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Neuronal activity evokes a vascular response that is essential to sustain brain function. We show that neurovascular coupling (NVC) is mediated by long-range projecting GABAergic neurons that express Tacr1. Whisker stimulation elicited Tacr1 neuron activity in the barrel cortex through feed-forward excitatory pathways. Optogenetic activation of Tacr1 neurons elicited vasodilation, whereas inhibition significantly reduced whisker-evoked hemodynamic responses. Moreover, vasodilation was preceded by capillary pericyte activity, demonstrating a mechanism for NVC.

Opioids are a mainstay of treatment for pain worldwide. Pruritus, a common side effect of opioids, is a patient dissatisfier that limits their use in many clinical settings. Both parenteral and neuraxial administration of opioids frequently evoke pruritus. The ability of opioids to suppress pain while causing itch continues to perplex clinicians and researchers alike. Several mechanisms have been proposed to explain how opioids can give rise to pruritus, but specific knowledge gaps perpetuate debate. This review summarizes the clinical burden of opioid-induced pruritus and emphasizes recent discoveries of peripheral and central mechanisms for opioid-induced pruritus, particularly with respect to scientific and conceptual advances in spinal cord circuitry and mast cell biology. The mechanisms and effectiveness of existing medications used for clinical management of pruritus will be evaluated, and we will highlight the emerging preclinical utility of selective κ-opioid receptor agonists, such as nalfurafine, for the management of opioid-induced pruritus.

Itch is an aversive somatic sense that elicits the desire to scratch. In animal models of itch, scratching behavior is frequently used as a proxy for itch, and this behavior is typically assessed through visual quantification. However, manual scoring of videos has numerous limitations, underscoring the need for an automated approach. Here, we propose a novel automated method for acoustic detection of mouse scratching. Using this approach, we show that chloroquine-induced scratching behavior in C57BL/6 mice can be quantified with reasonable accuracy (85% sensitivity, 75% positive predictive value). This report is the first method to apply supervised learning techniques to automate acoustic scratch detection.

The rostral ventromedial medulla (RVM) is important in descending modulation of spinal nociceptive transmission, but it is unclear if the RVM also modulates spinal pruriceptive transmission. RVM ON cells are activated by noxious algesic and pruritic stimuli and are pronociceptive. Many RVM-spinal projection neurons express the neurokinin-1 receptor (Tacr1), and ON-cells are excited by local administration of substance P (SP). We hypothesized that Tacr1-expressing RVM ON cells exert an inhibitory effect on itch opposite to their pronociceptive action. Intramedullary microinjection of SP significantly potentiated RVM ON cells and reduced pruritogen-evoked scratching while producing mild mechanical sensitization. Chemogenetic activation of RVM Tacr1-expressing RVM neurons also reduced acute pruritogen-evoked scratching. Optotagging experiments confirmed RVM Tacr1-expressing neurons to be ON cells. We conclude that Tacr1-expressing ON cells in RVM play a significant role in the modulation of pruriceptive transmission.

Pharmacological manipulations directed at the periaqueductal gray (PAG) have revealed the importance of the mu-opioid receptor in the endogenous pain-modulatory system. Despite the clear role for opioidergic signaling within the PAG for the descending modulation of pain, the molecular and anatomical characterizations of neurons containing the mu-opioid receptor remain elusive. Using combinatorial anatomical, optogenetic, and chemogenetic approaches, we delineate a supraspinal pathway centered on PAGMOR neurons in the modulation of pain and itch behaviors. We found that chemogenetic manipulations of PAGMOR neurons in assays of nociception unveiled complex results; whereas activation of these neurons generally facilitated responses to noxious stimuli and jumping behaviors on the hotplate assay, opposing patterns were observed with reflexive responses to sensory testing. Activation of PAGMOR neurons also robustly inhibited itch. These dichotomous findings across distinct types of sensory testing emphasize the contextual behavioral expression of nociception using reflexive and noxious paradigms. Lastly, we uncovered the role for PBN projections in the PAG that modulate pain in an uninjured, post-surgical state of latent sensitization.

