Possible origins and distribution of immunoreactive nitric oxide synthase-containing nerve fibers in cerebral arteries

Neuronal nitric oxide synthase is localized in extrinsic nerves regulating perireceptor processes in the chemosensory nasal mucosae of rats and humans

Nitric oxide synthase is the enzyme responsible for the production of the free radical gas nitric oxide, which has been implicated as an intercellular messenger in both the central and peripheral nervous systems. Immunoreactivity for nitric oxide synthase is often coincident with the histochemical demonstration of NADPH-diaphorase activity. Using an antibody to the neuronal form of nitric oxide synthase and a histochemical technique for NADPH-diaphorase, we have compared the localization of immunoreactivity and histochemical reaction product in the nasal mucosae of rats and humans. Immunoreactivity for neuronal nitric oxide synthase was localized in the extrinsic perivascular innervation of the olfactory and vomeronasal mucosae of rats and in the olfactory mucosa of humans. In the rat nasal mucosa, specific groups of glands were also innervated; the density of nitrinergic innervation varied among them, with vomeronasal glands and posterior glands of the nasal septum being the most densely innervated. In contrast, NADPH-diaphorase activity was present in olfactory, vomeronasal, and septal organ receptor neurons in rats and in olfactory receptor neurons in humans as well as in numerous nerve fibers, glands, and surface epithelial cells. The localization of neuronal nitric oxide synthase in extrinsic perivascular and periglandular nerve fibers suggests that nitric oxide may modulate the perireceptor processes of local blood flow and mucus secretion that influence the access to and clearance of chemical stimuli from rat and human chemosensory mucosae.

Blockade of nitric oxide synthesis inhibits hippocampal hyperemia in kainic acid-induced seizures

We investigated whether the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) affects the cerebrovascular changes occurring in seizures induced by kainic acid (KA) in awake, spontaneously breathing rats. Blood flow and tissue PO2 and PCO2 were continuously and simultaneously measured by mass spectrometry from a cannula chronically implanted into the dorsal hippocampus, L-NAME (20 mg/kg; n = 8) or saline (n = 9) was administered i.p. 30 min prior to i.p. KA (10 mg/kg) injection. L-NAME significantly decreased hippocampal blood flow and PO2 and increased mean arterial blood pressure (MABP). In L-NAME-treated rats, seizure activity occurred about 10 min sooner than in control rats, and status epilepticus was inevitably followed by a flat electroencephalogram and sudden death. In contrast, control rats survival KA-induced seizures. Hippocampal blood flow was significantly less elevated during the seizures in L-NAME-treated rats than in control rats (maximal levels, 170 and 450%, respectively, of baseline values), though MABP remained significantly higher. Hippocampal PO2 was significantly decreased at all times after KA injection in L-NAME-treated rats, whereas it remained at or above normoxic levels in control rats. The present results show that L-NAME markedly attenuates the hippocampal blood flow and tissue PO2 changes in response to enhanced metabolic activity due to limbic seizures and suggest that NO is of major importance in cerebral blood flow control during KA-induced seizures.

Projections of nitric oxide synthase-containing fibers from the sphenopalatine ganglion to cerebral arteries in the rat

The origin and distribution of cerebral perivascular nerves containing nitric oxide, a short-acting messenger or neurotransmitter, have been studied in the rat by histochemistry for reduced nicotinamide adenine dinucleotide phosphate-diaphorase activity, a specific marker for neuronal nitric oxide synthase. Positively stained nerve fibers were distributed throughout the major vessels of the cerebral arteries, though the fiber density was higher in the anterior circulation, including the circle of Willis, than in the posterior arteries. Examination using axonal transport methods indicated that nitric oxide-containing neurons in the sphenopalatine ganglion innervate the cerebral arteries bilaterally. Nitric oxide synthase in these ganglionic cells often co-existed with vasoactive intestinal polypeptide. The anatomical information obtained is discussed in terms of non-adrenergic, non-cholinergic neuronal transmission in the cerebral arteries.

Neuroprotective efficacy of N omega-nitro-L-arginine after focal cerebral ischemia in the mouse and inhibition of cortical nitric oxide synthase

The neuroprotective effects of various doses of N omega-nitro-L-arginine have been correlated with the degree of N omega-nitro-L-arginine-induced inhibition of cortical nitric oxide synthase activity measured ex vivo. Following focal cerebral ischemia induced by permanent occlusion of middle cerebral artery in the mouse, repeated administration of 1 mg/kg i.p. of N omega-nitro-L-arginine (beginning 5 min after surgery) reproducibly decreased by 66-76% the infarct volume measured at 6 days post-occlusion. This dose of N omega-nitro-L-arginine decreased cortical nitric oxide (NO) synthase activity by 70-73%. The neuroprotective efficacy of N omega-nitro-L-arginine increased dose-dependently over the range of doses of 0.1-1 mg/kg. Within this dose range of N omega-nitro-L-arginine, there was a good parallelism between the extent of inhibition of cortical NO synthase activity measured ex vivo and the degree of neuroprotection. However, higher doses of N omega-nitro-L-arginine (3 and 10 mg/kg i.p.), which inhibited NO synthase activity more effectively (up to 94%) failed to significantly reduce the infarct size. Repeated administrations of increasing doses of L-arginine (up to 30 mg/kg i.p.) with a low dose of N omega-nitro-L-arginine (1 mg/kg i.p.) caused a dose-dependent reduction in the neuroprotective efficacy of N omega-nitro-L-arginine while the extent of NO synthase inhibition measured ex vivo did not decrease significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of nitric oxide in regulating cerebrocortical oxygen consumption and blood flow during hypercapnia

The effect of the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the response of cerebrocortical oxygen consumption (CMRO2) and blood flow (CBF) to two levels of hypercapnia (PaCO2 approximately 60 mm Hg and PaCO2 approximately 90 mm Hg) was investigated in ketamine-anesthetized rats. CBF was calculated using the Kety-Schmidt approach and CMRO2 was calculated from the product of CBF and the arteriovenous (superior sagittal sinus) difference for oxygen. L-NAME treatment did not have a significant effect on either CMRO2 or CBF under normocapnic conditions but inhibited the hypercapnic increase of CMRO2 and the hypercapnic increase in CBF. These results suggest that NO plays a role in the response of CMRO2 and CBF during hypercapnia and are consistent with the suggestion that at least part of the increase in CBF observed during hypercapnia is coupled to an increase in CMRO2.

