Rubiscolin-6, a delta opioid peptide derived from spinach Rubisco, has anxiolytic effect via activating sigma1 and dopamine D1 receptors

Rubiscolin-6 (Tyr-Pro-Leu-Asp-Leu-Phe) is a delta opioid peptide derived from the large subunit of spinach d-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We previously reported that rubiscolin-6 had an analgesic effect and stimulated memory consolidation. Here we show that intraperitoneally (i.p.) or orally administered rubiscolin-6 has an anxiolytic effect at a dose of 10 mg/kg or 100 mg/kg, respectively, in the elevated plus-maze test in mice. The anxiolytic effects of rubscolin-6 after i.p. (10 mg/kg) and oral (100 mg/kg) administration were blocked by a delta opioid receptor antagonist, naltrindole (1 mg/kg, s.c.), suggesting that the anxiolytic activity of rubiscolin-6 is mediated by delta opioid receptor. The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was also blocked by a dopamine D(1) antagonist, SCH23390 (30 microg/kg, i.p.), but not by a dopamine D(2) antagonist, raclopride (15 microg/kg, i.p.). The anxiolytic effect of rubiscolin-6 (10 mg/kg, i.p.) was blocked by sigma(1) receptor antagonist, BMY14802 (0.5 mg/kg, i.p.) or BD1047 (10 mg/kg, i.p.). Taken together, the anxiolytic effect of rubiscolin-6 is mediated by sigma(1) and dopamine D(1) receptors downstream of delta opioid receptor.     

Antidepressant-like effect of 17beta-estradiol: involvement of dopaminergic, serotonergic, and (or) sigma-1 receptor systems

17beta-estradiol has been reported to possess antidepressant-like activity in animal models of depression, although the mechanism for its effect is not well understood. The present study is an effort in this direction to explore the mechanism of the antidepressant-like effect of 17beta-estradiol in a mouse model(s) of behavioral depression (despair behavior). Despair behavior, expressed as helplessness to escape from a situation (immobility period), as in a forced swim test in which the animals are forced to swim for a total of 6 min, was recorded. The antiimmobility effects (antidepressant-like) of 17beta-estradiol were compared with those of standard drugs like venlafaxine (16 mg/kg, i.p.). 17beta-estradiol produced a U-shaped effect in decreasing the immobility period. It had no effect on locomotor activity of the animal. The antidepressant-like effect was comparable to that of venlafaxine (16 mg/kg, i.p.). 17beta-estradiol also exhibited a similar profile of antidepressant action in the tail suspension test. When coadministered with other antidepressant drugs, 17beta-estradiol (5 microg/kg, i.p.) potentiated the antiimmobility effect of subeffective doses of fluoxetine (5 mg/kg, i.p.), venlafaxine (2 mg/kg, i.p.), or bupropion (10 mg/kg, i.p.), but not of desipramine (5 mg/kg, i.p.) or tranylcypromine (2 mg/kg, i.p.), in the forced swim test. The reduction in the immobility period elicited by 17beta-estradiol (20 microg/kg, i.p.) was reversed by haloperidol (0.5 mg/kg, i.p.; a D(2) dopamine receptor antagonist), SCH 23390 (0.5 mg/kg, i.p.; a D(1) dopamine receptor antagonist), and sulpiride (5 mg/kg, i.p.; a specific dopamine D(2) receptor antagonist). In mice pretreated with (+)-pentazocine (2.5 mg/kg, i.p.; a high-affinity sigma-1 receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced a synergistic effect. In contrast, pretreatment with progesterone (10 mg/kg, s.c.; a sigma-1 receptor antagonist neurosteroid), rimcazole (5 mg/kg, i.p.; another sigma-1 receptor antagonist), or BD 1047 (1 mg/kg, i.p.; a novel sigma-1 receptor antagonist) reversed the antiimmobility effects of 17beta-estradiol (20 microg/kg, i.p.). Similarly, in mice pretreated with a subthreshold dose of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a 5-HT1A serotonin receptor agonist), 17beta-estradiol (5 microg/kg, i.p.) produced an antidepressant-like effect. These findings demonstrate that 17beta-estradiol exerted an antidepressant-like effect preferentially through the modulation of dopaminergic and serotonergic receptors. This action may also involve the participation of sigma-1 receptors.     

