Leptin action on GABAergic neurons prevents obesity and reduces inhibitory tone to POMC neurons

The TRPM2 channel is a hypothalamic heat sensor that limits fever and can drive hypothermia

Body temperature homeostasis is critical for survival and requires precise regulation by the nervous system. The hypothalamus serves as the principal thermostat that detects and regulates internal temperature. We demonstrate that the ion channel TRPM2 [of the transient receptor potential (TRP) channel family] is a temperature sensor in a subpopulation of hypothalamic neurons. TRPM2 limits the fever response and may detect increased temperatures to prevent overheating. Furthermore, chemogenetic activation and inhibition of hypothalamic TRPM2-expressing neurons in vivo decreased and increased body temperature, respectively. Such manipulation may allow analysis of the beneficial effects of altered body temperature on diverse disease states. Identification of a functional role for TRP channels in monitoring internal body temperature should promote further analysis of molecular mechanisms governing thermoregulation and foster the genetic dissection of hypothalamic circuits involved with temperature homeostasis.

Dynamic GABAergic afferent modulation of AgRP neurons

Agouti-related peptide (AgRP) neurons of the arcuate nucleus of the hypothalamus (ARC) promote homeostatic feeding at times of caloric insufficiency, yet they are rapidly suppressed by food-related sensory cues prior to ingestion. Here we identify a highly selective inhibitory afferent to AgRP neurons that serves as a neural determinant of this rapid modulation. Specifically, GABAergic projections arising from the ventral compartment of the dorsomedial nucleus of the hypothalamus (vDMH) contribute to the pre-consummatory modulation of ARC^AgRP neurons. In a manner reciprocal to ARC^AgRP neurons, ARC-projecting leptin receptor (LepR)-expressing GABAergic DMH neurons exhibit rapid activation upon availability of food that additionally reflects the relative value of the food. Thus, DMH^LepR neurons form part of the sensory network that relays real-time information about the nature and availability of food to dynamically modulate ARC^AgRP neuron activity and feeding behavior.

Tumour biology of obesity-related cancers: understanding the molecular concept for better diagnosis and treatment

Obesity continues to be a major global problem. Various cancers are related to obesity and proper understanding of their aetiology, especially their molecular tumour biology is important for early diagnosis and better treatment. Genes play an important role in the development of obesity. Few genes such as leptin, leptin receptor encoded by the db (diabetes), pro-opiomelanocortin, AgRP and NPY and melanocortin-4 receptors and insulin-induced gene 2 were linked to obesity. MicroRNAs control gene expression via mRNA degradation and protein translation inhibition and influence cell differentiation, cell growth and cell death. Overexpression of miR-143 inhibits tumour growth by suppressing B cell lymphoma 2, extracellular signal-regulated kinase-5 activities and KRAS oncogene. Cancers of the breast, uterus, renal, thyroid and liver are also related to obesity. Any disturbance in the production of sex hormones and insulin, leads to distortion in the balance between cell proliferation, differentiation and apoptosis. The possible mechanism linking obesity to cancer involves alteration in the level of adipokines and sex hormones. These mediators act as biomarkers for cancer progression and act as targets for cancer therapy and prevention. Interestingly, many anti-cancerous drugs are also beneficial in treating obesity and vice versa. We also reviewed the possible link in the mechanism of few drugs which act both on cancer and obesity. The present review may be important for molecular biologists, oncologists and clinicians treating cancers and also pave the way for better therapeutic options.

An integrative study identifies KCNC2 as a novel predisposing factor for childhood obesity and the risk of diabetes in the Korean population

Obesity is a major risk factor for type 2 diabetes. To unravel the genetic determinants of obesity-associated diabetes, we performed a genome-wide study using the 1,000 Genomes-based imputation in a Korean childhood cohort (KoCAS-1, n = 484) and carried out de novo replication in an independent population (KoCAS-2, n = 1,548). A novel variant (rs10879834) with multiple diverse associations for obesity-related traits was also found to be replicated in an adult cohort (KARE, n = 8,842). Functional annotations using integrative epigenetic analyses identified biological significance and regulatory effects with an inverse methylation-expression correlation (cg27154343 in the 5′-UTR of the KCNC2 gene), tissue-specific enhancer mark (H3K4me1), and pathway enrichment (insulin signaling). Further functional studies in cellular and mouse models demonstrated that KCNC2 is associated with anti-obesogenic effects in the regulation of obesity-induced insulin resistance. KCNC2 shRNA transfection induced endoplasmic reticulum (ER) stress and hepatic gluconeogenesis. Overproduction of KCNC2 decreased ER stress, and treatment with metformin enhanced KCNC2 expression. Taken together, these data suggest that reduction of KCNC2 is associated with modified hepatic gluconeogenesis and increased ER stress on obesity-mediated diabetic risk. An integrative multi-omics analysis might reveal new functional and clinical implications related to the control of energy and metabolic homeostasis in humans.

Spatiotemporal SERT expression in cortical map development

The cerebral cortex is organized into morphologically distinct areas that provide biological frameworks underlying perception, cognition, and behavior. Profiling mouse and human cortical transcriptomes have revealed temporal-specific differential gene expression modules in distinct neocortical areas during cortical map establishment. However, the biological roles of spatiotemporal gene expression in cortical patterning and how cortical topographic gene expression is regulated are largely unknown. Here, we characterize temporal- and spatial-defined expression of serotonin (5-HT) transporter (SERT) in glutamatergic neurons during sensory map development in mice. SERT is transiently expressed in glutamatergic thalamic neurons projecting to sensory cortices and in pyramidal neurons in the prefrontal cortex (PFC) and hippocampus (HPC) during the period that lays down the basic functional neural circuits. We previously identified that knockout of SERT in the thalamic neurons blocks 5-HT uptake by their thalamocortical axons, resulting in excessive 5-HT signaling that impairs sensory map architecture. In contrast, here we show that selective SERT knockout in the PFC and HPC neurons does not perturb sensory map patterning. These data suggest that transient SERT expression in specific glutamatergic neurons provides area-specific instructions for cortical map patterning. Hence, genetic and pharmacological manipulations of this SERT function could illuminate the fundamental genetic programming of cortex-specific maps and biological roles of temporal-specific cortical topographic gene expression in normal development and mental disorders.

Hunger-Dependent Enhancement of Food Cue Responses in Mouse Postrhinal Cortex and Lateral Amygdala

The needs of the body can direct behavioral and neural processing toward motivationally relevant sensory cues. For example, human imaging studies have consistently found specific cortical areas with biased responses to food-associated visual cues in hungry subjects, but not in sated subjects. To obtain a cellular-level understanding of these hunger-dependent cortical response biases, we performed chronic two-photon calcium imaging in postrhinal association cortex (POR) and primary visual cortex (V1) of behaving mice. As in humans, neurons in mouse POR, but not V1, exhibited biases toward food-associated cues that were abolished by satiety. This emergent bias was mirrored by the innervation pattern of amygdalo-cortical feedback axons. Strikingly, these axons exhibited even stronger food cue biases and sensitivity to hunger state and trial history. These findings highlight a direct pathway by which the lateral amygdala may contribute to state-dependent cortical processing of motivationally relevant sensory cues.

Reciprocal Control of Drinking Behavior by Median Preoptic Neurons in Mice

Stimulation of glutamatergic neurons in the subfornical organ drives drinking behavior, but the brain targets that mediate this response are not known. The densest target of subfornical axons is the anterior tip of the third ventricle, containing the median preoptic nucleus (MnPO) and organum vasculosum of the lamina terminalis (OVLT), a region that has also been implicated in fluid and electrolyte management. The neurochemical composition of this region is complex, containing both GABAergic and glutamatergic neurons, but the possible roles of these neurons in drinking responses have not been addressed. In mice, we show that optogenetic stimulation of glutamatergic neurons in MnPO/OVLT drives voracious water consumption, and that optogenetic stimulation of GABAergic neurons in the same region selectively reduces water consumption. Both populations of neurons have extensive projections to overlapping regions of the thalamus, hypothalamus, and hindbrain that are much more extensive than those from the subfornical organ, suggesting that the MnPO/OVLT serves as a key link in regulating drinking responses.

