Analgesic effect of intrathecally administered orexin-A in the rat formalin test and in the rat hot plate test

The involvement of orexin-1 receptors in modulation of feeding and anxiety-like behavior in rats with complete Freund's adjuvant-induced temporomandibular joint disorder

Orexin-A (OXA), a neuropeptide produced in the hypothalamus, is recognized for its role in modulating orofacial nociception and regulating feeding behaviors, as well as its impact on psychophysiological responses. This study investigated the role of orexin-1 receptors (OX1R) in modulating nociceptive behaviors induced by noxious stimulation of the temporomandibular joint (TMJ) and the associated changes in mood and feeding behaviors in rats with complete Freund's adjuvant (CFA)-induced temporomandibular disorders (TMDs). Bilateral cannulation of the lateral ventricles was performed in rats. To induce nociception, CFA was injected unilaterally into the left TMJ of the rats. Nociceptive behaviors were assessed using the hot plate and tail flick tests, while anxiety-like behavior and food intake were evaluated using an elevated plus maze (EPM) and a food preference device, respectively. The results demonstrated a significant increase in nociceptive scores and anxiety-like behaviors, along with reductions in water and food consumption following CFA injection. However, post-treatment with OXA at concentrations of 50 and 100 pM/rat significantly decreased thermal nociceptive scores, alleviated anxiety-like behavior, and increased water and food intake. These beneficial effects were reversed when OXA was co-administered with SB-334867 (40 nM/rat), an OX1R antagonist. Collectively, our findings suggest that OX1R signaling plays a role in the modulation of anxiety-like behavior and abnormalities in food intake in CFA-treated rats. Understanding the involvement of OXA and its receptors in CFA-induced TMJ nociception and behavioral changes may pave the way for potential therapeutic interventions targeting OX1R signaling in the management of TMD-associated symptoms.

Fisetin mitigates cisplatin-induced peripheral neuropathy: a behavioral and immunohistochemical study

BACKGROUND

Cisplatin (CIS), a commonly used chemotherapeutic drug, often causes peripheral neuropathy, considerably affecting patients' quality of life. The present study investigated the neuroprotective effects of fisetin, a natural flavonoid with antioxidant and anti-inflammatory features, in a rat model of cisplatin-induced peripheral neuropathy.

METHODS AND RESULTS

Male Wistar rats were divided into six groups: sham, neuropathy (CIS, 3 mg/kg, 5 weeks), fisetin treatment (CIS + 10 mg/kg and CIS + 20 mg/kg), and drugs control groups (10 mg/kg and 20 mg/kg fisetin alone). Behavioural experiments were conducted to evaluate motor coordination and sensory function, electrophysiologically measured nerve conduction velocity (NCV). Gene expression studies were conducted for NF-kB and GPX4 to investigate oxidative stress and inflammation. Finally, confocal microscopy studies were used to evaluate the structure of the sciatic nerve. Cisplatin induced motor impairments, sensory dysfunction, mechanical allodynia, diminished nerve conduction velocity, myelin deterioration (decreased MBP), and increased neuroinflammation (elevated GFAP and NF-kB, decreased GPX4). Fisetin, specifically at a dose of 10 mg/kg, markedly enhanced motor coordination, sensory thresholds, NCV, maintained myelin integrity, reduced glial activation, and restored oxidative and inflammatory balance by elevating GPX4 levels and decreasing NF-kB expression.

CONCLUSIONS

These results highlight fisetin's potential as a therapeutic agent for cisplatin-induced neuropathy, emphasising its role in restoring molecular, structural, and functional integrity within the peripheral nervous system.

Narcolepsy: Beyond the Classic Pentad

Narcolepsy is a rare, disabling, chronic neurologic disorder that requires lifelong management of symptoms with pharmacologic and nonpharmacologic methods. The pentad symptoms of narcolepsy include excessive daytime sleepiness, cataplexy, disrupted nighttime sleep, sleep paralysis, and hypnagogic/hypnopompic hallucinations. However, people with narcolepsy often experience additional symptoms and disability related to nonpentad symptoms and comorbidities, such as cognitive, psychiatric, metabolic, and sleep disturbances. Current treatment strategies have focused primarily on addressing two of the pentad symptoms, excessive daytime sleepiness, and cataplexy, mainly owing to medication options being approved by the US Food and Drug Administration for these specific indications, neglecting the full 24-h impact and spectrum of symptoms. Meanwhile, the burden of disease extends far beyond these symptoms, and optimal management should reflect a comprehensive, patient-specific approach that not only addresses the entire pentad, but also goes beyond it to include the complete clinical presentation and manifestations of the disease. Individualized treatment must consider the patient's age and stage of life, most debilitating symptoms, support system and structure, comorbid conditions, treatment goals, and overall health. This review discusses care considerations for people living with narcolepsy in the context of their clinical characteristics beyond the hallmark features of narcolepsy.

Molecular Transformers: Adaptive Multitarget Ligands for Esterase-Induced Transition from Analgesics to Anesthetics

Multitarget strategies are essential in addressing complex diseases, yet developing multitarget-directed ligands (MTDLs) is particularly challenging when aiming to engage multiple therapeutic targets across different tissues. Here, we present a molecular transformer strategy, enhancing traditional MTDLs. By utilizing esterase-driven hydrolysis, this approach mimics the adaptive nature of transformers for enabling molecules to modify their pharmacological effects in response to the biological milieu. By virtual screening and biological evaluation, we identified KGP-25, a novel compound initially targeting the voltage-gated sodium channel 1.8 (Nav1.8) in the peripheral nervous system (PNS) for analgesia, and later the γ-aminobutyric acid subtype A receptor (GABAA) in the central nervous system (CNS) for general anesthesia. Our findings confirm KGP-25's dual efficacy in cellular and animal models, effectively reducing opioid-related side effects. This study validates the molecular transformer approach in drug design and highlights its potential to overcome the limitations of conventional MTDLs, paving new avenues in innovative therapeutic strategies.

The fentanyl-specific antibody FenAb024 can shield against carfentanil effects

The surge in opioid-related deaths, driven predominantly by fentanyl and its synthetic derivatives, has become a critical public health concern, which is particularly evident in the United States. While the situation is less severe in Europe, the European Monitoring Centre for Drugs and Drug Addiction reports a rise in drug overdose deaths, with emerging concerns about the impact of fentanyl-related molecules. Synthetic opioids, initially designed for medical use, have infiltrated illicit markets due to their low production costs and high potency, with carfentanil posing additional threats, including potential chemical weaponization. Existing overdose mitigation heavily relies on naloxone, requiring timely intervention and caregiver presence, while therapeutic prevention strategies face many access challenges. To provide an additional treatment option, we propose the use of a fentanyl-specific monoclonal antibody (mAb), as a non-opioid method of prophylaxis against fentanyl and carfentanil. This mAb shows protection from opioid effects in a pre-clinical murine model. mAbs could emerge as a versatile countermeasure in civilian and biodefense settings, offering a novel approach to combat opioid-associated mortality.

Most dynorphin neurons in the zona incerta-perifornical area are active in waking relative to non-rapid-eye movement and rapid-eye movement sleep

Dynorphin is an endogenous opiate localized in many brain regions and spinal cord, but the activity of dynorphin neurons during sleep is unknown. Dynorphin is an inhibitory neuropeptide that is coreleased with orexin, an excitatory neuropeptide. We used microendoscopy to test the hypothesis that, like orexin, the dynorphin neurons are wake-active. Dynorphin-cre mice (n = 3) were administered rAAV8-Ef1a-Con/Foff 2.0-GCaMP6M into the zona incerta-perifornical area, implanted with a GRIN lens (gradient reflective index), and electrodes to the skull that recorded sleep. One month later, a miniscope imaged calcium fluorescence in dynorphin neurons during multiple bouts of wake, non-rapid-eye movement (NREM), and rapid-eye movement (REM) sleep. Unbiased data analysis identified changes in calcium fluorescence in 64 dynorphin neurons. Most of the dynorphin neurons (72%) had the highest fluorescence during bouts of active and quiet waking compared to NREM or REM sleep; a subset (20%) were REM-max. Our results are consistent with the emerging evidence that the activity of orexin neurons can be classified as wake-max or REM-max. Since the two neuropeptides are coexpressed and coreleased, we suggest that dynorphin-cre-driven calcium sensors could increase understanding of the role of this endogenous opiate in pain and sleep.