Opioid signaling has been shown to be critically important in the neuromodulation of sensory circuits in the superficial spinal cord. Agonists of the mu-opioid receptor (MOR) elicit itch, whereas agonists of the kappa-opioid receptor (KOR) have been shown to inhibit itch. Despite the clear roles of MOR and KOR for the modulation itch, whether the delta-opioid receptor (DOR) is involved in the regulation of itch remained unknown. Here, we show that intrathecal administration of DOR agonists suppresses chemical itch and that intrathecal application of DOR antagonists is sufficient to evoke itch. We identify that spinal enkephalin neurons co-express neuropeptide Y (NPY), a peptide previously implicated in the inhibition of itch. In the spinal cord, DOR overlapped with both the NPY receptor (NPY1R) and KOR, suggesting that DOR neurons represent a site for convergent itch information in the dorsal horn. Lastly, we found that neurons co-expressing DOR and KOR showed significant Fos induction following pruritogen-evoked itch. These results uncover a role for DOR in the modulation of itch in the superficial dorsal horn.PerspectiveThis article reveals the role of the delta opioid receptor in itch. Intrathecal administration of delta agonists suppresses itch whereas the administration of delta antagonists is sufficient to induce itch. These studies highlight the importance of delta-opioid signaling for the modulation of itch behaviors, which may represent new targets for the management of itch disorders.

Supplemental Digital Content is Available in the Text. This study suggests that activation of nonpeptidergic afferents becomes aversive after spared nerve injury through the recruitment of a normally silent polysynaptic pathway., Most cutaneous C fibers, including both peptidergic and nonpeptidergic subtypes, are presumed to be nociceptors and respond to noxious input in a graded manner. However, mechanically sensitive, nonpeptidergic C fibers also respond to mechanical input in the innocuous range, so the degree to which they contribute to nociception remains unclear. To address this gap, we investigated the function of nonpeptidergic afferents using the MrgprdCre allele. In real-time place aversion studies, we found that low-frequency optogenetic activation of MrgrpdCre lineage neurons was not aversive in naive mice but became aversive after spared nerve injury (SNI). To address the underlying mechanisms of this allodynia, we recorded responses from lamina I spinoparabrachial (SPB) neurons using the semi-intact ex vivo preparation. After SNI, innocuous brushing of the skin gave rise to abnormal activity in lamina I SPB neurons, consisting of an increase in the proportion of recorded neurons that responded with excitatory postsynaptic potentials or action potentials. This increase was likely due, at least in part, to an increase in the proportion of lamina I SPB neurons that received input on optogenetic activation of MrgprdCre lineage neurons. Intriguingly, in SPB neurons, there was a significant increase in the excitatory postsynaptic current latency from MrgprdCre lineage input after SNI, consistent with the possibility that the greater activation post-SNI could be due to the recruitment of a new polysynaptic circuit. Together, our findings suggest that MrgprdCre lineage neurons can provide mechanical input to the dorsal horn that is nonnoxious before injury but becomes noxious afterwards because of the engagement of a previously silent polysynaptic circuit in the dorsal horn.

Intracortical inhibition in motor cortex (M1) regulates movement and motor learning. If cortical and thalamic inputs target different inhibitory cell types in different layers, then these afferents may play different roles in regulating M1 output. Using mice of both sexes, we quantified input to two main classes of M1 interneurons, parvalbumin+ (PV+) cells and somatostatin+ (SOM+) cells, using monosynaptic rabies tracing. We then compared anatomic and functional connectivity based on synaptic strength from sensory cortex and thalamus. Functionally, each input innervated M1 interneurons with a unique laminar profile. Different interneuron types were excited in a distinct, complementary manner, suggesting feedforward inhibition proceeds selectively via distinct circuits. Specifically, somatosensory cortex (S1) inputs primarily targeted PV+ neurons in upper layers (L2/3) but SOM+ neurons in middle layers (L5). Somatosensory thalamus [posterior nucleus (PO)] inputs targeted PV+ neurons in middle layers (L5). In contrast to sensory cortical areas, thalamic input to SOM+ neurons was equivalent to that of PV+ neurons. Thus, long-range excitatory inputs target inhibitory neurons in an area and a cell type-specific manner, which contrasts with input to neighboring pyramidal cells. In contrast to feedforward inhibition providing generic inhibitory tone in cortex, circuits are selectively organized to recruit inhibition matched to incoming excitatory circuits.SIGNIFICANCE STATEMENTM1 integrates sensory information and frontal cortical inputs to plan and control movements. Although inputs to excitatory cells are described, the synaptic circuits by which these inputs drive specific types of M1 interneurons are unknown. Anatomical results with rabies tracing and physiological quantification of synaptic strength shows that two main classes of inhibitory cells (PV+ and SOM+ interneurons) both receive substantial cortical and thalamic input, in contrast to interneurons in sensory areas (where thalamic input strongly prefers PV+ interneurons). Further, each input studied targets PV+ and SOM+ interneurons in a different fashion, suggesting that separate, specific circuits exist for recruitment of feedforward inhibition.