SIGNIFICANCE STATEMENT

Neurons in the median preoptic nucleus (MnPO) and organum vasculosum of the lamina terminalis (OVLT) are known to regulate fluid/electrolyte homeostasis, but few studies have examined this issue with an appreciation for the neurochemical heterogeneity of these nuclei. Using Cre-Lox genetic targeting of Channelrhodospin-2 in transgenic mice, we demonstrate that glutamate and GABA neurons in the MnPO/OVLT reciprocally regulate water consumption. Stimulating glutamatergic MnPO/OVLT neurons induced water consumption, whereas stimulating GABAergic MnPO neurons caused a sustained and specific reduction in water consumption in dehydrated mice, the latter highlighting a heretofore unappreciated role of GABAergic MnPO neurons in thirst regulation. These observations represent an important advance in our understanding of the neural circuits involved in the regulation of fluid/electrolyte homeostasis.

Plasma zinc alpha2-glycoprotein levels correlate positively with frailty severity in female elders

Frailty is a geriatric syndrome associated with adiposity. Zinc alpha2-glycoprotein (ZAG), a novel adipokine, is a modulator of body fat mass and positively correlates with age. This observational study aims to investigate the relationship between plasma ZAG levels and frailty in the elderly.We enrolled 189 elder participants from a hospital-based comprehensive geriatric assessment program in Taiwan from January 2007 to June 2008. The demographic data, body weight, body mass index, appendicular skeletal muscle mass index (ASMI), body fat mass percentage, metabolic and inflammatory parameters including plasma tumor-necrosis factor alpha, C-reactive protein and ZAG levels, were assessed. The frailty score was assessed by Fried Frailty Index.The mean age of all participants (91 [48.1%] men and 98 [51.9%] women) was 77.19 ± 6.12 years. Judged by the FFI score, 46 (24.34%) elders were robust, 106 (56.08%) were pre-frail, and 37 (19.58%) were frail. Older men showed greater ASMI and lower fat mass percentage in comparison to older women (P < 0.0001). The log-transformed mean plasma ZAG (μg/mL) level of overall was 1.82 ± 0.11, and it was higher in men than in women (1.85 ± 0.12 vs 1.79 ± 0.1, P = 0.0006). Plasma ZAG levels were different among the robust, pre-frail and frail subgroups (1.78 ± 0.09, 1.83 ± 0.12, 1.83 ± 1.10, respectively, P = 0.028), and the differences were more significant in woman elders (P = 0.005). Further multiple linear regression analysis showed plasma ZAG levels positively correlated with frailty severity in women (P for trend = 0.0435).Plasma ZAG levels positively correlated with frailty severity in woman elders. The difference between sexes suggests certain sex-specific mechanisms may exist to affect the association between plasma ZAG levels and frailty.

Hubs and spokes of the lateral hypothalamus: cell types, circuits and behaviour

The hypothalamus is among the most phylogenetically conserved regions in the vertebrate brain, reflecting its critical role in maintaining physiological and behavioural homeostasis. By integrating signals arising from both the brain and periphery, it governs a litany of behaviourally important functions essential for survival. In particular, the lateral hypothalamic area (LHA) is central to the orchestration of sleep-wake states, feeding, energy balance and motivated behaviour. Underlying these diverse functions is a heterogeneous assembly of cell populations typically defined by neurochemical markers, such as the well-described neuropeptides hypocretin/orexin and melanin-concentrating hormone. However, anatomical and functional evidence suggests a rich diversity of other cell populations with complex neurochemical profiles that include neuropeptides, receptors and components of fast neurotransmission. Collectively, the LHA acts as a hub for the integration of diverse central and peripheral signals and, through complex local and long-range output circuits, coordinates adaptive behavioural responses to the environment. Despite tremendous progress in our understanding of the LHA, defining the identity of functionally discrete LHA cell types, and their roles in driving complex behaviour, remain significant challenges in the field. In this review, we discuss advances in our understanding of the neurochemical and cellular heterogeneity of LHA neurons and the recent application of powerful new techniques, such as opto- and chemogenetics, in defining the role of LHA circuits in feeding, reward, arousal and stress. From pioneering work to recent developments, we review how the interrogation of LHA cells and circuits is contributing to a mechanistic understanding of how the LHA coordinates complex behaviour.

Population imaging at subcellular resolution supports specific and local inhibition by granule cells in the olfactory bulb

Information processing in early sensory regions is modulated by a diverse range of inhibitory interneurons. We sought to elucidate the role of olfactory bulb interneurons called granule cells (GCs) in odor processing by imaging the activity of hundreds of these cells simultaneously in mice. Odor responses in GCs were temporally diverse and spatially disperse, with some degree of non-random, modular organization. The overall sparseness of activation of GCs was highly correlated with the extent of glomerular activation by odor stimuli. Increasing concentrations of single odorants led to proportionately larger population activity, but some individual GCs had non-monotonic relations to concentration due to local inhibitory interactions. Individual dendritic segments could sometimes respond independently to odors, revealing their capacity for compartmentalized signaling in vivo. Collectively, the response properties of GCs point to their role in specific and local processing, rather than global operations such as response normalization proposed for other interneurons.

Optogenetic activation of leptin- and glucose-regulated GABAergic neurons in dorsomedial hypothalamus promotes food intake via inhibitory synaptic transmission to paraventricular nucleus of hypothalamus

OBJECTIVE

The dorsomedial hypothalamus (DMH) has been considered an orexigenic nucleus, since the DMH lesion reduced food intake and body weight and induced resistance to diet-induced obesity. The DMH expresses feeding regulatory neuropeptides and receptors including neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART), cholecystokinin (CCK), leptin receptor, and melanocortin 3/4 receptors. However, the principal neurons generating the orexigenic function in the DMH remain to be defined. This study aimed to clarify the role of the DMH GABAergic neurons in feeding regulation by using optogenetics and electrophysiological techniques.

METHODS

We generated the mice expressing ChRFR-C167A, a bistable chimeric channelrhodopsin, selectively in GABAergic neurons of DMH via locally injected adeno-associated virus 2. Food intake after optogenetic activation of DMH GABAergic neurons was measured. Electrophysiological properties of DMH GABAergic neurons were measured using slice patch clamp.

RESULTS

Optogenetic activation of DMH GABAergic neurons promoted food intake. Leptin hyperpolarized and lowering glucose depolarized half of DMH GABAergic neurons, suggesting their orexigenic property. Optical activation of axonal terminals of DMH GABAergic neurons at the paraventricular nucleus of hypothalamus (PVN), where anorexigenic neurons are localized, increased inhibitory postsynaptic currents on PVN neurons and promoted food intake.

CONCLUSION

DMH GABAergic neurons are regulated by metabolic signals leptin and glucose and, once activated, promote food intake via inhibitory synaptic transmission to PVN.

Manipulations of MeCP2 in glutamatergic neurons highlight their contributions to Rett and other neurological disorders

Many postnatal onset neurological disorders such as autism spectrum disorders (ASDs) and intellectual disability are thought to arise largely from disruption of excitatory/inhibitory homeostasis. Although mouse models of Rett syndrome (RTT), a postnatal neurological disorder caused by loss-of-function mutations in MECP2, display impaired excitatory neurotransmission, the RTT phenotype can be largely reproduced in mice simply by removing MeCP2 from inhibitory GABAergic neurons. To determine what role excitatory signaling impairment might play in RTT pathogenesis, we generated conditional mouse models with Mecp2 either removed from or expressed solely in glutamatergic neurons. MeCP2 deficiency in glutamatergic neurons leads to early lethality, obesity, tremor, altered anxiety-like behaviors, and impaired acoustic startle response, which is distinct from the phenotype of mice lacking MeCP2 only in inhibitory neurons. These findings reveal a role for excitatory signaling impairment in specific neurobehavioral abnormalities shared by RTT and other postnatal neurological disorders.

