Distribution of intracardiac neurones and nerve terminals that contain a marker for nitric oxide, NADPH-diaphorase, in the guinea-pig heart

The role of the tripartite synapse in the heart: how glial cells may contribute to the physiology and pathophysiology of the intracardiac nervous system

One of the major roles of the intracardiac nervous system (ICNS) is to act as the final site of signal integration for efferent information destined for the myocardium to enable local control of heart rate and rhythm. Multiple subtypes of neurons exist in the ICNS where they are organized into clusters termed ganglionated plexi (GP). The majority of cells in the ICNS are actually glial cells; however, despite this, ICNS glial cells have received little attention to date. In the central nervous system, where glial cell function has been widely studied, glia are no longer viewed simply as supportive cells but rather have been shown to play an active role in modulating neuronal excitability and synaptic plasticity. Pioneering studies have demonstrated that in addition to glia within the brain stem, glial cells within multiple autonomic ganglia in the peripheral nervous system, including the ICNS, can also act to modulate cardiovascular function. Clinically, patients with atrial fibrillation (AF) undergoing catheter ablation show high plasma levels of S100B, a protein produced by cardiac glial cells, correlated with decreased AF recurrence. Interestingly, S100B also alters GP neuron excitability and neurite outgrowth in the ICNS. These studies highlight the importance of understanding how glial cells can affect the heart by modulating GP neuron activity or synaptic inputs. Here, we review studies investigating glia both in the central and peripheral nervous systems to discuss the potential role of glia in controlling cardiac function in health and disease, paying particular attention to the glial cells of the ICNS.

Myths and realities of the cardiac vagus

There is continuing belief that cardiac parasympathetic postganglionic fibres are sparse or absent from the ventricles. This review of the literature shows that the supposition is a myth. Early studies considered that fine silver-stained fibres coursing amongst ventricle myocardial cells were most likely cardiac parasympathetic postganglionic fibres. The conclusions were later supported by acetyl cholinesterase staining using a method that appeared not to be associated with noradrenaline nerve fibres. The conclusion is critically examined in the light of several recent histological studies using the acetyl cholinesterase method and also a more definitive technique (CHAT), that suggest a widespread location of parasympathetic ganglia and a relatively dense parasympathetic innervation of ventricular muscle in a range of mammals including man. The many studies demonstrating acetylcholine release in the ventricle on vagal nerve stimulation and a high density of acetylcholine M2 receptors is in accord with this as are tests of ventricular performance from many physiological studies. Selective control of cardiac functions by anatomically segregated parasympathetic ganglia is discussed. It is argued that the influence of vagal stimulation on ventricular myocardial action potential refractory period, duration, force and rhythm is evidence that vagal fibres have close apposition to myocardial fibres. This is supported by clear evidence of accentuated antagonism between sympathetic activity and vagal activity in the ventricle and also by direct effects of vagal activity independent of sympathetic activity. The idea of differential control of atrial and ventricular physiology by vagal C and vagal B preganglionic fibres is examined as well as differences in chemical phenotypes and their function. The latter is reflected in medullary and supramedullary control. Reference is made to the importance of this knowledge to understanding the normal physiology of cardiac autonomic control and significance to pathology.

Distribution and neurotransmitter localization in the heart of the ray-finned fish, bichir (Polypterus bichir bichir Geoffroy St. Hilaire, 1802)

Anatomical and physiological studies of cardiovascular control are lacking in the ray-finned fish, the bichirs. The present immunohistochemical studies on the bichir (Polypterus bichir bichir) demonstrated the occurrence of intracardiac neurons and nerve fibers in the heart. Immunoreactivity to tyrosine hydroxylase (TH) and acetylcholinesterase (AchE) and various neuropeptides (substance P, galanin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP)), including neuronal nitric oxide synthase (nNOS), was found in the nerve cell bodies lying close to the Sinus venosus and the sino-atrial region. The main intracardiac localization of the nervous tissue is a network of nerve fibers, presumably corresponding to the postganglionic outflow giving rise to nerve terminals and the nerve cell bodies. In addition, the heart is innervated by extrinsic monoamine-containing nerve fibers supplying the Conus arteriosus and Sinus venosus, and substance P and galanin immunopositive fibers probably originating from cranial and spinal ganglia. The adrenergic innervation of the heart of the bichir is similar to that of the teleosts, but further studies are required on nervous control of the heart.