Orexins and primary headaches: an overview of the neurobiology and clinical impact

INTRODUCTION

Primary headaches, including migraines and cluster headaches, are highly prevalent disorders that significantly impact quality of life. Several factors suggest a key role for the hypothalamus, including neuroimaging studies, attack periodicity, and the presence of altered homeostatic regulation. The orexins are two neuropeptides synthesized almost exclusively in the lateral hypothalamus with widespread projections across the central nervous system. They are involved in an array of functions including homeostatic regulation and nociception, suggesting a potential role in primary headaches.

AREAS COVERED

This review summarizes current knowledge of the neurobiology of orexins, their involvement in sleep-wake regulation, nociception, and functions relevant to the associated symptomology of headache disorders. Preclinical reports of the antinociceptive effects of orexin-A in preclinical models are discussed, as well as clinical evidence for the potential involvement of the orexinergic system in headache.

EXPERT OPINION

Several lines of evidence support the targeted modulation of orexinergic signaling in primary headaches. Critically, orexins A and B, acting differentially via the orexin 1 and 2 receptors, respectively, demonstrate differential effects on trigeminal pain processing, indicating why dual-receptor antagonists failed to show clinical efficacy. The authors propose that orexin 1 receptor agonists or positive allosteric modulators should be the focus of future research.

Effects of the orexin receptor 2 agonist danavorexton on emergence from general anaesthesia and opioid-induced sedation, respiratory depression, and analgesia in rats and monkeys

BACKGROUND

Delayed emergence from general anaesthesia, opioid-induced sedation, and opioid-induced respiratory depression is associated with perioperative complications. We characterised the preclinical effects of the orexin receptor 2 (OX2R)-selective agonist danavorexton (TAK-925) on emergence from anaesthesia and reversal of fentanyl-induced sedation, respiratory depression, and analgesia.

METHODS

Emergence from isoflurane- or propofol-induced anaesthesia and fentanyl-induced sedation were investigated by righting reflex, rotarod, and electroencephalography in rats or monkeys. Fentanyl-induced respiratory depression was assessed by arterial blood gas analysis and whole-body plethysmography in rats and monkeys. Analgesia was evaluated using formalin- and skin incision-induced pain models in rats.

RESULTS

Danavorexton shortened emergence from isoflurane- or propofol-induced anaesthesia and from fentanyl-induced sedation at 1 (P=0.005), 3 (P=0.006), and 3 mg kg-1 s.c. (P=0.022), respectively, by righting reflex in rats. Danavorexton (10 mg kg-1 s.c.) accelerated recovery from isoflurane-, propofol- and fentanyl-induced motor impairment in separate rotarod tests in rats (P=0.008, P=0.007, P=0.017, respectively), and reversed anaesthesia and fentanyl-induced delta-power increases. Danavorexton shortened emergence (return of righting reflex) from isoflurane- or propofol-induced anaesthesia at 1 (P=0.002) and 3 mg kg-1 (P=0.004), respectively, in cynomolgus monkeys. Danavorexton (10 mg kg-1 s.c.) reversed fentanyl-induced increase in Pco2 (P=0.006), and decrease in Po2 (P=0.015) and pH (P<0.001) in rats, and at 3 mg kg-1 s.c. reversed fentanyl-induced increase in Pco2 (P=0.007), and decrease in Po2 (P=0.013) and SO2 (P=0.036) in monkeys. Danavorexton increased minute volume and tidal volume in fentanyl-treated animals. Danavorexton at ≤10 mg kg-1 s.c. did not compromise fentanyl analgesia in rat formalin- and skin incision-induced pain models.

CONCLUSIONS

Danavorexton promoted recovery from anaesthesia and fentanyl-induced sedation, and antagonised fentanyl-induced respiratory depression without compromising fentanyl analgesia.

Orexin-1 Receptor Antagonist SB-334867 Enhances Formalin-Induced Nociceptive Behaviors in Adult Male Rats

Background

Orexin (hypocretin) is one of the hypothalamic neuropeptides that plays a critical role in some behaviors including feeding, sleep, arousal, reward processing, and drug addiction. Neurons that produce orexin are scattered mediolaterally within the Dorsomedial Hypothalamus (DMH) and the lateral hypothalamus. In the current research, we assessed the impact of prolonged application of the antagonist of Orexin Receptor 1 (OXR1) on nociceptive behaviors in adult male rats.

Methods

Sixteen Wistar rats received subcutaneous (s.c.) injections of the OXR1 antagonist, SB-334867 (20 mg/kg, i.p.), or its vehicle repetitively from Postnatal Day 1 (PND1)-PND30. On the 30th day following the final application of the OXR1 antagonist formalin-provoked pain was evaluated by injecting formalin.

Results

Administration of the OXR1 antagonist in the long-term augmented the formalin-provoked nociceptive behaviors in interphase and phase II of the formalin-induced pain.

Conclusion

Current results showed that the continued inhibiting OXR1 might be implicated in formalin-induced nociceptive behaviors. Therefore, the present study highlighted the effect of orexin on analgesia.

In Silico, In Vitro, and In Vivo Evaluation of Caffeine-Coated Nanoparticles as a Promising Therapeutic Avenue for AML through NF-Kappa B and TRAIL Pathways Modulation

BACKGROUND

Advancements in nanoscience have led to a profound paradigm shift in the therapeutic applications of medicinally important natural drugs. The goal of this research is to develop a nano-natural product for efficient cancer treatment.

METHODS AND RESULTS

For this purpose, mesoporous silica nanoparticles (MSNPs) were formulated, characterized, and loaded with caffeine to develop a targeted drug delivery system, i.e., caffeine-coated nanoparticles (CcNPs). In silico docking studies were conducted to examine the binding efficiency of the CcNPs with different apoptotic targets followed by in vitro and in vivo bioassays in respective animal models. Caffeine, administered both as a free drug and in nanomedicine form, along with doxorubicin, was delivered intravenously to a benzene-induced AML model. The anti-leukemic potential was assessed through hematological profiling, enzymatic biomarker analysis, and RT-PCR examination of genetic alterations in leukemia markers. Docking studies show strong inter-molecular interactions between CcNPs and apoptotic markers. In vitro analysis exhibits statistically significant antioxidant activity, whereas in vivo analysis exhibits normalization of the genetic expression of leukemia biomarkers STMN1 and S1009A, accompanied by the restoration of the hematological and morphological traits of leukemic blood cells in nanomedicine-treated rats. Likewise, a substantial improvement in hepatic and renal biomarkers is also observed. In addition to these findings, the nanomedicine successfully normalizes the elevated expression of GAPDH and mTOR induced by exposure to benzene. Further, the nanomedicine downregulates pro-survival components of the NF-kappa B pathway and upregulated P53 expression. Additionally, in the TRAIL pathway, it enhances the expression of pro-apoptotic players TRAIL and DR5 and downregulates the anti-apoptotic protein cFLIP.

CONCLUSIONS

Our data suggest that MSNPs loaded with caffeine, i.e., CcNP/nanomedicine, can potentially inhibit transformed cell proliferation and induce pro-apoptotic TRAIL machinery to counter benzene-induced leukemia. These results render our nanomedicine as a potentially excellent therapeutic agent against AML.

