A novel spinal neuron connection for heat sensation

Deficiency of KIF15 contributes to oxaliplatin-induced cold hypersensitivity by limiting annexin A2 and enhancing TRPA1 localization in DRG neuronal membrane

Effective treatments for oxaliplatin-induced cold hypersensitivity remain a significant clinical challenge, primarily due to gaps in our understanding of the underlying pathophysiology. Our previous studies have indicated that kinesin-12 (KIF15) is expressed in neurons, suggesting its potential involvement in neurodevelopment and neuronal plasticity. However, its role in mediating chemotherapy-induced pain in primary sensory neurons has not yet been reported. In this study, we found that KIF15-knockout (Kif15-KO) mice showed an increase in cold sensitivity, with this heightened cold hypersensitivity being dependent on the accumulation of the TRP ankyrin 1 (TRPA1) channel on the cell membrane. We further demonstrated that in a model of oxaliplatin-induced peripheral neuropathy (OIPN), KIF15 expression was markedly reduced, coinciding with an increase in TRPA1 membrane localization and a physical interaction between KIF15 and Annexin A2 in peripheral sensory neurons. This suggests a mechanistic link where the loss of KIF15 disrupts the function of Annexin A2, enhancing the localization of TRPA1 on the cell membrane of dorsal root ganglion (DRG) neurons, thereby contributing to cold hypersensitivity. Our results offer a new understanding of the molecular mechanisms underlying chemotherapy-induced cold hypersensitivity, highlighting KIF15 as a key regulator and a potential therapeutic target for conditions like OIPN.

Neural ensembles that encode nocifensive mechanical and heat pain in mouse spinal cord

Acute pain is an unpleasant experience caused by noxious stimuli. How the spinal neural circuits attribute differences in quality of noxious information remains unknown. By means of genetic capturing, activity manipulation and single-cell RNA sequencing, we identified distinct neural ensembles in the adult mouse spinal cord encoding mechanical and heat pain. Reactivation or silencing of these ensembles potentiated or stopped, respectively, paw shaking, lifting and licking within but not across the stimuli modalities. Within ensembles, polymodal Gal+ inhibitory neurons with monosynaptic contacts to A-fiber sensory neurons gated pain transmission independent of modality. Peripheral nerve injury led to inferred microglia-driven inflammation and an ensemble transition with decreased recruitment of Gal+ inhibitory neurons and increased excitatory drive. Forced activation of Gal+ neurons reversed hypersensitivity associated with neuropathy. Our results reveal the existence of a spinal representation that forms the neural basis of the discriminative and defensive qualities of acute pain, and these neurons are under the control of a shared feed-forward inhibition.

The Burning Pain Transcriptome in the Mouse Primary Somatosensory Cortex

Our previous research has demonstrated that the spinal cord undergoes epigenetic and molecular alterations following non-severe burn injury (BI). However, the primary somatosensory cortex (S1), crucial for pain perception, remains unexplored in this context. Here, we investigated transcriptomic alterations in the S1 cortex of mice subjected to BI or formalin application (FA) to the hind paw, utilizing RNA sequencing (RNA-seq) one hour after injury. RNA-seq identified 1116 differentially expressed genes (DEGs) in BI and 136 DEGs in formalin-induced inflammatory pain. Notably, 82.4% of DEGs in BI and 32.4% in FA were downregulated. A total of 42 upregulated and 17 downregulated overlapping DEGs were identified, indicating significant differences in the cortical processing of pain based on its origins. Gene Ontology analysis reveals that BI upregulated mitochondrial functions and ribosome synthesis, whereas axon guidance, synaptic plasticity, and neurotransmission-related processes were downregulated. By contrast, formalin treatment mainly impacted metabolic processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis highlights the significance of retrograde endocannabinoid signaling (REC) in the response to burn injury. These findings demonstrate that transcriptomic remodeling in the S1 cortex is dependent on the sensory modality and suggest that the REC network is activated during acute pain responses following BI.

