Peripheral Sensory Neurons Research Articles

Neuromedin B Induces Acute Itch in Mice via the Activation of Peripheral Sensory Neurons.

Neuromedin B is expressed in nociceptive and itch-sensitive dorsal root ganglia neurons, but its peripheral pruritogenic potential is not well described. The potential of neuromedin B as a pruritogen and pro-inflammatory peptide in the skin was tested in vivo in an acute model in mice and monkeys as well as an allergic dermatitis model in mice. To identify the underlying mechanisms in vitro real time PCR analysis for neuromedin B and its receptor expression in murine mast cells and dorsal root ganglia as well as functional calcium imaging in the ganglia was applied. Neuromedin B induces itch when injected intradermally, and the peripheral signal is likely transmitted through the activation of dorsal root ganglia. Thus, neuromedin B could be an interesting new therapeutic target for peripheral processing of itch at the level of sensory neurons.

Potency of descending pain modulatory system is linked with peripheral sensory dysfunction in fibromyalgia: An exploratory study.

Fibromyalgia (FM) is characterized by chronic widespread pain whose pathophysiological mechanism is related to central and peripheral nervous system dysfunction. Neuropathy of small nerve fibers has been implicated due to related pain descriptors, psychophysical pain, and neurophysiological testing, as well as skin biopsy studies. Nevertheless, this alteration alone has not been previously associated to the dysfunction in the descending pain modulatory system (DPMS) that is observed in FM. We hypothesize that they associated, thus, we conducted a cross-sectional exploratory study.To explore small fiber dysfunction using quantitative sensory testing (QST) is associated with the DPMS and other surrogates of nociceptive pathways alterations in FM.We run a cross-sectional study and recruited 41 women with FM, and 28 healthy female volunteers. We used the QST to measure the thermal heat threshold (HTT), heat pain threshold (HPT), heat pain tolerance (HPT), heat pain tolerance (HPTo), and conditional pain modulation task (CPM-task). Algometry was used to determine the pain pressure threshold (PPT). Scales to assess catastrophizing, anxiety, depression, and sleep disturbances were also applied. Serum brain-derived neurotrophic factor (BDNF) was measured as a marker of neuroplasticity. We run multivariate linear regression models by group to study their relationships.Samples differed in their psychophysical profile, where FM presented lower sensitivity and pain thresholds. In FM but not in the healthy subjects, regression models revealed that serum BDNF was related to HTT and CPM-Task (Hotelling Trace = 1.80, P < .001, power = 0.94, R2 = 0.64). HTT was directly related to CPM-Task (B = 0.98, P = .004, partial-η2 = 0.25), and to HPT (B = 1.61, P = .008, partial η2 = 0.21), but not to PPT. Meanwhile, BDNF relationship to CPM-Task was inverse (B = –0.04, P = .043, partial-η2 = 0.12), and to HPT was direct (B = –0.08, P = .03, partial-η2 = 0.14).These findings high spot that in FM the disinhibition of the DPMS is positively correlated with the dysfunction in peripheral sensory neurons assessed by QST and conversely with serum BDNF.

Regenerative activity of Hericium erinaceus on axonal injury model using in vitro laser microdissection technique

ABSTRACTObjective: Peripheral nerve injury (PNI) is an important global health problem. Nerve Growth Factor (NGF) plays crucial role in the survival, growth, and maintenance of various neurons in the mammalian nervous system, human included. Hericium erinaceus (HE), an edible and medicinal mushroom, has been extensively studied for its neuroprotective properties. In this study, the neuroprotective and neurotogenic effects of HE and NGF were compared on mouse PNI model by using a laser microdissection technique.Methods: Neuronal cultures were prepared from dorsal root ganglia (DRG) of 6–8 week aged mice, pretreated them with phosphate-buffered saline (PBS), NGF, HE, or the combination of NGF and HE. To model axonal injury in vitro, axons were cut (axotomy) with a microscope-controlled laser beam. Axotomized neurons were imaged under the microscope. Axotomized neurons’ survival ratios were calculated using the propidium iodide (PI), which is a red-fluorescent nuclear dye. Their axon lengths were measured using the AxioVision 4.8 software.Results: Although both HE and NGF have neuroprotective and regenerative effects on axotomized peripheral sensory neurons, HE exhibits a higher neuroprotective activity compared to the NGF. The combination of HE and NGF maximizes axonal regeneration ability of axotomized neurons.Conclusion: HE has capabilities of preventing the death of neurons and regenerating their axons in the experimental axonal injury model. Our findings provide experimental evidence that HE may serve as a neuroprotective and regenerative candidate for treating peripheral nerve injuries. Present study warrants further investigation of HE as a potential natural compound to remedy PNI.