Similar functional roles of the Orexin-1 and Orexin-2 receptors within the dentate gyrus area of the hippocampus in the stress-induced antinociceptive responses in the acute pain model in the rat

Studies establish that the brain's Orexin system is involved in pain modulation. Orexin-1 and orexin-2 receptors (OX1 and OX2r, respectively) are essential in responsiveness to stressful stimuli. Some evidence indicates that the hippocampus's dentate gyrus (DG) potentially modulates pain and stress. The present study examined the involvement of OX1 and OX2 receptors within the DG in response to acute pain after exposure to forced swim stress (FSS). Five to seven days post-stereotaxic surgery, the baseline tail-flick latency (TFL) was taken from the animal, then rats unilaterally received through an implanted cannula either different doses of OX1r antagonist (SB334867; 1, 3, 10, and 30 nmol), OX2r antagonist (TCS OX2 29; 1, 3, 10 and 30 nmol), or vehicle (0.5 μl solution of 12% DMSO). After 5 min, rats were exposed to the FSS for six minutes. Subsequently, the tail-flick test was conducted, and the TFLs were measured at the 60-min time set intervals. Results indicated that FSS produces antinociceptive responses in the tail-flick test. Two-way ANOVA analysis showed that Microinjection of OX1r and OX2r antagonists into the DG region of the brain reduced FSS-induced analgesia in the tail-flick test. The decrement effects of these two antagonists were almost the same. Additionally, results showed that the role of both receptors was the same in modulating stress-induced analgesia (SIA). These findings show that the orexin system in the hippocampal DG region might be partially involved in the SIA in acute pain.

Evaluation of the antinociceptive effect generated by citronellal monoterpene isomers

Due to the complex nature of pain and the participation of physical, cognitive, psychological and behavioral aspects, pain management has several approaches. The use of medicinal plants in developing countries is quite expressive. Seeking new options for the treatment of emerging or debilitating diseases. Therefore, the present study seeks to elucidate the effects of the monoterpene, citronellal, differentiating its activity by isomers (R)-(+) and (S)-(-) citronellal. The study used several methods to evaluate the effects of citronellal isomers on motor coordination, nociceptive response, and the involvement of opioid, glutamatergic, and transient receptor pathways. The methods included rota-rod, hot-plate, and formalin tests, as well as the use of specific inhibitors and agonists. Data were analyzed using inferential statistics with a 95% confidence level. Both isomers did not significantly affect the motor coordination of the studied animals. The isomer (S)-(-) citronellal showed better results in relation to its structural counterpart, managing to have an antinociceptive effect in the formalin and hot plate tests with a lower concentration (100 mg/kg) and presenting fewer side effects, however, the this study was not able to elucidate the mechanism of action of this isomer despite having activity in studies with substances that act on specific targets such as glutamate and capsaicin, its activity was not reversed with the use of antagonists for pathways related to nociception. While the (R)-(+) citronellal isomer, despite showing total activity only at a concentration of 150 mg/kg, was able to determine its mechanism of action related to the opioid pathway by reversing its activity by the antagonist naloxone, being this is a pathway already correlated with nociception control treatments, however, it is also related to some unwanted side effects. In this way, new studies are sought to elucidate the mechanism related to the isomer (S)-(-) citronellal and a possibility of use in other areas related to the treatment of pain or inflammation.

Blockade of orexin receptor type-1 by SB-334867 and activation of orexin receptor type-2 attenuate morphine tolerance in rats

Purpose

The interaction of orexinergic neurons with the opioidergic system and their effects on morphine analgesia and tolerance have not been fully elucidated. The purpose of the study was to evaluate the effects of the orexin-1 and orexin-2 receptor (OX1R and OX2R) agonist and antagonist on morphine analgesia and tolerance in rats.

Material and methods

A total of 90 Wistar albino male rats weighing 180–220 g were used in the experiments. To induce morphine tolerance, rats were injected with a single dose of morphine (50 mg kg−1, s.c.) for 3 days. Morphine tolerance was assessed on day 4 in randomly selected rats by analgesia tests. In order to evaluate morphine tolerance situation, orexin-A, SB-334867, orexin-B and TCS OX2 29 were administered together with morphine for 3 days. The analgesic effects of orexin-A (10 μg kg−1), OXR1 antagonist SB-334867 (10 mg kg−1), OXR2 agonist orexin-B (15 μg kg−1), OXR2 antagonist TCS OX2 29 (0.5 mg kg−1) and morphine (5 mg kg−1) were measured at 15 or 30-min intervals by tail-flick and hot-plate antinociceptive tests.

Results

The results suggested that the combination of orexin-1 receptor antagonist SB-334867 and orexin-B with morphine significantly increased the analgesic effect compared to morphine-tolerant rats. In addition, administration of orexin-A and -B alone showed significant analgesic effects compared to the saline group. However, co-administration of orexin-A and -B with morphine did not increase the analgesic efficacy of morphine.

Conclusions

The results of this study demonstrated that co-administration of SB-334867 and orexin-B with morphine attenuated morphine tolerance. Further studies are needed to elucidate the details of the interaction between orexin receptors and the opioidergic system.

Spinal orexin A attenuates opioid-induced mechanical hypersensitivity in the rat

Background

Repeated administration of opioid analgesics for pain treatment can produce paradoxical hyperalgesia via peripheral and/or central mechanisms. Thus, this study investigated whether spinally (centrally) administered orexin A attenuates opioid-induced hyperalgesia (OIH).

Methods

[D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO), a selective μ-opioid receptor agonist, was used to induce mechanical hypersensitivity and was administered intradermally (4 times, 1-hour intervals) on the rat hind paw dorsum. To determine whether post- or pretreatments with spinal orexin A, dynorphin A, and anti-dynorphin A were effective in OIH, the drugs were injected through an intrathecal catheter whose tip was positioned dorsally at the L3 segment of the spinal cord (5 μg for all). Mechanical hypersensitivity was assessed using von Frey monofilaments.

Results

Repeated intradermal injections of DAMGO resulted in mechanical hypersensitivity in rats, lasting more than 8 days. Although the first intrathecal treatment of orexin A on the 6th day after DAMGO exposure did not show any significant effect on the mechanical threshold, the second (on the 8th day) significantly attenuated the DAMGO-induced mechanical hypersensitivity, which disappeared when the type 1 orexin receptor (OX1R) was blocked. However, intrathecal administration of dynorphin or an anti-dynorphin antibody (dynorphin antagonists) had no effect on DAMGO-induced hypersensitivity. Lastly, pretreatment with orexin A, dynorphin, or anti-dynorphin did not prevent DAMGO-induced mechanical hypersensitivity.

Conclusions

Spinal orexin A attenuates mechanical hyperalgesia induced by repetitive intradermal injections of DAMGO through OX1R. These data suggest that OIH can be potentially treated by activating the orexin A-OX1R pathway in the spinal dorsal horn.

Endogenous oxytocin exerts anti-nociceptive and anti-inflammatory effects in rats

Oxytocin is involved in pain transmission, although the detailed mechanism is not fully understood. Here, we generate a transgenic rat line that expresses human muscarinic acetylcholine receptors (hM3Dq) and mCherry in oxytocin neurons. We report that clozapine-N-oxide (CNO) treatment of our oxytocin-hM3Dq-mCherry rats exclusively activates oxytocin neurons within the supraoptic and paraventricular nuclei, leading to activation of neurons in the locus coeruleus (LC) and dorsal raphe nucleus (DR), and differential gene expression in GABA-ergic neurons in the L5 spinal dorsal horn. Hyperalgesia, which is robustly exacerbated in experimental pain models, is significantly attenuated after CNO injection. The analgesic effects of CNO are ablated by co-treatment with oxytocin receptor antagonist. Endogenous oxytocin also exerts anti-inflammatory effects via activation of the hypothalamus-pituitary-adrenal axis. Moreover, inhibition of mast cell degranulation is found to be involved in the response. Taken together, our results suggest that oxytocin may exert anti-nociceptive and anti-inflammatory effects via both neuronal and humoral pathways.

