Pharmacological evidence of involvement of nitric oxide pathway in anti‐pruritic effects of sumatriptan in chloroquine‐induced scratching in mice

Chloroquine (CQ) induces histamine‐independent itch in human and mice. We recently reported the role of intradermal nitric oxide (NO)/cyclic guanosine monophosphate pathway in CQ‐evoked scratching in mice. Chloroquine stimulates neuronal nitric oxide synthase (nNOS) activity to over‐producing NO in the skin. Sumatriptan, a 5‐hydroxytryptamine 1b/1d receptors (5‐HTR1b/1d) agonist, is involved in pain and used to treat migraine and cluster headaches. According to previous studies, sumatriptan inhibits NOS activity. Thus, we aimed to investigate the effect of sumatriptan on CQ‐induced scratching. We used the rostral back model of itch. Chloroquine was injected intradermally into the rostral back of NMRI mice, and the scratching behavior was evaluated by measuring the number of bouts over 30 min. We evaluated the effect of sumatriptan and combination of sumatriptan and a non‐selective NO synthase inhibitor, L‐N‐nitro arginine methyl ester (L‐NAME), on the scratching behavior. Additionally, the changes of skin, hippocampus, and cortical nitrite level after different treatments were studied. Intraperitoneal and intradermal sumatriptan attenuates CQ‐induced itch which reversed by GR‐127935, the selective 5‐HTR1b and 5‐HTR1d antagonist. Co‐administration of subeffective doses of sumatriptan and L‐NAME significantly decreases the scratching behavior. Intradermal injection of CQ significantly increases the intradermal nitrite levels while it does not have any significant effects on hippocampal or cortical nitrite concentrations. Likewise, the effective doses of intraperitoneal and intradermal sumatriptan significantly reduce intradermal nitrite levels. We concluded that sumatriptan suppresses CQ‐induced itch most likely by activating 5‐HT1b/1d receptors. This effect probably mediates through NO pathway.     

The nociceptive mechanism of 5‐hydroxytryptamine released into the peripheral tissue in acute inflammatory pain in rats

The present study examined the contribution of 5‐hydroxytryptamine (5‐HT) to acute peripheral inflammatory pain in rats. We used formalin test in this study. After formalin injection into the rat hind paw, biphasic pain‐related behavior (phases 1 and 2) was observed. A microdialysis study revealed that 5‐HT was released into the formalin injection site in a formalin concentration‐dependent manner (1.25–5%), and its peak time was 18min after the injection. Previous studies suggest that peripheral 5‐HT2 receptors are involved in inflammatory pain. Therefore, we next examined whether 5‐HT2A and 5‐HT2C receptors are involved, and from where 5‐HT is released in the formalin test. Local pretreatment with a selective 5‐HT2A receptor antagonist, ketanserin, and selective 5‐HT2C receptor antagonists, RS102221 and SB242084, inhibited the number of flinches in early part of phase 2 (phase 2A) of the formalin test in a dose‐dependent manner. Peripheral pretreatment with sodium cromoglycate (cromolyn), a mast cell membrane stabilizer, completely suppressed 5‐HT release and inhibited phase 2 responses of the formalin test. These drugs inhibited c‐fos expression in the superficial layer of the spinal dorsal horn of segments L4‐5 at 2h after formalin injection. These results indicate that 5‐HT released into peripheral tissue and its receptors, 5‐HT2A as well as 5‐HT2C, at the periphery have an important role in pain‐related behaviors during acute peripheral inflammation.     

5‐HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5‐HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5‐HT) receptors, the 5‐HT transporter (SERT), and 5‐HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5‐HT system in humans include antagonists for the 5‐HT_1A, 5‐HT_1B, 5‐HT_2A, and 5‐HT₄ receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging. © 2011 Wiley Periodicals, Inc.     

