Immunohistochemical study on the development of cholinergic and nitrergic nerve structures in the bovine esophageal groove

The proper functioning of the perinatal sucking reflex in calves is essential for the prevention of milk leakage into the rumen. The complex process behind its regulation is mediated at the gut level via multiple excitatory and inhibitory neurotransmitters, of which acetylcholine and nitric oxide are of fundamental importance. The aim of our study was to depict age-related alterations in the cholinergic and nitrergic innervation of the esophageal groove (EG) using immunohistochemistry and Real-Time PCR methods. We found out that the highest number of cholinergic nerve cells was present in the second trimester fetuses. From this developmental stage onward, their amount was gradually decreasing and reached the lowest value in 4-year-old cows. The same developmental pattern was observed for nitrergic nerve structures with the highest percentage of nitrergic neurons in the third trimester fetuses. Our observations prove that both neuronal populations are crucial for a proper closure of EG in calves. Therefore, their contribution to a general neuronal activity in the ENS diminishes with age as the high motility of a gastric groove is not necessarily required in older cattle.

The Influence of Bisphenol a on the Nitrergic Nervous Structures in the Domestic Porcine Uterus

Bisphenol A (BPA) is one of the most common environmental pollutants among endocrine disruptors. Due to its similarity to estrogen, BPA may affect estrogen receptors and show adverse effects on many internal organs. The reproductive system is particularly vulnerable to the impact of BPA, but knowledge about BPA-induced changes in the innervation of the uterus is relatively scarce. Therefore, this study aimed to investigate the influence of various doses of BPA on nitrergic nerves supplying the uterus with the double immunofluorescence method. It has been shown that even low doses of BPA caused an increase in the number of nitrergic nerves in the uterine wall and changed their neurochemical characterization. During the present study, changes in the number of nitrergic nerves simultaneously immunoreactive to substance P, vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating peptide, and/or cocaine- and amphetamine-regulated transcript were found under the influence of BPA. The obtained results strongly suggest that nitrergic nerves in the uterine wall participate in adaptive and/or protective processes aimed at homeostasis maintenance in the uterine activity under the impact of BPA.

Berberine restored nitrergic and adrenergic function in mesenteric and iliac arteries from streptozotocin-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Perivascular neuropathy was reported to involve in the vascular disorders associated with diabetes. The dried rhizomes of Coptis chinensis Franch. (Latin name: Coptidis Rhizoma; common name: Huang Lian in China), used frequently in Traditional Chinese medicine to treat diabetes (Xiaoke), have been confirmed to possess beneficial effects on diabetic peripheral neuropathy by modern clinical and pharmacological studies. Berberine (BBR), the main effective component of Huang Lian in the treatment of diabetes, is reported to ameliorate diabetic central and peripheral neuropathy. However, the effects of BBR on nerve function of mesenteric and iliac arteries are unclear.

AIM OF THE STUDY

To investigate the effects of BBR on the diabetes-induced changes in nitrergic and adrenergic function in mesenteric and iliac arteries.

MATERIALS AND METHODS

In this study, the animals were randomized into three groups: control rats, diabetic rats, and diabetic rats gavaged with BBR. We established diabetic rat model using intraperitoneal injection of streptozotocin (STZ, 55 mg kg^-1). Two weeks after model establishment, those in the BBR-treated groups were gavaged with berberine chloride (Sichuan Xieli Fharmaceutical. Co., Ltd; 200 mg·kg^-1·day^-1) diluted in distilled water for another 2 weeks. The superior mesenteric artery and iliac artery were excised. Electric field stimulation (EFS) was used to induce arterial vasoconstriction and explore (1) the diabetes-induced changes in neurogenic function of the superior mesenteric artery and iliac artery; (2) the effects of BBR on neurovascular dysfunction in the early stage of STZ-induced diabetic rats. Nitric oxide (NO) and noradrenaline (NA) released from the nitrergic and adrenergic nerves were quantified using fluorescence assays and ELISA, respectively.

RESULTS

EFS induced frequency-dependent vasoconstrictions in both superior mesenteric and iliac artery, and the contractile responses of arteries were abolished by 0.1 μmol·L^-1 tetrodotoxin (TTX), or inhibited by 1 μmol·L^-1 phentolamine or increased by 0.1 mmol·L^-1 N^ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME). In superior mesenteric artery, but not in iliac artery, the changes of contractile responses with L-NAME were significantly decreased in diabetic rats, and NO release was less also. In contrast, in iliac artery of diabetic rats, but not in superior mesenteric artery, the changes of contractile responses with phentolamine were increased, and NA release was increased significantly. All these changes in diabetic rats on both superior mesenteric artery and iliac artery were reversed by treated with BBR.

CONCLUSIONS

In the STZ-induced early diabetic rats, neural control of mesenteric and iliac vasomotor tone are altered differently. The diminished nitrergic nerve in superior mesenteric artery and enhanced adrenergic nerve in iliac artery both contributed to increased vasocontrictor responses. All these changes in diabetic rats were reversed by BBR, suggesting a novel mechanism of BBR in balance of neural regulation of vascular tone.

Monosodium glutamate impairs the contraction of uterine visceral smooth muscle ex vivo of rat through augmentation of acetylcholine and nitric oxide signaling pathways

The aim of the study was to examine the toxic effects of Monosodium glutamate (MSG), an extensively used food additive, on the contraction of uterine visceral smooth muscle (UVSM) in rat and to elucidate the probable neurocrine mechanism involved in it. MSG produced significant potentiation of the force and inhibition of frequency of uterus recorded ex vivo in chronic MSG exposure and in single dose acute experiments. MSG also produced significant potentiation of force of acetylcholine induced contraction and no alterations in atropine induced contraction of uterus. Further, MSG produced significant increase in force and frequency of contraction of neostigmine incubated uterus. We have found significant potentiation of the post pause force of contraction of uterus when MSG was applied in adrenaline incubated uterus. MSG also produced significant decrease in frequency of contraction of sodium nitroprusside incubated uterus; increase in frequency of N-ω-Nitro-l-Arginine Methyl Ester incubated uterus and no significant changes in frequency of contraction of methylene blue incubated uterus. These results indicate that MSG potentiates the force of contraction of UVSM predominantly by augmenting the activity of cholinergic intrinsic efferents and inhibits the frequency of contraction probably by augmenting the activity of nitrergic efferents. In conclusion, MSG potentiates the force and inhibits the frequency of contraction of UVSM, and the MSG induced effect is probably mediated through the augmentation of acetylcholine and nitric oxide signaling pathways.

Cholinergic and nitrergic neuronal networks in the goldfish telencephalon

The general organization of cholinergic and nitrergic elements in the central nervous system seems to be highly conserved among vertebrates, with the involvement of these neurotransmitter systems now well established in sensory, motor and cognitive processing. The goldfish is a widely used animal model in neuroanatomical, neurophysiological, and behavioral research. The purpose of this study was to examine pallial and subpallial cholinoceptive, cholinergic and nitrergic populations in the goldfish telencephalon by means of histochemical and immunohistochemical techniques in order to identify neurons containing acetylcholinesterase (AChE), choline acetyltransferase (ChAT), NADPH-diaphorase (NADPHd), and neuronal nitric oxide synthase (nNOS), and to relate their distribution to their putative functional significance. Regions containing AChE-labeled neurons represented terminal fields of cholinergic inputs as well as a widespread distribution of AChE-related enzymes; these regions also usually contained NADPHd-labeled neurons and often contained small numbers of nNOS-positive cells. However, the ventral subdivisions of the medial and lateral parts of the dorsal telencephalic area, and the ventral and lateral parts of the ventral telencephalic area, were devoid of nNOS-labeled cells. ChAT-positive neurons were found only in the lateral part of the ventral telencephalic area. ChAT- and nNOS-positive fibers exhibited a radial orientation, and were seen as thin axons with en-passant boutons. The distribution of these elements could help to elucidate the role of cholinergic and nitrergic neuronal networks in the goldfish telencephalon.

Autonomic boundary conditions for ventricular fibrillation and their implications for a novel defibrillation technique

The sympathetic and parasympathetic divisions of the autonomic nervous system modulate cardiac rhythm and the probability of arrhythmia occurrence. Both increased sympathetic drive and hypoxia increase the likelihood for ventricular fibrillation (VF). Vagus nerve stimulation (VNS) can protect from fatal arrhythmias via cholinergic and nitrergic action. We sought to determine boundary conditions for VF and defibrillation by autonomic manipulations accompanied or not by hypoxic changes in urethane-anesthetized rats. VF was induced with (1) vagotomy, (2) systemic high-dose (>15 mg/kg) isoproterenol, and (3) hypoxemia. When VNS (50 Hz) produced cardiac standstill, it converted every VF episode (59/59). A nitric oxide synthase inhibitor did not reduce VNS efficacy (13/14 episodes converted), but addition of atropine reduced VNS efficacy (11/27 episodes converted). VF can be induced by autonomic derangements only under constrained conditions, including sympathetic over-activation, reduced parasympathetic input, and hypoxemia. VNS can provide an alternative method to defibrillate via its cholinergic action.

