Supraspinal Level Research Articles

Supraspinal facilitation of painful stimuli by glutamatergic innervation from the retrosplenial to the anterior cingulate cortex.

The anterior cingulate cortex (ACC) is recognized as a pivotal cortical region involved in the perception of pain. The retrosplenial cortex (RSC), located posterior to the ACC, is known to play a significant role in navigation and memory processes. Although the projections from the RSC to the ACC have been found, the specifics of the synaptic connections and the functional implications of the RSC-ACC projections remain less understood. In this study, we employed a combination of whole-brain imaging, in vitro electrophysiology, and two-photon calcium imaging techniques to confirm the presence of direct excitatory glutamatergic projections from the RSC to the ACC in mice. This excitatory transmission is predominantly mediated by the postsynaptic AMPA receptors. Furthermore, the activation of the RSC-ACC projections through opto-/chemogenetics significantly facilitated the behavioral responses to both mechanical and thermal nociceptive stimuli in adult mice. Notably, this activation did not influence spinal nociceptive responses in the tail-flick test, nor did it affect anxiety-like or aversive behaviors. These findings indicate that the RSC-ACC glutamatergic pathway modulates nociceptive perception primarily at the supraspinal cortical level. We have identified a novel cortico-cortical facilitatory pathway that contributes to nociceptive processing in the cingulate cortex. The RSC-ACC pathway probably serves to integrate memory engrams with pain perception in both humans and animals.

Effect of somatic afferent nerve-visceral nerve circuit in the regulation of the gastrointestinal function with acupuncture and moxibustion

The distribution of the common acupoints of acupuncture-moxibustion for gastrointestinal diseases conforms to the rule of the segmental homology of somatic afferent nerve-visceral nerve circuit at the spinal cord level. Acupuncture-moxibustion regulates the gastrointestinal function through the nerve-endocrine-immune system, and especially depending on the integrity of the structure and function of nervous system. The somatic afferent nerve-visceral nerve circuit plays an important role in the process of acupuncture and moxibustion for regulating the gastrointestinal function. There are three dimensions. ① The somatic afferent nerve-visceral nerve circuit at the peripheral level, including the somatic afferent nerve-visceral afferent nerve circuit centered on the dorsal root ganglion, and the somatic afferent nerve-visceral efferent nerve circuit centered on the sympathetic ganglia; ② that at the spinal cord level; ③ that at the supra-spinal cord level, focusing on the various reflex circuits with the solitary nucleus involved. The somatic afferent nerve-visceral nerve circuit at the spinal level and inferior to it determines the segmental regulation of acupuncture-moxibustion in the gastrointestinal system, while that at the level superior to the spinal cord determines the supersegmental action of acupuncture-moxibustion in regulating the gastrointestinal system. The neurophysiological mechanism of acupuncture-moxibustion is multi-circuits and multi-targets in regulating gastrointestinal function.

Spinal Regulation of Posture: Effects of Transcutaneous Spinal Cord and Affective Sound Stimulation.

The combined effects of transcutaneous electrical stimulation (tES) of the spinal cord and affective sound stimulation on postural control were investigated to elucidate the involvement of spinal networks in the maintenance of vertical stability. Healthy volunteers (n = 27) underwent tES and sound stimulation separately and combined quasi-randomly. All participants were field-dependent; i.e., participants used the exteroceptive afferent stream for spatial orientation. Centre-of-pressure parameters were analysed to assess postural stability. Results showed that tES at the T11-T12 vertebrae stabilised posture, tES at the L1-L2 vertebrae had no postural effect, and sound stimulation from the left destabilised posture. To assess the role of spinal regulation of postural disturbances, we compared the effects of combined tES with sound stimulation to those of sound stimulation alone. Stimulation at the T11-T12 level reduced the lateral sway induced by affective sounds, whereas L1-L2 tES did not. These results suggest that, in healthy individuals, spinal networks located at the T11-T12 and L1-L2 vertebral levels have distinct roles in maintaining upright posture, both when a person is standing still and when they are actively stabilising their posture during destabilising perturbations. T11-T12 spinal networks stabilise upright posture when destabilising information is solely transmitted from the supraspinal level.

