Inhibition Of Nociception Research Articles

Ah-type Baroreceptor Neurons Expressing Estrogen Dependent mGluR7 Mediate Descending Inhibition of Cardiac Nociception

Silent myocardial infarction (MI) is critical for clinical practice with increasing risk for women and the cause remains a medical mystery. Upon the discovery of female-specific Ah-type baroreceptor neurons (BRNs), we hypothesize that glutamate mediates depressor response through afferent-specific expression of particular glutamate receptors (mGluRs) leading descending inhibition of cardiac nociception. In vivo, tail-flick reflex and electromyography were assessed to evaluate glutamate-mediated blood pressure regulation, peripheral and cardiac nociception. The results showed that glutamate decreased mean arterial pressure (MAP) and increased peripheral nociception. Interestingly, glutamate-mediated capsaicin-induced cardiac nociception was strongly reduced in female rats compared with males. Furthermore, Nodose (NG) microinjection of mGluR7 agonist significantly increased MAP in males and slightly decreased that in females. Even though mGluR8 direct activation intensified baroreceptor activation, the sensitivity was similar between sexes. In vitro, the expression profiles of mGluRs were investigated using Western blot and identified BRNs using single-cell qRT-PCR under ischemic conditions. Glutamate in serum, NG and nucleus tractus solitary (NTS) was raised significantly in the model rats of both sexes vs. sham-controls. Female-specific expression of mGluR7 in the baroreflex afferent pathway, especially higher expression in Ah-type BRNs, contributes significantly to cardiac analgesia, which may explain that the pathogenesis of silent MI occurs mainly in female patients. Therefore, higher expression of mGluR7 in female-specific subpopulation of Ah-type BRNs plays a critical role in cardiac analgesia and peripheral nociception.

Activation of the Locus Coeruleus Mediated by Designer Receptor Exclusively Activated by Designer Drug Restores Descending Nociceptive Inhibition after Traumatic Brain Injury in Rats.

Disruption of endogenous pain control mechanisms including descending pain inhibition has been linked to several forms of pain including chronic pain after traumatic brain injury (TBI). The locus coeruleus (LC) is the principal noradrenergic (NA) nucleus participating in descending pain inhibition. We therefore hypothesized that selectively stimulating LC neurons would reduce nociception after TBI. All experiments used a well-characterized rat lateral fluid percussion model of TBI. NA neurons were stimulated by administering clozapine N-oxide (CNO) to rats selectively expressing a designer receptor exclusively activated by designer drug (DREADD) viral construct in their LC's. Mechanical nociceptive thresholds were measured using von Frey fibers. The efficacy of diffuse noxious inhibitory control (DNIC), a critical endogenous pain control mechanism, was assessed using the hindpaw administration of capsaicin. Immunohistochemical analyses demonstrated the selective expression of the DREADD construct in LC neurons after stereotactic injection. During the 1st week after TBI, when rats demonstrated hindlimb (HL) nociceptive sensitization, CNO administration provided transient anti-allodynia in DREADD-expressing rats but not in rats injected with control virus. Seven weeks after TBI we observed a complete loss of DNIC in response to capsaicin. However, CNO administration largely restored DNIC in TBI DREADD-expressing rats but not those injected with control virus. Unexpectedly, the effects of LC activation in the DREADD-expressing rats were blocked by the α-1 adrenergic receptor antagonist prazosin, but not the α-2 adrenergic receptor antagonist atipamezole. These results suggest that directly stimulating the LC after TBI can reduce both early and late manifestations of dysfunctional endogenous pain regulation. Clinical approaches to activating descending pain circuits may reduce suffering in those with pain after TBI.

Anti-Nociceptive and Anti-Inflammatory Activities of the Ethyl Acetate Extract of Belamcanda chinensis (L.) Redouté in Raw 264.7 Cells in vitro and Mouse Model in vivo.

