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The superior colliculus (SC), a midbrain sensorimotor hub, is anatomically and functionally similar across vertebrates, but how its cell types have evolved is unclear. Using single-nucleus transcriptomics, we compared the SC's molecular and cellular organization in mice, tree shrews, and humans. Despite over 96 million years of evolutionary divergence, we identified ~30 consensus neuronal subtypes, including Cbln2 + neurons that form the SC-pulvinar circuit in mice and tree shrews. Synapse-related genes were among the most conserved, unlike neocortex, suggesting co-conservation of synaptic genes and circuitry. In contrast, cilia-related genes diverged significantly across species, highlighting the potential importance of the neuronal primary cilium in SC evolution. Additionally, we identified a novel inhibitory SC neuron in tree shrews and humans but not mice. Our findings reveal that the SC has evolved by conserving neuron subtypes, synaptic genes, and circuitry, while diversifying ciliary gene expression and an inhibitory neuron subtype., Competing Interests: DECLARATION OF INTERESTS The authors declare no competing interests.

Glucagon-like peptide-1 receptor agonists (GLP1RAs) effectively reduce body weight and improve metabolic outcomes, yet established peptide-based therapies require injections and complex manufacturing. Small-molecule GLP1RAs promise oral bioavailability and scalable manufacturing, but their selective binding to human versus rodent receptors has limited mechanistic studies. The neural circuits through which these emerging therapeutics modulate feeding behavior remain undefined, particularly in comparison to established peptide-based GLP1RAs. Here, we developed humanized GLP1R mouse models to investigate how small- molecule GLP1RAs influence feeding behavior. Integrating genetic manipulations, calcium imaging, and behavior profiling, we discovered that these compounds regulate both homeostatic and hedonic feeding through parallel neural circuits. Beyond engaging canonical hypothalamic and hindbrain networks that control metabolic homeostasis, GLP1RAs recruit a discrete population of Glp1r-expressing neurons in the central amygdala, which selectively suppress the consumption of palatable foods by reducing dopamine release in the nucleus accumbens. Stimulating these central amygdalar neurons curtail hedonic feeding, whereas targeted deletion of the receptor in this cell population specifically diminishes the anorectic efficacy of GLP1RAs for reward-driven intake. These findings reveal a dedicated neural circuit through which small molecule GLP1RAs modulate reward processing, suggesting broad therapeutic potential in conditions of dysregulated dopamine signaling including substance use disorder and binge eating.

Liraglutide and other glucagon-like peptide 1 receptor agonists (GLP-1RAs) are effective weight loss drugs, but how they suppress appetite remains unclear. One potential mechanism is by activating neurons that inhibit the hunger-promoting Agouti-related peptide (AgRP) neurons of the arcuate hypothalamus (Arc). To identify these afferents, we developed a method combining rabies-based connectomics with single-nucleus transcriptomics. Here, we identify at least 21 afferent subtypes of AgRP neurons in the mouse mediobasal and paraventricular hypothalamus, which are predicted by our method. Among these are thyrotropin-releasing hormone (TRH) + Arc (TRH Arc ) neurons, inhibitory neurons that express the Glp1r gene and are activated by the GLP-1RA liraglutide. Activating TRH Arc neurons inhibits AgRP neurons and feeding, probably in an AgRP neuron-dependent manner. Silencing TRH Arc neurons causes overeating and weight gain and attenuates liraglutide's effect on body weight. Our results demonstrate a widely applicable method for molecular connectomics, comprehensively identify local inputs to AgRP neurons and reveal a circuit through which GLP-1RAs suppress appetite., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The ventrolateral medulla (VLM) is a crucial region in the brain for visceral and somatic control, serving as a significant source of synaptic input to the spinal cord. Experimental studies have shown that gene expression in individual VLM neurons is predictive of their function. However, the molecular and cellular organization of the VLM has remained uncertain. This study aimed to create a comprehensive dataset of VLM cells using single-cell RNA sequencing in male and female mice. The dataset was enriched with targeted sequencing of spinally-projecting and adrenergic/noradrenergic VLM neurons. Based on differentially expressed genes, the resulting dataset of 114,805 VLM cells identifies 23 subtypes of neurons, excluding those in the inferior olive, and five subtypes of astrocytes. Spinally-projecting neurons were found to be abundant in seven subtypes of neurons, which were validated through in situ hybridization. These subtypes included adrenergic/noradrenergic neurons, serotonergic neurons, and neurons expressing gene markers associated with premotor neurons in the ventromedial medulla. Further analysis of adrenergic/noradrenergic neurons and serotonergic neurons identified nine and six subtypes, respectively, within each class of monoaminergic neurons. Marker genes that identify the neural network responsible for breathing were concentrated in two subtypes of neurons, delineated from each other by markers for excitatory and inhibitory neurons. These datasets are available for public download and for analysis with a user-friendly interface. Collectively, this study provides a fine-scale molecular identification of cells in the VLM, forming the foundation for a better understanding of the VLM's role in vital functions and motor control., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 the authors.)

Schwann cells (SCs) transition into a repair phenotype after peripheral nerve injury, which is crucial for supporting axon regeneration. However, the early SC injury response preceding the repair state remains poorly understood. Here, we demonstrate that Sarm1, a key regulator of axon degeneration, is expressed in SCs and has a critical role in the early SC injury response. Leveraging the fact that Sarm1 deletion impairs the SC transition to the repair state, we used single-nucleus RNA sequencing to compare the transcriptional responses of wild-type and Sarm1 knockout SCs 24 hours after nerve injury. Remarkably, Sarm1-deficient SCs, unlike wild-type SCs, showed increased expression of genes involved in oxidative phosphorylation and the TCA cycle. These findings were functionally validated, revealing that Sarm1 knockout SCs displayed increased mitochondrial respiration in response to injury. Intriguingly, Sarm1 knockout SCs also exhibited enhanced axon protection compared to wild-type SCs in an in vitro model of axon degeneration. We propose that Sarm1 gates the transition of SCs from a protective, oxidative phosphorylation-dependent state (which we term Protection Associated Schwann Cells or PASCs) to a glycolytic, pro-regenerative repair phenotype after injury. Our findings challenge the prevailing view of Sarm1 as an exclusively axon-autonomous regulator of degeneration and reveal a paradigm shift in understanding the role of Sarm1 in the SC injury response, with broad implications for the treatment of peripheral neuropathies and neurodegenerative diseases.

