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

Ultrastructure of NADPH diaphorase-positive nerve fibers and their terminals in the rat cerebral arterial system

To investigate how perivascular NO synthase (NOS)-containing nerves in the cerebral arterial system are involved in controlling the cerebral circulation, we observed the ultrastructure of NOS-containing nerve fibers and their terminals by means of nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH-d) histochemistry. We also observed the correlation between NADPH-d stained perivascular nerves and the perivascular sympathetic nerves, by means of double staining with NADPH-d histochemistry and tyrosine hydroxylase (TH) immunohistochemistry at the light microscopic level. NADPH-d-positive nerve fibers showed dense distribution mainly in the rostral portion of the circle of Willis and proximal portions of its main branches, where some of the NADPH-d-positive fibers coexisted with TH-positive fibers in a single nerve bundle. NADPH-d-positive nerve fibers were unmyelinated and had close contact with NADPH-d-negative myelinated and unmyelinated nerve fibers in a single nerve bundle, and NADPH-d-positive nerve terminals also existed closely with NADPH-d-negative nerve terminals. The number of NADPH-d-positive nerve terminals and their ratio to all other terminals were significantly higher in the rostral portion of the circle of Willis and the proximal portion of its branches, than the caudal portion of the circle of Willis and the distal portion of its branches. Nerve terminals were observed to locate within 250 nm from the basal lamina of arterial smooth muscle cells in the rostral portion of the circle of Willis and proximal portion of its branching arteries. The present observation confirmed that NOS-containing nerve fibers truly innervate the smooth muscle cells of the arterial wall in the circle of Willis and its main branches. Close contact between NADPH-d-positive and -negative nerve fibers and terminals in these arterial portions may indicate that NOS-containing perivascular nerves may work to modulate the rest of the other perivascular nervous system, such as the sympathetic nerves, to regulate the homeostasis of the arterial tonus.

Origin and Co-localization of nitric oxide synthase, CGRP, PACAP, and VIP in the cerebral circulation of the rat

The origin of perivascular nerve fibres storing nitric oxide synthase (NOS) and co-localisation with perivascular neuropeptides were examined in the rat middle cerebral artery (MCA) by retrograde tracing with True Blue (TB) in combination with immunocytochemistry. Application of TB to the proximal part of the middle cerebral artery labelled nerve cell bodies ipsilaterally in the trigeminal, sphenopalatine, otic, and superior cervical ganglia. A few labelled cell bodies were seen contralaterally, suggesting bilateral innervation. In the parasympathetic sphenopalatine and otic ganglia, numerous TB-labelled cell bodies contained neuronal NOS (C- and N-terminal), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase activating peptide (PACAP). In the trigeminal ganglion, almost all TB-labelled cell bodies contained calcitonin gene-related peptide (CGRP) but only a few cells contained NOS. In the superior cervical ganglion, the majority of the TB-labelled nerve cells contained neuropeptide Y (NPY) but none of them contained NOS. Removal of the ipsilateral sphenopalatine ganglion caused a slight reduction in the number of perivascular VIP-, PACAP-, and NOS-containing fibres after 3 days in the MCA while there was no difference at 2 and 4 weeks after the denervation as compared to control. This indicates that the parasympathetic VIP-, PACAP-, and NOS-immunoreactive nerve fibres in the rat MCA originate from several sources.

Innervation of cerebral blood vessels: morphology, plasticity, age-related, and Alzheimer's disease-related neurodegeneration

The light microscopical and ultrastructural morphology of the innervation of the major cerebral arteries and pial vessels is described, including the origins of the different groups of nerve fibres and their characteristic neurotransmitter phenotype. Species and region specific variations are described and novel data regarding the parasympathetic innervation of cerebral vessels are presented. The dynamic nature, or plasticity, of cerebrovascular innervation is emphasized in describing changes affecting particular subpopulations of neurons during normal ageing and in Alzheimer's disease. The molecular controls on plasticity are discussed with particular reference to target-associated factors such as the neurotrophins and their neuronal receptors, as well as extracellular matrix related factors such as laminin. Hypotheses are presented regarding the principal extrinsic and intrinsic influences on plasticity of the cerebrovascular innervation.

Cholinergic-nitrergic transmitter mechanisms in the cerebral circulation

Cerebral blood vessels from several species are innervated by vasodilator nerves. Acetylcholine (ACh) released from parasympathetic cholinergic nerves was first suggested to be the transmitter for vasodilation. Results from pharmacological studies in isolated cerebral arterial ring preparations, however, have demonstrated that nitric oxide (NO) but not ACh mediates the major component of neurogenic vasodilation. More recently, ACh and NO have been shown to co-release from the same cholinergic-nitrergic nerves, and that ACh acts as a presynaptic transmitter in modulating NO release. In this communication, evidence for the neuronal origin of NO and possible role of ACh in modulating NO release in large cerebral arteries at the base of the brain will be discussed.

Cavernous sinus ganglia are sources for parasympathetic innervation of cerebral arteries in rat

Retrograde tracing and immunohistochemistry was used in rats to investigate whether the ganglia in the cavernous sinus contribute to cerebrovascular innervation. The cavernous sinus ganglia in rat include the cavernous part of the pterygopalatine ganglion (PGC) and small cavernous ganglia (CG). The tracers, fluorogold and fast blue, were applied to the middle cerebral artery in eight rats. After 1 to 4 days, the cavernous sinuses were dissected out and studied as whole mount preparations and sections. A moderate number of labeled neurons were visible in the ipsilateral PGC and CG. Furthermore, fibers in the cavernous nerve plexus and abducens nerve were labeled, suggesting that the pathway from the cavernous sinus ganglia to the cerebral arteries runs through the cavernous plexus and then retrogradely along the abducens nerve to the internal carotid artery. Selected sections were immunohistochemically stained for the cholinergic marker, vesicular acetylcholine transporter (VAChT). Most cells in the PGC and CG were VAChT-immunoreactive, some of which also contained tracer. It is concluded that in rat, the cavernous sinus ganglia, consisting of the PGC and small CG, contribute to parasympathetic cerebrovascular innervation and that the cavernous nerve plexus and abducens nerve are involved in the pathway from these ganglia to the cerebral arteries.

Dynamic cerebral microcirculatory changes in transient forebrain ischemia in rats: involvement of type I nitric oxide synthase

The diameter of surface microvessels and the erythrocyte velocity and flux through intraparenchymal capillaries in the parietal cortex were measured during transient global cerebral ischemia and reperfusion using laser-scanning confocal fluorescence microscopy in anesthetized rats. The role of nitric oxide (NO) from neurons in the microcirculatory changes was also investigated using 7-nitro-indazole (7-NI, 25 mg/kg, i.p.). Wistar rats (4 per group) equipped with a closed cranial window were given fluorescein isothiocyanate (FITC)-Dextran and FITC-labeled erythrocytes intravenously to respectively visualize the microvessels and the erythrocytes in the capillaries. Experiments were videorecorded on-line. Forebrains were made ischemic for 15 minutes and then reperfused for 120 minutes under the microscope. Ischemia was associated with a flattened EEG, a low persistent blood flow, and a transient leakage of fluorescein across the arteriole wall. Unclamping the carotid arteries led to immediate high blood flow in the arterioles, but it was not until 5 minutes later that the arterioles dilated significantly (181% +/- 27%) and erythrocyte velocity in the capillaries increased significantly (460% +/- 263%). Neither nonperfused capillaries nor erythrocyte capillary recruitment occurred. 7-Nitro-indazole significantly reduced the arteriole dilatation and prevented the increase in erythrocyte velocity and flux through capillaries in early reperfusion. 7-Nitroindazole had no influence on the fluorescein leakage. The current study suggests a partial role for NO released from neurons in the postischemic microcirculatory changes and provides new findings on the timing of arteriole dilatation and blood-brain barrier opening, and on erythrocyte capillary circulation in global ischemia.

Fluorescent imaging of nitric oxide production in neuronal varicosities associated with intraparenchymal arterioles in rat hippocampal slices

The fluorescent indicator 4,5-diaminofluorescein (DAF-2) has been used to investigate the production of nitric oxide in the vicinity of intraparenchymal cerebral blood vessels. Slices of rat hippocampus 300-350 microm thick, were loaded with 5 microM DAF-2 diacetate. On exposure to light of 450-490 nm wavelength, point sources of fluorescence, 1.8+/-0.2 microm in diameter (mean+/-SEM), were observed in close apposition to the outer surface of the vascular smooth muscle wall of 10/15 arterioles. In fixed slices, resectioned and processed for nicotinamide adenine dinucleotide phosphate-dependent diaphorase, stained varicose fibres were also seen in close association with the smooth muscle wall of small arterioles. These findings suggest that tonic activity in perivascular nitrergic nerve fibres lying in close proximity to intraparenchymal microvessels may be a source of dilator tone within the parenchyma.