Mu-Opioid Receptor Agonist Induces Kir3 Currents in Mouse Peripheral Sensory Neurons - Effects of Nerve Injury.

Neuropathic pain often arises from damage to peripheral nerves and is difficult to treat. Activation of opioid receptors in peripheral sensory neurons is devoid of respiratory depression, sedation, nausea, and addiction mediated in the brain, and ameliorates neuropathic pain in animal models. Mechanisms of peripheral opioid analgesia have therefore gained interest, but the role of G protein-coupled inwardly rectifying potassium (Kir3) channels, important regulators of neuronal excitability, remains unclear. Whereas functional Kir3 channels have been detected in dorsal root ganglion (DRG) neurons in rats, some studies question their contribution to opioid analgesia in inflammatory pain models in mice. However, neuropathic pain can be diminished by activation of peripheral opioid receptors in mouse models. Therefore, here we investigated effects of the selective μ-opioid receptor (MOR) agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) on potassium conductance in DRG neurons upon a chronic constriction injury (CCI) of the sciatic nerve in mice. For verification, we also tested human embryonic kidney (HEK) 293 cells transfected with MOR and Kir3.2. Using patch clamp, we recorded currents at -80 mV and applied voltage ramps in high extracellular potassium concentrations, which are a highly sensitive measures of Kir3 channel activity. We found a significantly higher rate of HEK cells responding with potassium channel blocker barium-sensitive inward current (233 ± 51 pA) to DAMGO application in transfected than in untransfected group, which confirms successful recordings of inward currents through Kir3.2 channels. Interestingly, DAMGO induced similar inward currents (178 ± 36–207 ± 56 pA) in 15–20% of recorded DRG neurons from naïve mice and in 4–27% of DRG neurons from mice exposed to CCI, measured in voltage clamp or voltage ramp modes. DAMGO-induced currents in naïve and CCI groups were reversed by barium and a more selective Kir3 channel blocker tertiapin-Q. These data indicate the coupling of Kir3 channels with MOR in mouse peripheral sensory neuron cell bodies, which was unchanged after CCI. A comparative analysis of opioid-induced potassium conductance at the axonal injury site and peripheral terminals of DRG neurons could clarify the role of Kir3 channel–MOR interactions in peripheral nerve injury and opioid analgesia.

Epigenetic regulator UHRF1 inactivates REST and growth suppressor gene expression via DNA methylation to promote axon regeneration.

Injured peripheral sensory neurons switch to a regenerative state after axon injury, which requires transcriptional and epigenetic changes. However, the roles and mechanisms of gene inactivation after injury are poorly understood. Here, we show that DNA methylation, which generally leads to gene silencing, is required for robust axon regeneration after peripheral nerve lesion. Ubiquitin-like containing PHD ring finger 1 (UHRF1), a critical epigenetic regulator involved in DNA methylation, increases upon axon injury and is required for robust axon regeneration. The increased level of UHRF1 results from a decrease in miR-9. The level of another target of miR-9, the transcriptional regulator RE1 silencing transcription factor (REST), transiently increases after injury and is required for axon regeneration. Mechanistically, UHRF1 interacts with DNA methyltransferases (DNMTs) and H3K9me3 at the promoter region to repress the expression of the tumor suppressor gene phosphatase and tensin homolog (PTEN) and REST. Our study reveals an epigenetic mechanism that silences tumor suppressor genes and restricts REST expression in time after injury to promote axon regeneration.

Resilience to Pain: A Peripheral Component Identified Using Induced Pluripotent Stem Cells and Dynamic Clamp.