Parachlorophenylalanine‐induced 5‐HT depletion alters behavioral and brain neurotransmitters levels in 6‐Hz psychomotor seizure model in mice

The present study was designed to investigate the role of serotonin and other neurotransmitters namely dopamine (DA), histamine, nor‐epinephrine (NE), glutamate, and γ‐aminobutyric acid (GABA) in the 6‐Hz‐induced psychomotor seizures in Swiss albino mice. Parachlorophenylalanine (PCPA, 300 mg/kg/day, i.p for 3 days)‐treated mice were given 6‐Hz stimulation. Sodium valproate (SVP) (200 mg/kg/day, p.o for 3 days) was used as a reference antiepileptic drug. The behavioral changes induced by 6 Hz including increased rearing and grooming, Straub's tail, behavioral arrest, stun position were amplified by PCPA. The 6‐Hz‐induced seizures were accompanied by reduced brain 5‐HT, DA, NE, histamine, GABA, and enhanced glutamate levels. PCPA facilitated further reduction of endogenous 5‐HT and DA levels but not NE, histamine, GABA, and glutamate levels. Pre‐ and post‐treatment with SVP protected the mice from 6‐Hz seizures and attenuated PCPA‐induced changes in the levels of 5‐HT and DA in the mice brain suggesting the protective effect of SVP in the pharmacoresistant model of epilepsy involving mainly serotonergic mechanism. However, the study also suggests modulation of other neurotransmitters both in 6‐Hz psychomotor seizures and in the action of SVP against such seizures.     

Effects of acute stressors on itch- and pain-related behaviors in rats

Many acute stressors reduce pain, a phenomenon called stress-induced antinociception (SIA). Stress also is associated with increased scratching in chronic itch conditions. We investigated effects of acute stressors on facial itch and pain using a recently introduced rat model. Under baseline (no-swim) conditions, intradermal (id) cheek microinjection of the pruritogen serotonin (5-HT) selectively elicited hindlimb scratch bouts, whereas the algogen mustard oil (allyl isothiocyanate [AITC]) selectively elicited ipsilateral forepaw swipes, directed to the cheek injection site. To test effects of swim stress, rats received id cheek microinjection of 5-HT (1%), AITC (10%), or vehicle, and were then subjected to one of the following swim conditions: (1) weak SIA (W-SIA), (2) naltrexone-sensitive SIA (intermediate or I-SIA), or (3) naltrexone-insensitive SIA (strong or S-SIA). After the swim, we recorded the number of hindlimb scratch bouts and forelimb swipes directed to the cheek injection site, as well as facial grooming by both forepaws. Under S-SIA, AITC-evoked swiping and 5-HT-evoked scratching were both reduced. I-SIA reduced AITC-evoked swiping with no effect on 5-HT-evoked scratching. Facial grooming immediately post-swim was suppressed by S-SIA, but not I- or W-SIA. W-SIA tended to equalize scratching and swiping elicited by 5-HT and AITC compared with no-swim controls, suggesting altered itch and pain processing. Exercise (wheel-running), novelty, cold exposure, and fear (shaker table), key components of swim stress, differentially affected tail-flick latencies and 5-HT-evoked swiping and scratching behavior. Thus, itch and pain can be simultaneously suppressed by a combination of acute stress-related factors via an opioid-independent mechanism.     

N‐feruloylserotonin in preventive combination therapy with methotrexate reduced inflammation in adjuvant arthritis

Many of disease‐modifying anti‐rheumatic drugs often have side effects at high doses and/or during long‐term administration. Increased efficacy without increased toxicity is expected for combination therapy of rheumatoid arthritis (RA). The aim of the study was to examine the effect of N‐feruloylserotonin (N‐f‐5HT) and methotrexate (MTX) in monotherapy and in combination therapy on disease progression and inflammation in arthritic rats. Adjuvant arthritis was induced by intradermal injection of Mycobacterium butyricum in incomplete Freund′s adjuvant in Lewis rats. The experiment included healthy animals, arthritic animals without any drug administration, arthritic animals with administration of N‐f‐5HT in the oral daily dose of 15 mg/kg b.w., arthritic animals with administration of MTX in the oral dose of 0.3 mg/kg b.w. twice a week and arthritic animals treated with the combination of N‐f‐5HT and MTX. N‐f‐5HT in monotherapy reduced only activation of NF‐κB and did not have any significant effect on other parameters monitored. Low‐dose treatment of MTX decreased the level of IL‐1β and MCP‐1 on day 14 and activation of NF‐κB in liver without significant effect on other parameters. N‐f‐5HT and MTX combination showed both the anti‐arthritic (hind paw volume and arthritic score) and anti‐inflammatory effect (plasmatic levels of IL‐1β, IL‐17, MCP‐1, CRP, and activation of NF‐κB in liver). In combination with MTX, N‐f‐5HT markedly potentiated the therapeutic effect of MTX low dose, which resulted in significant improvement of all parameters measured. The findings showed that the combination therapy simultaneously decreased multiple markers of inflammation, a result crucial for future therapy of RA.     