The vagus nerve vitally connects the brain and body to coordinate digestive, cardiorespiratory, and immune functions. Its efferent neurons, which project their axons from the brainstem to the viscera, are thought to comprise "functional units" - neuron populations dedicated to the control of specific vagal reflexes or organ functions. Previous research indicates that these functional units differ from one another anatomically, neurochemically, and physiologically but have yet to define their identity in an experimentally tractable way. However, recent work with genetic technology and single-cell genomics suggests that genetically distinct subtypes of neurons may be the functional units of the efferent vagus. Here we review how these approaches are revealing the organizational principles of the efferent vagus in unprecedented detail., Competing Interests: Declaration of Competing Interest The authors have no conflicts of interest to disclose., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Cardiovagal neurons (CVNs) innervate cardiac ganglia through the vagus nerve to control cardiac function. Although the cardioinhibitory role of CVNs in nucleus ambiguus (CVN NA ) is well established, the nature and functionality of CVNs in dorsal motor nucleus of the vagus (CVN DMV ) is less clear. We therefore aimed to characterize CVN DMV anatomically, physiologically, and functionally. Optogenetically activating cholinergic DMV neurons resulted in robust bradycardia through peripheral muscarinic (parasympathetic) and nicotinic (ganglionic) acetylcholine receptors, but not beta-1-adrenergic (sympathetic) receptors. Retrograde tracing from the cardiac fat pad labeled CVN NA and CVN DMV through the vagus nerve. Using whole-cell patch-clamp, CVN DMV demonstrated greater hyperexcitability and spontaneous action potential firing ex vivo despite similar resting membrane potentials, compared to CVN NA . Chemogenetically activating DMV also caused significant bradycardia with a correlated reduction in anxiety-like behavior. Thus, DMV contains uniquely hyperexcitable CVNs and is capable of cardioinhibition and robust anxiolysis., Competing Interests: Authors declare no competing interest., (© 2024 The Authors.)

Cardiovagal neurons (CVNs) innervate cardiac ganglia through the vagus nerve to control cardiac function. Although the cardioinhibitory role of CVNs in nucleus ambiguus (CVN NA ) is well established, the nature and functionality of CVNs in dorsal motor nucleus of the vagus (CVN DMV ) is less clear. We therefore aimed to characterize CVN DMV anatomically, physiologically, and functionally. Optogenetically activating cholinergic DMV neurons resulted in robust bradycardia through peripheral muscarinic (parasympathetic) and nicotinic (ganglionic) acetylcholine receptors, but not beta-1-adrenergic (sympathetic) receptors. Retrograde tracing from the cardiac fat pad labeled CVN NA and CVN DMV through the vagus nerve. Using whole cell patch clamp, CVN DMV demonstrated greater hyperexcitability and spontaneous action potential firing ex vivo despite similar resting membrane potentials, compared to CVN NA . Chemogenetically activating DMV also caused significant bradycardia with a correlated reduction in anxiety-like behavior. Thus, DMV contains uniquely hyperexcitable CVNs capable of cardioinhibition and robust anxiolysis., Competing Interests: DECLARATION OF INTEREST Authors declare no competing interest.

The nucleus ambiguus (nAmb) provides parasympathetic control of cardiorespiratory functions as well as motor control of the upper airways and striated esophagus. A subset of nAmb neurons innervates the heart through the vagus nerve to control cardiac function at rest and during key autonomic reflexes such as the mammalian diving reflex. These cardiovagal nAmb neurons may be molecularly and anatomically distinct, but how they differ from other nAmb neurons in the adult brain remains unclear. We therefore classified adult mouse nAmb neurons based on their genome-wide expression profiles, innervation of cardiac ganglia, and ability to control HR. Our integrated analysis of single-nucleus RNA-sequencing data predicted multiple molecular subtypes of nAmb neurons. Mapping the axon projections of one nAmb neuron subtype, Npy2r-expressing nAmb neurons, showed that they innervate cardiac ganglia. Optogenetically stimulating all nAmb vagal efferent neurons dramatically slowed HR to a similar extent as selectively stimulating Npy2r+ nAmb neurons, but not other subtypes of nAmb neurons. Finally, we trained mice to perform voluntary underwater diving, which we use to show Npy2r+ nAmb neurons are activated by the diving response, consistent with a cardiovagal function for this nAmb subtype. These results together reveal the molecular organization of nAmb neurons and its control of heart rate., Competing Interests: DECLARATION OF INTERESTS The authors declare no competing interests.

Ghrelin exerts key effects on islet hormone secretion to regulate blood glucose levels. Here, we sought to determine whether ghrelin's effects on islets extend to the alteration of islet size and β cell mass. We demonstrate that reducing ghrelin - by ghrelin gene knockout (GKO), conditional ghrelin cell ablation, or high-fat diet (HFD) feeding - was associated with increased mean islet size (up to 62%), percentage of large islets (up to 854%), and β cell cross-sectional area (up to 51%). In GKO mice, these effects were more apparent in 10- to 12-week-old mice than in 4-week-old mice. Higher β cell numbers from decreased β cell apoptosis drove the increase in β cell cross-sectional area. Conditional ghrelin cell ablation in adult mice increased the β cell number per islet by 40% within 4 weeks. A negative correlation between islet size and plasma ghrelin in HFD-fed plus chow-fed WT mice, together with even larger islet sizes in HFD-fed GKO mice than in HFD-fed WT mice, suggests that reduced ghrelin was not solely responsible for diet-induced obesity-associated islet enlargement. Single-cell transcriptomics revealed changes in gene expression in several GKO islet cell types, including upregulation of Manf, Dnajc3, and Gnas expression in β cells, which supports decreased β cell apoptosis and/or increased β cell proliferation. These effects of ghrelin reduction on islet morphology might prove useful when designing new therapies for diabetes.