Melanocortin-4 receptor-regulated energy homeostasis

The melanocortin system provides a conceptual blueprint for the central control of energetic state. Defined by four principal molecular components--two antagonistically acting ligands and two cognate receptors--this phylogenetically conserved system serves as a prototype for hierarchical energy balance regulation. Over the last decade the application of conditional genetic techniques has facilitated the neuroanatomical dissection of the melanocortinergic network and identified the specific neural substrates and circuits that underscore the regulation of feeding behavior, energy expenditure, glucose homeostasis and autonomic outflow. In this regard, the melanocortin-4 receptor is a critical coordinator of mammalian energy homeostasis and body weight. Drawing on recent advances in neuroscience and genetic technologies, we consider the structure and function of the melanocortin-4 receptor circuitry and its role in energy homeostasis.

Voltage-Dependent Rhythmogenic Property of Respiratory Pre-Bötzinger Complex Glutamatergic, Dbx1-Derived, and Somatostatin-Expressing Neuron Populations Revealed by Graded Optogenetic Inhibition

The rhythm of breathing in mammals, originating within the brainstem pre-Bötzinger complex (pre-BötC), is presumed to be generated by glutamatergic neurons, but this has not been directly demonstrated. Additionally, developmental expression of the transcription factor Dbx1 or expression of the neuropeptide somatostatin (Sst), has been proposed as a marker for the rhythmogenic pre-BötC glutamatergic neurons, but it is unknown whether these other two phenotypically defined neuronal populations are functionally equivalent to glutamatergic neurons with regard to rhythm generation. To address these problems, we comparatively investigated, by optogenetic approaches, the roles of pre-BötC glutamatergic, Dbx1-derived, and Sst-expressing neurons in respiratory rhythm generation in neonatal transgenic mouse medullary slices in vitro and also more intact adult perfused brainstem-spinal cord preparations in situ. We established three different triple-transgenic mouse lines with Cre-driven Archaerhodopsin-3 (Arch) expression selectively in glutamatergic, Dbx1-derived, or Sst-expressing neurons for targeted photoinhibition. In each line, we identified subpopulations of rhythmically active, Arch-expressing pre-BötC inspiratory neurons by whole-cell recordings in medullary slice preparations in vitro, and established that Arch-mediated hyperpolarization of these inspiratory neurons was laser power dependent with equal efficacy. By site- and population-specific graded photoinhibition, we then demonstrated that inspiratory frequency was reduced by each population with the same neuronal voltage-dependent frequency control mechanism in each state of the respiratory network examined. We infer that enough of the rhythmogenic pre-BötC glutamatergic neurons also have the Dbx1 and Sst expression phenotypes, and thus all three phenotypes share the same voltage-dependent frequency control property.

Modulatory influences of estradiol and other anorexigenic hormones on metabotropic, Gi/o-coupled receptor function in the hypothalamic control of energy homeostasis

The appetite suppressant actions of estradiol are due to its ability to attenuate orexigenic signals and potentiate anorexigenic signals. The work from my laboratory has shown that male guinea pigs are more sensitive to the hyperphagic and hypothermic effects of cannabinoids than their female counterparts. Cannabinoid sensitivity is further dampened by the activational effects of estradiol. This occurs via the hypothalamic feeding circuitry, where estradiol rapidly attenuates the cannabinoid CB1 receptor-mediated presynaptic inhibition of glutamatergic input onto anorexigenic proopiomelanocortin (POMC) neurons in the arcuate nucleus. This disruption is blocked by the estrogen receptor antagonist ICI 182,780, and associated with increased expression of phosphatidylinositol-3-kinase (PI3K). Moreover, the ability of estradiol to reduce both the cannabinoid-induced hyperphagia and glutamate release onto POMC neurons is abrogated by the PI3K inhibitor PI 828. The peptide orphanin FQ/nociceptin (OFQ/N) activates opioid receptor-like (ORL)1 receptors to hyperpolarize and inhibit POMC neurons via the activation of postsynaptic G protein-gated, inwardly-rectifying (GIRK) channels. We have demonstrated that the fasting-induced hyperphagia observed in ORL1-null mice is blunted compared to wild type controls. In addition, the ORL1 receptor-mediated activation of GIRK channels in POMC neurons from ovariectomized female rats is markedly impaired by estradiol. The estrogenic attenuation of presynaptic CB1 and postsynaptic ORL1 receptor function may be part of a more generalized mechanism through which anorexigenic hormones suppress orexigenic signaling. Indeed, we have found that leptin robustly suppresses the OFQ/N-induced activation of GIRK channels in POMC neurons. Furthermore, its ability to augment excitatory input onto POMC neurons is blocked by PI 828. Thus, estradiol and other hormones like leptin reduce energy intake at least partly by activating PI3K to disrupt the pleiotropic functions of Gi/o-coupled receptors that inhibit anorexigenic POMC neurons.

Lateral Hypothalamic Area Glutamatergic Neurons and Their Projections to the Lateral Habenula Regulate Feeding and Reward

The overconsumption of calorically dense, highly palatable foods is thought to be a major contributor to the worldwide obesity epidemic; however, the precise neural circuits that directly regulate hedonic feeding remain elusive. Here, we show that lateral hypothalamic area (LHA) glutamatergic neurons, and their projections to the lateral habenula (LHb), negatively regulate the consumption of palatable food. Genetic ablation of LHA glutamatergic neurons increased daily caloric intake and produced weight gain in mice that had access to a high-fat diet, while not altering general locomotor activity. Anterior LHA glutamatergic neurons send a functional glutamatergic projection to the LHb, a brain region involved in processing aversive stimuli and negative reward prediction outcomes. Pathway-specific, optogenetic stimulation of glutamatergic LHA-LHb circuit resulted in detectable glutamate-mediated EPSCs as well as GABA-mediated IPSCs, although the net effect of neurotransmitter release was to increase the firing of most LHb neurons. In vivo optogenetic inhibition of LHA-LHb glutamatergic fibers produced a real-time place preference, whereas optogenetic stimulation of LHA-LHb glutamatergic fibers had the opposite effect. Furthermore, optogenetic inhibition of LHA-LHb glutamatergic fibers acutely increased the consumption of a palatable liquid caloric reward. Collectively, these results demonstrate that LHA glutamatergic neurons are well situated to bidirectionally regulate feeding and potentially other behavioral states via their functional circuit connectivity with the LHb and potentially other brain regions.

SIGNIFICANCE STATEMENT

In this study, we show that the genetic ablation of LHA glutamatergic neurons enhances caloric intake. Some of these LHA glutamatergic neurons project to the lateral habenula, a brain area important for generating behavioral avoidance. Optogenetic stimulation of this circuit has net excitatory effects on postsynaptic LHb neurons. This is the first study to characterize the functional connectivity and behavioral relevance of this circuit within the context of feeding and reward-related behavior.

Shared and distinct retinal input to the mouse superior colliculus and dorsal lateral geniculate nucleus

Our results suggest that the mouse superior colliculus (SC) has access to input from most of the retinal ganglion cells (RGCs) that innervate the dorsal lateral geniculate nucleus (dLGN). By comparison, a number of RGC types appear to innervate the SC but not the dLGN; these RGCs generally exhibit more transient responses and respond best to small stimuli.

The mammalian retina conveys the vast majority of information about visual stimuli to two brain regions: the dorsal lateral geniculate nucleus (dLGN) and the superior colliculus (SC). The degree to which retinal ganglion cells (RGCs) send similar or distinct information to the two areas remains unclear despite the important constraints that different patterns of RGC input place on downstream visual processing. To resolve this ambiguity, we injected a glycoprotein-deficient rabies virus coding for the expression of a fluorescent protein into the dLGN or SC; rabies virus labeled a smaller fraction of RGCs than lipophilic dyes such as DiI but, crucially, did not label RGC axons of passage. Approximately 80% of the RGCs infected by rabies virus injected into the dLGN were colabeled with DiI injected into the SC, suggesting that many dLGN-projecting RGCs also project to the SC. However, functional characterization of RGCs revealed that the SC receives input from several classes of RGCs that largely avoid the dLGN, in particular RGCs in which 1) sustained changes in light intensity elicit transient changes in firing rate and/or 2) a small range of stimulus sizes or temporal fluctuations in light intensity elicit robust activity. Taken together, our results illustrate several unexpected asymmetries in the information that the mouse retina conveys to two major downstream targets and suggest that differences in the output of dLGN and SC neurons reflect, at least in part, differences in the functional properties of RGCs that innervate the SC but not the dLGN.

