Lipoxin A4 inhibits cholinergic neurotransmission through nitric oxide generation in the rabbit trachea

The effect of lipoxin A₄ and lipoxin B₄ on cholinergic neurotransmission in rabbit tracheal segments was studied under isometric conditions in vitro. Lipoxin A₄ attenuated the contractile responses to electrical field stimulation and caused a rightward shift of the frequency-response curves, so that the stimulus frequency required to produce a half-maximal effect (ES₅₀) increased from 8.1 ± 0.8 to 25.7 ± 1.9 Hz (P < 0.001), whereas lipoxin B₄ had no effect. In contrast, lipoxin A₄ did not alte contractile responses to acetylcholine. Pretreatment of tissues with N^G-nitro- -arginine methylester inhibited the effect of lipoxin A₄ on electrical field stimulation, but N^G-nitro- -arginine methylester did not. This inhibition by N^G-nitro- -arginine methylester was reversed by -arginine but not by -arginine. These results suggest that lipoxin A₄ prejunctionally reduces the vagal nerve-mediated contraction of airway smooth muscle, probably by inhibiting the release of acetylcholine, and that this effect may be exerted through stimulation of nitric oxide generation.     

Nitric oxide and sensory afferent neurones modulate the protective effects of low-dose endotoxin on rat gastric mucosal damage

Pretreatment (1 h) with low doses (5–40 μg/kg i.p.) of Escherichia coli endotoxin dose dependently reduced the gastric mucosal damage induced by a 10 min challenge with 1 ml ethanol (50% and 100%) in conscious rats. Treatment with the nitric oxide synthesis inhibitor, oxide synthesis inhibitor, N^G-nitro- -arginine methyl ester (L-NAME, 5 and 10 mg/kg i.p.), significantly inhibited the protective effects of endotoxin (40 μg/kg i.p.). The actions of L-NAME were reversed by the prior administration of -arginine (100 mg/kg i.p.). The protective effects of endotoxin were not influenced by pretreatment with dexamethasone (5 mg/kg s.c. twice) or indomethacin (5 mg/kg s.c.). However, ablation of sensory afferent neurones by capsaicin pretreatment (20, 30 and 50 mg/kg s.c.) abolished the mucosa protective effects of endotoxin (40 μg/kg). These findings suggest that the protection elicited by low doses of endotoxin against ethanol-induced mucosal damage involves synthesis of nitric oxide and activation of sensory neurones.     

Contractile responses of human deferential artery and vas deferens to vasopressin

We studied the effects of vasopressin on isolated rings of human deferential artery and vas deferens (prostatic portion) obtained from patients undergoing radical cystectomy (n = 11) or prostatectomy (n = 10). Ring segments of artery or vas deferens were studied in organ bath experiments at optimal resting tension. In artery rings, vasopressin produced concentration-dependent, endothelium-independent contractions with an EC₅₀ of 4.5 × 10⁻¹⁰ M. The presence of N^G-nitro- -arginine methyl ester hydrochloride (10⁻⁴ M), an inhibitor of nitric oxide synthase, did not change significantly (P > 0.05) the vasopressin-induced contraction. In ring preparations of the prostatic part of the vas deferens, vasopressin induced phasic contractions with an EC₅₀ of 7.0 × 10⁻⁹ M. The vasopressin V₁ receptor antagonist, d(CH₂)₅Tyr(Me)AVP (10⁻⁸ and 10⁻⁶), displaced to the right in parallel the control curve to vasopressin in artery and vas deferens rings. These results indicate that vasopressin exerts a powerful constrictor action on human deferential artery and vas deferens by direct stimulation of V₁ receptors. It is concluded that the deferential artery may dampen the passage of blood to the vas deferens in circumstances characterized by increased plasma vasopressin levels.     

Role of nitric oxide in myotoxic activity induced by crotoxin in vivo.