Heterogeneity of Layer 1 Interneurons in the Mouse Medial Prefrontal Cortex

Cortical Layer 1 (L1) acts as a critical relay for processing long-range inputs. GABAergic inhibitory interneurons (INs) in this layer (Layer 1 interneurons [L1INs]) function as inhibitory gates, regulating these inputs and modulating the activity of deeper cortical layers. However, their characteristics and circuits in the medial prefrontal cortex (mPFC) remain poorly understood. Using biocytin labeling, we identified three distinct morphological types of mPFC L1INs: neurogliaform cells (NGCs), elongated NGCs (eNGCs), and single-bouquet cell-like (SBC-like) cells. Whole-cell recordings revealed distinct firing patterns across these subtypes: NGCs and eNGCs predominantly exhibited late-spiking (LS) patterns, and SBC-like cells displayed a higher prevalence of non-LS (NLS) patterns. We observed both electrical and chemical connections among mPFC L1INs. Optogenetic activation of NDNF+ L1INs demonstrated broad inhibitory effects on deeper layer neurons. The strength of inhibition on pyramidal neurons (PyNs) and INs displayed layer-specific preference. These findings highlight the functional diversity of L1INs in modulating mPFC circuits and suggest their potential role in supporting higher order cognitive functions.

NRG1-ErbB4 signaling in the cerebrospinal fluid-contacting nucleus regulates thermal pain in mice

The cerebrospinal fluid-contacting nucleus(CSF-contacting nucleus) is a pair of unique nuclei in the brain parenchyma which has long been demonstrated to play an important role in pain signal processing. However, the mechanisms by which the CSF-contacting nucleus intervenes in pain is unclear. The NRG1-ErbB4 signaling plays an important role in the nervous system and has been shown to be involved in the regulation of pain. Whether there is an involvement of NRG1-ErbB4 signaling in the regulation of pain in the CSF-contacting nucleus is currently unknown. Here, our works showed that c-Fos expression in the CSF-contacting nucleus was increased in response to incisional pain. The activation of the CSF-contacting nucleus by chemogenetics could induce thermal hyperalgesia in naive mice without effecting the pain in mice suffering from incision pain. The inhibition of the CSF-contacting nucleus alleviated incision pain, but had no effect on the pain response in naive mice. With immunofluorescence staining and Western blot, the NRG1-ErbB4 signaling in the CSF-contacting nucleus showed upregulated during the acute pain phase. And, activating NRG1-ErbB4 signaling in the CSF-contacting nucleus specifically by intracranial injection of drugs, the naïve mice displayed thermal hyperalgesia while inhibiting this signaling by intracranial injection could reverse the hyperalgesia caused by CSF-contacting nucleus activation, and execute an analgesic effect during the painful phase in mice. Our study suggested that the CSF-contacting nucleus plays a regulatory role in thermal pain in mice via NRG1-ErbB4 signaling.

Intrinsic anti-inflammatory nanomedicines for enhanced pain management

Introduction

Effective postoperative pain management remains a significant challenge due to the severe side effects of opioids and the limitations of existing analgesic delivery systems. Inflammation plays a critical role in pain exacerbation, highlighting the need for therapies that combine analgesic effects with intrinsic anti-inflammatory properties.

Methods

Herein, we develop an intrinsic anti-inflammatory nanomedicine designed to enhance pain management by integrating controlled anesthetic release with inherent anti-inflammatory activity. Our nanoplatform utilizes dendritic mesoporous silica nanoparticles (MSNs) loaded with levobupivacaine and coated with Rg3-based liposomes derived from ginsenoside Rg3, termed LMSN-bupi.

Results

The MSNs enable sustained and controlled release of the local anesthetic, while the Rg3-liposome coating provides intrinsic anti-inflammatory effects by inhibiting macrophage activation. In animal models, LMSN-bupi demonstrates significantly prolonged analgesic effects and attenuated inflammatory responses compared to traditional liposome-decorated nanoparticles (TMSN-bupi) (n = 5).

Discussion

These findings underscore the potential of intrinsic anti-inflammatory nanomedicines in enhancing pain management, offering a promising strategy to overcome the limitations of current therapies and improve patient outcomes in postoperative care.

