Hepatic danger signaling triggers TREM2+ macrophage induction and drives steatohepatitis via MS4A7-dependent inflammasome activation

Metabolic dysfunction-associated steatohepatitis (MASH), formerly known as nonalcoholic steatohepatitis (NASH), is an advanced stage of metabolic fatty liver disease. The pathogenic mechanisms of MASH center on hepatocyte injury and the ensuing immune response within the liver microenvironment. Recent work has implicated TREM2+ macrophages in various disease conditions, and substantial induction of TREM2+ NASH-associated macrophages (NAMs) serves as a hallmark of metabolic liver disease. Despite this, the mechanisms through which NAMs contribute to MASH pathogenesis remain poorly understood. Here, we identify membrane-spanning 4-domains a7 (MS4A7) as a NAM-specific pathogenic factor that exacerbates MASH progression in mice. Hepatic MS4A7 expression was strongly induced in mouse and human MASH and associated with the severity of liver injury. Whole-body and myeloid-specific ablation of Ms4a7 alleviated diet-induced MASH pathologies in male mice. We demonstrate that exposure to lipid droplets (LDs), released upon injury of steatotic hepatocytes, triggered NAM induction and exacerbated MASH-associated liver injury in an MS4A7-dependent manner. Mechanistically, MS4A7 drove NLRP3 inflammasome activation via direct physical interaction and shaped disease-associated cell states within the liver microenvironment. This work reveals the LD-MS4A7-NLRP3 inflammasome axis as a pathogenic driver of MASH progression and provides insights into the role of TREM2+ macrophages in disease pathogenesis.

Suppression of food intake by Glp1r/Lepr-coexpressing neurons prevents obesity in mouse models

The adipose-derived hormone leptin acts via its receptor (LepRb) in the brain to control energy balance. A potentially unidentified population of GABAergic hypothalamic LepRb neurons plays key roles in the restraint of food intake and body weight by leptin. To identify markers for candidate populations of LepRb neurons in an unbiased manner, we performed single-nucleus RNA-Seq of enriched mouse hypothalamic LepRb cells, identifying several previously unrecognized populations of hypothalamic LepRb neurons. Many of these populations displayed strong conservation across species, including GABAergic Glp1r-expressing LepRb (LepRbGlp1r) neurons, which expressed more Lepr than other LepRb cell populations. Ablating Lepr from LepRbGlp1r cells provoked hyperphagic obesity without impairing energy expenditure. Similarly, improvements in energy balance caused by Lepr reactivation in GABA neurons of otherwise Lepr-null mice required Lepr expression in GABAergic Glp1r-expressing neurons. Furthermore, restoration of Glp1r expression in LepRbGlp1r neurons in otherwise Glp1r-null mice enabled food intake suppression by the GLP1R agonist, liraglutide. Thus, the conserved GABAergic LepRbGlp1r neuron population plays crucial roles in the suppression of food intake by leptin and GLP1R agonists.

Resting state brain dynamics: Associations with childhood sexual abuse and major depressive disorder

Early life stress (ELS) and major depressive disorder (MDD) share neural network abnormalities. However, it is unclear how ELS and MDD may separately and/or jointly relate to brain networks, and whether neural differences exist between depressed individuals with vs without ELS. Moreover, prior work evaluated static versus dynamic network properties, a critical gap considering brain networks show changes in coordinated activity over time. Seventy-one unmedicated females with and without childhood sexual abuse (CSA) histories and/or MDD completed a resting state scan and a stress task in which cortisol and affective ratings were collected. Recurring functional network co-activation patterns (CAPs) were examined and time in CAP (number of times each CAP is expressed) and transition frequencies (transitioning between different CAPs) were computed. The effects of MDD and CSA on CAP metrics were examined and CAP metrics were correlated with depression and stress-related variables. Results showed that MDD, but not CSA, related to CAP metrics. Specifically, individuals with MDD (N = 35) relative to HCs (N = 36), spent more time in a posterior default mode (DMN)-frontoparietal network (FPN) CAP and transitioned more frequently between posterior DMN-FPN and prototypical DMN CAPs. Across groups, more time spent in a posterior DMN-FPN CAP and greater DMN-FPN and prototypical DMN CAP transition frequencies were linked to higher rumination. Imbalances between the DMN and the FPN appear central to MDD and might contribute to MDD-related cognitive dysfunction, including rumination. Unexpectedly, CSA did not modulate such dysfunctions, a finding that needs to be replicated by future studies with larger sample sizes.

ASB4 modulates central melanocortinergic neurons and calcitonin signaling to control satiety and glucose homeostasis

Variants in the gene encoding ankyrin repeat and SOCS box-containing 4 (ASB4) are linked to human obesity. Here, we characterized the pathways underlying the metabolic functions of ASB4. Hypothalamic Asb4 expression was suppressed by fasting in wild-type mice but not in mice deficient in AgRP, which encodes Agouti-related protein (AgRP), an appetite-stimulating hormone, suggesting that ASB4 is a negative target of AgRP. Many ASB4 neurons in the brain were adjacent to AgRP terminals, and feeding induced by AgRP neuronal activation was disrupted in Asb4-deficient mice. Acute knockdown of Asb4 in the brain caused marked hyperphagia due to increased meal size, and Asb4 deficiency led to increased meal size and food intake at the onset of refeeding, when very large meals were consumed. Asb4-deficient mice were resistant to the meal-terminating effects of exogenously administered calcitonin and showed decreased neuronal expression of Calcr, which encodes the calcitonin receptor. Pro-opiomelanocortin (POMC) neurons in the arcuate nucleus in mice are involved in glucose homeostasis, and Asb4 deficiency specifically in POMC neurons resulted in glucose intolerance that was independent of obesity. Furthermore, individuals with type 2 diabetes showed reduced ASB4 abundance in the infundibular nuclei, the human equivalent of the arcuate nucleus. Together, our results indicate that ASB4 acts in the brain to improve glucose homeostasis and to induce satiety after substantial meals, particularly those after food deprivation.

Single-Cell Mapping of GLP-1 and GIP Receptor Expression in the Dorsal Vagal Complex

The dorsal vagal complex (DVC) in the hindbrain, composed of the area postrema, nucleus of the solitary tract, and dorsal motor nucleus of the vagus, plays a critical role in modulating satiety. The incretins glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) act directly in the brain to modulate feeding, and receptors for both are expressed in the DVC. Given the impressive clinical responses to pharmacologic manipulation of incretin signaling, understanding the central mechanisms by which incretins alter metabolism and energy balance is of critical importance. Here, we review recent single-cell approaches used to detect molecular signatures of GLP-1 and GIP receptor-expressing cells in the DVC. In addition, we discuss how current advancements in single-cell transcriptomics, epigenetics, spatial transcriptomics, and circuit mapping techniques have the potential to further characterize incretin receptor circuits in the hindbrain.

NTS Prlh overcomes orexigenic stimuli and ameliorates dietary and genetic forms of obesity

Calcitonin receptor (Calcr)-expressing neurons of the nucleus tractus solitarius (NTS; Calcr^NTS cells) contribute to the long-term control of food intake and body weight. Here, we show that Prlh-expressing NTS (Prlh^NTS) neurons represent a subset of Calcr^NTS cells and that Prlh expression in these cells restrains body weight gain in the face of high fat diet challenge in mice. To understand the relationship of Prlh^NTS cells to hypothalamic feeding circuits, we determined the ability of Prlh^NTS-mediated signals to overcome enforced activation of AgRP neurons. We found that Prlh^NTS neuron activation and Prlh overexpression in Prlh^NTS cells abrogates AgRP neuron-driven hyperphagia and ameliorates the obesity of mice deficient in melanocortin signaling or leptin. Thus, enhancing Prlh-mediated neurotransmission from the NTS dampens hypothalamically-driven hyperphagia and obesity, demonstrating that NTS-mediated signals can override the effects of orexigenic hypothalamic signals on long-term energy balance.

Calcitonin receptor-expressing neurons of the nucleus tractus solitarius contribute to long-term control of food intake and body weight. The authors show that a subset of these cells expresses Prlh and that enhancing Prlh-mediated neurotransmission from the NTS dampens hypothalamically-driven hyperphagia and obesity in mice.

