5-HT3/7 and GABAB receptors mediate inhibition of trigeminal nociception by dietary supplementation of grape seed extract.

Background: Temporomandibular joint disorder is a prevalent orofacial pain condition involving sensitization and activation of trigeminal nociceptive neurons. Dietary supplementation with a proanthocyanin-enriched grape seed extract (GSE) was found to inhibit trigeminal nociception in a chronic TMD model. In this study, the cellular mechanisms by which GSE inhibits sustained trigeminal nociception in male and female Sprague Dawley rats were investigated.Methods: Some animals were supplemented with 0.5% GSE dissolved in their water one week prior to neck muscle inflammation induced by injection of complete Freund's adjuvant into the trapezius. To investigate the mechanism of GSE, some animals were injected intracisternally with antagonists of 5-HT3, 5-HT7, GABAA, or GABAB, receptor prior to jaw opening.Results: In males and females, trapezius inflammation prior to jaw opening resulted in sustained mechanical hypersensitivity of trigeminal nociceptors that was significantly inhibited by GSE. Further, GSE beginning 14 days post jaw opening also inhibited trigeminal nociception. Intracisternal injection of antagonists of the 5-HT3/7 and GABAB, but not GABAA receptors reduced the anti-nocifensive effect of GSE in both sexes. Neuronal expression of GABAB protein and mRNA in the spinal cord and trigeminal ganglion were detected.Conclusions: The inhibitory effect of GSE is mediated via activation of 5-HT3/7 receptors and GABAB to enhance central descending inhibitory pain pathways and suppress ongoing trigeminal nociception. Further, our findings support the use of GSE as a dietary supplement in the management of pain associated with TMD and other orofacial pain conditions involving central sensitization and dysfunction of descending pain modulation.

Noninvasive vagus nerve stimulation and morphine transiently inhibit trigeminal pain signaling in a chronic headache model.

INTRODUCTION: Chronic headache conditions are characterized by persistent sensitization of the trigeminal system, which involves dysfunction of descending pain modulation. We previously reported that noninvasive vagus nerve stimulation (nVNS) inhibits trigeminal nociception in models of episodic migraine through a mechanism involving enhanced serotonergic and GABAergic descending pain signaling. OBJECTIVES: The analgesic effectiveness of nVNS and morphine were investigated in an animal model of chronic headache mediated by the combination of the 3 migraine risk factors of neck muscle tension, paradoxical sleep deprivation, and pungent odors. METHODS: Sprague-Dawley rats were injected with complete Freund's adjuvant in the trapezius and sleep deprived for 1 night to promote trigeminal sensitization. After 7 days, animals were exposed to a pungent odor, and mechanical nocifensive head withdrawal responses were determined using von Frey filaments. Beginning on day 3 after odor exposure, animals were treated daily with either nVNS or morphine for 7 days. RESULTS: Exposure of animals sensitized by neck inflammation and sleep deprivation to a pungent odor resulted in a prolonged state of trigeminal nociception. Daily administration of nVNS or morphine significantly repressed the nocifensive response; however, cessation resulted in a return to heightened pretreatment nocifensive levels. CONCLUSIONS: The combination of reported migraine risk factors promotes a state of sustained trigeminal hypersensitivity characteristic of chronic headache. Daily nVNS was similarly effective as morphine in inhibiting nociception and may represent a safer, opioid-sparing therapeutic option for other chronic pain disorders involving sensitization of the trigeminal system by promoting descending pain modulation.

Dietary supplementation with grape seed extract prevents development of trigeminal sensitization and inhibits pain signaling in a preclinical chronic temporomandibular disorder model.

BACKGROUND: The risk factors neck muscle tension, prolonged jaw opening, and female gender are associated with developing temporomandibular disorders (TMD), which are characterized by persistent sensitization of trigeminal neurons and enhanced pain signaling. Dietary supplementation with a grape seed extract (GSE) can modulate expression of proteins that decrease neuronal excitability and trigeminal sensitization. METHODS: Mechanical nocifensive thresholds over the masseter were determined using von Frey filaments in male and female adult Sprague Dawley rats. To promote trigeminal sensitization, animals were injected with complete Freund's adjuvant in the upper trapezius. After 8 days, animals were subjected to near maximal jaw opening and head withdrawal responses were determined for 28 days. Some animals received continuous supplementation with 0.5% GSE in their drinking water two weeks prior to trapezius injections. RESULTS: Prolonged jaw opening increased the average number of nocifensive responses to mechanical stimuli for 14 days in males and females. However, trapezius inflammation prior to jaw opening promoted persistent mechanical sensitivity up to 28 days post-jaw opening in females, while in males nociceptive levels were still elevated at day 21. Supplementation with GSE, which is enriched in polyphenols and exhibits antioxidant and COX-2 activity, inhibited trigeminal nociception in response to jaw opening in both male and female sensitized animals. CONCLUSIONS: Our findings provide evidence that multiple risk factors contribute to the development of a prolonged state of trigeminal sensitization that is more severe in females and provide preclinical evidence that supplementation with GSE could be beneficial in the management of TMD.