Establishment of a Magnetically Controlled Scalable Nerve Injury Model

Animal models of peripheral nerve injury (PNI) serve as the fundamental basis for the investigations of nerve injury, regeneration, and neuropathic pain. The injury properties of such models, including the intensity and duration, significantly influence the subsequent pathological changes, pain development, and therapeutic efficacy. However, precise control over the intensity and duration of nerve injury remains challenging within existing animal models, thereby impeding accurate and comparative assessments of relevant cases. Here, a new model that provides quantitative and off-body controllable injury properties via a magnetically controlled clamp, is presented. The clamp can be implanted onto the rat sciatic nerve and exert varying degrees of compression under the control of an external magnetic field. It is demonstrated that this model can accurately simulate various degrees of pathology of human patients by adjusting the magnetic control and reveal specific pathological changes resulting from intensity heterogeneity that are challenging to detect previously. The controllability and quantifiability of this model may significantly reduce the uncertainty of central response and inter-experimenter variability, facilitating precise investigations into nerve injury, regeneration, and pain mechanisms.

The role and mechanism of NRG1/ErbB4 in inducing the differentiation of induced pluripotent stem cells into cardiomyocytes

BACKGROUND

We aimed to investigate the effect and potential mechanism of enhancing Neuregulin1 (NRG1)/v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 4 (ErbB4) expression on the differentiation of induced pluripotent stem cells (iPSCs) into cardiomyocytes.

METHODS

We utilized CRISPR-CAS9 technology to knock in ErbB4 and obtained a single-cell clone IPSN-AAVS1-CMV-ErbB4 (iPSCs-ErbB4). Subsequently, we induced the differentiation of iPSCs into cardiomyocytes and quantified the number of beating embryoid bodies. Furthermore, quantitative real-time PCR assessed the expression of cardiomyocyte markers, including ANP (atrial natriuretic peptide), Nkx2.5 (NK2 transcription factor related locus 5), and GATA4 (GATA binding protein 4). On the 14th day of differentiation, we observed the α-MHC (α-myosin heavy chain)-positive area using immunofluorescent staining and conducted western blotting to detect the expression of cTnT (cardiac troponin) protein and PI3K/Akt signaling pathway-related proteins. Additionally, we intervened the iPSCs-ErbB4 + NRG1 group with the PI3K/Akt inhibitor LY294002 and observed alterations in the expression of cardiomyocyte differentiation-related genes.

RESULTS

The number of beating embryoid bodies increased after promoting the expression of NRG1/ErbB4 compared to the iPSCs control group. Cardiomyocyte markers ANP, Nkx2.5, and GATA4 significantly increased on day 14 of differentiation, and the positive area of α-MHC was three times that of the iPSCs control group. Moreover, there was a marked increase in cTnT protein expression. However, there was no significant difference in cardiomyocyte differentiation between the iPSCs-ErbB4 group and the iPSCs control group. Akt phosphorylation was significantly increased in the iPSCs-ErbB4 + NRG1 group. LY294002 significantly reversed the enhancing effect of NRG1/ErbB4 overexpression on Akt phosphorylation as well as the increase in α-MHC and cTnT expression.

CONCLUSIONS

In conclusion, promoting the expression of NRG1/ErbB4 induced the differentiation of iPSC into cardiomyocytes, possibly through modulation of the PI3K/Akt signaling pathway.

Influence of Early-Life Stress on the Excitability of Dynorphin Neurons in the Adult Mouse Dorsal Horn