Salient cues, such as the rising sun or availability of food, entrain biological clocks for behavioral adaptation. The mechanisms underlying entrainment to food availability remain elusive. Using single-nucleus RNA sequencing during scheduled feeding, we identified a dorsomedial hypothalamus leptin receptor-expressing (DMH LepR ) neuron population that up-regulates circadian entrainment genes and exhibits calcium activity before an anticipated meal. Exogenous leptin, silencing, or chemogenetic stimulation of DMH LepR neurons disrupts the development of molecular and behavioral food entrainment. Repetitive DMH LepR neuron activation leads to the partitioning of a secondary bout of circadian locomotor activity that is in phase with the stimulation and dependent on an intact suprachiasmatic nucleus (SCN). Last, we found a DMH LepR neuron subpopulation that projects to the SCN with the capacity to influence the phase of the circadian clock. This direct DMH LepR -SCN connection is well situated to integrate the metabolic and circadian systems, facilitating mealtime anticipation.

The superficial superior colliculus (sSC) carries out diverse roles in visual processing and behaviors, but how these functions are delegated among collicular neurons remains unclear. Here, using single-cell transcriptomics, we identified 28 neuron subtypes and subtype-enriched marker genes from tens of thousands of adult mouse sSC neurons. We then asked whether the sSC's molecular subtypes are tuned to different visual stimuli. Specifically, we imaged calcium dynamics in single sSC neurons in vivo during visual stimulation and then mapped marker gene transcripts onto the same neurons ex vivo. Our results identify a molecular subtype of inhibitory neuron accounting for ∼50% of the sSC's direction-selective cells, suggesting a genetic logic for the functional organization of the sSC. In addition, our studies provide a comprehensive molecular atlas of sSC neuron subtypes and a multimodal mapping method that will facilitate investigation of their respective functions, connectivity, and development., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Salient cues, such as the rising sun or the availability of food, play a crucial role in entraining biological clocks, allowing for effective behavioral adaptation and ultimately, survival. While the light-dependent entrainment of the central circadian pacemaker (suprachiasmatic nucleus, SCN) is relatively well defined, the molecular and neural mechanisms underlying entrainment associated with food availability remains elusive. Using single nucleus RNA sequencing during scheduled feeding (SF), we identified a leptin receptor (LepR) expressing neuron population in the dorsomedial hypothalamus (DMH) that upregulates circadian entrainment genes and exhibits rhythmic calcium activity prior to an anticipated meal. We found that disrupting DMH LepR neuron activity had a profound impact on both molecular and behavioral food entrainment. Specifically, silencing DMH LepR neurons, mis-timed exogenous leptin administration, or mis-timed chemogenetic stimulation of these neurons all interfered with the development of food entrainment. In a state of energy abundance, repetitive activation of DMH LepR neurons led to the partitioning of a secondary bout of circadian locomotor activity that was in phase with the stimulation and dependent on an intact SCN. Lastly, we discovered that a subpopulation of DMH LepR neurons project to the SCN with the capacity to influence the phase of the circadian clock. This leptin regulated circuit serves as a point of integration between the metabolic and circadian systems, facilitating the anticipation of meal times., Competing Interests: DECLARATION OF INTERESTS The authors declare no competing interests.

Obesity comorbidities such as diabetes and cardiovascular disease are pressing public health concerns. Overconsumption of calories leads to weight gain; however, neural mechanisms underlying excessive food consumption are poorly understood. Here, we demonstrate that dopamine receptor D1 (Drd1) expressed in the agouti-related peptide/neuropeptide Y (AgRP/NPY) neurons of the arcuate hypothalamus is required for appropriate responses to a high-fat diet (HFD). Stimulation of Drd1 and AgRP/NPY co-expressing arcuate neurons is sufficient to induce voracious feeding. Delivery of a HFD after food deprivation acutely induces dopamine (DA) release in the ARC, whereas animals that lack Drd1 expression in ARC AgRP/NPY neurons (Drd1 AgRP -KO) exhibit attenuated foraging and refeeding of HFD. These results define a role for the DA input to the ARC that encodes acute responses to food and position Drd1 signaling in the ARC AgRP/NPY neurons as an integrator of the hedonic and homeostatic neuronal feeding circuits., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Axons of retinal ganglion cells (RGCs) play critical roles in the development of inhibitory circuits in visual thalamus. We previously reported that RGC axons signal astrocytes to induce the expression of fibroblast growth factor 15 (FGF15), a motogen required for GABAergic interneuron migration into visual thalamus. However, how retinal axons induce thalamic astrocytes to generate Fgf15 and influence interneuron migration remains unknown. Here, we demonstrate that impairing RGC activity had little impact on interneuron recruitment into mouse visual thalamus. Instead, our data show that retinal-derived sonic hedgehog (SHH) is essential for interneuron recruitment. Specifically, we show that thalamus-projecting RGCs express SHH and thalamic astrocytes generate downstream components of SHH signaling. Deletion of RGC-derived SHH leads to a significant decrease in Fgf15 expression, as well as in the percentage of interneurons recruited into visual thalamus. Overall, our findings identify a morphogen-dependent neuron-astrocyte signaling mechanism essential for the migration of thalamic interneurons., Competing Interests: RS, KS, EG, HX, JC, AG, MF No competing interests declared, (© 2022, Somaiya et al.)

In mammals, the pontine noradrenergic system influences nearly every aspect of central nervous system function. A subpopulation of pontine noradrenergic neurons, called A5, are thought to be important in the cardiovascular response to physical stressors, yet their function is poorly defined. We hypothesized that activation of A5 neurons drives a sympathetically mediated increase in blood pressure (BP). To test this hypothesis, we conducted a comprehensive assessment of the cardiovascular effects of chemogenetic stimulation of A5 neurons in male and female adult rats using intersectional genetic and anatomical targeting approaches. Chemogenetic stimulation of A5 neurons in freely behaving rats elevated BP by 15 mmHg and increased cardiac baroreflex sensitivity with a negligible effect on resting HR. Importantly, A5 stimulation had no detectable effect on locomotor activity, metabolic rate, or respiration. Under anesthesia, stimulation of A5 neurons produced a marked elevation in visceral sympathetic nerve activity (SNA) and no change in skeletal muscle SNA, showing that A5 neurons preferentially stimulate visceral SNA. Interestingly, projection mapping indicates that A5 neurons target sympathetic preganglionic neurons throughout the spinal cord and parasympathetic preganglionic neurons throughout in the brainstem, as well as the nucleus of the solitary tract, and ventrolateral medulla. Moreover, in situ hybridization and immunohistochemistry indicate that a subpopulation of A5 neurons coreleases glutamate and monoamines. Collectively, this study suggests A5 neurons are a central modulator of autonomic function with a potentially important role in sympathetically driven redistribution of blood flow from the visceral circulation to critical organs and skeletal muscle.