New in vitro highly cytotoxic platinum and palladium cyanoximates with minimal side effects in vivo.

Several biologically active bivalent Pd and Pt complexes with two structurally similar cyanoxime ligands abbreviated as H(DECO): 2-oximino-2-cyano-N,N'-diethylacetamide, and H(PyrCO): 2-oximino-2-cyan-N-pyrrolidine acetamide were synthesized and characterized using spectroscopic methods, thermal analysis and X-ray crystallography. Structures revealed planar cis-geometry of studied complexes. Freshly obtained Pt(DECO)2, Pd(DECO)2, Pt(PyrCO)2 and Pd(PyrCO)2 complexes were used in for in vitro cytotoxicity assays using two different etiology human cancer cell lines HeLa and WiDr cells. Investigated compounds showed cytotoxicity levels at or above cisplatin. Pt(DECO)2 was also tested in vivo in healthy C57BL/6 mice. The complex was administered at three different dosage (0, 7.5, 15 mg/kg, i.p. once/week), over a total period of 8 weeks. No changes were observed in the animal weight in the treated mice compared to the control dextrose-treated group. The levels of erythrocytes, leukocytes, and hemoglobin were within the normal level suggesting low myelotoxicity. Negligible cardiotoxicity was observed from the histological evaluation of the hearts from the treated animals. Results from the tail nerve conduction velocity (NCV) and nerve histomorphometry suggested no impact of Pt(DECO)2 on peripheral nerves. The complex, however, induced certain hepatotoxicity and lead to the elevation of IL-6, a pro-inflammatory cytokine. Overall, Pt(DECO)2 showed minimal in vivo toxicity, thus presenting a promising candidate for future testing in animal models of cancer.

Neuroprotective Effect of Enriched Chicken Bone Broth as a Dietary Supplement in a Model of Migraine Mediated by Early Life Stress.

Early life stress is a risk factor for development of migraine, a prevalent painful neurological disease characterized by sensitization and activation of trigeminal neurons. Secondary early life stress was previously shown to cause increased expression of neuronal proteins implicated in peripheral and central sensitization. Recently, dietary supplementation of chicken bone broth was shown to attenuate trigeminal nociception in an orofacial pain model. Accordingly, the focus of this study was to determine the effects of early life stress and dietary inclusion of bone broth on trigeminal nociceptor sensitization and activation in a model of episodic migraine. Adult Sprague-Dawley male sender rats subjected to primary traumatic stress were placed next to breeding or pregnant female rats that served as receiver rats (secondary traumatic stress) and in proximity to the offspring until weaning. Unstressed and stressed young adult offspring were tested for mechanical nocifensive response after exposure to a pungent odor known to be a migraine trigger, and in response to daily supplementation of bone broth. Early life stress promoted a primed state of trigeminal nociceptors that were activated by the pungent odor in both genders. Female animals exhibited a higher basal sensitization level and prolonged nociception compared with males. Supplementation of bone broth beginning at the time of weaning inhibited basal and triggered trigeminal mechanical sensitivity. Early life stress caused development of a sensitized trigeminal system that is implicated in migraine pathology and dietary supplementation with bone broth suppressed trigeminal sensitization, and thus may provide neuroprotective activity for reducing migraine risk.

Inhibition of Trigeminal Nociception by Non-invasive Vagus Nerve Stimulation: Investigating the Role of GABAergic and Serotonergic Pathways in a Model of Episodic Migraine.

Migraine is a prevalent neurological disease that is characterized by unpredictable episodic attacks of intense head pain. The underlying pathology involves sensitization and activation of the trigeminal system. Although non-invasive vagus nerve stimulation (nVNS) is recommended for the treatment of migraine, the abortive mechanism of action is not well-understood. The goal of this study was to compare the ability of nVNS and sumatriptan to inhibit trigeminal activation in two animal models of episodic migraine and to investigate the receptor mechanism of action of nVNS. Nocifensive head withdrawal response was investigated in adult male Sprague Dawley rats using von Frey filaments. To induce trigeminal nociceptor sensitization, complete Freund's adjuvant was injected in the trapezius muscle and trigeminal neurons were activated by exposure to a pungent odor or injection of the nitric oxide donor sodium nitroprusside. Some animals received nVNS or sumatriptan as treatment. Some animals were injected intracisternally with antagonists of GABAA, 5-HT3 or 5-HT7 receptors prior to nVNS since these receptors are implicated in descending modulation. While unsensitized animals exposed to the pungent odor or nitric oxide alone did not exhibit enhanced mechanical nociception, sensitized animals with neck muscle inflammation displayed increased trigeminal nocifensive responses. The enhanced nociceptive response to both stimuli was attenuated by nVNS and sumatriptan. Administration of antagonists of GABAA, 5-HT3, and 5-HT7 receptors in the upper spinal cord suppressed the anti-nocifensive effect of nVNS. Our findings suggest that nVNS inhibits trigeminal activation to a similar degree as sumatriptan in episodic migraine models via involvement of GABAergic and serotonergic signaling to enhance central descending pain modulation.

Central Role of Protein Kinase A in Promoting Trigeminal Nociception in an In Vivo Model of Temporomandibular Disorders.