PurposeInflammation and accompanying pain is a common global health problem that seriously affects human quality of life worldwide. Here, we aimed to investigate the anti-nociceptive and anti-inflammatory activities of the ethyl acetate extract of B. chinensis (EAEBc) along with the underlying mechanisms of action.MethodsThe in vitro anti-inflammatory activity of EAEBc was explored using an LPS-induced RAW264.7 cell inflammatory model. Nitric oxide (NO) production, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 levels were evaluated. In vivo anti-nociceptive and anti-inflammatory activities of EAEBc were assessed with the aid of classical experimental mouse models. In addition, LPS-induced biomarker contents (TNF-α, IL-1β, IL-6, NO, iNOS, and PGE2) and formalin-induced serum inflammatory factors (NO, PGE2, 5-HT, β-EP, substance P, and NE) were determined in mice.ResultsIn vitro, EAEBc significantly reduced LPS-induced NO generation and suppressed the production of TNF-α, IL-1β, and IL-6 in RAW264.7 cells in a concentration-dependent manner. In vivo, EAEBc downregulated serum TNF-α, IL-1β, IL-6, NO, iNOS, and PGE2 contents in mice with LPS-induced inflammation in a dose-dependent manner. EAEBc displayed anti-inflammatory activity in carrageenan-induced paw edema and xylene ear edema tests. Intragastric administration of EAEBc at test doses of 100 and 200 mg/kg led to inhibition of nociception and capillary permeability induced by acetic acid to varying degrees. Similarly, EAEBc exerted analgesic effects in the formalin and hot plate tests. In particular, the administration of EAEBc reversed the changes in the levels of inflammatory indicators NO, PGE2, 5-HT, β-EP, substance P, and NE in a mouse model of formalin-induced pain.ConclusionOur findings provide considerable evidence to support the extensive application of B. chinensis in traditional medicine and demonstrate the utility of this plant species as an effective candidate for prevention or treatment of various pain and inflammation-related conditions.

Adjunctive treatment of chronic migraine using an oral dental device: overview and results of a randomized placebo-controlled crossover study

ObjectiveTo assess the nocioceptive input of habitual nocturnal jaw clenching that acts as a contributing factor in migraine pathogenesis.BackgroundHabitual nocturnal jaw clenching has been implicated as a trigger, particularly in those whose headaches are present upon waking or shortly thereafter. Nocturnal EMG studies of patients diagnosed with migraine show nearly twice the temporalis clenching EMG levels and double the bite force as matched asymptomatic controls, leading to the speculation that parafunctional clenching activity may have some role in headache pathogenesis. The NTI (Nociceptive Trigeminal Inhibition) oral device is a dental splint designed to reduce nocturnal jaw clenching intensity and is FDA approved for the prevention of medically diagnosed migraine pain based on open label studies. There are no prior placebo-controlled trials to assess the migraine prevention efficacy of the NTI splint. This is the first placebo-controlled cross-over study to assess the efficacy of the NTI splint in patients with Chronic Migraine.MethodA placebo controlled, single-blinded cross-over study was done with IRB oversight assessing the efficacy of the NTI splint compared to placebo using the change in the HIT-6 score as the outcome measure.Results68% of refractory chronic migraine sufferers using the NTI as measured by sequential HIT 6 scores had at least a one-category improvement (severe to substantial, or substantial to some, or some to none) compared to 12% when using a placebo device. 36% of subjects using the NTI device reported a two-category improvement in their HIT-6 score, compared to 0% when using placebo.ConclusionThe improvement in HIT-6 scores produced by the NTI device, suggests that patients with Chronic Migraine may have intense nocturnal jaw clenching as a contributing factor to their headache related disability. An NTI device is one method of assessing whether jaw-clenching is a contributing factor to ongoing migraine.Trial registrationCurrent Controlled Trials NCT04871581. 04/05/2021. Retrospectively registered.

Inhibition of Nociception in a Preclinical Episodic Migraine Model by Dietary Supplementation of Grape Seed Extract Involves Activation of Endocannabinoid Receptors.

