SqueakOut: Autoencoder-based segmentation of mouse ultrasonic vocalizations

Mice emit ultrasonic vocalizations (USVs) that are important for social communication. Despite great advancements in tools to detect USVs from audio files in the recent years, highly accurate segmentation of USVs from spectrograms (i.e., removing noise) remains a significant challenge. Here, we present a new dataset of 12,954 annotated spectrograms explicitly labeled for mouse USV segmentation. Leveraging this dataset, we developed SqueakOut, a lightweight (4.6M parameters) fully convolutional autoencoder that achieves high accuracy in supervised segmentation of USVs from spectrograms, with a Dice score of 90.22. SqueakOut combines a MobileNetV2 backbone with skip connections and transposed convolutions to precisely segment USVs. Using stochastic data augmentation techniques and a hybrid loss function, SqueakOut learns robust segmentation across varying recording conditions. We evaluate SqueakOut's performance, demonstrating substantial improvements over existing methods like VocalMat (63.82 Dice score). The accurate USV segmentations enabled by SqueakOut will facilitate novel methods for vocalization classification and more accurate analysis of mouse communication. To promote further research, we release the annotated 12,954 spectrogram USV segmentation dataset and the SqueakOut implementation publicly.

Immune sensing of food allergens promotes avoidance behaviour

In addition to its canonical function of protection from pathogens, the immune system can also alter behaviour1,2. The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Here, using mouse models of food allergy, we show that allergic sensitization drives antigen-specific avoidance behaviour. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus and central amygdala. Allergen avoidance requires immunoglobulin E (IgE) antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote avoidance requires cysteinyl leukotrienes and growth and differentiation factor 15. Finally, a comparison of C57BL/6 and BALB/c mouse strains revealed a strong effect of the genetic background on the avoidance behaviour. These findings thus point to antigen-specific behavioural modifications that probably evolved to promote niche selection to avoid unfavourable environments.

Immune sensing of food allergens promotes aversive behaviour

In addition to its canonical function in protecting from pathogens, the immune system can also promote behavioural alterations ^1â€"3 . The scope and mechanisms of behavioural modifications by the immune system are not yet well understood. Using a mouse food allergy model, here we show that allergic sensitization drives antigen-specific behavioural aversion. Allergen ingestion activates brain areas involved in the response to aversive stimuli, including the nucleus of tractus solitarius, parabrachial nucleus, and central amygdala. Food aversion requires IgE antibodies and mast cells but precedes the development of gut allergic inflammation. The ability of allergen-specific IgE and mast cells to promote aversion requires leukotrienes and growth and differentiation factor 15 (GDF15). In addition to allergen-induced aversion, we find that lipopolysaccharide-induced inflammation also resulted in IgE-dependent aversive behaviour. These findings thus point to antigen-specific behavioural modifications that likely evolved to promote niche selection to avoid unfavourable environments.

AgRP neurons control structure and function of the medial prefrontal cortex

Hypothalamic agouti-related peptide and neuropeptide Y-expressing (AgRP) neurons have a critical role in both feeding and non-feeding behaviors of newborn, adolescent, and adult mice, suggesting their broad modulatory impact on brain functions. Here we show that constitutive impairment of AgRP neurons or their peripubertal chemogenetic inhibition resulted in both a numerical and functional reduction of neurons in the medial prefrontal cortex (mPFC) of mice. These changes were accompanied by alteration of oscillatory network activity in mPFC, impaired sensorimotor gating, and altered ambulatory behavior that could be reversed by the administration of clozapine, a non-selective dopamine receptor antagonist. The observed AgRP effects are transduced to mPFC in part via dopaminergic neurons in the ventral tegmental area and may also be conveyed by medial thalamic neurons. Our results unmasked a previously unsuspected role for hypothalamic AgRP neurons in control of neuronal pathways that regulate higher-order brain functions during development and in adulthood.

Deficiency of the paternally inherited gene Magel2 alters the development of separation-induced vocalization and maternal behavior in mice

The behavior of offspring results from the combined expression of maternal and paternal genes. Genomic imprinting silences some genes in a parent-of-origin specific manner, a process that, among all animals, occurs only in mammals. How genomic imprinting affects the behavior of mammalian offspring, however, remains poorly understood. Here, we studied how the loss of the paternally inherited gene Magel2 in mouse pups affects the emission of separation-induced ultrasonic vocalizations (USV). Using quantitative analysis of more than 1000 USVs, we characterized the rate of vocalizations as well as their spectral features from postnatal days 6-12 (P6-P12), a critical phase of mouse development that covers the peak of vocal behavior in pups. Our analyses show that Magel2 deficient offspring emit separation-induced vocalizations at lower rates and with altered spectral features mainly at P8. We also show that dams display altered behavior towards their own Magel2 deficient offspring at this age. In a test to compare the retrieval of two pups, dams retrieve wildtype control pups first and faster than Magel2 deficient offspring. These results suggest that the loss of Magel2 impairs the expression of separation-induced vocalization in pups as well as maternal behavior at a specific age of postnatal development, both of which support the pups' growth and development.