Adult NG2-Glia Are Required for Median Eminence-Mediated Leptin Sensing and Body Weight Control

While leptin is a well-known regulator of body fat mass, it remains unclear how circulating leptin is sensed centrally to maintain energy homeostasis. Here we show that genetic and pharmacological ablation of adult NG2-glia (also known as oligodendrocyte precursors), but not microglia, leads to primary leptin resistance and obesity in mice. We reveal that NG2-glia contact the dendritic processes of arcuate nucleus leptin receptor (LepR) neurons in the median eminence (ME) and that these processes degenerate upon NG2-glia elimination, which explains the consequential attenuation of these neurons' molecular and electrical responses to leptin. Our data therefore indicate that LepR dendrites in the ME represent the principal conduits of leptin's anorexigenic action and that NG2-glia are essential for their maintenance. Given that ME-directed X-irradiation confirmed the pharmacological and genetically mediated ablation effects on body weight, our findings provide a rationale for the known obesity risk associated with cranial radiation therapy.

Lateral Hypothalamus GABAergic Neurons Modulate Consummatory Behaviors Regardless of the Caloric Content or Biological Relevance of the Consumed Stimuli

It was recently reported that activation of a subset of lateral hypothalamus (LH) GABAergic neurons induced both appetitive (food-seeking) and consummatory (eating) behaviors in vGat-ires-cre mice, while inhibition or deletion of GABAergic neurons blunted these behaviors. As food and caloric-dense liquid solutions were used, the data reported suggest that these LH GABAergic neurons may modulate behaviors that function to maintain homeostatic caloric balance. Here we report that chemogenetic activation of this GABAergic population in vGat-ires-cre mice increased consummatory behavior directed at any available stimulus, including those entailing calories (food, sucrose, and ethanol), those that do not (saccharin and water), and those lacking biological relevance (wood). Chemogenetic inhibition of these neurons attenuated consummatory behaviors. These data indicate that LH GABAergic neurons modulate consummatory behaviors regardless of the caloric content or biological relevance of the consumed stimuli.

Computational Analysis of the Hypothalamic Control of Food Intake

Food-intake control is mediated by a heterogeneous network of different neural subtypes, distributed over various hypothalamic nuclei and other brain structures, in which each subtype can release more than one neurotransmitter or neurohormone. The complexity of the interactions of these subtypes poses a challenge to understanding their specific contributions to food-intake control, and apparent consistencies in the dataset can be contradicted by new findings. For example, the growing consensus that arcuate nucleus neurons expressing Agouti-related peptide (AgRP neurons) promote feeding, while those expressing pro-opiomelanocortin (POMC neurons) suppress feeding, is contradicted by findings that low AgRP neuron activity and high POMC neuron activity can be associated with high levels of food intake. Similarly, the growing consensus that GABAergic neurons in the lateral hypothalamus suppress feeding is contradicted by findings suggesting the opposite. Yet the complexity of the food-intake control network admits many different network behaviors. It is possible that anomalous associations between the responses of certain neural subtypes and feeding are actually consistent with known interactions, but their effect on feeding depends on the responses of the other neural subtypes in the network. We explored this possibility through computational analysis. We made a computer model of the interactions between the hypothalamic and other neural subtypes known to be involved in food-intake control, and optimized its parameters so that model behavior matched observed behavior over an extensive test battery. We then used specialized computational techniques to search the entire model state space, where each state represents a different configuration of the responses of the units (model neural subtypes) in the network. We found that the anomalous associations between the responses of certain hypothalamic neural subtypes and feeding are actually consistent with the known structure of the food-intake control network, and we could specify the ways in which the anomalous configurations differed from the expected ones. By analyzing the temporal relationships between different states we identified the conditions under which the anomalous associations can occur, and these stand as model predictions.

Awake dynamics and brain-wide direct inputs of hypothalamic MCH and orexin networks

The lateral hypothalamus (LH) controls energy balance. LH melanin-concentrating-hormone (MCH) and orexin/hypocretin (OH) neurons mediate energy accumulation and expenditure, respectively. MCH cells promote memory and appropriate stimulus-reward associations; their inactivation disrupts energy-optimal behaviour and causes weight loss. However, MCH cell dynamics during wakefulness are unknown, leaving it unclear if they differentially participate in brain activity during sensory processing. By fiberoptic recordings from molecularly defined populations of LH neurons in awake freely moving mice, we show that MCH neurons generate conditional population bursts. This MCH cell activity correlates with novelty exploration, is inhibited by stress and is inversely predicted by OH cell activity. Furthermore, we obtain brain-wide maps of monosynaptic inputs to MCH and OH cells, and demonstrate optogenetically that VGAT neurons in the amygdala and bed nucleus of stria terminalis inhibit MCH cells. These data reveal cell-type-specific LH dynamics during sensory integration, and identify direct neural controllers of MCH neurons.

Hypothalamic neurons expressing melanin-concentrating-hormone (MCH) maintain body weight by orchestrating behaviour and metabolism, but little is known about their intrinsic regulation. Here, Gonzalez and colleagues reveal their behaviour-related dynamics during wakefulness, and map their brain-wide neural inputs.

Silencing spinal interneurons inhibits immune suppressive autonomic reflexes caused by spinal cord injury

Spinal cord injury (SCI) at high spinal levels (e.g., above thoracic level 5) causes systemic immune suppression; however, the underlying mechanisms are unknown. Here, we show that profound plasticity develops within spinal autonomic circuitry below the injury, creating a sympathetic anti-inflammatory reflex, and that chemogenetic silencing of this reflex circuitry blocks post-SCI immune suppression. These data provide new insights and potential therapeutic options for limiting the devastating consequences of post-traumatic autonomic hyperreflexia and post-injury immune suppression.

The elegance of energy balance: Insight from circuit-level manipulations

Mechanisms of energy balance were first examined using very powerful neuroscience techniques such as lesions and electrical stimulation. This early work identified the hypothalamus as a key structure involved in hunger and feeding; however, neural resolution of cell-defined populations contributing to appetite regulation remained elusive. Recent innovations in neuroscience have produced constructs that allow for a high degree of specificity in loss- and gain-of-function manipulations in molecularly circumscribed neural subsets as well as monosynaptic circuit mapping and in vivo neurophysiology. These complimentary techniques have provided researchers an unprecedented amount of empirical agility. As a result, cell populations in two subregions of the hypothalamus have emerged as key players in the physiological control of feeding behavior. The arcuate nucleus of the hypothalamus and the paraventricular nucleus of the hypothalamus contain neural populations that have a direct role in the promotion of hunger and satiety. These include neurons that express agouti-related peptide, pro-opiomelanocortin, single-minded homolog 1 protein, and the melanocortin-4 receptor. This review focuses on how these neural subsets communicate with one another, link up to build elaborate networks, and ultimately contribute to alterations in food intake. The continuing advancement of neuroscience tools, as well as a multimodal integration of findings, will be critical in illuminating an exhaustive and clinically relevant hunger circuit.

Neurotrophic factor control of satiety and body weight

Energy balance--that is, the relationship between energy intake and energy expenditure--is regulated by a complex interplay of hormones, brain circuits and peripheral tissues. Leptin is an adipocyte-derived cytokine that suppresses appetite and increases energy expenditure. Ironically, obese individuals have high levels of plasma leptin and are resistant to leptin treatment. Neurotrophic factors, particularly ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF), are also important for the control of body weight. CNTF can overcome leptin resistance in order to reduce body weight, although CNTF and leptin activate similar signalling cascades. Mutations in the gene encoding BDNF lead to insatiable appetite and severe obesity.