Pain is a complex process that involves both detection in the peripheral nervous system and perception in the CNS. Individual-to-individual differences in pain are well documented, but not well understood. Here we capitalized on inherited erythromelalgia (IEM), a well characterized human genetic model of chronic pain, and studied a unique family containing related IEM subjects with the same disease-causing NaV1.7 mutation, which is known to make dorsal root ganglion (DRG) neurons hyperexcitable, but different pain profiles (affected son with severe pain, affected mother with moderate pain, and an unaffected father). We show, first, that, at least in some cases, relative sensitivity to pain can be modeled in subject-specific induced pluripotent stem cell (iPSC)-derived sensory neurons in vitro; second, that, in some cases, mechanisms operating in peripheral sensory neurons contribute to interindividual differences in pain; and third, using whole exome sequencing (WES) and dynamic clamp, we show that it is possible to pinpoint a specific variant of another gene, KCNQ in this particular kindred, that modulates the excitability of iPSC-derived sensory neurons in this family. While different gene variants may modulate DRG neuron excitability and thereby contribute to interindividual differences in pain in other families, this study shows that subject-specific iPSCs can be used to model interindividual differences in pain. We further provide proof-of-principle that iPSCs, WES, and dynamic clamp can be used to investigate peripheral mechanisms and pinpoint specific gene variants that modulate pain signaling and contribute to interindividual differences in pain.SIGNIFICANCE STATEMENT Individual-to-individual differences in pain are well documented, but not well understood. In this study, we show, first, that, at least in some cases, relative sensitivity to pain can be modeled in subject-specific induced pluripotent stem cell-derived sensory neurons in vitro; second, that, in some cases, mechanisms operating in peripheral sensory neurons contribute to interindividual differences in pain; and third, using whole exome sequencing and dynamic clamp, we show that it is possible to pinpoint a specific gene variant that modulates pain signaling and contributes to interindividual differences in pain.

High-resolution ultramicroscopy of the developing and adult nervous system in optically cleared Drosophila melanogaster

The fruit fly, Drosophila melanogaster, is an important experimental model to address central questions in neuroscience at an organismic level. However, imaging of neural circuits in intact fruit flies is limited due to structural properties of the cuticle. Here we present a novel approach combining tissue clearing, ultramicroscopy, and data analysis that enables the visualisation of neuronal networks with single-cell resolution from the larval stage up to the adult Drosophila. FlyClear, the signal preserving clearing technique we developed, stabilises tissue integrity and fluorescence signal intensity for over a month and efficiently removes the overall pigmentation. An aspheric ultramicroscope set-up utilising an improved light-sheet generator allows us to visualise long-range connections of peripheral sensory and central neurons in the visual and olfactory system. High-resolution 3D reconstructions with isotropic resolution from entire GFP-expressing flies are obtained by applying image fusion from orthogonal directions. This methodological integration of novel chemical, optical, and computational techniques allows a major advance in the analysis of global neural circuit organisation.

In vitro effects of soluble epoxide hydrolase inhibition on chondrocyte apoptosis and sensitization of peripheral sensory neurons

Introduction: Chondrocyte apoptosis and neuronal sensitization are prominent features of osteoarthritis (OA) that are difficult to control with currently available therapies.

Development and validation of an in vitro model system to study peripheral sensory neuron development and injury

The ability to discriminate between diverse types of sensation is mediated by heterogeneous populations of peripheral sensory neurons. Human peripheral sensory neurons are inaccessible for research and efforts to study their development and disease have been hampered by the availability of relevant model systems. The in vitro differentiation of peripheral sensory neurons from human embryonic stem cells therefore provides an attractive alternative since an unlimited source of biological material can be generated for studies that specifically address development and injury. The work presented in this study describes the derivation of peripheral sensory neurons from human embryonic stem cells using small molecule inhibitors. The differentiated neurons express canonical- and modality-specific peripheral sensory neuron markers with subsets exhibiting functional properties of human nociceptive neurons that include tetrodotoxin-resistant sodium currents and repetitive action potentials. Moreover, the derived cells associate with human donor Schwann cells and can be used as a model system to investigate the molecular mechanisms underlying neuronal death following peripheral nerve injury. The quick and efficient derivation of genetically diverse peripheral sensory neurons from human embryonic stem cells offers unlimited access to these specialised cell types and provides an invaluable in vitro model system for future studies.

Hypoxia-inducible factor 1α protects peripheral sensory neurons from diabetic peripheral neuropathy by suppressing accumulation of reactive oxygen species.