The impact of habitual physical activity on vagal-cardiac function and baroreflex sensitivity in elderly women is poorly characterized. This study compared vagal-cardiac modulation and carotid baroreflex (CBR) function in eight physically active (67.6 ± 1.9 years; peak O2 uptake 29.1 ± 2.5 mL/min/kg) versus eight sedentary (67.3 ± 1.8 years; peak O2 uptake 18.6 ± 0.9 mL/min/kg) elderly women. Heart rate (HR) variabilities and maximal changes of HR and mean arterial pressure (MAP) elicited by 5-s pressure pulses between +40 and −80 mmHg applied to the carotid sinus were measured at rest and during carotid baroreceptor unloading effected by −15 mmHg lower-body negative pressure (LBNP). HR variability was greater in active than sedentary women in both low (0.998 ± 0.286 versus 0.255 ± 0.063 bpm2; P = 0.036) and high (0.895 ± 0.301 versus 0.156 ± 0.045 bpm2; P = 0.044) frequency domains. CBR-HR gains (bpm/mmHg) were greater (fitness factor P

In perilous and stressful situations, the ability to suppress pain can be critical for survival. The rostral ventromedial medulla contains neurons that robustly inhibit nocioception at the level of the spinal cord through a top-down modulatory pathway. Although much is known about the role of the rostral ventromedial medulla in the inhibition of pain, the precise ability to directly manipulate pain-inhibitory neurons in the rostral ventromedial medulla has never been achieved. We now expose a cellular circuit that inhibits nocioception and itch in mice. Through a combination of molecular, tracing and behavioural approaches, we found that rostral ventromedial medulla neurons containing the kappa-opioid receptor inhibit itch and nocioception. With chemogenetic inhibition, we uncovered that these neurons are required for stress-induced analgesia. Using intersectional chemogenetic and pharmacological approaches, we determined that rostral ventromedial medulla kappa-opioid receptor neurons inhibit nocioception and itch through a descending circuit. Lastly, we identified a dynorphinergic pathway arising from the periaqueductal grey that modulates nociception within the rostral ventromedial medulla. These discoveries highlight a distinct population of rostral ventromedial medulla neurons capable of broadly and robustly inhibiting itch and nocioception.

Capsaicin applied locally to the skin causes central sensitization that results in allodynia, a state in which pain is elicited by innocuous stimuli. Here, we used two-photon calcium imaging of neurons in the dorsal spinal cord to visualize central sensitization across excitatory interneurons and spinal projection neurons. To distinguish among excitatory neuron subtypes, we developed CICADA, a cell profiling approach that leverages the expression of distinct Gq-coupled receptors. We then identified capsaicin-responsive and capsaicin-sensitized neuronal populations. Capsaicin-sensitized neurons showed emergent responses to low threshold input and increased receptive field sizes consistent with the psychophysical phenomenon that allodynia is observed across an extended secondary zone. Finally, we identified spinal projection neurons that showed a shift in tuning toward low threshold input. These experiments provide a population-level view of central sensitization and a framework with which to model somatosensory integration in the dorsal horn.HighlightWarwick et al. use two-photon calcium imaging coupled with pharmacological profiling to identify neuronal populations in the spinal dorsal horn that mediate capsaicin-induced central sensitization.

Purpose A high-velocity low-amplitude thrust joint manipulation (HVLAT) is an intervention used by clinicians to treat spine pain. HVLAT is an entry-level skill included in the curriculum of physical therapist education programs. The objective of this study was to investigate the effects of utilizing a motor learning theory assisted teaching strategy on physical therapy student HVLAT confidence and skill acquisition as compared to a traditional lab. Method Thirty physical therapy students were divided into two groups. One group received a traditional lab. The other group received a lab involving sequential partial task practice (SPTP) strategy in which students engaged in partial task practice over several repetitions with different partners. Student confidence and skill acquisition was determined through comparison of pretest and posttest surveys and performance on skills assessments. Results The traditional lab and SPTP lab groups demonstrated similar response from pretest to posttest related to their HVLAT confidence. Student grades on their skills assessment measuring skill acquisition showed no significant differences between the lab groups. Discussion The findings suggest that the SPTP lab strategy was as effective as a traditional lab structure for developing physical therapy student HVLAT confidence and skill acquisition. The majority of students in both lab groups reached a level of confidence that allowed them to feel comfortable teaching someone else these HVLAT skills. It is up to the instructors involved in delivering HVLAT content in physical therapist education programs to determine what learning activities are best suited to meet their specific objectives.