Motor control of the striated esophagus originates in the nucleus ambiguus (nAmb), a vagal motor nucleus that also contains upper airway motor neurons and parasympathetic preganglionic neurons for the heart and lungs. We disambiguate nAmb neurons based on their genome-wide expression profiles, efferent circuitry, and ability to control esophageal muscles. Our single-cell RNA sequencing analysis predicts three molecularly distinct nAmb neuron subtypes and annotates them by subtype-specific marker genes: Crhr2, Vipr2, and Adcyap1. Mapping the axon projections of the nAmb neuron subtypes reveals that Crhr2 nAmb neurons innervate the esophagus, raising the possibility that they control esophageal muscle function. Accordingly, focal optogenetic stimulation of cholinergic Crhr2 + fibers in the esophagus results in contractions. Activating Crhr2 nAmb neurons has no effect on heart rate, a key parasympathetic function of the nAmb, whereas activating all of the nAmb neurons robustly suppresses heart rate. Together, these results reveal a genetically defined circuit for motor control of the esophagus., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

The vagus nerve innervates many organs, and most, if not all, of its motor fibers are cholinergic. However, no one knows its organizing principles-whether or not there are dedicated neurons with restricted targets that act as "labeled lines" to perform certain functions, including two opposing ones (gastric contraction versus relaxation). By performing unbiased transcriptional profiling of DMV cholinergic neurons, we discovered seven molecularly distinct subtypes of motor neurons. Then, by using subtype-specific Cre driver mice, we show that two of these subtypes exclusively innervate the glandular domain of the stomach where, remarkably, they contact different enteric neurons releasing functionally opposing neurotransmitters (acetylcholine versus nitric oxide). Thus, the vagus motor nerve communicates via genetically defined labeled lines to control functionally unique enteric neurons within discrete subregions of the gastrointestinal tract. This discovery reveals that the parasympathetic nervous system utilizes a striking division of labor to control autonomic function., Competing Interests: Declaration of interests S.D.L. is a consultant for Kallyope, Inc., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Capsaicin, the pungent ingredient in chili peppers, produces intense burning pain in humans. Capsaicin selectively activates the transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptive primary afferents, and underpins the mechanism for capsaicin-induced burning pain. Paradoxically, capsaicin has long been used as an analgesic. The development of topical patches and injectable formulations containing capsaicin has led to application in clinical settings to treat chronic pain conditions, such as neuropathic pain and the potential to treat osteoarthritis. More detailed determination of the neurobiological mechanisms of capsaicin-induced analgesia should provide the logical rationale for capsaicin therapy and help to overcome the treatment's limitations, which include individual differences in treatment outcome and procedural discomfort. Low concentrations of capsaicin induce short-term defunctionalization of nociceptor terminals. This phenomenon is reversible within hours and, hence, likely does not account for the clinical benefit. By contrast, high concentrations of capsaicin lead to long-term defunctionalization mediated by the ablation of TRPV1-expressing afferent terminals, resulting in long-lasting analgesia persisting for several months. Recent studies have shown that capsaicin-induced Ca 2+ /calpain-mediated ablation of axonal terminals is necessary to produce long-lasting analgesia in a mouse model of neuropathic pain. In combination with calpain, axonal mitochondrial dysfunction and microtubule disorganization may also contribute to the longer-term effects of capsaicin. The analgesic effects subside over time in association with the regeneration of the ablated afferent terminals. Further determination of the neurobiological mechanisms of capsaicin-induced analgesia should lead to more efficacious non-opioidergic analgesic options with fewer adverse side effects., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Capsaicin is a potent agonist of the TRPV1 channel, a transduction channel that is highly expressed in nociceptive fibers (pain fibers) throughout the peripheral nervous system. Given the importance of TRPV1 as one of several transduction channels in nociceptive fibers, much research has been focused on the potential therapeutic benefits of using TRPV1 antagonists for the management of pain. However, an antagonist has two limitations. First, an antagonist in principle generally only affects one receptor. Secondly, most antagonists must have an ongoing presence on the receptor to have an effect. Capsaicin overcomes both liabilities by disrupting peripheral terminals of nociceptive fibers that express TRPV1, and thereby affects all of the potential means of activating that pain fiber (not just TRPV1 function). This disruptive effect is dependent on the dose and can occur within minutes. Thus, unlike a typical receptor antagonist, continued bioavailability at the level of the receptor is not necessary. By disrupting the entire terminal of the TRPV1-expressing nociceptive fiber, capsaicin blocks all the activation mechanisms within that fiber, and not just TRPV1 function. Topical capsaicin, an FDA approved treatment for neuropathic pain, addresses pain from abnormal nociceptor activity in the superficial layers of the skin. Effects after a single administration are evident over a period of weeks to months, but in time are fully reversible. This review focuses on the rationale for using capsaicin by injection for painful conditions such as osteoarthritis (OA) and provides an update on studies completed to date.

Low-density lipoprotein receptor-related protein 1 (LRP1) is a member of LDL receptor family that plays a key role in systemic glucose and lipid homeostasis. LRP1 also regulates energy balance in the hypothalamus by mediating leptin's anorexigenic action, although the underlying neurocircuitry involved is still unclear. Because GABAergic neurons are a major mediator of hypothalamic leptin action, we studied the role of GABAergic LRP1 in energy balance and leptin action using mice lacking LRP1 in Vgat- or AgRP-expressing neurons (Vgat-Cre; LRP1 loxP/loxP or AgRP-Cre; LRP1 loxP/loxP ). Here, we show that LRP1 deficiency in GABAergic neurons results in severe obesity in male and female mice fed a normal-chow diet. This effect is most likely due to increased food intake and decreased energy expenditure and locomotor activity. Increased adiposity in GABAergic neuron-specific LRP1-deficient mice is accompanied by hyperleptinemia and hyperinsulinemia. Insulin resistance and glucose intolerance in these mice are occurred without change in body weight. Importantly, LRP1 in GABAergic neurons is not required for leptin action, as evidenced by normal leptin's anorexigenic action and leptin-induced hypothalamic Stat3 phosphorylation. In contrast, LRP1 deficiency in AgRP neurons has no effect on adiposity and caloric intake. In conclusion, our data identify GABAergic neurons as a key neurocircuitry that underpins LRP1-dependent regulation of systemic energy balance and body-weight homeostasis. We further find that the GABAergic LRP1 signaling pathway modulates food intake and energy expenditure independently of leptin signaling and AgRP neurons.