The participation of monoamines in the realization of vasopressin analgesic effects during electrical stimulation of paws in rats

BACKGROUND: Arginine vasopressin has been implicated in the modulation of stress and pain. The influence of a synthetic analogue of arginine vasopressin, 1-deamino-8-D-arginine-vasopressin, оn pain sensitivity, stress reactivity, levels of monoamines and brain neurotrophic factor in a model of paw electrical stimulation in rats has not been studied. AIM: The aim was to evaluate the effect of a synthetic vasopressin analog, 1-deamino-8-D-arginine-vasopressin, on pain sensitivity and the content of norepinephrine, serotonin, dopamine, brain neurotrophic factor in the parietal cortex and spinal cord in electrocutaneous paw stimulation test in rats. MATERIALS AND METHODS: The study was conducted on male Wistar rats who were injected with 1-deamino-8-D-arginine-vasopressin intranasally once a day for 5 days in small (single 20 ng, course 100 ng) and large doses (single 2 ug, course 10 ug). The content of brain neurotrophic factor in the parietal cortex and spinal cord, and corticosterone in blood serum were determined using enzyme immunoassay. The levels of norepinephrine, serotonin, dopamine and their metabolites in the brain were evaluated using high-performance liquid chromatography. RESULTS: 1-Deamino-8-D-arginine-vasopressin in different doses reduced pain sensitivity in rats, more pronounced when administered in large doses. The peptide in small doses in the parietal cortex increased the content of dopamine and reduced the levels of 5-hydroxyindolacetic acid, a metabolite of serotonin; in the spinal cord, it reduced the content of 5-hydroxyindolacetic acid. 1-Deamino-8-D-arginine-vasopressin in high doses in the parietal cortex increased the content of dopamine and reduced the levels of 5-hydroxyindolacetic acid; in the spinal cord ― reduced the content of serotonin and 3,4-dihydroxyphenylacetic acid, a metabolite of dopamine; increased the levels of norepinephrine and homovanilic acid, a metabolite of dopamine. The peptide had no effect on corticosterone levels in the blood and brain neurotrophic factor levels in the brain in rats. CONCLUSIONS: The analgesic effects of 1-deamino-8-D-arginine-vasopressin were revealed with intranasal administration in different subendocrine doses. Regardless of the administered doses, dopamine and serotonin at the supraspinal level were involved in peptide-induced anesthesia; serotonin at the spinal cord level. More pronounced analgesia with the administration of 1-deamino-8-D-arginine-vasopressin in high doses was due to the additional involvement of dopamine and norepinephrine at the spinal cord level.

Short Lysine-Containing Tripeptide as Analgesic Substance: The Possible Mechanism of Ligand–Receptor Binding to the Slow Sodium Channel

A possible molecular mechanism of the ligand–receptor binding of Ac-Lys-Lys-Lys-NH2 (Ac-KKK-NH2) to the NaV1.8 channel that is responsible for nociceptive signal coding in the peripheral nervous system is investigated by a number of experimental and theoretical techniques. Upon Ac-KKK-NH2 application at 100 nM, a significant decrease in the effective charge carried by the NaV1.8 channel activation gating system Zeff is demonstrated in the patch-clamp experiments. A strong Ac-KKK-NH2 analgesic effect at both the spinal and supraspinal levels is detected in vivo in the formalin test. The distances between the positively charged amino groups in the Ac-KKK-NH2 molecule upon binding to the NaV1.8 channel are 11–12 Å, as revealed by the conformational analysis. The blind docking with the NaV1.8 channel has made it possible to locate the Ac-KKK-NH2 binding site on the extracellular side of the voltage-sensing domain VSDI. The Ac-KKK-NH2 amino groups are shown to form ionic bonds with Asp151 and Glu157 and a hydrogen bond with Thr161, which affects the coordinated movement of the voltage sensor up and down, thus modulating the Zeff value. According to the results presented, Ac-KKK-NH2 is a promising candidate for the role of an analgesic medicinal substance that can be applied for pain relief in humans.