Ketogenic diet restrains aging-induced exacerbation of coronavirus infection in mice

Increasing age is the strongest predictor of risk of COVID-19 severity and mortality. Immunometabolic switch from glycolysis to ketolysis protects against inflammatory damage and influenza infection in adults. To investigate how age compromises defense against coronavirus infection, and whether a pro-longevity ketogenic diet (KD) impacts immune surveillance, we developed an aging model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain-A59 (MHV-A59). When inoculated intranasally, mCoV is pneumotropic and recapitulates several clinical hallmarks of COVID-19 infection. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue, and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Activation of ketogenesis in aged mice expands tissue protective γδ T cells, deactivates the NLRP3 inflammasome, and decreases pathogenic monocytes in lungs of infected aged mice. These data establish harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against coronavirus infection in the aged.

Deciphering an AgRP-serotoninergic neural circuit in distinct control of energy metabolism from feeding

Contrasting to the established role of the hypothalamic agouti-related protein (AgRP) neurons in feeding regulation, the neural circuit and signaling mechanisms by which they control energy expenditure remains unclear. Here, we report that energy expenditure is regulated by a subgroup of AgRP neurons that send non-collateral projections to neurons within the dorsal lateral part of dorsal raphe nucleus (dlDRN) expressing the melanocortin 4 receptor (MC4R), which in turn innervate nearby serotonergic (5-HT) neurons. Genetic manipulations reveal a bi-directional control of energy expenditure by this circuit without affecting food intake. Fiber photometry and electrophysiological results indicate that the thermo-sensing MC4RdlDRN neurons integrate pre-synaptic AgRP signaling, thereby modulating the post-synaptic serotonergic pathway. Specifically, the MC4RdlDRN signaling elicits profound, bi-directional, regulation of body weight mainly through sympathetic outflow that reprograms mitochondrial bioenergetics within brown and beige fat while feeding remains intact. Together, we suggest that this AgRP neural circuit plays a unique role in persistent control of energy expenditure and body weight, hinting next-generation therapeutic approaches for obesity and metabolic disorders.

Analysis of ultrasonic vocalizations from mice using computer vision and machine learning

Mice emit ultrasonic vocalizations (USVs) that communicate socially relevant information. To detect and classify these USVs, here we describe VocalMat. VocalMat is a software that uses image-processing and differential geometry approaches to detect USVs in audio files, eliminating the need for user-defined parameters. VocalMat also uses computational vision and machine learning methods to classify USVs into distinct categories. In a data set of >4000 USVs emitted by mice, VocalMat detected over 98% of manually labeled USVs and accurately classified ≈86% of the USVs out of 11 USV categories. We then used dimensionality reduction tools to analyze the probability distribution of USV classification among different experimental groups, providing a robust method to quantify and qualify the vocal repertoire of mice. Thus, VocalMat makes it possible to perform automated, accurate, and quantitative analysis of USVs without the need for user inputs, opening the opportunity for detailed and high-throughput analysis of this behavior.

AgRP neurons control compulsive exercise and survival in an activity-based anorexia model

Hypothalamic agouti-related peptide (AgRP) and neuropeptide Y-expressing neurons have a critical role in driving food intake, but also in modulating complex, non-feeding behaviours1. We interrogated whether AgRP neurons are relevant to the emergence of anorexia nervosa symptomatology in a mouse model. Here we show, using in vivo fibre photometry, a rapid inhibition of AgRP neuronal activity following voluntary cessation of running. All AgRP neuron-ablated, food-restricted mice die within 72 h of compulsive running, while daily activation of AgRP neurons using a chemogenetic tool increases voluntary running with no lethality of food-restricted animals. Animals with impaired AgRP neuronal circuits are unable to properly mobilize fuels during food-restriction-associated exercise; however, when provided with elevated fat content through diet, their death is completely prevented. Elevated fat content in the diet also prevents the long-term behavioural impact of food-restricted fit mice with elevated exercise volume. These observations elucidate a previously unsuspected organizational role of AgRP neurons, via the mediation of the periphery, in the regulation of compulsive exercise and its related lethality with possible implications for psychiatric conditions, such as anorexia nervosa.

Ketogenesis restrains aging-induced exacerbation of COVID in a mouse model

Increasing age is the strongest predictor of risk of COVID-19 severity. Unregulated cytokine storm together with impaired immunometabolic response leads to highest mortality in elderly infected with SARS-CoV-2. To investigate how aging compromises defense against COVID-19, we developed a model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain MHV-A59 (mCoV-A59) that recapitulated majority of clinical hallmarks of COVID-19. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Ketogenic diet increases beta-hydroxybutyrate, expands tissue protective γδ T cells, deactivates the inflammasome and decreases pathogenic monocytes in lungs of infected aged mice. These data underscore the value of mCoV-A59 model to test mechanism and establishes harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against COVID-19 in the elderly.

Highlights

- Natural MHV-A59 mouse coronavirus infection mimics COVID-19 in elderly.- Aged infected mice have systemic inflammation and inflammasome activation.- Murine beta coronavirus (mCoV) infection results in loss of pulmonary γδ T cells.- Ketones protect aged mice from infection by reducing inflammation.

eTOC Blurb

Elderly have the greatest risk of death from COVID-19. Here, Ryu et al report an aging mouse model of coronavirus infection that recapitulates clinical hallmarks of COVID-19 seen in elderly. The increased severity of infection in aged animals involved increased inflammasome activation and loss of γδ T cells that was corrected by ketogenic diet.