Protocol to extract actively translated mRNAs from mouse hypothalamus by translating ribosome affinity purification

Here, we present an in-depth protocol for extracting ribosome-bound mRNAs in low-abundance cells of hypothalamic nuclei. mRNAs are extracted from the micropunched tissue using refined translating ribosome affinity purification. Isolated RNAs can be used for sequencing or transcript quantification. This protocol enables the identification of actively translated mRNAs in varying physiological states and can be modified for use in any neuronal subpopulation labeled with a ribo-tag. We use leptin receptor-expressing neurons as an example to illustrate the protocol. For complete details on the use and execution of this protocol, please refer to Han et al. (2020).

Paraventricular Calcitonin Receptor-Expressing Neurons Modulate Energy Homeostasis in Male Mice

The paraventricular nucleus of the hypothalamus (PVH) is a heterogeneous collection of neurons that play important roles in modulating feeding and energy expenditure. Abnormal development or ablation of the PVH results in hyperphagic obesity and defects in energy expenditure whereas selective activation of defined PVH neuronal populations can suppress feeding and may promote energy expenditure. Here, we characterize the contribution of calcitonin receptor-expressing PVH neurons (CalcRPVH) to energy balance control. We used Cre-dependent viral tools delivered stereotaxically to the PVH of CalcR2Acre mice to activate, silence, and trace CalcRPVH neurons and determine their contribution to body weight regulation. Immunohistochemistry of fluorescently-labeled CalcRPVH neurons demonstrates that CalcRPVH neurons are largely distinct from several PVH neuronal populations involved in energy homeostasis; these neurons project to regions of the hindbrain that are implicated in energy balance control, including the nucleus of the solitary tract and the parabrachial nucleus. Acute activation of CalcRPVH neurons suppresses feeding without appreciably augmenting energy expenditure, whereas their silencing leads to obesity that may be due in part due to loss of PVH melanocortin-4 receptor signaling. These data show that CalcRPVH neurons are an essential component of energy balance neurocircuitry and their function is important for body weight maintenance. A thorough understanding of the mechanisms by which CalcRPVH neurons modulate energy balance might identify novel therapeutic targets for the treatment and prevention of obesity.

Cross-species analysis defines the conservation of anatomically segregated VMH neuron populations

The ventromedial hypothalamic nucleus (VMH) controls diverse behaviors and physiologic functions, suggesting the existence of multiple VMH neural subtypes with distinct functions. Combing translating ribosome affinity purification with RNA-sequencing (TRAP-seq) data with single-nucleus RNA-sequencing (snRNA-seq) data, we identified 24 mouse VMH neuron clusters. Further analysis, including snRNA-seq data from macaque tissue, defined a more tractable VMH parceling scheme consisting of six major genetically and anatomically differentiated VMH neuron classes with good cross-species conservation. In addition to two major ventrolateral classes, we identified three distinct classes of dorsomedial VMH neurons. Consistent with previously suggested unique roles for leptin receptor (Lepr)-expressing VMH neurons, Lepr expression marked a single dorsomedial class. We also identified a class of glutamatergic VMH neurons that resides in the tuberal region, anterolateral to the neuroanatomical core of the VMH. This atlas of conserved VMH neuron populations provides an unbiased starting point for the analysis of VMH circuitry and function.

tTARGIT AAVs mediate the sensitive and flexible manipulation of intersectional neuronal populations in mice

While Cre-dependent viral systems permit the manipulation of many neuron types, some cell populations cannot be targeted by a single DNA recombinase. Although the combined use of Flp and Cre recombinases can overcome this limitation, insufficient recombinase activity can reduce the efficacy of existing Cre+Flp-dependent viral systems. We developed a sensitive dual recombinase-activated viral approach: tTA-driven Recombinase-Guided Intersectional Targeting (tTARGIT) adeno-associated viruses (AAVs). tTARGIT AAVs utilize a Flp-dependent tetracycline transactivator (tTA) ‘Driver’ AAV and a tetracycline response element-driven, Cre-dependent ‘Payload’ AAV to express the transgene of interest. We employed this system in Slc17a6^FlpO;Lepr^Cre mice to manipulate LepRb neurons of the ventromedial hypothalamus (VMH; LepRb^VMH neurons) while omitting neighboring LepRb populations. We defined the circuitry of LepRb^VMH neurons and roles for these cells in the control of food intake and energy expenditure. Thus, the tTARGIT system mediates robust recombinase-sensitive transgene expression, permitting the precise manipulation of previously intractable neural populations.

The brain contains hundreds of types of neurons, which differ in size, shape and behavior. But neuroscientists often wish to study individual neuronal types in isolation. They are able to do this with the aid of a toolkit made up of two parts: viral vectors and genetically modified mice.

Viral vectors are viruses that have been modified so that they are no longer harmful and can instead be used to introduce genetic material into cells on demand. To create a viral vector, the virus’ own genetic material is replaced with a ‘cargo’ gene, such as the gene for a fluorescent protein. The virus is then introduced into a new host such as a mouse. Importantly, the virus only produces the protein encoded by its ‘cargo’ gene if it is inside a cell that also contains one of two specific enzymes. These enzymes are called Cre and Flp.

This is where the second part of the toolkit comes in. Mice can be genetically engineered to produce either Cre or Flp exclusively in specific cell types. By introducing a viral vector into mice that produce either Cre or Flp only in one particular type of neuron, researchers can limit the activity of the cargo gene to that neuronal type.

But sometimes even this approach is not selective enough. Researchers may wish to limit the activity of the cargo gene to a subpopulation of cells that produce Cre or Flp. Or they may wish to target only Cre- or Flp-producing cells in a small area of the brain, while leaving cells in neighboring areas unaffected.

Sabatini et al. have now overcome this limitation by developing and testing a new set of viral vectors that are active only in neurons that produce both Cre and Flp. The vectors are called tTARGIT AAVs and allow researchers to target cells more precisely than was possible with the previous version of the toolkit.

Sabatini et al. show tTARGIT AAVs in action by using them to identify a group of neurons that control how much energy mice use and how much food they eat. As well as applying the vectors to their own research on obesity, Sabatini et al. have also made them freely available for other researchers to use in their own projects.

GFRAL-expressing neurons suppress food intake via aversive pathways

The TGFβ cytokine family member, GDF-15, reduces food intake and body weight and represents a potential treatment for obesity. Because the brainstem-restricted expression pattern of its receptor, GDNF Family Receptor α-like (GFRAL), presents an exciting opportunity to understand mechanisms of action for area postrema neurons in food intake; we generated GfralCre and conditional GfralCreERT mice to visualize and manipulate GFRAL neurons. We found infection or pathophysiologic states (rather than meal ingestion) stimulate GFRAL neurons. TRAP-Seq analysis of GFRAL neurons revealed their expression of a wide range of neurotransmitters and neuropeptides. Artificially activating GfralCre -expressing neurons inhibited feeding, decreased gastric emptying, and promoted a conditioned taste aversion (CTA). GFRAL neurons most strongly innervate the parabrachial nucleus (PBN), where they target CGRP-expressing (CGRPPBN) neurons. Silencing CGRPPBN neurons abrogated the aversive and anorexic effects of GDF-15. These findings suggest that GFRAL neurons link non-meal-associated pathophysiologic signals to suppress nutrient uptake and absorption.

Decreased sensitivity to the anorectic effects of leptin in mice that lack a Pomc-specific neural enhancer

Enhancer redundancy has been postulated to provide a buffer for gene expression against genetic and environmental perturbations. While work in Drosophila has identified functionally overlapping enhancers, work in mammalian models has been limited. Recently, we have identified two partially redundant enhancers, nPE1 and nPE2, that drive proopiomelanocortin gene expression in the hypothalamus. Here we demonstrate that deletion of nPE1 produces mild obesity while knockout of nPE2 has no discernible metabolic phenotypes. Additionally, we show that acute leptin administration has significant effects on nPE1 knockout mice, with food intake and body weight change significantly impacted by peripheral leptin treatment. nPE1 knockout mice became less responsive to leptin treatment over time as percent body weight change increased over 2 week exposure to peripheral leptin. Both Pomc and Agrp mRNA were not differentially affected by chronic leptin treatment however we did see a decrease in Pomc and Agrp mRNA in both nPE1 and nPE2 knockout calorie restricted mice as compared to calorie restricted PBS-treated WT mice. Collectively, these data suggest dynamic regulation of Pomc by nPE1 such that mice with nPE1 knockout become less responsive to the anorectic effects of leptin treatment over time. Our results also support our earlier findings in which nPE2 may only be critical in adult mice that lack nPE1, indicating that these neural enhancers work synergistically to influence metabolism.