This study was aimed to determine the role of nitric oxide on the skeletal myotoxic activity induced by crotoxin, the major component of the venom of Crotalus durissus terrificus. Rats were treated with N(G)-nitro-L-arginine methyl ester (L-NAME), a non-selective inhibitor of nitric oxide synthase or vehicle for 4 days, and on the 5th day received an intramuscular injection of crotoxin into the tibialis anterior muscle. Rats were also treated with aminoguanidine bicarbonate salt or 7-nitroindazole, inhibitors of the inducible and neuronal isoforms of nitric oxide synthase, respectively, for 4 days and on the 5th day injected with crotoxin. All treated groups were sacrificed 24 h after injection of crotoxin. Tibialis anterior and soleus muscles were removed, frozen and stored in liquid nitrogen. Histological sections were stained with toluidine blue and assayed for acid phosphatase. The results show that L-NAME significantly minimizes myonecrosis induced by crotoxin and both aminoguanidine and 7-nitroindazole partially prevented myonecrosis induced by crotoxin. Based on the present results we conclude that nitric oxide is a very important intracellular signaling molecule that mediates crotoxin myotoxic activity.     

NG-Nitro-L-Arginine-Methyl-Ester Protects against Ischaemia-Induced Biochemical Changes and Hippocampal Neurodegeneration in the Gerbil

To assess the effects of the nitric oxide inhibitor N^G-nitro-l -arginine methyl ester (L-NAME) on behavioural, biochemical and histological changes following global ischaemia, the Mongolian gerbil was used. Ischaemia was induced by bilateral carotid occlusion (BCO) for 5 min. N^G-nitro-l -arginine methyl ester was administered i.p. at 10 mg/kg 30 min, 6, 24, and 48 h after surgery. Results indicated that 5 min BCO caused a large increase in home cage activity. N^G-nitro-l -arginine methyl ester caused some attenuation in this hyperactivity. The activity of nitric oxide synthase (NOS) was increased in the cerebellum, brain stem, striatum, cerebral cortex and hippocampus of 5-min bilateral carotid occluded animals. N^G-nitro-l -arginine methyl ester reversed the increase in nitric oxide synthase activity in all brain regions. Extensive neuronal death was observed in the CA₁ layer of the hippocampus in 5-min BCO animals 96 h after surgery. N^G-nitro-l -arginine methyl ester significantly protected against the neuronal death of cells in the CA₁ layer.     

Inhibition of nitric oxide synthase reduces ultrasonic vocalizations of rat pups.

The present study investigated the effects of drugs acting on the brain nitric oxide pathway on ultrasonic vocalizations, body temperature and locomotion in 7-8-day-old rat pups. Both a selective neuronal nitric oxide synthase (NOS) inhibitor (7-nitroindazole) and a non-selective NOS inhibitor (nitro-L-arginine-methyl ester, L-NAME) decreased the number of ultrasonic vocalizations in a dose-dependent manner. The non-selective NOS inhibitor, L-NAME, suppressed not only ultrasonic vocalizations but also locomotion. The inactive isomer of the NOS inhibitor, nitro-D-arginine-methyl ester (D-NAME), and the biological precursor of nitric oxide, L-arginine, had no effect on ultrasonic vocalizations or locomotion. These data indicate that drugs suppressing nitric oxide synthesis produced an anxiolytic effect in rat pups. However, only the selective NOS inhibitor, 7-nitroindazole, was 'anxioselective', i.e., reduced ultrasonic vocalizations without causing sedation. Increased synthesis of nitric oxide in the brain had no apparent behavioral effect in this model.     

Discriminative stimulus properties of ethanol in rats: studies on the role of nitric oxide

The present study examined the role of the L-arginine-nitric oxide pathway in mediation of the ethanol interoceptive (discriminative) cue. Adult male Wistar rats (n = 16) were trained to discriminate ethanol (1 g/kg, 10% v/v) from saline under a fixed-ratio 10 (FR10) schedule of sweetened milk reinforcement. A nonselective nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 10-540 mg/kg) did not substitute for ethanol. Similarly, a relatively selective neuronal NOS inhibitor, 7-nitroindazole (7-NI; 10-80 mg/kg), did not mimic the ethanol cue. However, both L-NAME and 7-NI produced significant reduction in the rate of operant responding. A nitric oxide precursor, L-arginine (100-500 mg/kg) neither substituted for nor antagonize the ethanol stimulus. Taken together, these results suggest that the L-arginine-nitric oxide pathway is not involved in mediation of the discriminative stimulus effects of ethanol in the rat.     

