Ghrelin attenuates hyperalgesia and light aversion-induced by nitroglycerin in male rats

Levcromakalim provokes an acute rapid-onset migraine-like phenotype without inducing cortical spreading depolarization

BACKGROUND

Migraine headache attacks and accompanying sensory augmentation can be induced by several agents including levcromakalim (LVC), that is also capable of provoking aura-like symptoms in migraineurs. We investigated whether single LVC injection causes acute migraine-like phenotype in rats and induces/modulates cortical spreading depolarization (CSD), a rodent model of migraine aura.

METHODS

Wistar rats were administered LVC (1 mg/kg, i.p.) and compared to control (CTRL, vehicle, i.p.) and nitroglycerin (NTG, 10 mg/kg, i.p.) groups. Von Frey filaments were used to examine the periorbital and hind paw mechanical allodynia. Dark-light box (DLB), elevated plus maze (EPM), and open field arena (OFA) were used to evaluate light sensitivity and anxiety-related behaviors. The effects of LVC on CSD parameters, somatosensory evoked potentials, and baseline dural EEG (electroencephalography) were investigated. Possible CSD-induced c-fos expression was studied with Western Blot. Blood-brain barrier integrity in cortex was examined with Evans blue assay.

RESULTS

LVC and NTG administration robustly reduced periorbital mechanical thresholds in rats and induced anxiety-like behaviors and photophobia within 30 and 120 min, respectively. LVC induced migraine-like phenotype recovered in 2 h while NTG group did not fully recover before 4 h. Both LVC and NTG did not provoke DC (direct current) shift, EEG alterations or cortical c-fos expression characteristic to CSD. LVC did not induce de novo CSD and affect KCl (potassium chloride)-induced CSD parameters except for an increase in propagation failure. However, NTG significantly increased both CSD susceptibility and propagation failure. Somatosensory evoked potential (SSEP) configurations were not altered in both LVC and NTG groups, but SSEP latencies were prolonged after CSD. Acute LVC or NTG injection did not increase cortical BBB permeability.

CONCLUSIONS

Single LVC administration induced the fastest manifestation and recovery of acute migraine-like phenotype which was not mediated by CSD waves in the cerebral cortex. We suppose LVC triggered rapid-onset migraine-like symptoms are probably related to functional alterations in the trigeminal nociceptive system and K⁺ channel opening properties of LVC. Understanding the neurobiological mechanisms of this nociceptive window, may provide a novel target in migraine treatment.

Repeated gentle handling or maternal deprivation during the neonatal stage increases adult male rats' baseline orofacial pain responsiveness

OBJECTIVE

Early life experiences have been found to have a long-lasting effect on brain development in adult life. The purpose of this study was to determine whether neonatal manipulation could alter orofacial pain responsiveness in adult rats METHODS: In the first 21 days of life, male rats were exposed to gentle handling or maternal deprivation (MD) procedures to establish models of handled and MD rats, respectively. The rats were assigned to three of the following experimental groups at the age of two months: intra-dental capsaicin (100 µg), intra-lip formalin (50 µL), and repeated nitroglycerin (NTG) (5 mg/rat/ip) infusion. In addition, there were three drug vehicle groups and three groups that received capsaicin, formalin, or NTG without prior handling or MD procedures. The behaviors were recorded following the pain induction.

RESULTS

Spontaneous pain behaviors in the first phase of formalin test was significantly increased in MD (p < 0.01) and handled rats in comparison with the vehicle group (p < 0.05). The second-phase data showed that formalin-induced spontaneous pain behaviors was increased in rats- treated with MD as compared to either vehicle or handled+formalin groups (p < 0.001). Capsaicin-induced dental pulp nociception was increased in the MD group in comparison with the capsaicin (p < 0.001) and capsaicin+handled (p < 0.001) groups. Moreover, NTG-induced migraine-like behaviors symptoms were increased in the MD group as compared to control and handled groups (p < 0.05).

CONCLUSIONS

In this study neonatal gentle handling or MD treatment increased orofacial pain in adulthood, showing early life experiences permanent effects on the development of trigeminal circuits in the brain.