Nitric oxide is a key molecule in migraine and other vascular headaches

Nitric oxide (NO) may play a key role in migraine and other vascular headaches since glyceryl trinitrate (a donor of NO) and histamine (which probably activates endothelial NO formation) both cause a pulsating dose-dependent headache with several migrainous characteristics. At relatively high doses of glyceryl trinitrate, migraine sufferers develop stronger and more migraine-like headaches and more pronounced cerebral arterial dilatation than controls. After the infusion of glyceryl trinitrate, non-migraineurs remain headache-free while migraineurs develop a migraine-like attack. In this review, Jes Olesen, Lars Thomsen and Helle Iversen suggest that migraine may be caused by increased amounts and/or affinity of an enzyme in the NO-triggered cascade of reactions. NO may also be involved in the pathogenesis of other vascular headaches.

Nitric oxide synthase inhibition reduces caudate injury following transient focal ischemia in cats

BACKGROUND AND PURPOSE

We tested the hypothesis that inhibiting nitric oxide production either before or during transient focal ischemia affects early postischemic brain injury.

METHODS

Halothane-anesthetized cats underwent 1 hour of left middle cerebral artery occlusion plus 3 hours of reperfusion. Pretreatment groups received either intravenous N omega-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg, n = 10) or an equal volume of diluent (10 mL saline, n = 10) over 30 minutes before ischemia. Posttreatment groups received intravenous L-NAME (10 mg/kg) over 30 minutes from 45 minutes of ischemia to 15 minutes of reperfusion (n = 10) or intravenous L-NAME (10 mg/kg) plus L-arginine (200 mg/kg) over the same period followed by continuous L-arginine infusion (200 mg/kg per hour) for the remainder of reperfusion (n = 10).

RESULTS

Microsphere-determined blood flow to ipsilateral caudate nucleus and inferior temporal cortex decreased to the same extent during ischemia and recovered to the same extent during reperfusion in the four groups. Triphenyltetrazolium-determined injury volume of ipsilateral caudate nucleus in cats treated with L-NAME before or during ischemia (42 +/- 7% and 42 +/- 3% of caudate nucleus, respectively; mean +/- SE) was less (P < .05) compared with that in cats pretreated with saline (72 +/- 5%) or cats treated with L-NAME plus L-arginine (68 +/- 5%). Ipsilateral cerebral hemispheric injury volume was similar among the four groups (23 +/- 5%, 13 +/- 3%, 18 +/- 5%, and 29 +/- 5% of hemisphere in groups treated with L-NAME before ischemia and during ischemia, the saline-treated group, and the group treated with L-NAME plus L-arginine, respectively).

CONCLUSIONS

Inhibition of nitric oxide synthase decreases caudate injury volume from transient focal cerebral ischemia in cats. The beneficial effect is reversed by L-arginine and is not caused by favorable redistribution of blood flow during ischemia and reperfusion. Because L-NAME was efficacious when administered at reperfusion, nitric oxide generated during reperfusion appears to contribute to caudate injury.

Nitric oxide synthase inhibition and cerebrovascular regulation

There is increasing evidence that nitric oxide (NO) is an important molecular messenger involved in a wide variety of biological processes. Recent data suggest that NO is also involved in the regulation of the cerebral circulation. Thus, NO participants in the maintenance of resting cerebrovascular tone and may play an important role in selected vasodilator responses of the cerebral circulation. Furthermore, evidence has been presented suggesting that NO participates in the mechanisms of cerebral ischemic damage. Despite the widespread attention that NO has captured in recent years and the large number of studies that have been published on the subject, there is considerable controversy regarding the role of this agent in cerebrovascular regulation and in ischemic damage. In this paper the results of investigations on NO and the cerebral circulation are reviewed and the evidence for and against a role of NO is critically examined.

Combined effect of L-arginine and superoxide dismutase on the spastic basilar artery after subarachnoid hemorrhage in dogs

To investigate the function of nitric oxide (a major endothelium-derived relaxing factor) in cerebral arteries after subarachnoid hemorrhage (SAH) in vivo, several nitric oxide-related substances were administered to dogs that had undergone double SAH. These included L-arginine (a substrate for the formation of nitric oxide), NG-monomethyl-L-arginine (L-NMMA, an analog of L-arginine that inhibits the formation of nitric oxide from L-arginine), and superoxide dismutase (SOD, which protects nitric oxide from oxidation by superoxide anion), which were given via intracisternal injection. The diameter of the basilar artery was assessed angiographically. In intact dogs, intracisternal bolus injections of L-arginine (1, 10, or 100 mumol) produced a dose-dependent increase in the internal diameter of the basilar artery; conversely, L-NMMA reduced the diameter of the basilar artery from baseline in a dose-dependent manner. On Days 4 and 7, after two intracisternal injections of autologous blood, L-arginine produced transient vasodilation of the spastic basilar artery, whereas L-NMMA produced no significant vasoconstriction. The vasodilator effect of L-arginine after SAH was stronger on Day 4 than on Day 7, but less than in intact dogs. Intracisternal injection of SOD, which caused no effect per se, enhanced the duration of the vasodilator effect of L-arginine on the basilar artery on Day 4 and both the magnitude and duration of that effect on Day 7. Thus, the basal release of nitric oxide was impaired after SAH, but the ability to synthesize nitric oxide in the vascular wall was not abolished. The finding that the simultaneous injection of SOD enhanced and prolonged the vasodilation induced by sufficient exogenous L-arginine suggests that the inactivation of nitric oxide by superoxide anion contributes to the development of vasospasm.