Region-related modular nerve-dependent motor activity in anorectum--cholinergic and nitrergic contribution to rat model

Disturbances of enteric nerve-mediated anorectal evacuation mechanisms have medical and social impact. The study aimed at further eliciting the contribution of cholinergic and nitrergic neurotransmission systems to modular nerve networks in different regions of Wistar rat anorectum. Electrical field stimulation (EFS, 0.8 ms, 40 V, 2, 5 or 10 Hz, 20 s), computerized mechanographic on-line setup and drugs were used to evaluate the motor responses of isolated rings from circular muscle of rectum (proximal, middle, and distal part), internal anal sphincter, and anal canal. Twitch-like frequency-dependent contractions, more pronounced in rectal preparations, characterized the modular motor responses of rectal circular muscle rings and anal canal. Depending on the frequency of stimulation, the motor activity of internal anal sphincter varied from deep long-lasting relaxation to initial short-lasting relaxation, followed by a contraction. Electrically-evoked responses of anorectal preparations were tetrodotoxin (0.1 microM)-sensitive. In the presence of atropine (0.3 microM) the contractions of rectal rings decreased, relaxation of internal anal sphincter increased and inhibition of the contractions of the anal canal occurred, followed by relaxation. During atropine treatment, NG-nitro-L-arginine (0.5 microM) increased the contractile responses and suppressed internal anal sphincter relaxations. L-arginine (0.5 microM) decreased the contractions and extended the relaxations of internal anal sphincter and anal canal. Our results suggest that cholinergic and nitrergic systems are not equally involved in modular nerve networks of various regions of anorectum. Cholinergic transmission is more expressed in distal rectum, underlying its contractile potency, while nitric oxide-dependent transmission(s) control the relaxation ability of the internal anal sphincter and anal canal.

Neurons controlling Aplysia feeding inhibit themselves by continuous NO production

BACKGROUND

Neural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?

METHODOLOGY/PRINCIPAL FINDINGS

Applying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.

CONCLUSION/SIGNIFICANCE

Self-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior.

Effects of diabetes and elevated glucose on nitrergic relaxations in the isolated duodenum of the rat

Nitrergic relaxations of the isolated duodenum, induced by streptozotocin, were investigated in the experimental 8-week diabetes rat model. The effects of elevated glucose were also examined in the incubated duodenal muscles (in Krebs-Henseleit solution containing 44 mM glucose for 6 h) taken from nondiabetic rats. The relaxations induced by electrical field stimulation (EFS) and nicotine were significantly reduced in diabetic rats compared with control rats. Incubating of duodenal tissues in medium containing elevated glucose revealed significantly impaired relaxations to EFS and nicotine compared to responses obtained after normal glucose incubation. However, the relaxant responses to sodium nitroprusside and papaverine were similar in all groups. Incubating in hyperosmolar solutions containing sucrose, the relaxant responses were not affected. In conclusion, impairment of NO-mediated relaxations in diabetes may be related to hyperglycemia. The alterations caused by elevated glucose are not due to a hyperosmotic effect because the same concentration of sucrose had no effect on the relaxations.

Does tourniquet application alter the nitrergic responses of rabbit corpus cavernosum penis? A functional study

OBJECTIVE

To investigate the effects of short and long periods of tourniquet application on corporal nerves, endothelium and smooth muscle responses.

METHODS

After the rabbits were anesthetized with xylazine (5 mg/kg) and ketamine hydrochloride (35 mg/kg), a standard rubber circular band was applied to the base of the penis. After waiting for 20, 40 and 60 min, the tourniquets were removed and the penil tissue was reperfused for 5 min. In all groups, relaxation [carbachol, sodium nitroprusside (SNP) and electrical field stimulation (EFS) and contraction (phenylephrine and EFS)] responses were examined. In another set of experiments, the rabbits were killed 24 h after the tourniquet period of 60 min and carbachol-induced relaxation responses were obtained.

RESULTS

SNP- and EFS-induced relaxation responses were similar in all groups. Carbachol-induced relaxation responses were not altered in tissues from 20 min tourniquet group, but they were significantly reduced in tissues from 40 and 60 min tourniquet group compared to that from control group. The impaired endothelium-mediated relaxation responses did not return to control levels after 24 h of reperfusion period. Neither phenylephrine nor EFS-mediated contraction responses were altered with tourniquet application.

CONCLUSIONS

The results suggest that long period of tourniquet application altered endothelium-dependent muscarinic receptor-mediated relaxation responses. This is the first functional study that examined the effects of tourniquet application on corpus cavernosum tissue. In conclusion, it can be suggested that if tourniquet is necessary in penile surgery the application time of up to 20 min is more appropriate instead of prolonged usage.

[Relationship between gastrointestinal dyskinesis and gastrointestinal neurons in diabetic mellitus: experiment with rats]

OBJECTIVE

To investigate the relationship between gastrointestinal dyskinesis and histologic changes of gastrointestinal myenteric plexus cholinergic and nitrergic neurons in STZ-induced diabetic rats.

METHODS

45 SD rats were randomly divided into control group, diabetic group and insulin group. 16 weeks after diabetic model established, gastrointestinal motility of rats was measured and histologic changes of myenteric plexus cholinergic neuron and nitrergic neuron was observed.

RESULTS

Compared with control group, gastrointestinal motility of diabetic group was markedly slow (P < 0.01), the myenteric plexus cholinergic neuron counting of gastric antrum and small intestine were significantly decreased (6.6 +/- 2.9 vs 15.7 +/- 3.8 15.6 +/- 10.3 vs 22.6 +/- 7.4, P < 0.01), yet the number of nitrergic neuron only markedly reduced in gastric antrum (5.3 +/- 1.2 vs 11.8 +/- 2.2, P < 0.01). The gastrointestinal mobility, gastric antrum nitrergic neuron and small intestine cholinergic neuron counting of insulin group were markedly higher than that of diabetic group (P < 0.05), yet lower than that of control group (P < 0.01).

CONCLUSION

The gastrointestinal dyskinesis of STZ-induced diabetic rats might be associated with lesions of gastrointestinal myenteric plexus cholinergic neuron and nitrergic neuron. Insulin intensive therapy can partly ameliorate diabetic gastrointesternal dyskinesis.

Nitrergic and purinergic interplay in inhibitory transmission in rat gastric fundus

1 This study was undertaken to analyse the involvement of ATP in non-adrenergic non- cholinergic (NANC) relaxation and possible interplay between nitrergic and purinergic systems in rat gastric fundus. 2 Experiments were performed in vitro on strips of longitudinal muscle from rat gastric fundus, recording the mechanical activity as changes in isometric force. In addition, NO release induced by different experimental conditions was assayed. 3 Under NANC conditions in serotonin-precontracted strips, electrical field stimulation (EFS) elicited a tetrodotoxin (TTX)-sensitive relaxation accompanied by nitric oxide (NO) release. This effect was antagonized by pretreatment with the NO synthase antagonist Nomega-nitro-L-arginine (L-NA) or by desensitization of purinergic receptors. Purinergic desensitization was also able to further antagonize the residual EFS-induced relaxation remaining after L-NA treatment. Exogenously applied NO [delivered as sodium nitroprusside (SNP)] or ATP (and related purines) induced concentration-dependent, TTX-insensitive relaxant responses. ATP also induced the release of NO. A reduction in the responses to ATP was observed in the presence of L-NA. In contrast, SNP-induced relaxation remained unchanged after desensitization of purinergic receptors. Finally, apamin, a blocker of the small conductance Ca2+ -dependent K+ channels, reduced the amplitude of the muscular relaxation evoked by either EFS, ATP or SNP. 4 In conclusion, this study provides evidence that in rat gastric fundus, ATP is one of the inhibitory transmitters released from NANC intramural neurones acting directly on the muscle, through receptors coupled to apamin-sensitive Ca2+ -dependent K+ channels and, indirectly, through the stimulation of NO production.