Acute inhibition of glutathione biosynthesis alters endothelial function and blood pressure in rats

The present study investigated the role of nitric oxide (NO) in the rewarding effects of D-methamphetamine using 7-nitroindazole, a potent inhibitor of neuronal nitric oxide synthase (nNOS), as determined by the conditioned place preference paradigm. Male Sprague-Dawley rats treated with D-methamphetamine (1 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed marked place preference for the drug-paired side. The administration of 7-nitroindazole (12.5-50 mg/kg) 30 min prior to the exposure to D-methamphetamine dose-dependently attenuated the acquisition of D-methamphetamine-induced conditioned place preference. In addition, when it was acutely administered 30 min prior to the testing session of an already established D-methamphetamine-induced conditioned place preference, 7-nitroindazole (12.5-50 mg/kg) attenuated the expression of this conditioned response in a dose-dependent manner, while 7-nitroindazole (25 and 50 mg/kg) alone showed no place preference effects. These findings indicate that nitric oxide (NO) is involved in the rewarding properties of methamphetamine and suggest that selective nNOS inhibitors maybe useful in the management of methamphetamine abuse.     

Factors that determine acetylcholine responsiveness of guinea pig tracheal tubes

Acetylcholine administered to the inside of epithelium-denuded tracheal tubes did cause a potent contraction (2486±120 mg). In contrast, a response was hardly observed in tissues with an intact epithelial layer (674±81 mg), which was due to both the synthesis of nitric oxide and the activity of acetylcholinesterase, since the contractions to acetylcholine were significantly enhanced after preincubation with N^ω-nitro- -arginine methyl ester ( -NAME) or physostigmine (1374±65 and 1120±65 mg, respectively). In addition, the suppressive effect was caused by the barrier function of the epithelial layer, since preincubation of epithelium-denuded tissues with physostigmine significantly increased the pD₂ value for acetylcholine (7.48±0.04) compared to intact tissues preincubated with physostigmine (6.32±0.10) and epithelium-denuded preparations without physostigmine (6.37±0.06). Increasing concentrations of physostigmine administered to the inside of tissues with epithelium did induce a potent spontaneous contraction (1440±350 mg) that was prevented by atropine. In contrast to what was expected, the contractile response was diminished in tracheal tubes without epithelium (665±221 mg). It is concluded that contractions of epithelium-denuded tissues are more pronounced to exogenous than to endogenous acetylcholine, and that the production and breakdown of this neurotransmitter is very rapid in intact guinea pig airways. Moreover, the release of nitric oxide and the barrier function of the epithelium did suppress the responsiveness to acetylcholine.     

7-Nitroindazole reduces nitric oxide concentration in rat hippocampus after transient forebrain ischemia

We investigated the effects of 7-nitroindazole, a specific inhibitor of neuronal nitric oxide (NO) synthase, on NO concentration and on blood flow in rat hippocampus after transient forebrain ischemia which was induced by 4-vessel occlusion for 10 min. NO concentration was measured directly by an NO-selective electrode method. Hippocampal blood flow was also estimated by laser Doppler flowmetry. 7-Nitroindazole [0 (vehicle), 12.5, 25, 50 or 100 mg/kg] was administered intraperitoneally 20 min before ischemia. 7-Nitroindazole at any dose used did not affect basal NO levels before ischemia. 7-Nitroindazole (25, 50 and 100 mg/kg) reduced the NO concentration significantly during post-ischemic early reperfusion. Before 10 min of ischemia and during post-ischemic early reperfusion, there were no significant differences in hippocampal basal blood flow and reactive hyperemia between vehicle- and 7-nitroindazole-treated groups. These results demonstrate that the neuronal NO synthase inhibitor, 7-nitroindazole, can effectively inhibit NO synthesis in rat hippocampus during post-ischemic early reperfusion.     