Inhibition of nitric oxide biosynthesis and carotid arteriovenous anastomotic shunting in the pig

1. The role of nitric oxide (NO) biosynthesis in the regulation of blood flow through arteriovenous anastomoses was evaluated in the carotid circulation of the anaesthetized pig. For this purpose, the effect of intracarotid (i.c.) administration of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME: 0.1, 0.3 and 1.0 mg kg-1; n = 6) or saline (n = 6) was studied on the distribution of common carotid blood flow, using the radioactive microsphere method. 2. Apart from the highest dose, L-NAME caused no major changes in the systemic haemodynamic variables. Both cardiac output and systemic vascular conductance were reduced by L-NAME (1 mg kg-1), being reversed partly by L-arginine (100 mg kg-1, i.c.). In both groups, L-arginine slightly reduced mean arterial blood pressure. 3. Total common carotid artery blood flow as well as its distribution over the capillary and arteriovenous anastomotic fraction remained stable after saline injection. In contrast, L-NAME caused a dose-dependent decline in common carotid artery blood flow and conductance and this decline was confined entirely to its arteriovenous anastomotic part. 4. Subsequent intracarotid injection of L-arginine (100 mg kg-1) reversed the reduction in total carotid conductance almost completely and that in the arteriovenous anastomotic region partially. Additionally, L-arginine increased capillary conductance significantly in the L-NAME--as well as the saline-treated animals. 5. These results indicate that the L-arginine-NO pathway contributes little to the regulation of tissue perfusion in the porcine carotid circulation. In contrast, NO seems to play an important role in shunting arterial blood through arteriovenous anastomoses in the anaesthetized pig.

Nitric oxide and the cerebral circulation

BACKGROUND

Nitric oxide (NO) is a potent vasodilator that was initially described as the mediator of endothelium-dependent relaxation (endothelium-derived relaxing factor, EDRF). It is now known that NO is produced by a variety of other cell types.

SUMMARY OF REVIEW

Endothelium produces NO (EDRF) under basal conditions and in response to a variety of vasoactive stimuli in large cerebral arteries and the cerebral microcirculation. Endothelium-dependent relaxation is impaired in the presence of several pathophysiological conditions. This impairment may contribute to cerebral ischemia or stroke. Activation of glutamate receptors appears to be a major stimulus for production of NO by neurons. Neuronally derived NO may mediate local increases in cerebral blood flow during increases in cerebral metabolism. NO synthase-containing neurons also innervate large cerebral arteries and cerebral arterioles on the brain surface. Activation of parasympathetic fibers that innervate cerebral vessels produces NO-dependent increases in cerebral blood flow. Increases in cerebral blood flow during hypercapnia also appear to be dependent on production of NO. Astrocytes may release some NO constitutively, but astrocytes and microglia can release relatively large quantities of NO after induction of NO synthase in response to endotoxin or some cytokines. Expression of inducible NO synthase, perhaps in response to local production of cytokines, may exert cytotoxic effects in brain during or after ischemia.

CONCLUSIONS

Because endothelium, neurons, and glia can all produce NO in response to some stimuli, the influence of NO on the cerebral circulation appears to be very important. Under normal conditions, constitutively produced NO influences basal cerebral vascular tone and mediates vascular responses to a diverse group of stimuli. The inducible form of NO synthase produces much greater amounts of NO that may be an important mediator of cytotoxicity in brain.

Involvement of calcitonin gene-related peptide (CGRP) and nitric oxide (NO) in the pial artery dilatation elicited by cortical spreading depression

The aim of the present study was to examine whether the initial transient arterial dilatation during cortical spreading depression (CSD) was mediated by the release of calcitonin gene-related peptide (CGRP) and/or nitric oxide (NO). This question is of interest as the initial phase of CSD appears to be a model of events occurring during functional hyperemia and during the first period of classic migraine. Using an open cranial window technique, pial arterial diameter in the parietal cortex of cats was recorded with an image splitting method. Employing micropuncture technique, perivascularly applied CGRP8-37 did not alter the resting diameter of pial arteries but antagonized concentration dependently (5 x 10(-9)-10(-6) M) the dilatation (35%) due to 5 x 10(-8) M CGRP. NG-Nitro-L-Arginine (NOLAG, 10(-4) M) also had no effect on resting diameter of pial arteries, indicating that their resting tone is neither mediated by a continuous release of CGRP nor of NO. CSD was triggered by a remote intracortical injection of KCl (150 mM) and recorded by a microelectrode placed adjacent to the artery under investigation. CSD elicited a transient negative DC shift which was accompanied by a peak dilatation of 44 +/- 5.2% (S.E.M.). This dilatation was reduced by approximately 50% during topical application of 10(-7) M CGRP8-37 and 10(-4) M NOLAG each. A 75% inhibition of the CSD-induced dilatation was found during simultaneous application of both compounds. These data indicate that the initial dilatation during CSD is mediated, at least in part, by a release of CGRP and NO.(ABSTRACT TRUNCATED AT 250 WORDS)

L-arginine infusion promotes nitric oxide-dependent vasodilation, increases regional cerebral blood flow, and reduces infarction volume in the rat

BACKGROUND AND PURPOSE

We previously reported that L-arginine infusion increased pial vessel diameter by nitric oxide-dependent mechanisms, improved regional cerebral blood flow (rCBF) distal to middle cerebral artery (MCA) occlusion, and reduced infarction volume in spontaneously hypertensive rats when administered intraperitoneally before and after MCA occlusion. In this report we extend our findings (1) by examining the time course of L-arginine on rCBF and pial vessel diameter under basal conditions and on rCBF after MCA occlusion and (2) by reproducing the protective effect of L-arginine on infarct volume when given intravenously immediately after the onset of MCA occlusion in both normotensive and hypertensive models of focal cerebral ischemia.