P2 purinoceptor antagonists inhibit the non-adrenergic, non-cholinergic relaxation of the human colon in vitro

Neurotransmitters released by myenteric neurons regulate movements of intestinal smooth muscles. There has been little pharmacological evidence for a role of purinergic mechanisms in the non-adrenergic, non-cholinergic (NANC) relaxation of the human large intestine. We used P(2) purinoceptor antagonists to assess whether such receptors are involved in the NANC relaxation of the circular muscle of the human sigmoid colon. It was also investigated whether the guanylate cyclase enzyme mediates the NANC response. Human colonic circular strips were tested in organ bath experiments with isotonic recording. NANC, non-nitrergic relaxations induced by electrical field stimulation (1 and 10 Hz, in the presence of atropine, guanethidine, and 100 microM N(G)-nitro-L-arginine [L-NOARG]) were strongly inhibited by a combination of the P(2) purinoceptor antagonists pyridoxal-phosphate-6-azophenyl-2',4'-sulfonic acid (PPADS) (50 microM) and suramin (100 microM). PPADS plus suramin was ineffective in the absence of L-NOARG. L-NOARG alone significantly reduced the NANC relaxation to electrical stimulation. PPADS plus suramin strongly inhibited the relaxation in response to exogenous alpha,beta-methylene ATP. The guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (3 microM) inhibited the NANC relaxation, but did not add to its reduction by L-NOARG. L-NOARG was still slightly effective in the presence of ODQ. Vasoactive intestinal polypeptide tachyphylaxis failed to influence the non-nitrergic NANC relaxation. It is concluded that nitric oxide (NO) and ATP co-mediate, in a non-additive manner, the NANC relaxation. NO probably acts through the guanylate cyclase, though a small fraction of its effect might be mediated by other mechanisms. Activators of the guanylate cyclase other than NO do not seem to participate in the NANC relaxation.

Exposure to a hot environment can activate spinally projecting and nitrergic neurones in the lower brainstem in the rat

Reflex responses to hyperthermia include sweating, salivation and a redirection of blood flow from the viscera to the periphery, and involve changes in peripheral nerve activity mediated by the central nervous system (CNS), including specific areas of the ventral lower brainstem. The lower brainstem contains nitrergic neurones and neurones that project to intermediolateral cell column; however, it is not known whether these populations of neurones in the lower brainstem are activated following hyperthermia. The aims of the present study were to determine whether lower brainstem neurones activated by acute hyperthermia are nitrergic and/or whether they also project to the spinal cord. Retrogradely transported rhodamine-tagged beads were microinjected into the spinal cord. The rats were heated (environmental temperature 39 degrees C) for 1 h. Following perfusion/fixation, brain sections were processed to detect Fos (a marker of neuronal activation) and NADPH-diaphorase activity (a marker of nitrergic neurones). The results showed a significant increase in activated neurones in the mid-line (by fivefold), ventromedial (by eightfold) and ventrolateral lower brainstem (by ninefold). Some of these neurones were nitrergic, particularly in the ventromedial lower brainstem (5% of the activated neurones in this region were nitrergic). A small proportion of activated neurones were spinally projecting neurones (2-3% of activated neurones were spinally projecting). There were no triple-labelled neurones at any level of the lower brainstem examined. These findings indicate that only a small proportion of nitrergic neurones and spinally projecting neurones are activated by hyperthermia.

Parasympathetic stimulation elicits cerebral vasodilatation in rat

Forebrain arteries receive nitroxidergic input from parasympathetic ganglionic fibers that arise from the pterygopalatine ganglia. Previous studies have shown that ganglionic stimulation in some species led to cerebral vasodilatation while interruption of those fibers interfered with vasodilatation seen during acute hypertension. Because the ganglionic fibers are quite delicate and are easily damaged when the ganglia are approached with published techniques we sought to develop a method that allowed clear exposure of the ganglia and permitted demonstration of cerebral vasodilatation with electrical stimulation of the ganglia in the rat. We had found that an orbital approach during which the eye was retracted for visualization of the ganglion precluded eliciting vasodilatation with ganglionic stimulation. In the current study approaching the ganglion through an incision over the zygomatic arch provided clear exposure of the ganglion and stimulation of the ganglion with that approach led to vasodilatation.

Regulation of common carotid arterial blood flow by nitrergic neurons in the medulla of cats

Glutamate stimulation of the dorsal facial area, an area located dorsal to the facial nucleus, increases common carotid arterial blood flow. Nitrergic neurons are important in cardiovascular regulatory areas. We investigated whether the nitrergic neurons might be present and play a role in the dorsal facial area to regulate the arterial blood flow. Injections of L-arginine (an NO precursor) and sodium nitroprusside (an NO donor) into the area caused dose-dependent increases in the arterial blood flow. Injection of N(G)-nitro-arginine methyl ester (L-NAME, an NO synthase inhibitor) or methylene blue (a guanylate cyclase inhibitor) decreased the arterial blood flow. Nitrergic neurons and fibers were found in the dorsal facial area by histochemical staining of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, a maker of NO synthase. In conclusion, nitrergic neurons are present in the dorsal facial area and appear to release NO tonically in stimulating the area to cause increase in common carotid arterial blood flow.

The effects of endogenous and exogenous nitric oxide on gut motility in zebrafish Danio rerio embryos and larvae

Using motion analysis, the ontogeny of the nitrergic control system in the gut was studied in vivo in zebrafish Danio rerio embryos and larvae. For the first time we show the presence of a nitrergic tonus,modulating both anterograde and retrograde contraction waves in the intestine of developing zebrafish. At 4 d.p.f. (days post fertilisation), the nitric oxide synthase (NOS) inhibitor l-NAME (three boluses of 50–100 nl, 10–3 mol l–1) increased the anterograde contraction wave frequency by 0.50±0.10 cycles min–1. Subsequent application of the NO donor sodium nitroprusside (SNP; three boluses of 50–100 nl, 10–4mol l–1) reduced the frequency of propagating anterograde waves (–0.71±0.20 cycles min–1). This coincided with the first appearance of an excitatory cholinergic tonus, observed in an earlier study. One day later, at 5 d.p.f., in addition to the effect on anterograde contraction waves, application of l-NAME increased(0.39±0.15 cycles min–1) and following SNP application reduced (–1.61±0.36 cycles min–1) the retrograde contraction wave frequency. In contrast, at 3 d.p.f., when no spontaneous motility is observed, application of l-NAME did not induce contraction waves in either part of the gut, indicating the lack of a functional inhibitory tonus at this early stage. Gut neurons expressing NOS-like immunoreactivity were present in the distal and middle intestine as early as 2 d.p.f., and at 1 day later in the proximal intestine. In conclusion, the present study suggests that a nitrergic inhibitory tonus develops shortly before or at the time for onset of exogenous feeding.

Nitrergic Proprioceptive Afferents Originating from Quadriceps Femoris Muscle are Related to Monosynaptic Ia-Motoneuron Stretch Reflex Circuit in the Dog

1. The aim of the present study was to examine the occurrence of the neuronal nitric oxide synthase immunoreactivity in the stretch reflex circuit pertaining to the quadriceps femoris muscle in the dog. 2. Immunohistochemical processing for neuronal nitric oxide synthase and histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase were used to demonstrate the presence of neuronal nitric oxide synthase in the proprioceptive afferents issuing in the quadriceps femoris muscle. The retrograde tracer Fluorogold injected into the quadriceps femoris muscle was used to detect the proprioceptive afferents and their entry into the L5 and L6 dorsal root ganglia. 3. A noticeable number of medium-sized intensely nitric oxide synthase immunolabelled somata (1000-2000 microm(2) square area) was found in control animals in the dorsolateral part of L5 and L6 dorsal root ganglia along with large-caliber intraganglionic nitric oxide synthase immunolabelled fibers, presumed to be Ia axons. Before entering the dorsal funiculus the large-caliber nitric oxide synthase immunolabelled fibers of the L5 and L6 dorsal roots formed a massive medial bundle, which upon entering the dorsal root entry zone reached the dorsolateral part of the dorsal funiculus and were distributed here in a funnel-shaped fashion. The largest nitric oxide synthase immunolabelled fibers, 8.0-9.2 microm in diameter, remained close to the dorsal horn, while medium-sized fibers were seen dispersed across the medial portion of the dorsal funiculus. Single, considerably tapered nitric oxide synthase immunolabelled fibers, 2.2-4.6 microm in diameter, were seen to proceed in ventrolateral direction until they reached the mediobasal portion of the dorsal horn and the medial part of lamina VII. In lamina IX, only short fragments of nitric oxide synthase immunoreactive fibers and their terminal ramifications could be seen. Nitric oxide synthase immunolabelled terminals varying greatly in size were identified in control material at the base of the dorsal horn, in the vicinity of motoneurons ventrally and ventrolaterally in L5 and L6 segments and in Clarke's column of L3 and L4 segments. Injections of the retrograde tracer Fluorogold into the quadriceps femoris muscle and cut femoral nerve, combined with nitric oxide synthase immunohistochemistry of the L5 and L6 dorsal root ganglia, confirmed the existence of a number of medium-sized nitric oxide synthase immunoreactive and Fluorogold-fluorescent somata presumed to be proprioceptive Ia neurons (1000-2000 microm(2) square area) in the dorsolateral part of both dorsal root ganglia. L5 and L6 dorsal rhizotomy caused a marked depletion of nitric oxide synthase immunoreactivity in the medial bundle of the L5 and L6 dorsal roots and in the dorsal funiculus of L5 and L6 segments. 4. The analysis of control material and the degeneration of the large- and medium-caliber nitric oxide synthase immunoreactive Ia fibers in the dorsal funiculus of L5 and L6 segments confirmed the presence of nitric oxide synthase in the afferent limb of the monosynaptic Ia-motoneuron stretch reflex circuit related to the quadriceps femoris muscle.