Pharmacological evaluation of carvacrol anti-migraine potential

Migraine is a devitalizing neurovascular disorder that affects millions of people worldwide. This study was directed against the determination of the effectiveness of carvacrol against migraine. In silico results revealed that carvacrol possesses specific scoring values of - 4.4 to - 6 against selected targets. In vivo studies showed that carvacrol (25-50 mg/Kg) decreased migraine pain by reversing thermal allodynia, mechanical allodynia, number of head-scratching, and light phobicity in rats. Levels of glutathione, glutathione-s-transferase, and catalase enhanced in the cortex and trigeminal nucleus caudalis of the animal's brain tissues, i.e., cortex and trigeminal nucleus caudalis with the use of carvacrol, while a significant decrease in lipid peroxide level was seen. Histopathological evaluation showed improvement in cellular architecture and a decrease in expression of certain inflammatory markers such as tumor necrosis factor-alpha, nuclear factor kappa B, interleukin-18, and prostaglandin E2 validated by enzyme-linked immune sorbent assay, immunohistochemistry, and western blot analysis. This study indicates that carvacrol exhibits binding affinities against different targets involved in migraine pathology and possesses anti-migraine action, mediated through anti-inflammatory and anti-oxidant pathways.

Rodent behavior following a dural inflammation model with anti-CGRP migraine medication treatment

Background

Migraine is a widespread and prevalent disease with a complex pathophysiology, of which neuroinflammation and increased pain sensitivity have been suggested to be involved. Various studies have investigated the presence of different inflammatory markers in migraineurs and investigated the role of inflammation in inflammatory models with complete Freund's adjuvant (CFA) or inflammatory soup added to the dura mater.

Objective

The aim of the current study was to examine whether application of CFA to the dura mater would cause behavioral alterations that are migraine relevant. In addition, we investigated the potential mitigating effects of fremanezumab, a CGRP (calcitonin gene-related peptide) specific antibody, following CFA application.

Methods

Male Sprague-Dawley rats were randomly divided into six groups: fresh (n = 7), fresh + carprofen (n = 6), fresh + anti-CGRP (n = 6), sham (n = 7), CFA (n = 16), CFA + anti-CGRP (n = 8). CFA was applied for 15 min on a 3 × 3 mm clearing of the skull exposing the dura mater of male Sprague-Dawley rats. We applied the Light/Dark box and Open Field test, combined with the electronic von Frey test to evaluate outcomes. Finally, we observed CGRP immunoreactivity in the trigeminal ganglion.

Results

No differences were observed in the Light/Dark box test. The Open Field test detected behavior differences, notably that sham rats spend less time in the central zone, reared less and groomed more than fresh + carprofen rats. The other groups were not significantly different compared to sham rats, indicating that activation of the TGVS is present in sham surgery and cannot be exacerbated by CFA. However, for the allodynia, we observed specific periorbital sensitization, not observed in the sham animals. This could not be mitigated by fremanezumab, although it clearly reduced the amount of CGRP positive fibers.

Conclusion

CFA surgically administered to the dura causes periorbital allodynia and increases CGRP positive fibers in the trigeminal ganglion. Fremanezumab does not reduce periorbital allodynia even though it reduces CGRP positive fibers in the TG. Further work is needed to investigate whether CFA administered to the dura could be used as a non-CGRP inflammatory migraine model.

The neurobiology of pain and facial movements in rodents: Clinical applications and current research

One of the most controversial aspects of the use of animals in science is the production of pain. Pain is a central ethical concern. The activation of neural pathways involved in the pain response has physiological, endocrine, and behavioral consequences, that can affect both the health and welfare of the animals, as well as the validity of research. The strategy to prevent these consequences requires understanding of the nociception process, pain itself, and how assessment can be performed using validated, non-invasive methods. The study of facial expressions related to pain has undergone considerable study with the finding that certain movements of the facial muscles (called facial action units) are associated with the presence and intensity of pain. This review, focused on rodents, discusses the neurobiology of facial expressions, clinical applications, and current research designed to better understand pain and the nociceptive pathway as a strategy for implementing refinement in biomedical research.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Could Experimental Inflammation Provide Better Understanding of Migraines?