METHODS

Changes in pial vessel diameter (closed cranial window) and rCBF (laser-Doppler flowmetry) were measured over time after L-arginine infusion into anesthetized Sprague-Dawley rats. rCBF was also measured distal to MCA occlusion in a brain region showing rCBF reductions in the range of 80% of baseline. The effects of infusing L-arginine (300 mg/kg for 10 minutes beginning 5 minutes after occlusion) were assessed on infarction volume in Sprague-Dawley rats after proximal MCA occlusion and in spontaneously hypertensive rats after common carotid artery plus distal MCA occlusion.

RESULTS

L-Arginine (300 mg/kg IV) elevated rCBF by 20% when measured in the dorsolateral cortex of Sprague-Dawley rats and caused L-nitroarginine-methyl ester-inhibitable increases in pial vessel diameter. L-Arginine (> or = 30 mg/kg IV) increased blood flow distal to MCA occlusion by 50%. These effects were sustained throughout the observation period (70 to 105 minutes). Changes in mean arterial blood pressure were not observed. L-Arginine (300 mg/kg IV) reduced infarction volume by 35% and 28% in Sprague-Dawley and spontaneously hypertensive rats, respectively, when examined 24 hours after vessel occlusion.

CONCLUSIONS

These studies extend our previous findings by demonstrating that exogenous L-arginine induces sustained rCBF increases in normal brain as well as in a marginally perfused brain region distal to MCA occlusion. Our data in Sprague-Dawley rats support the conclusion that L-arginine-induced increases in rCBF can decrease infarction volume. We conclude that nitric oxide-mediated mechanisms increase rCBF and decrease infarction volume after MCA occlusion in both normotensive and hypertensive animals.

An ultrastructural study of NADPH-diaphorase and nitric oxide synthase in the perivascular nerves and vascular endothelium of the rat basilar artery

This is the first report on the ultrastructural distribution of nicotinamide adenine dinucleotide phosphate-diaphorase activity and neuronal isoform (Type I) of nitric oxide synthase immunoreactivity in perivascular nerves (axons) and vascular endothelial cells. In the Sprague-Dawley rat cerebral basilar artery, positive labelling for nicotinamide adenine dinucleotide phosphate-diaphorase and nitric oxide synthase was localized in axons and the endothelium. Over half (approximately 53%) of the axon profiles examined were positive for nicotinamide adenine dinucleotide phosphate-diaphorase. Labelling of nicotinamide adenine dinucleotide phosphate-diaphorase activity in the axons and endothelial cells was mostly distributed in patches within the cytoplasm. In endothelial cells, a relation between the nicotinamide adenine dinucleotide phosphate-diaphorase-labelling and cytoplasmic vesicle-like structures was seen. In both axons and the endothelium, nitric oxide synthase immunoreactivity was seen throughout the cell cytoplasm and in association with the membranes of mitochondria, endoplasmic reticulum and cytoplasmic/synaptic vesicles (the lumen/content of the vesicles was negative for nitric oxide synthase). Also, microtubules were labelled in nitric oxide synthase positive axon profiles. The nitric oxide synthase-positive axon varicosities were characterized by the presence of spherical agranular vesicles with a diameter of 40-50 nm. Approximately 30% of the axon profiles examined were positive for nitric oxide synthase. The nicotinamide adenine dinucleotide phosphate-diaphorase-positive endothelial cells (approximately 20% of all observed endothelial cell profiles) were more frequently seen than those positive for nitric oxide synthase (approximately 7%). It is suggested that nitric oxide released from both perivascular nerves and endothelial cells may be involved in vasomotor control of cerebral circulation.

The complex role of nitric oxide in the pathophysiology of focal cerebral ischemia

Nitrogen monoxide (NO) has recently emerged as an important mediator of cellular and molecular events which impacts the pathophysiology of cerebral ischemia. Although tempting to ask whether NO is "good or bad" for cerebral ischemia, the question underestimates the complexities of NO chemistry and physiology as well as oversimplifies the pathophysiology of focal cerebral ischemia. Important vascular and neuronal actions of NO have been defined which both enhance tissue survival and mediate cellular injury and death, and these will be reviewed. Strategies which modify NO synthesis and/or metabolism may someday assume therapeutic importance, but not until the tissue compartments generating NO, the activities of the enzymes that are inducibly and constitutively expressed, and the redox state of NO during the stages of ischemic injury, are defined with greater precision. Our knowledge of these processes is rudimentary. This review will summarize the evidence from animal models which supports an emerging role for NO in ischemic pathophysiology. Important aspects of NO synthesis and inhibitors of this process will also be discussed.

Differing effects of vasopressin on regional cerebral blood flow of dogs following intracisternal vs. intra-arterial administration

We investigated the differential effect of the intracisternal and intraarterial administration of vasopressin on the regional cerebral blood flow (rCBF) in the parietal cortex of dogs. Regional CBF, velocity and blood volume were assayed by laser flowmetry. The intracisternal injection of 1 nmol vasopressin significantly increased the rCBF and velocity, without affecting blood volume. However, the intravertebral arterial injection of 1 nmol vasopressin significantly decreased the rCBF and velocity. This discrepancy can be explained by a difference in the affected vasculature; large blood vessels in the subarachnoid space vs. whole cerebral vascular system. The intracisternal and intraarterial injection of the nitric oxide inhibitor NG-monomethyl-L-arginine reduced the rCBF from the base line, and significantly suppressed the rCBF elevation induced by vasopressin. The effect of vasopressin may be considered as the summation of the increased flow from the dilated large vessels via the release of nitric oxide from the endothelium, and of the decreased flow from the contracted small vessels.