Inflammation and depressive phenotypes: evidence from medical records from over 12 000 patients and brain morphology

BACKGROUND

Preclinical and human studies suggest an association between chronic inflammation and the development of depressive behaviors. This is proposed to occur through downstream effects of inflammatory cytokines on neuroplasticity, neurogenesis and neurotransmitter function, although the neural correlates remain poorly understood in humans.

METHODS

In Study 1, structural magnetic resonance imaging and serum inflammatory cytokine data were analyzed from 53 psychiatrically healthy female participants. Correlational analyses were conducted between interleukin-6 (IL-6) and volume in a priori regions implicated in the pathophysiology of major depressive disorder (MDD). In Study 2, medical data [including serum inflammatory acute phase reactants (C-reactive protein)] were analyzed for 12 589 participants. Participants were classified as having (n = 2541) v. not having (n = 10 048) probable lifetime MDD using phenotypes derived using machine-learning approaches. Non-parametric analyses compared inflammation between groups, whereas regression analyses probed whether inflammation predicted probable MDD classification while accounting for other variables.

RESULTS

In Study 1, significant negative correlations emerged between IL-6 and hippocampal, caudate, putamen and amygdalar volume. In Study 2, the MDD group showed a higher probability of elevated inflammation than the non-MDD group. Moreover, elevated inflammation was a significant predictor of probable MDD classification.

CONCLUSIONS

Findings indicate that inflammation is cross-sectionally related to reduced volume in brain regions implicated in MDD phenotypes among a sample of psychiatrically healthy women, and is associated with the presence of probable MDD in a large clinical dataset. Future investigations may identify specific inflammatory markers predicting first MDD onset.

Prenatal Androgenization Alters the Development of GnRH Neuron and Preoptic Area RNA Transcripts in Female Mice

Polycystic ovary syndrome (PCOS) is the most common form of infertility in women. The causes of PCOS are not yet understood and both genetics and early-life exposure have been considered as candidates. With regard to the latter, circulating androgens are elevated in mid-late gestation in women with PCOS, potentially exposing offspring to elevated androgens in utero; daughters of women with PCOS are at increased risk for developing this disorder. Consistent with these clinical observations, prenatal androgenization (PNA) of several species recapitulates many phenotypes observed in PCOS. There is increasing evidence that symptoms associated with PCOS, including elevated luteinizing hormone (LH) (and presumably gonadotropin-releasing hormone [GnRH]) pulse frequency emerge during the pubertal transition. We utilized translating ribosome affinity purification coupled with ribonucleic acid (RNA) sequencing to examine GnRH neuron messenger RNAs from prepubertal (3 weeks) and adult female control and PNA mice. Prominent in GnRH neurons were transcripts associated with protein synthesis and cellular energetics, in particular oxidative phosphorylation. The GnRH neuron transcript profile was affected more by the transition from prepuberty to adulthood than by PNA treatment; however, PNA did change the developmental trajectory of GnRH neurons. This included families of transcripts related to both protein synthesis and oxidative phosphorylation, which were more prevalent in adults than in prepubertal mice but were blunted in PNA adults. These findings suggest that prenatal androgen exposure can program alterations in the translatome of GnRH neurons, providing a mechanism independent of changes in the genetic code for altered expression.

Dual-Color Single-Cell Imaging of the Suprachiasmatic Nucleus Reveals a Circadian Role in Network Synchrony

The suprachiasmatic nucleus (SCN) acts as a master pacemaker driving circadian behavior and physiology. Although the SCN is small, it is composed of many cell types, making it difficult to study the roles of particular cells. Here we develop bioluminescent circadian reporter mice that are Cre dependent, allowing the circadian properties of genetically defined populations of cells to be studied in real time. Using a Color-Switch PER2::LUCIFERASE reporter that switches from red PER2::LUCIFERASE to green PER2::LUCIFERASE upon Cre recombination, we assess circadian rhythms in two of the major classes of peptidergic neurons in the SCN: AVP (arginine vasopressin) and VIP (vasoactive intestinal polypeptide). Surprisingly, we find that circadian function in AVP neurons, not VIP neurons, is essential for autonomous network synchrony of the SCN and stability of circadian rhythmicity.

Whole-brain efferent and afferent connectivity of mouse ventral tegmental area melanocortin-3 receptor neurons

The mesolimbic dopamine (DA) system is involved in the regulation of multiple behaviors, including feeding, and evidence demonstrates that the melanocortin system can act on the mesolimbic DA system to control feeding and other behaviors. The melanocortin-3 receptor (MC3R) is an important component of the melanocortin system, but its overall role is poorly understood. Because MC3Rs are highly expressed in the ventral tegmental area (VTA) and are likely to be the key interaction point between the melanocortin and mesolimbic DA systems, we set out to identify both the efferent projection patterns of VTA MC3R neurons and the location of the neurons providing afferent input to them. VTA MC3R neurons were broadly connected to neurons across the brain but were strongly connected to a discrete set of brain regions involved in the regulation of feeding, reward, and aversion. Surprisingly, experiments using monosynaptic rabies virus showed that proopiomelanocortin (POMC) and agouti-related protein (AgRP) neurons in the arcuate nucleus made few direct synapses onto VTA MC3R neurons or any of the other major neuronal subtypes in the VTA, despite being extensively labeled by general retrograde tracers injected into the VTA. These results greatly contribute to our understanding of the anatomical interactions between the melanocortin and mesolimbic systems and provide a foundation for future studies of VTA MC3R neurons and the circuits containing them in the control of feeding and other behaviors.

Ventromedial hypothalamic nucleus neuronal subset regulates blood glucose independently of insulin

To identify neurons that specifically increase blood glucose from among the diversely functioning cell types in the ventromedial hypothalamic nucleus (VMN), we studied the cholecystokinin receptor B-expressing (CCKBR-expressing) VMN targets of glucose-elevating parabrachial nucleus neurons. Activation of these VMNCCKBR neurons increased blood glucose. Furthermore, although silencing the broader VMN decreased energy expenditure and promoted weight gain without altering blood glucose levels, silencing VMNCCKBR neurons decreased hIepatic glucose production, insulin-independently decreasing blood glucose without altering energy balance. Silencing VMNCCKBR neurons also impaired the counterregulatory response to insulin-induced hypoglycemia and glucoprivation and replicated hypoglycemia-associated autonomic failure. Hence, VMNCCKBR cells represent a specialized subset of VMN cells that function to elevate glucose. These cells not only mediate the allostatic response to hypoglycemia but also modulate the homeostatic setpoint for blood glucose in an insulin-independent manner, consistent with a role for the brain in the insulin-independent control of glucose homeostasis.

The acute effects of nicotine on corticostriatal responses to distinct phases of reward processing

Nicotine enhances the reinforcement of non-drug rewards by increasing nucleus accumbens (NAcc) reactivity to anticipatory cues. This anticipatory effect is selective as no clear evidence has emerged showing that nicotine acutely changes reward receipt reactivity. However, repeated rewarding experiences shift peak brain reactivity from hedonic reward outcome to the motivational anticipatory cue yielding more habitual cue-induced behavior. Given nicotine's influence on NAcc reactivity and connectivity, it is plausible that nicotine acutely induces this shift and alters NAcc functional connectivity during reward processing. To evaluate this currently untested hypothesis, a randomized crossover design was used in which healthy non-smokers were administered placebo and nicotine (2-mg lozenge). Brain activation to monetary reward anticipation and outcome was evaluated with functional magnetic resonance imaging. Relative to placebo, nicotine induced more NAcc reactivity to reward anticipation. Greater NAcc activation during anticipation was significantly associated with lower NAcc activation to outcome. During outcome, nicotine reduced NAcc functional connectivity with cortical regions including the anterior cingulate cortex, orbitofrontal cortex, and insula. These regions showed the same negative relationship between reward anticipation and outcome as noted in the NAcc. The current findings significantly improve our understanding of how nicotine changes corticostriatal circuit function and communication during distinct phases of reward processing and critically show that these alterations happen acutely following a single dose. The implications of this work explain nicotinic modulation of general reward function, which offer insights into the initial drive to smoke and the subsequent difficulty in cessation.