Recent advances in acupuncture for pain relief.

Acupuncture therapy has achieved global expansion and shown promise for health promotion and treatment of acute/chronic pain. To present an update on the existing evidence base for research and clinical practice supporting acupuncture analgesia. This Clinical Update elaborates on the 2023 International Association for the Study of Pain Global Year for Integrative Pain Care "Factsheet Acupuncture for Pain Relief" and reviews best evidence and practice. Acupuncture is supported by a large research evidence base and growing utilization. Mechanisms of acupuncture analgesia include local physiological response at the needling site, suppression of nociceptive signaling at spinal and supraspinal levels, and peripheral/central release of endogenous opioids and other biochemical mediators. Acupuncture also produces pain relief by modulating specific brain networks, integral for sensory, affective, and cognitive processing, as demonstrated by neuroimaging research. Importantly, acupuncture does not just manage pain symptoms but may target the sources that drive pain, such as inflammation, partially by modulating autonomic pathways. Contextual factors are important for acupuncture analgesia, which is a complex multifaceted intervention. In clinical practice, historical records and many providers believe that acupuncture efficacy depends on specific acupoints used, the technique of needle placement and stimulation, and the person who delivers the procedure. Clinical research has supported the safety and effectiveness of acupuncture for various pain disorders, including acupuncture as a complementary/integrative therapy with other pain interventions. Although the quality of supportive evidence is heterogeneous, acupuncture's potential cost-effectiveness and low risk profile under standardized techniques suggest consideration as a neuromodulatory and practical nonpharmacological pain therapy.

BNT12, a novel hybrid peptide of opioid and neurotensin pharmacophores, produces potent central antinociception with limited side effects

The development of multitarget opioid drugs has emerged as an attractive approach for innovative pain management with reduced side effects. In the present study, a novel hybrid peptide BNT12 containing the opioid and neurotensin (NT)-like fragments was synthesized and pharmacologically characterized. In acute radiant heat paw withdrawal test, intracerebroventricular (i.c.v.) administration of BNT12 produced potent antinociception in mice. The central antinociceptive activity of BNT12 was mainly mediated by μ-, δ-opioid receptor, neurotensin receptor type 1 (NTSR1) and 2 (NTSR2), supporting a multifunctional agonism of BNT12 in the functional assays. BNT12 also exhibited significant antinociceptive effects in spared nerve injury (SNI)-neuropathic pain, complete Freund's adjuvant (CFA)-induced inflammatory pain, acetic acid-induced visceral and formalin-induced pain after i.c.v. administration. Furthermore, BNT12 exhibited substantial reduction of acute antinociceptive tolerance, shifted the dose-response curve to the right by only 1.3-fold. It is noteworthy that BNT12 showed insignificant chronic antinociceptive tolerance at the supraspinal level. In addition, BNT12 exhibited reduced or no opioid-like side effects on conditioned place preference (CPP) response, naloxone-precipitated withdrawal response, acute hyperlocomotion, motor coordination, gastrointestinal transit, and cardiovascular responses. The present investigation demonstrated that the novel hybrid peptide BNT12 might serve as a promising analgesic candidate with limited opioid-like side effects.

The Analgesic Potential of Litsea Species: A Systematic Review.