5-Hydroxytryptamine (5-HT)2 receptor involvement in acute 5-HT-evoked scratching but not in allergic pruritus induced by dinitrofluorobenzene in rats

We investigated the role of serotonin (5-hydroxytryptamine; 5-HT)2 and 5-HT3 receptor subtypes in acute itch-associated scratching behavior as well as in an allergic pruritus model in rats. Intradermal 5-HT evoked hind limb scratching directed toward the injection site in na?ve rats. Scratching behavior was significantly reduced by pretreatment with the 5-HT2 receptor antagonist ketanserin. Intradermal injection of alpha-methylserotonin, a 5-HT2 receptor agonist, also elicited scratching behavior in a dose-dependent manner, indicating that acute 5-HT-induced scratching is mediated via peripheral 5-HT2 receptors. To produce a model of allergic pruritus, skin was sensitized by topical application of 5% dinitrofluorobenzene (DNFB). One month later, repeated challenge of the skin with 0.2% DNFB at weekly intervals elicited scratching as part of the immediate allergic response. Scratching was not affected by ketanserin or by the 5-HT3 receptor antagonist ondansetron, indicating that neither 5-HT2 nor 5-HT3 receptors is involved in itch-associated scratching behavior caused by allergic skin dermatitis in rats.     

Cannabidiol reverses the mCPP‐induced increase in marble‐burying behavior

Cannabidiol (CBD), one of the main components of Cannabis sp., presents clinical and preclinical anxiolytic properties. Recent results using the marble‐burying test (MBT) suggest that CBD can also induce anticompulsive‐like effects. Meta‐chloro‐phenyl‐piperazine (mCPP) is a nonspecific serotonergic agonist (acting mainly at 5HT1A, 5HT2C and 5HT1D receptors) reported to increase symptoms in OCD patients and block the anticompulsive‐like effect of serotonin reuptake inhibitors (SRIs) in animal models. The aim of this study was to investigate the interference of CBD on mCPP effects in repetitive burying. Administration of mCPP showed dual effects in the MBT, increasing the number of buried marbles at lower (0.1 mg/kg) while decreasing it at higher doses (1 mg/kg), an effect not related to a general increase in anxiety‐like behavior. As found previously, CBD (30 mg/kg) and the positive control fluoxetine (FLX; 10 mg/kg) decreased burying behavior without changing general exploratory activity. A similar effect was found when subeffective doses of CBD (15 mg/kg) and FLX (3 mg/kg) were administered together. These subeffective doses alone were also able to block mCPP‐induced repetitive burying. The results, in addition to reinforcing a possible anticompulsive effect of CBD, also suggest that mCPP‐induced repetitive burying could be a useful test for the screening of compounds with presumed anticompulsive properties.     

Enhanced scratching evoked by PAR-2 agonist and 5-HT but not histamine in a mouse model of chronic dry skin itch

Chronic itch is a symptom of many skin conditions and systemic disease, and it has been hypothesized that the chronic itch may result from sensitization of itch-signaling pathways. We induced experimental chronic dry skin on the rostral back of mice, and observed a significant increase in spontaneous hindlimb scratches directed to the dry skin. Spontaneous scratching was significantly attenuated by a PAR-2 antibody and 5-HT2A receptor antagonist, indicating activation of these receptors by endogenous mediators released under dry skin conditions. We also observed a significant increase in the number of scratch bouts evoked by acute intradermal injections of a protease-activated receptor (PAR)-2 agonist and serotonin (5-HT), but not histamine. We additionally investigated if pruritogen-evoked activity of dorsal root ganglion (DRG) neurons is enhanced in this model. DRG cells from dry skin mice exhibited significantly larger responses to the PAR-2 agonist and 5-HT, but not histamine. Spontaneous scratching may reflect ongoing itch, and enhanced pruritogen-evoked scratching may represent hyperknesis (enhanced itch), both potentially due to sensitization of itch-signaling neurons. The correspondence between enhanced behavioral scratching and DRG cell responses suggest that peripheral pruriceptors that respond to proteases and 5-HT, but not histamine, may be sensitized in dry skin itch.     