Activation of NADPH-diaphorase-positive projections to the rostral ventrolateral medulla following cardiac mechanoreceptor stimulation in the conscious rat

Stimulation of cardiac mechanoreceptors during volume expansion elicits reflex compensatory changes in sympathetic nerve activity (SNA). The hypothalamic paraventricular nucleus (PVN) and nucleus of the tractus solitarius (NTS) are autonomic regions known to contribute to this reflex. Both of these nuclei project to the rostral ventrolateral medulla (RVLM), critical in the tonic generation of SNA. Recent reports from our laboratory show that these pathways 1) are activated following cardiac mechanoreceptor stimulation, and 2) produce nitric oxide, known to influence SNA. The aims of the present study were to determine whether 1) the activated neurons within the PVN and NTS were nitrergic and 2) these neurons projected to the RVLM. Animals were prepared, under general anesthesia, by microinjection of a retrogradely transported tracer into the pressor region of the RVLM and the placement of a balloon at the right venoatrial junction. In conscious rats, the balloon was inflated to stimulate the cardiac mechanoreceptors or was left uninflated. Balloon inflation elicited a significant increase in Fos-positive neurons in the parvocellular PVN (sevenfold) and NTS (fivefold). In the PVN, 51% of nitrergic neurons and 61% of RVLM-projecting nitrergic neurons were activated. In the NTS, these proportions were 8 and 18%, respectively. The data suggest that nitrergic neurons within the PVN and, to a lesser extent, in the NTS, some of which project to the RVLM, may contribute to the central pathways influencing SNA elicited by cardiac mechanoreceptor stimulation.

The calpain inhibitor, A-705253, corrects penile nitrergic nerve dysfunction in diabetic mice

Calpains, a superfamily of Ca(2+)-activated proteases, are associated with an array of physiological and pathological events, including susceptibility to diabetes. Recently, increased calpain activity has been linked to reduced endothelium-derived nitric oxide-mediated vasodilatation in diabetes. However, a similar mechanism for neuronal-derived nitric oxide has not been examined. Thus, the aim was to investigate effects of the calpain inhibitor A-705253, N-(1-benzyl-2-carbamoyl-2-oxoethyl)-2-[E-2-(4-diethyl-aminomethylphenyl)ethen-1-yl]benzamide, on nitrergic neurovascular function in diabetic mice. Diabetes was induced by streptozotocin; duration was 6 weeks. Intervention A-705253 treatment (30 mg/kg/day) was given for 2 weeks following 4 weeks of untreated diabetes. After 6 weeks of diabetes, corpus cavernosa were isolated in organ baths for measurement of agonist- and electrical stimulation-evoked smooth muscle tensions. Adrenergic nerve- and phenylephrine-mediated contractions were not altered by diabetes or calpain inhibition. In contrast, maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 29% reduced by diabetes (P<0.001). This neurological deficit was 66% corrected by A-705253 treatment (P<0.05). Maximum nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was attenuated approximately 39% by diabetes (P<0.01). Similarly, maximum endothelium-independent relaxation to the nitric oxide donor, sodium nitroprusside, was blunted approximately 23% by diabetes (P<0.001). A-705253 treatment partially improved endothelium-dependent relaxation to acetylcholine but had no effect on the deficit in response to nitroprusside. The data suggest that calpain contributes to the aetiology of diabetic nitrergic autonomic neuropathy and endothelial dysfunction, which may provide a novel therapeutic target for neurovascular complications.

Novel mechanism for impaired nitrergic relaxation in achalasia

New insights into the pathogenesis of achalasia indicate that incubation with serum from patients with achalasia leads to altered neurochemical coding of the myenteric plexus and impairs the nitrergic response to nerve stimulation

Serum from achalasia patients alters neurochemical coding in the myenteric plexus and nitric oxide mediated motor response in normal human fundus

BACKGROUND AND AIMS

Achalasia is a disease of unknown aetiology. An immune mechanism has been suggested on the basis of previous morphological observations. The objective of this study was to test whether the serum of achalasia patients could reproduce the phenotype and functional changes that occur with disease progression in an ex vivo human model.

METHODS

Specimens of normal human fundus were maintained in culture in the presence of serum from patients with achalasia, gastro-oesophageal reflux disease (GORD), or healthy subjects (controls). Immunohistochemical detection of choline acetyltransferase (ChAT), neurone specific enolase (NSE), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), and substance P was carried out in whole mounts of gastric fundus myenteric plexus. In addition, the effects of achalasia serum on electrical field stimulation (EFS) induced contractions were measured in circular muscle preparations.

RESULTS

Serum from achalasia patients did not affect the number of myenteric neurones. Tissues incubated with serum from achalasia patients showed a decrease in the proportion of NOS (-26% of NSE positive neurones; p=0.016) and VIP (-54%; p=0.09) neurones, and a concomitant increase in ChAT neurones (+16%; p<0.001) compared with controls. In contrast, GORD serum did not modify the phenotype of myenteric neurones. Area under the curve of EFS induced relaxations (abolished by N-nitro-L-arginine methyl ester) was significantly decreased following incubation with serum from achalasia patients compared with controls (-7.6 (2.6) v -14.5 (5.0); p=0.036).

CONCLUSIONS

Serum from achalasia patients can induce phenotypic and functional changes which reproduce the characteristics of the disease. Further identification of putative seric factors and mechanisms involved could lead to the development of novel diagnostic and/or therapeutic strategies in achalasia.

Esophageal-gastric relaxation reflex in rat: dual control of peripheral nitrergic and cholinergic transmission

It has long been known that the esophageal distension produced by swallowing elicits a powerful proximal gastric relaxation. Gastroinhibitory control by the esophagus involves neural pathways from esophageal distension-sensitive neurons in the nucleus tractus solitarius centralis (cNTS) with connections to virtually all levels of the dorsal motor nucleus of the vagus (DMV). We have shown recently that cNTS responses are excitatory and primarily involve tyrosine hydroxylase-immunoreactive cells, whereas the DMV response involves both an alpha1 excitatory and an alpha2 inhibitory response. In the present study, using an esophageal balloon distension to evoke gastric relaxation (esophageal-gastric reflex, EGR), we investigated the peripheral pharmacological basis responsible for this reflex. Systemic administration of atropine methyl nitrate reduced the amplitude of the gastric relaxation to 52.0+/-4.4% of the original EGR, whereas NG-nitro-L-arginine methyl ester (L-NAME) reduced it to 26.3+/-7.2% of the original EGR. Concomitant administration of atropine methyl nitrate and L-NAME reduced the amplitude of the gastric relaxation to 4.0+/-2.5% of control. This reduction in the amplitude of induced EGR is quite comparable (4.3+/-2.6%) to that seen when the animal was pretreated with the nicotinic ganglionic blocker hexamethonium. In the presence of bethanechol, the amplitude of the esophageal distension-induced gastric relaxation was increased to 177.0+/-10.0% of control; administration of L-NAME reduced this amplitude to 19.9+/-9.5%. Our data provide a clear demonstration that the gastroinhibitory control by the esophagus is mediated via a dual vagal innervation consisting of inhibitory nitrergic and excitatory cholinergic transmission.