Various plant species from the Litsea genus have been claimed to be beneficial for pain relief. The PRISMA approach was adopted to identify studies that reported analgesic properties of plants from the Litsea genus. Out of 450 records returned, 19 primary studies revealed the analgesic potential of nine Litsea species including (1) Litsea cubeba, (2) Litsea elliptibacea, (3) Litsea japonica, (4) Litsea glutinosa, (5) Litsea glaucescens, (6) Litsea guatemalensis, (7) Litsea lancifolia, (8) Litsea liyuyingi and (9) Litsea monopetala. Six of the species, 1, 3, 4, 7, 8 and 9, demonstrated peripheral antinociceptive properties as they inhibited acetic-acid-induced writhing in animal models. Species 1, 3, 4, 8 and 9 further showed effects via the central analgesic route at the spinal level by increasing the latencies of heat stimulated-nocifensive responses in the tail flick assay. The hot plate assay also revealed the efficacies of 4 and 9 at the supraspinal level. Species 6 was reported to ameliorate hyperalgesia induced via partial sciatic nerve ligation (PSNL). The antinociceptive effects of 1 and 3 were attributed to the regulatory effects of their bioactive compounds on inflammatory mediators. As for 2 and 5, their analgesic effect may be a result of their activity with the 5-hydroxytryptamine 1A receptor (5-HT1AR) which disrupted the pain-stimulating actions of 5-HT. Antinociceptive activities were documented for various major compounds of the Litsea plants. Overall, the findings suggested Litsea species as good sources of antinociceptive compounds that can be further developed to complement or substitute prescription drugs for pain management.

Hypothalamic Paraventricular Stimulation Inhibits Nociceptive Wide Dynamic Range Trigeminocervical Complex Cells via Oxytocinergic Transmission.

Oxytocinergic transmission blocks nociception at the peripheral, spinal, and supraspinal levels through the oxytocin receptor (OTR). Indeed, a neuronal pathway from the hypothalamic paraventricular nucleus (PVN) to the spinal cord and trigeminal nucleus caudalis (Sp5c) has been described. Hence, although the trigeminocervical complex (TCC), an anatomical area spanning the Sp5c, C1, and C2 regions, plays a role in some pain disorders associated with craniofacial structures (e.g., migraine), the role of oxytocinergic transmission in modulating nociception at this level has been poorly explored. Hence, in vivo electrophysiological recordings of TCC wide dynamic range (WDR) cells sensitive to stimulation of the periorbital or meningeal region were performed in male Wistar rats. PVN electrical stimulation diminished the neuronal firing evoked by periorbital or meningeal electrical stimulation; this inhibition was reversed by OTR antagonists administered locally. Accordingly, neuronal projections (using Fluoro-Ruby) from the PVN to the WDR cells filled with Neurobiotin were observed. Moreover, colocalization between OTR and calcitonin gene-related peptide (CGRP) or OTR and GABA was found near Neurobiotin-filled WDR cells. Retrograde neuronal tracers deposited at the meningeal (True-Blue, TB) and infraorbital nerves (Fluoro-Gold, FG) showed that at the trigeminal ganglion (TG), some cells were immunopositive to both fluorophores, suggesting that some TG cells send projections via the V1 and V2 trigeminal branches. Together, these data may imply that endogenous oxytocinergic transmission inhibits the nociceptive activity of second-order neurons via OTR activation in CGRPergic (primary afferent fibers) and GABAergic cells.

Novel endomorphin analogues CEMR-1 and CEMR-2 produce potent and long-lasting antinociception with a favourable side effect profile at the spinal level.

Endomorphins have shown great promise as pharmaceutics for the treatment of pain. We have previously confirmed that novel endomorphin analogues CEMR-1 and CEMR-2 behaved as potent μ agonists and displayed potent antinociceptive activities at the supraspinal and peripheral levels. The present study was undertaken to evaluate the antinociceptive properties of CEMR-1 and CEMR-2 following intrathecal (i.t.) administration. Furthermore, their antinociceptive tolerance and opioid-like side effects were also determined. The spinal antinociceptive effects of CEMR-1 and CEMR-2 were determined in a series of pain models, including acute radiant heat paw withdrawal test, spared nerve injury-induced neuropathic pain, complete Freund's adjuvant-induced inflammatory pain, visceral pain and formalin pain. Antinociceptive tolerance was evaluated in radiant heat paw withdrawal test. Spinal administration of CEMR-1 and CEMR-2 produced potent and prolonged antinociceptive effects in acute pain. CEMR-1 and CEMR-2 may produce their antinociception through distinct μ receptor subtypes. These two analogues also exhibited significant analgesic activities in neuropathic, inflammatory, visceral and formalin pain at the spinal level. It is noteworthy that CEMR-1 showed non-tolerance-forming analgesic properties, while CEMR-2 exhibited substantially reduced antinociceptive tolerance. Furthermore, both analogues displayed no or reduced side effects on conditioned place preference response, physical dependence, locomotor activity and gastrointestinal transit. The present investigation demonstrated that CEMR-1 and CEMR-2 displayed potent and long-lasting antinociception with a favourable side effect profile at the spinal level. Therefore, CEMR-1 and CEMR-2 might serve as promising analgesic compounds with minimal opioid-like side effects.

