Sensory Neurons Of Trigeminal Ganglia Research Articles

Stress Can Induce Bovine Alpha-Herpesvirus 1 (BoHV-1) Reactivation from Latency.

Bovine alpha-herpesvirus 1 (BoHV-1) is a significant problem for the cattle industry, in part because the virus establishes latency, and stressful stimuli increase the incidence of reactivation from latency. Sensory neurons in trigeminal ganglia and unknown cells in pharyngeal tonsils are importantsites for latency. Reactivation from latency can lead to reproductive problems in pregnant cows, virus transmission to young calves, suppression of immune responses, and bacterial pneumonia. BoHV-1 is also a significant cofactor in bovine respiratory disease (BRD). Stress, as mimicked by the synthetic corticosteroid dexamethasone, reproducibly initiates reactivation from latency. Stress-mediated activation of the glucocorticoid receptor (GR) stimulates viral replication and transactivation of viral promoters that drive the expression of infected cell protein 0 (bICP0) and bICP4. Notably, GR and Krüppel-like factor 15 (KLF15) form a feed-forward transcription loop that cooperatively transactivates immediate early transcription unit 1 (IEtu1 promoter). Two pioneer transcription factors, GR and KLF4, cooperatively transactivate the bICP0 early promoter. Pioneer transcription factors bind silent viral heterochromatin, remodel chromatin, and activate gene expression. Thus, wepredict that these novel transcription factors mediate early stages of BoHV-1 reactivation from latency.

Examination of neuro-inflammation and senescence in brainstem of aged mice latently infected with human alphaherpesvirus 1 (HSV-1)

Human alphaherpesvirus 1 (HSV-1) establishes life-long latency in sensory neurons in trigeminal ganglia (TG), brainstem neurons, and other CNS neurons. Two important segments of the brainstem were examined in this study: principal sensory nucleus of the spinal trigeminal tract (Pr5) because it receives direct afferent inputs from TG, and locus coeruleus (LC) because it is indirectly connected to Pr5 and LC sends axonal projections to cortical structures, which may facilitate viral spread from brainstem to the brain. The only viral gene abundantly expressed during latency is the latency associated transcript (LAT). Previous studies revealed 8-week old female C57Bl/6 mice infected with a LAT null mutant (dLAT2903) versus wild-type (wt) HSV-1 exhibit higher levels of senescence markers and inflammation in LC of females. New studies revealed 1-year old mice latently infected with wt HSV-1 or dLAT2903 contained differences in neuroinflammation and senescence in Pr5 and LC versus young mice. In summary, these studies confirm HSV-1 promotes neuro-inflammation in the brainstem, which may accelerate neurodegenerative disease.

Quercetin, Main Active Ingredient of Moutan Cortex, Alleviates Chronic Orofacial Pain via Block of Voltage-Gated Sodium Channel.

