Further analysis of acute antinociceptive and anti‐inflammatory actions of 4‐phenylselenyl‐7‐chloroquinoline in mice

A new quinoline containing selenium, 4‐phenylselenyl‐7‐chloroquinoline (4‐PSQ), was described and synthetized by our research group. Recently, we demonstrated the potential antinociceptive and anti‐inflammatory of 4‐PSQ. For this reason, the first objective of this study was to expand our previous findings by investigating the contribution of glutamatergic, serotonergic, and nitrergic systems to the acute antinociceptive action of this compound. Pretreatment with 4‐PSQ (0.01–25 mg/kg, p.o.) reduced the nociception induced by glutamate. MK‐801 (an uncompetitive antagonist of the N‐Methyl‐d ‐aspartate (NMDA) receptor) blocked the antinociceptive effect exerted by 4‐PSQ (25 mg/kg, p.o.) in the acetic acid‐induced abdominal writhing test. The pretreatment with WAY100635 (a selective antagonist of 5‐HT_1A receptor), ketanserin (a selective antagonist of 5‐HT_2A/2C receptor), and pindolol (a nonselective antagonist of 5‐HT_1A/1B receptors) partially blocked the antinociceptive effect caused by 4‐PSQ (25 mg/kg, per oral, p.o.) in the acetic acid‐induced abdominal writhing test. Nitric oxide precursor, l ‐arginine hydrochloride, partially reversed antinociception caused by 4‐PSQ or ω‐nitro‐l ‐arginine (l ‐NOARG). Treatments did not modify the locomotor and exploratory activities of mice. Additionally, the acute anti‐inflammatory effect of 4‐PSQ in a model of pleurisy induced by carrageenan in mice was investigated. 4‐PSQ reduced the cellular migration, pleural exudate accumulation, and myeloperoxidase activity induced by carrageenan exposure. 4‐PSQ protected against the increase in reactive species levels and reduction of nonprotein thiol levels induced by carrageenan. Data presented here showed that the modulation of serotonergic, nitrergic, and glutamatergic systems contributed to the antinociceptive effect of 4‐PSQ and it reinforced the therapeutic potential of this quinolinic compound for acute inflammation.     

Relations between open‐field,elevated plus‐maze,and emergence tests in C57BL/6J and BALB/c mice injected with GABA‐ and 5HT‐anxiolytic agents

Two 5HT_1A receptor agonists and chlordiazepoxide were examined in open‐field, elevated plus maze, and emergence tests. At doses with no effect in the open‐field, chlordiazepoxide increased open and open/total arm visits as well as open arm duration in the elevated plus maze, whereas 5HT_1A receptor agonists showed an anxiolytic response on a single measure. The anxiolytic action of chlordiazepoxide was limited to the less active BALB/c strain. Unlike the 5HT_1A receptor agonists, chlordiazepoxide was also anxiolytic in the emergence test, once again only in BALB/c and not C57BL/6J mice. Significant correlations were found between emergence latencies and specific indicators of anxiety in the elevated plus‐maze in chlordiazepoxide‐treated but not in mice treated with buspirone and 8‐OH‐DPAT. These results indicate that elevated plus‐maze and emergence tests depend on benzodiazepine receptors. In contrast, 5HT_1A receptor agonists were ineffective in the emergence test and no correlation was found between emergence latencies and specific indicators of anxiety in the elevated plus‐maze. Though superficially similar, the emergence test seems to tap into a partially separate facet of anxiety.     

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.     

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.     