The role of adrenomedullin in varicocele and impotence

OBJECTIVE

To assess the levels of adrenomedullin (a vasodilatory peptide) in penile blood before and after injection with papaverine in impotent men, and in the internal spermatic vein in infertile patients with varicocele, comparing the results with levels in the brachial vein in the same patients.

PATIENTS AND METHODS

Intracavernosal levels of adrenomedullin were determined in 14 impotent men (with no vascular pathology, as assessed by colour Doppler ultrasonography) before and after papaverine-induced penile erection. The effect of needle puncture alone was assessed in eight control patients. The level of adrenomedullin was also measured in the internal spermatic vein and brachial vein in 14 infertile men with varicocele.

RESULTS

The mean (SD) intracavernosal adrenomedullin levels in the 14 impotent men were significantly different between the flaccid and papaverine-induced erectile state, at 93.5 (33.0) and 135.8 (34.9) pmol/mL, respectively, (P < 0.05). Needle puncture alone had no effect on adrenomedullin levels. In men with varicocele, the adrenomedullin level of 139.0 (34.3) pmol/mL within the internal spermatic vein was significantly higher than that in the brachial vein, at 103.9 (37.6) pmol/mL (P < 0.05).

CONCLUSION

Injection with papaverine increases adrenomedullin release into penile blood; this release may be responsible for the increase in penile blood flow and penile erection. Higher levels of adrenomedullin within the internal spermatic vein of patients with varicocele may result from the retrograde flow of venous blood from the left adrenal gland and kidney. Further studies are needed to determine the role of adrenomedullin in male infertility and impotence.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Functional importance of neuronal nitric oxide synthase in the endothelium of rat basilar arteries

The function of the neuronal isoform of nitric oxide synthase (nNOS) was studied by comparing the effects of the specific nNOS blocker 7-nitro indazole monosodium salt (7-NINA) with that of the general NOS inhibitor N(G)-nitro-L-arginine (L-NA) in isolated rat basilar arteries (BAs). 7-NINA had no significant effect on the resting tone of the vessels, while both L-NA and 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ), a selective inhibitor of the soluble guanylyl cyclase, induced contraction. The relaxant effect of bradykinin was attenuated in the presence of L-NA but was not changed by 7-NINA. In contrast, 7-NINA markedly reduced the acetylcholine-induced, endothelium-dependent relaxation. These results demonstrate that nNOS contributes significantly to the relaxant effect of acetylcholine, indicating the functional importance of this isoenzyme in the cerebrovascular endothelium.

Effect of testosterone on the number of NADPH diaphorase-stained nerve fibers in the rat corpus cavernosum and dorsal nerve

OBJECTIVES

To elucidate the effect of testosterone on penile nerve supply.

METHODS

Three groups of 10 rats each were assessed; two groups were castrated and the third underwent a sham operation (control). After castration, one group received subcutaneous injection of testosterone while the others received sesame oil. At 8 weeks, the rats underwent a functional analysis. The evaluation included a subcutaneous injection with apomorphine to study centrally mediated erection, and cavernous nerve electrostimulation and papaverine injection to study peripherally mediated erection. At death, a penile midshaft specimen was taken for nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining.

RESULTS

In the apomorphine study, castrated rats had no erections, but the erectile function of those receiving testosterone was restored to the level of the controls. The mean numbers of NADPH-diaphorase-stained nerve fibers in the copora cavernosa and both dorsal nerves of castrated rats, at 165.8 +/- 20.0 and 271.3 +/- 21.1, respectively, were significantly lower than those of the controls, at 271.7 +/- 14.6 and 471.2 +/- 27.6, respectively. Those of the testosterone replacement group, at 290.7 +/- 10.1 and 500.7 +/- 23.9, respectively, recovered to the control level. The intracavernosal pressure decreased significantly in the absence of testosterone, both after electrostimulation and intracavernosal papaverine injection, and recovered to the control level after testosterone replacement.

CONCLUSIONS

Our results indicate that testosterone acts on the nervous system to mediate erection. When it is absent, there may be downregulation of both the production and activity of nitric oxide (NO), thereby decreasing the response to peripheral stimulation via the NO pathway. Testosterone replacement may upregulate NO activity to the control level.

Parasympathetic nerves influence cerebral blood flow during hypertension in rat

This study tested the hypothesis that cerebral vasodilatation during marked acute hypertension is mediated in part through the influence of parasympathetic nerves from the pterygopalatine ganglia. Blood pressure was increased slowly in anesthetized rats after bilateral transection of the parasympathetic nerves. Cerebral blood flow was measured by laser flowmetry. Acutely hypertensive denervated animals developed significantly less cerebral vasodilatation than did control animals with intact nerves. Thus, parasympathetic vasodilator nerves contribute to vasodilatation seen with acute hypertension.

Delayed testosterone replacement restores nitric oxide synthase-containing nerve fibres and the erectile response in rat penis

OBJECTIVE

To elucidate the effect of testosterone on penile innervation. Materials and methods Three groups of six rats each were assessed; two groups (1 and 2) were castrated and the third (group 3) underwent a sham operation (control). Eight weeks after castration, group 2 received a subcutaneous injection with testosterone. At 8 weeks, the rats in group 1 and 3 underwent a final functional analysis while those in group 2 did so at 12 weeks. The evaluation included a subcutaneous injection with apomorphine to study centrally mediated erection, and cavernosal nerve electrostimulation and papaverine injection to study peripherally mediated erection. At death a penile mid-shaft specimen was taken for NADPH-diaphorase staining.

RESULTS

In the apomorphine study, castration resulted in significantly fewer yawns and erections than in the control, and those in group 2 significantly better central erectile function than in the controls. The mean (SEM) number of nitric oxide synthase (NOS)-containing nerve fibres in the corpora cavernosa and both dorsal nerves of castrated rats, at 46.2 (9.1) and 203 (32.1), respectively, were significantly lower than in rats in group 2, at 84.1 (11.2) and 300.6 (17.1), and than in the controls, at 88.6 (10.9) and 306.3 (22.9), respectively. The intracavernosal pressure decreased significantly in the absence of testosterone, both after electrostimulation and intracavernosal papaverine injection. However, there was no difference between the control and group 2 rats in either the number of NOS-containing nerve fibres or in the peripheral erectile functional study.

CONCLUSIONS

Testosterone acts on the nervous system to mediate erection; when it is absent there may be down-regulation of both the production and activity of NO, thereby decreasing the response to peripheral stimulation via the NO pathway. The restoration of erectile function seen in rats in group 2 supports this phenomenon. Delayed testosterone replacement has no detrimental effect on the restoration of the erectile mechanism after castration.

Preganglionic and postganglionic neurons responsible for cerebral vasodilation mediated by nitric oxide in anesthetized dogs

The authors performed investigations to functionally determine the route of efferent innervation in vivo responsible for cerebral vasodilation mediated by nitric oxide (NO). In anesthetized beagles, electrical stimulation of the pterygopalatine ganglion vasodilated ipsilateral cerebral arteries such as the middle cerebral and posterior communicating arteries. Intravenous injections of NG-nitro-L-arginine (L-NA) markedly inhibited the response to nerve stimulation, and the effect was reversed by L-arginine. Stimulation of the proximal portion of the greater superficial petrosal nerve, upstream of the pterygopalatine ganglion, also produced cerebral vasodilation, which was abolished by L-NA and restored by L-arginine. Treatment with hexamethonium abolished the response to stimulation of the petrosal nerve but did not affect the response to pterygopalatine ganglion stimulation. Destruction of the pterygopalatine ganglion by cauterization constricted the cerebral arteries. Postganglionic denervation abolished the vasodilation, lacrimation, and nasal secretion induced on the ipsilateral side by stimulation of the pterygopalatine ganglion and petrosal nerve. The vasodilator response was suppressed by L-NA but unaffected by atropine, whereas lacrimation and nasal secretion were abolished solely by atropine. It is concluded that postganglionic neurons from the pterygopalatine ganglion play crucial roles in cerebral vasodilation mediated by NO from the nerve, and preganglionic neurons, possibly from the superior salivatory nucleus through the greater superficial petrosal nerve, innervate the pterygopalatine ganglion. Tonic discharges from the vasomotor center participate significantly in the maintenance of cerebral vasodilation.