Effect of curcumin on formalin-induced muscle pain in male rats: role of local cyclooxygenase system.

Investigating the mechanisms responsible for pain processing of natural and synthetic chemical compounds is necessary to optimize pain management. Curcumin (Cur), the active ingredient of turmeric, exhibits potent analgesic and anti-inflammatory properties by employing multiple mechanisms at the local peripheral, spinal and supra-spinal levels. This study was aimed to investigate the effect of oral administration of Cur on muscle pain induced by intramuscular (IM) injection of formalin. To explore the possible local mechanisms, a cyclooxygenase (COX) inhibitor, diclofenac (Dic) and a COX product, prostaglandin E2 (PGE2), were applied. The IM injection of formalin (25.00 µL, 2.50%) into the gastrocnemius muscle induced two distinct phases of hind leg flinching. A short-lasting (10 min) hind leg lifting was observed following IM injection of PGE2 (2 µg kg-1, 25.00 µL). Oral administration of Cur (25.00 and 100 mg kg-1) and IM injection of 40.00 µg kg-1 Dic attenuated formalin and PGE2 induced nociceptive behaviors. Contra-lateral IM injection of Dic did not change muscle pain induced by ipsilateral IM injection of formalin and PGE2. The second phase of formalin induced flinching as well as PGE2 evoked lifting were more suppressed when 40.00 µg kg-1 Dic and 100 mg kg-1 Cur were used together. Locomotor activity was not changed by the above-mentioned treatments. It was concluded that the reducing effect of muscle pain of Cur might be related to the local inhibition of COX.

Peripheral Branch Injury Induces Oxytocin Receptor Expression at the Central Axon Terminals of Primary Sensory Neurons.

Considerable evidence suggests that oxytocin, as a regulatory nonapeptide, participates in modulatory mechanisms of nociception. Nonetheless, the role of this hypothalamic hormone and its receptor in the sensory pathway has yet to be fully explored. The present study performed immunohistochemistry, enzyme-linked immunosorbent assay, and RT-qPCR analysis to assess changes in the expression of the neuronal oxytocin receptor in female rats following tight ligation of the sciatic nerve after 1, 3, and 7 days of survival. Oxytocin receptor immunoreactivity was present in both dorsal root ganglia and lumbar spinal cord segments, but not accumulated at the site of the ligation of the peripheral nerve branch. We found a time-dependent change in the expression of oxytocin receptor mRNA in L5 dorsal root ganglion neurons, as well as an increase in the level of the receptor protein in the lumbar segment of the spinal cord. A peak in the expression was observed on day 3, which downturned slightly by day 7 after the nerve ligation. These results show that OTR expression is up-regulated in response to peripheral nerve lesions. We assume that the importance of OTR is to modify spinal presynaptic inputs of the sensory neurons upon injury-induced activation, thus to be targets of the descending oxytocinergic neurons from supraspinal levels. The findings of this study support the concept that oxytocin plays a role in somatosensory transmission.

