Role of nitric oxide in the stress-induced release of serotonin in the locus coeruleus

Serotonergic mechanisms within the locus coeruleus (LC) are thought to be important in various functions including the stress response. In this study we investigated a possible role of nitric oxide (NO) as an intermediary messenger in the regulation of the serotonin (5-HT) neurotransmission within the LC. Using the push-pull superfusion technique coupled with HPLC and electrochemical detection, the in vivo release of 5-HT was determined in time periods of 10 min in the LC of freely moving rats. Superfusion with three different NO donors, SIN-1 (linsidomine), S-nitroso-N-penicillamine (SNAP) or 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPANO) increased 5-HT release in the LC. Superfusion with the precursor of NO, L-arginine, for 1 h led to a sustained increase in 5-HT release. On the other hand, the NOS inhibitor N-methyl-L-arginine methyl ester (L-NAME) did not significantly change the release of 5-HT. Infusion of N-methyl-D-aspartate (NMDA) or kainic acid, as well as exposure of rats to noise stress or tail pinch increased the release of 5-HT in the LC. Superfusion with L-NAME prevented the increase in 5-HT outflow by all these procedures, while the inactive isomer D-NAME had no effect. Taken together, the results of this study suggest that the release of 5-HT in the LC is facilitated by NO. Under resting conditions inhibition of NOS does not appear to substantially influence the release of 5-HT in the LC. However, there seems to be a facilitatory nitrergic influence on serotonergic responses evoked by excitatory amino acid receptor stimulation or various stress stimuli.     

Stimulatory effects of clonidine,cirazoline and rilmenidine on locus coeruleus noradrenergic neurones: possible involvement of imidazoline-preferring receptors

Summary Clonidine and related drugs not only interact with ₂-adrenoceptors but also recognise non-adrenoceptor sites in the brain. The involvement of these imidazoline-preferring receptors in the regulation of the activity of locus coeruleus noradrenergic neurones (NA-LC) was investigated after inactivation of ₂-adrenoceptors with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). In EEDQ-pretreated rats (6 mg/kg, i.p., 6 h), the characteristic inhibitory effect of low doses of clonidine on these neurones was abolished and a paradoxical, dose-dependent increase in firing rate was observed at higher doses (640–5120 g/kg, i.v.) (ED₅₀ = 702 g/kg, E_max = 83 %, n = 14). Guanfacine (0.3–20 mg/kg) did not modify neuronal activity but antagonised the stimulatory effect of clonidine. Cirazoline (80–640 g/kg) and rilmenidine (0.3–10 mg/kg) also stimulatedneuronal activity(ED₅₀ = 192 g/kg, E_max = 102%, n = 5; ED₅₀ = 1563 g/kg, E_max = 70%, n = 1–5, respectively) by an ₂-adrenoceptor-independent mechanism. The results suggest that these drugs can modulate the activity of locus coeruleus noradrenergic neurones through the activation of I₁-imidazoline-preferring receptors.     

Cytoprotective effect of rabeprazole against ethanol-induced gastric mucosal damage: possible involvement of nitric oxide

The cytoprotective effect of rabeprazole, a new proton pump inhibitor, against ethanol-induced gastric mucosal damage was investigated in rats. Rats received intraperitoneal injections of rabeprazole once only or once daily for 3 days. Subsequently, the rats were given 1 ml of absolute ethanol by oral intubation. Some rats given rabeprazole were treated with N-omega-nitro-L-arginine methyl ester (L-NAME) or indomethacin. Repeated administration of rabeprazole significantly inhibited ethanol-induced gastric mucosal damage, although single administration of this drug did not. Pretreatment with L-NAME abolished the cytoprotective effect of rabeprazole. This inhibitory effect of L-NAME was reversed by L-arginine but not by D-arginine. Pretreatment with indomethacin did not influence the cytoprotective effect of rabeprazole. These results suggest that repeated intraperitoneal administration of rabeprazole has a cytoprotective effect against ethanol-induced gastric mucosal damage and that this effect may be mediated via nitric oxide but not via prostaglandins.     