Different effects of 7-nitroindazole in reserpine-induced hypolocomotion in two strains of mice

There are a number of reasons for believing that nitric oxide participates in motor control in the striatum. Therefore, effects of neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) were studied on the reserpine model of Parkinson's disease in Swiss and C57BL/6 mice using the open-field test. Mice received reserpine (1 mg/kg administered intraperitoneally). A significant hypolocomotion was observed 24 h and 48 h after reserpine injection. The treatment with 7-nitroindazole (25 mg/kg, administered intraperitoneally, 30 min after reserpine) attenuated reserpine-induced hypolocomotion 24 h and 48 h after the treatment in Swiss mice, but not completely in C57BL/6 mice. These results suggest that nitric oxide functions as an intercellular messenger in motor circuits in the brain. Moreover, our data suggests that the comparison of such mouse strains may provide information on genetic basis for strain differences in different sensitivity to these drugs.     

Possible role of nitric oxide in the development of L-2-chloropropionic acid-induced cerebellar granule cell necrosis.

1. L-2-Chloropropionic acid (L-CPA) produces selective neuronal cell necrosis in rat cerebellum when administered orally at 750 mg kg-1 that is mediated in part through activation of N-methyl-D-aspartate (NMDA) receptors. Cerebellar granule cell death occurs between 30 and 36 h following L-CPA administration exhibiting a number of features in common with excitatory amino acid-induced cell death. We have used this in vivo model to examine the neurochemical processes following L-CPA-induced activation of NMDA receptors leading to neuronal cell death in the rat cerebellum. 2. The effects of a number of compounds which potently block nitric oxide synthase in vitro were examined on L-CPA-induced neurotoxicity 48 h following L-CPA dosing, to discover whether the neuronal cell death is mediated in part by excessive nitric oxide generation. Four inhibitors were studied, NG-nitro-L-arginine (L-NOARG), NG-nitro-L-arginine methyl ester (L-NAME), NG-iminoethyl-L-ornithine (L-NIO) and 3-bromo-7-nitroindazole (BrNI). 3. L-NAME (50 mg kg-1, i.p. twice daily) and BrIN (50 mg kg-1, i.p. twice daily) administration prevented the L-CPA-induced loss of granule cells which can reach up to 80-90% of the total cell number in rats treated with L-CPA alone. L-NOARG (50 mg kg-1, i.p. twice daily) and L-NIO administered at either 25 or 100 mg kg-1, twice daily did not produce any significant protection against L-CPA-induced neurotoxicity. 4. Both L-NAME and BrIN also prevented the L-CPA-induced increase in cerebellar water content and sodium concentrations. L-NIO when administered at the highest doses prevented the increase in cerebellar sodium concentration but not water content. L-NIO and L-NOARG were ineffective in preventing the L-CPA-induced increases in cerebellar water and sodium concentrations. 5. L-CPA-induced reductions in cerebellar aspartate and glutamate concentrations and increases in glutamine and GABA concentrations were prevented by L-NAME and BrIn, but not by L-NIO or L-NOARG. Also reductions in L-[3H]-glutamate binding to glutamate ionotrophic and metabotrophic receptors in the granule cell layer of rat cerebellum was prevented by L-NAME and BrIN, but not L-NIO or L-NOARG. 6. In conclusion, the neuroprotection offered by L-NAME and BrIN suggests that L-CPA-induced cerebellar granule cell necrosis is possibly mediated by or associated with excessive generation of nitric oxide. The inability of nitric oxide synthase inhibitors, L-NOARG and L-NIO to afford protection may result from their limited penetration into the brain (L-NIO) or rapid dissociation from the enzyme.     