While early-life adversity has been associated with a higher risk of developing chronic pain in adulthood, the cellular and molecular mechanisms by which chronic stress during the neonatal period can persistently sensitize developing nociceptive circuits remain poorly understood. Here, we investigate the effects of early-life stress (ELS) on synaptic integration and intrinsic excitability in dynorphin-lineage (DYN) interneurons within the adult mouse superficial dorsal horn (SDH), which are important for inhibiting mechanical pain and itch. The administration of neonatal limited bedding between postnatal days (P)2 and P9 evoked sex-dependent effects on spontaneous glutamatergic signaling, as female SDH neurons exhibited a higher amplitude of miniature excitatory postsynaptic currents (mEPSCs) after ELS, while mEPSC frequency was reduced in DYN neurons of the male SDH. Furthermore, ELS decreased the frequency of miniature inhibitory postsynaptic currents selectively in female DYN neurons. As a result, ELS increased the balance of spontaneous excitation versus inhibition (E:I ratio) in mature DYN neurons of the female, but not male, SDH network. Nonetheless, ELS weakened the total primary afferent-evoked glutamatergic drive onto adult DYN neurons selectively in females, without modifying afferent-evoked inhibitory signaling onto the DYN population. Finally, ELS failed to significantly change the intrinsic membrane excitability of mature DYN neurons in either males or females. Collectively, these data suggest that ELS exerts a long-term influence on the properties of synaptic transmission onto DYN neurons within the adult SDH, which includes a reduction in the overall strength of sensory input onto this important subset of inhibitory interneurons. PERSPECTIVE: This study suggests that chronic stress during the neonatal period influences synaptic function within adult spinal nociceptive circuits in a sex-dependent manner. These findings yield new insight into the potential mechanisms by which early-life adversity might shape the maturation of pain pathways in the central nervous system (CNS).

Spinal Nmur2-positive Neurons Play a Crucial Role in Mechanical Itch

The dorsal spinal cord is crucial for the transmission and modulation of multiple somatosensory modalities, such as itch, pain, and touch. Despite being essential for the well-being and survival of an individual, itch and pain, in their chronic forms, have increasingly been recognized as clinical problems. Although considerable progress has been made in our understanding of the neurochemical processing of nociceptive and chemical itch sensations, the neural substrate that is crucial for mechanical itch processing is still unclear. Here, using genetic and functional manipulation, we identified a population of spinal neurons expressing neuromedin U receptor 2 (Nmur2+) as critical elements for mechanical itch. We found that spinal Nmur2+ neurons are predominantly excitatory neurons, and are enriched in the superficial laminae of the dorsal horn. Pharmacogenetic activation of cervical spinal Nmur2+ neurons evoked scratching behavior. Conversely, the ablation of these neurons using a caspase-3-based method decreased von Frey filament-induced scratching behavior without affecting responses to other somatosensory modalities. Similarly, suppressing the excitability of cervical spinal Nmur2+ neurons via the overexpression of functional Kir2.1 potassium channels reduced scratching in response to innocuous mechanical stimuli, but not to pruritogen application. At the lumbar level, pharmacogenetic activation of these neurons evoked licking and lifting behaviors. However, ablating these neurons did not affect the behavior associated with acute pain. Thus, these results revealed the crucial role of spinal Nmur2+ neurons in mechanical itch. Our study provides important insights into the neural basis of mechanical itch, paving the way for developing novel therapies for chronic itch. PERSPECTIVE: Excitatory Nmur2+ neurons in the superficial dorsal spinal cord are essential for mechanical but not chemical itch information processing. These spinal Nmur2+ neurons represent a potential cellular target for future therapeutic interventions against chronic itch. Spinal and supraspinal Nmur2+ neurons may play different roles in pain signal processing.

Deep sequencing of Phox2a nuclei reveals five classes of anterolateral system neurons

The anterolateral system (ALS) is a major ascending pathway from the spinal cord that projects to multiple brain areas and underlies the perception of pain, itch, and skin temperature. Despite its importance, our understanding of this system has been hampered by the considerable functional and molecular diversity of its constituent cells. Here, we use fluorescence-activated cell sorting to isolate ALS neurons belonging to the Phox2a-lineage for single-nucleus RNA sequencing. We reveal five distinct clusters of ALS neurons (ALS1-5) and document their laminar distribution in the spinal cord using in situ hybridization. We identify three clusters of neurons located predominantly in laminae I-III of the dorsal horn (ALS1-3) and two clusters with cell bodies located in deeper laminae (ALS4 and ALS5). Our findings reveal the transcriptional logic that underlies ALS neuronal diversity in the adult mouse and uncover the molecular identity of two previously identified classes of projection neurons. We also show that these molecular signatures can be used to target groups of ALS neurons using retrograde viral tracing. Overall, our findings provide a valuable resource for studying somatosensory biology and targeting subclasses of ALS neurons.