Reduced Adverse Event Profile of Orally Inhaled DHE (MAP0004) vs IV DHE: Potential Mechanism

Background.— MAP0004 is a novel orally inhaled formulation of dihydroergotamine mesylate (DHE) currently in development that has been clinically observed to provide rapid (～10 minutes) therapeutic levels of DHE but with lower rates of adverse effects (dizziness, nausea, and paresthesia) compared with intravenous (IV) dosing. Receptor‐based mechanistic studies were conducted to determine if differences between IV DHE and inhaled DHE (MAP0004) binding and functional activity were responsible for the improved adverse event profile. Methods.— Radioligand competitive binding assays were performed at adrenergic (α1 [non‐specific], α2A, α2B, α2C, β), dopaminergic (D; D₁, D₂, D₃), and at serotonergic (5‐HT; 5‐HT_1A, 5‐HT_1B, 5‐HT_1D, 5‐HT_2A, 5‐HT_2C, 5‐HT₃, 5‐HT₄, 5‐HT_5A, 5‐HT₆, 5‐HT₇) receptors. Binding assays were also conducted for the major metabolite of DHE, 8’‐hydroxy‐DHE (8’‐OH‐DHE). Subsequent functional receptor assays were also performed at 5‐HT_1B, 5‐HT_1D, 5‐HT_2A, 5‐HT_2C, 5‐HT₃, D₂, α1A, α2A, α2B, β1, and β2 and muscarinic receptors to ensure that observed receptor binding translated into potential functional response. Results.— For competitive binding studies, DHE demonstrated extensive activity at IV C_max for all 5‐HT receptors tested, except 5‐HT₃ and 5‐HT₄, and α1, α2A, α2B, α2C, and D₃ receptors. DHE concentrations used in the studies were equal to the peak plasma concentrations (C_max) observed in human subjects following IV DHE 1.0 mg (the standard approved dose), and 2 and 4 inhalations MAP0004 which, respectively, produced systemic circulation levels of DHE equivalent to 0.44 mg and 0.88 mg administered IV. MAP0004 binding activity at the C_max concentrations was lower than IV DHE and no binding was observed for the 8’‐OH‐DHE metabolite. However, MAP0004 preserved potent agonist action at key anti‐migraine 5‐HT_1B and 5‐HT_1D receptors, even at the lower C_max concentrations. Functional binding studies displayed similar results whereby IV DHE C_max concentrations invoked strong agonist/antagonist responses, for instance at adrenergic and 5‐HT_2C receptors, which could have been responsible for dizziness. Conversely, at C_max concentrations of MAP0004, inhaled DHE achieved a significantly lower response or no response at the adrenergic and 5‐HT_2C receptors. Conclusions.— The mechanism by which nausea was experienced with IV DHE – yet not with MAP0004 – was not associated with classic nausea pathways/targets (dopamine, 5‐HT₃, or muscarinic receptors) or with peripheral action in the intestine via enterochromaffin cells. Importantly, the maximum DHE concentrations following MAP0004 administration were insufficient to interact with receptors implicated in cardiovascular (5‐HT_2B and β₁) and pulmonary effects (β₂, adenosine, muscarinic, and leukotriene).     

Therapeutic effects of metabotropic glutamate receptor 5 positive allosteric modulator CDPPB on phencyclidine‐induced cognitive deficits in mice

This study was undertaken to examine the effects of CDPPB (3‐cyano‐N‐(1,3‐diphenyl‐1H‐pyrazol‐5‐yl)benzamide), a positive allosteric modulator (PAM) of metabotropic glutamate receptor 5 (mGlu₅), on cognitive deficits in mice after repeated administration of the N‐methyl‐D‐aspartate (NMDA) receptor antagonist phencyclidine (PCP). In the novel object recognition test, PCP (10 mg/kg/day for 10 days)‐induced cognitive deficits in mice were not improved by a single administration of CDPPB (10 mg/kg/day). However, PCP (10 mg/kg/day for 10 days)‐induced cognitive deficits in mice were significantly improved by subsequent subchronic (14 days) administration of CDPPB (10 mg/kg/day), but not of CDPPB (1.0 mg/kg/day). This study suggests that PCP‐induced cognitive deficits in mice are improved by subsequent subchronic administration of CDPPB. Therefore, mGlu₅ PAMs would be potential therapeutic drugs for cognitive deficits in schizophrenia.     

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)     

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.     