The impact of different neuronal populations on local cerebral blood flow (CBF) regulation is not well known and insight into these relationships could enhance the interpretation of brain function and dysfunction from brain imaging data. We investigated the role of sub-types of inhibitory neuron activity on the regulation of CBF using optogenetics, laser Doppler flowmetry and different transgenic mouse models (parvalbumin (PV), vasoactive intestinal peptide (VIP), somatostatin (SOM) and nitric oxide synthase (NOS)). Whisker stimulation was used to verify that typical CBF responses were obtained in all mice. Photo-stimulation of SOM-cre and NOS-cre mice produced significant increases in CBF that were similar to whisker responses. In NOS-cre mice, CBF responses scaled with the photo-stimulus pulse duration and frequency. In SOM-cre mice, CBF increases were followed by decreases. In VIP-cre mice, photo-stimulation did not consistently produce significant changes in CBF, while slower increases in CBF that peaked 14–18 s after stimulation onset were observed in PV-cre mice. Control experiments performed in non-expressing regions showed no changes in CBF. These findings suggest that dysfunction in NOS or SOM neurons can have a significant impact on vascular responses that are detected by brain imaging methods like functional magnetic resonance imaging (fMRI).

The rostral ventromedial medulla (RVM) is important in descending modulation of spinal nociceptive transmission, but it is unclear if these descending pathways also modulate spinal pruriceptive transmission. RVM ON cells are activated by noxious algesic and pruritic stimuli and are pronociceptive. Many RVM-spinal projection neurons express the neurokinin-1 receptor (Tacr1), and ON-cells are excited by local administration of substance P (SP). We hypothesized that Tacr1-expressing RVM ON cells exert an inhibitory effect on itch opposite to their pronociceptive action. Intramedullary microinjection of SP significantly potentiated RVM ON cells and reduced pruritogen-evoked scratching while facilitating mechanical nociception. Chemogenetic activation of RVM Tacr1-expressing RVM neurons also reduced acute pruritogen-evoked scratching behavior while enhancing mechanonociception. Optotagging experiments confirmed RVM Tacr1-expressing neurons to be ON cells. We conclude that Tacr1-expressing ON cells in RVM play a significant role in the descending inhibition of spinal pruriceptive transmission.

Morphine-induced itch is a very common and debilitating side effect that occurs in laboring women who receive epidural analgesia and in patients who receive spinal morphine for relief of perioperative pain. Although antihistamines are still widely prescribed for the treatment of morphine-induced itch, their use is controversial because the cellular basis for morphine-induced itch remains unclear. Here, we used animal models and show that neuraxial morphine causes itch through neurons and not mast cells. In particular, we found that spinal dynorphin (Pdyn) neurons are both necessary and sufficient for morphine-induced itch in mice. Agonism of the kappa-opioid receptor alleviated morphine-induced itch in mice and nonhuman primates. Thus, our findings not only reveal that morphine causes itch through a mechanism of disinhibition but also challenge the long-standing use of antihistamines, thereby informing the treatment of millions worldwide.

International audience; The spinal dorsal horn is a major site for the induction and maintenance of mechanical allodynia, but the circuitry that underlies this clinically important form of pain remains unclear. The studies presented here provide strong evidence that the neural circuits conveying mechanical allodynia in the dorsal horn differ by the nature of the injury. Calretinin (CR) neurons in lamina II inner convey mechanical allodynia induced by inflammatory injuries, while protein kinase C gamma (PKCg) neurons at the lamina II/III border convey mechanical allodynia induced by neuropathic injuries. Cholecystokinin (CCK) neurons located deeper within the dorsal horn (laminae III–IV) are important for both types of injuries. Interestingly, the Maf+ subset of CCK neurons is composed of transient vesicular glutamate transporter 3 (tVGLUT3) neurons, which convey primarily dynamic allodynia. Identification of an etiology-based circuitry for mechanical allodynia in the dorsal horn has important implications for the mechanistic and clinical understanding of this condition.

In perilous and stressful situations, the ability to suppress pain can be critical for survival. The rostral ventromedial medulla (RVM) contains neurons that robustly inhibit pain processing in the spinal cord through a top-down modulatory pathway. Although much is known about the role of the RVM in the inhibition of pain, the precise identities and mechanisms of pain-inhibitory neurons in the RVM have never been identified. We now expose a cellular circuit that inhibits pain and itch in mice. Through a combination of molecular, tracing, and behavioral approaches, we found that RVM neurons containing the kappa-opioid receptor (KOR) inhibit itch and pain. With chemogenetic inhibition, we uncovered that these neurons are required for stress-induced analgesia. Using intersectional chemogenetic and pharmacological approaches, we determined that RVM KOR neurons inhibit pain and itch through a descending circuit. Lastly, we identified a dynorphinergic pathway arising from the PAG that modulates nociception within the RVM. These discoveries highlight a distinct population of RVM neurons capable of broadly and robustly inhibiting itch and pain.