Functional Ontogeny of Hypothalamic Agrp Neurons in Neonatal Mouse Behaviors

Hypothalamic Agrp neurons regulate food ingestion in adult mice. Whether these neurons are functional before animals start to ingest food is unknown. Here, we studied the functional ontogeny of Agrp neurons during breastfeeding using postnatal day 10 mice. In contrast to adult mice, we show that isolation from the nursing nest, not milk deprivation or ingestion, activated Agrp neurons. Non-nutritive suckling and warm temperatures blunted this effect. Using in vivo fiber photometry, neonatal Agrp neurons showed a rapid increase in activity upon isolation from the nest, an effect rapidly diminished following reunion with littermates. Neonates unable to release GABA from Agrp neurons expressed blunted emission of isolation-induced ultrasonic vocalizations. Chemogenetic overactivation of these neurons further increased emission of these ultrasonic vocalizations, but not milk ingestion. We uncovered important functional properties of hypothalamic Agrp neurons during mouse development, suggesting these neurons facilitate offspring-to-caregiver bonding.

Activation of Agrp neurons modulates memory-related cognitive processes in mice

Hypothalamic Agrp neurons are critical regulators of food intake in adult mice. In addition to food intake, these neurons have been involved in other cognitive processes, such as the manifestation of stereotyped behaviors. Here, we evaluated the extent to which Agrp neurons modulate mouse behavior in spatial memory-related tasks. We found that activation of Agrp neurons did not affect spatial learning but altered behavioral flexibility using a modified version of the Barnes Maze task. Furthermore, using the Y-maze test to probe working memory, we found that chemogenetic activation of Agrp neurons reduced spontaneous alternation behavior mediated by the neuropeptide Y receptor-5 signaling. These findings suggest novel functional properties of Agrp neurons in memory-related cognitive processes.

Regulation of substrate utilization and adiposity by Agrp neurons

The type of nutrient utilized by the organism at any given time—substrate utilization—is a critical component of energy metabolism. The neuronal mechanisms involved in the regulation of substrate utilization in mammals are largely unknown. Here, we found that activation of hypothalamic Agrp neurons rapidly altered whole-body substrate utilization, increasing carbohydrate utilization, while decreasing fat utilization. These metabolic changes occurred even in the absence of caloric ingestion and were coupled to increased lipogenesis. Accordingly, inhibition of fatty acid synthase—a key enzyme that mediates lipogenesis—blunted the effects of Agrp neuron activation on substrate utilization. In pair-fed conditions during positive energy balance, activation of Agrp neurons improved metabolic efficiency, and increased weight gain and adiposity. Conversely, ablation of Agrp neurons impaired fat mass accumulation. These results suggest Agrp neurons regulate substrate utilization, contributing to lipogenesis and fat mass accumulation during positive energy balance.

Agouti-related peptide (AgRP) producing neurons regulate food intake and metabolic processes in peripheral organs. Here, the authors show that hypothalamic AgRP neurons alter whole body substrate utilization to favour carbohydrate usage and lipid storage.

Plasticity of calcium-permeable AMPA glutamate receptors in Pro-opiomelanocortin neurons

POMC neurons integrate metabolic signals from the periphery. Here, we show in mice that food deprivation induces a linear current-voltage relationship of AMPAR-mediated excitatory postsynaptic currents (EPSCs) in POMC neurons. Inhibition of EPSCs by IEM-1460, an antagonist of calcium-permeable (Cp) AMPARs, diminished EPSC amplitude in the fed but not in the fasted state, suggesting entry of GluR2 subunits into the AMPA receptor complex during food deprivation. Accordingly, removal of extracellular calcium from ACSF decreased the amplitude of mEPSCs in the fed but not the fasted state. Ten days of high-fat diet exposure, which was accompanied by elevated leptin levels and increased POMC neuronal activity, resulted in increased expression of Cp-AMPARs on POMC neurons. Altogether, our results show that entry of calcium via Cp-AMPARs is inherent to activation of POMC neurons, which may underlie a vulnerability of these neurons to calcium overload while activated in a sustained manner during over-nutrition.

DOI:http://dx.doi.org/10.7554/eLife.25755.001

A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages

Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood-brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood-brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system.

AgRP Neurons Regulate Bone Mass

The hypothalamus has been implicated in skeletal metabolism. Whether hunger-promoting neurons of the arcuate nucleus impact the bone is not known. We generated multiple lines of mice to affect AgRP neuronal circuit integrity. We found that mice with Ucp2 gene deletion, in which AgRP neuronal function was impaired, were osteopenic. This phenotype was rescued by cell-selective reactivation of Ucp2 in AgRP neurons. When the AgRP circuitry was impaired by early postnatal deletion of AgRP neurons or by cell autonomous deletion of Sirt1 (AgRP-Sirt1(-/-)), mice also developed reduced bone mass. No impact of leptin receptor deletion in AgRP neurons was found on bone homeostasis. Suppression of sympathetic tone in AgRP-Sirt1(-/-) mice reversed osteopenia in transgenic animals. Taken together, these observations establish a significant regulatory role for AgRP neurons in skeletal bone metabolism independent of leptin action.