Cellular architecture and transmitter phenotypes of neurons of the mouse median raphe region

The median raphe region (MRR, which consist of MR and paramedian raphe regions) plays a crucial role in regulating cortical as well as subcortical network activity and behavior, while its malfunctioning may lead to disorders, such as schizophrenia, major depression, or anxiety. Mouse MRR neurons are classically identified on the basis of their serotonin (5-HT), vesicular glutamate transporter type 3 (VGLUT3), and gamma-aminobutyric acid (GABA) contents; however, the exact cellular composition of MRR regarding transmitter phenotypes is still unknown. Using an unbiased stereological method, we found that in the MR, 8.5 % of the neurons were 5-HT, 26 % were VGLUT3, and 12.8 % were 5-HT and VGLUT3 positive; whereas 37.2 % of the neurons were GABAergic, and 14.4 % were triple negative. In the whole MRR, 2.1 % of the neurons were 5-HT, 7 % were VGLUT3, and 3.6 % were 5-HT and VGLUT3 positive; whereas 61 % of the neurons were GABAergic. Surprisingly, 25.4 % of the neurons were triple negative and were only positive for the neuronal marker NeuN. PET-1/ePET-Cre transgenic mouse lines are widely used to specifically manipulate only 5-HT containing neurons. Interestingly, however, using the ePET-Cre transgenic mice, we found that far more VGLUT3 positive cells expressed ePET than 5-HT positive cells, and about 38 % of the ePET cells contained only VGLUT3, while more than 30 % of 5-HT cells were ePET negative. These data should facilitate the reinterpretation of PET-1/ePET related data in the literature and the identification of the functional role of a putatively new type of triple-negative neuron in the MRR.

A GABAergic nigrotectal pathway for coordination of drinking behavior

The contribution of basal ganglia outputs to consummatory behavior remains poorly understood. We recorded from the substantia nigra pars reticulata (SNR), the major basal ganglia output nucleus, during self-initiated drinking. The firing rates of many lateral SNR neurons were time-locked to individual licks. These neurons send GABAergic projections to the deep layers of the orofacial region of the lateral tectum (superior colliculus, SC). Many tectal neurons are also time-locked to licking, but their activity is usually antiphase to that of SNR neurons, suggesting inhibitory nigrotectal projections. We used optogenetics to selectively activate the GABAergic nigrotectal afferents in the deep layers of the SC. Photo-stimulation of the nigrotectal projections transiently inhibited the activity of the lick-related tectal neurons, disrupted their licking-related oscillatory pattern, and suppressed self-initiated drinking. These results demonstrate that GABAergic nigrotectal projections play a crucial role in coordinating drinking behavior.

Euglycemia Restoration by Central Leptin in Type 1 Diabetes Requires STAT3 Signaling but Not Fast-Acting Neurotransmitter Release

Central leptin action is sufficient to restore euglycemia in insulinopenic type 1 diabetes (T1D); however, the underlying mechanism remains poorly understood. To examine the role of intracellular signal transducer and activator of transcription 3 (STAT3) pathways, we used LepRs/s mice with disrupted leptin-phosphorylated STAT3 signaling to test the effect of central leptin on euglycemia restoration. These mice developed streptozocin-induced T1D, which was surprisingly not associated with hyperglucagonemia, a typical manifestation in T1D. Further, leptin action on euglycemia restoration was abrogated in these mice, which was associated with refractory hypercorticosteronemia. To examine the role of fast-acting neurotransmitters glutamate and γ-aminobutyric acid (GABA), two major neurotransmitters in the brain, from leptin receptor (LepR) neurons, we used mice with disrupted release of glutamate, GABA, or both from LepR neurons. Surprisingly, all mice responded normally to leptin-mediated euglycemia restoration, which was associated with expected correction from hyperglucagonemia and hyperphagia. In contrast, mice with loss of glutamate and GABA appeared to develop an additive obesity effect over those with loss of single neurotransmitter release. Thus, our study reveals that STAT3 signaling, but not fast-acting neurotransmitter release, is required for leptin action on euglycemia restoration and that hyperglucagonemia is not required for T1D.

Leptin signalling pathways in hypothalamic neurons

Leptin is the most critical hormone in the homeostatic regulation of energy balance among those so far discovered. Leptin primarily acts on the neurons of the mediobasal part of hypothalamus to regulate food intake, thermogenesis, and the blood glucose level. In the hypothalamic neurons, leptin binding to the long form leptin receptors on the plasma membrane initiates multiple signaling cascades. The signaling pathways known to mediate the actions of leptin include JAK-STAT signaling, PI3K-Akt-FoxO1 signaling, SHP2-ERK signaling, AMPK signaling, and mTOR-S6K signaling. Recent evidence suggests that leptin signaling in hypothalamic neurons is also linked to primary cilia function. On the other hand, signaling molecules/pathways mitigating leptin actions in hypothalamic neurons have been extensively investigated in an effort to treat leptin resistance observed in obesity. These include SOCS3, tyrosine phosphatase PTP1B, and inflammatory signaling pathways such as IKK-NFκB and JNK signaling, and ER stress-mitochondrial signaling. In this review, we discuss leptin signaling pathways in the hypothalamus, with a particular focus on the most recently discovered pathways.

Activation of Pyramidal Neurons in Mouse Medial Prefrontal Cortex Enhances Food-Seeking Behavior While Reducing Impulsivity in the Absence of an Effect on Food Intake

The medial prefrontal cortex (mPFC) is involved in a wide range of executive cognitive functions, including reward evaluation, decision-making, memory extinction, mood, and task switching. Manipulation of the mPFC has been shown to alter food intake and food reward valuation, but whether exclusive stimulation of mPFC pyramidal neurons (PN), which form the principle output of the mPFC, is sufficient to mediate food rewarded instrumental behavior is unknown. We sought to determine the behavioral consequences of manipulating mPFC output by exciting PN in mouse mPFC during performance of a panel of behavioral assays, focusing on food reward. We found that increasing mPFC pyramidal cell output using designer receptors exclusively activated by designer drugs (DREADD) enhanced performance in instrumental food reward assays that assess food seeking behavior, while sparing effects on affect and food intake. Specifically, activation of mPFC PN enhanced operant responding for food reward, reinstatement of palatable food seeking, and suppression of impulsive responding for food reward. Conversely, activation of mPFC PN had no effect on unconditioned food intake, social interaction, or behavior in an open field. Furthermore, we found that behavioral outcome is influenced by the degree of mPFC activation, with a low drive sufficient to enhance operant responding and a higher drive required to alter impulsivity. Additionally, we provide data demonstrating that DREADD stimulation involves a nitric oxide (NO) synthase dependent pathway, similar to endogenous muscarinic M3 receptor stimulation, a finding that provides novel mechanistic insight into an increasingly widespread method of remote neuronal control.

Ion Channels in Obesity: Pathophysiology and Potential Therapeutic Targets

Obesity is a multifactorial disease related to metabolic disorders and associated with genetic determinants. Currently, ion channels activity has been linked to many of these disorders, in addition to the central regulation of food intake, energetic balance, hormone release and response, as well as the adipocyte cell proliferation. Therefore, the objective of this work is to review the current knowledge about the influence of ion channels in obesity development. This review used different sources of literature (Google Scholar, PubMed, Scopus, and Web of Science) to assess the role of ion channels in the pathophysiology of obesity. Ion channels present diverse key functions, such as the maintenance of physiological homeostasis and cell proliferation. Cell biology and pharmacological experimental evidences demonstrate that proliferating cells exhibit ion channel expression, conductance, and electrical properties different from the resting cells. Thereby, a large variety of ion channels has been identified in the pathogenesis of obesity such as potassium, sodium, calcium and chloride channels, nicotinic acetylcholine receptor and transient receptor potential channels. The fundamental involvement of these channels on the generation of obesity leads to the progress in the knowledge about the mechanisms responsible for the obesity pathophysiology, consequently emerging as new targets for pharmacological modulation.

Evolution of mammalian sound localization circuits: A developmental perspective

Localization of sound sources is a central aspect of auditory processing. A unique feature of mammals is the smooth, tonotopically organized extension of the hearing range to high frequencies (HF) above 10kHz, which likely induced positive selection for novel mechanisms of sound localization. How this change in the auditory periphery is accompanied by changes in the central auditory system is unresolved. I will argue that the major VGlut2(+) excitatory projection neurons of sound localization circuits (dorsal cochlear nucleus (DCN), lateral and medial superior olive (LSO and MSO)) represent serial homologs with modifications, thus being paramorphs. This assumption is based on common embryonic origin from an Atoh1(+)/Wnt1(+) cell lineage in the rhombic lip of r5, same cell birth, a fusiform cell morphology, shared genetic components such as Lhx2 and Lhx9 transcription factors, and similar projection patterns. Such a parsimonious evolutionary mechanism likely accelerated the emergence of neurons for sound localization in all three dimensions. Genetic analyses indicate that auditory nuclei in fish, birds, and mammals receive contributions from the same progenitor lineages. Anatomical and physiological differences and the independent evolution of tympanic ears in vertebrate groups, however, argue for convergent evolution of sound localization circuits in tetrapods (amphibians, reptiles, birds, and mammals). These disparate findings are discussed in the context of the genetic architecture of the developing hindbrain, which facilitates convergent evolution. Yet, it will be critical to decipher the gene regulatory networks underlying development of auditory neurons across vertebrates to explore the possibility of homologous neuronal populations.