Brain nitric oxide changes after controlled cortical impact injury in rats

Nitric oxide (NO) and the NO end products, nitrate and nitrite, were measured at the impact site after a 5-m/s, 3-mm deformation controlled cortical impact injury in rats. Immediately after the impact injury and the NO and microdialysis probes could be replaced, there was an increase from baseline in NO concentration of 83 +/- 16 (SE) nM, compared with 0.5 +/- 4 nM in the sham injured animals (P < 0.001). This marked increase in NO occurred at the time of the initial rise in blood pressure (BP) and intracranial pressure (ICP) in response to the injury. After the initial increase in BP and ICP, the BP decreased and stabilized at a value which was approximately 20 mmHg below the preinjury values, and ICP plateaued at an average value of 20 mmHg, compared with 8 mmHg in the sham-injured animals. This provided an average cerebral perfusion pressure of 40-50 mmHg, compared with 65-75 mmHg for the sham-injured animals. These values were relatively constant for the remainder of the 3-h monitoring period. The NO values also stabilized during this time period. By 1 h after the impact injury the NO concentration measured directly using the NO electrode had decreased from baseline values by an average value of 25 +/- 6 nM. NO concentration remained significantly lower than baseline values throughout the remainder of the 3-h monitoring period. The concentration of nitrate/nitrite in the dialysate fluid also decreased by an average value of 341 +/- 283 nM 20-40 min after the injury. Dialysate nitrite/nitrate concentrations remained less than the preinjury baseline values throughout the remainder of the 3-h monitoring period. Preinjury treatment with L-nitro-arginine methyl ester (L-NAME) blunted the injury-induced increase in NO and resulted in more severe immediate intracranial hypertension and more severe systemic hypotension at one hour after injury. Mortality was also 67% with L-NAME pretreatment, compared with 1% in untreated animals.

The effect of intranasal cocaine and lidocaine on nitroglycerin-induced attacks in cluster headache

The administration of nitroderivatives in cluster headache (CH) sufferers is the most reproducible experimental paradigm to induce spontaneous-like pain attacks. Previous uncontrolled studies have reported that the local use of anaesthetic agents in the area of the sphenopalatine fossa is able to extinguish nitroglycerin (NTG)-induced pain in CH. The present study, carried out according to a double-blind placebo-controlled design, included 15 CH patients, six with episodic CH (mean +/- SD age of 36.8+/-5.6 years), and nine with chronic CH (37.8+/-10.4 years). Patients had undergone a standard NTG test (0.9 mg sublingually), during which the intensity of pain was scored using a visuoanalogic scale (VAS, range 0-10). Nine patients (two with the episodic form, seven with the chronic form) experienced a typical, spontaneous-like attack on the usual side, occurring in all cases within 45 min. In these patients, the test was repeated with an interval of 2 days, and once pain intensity reached 5 on the VAS, a 10% solution of cocaine hydrochloride (1 ml, mean amount per application 40-50 mg), or 10% lidocaine (1 ml), or saline was applied using a cotton swab in the area corresponding to the sphenopalatine fossa, under anterior rhinoscopy. This was done in both the symptomatic and the non-symptomatic side, for 5 min. Treatments were always performed randomly, in separate sessions. All patients responded promptly to both anaesthetic agents, with complete cessation of induced pain occurring after 31.3+/-13.1 min for cocaine and 37.0+/-7.8 min for lidocaine (M+/-SD). In the case of saline application, pain severity increased thereafter, and extinction of the provoked attacks occurred with a latency of 59.3+/-12.3 min (P<0.01 and P<0.01 vs. cocaine and lidocaine, respectively, Mann-Whitney U-test). While further suggesting that the sphenopalatine ganglion participates in the mechanisms of pain, these findings indicate that the local administration of the anaesthetic agents cocaine and lidocaine is effective on NTG-induced CH attacks, and may be used in the symptomatic treatment of this disorder.

Maturational differences in soluble guanylate cyclase activity in ovine carotid and cerebral arteries

Basal cGMP concentrations are greater in immature than in mature cranial arteries, which may help explain why cerebrovascular resistance is lower in neonates than in adults. The present studies explore the hypothesis that this difference derives from age-related differences in soluble guanylate cyclase (sGC) activity. Maturation depressed (p < 0.01) maximal sGC activity (pmol cGMP/mg/min) in both carotid (from 11.10 +/- 0.50 to 3.60 +/- 0.20) and cerebral (from 3.10 +/- 0.31 to 1.45 +/- 0.08) arteries. Western blot analysis of relative sGC abundance (relative to sGC expression in adult kidney) found that sGC abundance was significantly greater (p < 0.05) in newborn carotid (0.38 +/- 0.04) and cerebral arteries (0.37 +/- 0.06) than in adult arteries (0.25 +/- 0.05 and 0.17 +/- 0.03, respectively). Basal Km values in carotid and cerebral arteries did not differ significantly between newborns (3- to 7-d old) and adults. Activation of sGC with nitrosylated heme significantly reduced Km values 3- to 5-fold in both types of artery and in both age groups. Within artery type, maturation had no significant effect on activated Km. Between artery types, activated Km values were greater (p < 0.05) in cerebral (200 +/- 40 microM) than in carotid (80 +/- 10 microM) arteries. Together, these data suggest that variations in sGC substrate affinity contribute to observed differences in sGC activity between artery types but not those between age groups. In contrast, variations in enzyme abundance, and possibly also enzyme-specific activity, appear responsible for differences in sGC activity associated with both age and artery type.

Increased cerebral blood flow but no reversal or prevention of vasospasm in response to L-arginine infusion after subarachnoid hemorrhage

OBJECT

The reduction in the level of nitric oxide (NO) is a purported mechanism of delayed vasospasm after subarachnoid hemorrhage (SAH). Evidence in support of a causative role for NO includes the disappearance of nitric oxide synthase (NOS) from the adventitia of vessels in spasm, the destruction of NO by hemoglobin released from the clot into the subarachnoid space, and reversal of vasospasm by intracarotid NO. The authors sought to establish whether administration of L-arginine, the substrate of the NO-producing enzyme NOS, would reverse and/or prevent vasospasm in a primate model of SAH.

METHODS

The study was composed of two sets of experiments: one in which L-arginine was infused over a brief period into the carotid artery of monkeys with vasospasm, and the other in which L-arginine was intravenously infused into monkeys over a longer period of time starting at onset of SAH. In the short-term infusion experiment, the effect of a 3-minute intracarotid infusion of L-arginine (intracarotid concentration 10(-6) M) on the degree of vasospasm of the right middle cerebral artery (MCA) and on regional cerebral blood flow (rCBF) was examined in five cynomolgus monkeys. In the long-term infusion experiment, the effect of a 14-day intravenous infusion of saline (control group, five animals) or L-arginine (10(-3) M; six animals) on the occurrence and degree of cerebral vasospasm was examined in monkeys. The degree of vasospasm in all experiments was assessed by cerebral arteriography, which was performed preoperatively and on postoperative Days 7 (short and long-term infusion experiments) and 14 (long-term infusion experiment). In the long-term infusion experiment, plasma levels of L-arginine were measured at these times in the monkeys to confirm L-arginine availability. Vasospasm was not affected by the intracarotid infusion of L-arginine (shown by the reduction in the right MCA area on an anteroposterior arteriogram compared with preoperative values). However, intracarotid L-arginine infusion increased rCBF by 21% (p < 0.015; PCO2 38-42 mm Hg) in all vasospastic monkeys compared with rCBF measured during the saline infusions. In the long-term infusion experiment, vasospasm of the right MCA occurred with similar intensity with or without continuous intravenous administration of L-arginine on Day 7 and had resolved by Day 14. The mean plasma L-arginine level increased during infusion from 12.7+/-4 microg/ml on Day 0 to 21.9+/-13.1 microg/ml on Day 7 and was 18.5+/-3.1 microg/ml on Day 14 (p < 0.05).

CONCLUSIONS

Brief intracarotid and continuous intravenous infusion of L-arginine did not influence the incidence or degree of cerebral vasospasm. After SAH, intracarotid infusion of L-arginine markedly increased rCBF in a primate model of SAH. These findings discourage the use of L-arginine as a treatment for vasospasm after SAH.