Diabetic peripheral neuropathy (DPN) is one of the most common diabetic complications. Mechanisms underlying nerve damage and sensory loss following metabolic dysfunction remain largely unclear. Recently, hyperglycemia-induced mitochondrial dysfunction and the generation of reactive oxygen species (ROS) have gained attention as possible mechanisms of organ damage in diabetes. Hypoxia-inducible factor 1 (HIF1α) is a key transcription factor activated by hypoxia, hyperglycemia, nitric oxide as well as ROS, suggesting a fundamental role in DPN susceptibility. We analyzed regulation of HIF1α in response to prolonged hyperglycemia. Genetically modified mutant mice, which conditionally lack HIF1α in peripheral sensory neurons (SNS-HIF1α-/-), were analyzed longitudinally up to 6months in the streptozotocin (STZ) model of type1 diabetes. Behavioral measurements of sensitivity to thermal and mechanical stimuli, quantitative morphological analyses of intraepidermal nerve fiber density, measurements of ROS, ROS-induced cyclic GMP-dependent protein kinase 1α (PKG1α), and levels of vascular endothelial growth factor (VEGF) in sensory neurons in vivo were undertaken over several months post-STZ injections to delineate the role of HIF1α in DPN. Longitudinal behavioral and morphological analyses at 5, 13, and 24weeks post-STZ treatment revealed that SNS-HIF1α-/- developed stronger hyperglycemia-evoked losses of peripheral nociceptive sensory axons associated with stronger losses of mechano- and heat sensation with a faster onset than HIF1αfl/fl mice. Mechanistically, these histomorphologic, behavioral, and biochemical differences were associated with a significantly higher level of STZ-induced production of ROS and ROS-induced PKG1α dimerization in sensory neurons of SNS-HIF1α-/- mice as compared with HIF1αfl/fl. We found that prolonged hyperglycemia induced VEGF expression in the sciatic nerve which is impaired in SNS-HIF1α mice. Our results indicate that HIF1α is as an upstream modulator of ROS in peripheral sensory neurons and exerts a protective function in suppressing hyperglycemia-induced nerve damage by limiting ROS levels and by inducing expression of VEGF which may promote peripheral nerve survival. Our data suggested that HIF1α stabilization may be thus a new strategy target for limiting sensory loss, a debilitating late complication of diabetes. KEY MESSAGES: • Impaired hypoxia-inducible factor 1α (HIF1α) signaling leads to early onset of STZ-induced loss of sensation in mice. • STZ-induced loss of sensation in HIF1α mutant mice is associated with loss of sensory nerve fiber in skin. • Activation of HIF1α signaling in diabetic mice protects the sensory neurons by limiting ROS formation generated due to mitochondrial dysfunction and by inducing VEGF expression.

Transient receptor potential vanilloid 1-6 (Trpv1-6) gene expression in the mouse brain during estrous cycle

In recent years estradiol has emerged as a potential regulator of transient receptor potential vanilloid (TRPV) cationic channels in the peripheral tissues and sensory neurons, however, its analogous role in the CNS is poorly understood. TRPV channels modulate Ca2+ signalling, neurotransmission and behaviour, and expression of these ion channels and estrogen receptors show a great degree of overlap in different brain regions. Herein, we probe if Trpv1-6 genes contain estrogen receptor-binding sites and if their expression in different brain regions is modulated during estrous cycle. Bioinformatics analysis of the mouse Trpv1-6 gene sequences showed presence of putative functional estrogen response element in their promoter regions. Using qRT-PCR, Trpv1-6 mRNA expression was observed in the olfactory bulb, cortex, hypothalamus, hippocampus, brainstem, and cerebellum of mouse. In these regions, compared to estrus, metestrus, and diestrus, reduced levels of Trpv1 and Trpv5 but elevated Trpv2 and Trpv6 mRNA levels were observed during proestrus. Lower levels of Trpv3 and Trpv4 mRNAs were seen during estrus but higher expression of Trpv3 during metestrus and diestrus, and Trpv4 during proestrus was observed. Estradiol seems to regulate Trpv1/Trpv5 and Trpv2/Trpv6 mRNA expression in opposite manner. Except Trpv4 mRNA expression in the hippocampus and Trpv6 expression in the olfactory bulb, hippocampus and brainstem, expression of other members of TRPV subfamily in distinct brain regions of male mice was comparable to those in metestrus and diestrus mice. We suggest that the circulating levels of estradiol during the estrous cycle may differentially regulate the activity of TRPV1-6 ion channels in the brain.