O-GlcNAc transferase enables AgRP neurons to suppress browning of white fat

Induction of beige cells causes the browning of white fat and improves energy metabolism. However, the central mechanism that controls adipose tissue browning and its physiological relevance are largely unknown. Here, we demonstrate that fasting and chemical-genetic activation of orexigenic AgRP neurons in the hypothalamus suppress the browning of white fat. O-linked β-N-acetylglucosamine (O-GlcNAc) modification of cytoplasmic and nuclear proteins regulates fundamental cellular processes. The levels of O-GlcNAc transferase (OGT) and O-GlcNAc modification are enriched in AgRP neurons and are elevated by fasting. Genetic ablation of OGT in AgRP neurons inhibits neuronal excitability through the voltage-dependent potassium channel, promotes white adipose tissue browning, and protects mice against diet-induced obesity and insulin resistance. These data reveal adipose tissue browning as a highly dynamic physiological process under central control, in which O-GlcNAc signaling in AgRP neurons is essential for suppressing thermogenesis to conserve energy in response to fasting.

Leptin signaling in astrocytes regulates hypothalamic neuronal circuits and feeding

We found that leptin receptors were expressed in hypothalamic astrocytes and that their conditional deletion led to altered glial morphology and synaptic inputs onto hypothalamic neurons involved in feeding control. Leptin-regulated feeding was diminished, whereas feeding after fasting or ghrelin administration was elevated in mice with astrocyte-specific leptin receptor deficiency. These data reveal an active role of glial cells in hypothalamic synaptic remodeling and control of feeding by leptin.

Hypothalamic melanin concentrating hormone neurons communicate the nutrient value of sugar

Sugars that contain glucose, such as sucrose, are generally preferred to artificial sweeteners owing to their post-ingestive rewarding effect, which elevates striatal dopamine (DA) release. While the post-ingestive rewarding effect, which artificial sweeteners do not have, signals the nutrient value of sugar and influences food preference, the neural circuitry that mediates the rewarding effect of glucose is unknown. In this study, we show that optogenetic activation of melanin-concentrating hormone (MCH) neurons during intake of the artificial sweetener sucralose increases striatal dopamine levels and inverts the normal preference for sucrose vs sucralose. Conversely, animals with ablation of MCH neurons no longer prefer sucrose to sucralose and show reduced striatal DA release upon sucrose ingestion. We further show that MCH neurons project to reward areas and are required for the post-ingestive rewarding effect of sucrose in sweet-blind Trpm5(-/-) mice. These studies identify an essential component of the neural pathways linking nutrient sensing and food reward. DOI: http://dx.doi.org/10.7554/eLife.01462.001.

Mitofusin 2 in POMC neurons connects ER stress with leptin resistance and energy imbalance

Mitofusin 2 (MFN2) plays critical roles in both mitochondrial fusion and the establishment of mitochondria-endoplasmic reticulum (ER) interactions. Hypothalamic ER stress has emerged as a causative factor for the development of leptin resistance, but the underlying mechanisms are largely unknown. Here, we show that mitochondria-ER contacts in anorexigenic pro-opiomelanocortin (POMC) neurons in the hypothalamus are decreased in diet-induced obesity. POMC-specific ablation of Mfn2 resulted in loss of mitochondria-ER contacts, defective POMC processing, ER stress-induced leptin resistance, hyperphagia, reduced energy expenditure, and obesity. Pharmacological relieve of hypothalamic ER stress reversed these metabolic alterations. Our data establish MFN2 in POMC neurons as an essential regulator of systemic energy balance by fine-tuning the mitochondrial-ER axis homeostasis and function. This previously unrecognized role for MFN2 argues for a crucial involvement in mediating ER stress-induced leptin resistance.

Mitochondrial dynamics controlled by mitofusins regulate Agrp neuronal activity and diet-induced obesity

Mitochondria are key organelles in the maintenance of cellular energy metabolism and integrity. Here, we show that mitochondria number decrease but their size increase in orexigenic agouti-related protein (Agrp) neurons during the transition from fasted to fed to overfed state. These fusion-like dynamic changes were cell-type specific, as they occurred in the opposite direction in anorexigenic pro-opiomelanocortin (POMC) neurons. Interfering with mitochondrial fusion mechanisms in Agrp neurons by cell-selectively knocking down mitofusin 1 (Mfn1) or mitofusin 2 (Mfn2) resulted in altered mitochondria size and density in these cells. Deficiency in mitofusins impaired the electric activity of Agrp neurons during high-fat diet (HFD), an event reversed by cell-selective administration of ATP. Agrp-specific Mfn1 or Mfn2 knockout mice gained less weight when fed a HFD due to decreased fat mass. Overall, our data unmask an important role for mitochondrial dynamics governed by Mfn1 and Mfn2 in Agrp neurons in central regulation of whole-body energy metabolism.

Hypothalamic control of energy balance: insights into the role of synaptic plasticity

The past 20 years witnessed an enormous leap in understanding of the central regulation of whole-body energy metabolism. Genetic tools have enabled identification of the region-specific expression of peripheral metabolic hormone receptors and have identified neuronal circuits that mediate the action of these hormones on behavior and peripheral tissue functions. One of the surprising findings of recent years is the observation that brain circuits involved in metabolism regulation remain plastic through adulthood. In this review, we discuss these findings and focus on the role of neurons and glial cells in the dynamic process of plasticity, which is fundamental to the regulation of physiological and pathological metabolic events.