Platelet serotonin 5‐HT2A receptor binding in patients with carcinoid tumor

Background: As carcinoid tumors produce and secrete serotonin, various serotonin markers in blood, plasma and urine have been used as diagnostic tools, and quantification of the urinary excretion of the serotonin metabolite 5‐hydroxyindoleacetic acid (5‐HIAA) is the method most frequently used. Methods: [³H]lysergic acid diethylamide ([³H]LSD) binding to the platelet serotonin 5‐HT_2A receptor was investigated in nine patients with carcinoid tumors. The possible effect of serotonin‐rich food on the receptor binding was also investigated. Results: B_max for [³H]LSD binding was significantly lower in the carcinoid group than in the control group (mean±SD: 17.6±1.3 vs. 23.9±5.2?fmol/mg protein; p=0.007). K_d for [³H]LSD binding was significantly higher in the carcinoid group than in the control group (median: 1.14 vs. 0.71?nmol/L; p=0.03). B_max was inversely related to the urinary 5‐HIAA excretion, but the correlation did not reach statistical significance (r_s=?0.57; p=0.14). Intake of five bananas per day for one week had no effect on B_max or K_d in healthy volunteers. Conclusions: The results are consistent with a down‐regulation of the 5‐HT_2A receptor as a response to the high serotonin levels found in patients with carcinoid tumors. Intake of serotonin‐rich food does not affect the receptor characteristics. Further studies are needed to determine whether the platelet 5‐HT_2A receptor status can be used as a supplement to urinary 5‐HIAA and other biochemical variables in carcinoid tumors.     

A report of a galactan from marine alga Gelidium crinale with in vivo anti‐inflammatory and antinociceptive effects

The sulfated galactan of the red marine alga Gelidium crinale (SG‐Gc) was purified by ion exchange chromatography and tested by intravenous (i.v.) route in rodent experimental models of inflammation and nociception. The anti‐inflammatory activity of SG‐Gc (0.01, 0.1 and 1 mg/kg) was evaluated in the model of rat paw edema induced by different inflammatory stimuli, while SG‐Gc (0.1, 1 and 10 mg/kg) antinociceptive effect was assessed in models of nociception/hyperalgesia elicited by chemical (formalin test), thermal (hot plate), and mechanical (von Frey) stimuli in mice. In addition, the toxicity was evaluated after rat treatment with SG‐Gc (1 mg/kg; i.v.) during 10 days, followed by analysis of the wet weight of animal’s body/organs and hematological/biochemical parameters. Sulfated galactan of G. crinale inhibited the time course of dextran‐induced paw edema, at all doses, showing maximal effect at 1 mg/kg (42%) and that induced by carrageenan at 0.01 (18%) and 1 mg/kg (20%), but was ineffective on the edema elicited by zymosan. At the highest dose, SG‐Gc also inhibited the paw edema induced by histamine (49%), compound 48/80 (32%), and phospholipase A₂ (44%). Sulfated galactan of G. crinale inhibited both neurogenic and inflammatory phases of the formalin test, at all doses, and at 10 mg/kg, the animals flinch reaction in the von Frey test in the 1st and 3rd h by 19 and 26%, respectively. Additionally, SG‐Gc treatment was well tolerated by animals. In conclusion, SG‐Gc presents anti‐inflammatory effect involving the inhibition of histamine and arachidonic acid metabolites and also antinociceptive activity, especially the inflammatory pain with participation of the opioid system.     

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.     

Interactions between angiotensin AT1 receptor antagonists and second‐generation antiepileptic drugs in the test of maximal electroshock