The hypothalamic suprachiasmatic (SCN) clock contains several neurochemically defined cell groups that contribute to the genesis of circadian rhythms. Using cell-specific and genetically targeted approaches we have confirmed an indispensable role for vasoactive intestinal polypeptide-expressing SCN (SCN VIP ) neurons, including their molecular clock, in generating the mammalian locomotor activity (LMA) circadian rhythm. Optogenetic-assisted circuit mapping revealed functional, di-synaptic connectivity between SCN VIP neurons and dorsomedial hypothalamic neurons, providing a circuit substrate by which SCN VIP neurons may regulate LMA rhythms. In vivo photometry revealed that while SCN VIP neurons are acutely responsive to light, their activity is otherwise behavioral state invariant. Single-nuclei RNA-sequencing revealed that SCN VIP neurons comprise two transcriptionally distinct subtypes, including putative pacemaker and non-pacemaker populations. Altogether, our work establishes necessity of SCN VIP neurons for the LMA circadian rhythm, elucidates organization of circadian outflow from and modulatory input to SCN VIP cells, and demonstrates a subpopulation-level molecular heterogeneity that suggests distinct functions for specific SCN VIP subtypes.

The estimated probability of progressing from phase 3 analgesic clinical trials to regulatory approval is approximately 57%, suggesting that a considerable number of treatments with phase 2 trial results deemed sufficiently successful to progress to phase 3 do not yield positive phase 3 results. Deficiencies in the quality of clinical trial conduct could account for some of this failure. An Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting was convened to identify potential areas for improvement in trial conduct in order to improve assay sensitivity (ie, ability of trials to detect a true treatment effect). We present recommendations based on presentations and discussions at the meeting, literature reviews, and iterative revisions of this article. The recommendations relate to the following areas: 1) study design (ie, to promote feasibility), 2) site selection and staff training, 3) participant selection and training, 4) treatment adherence, 5) data collection, and 6) data and study monitoring. Implementation of these recommendations may improve the quality of clinical trial data and thus the validity and assay sensitivity of clinical trials. Future research regarding the effects of these strategies will help identify the most efficient use of resources for conducting high quality clinical trials. PERSPECTIVE: Every effort should be made to optimize the quality of clinical trial data. This manuscript discusses considerations to improve conduct of pain clinical trials based on research in multiple medical fields and the expert consensus of pain researchers and stakeholders from academia, regulatory agencies, and industry., (Copyright © 2020. Published by Elsevier Inc.)

Objectives: To independently assess quality of care among patients who died in hospital and whose next-of-kin submitted a letter of complaint and make comparisons with matched controls. To identify whether use of a treatment escalation limitation plan (TELP) during the terminal illness was a relevant background factor., Design: The study was an investigator-blinded retrospective case-note review of 42 complaints cases and 72 controls matched for age, sex, ward location and time of death., Setting: The acute medical and surgical wards of three District General Hospitals administered by NHS Lanarkshire, Scotland., Participants: None., Intervention: None., Outcome Measures: Quality of care: clinical 'problems', non-beneficial interventions (NBIs) and harms were evaluated using the Structured Judgment Review Method. Complaints were categorized using the Healthcare Complaints Analysis Tool., Results: The event frequencies and rate ratios for clinical 'problems', NBIs and harms were consistently higher in complaint cases compared to controls. The difference was only significant for NBIs (P = 0.05). TELPs were used less frequently in complaint cases compared to controls (23.8 versus 47.2%, P = 0.013). The relationship between TELP use and the three key clinical outcomes was nonsignificant., Conclusions: Care delivered to patients at end-of-life whose next-of-kin submitted a complaint was poorer overall than among control patients when assessed independently by blinded reviewers. Regular use of a TELP in acute clinical settings has the potential to influence complaints relating to end-of-life care, but this requires further prospective study., (© The Author(s) 2020. Published by Oxford University Press in association with the International Society for Quality in Health Care. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Objective: To assess the efficacy and safety of high-purity synthetic trans-capsaicin (CNTX-4975) in patients with chronic moderate-to-severe osteoarthritis (OA)-associated knee pain., Methods: In this phase II multicenter double-blind study, patients ages 45-80 years who had stable knee OA were randomized in a 2:1:2 ratio to receive a single intraarticular injection of placebo, CNTX-4975 0.5 mg, or CNTX-4975 1.0 mg. The primary efficacy end point was area under the curve (AUC) for change from baseline in daily Western Ontario and McMaster Universities Osteoarthritis Index pain with walking score (range 0-10, 0 = none and 10 = extreme) through week 12. Secondary efficacy end points included a similar AUC analysis of outcomes in patients treated with CNTX-4975 0.5 mg, and evaluations extending to 24 weeks., Results: Efficacy was evaluated in 172 patients (placebo group, n = 69; CNTX-4975 0.5 mg group, n = 33; CNTX-4975 1.0 mg group, n = 70). At week 12, greater decreases in the AUC for the pain score were observed with CNTX-4975 in the 0.5 mg and 1.0 mg groups versus placebo (0.5 mg group least squares mean difference [LSMD] -0.79, P = 0.0740; 1.0 mg group LSMD -1.6, P < 0.0001). Significant improvements were maintained at week 24 in the 1.0 mg group (LSMD -1.4, P = 0.0002). Treatment-emergent adverse events were similar in the placebo and CNTX-4975 1.0 mg groups., Conclusion: In this study, CNTX-4975 provided dose-dependent improvement in knee OA-associated pain. CNTX-4975 1.0 mg produced a significant decrease in OA knee pain through 24 weeks; CNTX-4975 0.5 mg significantly improved pain at 12 weeks, but the effect was not evident at 24 weeks., (© 2019 Centrexion Therapeutics Corporation. Arthritis & Rheumatology published by Wiley Periodicals, Inc. on behalf of American College of Rheumatology.)