Leptin regulates glutamate and glucose transporters in hypothalamic astrocytes

Glial cells perform critical functions that alter the metabolism and activity of neurons, and there is increasing interest in their role in appetite and energy balance. Leptin, a key regulator of appetite and metabolism, has previously been reported to influence glial structural proteins and morphology. Here, we demonstrate that metabolic status and leptin also modify astrocyte-specific glutamate and glucose transporters, indicating that metabolic signals influence synaptic efficacy and glucose uptake and, ultimately, neuronal function. We found that basal and glucose-stimulated electrical activity of hypothalamic proopiomelanocortin (POMC) neurons in mice were altered in the offspring of mothers fed a high-fat diet. In adulthood, increased body weight and fasting also altered the expression of glucose and glutamate transporters. These results demonstrate that whole-organism metabolism alters hypothalamic glial cell activity and suggest that these cells play an important role in the pathology of obesity.

Sirtuin 1 and sirtuin 3: physiological modulators of metabolism

The sirtuins are a family of highly conserved NAD(+)-dependent deacetylases that act as cellular sensors to detect energy availability and modulate metabolic processes. Two sirtuins that are central to the control of metabolic processes are mammalian sirtuin 1 (SIRT1) and sirtuin 3 (SIRT3), which are localized to the nucleus and mitochondria, respectively. Both are activated by high NAD(+) levels, a condition caused by low cellular energy status. By deacetylating a variety of proteins that induce catabolic processes while inhibiting anabolic processes, SIRT1 and SIRT3 coordinately increase cellular energy stores and ultimately maintain cellular energy homeostasis. Defects in the pathways controlled by SIRT1 and SIRT3 are known to result in various metabolic disorders. Consequently, activation of sirtuins by genetic or pharmacological means can elicit multiple metabolic benefits that protect mice from diet-induced obesity, type 2 diabetes, and nonalcoholic fatty liver disease.

Ghrelin-immunopositive hypothalamic neurons tie the circadian clock and visual system to the lateral hypothalamic arousal center

Ghrelin, a circulating gut-hormone, has emerged as an important regulator of growth hormone release and appetite. Ghrelin-immunopositive neurons have also been identified in the hypothalamus with a unique anatomical distribution. Here, we report that ghrelin-labeled neurons receive direct synaptic input from the suprachiasmatic nucleus, the central circadian timekeeper of the brain, and lateral geniculate nucleus, a visual center, and project synaptically to the lateral hypothalamic orexin/hypocretin system, a region of the brain critical for arousal. Hypothalamic ghrelin mRNA oscillates in a circadian pattern peaking in the dark phase prior to the switch from arousal to sleep. Ghrelin inhibits the electrophysiological activity of identified orexin/hypocretin neurons in hypothalamic slices. These observations indicate that the hypothalamic neurons identified by ghrelin immunolabeling may be a key mediator of circadian and visual cues for the hypothalamic arousal system.

UCP2 induced by natural birth regulates neuronal differentiation of the hippocampus and related adult behavior

Mitochondrial uncoupling protein 2 (UCP2) is induced by cellular stress and is involved in regulation of fuel utilization, mitochondrial bioenergetics, cell proliferation, neuroprotection and synaptogenesis in the adult brain. Here we show that natural birth in mice triggers UCP2 expression in hippocampal neurons. Chemical inhibition or genetic ablation of UCP2 lead to diminished neuronal number and size, dendritic growth and synaptogenezis in vitro and impaired complex behaviors in the adult. These data reveal a critical role for Ucp2 expression in the development of hippocampal neurons and circuits and hippocampus-related adult behaviors.

AgRP neurons regulate development of dopamine neuronal plasticity and nonfood-associated behaviors

It is not known whether behaviors unrelated to feeding are affected by hypothalamic regulators of hunger. We found that impairment of Agouti-related protein (AgRP) circuitry by either Sirt1 knockdown in AgRP-expressing neurons or early postnatal ablation of these neurons increased exploratory behavior and enhanced responses to cocaine. In AgRP circuit-impaired mice, ventral tegmental dopamine neurons exhibited enhanced spike timing-dependent long-term potentiation, altered amplitude of miniature postsynaptic currents and elevated dopamine in basal forebrain. Thus, AgRP neurons determine the set point of the reward circuitry and associated behaviors.

Obesity is associated with hypothalamic injury in rodents and humans

Rodent models of obesity induced by consuming high-fat diet (HFD) are characterized by inflammation both in peripheral tissues and in hypothalamic areas critical for energy homeostasis. Here we report that unlike inflammation in peripheral tissues, which develops as a consequence of obesity, hypothalamic inflammatory signaling was evident in both rats and mice within 1 to 3 days of HFD onset, prior to substantial weight gain. Furthermore, both reactive gliosis and markers suggestive of neuron injury were evident in the hypothalamic arcuate nucleus of rats and mice within the first week of HFD feeding. Although these responses temporarily subsided, suggesting that neuroprotective mechanisms may initially limit the damage, with continued HFD feeding, inflammation and gliosis returned permanently to the mediobasal hypothalamus. Consistent with these data in rodents, we found evidence of increased gliosis in the mediobasal hypothalamus of obese humans, as assessed by MRI. These findings collectively suggest that, in both humans and rodent models, obesity is associated with neuronal injury in a brain area crucial for body weight control.

Synaptic plasticity of feeding circuits: hormones and hysteresis

The drive to eat is controlled by neuronal circuits in the hypothalamus that respond to hormones signaling hunger or satiety. In this issue of Cell, Yang et al. (2011) reveal an AMPK-dependent synaptic pathway that sustains excitatory stimulation of the NPY/AgRP neurons that promote feeding behavior until satiety signals kick in.