Migraine is associated with peripheral and central sensitization of the trigeminal system and dysfunction of descending pain modulation pathways. Recently, dietary inclusion of grape seed extract (GSE) was shown to inhibit mechanical nociception in a preclinical model of chronic temporomandibular joint disorder, a condition often comorbid with migraine, with the antinociceptive effect mediated, in part, by activation of 5-HT3/7 and GABAB receptors. This study further investigated the mechanisms by which GSE inhibits mechanical nociception in a preclinical model of episodic migraine. Hyperalgesic priming of female and male Sprague Dawley rats was induced by three consecutive daily two-hour episodes of restraint stress. Seven days after the final restraint stress, rats were exposed to pungent odors from an oil extract that contains the compound umbellulone, which stimulates CGRP release and induces migraine-like pain. Some animals received dietary supplementation of GSE in their drinking water beginning one week prior to restraint stress. Changes in mechanical sensitivity in the orofacial region and hindpaw were determined using von Frey filaments. To investigate the role of the endocannabinoid receptors in the effect of GSE, some animals were injected intracisternally with the CB1 antagonist AM 251 or the CB2 antagonist AM 630 prior to odor inhalation. Changes in CGRP expression in the spinal trigeminal nucleus (STN) in response to stress, odor and GSE supplementation were studied using immunohistochemistry. Exposure of stress-primed animals to the odor caused a significant increase in the average number of withdrawal responses to mechanical stimulation in both the orofacial region and hindpaw, and the effect was significantly suppressed by daily supplementation with GSE. The anti-nociceptive effect of GSE was inhibited by intracisternal administration of antagonists of CB1 and CB2 receptors. GSE supplementation inhibited odor-mediated stimulation of CGRP expression in the STN in sensitized animals. These results demonstrate that GSE supplementation inhibits trigeminal pain signaling in an injury-free model of migraine-like pain via activation of endocannabinoid receptors and repression of CGRP expression centrally. Hence, we propose that GSE may be beneficial as a complementary migraine therapeutic.

The Relationship Between Experienced Discrimination and Pronociceptive Processes in Native Americans: Results From the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) have higher pain rates than the general U.S. population. It has been found that increased central sensitization and reduced pain inhibition are pronociceptive processes that increase pain risk; yet, little attention has focused on the influence of psychosocial factors. Discrimination is a psychosocial factor associated with increased pain in other minoritized groups; however, it is unclear whether it also promotes pain in NAs. This study analyzed data from 269 healthy, pain-free participants (N = 134 non-Hispanic whites [NHWs], N = 135 NAs) from the Oklahoma Study of Native American Pain Risk. Experienced discrimination was measured using the Everyday Discrimination Scale (EDS). Nociceptive processes were measured via static measures of spinal sensitivity (nociceptive flexion reflex [NFR] threshold, 3-stimulation NFR threshold), temporal summation of pain (TS-Pain) and nociceptive flexion reflex (TS-NFR), and conditioned pain modulation of pain (CPM-Pain) and NFR (CPM-NFR). Results demonstrated that greater discrimination was associated with enhanced TS-NFR and impaired CPM-NFR but not static measures of spinal sensitivity or measures of pain modulation (TS-Pain, CPM-Pain). Although the effects of discrimination on outcomes were similar in both groups (not moderated by ethnicity), NAs experienced higher levels of discrimination and therefore discrimination mediated a relationship between ethnicity and impaired CPM-NFR. This indicates experienced discrimination may promote a pain risk phenotype in NAs that involves spinal sensitization resulting from impaired inhibition of spinal nociception without sensitization of pain experience. PerspectiveThis study found that discrimination was associated with spinal sensitization and impaired descending inhibition of spinal nociception. These findings bolster our understanding of how social stressors experienced disproportionately by minoritized groups can contribute to pain outcomes.

Antihyperlipidemic, anti-inflammatory, analgesic, and antipyretic activities of "dimethyl dimethoxy biphenyl dicarboxylate" in male Wistar rats.

Dimethyl dimethoxy biphenyl (DDB) dicarboxylate has been applied as a therapeutic modality for curing liver diseases, particularly hepatitis virus. The objective of this study was to assess the protective potential against Triton X-100 induced abnormal fat metabolism in addition to anti-inflammatory, analgesic, and antipyretic effects of DDB. The anti-inflammatory, antinociceptive, and antipyretic of DDB were investigated through induction of paw edema, pain, and fever in experimental rats. DDB decreased cholesterol and triglyceride contents. DDB resulted in inhibition of inflammation, nociception, and fever in the experimental models. DDB improved lipid profile, as evidence of hypolipidemic potential. It also showed anti-inflammatory, analgesic, and antipyretic properties.