Chronic orofacial pain (COP) therapy is challenging, as current medical treatments are extremely lacking. Moutan Cortex (MC) is a traditional Chinese medicine herb widely used for chronic inflammatory diseases. However, the mechanism behind MC in COP therapy has not been well-established. The purpose of this study was to identify the active ingredients of MC and their specific underlying mechanisms in COP treatment. In this study, the main active ingredients and compound-target network of MC in COP therapy were identified through network pharmacology and bioinformatics analysis. Adult male Sprague-Dawley rats received oral mucosa lipopolysaccharide (LPS) injection to induce COP. Pain behaviors were evaluated by orofacial mechanical nociceptive assessment after intraganglionar injection. In vitro inflammatory cytokines in LPS-pretreated human periodontal ligament stem cells (hPDLSCs) and rat primary cultural trigeminal ganglion (TG) neurons were quantified by real-time quantitative polymerase chain reaction (RT-qPCR). Schrödinger software was used to verify the molecular docking of quercetin and critical targets. Whole-cell recording electrophysiology was used to evaluate the effect of quercetin on voltage-gated sodium (Na v ) channel in rat TG neurons. The assembled compound-target network consisted of 4 compounds and 46 targets. As 1 of the active components of MC correlated with most related targets, quercetin alleviated mechanical allodynia in LPS-induced rat model of COP (mechanical allodynia threshold median [interquartile range (IQR) 0.5 hours after drug administration: vehicle 1.3 [0.6-2.0] g vs quercetin 7.0 [6.0-8.5] g, P = .002). Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that immune response and membrane functions play essential roles in MC-COP therapy. Five of the related targets were identified as core targets by protein-protein interaction analysis. Quercetin exerted an analgesic effect, possibly through blocking Na v channel in TG sensory neurons (peak current density median [IQR]: LPS -850.2 [-983.6 to -660.7] mV vs LPS + quercetin -589.6 [-711.0 to -147.8] mV, P = .006) while downregulating the expression level of proinflammatory cytokines-FOS (normalized messenger RNA [mRNA] level mean ± standard error of mean [SEM]: LPS [2. 22 ± 0.33] vs LPS + quercetin [1. 33 ± 0.14], P = .034) and TNF-α (normalized mRNA level mean ± SEM: LPS [8. 93 ± 0.78] vs LPS + quercetin [3. 77 ± 0.49], P < .0001). Identifying Na v as the molecular target of quercetin clarifies the analgesic mechanism of MC, and provides ideas for the development of novel selective and efficient chronic pain relievers.

The miR-183/96/182 cluster regulates sensory innervation, resident myeloid cells and functions of the cornea through cell type-specific target genes

The conserved miR-183/96/182 cluster (miR-183C) is expressed in both corneal resident myeloid cells (CRMCs) and sensory nerves (CSN) and modulates corneal immune/inflammatory responses. To uncover cell type-specific roles of miR-183C in CRMC and CSN and their contributions to corneal physiology, myeloid-specific miR-183C conditional knockout (MS-CKO), and sensory nerve-specific CKO (SNS-CKO) mice were produced and characterized in comparison to the conventional miR-183C KO. Immunofluorescence and confocal microscopy of flatmount corneas, corneal sensitivity, and tear volume assays were performed in young adult naïve mice; 3′ RNA sequencing (Seq) and proteomics in the trigeminal ganglion (TG), cornea and CRMCs. Our results showed that, similar to conventional KO mice, the numbers of CRMCs were increased in both MS-CKO and SNS-CKO vs age- and sex-matched WT control littermates, suggesting intrinsic and extrinsic regulations of miR-183C on CRMCs. The number of CRMCs was increased in male vs female MS-CKO mice, suggesting sex-dependent regulation of miR-183C on CRMCs. In the miR-183C KO and SNS-CKO, but not the MS-CKO mice, CSN density was decreased in the epithelial layer of the cornea, but not the stromal layer. Functionally, corneal sensitivity and basal tear volume were reduced in the KO and SNS-CKO, but not the MS-CKO mice. Tear volume in males is consistently higher than female WT mice. Bioinformatic analyses of the transcriptomes revealed a series of cell-type specific target genes of miR-183C in TG sensory neurons and CRMCs. Our data elucidate that miR-183C imposes intrinsic and extrinsic regulation on the establishment and function of CSN and CRMCs by cell-specific target genes. miR-183C modulates corneal sensitivity and tear production through its regulation of corneal sensory innervation.

Specificity protein 1 (Sp1) and glucocorticoid receptor (GR) stimulate bovine alphaherpesvirus 1 (BoHV-1) replication and cooperatively transactivate the immediate early transcription unit 1 promoter.