OR04-03 Calcitonin Receptor Expressing Neurons in the PVH Regulate Feeding Behavior

The paraventricular nucleus of the hypothalamus (PVH) is a brain region crucial for energy homeostasis. Abnormal PVH development or damage leads to hyperphagic obesity and energy expenditure deficits underscoring the importance of PVH neuronal activity in energy balance control. Application of salmon calcitonin (sCT) to the PVH suppresses feeding and calcitonin receptor (CalcR) is highly expressed in the PVH of rodents suggesting that CalcR-expressing PVH neurons contribute to energy homeostasis. In situ hybridization reveals that many CalcR^PVH neurons express melanocortin-4 receptor (MC4R), a receptor required for normal feeding behavior. To investigate the physiologic roles of CalcR^PVH neurons, we generated CalcR-2a-Cre knock-in mice to manipulate CalcR-expressing cells. Deletion of MC4R from CalcR expressing cells using Cre-loxP technology resulted in profound obesity in both male and female mice by 16 weeks of age. This weight gain was attributable to hyperphagia, as cumulative food intake of the MC4R deleted mice was significantly greater than the controls and energy expenditure measurements acquired through CLAMS analysis were not significantly different. To determine the brain regions engaged by CalcR^PVH neurons, we used anterograde Cre-dependent viral tracing reagents injected into the PVH of CalcR-Cre mice, and found that CalcR^PVH neurons project to brain regions implicated in energy balance control, including the nucleus of the solitary tract and the parabrachial nucleus. To assess the acute effects of activating CalcR^PVH neurons, we used DREADD technology to chemogenetically activate CalcR^PVH neurons. CalcR^PVH neuron activation suppressed feeding but had no significant effect on energy expenditure. To determine if the activity of CalcR^PVH neurons is required for energy homeostasis, we silenced them using Cre-dependent tetanus toxin virus. Male mice with tetanus toxin silenced CalcR^PVH neurons were obese 7 weeks following injection in part due to greater cumulative food intake; CLAMS analysis revealed no differences in energy expenditure. Mice with silenced CalcR^PVH neurons as well as mice with CalcR deleted from the PVH had normal anorectic responses to sCT, suggesting sCT-induced anorexia does not require CalcR^PVH neurons or CalcR expression in the PVH. Taken together, these findings suggest CalcR^PVH neurons are an essential component of feeding and energy homeostatic circuitry.

Leptin receptor-expressing nucleus tractus solitarius neurons suppress food intake independently of GLP1 in mice

Leptin receptor-expressing (LepRb-expressing) neurons of the nucleus tractus solitarius (NTS; LepRbNTS neurons) receive gut signals that synergize with leptin action to suppress food intake. NTS neurons that express preproglucagon (Ppg) (and that produce the food intake-suppressing PPG cleavage product glucagon-like peptide-1 [GLP1]) represent a subpopulation of mouse LepRbNTS cells. Using Leprcre, Ppgcre, and Ppgfl mouse lines, along with Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), we examined roles for Ppg in GLP1NTS and LepRbNTS cells for the control of food intake and energy balance. We found that the cre-dependent ablation of NTS Ppgfl early in development or in adult mice failed to alter energy balance, suggesting the importance of pathways independent of NTS GLP1 for the long-term control of food intake. Consistently, while activating GLP1NTS cells decreased food intake, LepRbNTS cells elicited larger and more durable effects. Furthermore, while the ablation of NTS Ppgfl blunted the ability of GLP1NTS neurons to suppress food intake during activation, it did not impact the suppression of food intake by LepRbNTS cells. While Ppg/GLP1-mediated neurotransmission plays a central role in the modest appetite-suppressing effects of GLP1NTS cells, additional pathways engaged by LepRbNTS cells dominate for the suppression of food intake.

Paraventricular, subparaventricular and periventricular hypothalamic IRS4-expressing neurons are required for normal energy balance

Understanding the neural components modulating feeding-related behavior and energy expenditure is crucial to combating obesity and its comorbidities. Neurons within the paraventricular nucleus of the hypothalamus (PVH) are a key component of the satiety response; activation of the PVH decreases feeding and increases energy expenditure, thereby promoting negative energy balance. In contrast, PVH ablation or silencing in both rodents and humans leads to substantial obesity. Recent studies have identified genetically-defined PVH subpopulations that control discrete aspects of energy balance (e.g. oxytocin (OXT), neuronal nitric oxide synthase 1 (NOS1), melanocortin 4-receptor (MC4R), prodynorphin (PDYN)). We previously demonstrated that non-OXT NOS1^PVH neurons contribute to PVH-mediated feeding suppression. Here, we identify and characterize a non-OXT, non-NOS1 subpopulation of PVH and peri-PVH neurons expressing insulin-receptor substrate 4 (IRS4^PVH) involved in energy balance control. Using Cre-dependent viral tools to activate, trace and silence these neurons, we highlight the sufficiency and necessity of IRS4^PVH neurons in normal feeding and energy expenditure regulation. Furthermore, we demonstrate that IRS4^PVH neurons lie within a complex hypothalamic circuitry that engages distinct hindbrain regions and is innervated by discrete upstream hypothalamic sites. Overall, we reveal a requisite role for IRS4^PVH neurons in PVH-mediated energy balance which raises the possibility of developing novel approaches targeting IRS4^PVH neurons for anti-obesity therapies.

Calcitonin Receptor Neurons in the Mouse Nucleus Tractus Solitarius Control Energy Balance via the Non-aversive Suppression of Feeding

To understand hindbrain pathways involved in the control of food intake, we examined roles for calcitonin receptor (CALCR)-containing neurons in the NTS. Ablation of NTS Calcr abrogated the long-term suppression of food intake, but not aversive responses, by CALCR agonists. Similarly, activating Calcr^NTS neurons decreased food intake and body weight but (unlike neighboring Cck^NTS cells) failed to promote aversion, revealing that Calcr^NTS neurons mediate a non-aversive suppression of food intake. While both Calcr^NTS and Cck^NTS neurons decreased feeding via projections to the PBN, Cck^NTS cells activated aversive CGRP^PBN cells while Calcr^NTS cells activated distinct non-CGRP PBN cells. Hence, Calcr^NTS cells suppress feeding via non-aversive, non-CGRP PBN targets. Additionally, silencing Calcr^NTS cells blunted food intake suppression by gut peptides and nutrients, increasing food intake and promoting obesity. Hence, Calcr^NTS neurons define a hindbrain system that participates in physiological energy balance and suppresses food intake without activating aversive systems.

Alpha-melanocyte stimulating hormone increases the activity of melanocortin-3 receptor-expressing neurons in the ventral tegmental area

KEY POINTS

Alpha-melanocyte stimulating hormone (α-MSH) is an anorexigenic peptide. Injection of the α-MSH analog MTII into the ventral tegmental area (VTA) decreases food and sucrose intake and food reward. Melanocortin-3 receptors (MC3R) are highly expressed in the VTA, suggesting that the effects of intra-VTA α-MSH may be mediated by α-MSH changing the activity of MC3R-expressing VTA neurons. α-MSH increased the firing rate of MC3R VTA neurons in acute brain slices from mice, although it did not affect the firing rate of non-MC3R VTA neurons. The α-MSH induced increase in MC3R neuron firing rate is probably activity-dependent, and was independent of fast synaptic transmission and intracellular Ca²⁺ levels. These results help us to better understand how α-MSH acts in the VTA to affect feeding and other dopamine-dependent behaviours.