Secret talk between adipose tissue and central nervous system via secreted factors-an emerging frontier in the neurodegenerative research

First seen as a storage organ, the white adipose tissue (WAT) is now considered as an endocrine organ. WAT can produce an array of bioactive factors known as adipokines acting at physiological level and playing a vital role in energy metabolism as well as in immune response. The global effect of adipokines in metabolic activities is well established, but their impact on the physiology and the pathophysiology of the central nervous system (CNS) remains poorly defined. Adipokines are not only produced by the WAT but can also be expressed in the CNS where receptors for these factors are present. When produced in periphery and to affect the CNS, these factors may either cross the blood brain barrier (BBB) or modify the BBB physiology by acting on cells forming the BBB. Adipokines could regulate neuroinflammation and oxidative stress which are two major physiological processes involved in neurodegeneration and are associated with many chronic neurodegenerative diseases. In this review, we focus on four important adipokines (leptin, resistin, adiponectin, and TNFα) and one lipokine (lysophosphatidic acid-LPA) associated with autotaxin, its producing enzyme. Their potential effects on neurodegeneration and brain repair (neurogenesis) will be discussed. Understanding and regulating these adipokines could be an interesting lead to novel therapeutic strategy in order to counteract neurodegenerative disorders and/or promote brain repair.

A specific area of olfactory cortex involved in stress hormone responses to predator odours

Instinctive reactions to danger are critical to the perpetuation of species and are observed throughout the animal kingdom. The scent of predators induces an instinctive fear response in mice that includes behavioural changes, as well as a surge in blood stress hormones that mobilizes multiple body systems to escape impending danger. How the olfactory system routes predator signals detected in the nose to achieve these effects is unknown. Here we identify a specific area of the olfactory cortex in mice that induces stress hormone responses to volatile predator odours. Using monosynaptic and polysynaptic viral tracers, we found that multiple olfactory cortical areas transmit signals to hypothalamic corticotropin-releasing hormone (CRH) neurons, which control stress hormone levels. However, only one minor cortical area, the amygdalo-piriform transition area (AmPir), contained neurons upstream of CRH neurons that were activated by volatile predator odours. Chemogenetic stimulation of AmPir activated CRH neurons and induced an increase in blood stress hormones, mimicking an instinctive fear response. Moreover, chemogenetic silencing of AmPir markedly reduced the stress hormone response to predator odours without affecting a fear behaviour. These findings suggest that AmPir, a small area comprising <5% of the olfactory cortex, plays a key part in the hormonal component of the instinctive fear response to volatile predator scents.

Postnatal undernutrition delays a key step in the maturation of hypothalamic feeding circuits

OBJECTIVE

Humans and animals exposed to undernutrition (UN) during development often experience accelerated "catch-up" growth when food supplies are plentiful. Little is known about the mechanisms regulating early growth rates. We previously reported that actions of leptin and presynaptic inputs to orexigenic NPY/AgRP/GABA (NAG) neurons in the arcuate nucleus of the hypothalamus are almost exclusively excitatory during the lactation period, since neuronal and humoral inhibitory systems do not develop until after weaning. Moreover, we identified a critical step that regulates the maturation of electrophysiological responses of NAG neurons at weaning - the onset of genes encoding ATP-dependent potassium (KATP) channel subunits. We explored the possibility that UN promotes subsequent catch-up growth, in part, by delaying the maturation of negative feedback systems to neuronal circuits driving food intake.

METHODS

We used the large litter (LL) size model to study the impacts of postnatal UN followed by catch-up growth. We evaluated the maturation of presynaptic and postsynaptic inhibitory systems in NAG neurons using a combination of electrophysiological and molecular criteria, in conjunction with leptin's ability to suppress fasting-induced hyperphagia.

RESULTS

The onset of KATP channel subunit expression and function, the switch in leptin's effect on NAG neurons, the ingrowth of inhibitory inputs to NAG neurons, and the development of homeostatic feedback to feeding circuits were delayed in LL offspring relative to controls. The development of functional KATP channels and the establishment of leptin-mediated suppression of food intake in the peri-weaning period were tightly linked and were not initiated until growth and adiposity of LL offspring caught up to controls.

CONCLUSIONS

Our data support the idea that initiation of KATP channel subunit expression in NAG neurons serves as a molecular gatekeeper for the maturation of homeostatic feeding circuits.

Leptin Responsive and GABAergic Projections to the Rostral Preoptic Area in Mice

The adipocyte-derived hormone leptin plays a critical role in the control of reproduction via signalling in hypothalamic neurones. The drivers of the hypothalamic-pituitary-gonadal axis, the gonadotrophin-releasing hormone (GnRH) neurones, do not have the receptors for leptin. Therefore, intermediate leptin responsive neurones must provide leptin-to-GnRH signalling. We investigated the populations of leptin responsive neurones that provide input to the rostral preoptic area (rPOA) where GnRH cell bodies reside. Fluorescent retrograde tracer beads (RetroBeads; Lumafluor Inc., Naples, FL, USA) were injected into the rPOA of transgenic leptin receptor enhanced green fluorescent protein (Lepr-eGFP) reporter mice. Uptake of the RetroBeads by Lepr-eGFP neurones was assessed throughout the hypothalamus. RetroBead uptake was most evident in the medial arcuate nucleus (ARC), the dorsomedial nucleus (DMN) and the ventral premammillary nucleus (PMV) of the hypothalamus. The uptake of RetroBeads specifically by Lepr-eGFP neurones was highest in the medial ARC (18% of tracer-labelled neurones Lepr-eGFP-positive). Because neurones that are both leptin responsive and GABAergic play a critical role in the regulation of fertility by leptin, we next focussed on the location of these populations. To address whether GABAergic neurones in leptin-responsive hypothalamic regions project to the rPOA, the experiment was repeated in GABA neurone reporter mice (Vgat-tdTomato). Between 10% and 45% of RetroBead-labelled neurones in the ARC were GABAergic, whereas uptake of tracer by GABAergic neurones in the DMN and PMV was very low (< 5%). These results show that both leptin responsive and GABAergic neurones from the ARC project to the region of the GnRH cell bodies. Our findings suggest that LEPR-expressing GABA neurones from the ARC may be mediators of leptin-to-GnRH signalling.

GRK2: putting the brakes on the circadian clock

G protein-coupled receptor kinases (GRKs) are a family of serine/threonine protein kinases that terminate G protein-coupled receptor (GPCR) signaling by phosphorylating the receptor and inducing its internalization. In addition to their canonical function, some GRKs can phosphorylate non-GPCR substrates and regulate GPCR signaling in a kinase-independent manner. GPCRs are abundantly expressed in the suprachiasmatic nucleus (SCN), a structure in the mammalian brain that serves as the central circadian pacemaker. Various facets of circadian timekeeping are under the influence of GPCR signaling, and thus are potential targets for GRK regulation. Despite this, little attention has been given to the role of GRKs in circadian rhythms. In this research highlight, we discuss our latest findings on the functional involvement of GRK2 in mammalian circadian timekeeping in the SCN. Using grk2 knockout mice, we demonstrate that GRK2 is critical for maintaining proper clock speed and ensuring that the clock is appropriately synchronized to environmental light cycles. Although grk2 deficiency expectedly alters the expression of a key GPCR in the SCN, our study also reveals that GRK2 has a more direct function that touches the heart of the circadian clock.