Role of benzodiazepine-GABAA receptor complex in attenuation of U-50,488H-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin in mice

In the present study, the role of benzodiazepine-GABAA receptor complex in the attenuation of U-50,488H (U50), a selective kappa opioid agonist-induced analgesia and inhibition of tolerance to its analgesia by ginseng total saponin (GTS) was investigated using the mice tail-flick test. The intraperitoneal (i.p.) treatment of GTS (100 and 200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently attenuated the U50 (40 mg/kg, i.p.)-induced analgesia. GTS (0.001-10 microg/ml) did not alter binding of [3H]naloxone to mice whole brain membrane. The attenuation effect of GTS (100 mg/ kg) and diazepam (0.5 mg/kg) on U50-induced analgesia was blocked by flumazenil (0.1 mg/kg, i.p.), a benzodiazepine receptor antagonist, and picrotoxin (1 mg/kg, i.p.), a GABAA-gated chloride channel blocker. However, bicuculline (1 mg/kg, i.p.), a GABAA receptor antagonist blocked the attenuation effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on U50-induced analgesia. Chronic treatment (day 4-day 6) of GTS (50-200 mg/kg) and diazepam (0.1-1 mg/kg) dose-dependently inhibited the tolerance to U50-induced analgesia. Flumazenil (0.1 mg/kg) and picrotoxin (1 mg/kg) on chronic treatment blocked the inhibitory effect of GTS (100 mg/kg) and diazepam (0.5 mg/kg) on tolerance to U50-induced analgesia. On the other hand, chronic treatment of bicuculline (1 mg/kg) blocked the inhibitory effect of diazepam (0.5 mg/kg) but not GTS (100 mg/kg) on tolerance to U50-induced analgesia. In conclusion, the findings suggest that GTS attenuates U50-induced analgesia and inhibits tolerance to its analgesia and this action involves benzodiazepine receptors and GABAA-gated chloride channels.     

Peripheral GLP-1 gastroprotection against ethanol: the role of exendin, NO, CGRP, prostaglandins and blood flow

The aim of this study was to investigate the effects of peripherally injected glucagon like peptide-1 (GLP-1) on ethanol-induced gastric mucosal damage and the mechanisms included in the effect. Absolute ethanol was administered through an orogastric cannula right after the injection of GLP-1 (1, 10, 100, 1000 or 10,000 ng/kg; i.p.). The rats were decapitated an hour later, the stomachs removed and the gastric mucosal damage scored. 1000 ng GLP-1 inhibited gastric mucosal damage by 45% and 10,000 ng GLP-1 by 60%. The specific receptor antagonist exendin-(9-39) (2500 ng/kg; i.p.), calcitonin gene related peptide (CGRP) receptor antagonist CGRP-(8-37) (10 microg/kg; i.p.), nitric oxide (NO) synthase inhibitor l-NAME (30 mg/kg; s.c.) and cyclooxygenase inhibitor indomethacin (5 mg/kg; i.p.) inhibited the preventive effect of GLP-1 on ethanol-induced gastric mucosal damage. GLP-1 also prevented the decrease in gastric mucosal blood flow caused by ethanol when administered at gastroprotective doses (1000 and 10,000 ng/kg; i.p.). In conclusion, GLP-1 administered peripherally prevents the gastric mucosal damage caused by ethanol in rats. CGRP, NO, prostaglandin and gastric mucosal blood flow are thought to play a role in this effect, mediated through receptors specific to GLP-1.     

Attenuation of capsaicin-induced acute and visceral nociceptive pain by alpha- and beta-amyrin, a triterpene mixture isolated from Protium heptaphyllum resin in mice

The triterpene mixture, alpha- and beta-amyrin, isolated from Protium heptaphyllum resin was evaluated on capsaicin-evoked nociception in mice. Orally administered alpha- and beta-amyrin (3 to 100 mg/kg) significantly suppressed the nociceptive behaviors--evoked by either subplantar (1.6 microg) or intracolonic (149 microg) application of capsaicin. The antinociception produced by alpha- and beta-amyrin against subplantar capsaicin-induced paw-licking behavior was neither potentiated nor attenuated by ruthenium red (1.5 mg/kg, s.c.), a non-specific antagonist of vanilloid receptor (TRPV1), but was greatly abolished in animals pretreated with naloxone (2 mg/kg, s.c.), suggesting an opioid mechanism. However, participation of alpha2-adrenoceptor involvement was unlikely since yohimbine (2 mg/kg, i.p.) pretreatment failed to block the antinociceptive effect of alpha- and beta-amyrin in the experimental model of visceral nociception evoked by intracolonic capsaicin. The triterpene mixture (3 to 30 mg/kg, p.o.) neither altered significantly the pentobarbital sleeping time, nor impaired the ambulation or motor coordination in open-field and rota-rod tests, respectively, indicating the absence of sedative or motor abnormality that could account for its antinociception. Nevertheless, alpha- and beta-amyrin could significantly block the capsaicin (10 mg/kg, s.c.)-induced hyperthermic response but not the initial hypothermia. These results suggest that the triterpene mixture, alpha- and beta-amyrin has an analgesia inducing effect, possibly involving vanilloid receptor (TRPV1) and an opioid mechanism.     