Basic fibroblast growth factor dilates rat pial arterioles

Basic fibroblast growth factor (bFGF) is a polypeptide that promotes the survival and differentiation of brain neurons, glia, and endothelial cells. It has been shown recently that intravenously administered bFGF lowers blood pressure by systemic vasodilation; this effect is mediated, in part, by nitric oxide (NO)-dependent mechanisms. In the current study, we directly evaluated the effect of bFGF on pial arterioles of pentobarbital-anesthetized Sprague-Dawley rats (n = 18) using the closed cranial window technique. Basic FGF (5-200 ng/ml) produced dose-dependent vasodilation; maximal vessel diameter (approximately 120% of control) was reached at 100 ng/ml. No vasodilation was found when bFGF was heat inactivated, or preincubated with blocking antibody. Moreover, bFGF-induced vasodilation was attenuated by coadministration of the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), consistent with an NO-dependent mechanism. These results suggest that bFGF may play an important role in the regulation of cerebrovascular tone and cerebral blood flow.

Targeted disruption of the neuronal nitric oxide synthase gene

By homologous recombination, we have generated mice that lack the neuronal nitric oxide synthase (NOS) gene. Neuronal NOS expression and NADPH-diaphorase (NDP) staining are absent in the mutant mice. Very low level residual catalytic activity suggests that other enzymes in the brain may generate nitric oxide. The neurons normally expressing NOS appear intact, and the mutant NOS mice are viable, fertile, and without evident histopathological abnormalities in the central nervous system. The most evident effect of disrupting the neuronal NOS gene is the development of grossly enlarged stomachs, with hypertrophy of the pyloric sphincter and the circular muscle layer. This phenotype resembles the human disorder infantile pyloric stenosis, in which gastric outlet obstruction is associated with the lack of NDP neurons in the pylorus.

Enhanced expression of nitric oxide synthase by rat retina following pterygopalatine parasympathetic denervation

Removal of the pterygopalatine ganglion enhanced the expression of nitric oxide synthase (NOS) in the ipsilateral rat retina and optic nerve by immunohistochemical and biochemical criteria. The denervation procedure did not alter the apparent histochemical reactivity of retinal cells normally immunoreactive for NOS but did induce expression in retinal ganglion cells and their axons in the retinal nerve fiber layer and optic nerve. After denervation, the induced NOS immunohistochemical reactivity was consistently visualized by day 7, reached a maximum intensity during days 14 to 28, and thereafter gradually attenuated to become barely detectable by microscopy at 10 weeks. Biochemical assays performed two weeks after pterygopalatine denervation confirmed the immunohistochemical observations, especially with regard to the optic nerve. The induced enzyme activity in both retina and optic nerve showed calcium dependency. These results point towards interactions of the ocular parasympathetic innervation and the retina, between which no known neuronal connections exist.

Nitric oxide: a new messenger in the brain

The important role played by nitric oxide (NO) in the central nervous system has largely been emphasized in the recent literature. It can originate at least from four different sources: the endothelium of cerebral vessels, the immunostimulated microglia and astrocytes, the nonadrenergic noncholinergic nerve, and the glutamate neuron. NO has been implicated in a large number of pathologies (such as neurotoxicity in Alzheimer's disease and Huntington's disease, cerebral ischemia, stroke, and anxiety) and also in normal physiological functions (such as memory and learning, regulation of the cerebrovascular system, modulation of the wakefulness, mediation of nociception, olfaction, food intake and drinking, regulation of noradrenaline, and dopamine release). The aim of this paper is to review and to integrate the most recent advances in our understanding of the roles of NO in the brain.

Arterial supersensitivity to nitric oxide (nitroglycerin) in migraine sufferers

The sensitivity to nitroglycerin-induced dilatation of large intracranial arteries was studied in 17 patients with migraine without aura, 17 age and sex-matched healthy subjects and 9 patients with episodic tension-type headache. Nitroglycerin in the doses of 0.015, 0.03, 0.25 microgram/kg/min was successively infused for 15 min per dose. Blood velocity (Vmean) in the middle cerebral artery (MCA) was recorded with transcranial Doppler before and at the end of every infusion period, and 30 and 60 min after end of the last infusion. In all three groups Vmean decreased with increasing doses (p < 0.001). The response was more pronounced in migraine patients at the two higher doses (p < 0.05). Since nitroglycerin acts as an exogenous source of nitric oxide (NO), these data support that NO supersensitivity may be an important molecular mechanism of migraine pain.

Nitric oxide synthase-immunoreactive nerve fibers in dog cerebral and peripheral arteries

Nitric oxide synthase (NOS)-immunoreactive fibers innervating the dog arterial wall were histochemically determined by the use of NOS antiserum. NOS-immunoreactive fibers were consistently found in every arterial wall examined. In a whole-mount preparation, NOS-positive fibers were detectable in the small pial artery having a diameter of about 100 microns as well as the proximal middle cerebral artery. Further detailed analyses in thin cryostat sections indicated that in middle cerebral, basilar, temporal, mesenteric and femoral arteries, fine NOS-positive fibers were detected in outer zones of the media in addition to many thicker fibers in the adventitia. However, in the coronary artery, many thick fibers were situated in the adventitia, and fine NOS-positive fibers were not found in the media. Injection of ethanol to the pterygopalatine ganglion markedly decreased or abolished the NOS immunoreactivity in nerve cells and fibers and abolished the innervation of NOS-positive fibers in the wall of middle cerebral artery of the ipsilateral side. Together with findings in our previous publications concerning the functional role of nitroxidergic nerve in the control of arterial tone, we conclude that perivascular nerves containing NOS are crucial in eliciting the neurally induced, NO-mediated arterial relaxation.