N-type Ca2+ channels in cultured rat sphenopalatine ganglion neurons: an immunohistochemical and electrophysiological study

Results from pharmacological studies have suggested that presynaptic N-type Ca2+ channels play an important role in regulating neuronal Ca2+ influx and transmitter nitric oxide (NO) release in isolated cerebral arteries. However, the presence of N-type Ca2+ channels in cerebral perivascular nerves has not been directly demonstrated. As a major source of cerebral perivascular NOergic innervation is the sphenopalatine ganglion (SPG), adult rat SPGs were cultured and examined by whole-cell patch-clamp technique. One week after growing in the culture medium, significant neurite outgrowth from the SPG neuronal cells was observed. Both soma and neurites of these cells were immunoreactive for N-type Ca2+ channels, transmitter-synthesizing enzymes (choline acetyltransferase and NO synthase), and several neuropeptides (vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and pituitary adenylate cyclase-activating peptide-38) that had been found in cerebral perivascular nerves in whole-mount vascular preparations. In current-clamp recordings, injection of a small depolarizing current caused action potential firing. In voltage-clamp recordings, the fast inward currents were blocked by tetrodotoxin and outward currents by tetraethylammonium, which is typical for neurons. Most Ca2+ currents isolated by blockade of sodium and potassium currents were blocked by omega-conotoxin, indicating that N-type Ca2+ channels are the dominant voltage-dependent Ca2+ channels regulating Ca2+ influx during membrane depolarization of SPG neurons. The ability to culture postganglionic SPG neurons provides an opportunity to directly study the electrophysiological and pharmacological properties of these neurons.

Nitric oxide and the cerebral vascular function

The presence of a cholinergic vasodilator innervation to cerebral circulation is well established. Despite its high endogenous concentration in cerebral blood vessels, acetylcholine (ACh) is not the transmitter for vasodilation. This finding has led to the discovery that nitric oxide (NO), which is coreleased with ACh and neural peptides such as vasoactive intestinal polypeptide (VIP) from the respective cholinergic-nitrergic (nitric oxidergic) nerves and the VIPergic-nitrergic nerves, is the primary transmitter in relaxing smooth muscle. ACh and VIP act presynaptically to inhibit and facilitate, respectively, the release of NO. Release of NO from cerebral vascular endothelial cells is also well established. A similar system for recycling L-citrulline to L-arginine for synthesizing more NO has been demonstrated in both cerebral perivascular nerves and endothelial cells. Neuronal and endothelial NO appears to play an important role in controlling cerebral vascular tone and circulation in health and disease.

Endogenous nitric oxide synthesis: biological functions and pathophysiology

Modern molecular biology has revealed vast numbers of large and complex proteins and genes that regulate body function. By contrast, discoveries over the past ten years indicate that crucial features of neuronal communication, blood vessel modulation and immune response are mediated by a remarkably simple chemical, nitric oxide (NO). Endogenous NO is generated from arginine by a family of three distinct calmodulin- dependent NO synthase (NOS) enzymes. NOS from endothelial cells (eNOS) and neurons (nNOS) are both constitutively expressed enzymes, whose activities are stimulated by increases in intracellular calcium. Immune functions for NO are mediated by a calcium-independent inducible NOS (iNOS). Expression of iNOS protein requires transcriptional activation, which is mediated by specific combinations of cytokines. All three NOS use NADPH as an electron donor and employ five enzyme cofactors to catalyze a five-electron oxidation of arginine to NO with stoichiometric formation of citrulline. The highest levels of NO throughout the body are found in neurons, where NO functions as a unique messenger molecule. In the autonomic nervous system NO functions NO functions as a major non-adrenergic non-cholinergic (NANC) neurotransmitter. This NANC pathway plays a particularly important role in producing relaxation of smooth muscle in the cerebral circulation and the gastrointestinal, urogenital and respiratory tracts. Dysregulation of NOS activity in autonomic nerves plays a major role in diverse pathophysiological conditions including migraine headache, hypertrophic pyloric stenosis and male impotence. In the brain, NO functions as a neuromodulator and appears to mediate aspects of learning and memory. Although endogenous NO was originally appreciated as a mediator of smooth muscle relaxation, NO also plays a major role in skeletal muscle. Physiologically muscle-derived NO regulates skeletal muscle contractility and exercise-induced glucose uptake. nNOS occurs at the plasma membrane of skeletal muscle which facilitates diffusion of NO to the vasculature to regulate muscle perfusion. nNOS protein occurs in the dystrophin complex in skeletal muscle and NO may therefore participate in the pathophysiology of muscular dystrophy. NO signalling in excitable tissues requires rapid and controlled delivery of NO to specific cellular targets. This tight control of NO signalling is largely regulated at the level of NO biosynthesis. Acute control of nNOS activity is mediated by allosteric enzyme regulation, by posttranslational modification and by subcellular targeting of the enzyme. nNOS protein levels are also dynamically regulated by changes in gene transcription, and this affords long-lasting changes in tissue NO levels. While NO normally functions as a physiological neuronal mediator, excess production of NO mediates brain injury. Overactivation of glutamate receptors associated with cerebral ischemia and other excitotoxic processes results in massive release of NO. As a free radical, NO is inherently reactive and mediates cellular toxicity by damaging critical metabolic enzymes and by reacting with superoxide to form an even more potent oxidant, peroxynitrite. Through these mechanisms, NO appears to play a major role in the pathophysiology of stroke, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis.

Effect of AR-R 17477, a potent neuronal nitric oxide synthase inhibitor, on infarction volume resulting from permanent focal ischemia in rats

OBJECTIVE

We tested whether AR-R 17477, a selective inhibitor of neuronal nitric oxide synthase, reduces brain injury in rats subjected to permanent focal ischemia.

DESIGN

Randomized within cohort; nonblinded study.

SETTING

University basic science laboratory.

SUBJECTS

Halothane-anesthetized male Wistar rats (n = 53).

INTERVENTIONS

Rats were treated with either intravenous saline (diluent) or AR-R 17477 (1 or 3 mg/kg) 30 mins before or 60 mins after the onset of permanent focal cerebral ischemia. Infarction volume was determined at 18 or 48 hrs of ischemia.

MEASUREMENTS AND MAIN RESULTS

Pretreatment with 1 mg/kg AR-R 17477 was associated with a decreased infarct volume (2,3,5-triphenyltetrazolium chloride staining) in the striatum (saline, 81+/-7 mm3; AR-R 17477, 55+/-3 mm3) but not in the cortex at 18 hrs of occlusion (saline, 302+/-29 mm3; AR-R 17477, 237+/-36 mm3). However, this therapeutic effect of AR-R 17477 was no longer evident if the rats were allowed to survive for 48 hrs before analysis of infarction volume. In fact, in this separate cohort of animals, three of eight AR-R 17477-treated and five of eight saline-treated rats died before completing 48 hrs of ischemia. Efficacy of AR-R 17477 was completely absent (even at 18 hrs of ischemia) when drug treatment was delayed until 1 hr after the onset of ischemia. Infarction volume at 18 hrs of ischemia was similar between rats treated with saline, 1 mg/kg (cortex, 229+/-43 mm3; striatum, 67+/-8 mm3) or 3 mg/kg AR-R 17477 (cortex, 284+/-34 mm3; striatum, 75+/-5 mm3). In addition, only one of eight rats treated with 3 mg/kg AR-R 17477 at 1 hr of ischemia survived 48 hrs of occlusion, compared with three of eight rats treated with saline.

CONCLUSIONS

Neuronally generated nitric oxide is a mediator of brain injury during permanent focal ischemia in rats. However, severity of the ischemic insult appears to limit the therapeutic efficacy of the specific neuronal nitric oxide synthase inhibitor, AR-R 17477.

Effects of some guanidino compounds on human cerebral arteries

BACKGROUND AND PURPOSE

Accumulation of endogenous guanidino-substituted analogues of L-arginine in chronic renal failure might contribute to some of the vascular and neurological disorders of this pathology. We tested the hypothesis that in human cerebral arteries, some guanidino compounds may increase vascular tone, through nitric oxide (NO) synthase inhibition, and impair endothelium-dependent relaxation.

METHODS

Rings of human middle cerebral artery were obtained during autopsy of 26 patients who had died 3 to 12 hours before. The rings were suspended in organ baths for isometric recording of tension. We then studied the responses to N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetrical dimethylarginine; ADMA), aminoguanidine (AG), and methylguanidine (MG).

RESULTS

L-NMMA (10(-6) to 3x10(-4) mol/L) and ADMA (10(-6) to 3x10(-4) mol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC(50)]=1.1x10(-5) and 1.6x10(-5) mol/L, respectively; E(max)=35. 5+/-7.9% and 43.9+/-5.9% of the response to 100 mmol/L KCl). AG (10(-5) to 3x10(-3) mol/L) and MG (10(-5) to 3x10(-3) mol/L) produced endothelium-independent contractions (E(max)=44.3+/-8.8% and 45.7+/-5.8% of the response to 100 mmol/L KCl, respectively). L-Arginine (10(-3) mol/L) prevented the contractions by L-NMMA and ADMA but did not change contractions induced by AG and MG. L-NMMA and ADMA inhibited endothelium-dependent relaxation induced by acetylcholine in a concentration-dependent manner; AG and MG were without effect.