N-Ethylnorketamine has anesthetic and analgesic effects with abuse liability

Arylcyclohexylamines is an ever-growing class of new psychoactive substances, including an increasing number of ketamine analogs. N-Ethylnorketamine (NENK) is a new synthetic ketamine analog that has emerged as an abused drug, but little is known about the pharmacological profile of NENK. In this study, we investigated the anesthetic and analgesic activity, abuse liability of NENK compared with ketamine. The ED₅₀ values of anesthetic activity for NENK and ketamine were 96.9, 69.4 mg/kg, respectively. The ED₅₀ values of analgesic activity for NENK and ketamine were 45.9 and 23.6 mg/kg, respectively. NENK induced significant conditioned place preference at a minimum dose of 10.0 mg/kg in mice, an effect comparable to that of ketamine (3.0 mg/kg). Acute injections of NENK or ketamine at 30.0 mg/kg enhanced locomotor activity, and repeated treatments with this dose induced locomotor sensitization after withdrawal. Taken together, these results clearly demonstrated that NENK has lower anesthetic and analgesic activity compared to ketamine, but has significant abuse liability.

Dezocine as a potent analgesic: overview of its pharmacological characterization

Dezocine, a synthetic opioid, introduced in 1970s as an analgesic, was redeveloped for relieving moderate to severe pain by Yangtze River Pharmaceutical Group in China in 2009. To date, dezocine occupies 45% of China's opioid analgesic market. Along with dezocine being a dominated painkiller, a certain amount of research was conducted to elucidate dezocine's action. In this review we summarize the current knowledge on the receptor, preclinical and clinical pharmacology of dezocine. Briefly, preclinical data show that dezocine is effective under varying pain conditions, particularly chronic neuropathic pain and cancer pain, through activation of opioid receptors, and inhibition of norepinephrine reuptake. Clinical data establish the effectiveness of dezocine either as a primary analgesic for postoperative pain management or a supplement for balanced analgesia. The receptor profile of dezocine is different from known pure μ agonists, and allows it to be used in combination with other opioids for additivity in efficacy or lower incidence of adverse effects.

From basic mechanisms to therapeutic perspectives in cluster headache

PURPOSE OF REVIEW

The pathophysiological understanding of cluster headache has evolved significantly over the past years. Although it is now well known that the trigeminovascular system, the parasympathetic system and the hypothalamus play important roles in its pathomechanism, we increasingly understand the functional role several neurotransmitters and hormones play in the communication between these structures.

RECENT FINDINGS

This work will give an overview of the current understanding of the role of calcitonin gene-related peptide, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, melatonin and orexins in cluster headache. On the basis of recent evidence, this study will also review the relevance of the monoclonal calcitonin gene-related peptide antibody galcanezumab as well as the sleep-regulating hormone melatonin in the treatment of cluster headache.

SUMMARY

Herein, we aim to review the basic mechanisms implicated in the pathophysiology of cluster headache and how the increased mechanistic understanding may lead to the discovery of novel therapeutic targets.

Boric acid improves the behavioral, electrophysiological and histological parameters of cisplatin-induced peripheral neuropathy in rats

Boric acid (BA) has been used in many diseases because it increases the amount of reduced glutathione in the body and reduces oxidative damage. This study aims to investigate the effects of boric acid in cisplatin-induced neuropathy, in which oxidative stress is also effective in its pathophysiology. In this study, 8-10 weeks old, 170-190 g Wistar Albino rats were used. Each group contained seven rats (n = 35). Experimental groups consist of control, sham, neuropathy, treatment, and boric acid groups. For the neuropathy model, a single dose of cisplatin (3 mg/kg, i.p) was administered once a week for five weeks, and for the treatment group, boric acid was administered daily (100 mg/kg, intragastric) for five weeks. After drug administration, the rotarod test to evaluate motor performance, the tail-flick and hot/cold plate tests to evaluate sensory conduction states, the von Frey filament test to evaluate the mechanical allodynia, and the adhesive removal test to assess sensorimotor function were performed. The sciatic nerve's motoric conduction velocity was also assessed electrophysiologically. Oxidative stress parameters were also assessed biochemically in sciatic nerve tissue and serum. Hematoxylin and eosin staining was used to evaluate the sciatic nerve tissue histopathologically. The motor conduction velocity of the sciatic nerve, impaired by cisplatin, was increased considerably by boric acid (p < 0.05). It also reduced the latency time of the compound muscle action potential (CMAP), which was increased by cisplatin. (p < 0.05). The von Frey filament test results demonstrated increased pain sensitivity of the cisplatin group increased, and mechanical allodynia was observed. Boric acid significantly alleviated this condition (p < 0.05). In the cold plate, adhesive removal, and rotarod tests, boric acid attenuated the adverse effects of cisplatin (p < 0.05). Biochemically, BA reduced the level of MDA, which was raised by cisplatin, and significantly increased the level of SOD, which was lowered by cisplatin (p < 0.05). Histopathologically; BA reduced neuronal degeneration and vacuolization caused by cisplatin. As a consequence, it has been determined that boric acid alleviates the adverse effects of cisplatin. BA reduced the destructive effect of cisplatin by reducing oxidative stress, and this effect was verified electrophysiologically, behaviorally, and histopathologically.

Orexin receptors in GtoPdb v.2021.3

Orexin receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Orexin receptors [42]) are activated by the endogenous polypeptides orexin-A and orexin-B (also known as hypocretin-1 and -2; 33 and 28 aa) derived from a common precursor, preproorexin or orexin precursor, by proteolytic cleavage and some typical peptide modifications [109]. Currently the only orexin receptor ligands in clinical use are suvorexant and lemborexant, which are used as hypnotics. Orexin receptor crystal structures have been solved [134, 133, 54, 117, 46].

An overview of the orexinergic system in different animal species

Orexin (hypocretin), is a neuropeptide produced by a subset of neurons in the lateral hypothalamus. From the lateral hypothalamus, the orexin-containing neurons project their fibres extensively to other brain structures, and the spinal cord constituting the central orexinergic system. Generally, the term ''orexinergic system'' usually refers to the orexin peptides and their receptors, as well as to the orexin neurons and their projections to different parts of the central nervous system. The extensive networks of orexin axonal fibres and their terminals allow these neuropeptidergic neurons to exert great influence on their target regions. The hypothalamic neurons containing the orexin neuropeptides have been implicated in diverse functions, especially related to the control of a variety of homeostatic functions including feeding behaviour, arousal, wakefulness stability and energy expenditure. The broad range of functions regulated by the orexinergic system has led to its description as ''physiological integrator''. In the last two decades, the orexinergic system has been a topic of great interest to the scientific community with many reports in the public domain. From the documentations, variations exist in the neuroanatomical profile of the orexinergic neuron soma, fibres and their receptors from animal to animal. Hence, this review highlights the distinct variabilities in the morphophysiological aspects of the orexinergic system in the vertebrate animals, mammals and non-mammals, its presence in other brain-related structures, including its involvement in ageing and neurodegenerative diseases. The presence of the neuropeptide in the cerebrospinal fluid and peripheral tissues, as well as its alteration in different animal models and conditions are also reviewed.

Orexin-2 receptor antagonism in the cornu ammonis 1 region of hippocampus prevented the antinociceptive responses induced by chemical stimulation of the lateral hypothalamus in the animal model of persistent pain

Orexins are excitatory neuropeptides, mainly produced by neurons located in the lateral hypothalamus, which project to many brain areas. The orexinergic system plays a fundamental role in arousal, sleep/wakefulness, feeding, energy homeostasis, motivation, reward, stress and pain modulation. As a prominent part of the limbic system, the hippocampus has been involved in formalin-induced nociception modulation. Moreover, hippocampus regions express both orexin-1 (OX1) and orexin-2 (OX2) receptors. The present study investigated the role of OX2 receptors (OX2R) within the cornu ammonis 1 (CA1) region of the hippocampus in the mediation of lateral hypothalamus-induced antinociception. Fifty-three male Wistar rats were unilaterally implanted with two separate cannulae into the lateral hypothalamus and CA1. Animals were pretreated with intra-CA1 TCS OX2 29 as an OX2R antagonist before intra-lateral hypothalamus administration of carbachol (250 nM) as a muscarinic agonist for chemical stimulation of orexinergic neurons. Formalin test was used as an animal model of persistent pain, following intra-lateral hypothalamus carbachol microinjection. Results showed that the chemical stimulation of the lateral hypothalamus significantly attenuated formalin-evoked nociceptive behaviors during both phases of the formalin test, and administration of TCS OX2 29 into the CA1 blocked these antinociceptive responses in both phases, especially in the late phase. These findings suggest that OX2 receptors in the CA1 partially mediate the lateral hypothalamus-induced antinociceptive responses in persistent inflammatory pain.