Peroxisome proliferation-associated control of reactive oxygen species sets melanocortin tone and feeding in diet-induced obesity

Previous studies have proposed roles for hypothalamic reactive oxygen species (ROS) in the modulation of circuit activity of the melanocortin system. Here we show that suppression of ROS diminishes pro-opiomelanocortin (POMC) cell activation and promotes the activity of neuropeptide Y (NPY)- and agouti-related peptide (AgRP)-co-producing (NPY/AgRP) neurons and feeding, whereas ROS-activates POMC neurons and reduces feeding. The levels of ROS in POMC neurons were positively correlated with those of leptin in lean and ob/ob mice, a relationship that was diminished in diet-induced obese (DIO) mice. High-fat feeding resulted in proliferation of peroxisomes and elevated peroxisome proliferator-activated receptor γ (PPAR-γ) mRNA levels within the hypothalamus. The proliferation of peroxisomes in POMC neurons induced by the PPAR-γ agonist rosiglitazone decreased ROS levels and increased food intake in lean mice on high-fat diet. Conversely, the suppression of peroxisome proliferation by the PPAR antagonist GW9662 increased ROS concentrations and c-fos expression in POMC neurons. Also, it reversed high-fat feeding-triggered elevated NPY/AgRP and low POMC neuronal firing, and resulted in decreased feeding of DIO mice. Finally, central administration of ROS alone increased c-fos and phosphorylated signal transducer and activator of transcription 3 (pStat3) expression in POMC neurons and reduced feeding of DIO mice. These observations unmask a previously unknown hypothalamic cellular process associated with peroxisomes and ROS in the central regulation of energy metabolism in states of leptin resistance.

Feeding signals and brain circuitry

Food intake is a major physiological function in animals and must be entrained to the circadian oscillations in food availability. In the last two decades a growing number of reports have shed light on the hormonal, cellular and molecular mechanisms involved in the regulation of food intake. Brain areas located in the hypothalamus have been shown to play a pivotal role in the regulation of energy metabolism, controlling energy balance. In these areas, neuronal plasticity has been reported that is dependent upon key hormones, such as leptin and ghrelin, that are produced by peripheral organs. This review will provide an overview of recent discoveries relevant to understanding these issues.

The role of mitochondrial uncoupling proteins in lifespan

The increased longevity in modern societies raised the attention to biological interventions that could promote a healthy aging. Mitochondria are main organelles involved in the production of adenosine triphosphate (ATP), the energetic substrate for cellular biochemical reactions. The production of ATP occurs through the oxidative phosphorylation of intermediate substrates derived from the breakdown of lipids, sugars, and proteins. This process is coupled to production of oxygen reactive species (ROS) that in excess will have a deleterious role in cellular function. The damage promoted by ROS has been emphasized as one of the main processes involved in senescence. In the last decades, the discovery of specialized proteins in the mitochondrial inner membrane that promote the uncoupling of proton flux (named uncoupling proteins-UCPs) from the ATP synthase shed light on possible mechanisms implicated in the buffering of ROS and consequently in the process of aging. UCPs are responsible for a physiological uncoupling that leads to decrease in ROS production inside the mitochondria. Thus, induction of uncoupling through UCPs could decrease the cellular damage that occurs during aging due to excess of ROS. This review will focus on the evidence supporting these mechanisms.

GABA keeps up an appetite for life

In the arcuate nucleus of the hypothalamus, neurons that produce the neuropeptides NPY and AgRP play a vital role in the maintenance of energy homeostasis. In this issue, Wu et al. (2009) show that these neurons modulate feeding behavior in mice by providing GABAergic input to the parabrachial nucleus in the brainstem.

Megalin mediates the transport of leptin across the blood-CSF barrier

Leptin, a peptide hormone secreted by adipose tissue, exhibits a large range of central and peripheral actions. It has been proposed that the participation of leptin in diseases such as obesity is due to, at least in part, its impaired transport across the blood-brain barrier (BBB). Since, the mechanisms by which brain takes up leptin remain unclear, we set out to study how leptin may cross the BBB. We have used different immunoassays and lentiviral vectors to analyze the role of megalin in the transport of leptin in rodents and humans. We demonstrate that circulating leptin is transported into the brain by binding to megalin at the choroid plexus epithelium. Indeed, the downregulation of megalin expression in physiological and pathological situations such as aging and Alzheimer's disease was correlated with poor entry of leptin into the brain. Moreover, amyloid beta (Abeta) deposits of choroid plexus could be disturbing megalin function. The present data indicate that leptin represents a novel megalin ligand of importance in the levels and therapeutic actions of leptin into the brain.

Disturbed cross talk between insulin-like growth factor I and AMP-activated protein kinase as a possible cause of vascular dysfunction in the amyloid precursor protein/presenilin 2 mouse model of Alzheimer's disease