Pharmacological modulation of the bronchopulmonary action of the vasoactive peptide, endothelin, administered by aerosol in the guinea-pig

Administration by aerosol for 1 min of solutions of endothelin (ENDO; 1, 5 or 10 micrograms/ml) to anaesthetized and ventilated guinea-pigs induced a dose-dependent bronchopulmonary response (BR) which was maximal within 4 to 5 min. In contrast, no significant change of the mean arterial blood pressure was observed. Pretreatment of guinea-pigs with propranolol (1 mg/kg, i.v.), mepyramine (1 mg/kg, i.v.), nifedipine (50 mg/kg, i.p.) or verapamil (0.3 mg/kg, i.v.) did not significantly affect the BR induced by an aerosol of a solution of 10 micrograms/ml ENDO. In contrast, BR was significantly reduced when the animals were pretreated with the cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.v.) or the platelet-activating factor (PAF) receptor antagonist, BN 52021 (10 mg/kg, i.v.). These results indicate that aerosolized ENDO induces a BR via the generation of secondary mediators such as cyclooxygenase products and PAF in a process which is unaffected by the blockers of the voltage-dependent calcium channels.     

Central antidopaminergic properties of 2-bromolisuride, an analogue of the ergot dopamine agonist lisuride

2-Bromolisuride (2-Br-LIS), a derivative of the ergot dopamine (DA) agonist lisuride, was investigated in rodents in comparison with the DA antagonist haloperidol with regard to its influence on DA related behaviour, cerebral DA metabolism and prolactin (PRL) secretion. 2-Br-LIS produced catalepsy in mice (ED50 3.3 mg/kg i.p.), antagonized apomorphine-induced stereotypies in mice (ED50 0.4 mg/kg i.p.), antagonized DA agonist-induced stereotypies in rats (0.1-1.56 mg/kg i.p.), inhibited locomotor activity in rats (0.025-6.25 mg/kg i.p.), antagonized the hyperactivity produced by various DA agonists in rats (0.025-6.25 mg/kg i.p.) and inhibited the apomorphine-induced hypothermia in mice (0.05-0.78 mg/kg i.p.). 2-Br-LIS (0.03-10 mg/kg i.p.) stimulated DA biosynthesis and DOPAC formation in the striatum and DA rich limbic system of rats, but had no effect on serotonin turnover. In striatum and limbic forebrain of gamma-butyrolactone-pretreated rats 2-Br-LIS reversed the apomorphine-induced inhibition of DOPA accumulation. 2-Br-LIS (0.03 - 3 mg/kg) enhanced PRL secretion in intact male rats. These findings indicate DA antagonistic properties of 2-Br-LIS presumably due to blockade of central pre- and postsynaptic DA receptors being of approximately the same order of potency as haloperidol. 2-Br-LIS is the first ergot compound with definite antidopaminergic properties suggesting its potential usefulness as a neuroleptic.     

Effects of the non-competitive NMDA receptor antagonist ketamine on morphine-induced place preference in mice

The effects of ketamine, a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, on morphine-induced place preference were examined in mice. Morphine (1-5 mg/kg, s.c.) produced a dose-related place preference in mice. Ketamine alone (3, 10 mg/kg, i.p.), like dizocilpine alone (0.2 mg/ kg, i.p.), also produced a preference for the drug-associated place. Pretreatment with ketamine (10 mg/ kg, i.p.) or dizocilpine (0.1 and 0.2 mg/kg, i.p) suppressed the place preference produced by morphine in a dose-dependent manner. These findings provide the first demonstration that ketamine alone produces a place preference using the conditioned place preference (CPP) paradigm, but that mice treated with ketamine combined with morphine show neither a morphine- nor a ketamine-induced place preference.     