Migraines constitute a common neurological and headache disorder affecting around 15% of the world’s population. In addition to other mechanisms, neurogenic neuroinflammation has been proposed to play a part in migraine chronification, which includes peripheral and central sensitization. There is therefore considerable evidence suggesting that inflammation in the intracranial meninges could be a key element in addition to calcitonin gene-related peptide (CGRP), leading to sensitization of trigeminal meningeal nociceptors in migraines. There are several studies that have utilized this approach, with a strong focus on using inflammatory animal models. Data from these studies show that the inflammatory process involves sensitization of trigeminovascular afferent nerve terminals. Further, by applying a wide range of different pharmacological interventions, insight has been gained on the pathways involved. Importantly, we discuss how animal models should be used with care and that it is important to evaluate outcomes in the light of migraine pathology.

The active fragments of ghrelin cross the blood-brain barrier and enter the brain to produce antinociceptive effects after systemic administration

G (1-5)-NH₂, G (1-7)-NH₂, and G (1-9) are the active fragments of ghrelin. The aim of this study was to investigate the antinociceptive effects, their ability to cross the blood-brain barrier, and the receptor mechanism(s) of these fragments using the tail withdrawal test in male Kunming mice. The antinociceptive effects of these fragments (2, 6, 20, and 60 nmol/mouse) were tested at 5, 10, 20, 30, 40, 50, and 60 min after intravenous (i.v.) injection. These fragments induced dose- and time-related antinociceptive effects relative to saline. Using the near infrared fluorescence imaging experiments, our results showed that these fragments could cross the brain-blood barrier and enter the brain. The antinociceptive effects of these fragments were completely antagonized by naloxone (intracerebroventricular, i.c.v.); however, naloxone methiodide (intraperitoneal, i.p.), which is the peripheral restricted opioid receptor antagonist, did not antagonize these antinociceptive effects. Furthermore, the GHS-R1α antagonist [D-Lys³]-GHRP-6 (i.c.v.) completely antagonized these antinociceptive effects, too. These results suggested that these fragments induced antinociceptive effects through central opioid receptors and GHS-R1α. In conclusion, our studies indicated that these active fragments of ghrelin could cross the brain-blood barrier and enter the brain and induce antinociceptive effects through central opioid receptors and GHS-R1α after intravenous injection.

Investigating Migraine-Like Behavior using Light Aversion in Mice

Migraine is a complex neurological disorder characterized by headache and sensory abnormalities, such as hypersensitivity to light, observed as photophobia. Whilst it is impossible to confirm that a mouse is experiencing migraine, light aversion can be used as a behavioral surrogate for the migraine symptom of photophobia. To test for light aversion, we utilize the light/dark assay to measure the time mice freely choose to spend in either a light or dark environment. The assay has been refined by introducing two critical modifications: pre-exposures to the chamber prior to running the test procedure and adjustable chamber lighting, permitting the use of a range of light intensities from 55 lux to 27,000 lux. Because the choice to spend more time in the dark is also indicative of anxiety, we also utilize a light-independent anxiety test, the open field assay, to distinguish anxiety from light-aversive behavior. Here, we describe a modified test paradigm for the light/dark and open field assays. The application of these assays is described for intraperitoneal injection of calcitonin gene-related peptide (CGRP) in two mouse strains and for optogenetic brain stimulation studies.

Orexin one receptors within the basolateral amygdala are involved in the modulation of cognitive deficits associated with a migraine-like state in rats

OBJECTIVES

This study explored the possible role of orexin one receptors (Orx1R) in the basolateral amygdala (BLA) on the modulation of nitroglycerin (NTG)-induced migraine-like symptoms. In addition, pain-induced subsequent alteration in learning and memory competence was evaluated in the adult male Wistar rats.