SIM1-expressing paraventricular hypothalamus (PVH) neurons are key regulators of energy balance. Within the PVH SIM1 population, melanocortin-4 receptor-expressing (PVH MC4R ) neurons are known to regulate satiety and bodyweight, yet they account for only half of PVH SIM1 neuron-mediated regulation. Here we report that PVH prodynorphin-expressing (PVH PDYN ) neurons, which notably lack MC4Rs, function independently and additively with PVH MC4R neurons to account for the totality of PVH SIM1 neuron-mediated satiety. Moreover, PVH PDYN neurons are necessary for prevention of obesity in an independent but equipotent manner to PVH MC4R neurons. While PVH PDYN and PVH MC4R neurons both project to the parabrachial complex (PB), they synaptically engage distinct efferent nodes, the pre-locus coeruleus (pLC), and central lateral parabrachial nucleus (cLPBN), respectively. PB-projecting PVH PDYN neurons, like PVH MC4R neurons, receive input from interoceptive ARC AgRP neurons, respond to caloric state, and are sufficient and necessary to control food intake. This expands the CNS satiety circuitry to include two non-overlapping PVH to hindbrain circuits., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Objectives: To assess the effect of using a treatment escalation/limitation plan (TELP) on the frequency of harms in 300 patients who died following admission to hospital., Design: A retrospective case note review of 300 unselected, consecutive deaths comprising: (1) patients with a TELP in addition to a do-not-attempt cardiopulmonary resuscitation order (DNACPR); (2) those with DNACPR only; and (3) those with neither. Patient deaths were classified retrospectively as 'expected' or 'unexpected' using the Gold Standard Framework Prognostic Indicator Guidance., Setting: Medical, surgical and intensive care units of a district general hospital., Outcomes: The primary outcome was the between-group difference in rates of harms, non-beneficial interventions (NBIs) and clinical 'problems' identified using the Structured Judgement Review Method., Results: 289 case records were evaluable. 155 had a TELP and DNACPR (54%); 113 had DNACPR only (39%); 21 had neither (7%). 247 deaths (86%) were 'expected'. Among patients with 'expected' deaths and using the TELP/DNACPR as controls (incidence rate ratio (IRR)=1.00), the IRRs were: for harms, 2.99 (DNACPR only) and 4.00 (neither TELP nor DNACPR) (p<0.001 for both); for NBIs, the corresponding IRRs were 2.23 (DNACPR only) and 2.20 (neither) (p<0.001 and p<0.005, respectively); for 'problems', 2.30 (DNACPR only) and 2.76 (neither) (p<0.001 for both). The rates of harms, NBIs and 'problems' were significantly lower in the group with a TELP/DNACPR compared with 'DNACPR only' and 'neither': harms (per 1000 bed days) 17.1, 76.9 (p<0.001) and 197.8 (p<0.001) respectively; NBIs: 27.4, 92.1 (p<0.001) and 172.4 (p<0.001); and 'problems': 42.3, 146.2 (p<0.01) and 333.3 (p<0.001)., Conclusions: The use of a TELP was associated with a significant reduction in harms, NBIs and 'problems' in patients admitted acutely and who subsequently died, especially if they were likely to be in the last year of life., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2018. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Sodium deficiency increases angiotensin II (ATII) and aldosterone, which synergistically stimulate sodium retention and consumption. Recently, ATII-responsive neurons in the subfornical organ (SFO) and aldosterone-sensitive neurons in the nucleus of the solitary tract (NTS HSD2 neurons) were shown to drive sodium appetite. Here we investigate the basis for NTS HSD2 neuron activation, identify the circuit by which NTS HSD2 neurons drive appetite, and uncover an interaction between the NTS HSD2 circuit and ATII signaling. NTS HSD2 neurons respond to sodium deficiency with spontaneous pacemaker-like activity-the consequence of "cardiac" HCN and Na v 1.5 channels. Remarkably, NTS HSD2 neurons are necessary for sodium appetite, and with concurrent ATII signaling their activity is sufficient to produce rapid consumption. Importantly, NTS HSD2 neurons stimulate appetite via projections to the vlBNST, which is also the effector site for ATII-responsive SFO neurons. The interaction between angiotensin signaling and NTS HSD2 neurons provides a neuronal context for the long-standing "synergy hypothesis" of sodium appetite regulation., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Capsaicin is an ingredient in spicy peppers that produces burning pain by activating transient receptor potential vanilloid 1 (TRPV1), a Ca 2+ -permeable ion channel in nociceptors. Capsaicin has also been used as an analgesic, and its topical administration is approved for the treatment of certain pain conditions. The mechanisms underlying capsaicin-induced analgesia likely involve reversible ablation of nociceptor terminals. However, the mechanisms underlying these effects are not well understood. To visualize TRPV1-lineage axons, a genetically engineered mouse model was used in which a fluorophore is expressed under the TRPV1 promoter. Using a combination of these TRPV1-lineage reporter mice and primary afferent cultures, we monitored capsaicin-induced effects on afferent terminals in real time. We found that Ca 2+ influx through TRPV1 is necessary for capsaicin-induced ablation of nociceptive terminals. Although capsaicin-induced mitochondrial Ca 2+ uptake was TRPV1-dependent, dissipation of the mitochondrial membrane potential, inhibition of the mitochondrial transition permeability pore, and scavengers of reactive oxygen species did not attenuate capsaicin-induced ablation. In contrast, MDL28170, an inhibitor of the Ca 2+ -dependent protease calpain, diminished ablation. Furthermore, overexpression of calpastatin, an endogenous inhibitor of calpain, or knockdown of calpain 2 also decreased ablation. Quantitative assessment of TRPV1-lineage afferents in the epidermis of the hind paws of the reporter mice showed that EGTA and MDL28170 diminished capsaicin-induced ablation. Moreover, MDL28170 prevented capsaicin-induced thermal hypoalgesia. These results suggest that TRPV1/Ca 2+ /calpain-dependent signaling plays a dominant role in capsaicin-induced ablation of nociceptive terminals and further our understanding of the molecular mechanisms underlying the effects of capsaicin on nociceptors., (© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.)

We report the case of a 12-year-old boy who experienced recurrent suppurative arthritis of the distal interphalangeal joint after near simultaneous exposure to a frog, a dog bite and lake water. Anaerobic cultures of synovial fluid obtained during operative debridement grew small round gray colonies ultimately identified as Erysipelothrix rhusiopathiae by routine laboratory tests and mass spectrometry.