Evidence strongly supports simulation-based learning activities as an effective instructional intervention. The debriefing session associated with a simulation event is one of, if not the critical, learning component within the learning activity. Because of its importance, the debriefing portion of a simulation should demand as much planning and forethought as the rest of the event; however, it is often overlooked in the planning process. These twelve steps will help guide faculty who are planning simulation-based learning activities to ensure that their debriefing sessions are effective and successful learning opportunities.

Most cutaneous C-fibers, including both peptidergic and non-peptidergic subtypes are presumed to be nociceptors and respond to noxious input in a graded manner. However, mechanically sensitive, non-peptidergic C-fibers also respond to mechanical input in the innocuous range, and so the degree to which they contribute to nociception remains unclear. To address this gap, we investigated the function of non-peptidergic afferents using theMrgprdCreallele. In real time place aversion studies, we found that low frequency optogenetic activation ofMrgrpdCrelineage neurons was not aversive in naïve mice, but became aversive after spared nerve injury (SNI). To address the underlying mechanisms of this allodynia, we recorded from lamina I spinoparabrachial (SPB) neurons using the semi-intactex vivopreparation. Following SNI, innocuous brushing of the skin gave rise to abnormal activity in lamina I SPB neurons, consisting of an increase in the proportion of recorded neurons that responded with excitatory post synaptic potentials or action potentials. This increase was likely due, at least in part, to an increase in the proportion of lamina I (LI) SPB neurons that received input upon optogenetic activation ofMrgprdCrelineage neurons. Intriguingly, in SPB neurons there was a significant increase in the EPSC latency fromMrgprdCrelineage input following SNI, consistent with the possibility that the greater activation post SNI could be due to the recruitment of a new polysynaptic circuit. Together, our findings suggestMrgprdCrelineage neurons can provide mechanical input to the dorsal horn that is non-noxious before injury but becomes noxious afterwards due the engagement of a previously silent polysynaptic circuit in the dorsal horn.

The neurokinin-1 receptor (NK1R; encoded byTacr1) is expressed in spinal dorsal horn neurons and has been suggested to mediate itch in rodents. However, previous studies relied heavily on neurotoxic ablation of NK1R spinal neurons, which limited further dissection of their function in spinal itch circuitry. To address this limitation, we leveraged a newly developedTacr1CreERmouse line to characterize the role of NK1R spinal neurons in itch. We show that pharmacological activation of spinal NK1R and chemogenetic activation ofTacr1CreERspinal neurons increases itch behavior in male and female mice, whereas pharmacological inhibition of spinal NK1R suppresses itch behavior. We use fluorescencein situhybridization (FISH) to characterize the endogenous expression ofTacr1throughout the superficial and deeper dorsal horn (DDH), as well as the lateral spinal nucleus (LSN), of mouse and human spinal cord. Retrograde labeling studies in mice from the parabrachial nucleus (PBN) show that less than 20% of superficialTacr1CreERdorsal horn neurons are spinal projection neurons, and thus the majority ofTacr1CreERare local interneurons. We then use a combination ofin situhybridization andex vivotwo-photon Ca2+imaging of the mouse spinal cord to establish that NK1R and the gastrin-releasing peptide receptor (GRPR) are coexpressed within a subpopulation of excitatory superficial dorsal horn (SDH) neurons. These findings are the first to suggest a role for NK1R interneurons in itch and extend our understanding of the complexities of spinal itch circuitry.SIGNIFICANCE STATEMENTThe spinal cord is a critical hub for processing somatosensory input, yet which spinal neurons process itch input and how itch signals are encoded within the spinal cord is not fully understood. We demonstrate neurokinin-1 receptor (NK1R) spinal neurons mediate itch behavior in mice and that the majority of NK1R spinal neurons are local interneurons. These NK1R neurons comprise a subset of gastrin-releasing peptide receptor (GRPR) interneurons and are thus positioned at the center of spinal itch transmission. We show NK1R mRNA expression in human spinal cord, underscoring the translational relevance of our findings in mice. This work is the first to suggest a role for NK1R interneurons in itch and extends our understanding of the complexities of spinal itch circuitry.

Wind-up is a frequency-dependent increase in the response of spinal cord neurons, which is thought to underlie temporal summation of nociceptive input. However, whether spinoparabrachial neurons, which likely contribute to the affective component of pain, undergo wind-up was unknown. Here, we addressed this question and investigated the underlying neural circuit. We show that one-fifth of lamina I spinoparabrachial (SPB) neurons undergo wind-up, and provide evidence that wind-up in these cells is mediated in part by a network of spinal excitatory interneurons that show reverberating activity. These findings provide insight into a polysynaptic circuit of sensory augmentation that may contribute to the wind-up of pain’s unpleasantness.