Biphasic neurogenic vasodilatation in the bovine intraocular long posterior ciliary artery: involvement of nitric oxide and an additional unidentified neurotransmitter

We have investigated the neurogenic factors inducing relaxation in the intraocular segment of the bovine long posterior ciliary artery. In precontracted vessels, electrical field stimulation (EFS, 0.5-128 Hz, 10 s trains) in the presence of guanethidine (30 microM) evoked biphasic relaxation: optimal relaxation for the first and second components occurred at 10 and 50 s, respectively. The first component, but not the second, was abolished by L-NAME (100 microM) or ODQ (3 microM). Relaxation to exogenous CGRP (0.1-300 nM) was inhibited by the CGRP antagonist, CGRP(8-37) (1-5 microM), but neither component of neurogenic relaxation was affected. Preincubation with the sensory nerve excitotoxin, capsaicin (1 microM), had no effect on either the first or second components of neurogenic relaxation. Substance P (0.1 nM-0.1 microM) induced relaxation, but rapid and complete desensitisation occurred within minutes. Neither desensitisation to substance P (0.1 microM) nor incubation with the NK(1) antagonist, L-733,060 (0.3 microM), had any effect on the first or second components of neurogenic relaxation.VIP (0.1 nM-0.3 microM) induced relaxation and this was followed by substantial desensitisation. Neither desensitisation to VIP (0.6 microM) nor treatment with the protease, alpha-chymotrypsin (10 U ml(-1)), had any effect on the first or second components of neurogenic relaxation. The results indicate that nitric oxide mediates the first component of neurogenic relaxation in the bovine intraocular ciliary artery. The neurotransmitter mediating the second component remains to be determined but is unlikely to be CGRP, substance P or VIP.

Influence of the selective neuronal NO synthase inhibitor ARL 17477 on nitrergic neurotransmission in porcine stomach

Selective neuronal NOS (nNOS) inhibitors have been developed for possible application in cerebral ischemia and neurodegenerative disorders. To investigate the degree of interference with peripheral nNOS, the influence of the selective nNOS inhibitor ARL 17477 was studied on electrically induced nitrergic relaxations in pig gastric fundus strips and on gastric fundic compliance in conscious pig. Circular muscle strips of porcine gastric fundus were electrically stimulated (10 s trains at 4 Hz, 0.1 ms and 40 V). ARL 17477 inhibited the electrically induced relaxations in a concentration-dependent way (3x10(-6) M-10(-4) M). The inhibitory effect of ARL 17477 developed more progressively than that of N(G)-nitro-L-arginine methyl ester (L-NAME; 3x10(-4) M). In conscious pigs, instrumented with a fundic cannula, L-NAME (20 mg/kg i.v.) significantly increased mean arterial blood pressure and decreased fundic compliance in the fasted state (71+/-13 ml/mm Hg versus 185+/-37 ml/mm Hg after saline; P<0.05). ARL 17477 (3 mg/kg, i.v.) did not influence blood pressure but influenced gastric fundic volume-pressure curves in a similar way as L-NAME. Plasma concentration analysis of ARL 17477 indicated a half-life of less than 30 min in pig. ARL 17477 thus inhibits the effect of nitrergic neurons in the pig gastric fundus in vitro, leading to inhibited gastric compliance in the conscious pig. The study indicates that selective nNOS inhibitors, applied for cerebral disorders, might also interfere with neuronal nitrergic regulation of gastrointestinal motility.

Nitric oxide and adult neurogenesis in health and disease

Adult neurogenesis may be functionally important as a mechanism of brain plasticity in physiological conditions and brain repair after injury. Nitric oxide (NO), a diffusible intracellular and intercellular messenger in the mammalian nervous system, has been shown to affect adult neurogenesis in different ways. In the normal brain, NO, synthesized by the neuronal isoform of NO synthase in nitrergic neurons, is a negative regulator of precursor cell proliferation. However, after brain damage, NO overproduction in different neural and nonneural cell types promotes neurogenesis. Recently reported results on the effects of NO on new neuron generation in the adult brain are reviewed, with special attention to the proposed mechanisms of action and functional consequences in health and disease.

Enhanced responsiveness to nitric oxide, nitroxyl anions, and nitrergic transmitter by 3-(5′-hydroxymethyl-2′-furyl)-1-benzyl indazole in the rat anococcygeus muscle

The effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) on responses to sodium nitroprusside (SNP), S-nitroso-N-acetyl-penicillamine (SNAP), the nitroxyl anion donor Angeli's salt, and nitrergic nerve stimulation, as well as the release of NO from nitrergic nerves, were studied in the rat isolated anococcygeus muscle. YC-1 (1-100 microM) produced concentration-dependent relaxations in contracted muscles, which were partially but significantly reduced by the inhibitor of soluble guanylate cyclase (sGC), 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 1 and 10 microM). At a concentration that did not affect tissue tension, YC-1 (1 microM) significantly enhanced relaxations to SNP, SNAP, and Angeli's salt but did not affect relaxations to papaverine (10 microM). Nitrergic relaxations elicited by short periods (1 Hz for 10 s, 15 V) and long periods of EFS (5 Hz for 5 min, 15 V) were also enhanced by YC-1. YC-1 (100 microM), in an l-NAME and tetrodotoxin-insensitive manner, also increased the amount of NO detected in the organ bath media after the tissue was field stimulated (5 Hz for 5 min), which may have resulted from the electrolytic degradation of YC-1, as this effect was also seen in the absence of tissue. In summary, YC-1 enhanced relaxations to donors of NO, Angeli's salt, and nitrergic nerve stimulation in the rat anococcygeus muscle; however, the enhanced release of NO by YC-1 following nitrergic nerve stimulation was not a tissue-dependent effect.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Sulfur-containing amino acids block stretch-dependent K+ channels and nitrergic responses in the murine colon

1. Efforts to determine the role of stretch-dependent K(+) (SDK) channels in enteric inhibitory neural responses in gastrointestinal muscles are difficult due to a lack of blocking drugs for SDK channels. 2. SDK channels are blocked by sulfur-containing amino acids. These compounds reduced the open probability of SDK channels in on and off-cell patches of murine colonic myocytes. L-Methionine was the most selective and had little or no effect on other known K(+) conductances in colonic myocytes. 3. Application of L-cysteine, L-methionine or DL-homocysteine depolarized intact muscles and enhanced spontaneous contractions. D-Stereoisomers of these amino acids were less effective than L-stereoisomers. 4. Pretreatment of muscles with tetrodotoxin, N(W)-nitro-L-arginine or 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one reduced the depolarization responses to these compounds, suggesting that spontaneous neural activity and release of NO tonically activates SDK channels. 5. Nitrergic responses to nerve stimulation were reduced by sulfur-containing amino acids. 6. These data suggest that nitrergic inhibitory junction potentials are mediated, in part, by activation of SDK channels in murine colonic muscles.

Nitric oxide and penile erectile function

The discovery of nitric oxide (NO) as an intercellular messenger or neurotransmitter opened a new era for identifying the important mechanisms underlying physiological and pathophysiological events in autonomically innervated organs and tissues; it also provided the way for development of new therapeutics based on a novel concept of molecule and cell interaction. Endothelium-derived relaxing factor (EDRF) discovered by Furchgott and Zawadzki has been proved to be NO, a labile gaseous molecule, that modulates vascular tone, platelet aggregation and adhesion, and vascular smooth muscle proliferation. Later, NO was determined to act as a non-adrenergic, non-cholinergic (NANC) neurotransmitter of postganglionic parasympathetic nerve fibers, innervating a variety of smooth muscles including the penile corpus cavernosum (CC). The nerve is called "nitrergic" or "nitroxidergic". Although CC sinusoidal endothelial cells also produce and liberate NO in response to chemical and possibly physical stimuli, roles of neurogenic NO in penile erection appear to be more attractive and convincing. NO is formed from L-arginine via catalysis by NO synthase (NOS) isoforms, neuronal (nNOS), endothelial (eNOS), and inducible NOS. NO from nerves and possibly endothelia plays a crucial role in initiating and maintaining intracavernous pressure increase, penile vasodilatation, and penile erection that are dependent on cyclic GMP synthesized with activation of soluble guanylyl cyclase by NO in smooth muscle cells. Erectile dysfunction (ED) is caused by a variety of pathogenic factors, particularly impaired formation and action of NO. Thus, replenishment of this molecule or intracellular cyclic GMP is expected so far to be the most promising therapeutic measures for patients with ED. This article includes recent advances in research on physiological roles and pathophysiological implications of NO in penile erection and on novel therapy for ED in reference to NO.