Nitric oxide synthase inhibitors do not substitute in rats trained to discriminate phencyclidine from saline

Release of nitric oxide occurs as a consequence of glutamate stimulation of NMDA receptors and is dependent upon calcium-calmodulin activation of the enzyme nitric oxide synthase. Since nitric oxide may serve as an intracellular messenger for NMDA glutamatergic neurons, it could be hypothesized that blockade of its synthesis may produce pharmacological effects similar to those of NMDA receptor antagonists. The purpose of the present study was to compare the effects of nitric oxide synthase inhibitors to those of the high affinity NMDA open channel blocker phencyclidine in drug discrimination, a pharmacologically selective procedure in which phencyclidine produces distinctive effects. Rats were trained to discriminate 2 mg/kg phencyclidine from saline in a standard two-lever discrimination task with food reward. Whereas phencyclidine dose-dependently substituted for itself, 7-nitroindazole, L-NAME (N(G)-nitro-L-arginine methyl ester), and L-NOARG (N(G)-nitro-L-arginine) failed to substitute for phencyclidine when administered intraperitoneally. L-NAME and 7-nitroindazole were tested up to doses that disrupted responding, providing evidence that a behaviorally-relevant dosage range was evaluated. Although these results conflict with those of a previous study which found that nitric oxide synthase inhibitors substituted for phencyclidine and produced phencyclidine-like catalepsy in pigeons, they are consistent with research showing that these drugs did not produce phencyclidine-like pharmacological effects in behavioral procedures in rats.     

Oxidative stress in methamphetamine-induced self-injurious behavior in mice

Previous studies have shown that N-methyl-D-aspartate, the formation of free radicals and poly(ADP-ribose) polymerase are related to methamphetamine-induced neurotoxicity. This study was designed to investigate the involvement of oxidative stress in methamphetamine-induced self-injurious behavior in mice. In this study, methamphetamine (20 mg/kg) induced continuous self-injurious behavior in six of seven mice. N-methyl-D-aspartate-receptor antagonists (MK801 and 3-((R)-2-carboxypiperazin-4-yl) propyl-1-phosphonic acid) significantly attenuated this methamphetamine-induced self-injurious behavior. These results suggest that the activation of N-methyl-D-aspartate receptors is involved in methamphetamine-induced self-injurious behavior. Furthermore, we found that the nonselective nitric oxide synthase inhibitor l-N-nitro-L-arginine methyl ester hydrochloride and the neuronal nitric oxide synthase inhibitor 7-nitroindazole, but not the inducible nitric oxide synthase inhibitor aminoguanidine, the free-radical inhibitors fullerene and 3-methyl-1-phenyl-2-pyrazolin-5-one-186, or the poly(ADP-ribose) polymerase inhibitor benzamide, significantly attenuated methamphetamine-induced self-injurious behavior. The present results show that oxidative stress, which is mediated by the activation of neuronal nitric oxide synthase, is associated with methamphetamine-induced self-injurious behavior. These findings may help us to better understand the clinical phenomenon of self-injurious behavior.     

Behavioral effects of NMDA receptor agonists and antagonists in combination with nitric oxide-related compounds

Responding of rats was maintained under a 120-response fixed ratio (FR) schedule of food delivery, and animals received individual and combined injections of N-methyl-D-aspartic acid (NMDA), phencyclidine hydrochloride, (+)-MK-801 hydrogen maleate (MK-801), (+/-)-2-amino-5-phosphonopentanoic acid (AP5), 7-chlorokynurenic acid (7CK), ifenprodil tartrate, N(G)-nitro-L-arginine methyl ester hydorchloride (L-NAME), 7-nitroindazole, aminoguanidine hemisulfate, L-arginine, molsidomine, sodium nitroprusside, and 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8). Behavioral suppression after NMDA was completely and dose-dependently reversed by MK-801, phencyclidine, AP5, and aminoguanidine; partially and dose-dependently attenuated by molsidomine, ifenprodil, and 7CK; and not attenuated at all by L-NAME, 7-nitroindazole, or TMB-8. These findings suggested that behavioral suppression after NMDA was associated with nitric oxide from the inducible synthase. In a second series of experiments, comparable behavioral suppression by 0.1 mg/kg MK-801, but not 3 mg/kg phencyclidine, was attenuated by nitroprusside, molsidomine, and L-arginine, suggesting that suppressions from MK-801 and phencyclidine were mediated by different final common pathways, and that behavioral suppression from MK-801, but not phencyclidine, may be associated with Ca(2+)-dependent nitric oxide.     