The anticonvulsant activity of angiotensin AT₁ receptor antagonists, losartan (2‐n‐butyl‐4‐chloro‐5‐hydroxymethyl‐1‐[(2′(1H‐tetrazol‐5‐yl)‐biphenil‐4‐yl)methyl]imidazole) and telmisartan (49‐[(1,49‐dimethyl‐29‐propyl[2,69‐bi‐1H‐benzimidazo]‐19‐yl)methyl]‐[1,19‐biphenyl]‐2‐carboxylic acid), has been reported recently. It is suggested that AT₁ receptor antagonists may affect the protective action of antiepileptic drugs. The aim of this study was to determine the influence of losartan and telmisartan on the anticonvulsant activity of some second‐generation antiepileptics (lamotrigine – LTG, oxcarbazepine – OXC, and topiramate – TPM). For this purpose, the maximal electroshock seizure (MES) test in mice was used. Additionally, the drug combinations were checked for adverse effects in the passive avoidance and chimney tests. In the MES test, losartan at the doses of 30 and 50 mg/kg, administered intraperitoneally (i.p.), potentiated the protective action of LTG (P < 0.01). This interaction was not accompanied by a significant change of LTG level either in plasma or in the brain. Telmisartan at the dose of 30 mg/kg i.p. enhanced the anticonvulsant action of TPM (P < 0.01). However, this interaction was pharmacokinetic in nature, as telmisartan significantly increased plasma and total brain concentrations of TPM (P < 0.001). The combinations of AT₁ receptor antagonists with antiepileptic drugs did not affect retention in the passive avoidance test or motor coordination in the chimney test. The potentiation of the anticonvulsant action of LTG by losartan probably on account of pharmacodynamic interactions, make this combination important for further experimental and clinical studies. The combination of telmisartan and TPM is less beneficial due to pharmacokinetic interactions.     

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.     

Adenosine A1 Antagonism Attenuates β-adrenergic–resistant Sudden Hypoxic Cardiac Insufficiency

Objectives: In states such as hypoxia, shock, and cardiac arrest, compromised systemic oxygenation or perfusion appears to induce cardiac insufficiency that can be resistant to β‐adrenergic drugs. Elevated levels of adenosine may mediate such β‐adrenergic–resistant cardiac insufficiency via the adenosine A₁ receptor (A₁AdoR). The objective of this study was to test the hypothesis that selective A₁AdoR antagonism attenuates hypoxic cardiac insufficiency more efficaciously than β₁‐adrenergic agonism or nonselective adenosine antagonism. Methods: Rats were paralyzed and ventilated to a pCO₂ level of 35–40 mm Hg. Ten minutes before hypoxia (inspired O₂ concentration = 5%), rats were treated intravenously with one of the following: 0.1 mg/kg BG‐9719 (n= 9), 10 mg/kg NPC‐205 (n= 10; BG‐9719 and NPC‐205 are selective A₁AdoR antagonists, with durations of action of 30–60 minutes and 60–90 minutes, respectively), 10 mg/kg aminophylline (n= 12), 5 μg/kg/min dobutamine (n= 11), or control solutions. These drug doses maximized survival duration in dose‐response studies. Results: Before hypoxia, cardiac work was increased more by aminophylline and dobutamine than by BG‐9719. Mean (±SEM) duration of survival (in minutes) after hypoxia increased from <13 (control solutions) to 13.8 (±1.4) (dobutamine), 20.0 (±1.6) (aminophylline), 31.7 (±4.6) (BG‐9719), and 40.5 (±7.5) (NPC‐205) (p < 0.0001). Heart rate and dP/dt decreased rapidly after hypoxia, but decreases were attenuated with BG‐9719 and NPC‐205 compared with dobutamine (p < 0.05) and tended toward attenuation with aminophylline. Conclusions: BG‐9719 and NPC‐205 improved survival duration, heart rate, and left ventricular contractility during hypoxia more efficaciously than dobutamine and possibly aminophylline. Selective A₁AdoR antagonists warrant further study as alternatives to β‐adrenergic agonists in hypoxia, shock, and cardiac arrest, in which compromised systemic perfusion or oxygenation impairs cardiac output.     

Do Adenosine Receptors Play a Role in Amitriptyline‐Induced Cardiovascular Toxicity in Rats?