Different modulation of spontaneous activities by nitrergic inhibitory nerves between ileum and jejunum in W/Wv mutant mice

We compared the spontaneous electrical and mechanical activities between the jejunum and ileum in the W/Wv mutant mouse, where ICC in the myenteric region (ICC-MY) are deficient. Electrical slow waves (SWs) superimposed with spike potentials, and synchronous circular and longitudinal muscle mechanical activities at a regular rhythm under approximately 1 cm H2O were recorded in the jejunum and ileum of wild-type mice. However, in the jejunum and ileum of W/Wv mice, irregular electrical and mechanical activities without discernable SWs were recorded. N-nitro-L-arginine methyl ester (L-NAME) significantly decreased the mean interval of longitudinal muscle contractions from 4.43+/-3.39 to 2.50+/-1.23 s in the ileum of W/W(V) mice. L-NAME also significantly decreased mean coefficient of variance (decreased irregularity) in the intervals from 2.59+/-0.84 to 0.48+/-0.46 in the ileum. Tetrodotoxin also significantly decreased mean interval and coefficient of variance in the ileum. Neither L-NAME nor tetrodotoxin affected contractile activity in the jejunum. These results suggest that enteric nitrergic nerves in the ileum, but not the jejunum, mediate a steady-state inhibition of myogenic activity in W/Wv mice.

The origin of extrinsic nitrergic axons supplying the human eye

Nitrergic nerve fibres of intrinsic and extrinsic origin constitute an important component of the autonomic innervation in the human eye. The intrinsic source of nitrergic nerves are the ganglion cells in choroid and ciliary muscle. In order to obtain more information on the origin of extrinsic nitrergic nerves in the human eye, we obtained superior cervical, ciliary, pterygopalatine and trigeminal ganglia from six human donors, and stained them for neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D). In the superior cervical ganglia, nNOS/NADPH-D-positive varicose axons were observed whereas perikarya were consistently negative. Fewer than 1% of perikarya in the ciliary ganglia were labelled for nNOS/NADPH-D. The diameter of nNOS/NADPH-D-positive ciliary perikarya was between 8 and 10 microm, which was markedly smaller than the diameter of the vast majority of negative perikarya in the ciliary ganglion. More than 70% of perikarya in the pterygopalatine ganglia were intensely labelled for both nNOS and NADPH-D. In trigeminal ganglia, 18% of perikarya were nNOS/NADPH-D-positive. The average diameter of trigeminal nNOS/NADPH-D perikarya was between 25 and 45 microm. Pterygopalatine and trigeminal ganglia are the most likely sources for extrinsic nerve fibres to the human eye.

Nitric oxide control of large veins in the toad Bufo marinus

This study examined the nitric oxide (NO) control of the vascular smooth muscle of the ventral abdominal vein and vena cava of the toad, Bufo marinus, by using anatomical and physiological approaches. Nicotinamide adenine di-nucleotide phosphate-diaphorase histochemistry and immunohistochemistry using endothelial nitric oxide synthase (NOS) and neural NOS antibodies produced no evidence for endothelial NOS in the veins, but, neural NOS-immunoreactive perivascular nerves were present. Acetylcholine (10(-5) M) caused a vasodilation in both veins that was endothelium-independent, and which was blocked by the soluble guanylyl cyclase inhibitor, ODQ (10(-5) M). The NOS inhibitors, L-NNA (10(-4) M) and L-NAME (10(-4) M), did not significantly reduce the vasodilatory effect of acetylcholine in the veins; this suggested that the vasodilation was not due to NO. However, in the presence of phenoxybenzamine (10(-7)-10(-8) M), L-NNA significantly reduced the vasodilatory effect of acetylcholine in the veins. This unusual response is due to phenoxybenzamine partially inactivating the muscarinic receptor pool in the veins. In addition, the neural NOS inhibitor, vinyl-L-NIO (10(-5) M), significantly reduced the acetylcholine-mediated vasodilation in the presence of phenoxybenzamine. The results show that in toad veins, nitrergic nerves rather than an endothelial NO system are involved in NO-mediated vasodilation.

A comparative study of sildenafil, NCX-911 and BAY41-2272 on the anococcygeus muscle of diabetic rats

We compared the effects of a nitric oxide (NO)-releasing sildenafil (NCX-911), NO-independent soluble guanylate cyclase activator (BAY41-2272) and sildenafil on the anococcygeus muscle from streptozotocin-induced 16-weeks diabetic rats. NCX-911, BAY41-2272 and sildenafil reduced the phenylephrine-induced tone in the control group (EC50=1088.8+/-165.0, 151.6+/-9.3 and 827.1+/-167.3 nM, respectively). The potencies of NCX-911 and BAY41-2272 were not altered, but that of sildenafil was significantly reduced in the diabetic group. EC50 values for NCX-911, BAY41-2272 and sildenafil in the diabetic group were 1765.9+/-303.5, 209.7+/-27.3 and 2842.2+/-640.3 nM, respectively (P<0.05 for sildenafil). Nitrergic relaxation responses were significantly decreased in the diabetic group. The remaining nitrergic relaxation responses were potentiated by BAY41-2272 but not by sildenafil or NCX-911. These results confirm that endogenous NO derived from nitrergic nerves is significantly decreased in diabetes, and suggest that NO-releasing PDE5 inhibitors and NO-independent soluble guanylate cyclase activators could be more useful than PDE5 inhibitors in the treatment of ED in long-term diabetes.

Changes in nitrergic innervation of defunctionalized rat colon after diversion colostomy

After 45 days of complete diversion colostomy in male Wistar rats, morphometry of soma and nuclei of NADPH diaphorase positive cells of the myenteric plexus was evaluated. There was a significant (P < 0.0001) diminution in the area, perimeter and volume-weighted mean volume of soma and nuclei of nitrergic myenteric neurones in the defunctionalized colon. In addition, there was a significant reduction in the neuronal density of the myenteric neurones, and increased distance between the ganglia. In addition, there was myenteric glial atrophy. Atrophy of colonic myenteric neurones was accompanied by significant reduction (P < 0.001) in the volume fraction of the muscularis externa, the prime targets of these neurones. The disturbances in the microecology of the colon may jeopardize the finely orchestrated functioning of the components of the Enteric nervous system (ENS) leading to colonic dysfunction. Our observations, by extrapolation, may explain the bowel dysmotility in humans after restoration of colonic continuity after colostomy.

Muscarinic modulation of nitrergic neurotransmission in guinea-pig gastric fundus

Muscarinic receptor activation by (4-Hydroxy-2-butynyl)-1-trimethylammonium-m-chlorocarbanilate chloride (McN-A-343) was investigated both on NADPH-d staining and on electrically induced responses in guinea-pig gastric fundus. McN-A-343 (10 micromol L(-1)) significantly increased the optical density of NADPH-d positive neurones, while blockade of nitric oxide synthase with N(omega)-nitro-L-arginine (L-NA) decreased it, suggesting facilitation of nitric oxide (NO) production. Electrical field stimulation (EFS; 2 Hz, 0.2 ms, supramaximal current intensity, 10 s train duration) elicited on-contraction followed by off-relaxation in the circular muscle strips. McN-A-343 (10 micromol L(-1)) transformed the EFS-evoked response from on-contraction into on-relaxation, which was neurogenic, tetrodotoxin-sensitive and hexamethonium-resistant. L-NA partly reduced the EFS-evoked relaxation, revealing two components: a nitrergic and a non-nitrergic one. The effect of McN-A-343 on the amplitude of the EFS-evoked relaxation was not changed by the M(3) receptor antagonist para-fluoro-hexahydro-sila-difenidol hydrochloride, but was significantly enhanced by M(1) receptor blockade with telenzepine. In the presence of telenzepine, the L-NA-dependent nitrergic component of the EFS-induced relaxation predominates. We suggest that cholinergic receptor activation has a dual effect on nitrergic neurotransmission: (i) stimulation of NOS by muscarinic receptor(s) different from M(1) and M(3) subtype, (ii) prejunctional inhibition of NO-mediated relaxation via M(1) receptors. In addition, M(1) receptors may facilitate the non-nitrergic relaxation.

Role of intrinsic nitrergic neurones on vagally mediated striated muscle contractions in the hamster oesophagus

Oesophageal peristalsis is controlled by vagal motor neurones, and intrinsic neurones have been identified in the striated muscle oesophagus. However, the effect(s) of intrinsic neurones on vagally mediated contractions of oesophageal striated muscles has not been defined. The present study was designed to investigate the role of intrinsic neurones on vagally evoked contractions of oesophageal striated muscles, using hamster oesophageal strips maintained in an organ bath. Stimulation (30 micros, 20 V) of the vagus nerve trunk produced twitch contractions. Piperine inhibited vagally evoked contractions, while capsaicin and NG-nitro-L-arginine methyl ester (L-NAME) abolished the inhibitory effect of piperine. The effect of L-NAME was reversed by subsequent addition of L-arginine, but not by D-arginine. L-NAME did not have any effect on the vagally mediated contractions and presumed 3H-ACh release. NONOate, a nitric oxide donor, and dibutyryl cyclic GMP inhibited twitch contractions. Inhibition of vagally evoked contractions by piperine and NONOate was fully reversed by ODQ, an inhibitor of guanylate cyclase. Immunohistochemical staining showed immunoreactivity for nitric oxide synthase (NOS) in nerve cell bodies and fibres in the myenteric plexus and the presence of choline acetyltransferase and NOS in the motor endplates. Only a few NOS-immunoreactive portions in the myenteric plexus showed vanilloid receptor 1 (VR1) immunoreactivity. Our results suggest that there is a local neural reflex that involves capsaicin-sensitive neurones, nitrergic myenteric neurones and vagal motor neurones.

