Effect of sumatriptan in different models of pain in rats

Effect of dural inflammatory soup application on activation and sensitization markers in the caudal trigeminal nucleus of the rat and the modulatory effects of sumatriptan and kynurenic acid

Background

The topical inflammatory soup can model the inflammation of the dura mater causing hypersensitivity and activation of the trigeminal system, a phenomenon present in migraineurs. Calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase are important in the sensitization process there.

5-HT_1B/1D receptor agonists, triptans are used as a treatment of migraine. Kynurenic acid an NMDA antagonist can act on structures involved in trigeminal activation.

Aim

We investigated the effect of inflammatory soup induced dural inflammation on the calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase levels in the caudal trigeminal nucleus. We also tested whether pretreatment with a well-known antimigraine drug, such as sumatriptan and kynurenic acid, a compound with a different mechanism of action, can affect these changes and if their modulatory effects are comparable.

Material and methods

After subcutaneous sumatriptan or intraperitoneal kynurenic acid the dura mater of adult male Sprague-Dawley rats (n = 72) was treated with inflammatory soup or its vehicle (synthetic interstitial fluid). Two and a half or four hours later perfusion was performed and the caudal trigeminal nucleus was removed for immunohistochemistry.

Results and conclusion

Inflammatory soup increased calcitonin gene-related peptide, transient receptor potential vanilloid-1 receptor, and neuronal nitric oxide synthase in the caudal trigeminal nucleus compared to placebo, which was attenuated by sumatriptan and kynurenic acid. This suggests the involvement of 5-HT_1B/1D and NMDA receptors in neurogenic inflammation development of the dura and thus in migraine attacks.

Role of 5-HT5A and 5-HT1B/1D receptors in the antinociception produced by ergotamine and valerenic acid in the rat formalin test

Sumatriptan, dihydroergotamine and methysergide inhibit 1% formalin-induced nociception by activation of peripheral 5-HT1B/1D receptors. This study set out to investigate the pharmacological profile of the antinociception produced by intrathecal and intraplantar administration of ergotamine (a 5-HT1B/1D and 5-HT5A/5B receptor agonist) and valerenic acid (a partial agonist at 5-HT5A receptors). Intraplantar injection of 1% formalin in the right hind paw resulted in spontaneous flinching behavior of the injected hindpaw of female Wistar rats. Intrathecal ergotamine (15nmol) or valerenic acid (1 nmol) blocked in a dose dependent manner formalin-induced nociception. The antinociception by intrathecal ergotamine (15nmol) or valerenic acid (1nmol) was partly or completely blocked by intrathecal administration of the antagonists: (i) methiothepin (non-selective 5-HT5A/5B; 0.01-0.1nmol); (ii) SB-699551 (selective 5-HT5A; up to 10nmol); (iii) anti-5-HT5A antibody; (iv) SB-224289 (selective 5-HT1B; 0.1-1nmol); or (v) BRL-15572 (selective 5-HT1D; 0.1-1nmol). Likewise, antinociception by intraplantar ergotamine (15nmol) and valerenic acid (10nmol) was: (i) partially blocked by methiothepin (1nmol), SB-699551 (10nmol) or SB-224289 (1nmol); and (ii) abolished by BRL-15572 (1nmol). The above doses of antagonists (which did not affect per se the formalin-induced nociception) were high enough to completely block their respective receptors. Our results suggest that ergotamine and valerenic acid produce antinociception via 5-HT5A and 5-HT1B/1D receptors located at both spinal and peripheral sites. This provides new evidence for understanding the modulation of nociceptive pathways in inflammatory pain.

Prophylactic effects of asiaticoside-based standardized extract of Centella asiatica (L.) Urban leaves on experimental migraine: Involvement of 5HT1A/1B receptors

The present study aimed at evaluation of prophylactic efficacy and possible mechanisms of asiaticoside (AS) based standardized extract of Centella asiatica (L.) Urban leaves (INDCA) in animal models of migraine. The effects of oral and intranasal (i.n.) pretreatment of INDCA (acute and 7-days subacute) were evaluated against nitroglycerine (NTG, 10 mg·kg(-1), i.p.) and bradykinin (BK, 10 μg, intra-arterial) induced hyperalgesia in rats. Tail flick latencies (from 0 to 240 min) post-NTG treatment and the number of vocalizations post-BK treatment were recorded as a measure of hyperalgesia. Separate groups of rats for negative (Normal) and positive (sumatriptan, 42 mg·kg(-1), s.c.) controls were included. The interaction of INDCA with selective 5-HT1A, 5-HT1B, and 5-HT1D receptor antagonists (NAN-190, Isamoltane hemifumarate, and BRL-15572 respectively) against NTG-induced hyperalgesia was also evaluated. Acute and sub-acute pre-treatment of INDCA [10 and 30 mg·kg(-1) (oral) and 100 μg/rat (i.n.) showed significant anti-nociception activity, and reversal of the NTG-induced hyperalgesia and brain 5-HT concentration decline. Oral pre-treatment with INDCA (30 mg·kg(-1), 7 d) showed significant reduction in the number of vocalization. The anti-nociceptive effects of INDCA were blocked by 5-HT1A and 5-HT1B but not 5-HT1D receptor antagonists. In conclusion, INDCA demonstrated promising anti-nociceptive effects in animal models of migraine, probably through 5-HT1A/1B medicated action.