The hypothalamic arcuate-median eminence complex (Arc-ME) controls energy balance, fertility and growth through molecularly distinct cell types, many of which remain unknown. To catalog cell types in an unbiased way, we profiled gene expression in 20,921 individual cells in and around the adult mouse Arc-ME using Drop-seq. We identify 50 transcriptionally distinct Arc-ME cell populations, including a rare tanycyte population at the Arc-ME diffusion barrier, a new leptin-sensing neuron population, multiple agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) subtypes, and an orexigenic somatostatin neuron population. We extended Drop-seq to detect dynamic expression changes across relevant physiological perturbations, revealing cell type-specific responses to energy status, including distinct responses in AgRP and POMC neuron subtypes. Finally, integrating our data with human genome-wide association study data implicates two previously unknown neuron populations in the genetic control of obesity. This resource will accelerate biological discovery by providing insights into molecular and cell type diversity from which function can be inferred.

Arcuate nucleus (ARC) neurons sense the fed or fasted state and regulate hunger. Agouti-related protein (AgRP) neurons in the ARC (ARC AgRP neurons) are stimulated by fasting and, once activated, they rapidly (within minutes) drive hunger. Pro-opiomelanocortin (ARC POMC ) neurons are viewed as the counterpoint to ARC AgRP neurons. They are regulated in an opposite fashion and decrease hunger. However, unlike ARC AgRP neurons, ARC POMC neurons are extremely slow in affecting hunger (many hours). Thus, a temporally analogous, rapid ARC satiety pathway does not exist or is presently unidentified. Here we show that glutamate-releasing ARC neurons expressing oxytocin receptor, unlike ARC POMC neurons, rapidly cause satiety when chemo- or optogenetically manipulated. These glutamatergic ARC projections synaptically converge with GABAergic ARC AgRP projections on melanocortin-4 receptor (MC4R)-expressing satiety neurons in the paraventricular hypothalamus (PVH MC4R neurons). Transmission across the ARC Glutamatergic →PVH MC4R synapse is potentiated by the ARC POMC neuron-derived MC4R agonist, α-melanocyte stimulating hormone (α-MSH). This excitatory ARC→PVH satiety circuit, and its modulation by α-MSH, provides insight into regulation of hunger and satiety., Competing Interests: The authors declare no competing financial interests.

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 before 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 preconsummatory modulation of ARC AgRP neurons. In a manner reciprocal to ARC AgRP neurons, ARC-projecting leptin receptor-expressing GABAergic vDMH neurons exhibit rapid activation upon availability of food that additionally reflects the relative value of the food. Thus, leptin receptor-expressing GABAergic vDMH 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.

Capsaicin is the pungent ingredient of chili peppers and is approved as a topical treatment of neuropathic pain. The analgesia lasts for several months after a single treatment. Capsaicin selectively activates TRPV1, a Ca 2+ -permeable cationic ion channel that is enriched in the terminals of certain nociceptors. Activation is followed by a prolonged decreased response to noxious stimuli. Interest also exists in the use of injectable capsaicin as a treatment for focal pain conditions, such as arthritis and other musculoskeletal conditions. Recently injection of capsaicin showed therapeutic efficacy in patients with Morton's neuroma, a painful foot condition associated with compression of one of the digital nerves. The relief of pain was associated with no change in tactile sensibility. Though injection evokes short term pain, the brief systemic exposure and potential to establish long term analgesia without other sensory changes creates an attractive clinical profile. Short-term and long-term effects arise from both functional and structural changes in nociceptive terminals. In this review, we discuss how local administration of capsaicin may induce ablation of nociceptive terminals and the clinical implications., Competing Interests: The authors declare no conflict of interest.

AMP-activated protein kinase (AMPK) plays an important role in regulating food intake. The downstream AMPK substrates and neurobiological mechanisms responsible for this, however, are ill defined. Agouti-related peptide (AgRP)-expressing neurons in the arcuate nucleus regulate hunger. Their firing increases with fasting, and once engaged they cause feeding. AgRP neuron activity is regulated by state-dependent synaptic plasticity: fasting increases dendritic spines and excitatory synaptic activity; feeding does the opposite. The signaling mechanisms underlying this, however, are also unknown. Using neuron-specific approaches to measure and manipulate kinase activity specifically within AgRP neurons, we establish that fasting increases AMPK activity in AgRP neurons, that increased AMPK activity in AgRP neurons is both necessary and sufficient for fasting-induced spinogenesis and excitatory synaptic activity, and that the AMPK phosphorylation target mediating this plasticity is p21-activated kinase. This provides a signaling and neurobiological basis for both AMPK regulation of energy balance and AgRP neuron state-dependent plasticity., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Intermetatarsal neuroma or Morton's neuroma is a painful condition of the foot resulting from an entrapment of the common digital nerve typically in the third intermetatarsal space. The pain can be severe and especially problematic with walking. Treatment options are limited and surgery may lead to permanent numbness in the toes. Capsaicin, the pungent ingredient of hot peppers, produces analgesia by inducing retraction of nociceptive afferents from the area of innervation and is effective in treating certain neuropathic pain disorders. A randomized double-blind placebo-controlled study was conducted to test the efficacy, tolerability, and safety of a single 0.1 mg dose of capsaicin vs placebo injected into the region of the neuroma. A total of 58 subjects diagnosed with Morton's neuroma with foot pain ≥4 (0-10 numerical pain rating scale) were injected with 2 mL of lidocaine into the intermetatarsal space proximal to the neuroma to provide local anesthesia. After 5 minutes, 0.1 mg capsaicin or placebo was injected into the intermetatarsal space containing the painful neuroma. Average foot pain was rated for 2 weeks before through 4 weeks after injection. At weeks 1 and 4, the decrease in pain was significantly greater in the subjects treated with capsaicin (P = 0.021 and P = 0.019, respectively). A trend toward significance was noted at weeks 2 and 3. Improvements in functional interference scores and reductions in oral analgesic use were also seen in the capsaicin-treated group. These findings suggest that injection of capsaicin is an efficacious treatment option for patients with painful intermetatarsal neuroma.