N‐methyl‐d‐aspartate receptor‐mediated modulations of the anti‐allodynic effects of 5‐HT1B/1D receptor stimulation in a rat model of trigeminal neuropathic pain

Previous studies showed that triptans and other 5‐HT_1B/1D‐receptor agonists attenuate hyper‐responsiveness to mechanical stimulation of the face in a rat model of trigeminal neuropathic pain, probably by activating 5‐HT_1B/1D‐receptors on primary afferent nociceptive fibers. We now tested whether blockade of post‐synaptic receptors for the excitatory amino acid glutamate released by these fibers would increase this action. We thus evaluated whether (±)1‐hydroxy‐3‐aminopyrrolidine‐2‐one (HA‐966), an antagonist at the glycine/d ‐serine site of N‐methyl‐d ‐aspartate (NMDA)‐receptors, would potentiate the anti‐allodynic action of dihydroergotamine and zolmitriptan in rats with chronic constriction injury to the infraorbital nerve (CCI‐ION). Complementary studies were performed with other NMDA‐receptor ligands and in rats with chronic constriction injury to the sciatic nerve (CCI‐SN) for comparison. Injury was produced by loose ligatures of the nerves. Responsiveness to mechanical stimulation (vibrissae or hindpaw territories) with von Frey filaments was used to evaluate allodynia 2 weeks after nerve ligature. Rats received NMDA‐receptor ligands or saline 20 min before dihydroergotamine (25–100μg/kg, i.v.) or zolmitriptan (25–100μg/kg, s.c.). HA‐966 (2.5 mg/kg, s.c.), inactive on its own, enhanced the anti‐allodynic effects of dihydroergotamine (eightfold increase) and zolmitriptan (threefold increase) in CCI‐ION rats, but these drugs exerted no effects in allodynic CCI‐SN rats. NMDA‐receptor blockade by memantine (5 mg/kg, i.p.) also enhanced, whereas activation at glycine/NMDA site by d ‐cycloserine (3 mg/kg, i.p.) reduced the anti‐allodynic properties of zolmitriptan in CCI‐ION rats. Combined administration of NMDA‐receptor antagonist and 5‐HT_1B/1D‐receptor agonist may be a promising approach for alleviating trigeminal neuropathic pain.     

Clinical correlates of blood serotonin levels in patients with mastocytosis

Background Mastocytosis is a clonal disorder associated with an increased mast cell burden. We have recently demonstrated the ability of human mast cells to express and be activated through multiple serotonin receptors; to synthesize and release serotonin; and that mastocytosis patients may have abnormal serotonin levels. As serotonin has been implicated in the genesis of clinical symptoms found in association with some chronic diseases, we have now determined the whole blood serotonin levels in 29 patients diagnosed with mastocytosis, and correlated these levels with multiple clinical and laboratory parameters. Materials and methods Patients with mastocytosis were categorized according to disease variant. Blood serotonin values were determined and correlated with values reported for normal subjects; and clinical and laboratory features of the disease. Results Total blood serotonin levels followed a bimodal distribution in line with our earlier report,unlike the normal distribution reported for normal individuals. Serotonin levels did not correlate with platelet numbers, liver function tests or serum tryptase levels. Patients with lower serotonin values had greater rates of fatigue (P = 0·0001), migraine headaches (P = 0·0028), psychiatric symptoms (P = 0·0001), diarrhoea (P = 0·0407), flushing (0·0085), and abdominal and bone pain (P = 0·0001). Conclusions Our study suggests that low blood serotonin levels help define a sub‐group of patients with mastocytosis that are more likely to present with neurological and gastrointestinal complaints, and suggests that the use of pharmacologic agents that alter blood serotonin levels could be explored in selected patients.     

Involvement of Pro‐Nociceptive 5‐HT2A Receptor in the Pathogenesis of Medication‐Overuse Headache