The GABAB receptor and recognition memory: possible modulation of its behavioral effects by the nitrergic system

Functional activation of the GABA(B) receptor inhibits learning and memory processes, though discrepant findings, in this context, have also been reported. The present study was designed to investigate the role of the GABA(B) receptor on recognition memory in the rat. For this purpose, the effects induced by the GABA(B) agonist baclofen and the GABA(B) antagonist P-(3-aminopropyl)-P-diethoxymethylphosphinic acid (CGP 35348) on memory were assessed by using the object-recognition task. In addition, the possible involvement of the nitrergic system on GABA(B) receptor's effects was also evaluated by using the same behavioral procedure. This is a working-memory paradigm based on the differential exploration of a new and familiar object. In a first dose-response study, baclofen (0.5, 2, and 4 mg/kg, i.p.), dose-dependently impaired animals' performance in this task, suggesting a modulation of acquisition and storage of information. CGP 35348 (100 and 300 mg/kg, i.p.), counteracted these baclofen-induced performance deficits. The nitric oxide donor molsidomine, at the dose of 4 but not 2 mg/kg, i.p, successfully antagonized the deficits on cognition induced by the highest dose of baclofen (4 mg/kg). These results indicate a) that the GABA(B) receptor is involved in recognition memory and b) that an NO component modulates the effects of the GABA(B) receptor on learning and memory.

Calyculin-A inhibits nitrergic relaxations of the mouse anococcygeus

The aim was to determine whether blockade of store-operated Ca(2+) entry, or inhibition of Ca(2+) sensitisation, is the predominant mechanism by which neuronally released nitric oxide mediates relaxation of the mouse anococcygeus. Nitrergic relaxations to field stimulation (10 Hz, 10 s trains) were unaffected by the sarcoplasmic reticulum Ca(2+) ATPase blocking agent thapsigargin (100 nM), known to prevent nitric-oxide-induced inhibition of store-operated Ca(2+) entry. Conversely, the myosin phosphatase inhibitor calyculin-A (1 microM) caused almost complete abolition of nitrergic relaxations. The results provide evidence that inhibition of Ca(2+) sensitisation is the major cellular mechanism underlying nitrergic relaxation of the mouse anococcygeus.

Role of copper in the relaxant action of S-nitrosothiols in the rat anococcygeus muscle

1. The effects of copper chelators were investigated on the relaxant actions of the S-nitrosothiols S-nitrosoglutathione (GSNO) and S-nitroso-N-acetyl-d,l-penicillamine (SNAP), the non-S-nitrosothiol nitric oxide (NO) donor sodium nitroprusside (SNP), free radical NO (NO.) and the nitrergic neurotransmitter in rat isolated anococcygeus muscle. 2. Cumulative additions of GSNO (0.01-100 micro mol/L), SNAP (0.001-10 micro mol/L), SNP (0.001-1 micro mol/L) and NO. (0.5-5 micro mol/L) and electrical field stimulation (EFS; 1-5 Hz, 10 s) of nitrergic nerves in preparations precontracted with guanethidine (10-30 micro mol/L) and clonidine (0.01-0.3 micro mol/L) produced concentration-dependent relaxations. 3. The Cu[I] chelator neocuproine (10-30 micro mol/L) produced concentration-dependent inhibitions of the relaxations to GSNO and SNAP. At 30 micro mol/L, neocuprinone had no effect on relaxations to SNP (0.001-1 micro mol/L), NO. (0.5-5 micro mol/L) or EFS (1-5 Hz, 10 s). 4. The Cu[II] chelator cuprizone (30 micro mol/L) slightly and significantly enhanced relaxations to GSNO and NO., but had no effect on relaxations to SNAP, SNP or EFS. 5. In conclusion, the results indicate that Cu[I], but not Cu[II], may be involved in the relaxant actions of GSNO and SNAP in the rat anococcygeus muscle.

Acute intracerebroventricular insulin microinjection after nitric oxide synthase inhibition of renal sodium handling in rats

The role of the central nervous system (CNS) in the control of hydrosaline homeostasis has been strikingly demonstrated by several studies. Recent and growing evidence suggests that insulin or a nonapeptide-derived from the C-terminus of the insulin beta-chain may influence many brain functions. However, there is little information on the insulin-activated neural pathways regulating urinary sodium excretion. Also, we examined the influence of nitric oxide synthase activity by chronic oral administration of N(omega)-nitro-l-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, after previous i.c.v. administration of insulin to unanesthetized, unrestrained rats that were randomly assigned to one of seven separated groups: (a) i.c.v. 0.15 M NaCl-injected (n = 11) and i.c.v. 126 ng (n = 11) insulin-injected rats; (b) i.c.v. insulin-injected in systemic L-NAME-treated (n = 10) and vehicle-treated insulin-injected rats (n = 10); and (c) subcutaneously (SC) insulin-injected rats (n = 5). We showed that centrally administered insulin produced increase in the urinary output of sodium (from 0.15 M NaCl: 855.6 +/- 85.1 Delta%.min(-1) to 126 ng insulin: 2055 +/- 310.6 Delta%.min(-1)) and potassium (126 ng: from 0.15 M NaCl: 460.4 +/- 100 Delta%.min(-1) to 126 ng insulin: 669 +/- 60.8 Delta%.min(-1)). The urinary sodium excretion response to i.c.v. 126 ng insulin microinjection was significantly abolished by previous systemic treatment of animals with 15 mg/kg/day L-NAME (from vehicle + 126 ng insulin: 1935 +/- 258.3 Delta%. min(-1) to L-NAME + 126 ng insulin: 582.3 +/- 69.6 Delta%. min(-1)). In addition, we showed that insulin-induced natriuresis occurred by increasing post-proximal tubule sodium rejection (FEPP(Na)), despite an unchanged glomerular filtration rate (C(Cr)). The current data suggests the novel concept that CNS NO-dependent neural pathways may play an instrumental role on efferent insulin-sensitive nerve activity from periventricular region. Speculatively, it seems interesting to suggest that perhaps one of the efferent signals triggered by insulin in the CNS may be nitrergic in nature, and that defects in this efferent signal could result in insulin central resistance, inability of renal tubules to handle the hydro electrolyte balance and hypertension.

Characterization of the rat isolated retractor penis muscle as a model for the study of nitrergic transmission

INTRODUCTION

The anococcygeus and retractor penis muscles are part of the erectile machinery in male rodents. The rat anococcygeus muscle is a widely used smooth muscle preparation for the study of the effects of test substances on adrenergic, nitrergic, and cholinergic transmission. There is, however, little information available on the process of autonomic transmission in the rat retractor penis muscle, although its autonomic innervation has generally been assumed to be similar to that of the anococcygeus muscle because of the contiguous nature of the two muscles. The present study investigated the involvement of nitrergic transmission in mediating relaxant responses of the rat retractor penis muscle to electrical field stimulation.

METHODS

The retractor penis muscle was isolated from Sprague-Dawley rats and mounted in Krebs solution. Phentolamine (5 microM) was added to the bath to block the adrenergic responses of the muscle, which was then precontracted with carbachol (10 microM).

RESULTS

Electrical field stimulation (20-30 V, 1 ms pulse width, at 0.5-20 Hz for 10 s) of the carbachol precontracted muscle elicited frequency-dependent relaxant responses (0.9-68%). Tetrodotoxin (1 microM), N(G)-nitro-L-arginine (L-NOARG) (50 microM), N(G)-nitro-L-arginine methylester (L-NAME) (100 microM), and haemoglobin (100 microM) inhibited these relaxant responses by 99.3%, 93.9%, 86.9%, and 77.5%, respectively. L-Arginine (250 microM) (but not its D-isomer) reversed the blockade produced by L-NOARG (72.7%) and L-NAME (81.5%).

DISCUSSION

Our results provide clear evidence that the inhibitory (relaxant) responses of the rat retractor penis muscle to electrical field stimulation are mediated by nitric oxide involving the L-arginine-nitric oxide synthase-nitric oxide pathway. The rat retractor penis muscle is a versatile preparation that can replace the cumbersome preparations from the pig, ox, and horse, hitherto used as pharmacological models for the study of the retractor penis muscle.