Pharmacodynamic/pharmacokinetic correlation of optimized ibuprofen nanosuspensions having enhanced anti-inflammatory and antinociceptive activity

The main objective of this study was to evaluate the antinociceptive and anti-inflammatory activity of ibuprofen (IB) nanoformulations which were developed in our previous study and showed enhanced in-vitro dissolution rate compared with the marketed formulation. The in-vivo pharmacodynamic (PD) studies were performed in mice. The antinociceptive effect of the formulations was evaluated using the formalin test, whereas the anti-inflammatory activity was evaluated by measuring oedema caused by formalin test. The optimized formulation exhibited nanosized particles with rapid dissolution compared with IB in water and marketed product. The antinociceptive and anti-inflammatory activity of IB was significantly improved in optimized nanosuspension compared with other formulations. A good correlation was observed between the pharmacokinetic and PD data: nanosuspension > freeze-dried nanoparticles > marketed product > unhomogenized formulation > IB suspension in water. There was a significantly good correlation between percentage inhibition of paw oedema with peak serum concentration (Cmax) and time at which the Cmax is observed (Tmax) but not area under the curve (AUC), whereas there was a good correlation between percentage inhibition of formalin-induced nociception in phase II, but not phase I, with AUC and Cmax but not Tmax. The development of IB nanoformulation by ultra-homogenization technique improved its dissolution and PD properties.

Psychosocial and cardiometabolic predictors of chronic pain onset in Native Americans: serial mediation analyses of 2-year prospective data from the Oklahoma Study of Native American Pain Risk.

Chronic pain results in considerable suffering, as well as significant economic and societal costs. Previous evidence suggests that Native Americans (NAs) have higher rates of chronic pain than other U.S. racial or ethnic groups, but the mechanisms contributing to this pain disparity are poorly understood. The Oklahoma Study of Native American Pain Risk was developed to address this issue and recruited healthy, pain-free NAs and non-Hispanic Whites. Cross-sectional analyses identified several measures of adversity (eg, trauma and discrimination), cognitive-affective factors (perceived stress and pain-related anxiety/catastrophizing), and cardiometabolic factors (eg, body mass index, blood pressure, and heart rate variability) that were associated with pronociceptive processes (eg, central sensitization, descending inhibition, and hyperalgesia). Every 6-months after enrollment, eligible participants (N = 277) were recontacted and assessed for the onset of chronic pain. This study examines predictors of chronic pain onset in the 222 participants (80%) who responded over the first 2 years. The results show that NAs developed chronic pain at a higher rate than non-Hispanic Whites (OR = 2.902, P < 0.05), even after controlling for age, sex, income, and education. Moreover, serial mediation models identified several potential pathways to chronic pain onset within the NA group. These paths included perceived discrimination, psychological stress, pain-related anxiety, a composite measure of cardiometabolic risk, and impaired descending inhibition of spinal nociception (assessed from conditioned pain modulation of the nociceptive flexion reflex). These results provide the first prospective evidence for a pain disparity in NAs that seems to be promoted by psychosocial, cardiometabolic, and pronociceptive mechanisms.

Anti-nociceptive Potential of Ethanol Extract of Terminalia macroptera Guill&amp;Perr (Combretaceae) Stem Bark in Mice

Background: Terminalia macroptera Guill. &amp;Perr. (Combretaceae) is a flowering plant with several ethno-medicinal claims. However, the dearth of information on its analgesic property has necessitated this study.Objectives: to evaluate the anti-nociceptive potential of ethanol extract of Terminalia macroptera stem bark (TMSB) in mice.Materials and Methods: Male and female mice of weight range 22 – 25g were randomly allotted into seven groups (n= 5) and treated as follows: Group I received 0.5 mL distilled water orally (negative control), Groups II-V were orally administered ethanol extract of T. macroptera stem bark (TMSB) at 50, 100, 200, and 400 mg/kg respectively while groups VI-VII received piroxicam 10 mg/kg and pentazocine 2 mg/kg intraperitoneally respectively as standards. The same treatment pattern was adopted for both pain models: tail immersion and acetic acid-induced writhing assays. Data were expressed as mean ± standard error of mean (SEM) using two-way analysis of variance (ANOVA) followed by Tukey’s and Bonferroni's multiple comparisons tests with p &lt; 0.05 taken as significance.Results: The ethanolic extract of Terminalia macroptera stem bark showed significant dose-dependent anti-nociceptive activity at 100 and 400 mg/kg (2.95±0.41 and 2.9±0.31 respectively) 60 min post-treatment compared to the negative control group in the tail immersion test. Significant inhibition of nociception (0.20±0.20) was obtained at 400 mg/kg compared to the negative control group in the acetic acid-induced writhing test.Conclusions: The ethanol extract of Terminalia macroptera stem bark exhibited dose-dependent anti-nociceptive potential in both tail immersion and acetic acid-induced writhing assays in mice.