Role of kappa- and delta-opioid receptors in the antinociceptive effect of oxytocin in formalin-induced pain response in mice

Oxytocin has been implicated in the modulation of somatosensory transmission such as nociception and pain. The present study investigates the effect of oxytocin on formalin-induced pain response, a model of tonic continuous pain. The animals were injected with 0.1 ml of 1% formalin in the right hindpaw and the left hindpaw was injected with an equal volume of normal saline. The time spent by the animals licking or biting the injected paw during 0-5 min (early phase) and 20-25 min (late phase) was recorded separately. Oxytocin (25, 50, 100 microg/kg, i.p.) dose dependently decreased the licking/biting response, both in the early as well as the late phases. The antinociceptive effect of oxytocin (100 microg/kg, i.p.) was significantly attenuated in both the phases by a higher dose of the non-selective opioid receptor antagonist naloxone (5 mg/kg, i.p.), MR 2266 (0.1 mg/kg, i.p.), a selective kappa-opioid receptor antagonist and naltrindole (0.5 mg/kg, i.p.), a selective delta-opioid receptor antagonist but not by a lower dose of naloxone (1 mg/kg, i.p.) or beta-funaltrexamine (2.5 microg/mouse, i.c.v.), a selective mu-opioid receptor antagonist. Nimodipine, a calcium channel blocker (1 and 5 mg/kg, i.p.) produced a dose-dependent analgesic effect. The antinociceptive effect of oxytocin was significantly enhanced by the lower dose of nimodipine (1 mg/kg, i.p.) in both the phases. Chronic treatment with oxytocin (100 microg/kg/day, i.p. daily for 7 days) did not produce tolerance in both the phases of formalin-induced pain response. The results thus indicate that oxytocin displays an important analgesic response in formalin test; both kappa- and delta-opioid receptors as well as voltage-gated calcium channels seem to be involved in the oxytocin-induced antinociception.     

Stimulatory effects of endogenous and exogenous nitric oxide on gastric acid secretion in anesthetized rats

We previously reported the stimulatory effect of endogenous nitric oxide (NO) on gastric acid secretion in the isolated mouse whole stomach and histamine release from gastric histamine-containing cells. In the present study, we investigated the effects of endogenous and exogenous NO on gastric acid secretion in urethane-anesthetized rats. Acid secretion was studied in gastric-cannulated rats stimulated with several secretagogues under urethane anesthesia. The acid secretory response to the muscarinic receptor agonist bethanechol (2 mg/kg, s.c.), the cholecystokinin(2) receptor agonist pentagastrin (20 microg/kg, s.c.) or the centrally acting secretagogue 2-deoxy-D-glucose (200 mg/kg, i.v.) was dose-dependently inhibited by the NO synthase inhibitor N(omega)-nitro-L-arginine (L-NNA, 10 or 50 mg/kg, i.v.). This inhibitory effect of L-NNA was reversed by a substrate of NO synthase, L-arginine (200 mg/kg, i.v.), but not by D-arginine. The histamine H(2) receptor antagonist famotidine (1 mg/kg, i.v.) completely inhibited the acid secretory response to bethanechol, pentagastrin or 2-deoxy-D-glucose, showing that all of these secretagogues induced gastric acid secretion mainly through histamine release from gastric enterochromaffin-like cells (ECL cells). On the other hand, histamine (10 mg/kg, s.c.)-induced gastric acid secretion was not inhibited by pretreatment with L-NNA. The NO donor sodium nitroprusside (0.3-3 mg/kg, i.v.) also dose-dependently induced an increase in acid secretion. The sodium nitroprusside-induced gastric acid secretion was significantly inhibited by famotidine or by the soluble guanylate cyclase inhibitor methylene blue (50 mg/kg, i.v.). These results suggest that NO is involved in the gastric acid secretion mediated by histamine release from gastric ECL cells.     

Repeated treatment with imipramine, fluvoxamine and tranylcypromine decreases the number of escape failures by activating dopaminergic systems in a rat learned helplessness test.