Anti-migraine effect of Areca Catechu L. nut extract in bradykinin-induced plasma protein extravasation and vocalization in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Areca catechu Linn. (Arecaceae) nut is a popular folk remedy for the treatment of migraine in Kerala and Tamil Nadu states of India.

AIM OF THE STUDY

This study was designed to investigate the effect of hydroalcoholic extract of A. catechu L. nut (ANE) treatment on migraine pain in rat models to strengthen its use as an anti-migraine therapy.

MATERIALS AND METHODS

Bradykinin (0.1 μmol/kg) injection in to left femoral vein of rat produced PPE which was measured with luminescence spectrometer. Vocalizations were produced in rats with 10 μg of bradykinin infusion into common carotid artery. Phonogram was recorded before, during and for 5min after bradykinin injection and sumatriptan was used as a standard anti-migraine drug. In both models, the ANE was orally administered at doses of 250 and 500 mg/kg, 60 min before bradykinin infusion.

RESULTS

The PPE was reduced in both ANE treated groups of rats. The percent fluorescein was significantly increased in positive control group (97.00±1.7%; p<0.0001) compared to negative control (63.87±1.2%). With ANE treatments (250 and 500 mg/kg) PPE was significantly decreased to 88.88±1.4% (p<0.01) and 83.55±0.1% (p<0.0001) compared to positive control group, respectively. On the other hand in the model of vocalization, with 250 and 500 mg/kg ANE treatment, vocalization was significantly reduced to 33.33% and 16.66%, respectively, compared to saline treated rats. The reduction in vocalization is comparable to the reference drug sumatriptan.

CONCLUSION

The findings provide the strong evidence for anti-migraine potential of ANE in rat models of migraine. In summary, therapeutic intervention with ANE treatment could be a promising strategy for prevention of migraine.

The complex actions of sumatriptan on rat dural afferents

AIM

To test the hypothesis that the clinical efficacy of triptans reflects convergent modulation of ion channels also involved in inflammatory mediator (IM)-induced sensitization of dural afferents.

METHODS

Acutely dissociated retrogradely labeled rat dural afferents were studied with whole cell and perforated patch techniques in the absence and presence of sumatriptan and/or IM (prostaglandin E2, bradykinin, and histamine).

RESULTS

Sumatriptan dose-dependently suppressed voltage-gated Ca²⁺ currents. Acute (2 min) sumatriptan application increased dural afferent excitability and occluded further IM-induced sensitization. In contrast, pre-incubation (30 min) with sumatriptan had no influence on dural afferent excitability and partially prevented IM-induced sensitization of dural afferents. The sumatriptan-induced suppression of voltage-gated Ca²⁺ currents and acute sensitization and pre-incubation-induced block of IM-induced sensitization were blocked by the 5-HT(1D) antagonist BRL 15572. Pre-incubation with sumatriptan failed to suppress the IM-induced decrease in action potential threshold and overshoot (which results from modulation of voltage-gated Na⁺ currents) and activation of Cl⁻ current, and had no influence on the Cl⁻ reversal potential. However, pre-incubation with sumatriptan caused a dramatic hyperpolarizing shift in the voltage dependence of K⁺ current activation.

DISCUSSION

These results indicate that although the actions of sumatriptan on dural afferents are complex, at least two distinct mechanisms underlie the antinociceptive actions of this compound. One of these mechanisms, the shift in the voltage dependence of K⁺ channel activation, may suggest a novel strategy for future development of anti-migraine agents.

Does single cortical spreading depression elicit pain behaviour in freely moving rats?

INTRODUCTION

Behavioural animal studies are critical, particularly to translate results to human beings. Cortical spreading depression (CSD) has been implicated in migraine pathogenesis. We aimed to investigate the effects of CSD on the behaviour of freely moving rats, since available CSD models do not include awake animals.

MATERIALS AND METHODS

We developed a new model to induce single CSD by applying topical N-methyl-D-aspartate (NMDA) and employed a combination of an automated behavioural analysis system, video camera and ultrasonic vocalisation (USV) calls for the first time. Electrocorticograms were also studied during CSD in freely moving rats. Behaviour associated with cephalic pain was assessed in a group of rats that received sumatriptan. Cortical c-fos immunoreactivity was performed in order to confirm CSD.

RESULTS

NMDA induced single CSD in ipsilateral cortex, evoked freezing behaviour (P < 0.01) and increased the number of wet dog shakes (WDS; P < 0.01). Grooming, locomotion, eating, drinking, and circling were not significantly altered among groups. Ultrasonic vocalisations compatible with pain calls (22-27 kHz) were only detected in 3 out of 25 rats. Sumatriptan did not significantly reduce the freezing behaviour. CSD induced significant c-fos expression in ipsilateral cerebral cortex and amygdala (P < 0.01).