Cerebrovascular dysfunction appears to be involved in Alzheimer's disease (AD). In double mutant amyloid precursor protein/presenilin 2 (APP/PS2) mice, a transgenic model of AD, vessel homeostasis is disturbed. These mice have elevated levels of vascular endothelial growth factor (VEGF) and increased brain endothelial cell division but abnormally low brain vessel density. Examination of the potential involvement of insulin-like growth factor I (IGF-I) in these alterations revealed that treatment with IGF-I, a potent vessel growth promoter in the brain that ameliorates cognitive dysfunction in APP/PS2 mice, counteracted vascular dysfunction as follows: VEGF levels and endothelial cell proliferation were reduced, whereas vascular density was normalized. Notably, abnormally elevated brain IGF-I receptor levels in APP/PS2 mice were also normalized by IGF-I treatment. Analysis of possible processes involved in these alterations indicated that AMP-activated protein kinase (AMPK), a cell energy sensor that intervenes in angiogenic signaling and interacts with IGF-I, was also abnormally activated in APP/PS2 brains. Examination of the consequences of AMPK activation on cultured brain endothelial cells revealed increased VEGF levels together with enhanced endothelial cell proliferation and metabolism. Although these effects were also independently elicited by IGF-I, when both IGF-I and AMPK pathways were simultaneously activated on brain endothelial cells, VEGF production and endothelial cell proliferation ceased while cells remained metabolically activated (glucose use, peroxide production, and mitochondrial activity were elevated) and became more resistant to oxidative stress. Therefore, high IGF-I receptor and phosphoAMPK levels in APP/PS2 brains may reflect imbalanced IGF-I and AMPK angiogenic cross talk that could underlie vascular dysfunction in this model of AD.

Decreased plasma brain derived neurotrophic factor levels in unmedicated bipolar patients during manic episode

BACKGROUND

Bipolar disorder (BD) has been increasingly associated with abnormalities in neuroplasticity and cellular resilience. Brain Derived Neurotrophic Factor (BDNF) gene has been considered an important candidate marker for the development of bipolar disorder and this neurotrophin seems involved in intracellular pathways modulated by mood stabilizers. Also, previous studies demonstrated a role for BDNF in the pathophysiology and clinical presentation of mood disorders.

METHODS

We investigated whether BDNF levels are altered during mania. Sixty subjects (14 M and 46 F) were selected and included in the study. Thirty patients meeting SCID-I criteria for manic episode were age and gender matched with thirty healthy controls. Young Mania Rating Scale (YMRS) evaluated the severity of manic episode and its possible association with the neurotrophin levels.

RESULTS

Mean BDNF levels were significantly decreased in drug free/naive (224.8 +/- 76.5 pg/ml) compared to healthy controls (318.5 +/- 114.2), p < .001]. Severity of the manic episode presented a significant negatively correlation to plasma BDNF levels (r= .78; p < .001; Pearson test).

CONCLUSIONS

Overall, these results suggest that the decreased plasma BDNF levels may be directly associated with the pathophysiology and severity of manic symptoms in BD. Further studies are necessary to clarify the role of BDNF as a putative biological marker in BD.

Exercise affects glutamate receptors in postsynaptic densities from cortical mice brain

Physical activity has been proposed as a behavior intervention that promotes mental health and some of the benefits induced by exercise have been related to the glutamatergic system. Indeed, glutamate is the most abundant excitatory neurotransmitter in brain. Thus, we evaluated if voluntary exercise in mice could modulate glutamatergic synapses at level of postsynaptic density (PSD). Through Western blot, we found that exercise during 1 month increased glutamatergic-related protein content in PSD from cortex of mice. Exercise increased the immunocontent of GluR1 (129%), SAP-97 (179%), GRIP-1 (129%), and in less extent, GluR2/3 (118%) and PSD-95 (112%) proteins. The overall content of NMDA subunits R1, R2A and R2B were not altered in mice that had exercised, however, the phosphorylated NMDA subunits, phospho-NMDAR1 (150%), and phospho-NMDAR2B (183%) showed a strong increase. Because exercise increased the content of phosphorylated forms of NMDA receptors, we evaluated the binding of MK-801, a specific ligand that binds to open NMDA channel. Exercise increased the binding of MK-801 in cortical cellular membranes in 51%. Altogether, our results point to a modulation of glutamatergic synapses by exercise with likely implications in the exercise-induced mental health.

Motor impairment induced by oral exposure to methylmercury in adult mice

The effects of oral exposure to methylmercury chloride (MeHg) on locomotor control and activity in adult mice were investigated in the present study. MeHg was diluted in drinking water (0, 20 and 40mg/L - as methylmercury chloride) and locomotion (spontaneous locomotor activity) and motor impairment tests (beam walking, footprint and clasping) were performed at 7, 14 and 21 days after the beginning of the treatment. MeHg exposure caused a significant decrease in spontaneous locomotor activity and this effect was dose- and time-dependent. Significant dose- and duration-dependent increases in beam walking latency were observed following chronic MeHg exposure. Furthermore, dose- and duration-dependent locomotor deficits on footprint coordination were also observed. Taken together, these results show that MeHg-induced impairment on locomotor activity is not limited to exposures that take place during neural development. We discuss the possible relationship between our findings and the similar clinical signs observed in adult humans exposed to MeHg.

Increased locomotor response to amphetamine, but not other psychostimulants, in adult mice submitted to a low-protein diet

Protein malnutrition results in a variety of brain dysfunctions, ultimately affecting cognitive functions. The effects of protein malnutrition in brain response to psychostimulants have been less studied in adult animals. We therefore aimed to study the response to psychoactive drugs on the locomotor activity (a behavior paradigm) of adult protein malnourished mice. Two-month-old mice were divided in two groups: (a) low-protein group (LP), which received 6% of protein diet, and (b) a control group that received a 25% of protein diet. After 3 months, they were tested for locomotor activity after an i.p. injection of one of psychoactive drugs: D-amphetamine (5.0 mg/kg), apomorphine (2.0 mg/kg), dizocilpine (0.25 mg/kg), or caffeine (30 mg/kg). Mice submitted to the LP diet presented prolonged induction of hyperlocomotion caused by amphetamine (about 350% between 90 and 180 min post drug injection as compared with well-nourished mice, p<0.01) but presented unaltered response to apomorphine, caffeine, and dizocilpine. These data point to altered catecholamine metabolism induced by protein restriction in adult mice. The results are discussed based on previous works, presenting theoretical hypotheses about the possible mechanisms involved in the present findings.