Chronic administration of antidepressants has been shown to reduce the number of escape failures in the rat learned helplessness test (LH). In the present study we investigated the role of D1, D2 and D3 receptors in mediating this effect. In our first series of experiments, we demonstrated that SKF38393, D1 receptor agonist, in a dose of 2.5 mg/kg (i.p.) and quinpirole, D2 receptor agonist in a dose of 0.5 mg/kg (i.p.), significantly decreased the number of escape failures in LH, and these were reversed by SCH23390 (0.015 mg/kg), D1 receptor antagonist, and by sulpiride (25 mg/kg), D2 receptor antagonist, respectively. In contrast, 7-OH-DPAT, a D3 receptor agonist, in a dose of 10 mg/kg (i.p.) did not affect the number of escape failures in LH. In a second series of experiments, we showed that eight days of repeated treatment with imipramine (10 mg/kg, p.o.), fluvoxamine (1.25 mg/kg, p.o.) and tranylcypromine (1.25 mg/kg, p.o.) significantly decreased the number of escape failures in LH. The decrease in escape failures seen with use of imipramine and tranylcypromine was reversed by sulpiride in LH, but not by SCH23390. On the other hand, the effect of fluvoxamine was reversed by both SCH23390 and sulpiride. These findings indicate that stimulation of D1 and D2 receptors decreased the number of escape failures in LH, respectively. Thus, D2 and/or D1 receptors are probably involved in the decreased number of escape failures in case of repeated treatment with antidepressants in LH.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Involvement of monoaminergic system in the antidepressant-like effect of the hydroalcoholic extract of Siphocampylus verticillatus

The antidepressant-like effect of the hydroalcoholic extract obtained from aerial parts of Siphocampylus verticillatus, a Brazilian medicinal plant, was investigated in two models of depression in mice and against synaptosomal uptake of serotonin, noradrenaline and dopamine. The immobility times in the forced swimming test (FST) and in the tail suspension test (TST) were significantly reduced by the extract (dose range 100-1000 mg/kg, i.p.), without accompanying changes in ambulation when assessed in an open-field. In addition when given orally the extract was also effective in reducing the immobility time in the TST. The efficacy of extract in the TST was comparable to that of the tricyclic antidepressant imipramine (15 mg/kg, i.p.) and with fluoxetine (32 mg/kg, i.p.). The anti-immobility effect of the extract (600 mg/kg, i.p.) assessed in the TST was not affected by pre-treatment with naloxone (1 mg/kg, i.p., a non-selective opioid receptor antagonist) or L-arginine (750 mg/kg, i.p., a nitric oxide precursor). In contrast, the extract (600 mg/kg, i.p.) antidepressant-like effect was significantly reduced by pre-treatment of animals with p-chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis), sulpiride (50 mg/kg, i.p., a selective D2 receptor antagonist), prazosin (62.5 microg/kg, i.p., an alpha1 adrenoreceptor antagonist) or by guanosine 5'-monophosphate (GMP, 250 mg/kg, i.p., a nucleotide known to block some actions elicited by NMDA). The biochemical data show that the extract of S. verticillatus inhibited in a graded manner the uptake of monoamines. However, at the IC50 level, the extract was approximately 3.2 to 3.4-fold more potent and also more efficacious in inhibiting the synaptosomal uptake of noradrenaline and serotonin than dopamine. Taken together these data demonstrate that the extract of S. verticillatus elicited a significant antidepressant-like effect, when assessed in the TST and FST in mice. Its action seems to involve an interaction with adrenergic, dopaminergic, glutamatergic and serotonergic systems.     

Chronic clonidine treatment and its termination: effects on penile erection and ejaculation in the dog.

The effects of chronic administration (4 weeks) of the alpha-2 adrenoceptor agonist clonidine (CL) and its termination on penile erection and ejaculation were investigated in male dogs. Penile erection and ejaculation were elicited by manual penile stimulation (for 5 min). CL (10 micrograms/kg/hr, s.c.) was delivered via osmotic minipump (Alza, 2ML-4). 3 or 7 days after the minipump implantation, CL caused a significant decrease in the amount of ejaculate produced by the genital stimulation without affecting the erectile potency. Ejaculatory ability returned to pretreatment levels despite continued CL administration, becoming evident in tests 14 days after initiation of treatment. Further, chronic CL (23 days) antagonized the inhibitory effects of acute administration of CL (0.05 mg/kg, i.p.). These data indicate tolerance to continued delivery of low doses as well as to acute administration of a higher dose. In the acute drug experiments, the ejaculatory inhibition elicited by CL (0.05 mg/kg, i.p.) was completely antagonized by pretreatment with yohimbine (0.05 and 0.10 mg/kg, i.p.), an alpha-2 adrenoceptor antagonist, but not with naloxone (1.0 mg/kg, i.p.), an opioid receptor antagonist. Furthermore, DG-5128 (1.0 and 2.0 mg/kg, i.p.), a selective alpha-2 adrenoceptor antagonist that poorly penetrates the blood-brain barrier, failed to antagonize the CL-induced ejaculatory inhibition. This study suggests that functional alterations in the central alpha-2 adrenoceptor mechanism may be related to the changes in the ejaculatory capacity during chronic treatment with CL.     