Bovine alphaherpesvirus 1 (BoHV-1) infections cause respiratory tract disorders and suppress immune responses, which can culminate in bacterial pneumonia. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons present in trigeminal ganglia (TG) and unknown cells in pharyngeal tonsil. Latently infected calves consistently reactivate from latency after an intravenous injection of the synthetic corticosteroid dexamethasone (DEX), which mimics the effects of stress. The immediate early transcription unit 1 (IEtu1) promoter drives expression of infected cell protein 0 (bICP0) and bICP4, two key viral transcriptional regulators. The IEtu1 promoter contains two functional glucocorticoid receptor (GR) response elements (GREs), and this promoter is transactivated by GR, DEX, and certain Krüppel transcription factors that interact with GC-rich motifs, including consensus specificity protein 1 (Sp1) binding sites. Based on these observations, we hypothesized that Sp1 stimulates productive infection and transactivates key BoHV-1 promoters. DEX treatment of latently infected calves increased the number of Sp1+ TG neurons and cells in pharyngeal tonsil indicating that Sp1 expression is induced by stress. Silencing Sp1 protein expression with siRNA or mithramycin A, a drug that preferentially binds GC-rich DNA, significantly reduced BoHV-1 replication. Moreover, BoHV-1 infection of permissive cells increased Sp1 steady-state protein levels. In transient transfection studies, GR and Sp1 cooperatively transactivate IEtu1 promoter activity unless both GREs are mutated. Co-immunoprecipitation studies revealed that GR and Sp1 interact in mouse neuroblastoma cells (Neuro-2A) suggesting this interaction stimulates IEtu1 promoter activity. Collectively, these studies suggested that the cellular transcription factor Sp1 enhances productive infection and stress-induced BoHV-1 reactivation from latency.IMPORTANCEFollowing acute infection, bovine alphaherpesvirus 1 (BoHV-1) establishes lifelong latency in sensory neurons in trigeminal ganglia (TG) and pharyngeal tonsil. The synthetic corticosteroid dexamethasone consistently induces BoHV-1 reactivation from latency. The number of TG neurons and cells in pharyngeal tonsil expressing the cellular transcription factor specificity protein 1 (Sp1) protein increases during early stages of dexamethasone-induced reactivation from latency. Silencing Sp1 expression impairs BoHV-1 replication in permissive cells. Interestingly, mithramycin A, a neuroprotective antibiotic that preferentially binds GC-rich DNA, impairs Sp1 functions and reduces BoHV-1 replication suggesting that it is a potential antiviral drug. The glucocorticoid receptor (GR) and Sp1 cooperatively transactivate the BoHV-1 immediate early transcript unit 1 (IEtu1) promoter, which drives expression of infected cell protein 0 (bICP0) and bICP4. Mithramycin A also reduced Sp1- and GR-mediated transactivation of the IEtu1 promoter. These studies revealed that GR and Sp1 trigger viral gene expression and replication following stressful stimuli.

Chemokine receptor CXCR2 in primary sensory neurons of trigeminal ganglion mediates orofacial itch.

The CXCR2 chemokine receptor is known to have a significant impact on the initiation and control of inflammatory processes. However, its specific involvement in the sensation of itch is not yet fully understood. In this study, we aimed to elucidate the function of CXCR2 in the trigeminal ganglion (TG) by utilizing orofacial itch models induced by incision, chloroquine (CQ), and histamine. Our results revealed a significant up-regulation of CXCR2 mRNA and protein expressions in the primary sensory neurons of TG in response to itch stimuli. The CXCR2 inhibitor SB225002 resulted in notable decrease in CXCR2 protein expression and reduction in scratch behaviors. Distal infraorbital nerve (DION) microinjection of a specific shRNA virus inhibited CXCR2 expression in TG neurons and reversed itch behaviors. Additionally, the administration of the PI3K inhibitor LY294002 resulted in a decrease in the expressions of p-Akt, Akt, and CXCR2 in TG neurons, thereby mitigating pruritic behaviors. Collectively, we report that CXCR2 in the primary sensory neurons of trigeminal ganglion contributes to orofacial itch through the PI3K/Akt signaling pathway. These observations highlight the potential of molecules involved in the regulation of CXCR2 as viable therapeutic targets for the treatment of itch.

Impaired glucocorticoid receptor function attenuates herpes simplex virus 1 production during explant-induced reactivation from latency in female mice.