CONCLUSIONS

The results suggest that the contractions induced by L-NMMA and ADMA are due to inhibition of endothelial NO synthase activity, whereas AG and MG do not affect the synthesis of NO. An increase in the plasma concentration of L-NMMA and ADMA associated with uremia is likely to represent a diminished release or effect of NO, and consequently, an increased cerebrovascular tone in uremic patients is highly conceivable.

Characteristics of heterogeneity in the expression of vasoconstriction in response to N(G)-monomethyl-L-arginine in isolated canine arteries

We characterized the contractile effect of a nitric oxide (NO) synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), in isolated canine arteries. L-NMMA induced a heterogenous response: potent vasoconstriction in the cerebral arteries, and weak or no vasoconstrictor responses in different peripheral arteries. The vasoconstriction of the cerebral artery was inhibited by L-arginine but not D-arginine. L-NMMA (1(-4) M) caused a 53% decrease in guanosine 3'5'-cyclic monophosphate (cGMP) levels in the cerebral artery, but it was not significant compared with that in peripheral arteries. The L-NMMA-induced vasoconstriction was inhibited by diltiazem and nicardipine, and the heterogeneity was mimicked by treatment with charybdotoxin, a Ca2+-activated K+ (BK(Ca)) channel blocker, channels which are regulated by NO/cGMP. Both L-NMMA and charybdotoxin caused a potent vasoconstriction in the mesenteric artery precontracted with 20 mM KCl. 1 H-[1,2,4]oxadiazolo[4,3-alpha] quinoxalin-1-one (ODQ) (10(-5) M), a selective guanylate cyclase inhibitor, caused vasoconstriction in the presence of nitroprusside in the endothelium-denuded basilar artery, but not in the endothelium-denuded mesenteric artery. In conclusion, LNMMA-induced heterogenous vasoconstriction was due to the different sensitivities of vascular smooth muscles to NO/cGMP. The heterogeneity may result from a difference in the basal state of ion channels such as the voltage-dependent Ca2+ channel and the BK(Ca) channel in vascular smooth muscles.

Vipergic innervation of the mammalian pineal gland

The present article reviews the literature relative to VIP- and PHI-containing nerve fibers in the pineal gland of mammals. The article summarizes data on the presence and distribution of the two peptides in the brain of mammals, their role in neuronal metabolism, and the significance and origin of VIPergic and PHIergic cerebrovascular nerve fibers. Special emphasis is placed on VIP- and PHI-containing nerves in the pineal gland. The morphology of the fibers, the nature of the innervation, and the distribution of immunoreactive nerves within the pineal gland are examined. The review discusses the nature of the classical and "central" innervation of the pineal gland. The possible site of origin of pinealopetal VIPergic and PHIergic fibers is investigated, with special reference to ganglia of the head, and particularly to the pterygopalatine, otic, and trigeminal ganglia. The nature of VIP (and PHI) receptors is examined with reference to the most recent acquisitions in the field. Based on the data, a role for VIP (and PHI) in pineal metabolism is discussed.

Electron-immunocytochemical studies of perivascular nerves of mesenteric and renal arteries of golden hamsters during and after arousal from hibernation

Electron immunocytochemistry was used to examine perivascular nerves of hamster mesenteric and renal arteries during hibernation and 2 h after arousal from hibernation. Vessels from cold-exposed but nonhibernating, and normothermic control hamsters were also examined. During hibernation the percentage of axon profiles in mesenteric and renal arteries that were immunopositive for markers of sympathetic nerves, tyrosine hydroxylase (TH) and neuropeptide Y (NPY), were increased 2-3 fold compared with normothermic and cold control animals. This increase was reduced markedly only 2 h after arousal from hibernation. The small percentage of nitric oxide synthase-1-positive axon profiles found in mesenteric (but not renal) arteries was also increased during hibernation and returned towards control values after arousal. In contrast, the percentage of perivascular axons immunostaining for vasoactive intestinal polypeptide (VIP), a marker for parasympathetic nerves, was reduced in mesenteric arteries during hibernation. There was no labelling of perivascular nerves for substance P in either mesenteric or renal arteries. It is suggested that the increase in percentage of TH- and NPY-immunostained perivascular nerves may account for the increased vasoconstriction associated with high vascular resistance that is known to occur during hibernation. The reduction in the percentage of axons positive for VIP in hibernating animals would contribute to this mechanism since this neuropeptide is a vasodilator.

Occurrence and distribution of substance P receptors in the cerebral blood vessels of the rat

The distribution of immunoreactivity to the receptor for substance P was examined in the cerebral blood vessels of the rat. Substance P immunoreactivity has been demonstrated in the nerve fibers of the cerebral blood vessels. Recently, the production of substance P receptor specific antibody has enabled the detection of localization of the substance P receptor in the central nervous system. In this study, we examined the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia innervating the cerebral blood vessels. Sprague-Dawley rats were perfused with fixative and the pial arteries and the cranial ganglia known to innervate the cerebral blood vessels, i.e., trigeminal, sphenopalatine, internal carotid, otic and superior cervical ganglia, were dissected. All specimens were incubated with anti-substance P receptor IgG, then stained by the avidin-biotin-peroxidase complex method. Numerous nerve fibers with varicosities forming plexuses, with substance P receptor immunoreactivity were observed on the walls of the major extracerebral arteries forming the circle of Willis and its branches. Substance P receptor immunoreactivity was also detected in the endothelium of the cerebral arteries. Substance P receptor immunoreactivity was positive in many neurons of the sphenopalatine ganglion, otic ganglion, trigeminal ganglion, superior cervical ganglion and internal carotid ganglion. The present study demonstrated the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia that innervate the cerebral blood vessels. These findings are important in understanding the responsiveness of the cerebral blood vessels to substance P.

Inducible nitric oxide synthase: a possible key factor in the pathogenesis of chronic vasospasm after experimental subarachnoid hemorrhage

OBJECT

The role of nitric oxide (NO) in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH) is not well understood. Nitric oxide is a well-established vasodilatory substance; however, in SAH, NO may become a major source for the production of injurious free-radical species, leading to chronic cerebral vasospasm. Reactive overproduction of NO to counteract vascular narrowing might potentiate the detrimental effects of NO. The focus of the present study is to determine the extent of reactive induction of inducible nitric oxide synthase (iNOS) after experimental SAH.

METHODS

Chronic vasospasm was induced in male Wistar rats by an injection of autologous blood (100 microl) into the cisterna magna followed by a second injection 24 hours later. A control group of 10 animals was treated with injections of 0.9% sodium chloride solution. Vasospasm was verified by pressure-controlled angiography after retrograde cannulation of the external carotid artery 7 days later. In 11 of 15 animals radiographic evidence of cerebral vasospasm was seen. The animals were perfusion fixed and their brains were removed for immunohistochemical assessment. With the aid of a microscope, staining for iNOS was quantified in 40-microm floating coronal sections. Immunohistochemical staining for iNOS was markedly more intense in animals with significant angiographic evidence of vasospasm. Virtually no staining was observed in control animals. Seven days after the second experimental SAH, labeling of iNOS was found in endothelial cells, in vascular smooth-muscle cells, and, above all, in adventitial cells. Some immunohistochemical staining of iNOS was observed in rod cells (activated microglia), in glial networks, and in neurons.

CONCLUSIONS

The present study demonstrates induction of iNOS after experimental SAH.

Messenger molecules and receptor mRNA in the human trigeminal ganglion

The presence and distribution of neuromessenger molecules and receptor mRNA in human trigeminal ganglion was studied with immunocytochemical, in situ hybridisation and RT-PCR techniques. Immunofluorescence staining revealed that calcitonin gene-related peptide (CGRP) immunoreactive (-ir) neurons occurred in high numbers, constituting 36-40% of all nerve cell bodies in the ganglion. Accordingly, in situ hybridisation demonstrated CGRP mRNA in a large portion of the trigeminal neurons. A small number of the nerve cell bodies showed substance P (SP)-ir, (18%), nitric oxide synthase (NOS)-ir (15%), and pituitary adenylate cyclase activating peptide (PACAP)-ir (20%). Double immunostaining revealed that only few CGRP-ir neurons also were NOS-ir (less than 5%). The C-terminal flanking peptide of neuropeptide Y, C-PON, was not visible in any of the nerve cell bodies studied. Agarose gel electrophoresis of the RT-PCR products from the ganglia demonstrated the presence of mRNA corresponding to CGRP1, NPY Y1 and Y2, and VIP1 receptors. These results suggest both sympathetic and parasympathetic influence on the activity in the trigeminal ganglion.