Inhibition of nitric oxide synthase attenuates the cerebral blood flow response to stimulation of postganglionic parasympathetic nerves in the rat

Stimulation of cerebrovascular parasympathetic nerves markedly increases cortical blood flow. Nitric oxide (NO) or a NO-containing compound is present in these nerves and may therefore, upon release, be partly responsible for the flow increase. In addition, transmitters released from the nerves may cause synthesis and release of this compound from the endothelium. The contribution of NO synthesis to the cortical blood flow (CoBF) increase during parasympathetic stimulation was elucidated in rat by laser-Doppler flowmetry. Thirty-minute exposure to circulating N omega-nitro-L-arginine methyl ester (L-NAME) 50 mg kg-1 eliminated most of the response (from 104 to 8% increase), whereas 10-min exposure to this dose or 30-min exposure to 5 mg kg-1 caused a less marked reduction. The reducing effect was particularly evident after elimination of the systemic blood pressure increase caused by L-NAME (only 3% increase after the high dose). Infusion of L-arginine restored the flow response. Resting CoBF was not substantially affected by blockade of NO formation. Thus, release of an NO-containing compound constitutes a major component of the increase in CoBF caused by parasympathetic nerve stimulation but does not seem to contribute to cortical flow regulation during resting conditions.

Histochemical localization of NADPH-dependent diaphorase (nitric oxide synthase) activity in vascular endothelial cells in the rat brain

This study investigated the localization of NADPH-dependent diaphorase activity within vascular endothelial cells in the rat brain. Light microscope observations showed that in addition to neurons and neuronal processes stained histochemically for NADPH-dependent diaphorase activity, endothelial cells in many medium to large diameter (20-100 microns) blood vessels were also stained. These vessels were either attached to the pial surface or contained within the substance of the tissue. In vascular endothelia, the formazan end-product of the diaphorase reaction was deposited as discrete clusters of darkly stained punctae that were located around the nucleus of these cells. Correlated light- and electron-microscopical examination revealed that the sites of formazan deposition occurred in regions of endothelial cytoplasm devoid of smooth and rough endoplasmic reticulum and of mitochondria. Since endothelial NADPH dependent diaphorase activity co-localizes with the activity of nitric oxide synthase (the synthetic enzyme for nitric oxide) these observations suggest that in vascular endothelial cells nitric oxide synthase may be a highly localized soluble cytosolic enzyme not structurally associated with any subcellular organelle. In addition, specific regions of the smooth muscle cells encircling the larger diameter blood vessels clearly demonstrated NADPH dependent diaphorase activity. Unmyelinated fibres and fibre-plexi surrounding blood vessels on the pial surface were also stained. The results of this study show specific NADPH dependent diaphorase activity in vascular endothelial cells in the rat brain. Therefore, together with neurons, endothelial cells may control nitric oxide-dependent vasodilation thereby regulating local blood flow in the brain.

Local NADPH-diaphorase neurons innervate pial arteries and lie close or project to intracerebral blood vessels: a possible role for nitric oxide in the regulation of cerebral blood flow

Electrical stimulation of perivascular nerves induced a relaxation of endothelium-denuded cat pial arteries that was significantly reduced by nitric oxide (NO) synthase inhibition, indicating that NO was involved in the neurogenic relaxation of these vessels. Histochemical staining of the pial arteries for NADPH-diaphorase (NADPH-d), used as a marker for NO synthase, showed positive nerve fibers in the adventitial layer. Interestingly, in some restricted areas stained neuronal cell bodies were also observed. These neurons were scattered or distributed in small groups in a ganglion-like manner, and they sent fibers to the vessel wall. No NADPH-d-positive nerve fibers or cell bodies were detected in forelimb, pulmonary, or coronary arteries. Within the brain parenchyma, blood vessels also showed positive fibers around their walls. These fibers were organized in a branching pattern and presented varicosities. NADPH-d-positive neurons were found in the proximity of the intracerebral vascular profiles, sending processes to the vessels and/or being directly apposed to their wall. The neurovascular contacts were preferentially located close to the interface between the cerebral cortex and white matter. The anatomical relationship between NADPH-d-positive neurons and fibers and the cerebral blood vessels, together with the participation of NO in the neurogenic relaxation of pial arteries, suggests that NO is involved in the regulation of cerebral blood flow.

Nitric oxide synthase immunoreactive neurons in the rat kidney

The presence of neurons with nitric oxide synthase (NOS) immunoreactivity was investigated in the rat kidney. Whole kidneys were examined by means of serial sections. The indirect immunocytochemical technique using polyclonal antibody raised against rat brain type Ia NOS and the histochemical technique for nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase are used in this study. NOS-immunoreactive (NOS-IR) neurons varied in size and were observed: (1) associated with nerve bundles at the hilus of the kidney, (2) in the proximity of the lower or middle portion of the interlobar arteries, and (3) on the wall of the renal pelvis. We are presenting anatomic evidence for the presence of neurons in the rat kidney. Their location is consistent with the existence of a parasympathetic innervation of the rat kidney.

Pathophysiology of erectile dysfunction

During the past decade, our knowledge of the hemodynamics, functional anatomy, neurophysiology, and neuropharmacology of erectile function has evolved substantially. The change of smooth muscle tone has emerged as a key factor in erection and detumescence. However, future studies are needed to elucidate the cellular and molecular basis of erectile physiology. With insight into normal physiology we will understand the pathologic process and be able to treat it.