A correlation exists between stress and increased episodes of human alpha-herpes virus 1 reactivation from latency. Stress increases corticosteroid levels; consequently, the glucocorticoid receptor (GR) is activated. Recent studies concluded that a GR agonist, but not an antagonist, accelerates productive infection and reactivation from latency. Furthermore, GR and certain stress-induced transcription factors cooperatively transactivate promoters that drive the expression of infected cell protein 0 (ICP0), ICP4, and VP16. This study revealed female mice expressing a GR containing a serine to alanine mutation at position 229 (GRS229A) shed significantly lower levels of infectious virus during explant-induced reactivation compared to male GRS229A or wild-type parental C57BL/6 mice. Furthermore, female GRS229A mice contained fewer VP16 + TG neurons compared to male GRS229A mice or wild-type mice during the early stages of explant-induced reactivation from latency. Collectively, these studies revealed that GR transcriptional activity has female-specific effects, whereas male mice can compensate for the loss of GR transcriptional activation.

Silencing of TRPV4-expressing sensory neurons attenuates temporomandibular disorders pain.

Identification of potential therapeutic targets is needed for temporomandibular disorders (TMD) pain, the most common form of orofacial pain, because current treatments lack efficacy. Considering TMD pain is critically mediated by the trigeminal ganglion (TG) sensory neurons, functional blockade of nociceptive neurons in the TG may provide an effective approach for mitigating pain associated with TMD. We have previously shown that TRPV4, a polymodally-activated ion channel, is expressed in TG nociceptive neurons. Yet, it remains unexplored whether functional silencing of TRPV4-expressing TG neurons attenuates TMD pain. In this study, we demonstrated that co-application of a positively charged, membrane-impermeable lidocaine derivative QX-314 with the TRPV4 selective agonist GSK101 suppressed the excitability of TG neurons. Moreover, co-administration of QX-314 and GSK101 into the TG significantly attenuated pain in mouse models of temporomandibular joint (TMJ) inflammation and masseter muscle injury. Collectively, these results suggest TRPV4-expressing TG neurons represent a potential target for TMD pain.

OnabotulinumtoxinA effects on trigeminal nociceptors.

OnabotulinumtoxinA (onabotA) is approved globally for prevention of chronic migraine; however, the classical mechanism of action of onabotA in motor and autonomic neurons cannot fully explain the effectiveness of onabotulinumtoxinA in this sensory neurological disease. We sought to explore the direct effects of onabotulinumtoxinA on mouse trigeminal ganglion sensory neurons using an inflammatory soup-based model of sensitization. Primary cultured trigeminal ganglion neurons were pre-treated with inflammatory soup, then treated with onabotulinumtoxinA (2.75 pM). Treated neurons were used to examine transient receptor potential vanilloid subtype 1 and transient receptor potential ankyrin 1 cell-surface expression, calcium influx, and neuropeptide release. We found that onabotulinumtoxinA cleaved synaptosomal-associated protein-25 kDa in cultured trigeminal ganglion neurons; synaptosomal-associated protein-25 kDa cleavage was enhanced by inflammatory soup pre-treatment, suggesting greater uptake of toxin under sensitized conditions. OnabotulinumtoxinA also prevented inflammatory soup-mediated increases in TRPV1 and TRPA1 cell-surface expression, without significantly altering TRPV1 or TRPA1 protein expression in unsensitized conditions. We observed similar inhibitory effects of onabotulinumtoxinA on TRP-mediated calcium influx and TRPV1- and TRPA1-mediated release of calcitonin gene-related peptide and prostaglandin 2 under sensitized, but not unsensitized control, conditions. Our data deepen the understanding of the sensory mechanism of action of onabotulinumtoxinA and support the notion that, once endocytosed, the cytosolic light chain of onabotulinumtoxinA cleaves synaptosomal-associated protein-25 kDa to prevent soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated processes more generally in motor, autonomic, and sensory neurons.