Neuronal messengers and peptide receptors in the human sphenopalatine and otic ganglia

A majority of the parasympathetic nerve fibers to cranial structures derive from the sphenopalatine and otic ganglia. In particular, blood vessels are invested with a rich supply of dilator fibers of parasympathetic origin. In the present study, we have examined the occurrence of noncholinergic neuromessengers and neuropeptide receptors in the human sphenopalatine and otic ganglia. Vasoactive intestinal peptide (VIP)-immunoreactive (ir) nerve cell bodies occurred in high numbers in the sphenopalatine and otic ganglia. Likewise, high numbers of NOS- and PACAP-containing nerve cell bodies were seen in both ganglia. Autofluorescent lipofuscin, characteristic of adult human nervous tissue, was present within many nerve cell bodies in both ganglia. Receptor mRNA was studied with reverse transcriptase-polymerase chain reaction (RT-PCR). Total RNA from the sphenopalatine and otic ganglia was successfully extracted. By using appropriate sense and antisense primers, oligonucleotides were designed from the human sequences derived from GenBank, corresponding to human NPY Y1, CGRP1 and VIP1 receptors. In the sphenopalatine ganglion, we revealed the presence of mRNA for the human NPY Y1 and VIP1 receptors but not the CGRP1 receptor. The otic ganglion was found to react positively only for primers to mRNA for VIP1 but not for CGRP1 or NPY Y1 receptors.

Histopathological changes and nitric oxide synthase activity in corpus cavernosum from rats with neurogenic erectile dysfunction

OBJECTIVE

To investigate changes in histology and nitric oxide synthase (NOS) activity in cavernosal tissues from rats with neurogenic erectile dysfunction induced experimentally.

MATERIALS AND METHODS

Twenty-four adult male Sprague-Dawley rats were divided equally into three groups and underwent a sham operation (control, group 1), unilateral (group 2) or bilateral (group 3) cavernosal nerve resection. Three months later they were killed and the cavernosal tissues analysed histologically by light and transmission electron microscopy, with NOS activity detected using an NADPH-diaphorase staining technique.

RESULTS

On light and electron microscopy, while penile nerves and cavernosal smooth muscle cells had a normal morphological appearance in the eight control rats, there were degenerative changes of the myelinated penile nerves and axonal fibrosis in groups 2 and 3. However, these changes were not significant. Using NADPH-diaphorase staining, NOS activity was detected in all three groups in endothelial cells and cavernosal structures. However, the staining was more intense in endothelial cells and cavernosal muscles of rats in group 2 than in the other groups.

CONCLUSION

NOS activity was increased in the cavernosal tissue after cavernosal denervation, but the pharmacological action of nitric oxide may be impaired.

Role of nitric oxide in traumatic brain injury in the rat

OBJECT

Although nitric oxide (NO) has been shown to play an important role in the pathophysiological process of cerebral ischemia, its contribution to the pathogenesis of traumatic brain injury (TBI) remains to be clarified. The authors investigated alterations in constitutive nitric oxide synthase (NOS) activity after TBI and the histopathological response to pharmacological manipulations of NO.

METHODS

Male Sprague-Dawley rats underwent moderate (1.7-2.2 atm) parasagittal fluid-percussion brain injury. Constitutive NOS activity significantly increased within the ipsilateral parietal cerebral cortex, which is the site of histopathological vulnerability, 5 minutes after TBI occurred (234.5+/-60.2% of contralateral value [mean+/-standard error of the mean ¿SEM¿], p < 0.05), returned to control values by 30 minutes (114.1+/-17.4%), and was reduced at 1 day after TBI (50.5+/-13.1%, p < 0.01). The reduction in constitutive NOS activity remained for up to 7 days after TBI (31.8+/-6.0% at 3 days, p < 0.05; 20.1+/-12.7% at 7 days, p < 0.01). Pretreatment with 3-bromo-7-nitroindazole (7-NI) (25 mg/kg), a relatively specific inhibitor of neuronal NOS, significantly decreased contusion volume (1.27+/-0.17 mm3 [mean+/-SEM], p < 0.05) compared with that of control (2.52+/-0.35 mm3). However, posttreatment with 7-NI or pre- or posttreatment with nitro-L-arginine-methyl ester (L-NAME) (15 mg/kg), a nonspecific inhibitor of NOS, did not affect the contusion volume compared with that of control animals (1.87+/-0.46 mm3, 2.13+/-0.43 mm3, and 2.18+/-0.53 mm3, respectively). Posttreatment with L-arginine (1.1+/-0.3 mm3, p < 0.05), but not 3-morpholino-sydnonimine (SIN-1) (2.48+/-0.37 mm3), significantly reduced the contusion volume compared with that of control animals.

CONCLUSIONS

These data indicate that constitutive NOS activity is affected after moderate parasagittal fluid percussion brain injury in a time-dependent manner. Inhibition of activated neuronal NOS and/or enhanced endothelial NOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Effects of endothelin receptor type A antagonism and nitric oxide synthase inhibition on cerebral blood flow in hypertensive rats

Effects of the endothelin receptor type A antagonist BQ 123 and the NO synthase inhibitor L-NMMA on cerebral blood flow were studied in vivo in anaesthetized hypertensive (SHR) and normotensive (WKY) rats. The effects of acetylcholine following pre-treatment with these drugs were also studied with the microsphere method for blood flow determination in the cortex, thalamus, caudatus, pons, medulla, cerebellum and hypophysis. BQ 123 (1 mg kg-1) induced only minor effects on cerebral blood flow in both strains (n = 8), whereas L-NMMA (N = 8; 20 mg kg-1) reduced regional cerebral blood flow significantly in most regions (21-54%) in the hypertensive, but not in the normotensive rat. In normotensive rats pre-treated with BQ 123 intravenous administration of acetylcholine (2 micrograms kg-1 min-1) induced a widespread significant increase (20-50%) in cerebral blood flow despite a reduction of the mean arterial blood pressure, while no significant effects were seen in hypertensive animals. Intravenous infusion of acetylcholine in animals pre-treated with L-NMMA did not affect cerebral blood flow in most regions in either of the two rat strains. In conclusion, a vasodilatory response to acetylcholine was found following endothelin receptor A antagonism in the WKY rat only, suggesting a role for endothelin in the control of cerebral blood flow in this strain. Furthermore, a higher basal vasodilating nitric oxide-tone seems to be present in the hypertensive rat compared with the normotensive rat.

Developmental characteristics of neuronal nitric oxide synthase (nNOS) immunoreactive neurons in fetal to adolescent human brains

The developmental characteristics of the neuronal nitric oxide synthase (nNOS) immunoreactive neurons in the human brain were studied. In the frontal lobe, nNOS immunoreactive cells appeared as early as 18 gestational weeks (GW) in the subcortical plate and then increased predominantly in the subcortical white matter during the fetal period, while weakly immunoreactive neurons were found in the cortical II-IV layers after 26 GW. In the basal ganglia, immunoreactive neurons could be detected in the striatum as early as 13 GW, and then showed a transient increase with peaks at 23-24 GW and 33-36 GW in the putamen and caudate nucleus, respectively. In the cerebellum, immunoreactivity was detected in the Purkinje and basket cells after 23 GW and 31 GW, respectively. The immunoreactivity of internal granule cells was constantly weak. In the brain stem, constant and intense immunoreactive neurons were found in the central gray, pedunculopontine tegmental nucleus, solitary tract nucleus, and lateral reticular nucleus. The immunoreactivity in the neurons of the pontine nucleus and inferior olivary nucleus was transiently increased, with peaks at 38-40 GW and 23-24 GW, respectively. This characteristic nNOS development suggests that transient nNOS hyperproduction may contribute to neuron maturation as well as vulnerability in each period and region, and NO may play an important role in the basic development of human brain functions.

Role of nitric oxide and thromboxane in the maintenance of cerebrovascular tone

This study investigated the role of thromboxane A2 (TXA2) and neuronal nitric oxide (NO) synthase (nNOS)-derived NO in the maintenance of resting cerebrovascular tone. Rat basilar artery (BA) segments were mounted in myographs to study their isometric tension development. 7-Nitro indazole monosodium salt (7-NINA), a specific inhibitor of nNOS, had no significant effect on the resting tone, whereas the general NOS blocker N(G)-nitro-L-arginine (L-NA) induced strong contraction. The thromboxane (TP) receptor antagonist ICI 192605 induced weak vasodilation, and this effect was significantly enhanced after precontraction of the vessels with uridine-5'-triphosphate (UTP). Incubation of BA segments with ICI 192605 attenuated the contractile effect of UTP. These data indicate that nNOS is not involved in resting cerebrovascular NO production and that basal TXA2 release induces a weak contractile tone in the rat BA. Activation of P2U receptors by UTP appears to stimulate TXA2 release in these vessels.