ABSTRACT

The mesocorticolimbic dopamine system, the brain's reward system, regulates multiple behaviours, including food intake and food reward. There is substantial evidence that the melanocortin system of the hypothalamus, an important neural circuit controlling feeding and body weight, interacts with the mesocorticolimbic dopamine system to affect feeding, food reward and body weight. For example, melanocortin-3 receptors (MC3Rs) are expressed in the ventral tegmental area (VTA) and our laboratory previously showed that intra-VTA injection of the MC3R agonist, MTII, decreases home-cage food intake and operant responding for sucrose pellets. However, the cellular mechanisms underlying the effects of intra-VTA alpha-melanocyte stimulating hormone (α-MSH) on feeding and food reward are unknown. To determine how α-MSH acts in the VTA to affect feeding, we performed electrophysiological recordings in acute brain slices from mice expressing enhanced yellow fluorescent protein in MC3R neurons to test how α-MSH affects the activity of VTA MC3R neurons. α-MSH significantly increased the firing rate of VTA MC3R neurons without altering the activity of non-MC3R expressing VTA neurons. In addition, the α-MSH-induced increase in MC3R neuron activity was independent of fast synaptic transmission and intracellular Ca²⁺ levels. Finally, we show that the effect of α-MSH on MC3R neuron firing rate is probably activity-dependent. Overall, these studies provide an important advancement in the understanding of how α-MSH acts in the VTA to affect feeding and food reward.

Respiratory Phenomics across Multiple Models of Protein Hyperacylation in Cardiac Mitochondria Reveals a Marginal Impact on Bioenergetics

Acyl CoA metabolites derived from the catabolism of carbon fuels can react with lysine residues of mitochondrial proteins, giving rise to a large family of post-translational modifications (PTMs). Mass spectrometry-based detection of thousands of acyl-PTMs scattered throughout the proteome has established a strong link between mitochondrial hyperacylation and cardiometabolic diseases; however, the functional consequences of these modifications remain uncertain. Here, we use a comprehensive respiratory diagnostics platform to evaluate three disparate models of mitochondrial hyperacylation in the mouse heart caused by genetic deletion of malonyl CoA decarboxylase (MCD), SIRT5 demalonylase and desuccinylase, or SIRT3 deacetylase. In each case, elevated acylation is accompanied by marginal respiratory phenotypes. Of the >60 mitochondrial energy fluxes evaluated, the only outcome consistently observed across models is a ∼15% decrease in ATP synthase activity. In sum, the findings suggest that the vast majority of mitochondrial acyl PTMs occur as stochastic events that minimally affect mitochondrial bioenergetics.

Lateral Hypothalamic Mc3R-Expressing Neurons Modulate Locomotor Activity, Energy Expenditure, and Adiposity in Male Mice

The central melanocortin system plays a crucial role in the control of energy balance. Although the decreased energy expenditure and increased adiposity of melanocortin-3 receptor (Mc3R)-null mice suggest the importance of Mc3R-regulated neurons in energy homeostasis, the roles for specific subsets of Mc3R neurons in energy balance have yet to be determined. Because the lateral hypothalamic area (LHA) contributes to the control of energy expenditure and feeding, we generated Mc3rcre mice to determine the roles of LHA Mc3R (Mc3RLHA) neurons in energy homeostasis. We found that Mc3RLHA neurons overlap extensively with LHA neuron markers that contribute to the control of energy balance (neurotensin, galanin, and leptin receptor) and project to brain areas involved in the control of feeding, locomotion, and energy expenditure, consistent with potential roles for Mc3RLHA neurons in these processes. Indeed, selective chemogenetic activation of Mc3RLHA neurons increased locomotor activity and augmented refeeding after a fast. Although the ablation of Mc3RLHA neurons did not alter food intake, mice lacking Mc3RLHA neurons displayed decreased energy expenditure and locomotor activity, along with increased body mass and adiposity. Thus, Mc3R neurons lie within LHA neurocircuitry that modulates locomotor activity and energy expenditure and contribute to energy balance control.

Sex differences in tobacco smokers: Executive control network and frontostriatal connectivity

BACKGROUND

Women experience greater difficulty quitting smoking than men, which may be explained by sex differences in brain circuitry underlying cognitive control. Prior work has linked reduced interhemispheric executive control network (ECN) coupling with poor executive function, shorter time to relapse, and greater substance use. Lower structural connectivity between a key ECN hub, the dorsolateral prefrontal cortex (DLPFC), and the dorsal striatum (DS) also contributes to less efficient cognitive control recruitment, and reduced intrahemispheric connectivity between these regions has been associated with smoking relapse. Therefore, sex differences were probed by evaluating interhemispheric ECN and intrahemispheric DLPFC-DS connectivity. To assess the potential sex by nicotine interaction, a pilot sample of non-smokers was evaluated following acute nicotine and placebo administration.

METHODS

Thirty-five smokers (19 women) completed one resting state functional magnetic resonance imaging scan. Seventeen non-smokers (8 women) were scanned twice using a repeated measures design where they received 2 and 0 mg nicotine.

RESULTS

In smokers, women had less interhemispheric ECN and DLPFC-DS coupling than men. In non-smokers, there was a drug x sex interaction where women, relative to men, had weaker ECN coupling following nicotine but not placebo administration.

CONCLUSIONS

The current work indicates that nicotine-dependent women, versus men, have weaker connectivity in brain networks critically implicated in cognitive control. How these connectivity differences contribute to the behavioral aspects of smoking requires more testing. However, building on the literature, it is likely these deficits in functional connectivity contribute to the lower abstinence rates noted in women relative to men.

Transcriptional and physiological roles for STAT proteins in leptin action

Objectives

Leptin acts via its receptor LepRb on specialized neurons in the brain to modulate food intake, energy expenditure, and body weight. LepRb activates signal transducers and activators of transcription (STATs, including STAT1, STAT3, and STAT5) to control gene expression.

Methods

Because STAT3 is crucial for physiologic leptin action, we used TRAP-seq to examine gene expression in LepRb neurons of mice ablated for Stat3 in LepRb neurons (Stat3^LepRbKO mice), revealing the STAT3-dependent transcriptional targets of leptin. To understand roles for STAT proteins in leptin action, we also ablated STAT1 or STAT5 from LepRb neurons and expressed a constitutively-active STAT3 (CASTAT3) in LepRb neurons.

Results

While we also found increased Stat1 expression and STAT1-mediated transcription of leptin-regulated genes in Stat3^LepRbKO mice, ablating Stat1 in LepRb neurons failed to alter energy balance (even on the Stat3^LepRbKO background); ablating Stat5 in LepRb neurons also failed to alter energy balance. Importantly, expression of a constitutively-active STAT3 (CASTAT3) in LepRb neurons decreased food intake and body weight and improved metabolic parameters in leptin-deficient (ob/ob) mice, as well as in wild-type animals.

Conclusions

Thus, STAT3 represents the unique STAT protein required for leptin action and STAT3 suffices to mediate important components of leptin action in the absence of other LepRb signals.

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We used TRAP-seq to define the STAT3-dependent and independent control of gene expression in LepRb neurons.

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We deleted multiple STAT proteins from LepRb neurons, revealing the unique role for STAT3 in leptin action.

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Constitutively-active STAT3 in LepRb neurons controlled body weight and glucose in ob/ob and wild-type mice.

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STAT3 represents the only STAT protein required for leptin action and suffices to mediate components of leptin action.

Specific subpopulations of hypothalamic leptin receptor-expressing neurons mediate the effects of early developmental leptin receptor deletion on energy balance

OBJECTIVE

To date, early developmental ablation of leptin receptor (LepRb) expression from circumscribed populations of hypothalamic neurons (e.g., arcuate nucleus (ARC) Pomc- or Agrp-expressing cells) has only minimally affected energy balance. In contrast, removal of LepRb from at least two large populations (expressing vGat or Nos1) spanning multiple hypothalamic regions produced profound obesity and metabolic dysfunction. Thus, we tested the notion that the total number of leptin-responsive hypothalamic neurons (rather than specific subsets of cells with a particular molecular or anatomical signature) subjected to early LepRb deletion might determine energy balance.

METHODS

We generated new mouse lines deleted for LepRb in ARC GhrhCre neurons or in Htr2cCre neurons (representing roughly half of all hypothalamic LepRb neurons, distributed across many nuclei). We compared the phenotypes of these mice to previously-reported models lacking LepRb in Pomc, Agrp, vGat or Nos1 cells.

RESULTS

The early developmental deletion of LepRb from vGat or Nos1 neurons produced dramatic obesity, but deletion of LepRb from Pomc, Agrp, Ghrh, or Htr2c neurons minimally altered energy balance.