Effects of oleuropein on pentylenetetrazol-induced seizures in mice: involvement of opioidergic and nitrergic systems

Oleuropein, a well-known olive polyphenol, has been shown to mediate neuroprotection in Alzheimer’s disease and cerebral ischemia. We investigated the effects of oleuropein on pentylenetetrazole (PTZ)-induced seizures in male NMRI mice, with diazepam as the standard drug. We also examined the possible involvement of opioidergic/nitrergic pathways in the probable effects of oleuropein. Intraperitoneal (i.p.) administration of different doses of oleuropein (10, 20 and 30 mg/kg) significantly increased the seizure threshold 60 min prior to induction of seizure, in a dose-dependent manner. Administration of naltrexone (10 mg/kg, i.p.), an opioid receptor antagonist, completely reversed the anticonvulsant effects of oleuropein (10 mg/kg). On the other hand, the anticonvulsant effect of oleuropein (10 mg/kg) was blocked by a non-effective dose of nonspecific inhibitor of nitric oxide synthase (NOS), L-NAME (1 and 10 mg/kg, i.p) and a selective inhibitor of neuronal NOS, 7-nitroindazole (30 mg/kg, i.p.). However, the nitric oxide precursor, l-arginine (30 and 60 mg/kg, i.p.) potentiated the anticonvulsant activity of oleuropein (10 mg/kg). A selective inducible NOS inhibitor, aminoguanidine (100 mg/kg, i.p.) did not change the anticonvulsant activity of oleuropein. It seems that the opioidergic system and constitutive neuronal NOS may be involved in the anticonvulsant properties of oleuropein.     

Evidence that A(2a) and not A(2b) purinoceptors are coupled to production of nitric oxide in the central regulation of blood pressure

In a previous study we reported that nitric oxide (NO) partially mediates centrally the decrease of arterial blood pressure induced by adenosine A₂ subtype receptor stimulation. The present study confirms the earlier suggestion and shows that in adult male normotensive anaesthetized rats 5′-N-ethylcarboxamidoadenosine (NECA), a non-selective adenosine receptor agonist, centrally injected induced a significant decrease of arterial blood pressure. Moreover, the observation that intracerebroventricular (i.c.v.) administration of N^ω-nitro- -arginine methyl ester ( -NAME), a NO synthase inhibitor, +8-(3-chlorostyryl)-caffeine (CSC), antagonist of A_2a receptors, did not reduce furthermore the hypotensive effect induced by NECA injection, demonstrated that NO is involved only via A_2a and not via A_2b adenosine subtype receptors in the central regulation of blood pressure.     

Effects of intrathecal administration of nitric oxide synthase inhibitors on carrageenan-induced thermal hyperalgesia.

1. We examined the effects of various nitric oxide synthase (NOS) inhibitors on carrageenan-induced thermal hyperalgesia. 2. First, we determined the time point at which a subcutaneous plantar injection of carrageenan into the rat hindpaw produced maximum thermal hyperalgesia. Subsequently, we demonstrated that intrathecal administration of the non-selective NOS inhibitor L-N(G)-nitro-arginine methyl ester (L-NAME) produces a dose-dependent reduction of carrageenan-induced thermal hyperalgesia. 3. Four relatively selective NOS inhibitors were then tested for their efficacy at reducing carrageenan-induced thermal hyperalgesia. Initially, the effects of prolonged treatment with inhibitors of neuronal [7-nitroindazole (7-NI) and 3-bromo-7-nitroindazole (3-Br)] and inducible [aminoguanidine (AG) and 2-amino-5,6-dihydro-methylthiazine (AMT)] NOS were examined. All agents were injected three times intrathecally during the course of inflammation caused by the plantar injection of carrageenan, and thermal hyperalgesia was measured at 6 h post-carrageenan using a plantar apparatus. 4. All inhibitors, except for 7-NI, were effective at attenuating the carrageenan-induced thermal hyperalgesia when compared with vehicle treatment. 5. Finally, the effects of early versus late administration of neuronal and inducible NOS inhibitors on carrageenan-induced thermal hyperalgesia were examined. We found that neither 3-Br nor AG significantly affected thermal hyperalgesia when administered during the early phase of carrageenan inflammation, while only AG was able to reduce thermal hyperalgesia when administered during the late phase of the injury. 6. Our results suggest that inducible NOS contributes to thermal hyperalgesia in only the late stages of the carrageenan-induced inflammatory response, while neuronal NOS likely plays a role throughout the entire time course of the injury.     