Segregation of VIPergic-nitric oxidergic and cholinergic-nitric oxidergic innervation in porcine middle cerebral arteries

The distribution of nitric oxide synthase (NOS)-, choline acetyltransferase (ChAT)-, and vasoactive intestinal polypeptide (VIP)-immunoreactivities, and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-reactivities in the sphenopalatine ganglia (SPG), and perivascular nerves in middle cerebral arteries of the pig was investigated by double-staining techniques using combined immunofluorescence and histochemistry methods. In the SPG, almost all ganglionic cells were NOS-immunoreactive (I) and NADPHd-positive, and both NOS immunoreactivities and NADPHd reactivities were completely co-localized. ChAT-I ganglionic cells accounted for 75%, while VIP-I ganglionic cells represented 42% of all ganglionic cells. Almost all VIP immunoreactivities were co-localized with ChAT immunoreactivities, and all ganglionic cells that were VIP-I and/or ChAT-I were NOS-I and NADPHd-reactive. None of the ganglionic cells in the SPG were immunoreactive to calcitonin gene-related peptide (CGRP). CGRP immunoreactivities, however, were found to surround some ganglionic cells. In middle cerebral arteries, all adventitial NOS-I bundles and fine fibers were coincident with NADPHd fibers. Almost all adventitial ChAT-I bundles and thin fibers, and VIP-I mesh-like fibers stained positively for NADPHd, while the mesh-like NADPHd fine fibers were not ChAT-I. Simultaneous labeling using antibodies against VIP and ChAT further indicated that VIP-I fibers were closer than ChAT-I fibers to the smooth muscle. In rare occasions, perivascular fibers were found to be stained for both ChAT and VIP, showing that most ChAT-I and VIP-I fibers were not coincident. These results suggest that ChAT and VIP are rarely co-localized in perivascular nerves in middle cerebral arteries, and point out that the neurotransmitter and the modulator that are co-localized within the same nerve cell body may distribute totally independently and differently at the terminal level. The present results also indicate that in cerebral perivascular nerves, the combination of nitric oxide (NO) and acetylcholine (ACh), as well as the combination of NO and VIP, are localized in the same nerve with different axons containing either NO plus ACh, or NO plus VIP. These findings support the hypothesis that ACh and VIP may act as modulators in regulating presynaptic release of NO, and therefore, cerebral neurogenic vasodilation, from their respective perivascular cholinergic-nitric oxidergic and VIPergic-nitric oxidergic nerves.

Modulation of myofascial pain by the reproductive hormones: a preliminary report

STATEMENT OF PROBLEM

The predominance of myofascial pain in women in childbearing years suggests that the reproductive hormones may play a role in this pain disorder.

PURPOSE

The potential influence of these hormones on myofascial pain was evaluated.

METHODS

Pain patterns were compared across three consecutive menstrual cycles in oral contraceptives users (OC group) and nonusers (Non-OC group).

RESULTS

Preliminary results showed that within menstrual cycle variability of daily pain was higher than the nonusers group. In addition to their low variation, pain levels of oral contraceptives users remained positive across the hormonal cycle, whereas in nonusers, peaks of pain alternated frequently with pain-free periods. These data suggest that pain levels in oral contraceptives users may be more constant than those of nonusers.

CONCLUSIONS

This potential hormonal influence on myofascial pain levels among oral contraceptives users may represent one of the various adverse effects induced by oral contraceptives at the trigeminal area in sensitive subjects. Evidence supporting the link between estrogen, nitric oxide, and inflammatory processes is presented.

Perivascular nerves contribute to cortical spreading depression-associated hyperemia in rats

We investigated the contribution of perivascular nerves and neurotransmitters to cortical spreading depression (CSD)-associated hyperperfusion in the rat. Chronic transection of the nasociliary nerve (NCN, 2 wk before) decreased ipsilateral CSD-associated hyperperfusion by 23 +/- 13% (mean +/- SD; n = 5, P < 0.05), whereas acute transection of the NCN or sham surgery had no effect (n = 8). When the NCN and parasympathetic nerve fibers (PSN) were both chronically transected, CSD hyperperfusion was attenuated by 55 +/- 19% (n = 5, P < 0.05). Cerebrovascular reactivity to hypercapnia was not significantly affected. Brain topical superfusion of the muscarinic receptor antagonist atropine (10(-4) M) caused a reduction of CSD hyperperfusion by 41 +/- 13% (n = 5, P < 0.05). The competitive blockade of calcitonin gene-related peptide (CGRP) receptors by CGRP-(8-37) (5 x 10(-7) M) afforded a decrease by 49 +/- 19% (n = 5, P < 0.05), without affecting CO2 reactivity (n = 4). The combined application of both CGRP-(8-37) and atropine further attenuated CSD hyperperfusion (by 69 +/- 17%, n = 5, P < 0.05). After chronic NCN and PSN transection brain topical superfusion of CGRP-(8-37) (5 x 10(-7) M) reduced CSD hyperperfusion slightly by 9.5 +/- 5% (n = 3). Atropine (10(-4) M) afforded a decrease by 17 +/- 6% (n = 3). These reductions were not statistically significant. We conclude that CSD-associated hyperperfusion is mediated in part by a depolarization of trigeminal sensory and parasympathetic nerve fibers, resulting in a release of vasoactive trigeminal and parasympathetic neurotransmitters.

Calcitonin gene-related peptide and nitric oxide in the trigeminal ganglion: cerebral vasodilatation from trigeminal nerve stimulation involves mainly calcitonin gene-related peptide

Nitric oxide (NO) is a novel neurotransmitter candidate to which a large number of physiological roles has been ascribed. In the present study, immunocytochemistry was used to demonstrate NO synthase (NOS) and to investigate possible co-localization with other neurotransmitters. In the trigeminal ganglion of the cat, a moderate number of NOS immunoreactive nerve cell bodies was seen, of which the major part also expressed calcitonin gene-related peptide (CGRP). The nerve cell bodies expressing NOS in the trigeminal ganglion were predominantly of small to medium size; while numerous cell bodies of varying size contained CGRP. With in situ hybridization using oligonucleotide probes, CGRP mRNA was demonstrated in almost all trigeminal neurons of the cat. Stimulation of the nasociliary nerve resulted in a frequency-dependent increase in ipsilateral local cortical blood flow by 30 +/- 6%. Administration of the NOS inhibitor NG-nitro-L-arginine-methylester (L-NAME) did not significantly alter this response when applied intravenously or on the cortical surface. Local cortical administration of the CGRP blocker h-CGRP (8-37) did not alter the cerebral vasodilator response to hypercapnia or resting flow. However, the nasociliary nerve response was reduced by 50% after h-CGRP (8-37), with a general shift to the right of the frequency-response curve. These data suggest that although NOS is seen in several trigeminal ganglion cells and coexists with CGRP in a subpopulation of the sensory neurons, its role in trigeminally mediated vasodilatation was not significant.

Direct evidence for nitric oxide synthase in vagal afferents to the nucleus tractus solitarii

The anatomical relationship between vagal afferents and brain nitric oxide synthase containing terminals in the nucleus tractus solitarii was studied by means of anterograde tracing combined with immunocytochemistry and immuno-electron microscopy. Biotinylated dextran amine was injected into the nodose ganglion with a glass micropipette. Four to eight days following the injection, regions of the nucleus tractus solitarii containing biotinylated dextran amine-labelled vagal afferents and those containing nitric oxide synthase-immunopositive terminals were congruent. Many neurons exhibiting nitric oxide synthase immunoreactivity were found within the biotinylated dextran amine-containing terminal field. However dense labeling of terminals with biotinylated dextran amine precluded determination if the terminals were nitric oxide synthase-immunoreactive. Therefore, we combined degeneration of vagal afferents after removal of one nodose ganglion with nitric oxide synthase immuno-electron microscopy. Axon terminals that possessed characteristic vesicle clusters and were partially or completely engulfed by glial processes were identified as degenerating vagal afferents. Degenerating axon terminals comprised 38% of the total axon terminals in the nucleus tractus solitarii in a sample of sections; and of the degenerating axon terminals, 67% were nitric oxide synthase-immunoreactive. Nitric oxide synthase immunoreactivity was present in 41% of the non-degenerating axon terminals. Prominent staining of dendrites for nitric oxide synthase immunoreactivity indicated that much of the nitric oxide synthase in the nucleus tractus solitarii is not derived from peripheral afferents. Of the total number of dendritic profiles sampled, half were nitric oxide synthase-immunoreactive. Our data support the hypothesis that nitric oxide or nitric oxide donors may be present in primary vagal afferents that terminate in the nucleus tractus solitarii. While this study confirms that vagal afferents contain brain nitric oxide synthase, it demonstrates for the first time that the majority of nitric oxide synthase immunoreactivity in the nucleus tractus solitarii is found in intrinsic structures in the nucleus. In addition, our data show that second or higher order neurons in the nucleus tractus solitarii may be nitroxidergic and receive both nitroxidergic and non-nitroxidergic vagal input.