Effect of cyclosporin A on morphine-induced place conditioning in mice: involvement of nitric oxide

Cyclosporin A is shown to attenuate antinociceptive effects of morphine, development and expression of morphine-induced tolerance and dependency via nitric oxide (NO) pathway. In the present study, the effect of systemic cyclosporin A on morphine-induced conditioned place preference (CPP) and the probable involvement of nitric oxide were assessed in mice. Our data showed that administration of morphine (1, 2.5, 5, 7.5, 10 mg/kg) significantly increased the time spent in the drug-paired compartment in a dose-dependent manner. The maximum response was obtained with 5 mg/kg of morphine. Cyclosporin A (5, 10 mg/kg) and N(G)-nitro-L-arginine methyl ester (L-NAME; 2.5, 5, 10 mg/kg), a nonselective nitric oxide synthase (NOS) inhibitor, did not induce either conditioned place preference or conditioned place aversion (CPA), while cyclosporin A (20 mg/kg) induced CPA. Both cyclosporin A (10, 20 mg/kg) and L-NAME (5, 10 mg/kg), in combination with morphine (5 mg/kg) during conditioning, significantly suppressed acquisition of morphine-induced place preference. Lower and per se noneffective doses of Cyclosporin A (1, 2.5, 5 mg/kg) and L-NAME (2.5 mg/kg), when coadministered, exerted a significant potentiating effect on the attenuation of morphine-induced place preference. Aminoguanidine (50, 100 mg/kg), the specific inducible nitric oxide synthase (iNOS) inhibitor, whether alone or in combination with cyclosporin A failed to show this inhibitory effect on morphine-induced place preference. In conclusion, decreasing nitric oxide production through inhibiting constitutive nitric oxide synthase may be a mechanism through which cyclosporin A attenuates morphine-induced place preference.     

17B-estradiol and hypercholesterolemia: involvement of nitric oxide

The mechanisms of the protective effect of 17B-estradiol were investigated in the middle cerebral artery (MCA) and aorta isolated from cholesterol-fed rabbits. Three groups were assigned: control group (standard chow), cholesterol group (standard chow+1% cholesterol) and estradiol group (1% cholesterol+17B-estradiol). The MCA and the aorta were isolated, precontracted respectively with high K(+) solution or with phenylephrine and exposed to cumulative acetylcholine concentrations. In the control group, acetylcholine induced a concentration-dependent relaxation in the aorta and the MCA. Cholesterol diet for eight months reduced significantly the maximal response to acetylcholine by about 50% in the aorta and by about 30% in the MCA. The chronic treatment with 17B-estradiol restored this impaired relaxations to acetylcholine. Incubation of arteries from estradiol group with N(omega)-nitro L-arginine methyl-ester (L-NAME), a potent inhibitor of constitutive nitric oxide synthase, entirely abolished the relaxation to acetylcholine while aminoguanidine, a potent inhibitor of inducible nitric oxide synthase, did not affect this relaxation. These observations suggest that the protective effect of 17B-estradiol against hypercholesterolemia is mediated via a release of endothelial nitric oxide.     

Effect of vinpocetine on noradrenergic neurons in rat locus coeruleus

Conventional extracellular single unit recordings were used to investigate the effect of vinpocetine on locus coeruleus noradrenergic neurons in chloral hydrate-anesthetized rats. Vinpocetine produced a significant and dose-dependent increase in the firing rate of locus coeruleus neurons (ED30 = 0.75 mg/kg i.v.) up to 1 mg/kg i.v., followed by a complete blockade of spiking activity at doses higher than this. The effective dose range was in very good agreement with the dose range corresponding to the memory-enhancing effects of the compound. Our results supplied direct electrophysiological evidence that vinpocetine increases the activity of ascending noradrenergic pathways. This effect can be related to the cognitive-enhancing characteristics of the compound.     