Capsiate, a nonpungent capsaicin analog, increases endurance swimming capacity of mice by stimulation of vanilloid receptors

We investigated the effect of capsiate, a nonpungent natural capsaicin analog, on the swimming capacity of mice in an adjustable-current water pool. Male BALB/c mice orally given capsiate (10 mg/kg) were able to keep swimming longer before exhaustion than the control mice. After 30 min of swimming, the residual glycogen in the gastrocnemius muscle was higher, the serum free fatty acid concentration tended to be higher, and the serum lactic acid concentration was significantly lower in the capsiate-administered mice. The value for the respiratory exchange ratio of the capsiate group was significantly lower during both resting and treadmill running. These physiological differences were abolished by administering the vanilloid receptor antagonist, capsazepin (0.17 mmol/kg, i.p.). The mice were not averse to the capsiate solution during a 4-h two-bottle choice test. These results suggest that the oral administration of capsiate enhanced fat oxidation and spared carbohydrate utilization, and consequently increased the endurance swimming capacity of the mice via stimulation of their vanilloid receptors. Practical application of capsiate is expected.     

Effects of Modafinil on Clonic Seizure Threshold Induced by Pentylenetetrazole in Mice: Involvement of Glutamate,Nitric oxide,GABA, and Serotonin Pathways

Epilepsy is the third most common chronic brain disorder. Modafinil is an awakening agent approved for narcolepsy. In addition to its clinical uses some reports revealed that modafinil was associated with some alterations in seizure threshold. The purpose of this study was to clarify the effect of acute administration of modafinil in clonic seizure threshold (CST) induced by pentylenetetrazole in mice and the involvement of glutamate, nitric oxide, gamma amino butyric acid (GABA), and serotonin systems in this feature. Modafinil at 80 and 150 mg/kg showed anti- and pro-convulsant effects respectively and expressed maximum anti- and pro-convulsant activities at 30 min after injection. Both modulatory effects were blunted by pretreatment of l-NAME [nonspecific nitric oxide synthase (NOS) inhibitor; 10 mg/kg, i.p.], 7-nitroindazole (a neuronal NOS inhibitor; 40 mg/kg, i.p.), and aminoguanidine (an inducible NOS inhibitor; 50 mg/kg, i.p.). Injection of the NOS precursor l-arginine (60 mg/kg, i.p.) before modafinil did not change the anti-convulsant effect, while thoroughly reversed the pro-convulsant one. Our experiments displayed that administration of diazepam (a GABA_A receptor agonist; 0.02 mg/kg, i.p.) and MK-801 (a NMDA receptor antagonist; 0.05 mg/kg, i.p.) before different doses of modafinil significantly increased CST. Finally, pretreatment of citalopram (a selective serotonin reuptake inhibitor; 0.1 mg/kg, i.p.) did not modify the convulsant activities of modafinil. Therefore, nitric oxide system may mediate anti-convulsant activity, while glutamate, nitric oxide, and GABA pathways may involve in pro-convulsant property. Serotonin receptors have no role on convulsant effects of modafinil.     

Capsaicin-, resiniferatoxin-, and olvanil-induced adrenaline secretions in rats via the vanilloid receptor.

The effects of capsaicin analogs on adrenaline secretion were investigated in rats. Capsaicin (20-100 microg/kg, i.v.) caused biphasic adrenaline secretion. Capsazepine (20 mg/kg, i.v.), a specific competitive antagonist of the vanilloid (capsaicin) receptor, strongly inhibited both phases of adrenaline secretion by capsaicin (50 microg/kg). Next, the effects of two capsaicin analogs on the adrenal catecholamine secretion were examined. Resiniferatoxin (20-200 ng/kg, i.v.), a naturally occurring phorbolester-like compound, provoked slow onset adrenaline secretion in a dose-dependent manner. Olvanil (2.46-246 microg/kg, i.v.), a synthesized non pungent capsaicin analog, also stimulated delayed catecholamine secretion dose-dependently. Capsazepine (20 mg/kg, i.v.) pretreatment prevented the resiniferatoxin (50 ng/kg)- and olvanil (24.6 microg/kg)-induced catecholamine secretion. These results suggest that some vanilloids (capsaicin, resiniferatoxin, olvanil) excite adrenaline secretion and such excitation is via the vanilloid receptor.     