METHODS

The rats were given NTG (5 mg/kg, i.p.) every two days (for nine-day) to induce a migraine-like state. The migraine animals were treated with intra-BLA infusion of an Orx1R antagonist SB 334,867 (10, 20, and 40 nM/rat) or its vehicle DMSO. The NTG-induced migraine symptoms were recorded for 90 min. Spatial and passive avoidance performances were assessed by Morris water maze (MWM) and shuttle box tasks, respectively.

RESULTS

In comparison with control, NTG produced significant migraine-like symptoms characterized by a decrease in cage climbing and an increase in head-scratching, freezing, and facial grooming behavior. Intra-BLA infusion of SB 334,867 (40 nM/rat) significantly decreased cage climbing and increased facial grooming responses in NTG-treated rats. Moreover, all administrated doses of SB 334,867 increased NTG-evoked head-scratching and freezing behavior. Besides, NTG impaired learning and memory performances in both tests, which were exaggerated by post-injection of SB 334,867 (40 nM/rat).

CONCLUSIONS

Overall, the data provided an emerging role for the orexin system within BLA in the modulation of cognitive decline comorbid with migraine in rats.

The Effectiveness of Scutellaria baicalensis on Migraine: Implications from Clinical Use and Experimental Proof

Background

Scutellaria baicalensis (SB), a traditional Chinese medicine, is commonly used for the treatment of inflammatory and painful conditions. The purpose of the present study was to examine the effects of SB on migraine.

Materials and Methods

We examined the clinical applications of SB based on the data obtained from Taiwan's National Health Insurance Research Database and confirmed that it was frequently used in Taiwan for the treatment of headaches. An experimental migraine model was established in rats by an intraperitoneal injection of nitroglycerin (NTG, 10 mg/kg). Pretreatment with SB was given orally 30 min before NTG administration. The rats were subjected to migraine-related behaviour tests that were video-recorded and analysed using EthoVision XT 12.0 software.

Results

The frequency of exploratory and locomotor behaviour was comparatively lower in the NTG group than that in the control group, while the frequency of resting and grooming behaviour increased. These phenomena were ameliorated by pretreatment with 1.0 g/kg SB. The total time spent on the smooth surface was longer in the NTG group than that in the control group, but the time was shortened by pretreatment with 1.0 g/kg SB.

Conclusions

Pretreatment with 1.0 g/kg SB relieved migraine-related behaviours in the experimental NTG-induced migraine model. The outcome therefore demonstrated that pretreatment with 1.0 g/kg SB is beneficial for migraine treatment.

Exacerbated Headache-Related Pain in the Single Prolonged Stress Preclinical Model of Post-traumatic Stress Disorder

Chronic headache pain is one of the most commonly reported comorbid pain conditions with post-traumatic stress disorder (PTSD) patients and resistant to effective treatment, yet no combined preclinical model of the two disorders has been reported. Here, we used a modified chronic headache pain model to investigate the contribution of single prolonged stress (SPS) model of PTSD with sodium nitroprusside (SNP)-induced hyperalgesia. Injection of SNP (2 mg/kg, i.p.) occurred every other day from day 7 to day 15 after initiation of SPS in rats. Paw withdrawal threshold (PWT) to von Frey stimuli and tail flick latencies (TFL) dramatically decreased as early as 7 days after SPS and lasted until at least day 21. Basal PWT and TFL also significantly decreased during the SNP treatment period. The lower nociceptive thresholds recovered in 6 days following the final SNP injection in SNP group, but not in SPS + SNP group. Elevated nociceptin/OFQ (N/OFQ) levels observed in cerebrospinal fluid of SPS rats were even higher in SPS + SNP group. Glial fibrillary acidic protein (GFAP) and N/OFQ peptide (NOP) receptor mRNA expression increased in dorsal root ganglia (DRG) 21 days after SPS exposure; mRNA increases in the SPS/SNP group was more pronounced than SPS or SNP alone. GFAP protein expression was upregulated in trigeminal ganglia by SPS. Our results indicate that traumatic stress exaggerated chronic SNP-induced nociceptive hypersensitivity, and that N/OFQ and activated satellite glia cells may play an important role in the interaction between both conditions.