Guanosine selectively inhibits locomotor stimulation induced by the NMDA antagonist dizocilpine

Guanosine has been shown to modulate glutamate system by stimulating astrocytic glutamate uptake. Recent evidence suggest that the locomotor effects of NMDA receptor antagonists, an animal model of schizophrenia, is associated with activation of non-NMDA glutamatergic receptors caused by increased glutamate release. The present work was undertaken to evaluate whether guanosine could have influence on the hyperlocomotion induced in mice by dizocilpine (MK-801), a NMDA antagonist. We also evaluated the effect of guanosine on the hyperlocomotion induced by the indirect dopamine agonist amphetamine, and by the non-selective adenosine receptor antagonist caffeine. Guanosine (7.5 mg/kg) produced an attenuation of about 60% on the hyperlocomotion induced by dizocilpine (0.25 mg/kg), whereas it did not affect the hyperlocomotion induced by amphetamine (5 mg/kg) or caffeine (30 mg/kg). Guanosine pre-treatment did not affect total spontaneous locomotion in all experiments. To test neuronal pathway selectivity, we evaluated MK-801 against guanosine in a working memory paradigm (spontaneous alternation task). Guanosine did not reverted the impairment caused by MK-801 in the spontaneous alternation test, and when administered alone also presented an amnesic effect. The results are discussed based on the current hypothesis of locomotor activation induced by the psychoactive drugs studied. Further studies are necessary to evaluate if guanosine could have clinical utility for the treatment of schizophrenia.

Influence of anticoagulants on the measurement of S100B protein in blood

OBJECTIVE

Evaluate anticoagulants influence on blood S100B levels.

DESIGN AND METHODS

Blood from 18 healthy adult subjects were collected using: no anticoagulants; EDTA; heparin; and citrate. S100B levels were determined using LIA-mat assay.

RESULTS

Heparin and citrate increased S100B levels (p<0.001), whereas EDTA had no effect (p=0.24). Heparin samples were highly (r2=0.97, p<0.001), citrate samples were moderately (r2=0.49, p<0.001), and EDTA samples were not (r2=0.22, p=0.059) correlated with serum samples.

CONCLUSION

When anticoagulant is required, heparin should be the primary choice.

Ebselen protects against methylmercury-induced inhibition of glutamate uptake by cortical slices from adult mice

Methylmercury (MeHg) is a highly neurotoxic compound and the inhibition of glutamate uptake by astrocytes has been pointed as an important mechanism involved in MeHg-induced glutamate excitotoxicity. We examined the effect of oral exposure to MeHg (10 and 40 mg/l in drinking water) on glutamate uptake by brain cortical slices of adult mice. Moreover, the possible protective role of ebselen (20 mg/kg, subcutaneously) against MeHg effect was also examined. In addition, it was measured the glutathione peroxidase and catalase activities in mice brain. Our results demonstrated, for the first time, that in vivo exposure to MeHg causes a dose-dependent decrease in glutamate uptake and that ebselen, which did not affect the uptake per se, reverted this effect. MeHg decreased glutathione peroxidase activity and increased catalase activity, effects which were also prevented by ebselen. These results may indirectly indicate that: (i) the in vivo inhibitory effect of MeHg on glutamate uptake could be probably related to overproduction of H(2)O(2); (ii) the protective effect of ebselen on MeHg-induced inhibition of glutamate uptake could be related to its ability to detoxify H(2)O(2).

Influence of anticoagulants on the measurement of S100B protein in blood

OBJECTIVE

Evaluate anticoagulants influence on plasma S100B levels.

DESIGN AND METHODS

Blood were collected from 18 healthy adult subjects using: no anticoagulants, EDTA, heparin, and citrate. S100B levels were determined using LIA-mat assay.

RESULTS

Heparin plasma and citrate increased plasma S100B levels (p < 0.001), whereas EDTA had no effect (p = 0.24). Heparin plasma samples were highly (r2 = 0.97, p < 0.001), citrate samples were moderately (r2 = 0.49, p < 0.001), and EDTA samples were not (r2 = 0.22, p = 0.059) correlated with serum samples.

CONCLUSIONS

When anticoagulant is required, heparin plasma should be the primary choice for measurement of S100 B levels.

Increase in Serum S100B Protein Level After a Swimming Race

Physical activity has been shown to be a beneficial stimulus to the central and peripheral nervous systems. The S100B is a cytokine physiologically produced and released predominantly by astrocytes on the central nervous system (CNS). In order to study the possible influence of a nonimpact exercise on S100B serum levels, we measured this protein serum level after a 7,600-meter swimming race. We observed an increase in S100B levels in athletes post-race compared with their baseline values, pointing to a potential acute influence of physical exercise on serum S100B levels not related with CNS injury. We discuss this result and emphasize the possible central and peripheral origins of S100B serum levels. Key words: exercise, serotonin, astrocytes