Roles of Thermosensitive Transient Receptor Channels TRPV1 and TRPM8 in Paclitaxel-Induced Peripheral Neuropathic Pain

Paclitaxel, a microtubule-stabilizing chemotherapy drug, can cause severe paclitaxel-induced peripheral neuropathic pain (PIPNP). The roles of transient receptor potential (TRP) ion channel vanilloid 1 (TRPV1, a nociceptor and heat sensor) and melastatin 8 (TRPM8, a cold sensor) in PIPNP remain controversial. In this study, Western blotting, immunofluorescence staining, and calcium imaging revealed that the expression and functional activity of TRPV1 were upregulated in rat dorsal root ganglion (DRG) neurons in PIPNP. Behavioral assessments using the von Frey and brush tests demonstrated that mechanical hyperalgesia in PIPNP was significantly inhibited by intraperitoneal or intrathecal administration of the TRPV1 antagonist capsazepine, indicating that TRPV1 played a key role in PIPNP. Conversely, the expression of TRPM8 protein decreased and its channel activity was reduced in DRG neurons. Furthermore, activation of TRPM8 via topical application of menthol or intrathecal injection of WS-12 attenuated the mechanical pain. Mechanistically, the TRPV1 activity triggered by capsaicin (a TRPV1 agonist) was reduced after menthol application in cultured DRG neurons, especially in the paclitaxel-treated group. These findings showed that upregulation of TRPV1 and inhibition of TRPM8 are involved in the generation of PIPNP, and they suggested that inhibition of TRPV1 function in DRG neurons via activation of TRPM8 might underlie the analgesic effects of menthol.

Construction of functional neural network tissue combining CBD-NT3-modified linear-ordered collagen scaffold and TrkC-modified iPSC-derived neural stem cells for spinal cord injury repair

Induced pluripotent stem cells (iPSCs) can be personalized and differentiated into neural stem cells (NSCs), thereby effectively providing a source of transplanted cells for spinal cord injury (SCI). To further improve the repair efficiency of SCI, we designed a functional neural network tissue based on TrkC-modified iPSC-derived NSCs and a CBD-NT3-modified linear-ordered collagen scaffold (LOCS). We confirmed that transplantation of this tissue regenerated neurons and synapses, improved the microenvironment of the injured area, enhanced remodeling of the extracellular matrix, and promoted functional recovery of the hind limbs in a rat SCI model with complete transection. RNA sequencing and metabolomic analyses also confirmed the repair effect of this tissue from multiple perspectives and revealed its potential mechanism for treating SCI. Together, we constructed a functional neural network tissue using human iPSCs-derived NSCs as seed cells based on the interaction of receptors and ligands for the first time. This tissue can effectively improve the therapeutic effect of SCI, thus confirming the feasibility of human iPSCs-derived NSCs and LOCS for SCI repair and providing a valuable direction for SCI research.

Spatial transcriptomics and single-nucleus RNA sequencing reveal a transcriptomic atlas of adult human spinal cord

Despite the recognized importance of the spinal cord in sensory processing, motor behaviors, and neural diseases, the underlying organization of neuronal clusters and their spatial location remain elusive. Recently, several studies have attempted to define the neuronal types and functional heterogeneity in the spinal cord using single-cell or single-nucleus RNA sequencing in animal models or developing humans. However, molecular evidence of cellular heterogeneity in the adult human spinal cord is limited. Here, we classified spinal cord neurons into 21 subclusters and determined their distribution from nine human donors using single-nucleus RNA sequencing and spatial transcriptomics. Moreover, we compared the human findings with previously published single-nucleus data of the adult mouse spinal cord, which revealed an overall similarity in the neuronal composition of the spinal cord between the two species while simultaneously highlighting some degree of heterogeneity. Additionally, we examined the sex differences in the spinal neuronal subclusters. Several genes, such as SCN10A and HCN1, showed sex differences in motor neurons. Finally, we classified human dorsal root ganglia (DRG) neurons using spatial transcriptomics and explored the putative interactions between DRG and spinal cord neuronal subclusters. In summary, these results illustrate the complexity and diversity of spinal neurons in humans and provide an important resource for future research to explore the molecular mechanisms underlying spinal cord physiology and diseases.