CONCLUSIONS

Although early developmental deletion of LepRb from known populations of ARC neurons fails to substantially alter body weight, the minimal phenotype of mice lacking LepRb in Htr2c cells suggests that the phenotype that results from early developmental LepRb deficiency depends not simply upon the total number of leptin-responsive hypothalamic LepRb cells. Rather, specific populations of LepRb neurons must play particularly important roles in body energy homeostasis; these as yet unidentified LepRb cells likely reside in the DMH.

Liraglutide Modulates Appetite and Body Weight Through Glucagon-Like Peptide 1 Receptor-Expressing Glutamatergic Neurons

Glucagon-like peptide 1 receptor (GLP-1R) agonists are U.S. Food and Drug Administration-approved weight loss drugs. Despite their widespread use, the sites of action through which GLP-1R agonists (GLP1RAs) affect appetite and body weight are still not fully understood. We determined whether GLP-1Rs in either GABAergic or glutamatergic neurons are necessary for the short- and long-term effects of the GLP1RA liraglutide on food intake, visceral illness, body weight, and neural network activation. We found that mice lacking GLP-1Rs in vGAT-expressing GABAergic neurons responded identically to controls in all parameters measured, whereas deletion of GLP-1Rs in vGlut2-expressing glutamatergic neurons eliminated liraglutide-induced weight loss and visceral illness and severely attenuated its effects on feeding. Concomitantly, deletion of GLP-1Rs from glutamatergic neurons completely abolished the neural network activation observed after liraglutide administration. We conclude that liraglutide activates a dispersed but discrete neural network to mediate its physiological effects and that these effects require GLP-1R expression on glutamatergic but not GABAergic neurons.

Defining the Transcriptional Targets of Leptin Reveals a Role for Atf3 in Leptin Action

Leptin acts via its receptor (LepRb) to modulate gene expression in hypothalamic LepRb-expressing neurons, thereby controlling energy balance and glucose homeostasis. Despite the importance of the control of gene expression in hypothalamic LepRb neurons for leptin action, the transcriptional targets of LepRb signaling have remained undefined because LepRb cells contribute a small fraction to the aggregate transcriptome of the brain regions in which they reside. We thus employed translating ribosome affinity purification followed by RNA sequencing to isolate and analyze mRNA from the hypothalamic LepRb neurons of wild-type or leptin-deficient (Lepob/ob) mice treated with vehicle or exogenous leptin. Although the expression of most of the genes encoding the neuropeptides commonly considered to represent the main targets of leptin action were altered only following chronic leptin deprivation, our analysis revealed other transcripts that were coordinately regulated by leptin under multiple treatment conditions. Among these, acute leptin treatment increased expression of the transcription factor Atf3 in LepRb neurons. Furthermore, ablation of Atf3 from LepRb neurons (Atf3LepRbKO mice) decreased leptin efficacy and promoted positive energy balance in mice. Thus, this analysis revealed the gene targets of leptin action, including Atf3, which represents a cellular mediator of leptin action.

Childhood stress, grown-up brain networks: corticolimbic correlates of threat-related early life stress and adult stress response

BACKGROUND

Exposure to threat-related early life stress (ELS) has been related to vulnerability for stress-related disorders in adulthood, putatively via disrupted corticolimbic circuits involved in stress response and regulation. However, previous research on ELS has not examined both the intrinsic strength and flexibility of corticolimbic circuits, which may be particularly important for adaptive stress responding, or associations between these dimensions of corticolimbic dysfunction and acute stress response in adulthood.

METHODS

Seventy unmedicated women varying in history of threat-related ELS completed a functional magnetic resonance imaging scan to evaluate voxelwise static (overall) and dynamic (variability over a series of sliding windows) resting-state functional connectivity (RSFC) of bilateral amygdala. In a separate session and subset of participants (n = 42), measures of salivary cortisol and affect were collected during a social-evaluative stress challenge.

RESULTS

Higher severity of threat-related ELS was related to more strongly negative static RSFC between amygdala and left dorsolateral prefrontal cortex (DLPFC), and elevated dynamic RSFC between amygdala and rostral anterior cingulate cortex (rACC). Static amygdala-DLPFC antagonism mediated the relationship between higher severity of threat-related ELS and blunted cortisol response to stress, but increased dynamic amygdala-rACC connectivity weakened this mediated effect and was related to more positive post-stress mood.

CONCLUSIONS

Threat-related ELS was associated with RSFC within lateral corticolimbic circuits, which in turn was related to blunted physiological response to acute stress. Notably, increased flexibility between the amygdala and rACC compensated for this static disruption, suggesting that more dynamic medial corticolimbic circuits might be key to restoring healthy stress response.

Identification of Genes Enriched in GnRH Neurons by Translating Ribosome Affinity Purification and RNAseq in Mice

Gonadotropin-releasing hormone (GnRH) neurons are a nexus of fertility regulation. We used translating ribosome affinity purification coupled with RNA sequencing to examine messenger RNAs of GnRH neurons in adult intact and gonadectomized (GDX) male and female mice. GnRH neuron ribosomes were tagged with green fluorescent protein (GFP) and GFP-labeled polysomes isolated by immunoprecipitation, producing one RNA fraction enhanced for GnRH neuron transcripts and one RNA fraction depleted. Complementary DNA libraries were created from each fraction and 50-base, paired-end sequencing done and differential expression (enhanced fraction/depleted fraction) determined with a threshold of >1.5- or <0.66-fold (false discovery rate P ≤ 0.05). A core of ∼840 genes was differentially expressed in GnRH neurons in all treatments, including enrichment for Gnrh1 (∼40-fold), and genes critical for GnRH neuron and/or gonadotrope development. In contrast, non-neuronal transcripts were not enriched or were de-enriched. Several epithelial markers were also enriched, consistent with the olfactory epithelial origins of GnRH neurons. Interestingly, many synaptic transmission pathways were de-enriched, in accordance with relatively low innervation of GnRH neurons. The most striking difference between intact and GDX mice of both sexes was a marked downregulation of genes associated with oxidative phosphorylation and upregulation of glucose transporters in GnRH neurons from GDX mice. This may suggest that GnRH neurons switch to an alternate fuel to increase adenosine triphosphate production in the absence of negative feedback when GnRH release is elevated. Knowledge of the GnRH neuron translatome and its regulation can guide functional studies and can be extended to disease states, such as polycystic ovary syndrome.

Essential Role for Hypothalamic Calcitonin Receptor‒Expressing Neurons in the Control of Food Intake by Leptin

The adipocyte-derived hormone leptin acts via its receptor (LepRb) on central nervous system neurons to communicate the repletion of long-term energy stores, to decrease food intake, and to promote energy expenditure. We generated mice that express Cre recombinase from the calcitonin receptor (Calcr) locus (Calcrcre mice) to study Calcr-expressing LepRb (LepRbCalcr) neurons, which reside predominantly in the arcuate nucleus (ARC). Calcrcre-mediated ablation of LepRb in LepRbCalcrknockout (KO) mice caused hyperphagic obesity. Because LepRb-mediated transcriptional control plays a crucial role in leptin action, we used translating ribosome affinity purification followed by RNA sequencing to define the transcriptome of hypothalamic Calcr neurons, along with its alteration in LepRbCalcrKO mice. We found that ARC LepRbCalcr cells include neuropeptide Y (NPY)/agouti-related peptide (AgRP)/γ-aminobutyric acid (GABA) ("NAG") cells as well as non-NAG cells that are distinct from pro-opiomelanocortin cells. Furthermore, although LepRbCalcrKO mice exhibited dysregulated expression of several genes involved in energy balance, neither the expression of Agrp and Npy nor the activity of NAG cells was altered in vivo. Thus, although direct leptin action via LepRbCalcr cells plays an important role in leptin action, our data also suggest that leptin indirectly, as well as directly, regulates these cells.