Fluvastatin reduces pulmonary vein spontaneous activity through nitric oxide pathway

INTRODUCTION

Pulmonary veins (PVs) are the most important focus for the generation of atrial fibrillation. The HMG-CoA reductase inhibitors (statins) can reduce the occurrence of atrial fibrillation. The purposes of this study were to evaluate whether statins may inhibit the PV arrhythmogenic activity to prevent atrial arrhythmias from PVs and to investigate the link between fluvastatin, nitric oxide synthase (NOS) activity, mechanical activity, and electrical activity.

METHODS

Conventional microelectrodes and Western blot were used to record the electrical activity, diastolic tension, contractility and expression of Akt, endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), and phosphorylated Akt and eNOS before and after the administration of fluvastatin in rabbit PVs or atria.

RESULTS

Fluvastatin decreased the PV spontaneous activity, diastolic tension, and contractility, but did not change the action potential duration or resting membrane potential. The effects of fluvastatin on the PV firing rate and diastolic tension were attenuated in the presence of L-NAME (100 microM), wortmannin (100 nM), and ODQ (3 microM). Fluvastatin (1 muM) increased the phosphorylated Akt and eNOS, but did not change the total Akt or eNOS in the PVs and atria. In contrast, fluvastatin (1 microM) decreased the total nNOS in the PVs and atria.

CONCLUSIONS AND IMPLICATIONS

Fluvastatin produced nitric oxide through the PI3kinase/Akt pathway, thus reducing the PV vascular diastolic tension and PV spontaneous activity. These results may contribute to the beneficial effects of statins.

Architecture and age-related analysis of the neuronal number of the guinea pig intrinsic cardiac nerve plexus

The aims of the present study have been to determine the architecture of the guinea pig intrinsic cardiac nerve plexus (ICNP) and to test whether or not the heart of this species undergoes decrease in neuronal number with aging. Nine young (3-4 weeks of age) and nine adult (18-24 months of age) animals were examined employing histochemistry for acetylcholinesterase to reveal the ICNP in total hearts. The number of intracardiac neurons in seven animals was assessed via counting of the nerve cells both on total hearts and in serial sections of the atrial walls. The intracardiac neurons from adult guinea pigs were amassed within 329 +/- 15 ganglia. The hearts of young animals contained significantly fewer ganglia, only 211 +/- 27. In adult guinea pigs approximately 60% of the intracardiac neurons were distributed within ganglia of not more than 20 neurons, but the ganglia of such size accumulated only 45% of the neurons in young animals. The total number of the intracardiac neurons estimated per guinea pig heart was 2321 +/- 215, and this number did not differ significantly between young and adult animals. The nerves entering the guinea pig heart were found both in the arterial and venous part of the heart hilum. The nerves from the arterial part of the heart hilum proceeded into the ventricles, but the nerves from the venous part of the hilum formed a nerve plexus of the cardiac hilum located on the heart base. Within the guinea pig epicardium, intrinsic nerves divided into six routes and proceeded to separate atrial, ventricular and septal regions. In conclusion, findings of this study contradict the age-related decrease of the neuronal number in the guinea pig heart and illustrate the remarkable similarity in the architecture of the intracardiac nerve plexuses between guinea pig and rat.

The role of neuronal nitric oxide in the vagal control of cardiac interval of the rat heart in vitro