Modulatory role of the orexin system in stress-induced analgesia: Involvement of the ventral tegmental area

BACKGROUND

Exposure to stressful experiences is often accompanied by suppressing pain perception, referred to as stress-induced analgesia. The neuropeptides orexins are essential in regulating the mechanism that responds to stressful and painful stimuli. Meanwhile, the ventral tegmental area (VTA), as a part of descending pain inhibitory system, responds to noxious stimuli. This study aimed to investigate the role of intra-VTA administration of orexin receptor antagonists on stress-induced antinociceptive responses in the animal model of acute pain.

METHOD

Ninety-three adult Wistar rats weighing 230-250 g were unilaterally implanted by a cannulae above the VTA. Animals were pretreated with different doses (1, 3, 10 and 30 nM/0.3 μl) of SB334867 as the orexin-1 receptor antagonist and TCS OX2 29 as the orexin-2 receptor antagonist into the VTA, just 5 min before 6 min exposure to forced swim stress (FSS). Nociceptive threshold was measured using the tail-flick test as a model of acute pain.

RESULTS

The results showed that exposure to FSS could significantly increase analgesic responses. Moreover, intra-VTA administration of SB334768 and TCS OX2 29 blocked the antinociceptive effect of FSS in the tail-flick test.

CONCLUSION

The findings suggest that OX1 and OX2 receptors in the VTA might modulate the antinociceptive behaviours induced by FSS in part.

SIGNIFICANCE

Acute exposure to physical stress suppresses pain-related behaviors in the animal model of acute pain. Blockade of the OX1 and OX2 receptors in the VTA attenuates antinociceptive responses induced by FSS. The contribution of the OX2 receptors in the VTA is more predominant than OX1 receptors in stress-induced analgesia.

Activation of Hypocretin Neurons in Endometriosis

Endometriosis is a gynecological disease affecting 6-10% of women of reproductive age. In addition to gynecologic symptoms, endometriosis is associated with various systemic effects, including inflammation, altered body weight, and behavioral changes. Previous murine studies demonstrate that endometriosis is causally inked to increased pain sensitization, behavioral changes, and low body mass index (BMI). One possible cellular target that may mediate some of these findings is the hypocretin/orexin neurons. This neuronal system plays a role in regulating wakefulness/sleep cycles, pain perception, and appetite. We hypothesize that endometriosis alters activity level of the hypocretin/orexin (Hcrt) neuronal system. Mice underwent endometriosis induction surgeries (endo) or sham surgeries (sham) for the development of the experimental model. Immunocytochemistry was performed on harvested samples from the lateral hypothalamus, and activation levels of Hcrt cells were examined by quantifying the expression of phosphorylation of cAMP-responsive element binding protein (CREB) in these cells after an acute stress in sham and endo mice. Mice with endometriosis had greater Hcrt neurons activation than sham mice. Mice with endometriosis fed with high fat diet showed a lower fat/body weight and fat/lean tissue ratio compared to mice without endometriosis. There was no significant difference in food intake between sham and endometriosis mice. These results demonstrate that endometriosis is associated with low body mass and increased hypocretin/orexin activity, which could be implicated in the behavioral changes and to differences in body composition.

Antinociceptive Effect of BPC-157 in the Formalin-induced Pain Model

Objectives Body protective compound-157 (BPC-157) is a stable gastric pentadecapeptide that has been effective in trials aiming to increase wound healing capabilities and decrease inflammatory cell influx, including studies on the healing of muscles and tendons. There are no studies about the effect of BPC-157 on pain transmission via nociception. This study examined the antinociceptive effects of BPC-157 using formalin tests and immunohistochemistry. Methods Rats were randomly divided into the control, morphine and BPC-157 groups. Pain behavior was quantified periodically at 5- and 35- min intervals (representative values of phases 1 and 2) by counting the number of flinches exhibited by the injected paw after injection. The dorsal root ganglia (DRG) and spinal cords (SC) were collected, and then, the number of cytokine-positive cells was determined via immunostaining. Results BPC-157 dose-dependently decreased the number of flinches during phase 1 but did not decrease the number of flinches during phase 2. During phase 1, interleukin-1β (IL-1β) in the DRG tissue was significantly different in the morphine, 10 μg/kg BPC-157, and 20 μg/kg BPC-157 groups. During phase 2, statistical significance was achieved in the DRG tissue in the morphine, 20 μg/kg BPC-157, and 40 μg/kg BPC-157 groups. During phase 1, interleukin-6 was significantly different in the DRG tissue in the morphine group and the SC tissue in the 10 μg/kg BPC-157 group. During phase 2, statistical significance was achieved in the morphine group and the BPC-157 20 μg/kg group in both the DRG and SC tissues. There were no significant differences in tumor necrosis factor-α between the DRG and SC tissues. Conclusions BPC-157 was effective during phase 1 but not during phase 2, as determined by the formalin test. BPC-157 decreased the expression of IL-1β in the DRG tissue in phases 1 and 2.

Emerging Targets for Migraine Treatment

Background

While understanding the pathophysiology of migraine has led to CGRP-based treatments, other potential targets have also been implicated in migraine.

Objectives

To catalog new promising targets for the treatment of migraine.

Methods

We completed a literature review focusing on 5HT_1F, PACAP, melatonin, and orexins.

Results

The 5HT_1F receptor agonist lasmiditan, following two positive randomized placebo-controlled trials, was FDA-approved for the acute treatment of migraine. PACAP-38 has shown analogous evidence to what was obtained for CGRP with its localization in key structures, provocation tests, and positive studies when antagonizing its receptor in animal models, although a PAC-1 receptor monoclonal antibody study was negative. Melatonin has undergone several randomized controlled trials showing a positive trend. Filorexant is the only dual orexin receptor antagonist, which was tested in humans with negative results.

Conclusions

Further and ongoing studies will determine the utility of these new therapies with lasmiditan and melatonin having demonstrated efficacy for the treatment of migraine.

Post-traumatic stress disorder increases pain sensitivity by reducing descending noradrenergic and serotoninergic modulation

Exposure to stress might influence pain sensitivity; however, little is known about whether post-traumatic stress disorder (PTSD)-like symptoms alter pain sensitivity and how it can happen. Male rats were exposed to the inescapable footshock paired with either social isolation or a control condition (not exposed to footshock but subjected to social isolation). After 7, 14, or 21 days, memory retention was evaluated. In the following three days, animals underwent the following tests: open-field, social interaction and formalin tests. Another group of animals were subjected to the object recognition test and to von Frey filaments. In other cohorts of animals, saline, fluoxetine, or desipramine were injected intrathecally and immunohistochemistry was performed to investigate whether PTSD-like symptoms alter the expression of c-Fos in serotonergic and noradrenergic neurons. Inescapable footshock induced the development of PTSD-like symptoms. Animals with PTSD-like symptoms showed an increase in the number of flinches in the formalin test and a reduction in mechanical threshold in the von Frey test at both retention intervals. The social interaction was negatively correlated with the nociceptive response in the formalin test. Fluoxetine or desipramine prevented the nociceptive response to chemical stimulus in the formalin test. In addition, in animals with PTSD-like symptoms, there was a reduction in c-Fos expression in serotonergic and noradrenergic neurons. Our results are important for the association of increased sensitivity to pain as one of the clinical manifestations that are present in the development of PTSD, and a possible treatment for increased pain sensitivity in male individuals with PTSD.