AIMS: To investigate cellular changes in the spinal trigeminal nucleus (STN) and trigeminal ganglion (TG) associated with trigeminal nociception mediated by inflammation in the temporomandibular joint (TMJ). METHODS: Male Sprague-Dawley rats (n = 86) were utilized to investigate cellular and behavioral responses to prolonged TMJ inflammation caused by bilateral injection of Complete Freund's Adjuvant (CFA) in the TMJ capsules. To investigate the cellular effects of protein kinase A (PKA) in the STN, rats were injected intrathecally with the selective PKA inhibitor KT5720 prior to injection of CFA into both TMJ capsules. Levels of calcitonin gene-related peptide (CGRP), active PKA, and ionized calcium-binding adapter molecule 1 (Iba1) in the STN and expression of phosphorylated extracellular regulated kinases (p-ERK) in the TG were determined with immunohistochemistry (n ≥ 3 experiments per test condition). Nocifensive head withdrawal responses to mechanical stimulation of the cutaneous tissue over the TMJ were monitored following CFA injection in the absence or presence of KT5720 (n = 7). Statistical analysis was performed using parametric analysis of variance (ANOVA) tests. RESULTS: Intrathecal injection of KT5720 significantly inhibited the stimulatory effect of CFA on levels of CGRP, PKA, and Iba1 in the STN. In addition, administration of KT5720 decreased the average number of CFA-induced nocifensive withdrawal responses to mechanical stimulation and the CFA-mediated increase in p-ERK expression in the ganglion. CONCLUSION: These findings provide evidence that elevated PKA activity in the STN promotes cellular events temporally associated with trigeminal nociception caused by prolonged TMJ inflammation.

Vagus nerve stimulation inhibits trigeminal nociception in a rodent model of episodic migraine.

INTRODUCTION: Although neck muscle tension is considered a risk factor for migraine, pungent odors can act as a trigger to initiate an attack in sensitized individuals. Although noninvasive vagus nerve stimulation (nVNS) is now an approved treatment for chronic migraine, how it functions to inhibit trigeminal nociception in an episodic migraine model is not known. OBJECTIVES: The objectives of this study were to determine if nVNS could inhibit trigeminal nociception in a novel model of episodic migraine and investigate changes in the expression of proteins implicated in peripheral and central sensitization. METHODS: Sprague-Dawley male rats were injected with an inflammatory agent in the trapezius muscle before exposure to pungent volatile compounds, which was used to initiate trigeminal nociceptor activation. The vagus nerve was stimulated transdermally by a 1-ms pulse of 5 kHz sine waves, repeated at 25 Hz for 2 minutes. Nocifensive head withdrawal response to von Frey filaments was determined and immunoreactive protein levels in the spinal cord and trigeminal ganglion (TG) were investigated. RESULTS: Exposure to the pungent odor significantly increased the number of nocifensive withdrawals in response to mechanical stimulation of sensitized TG neurons mediated by neck muscle inflammation. Noninvasive vagus nerve stimulation inhibited nociception and repressed elevated levels of P-ERK in TG, Iba1 in microglia, and GFAP in astrocytes from sensitized animals exposed to the pungent odor. CONCLUSION: Our findings demonstrate that nVNS inhibits mechanical nociception and represses expression of proteins associated with peripheral and central sensitization of trigeminal neurons in a novel rodent model of episodic migraine.

Elevated levels of calcitonin gene-related peptide in upper spinal cord promotes sensitization of primary trigeminal nociceptive neurons.

Orofacial pain conditions including temporomandibular disorder (TMD) and migraine are characterized by peripheral and central sensitization of trigeminal nociceptive neurons. The goal of this study was to investigate the role of calcitonin gene-related peptide (CGRP) in promoting bidirectional signaling within the trigeminal system to mediate sensitization of primary nociceptive neurons. Adult male Sprague-Dawley rats were injected intercisternally with CGRP or co-injected with the receptor antagonist CGRP8-37 or KT 5720, a protein kinase A (PKA) inhibitor. Nocifensive head withdrawal response to mechanical stimulation was investigated using von Frey filaments. Expression of PKA, glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba1) in the spinal cord and phosphorylated extracellular signal-regulated kinase (P-ERK) in the ganglion was studied using immunohistochemistry. Some animals were co-injected with CGRP and Fast Blue dye and the ganglion was imaged using fluorescent microscopy. CGRP increased nocifensive responses to mechanical stimulation when compared to control. Co-injection of CGRP8-37 or KT 5720 with CGRP inhibited the nocifensive response. CGRP stimulated PKA and GFAP expression in the spinal cord, and P-ERK in ganglion neurons. Seven days post injection, Fast Blue was observed in ganglion neurons and satellite glial cells. Our results demonstrate that elevated levels of CGRP in the upper spinal cord promote sensitization of primary nociceptive neurons via a mechanism that involves activation of PKA centrally and P-ERK in ganglion neurons. Our findings provide evidence of bidirectional signaling within the trigeminal system that facilitate increased neuron-glia communication within the ganglion associated with trigeminal sensitization.