Neuropathic itch is a pathological condition that is due to damage within the nervous system. This type of itch can be severe and unrelenting, which has a very negative impact on quality of life. Neuropathic itch is more common than generally appreciated because most types of neuropathic pain have a neuropathic itch counterpart. Unfortunately, much like neuropathic pain, there is a lack of effective treatments for neuropathic itch. Here, we consider the neural basis of itch and then describe how injuries within these neural circuits can lead to neuropathic itch in both animal models and human disease states.

Spinal projection neurons are a major pathway through which somatic stimuli are conveyed to the brain. However, the manner in which this information is coded is poorly understood. Here, we report the identification of a modality-selective spinoparabrachial (SPB) neuron subtype with unique properties. Specifically, we find that cold-selective SPB neurons are differentiated by selective afferent input, reduced sensitivity to substance P, distinct physiological properties, small soma size, and low basal drive. In addition, optogenetic experiments reveal that cold-selective SPB neurons do not receive input from Nos1 inhibitory interneurons and, compared with other SPB neurons, show significantly smaller inhibitory postsynaptic currents upon activation of Pdyn inhibitory interneurons. Together, these data suggest that cold output from the spinal cord to the parabrachial nucleus is mediated by a specific cell type with distinct properties.

The anterolateral pathway consists of ascending spinal tracts that convey pain, temperature and touch information from the spinal cord to the brain1–4. Projection neurons of the anterolateral pathway are attractive therapeutic targets for pain treatment because nociceptive signals emanating from the periphery are channelled through these spinal projection neurons en route to the brain. However, the organizational logic of the anterolateral pathway remains poorly understood. Here we show that two populations of projection neurons that express the structurally related G-protein-coupled receptors (GPCRs) TACR1 and GPR83 form parallel ascending circuit modules that cooperate to convey thermal, tactile and noxious cutaneous signals from the spinal cord to the lateral parabrachial nucleus of the pons. Within this nucleus, axons of spinoparabrachial (SPB) neurons that express Tacr1 or Gpr83 innervate distinct sets of subnuclei, and strong optogenetic stimulation of the axon terminals induces distinct escape behaviours and autonomic responses. Moreover, SPB neurons that express Gpr83 are highly sensitive to cutaneous mechanical stimuli and receive strong synaptic inputs from both high- and low-threshold primary mechanosensory neurons. Notably, the valence associated with activation of SPB neurons that express Gpr83 can be either positive or negative, depending on stimulus intensity. These findings reveal anatomically, physiologically and functionally distinct subdivisions of the SPB tract that underlie affective aspects of touch and pain. Two populations of neurons with distinct anatomy and receptor expression that convey information from the spinal cord to the brain have different functional properties with respect to touch and pain.

Spinal projection neurons are a major pathway through which somatic stimuli are conveyed to the brain. However, the manner in which this information is coded is poorly understood. Here, we report the identification of a modality-selective spinoparabrachial (SPB) neuron subtype with unique properties. Specifically, we find that cold-selective SPB neurons are differentiated by selective afferent input, reduced neuropeptide sensitivity, distinct physiological properties, small soma size, and low basal drive. In addition, optogenetic experiments reveal that cold-selective SPB neurons are distinctive with respect to their connectivity, with little to no input from either Pdyn or Nos1 inhibitory interneurons. Together, these data define a neural substrate supporting a labeled-line for cold from the periphery to the brain.

Objectives This study examines how the perceived role of poor lifestyle and irresponsible behaviour in contracting HIV, human papilloma virus (HPV) and diabetes affects public support for government-provisioned prevention efforts in Britain. It assesses whether public attitudes on healthcare spending are broadly sensitive to ‘lifestyle stigmas’. Methods We conducted an online survey of 738 respondents in Britain and embedded three separate survey experiments to measure support for government-provisioned interventions for HIV, HPV and type 2 diabetes. In each experiment, we manipulated language used to describe the extent to which the diseases are caused by lifestyle choices. Most respondents participated in all three experiments, but assignment was randomised within each condition. Analysis compared support among respondents exposed to ‘lifestyle’ treatment (information emphasising the disease’s lifestyle causes) versus control treatment. We estimated three separate t-tests in which support for government provision of interventions is the dependent variable. Results Support for government-provisioned prevention was high for all three diseases. There was no statistical difference between treatment and control conditions for HIV (treatment mean=3.73, control mean=3.86, p=0.38). But in both HPV (treatment mean=3.96, control mean=4.43, p Conclusions Public opinion on healthcare expenditures in Britain is unexpected and uneven. Consistent participant support for pre-exposure prophylaxis (PrEP) shows public attitudes are not always sensitive to lifestyle stigmas—but for other diseases, perceived relationships between individual behaviour and poor health can still shape public opinion about health expenditures. Policymakers and practitioners should remain attentive to how health problems are framed and discussed to ensure broad public support, and take advantage of policy windows like with PrEP as they may close.