Bone Health and Endocrine Comorbidities in Pediatric Epilepsy

Antiseizure medications and dietary therapies have associated effects on the endocrine system. We provided an overview of the relationship between epilepsy treatment and bone health in children with epilepsy. Additionally, we discussed the effects of epilepsy treatment on other endocrine systems including thyroid function, growth, reproduction, and weight. The effect of epilepsy on bone health is multifactorial; there are direct and indirect effects of medication and dietary treatments as well as a decrease in physical activity, decreased sunlight exposure, decreased vitamin D levels, and additional comorbidities. Some medications have a greater effect on vitamin D and bone health than others, however all antiseizure medical treatments are associated with lower vitamin D levels in pediatric patients. We have provided practical suggestions for vitamin D surveillance in children with epilepsy as well as replacement strategies. Children with epilepsy have an increased likelihood of additional endocrine disorders including subclinical hypothyroidism, decreased growth, weight abnormalities, reproductive and sexual dysfunction. To a great extent, this is medication specific. Though more studies are needed to elucidate optimal treatment and monitoring of bone health and other endocrinopathies in children with epilepsy, it is critical that caregivers pay close attention to these issues to provide optimal comprehensive care to their patients.

A leptin-regulated circuit controls glucose mobilization during noxious stimuli

Adipocytes secrete the hormone leptin to signal the sufficiency of energy stores. Reductions in circulating leptin concentrations reflect a negative energy balance, which augments sympathetic nervous system (SNS) activation in response to metabolically demanding emergencies. This process ensures adequate glucose mobilization despite low energy stores. We report that leptin receptor-expressing neurons (LepRb neurons) in the periaqueductal gray (PAG), the largest population of LepRb neurons in the brain stem, mediate this process. Application of noxious stimuli, which often signal the need to mobilize glucose to support an appropriate response, activated PAG LepRb neurons, which project to and activate parabrachial nucleus (PBN) neurons that control SNS activation and glucose mobilization. Furthermore, activating PAG LepRb neurons increased SNS activity and blood glucose concentrations, while ablating LepRb in PAG neurons augmented glucose mobilization in response to noxious stimuli. Thus, decreased leptin action on PAG LepRb neurons augments the autonomic response to noxious stimuli, ensuring sufficient glucose mobilization during periods of acute demand in the face of diminished energy stores.

Dopaminergic Enhancement of Striatal Response to Reward in Major Depression

OBJECTIVE

Major depressive disorder is characterized by reduced reward-related striatal activation and dysfunctional reward learning, putatively reflecting decreased dopaminergic signaling. The goal of this study was to test whether a pharmacological challenge designed to facilitate dopaminergic transmission can enhance striatal responses to reward and improve reward learning in depressed individuals.

METHOD

In a double-blind placebo-controlled design, 46 unmedicated depressed participants and 43 healthy control participants were randomly assigned to receive either placebo or a single low dose (50 mg) of the D₂/D₃ receptor antagonist amisulpride, which is believed to increase dopamine signaling through presynaptic autoreceptor blockade. To investigate the effects of increased dopaminergic transmission on reward-related striatal function and behavior, a monetary incentive delay task (in conjunction with functional MRI) and a probabilistic reward learning task were administered at absorption peaks of amisulpride.

RESULTS

Depressed participants selected previously rewarded stimuli less frequently than did control participants, indicating reduced reward learning, but this effect was not modulated by amisulpride. Relative to depressed participants receiving placebo (and control participants receiving amisulpride), depressed participants receiving amisulpride exhibited increased striatal activation and potentiated corticostriatal functional connectivity between the nucleus accumbens and the midcingulate cortex in response to monetary rewards. Stronger corticostriatal connectivity in response to rewards predicted better reward learning among depressed individuals receiving amisulpride as well as among control participants receiving placebo.

CONCLUSIONS

Acute enhancement of dopaminergic transmission potentiated reward-related striatal activation and corticostriatal functional connectivity in depressed individuals but had no behavioral effects. Taken together, the results suggest that targeted pharmacological treatments may normalize neural correlates of reward processing in depression; despite such acute effects on neural function, behavioral modification may require more chronic exposure. This is consistent with previous reports that antidepressant effects of amisulpride in depression emerged after sustained administration.

Joint Effects: A Pilot Investigation of the Impact of Bipolar Disorder and Marijuana Use on Cognitive Function and Mood

Marijuana is the most widely used illicit substance in those diagnosed with bipolar I disorder. However, there is conflicting evidence as to whether marijuana may alleviate or exacerbate mood symptomatology. As bipolar disorder and marijuana use are individually associated with cognitive impairment, it also remains unclear whether there is an additive effect on cognition when bipolar patients use marijuana. The current study aimed to determine the impact of marijuana on mood in bipolar patients and to examine whether marijuana confers an additional negative impact on cognitive function. Twelve patients with bipolar disorder who smoke marijuana (MJBP), 18 bipolar patients who do not smoke (BP), 23 marijuana smokers without other Axis 1 pathology (MJ), and 21 healthy controls (HC) completed a neuropsychological battery. Further, using ecological momentary assessment, participants rated their mood three times daily as well as after each instance of marijuana use over a four-week period. Results revealed that although the MJ, BP, and MJBP groups each exhibited some degree of cognitive impairment relative to HCs, no significant differences between the BP and MJBP groups were apparent, providing no evidence of an additive negative impact of BPD and MJ use on cognition. Additionally, ecological momentary assessment analyses indicated alleviation of mood symptoms in the MJBP group after marijuana use; MJBP participants experienced a substantial decrease in a composite measure of mood symptoms. Findings suggest that for some bipolar patients, marijuana may result in partial alleviation of clinical symptoms. Moreover, this improvement is not at the expense of additional cognitive impairment.

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.

TRAP-seq defines markers for novel populations of hypothalamic and brainstem LepRb neurons

OBJECTIVE

Leptin acts via its receptor (LepRb) on multiple subpopulations of LepRb neurons in the brain, each of which controls specific aspects of energy balance. Despite the importance of LepRb-containing neurons, the transcriptome and molecular identity of many LepRb subpopulations remain undefined due to the difficulty of studying the small fraction of total cells represented by LepRb neurons in heterogeneous brain regions. Here we sought to examine the transcriptome of LepRb neurons directly and identify markers for functionally relevant LepRb subsets.

METHODS

We isolated mRNA from mouse hypothalamic and brainstem LepRb cells by Translating Ribosome Affinity Purification (TRAP) and analyzed it by RNA-seq (TRAP-seq).

RESULTS

TRAP mRNA from LepRb cells was enriched for markers of peptidergic neurons, while TRAP-depleted mRNA from non-LepRb cells was enriched for markers of glial and immune cells. Genes encoding secreted proteins that were enriched in hypothalamic and brainstem TRAP mRNA revealed subpopulations of LepRb neurons that contained neuropeptide-encoding genes (including prodynorphin, Pdyn) not previously used as functional markers for LepRb neurons. Furthermore, Pdyn (cre) -mediated ablation of Lepr (flox) in Pdyn-expressing neurons (LepRb (Pdyn) KO mice) blunted energy expenditure to promote obesity during high-fat feeding.

CONCLUSIONS

TRAP-seq of CNS LepRb neurons defines the LepRb neuron transcriptome and reveals novel markers for previously unrecognized subpopulations of LepRb neurons.

Leptin-inhibited PBN neurons enhance responses to hypoglycemia in negative energy balance

Hypoglycemia initiates the counter regulatory response (CRR), in which the sympathetic nervous system, glucagon, and glucocorticoids restore glucose to appropriate concentrations. During starvation, low leptin restrains energy utilization, enhancing long-term survival. To ensure short-term survival during hypoglycemia in fasted animals, the CRR must overcome this energy-sparing program and nutrient depletion. Here, we identify in mice a previously unrecognized role for leptin and a population of leptin-regulated neurons that modulate the CRR to meet these challenges. Hypoglycemia activates leptin receptor (LepRb) and cholecystokinin (CCK)-expressing neurons of the parabrachial nucleus (PBN), which project to the ventromedial hypothalamic nucleus. Leptin inhibits these cells and Cck^cre-mediated ablation of LepRb enhances the CRR. Inhibition of PBN LepRb cells blunts the CRR, while their activation mimics the CRR in a CCK-dependent manner. PBN LepRb^CCK neurons represent a crucial component of the CRR system, and may represent a therapeutic target in hypoglycemia.