(Headache 2010;50:185‐197) Objectives.— To determine the involvement of 5‐HT_2A (5‐HT_2A) receptor in the process of trigeminal plasticity induced by chronic analgesic exposure and in the process of inflammatory‐induced thermal hyperalgesia. Background.— Derangement in 5‐HT_2A serotonin receptor has been reported to implicate in pathogenesis of medication‐overuse headache. No clear explanation concerning the precise roles of these receptors in the process. Methods.— Wistar rats were daily administered with paracetamol (200 mg/kg) for 30 days. On the next day, ketanserin, a 5‐HT_2A antagonist, or saline was given prior to cortical spreading depression (CSD) induction. Electrocorticogram, cortical blood flow, Fos and 5‐HT_2A‐immunoreactivity in cortex and trigeminal pathway were studied. In the other experiment, complete Freund's adjuvant was injected into the rat hind paw to induce tissue inflammation. Three days later, ketanserin was given and noxious heat was applied to both inflamed and noninflamed paws. The response between 2 sides was compared by measuring paw withdrawal latency. Results.— Chronic paracetamol exposure led to an increase in CSD frequency and CSD‐evoked Fos expression in cerebral cortex indicating the increase in neuronal excitability. Prolonged medication exposure also facilitated trigeminal nociception as evident by an increase in CSD‐evoked Fos expression in trigeminal nucleus caudalis. The expression of 5‐HT_2A receptor in cerebral cortex and trigeminal ganglia was enhanced by chronic paracetamol administration. Pretreatment with ketanserin significantly attenuated these effects. The second experiment showed that ketanserin was able to lengthen the paw withdrawal latency in the inflamed side but did not alter nociceptive response in the noninflamed side. Conclusion.— These findings suggest that up‐regulation of pro‐nociceptive 5‐HT_2A receptor is an important step in the process of cortical hyper‐excitation and nociceptive facilitation induced by chronic analgesic exposure.     

Sumatriptan reduces severity of status epilepticus induced by lithium–pilocarpine through nitrergic transmission and 5‐HT1B/D receptors in rats: A pharmacological‐based evidence

Status epilepticus (SE) is a life‐threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti‐inflammatory property of the anti‐migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole‐induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium–pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5‐hydroxytryptamin 1B/1D (5‐HT_1B/1D) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001‐1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5‐HT_1B/1D antagonist GR‐127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor‐α (TNF‐α) and NO levels were markedly elevated in the rats' brain tissues post‐SE induction, pre‐treatment with sumatriptan significantly reduced both TNF‐α (P < 0.05) and NO (P < 0.001) levels. Combined GR‐127935 and sumatriptan treatment inhibited these anti‐inflammatory effects of sumatriptan, whereas combined non‐specific NOS (L‐NAME) or selective neuronal NOS (7‐nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5‐HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.     

5‐HT2C receptor agonists attenuate pain‐related behaviour in a rat model of trigeminal neuropathic pain

Peripheral branches of the trigeminal nerve may be damaged during maxillofacial injury or surgical procedures and trigeminal trauma may induce severe pain that is very challenging to treat. Chronic constriction injury to the infraorbital nerve (ION‐CCI) by loose ligatures has proven a useful model for some types of trigeminal neuropathic pain disorder. Using ION‐CCI rats, we examined the antiallodynic effects of intrathecally administered agents which are selective for 5‐HT2C receptors. Allodynia was evaluated by applying von Frey filaments to skin innervated by the injured ION. Dose‐dependent antiallodynic effects followed administration of three 5‐HT2C receptor agonists, 6‐chloro‐2‐(1‐piperazinyl)‐pyrazine (MK212: 10, 30, and 100 μg); (S)‐2‐(chloro‐5‐fluoro‐indol‐l‐yl)‐1‐methyamine fumarate (RO 60‐0175: 10, 30, and 100 μg); (AaR)‐8,9‐dichloro‐2,3,4,4a‐tetrahydro‐1H‐pyrazino[1,2‐a]quinoxalin‐5(6H)‐one (WAY‐161503: 10, 30, and 100 μg). ED50 values for antiallodynic effects of MK212, RO 60‐0175, and WAY‐161503 were 39.62, 46.67, and 51.22 μg, respectively. Intrathecal administration of the 5‐HT2C receptor antagonist, 8‐[5‐2,4‐dimethoxy‐5‐(4‐trifluoromethylphenylsulphonamido)phenyl‐5‐oxopentyl]‐1,3,8‐triazaspiro[4,5]decane‐2,4‐dione (RS‐102221: 30 μg) did not alter the mechanical threshold. Intrathecal pretreatment with RS‐102221 (10 and 30 μg) reduced the antiallodynic effects of the highest dose of 5‐HT2C agonists. These results indicated that, in this rat model, the 5‐HT2C receptor plays a role in spinal inhibition of trigeminal neuropathic pain.     