Structured Dendritic Inhibition Supports Branch-Selective Integration in CA1 Pyramidal Cells

Neuronal circuit function is governed by precise patterns of connectivity between specialized groups of neurons. The diversity of GABAergic interneurons is a hallmark of cortical circuits, yet little is known about their targeting to individual postsynaptic dendrites. We examined synaptic connectivity between molecularly defined inhibitory interneurons and CA1 pyramidal cell dendrites using correlative light-electron microscopy and large-volume array tomography. We show that interneurons can be highly selective in their connectivity to specific dendritic branch types and, furthermore, exhibit precisely targeted connectivity to the origin or end of individual branches. Computational simulations indicate that the observed subcellular targeting enables control over the nonlinear integration of synaptic input or the initiation and backpropagation of action potentials in a branch-selective manner. Our results demonstrate that connectivity between interneurons and pyramidal cell dendrites is more precise and spatially segregated than previously appreciated, which may be a critical determinant of how inhibition shapes dendritic computation.

Involvement of the Acyl-CoA binding domain containing 7 in the control of food intake and energy expenditure in mice

Acyl-CoA binding domain-containing 7 (Acbd7) is a paralog gene of the diazepam-binding inhibitor/Acyl-CoA binding protein in which single nucleotide polymorphism has recently been associated with obesity in humans. In this report, we provide converging evidence indicating that a splice variant isoform of the Acbd7 mRNA is expressed and translated by some POMC and GABAergic-neurons in the hypothalamic arcuate nucleus (ARC). We have demonstrated that the ARC ACBD7 isoform was produced and processed into a bioactive peptide referred to as nonadecaneuropeptide (NDN) in response to catabolic signals. We have characterized NDN as a potent anorexigenic signal acting through an uncharacterized endozepine G protein-coupled receptor and subsequently via the melanocortin system. Our results suggest that ACBD7-producing neurons participate in the hypothalamic leptin signalling pathway. Taken together, these data suggest that ACBD7-producing neurons are involved in the hypothalamic control exerted on food intake and energy expenditure by the leptin-melanocortin pathway.

DOI:http://dx.doi.org/10.7554/eLife.11742.001

Obesity is an increasingly common problem worldwide. To treat it effectively, we must understand how the body controls how much food a person consumes and how much energy they expend. The hypothalamus is one region of the brain that plays a critical role in regulating this energy balance. Some of the neurons in the hypothalamus can change their activity when they detect satiety hormones including the leptin, which is produced by fat cells and suppresses appetite. However, it is not clear exactly how the neurons respond to leptin and other energy-related signals.

Recent studies have linked the gene that encodes a protein called ACBD7 with obesity, and showed that it is one of the genes that is overexpressed in neurons that are sensitive to leptin. Now, Lanfray et al. have discovered a population of neurons that produce a new variant of the protein in the hypothalamus of mice. When this protein variant matures, it can be cut down to form a small protein-like molecule called NDN. Further experiments showed that leptin stimulates the production of both the new ABCD7 variant and NDN.

Lanfray et al. then injected mice that had been denied food for a several hours with NDN. The injected mice ate less than untreated mice, and burn more energy.

NDN appears to form part of the signaling pathway through which leptin signals to the hypothalamus to control appetite. In the future, creating mice in which the activity of the gene that encodes ACBD7 can be easily disrupted could help to reveal more about how the hypothalamus helps to control energy balance.

DOI:http://dx.doi.org/10.7554/eLife.11742.002

Effective Modulation of Male Aggression through Lateral Septum to Medial Hypothalamus Projection

Aggression is a prevalent behavior in the animal kingdom that is used to settle competition for limited resources. Given the high risk associated with fighting, the central nervous system has evolved an active mechanism to modulate its expression. Lesioning the lateral septum (LS) is known to cause "septal rage," a phenotype characterized by a dramatic increase in the frequency of attacks. To understand the circuit mechanism of LS-mediated modulation of aggression, we examined the influence of LS input on the cells in and around the ventrolateral part of the ventromedial hypothalamus (VMHvl)-a region required for male mouse aggression. We found that the inputs from the LS inhibited the attack-excited cells but surprisingly increased the overall activity of attack-inhibited cells. Furthermore, optogenetic activation of the projection from LS cells to the VMHvl terminated ongoing attacks immediately but had little effect on mounting. Thus, LS projection to the ventromedial hypothalamic area represents an effective pathway for suppressing male aggression.

Expression of ESR1 in Glutamatergic and GABAergic Neurons Is Essential for Normal Puberty Onset, Estrogen Feedback, and Fertility in Female Mice

Circulating estradiol exerts a profound influence on the activity of the gonadotropin-releasing hormone (GnRH) neuronal network controlling fertility. Using genetic strategies enabling neuron-specific deletion of estrogen receptor α (Esr1), we examine here whether estradiol-modulated GABA and glutamate transmission are critical for the functioning of the GnRH neuron network in the female mouse. Using Vgat- and Vglut2-ires-Cre knock-in mice and ESR1 immunohistochemistry, we demonstrate that subpopulations of GABA and glutamate neurons throughout the limbic forebrain express ESR1, with ESR1-GABAergic neurons being more widespread and numerous than ESR1-glutamatergic neurons. We crossed Vgat- and Vglut2-ires-Cre mice with an Esr1(lox/lox) line to generate animals with GABA-neuron-specific or glutamate-neuron-specific deletion of Esr1. Vgat-ires-Cre;Esr1(lox/lox) mice were infertile, with abnormal estrous cycles, and exhibited a complete failure of the estrogen positive feedback mechanism responsible for the preovulatory GnRH surge. However, puberty onset and estrogen negative feedback were normal. Vglut2-ires-Cre;Esr1(lox/lox) mice were also infertile but displayed a wider range of deficits, including advanced puberty onset, abnormal negative feedback, and abolished positive feedback. Whereas <25% of preoptic kisspeptin neurons expressed Cre in Vgat- and Vglut2-ires-Cre lines, ∼70% of arcuate kisspeptin neurons were targeted in Vglut2-ires-Cre;Esr1(lox/lox) mice, possibly contributing to their advanced puberty phenotype. These observations show that, unexpectedly, ESR1-GABA neurons are only essential for the positive feedback mechanism. In contrast, we reveal the key importance of ESR1 in glutamatergic neurons for multiple estrogen feedback loops within the GnRH neuronal network required for fertility in the female mouse.

Lateral hypothalamic circuits for feeding and reward

In experiments conducted over 60 years ago, the lateral hypothalamic area (LHA) was identified as a critical neuroanatomical substrate for motivated behavior. Electrical stimulation of the LHA induces voracious feeding even in well-fed animals. In the absence of food, animals will work tirelessly, often lever-pressing thousands of times per hour, for electrical stimulation at the same site that provokes feeding, drinking and other species-typical motivated behaviors. Here we review the classic findings from electrical stimulation studies and integrate them with more recent work that has used contemporary circuit-based approaches to study the LHA. We identify specific anatomically and molecularly defined LHA elements that integrate diverse information arising from cortical, extended amygdala and basal forebrain networks to ultimately generate a highly specified and invigorated behavioral state conveyed via LHA projections to downstream reward and feeding-specific circuits.

Genetic cell targeting uncovers specific neuronal types and distinct subregions in the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) plays an important role in fear, stress, and anxiety. It contains a collection of subnuclei delineated by gross cytoarchitecture features; however, there has yet to be a systematic examination of specific BNST neuronal types and their associated neurochemical makeup. The present study focuses on improved characterization of the anterior BNST based on differing molecular and chemical expression aided by mouse genetics. Specific Cre driver lines crossed with a fluorescent reporter line were used for genetic cell targeting and immunochemical staining. Using this new approach, we were able to robustly identify specific excitatory and inhibitory cell types in the BNST. The presence and distribution of excitatory neurons were firmly established; glutamatergic neurons in the anterior BNST accounted for about 14% and 31% of dorsal and ventral BNST cells, respectively. GABAergic neurons expressing different isoforms of glutamic acid decarboxylase were found to have differential subregional distributions. Almost no parvalbumin-expressing cells were found in the BNST, while somatostatin-expressing cells and calretinin-expressing cells account for modest proportions of BNST cells. In addition, vasoactive intestinal peptide-expressing axonal plexuses were prominent in the oval and juxtacapsular subregions. In addition, we discovered that corticotropin-releasing hormone-expressing cells contain GABAergic and glutamatergic subpopulations. Together, this study reveals new information on excitatory and inhibitory neurons in the BNST, which will facilitate genetic dissection and functional studies of BNST subregions. J. Comp. Neurol. 524:2379-2399, 2016. © 2016 Wiley Periodicals, Inc.