Characterization of the non-nitrergic NANC relaxation responses in the rabbit vaginal wall

Electrical field stimulation (EFS)-induced non-adrenergic non-cholinergic (NANC) relaxation responses in the rabbit vaginal wall were investigated. These NANC responses were partially inhibited with the nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME; 500 microM), N(G)-nitro-L-arginine (300 microM) or N-iminoethyl-L-ornithine (500 microM) or the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM). Application of L-NAME and ODQ concomitantly did not increase the degree of inhibition. L-NAME or ODQ were observed to be more effective at low frequencies. The resistant part of the responses was more pronounced at higher frequencies and was completely inhibited by tetrodotoxin (1 microM). Exogenous application of the peptides vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27 and PACAP-38), peptide histidine methionine (PHM), peptide histidine valine (PHV), helospectin-I or -II induced a relaxation response. Calcitonin gene-related peptide or substance P did not cause any relaxation. The peptidase alpha-chymotrypsin (type II; 2 units ml(-1)) did not affect non-nitrergic NANC responses, although it did inhibit relaxation responses elicited by exogenous VIP, PACAP-27, PACAP-38, PHM, PHV, helospectin-I or -II. K(+) channel inhibitors apamin (1 microM) or charybdotoxin (100 nM) when used alone or in conjunction did not affect non-nitrergic NANC responses. The non-nitrergic NANC responses were not associated with any increase in intracellular cyclic adenosine-3', 5'-monophosphate (cyclic AMP) or cyclic guanosine-3', 5'-monophosphate (cyclic GMP) concentrations. The peptide-induced relaxations were all associated with increases in cyclic AMP concentrations. These results suggest that a neuronal factor elicits non-nitrergic NANC responses in the rabbit vaginal wall. The identity of this factor remains to be established.

Sympathetic modulation of nitrergic neurogenic vasodilation in cerebral arteries

The presence of close apposition between the adrenergic and the non-adrenergic or nitrergic nerve terminals in large cerebral arteries in several species is well documented. The axo-axonal distance between these different types of nerve terminals is substantially closer than the synaptic distance between the adventitial nerve terminals and the outermost layer of smooth muscle in the media. This feature suggests that a functional axo-axonal interaction between nerve terminals is more likely to occur than that between the nerve and muscle. Thus, transmitters released from one nerve terminal may modulate release of transmitters from the neighboring nerve terminals, resulting in a neurogenic response. We have reported that nicotine-induced nitric oxide (NO)-mediated neurogenic vasodilation is dependent on intact sympathetic innervation in porcine and cat cerebral arteries. Evidence also has been presented to indicate that nicotine acts on alpha7-nicotinic receptors located on sympathetic nerve terminals, resulting in release of norepinephrine which then diffuses to act on beta2-adrenoceptos located on the neighboring nitrergic nerve terminals to release NO and therefore vasodilation. The predominant facilitatory effect of beta2-adrenoceptors in releasing NO is compromised by presynaptic alpha2-adrenoceptors located on the same nerves. Activation of cerebral sympathetic nerves may cause NO-mediated dilation in large cerebral arteries at the base of the brain.

Neurogenic cerebral vasodilation mediated by nitric oxide

In cerebral arteries isolated from most of mammals, nerve stimulation produces relaxations in contrast to contractions in peripheral arteries. The relaxant mechanism is found to be non-adrenergic and non-cholinergic, but the neurotransmitter is not clarified until recently. Based on several functional and histological studies with isolated cerebral arteries, nitric oxide (NO) is now considered to be a neurotransmitter of the vasodilator nerve and the nerve has been called a nitroxidergic (nitrergic) nerve. Upon neural excitation, calcium influxed through N-type Ca2+ channels activates neuronal NO synthase, and then NO is produced by the enzyme from L-arginine. The released NO activates soluble guanylate cyclase in smooth muscle cells, resulting in relaxation with a cyclic GMP-dependent mechanism. The functional role and neuronal pathway have also been investigated in anesthetized dogs and Japanese monkeys. The nitroxidergic (nitrergic) nerves innervating the circulus arteriosus, including the anterior and middle cerebral and posterior communicating arteries, are found to be postganglionic nerves originated from the ipsilateral pterygopalatine ganglion and tonically dilate cerebral arteries in the resting condition. Our findings suggest that the nitroxidergic (nitrergic) nerve plays a physiologically important role to maintain a steady blood supply to the brain.

Nitrergic relaxation in urethral smooth muscle: involvement of potassium channels and alternative redox forms of NO

We examined the contribution of K+ channels to the relaxation responses induced by different redox forms of nitric oxide (NO., NO- and NO+) in comparison with those evoked by electrical field stimulation (EFS) of nitrergic nerves in the sheep urethra. K+ channel blockers with different selectivity profile were used. Sodium nitroprusside (SNP) and different S-nitrosothiols were used as NO+ donors, Angeli's salt as an NO- donor and nitroglycerin (GTN) was chosen as a representative compound known to require metabolic activation in the target tissue. Pure NO gas was used to prepare NO. solutions. Relaxation evoked by EFS of nitrergic nerves or by exogenous NO was not inhibited by any of the K+ channel blockers, but was enhanced by 4-aminopyridine [inhibitor of voltage-dependent K+ (KV) channels]. This suggests that, whereas K+ channel activation and hyperpolarization of the postsynaptic membrane do not contribute to relaxation, prejunctional modulation of the nitrergic neurotransmission by Kv channels may be relevant. Relaxation induced by NO+ or NO- donors was not affected by K+ channel blockade with the following exceptions: glybenclamide, a blocker of ATP-sensitive K+ channels (KATP), enhanced responses to SNP and Angeli's salt, 4-aminopyridine inhibited relaxation evoked by Angeli's salt and GTN, and charybdotoxin, a blocker of large-conductance, Ca2+-activated K+ channels (BKCa) inhibited those induced by the S-nitrosothiol S-nitrosoglutathione. These results do not suggest the existence of a general mechanism of action on K+ channels for compounds releasing either NO+ or NO- in the sheep urethra. None of the K+ channel blockers affected relaxation induced by the membrane-permeable analogue of cGMP, 8-bromo-cGMP. However, the fact that the addition of the phosphodiesterase inhibitor zaprinast (0.1 mM) enhanced the relaxation to Angeli's salt, while preventing the inhibition induced by 4-aminopyridine, suggests that involvement of guanylate cyclase activation in the action of NO donors on K+ channels can not be excluded. Accordingly, the guanylate cyclase inhibitors 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ, 10 microM) and 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028, 10 microM) almost abolished relaxations to EFS and Angeli's salt. In contrast, ODQ only moderately inhibited relaxations to NO.. In addition, the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO) effectively inhibited responses to NO. whilst not affecting those to EFS or NO-, suggesting a close similarity between the nitrergic transmitter and nitroxyl ion. We conclude that nitrergic relaxation induced either by the endogenous transmitter or by exogenous NO donors in the ovine urethra is not mediated by postsynaptic alterations in the K+ conductance; only a prejunctional modulation through Kv channels seems to be significant. In addition, the production and/or release of alternative redox forms of NO, such as NO-, may be involved in neurotransmission processes in the urethra.

Effects of some divalent cations on nitrergic relaxations in the mouse corpus cavernosum

Acute effects of some divalent cations (Cd2+, Ni2+, Co2+, Zn2+, Mn2+ and Sn2+) were investigated on neurogenic and endothelium-dependent relaxations in the isolated mouse corpus cavernosum. Neither neurogenic nor endothelium-dependent relaxation was affected by cations at the concentrations used (up to 100 microM), except Cd2+. Although Cd2+ (20 and 40 microM) did not cause any significant alteration in the acetylcholine- (ACh) or sodium nitroprusside- (SNP) induced relaxation, it inhibited electrical field stimulation- (EFS) produced relaxation significantly. Zn2+ and selenium could not reverse this inhibitory action. Cd2+ did block the EFS-evoked guanethidine-sensitive contraction in the presence of N(G)-nitro-L-arginine. Elevation of external Ca2+ content significantly reduced the inhibitions due to Cd2+ on the EFS-induced relaxation and on the EFS-evoked guanethidine-sensitive contraction. In the Ca2+-omitted medium, EFS-induced relaxation disappeared, while acetylcholine-elicited relaxation resisted. Verapamil was ineffective on the relaxation produced by EFS or acetylcholine. However, it significantly diminished phenylephrine-induced contractions. These findings suggest that unlike other cations at the concentrations used in the present study, Cd2+ may have an effect on an external Ca2+-dependent mechanism at the neuronal level, and this effect may be responsible for its acute inhibitory action on the neurogenic relaxation in the mouse corpus cavernosum.