Selective Inhibition of 5‐HT7 Receptor Reduces CGRP Release in an Experimental Model for Migraine

Objective.— To investigate the role of 5‐HT₇ receptors on the release of calcitonin gene‐related peptide (CGRP) in an animal model of migraine. Background.— Calcitonin gene‐related peptide has been identified as a key neuropeptide in the pathophysiology of migraine. It is elevated in the external jugular vein during migraine attacks in humans and after stimulation of the trigeminal ganglion in animal models of migraine. This can be treated with the 5‐HT_1B/1D receptor agonist sumatriptan concomitant with headache relief. Nevertheless, triptans, the most effective agents for the treatment of acute migraine attacks, are not effective in more than 1/3 of migraineurs and less than 50% of migraineurs achieve complete pain freedom. This indicates other serotonin receptors may be involved in the pathophysiology of migraine. Increasing evidence has shown that 5‐HT₇ receptors may be involved in migraine pathogenesis. However, direct evidence for the role of 5‐HT₇ receptors in migraine is still lacking. Methods.— Unilateral electrical stimulation of the trigeminal ganglion (TGES) was performed in anesthetized male Sprague‐Dawley rats. Animals were pretreated with sumatriptan (300 µg/kg, i.v.), selective 5‐HT₇ receptor antagonist SB269970 (5, 10 mg/kg, s.c.), potential 5‐HT₇ receptor agonist AS19 (5, 10 mg/kg, s.c.) or co‐administration of SB269970 and AS19 (10 mg/kg, s.c.). Serum CGRP concentrations in the ipsilateral jugular vein were determined before and at 2 and 5 minutes after the start of TGES. Results.— Our results showed that sumatriptan almost completely inhibited the release of CGRP evoked by TGES. Pre‐administration of SB269970 (5, 10 mg/kg) caused a significant decrease in serum CGRP concentrations at 2 and 5 minutes following the onset of TGES, with a less inhibitory effect compared with sumatriptan. AS19 had no significant effect on CGRP release, while the SB269970‐induced inhibitory effect was reversed by AS19. Conclusions.— Selective inhibition of 5‐HT₇ receptors partly reduced CGRP release evoked by TGES. These findings suggest that 5‐HT₇ receptors may play a role in the pathophysiology of migraine. (Headache 2010;50:579‐587)     

Treatment with either COX‐2 inhibitor or 5‐LOX inhibitor causes no compensation between COX‐2 pathway and 5‐LOX pathway in chronic aluminum overload‐induced liver injury in rats

This study was designed to observe the compensation between cyclooxygenase‐2 pathway and 5‐lipoxygenase pathway in chronic aluminum overload‐induced liver injury rats. A rat hepatic injury model of chronic aluminum injury was established by the intragastric administration of aluminum gluconate (Al3 + 200 mg/kg per day, 5 days a week for 20 weeks). The COX‐2 inhibitor [meloxicam (1 mg/kg)] and 5‐LOX inhibitor [caffeic acid (30 mg/kg)] were intragastrically administered 1 h after aluminum administration. The histopathology was detected by hematoxylin‐eosin staining. A series of biochemical indicators were measured with biochemistry assay or ELISAs. The expressions of COX‐2 and 5‐LOX were measured by immunohistochemistry. Our experimental results showed that aluminum overload caused a significant damage to the liver and also significantly increased the expressions of COX‐2, 5‐LOX and the levels of inflammation and oxidative stress. The administration of meloxicam and caffeic acid significantly protected livers against histopathological injury, significantly decreased plasma ALT, AST, and ALP levels, significantly decreased TNF‐α, IL‐6, IL‐1β levels, and oxidative stress. However, the administration of caffeic acid did not significantly increase the expression of COX‐2 compared with the model group. On the other hand, the administration of meloxicam also did not significantly increase the expression of 5‐LOX compared with the model group. Our results indicate that there is no compensation between COX‐2 pathway and 5‐LOX pathway by inhibiting either COX‐2 or 5‐LOX in chronic aluminum overload‐induced liver injury rat.     

Involvement of monoaminergic system in the antidepressant‐like effect of riparin I from Aniba riparia (Nees) Mez (Lauraceae) in mice