Endomorphin-2 analogs with C-terminal esterification display potent antinociceptive effects in the formalin pain test in mice

Previously, we have investigated three C-terminal esterified endomorphin-2 (EM-2) analogs EM-2-Me, EM-2-Et and EM-2-Bu with methyl, ethyl and tert-butyl ester modifications, respectively. These analogs produced significant antinociception in acute pain at the spinal and supraspinal levels, with reduced tolerance and gastrointestinal side effects. The present study was undertaken to determine the analgesic effects and opioid mechanisms of these three analogs in the formalin pain test. Our results demonstrated that intracerebroventricular (i.c.v.) administration of 0.67–20 nmol EM-2 analogs EM-2-Me, EM-2-Et and EM-2-Bu produced dose-dependent antinociceptive effects in both phase Ⅰ and phase Ⅱ of formalin pain. EM-2-Me and EM-2-Bu displayed more potent antinociception than morphine. Especially, EM-2-Bu exhibited the highest antinociception in phase Ⅱ of formalin pain, with the ED50 value being 2.1 nmol. Naloxone (80 nmol, i.c.v.) completely antagonized the antinociceptive effects of EM-2-Me, EM-2-Et and EM-2-Bu (20 nmol, i.c.v.) in both phase I and phase Ⅱ of formalin pain, suggesting a central opioid mechanism. Nevertheless, the antinociception induced by EM-2-Me might be involved in the release of dynorphin A, which subsequently acted on κ- opioid receptor. EM-2-Bu produced the antinociception probably by the direct activation of both μ- and δ-opioid receptors. EM-2-Me, EM-2-Et and EM-2-Bu also produced significant analgesic effects after peripheral administration, and the central opioid receptors were involved. Furthermore, EM-2-Bu had no influence on the locomotor activity after i.c.v. injection. The present investigation demonstrated that C-terminal esterified modifications of EM-2 will be beneficial for developing novel therapeutics in formalin pain.

Effect of Fenofibrate as PPARα Agonist in Suppressing the Development of Oxaliplatin-Induced Peripheral Neuropathy via TRPA1 Modulation

Background: CIPN (Chemotherapy-induced Peripheral Neuropathy) primarily affects the sensory system and is accompanied by pain, autonomic dysfunction, and motor impairments. Alterations of intracellular second messengers at the supraspinal level in CIPN needed to be explored more. In addition, there is a lack of evidence regarding implications for the supraspinal area through the propagation of pain via the ascending pathway. Objective: In this study, we evaluated the effect of fenofibrate as a PPARα agonist in suppressing the development of CIPN. Methods: Twenty-four mice were distributed to the normal control group, neuropathy group, and neuropathy with the treatment of fenofibrate 75 and 150 mg/kg groups, resulting in 6 animals per group. Oxaliplatin was injected on days 0, 2, 4, and 6. The hot plate test was performed before the oxaliplatin administration and then continued on the 7th, 14th, and 21st days. Thalamus tissues were collected to measure the TRPA1 mRNA expression using qPCR. Results: Fenofibrate 75 mg/kg co-treatment with oxaliplatin tended to prevent the enhancement of oxaliplatin-induced thermal hyperalgesia in hind-paw withdrawal and rubbing responses. Furthermore, fenofibrate 75 and 150 mg/kg co-treatment with oxaliplatin significantly reduced the relative TRPA1 mRNA expression but did not modulate the relative BDNF mRNA expression in the thalamus. Conclusion: PPARα agonist has a potential effect in suppressing the development of CIPN. However, given the various perspectives on the role of neurotrophins in CIPN, additional non-clinical investigations, are needed to provide more insight into other mechanisms of CIPN and the role of PPAR agonists.

Spinal displacement during thoracic manipulative therapy in mechanical neck pain patients: an observational study

ABSTRACT Introduction Thoracic manipulative therapy (TMT) is recommended for treating patients with mechanical neck pain (MNP). However, there are multiple proposed recommendations for the mechanism for neck pain reduction. Objective To investigate displacement of the cervicothoracic spine during the application of TMT in patients with MNP. Methods Thirty-five male patients with MNP were recruited. Displacements of C3, C5, C7, T2, T4 and T6 were measured using a motion capture system while a therapist applied a grade III central posteroanterior TMT (cpa-TMT) to T6. Results Mean (SD) displacement ranged from 2.2 (0.62) to 5.5 (1.1) mm. A significant decrease in neck pain intensity at rest was found after the application of the cpa-TMT (mean difference 17 mm, p < 0.001). A downward trend in spinal displacement was noted, with the largest and smallest displacement occurring at T6 and C3, respectively. Correlations between the displacement of T6 and adjacent spinal levels were moderate to high (Pearson’s r range 0.70–0.90, p < 0.001). It was showed that cpa-TMT applied to T6 produced the PA displacement toward the upper cervical spine. Conclusion TMT produces spinal segmental displacements toward the upper cervical spine in MNP patients. These segmental displacements would activate the alleviation effect at both the spinal and supraspinal levels resulting in neck pain reduction. These findings would provide supporting evidence for the use of TMT in neck pain reduction.