Alleviation of neuropathic pain with neuropeptide Y requires spinal Npy1r interneurons that coexpress Grp

Neuropeptide Y targets the Y1 receptor (Y1) in the spinal dorsal horn (DH) to produce endogenous and exogenous analgesia. DH interneurons that express Y1 (Y1-INs; encoded by Npy1r) are necessary and sufficient for neuropathic hypersensitivity after peripheral nerve injury. However, as Y1-INs are heterogenous in composition in terms of morphology, neurophysiological characteristics, and gene expression, we hypothesized that a more precisely defined subpopulation mediates neuropathic hypersensitivity. Using fluorescence in situ hybridization, we found that Y1-INs segregate into 3 largely nonoverlapping subpopulations defined by the coexpression of Npy1r with gastrin-releasing peptide (Grp/Npy1r), neuropeptide FF (Npff/Npy1r), and cholecystokinin (Cck/Npy1r) in the superficial DH of mice, nonhuman primates, and humans. Next, we analyzed the functional significance of Grp/Npy1r, Npff/Npy1r, and Cck/Npy1r INs to neuropathic pain using a mouse model of peripheral nerve injury. We found that chemogenetic inhibition of Npff/Npy1r-INs did not change the behavioral signs of neuropathic pain. Further, inhibition of Y1-INs with an intrathecal Y1 agonist, [Leu31, Pro34]-NPY, reduced neuropathic hypersensitivity in mice with conditional deletion of Npy1r from CCK-INs and NPFF-INs but not from GRP-INs. We conclude that Grp/Npy1r-INs are conserved in higher order mammalian species and represent a promising and precise pharmacotherapeutic target for the treatment of neuropathic pain.

Tyrosine Kinase Receptor ErbB4 in Advillin-Positive Neurons Contributes to Inflammatory Pain Hypersensitivity in Mouse DRG

Inflammatory pain is a common type of pathological pain. Although the dorsal root ganglion (DRG) is key to pathogenesis of inflammatory pain, the underlying specific molecular and cellular mechanisms remain unclear. In this study, we used mouse models of acute or chronic inflammatory pain, induced by formalin or complete Freund' s adjuvant (CFA), respectively, to explore whether tyrosine kinase receptor ErbB4 participates in the pathogenesis of inflammatory pain. Firstly, we found that both the expression of Neuregulin 1 (Nrg1) and phosphorylation of ErbB4 receptor were upregulated in DRG after inflammatory pain, implying the activation of ErbB4 in DRG. Using ErbB4-mutant mice, we found reduced pain sensitivity of mice when ErbB4 gene expression was largely ablated; furthermore, ErbB4 deletion decreased the inflammatory pain hypersensitivity of either formalin- or CFA-induced mouse models. Moreover, the pain sensitivity was reduced in mice with specific deletion of ErbB4 on advillin-positive neurons within DRG. Importantly, pain hypersensitivity also decreased in Advillin-Cre;ErbB4-/- cKO mice after formalin- or CFA-induced inflammatory pain. Finally, gene quantification differential expression analysis, using RNAseq technology in combination with GO and KEGG enrichment analysis, suggested that calcium signaling pathway possibly mediated the roles of ErbB4 on DRG sensory neurons in inflammatory pain models. Together, these results indicate that ErbB4 on advillin-positive sensory neurons enhances inflammatory pain sensitivity, providing new clues towards the pathogenic mechanisms of inflammatory pain.

Transient receptor potential M2 channel in the hypothalamic preoptic area and its impact on thermoregulation during menopause

BACKGROUND

Decreased estrogen levels can cause abnormal thermosensitivity of the preoptic area (POA) in the hypothalamus during menopause, which may cause hot flashes. Thermosensitive transient receptors (ThermoTRPs) affect the thermosensitivity of neurons. It is worth exploring whether ThermoTRPs change under low estrogen state and participate in the abnormal thermoregulation of POA.