A Pre-Existing Myogenic Temporomandibular Disorder Increases Trigeminal Calcitonin Gene-Related Peptide and Enhances Nitroglycerin-Induced Hypersensitivity in Mice

Migraine is commonly reported among patients with temporomandibular disorders (TMDs), especially myogenic TMD. The pathophysiologic mechanisms related to the comorbidity of the two conditions remain elusive. In the present study, we combined masseter muscle tendon ligation (MMTL)-produced myogenic TMD with systemic injection of nitroglycerin (NTG)-induced migraine-like hypersensitivity in mice. Facial mechanical allodynia, functional allodynia, and light-aversive behavior were evaluated. Sumatriptan, an FDA-approved medication for migraine, was used to validate migraine-like hypersensitivity. Additionally, we examined the protein level of calcitonin gene-related peptide (CGRP) in the spinal trigeminal nucleus caudalis using immunohistochemistry. We observed that mice with MMTL pretreatment have a prolonged NTG-induced migraine-like hypersensitivity, and MMTL also enabled a non-sensitizing dose of NTG to trigger migraine-like hypersensitivity. Systemic injection of sumatriptan inhibited the MMTL-enhanced migraine-like hypersensitivity. MMTL pretreatment significantly upregulated the protein level of CGRP in the spinal trigeminal nucleus caudalis after NTG injection. Our results indicate that a pre-existing myogenic TMD can upregulate NTG-induced trigeminal CGRP and enhance migraine-like hypersensitivity.

Targeted Nitric Oxide Synthase Inhibitors for Migraine

Nitric oxide (NO) is a small gaseous signaling molecule that has important biological effects. It has been heavily implicated in migraine; and the NO donor, nitroglycerin, has been used extensively as a human migraine trigger. Correspondingly, a number of components of the NO signaling cascade have been shown to be upregulated in migraine patients. NO is endogenously produced in the body by NO synthase (NOS), of which there are three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Based on the accumulating evidence that endogenous NO regulation is altered in migraine pathogenesis, global and isoform-selective inhibitors of NOS have been targeted for migraine drug development. This review highlights the evidence for the role of NO in migraine and focuses on the use of NOS inhibitors for the treatment of this disorder. In addition, we discuss other molecules within the NO signaling pathway that may be promising therapeutic targets for migraine.

Ghrelin attenuated hyperalgesia induced by chronic nitroglycerin: CGRP and TRPV1 as targets for migraine management

Background

According to the neurovascular theory of migraine, activation of the trigeminovascular system contributes to the development of migraine. This study examined the effects of chronic intraperitoneal ghrelin (150 µg/kg) treatment on the development of chronic migraine induced by intermittent injection of nitroglycerin 10 mg/kg.

Methods

Baseline and post-drug (2 h following nitroglycerin injection) mechanical and thermal sensitivity were assessed by von Frey hair and tail immersion tests, respectively on days 1, 3, 5, 7, 9 and 11. Moreover, we investigated the effect of ghrelin treatment on nitroglycerin-induced aversive behavior by using a two-chamber conditioned place aversion paradigm. At the end of behavioral testing, on day 11, animals were sacrificed and plasma concentration of calcitonin gene-related peptide was measured using a rat-specific enzyme-linked immunosorbent assay kit. Also, real time polymerase chain reaction was used to quantify mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid 1 in the trigeminal ganglion.

Results

Our results indicated that nitroglycerin activated the trigeminovascular system, which was reflected by mechanical and thermal hypersensitivity and elevation of mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid-1, as migraine markers, and plasma calcitonin gene-related peptide levels. Moreover, chronic nitroglycerin injection induced conditioned place aversion and body weight loss. Nevertheless, ghrelin modulated nitroglycerin-triggered changes in transient receptor potential vanilloid-1 and calcitonin gene-related peptide expression, and mitigated nitroglycerin-induced hyperalgesia.

Conclusion

These results provide the first convincing evidence that ghrelin has a modulating effect on central sensitization induced by chronic intermittent nitroglycerin, and its antinociceptive effect may be related to a reduction of these factors in the trigeminal ganglion.