Objective: The aim of the our study was to investigate the role of adenosine receptors on cardiovascular toxicity induced by amitriptyline, a tricyclic antidepressant agent. Therefore, the hypothesis of this study was that adenosine receptor antagonists would improve and/or prevent amitriptyline‐induced hypotension and conduction abnormalities in an anesthetized rat model of amitriptyline intoxication. Methods: Two separate experimental protocols were performed. Amitriptyline intoxication was induced by the infusion of amitriptyline 0.94 mg/kg/min until 40–45% reduction of mean arterial pressure (MAP). Sodium cromoglycate (10 mg/kg) was injected i.v. to inhibit the A₃ receptor‐mediated activation of mast cells. In protocol 1, after amitriptyline infusion, while control animals (n = 8) were given dextrose solution, treatment groups received a selective adenosine A₁ antagonist DPCPX (8‐cyclopentyl‐1,3‐Dipropylxanthine, 20 µg/kg/min, n = 8) or a selective A_2a antagonist CSC (8‐(3‐chlorostyryl) caffeine, 24 µg/kg/min, n = 8) for 60 minutes. In protocol 2, after the sodium cromoglycate, while control group of rats (n = 8) recevied a dextrose solution, treatment groups of rats were administered DPCPX (20 µg/kg/min, n = 8) or CSC (24 µg/kg/min, n = 8) infusion to block adenosine A₁ and A_2a receptors for 20 minutes before amitriptyline infusion. After pretreatment with adenosine antagonists, all rats were given a dose of 0.94 mg/kg/min of amitriptyline infusion during 60 minutes. Outcome measures were mean arterial pressure (MAP), heart rate (HR), QRS duration and survival rate. Results: In protocol 1, amitriptyline infusion significantly reduced MAP and prolonged QRS within 15 minutes. HR was not changed significantly during the experiments. While dextrose did not improve MAP and QRS prolongation, DPCPX or CSC administration developed a significant improvement in MAP compared to the dextrose group within 10 min (88.5 ± 2.8%, 75.6 ± 4.7% and 50.1 ± 14.7%, p < 0.01, p < 0.05, respectively). Both DPCPX and CSC decreased QRS prolongation (p < 0.05) and increased median survival time significantly (log‐rank test, p < 0.00001). In protocol 2, pretreatment with DPCPX or CSC prevented the reduction in MAP due to amitriptyline toxicity compared to rats administered dextrose infusion (99.5 ± 2.6%, 102.4 ± 2.6%, 81.8 ± 5.4, p < 0.01 at 30 min; 98.0 ± 2.9%, 93.5 ± 6.0%, 64.9 ± 4.7, p < 0.001, p < 0.01 at 40 min, respectively). Pretreatment with DPCPX or CSC also prevented the QRS prolongation (p < 0.05) and increased median survival time significantly (log‐rank test, p < 0.0001). Conclusion: Adenosine antagonists were found to be effective in improving hypotension, QRS prolongation and survival time in our rat model of amitriptyline toxicity. Additionally, amitriptyline‐induced cardiotoxicity was abolished by pretreatment with adenosine receptor antagonists. These results suggest that adenosine receptors may have a role in the pathophysiology of amitriptyline‐induced cardiovascular toxicity. Adenosine A₁ and A_2a receptor antagonists may be promising agents for reversing amitriptyline‐induced cardiovascular toxicity.     

Effects of chronic administration of adipokinetic and hypertrehalosemic hormone on animal behavior,BDNF, and CREB expression in the hippocampus and neurogenesis in mice