Effect of electroacupuncture on ocular surface sensory neuralgia and expression of P2X3 receptor and PKC in cornea and trigeminal ganglion of dry eye guinea pigs

To observe the effect of electroacupuncture (EA) on ocular surface sensory neuralgia and the expression of P2X3 receptor (P2X3R) and protein kinase C(PKC)in cornea and trigeminal ganglion (TG) in dry eye disease (DED) guinea pigs, so as to explore its mechanism underlying improvement of ocular surface sensory neuralgia in DED. Male British tricolor short haired guinea pigs were randomly divided into control, model, medication (pranoprofen), EA and sham acupuncture groups, with 8 guinea pigs in each group. The dry eye model was induced by subcutaneous injection of scopolamine hydrobromide solution (0.6 mg/0.2 mL,once daily) for 10 d. Guinea pigs in the medication group were treated by applying pranoprofen eye drops to eyes, 1 drop for one eye each time, three times a day. Guinea pigs of the EA group received EA stimulation (4 Hz/20 Hz,1 mA) of bilateral "Cuanzhu" (BL2) and "Taiyang" (HN5) and acupuncture at "Jingming" (BL1) "Sizhukong" (TE23), "Tongziliao" (GB1) for 15 min, once a day. Guinea pigs in the sham acupuncture group received blunt stimu-lation at the surface of the same acupoint with the tip of the acupuncture needle, once a day. All the treatments were conducted for 14 d. The corneal epithelium fluorescein staining score (0-3 points) was given according to the number of fluorescence-positive dots and flake-like coloration, the corneal mechanical perception thread (CMPT) detected using a corneal perception meter, and the palpebral fissure height measured. The number of sensory neurons in the cornea and TG was determined by using cholera toxin subunit B conjugated with Alexa Fluor 488 fluorescence labelling, and the expression levels of P2X3R and PKC in the cornea and TG detected by using immunohistochemistry and Western blot, separately. Compared with the control group, the corneal fluorescein staining score, immunoactivity and expression of P2X3R proteins in both cornea and TG, PKC proteins in TG were significantly increased (P<0.01), whereas the CMPT and the height of palpebral fissure and the number of TG neurons significantly decreased in the model group (P<0.05,P<0.01). In comparison with the model group, the fluorescein staining score in the medication and EA groups, the immunoactivity and expression of P2X3R in cornea and TG in the EA group, and that of TG PKC in the EA group and the sham acupuncture groups were significantly decreased (P<0.05, P<0.01), while the height of palpebral fissure and CMPT after EA and the number of labelling TG sensory neurons were remarkably increased in the EA group (P<0.01) rather than in the medication and sham acupuncture groups (P>0.05). EA can alleviate the damage of corneal epithelium and sensory neurons in dry eye model guinea pigs, which may be related to its functions in down-regu-lating the expression of P2X3R and PKC in the cornea and TG.

Sensory nerves promote corneal inflammation resolution via CGRP mediated transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway

ObjectivesTo explore the role of the corneal sensory nerves in Pseudomonas aeruginosa (P. aeruginosa) keratitis, the synergistic effect between the sensory neurons and macrophages in calcitonin gene-related peptide (CGRP) release, and the functional mechanisms of CGRP-mediated transformation of macrophages to the M2 phenotype. MethodsCorneal nerve loss, macrophage recruitment, and CGRP expression were evaluated. To explore the synergistic effect between the sensory neurons and macrophages, RAW 264.7 cells were challenged with lipopolysaccharide (LPS), then trigeminal ganglion (TG) sensory neurons were isolated and co-incubated with macrophages, and CGRP expression was tested. To investigate the biological function of cornea neuron-initiated immune responses mediated by CGRP, BIBN 4096BS was used to inhibit CGRP in vivo and α-CGRP was used to simulate CGRP in vitro. The expressions of inflammatory cytokines (IL-1β, IL-6, TNF-α, and IL-10), M1 (CD80/CD86), M2 (CD163/CD206) macrophage markers, and signal transducers (PI3K/AKT) were detected. ResultsP. aeruginosa infection induced corneal nerve loss, macrophage recruitment, and CGRP up-expression. CGRP was co-localized with macrophages. Co-culture showed that sensory neurons and macrophages can mediate CGRP release. More CGRP was released when the two types of cells were combined to respond to LPS. BIBN 4096BS promoted pro-inflammatory cytokines and inhibited the anti-inflammatory cytokines and signal transducers, while, α-CGRP inhibited the pro-inflammatory cytokines and M1 markers and promoted the anti-inflammatory cytokine, M2 markers, and signal transducers. ConclusionsP. aeruginosa infection induces corneal sensory neuron activation, macrophage recruitment, and CGRP up-expression. The synergistic effect between the sensory neurons and macrophages promotes CGRP release. CGRP inhibits corneal inflammation and promotes the transformation of macrophages to the M2 phenotype through the PI3K/AKT signaling pathway.