LY377770, a novel iGlu5 kainate receptor antagonist with neuroprotective effects in global and focal cerebral ischaemia

We have evaluated the neuroprotective effects of the decahydroisoquinoline LY377770, a novel iGlu5 kainate receptor antagonist, in two models of cerebral ischaemia.Global ischaemia, induced in gerbils by bilateral carotid artery occlusion (BCAO) for 5 min, produced a large increase in locomotor activity at 96 hr post-occlusion and a severe loss of CA1 cells in the hippocampus histologically at 120 hr post-occlusion. LY377770 (80 mg/kg i.p. 30 min before or 30 min after BCAO followed by 40 mg/kg i.p. administered at 3 and 6 hr after the initial dose) attenuated the ischaemia-induced hyperactivity and provided (92%) and (29%) protection in the CA1 cells respectively. This protection was greater than that seen with maximally tolerated doses of other glutamate receptor antagonists (CGS19755, CPP, MK-801, ifenprodil, eliprodil, HA-966, ACEA1021, L701,324, NBQX, LY293558, GYKI52466 and LY300164).Focal ischaemia was induced by infusing 200 pmol of endothelin-1 (Et-1) adjacent to the middle cerebral artery and LY377770 was administered at 80 mg/kg i.p. immediately, 1 or 2 hr post-occlusion followed by 40 mg/kg i.p. 3 and 6 hr after the first dose. The infarct volume, measured 72 hr later, was reduced by LY377770 when given immediately (P<0.01), at 1 hr (P<0.05) but not significantly at 2 hr post-occlusion. Reference compounds, LY293558 (20 mg/kg i.p. and then 10 mg/kg as above) and MK-801 (2.5 mg/kg i.p. ), both administered immediately post-occlusion produced significant (P<0.05) but somewhat less neuroprotection. In parallel microdialysis studies, LY377770 (75 mg/kg i.p.) attenuated ischaemia-induced increases in extracellular levels of glutamate, but not of dopamine.In conclusion, these results indicated that iGlu5 kainate receptors play a central role in ischaemic brain damage following global and focal cerebral ischaemia. LY377770 is a novel, soluble, systemically active iGlu5 antagonist with efficacy in global and focal ischaemia, even when administered post-occlusion. LY377770 may therefore be useful as a neuroprotectant in man.     

Nitric oxide synthase mediates delta opioid receptor-induced hypothermia in rats

The role of nitric oxide (NO) production in delta opioid receptor-induced hypothermia has not been reported. The present study investigated the effect of nitric oxide synthase (NOS) inhibitors on the hypothermic effect of (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80), a nonpeptide delta opioid agonist. SNC-80 (35 mg/kg, i.p.) administered to rats caused a significant hypothermia. N-nitro-L-arginine methyl ester (L-NAME) (10, 25 and 50 mg/kg, i.p.), a NOS inhibitor, and 7-nitroindazole (7-NI) (5 and 10 mg/kg, i.p.), a neuronal NOS inhibitor, were ineffective. For combined administration, L-NAME (50 mg/kg, i.p.) or 7-NI (10 mg/kg, i.p.) attenuated SNC-80-evoked hypothermia. To determine the involvement of central NOS, L-NAME (0.25, 0.5 and 1 mg/rat) was administered i.c.v. 30 min prior to SNC-80 (35 mg/kg, i.p.). Experiments revealed that L-NAME (1 mg/rat, i.c.v.) attenuated SNC-80-induced hypothermia. The present data demonstrate that central NO production is necessary for delta opioid receptor-induced hypothermia.