Anti-allodynic and medullary modulatory effects of a single dose of delta-9-tetrahydrocannabinol (THC) in neuropathic rats tolerant to morphine

Neuropathic pain (NP) is often treated with opioids, the prolonged use of which causes tolerance to their analgesic effect and can potentially cause death by overdose. The phytocannabinoid delta-9-tetrahydrocannabinol (THC) may be an effective alternative analgesic to treat NP in morphine-tolerant subjects. Male Wistar rats developed NP after spared nerve injury, and were then treated with increasing doses of THC (1, 1.5, 2, 2.5, and 5 mg/kg, intraperitoneally), which reduced mechanical allodynia at the dose of 2.5 and 5 mg/kg. Another group of NP rats were treated with morphine (5 mg/kg, twice daily for 7 days, subcutaneously), until tolerance developed, and on day 8 received a single dose of THC (2.5 mg/kg), which significantly reduced mechanical allodynia. To evaluate the modulation of THC in the descending pain pathway, in vivo electrophysiological recordings of pronociceptive ON cells and antinociceptive OFF cells in the rostroventral medulla (RVM) were recorded after intra-PAG microinjection of THC (10 μg/μl). NP rats with morphine tolerance, compared to the control one, showed a tonic reduction of the spontaneous firing rate of ON cells by 44%, but the THC was able to further decrease it (a hallmark of many analgesic drugs acting at supraspinal level). On the other hand, the firing rate, of the antinociceptive OFF cells was increased after morphine tolerance by 133%, but the THC failed to further activate it. Altogether, these findings indicate that a single dose of THC produces antiallodynic effect in individuals with NP who are tolerant to morphine, acting mostly on the ON cells of the descending pain pathways, but not on OFF cells.

Differences between brain responses to peroneal electrical transcutaneous neuromodulation and transcutaneous tibial nerve stimulation, two treatments for overactive bladder.

To compare brain responses to peroneal electrical transcutaneous neuromodulation (peroneal eTNM®) and transcutaneous tibial nerve stimulation (TTNS), two methods for treating overactive bladder (OAB), using functional magnetic resonance imaging (fMRI). The present study was not designed to compare their clinical efficacy. This study included 32 healthy adult female volunteers (average age 38.3 years (range 22-73)). Brain MRI using 3 T scanner was performed during three 8-min blocks of alternating sequences. During each 8-min block, the protocol alternated between sham stimulation (30 s) and rest (30 s) for 8 repeats; then peroneal eTNM® stimulation (30 s) and rest (30 s) for 8 repeats; then, TTNS stimulation (30 s) and rest (30 s) for 8 repeats. Statistical analysis was performed at the individual level with a threshold of p = 0.05, family-wise error (FWE)-corrected. The resulting individual statistical maps were analyzed in group statistics using a one-sample t-test, p = 0.05 threshold, false discovery rate (FDR)-corrected. During peroneal eTNM®, TTNS, and sham stimulations, we recorded activation in the brainstem, bilateral posterior insula, bilateral precentral gyrus, bilateral postcentral gyrus, left transverse temporal gyrus, and right supramarginal gyrus. During both peroneal eTNM® and TTNS stimulations, but not sham stimulations, we recorded activation in the left cerebellum, right transverse temporal gyrus, right middle frontal gyrus, and right inferior frontal gyrus. Exclusively during peroneal eTNM® stimulation, we observed activation in the right cerebellum, right thalamus, bilateral basal ganglia, bilateral cingulate gyrus, right anterior insula, right central operculum, bilateral supplementary motor cortex, bilateral superior temporal gyrus, and left inferior frontal gyrus. Peroneal eTNM®, but not TTNS, induces the activation of brain structures that were previously implicated in neural control of the of bladder filling and play an important role in the ability to cope with urgency. The therapeutic effect of peroneal eTNM® could be exerted, at least in part, at the supraspinal level of neural control.