TREK channel activation suppresses migraine pain phenotype

SummaryActivation and sensitization of trigeminal ganglia (TG) sensory neurons, leading to the release of pro-inflammatory peptides such as calcitonin gene-related peptide (CGRP), are likely a key component in migraine-related headache induction. Reducing TG neuron excitability represents therefore an attractive alternative strategy to relieve migraine pain. Here by using pharmacology and genetic invalidation ex vivo and in vivo, we demonstrate that activating TREK1 and TREK2 two-pore-domain potassium (K2P) channels inhibits TG neuronal firing sufficiently to fully reverse the migraine-like phenotype induced by NO-donors in rodents. Finally, targeting TREK is as efficient as treatment with CGRP antagonists, which represents one of the most effective migraine therapies. Altogether, our results demonstrate that inhibiting TG excitability by pharmacological activation of TREK channels should be considered as an alternative to the current migraine treatment.

Wnt antagonists suppress herpes simplex virus type 1 productive infection

Following acute infection of mucosal surfaces, herpes simplex virus 1 (HSV-1) establishes life-long latent infections within neurons, including sensory neurons in trigeminal ganglia (TG). Periodically, reactivation from latency occurs resulting in virus transmission and recurrent disease. In the absence of lytic cycle viral transcriptional proteins, host factors are predicted to mediate early stages of reactivation from latency. Previous studies suggested the canonical Wnt/β-catenin signaling pathway promotes productive infection. To further examine how the Wnt/β-catenin signaling pathway enhances productive infection, we examined two antagonists of the Wnt-signaling pathway. KYA1797K enhances formation of the β-catenin destruction complex, resulting in β-catenin degradation. Conversely, iCRT14 inhibits β-catenin dependent transcription by interfering with β-catenin interactions with T-cell factor/lymphoid enhancer factor (TCF)/Lef family of cellular transcription factors and interferes with TCF/Lef binding to DNA. iCRT14 and KYA1797K significantly inhibited HSV-1 productive infection in human and mouse neuronal cells and monkey kidney cells (VERO). Although iCRT14 was only effective when present throughout infection, delayed addition or early removal of KYA1797K did not significantly reduce its antiviral properties. KYA1797K had no effect on virus entry or penetration indicating it impairs certain aspects of viral replication. These studies demonstrated β-catenin promotes HSV-1 productive infection and indicate antagonists of the canonical Wnt/β-catenin signaling pathway may be effective anti-HSV therapeutic agents.

Disrupted Trigeminal Ganglion Development in a Mouse Model of Familial Dysautonomia