METHODS

Adult female Sprague-Dawley rats were randomly divided into sham operation (SHAM), ovariectomy (OVX) and estrogen treatment after ovariectomy (OVX+E) groups. Under 10 ℃, 18 ℃, 25 ℃, 37 ℃ and 45 ℃ incubations, their skin temperature was monitored and the expression of TRPA1, TRPM8, TRPM2, and TRPV1 in POA were investigated.

RESULTS

The skin temperature of ovariectomized rats changed faster and more dramatically under different incubation temperatures. The results at mRNA level show that only the expression of TRPM2 decreased in POA of OVX group compared with the other two groups at 25 ℃, TRPA1 expression in POA of the three groups increased at 10 ℃, TRPM8 increased at 10 ℃ and 18 ℃, TRPV1 increased at 10 ℃ and 45 ℃, while the expression of TRPM2 decreased at 10 ℃ and 18 ℃ and increased at 37 ℃ and 45 ℃. In all these cases, the magnitudes of the changes were less in the OVX group relative to the other two groups. The further immunohistochemical and Western blot results of TRPM2 and the activated TRPM2 positive cells labeled by c-Fos were consistent with the results of mRNA level.

CONCLUSIONS

The expression and thermosensitivity of TRPM2 in POA changed greatly under different incubation temperatures, but the changes in ovariectomized rats were less. This may be the key factor triggering thermoregulation dysfunction under low estrogen and may cause hot flashes.

Deep sequencing of Phox2a nuclei reveals five classes of anterolateral system neurons

The anterolateral system (ALS) is a major ascending pathway from the spinal cord that projects to multiple brain areas and underlies the perception of pain, itch and skin temperature. Despite its importance, our understanding of this system has been hampered by the considerable functional and molecular diversity of its constituent cells. Here we use fluorescence-activated cell sorting to isolate ALS neurons belonging to the Phox2a-lineage for single-nucleus RNA sequencing. We reveal five distinct clusters of ALS neurons (ALS1-5) and document their laminar distribution in the spinal cord using in situ hybridization. We identify 3 clusters of neurons located predominantly in laminae I-III of the dorsal horn (ALS1-3) and two clusters with cell bodies located in deeper laminae (ALS4 & ALS5). Our findings reveal the transcriptional logic that underlies ALS neuronal diversity in the adult mouse and uncover the molecular identity of two previously identified classes of projection neurons. We also show that these molecular signatures can be used to target groups of ALS neurons using retrograde viral tracing. Overall, our findings provide a valuable resource for studying somatosensory biology and targeting subclasses of ALS neurons.

Energy Expenditure Homeostasis Requires ErbB4, an Obesity Risk Gene, in the Paraventricular Nucleus

Obesity affects more than a third adult population in the United States; the prevalence is even higher in patients with major depression disorders. GWAS studies identify the receptor tyrosine kinase ErbB4 as a risk gene for obesity and for major depression disorders. We found that ErbB4 was enriched in the paraventricular nucleus of the hypothalamus (PVH). To investigate its role in metabolism, we deleted ErbB4 by injecting a Cre-expressing virus into the PVH of ErbB4-floxed male mice and found that PVH ErbB4 deletion increased weight gain without altering food intake. ErbB4 PVH deletion also reduced nighttime activity and decreased intrascapular brown adipose tissue (iBAT) thermogenesis. Analysis of covariance (ANCOVA) revealed that ErbB4 PVH deletion reduced O2 consumption, CO2 production and heat generation in a manner independent of body weight. Immunostaining experiments show that ErbB4+ neurons in the PVH were positive for oxytocin (OXT); ErbB4 PVH deletion reduces serum levels of OXT. We characterized mice where ErbB4 was specifically mutated in OXT+ neurons and found reduction in energy expenditure, phenotypes similar to PVH ErbB4 deletion. Taken together, our data indicate that ErbB4 in the PVH regulates metabolism likely through regulation of OXT expressing neurons, reveal a novel function of ErbB4 and provide insight into pathophysiological mechanisms of depression-associated obesity.