Expression and Manipulation of the APC-\u03b2-Catenin Pathway During Peripheral Neuron Regeneration

Molecules and pathways that suppress growth are expressed in postmitotic neurons, a potential advantage in mature neural networks, but a liability during regeneration. In this work, we probed the APC (adenomatous polyposis coli)-β-catenin partner pathway in adult peripheral sensory neurons during regeneration. APC had robust expression in the cytoplasm and perinuclear region of adult DRG sensory neurons both before and after axotomy injury. β-catenin was expressed in neuronal nuclei, neuronal cytoplasm and also in perineuronal satellite cells. In injured dorsal root ganglia (DRG) sensory neurons and their axons, we observed paradoxical APC upregulation, despite its role as an inhibitor of growth whereas β-catenin was downregulated. Inhibition of APC in adult sensory neurons and activation of β-catenin, LEF/TCF transcriptional factors were associated with increased neuronal plasticity in vitro. Local knockdown of APC, at the site of sciatic nerve crush injury enhanced evidence for electrophysiological, behavioural and structural regeneration in vivo. This was accompanied by upregulation of β-catenin. Collectively, the APC-β-catenin-LEF/TCF transcriptional pathway impacts intrinsic mechanisms of axonal regeneration and neuronal plasticity after injury, offering new options for addressing axon regeneration.

Peripheral Kappa Opioid Receptor Signaling Takes on a Central Role

With the current unmet demand for effective analgesics and the opioid crisis, pain relief without major central adverse effects is highly appealing. In this issue of Neuron, Snyder etal. (2018) report on the localization, functions, and therapeutic potential of kappa opioid receptors in peripheral sensory neurons.

Generation of iPSC-Derived Human Peripheral Sensory Neurons Releasing Substance P Elicited by TRPV1 Agonists.

Neural crest stem cells (NCPCs) have been shown to differentiate into various cell types and tissues during embryonic development, including sensory neurons. The few studies addressing the generation of NCPCs and peripheral sensory neurons (PSNs) from human induced pluripotent stem cells (hiPSCs), generated sensory cells without displaying robust activity. Here, we describe an efficient strategy for hiPSCs differentiation into NCPCs and functional PSNs using chemically defined media and factors to achieve efficient differentiation, confirmed by the expression of specific markers. After 10 days hiPSCs differentiated into NCPCs, cells were then maintained in neural induction medium containing defined growth factors for PSNs differentiation, followed by 10 days in neonatal human epidermal keratinocytes- (HEKn-) conditioned medium (CM). We observed a further increase in PSN markers expression and neurites length after CM treatment. The resulting neurons elicited action potentials after current injection and released substance P (SP) in response to nociceptive agents such as anandamide and resiniferatoxin. Anandamide induced substance P release via activation of TRPV1 and not CB1. Transcriptomic analysis of the PSNs revealed the main dorsal root ganglia neuronal markers and a transcriptional profile compatible with C fiber-low threshold mechanoreceptors. TRPV1 was detected by immunofluorescence and RNA-Seq in multiple experiments. In conclusion, the developed strategy generated PSNs useful for drug screening that could be applied to patient-derived hiPSCs, consisting in a powerful tool to model human diseases in vitro.

Reduced mitochondrial reactive oxygen species production in peripheral nerves of mice fed a ketogenic diet.

What is the central question of this study? Do peripheral sensory neurons metabolize fat-based fuel sources, and does a ketogenic diet modify these processes? What is the main finding and its importance We show that peripheral axons from mice fed a ketogenic diet respond to fat-based fuel sources with reduced respiration and H2 O2 emission compared with mice fed a control diet. These results add to our understanding of the responses of sensory neurons to neuropathy associated with poor diet, obesity and metabolic syndrome. These findings should be incorporated into current ideas of axonal protection and might identify how dietary interventions may change mitochondrial function in settings of sensory dysfunction. Metabolic syndrome and obesity are increasing epidemics that significantly impact the peripheral nervous system and lead to negative changes in sensation and peripheral nerve function. Research to understand the consequences of diet, obesity and fuel usage in sensory neurons has commonly focused on glucose metabolism. Here, we tested whether mouse sensory neurons and nerves have the capacity to metabolize fat-based fuels (palmitoyl-CoA) and whether these effects are altered by feeding of a ketogenic (90%kcal fat) diet compared with a control diet (14%kcal fat). Male C57Bl/6 mice were placed on the diets for 10weeks, and after the mice were killed, the dorsal root ganglion (DRG) and sciatic nerve (SN) were placed in an Oroboros oxygraph-2K to examine diet-induced alterations in metabolism (respiration) of palmitoyl-CoA and H2 O2 emission (fluorescence). In addition, RNAseq was performed on the DRG of mice fed a control or a ketogenic diet for 12weeks, and genes associated with mitochondrial respiratory function were analysed. Our results suggest that the sciatic nerves from mice fed a ketogenic diet display reduced O2 respiration and H2 O2 emission when metabolizing palmitoyl-CoA compared with mice fed a control diet. Assessments of changes in mRNA gene expression reveal alterations in genes encoding the NADH dehydrogenase complex and complexIV, which could alter production of reactive oxygen species. These new findings highlight the ability of sensory neurons and axons to oxidize fat-based fuel sources and show that these mechanisms are adaptable to dietary changes.