Neurons in the trigeminal ganglion (TG) relay somatosensory information from the face and oral cavity to the central nervous system. Arising from the differentiation of both neural crest cell and ectodermal placode cell precursors during embryogenesis, neurons in the TG ultimately encode one sensory modality (i.e., touch, pain, temperature). TG neuron identity is discernable by particular molecular markers, including the mutually exclusive expression of the neurotrophin receptors TrkA, TrkB, or TrkC, which are required for long-term neuronal function and survival. While little is known about the mechanisms that establish and maintain distinct neuronal subpopulations in the TG, disease studies offer some insight. Familial Dysautonomia (FD) is a hereditary neuropathy caused by a mutation in Elongator complex protein 1 (ELP1), which leads to reduced ELP1 protein levels in sensory and autonomic neurons. FD patients have clinical deficits that point to abnormal TG function, including impaired sensation of facial pain and temperature. Moreover, FD patients have smaller trigeminal nerves compared to healthy controls, in the absence of overt degeneration. Given these findings, we hypothesize that ELP1 is necessary for the development and survival of TG sensory neurons. Our initial results uncovered cytoplasmic Elp1 expression in both placode cell- and neural crest cell-derived neurons of the developing mouse TG starting from embryonic day (E)10.5. Using a conditional knockout mouse model in which Elp1 is deleted from Wnt1-positive neural crest cells and derivatives, including sensory neurons, we next examined the effect of Elp1 loss on TG development. Our preliminary data reveal Elp1 depletion from neural crest cells leads to abnormal TG morphology and fewer trigeminal nerve branches as early as embryonic day (E)11, a phenotype that persists throughout development and suggests defects in both neural crest- and placode cell-derived neurons in the TG. TrkA-expressing neurons, which typically function in pain perception, are especially vulnerable to Elp1 loss during this period of TG formation. By E12.5, we observe decreased TrkA expression in distal trigeminal nerve endings and fewer TrkA-positive neuron cell bodies in the TG. Analyses from TUNEL staining reveal increased cell death in the TG at E12.5, suggesting TrkA-expressing neurons, progenitor cells, and/or supporting cells may undergo aberrant apoptosis in Elp1 conditional knockout TG. Together, our results confirm a role for Elp1 in the development and survival of TG sensory neurons. These findings help explain the loss of facial sensation in FD and may guide future therapeutic interventions to increase quality of life for FD patients.

TREK Channel Activation Suppresses Migraine Pain Phenotype

Activation and sensitization of trigeminal (TG) ganglia sensory neurons, leading to the release of pro-inflammatory peptides such as calcitonin gene-related peptide (CGRP), are likely a key component in migraine-related headache induction. Reducing TG neuron excitability represents therefore an attractive alternative strategy to relieve migraine pain. Here by using pharmacology and genetic invalidation ex vivo and in vivo, we demonstrate that activating TREK1- and TREK2- Two-Pore-Domain potassium ( K 2P ) channels inhibits TG neuronal firing sufficiently to fully reverse the migraine-like phenotype induced by NO-donors in rodents. Finally, targeting TREK is as efficient as treatment with CGRP antagonists, which represents one of the most effective migraine therapies. Altogether, our results demonstrate that inhibiting TG excitability by pharmacological activation of TREK channels should be considered as an alternative to the current migraine treatment.

The effect of oral administration of monosodium glutamate on orofacial pain response and the estimated number of trigeminal ganglion sensory neurons of male Wistar rats

Monosodium glutamate (MSG) is a worldwide flavor enhancer. The excessive glutamate concentration in nerve tissue induces the death of nerve cells, known as excitotoxicity. In the orofacial region, the nerve cells’ death affects pain perception such as mechanical hyperalgesia and allodynia. The aim of the present study was to examine the pain response modification and the estimated total number of trigeminal ganglion sensory neurons after sub chronic oral administration of MSG. Twenty eight male Wistar rats, aged 6-8 weeks (100-150 grams) were divided into 4 groups: Control (2 mL NaCl 0.9%); 1 mg/gWB MSG; 2 mg/gWB MSG; 4 mg/gWB MSG groups. Daily oral administration of MSG was given for 30 days. The control group received NaCl per oral for the same period. The pin prick and air puff test were performed on days 1-2, days 41-42 and days 55-56. The number of trigeminal ganglion sensory neurons were estimated by the unbiased stereology method, using the approach of numerical density and organ volume reference. The results showed that the sub chronic oral administration of MSG does not modify either the orofacial pain response or the estimated total number of trigeminal ganglion sensory neurons. .

Role of CGRP in Neuroimmune Interaction via NF-κB Signaling Genes in Glial Cells of Trigeminal Ganglia.

