling.

Influence of feeding status on neuronal activity in the hypothalamus during lipopolysaccharide-induced anorexia in rats

Fasting attenuates disease-associated anorexia, but the mechanisms underlying this effect are not well understood. In the present study, we investigated the extent to which a 48 h fast alters hypothalamic neuronal activity in response to the anorectic effects of lipopolysaccharide in rats. Male rats were fed ad libitum or fasted, and were injected with i.p. saline or lipopolysaccharide (250 microg/kg). Immunohistochemistry for Fos protein was used to visualize neuronal activity in response to lipopolysaccharide within selected hypothalamic feeding regulatory nuclei. Additionally, food intake, body weight, plasma interleukin-1 and leptin levels, and the expression of mRNA for appetite-related neuropeptides (neuropeptide Y, proopiomelanocortin and cocaine-amphetamine-regulated transcript) were measured in a time-related manner. Our data show that the pattern of lipopolysaccharide-induced Fos expression was similar in most hypothalamic nuclei whatever the feeding status. However, we observed that fasting significantly reduced lipopolysaccharide-induced Fos expression in the paraventricular nucleus, in association with an attenuated lipopolysaccharide-induced anorexia and body weight loss. Moreover, lipopolysaccharide reduced fasting-induced Fos expression in the perifornical area of the lateral hypothalamus. Lipopolysaccharide-induced circulating levels of interleukin-1 were similar across feeding status. Finally, fasting, but not lipopolysaccharide, affected circulating level of leptin and appetite-related neuropeptides expression in the arcuate nucleus. Together, our data show that fasting modulates lipopolysaccharide-induced anorexia and body weight loss in association with neural changes in specific hypothalamic nuclei.

Induced expression of c-fos in the diencephalon and pituitary gland of goats following transportation1

To identify regions of the caprine diencephalone and pituitary gland related to transportation stress, the expression of c-fos protein was examined immunohistochemically as an indicator of neural activation. Ten castrated Shiba goats (Capra hircus), five transported and five controls, were used. Transported goats were trucked for 1 h and killed by transcardiac perfusion 1 h after the end of transportation. Control goats were housed in single pens killed in the same manner and at the same time as the transported goats. The diencephalon and the pituitary gland were removed after perfusion and used for immunostaining. Plasma cortisol concentrations during and after transportation also were investigated. During transportation, plasma cortisol concentrations increased (P < 0.05) compared with those in the controls. In the diencephalon, c-fos immunoreactive cells were detected in the subcallosa, the lateral septal area, the bed nucleus of stria terminalis (BNST), the preoptic hypothalamic area (POA), the suprachiasmatic nucleus (SCN), the supraoptic nucleus, the paraventricular hypothalamic nucleus parvocellular (PVNp), the paraventricular hypothalamic nucleus magnocellular (PVNm), the arcuate nucleus (ARC), the paraventricular thalamic nucleus, and the stria medullaris in both control and transported goats. The numbers of c-fos immunoreactive cells were increased (P < 0.05) by transportation in the PVNm, the PVNp, the BNST, the POA, the ARC, and the SCN (P < 0.10). In the anterior pituitary gland, the number of c-fos immunoreactive cells in transported goats was 4 to 30 times as much as in control goats; however, there were no differences in the intermediate and posterior lobes between control and transported goats. This study has identified regions in the caprine diencephalon and pituitary gland that show transport-induced increases in c-fos immunoreactive cells. In conclusion, the PVNm, the PVNp, the BNST, the POA, the SCN in the diencephalons, and the anterior lobe of pituitary gland may be involved in the stress responses of goats to transportation.