The extracellular matrix glycoprotein tenascin-X regulates peripheral sensory and motor neurones.

Key points Tenascin‐X (TNX) is an extracellular matrix glycoprotein with anti‐adhesive properties in skin and joints. Here we report the novel finding that TNX is expressed in human and mouse gut tissue where it is exclusive to specific subpopulations of neurones.Our studies with TNX‐deficient mice show impaired defecation and neural control of distal colonic motility that can be rescued with a 5‐HT4 receptor agonist. However, colonic secretion is unchanged. They are also susceptible to internal rectal intussusception. Colonic afferent sensitivity is increased in TNX‐deficient mice. Correspondingly, there is increased density of and sensitivity of putative nociceptive fibres in TNX‐deficient mucosa.A group of TNX‐deficient patients report symptoms highly consistent with those in the mouse model.These findings suggest TNX plays entirely different roles in gut to non‐visceral tissues – firstly a role in enteric motor neurones and secondly a role influencing nociceptive sensory neuronesStudying further the mechanisms by which TNX influences neuronal function will lead to new targets for future treatment. The extracellular matrix (ECM) is not only an integral structural molecule, but is also critical for a wide range of cellular functions. The glycoprotein tenascin‐X (TNX) predominates in the ECM of tissues like skin and regulates tissue structure through anti‐adhesive interactions with collagen. Monogenic TNX deficiency causes painful joint hypermobility and skin hyperelasticity, symptoms characteristic of hypermobility Ehlers Danlos syndrome (hEDS). hEDS patients also report consistently increased visceral pain and gastrointestinal (GI) dysfunction. We investigated whether there is a direct link between TNX deficiency and GI pain or motor dysfunction. We set out first to learn where TNX is expressed in human and mouse, then determine how GI function, specifically in the colon, is disordered in TNX‐deficient mice and humans of either sex. In human and mouse tissue, TNX was predominantly associated with cholinergic colonic enteric neurones, which are involved in motor control. TNX was absent from extrinsic nociceptive peptidergic neurones. TNX‐deficient mice had internal rectal prolapse and a loss of distal colonic contractility which could be rescued by prokinetic drug treatment. TNX‐deficient patients reported increased sensory and motor GI symptoms including abdominal pain and constipation compared to controls. Despite absence of TNX from nociceptive colonic neurones, neuronal sprouting and hyper‐responsiveness to colonic distension was observed in the TNX‐deficient mice. We conclude that ECM molecules are not merely support structures but an integral part of the microenvironment particularly for specific populations of colonic motor neurones where TNX exerts functional influences.

Therapeutic Applications of Capsaicin in Upper Airways.

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the substance responsible of the irritation caused by the contact of chili peppers with the skin or mucous membranes. This protoalkaloid acts by stimulating the transient receptor potential cation channel subfamily V member 1 (TRPV1), which is mainly expressed by nociceptive fibers of peripheral sensory neurons, but is also present in the central nervous system, and in some non-neuronal cells. Following the initial, intense neuronal excitation, a brief refractory period occurs. However, repeated and massive exposures to capsaicin can impair nociceptive fiber function for weeks or months. During this lapse of time, disorders related to the hyperreactivity of peripheral nociceptors are abolished or greatly reduced. Capsaicin has been utilized to treat several diseases of upper airways. The objective of this review was to report the latest findings on the use of Capsaicin in the treatment of upper airway diseases. Capsaicin effectiveness has been proved in non allergic rhinitis. Some studies suggest that this substance may be also effective in nasal polyposis and in the burning mouth syndrome. No clear evidence has been obtained about its use in allergic rhinitis. To date, the use of capsaicin to treat upper airway diseases is still limited in clinical practice. This may originate by the lack of strong, conclusive evidences of its effectiveness, by the variety of therapeutic schemes used in literature, and finally by the unpleasant effects of the exposure to capsaicin, which are only partly relieved by the pretreatment with local anesthetics.