Central medial thalamic nucleus dynamically participates in acute itch sensation and chronic itch-induced anxiety-like behavior in male mice

Itch is an annoying sensation consisting of both sensory and emotional components. It is known to involve the parabrachial nucleus (PBN), but the following transmission nodes remain elusive. The present study identified that the PBN-central medial thalamic nucleus (CM)-medial prefrontal cortex (mPFC) pathway is essential for itch signal transmission at the supraspinal level in male mice. Chemogenetic inhibition of the CM-mPFC pathway attenuates scratching behavior or chronic itch-related affective responses. CM input to mPFC pyramidal neurons is enhanced in acute and chronic itch models. Specifically chronic itch stimuli also alter mPFC interneuron involvement, resulting in enhanced feedforward inhibition and a distorted excitatory/inhibitory balance in mPFC pyramidal neurons. The present work underscores CM as a transmit node of the itch signal in the thalamus, which is dynamically engaged in both the sensory and affective dimensions of itch with different stimulus salience.

Altered Brain Expression of DNA Methylation and Hydroxymethylation Epigenetic Enzymes in a Rat Model of Neuropathic Pain.

The role of epigenetics in chronic pain at the supraspinal level is yet to be fully characterized. DNA histone methylation is crucially regulated by de novo methyltransferases (DNMT1-3) and ten-eleven translocation dioxygenases (TET1-3). Evidence has shown that methylation markers are altered in different CNS regions related to nociception, namely the dorsal root ganglia, the spinal cord, and different brain areas. Decreased global methylation was found in the DRG, the prefrontal cortex, and the amygdala, which was associated with decreased DNMT1/3a expression. In contrast, increased methylation levels and mRNA levels of TET1 and TET3 were linked to augmented pain hypersensitivity and allodynia in inflammatory and neuropathic pain models. Since epigenetic mechanisms may be responsible for the regulation and coordination of various transcriptional modifications described in chronic pain states, with this study, we aimed to evaluate the functional role of TET1-3 and DNMT1/3a genes in neuropathic pain in several brain areas. In a spared nerve injury rat model of neuropathic pain, 21 days after surgery, we found increased TET1 expression in the medial prefrontal cortex and decreased expression in the caudate-putamen and the amygdala; TET2 was upregulated in the medial thalamus; TET3 mRNA levels were reduced in the medial prefrontal cortex and the caudate-putamen; and DNMT1 was downregulated in the caudate-putamen and the medial thalamus. No statistically significant changes in expression were observed with DNMT3a. Our results suggest a complex functional role for these genes in different brain areas in the context of neuropathic pain. The notion of DNA methylation and hydroxymethylation being cell-type specific and not tissue specific, as well as the possibility of chronologically differential gene expression after the establishment of neuropathic or inflammatory pain models, ought to be addressed in future studies.

Preparations methods of tizanidine (API) and related compounds: A review

Tizanidine is an imidazoline derivative with the agonistic activity of central alpha 2 receptors at both the spinal and supra-spinal levels. It was prepared for the first time in 1978 and approved for use in 1996. The present review focuses on all methods used for the synthesis of tizanidine, related compounds and intermediates. This review article covers all the methods that have been used in the preparation of tizanidine since its discovery until now. Methods used for the preparation of tizanidine-related compounds are also covered. This review gives those interested in drug synthesis and designs the ability to form a complete picture of the preparation of this drug, as well as providing the opportunity for the synthesis of other drugs developed from this drug to increase activity and/or reduce side effects.