The Relationship Between Adverse Life Events and Endogenous Inhibition of Pain and Spinal Nociception: Findings From the Oklahoma Study of Native American Pain Risk (OK-SNAP)

Adverse life events (ALEs) are a risk factor for chronic pain; however, mechanisms underlying this association are not understood. This study examined whether cumulative ALE exposure impairs endogenous inhibition of pain (assessed from pain report) and spinal nociception (assessed from nociceptive flexion reflex; NFR) in healthy, pain-free Native Americans (n = 124) and non-Hispanic Whites (n = 129) during a conditioned pain modulation (CPM) task. Cumulative ALE exposure was assessed prior to testing by summing the number of potentially traumatic events experienced by each participant across their lifespan. Multilevel modeling found that ALEs were associated with NFR modulation during the CPM task even after controlling for general health, body mass index, sex, age, blood pressure, sleep quality, stimulation intensity, stimulus number, perceived stress, and psychological distress. Low exposure to ALEs was associated with NFR inhibition, whereas high exposure to ALEs was associated with NFR facilitation. By contrast, pain perception was inhibited during the CPM task regardless of the level of ALE exposure. Race/ethnicity did not moderate these results. Thus, ALEs may be pronociceptive for both Native Americans and non-Hispanic Whites by impairing descending inhibition of spinal nociception. This could contribute to a chronic pain risk phenotype involving latent spinal sensitization. PerspectiveThis study found that adverse life events were associated with impaired descending inhibition of spinal nociception in a sample of Native Americans and non-Hispanic Whites. These findings expand on previous research linking adversity to chronic pain risk by identifying a proximate physiological mechanism for this association.

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

ABSTRACT 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.

Transgenic Tarantula Toxin: A novel tool to study mechanosensitive ion channels in Drosophila

The tarantula venom toxin GsMTx4 is the only known specific inhibitor of cation-selective mechanosensitive ion channels (MSCs). Its specificity, potency, and ease of use on isolated tissues and cells have made it a powerful pharmacological tool to identify and probe the physiological function of MSCs. In some contexts, however, it would be desirable to deliver the toxin in a controlled way in vivo. Here we describe a novel tool to allow spatial and temporal control of GsMTx4 delivery in vivo in Drosophila. To test the tool, we targeted MSCs required for mechanical nociception in a specific subset of sensory neurons in intact larvae. Expression of GsMTx4 in these neurons results in robust inhibition of mechanical nociception, demonstrating the toxin is active when expressed in vivo. The tool will be particularly useful to manipulate MSC activity in a spatially and temporally-controlled manner to study their role in development, physiology and behaviour in intact, free moving animals.

5-(4H)-Oxazolones and Their Benzamides as Potential Bioactive Small Molecules.

The five membered heterocyclic oxazole group plays an important role in drug discovery. Oxazolones present a wide range of biological activities. In this article the synthesis of 4-substituted-2-phenyloxazol-5(4H)-ones from the appropriate substituted aldehydes via an Erlenmeyer–Plochl reaction is reported. Subsequently, the corresponding benzamides were produced via a nucleophilic attack of a secondary amine on the oxazolone ring applying microwave irradiation. The compounds are obtained in good yields up to 94% and their structures were confirmed using IR, 1H-NMR, 13C-NMR and LC/MS data. The in vitro anti-lipid peroxidation activity and inhibitory activity against lipoxygenase and trypsin induced proteolysis of the novel derivatives were studied. Inhibition of carrageenin-induced paw edema (CPE) and nociception was also determined for compounds 4a and 4c. Oxazolones 2a and 2c strongly inhibit lipid peroxidation, followed by oxazolones 2b and 2d with an average inhibition of 86.5%. The most potent lipoxygenase inhibitor was the bisbenzamide derivative 4c, with IC50 41 μM. The benzamides 3c, 4a–4e and 5c were strong inhibitors of proteolysis. The replacement of the thienyl moiety by a phenyl group does not favor the protection. Compound 4c inhibited nociception higher than 4a. The replacement of thienyl groups by phenyl ring led to reduced biological activity. Docking studies of the most potent LOX inhibitor highlight interactions through allosteric mechanism. All the potent derivatives present good oral bioavailability.