Activation of the trigeminal system causes the release of various neuropeptides, cytokines, and other immune mediators. Calcitonin gene-related peptide (CGRP), which is a potent algogenic mediator, is expressed in the peripheral sensory neurons of trigeminal ganglion (TG). It affects the inflammatory responses and pain sensitivity by modulating the activity of glial cells. The primary aim of this study was to use array analysis to investigate the effect of CGRP on the glial cells of TG in regulating nuclear factor kappa B (NF-κB) signaling genes and to further check if CGRP in the TG can affect neuron-glia activation in the spinal trigeminal nucleus caudalis. The glial cells of TG were stimulated with CGRP or Minocycline (Min) + CGRP. The effect on various genes involved in NF-κB signaling pathway was analyzed compared to no treatment control condition using a PCR array analysis. CGRP, Min + CGRP or saline was directly injected inside the TG and the effect on gene expression of Egr1, Myd88 and Akt1 and protein expression of cleaved Caspase3 (cleav Casp3) in the TG, and c-Fos and glial fibrillary acidic protein (GFAP) in the spinal section containing trigeminal nucleus caudalis was analyzed. Results showed that CGRP stimulation resulted in the modulation of several genes involved in the interleukin 1 signaling pathway and some genes of the tumor necrosis factor pathway. Minocycline pre-treatment resulted in the modulation of several genes in the glial cells, including anti-inflammatory genes, and neuronal activation markers. A mild increase in cleav Casp3 expression in TG and c-Fos and GFAP in the spinal trigeminal nucleus of CGRP injected animals was observed. These data provide evidence that glial cells can participate in neuroimmune interaction due to CGRP in the TG via NF-κB signaling pathway.

Longitudinal transcriptomic characterization of viral genes in HSV-1 infected tree shrew trigeminal ganglia

BackgroundFollowing acute infection, Herpes Simplex virus-1 (HSV-1) establishes lifelong latency and recurrent reactivation in the sensory neurons of trigeminal ganglia (TG). Infected tree shrew differs from mouse and show characteristics similar to human infection. A detailed transcriptomic analysis of the tree shrew model could provide mechanistic insights into HSV-1 infection in humans.MethodsWe sequenced the transcriptome of infected TGs from tree shrews and mice, and 4 human donors, then examined viral genes expression up to 58 days in infected TGs from mouse and tree shrew, and compare the latency data with that in human TGs.ResultsHere, we found that all HSV-1 genes could be detected in mouse TGs during acute infection, but 22 viral genes necessary for viral transcription, replication and viral maturation were not expressed in tree shrew TGs during this stage. Importantly, during latency, we found that LAT could be detected both in mouse and tree shrew, but the latter also has an ICP0 transcript signal absent in mouse but present in human samples. Importantly, we observed that infected human and tree shrew TGs have a more similar LAT region transcription peak. More importantly, we observed that HSV-1 spontaneously reactivates from latently infected tree shrews with relatively high efficiency.ConclusionsThese results represent the first longitudinal transcriptomic characterization of HSV-1 infection in during acute, latency and recurrent phases, and revealed that tree shrew infection has important similar features with human infection.

Sensory neurons directly promote angiogenesis in response to inflammation via substance P signaling.

Blood vessels and nerves travel together to supply most tissues in the body. However, there is a knowledge gap in the mechanisms underlying the direct regulation of angiogenesis by nerves. In the current study, we examined the regulation of angiogenesis by sensory nerves in response to inflammation using the cornea, a normally avascular and densely innervated ocular tissue, as a model. We used desiccating stress as an inflammatory stimulus in vivo and found that sub-basal and epithelial nerve densities in the cornea were reduced in dry eye disease (DED). We established a co-culture system of trigeminal ganglion sensory neurons and vascular endothelial cells (VEC) and found that neurons isolated from mice with DED directly promoted VEC proliferation and tube formation compared with normal controls. In addition, these neurons expressed and secreted higher levels of substance P (SP), a proinflammatory neuropeptide. SP potently promoted VEC activation in vitro and blockade of SP signaling with spantide I, an antagonist of SP receptor Neurokinin-1, significantly reduced corneal neovascularization in vivo. Spantide I and siRNA knockdown of SP abolished the promotion of VEC activation by DED neurons in vitro. Taken together, our data suggested that sensory neurons directly promote angiogenesis via SP signaling in response to inflammation in the cornea.

Peripheral serotonin receptor 2B and transient receptor potential channel 4 mediate pruritus to serotonergic antidepressants in mice

Peripheral serotonin receptor 2B and transient receptor potential channel 4 mediate pruritus to serotonergic antidepressants in mice