Activation of noradrenergic locus coeruleus neurons by clozapine and haloperidol: involvement of glutamatergic mechanisms

The major brain noradrenergic nucleus locus coeruleus (LC) has long been thought to be involved in states of alertness and cognitive processes. These functional characteristics make this nucleus interesting with regard to the signs of schizophrenia, especially the negative symptoms of the disease. In the present in-vivo electrophysiological study we analyse a putative interaction between endogenous kynurenic acid (KYNA) and the antipsychotic drugs clozapine and haloperidol on noradrenergic LC neurons. Previous studies have shown that systemically administered antipsychotic drugs increase the neuronal activity of LC noradrenaline (NA) neurons. In line with these findings, our results show that clozapine (1.25-10 mg/kg i.v.) and haloperidol (0.05-0.08 mg/kg i.v.) increased the firing rate of LC NA neurons in anaesthetized rats. Pretreatment with PNU 156561A (40 mg/kg i.v., 3 h), a potent inhibitor of kynurenine 3-hydroxylase, produced a 2-fold increase in rat brain KYNA levels. This treatment prevented the increase in firing rate of LC NA neurons induced by haloperidol (0.05-0.08 mg/kg i.v.) and clozapine in high doses (2.5-10 mg/kg i.v.). However, the excitatory action of the lowest dose of clozapine (1.25 mg/kg i.v.) was not abolished by elevated levels of brain KYNA. Furthermore, pretreatment with L-701,324 (4 mg/kg i.v.) a selective antagonist at the glycine site of the NMDA receptor prevented the excitatory effects of both clozapine and haloperidol. The present results suggest that the excitation of LC NA neurons by haloperidol and clozapine involves a glutamatergic component.     

Buspirone increases locus coeruleus noradrenergic neuronal activity in vitro

Buspirone, a non-benzodiazepine anxiolytic agent, produced dose-dependent increases in the activity of norepinephrine-containing locus coeruleus neurons recorded from mouse brain slices in vitro. The response was not changed in a low calcium/high magnesium incubation medium, indicating that the observed effects were the result of a direct action of buspirone on locus coeruleus neurons. These data suggest that noradrenergic neurons may not be as important in mediating anxiety states as previously suggested.     

线粒体ATP敏感性钾通道、一氧化氮合酶在四氢生物蝶呤保护再灌注心肌中的作用

目的研究线粒体三磷酸腺苷敏感性钾通道（mitoKATP）、一氧化氮合酶（NOS）在四氢生物蝶呤（BH4）减轻心肌缺血再灌注损伤（MIRI）中的作用。方法将64只成年大白兔随机分成4组,建立Langendorff模型灌注其离体心脏,加入不同成分的K-H液灌流、停跳、复灌,观察冠脉流量（CF）,测定冠脉流出液肌酸激酶（CK）的含量以及心室肌NO含量。结果用含BH4的K-H液灌注的组Ⅱ再灌注后的CF、心肌NO含量增加,冠脉流出液中CK的含量降低。使用含NOS抑制剂L-NAME或mitoKATP抑制剂5-HD预处理,使CF降低,冠脉流出液中CK的含量升高,同时L-NAME预处理后的心肌组织NO含量较其他组下降,各差异均有统计学意义（P〈0．05）。结论外源性BH4具有抗MIRI的作用,而mitoKATP、NOS参与了这种作用。提高NOS的活性,促进内源性NO的产生,mitoKATP的开放是保护作用的可能机制。     

A noradrenaline-induced inhibition from locus coeruleus of nucleus accumbens neuron receiving input from hippocampus