Optogenetic Dissection of the Basal Forebrain Neuromodulatory Control of Cortical Activation, Plasticity, and Cognition

The basal forebrain (BF) houses major ascending projections to the entire neocortex that have long been implicated in arousal, learning, and attention. The disruption of the BF has been linked with major neurological disorders, such as coma and Alzheimer's disease, as well as in normal cognitive aging. Although it is best known for its cholinergic neurons, the BF is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific BF cell types have led to a renaissance in the study of the BF and are beginning to yield new insights about cell-type-specific circuit mechanisms during behavior. These approaches enable us to determine the behavioral conditions under which cholinergic and noncholinergic BF neurons are activated and how they control cortical processing to influence behavior. Here we discuss recent advances that have expanded our knowledge about this poorly understood brain region and laid the foundation for future cell-type-specific manipulations to modulate arousal, attention, and cortical plasticity in neurological disorders.

SIGNIFICANCE STATEMENT

Although the basal forebrain is best known for, and often equated with, acetylcholine-containing neurons that provide most of the cholinergic innervation of the neocortex, it is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific cell types in the basal forebrain have led to a renaissance in this field and are beginning to dissect circuit mechanisms in the basal forebrain during behavior. This review discusses recent advances in the roles of basal forebrain cholinergic and noncholinergic neurons in cognition via their dynamic modulation of cortical activity.

Adult mouse cortical cell taxonomy revealed by single cell transcriptomics

Nervous systems are composed of various cell types, but the extent of cell type diversity is poorly understood. Here, we construct a cellular taxonomy of one cortical region, primary visual cortex, in adult mice based on single cell RNA-sequencing. We identify 49 transcriptomic cell types including 23 GABAergic, 19 glutamatergic and seven non-neuronal types. We also analyze cell-type specific mRNA processing and characterize genetic access to these transcriptomic types by many transgenic Cre lines. Finally, we show that some of our transcriptomic cell types display specific and differential electrophysiological and axon projection properties, thereby confirming that the single cell transcriptomic signatures can be associated with specific cellular properties.

The Role of PVH Circuits in Leptin Action and Energy Balance

Although it has been known for more than a century that the brain controls overall energy balance and adiposity by regulating feeding behavior and energy expenditure, the roles for individual brain regions and neuronal subtypes were not fully understood until recently. This area of research is active, and as such our understanding of the central regulation of energy balance is continually being refined as new details emerge. Much of what we now know stems from the discoveries of leptin and the hypothalamic melanocortin system. Hypothalamic circuits play a crucial role in the control of feeding and energy expenditure, and within the hypothalamus, the arcuate nucleus (ARC) functions as a gateway for hormonal signals of energy balance, such as leptin. It is also well established that the ARC is a primary residence for hypothalamic melanocortinergic neurons. The paraventricular hypothalamic nucleus (PVH) receives direct melanocortin input, along with other integrated signals that affect energy balance, and mediates the majority of hypothalamic output to control both feeding and energy expenditure. Herein, we review in detail the structure and function of the ARC-PVH circuit in mediating leptin signaling and in regulating energy balance.

Interacting Neural Processes of Feeding, Hyperactivity, Stress, Reward, and the Utility of the Activity-Based Anorexia Model of Anorexia Nervosa

Anorexia nervosa (AN) is a psychiatric illness with minimal effective treatments and a very high rate of mortality. Understanding the neurobiological underpinnings of the disease is imperative for improving outcomes and can be aided by the study of animal models. The activity-based anorexia rodent model (ABA) is the current best parallel for the study of AN. This review describes the basic neurobiology of feeding and hyperactivity seen in both ABA and AN, and compiles the research on the role that stress-response and reward pathways play in modulating the homeostatic drive to eat and to expend energy, which become dysfunctional in ABA and AN.

Inhibitory Gating of Input Comparison in the CA1 Microcircuit

Spatial and temporal features of synaptic inputs engage integration mechanisms on multiple scales, including presynaptic release sites, postsynaptic dendrites, and networks of inhibitory interneurons. Here we investigate how these mechanisms cooperate to filter synaptic input in hippocampal area CA1. Dendritic recordings from CA1 pyramidal neurons reveal that proximal inputs from CA3 as well as distal inputs from entorhinal cortex layer III (ECIII) sum sublinearly or linearly at low firing rates due to feedforward inhibition, but sum supralinearly at high firing rates due to synaptic facilitation, producing a high-pass filter. However, during ECIII and CA3 input comparison, supralinear dendritic integration is dynamically balanced by feedforward and feedback inhibition, resulting in suppression of dendritic complex spiking. We find that a particular subpopulation of CA1 interneurons expressing neuropeptide Y (NPY) contributes prominently to this dynamic filter by integrating both ECIII and CA3 input pathways and potently inhibiting CA1 pyramidal neuron dendrites.

Hypothalamic feedforward inhibition of thalamocortical network controls arousal and consciousness

During non-rapid eye movement (NREM) sleep, synchronous synaptic activity in the thalamocortical network generates predominantly low-frequency oscillations (<4 Hz) that are modulated by inhibitory inputs from the thalamic reticular nucleus (TRN). Whether TRN cells integrate sleep-wake signals from subcortical circuits remains unclear. We found that GABA neurons from the lateral hypothalamus (LHGABA) exert a strong inhibitory control over TRN GABA neurons (TRNGABA). We found that optogenetic activation of this circuit recapitulated state-dependent changes of TRN neuron activity in behaving mice and induced rapid arousal during NREM, but not REM, sleep. During deep anesthesia, activation of this circuit induced sustained cortical arousal. In contrast, optogenetic silencing of LHGABA-TRNGABA transmission increased the duration of NREM sleep and amplitude of delta (1-4 Hz) oscillations. Collectively, these results demonstrate that TRN cells integrate subcortical arousal inputs selectively during NREM sleep and may participate in sleep intensity.

A talk between fat tissue, gut, pancreas and brain to control body weight

The incidence of obesity and its related disorders are increasing at a rate of pandemic proportions. Understanding the mechanisms behind the maintenance of energy balance is fundamental in developing treatments for clinical syndromes including obesity and diabetes. A neural network located in the nucleus of the solitary tract-area postrema complex in the hindbrain and the hypothalamus in the forebrain has long been implicated in the control of energy balance. In the hypothalamus this central neuronal network consists of small populations of nuclei with distinct functions such as the arcuate nucleus (ARH), the paraventricular nuclei of the hypothalamus (PVH), the dorsomedial (DMH), the ventromedial (VMH) and the lateral hypothalamus (LH). These hypothalamic areas form interconnected neuronal circuits that respond to fluctuations in energy status by altering the expression of neuropeptides, leading to changes in energy intake and expenditure. Regulation of these hypothalamic nuclei involves the actions of orexigenic peptides (ie ghrelin), which act to stimulate energy intake and decrease energy expenditure, and anorexigenic peptides (ie. leptin and insulin), which act to reduce energy intake and stimulate energy expenditure. Here we review the role of the ARH, DMH and PVH in the control of energy homeostasis and how recent advances in research technologies (Cre-loxP technology, optogenetics and pharmacogenetics) have shed light on the role of these hypothalamic nuclei in the control of energy balance. Such novel findings include the implication of ARH POMC and AgRP neurons in the browning of white adipose tissue to regulate energy expenditure as well as the likely existence of divergent hypothalamic pathways in the DMH and PVH in the control of food intake and energy expenditure.

Genetic engineering of mammals

Historically, genetic engineering for mammalian reproductive questions has been accomplished primarily in the mouse. However, all the genetic manipulations that can be done in the mouse can now be accomplished in most domesticated mammals. Random integration of transgenes, homologous recombination and gene editing are now routine for several mammalian species. For livestock, queries related to fertility can be asked directly for the species in question, without a need for a mouse model. For human clinical concerns, the most appropriate model should be selected based on physiology, anatomy, or even size. The mouse will continue to be a useful genetically engineered model. However, other species are now amenable to the full range of genetic manipulations and should be considered as possible models for human conditions when appropriate.