Animal Model of Chronic Migraine-Associated Pain

Migraine is a debilitating condition that affects hundreds of millions of people worldwide. A subset of these patients experience chronic migraine, resulting in long-term disability and a severely lowered quality of life. The development of novel migraine therapies has been slow, partially due to the small number of predictive animal models. We have recently developed a novel model of chronic migraine-associated pain, using the known human migraine trigger, nitroglycerin. Injection of nitroglycerin evokes an acute mechanical hyperalgesia, which is sensitive to the acute migraine therapy sumatriptan. In addition, chronic administration of nitroglycerin produces a progressive and sustained decrease in basal mechanical responses, and this hypersensitivity is blocked by migraine preventatives such as topiramate. This mouse model of chronic migraine can be used to study the mechanisms underlying progression of migraine from an episodic to a chronic disorder, and for identifying and screening novel acute and preventive migraine therapies. © 2017 by John Wiley & Sons, Inc.

Recurrent administration of the nitric oxide donor, isosorbide dinitrate, induces a persistent cephalic cutaneous hypersensitivity: A model for migraine progression

Background

A subgroup of migraineurs experience an increase in attack frequency leading to chronic migraine.

Methods

We assessed in rats the roles of dose and repeat administration of systemic isosorbide dinitrate (ISDN), a nitric oxide donor, on the occurrence and development of cephalic/face and extracephalic/hindpaw mechanical allodynia as a surrogate of migraine pain, and the effect of acute systemic sumatriptan and olcegepant and chronic systemic propranolol on these behavioral changes.

Results

A single high (H-ISDN) but not low (L-ISDN) dose of ISDN induces a reversible cephalic and extracephalic mechanical allodynia. However, with repeat administration, L-ISDN produces reversible cephalic but never extracephalic allodynia, whereas H-ISDN induces cephalic and extracephalic allodynia that are both potentiated. H-ISDN-induced cephalic allodynia thus gains persistency. Sumatriptan and olcegepant block single H-ISDN-induced behavioral changes, but only olcegepant reduces these acute changes when potentiated by repeat administration. Neither sumatriptan nor olcegepant prevent chronic cephalic hypersensitivity. Conversely, propranolol blocks repeat H-ISDN-induced chronic, but not acute, behavioral changes.

Conclusions

Repeated ISDN administration appears to be a naturalistic rat model for migraine progression, suitable for screening acute and preventive migraine therapies. It suggests frequent and severe migraine attacks associated with allodynia may be a risk factor for disease progression.

Ghrelin Exerts Analgesic Effects through Modulation of IL-10 and TGF-β Levels in a Rat Model of Inflammatory Pain

BACKGROUND

Ghrelin is a peptide with attenuating effect on inflammatory pain. Both anti- and pro-inflammatory mediators have a role in the nociception and development of pain and hyperalgesia. IL-10 and TGF-β are anti-inflammatory cytokines and inhibit the expression of pro-inflammatory cytokines related to peripheral and central inflammatory pain. In this study, the effects of i.p. injection of ghrelin on the early and the late phases of pain, as well as serum levels of IL-10 and TGF-β, as anti-inflammatory cytokines, were investigated in formalin-induced pain in male rats.

METHODS

Adult male Wistar rats (n=48) were randomly divided into six groups: control, formalin+saline, ghrelin (40, 80, and 160 μg/kg), and morphine. Ghrelin was administered i.p. 30 min before inducing pain by formalin. Pain induced by intraplantar (i.pl.) injection of 50 µl formalin 5%, and pain behavior was studied for 60 min. Serum IL-10 and TGF-β levels were assessed by ELISA method.

RESULTS

The findings of the present study showed that ghrelin with high doses (80 and 160 μg/kg) significantly reduced pain intensity in both the early and the late phases of pain. The serum levels of cytokines, IL-10, and TGF-β1 showed a significant elevation with ghrelin at the dose of 160 μg/kg.

CONCLUSION

Ghrelin is effective in reducing the intensity of both the early and the late phases of inflammatory pain. It seems that ghrelin exerts its analgesic effects in part by increasing the serum levels of anti-inflammatory cytokines.