A recent flurry of genetic studies in mice have provided key insights into how the somatosensory system is organized at a cellular level to encode itch, pain, temperature, and touch. These studies are largely predicated on the idea that functional cell types can be identified by their unique developmental provenance and gene expression profile. However, the extent to which gene expression profiles can be correlated with functional cell types and circuit organization remains an open question. In this review, we focus on recent progress in characterizing the sensory afferent and dorsal horn neuron cell types that process cutaneous somatosensory information and ongoing circuit studies that are beginning to bridge the divide between cell type and function.

Each day we experience myriad somatosensory stimuli: hugs from loved ones, warm showers, a mosquito bite, and sore muscles after a workout. These tactile, thermal, itch, and nociceptive signals are detected by peripheral sensory neuron terminals distributed throughout our body, propagated into the spinal cord, and then transmitted to the brain through ascending spinal pathways. Primary sensory neurons that detect a wide range of somatosensory stimuli have been identified and characterized. In contrast, very little is known about how peripheral signals are integrated and processed within the spinal cord and conveyed to the brain to generate somatosensory perception and behavioral responses. We tackled this question by developing new mouse genetic tools to define projection neuron (PN) subsets of the anterolateral pathway, a major ascending spinal cord pathway, and combining these new tools with advanced anatomical, physiological, and behavioral approaches. We found that Gpr83+ PNs, a newly identified subset of spinal cord output neurons, and Tacr1+ PNs are largely non-overlapping populations that innervate distinct sets of subnuclei within the lateral parabrachial nucleus (PBNL) of the pons in a zonally segregated manner. In addition, Gpr83+ PNs are highly sensitive to cutaneous mechanical stimuli, receive strong synaptic inputs from primary mechanosensory neurons, and convey tactile information bilaterally to the PBNL in a non-topographically organized manner. Remarkably, Gpr83+ mechanosensory limb of the anterolateral pathway controls behaviors associated with different hedonic values (appetitive or aversive) in a scalable manner. Our study reveals a dedicated spinal cord output pathway that conveys affective touch signals to the brain as well as parallel ascending circuit modules that cooperate to convey tactile, thermal and noxious cutaneous signals from the spinal cord to the brain. Furthermore, our study provides an insight into the new therapeutic opportunities for developing treatments for neurological disorders associated with pain and affective touch. This work was supported by the Alice and Joseph E. Brooks Funds (S.C.), the Blavatnik Biomedical Accelerator Fund (S.C., D.G), NIH grants NS097344 and AT011447 (D.G.), AR063772 (S.R.), NS096705 (H.K.), the Bertarelli Foundation (D.G.), The Hock E. Tan and Lisa Yang Center for Autism Research at Harvard University (D.G.) and the Edward R. and Anne G. Lefler Center for Neurodegenerative Disorders (D.G). D.G. is an investigator of the Howard Hughes Medical Institute.

The Neurokinin 1 Receptor (NK1R), which binds Substance P, is expressed in discrete populations of neurons throughout the nervous system, where it has numerous roles including the modulation of pain and affective behaviors. Here, we report the generation of a NK1R-CreER knockin allele, in which CreERT2 replaces the coding sequence of the TACR1 gene (encoding NK1R) in order to gain genetic access to these cells. We find that the NK1R-CreER allele mediates recombination in many regions of the nervous system that are important in pain and anxiety including the amygdala, hypothalamus, frontal cortex, raphe nucleus, and dorsal horn of the spinal cord. Other cell types that are labeled by this allele include amacrine cells in the retina and fibroblasts in the skin. Thus, the NK1R-CreER mouse line is a valuable new tool for conditional gene manipulation enabling the visualization and manipulation of cells that express NK1R.