Nicotine stimulates secretion of corticosterone via both CRH and AVP receptors

Corticosterone-releasing hormone (CRH) and arginine vasopressin (AVP) are crucial components of the hypothalamic-pituitary-adrenal axis that stimulates the release of adrenocorticotropic hormone from the pituitary and mediate the stress response. CRH binds to two subtypes of CRH receptors (CRH-R1 and CRH-R2) that are present in both central and peripheral tissues. We used the CRH-R1-specific antagonist, antalarmin (ANT), the CRH-R1 and CRH-R2 peptide antagonist, astressin (AST), and the CRH-R2-specific peptide antagonist, astressin2b (AST2b), to determine which CRH receptor is involved in the nicotine-stimulated secretion of corticosterone. Male C57BL/6 mice were administered ANT (20 mg/kg, i.p.), AST (0.3 mg/kg, i.p.), AST2b (0.3 mg/kg, i.p.) or vehicle prior to administration of nicotine (1.0 mg/kg, s.c.), CRH (10 μg/kg, s.c.), AVP (10 μg/kg, s.c.) or saline (s.c.), killed 15 min later and trunk blood collected and assayed for corticosterone plasma levels. We found that CRH enhanced corticosterone release, and this response was blocked by both AST and ANT. Nicotine also increased corticosterone secretion, but this effect persisted in the presence of either CRH antagonist. Furthermore, AST but not ANT or AST2b decreased corticosterone levels associated with stress of handling and injection. We also assessed the role of AVP V(1b) -specific receptor antagonist, SSR149415 alone and in combination with AST and AST2b. Although the AVP antagonist did not alter basal or nicotine-stimulated corticosterone secretion, it attenuated the AVP-induced stimulation of corticosterone and its combination with AST but not AST2b completely abolished nicotine-mediated stimulation of corticosterone secretion. Our results demonstrate that the nicotine-induced stimulation of the hypothalamic-pituitary-adrenal axis is mediated by both the CRH-R and the AVP V(1b) receptor and when the CRH receptor is blocked, nicotine may utilize the AVP V(1b) receptor to mediate secretion of corticosterone. These results argue in favor of the development of specific antagonists that block both AVP and CRH receptors to decrease the pleasurable component of nicotine, which may be mediated by corticosterone.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Biochemical and pharmacological activities of SSR 146977, a new potent nonpeptide tachykinin NK3 receptor antagonist

SSR 146977 is a potent and selective antagonist of the tachykinin NK3 receptor. In Chinese hamster ovary cells expressing the human tachykinin NK3 receptor, SSR 146977 inhibited the binding of radioactive neurokinin B to NK3 receptors (Ki = 0.26 nM), senktide (10 nM) induced inositol monophosphate formation (IC50 = 7.8-13 nM), and intracellular calcium mobilization (IC50 = 10 nM). It antagonized [MePhe7]neurokinin B induced contractions of guinea pig ileum (pA2 = 9.07). Senktide (30 nM) induced firing rate increase of noradrenergic neurons in the guinea pig locus coeruleus and dopaminergic neurons in the guinea pig substantia nigra was also blocked by SSR 146977 (50 and 100 nM, respectively). In vivo, in the respiratory system, SSR 146977 inhibited bronchial hyperresponsiveness to acetylcholine, bronchial microvascular permeability hypersensitivity to histamine (doses of 0.1-1 mg/kg i.p.), and cough (doses of 0.03-1 mg/kg i.p.) provoked by citric acid in guinea pigs. In the central nervous system, SSR 146977 inhibited turning behaviour (ID50 = 0.2 mg/kg i.p. and 0.4 mg/kg p.o.) and prevented the decrease of locomotor activity (10 and 30 mg/kg i.p) mediated by the stimulation of NK3 receptors in gerbils. In guinea pigs, SSR 146977 antagonized senktide-induced acetylcholine release in the hippocampus (0.3 and 1 mg/kg i.p) and norepinephrine release in the prefrontal cortex (0.3 mg/kg i.p.). It also prevented haloperidol-induced increase of the number of spontaneously active dopamine A10 neurons (1 and 3 mg/kg i.p.).