Orexin (hypocretin) participates in central autonomic regulation during fight-or-flight response

Our daily life does not only involve a calm resting state but is rather full of perturbations that induce active states such as moving, eating, and communicating. During such active conditions, cardiorespiratory regulation should be adjusted according to bodily demand, which differs from that during the resting state, by modulating or resetting the operating point. To explore neural mechanisms in the state-dependent adjustment of central autonomic regulation, my research group has recently focused on the fight-or-flight response because the stressor induces not only cognitive, emotional, and behavioral changes but also autonomic changes. In this brief review, I will summarize our discovery using orexin knockout mice and orexin neuron-ablated mice for the possible contribution of orexin, a hypothalamic neuropeptide, to the state-dependent adjustment of the central autonomic regulation. In addition, I will introduce some recent discovery using optogenetic manipulation of the orexin and related systems. The diversity of synaptic control of the cardiovascular and respiratory neurons appears necessary for animals to adapt themselves to ever-changing life circumstances and behavioral states. The orexin system is likely to function as one of the essential modulators for coordinating the circuits controlling autonomic functions and behaviors.

Orexinergic descending inhibitory pathway mediates linalool odor-induced analgesia in mice

Linalool odor exposure induces an analgesic effect in mice. This effect disappeared in the anosmic model mice, indicating that olfactory input evoked by linalool odor triggered this effect. Furthermore, hypothalamic orexinergic neurons play a pivotal role in this effect. However, the neuronal circuit mechanisms underlying this effect have not been fully addressed. In this study, we focused on the descending orexinergic projection to the spinal cord and examined whether this pathway contributes to the effect. We assessed the effect of intrathecal administration of orexin receptor antagonists on linalool odor-induced analgesia in the tail capsaicin test. We found that the selective orexin type 1 receptor antagonist, but not the selective orexin type 2 receptor antagonist, prevented the odor-induced analgesic effect. Furthermore, immunohistochemical analyses of c-Fos expression induced by the capsaicin test revealed that neuronal activity of spinal cord neurons was suppressed by linalool odor exposure, which was prevented by intrathecal administration of the orexin 1 receptor antagonist. These results indicate that linalool odor exposure drives the orexinergic descending pathway and suppresses nociceptive information flow at the spinal level.

Targets for migraine treatment: beyond calcitonin gene-related peptide

PURPOSE OF REVIEW

Despite the development of several medications for the acute and preventive treatment of migraine, there are still many patients in whom lack of efficacy, tolerability, interactions or contraindications make other options necessary. CGRP-based drugs have opened the door to a new era of migraine-targeted treatments. Beyond CGRP, there are other promising targets covered here.

RECENT FINDINGS

For the acute treatment of migraine, 5-HT1F receptor agonists, ditans, are now available. Unlike triptans, 5-HT1B/1D receptor agonists, cardiovascular disease is not a contraindication for the use of ditans. The first study on a monoclonal antibody targeting PAC1 receptor was negative, although this may not be the end for the pituitary adenylate cyclase-activating polypeptide (PACAP) pathway as a target.

SUMMARY

Following positive phase-III clinical trials, lasmiditan is the first ditan to be FDA-approved. PACAP has experimental evidence suggesting a role in migraine pathophysiology. As for CGRP, the presence of PACAP in key migraine structures along with positive provocative tests for both PACAP-38 and PACAP-27 indicate this pathway may still be a pharmacological target. Glutamate-based targets have long been considered in migraine. Two clinical trials with memantine, an NMDA-R antagonist, for the preventive treatment of migraine have now been published. The hypothalamus has also been implicated in migraine pathophysiology: the potential role of orexins in migraine is discussed. Acid-sensing ion channels, as well as amylin-blocking drugs, may also become migraine treatments in the future: more research is warranted.

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT2A and 5-HT1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Insulin within the Arcuate Nucleus Has Paradoxical Effects on Nociception in Healthy and Diabetic Rats

Introduction

Broad neural circuits originate from the hypothalamic arcuate nucleus and project to many parts of the brain which are related to pain perception. Insulin receptors are found in the arcuate nucleus. Since nociception may be affected in type 1 diabetes, the present study aimed to investigate the intra-arcuate nucleus insulin role in pain perception in streptozotocin (STZ)-induced diabetic and healthy rats.

Methods

Regular insulin was microinjected within the arcuate nucleus and the pain tolerance was measured using the hot plate and the tail-flick apparatus in diabetic rats.

Results

The results showed that the arcuate nucleus suppression with lidocaine could increase thermal nociception in non-diabetic animals. Also, insulin within the arcuate nucleus decreased the acute thermal pain perception in these animals. STZ-induced diabetes produced hypoalgesia which the latency of these tests, progressively increased over time after induction of diabetes. Also, in the same animal group, intra-arcuate injection of insulin reduced the latency of nociception.

Conclusion

Intra-arcuate insulin has paradoxical and controversial effects in healthy and diabetic rats' nociception. These effects seem to be due to the insulin effect on releasing proopiomelanocortin and its derivatives.

The neurohypophysial oxytocin and arginine vasopressin system is activated in a knee osteoarthritis rat model

Osteoarthritis (OA) causes chronic joint pain and significantly impacts daily activities. Hence, developing novel treatment options for OA has become an increasingly important area of research. Recently, studies have reported that exogenous, as well as endogenous, hypothalamic-neurohypophysial hormones, oxytocin (OXT) and arginine-vasopressin (AVP), significantly contribute to nociception modulation. Moreover, the parvocellular OXT neurone (parvOXT) extends its projection to the superficial spinal dorsal horn, where it controls the transmission of nociceptive signals. Meanwhile, AVP produced in the magnocellular AVP neurone (magnAVP) is released into the systemic circulation where it contributes to pain management at peripheral sites. The parvocellular AVP neurone (parvAVP), as well as corticotrophin-releasing hormone (CRH), suppresses inflammation via activation of the hypothalamic-pituitary adrenal (HPA) axis. Previously, we confirmed that the OXT/AVP system is activated in rat models of pain. However, the roles of endogenous hypothalamic-neurohypophysial hormones in OA have not yet been characterised. In the present study, we investigated whether the OXT/AVP system is activated in a knee OA rat model. Our results show that putative parvOXT is activated and the amount of OXT-monomeric red fluorescent protein 1 positive granules in the ipsilateral superficial spinal dorsal horn increases in the knee OA rat. Furthermore, both magnAVP and parvAVP are activated, concurrent with HPA axis activation, predominantly modulated by AVP, and not CRH. The OXT/AVP system in OA rats was similar to that in systemic inflammation models, including adjuvant arthritis; however, magnocellular OXT neurones (magnOXT) were not activated in OA. Hence, localised chronic pain conditions, such as knee OA, activate the OXT/AVP system without impacting magnOXT.

Differential role of specific cardiovascular neuropeptides in pain regulation: Relevance to cardiovascular diseases

In many instances, the perception of pain is disproportionate to the strength of the algesic stimulus. Excessive or inadequate pain sensation is frequently observed in cardiovascular diseases, especially in coronary ischemia. The mechanisms responsible for individual differences in the perception of cardiovascular pain are not well recognized. Cardiovascular disorders may provoke pain in multiple ways engaging molecules released locally in the heart due to tissue ischemia, inflammation or cellular stress, and through neurogenic and endocrine mechanisms brought into action by hemodynamic disturbances. Cardiovascular neuropeptides, namely angiotensin II (Ang II), angiotensin-(1-7) [Ang-(1-7)], vasopressin, oxytocin, and orexins belong to this group. Although participation of these peptides in the regulation of circulation and pain has been firmly established, their mutual interaction in the regulation of pain in cardiovascular diseases has not been profoundly analyzed. In the present review we discuss the regulation of the release, and mechanisms of the central and systemic actions of these peptides on the cardiovascular system in the context of their central and peripheral nociceptive (Ang II) and antinociceptive [Ang-(1-7), vasopressin, oxytocin, orexins] properties. We also consider the possibility that they may play a significant role in the modulation of pain in cardiovascular diseases. The rationale for focusing attention on these very compounds was based on the following premises (1) cardiovascular disturbances influence the release of these peptides (2) they regulate vascular tone and cardiac function and can influence the intensity of ischemia - the factor initiating pain signals in the cardiovascular system, (3) they differentially modulate nociception through peripheral and central mechanisms, and their effect strongly depends on specific receptors and site of action. Accordingly, an altered release of these peptides and/or pharmacological blockade of their receptors may have a significant but different impact on individual sensation of pain and comfort of an individual patient.