Is the orofacial antinociceptive effect of lectins intrinsically related to their specificity to monosaccharides?

Lectins are proteins of non-immunological origin that may play several biological applications, of which we can highlight the anti-inflammatory and antinociceptive activities. In this work, we evaluated the possible effect of orofacial antinociceptive activity of three plant lectins, Dioclea violacea (DVL - Man/Glc-binding), Vatairea macrocarpa (VML - Gal-binding) and PPL (Parkia platycephala - Man/Glc-binding) in adult zebrafish. Acute nociception was induced by menthol (1.2 μM), or capsaicin (4.93 μM) applied into in the upper lip (5.0 μL) of adult wild zebrafish. Zebrafish were pretreated by intraperitoneal injection (20 μL) with vehicle (Control) or lectins (0.025; 0.05 or 0.1 mg/mL) 30 min before induction. The effect of lectins on zebrafish locomotor behavior was evaluated with the open field test. Naive groups (n = 8) were included in all tests. Our results indicate that only PPL presented antinociceptive induced by capsaicin, suggesting the potential clinical application of PPL as inhibitor of orofacial nociception and that this effect may be due to the modulation of TRPV1 channel. In conclusion, lectins that exhibit affinity to the same or different carbohydrates do not necessarily have an antinociceptive effect on the orofacial nociception model, indicating that the glycan carbohydrate binding pattern may be related to the effect on nociception inhibition.

Effects of Heating-needle Stimulation in Restoration of Weakened Descending Inhibition of Nociception in a Rat Model of Parkinson’s Disease

Here we investigated variations of endogenous descending modulation of nociception and therapeutic effects of intramuscular (i.m.) heating-needle stimulation in early stage of Parkinson’s disease (PD) induced by unilateral microinjection of 3.5 μl of 2.5 μg/μl 6-hydroxydopamine into the rat striatum. Paw withdrawal reflexes to noxious mechanical and heat stimuli in PD rats with and without exposure to i.m. 5.8% saline induced muscle nociception were evaluated. Experimental PD had no influence on mechanical or heat sensitivity in the baseline condition, whereas descending facilitation was stronger and descending inhibition was weaker in PD rats than vehicle-treated or naive rats during muscle nociception (P < 0.05). Striatal administration of 5 μg of dopamine failed to reverse the PD-associated changes in descending facilitation or inhibition, whereas dopamine in the thalamic mediodorsal (MD) nucleus and ventromedial (VM) nucleus significantly decreased the increase in descending facilitation and reversed the attenuation in descending inhibition, respectively (P < 0.05). I.m. 43 °C of heating-needle stimulation had no effects on the enhanced descending facilitation in PD rats, but it markedly increased descending inhibition and reversed the increase in the number of apomorphine-induced body rotations (P < 0.05), which effects were dose-dependently attenuated by raclopride, a dopamine 2 receptor antagonist, in the thalamic VM nucleus (P < 0.05). The results indicate that the early-stage PD is associated with enhanced descending facilitation and weakened descending inhibition. From clinical perspective, 43 °C heat therapeutic regime promises to selectively enhance descending inhibition that is accompanied by improvement of motor dysfunction in PD.

Does Motor Cortex Engagement During Movement Preparation Differentially Inhibit Nociceptive Processing in Patients with Chronic Whiplash Associated Disorders, Chronic Fatigue Syndrome and Healthy Controls? An Experimental Study.