The nucleus of the solitary tract (NTS) is a key gateway for meal-related signals entering the brain from the periphery. However, the chemical mediators crucial to this process have not been fully elucidated. We reveal that a subset of NTS neurons containing cholecystokinin (CCK(NTS)) is responsive to nutritional state and that their activation reduces appetite and body weight in mice. Cell-specific anterograde tracing revealed that CCK(NTS) neurons provide a distinctive innervation of the paraventricular nucleus of the hypothalamus (PVH), with fibers and varicosities in close apposition to a subset of melanocortin-4 receptor (MC4R(PVH)) cells, which are also responsive to CCK. Optogenetic activation of CCK(NTS) axon terminals within the PVH reveal the satiating function of CCK(NTS) neurons to be mediated by a CCK(NTS)→PVH pathway that also encodes positive valence. These data identify the functional significance of CCK(NTS) neurons and reveal a sufficient and discrete NTS to hypothalamus circuit controlling appetite.

Pro-opiomelanocortin (POMC)- and agouti-related peptide (AgRP)-expressing neurons of the arcuate nucleus of the hypothalamus (ARC) are oppositely regulated by caloric depletion and coordinately stimulate and inhibit homeostatic satiety, respectively. This bimodality is principally underscored by the antagonistic actions of these ligands at downstream melanocortin-4 receptors (MC4R) in the paraventricular nucleus of the hypothalamus (PVH). Although this population is critical to energy balance, the underlying neural circuitry remains unknown. Using mice expressing Cre recombinase in MC4R neurons, we demonstrate bidirectional control of feeding following real-time activation and inhibition of PVH(MC4R) neurons and further identify these cells as a functional exponent of ARC(AgRP) neuron-driven hunger. Moreover, we reveal this function to be mediated by a PVH(MC4R)→lateral parabrachial nucleus (LPBN) pathway. Activation of this circuit encodes positive valence, but only in calorically depleted mice. Thus, the satiating and appetitive nature of PVH(MC4R)→LPBN neurons supports the principles of drive reduction and highlights this circuit as a promising target for antiobesity drug development.

Epilepsy is a significant but potentially preventable complication of traumatic brain injury (TBI). Previous research in animal models of acquired epilepsy has implicated the calcium-sensitive phosphatase, calcineurin. In addition, our lab recently found that calcineurin activity in the rat hippocampus increases acutely after lateral TBI. Here we use a calcineurin inhibitor test whether an acute increase in calcineurin activity is necessary for the development of late post-traumatic seizures. Adult rats were administered the calcineurin inhibitor Tacrolimus (5mg/kg; i.p.) 1 hour after lateral fluid percussion TBI and then monitored by video-electrocorticography (video-ECoG) for spontaneous seizure activity 5 weeks or 33 weeks later. At 5 weeks post-TBI, we observed epileptiform activity on the video-ECoG of brain injured rats but no seizures. By 33 weeks post-TBI though, nearly all injured rats exhibited spontaneous seizures, including convulsive seizures which were infrequent but lasted minutes (18% of injured rats), and non-convulsive seizures which were frequent but lasted tens of seconds (94% of injured rats). We also identified non-convulsive seizures in a smaller subset of control and sham TBI rats (56%), reminiscent of idiopathic seizures described in other rats strains. Non-convulsive seizures in the brain injured rats, however, were four-times more frequent and two-times longer lasting than in their uninjured littermates. Interestingly, rats administered Tacrolimus acutely after TBI showed significantly fewer non-convulsive seizures than untreated rats, but a similar degree of cortical atrophy. The data thus indicate that administration of Tacrolimus acutely after TBI suppressed non-convulsive seizures months later.

Objective: Although poor sleep is a consequence of pain, sleep disturbance reciprocally induces hyperalgesia and exacerbates clinical pain. Conceptual models of chronic pain implicate dysfunctional supraspinal pain processing mechanisms, mediated in part by endogenous opioid peptides. Our preliminary work indicates that sleep disruption impairs psychophysical measures of descending pain modulation, but few studies have investigated whether insufficient sleep may be associated with alterations in endogenous opioid systems. This preliminary, exploratory investigation sought to examine the relationship between sleep and functioning of the cerebral mu opioid system during the experience of pain in healthy participants., Subjects and Design: Twelve healthy volunteers participated in a 90-minute positron emission tomography imaging scan using [11C]Carfentanil, a mu opioid receptors agonist. During the session, pain responses to a 10% topical capsaicin cream were continuously rated on a 0-100 scale. Participants also completed the Pittsburgh Sleep Quality Index (PSQI)., Results: Poor sleep quality (PSQI) was positively and significantly associated with greater binding potential (BP) in regions within the frontal lobes. In addition, sleep duration was negatively associated with BP in these areas as well as the temporal lobe and anterior cingulate., Conclusions: These findings suggest that poor sleep quality and short sleep duration are associated with endogenous opioid activity in these brain regions during the application of a noxious stimulus. Elucidating the role of the endogenous opioid system in mediating some of the associations between sleep and pain could significantly improve our understanding of the pathophysiology of chronic pain and might advance clinical practice by suggesting interventions that could buffer the adverse effects of poor sleep on pain., (Wiley Periodicals, Inc.)

A length-dependent neuropathy with pain in the feet is a common complication of diabetes (painful diabetic neuropathy). It was hypothesized that pain may arise from sensitized-hyperactive cutaneous nociceptors, and that this abnormal signaling may be reduced by topical administration of the α(2)-adrenergic agonist, clonidine, to the painful area. This was a randomized, double-blind, placebo-controlled, parallel-group, multicenter trial. Nociceptor function was measured by determining the painfulness of 0.1% topical capsaicin applied to the pretibial area of each subject for 30minutes during screening. Subjects were then randomized to receive 0.1% topical clonidine gel (n=89) or placebo gel (n=90) applied 3 times a day to their feet for 12weeks. The difference in foot pain at week 12 in relation to baseline, rated on a 0-10 numerical pain rating scale (NPRS), was compared between groups. Baseline NPRS was imputed for missing data for subjects who terminated the study early. The subjects treated with clonidine showed a trend toward decreased foot pain compared to the placebo-treated group (the primary endpoint; P=0.07). In subjects who felt any level of pain to capsaicin, clonidine was superior to placebo (P<0.05). In subjects with a capsaicin pain rating ⩾2 (0-10, NPRS), the mean decrease in foot pain was 2.6 for active compared to 1.4 for placebo (P=0.01). Topical clonidine gel significantly reduces the level of foot pain in painful diabetic neuropathy subjects with functional (and possibly sensitized) nociceptors in the affected skin as revealed by testing with topical capsaicin. Screening for cutaneous nociceptor function may help distinguish candidates for topical therapy for neuropathic pain., (Copyright © 2012 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)