CONCLUSIONS

CSD induces freezing behaviour by invoking anxiety/fear via amygdala activation in freely-moving rats. Single CSD is unlikely to lead to severe pain in freely-moving rats, though the development of mild or vague pain cannot be excluded. The relevance of rat behavioural responses triggered by CSD to migraine symptoms in humans needs further evaluation.

Reversal of inflammatory and noninflammatory visceral pain by central or peripheral actions of sumatriptan

BACKGROUND & AIMS

Sumatriptan is used specifically to relieve headache pain. The possible efficacy of sumatriptan was investigated in 2 models of visceral pain.

METHODS

Pancreatic inflammation was induced by intravenous injection of dibutyltin dichloride. Noninflammatory irritable bowel syndrome was induced by intracolonic instillation of sodium butyrate. The effects of systemic sumatriptan on referred hypersensitivity were tested in both models. Effects of sumatriptan within the rostral ventromedial medulla (RVM), a site of descending modulation of visceral pain, was determined by (1) testing the effects of RVM administration of 5HT1(B/D) antagonists on systemic sumatriptan action and (2) determining whether RVM application of sumatriptan reproduced the actions of systemic drug administration.

RESULTS

Systemic sumatriptan elicited a dose- and time-related blockade of referred hypersensitivity in both models that was blocked by systemic administration of either 5HT1(B) or 5HT1(D) antagonists. Sumatriptan administered into the RVM similarly produced dose- and time-related blockade of referred hypersensitivity in both visceral pain models. This was blocked by local microinjection of the 5HT1(B) antagonist but not the 5HT1(D) antagonist. Microinjection of 5HT1(B) or 5HT1(D) antagonists into the RVM did not block the effects of systemic sumatriptan.

CONCLUSIONS

Our findings suggest that sumatriptan suppresses either inflammatory or noninflammatory visceral pain, most likely through peripheral 5HT1(B)/(D) receptors. Actions at 5HT1(B) receptors within the RVM offer an additional potential site of action for the modulation of visceral pain by triptans. These studies offer new insights into the development of strategies that may improve therapy of visceral pain conditions using already available medications.

Serotonin type 1D receptors (5HTR) are differentially distributed in nerve fibres innervating craniofacial tissues

We tested the hypothesis that the 5HT(1D)R, the primary antinociceptive target of triptans, is differentially distributed in tissues responsible for migraine pain. The density of 5HT(1D)R was quantified in tissues obtained from adult female rats with Western blot analysis. Receptor location was assessed with immunohistochemistry. The density of 5HT(1D)R was significantly greater in tissues known to produce migraine-like pain (i.e. circle of Willis and dura) than in structures in which triptans have no antinociceptive efficacy (i.e. temporalis muscle). 5HT(1D)R-like immunoreactivity was restricted to neuronal fibres, where it colocalized with calcitonin gene-related peptide and tyrosine hydroxylase immunoreactive fibres. These results are consistent with our hypothesis that the limited therapeutic profile of triptans could reflect its differential peripheral distribution and that the antinociceptive efficacy reflects inhibition of neuropeptide release from sensory afferents. An additional site of action at sympathetic efferents is also suggested.

Activation of the 5-HT1B/D receptor reduces hindlimb neurogenic inflammation caused by sensory nerve stimulation and capsaicin

Activation of the 5-HT(1B/D) receptor inhibits cerebrovascular neurogenic inflammation (NI). The aim of this study was to determine if the 5-HT(1B/D) receptor agonist sumatriptan can also inhibit NI in other regions of the body. NI was assessed by measuring plasma extravasation (PE) and changes in blood flow in the rat hindpaw. Sumatriptan was administered locally (20 microl, 50 or 100 nM, s.c.) into the dorso-medial region of one hindpaw. The other paw was pre-treated with vehicle (20 microl of 0.9% saline) and served as a control. NI was induced after treatment with sumatriptan/vehicle by injecting capsaicin (15 microl, 1%, s.c.) into each paw or by electrically stimulating the saphenous nerve (4 Hz, 30s). Sumatriptan administered locally or systemically (300 microg/kg, i.v.) significantly reduced saphenous nerve and capsaicin-induced PE and vasodilation. The systemic and local inhibitory actions of sumatriptan are mediated by the 5-HT(1B/D) receptor as pre-treatment with the 5-HT(1B/D) antagonist GR127935 (GR; 15 microl, 1 microM, s.c. or 0.2 micromol/kg, i.v.) completely blocked the inhibitory effect of sumatriptan on capsaicin-induced vasodilation and reduced the inhibitory effect of sumatriptan on capsaicin and electrically induced-PE. Neither PE induced by local injection of substance P (SP) (20 pmol, 20 microl, s.c.) nor vasodilation induced by local CGRP injection was affected by pre-treatment with sumatriptan. These findings indicate that both local and systemic activation of the 5-HT(1B/D) receptor by sumatriptan reduce NI induced by nerve stimulation or capsaicin presumably by inhibiting neuropeptide release. 5-HT(1B/D) receptor agonists may be useful for the treatment of non-trigeminal pain conditions involving NI.