Electrophysiological studies using rats anesthetized with chloral hydrate were performed to determine whether or not noradrenaline originating in the locus coeruleus (LC) produces a beta-receptor-mediated inhibition of the nucleus accumbens (Acc) neurons receiving input from the hippocampus (HPC). When conditioning stimuli were applied to the LC preceding a test stimulus to the HPC, an inhibition of spike generation with HPC stimulation was observed during 20-100 msec of the conditioning-test time interval. This inhibition was observed when the stimulating electrode was located in the LC or its immediate vicinity. The spike generation upon HPC stimulation was also inhibited by iontophoretic application of noradrenaline, and the inhibition was antagonized by iontophoretically applied sotalol, a beta-adrenergic blocker, but not by phentolamine, an alpha-adrenergic blocker. These results suggest that noradrenaline derived from the LC produces a beta-receptor-mediated inhibition of the Acc neurons receiving input from the HPC.     

Hippocampus and locus coeruleus activity on rats chronically treated with diazepam

The neural mechanisms underlying benzodiazepine (BZD) dependence remain equivocal. The present studies tested the hypothesis that similar neural circuitry might be involved in the effects of chronic 7-chloro-1-methyl-5-phenyl-3H-1,4-benzodiazepine-2(1H)-one, diazepam (DZ, Roche), administration and withdrawal. The results of our study showed an increased hippocampal synaptic plasticity in slices from rats chronically treated with DZ (5 mg/kg/18 days), assessed as a decrease of the threshold in the stimulation rate for long-term potentiation (LTP) elicitation. Rats with the same schedule of DZ administration but without signs of withdrawal behaved similarly to vehicle-treated ones (VEH), in the threshold to induce LTP. Furthermore, the activity of locus coeruleus (LC) norepinephrine (NE) neurons in rats tested 24 h after the last DZ injection showed a significant increase. On the other hand, rats that after chronic DZ administration did not develop signs of withdrawal and exhibited a similar pattern of discharge on LC-NE nucleus compared with their controls. We conclude that chronic DZ administration enhances both hippocampal synaptic plasticity and activity of LC-NE neurons. This neural system could be the biological substrate underlying the behavioral alterations accompanying chronic DZ administration and withdrawal.     

Morphine increases locus coeruleus noradrenergic neuronal activity in vitro

Morphine produced a dose-dependent increase in the activity of norepinephrine-containing locus coeruleus neurons recorded from mouse brain slices in vitro. The response was not changed in a low calcium-high magnesium incubation medium, indicating that the observed effects are the result of a direct action of morphine on locus coeruleus neurons. When the mice were anesthetized with chloral hydrate prior to preparation of tissue slices, morphine produced a dose-dependent suppression of noradrenergic neuronal activity. These studies suggest that previous data showing a decrease in activity of locus coeruleus neurons following incubation with morphine in vitro are due to the use of anesthesia.     

Galanin decreases the activity of locus coeruleus neurons in vitro

A brain slice preparation was used to examine the effects of galanin on the spontaneous firing rate of locus coeruleus noradrenergic neurons. Galanin (10(-9)-10(-7) M), added to the bath, inhibited the firing of 14 out of 19 neurons in a concentration-dependent manner. The observed effect was quite variable, ranging from 20 to 100% at 10(-7) M. Experiments performed in low-Ca2+, high-Mg2+ medium also showed a significant inhibition by galanin (10(-7) M) in three out of five neurons, which suggests that the peptide acts directly.     

Excitatory mechanisms in neuroleptic-induced vacuous chewing movements (VCMs): possible involvement of calcium and nitric oxide