Involvement of Mrgprd-expressing nociceptors-recruited spinal mechanisms in nerve injury-induced mechanical allodynia

Mechanical allodynia and hyperalgesia are intractable symptoms lacking effective clinical treatments in patients with neuropathic pain. However, whether and how mechanically responsive non-peptidergic nociceptors are involved remains elusive. Here, we showed that von Frey-evoked static allodynia and aversion, along with mechanical hyperalgesia after spared nerve injury (SNI) were reduced by ablation of Mrgprd^CreERT2-marked neurons. Electrophysiological recordings revealed that SNI-opened Aβ-fiber inputs to laminae I-II_o and _vII_i, as well as C-fiber inputs to _vII_i, were all attenuated in Mrgprd-ablated mice. In addition, priming chemogenetic or optogenetic activation of Mrgprd⁺ neurons drove mechanical allodynia and aversion to low-threshold mechanical stimuli, along with mechanical hyperalgesia. Mechanistically, gated Aβ and C inputs to _vII_i were opened, potentially via central sensitization by dampening potassium currents. Altogether, we uncovered the involvement of Mrgprd⁺ nociceptors in nerve injury-induced mechanical pain and dissected the underlying spinal mechanisms, thus providing insights into potential therapeutic targets for pain management.

Representation and control of pain and itch by distinct prefrontal neural ensembles

Pain and itch are two closely related but essentially distinct sensations that elicit different behavioral responses. However, it remains mysterious how pain and itch information is encoded in the brain to produce differential perceptions. Here, we report that nociceptive and pruriceptive signals are separately represented and processed by distinct neural ensembles in the prelimbic (PL) subdivision of the medial prefrontal cortex (mPFC) in mice. Pain- and itch-responsive cortical neural ensembles were found to significantly differ in electrophysiological properties, input-output connectivity profiles, and activity patterns to nociceptive or pruriceptive stimuli. Moreover, these two groups of cortical neural ensembles oppositely modulate pain- or itch-related sensory and emotional behaviors through their preferential projections to specific downstream regions such as the mediodorsal thalamus (MD) and basolateral amygdala (BLA). These findings uncover separate representations of pain and itch by distinct prefrontal neural ensembles and provide a new framework for understanding somatosensory information processing in the brain.

Artificial nano-red blood cells nanoplatform with lysosomal escape capability for ultrasound imaging-guided on-demand pain management

Postoperative pain management would benefit significantly from an anesthetic that could take effect in an on-demand manner. An ultrasound would be an appropriate tool for such nanoplatform because it is widely used in clinical settings for ultrasound-guided anesthesia. Herein, we report a nanoplatform for postoperative on-demand pain management that can effectively enhance their analgesic time while providing ultrasonic imaging. Levobupivacaine and perfluoropentane were put into dendritic mesoporous silica and covered with red blood cell membranes to make the pain relief last longer in living organisms. The generated nanoplatform with gas-producing capability is ultrasonic responsive and can finely escape from the lysosomal in cells under ultrasound irradiation, maximizing the anesthetic effect with minimal toxicity. Using an incision pain model in vivo, levobupivacaine's sustained and controlled release gives pain reduction for approximately 3 days straight. The duration of pain relief is over 20 times greater than with a single injection of free levobupivacaine. Effective pain management was reached in vivo, and the pain reduction was enhanced by repeated ultrasonic irradiation. There was no detectable systemic or tissue injury under either of the treatments. Thus, our results suggest that nanoplatform with lysosomal escape capability can provide a practical ultrasound imaging-guided on-demand pain management strategy. STATEMENT OF SIGNIFICANCE: On-demand pain management is essential to postoperative patients. However, the traditional on-demand pain management strategy is hampered by the limited tissue penetration depth of near-infrared stimuli and the lack of proper imaging guidance. The proposed research is significant because it provides a nanoplatform for deep penetrated ultrasound controlled pain management under clinical applicable ultrasound imaging guidance. Moreover, the nanoplatform with prolonged retention time and lysosomal escape capability can provide long-term pain alleviation. Therefore, our results suggest that nanoplatform with lysosomal escape capability can provide an effective strategy for ultrasound imaging-guided on-demand pain management.

ErbB4+ spinal cord dorsal horn neurons process heat pain

How the spinal cord transmits heat signals from the periphery to the brain remains unclear. In this issue of Neuron, Wang et al. (2022) identify a population of spinal cord neurons functioning in this pathway.