Birthdating of myenteric neuron subtypes in the small intestine of the mouse

There are many different types of enteric neurons. Previous studies have identified the time at which some enteric neuron subtypes are born (exit the cell cycle) in the mouse, but the birthdates of some major enteric neuron subtypes are still incompletely characterized or unknown. We combined 5-ethynynl-2'-deoxyuridine (EdU) labeling with antibody markers that identify myenteric neuron subtypes to determine when neuron subtypes are born in the mouse small intestine. We found that different neurochemical classes of enteric neuron differed in their birthdates; serotonin neurons were born first with peak cell cycle exit at E11.5, followed by neurofilament-M neurons, calcitonin gene-related peptide neurons (peak cell cycle exit for both at embryonic day [E]12.5-E13.5), tyrosine hydroxylase neurons (E15.5), nitric oxide synthase 1 (NOS1) neurons (E15.5), and calretinin neurons (postnatal day [P]0). The vast majority of myenteric neurons had exited the cell cycle by P10. We did not observe any EdU+/NOS1+ myenteric neurons in the small intestine of adult mice following EdU injection at E10.5 or E11.5, which was unexpected, as previous studies have shown that NOS1 neurons are present in E11.5 mice. Studies using the proliferation marker Ki67 revealed that very few NOS1 neurons in the E11.5 and E12.5 gut were proliferating. However, Cre-lox-based genetic fate-mapping revealed a small subpopulation of myenteric neurons that appears to express NOS1 only transiently. Together, our results confirm a relationship between enteric neuron subtype and birthdate, and suggest that some enteric neurons exhibit neurochemical phenotypes during development that are different from their mature phenotype.

Rapid mood-elevating effects of low field magnetic stimulation in depression

BACKGROUND

We previously reported rapid mood elevation following an experimental magnetic resonance imaging procedure in depressed patients with bipolar disorder (BPD). This prompted the design, construction, and testing of a portable electromagnetic device that reproduces only the rapidly oscillating (1 kHz, <1 V/m) electromagnetic field of the experimental procedure, called low field magnetic stimulation (LFMS).

METHODS

We used a randomized, double blind, sham controlled treatment protocol to study the effects of LFMS in a large group of stably medicated, depressed patients with either BPD (n = 41) or major depressive disorder (n = 22). Subjects received a single, 20-minute treatment. Change in mood was assessed immediately afterward using a visual analog scale (VAS), the 17-item Hamilton Depression Rating Scale (HDRS-17), and the Positive and Negative Affect Schedule scales.

RESULTS

Substantial improvement (>10% of baseline) in mood was observed following LFMS treatment relative to sham treatment for both diagnostic subgroups for our primary outcomes, the VAS and the HDRS-17. These differences were not statistically significant in primary analyses stratifying by diagnosis but were significant in secondary analyses combining data across the two diagnostic groups (p = .01 VAS, p = .02 HDRS-17). Rapid improvement in mood was also observed using the Positive and Negative Affect Schedule scales as secondary measures (positive affect scale p = .02 BPD, p = .002 combined group). A finite element method calculation indicates a broad penetration of the LFMS electric field throughout the cerebral cortex.

CONCLUSIONS

Low field magnetic stimulation may produce rapid changes in mood using a previously unexplored range of electromagnetic fields.

Melanocortin 4 receptors in autonomic neurons regulate thermogenesis and glycemia

Melanocortin 4 receptors (Mc4rs) are expressed by extra-hypothalamic neurons including cholinergic autonomic pre-ganglionic neurons. However, whether Mc4rs in these neurons are required to control energy and glucose homeostasis is unclear. Here we report that Mc4rs in sympathetic, but not parasympathetic, pre-ganglionic neurons are required to regulate energy expenditure and body weight including brown and white adipose tissue thermogenic responses to diet and cold exposure. In addition, deletion of Mc4rs in both sympathetic and parasympathetic cholinergic neurons impairs glucose homeostasis.

An excitatory paraventricular nucleus to AgRP neuron circuit that drives hunger

Hunger is a hard-wired motivational state essential for survival. Agouti-related peptide (AgRP)-expressing neurons in the arcuate nucleus (ARC) at the base of the hypothalamus are crucial to the control of hunger. They are activated by caloric deficiency and, when naturally or artificially stimulated, they potently induce intense hunger and subsequent food intake. Consistent with their obligatory role in regulating appetite, genetic ablation or chemogenetic inhibition of AgRP neurons decreases feeding. Excitatory input to AgRP neurons is important in caloric-deficiency-induced activation, and is notable for its remarkable degree of caloric-state-dependent synaptic plasticity. Despite the important role of excitatory input, its source(s) has been unknown. Here, through the use of Cre-recombinase-enabled, cell-specific neuron mapping techniques in mice, we have discovered strong excitatory drive that, unexpectedly, emanates from the hypothalamic paraventricular nucleus, specifically from subsets of neurons expressing thyrotropin-releasing hormone (TRH) and pituitary adenylate cyclase-activating polypeptide (PACAP, also known as ADCYAP1). Chemogenetic stimulation of these afferent neurons in sated mice markedly activates AgRP neurons and induces intense feeding. Conversely, acute inhibition in mice with caloric-deficiency-induced hunger decreases feeding. Discovery of these afferent neurons capable of triggering hunger advances understanding of how this intense motivational state is regulated.

AVP neurons in the paraventricular nucleus of the hypothalamus regulate feeding

Melanocortins and their receptors are critical components of energy homeostasis and the paraventricular nucleus of the hypothalamus (PVH) is an important site of melanocortin action. Although best known for its role in osmoregulation, arginine vasopressin (AVP) has been implicated in feeding and is robustly expressed in the PVH. Since the anorectic melanocortin agonist MTII activates PVH-AVP neurons, we hypothesized that PVH-AVP neurons contribute to PVH-mediated anorexia. To test this, we used an AVP-specific Cre-driver mouse in combination with viral vectors to acutely manipulate PVH-AVP neuron function. Using designer receptors exclusively activated by designer drugs (DREADDs) to control PVH-AVP neuron activity, we show that activation of PVH-AVP neurons acutely inhibits food intake, whereas their inhibition partially reverses melanocortin-induced anorexia. We further show that MTII fails to fully suppress feeding in mice with virally-induced PVH-AVP neuron ablation. Thus PVH-AVP neurons contribute to feeding behaviors, including the acute anorectic response to MTII.

GABAergic RIP-Cre neurons in the arcuate nucleus selectively regulate energy expenditure

Neural regulation of energy expenditure is incompletely understood. By genetically disrupting GABAergic transmission in a cell-specific fashion, and by combining this with selective pharmacogenetic activation and optogenetic mapping techniques, we have uncovered an arcuate-based circuit that selectively drives energy expenditure. Specifically, mice lacking synaptic GABA release from RIP-Cre neurons have reduced energy expenditure, become obese and are extremely sensitive to high-fat diet-induced obesity, the latter due to defective diet-induced thermogenesis. Leptin's ability to stimulate thermogenesis, but not to reduce feeding, is markedly attenuated. Acute, selective activation of arcuate GABAergic RIP-Cre neurons, which monosynaptically innervate PVH neurons projecting to the NTS, rapidly stimulates brown fat and increases energy expenditure but does not affect feeding. Importantly, this response is dependent upon GABA release from RIP-Cre neurons. Thus, GABAergic RIP-Cre neurons in the arcuate selectively drive energy expenditure, contribute to leptin's stimulatory effect on thermogenesis, and protect against diet-induced obesity.

An obligate role of oxytocin neurons in diet induced energy expenditure

Oxytocin neurons represent one of the major subsets of neurons in the paraventricular hypothalamus (PVH), a critical brain region for energy homeostasis. Despite substantial evidence supporting a role of oxytocin in body weight regulation, it remains controversial whether oxytocin neurons directly regulate body weight homeostasis, feeding or energy expenditure. Pharmacologic doses of oxytocin suppress feeding through a proposed melanocortin responsive projection from the PVH to the hindbrain. In contrast, deficiency in oxytocin or its receptor leads to reduced energy expenditure without feeding abnormalities. To test the physiological function of oxytocin neurons, we specifically ablated oxytocin neurons in adult mice. Our results show that oxytocin neuron ablation in adult animals has no effect on body weight, food intake or energy expenditure on a regular diet. Interestingly, male mice lacking oxytocin neurons are more sensitive to high fat diet-induced obesity due solely to reduced energy expenditure. In addition, despite a normal food intake, these mice exhibit a blunted food intake response to leptin administration. Thus, our study suggests that oxytocin neurons are required to resist the obesity associated with a high fat diet; but their role in feeding is permissive and can be compensated for by redundant pathways.