Designer receptors exclusively activated by designer drugs (DREADDs) are an advanced experimental tool that could potentially provide a novel approach to pain management. In particular, expression of an inhibitory (Gi-coupled) DREADD in nociceptors might enable ligand-dependent analgesia. To test this possibility, TRPV1-cre mice were used to restrict expression of Gi-DREADDs to predominantly C-fibers. Whereas baseline heat thresholds in both male and female mice expressing Gi-DREADD were normal, 1 mg/kg clozapine-N-oxide (CNO) produced a significant 3 h increase in heat threshold that returned to baseline by 5 h after injection. Consistent with these behavioral results, CNO decreased action potential firing in isolated sensory neurons from Gi-DREADD mice. Unexpectedly, however, the expression of Gi-DREADD in sensory neurons caused significant changes in voltage-gated Ca2+and Na+currents in the absence of CNO, as well as an increase in Na+channel (NaV1.7) expression. Furthermore, CNO-independent excitatory and inhibitory second-messenger signaling was also altered in these mice, which was associated with a decrease in the analgesic effect of endogenous inhibitory G-protein-coupled receptor activation. These results highlight the potential of this exciting technology, but also its limitations, and that it is essential to identify the underlying mechanisms for any observed behavioral phenotypes.SIGNIFICANCE STATEMENTDREADD technology is a powerful tool enabling manipulation of activity and/or transmitter release from targeted cell populations. The purpose of this study was to determine whether inhibitory DREADDs in nociceptive afferents could be used to produce analgesia, and if so, how. DREADD activation produced a ligand-dependent analgesia to heatin vivoand a decrease in neuronal firing at the single-cell level. However, we observed that expression of Gi-DREADD also causes ligand-independent changes in ion channel activity and second-messenger signaling. These findings highlight both the potential and the limitations of this exciting technology as well as the necessity to identify the mechanisms underlying any observed phenotype.

Auditory information is initially processed in the cochlear nuclei before being relayed to the brain. The cochlear nuclei are subdivided into dorsal, anterior ventral, and posterior ventral domains, each containing several subtypes of neurons that are thought to play discrete roles in the processing of sound. However, the ontogeny of these neurons is poorly understood, and this gap in knowledge hampers efforts to understand the basic neural circuitry of this nucleus. Here, we reveal that Bhlhb5 is expressed in both excitatory (unipolar brush cells) and inhibitory neurons (cartwheel cells) of the DCN during development. To gain genetic access to Bhlhb5-expressing neurons in the DCN, we generated a Bhlhb5::flpo knockin allele. Using an intersectional genetic strategy, we labeled cartwheel cells, thereby providing proof of concept that subpopulations of Bhlhb5-expressing neurons can be genetically targeted. Moreover, fate-mapping experiments using this allele revealed that Bhlhb5 is required for the proper development of the DCN, since mice lacking Bhlhb5 showed a dramatically diminished number of neurons, including unipolar brush and cartwheel cells. Intriguingly, the Bhlhb5::flpo allele also genetically labels numerous other regions of the nervous system that process sensory input, including the dorsal horn, the retina, and the nucleus of the lateral olfactory tract, hinting at a more general role for Bhlhb5 in the development of neurons that mediate sensory integration.

The lateral parabrachial nucleus (lPBN) is a major target of spinal projection neurons conveying nociceptive input into supraspinal structures. However, the functional role of distinct lPBN efferents in diverse nocifensive responses have remained largely uncharacterized. Here we show that that the lPBN is required for escape behaviors and aversive learning to noxious stimulation. In addition, we find that two populations of efferent neurons from different regions of the lPBN collateralize to distinct targets. Activation of efferent projections to the ventromedial hypothalamus (VMH) or lateral periaqueductal gray (lPAG) drives escape behaviors, whereas activation of lPBN efferents to the bed nucleus stria terminalis (BNST) or central amygdala (CEA) generates an aversive memory. Finally, we provide evidence that dynorphin-expressing neurons, which span cytoarchitecturally distinct domains of the lPBN, are required for aversive learning.

Increasing evidence suggests that extracellular miRNAs may serve as biomarkers of diseases, but the physiological relevance of extracellular miRNA is unclear. We find that intradermal cheek injection of miR-711 induces TRPA1-depedent itch (scratching) without pain (wiping) in naïve mice. Extracellular perfusion of miR-711 induces TRPA1 currents in both Trpa1-expressing heterologous cells and native sensory neurons through the core sequence GGGACCC. Computer simulations reveal that the core sequence binds several residues at the extracellular S5-S6 loop of TRPA1, which are critical for TRPA1 activation by miR-711 but not allyl isothiocyanate. Intradermal inoculation of human Myla cells induces lymphoma and chronic itch in immune- deficient mice, associated with increased serum levels of miR-711, secreted from cancer cells. Lymphoma-induced chronic itch is suppressed by miR-711 inhibitor and a blocking peptide that disrupts the miR-711/TRPA1 interaction. Our findings demonstrated an unconventional physiological role of extracellular naked miRNAs as itch mediators and ion channel modulators.