In past studies conducted by our group, riparin I (rip I) isolated from the green fruit of Aniba riparia presented antianxiety effects in mice, while its analogs rip II and III showed anxiolytic and antidepressant‐like actions. This time around, we investigated a possible antidepressant activity of rip I using the forced swimming test (FST) and tail suspension test (TST) as predictive tests for antidepressant activity in rodents. In addition, the involvement of the monoaminergic system in this effect was also assessed. rip I was acutely administered by intraperitoneal (i.p.) and oral (p.o) routes to male mice at doses of 25 and 50 mg/kg. Results showed that rip I at both tested doses and administration routes produced a significant decrease in immobility time in FST and TST. The pretreatment of mice with prazosin (1 mg/kg, i.p., an α₁‐adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂‐adrenoceptor antagonist), SCH23390 (15 μg/kg, i.p., a dopamine D1 receptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist), p‐chlorophenylalanine (100 mg/kg, an inhibitor of serotonin synthesis) or ritanserin (4 mg/kg, a serotonin 5‐HT2_a/2_c receptor antagonist) blocked the anti‐immobility effects elicited by rip I (50 mg/kg, p.o.) in the FST. Taken together, results indicate that rip I produces significant antidepressant‐like activity in the FST and TST, and this effect seems to be dependent on its interaction with noradrenergic, dopaminergic and serotonergic systems.     

Dual effect of cAMP agonist on ameliorative function of PKA inhibitor in morphine‐dependent mice

The present study shows interactive effects of bucladesine (db‐cAMP) as a cyclic adenosine monophosphate (cAMP) agonist and H‐89 as a protein kinase A (PKA) inhibitor on naloxone‐induced withdrawal signs in morphine‐dependent mice. Animals were treated subcutaneously with morphine thrice daily with doses progressively increased from 50 to 125 mg/kg. A last dose of morphine (50 mg/kg) was administered on the 4th day. Several withdrawal signs were precipitated by intraperitoneal (i.p.) administration of naloxone (5 mg/kg). Different doses of bucladesine (50, 100, 200 nm /mouse) and H‐89 (0.05, 0.5, 1, 5 mg/kg) were administered (i.p.) 60 min before naloxone injection. In combination groups, bucladesine was injected 15 min before H‐89 injection. Single administration of H‐89 (0.5, 1, 5 mg/kg) and bucladesine (50, 100 nm /mouse) significantly attenuated prominent behavioral signs of morphine withdrawal. Lower doses of bucladesine (50, 100 nm /mouse) in combination with H‐89 (0.05 mg/kg) increased the inhibitory effects of H‐89 on withdrawal signs while in high dose (200 nm /mouse) decreased the ameliorative function of H‐89 (0.05 mg/kg) in morphine‐dependent animals. It is concluded that H‐89 and bucladesine could affect morphine withdrawal syndrome via possible interaction with cyclic nucleotide messengering systems, protein kinase A signaling pathways, and modified related neurotransmitters.     

Serotonin increases the functional activity of capsaicin-sensitive rat trigeminal nociceptors via peripheral serotonin receptors

Peripheral serotonin (5HT) has been implicated in migraine and temporomandibular pain disorders in humans and animal models and yet the mechanism(s) by which 5HT evokes pain remains unclear. Trigeminal pain can be triggered by activation of the transient receptor potential V1 channel (TRPV1), expressed by a subset of nociceptive trigeminal ganglia (TG) neurons and gated by capsaicin, noxious heat, and other noxious stimuli. As 5HT is released in the periphery during inflammation and evokes thermal hyperalgesia, and TRPV1 is essential for thermal hyperalgesia, we hypothesized that 5HT increases the activity of capsaicin-sensitive trigeminal neurons and that this increase can be attenuated by pharmacologically targeting peripheral 5HT receptors. TG cultures were pretreated with 5HT (10 nM-100 μM), sumatriptan (5HT_1B/1D agonist), ketanserin (5HT_2A antagonist), granisetron (5HT₃ antagonist), or vehicle prior to capsaicin (30-50 nM). Single-cell accumulation of intracellular calcium was recorded or calcitonin gene-related peptide (CGRP) release was measured following each treatment. In addition, using in situ hybridization and immunohistochemistry, we detected the colocalization of 5HT_1B, 5HT_1D, 5HT_2A, and 5HT_3A, but not 5HT_2C mRNA with TRPV1 in TG cells. 5HT pretreatment evoked a significant increase in calcium accumulation in capsaicin-sensitive trigeminal neurons and enhanced capsaicin-evoked CGRP release, but had no significant effect when given alone. Sumatriptan, ketanserin, and granisetron treatment attenuated calcium accumulation and 5HT enhancement of capsaicin-evoked CGRP release. Together these results indicate that 5HT increases the activity of capsaicin-sensitive peripheral nociceptors, which can be attenuated by pharmacologically targeting peripheral 5HT receptors, thereby providing a mechanistic basis for peripheral craniofacial pain therapy.