The aim of this study was to examine the role of neuronal nitric oxide (NO) on vagal regulation of the rat heart in vitro using the neuronal nitric oxide synthase (nNOS) inhibitor 1-(2-trifluoromethylphenyl) imidazole (TRIM). All experiments were carried out in the presence of the beta-adrenoreceptor antagonist atenolol (4 microM). Right thoracic vagus, or its cardiac branch, was stimulated at frequencies of 2, 4, 8, 16 and 32 Hz (pulse duration 1 ms, 20 V, for 20 s) before and after addition of TRIM (0.14 mM) and cardiac interval (ms) assessed. There was a significant positive linear correlation between cardiac interval and vagal frequency giving a slope of 2.76+/-0.8 ms/Hz (slope+/-S.E. slope; data pooled from eight rats) which was significantly attenuated following TRIM to 0.4+/-0.6 ms/Hz (P<0.05 ANOVA; n=8 rats). Nicotine applied in cumulative concentrations (0.03, 0.1, 0.3, 0.5, 1 mM) caused a linear concentration-dependent increase in cardiac interval, with a slope of 403+/-72 ms/mM (n=10 rats) which was significantly attenuated after treatment with hexamethonium (28 microM), to 190+/-36 ms/mM (n=10 rats, P<0.05 ANOVA), and atropine (3 microM) 100+/-31 ms/mM (n=9 rats, P<0.05 ANOVA) but not following TRIM (0.14 mM) 262+/-48 ms/mM (n=9 rats, P<0.05 ANOVA). These results suggest that NO facilitates vagal effects on the rat heart in vitro by an action at the pre-ganglionic/post-ganglionic synapse.

Evidence for a possible role for nitric oxide in the modulation of heart activity in Achatina fulica and Helix aspersa

The effects of nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine, S-nitroso-l-glutathione, sodium nitroprusside and sodium nitrite were investigated on the activity of the isolated hearts of Achatina fulica and Helix aspersa. NO donors inhibited heart activity in a concentration-dependent manner. The only exception was sodium nitroprusside, which excited H. aspersa heart. The inhibitory effects of these NO donors were reduced by the NO scavenger, methylene blue, the guanylyl cyclase inhibitor, 1H-(1,2,4) Oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), and potentiated by 8-Br-cGMP and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Acetylcholine also inhibited the heart activity, and this inhibition was reduced by methylene blue and ODQ. Positive NADPH-diaphorase staining was located in the outer pericardial layer of the heart of A. fulica. The present results provide evidence that NO may modulate the activity of gastropod hearts, and this modulation may modify the inhibitory action of acetylcholine on heart activity.

Localization of NOS-1 in the sarcolemma region of a subpopulation of atrial cardiomyocytes including myoendocrine cells and NOS-3 in vascular and endocardial endothelial cells of the rat heart

Cellular localization patterns of NOS isoforms 1 and 3 (nNOS and eNOS, respectively) in the mammalian heart under basal (non-stimulated) working conditions are still a matter of discussion. Therefore, this issue was reinvestigated in rats using RT-PCR, Western blotting, catalytic histochemistry, immunohistochemistry and image analysis. Tongue and extensor digitorum longus muscles served as positive controls for NOS-1 and NOS-3. RT-PCR revealed NOS-1 mRNA and NOS-3 mRNA in atria and ventricles. Western blotting showed NOS-1 protein in atria and NOS-3 protein in the walls of both heart chambers. Localization of the activity of urea-resistant (and therefore specific) NADPH diaphorase (NADPH-D) and NOS-1 immunohistochemistry showed that NOS-1 is present in the sarcolemma region of a subpopulation of atrial cardiomyocytes but not in working and impulse-conducting cardiomyocytes of atria and ventricles. Atrial natriuretic peptide (ANP) immunohistochemistry revealed that a minority of the NOS-1-expressing atrial cardiomyocytes are myoendocrine cells. eNOS immunostaining was present in endothelial cells of capillaries of the conducting and working myocardium and endocardial cells. Image analysis of the activity of urea-resistant NOS diaphorase showed that NOS-1 activity is lower in the sarcolemma region of atrial cardiomyocytes than in that of tongue and extensor digitorum longus myofibers. These data suggest that, in the non-stimulated rat heart. NOS-1 is expressed in a subpopulation of atrial cardiomyocytes including myoendocrine cells, and that NOS-3 is expressed in the vascular and endocardial endothelium.