Neurosecretory cells in corpus cardiacum of insects synthesize a set of hormones that are called adipokinetic, hypertrehalosaemic or hyperprolinaemic, depending on insect in question. This study investigated effects of chronic administration of Anax imperator adipokinetic hormone (Ani‐AKH), Libellula auripennis adipokinetic hormone (Lia‐AKH), and Phormia‐Terra hypertrehalosaemic hormone (Pht‐HrTH) on depression, anxiety, analgesy, locomotion in forced swimming (FST), elevated plus‐maze (EPM), hot plate, and locomotor activity tests. Ani‐AKH (1 and 2 mg/kg), Lia‐AKH (1 and 2 mg/kg), and Pht‐HrTH (1 and 2 mg/kg) had antidepressant effects in forced swimming test. Lia‐AKH (2 mg/kg) and Pht‐HrTH (1 and 2 mg/kg) had anxiolytic effects when given chronically in elevated plus‐maze test. Ani‐AKH (1 and 2 mg/kg) and Pht‐HrTH (2 mg/kg) had antinociceptive effects in hot plate test in male balb‐c mice. Ani‐AKH (2 mg/kg), Lia‐AKH (1 and 2 mg/kg), and Pht‐HrTH had locomotion‐enhancing effects in locomotor activity test in male balb‐c mice. Drug treatment significantly increased brain‐derived neurotrophic factor (BDNF) and cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) gene expression levels compared to control levels. Pht‐HrTH and Ani‐AKH groups had significantly increased numbers of BrdU‐labeled cells, while neurodegeneration was lower in the Pht‐HrTH group. Our study showed that AKH/RPCH family peptides may be used in treatment of psychiatric illness such as depression and anxiety, in treatment of pain and in diseases related to locomotion system. AKH/RPCH family peptides increase neurotrophic factors in brain and have potential proliferative and neuroprotective effects in hippocampal neurogenesis and neurodegeneration.     

Differential contribution of opioid and noradrenergic mechanisms of tapentadol in rat models of nociceptive and neuropathic pain

The novel analgesic tapentadol combines μ‐opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule and shows potent analgesia in various rodent models of pain. We analyzed the contribution of opioid and monoaminergic mechanisms to the activity of tapentadol in rat models of nociceptive and neuropathic pain. Antinociceptive efficacy was inferred from tail withdrawal latencies of experimentally naive rats using a tail flick test. Antihypersensitive efficacy was inferred from ipsilateral paw withdrawal thresholds toward an electronic von Frey filament in a spinal nerve ligation model of mononeuropathic pain. Dose–response curves of tapentadol (intravenous) were determined in combination with vehicle or a fixed dose (intraperitoneal) of the μ‐opioid receptor antagonist naloxone (1 mg/kg), the α2‐adrenoceptor antagonist yohimbine (2.15 mg/kg), or the serotonin 5‐HT_2A receptor antagonist ritanserin (0.316 mg/kg). Tapentadol showed clear antinociceptive and antihypersensitive effects (>90% efficacy) with median effective dose (ED₅₀) values of 3.3 and 1.9 mg/kg, respectively. While the antinociceptive ED₅₀ value of tapentadol was shifted to the right 6.4‐fold by naloxone (21.2 mg/kg) and only 1.7‐fold by yohimbine (5.6 mg/kg), the antihypersensitive ED₅₀ value was shifted to the right 4.7‐fold by yohimbine (8.9 mg/kg) and only 2.7‐fold by naloxone (5.2 mg/kg). Ritanserin did not affect antinociceptive or antihypersensitive ED₅₀ values of tapentadol. Activation of both μ‐opioid receptors and α2‐adrenoceptors contribute to the analgesic effects of tapentadol. The relative contribution is, however, dependent on the particular pain indication, as μ‐opioid receptor agonism predominantly mediates tapentadol's antinociceptive effects, whereas noradrenaline reuptake inhibition predominantly mediates its antihypersensitive effects.     

Targeted inhibition of the serotonin 5HT2A receptor improves coronary patency in an in vivo model of recurrent thrombosis

Summary. Background: Release of serotonin and activation of serotonin 5HT_2A receptors on platelet surfaces is a potent augmentative stimulus for platelet aggregation. However, earlier‐generation serotonin receptor antagonists were not successfully exploited as antiplatelet agents, possibly owing to their lack of specificity for the 5HT_2A receptor subtype. Objective: To assess whether targeted inhibition of the serotonin 5HT_2A receptor attenuates recurrent thrombosis and improves coronary patency in an in vivo canine model mimicking unstable angina. Methods: In protocol 1, anesthetized dogs were pretreated with a novel, selective inverse agonist of the 5HT_2A receptor (APD791) or saline. Recurrent coronary thrombosis was then initiated by coronary artery injury + stenosis, and coronary patency was monitored for 3 h. Protocol 2 was similar, except that: (i) treatment with APD791 or saline was begun 1 h after the onset of recurrent thrombosis; (ii) template bleeding time was measured; and (iii) blood samples were obtained for in vitro flow cytometric assessment of platelet responsiveness to serotonin. Results: APD791 attenuated recurrent thrombosis, irrespective of the time of treatment: in both protocols, flow–time area (index of coronary patency; normalized to baseline coronary flow) averaged 58–59% (P < 0.01) following administration of APD791 vs. 21–28% in saline controls. Moreover, the in vivo antithrombotic effect of APD791 was not accompanied by increased bleeding, but was associated with significant and selective inhibition of serotonin‐mediated platelet activation. Conclusion: 5HT_2A receptor inhibition with APD791, even when initiated after the onset of recurrent thrombosis, improves coronary patency in the in vivo canine model.     