Endothelium-derived vasoactive factors and regulation of the cerebral circulation

Vasoactive factors produced and released by endothelium exert a powerful influence on vascular tone in the cerebral circulation. Endothelium-derived relaxing factor (EDRF), which has been identified as nitric oxide (NO) or an NO-containing compound, is produced under basal conditions in cerebral blood vessels. EDRF mediates endothelium-dependent relaxation in response to a number of stimuli in the cerebral circulation. The influence of NO on the cerebral circulation appears to be particularly important and complex because both neurons and glia, in addition to endothelium, produce NO in response to some stimuli. Neuronally derived NO may mediate local vasodilation in response to increased neuronal activity. In addition to EDRF, cerebral endothelium may produce other relaxing factors, including prostacyclin, endothelium-derived hyperpolarizing factor, and oxygen-derived free radicals. Several pathophysiological conditions are associated with impaired endothelium-dependent responses that may involve the decreased production of EDRF and release of endothelium-derived contracting factors, such as the cyclooxygenase products of arachidonic acid and endothelin. The release of endothelin, an extremely potent and long-lasting vasoconstrictor peptide, may contribute to vasospasm after subarachnoid hemorrhage.

Nitric oxide synthase: a new diagnostic tool for neurogenic impotence

Cavernosal biopsy specimens obtained from men undergoing penile surgery permitted determination of the diagnostic value of nitric oxide synthase in neurogenic impotence. In biopsy specimens obtained from 25 men, the presence of nitric oxide synthase (NOS), as shown by nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining, was determined in nerve fibers, smooth muscle, and sinusoidal endothelium. Positive staining for NOS correlated significantly (p < or = 0.001) with a clinical history of cavernous nerve integrity. In comparison, staining with protein gene product (PGP 9.5), an excellent general nerve stain, lacked any degree of specificity as an indicator of nerve status. NADPH diaphorase may provide important insight into the cavernous nerve integrity of the patient. This report is the first to describe histologic features of human cavernosal tissue biopsies that will allow the direct diagnosis of neurogenic impotence owing to cavernous nerve damage.

Nitric oxide synthase-like immunoreactivity in lumbar dorsal root ganglia and spinal cord of rat and monkey and effect of peripheral axotomy

With the immunofluorescence technique, nitric oxide synthase (NOS)-like immunoreactivity (LI) was found in a few medium-sized and small sensory neurons in lumbar (L) 4 and L5 dorsal root ganglia (DRG) of normal rat, and in most of these neurons, NOS-LI coexisted with calcitonin gene-related peptide and sometimes with substance P and galanin. NOS-immunoreactive nerve fibers, terminals and small neurons were also located in the dorsal horn of the segments 4 and 5 of the rat lumbar spinal cord with the highest density in inner lamina II. Many NOS-positive neurons and fibers were seen in the area around the central canal. A sparse network of NOS-immunoreactive nerve fibers was found in the ventral horn. After unilateral sciatic nerve cut in the rat, the number of NOS-positive neurons increased in the ipsilateral L4 and L5 DRGs, mainly in medium and small neurons, but also in some large neurons and very small neurons. NOS-LI could now also be seen in the ipsilateral dorsal roots, and in an increased number of fibers and terminals in both outer and inner lamina II of the ipsilateral dorsal horn. The number of NOS-immunoreactive neurons in lamina II of the ipsilateral dorsal horn was reduced. In the monkey L4 and L5 DRGs, many small neurons were NOS-immunoreactive, but only a few weakly stained nerve fibers and terminals were found in laminae I-IV of the dorsal horn at L4 and L5 lumbar levels. A few NOS-positive neurons were present in lamina X. The number of NOS-immunoreactive neurons was somewhat reduced in DRGs 14 days after peripheral axotomy, but no certain effect was seen in the dorsal horn. These results, together with earlier in situ hybridization studies, demonstrate that axotomy in rat induces a marked upregulation of NOS synthesis in primary sensory neurons, thus suggesting a role for NO in lesioned sensory neurons. In contrast, no such effect was recorded in monkey, perhaps indicating distinct species differences.

Synthesis of nitric oxide in CNS glial cells

Attention has focused on particular neurons as the source of nitric oxide (NO) within the parenchyma of the CNS. In contrast, glial cells have been viewed mainly as potential reservoirs of L-arginine, the substrate for nitric oxide synthase (NOS), and as likely targets for neuronally derived NO because of their proximity and their expression of soluble guanylyl cyclase (sGC). However, it is becoming evident that astrocytes display both constitutive and inducible NOS activity under various conditions, and that activated microglia express an inducible NOS. The NO-producing capacity of oligodendrocytes is not yet known. Glial-derived NO has significant implications for CNS pathophysiology, given the anatomical location and abundance of these cells, and the wide variety of potential interactions that NO can have with cellular biochemistry. Our intention here is to evaluate the evidence for NO production from non-neuronal CNS sources and thus prompt discussion about potential 'nitrinergic' roles for glial cells.

Immunohistochemical localization of nitric oxide synthase in the autonomic innervation of the human penis

An improved understanding of the physiology of penile erection has resulted from recent evidence that implicates nitric oxide as the principal mediator of erectile function. Previously, the neuroanatomy of erection in man was established with descriptions of the autonomic innervation of the pelvic organs and external genitalia. The basis upon which novel physiological concepts of erection relate to earlier neuroanatomical principles remains to be determined. In the present study these relationships were explored with nitric oxide synthase immunohistochemistry and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry of select pelvic tissue specimens obtained from 4 men (3 at radical prostatectomy and 1 at autopsy). Nitric oxide synthase, the enzyme that catalyzes nitric oxide production, was identified in discrete neuronal locations, including the pelvic plexus, cavernous nerves and their terminal endings within the corporeal erectile tissue, branches of the dorsal penile nerves and nerve plexuses in the adventitia of the deep cavernous arteries. This distribution of nitric oxide synthase-containing nerves suggests that nitric oxide neuronally modulates local vascular smooth musculature of the penis. On this basis, nitric oxide is identified as a neuronal mediator of penile erection in man.

Regulation of the cerebral microcirculation during neural activity: is nitric oxide the missing link?