Background: Patients with chronic fatigue syndrome (CFS) and chronic whiplash associated disorders (cWAD) present a reduced ability to activate central descending nociceptive inhibition after exercise, compared to measurements before exercise. It was hypothesised that a dysfunctional motor-induced inhibition of nociception partly explains this dysfunctional exercise-induced hypoalgesia. This study investigates if engagement of the motor system during movement preparation inhibits nociception-evoked brain responses in these patients as compared to healthy controls (HC). Methods: The experiment used laser-evoked potentials (LEPs) during three conditions (no task, mental task, movement preparation) while recording brain activity with a 32-channel electroencephalogram in 21 patients with cWAD, 20 patients with CFS and 18 HC. Two-factor mixed design Analysis of variance were used to evaluate differences in LEP amplitudes and latencies. Results: No differences in N1, N2, N2P2, and P2 LEP amplitudes were found between the HC, CFS, and cWAD groups. After nociceptive stimulation, N1, N2 (only at hand location), N2P2, and P2 LEP amplitudes significantly decreased during movement preparation compared to no task (within group differences). Conclusion: Movement preparation induces a similar attenuation of LEPs in patients with CFS, patients with cWAD and HC. These findings do not support reduced motor-induced nociceptive inhibition in these patients.

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.

The Effect of Pain Catastrophizing on Endogenous Inhibition of Pain and Spinal Nociception in Native Americans: Results From the Oklahoma Study of Native American Pain Risk.

Conditioned pain modulation (CPM) is a task that involves measuring pain in response to a test stimulus before and during a painful conditioning stimulus (CS). The CS pain typically inhibits pain elicited by the test stimulus; thus, this task is used to assess endogenous pain inhibition. Moreover, less efficient CPM-related inhibition is associated with chronic pain risk. Pain catastrophizing is a cognitive-emotional process associated with negative pain sequelae, and some studies have found that catastrophizing reduces CPM efficiency. The current study examined the relationship between catastrophizing (dispositional and situation specific) and CPM-related inhibition of pain and the nociceptive flexion reflex (NFR; a marker of spinal nociception) to determine whether the catastrophizing-CPM relationship might contribute to the higher risk of chronic pain in Native Americans (NAs). CPM of pain and NFR was assessed in 124 NAs and 129 non-Hispanic Whites. Dispositional catastrophizing was assessed at the beginning of the test day, whereas situation-specific catastrophizing was assessed in response to the CS, as well as painful electric stimuli. Situation-specific, but not dispositional, catastrophizing led to less NFR inhibition but more pain inhibition. These effects were not moderated by race, but mediation analyses found that: (a) the NA race was associated with greater situation-specific catastrophizing, which led to less NFR inhibition and more pain inhibition, and (b) situation-specific catastrophizing was associated with greater CS pain, which led to more pain inhibition. Catastrophizing may contribute to NA pain risk by disrupting descending inhibition.

Anti-inflammatory, Antipyretic and Analgesic Activities of Persimmon (Diospyros kaki) Leaves in Animal Model

Diospyros kaki L. (Ebenaceae) fruit and leaves are traditionally used for the treatment of hypertension and angina, as well as for their antithrombotic and anti-inflammatory effects. We investigated the anti-inflammatory, analgesic and antipyretic activities of Diospyros kaki L. (Ebenaceae) in order to scientifically validate its pharmacological importance. In the current study, the anti-inflammatory, analgesic and antipyretic activities of ethyl acetate (Per-1), n-butanol (Per-2) and aqueous (Per-3) fractions of a methanol extract of Persimmon leaves were tested. Wistar rats weighing 190–210 g (for the anti-inflammatory assay) and male albino mice (Swiss) weighing 18–24 g (for the antipyretic and analgesic assays) were utilized as the experimental animals. The rats were separated into eight groups (for anti-inflammatory) and seven group (for antipyretic), each consisting of six rats. Each sample was treated orally and two doses: 100 and 200 mg/kg body weight were used in these experiments. The Per-3 sample at a dose of 200 mg/kg produced the highest inflammation inhibition at 59.28%. The same sample at a dose of 200 mg/kg lowered body temperature from 38°C of hyperthermia mice back to 36.65 ± 0.12°C after 120 min, close to the normal temperature (35.21 ± 0.29°C). In the tail flick model, sample Per-3 showed 67.74% highest nociception inhibition. Similar results were obtained with Acetic acid and hot-plate assay. These results confirm that the n-butanol and aqueous fractions of persimmon are active and may be used for further pharmacological screening.