Role of peripheral versus spinal 5‐HT7 receptors in the modulation of pain undersensitizing conditions

Several studies have suggested that 5‐HT₇ receptors are involved in nociceptive processing but the exact contribution of peripheral versus central 5‐HT₇ receptors still needs to be elucidated. In the present study, the respective roles of peripheral and spinal 5‐HT₇ receptors in the modulation of mechanical hypersensitivity were investigated under two different experimental pain conditions. In a first set of experiments, the selective 5‐HT₇ receptor agonist, E‐57431, was systemically, intrathecally or peripherally (intraplantarly) administered to rats sensitized by intraplantar injection of capsaicin. Oral administration of E‐57431 (1.25–10 mg/kg) was found to exert a clear‐cut dose‐dependent reduction of capsaicin‐induced mechanical hypersensitivity. Interestingly, intrathecal administration of E‐57431 (100 μg) also inhibited mechanical hypersensitivity secondary to capsaicin injection. In contrast, a dose‐dependent enhancement of capsaicin‐induced mechanical hypersensitivity was observed after local intraplantar injection of E‐57431 (0.01–1 μg). In a second set of experiments, E‐57431 was systemically or intrathecally administered to rats submitted to neuropathic pain (spared nerve injury model). Significant inhibition of nerve injury‐induced mechanical hypersensitivity was found after intraperitoneal (10 mg/kg) as well as intrathecal (100 μg) administration of E‐57431 in this chronic pain model. These studies provide evidence that, under sensitizing neurogenic/neuropathic conditions, activation of 5‐HT₇ receptors exerts antinociceptive effects at the level of the spinal cord and pronociceptive effects at the periphery. The antinociceptive effect mediated by central 5‐HT₇ receptors seems to predominate over the pronociceptive effect at the periphery when a selective 5‐HT₇ receptor agonist is systemically administered.     

Evaluation of the anxiolytic effects of chrysin, a Passiflora incarnata extract, in the laboratory rat

The definitive anxiolytic effects of Passiflora incarnata are unknown. We studied the potential anxiolytic effects of chrysin, a Passiflora extract, and the purported modulation of the benzodiazepine receptor on the GABA(A) receptor in laboratory rats. We hypothesized that chrysin decreases anxiety via interaction with the GABA(A) receptor in laboratory rats as measured by elevated plus-maze (EPM), corticosterone, and catecholamine assays. We randomized 44 male Sprague-Dawley rats in a double-blind, placebo-controlled, between-subjects experimental design. Each animal received an intraperitoneal injection of (1) vehicle (DMSO 4%), (2) chrysin, 2 mg/kg, (3) midazolam, 1.5 mg/kg, or (4) flumazenil, 3 mg/kg and chrysin, 2 mg/kg. The EPM was used to evaluate the behavioral component of anxiolysis, and catecholamine and corticosterone assays were examined to measure the neurohormonal effects of anxiety. No statistical difference was found among groups in catecholamine and corticosterone levels. Midazolam significantly decreased anxiety compared with control and flumazenil plus chrysin groups (P <.05); there was no significant difference compared with the chrysin group. These data suggest that chrysin may have anxiolytic properties similar to midazolam but to a lesser magnitude at the 2 mg/kg dose used in this study.