Although the mechanisms regulating the cerebral microcirculation during neural activity have been the subject of inquiry for a century or more, the mediators responsible for the changes in cerebral blood flow still remain to be clearly identified. The discovery that nitric oxide, a powerful cerebrovasodilator, is produced by active neurons has led to the hypothesis that this agent could be the long-sought mediator 'coupling' brain activity to cerebral blood flow. This hypothesis is supported by recent experimental data suggesting that nitric oxide participates in the maintenance of resting cerebral blood flow and in the cerebrovasodilatation elicited by increased neural activity. In this article, this evidence is critically reviewed and discussed in the context of general principles of cerebrovascular regulation.

The localization of nitric oxide synthase in the rat eye and related cranial ganglia

Nitric oxide synthase is the biosynthetic enzyme for the free radical neurotransmitter nitric oxide. Using an affinity-purified antiserum, nitric oxide synthase was found to be localized to peripheral ocular nerve fibers, related cranial ganglia, and the retina of the rat. In the eye, nitric oxide synthase-like immunoreactive peripheral nerve fibers were visualized mainly in the choroid and about limbal blood vessels. The anterior uvea was quite sparsely innervated, and the cornea was negative. Many principal neurons in the pterygopalatine ganglion were immunoreactive for nitric oxide synthase while very few cells stained in the superior cervical and trigeminal ganglia. Virtually all nitric oxide synthase-like immunoreactive pterygopalatine cells were also immunostained for vasoactive intestinal polypeptide; nitric oxide synthase also partially co-localized with neuropeptide Y in some of the neurons of this ganglion. Pterygopalatine ganglionectomy significantly reduced the number of peripheral nitric oxide synthase-like immunoreactive nerve fibers in the eye. A variety of immunoreactive retinal cells were seen. Most cells in the inner nuclear layer or ganglion cell layer corresponded morphologically to amacrine cells and displaced amacrine cells. Interplexiform cells and occasional faintly stained cells in the outer portion of the inner nuclear layer also were visualized. Nicotinamide adenine dinucleotide phosphate diaphorase histochemistry generally stained cells of similar distribution but did reveal somewhat more extensive localizations in peripheral ocular tissues, the ciliary ganglion, and the retina, compared with nitric oxide synthase immunohistochemistry. Nitric oxide synthase thus localizes to peripheral ocular nerve fibers, chiefly parasympathetic in nature and derived from the pterygopalatine ganglion, and to several cell types in the retina. Nitric oxide probably acts as a choroidal vasodilator of parasympathetic origin in the eye; the neuropeptide co-localizations in the pterygopalatine ganglion suggest complex neuromodulatory interactions. The retinal localizations imply potential neurotransmitter functions for nitric oxide in this tissue.

Blockade of nitric oxide synthesis in rats strongly attenuates the CBF response to extracellular acidosis

We tested the hypothesis that the CBF response to extracellular acidosis is mediated by nitric oxide (NO). A closed cranial window, superfused with artificial CSF (aCSF), was implanted over the parietal cortex in anesthetized and ventilated Wistar rats. Regional cerebral blood flow (rCBF) was measured continuously with laser-Doppler flowmetry (LDF). The reaction of rCBF to hypercapnia (PaCO2 from 30.5 +/- 1.8 to 61.3 +/- 5.8 mm Hg by adding CO2 to the inspiratory gas) was 2.9 +/- 1.4%/mm Hg, and the reaction of rCBF to H+ (superfusion of acidic aCSF, pH 7.07 +/- 0.05) was 101.7 +/- 24.7%/pH unit. The regional NO synthase (NOS) activity was blocked by superfusing aCSF containing 10(-3) M N omega-nitro-L-arginine (L-NA, n = 10). After 30 min of L-NA superfusion, rCBF was reduced to 80.1 +/- 6.5% of baseline, and the rCBF responses to hypercapnia (PaCO2 from 30.9 +/- 2.9 to 58.8 +/- 7.7 mm Hg) and extracellular acidosis (aCSF pH 7.08 +/- 0.06) were reduced to 0.8 +/- 1.1%/mm Hg and 10.1 +/- 23.0%/pH unit, respectively (both p < 0.001). This effect was stereospecific since aCSF containing 10(-3) M N omega-nitro-D-arginine affected neither baseline rCBF nor the response to H+ (n = 5). The NOS blockade did not affect the vasodilatation by the NO donor sodium nitroprusside (n = 5, 114.3 +/- 25.1% before vs. 130.2 +/- 24.7% after NOS blockade). The results confirm the involvement of NO in the CBF reaction to hypercapnia and demonstrate for the first time that NOS blockade also strongly attenuates the H+ response of the cerebral vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)

Projections and chemical coding of neurons with immunoreactivity for nitric oxide synthase in the guinea-pig small intestine

The distribution of nitric oxide synthase (NOS) immunoreactivity was investigated in the guinea-pig small intestine. There were many immunoreactive nerve cell bodies in the myenteric plexus but very few in submucous ganglia. NOS immunoreactivity was not found in non-neuronal cells except for rare mucosal endocrine cells. Abundant immunoreactive nerve fibres in both myenteric and submucous ganglia, and in the circular muscle, arose from myenteric nerve cells whose axons projected anally along the intestine. NOS immunoreactivity coexisted with VIP-immunoreactivity, but not with substance P immunoreactivity. We conclude that nitric oxide synthase is located in a sub-population of enteric neurons, amongst which are inhibitory motor neurons that supply the circular muscle layer.

Nitric oxide: a physiologic mediator of penile erection

Nitric oxide (NO) is a cytotoxic agent of macrophages, a messenger molecule of neurons, and a vasodilator produced by endothelial cells. NO synthase, the synthetic enzyme for NO, was localized to rat penile neurons innervating the corpora cavernosa and to neuronal plexuses in the adventitial layer of penile arteries. Small doses of NO synthase inhibitors abolished electrophysiologically induced penile erections. These results establish NO as a physiologic mediator of erectile function.