Tardive dyskinesia (TD) is a serious motor side-effect of chronic neuroleptic therapy. Chronic treatment with neuroleptics leads to the development of oral abnormal movements in rats known as vacuous chewing movements (VCMs). Vacuous chewing movements in rats have been widely accepted as an animal model of tardive dyskinesia. Chronic blockade of D2 inhibitory dopamine (DA) receptors localized on glutamatergic terminals in the striatum leads to the persistent enhanced release of glutamate that kills the striatal output neurons. The object of the present study was to explore the role of glutamatergic modulation on the neuroleptic-induced VCMs. Rats were chronically (for 21 days) treated with haloperidol (1.5 mg/kg, i.p.) to produce VCMs. The neuroleptic-induced VCMs viz., vertical jaw movements, tongue protrusions and bursts of jaw tremors, were counted during a 5 min observation period. Dizocilpine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, dose dependently (0.02 and 0.05 mg/kg) reduced haloperidol-induced VCMs. Felodipine (5 and 10 mg/kg), an L-type calcium-channel blocker, also significantly reduced the VCM count. N-omega-nitro-L-arginine methyl ester (L-NAME) (25 and 50 mg/kg), a nitric oxide synthase inhibitor, also reduced the VCM count in an L-arginine-sensitive manner. In conclusion, the findings of the present study indicated NMDA receptor involvement in haloperidol-induced VCMs, and also suggested the possible involvement of calcium and nitric oxide in haloperidol-induced VCMs.     

Effect of buspirone on single unit activity in locus coeruleus and dorsal raphe nucleus in behaving cats

The effects of administration of the non-benzodiazepine anxiolytic buspirone on the spontaneous and sensory evoked single unit activity of serotonergic (5-HT) neurons in the dorsal raphe nucleus and noradrenergic (NE) neurons in the locus coeruleus were examined in freely moving cats. Buspirone (1.0 mg/kg i.p.) strongly suppressed both the spontaneous and evoked activity of 5-HT dorsal raphe nucleus neurons. The spontaneous activity of NE neurons in the locus coeruleus was non-significantly increased by drug administration, while the evoked response was unaffected. These effects occurred during a period of mild behavioral activation. It is suggested that the anxiolytic effects of buspirone administration are not achieved through an action of NE neurons, but may be mediated in part by actions on 5-HT neurons in the dorsal raphe.     

Reduction of myocardial infarct size by tetrahydrobiopterin: possible involvement of mitochondrial KATP channels activation through nitric oxide production

This study examined whether intravenous administration of tetrahydrobiopterin (BH4) reduces myocardial infarct size following ischemia/reperfusion (I/R) in rats, and the mechanisms of its protective effect were also investigated. Rats were subjected to 30 minutes of ischemia by ligation of the left coronary artery and 2 hours of reperfusion. The infarct size was determined as a percentage of the area at risk by triphenyltetrazolium staining. Intravenous administration of BH4 (0.01 mg/kg-1 mg/kg) significantly reduced the myocardial infarct size. Nitrite plus nitrate (NOx) and cGMP levels in the hearts were significantly increased by the treatment with BH4, and the infarct size-limiting effect of BH4 was abolished by the co-administration of NG-nitro-L-arginine methyl ester, a specific inhibitor of nitric oxide synthase, or 5-hydroxydecanoic acid, a specific inhibitor of mitochondrial ATP-sensitive potassium channel (mitoKATP channel). These findings suggest that BH4 has a cardioprotective effect against I/R in vivo, and its protective effect appeared to be involved in the opening of mitoKATP channels through increased nitric oxide production.     

Retinal neurotoxicity of nitric oxide donors with different half-life of nitric oxide release: involvement of N-methyl-D-aspartate receptor

We compared the degree of neurotoxic outcome in the retina exposed to three nitric oxide (NO) donors with different half-life of NO release. Intravitreal injection of NO donors resulted in a significant decrease in cell density in the ganglion cell layer and thinning of the inner plexiform layer in a half-life time-dependent manner. Concurrent injection of an NO-trapping reagent with an NO donor abolished NO donor-induced retinal damage. (+)-MK-801 also prevented NO-induced retinal damage, indicating that N-methyl-D-aspartate receptors are partly involved in NO-induced neurodegeneration. These results may be relevant to a pathogenic role of NO - glutamate receptor in several ophthalmic disorders.