Nitric oxide supports atrial function in sepsis: relevance to side effects of inhibitors in shock

The mechanisms underlying myocardial dysfunction in sepsis remain poorly understood. The theoretical benefits of nitric oxide synthase (NOS) inhibition in reversing the haemodynamic changes that characterise septic shock have not been supported by clinical trials, some of which have demonstrated detrimental myocardial effects. We have therefore assessed the effects of endotoxaemia on NOS enzyme expression as well as a number of functional responses of myocardial tissue from rats. Atrial tissue expressed high levels of mRNA for inducible (i) NOS and released increased levels of nitrite after animals were treated with endotoxin. In parallel, the inotropic response stimulated by isoprenaline was reduced in atria from endotoxin-treated animals, an effect that was reversed when endogenous release of NO was maximised. Our results suggest that myocardial contractility is maintained by NO production and that inhibitors may compromise cardiac output; this may explain the deleterious effects of NOS inhibition on cardiac function in clinical trials.

The nitric oxide synthase-1 and nitric oxide synthase-3/nitric oxide signalling systems in the heart of wild type mice and mouse mutants

Recently, we have shown that nitric oxide synthase-1 (NOS-1) and thus its product NO are present in the sarcolemma region of a subpopulation of atrial cardiomyocytes in the rat heart. In order to find out whether this newly discovered sarcolemma-associated NOS/NO system represents a general signalling mechanism in the murine rodent heart and whether its properties are comparable to those in skeletal muscle fibres, immunohistochemical and catalytic histochemical methods (including image analysis) were applied to the heart and extensor digitorum longus (EDL) and tongue muscles of wild type and mutant mice. In different strains of wild type mice and NOS-3 knockouts, urea-resistant (and therefore specific) NOS NADPH diaphorase histochemistry and NOS-1 immunohistochemistry revealed that NOS-1 activity and protein were present in the sarcolemma region of a subpopulation of atrial and ventricular working cardiomyocytes, but not in those of the impulse conducting system. Using image analysis, NOS-1 showed similar activities in the sarcolemma region of cardiomyocytes and in EDL type I myofibres. In mdx and NOS-1 knockout mice, NOS-1 was absent from the sarcolemma region of atrial and ventricular cardiomyocytes and of EDL and tongue muscle fibres, whereas NOS-1 was present in the hearts of NOS-3 knockouts. Atrial natriuretic peptide immunohistochemistry identified part of the atrial NOS-1-expressing cardiomyocytes as myoendocrine cells. In mdx mice as well as in NOS-1 - and NOS-3-deficient animals, the peptide was found in greater abundance than in wild type mice. These data suggest that NOS-1 is expressed in a subpopulation of working cardiomyocytes in the murine rodent heart, that the myoendocrine cells may be negatively modulated by NOS-1 - and NOS-3-produced NO, and that the anchoring mechanisms for NOS-1 in these cells (i.e. their confinement to the sarcolemma region) are comparable to those in skeletal muscle fibres.

Analysis and neuronal modeling of the nonlinear characteristics of a local cardiac reflex in the rat

Previous experimental results have suggested the existence of a local cardiac reflex in the rat. In this study, the putative role of such a local reflex in cardiovascular regulation is quantitatively analyzed. A model for the local reflex is developed from anatomical experimental results and physiological data in the literature. Using this model, a systems-level analysis is conducted. Simulation results indicate that the neuromodulatory mechanism of the local reflex attenuates the nonlinearity of the relationship between cardiac vagal drive and arterial pressure. This behavior is characterized through coherence analysis. Furthermore, the modulation of phase-related characteristics of the cardiovascular system is suggested as a plausible mechanism for the nonlinear attenuation. Based on these results, it is plausible that the functional role of the local reflex is highly robust nonlinear compensation at the heart, which results in less complex dynamics in other parts of the reflex.

The intrinsic origin of nitric oxide synthase immunoreactive nerve fibers in the right atrium of the guinea pig

We previously reported three kinds of nitric oxide synthase-immunoreactive (NOS-ir) axons in the guinea pig heart: the sparse fiber network covering the right atrium, the basket-like endings around intracardiac neurons, and the axons in the septal region. The sparse NOS-ir nerve fiber network in the right atrium remained after vagotomy and has been suggested to be originated from intrinsic cardiac ganglia. Using Chorera toxin B as a retrograde tracer, we determined a part of them were derived from cardiac ganglionic neurons located in the area near the vena cavae.

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.