Regulation of ductus arteriosus patency by nitric oxide in fetal lambs: the role of gestation, oxygen tension, and vasa vasorum

We hypothesized that nitric oxide (NO) production by the fetal ductus arteriosus is limited because of low fetal PO2, but that at neonatal PO2, NO might be an important regulator of ductus arteriosus tone. We exposed isolated rings of fetal lamb ductus arteriosus to elevated PO2. L-NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), and methylene blue and 6-anilino-5,8-quinolinedione (LY83583), inhibitors of guanylate cyclase, produced constriction of the ductus arteriosus. When ductus arteriosus rings were exposed to low PO2, L-NAME had no effect, and methylene blue and LY83583 had only a small effect on ductus arteriosus tone. Sodium nitroprusside and calcium ionophore A23187 relaxed ductus arteriosus rings more than aortic rings, and relaxed ductus arteriosus rings from immature fetuses more than those from late gestation fetuses. In contrast, ductus arteriosus rings from both early and late gestation were equally sensitive to 8-bromo-cGMP. By both reverse transcriptase-polymerase chain reaction and immunohistochemistry, endothelial cell NOS and inducible calcium-independent NOS, but not nerve cell NOS, were detected in the ductus arteriosus. Inducible NOS was expressed only by endothelial cells lining the ductus arteriosus lumen; in contrast, endothelial cell NOS was expressed by both luminal and vasa vasorum endothelial cells. The role of inducible NOS in the ductus arteriosus is uncertain because the potency of a specific inducible NOS inhibitor in constricting the ductus arteriosus was negligible compared with that of an endothelial cell NOS inhibitor. We speculate that NO may be an important regulator of ductus arteriosus tone at high but not low PO2. The endothelial cell NOS isoform found in vasa vasorum may be an important source of NO because removal of ductus arteriosus luminal endothelium only partially blocks the effects of L-NAME, methylene blue, and LY83583.

Cerebral vasodilators

The vascular tone, vascular resistance and blood flow in the brain are regulated by neural and humoral factors in quite a different way from those of peripheral organs and tissues. In contrast to the dominant vasoconstrictor control in the periphery, the intracranial vascular tone is predominantly influenced by vasodilator mediators over vasoconstrictor ones. Recent studies have revealed that nitroxidergic vasodilator nerve and endothelium-derived hyperpolarizing factor (EDHF) or K+ channel opening substance appear to play important roles in the regulation of cerebral arterial and arteriolar tone in primate and subprimate mammals, in addition to the accepted information concerning the crucial contribution of endothelium-derived relaxing factor (EDRF) or nitric oxide (NO), polypeptides, prostanoids, etc. This article summarizes characteristic properties of vasodilator factors in controlling the cerebral arterial and arteriolar tone that undoubtedly contribute to circulatory homeostasis. The content includes vasodilator nerve, endogenous vasodilator substances, and vasodilator interventions such as hypoxia, hypercapnia and hyperosmolarity.

Temporal changes in perivascular concentrations of oxyhemoglobin, deoxyhemoglobin, and methemoglobin after subarachnoid hemorrhage

Hemoglobin released from hemolysed erythrocytes has been postulated to be responsible for delayed cerebral vasospasm after subarachnoid hemorrhage (SAH). However, the evidence is indirect and the mechanisms of action are unclear. Cerebrovascular tone is regulated by a dynamic balance of relaxing and contracting factors. Loss of the endothelium-derived relaxing factor-nitric oxide in the presence of oxyhemoglobin and overproduction of endothelin-1 stimulated by oxyhemoglobin have been postulated as causes of delayed cerebral vasospasm after SAH.

OBJECT

The authors aimed to investigate this hypothesis using in vivo microdialysis to examine time-dependent changes in the perivascular concentrations of oxyhemoglobin, deoxyhemoglobin, and methemoglobin in a primate model of SAH.

METHODS

Nine cynomolgus monkeys underwent right-sided frontotemporal craniectomy and placement of a semipermeable microdialysis catheter adjacent to the right middle cerebral artery (MCA). Saline (control group, three animals) or an arterial blood clot (SAH group, six animals) was then placed around the MCA and the catheter. Arteriographically confirmed vasospasm had developed in all animals with SAH but in none of the control animals on Day 7. The dialysate was collected daily for 12 days. Levels of oxyhemoglobin, deoxyhemoglobin, and methemoglobin were measured by means of spectrophotometry. Perivascular concentrations of oxyhemoglobin, deoxyhemoglobin, and methemoglobin peaked on Day 2 in the control monkeys and could not be detected on Days 5 to 12. Perivascular concentrations of oxyhemoglobin and deoxyhemoglobin peaked on Day 7 in the SAH group, at which time the concentrations in the dialysate were 100-fold higher than in any sample obtained from the control animals. Methemoglobin levels increased only slightly, peaking between Days 7 and 12, at which time the concentration in the dialysate was 10-fold higher than in samples from the control animals.

CONCLUSIONS

This study provides in vivo evidence that the concentrations of oxyhemoglobin and deoxyhemoglobin increase in the cerebral subarachnoid perivascular space during the development of delayed cerebral vasospasm. The results support the hypothesis that oxyhemoglobin is involved in the pathogenesis of delayed cerebral vasospasm after SAH and implicate deoxyhemoglobin as a possible vasospastic agent.

Neuronal NOS-cGMP-dependent ACh-induced relaxation in pial arterioles of endothelial NOS knockout mice

We evaluated the effects of superfusing 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), eNOS null (B) an inhibitor of soluble guanylyl cyclase, and 7-nitroindazole sodium (7-NI), a selective neuronal nitric oxide synthase (nNOS) inhibitor, on the acetylcholine (ACh) response in endothelial NOS (eNOS) null mice. Pial arteriolar diameter was measured by intravital microscopy through a closed cranial window under alpha-chloralose anesthesia. NOS activity was measured by [3H]arginine-to-[3H]citrulline conversion in subjacent cortex in vitro. The density and distribution of muscarinic receptors in the brain were determined by quantitative [3H]quinuclidinyl benzilate autoradiography and did not differ between the eNOS mutants and wild-type mice. ACh superfusion (1 and 10 microM) dose dependently dilated pial arterioles in eNOS null and wild-type mice. ODQ (10 microM) attenuated ACh-induced dilation in both eNOS mutants (41% decrease at 10 microM ACh, P < 0.01, n = 6) and wild-type strains (n = 5 per group). By contrast, topical superfusion of 7-NI (100 microM) attenuated the ACh response in eNOS mutants only (66%, P < 0.05, and 25% decrease, P < 0.05, at 1 and 10 microM ACh, respectively). Our findings suggest that nNOS-guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathways dilate pial arterioles by compensatory mechanisms after eNOS gene disruption.

Nitrergic innervation of the cerebral arterial tree in the bent-winged bat (mammalia: Microchiroptera)

The distribution and origin of cerebrovascular nitrergic nerves were studied immunohistochemically and histochemically in the bent-winged bat. The supply of nitric oxide synthase (NOS)-immunoreactive (IR) and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd)-positive nerves to the bat major cerebral arteries differs from the general mammalian pattern in that it is preferential for the vertebrobasilar system (VBS) as opposed to the internal carotid system. Interestingly, a few nerve cells with bright NOS immunofluorescence and intense NADPHd activity were localized in the walls of the vertebral artery (VA) and basilar artery (BA) from many individual bats. Cerebral perivascular NOS-IR nerves were generally immunoreactive for vasoactive intestinal polypeptide (VIP). NOS-IR neurons intrinsic to the BA and VA expressed variable degrees of VIP immunoreactivity and showed no acetylcholinesterase (AChE) activity. Most cell bodies of the microganglia (MG) in the carotid canal and tympanic cavity, and those of the cranial and cervical facial ganglia, showed both NOS and VIP immunoreactivities and were stained intensely for NADPHd. From these and other findings, it is suggested that, in the bent-winged bat at least, the BA and VA of the cerebral arterial tree are frequently dually innervated by two neurochemically defined nitrergic neurons, the cranial parasympathetic VIP-IR and AChE-positive neurons, which are derived mainly from the MG via the internal carotid artery, and the intrinsic neurons, either IR or immunonegative for VIP but negative for AChE, which form an outflow tract from some caudally located ganglia projecting to the VBS via the VA.