Involvement of descending pain control system regulated by orexin receptor signaling in the induction of central post-stroke pain in mice

Central post-stroke pain (CPSP) is a type of neuropathic pain for which the mechanism and relevant drug pathways remain unknown. Recently, it was reported that intracerebroventricular (ICV) administration of orexin-A suppresses pain and ischemia. In this study, we tested the role of orexin-A in CPSP induction in mice. Male ddY mice were subjected to 30 min of bilateral carotid artery occlusion (BCAO). CPSP was assessed by von Frey test. Colocalization of orexin 1 receptor (OX1R) with various neuron markers were determined by double-immunofluorescence. The hindpaw withdrawal responses to mechanical stimuli were significantly increased 3 days post-BCAO compared with those of sham groups. ICV injection of orexin-A dose-dependently suppressed BCAO-induced mechanical allodynia. These effects were inhibited by pre-treatment with SB334867 (an OX1R antagonist; ICV injection), yohimbine (a noradrenaline α₂ receptor antagonist; intrathecal (IT) injection), and WAY100635 (a serotonin 5-HT_1A receptor antagonist; IT injection), but not TCS OX2 29 (an OX2R antagonist; ICV injection). OX1R colocalized with TH (a noradrenergic neuron marker) and TPH (a serotonergic neuron marker) in the locus ceruleus (LC) and the rostral ventromedial medulla (RVM), respectively. The number of c-Fos positive cells in the LC and the RVM of BCAO mice was increased at 90 min after ICV injection of orexin-A compared to saline group. These results indicate that orexin-A/OX1R signaling plays an important role through activation of the descending pain control system in the induction of CPSP in mice.

Dimethyl fumarate alleviates the nitroglycerin (NTG)-induced migraine in mice

Background

Oxidative stress and inflammatory pathways are involved in migraine and endogenous antioxidant defense system has a role in the prevention of hyperalgesia in migraine. In this study, we aimed to evaluate the role of the most pharmacologically effective molecules among the fumaric acid esters (FAEs), dimethyl fumarate, nuclear factor E2-related factor 2/antioxidant response element (Nrf-2/ARE) pathway-mediated, in regulating the hypersensitivity in a mouse model of nitroglycerine (NTG)-induced migraine.

Methods

Mice were orally administered with DMF at the doses of 10, 30, and 100 mg/kg, 5 min after NTG intraperitoneal injections. We performed histological and molecular analysis on the whole brain and behavioral tests after 4 h by NTG-migraine induction. The expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кB) subunit p65, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα), inducible nitrite oxide synthase (iNOS), cyclooxygenase 2 (COX-2), Nrf-2, manganese superoxide dismutase (Mn-SOD), and heme-oxygenase-1 (HO-1) were detected by Western blot. Tail flick, hot plate, orofacial formalin, and photophobia tests were used to evaluate migraine-like pain and migraine-related light sensitivity.

Moreover, we evaluate Nrf-2-dependent mechanism by the in vitro stimulation of cells extracted by trigeminal ganglia with diethylenetriamine/nitric oxide (DETA/NO), a nitric oxide (NO) donor. The cells were pre-treated with DMF and an antagonist of Nrf-2, trigonelline (TR) 2 h before DETA/NO stimulation.

Results

DMF treatment notably reduced histological damage as showed by cresyl violet staining; also, regulating both NF-κB and Nrf-2 pathway, DMF treatment decreased the severity of inflammation and increased the protective antioxidant action. Moreover, the headache was significantly reduced. The protective effect of DMF treatment, via Nrf-2, was confirmed in in vitro studies, through inhibition of Nrf-2 by trigonelline. Cytotoxicity, iNOS, and MnSOD expression were evaluated.

Conclusion

These results provided the evidence that DMF, by Nrf-2 modulation, has a protective effect on central sensitization induced by NTG, suggesting a new insight into the potential application of DMF as novel candidates in drug development for migraine.

The Lateral Hypothalamus: An Uncharted Territory for Processing Peripheral Neurogenic Inflammation

The roles of the hypothalamus and particularly the lateral hypothalamus (LH) in the regulation of inflammation and pain have been widely studied. The LH consists of a parasympathetic area that has connections with all the major parts of the brain. It controls the autonomic nervous system (ANS), regulates feeding behavior and wakeful cycles, and is a part of the reward system. In addition, it contains different types of neurons, most importantly the orexin neurons. These neurons, though few in number, perform critical functions such as inhibiting pain transmission and interfering with the reward system, feeding behavior and the hypothalamic pituitary axis (HPA). Recent evidence has identified a new role for orexin neurons in the modulation of pain transmission associated with several inflammatory diseases, including rheumatoid arthritis and ulcerative colitis. Here, we review recent findings on the various physiological functions of the LH with special emphasis on the orexin/receptor system and its role in mediating inflammatory pain.

Significant Quantitative Differences in Orexin Neuronal Activation After Pain Assessments in an Animal Model of Sickle Cell Disease

Sickle cell disease is a hemoglobinopathy that causes sickling of red blood cells, resulting in vessel blockage, stroke, anemia, inflammation, and extreme pain. The development and treatment of pain, in particular, neuropathic pain in sickle cell disease patients is poorly understood and impedes our progress toward the development of novel therapies to treat pain associated with sickle cell disease. The orexin/hypocretin system offers a novel approach to treat chronic pain and hyperalgesia. These neuropeptides are synthesized in three regions: perifornical area (PFA), lateral hypothalamus (LH), and dorsomedial hypothalamus (DMH). Data suggest that orexin-A neuropeptide has an analgesic effect on inflammatory pain and may affect mechanisms underlying the maintenance of neuropathic pain. The purpose of this study was to determine whether there are neuronal activation differences in the orexin system as a result of neuropathic pain testing in a mouse model of sickle cell disease. Female transgenic sickle mice that express exclusively (99%) human sickle hemoglobin (HbSS-BERK) and age-/gender-matched controls (HbAA-BERK mice; n = 10/group, 20-30 g) expressing normal human hemoglobin A were habituated to each test protocol and environment before collecting baseline measurements and testing. Four measures were used to assess pain-related behaviors: thermal/heat hyperalgesia, cold hyperalgesia, mechanical hyperalgesia, and deep-tissue hyperalgesia. Hypothalamic brain sections from HbAA-BERK and HbSS-BERK mice were processed to visualize orexin and c-Fos immunoreactivity and quantified. The percentage of double labeled neurons in the PFA was significantly higher than the percentage of double labeled neurons in the LH orexin field of HbAA-BERK mice (* p < 0.05). The percentages of double labeled neurons in PFA and DMH orexin fields are significantly higher than those neurons in the LH of HbSS-BERK mice (* p < 0.05). These data suggest that DMH orexin neurons were preferentially recruited during neuropathic pain testing and a more diverse distribution of orexin neurons may be required to produce analgesia in response to pain in the HbSS-BERK mice. Identifying specific orexin neuronal populations that are integral in neuropathic pain processing will allow us to elucidate mechanisms that provide a more selective, targeted approach in treating of neuropathic pain in sickle cell disease.