Abstract 1057: Characterization and functional consequences of neuronal invasion in oral cancer

Abstract Most oral cancer patients suffer severe, chronic pain promoted by oral cancer-induced changes in sensory nerves innervating the oral cavity. However, the impact of sensory neurons on carcinogenesis beyond nociceptive signaling is an understudied problem in oral cancer. We hypothesize that oral cancer and sensory neurons interact, such that, oral cancer induces sensitization, sprouting and plasticity in neurons, and efferent neuronal activity promotes oral carcinogenesis. Using an oral cancer subcutaneous xenograft model, we tested the impact of peripheral nerve presence on squamous cell carcinoma tumor growth in the mouse hindpaw. Mice that received a sciatic nerve axotomy one week prior to HSC-3 oral cancer cell inoculation developed significantly smaller tumors (28.23 ± 6.6 % of total paw area) compared to mice that received sham surgery (50.71 ± 2.48 %). These data suggest that peripheral neuron innervation supports oral cancer growth. Additionally, neuropeptides are released from primary afferent neurons and suppression of the immune response has been linked to peripheral neurotransmission. Using flow cytometry, we tested whether inhibition of peripheral sensory neurons impacted inflammation in response to oral cancer. Temporary nerve block with 1% bupivacaine injection into the lingual nerve prior to injection of supernatant from HSC-3 oral cancer cells resulted in significantly more CD45+ immune cell infiltration (21.66 ± 3.4 %) into the tongue compared to HSC-3 supernatant with intact nerve function (9.10 ± 1.2 %). These results suggest neuron-mediated suppression of cancer-evoked inflammation and support the premise that neurons and neuronal activity modulates the oral cancer microenvironment. High-resolution imaging of neuronal innervation into tongue cancer and its remodeling in response to pathological changes is challenging due to dense neuronal innervation in the tongue. We utilized a recently developed optical clearing protocol (CLARITY) that preserves protein integrity and three-dimensional structure of tissue and high-resolution microscopy to visualize and characterize sensory neuron innervation in thick 1 mm tongue sections from an orthotopic xenograft mouse model of oral cancer. In a preliminary study of neuronal innervation in a tongue HSC-3 xenograft model, we observed that PGP9.5+ neuronal fiber density was greater in the cancer environment and diminished with distance from the cancer. These data suggest that oral cancer induces plasticity and sprouting of innervating peripheral neurons. A better understanding of the nerve-cancer interaction has potential for development of new therapeutic strategies to treat oral cancer and oral cancer pain by targeting sensory neurons. Citation Format: Nicole N. Scheff, Richard Klares, Brian L. Schmidt. Characterization and functional consequences of neuronal invasion in oral cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1057.

Evolution of a central neural circuit underlies Drosophila mate preferences.

Courtship rituals serve to reinforce reproductive barriers between closely related species. Drosophila melanogaster and D. simulans exhibit reproductive isolation due, in part, to the fact that D. melanogaster females produce 7,11-heptacosadiene (7,11-HD), a pheromone that promotes courtship in D. melanogaster males but suppresses courtship in D. simulans males. Here we compare pheromone-processing pathways in D. melanogaster and D. simulans males to define how these sister species endow 7,11-HD with the opposite behavioral valence to underlie species discrimination. We show that males of both species detect 7,11-HD using the homologous peripheral sensory neurons but this signal is differentially propagated to the P1 neurons that control courtship behavior. A change in the balance of excitation and inhibition onto courtship-promoting neurons transforms an excitatory pheromonal cue in D. melanogaster into an inhibitory cue in D. simulans. Our results reveal how species-specific pheromone responses can emerge from conservation of peripheral detection mechanisms and diversification of central circuitry and illustrate how flexible nodes in neural circuits can contribute to behavioral evolution.

Dialing down the opioids

Pain The pain relief afforded by morphine and other opioids comes with the cost of behavioral side effects and high addiction potential. He et al. found that the analgesic response to morphine could be enhanced by compounds that activate the peripheral sensory neuron–localized receptor MrgC11 in mice and MrgX1 in humans. Activation of MrgC11 promoted its interaction with the µ-opioid receptor. This interaction enabled the use of lower morphine doses to achieve pain relief in mice, without the tolerance and locomotor side effects typically associated with the drug. Sci. Signal. 11 , eaao3134 (2018).