Knowledge Gaps in the Perioperative Management of Adults With Narcolepsy: A Call for Further Research

There is increasing awareness that sleep disorders may be associated with increased perioperative risk. The Society of Anesthesia and Sleep Medicine created the Narcolepsy Perioperative Task Force: (1) to investigate the current state of knowledge of the perioperative risk for patients with narcolepsy, (2) to determine the viability of developing perioperative guidelines for the management of patients with narcolepsy, and (3) to delineate future research goals and clinically relevant outcomes. The Narcolepsy Perioperative Task Force established that there is evidence for increased perioperative risk in patients with narcolepsy; however, this evidence is sparse and based on case reviews, case series, and retrospective reviews. Mechanistically, there are a number of potential mechanisms by which patients with narcolepsy could be at increased risk for perioperative complications. These include aggravation of the disease itself, dysautonomia, narcolepsy-related medications, anesthesia interactions, and withdrawal of narcolepsy-related medications. At this time, there is inadequate research to develop an expert consensus or guidelines for the perioperative management of patients with narcolepsy. The paucity of available literature highlights the critical need to determine if patients with narcolepsy are at an increased perioperative risk and to establish appropriate research protocols and clearly delineated patient-centered outcomes. There is a real need for collaborative research among sleep medicine specialists, surgeons, anesthesiologists, and perioperative providers. This future research will become the foundation for the development of guidelines, or at a minimum, a better understanding how to optimize the perioperative care of patients with narcolepsy.

New 2-amino-pyridinyl-N-acylhydrazones: Synthesis and identification of their mechanism of anti-inflammatory action

AIMS

The main aim of this paper was the synthesis and the evaluation of the anti-inflammatory activity of LASSBio-1828 (an amino-pyridinyl-N-acylhydrazone) and its respective hydrochloride, based on a p38α MAPK inhibitor (LASSBio-1824) previously synthesized by our group.

MAIN METHODS

The compounds were tested regarding their cell viability effect and on acute models of inflammation such as formalin-induced licking test, cell migration and inflammatory mediators quantification.

KEY FINDINGS

Treatment with the compounds inhibited p38α, reduced inflammatory pain, cell migration and inflammatory mediators that participate on the MAPK pathway such as TNF-α and IL-1β.

SIGNIFICANCE

Taken together, these results suggest that the synthesis of the corresponding hydrochloride of LASSBio-1828 enhanced its potency as a p38 inhibitor, and also that this compound could be considered a good anti-inflammatory drug candidate after further studies.

Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications

Pain can be both a cause and a consequence of sleep deficiency. This bidirectional relationship between sleep and pain has important implications for clinical management of patients, but also for chronic pain prevention and public health more broadly. The review that follows will provide an overview of the neurobiological evidence of mechanisms thought to be involved in the modulation of pain by sleep deficiency, including the opioid, monoaminergic, orexinergic, immune, melatonin, and endocannabinoid systems; the hypothalamus-pituitary-adrenal axis; and adenosine and nitric oxide signaling. In addition, it will provide a broad overview of pharmacological and non-pharmacological approaches for the management of chronic pain comorbid with sleep disturbances and for the management of postoperative pain, as well as discuss the effects of sleep-disturbing medications on pain amplification.

Design, Synthesis and Pharmacological Evaluation of Novel Antiinflammatory and Analgesic O-Benzyloxime Compounds Derived From Natural Eugenol

Background: :

A new series of O-benzyloximes derived from eugenol was synthesized and was evaluated for its antinociceptive and anti-inflammatory properties.

Methods: :

The target compounds were obtained in good global 25-28% yields over 6 steps, which led us to identify compounds (Z)-5,6-dimethoxy-2,2-dimethyl-2,3-dihydro-1H-inden-1-one-O-(4- (methylthio)benzyloxime (8b), (Z)-5,6-dimethoxy-2,2-dimethyl-2,3-dihydro-1H-inden-1-one-O-4- bromobenzyloxime (8d) and (Z)-5,6-dimethoxy-2,2-dimethyl-2,3-dihydro-1H-inden-1-one-O-4- (methylsulfonyl)benzyloxime (8f) as promising bioactive prototypes.

Results::

These compounds have significant analgesic and anti-inflammatory effects, as evidenced by formalin-induced mice paw edema and carrageenan-induced mice paw edema tests. In the formalin test, compounds 8b and 8f evidenced both anti-inflammatory and direct analgesic activities and in the carrageenan-induced paw edema, with compounds 8c, 8d, and 8f showing the best inhibitory effects, exceeding the standard drugs indomethacin and celecoxib.

Conclusion: :

Molecular docking studies have provided additional evidence that the pharmacological profile of these compounds may be related to inhibition of COX enzymes, with slight preference for COX-1. These results led us to identify the new O-benzyloxime ethers 8b, 8d and 8f as orally bioactive prototypes, with a novel structural pattern capable of being explored in further studies aiming at their optimization and development as drug candidates.

Cellular Mechanisms for Antinociception Produced by Oxytocin and Orexins in the Rat Spinal Lamina II-Comparison with Those of Other Endogenous Pain Modulators

Much evidence indicates that hypothalamus-derived neuropeptides, oxytocin, orexins A and B, inhibit nociceptive transmission in the rat spinal dorsal horn. In order to unveil cellular mechanisms for this antinociception, the effects of the neuropeptides on synaptic transmission were examined in spinal lamina II neurons that play a crucial role in antinociception produced by various analgesics by using the whole-cell patch-clamp technique and adult rat spinal cord slices. Oxytocin had no effect on glutamatergic excitatory transmission while producing a membrane depolarization, γ-aminobutyric acid (GABA)-ergic and glycinergic spontaneous inhibitory transmission enhancement. On the other hand, orexins A and B produced a membrane depolarization and/or a presynaptic spontaneous excitatory transmission enhancement. Like oxytocin, orexin A enhanced both GABAergic and glycinergic transmission, whereas orexin B facilitated glycinergic but not GABAergic transmission. These inhibitory transmission enhancements were due to action potential production. Oxytocin, orexins A and B activities were mediated by oxytocin, orexin-1 and orexin-2 receptors, respectively. This review article will mention cellular mechanisms for antinociception produced by oxytocin, orexins A and B, and discuss similarity and difference in antinociceptive mechanisms among the hypothalamic neuropeptides and other endogenous pain modulators (opioids, nociceptin, adenosine, adenosine 5’-triphosphate (ATP), noradrenaline, serotonin, dopamine, somatostatin, cannabinoids, galanin, substance P, bradykinin, neuropeptide Y and acetylcholine) exhibiting a change in membrane potential, excitatory or inhibitory transmission in the spinal lamina II neurons.

Analgesic tolerance induced by repeated morphine injections induces cross-tolerance to the analgesic effect of orexin-A in rats

Repeated administration of morphine or orexin-A produces tolerance to their antinociceptive effects. We investigated the possible incidence of cross-tolerance between orexin-A and morphine. Adult male Sprague-Dawley rats (200-250 g) were used. Under deep anesthesia, a stereotaxic apparatus was used to implant a 23 G cannula into the lateral ventricle for an intracerebroventricular (ICV) microinjection. The antinociceptive effect of three different doses of orexin-A (5, 20, and 40 µM; dissolved in 5 µl sterile saline; ICV) was examined using the hot-plate test at 15, 30, 60, and 90 min after infusion. To evaluate tolerance, orexin-A (20 µM; ICV) or morphine (10 mg/kg; intraperitoneal) was administered for 7 consecutive days (twice per day) and the analgesic response was assessed at days 1, 4, and 7. Cross-tolerance was investigated at day 8 with a single injection of morphine (10 mg/kg; intraperitoneal) to the repeated orexin-A group and a single microinjection of orexin-A (20 µM; ICV) to the repeated morphine group. Analgesic responses were then examined. Administration of both orexin-A and morphine produced significant antinociception at day 1 (P<0.001 compared with the saline group). However, a significant reduction in the analgesic effects of both morphine and orexin-A appeared at day 7, following repeated administration (P<0.01). Orexin-A microinjection at day 8 in the repeated morphine group did not result in significant antinociception (P>0.05), whereas morphine injection in the repeated orexin-A group at day 8 showed a significant analgesic effect (P<0.001). These results indicate cross-tolerance to the analgesic effect of orexin-A following morphine tolerance.