Role of endothelium-derived nitric oxide in the regulation of cardiac oxygen metabolism: implications in health and disease

Endothelium-derived NO is considered to be primarily an important determinant of vascular tone and platelet activity; however, the modulation of myocardial metabolism by NO may be one of its most important roles. This modulation may be critical for the regulation of tissue metabolism. Several physiological processes act in concert to make endothelial NO synthase-derived NO potentially important in the regulation of mitochondrial respiration in cardiac tissue, including (1) the nature of the capillary network in the myocardium, (2) the diffusion distance for NO, (3) the low toxicity of NO at physiological (nanomolar) concentrations, (4) the fact that low PO(2) in tissue facilitates the action of NO on cytochrome oxidase, and (5) the formation of oxygen free radicals. A decrease in NO production is involved in the pathophysiological modifications that occur in heart failure and diabetes, disease states associated with altered cardiac metabolism that contributes to the evolution of the disease process. In contrast, several drugs (eg, angiotensin-converting enzyme inhibitors, amlodipine, and statins) can restore or maintain endogenous production of NO by endothelial cells, and this mechanism may explain part of their therapeutic efficiency. Thus, the purpose of this review is to critically evaluate the role of NO in the control of mitochondrial respiration, with special emphasis on its effect on cardiac metabolism.

Intense exercise causes decrease in expression of both endothelial NO synthase and tissue NOx level in hearts

Cardiac myocytes produce nitric oxide (NO). We studied the effects of intense exercise on the expression of NO synthase (NOS) and the tissue level of nitrite (NO(2)(-))/nitrate (NO(3)(-)) (i.e., NOx), which are stable end products of NO in the heart. Rats ran on a treadmill for 45 min. Immediately after this exercise, the heart was quickly removed. Control rats remained at rest during the same 45-min period. The mRNA level of endothelial NOS (eNOS) in the heart was markedly lower in the exercised rats than in the control rats. Western blot analysis confirmed downregulation of eNOS protein in the heart after exercise. Tissue NOx level in the heart was significantly lower in the exercised rats than in the control rats. The present study revealed for the first time that production of NO in the heart is decreased by intense exercise. Because NO attenuates positive inotropic and chronotropic responses to beta(1)-adrenergic stimulation in the heart, the decrease in cardiac production of NO by intense exercise may contribute to the acceleration of increase in myocardial contractility and heart rate during intense exercise.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.

3-D characterization of ganglion cells of the terminal nerve plexus of rat atrioventricular junction

Three-dimensional (3-D) morphology of neurons of the terminal nerve plexus of the atrioventricular junction was examined in a scanning electron microscope. Distributions of different cell types encountered as well as their relations to different structures of the atrioventricular specialized tissue were also studied. Most neurons were found disseminated in a thin connective tissue layer separating different segments of the atrioventricular conductive tissue from the interventricular septum. Sometimes, they formed small pluricellular ganglia (up to 5 neurons) but, frequently, they occurred isolated in the terminal ramifications of the intramural nerve plexus of specialized tissue. Some intranodal neurons could also be identified. According to their 3-D morphology, nerve cells of the perinodal ganglionated plexus could be divided into three categories: (1) Large unipolar neurons were scattered throughout the atrioventricular junction. Their long and thin axonal projections were often directed towards the interventricular septum. (2) Large pseudounipolar or bipolar neurons were located at a few specific loci, namely all along the bundle of His and its bifurcation into the right and left bundle branches. Frequently, they occurred solitary and immersed amongst strands of surrounding muscle cells. Only occasional synaptic impacts could be identified on the surface of neuronal bodies of these bipolar neurons. On the other hand, their dendritic varicosities were richly innervated. Due to their irregular shape, intimate association with muscular elements and their topographical superposition with occasional spindle-like structures, these nerve cells recall prospective sensory neurons involved in integration of mechanical and neural stimuli to the heart. (3) Small multipolar interneurons could be identified in the retronodal ganglion and within right and left bundle branches. The present description of morphological heterogeneity of intramural nerve cells agrees with recent morphological and functional classifications of autonomic neurons and supports the idea that, at the level of the atrioventricular junction, a self-governed neuronal network may be operating.

Proinflammatory cytokines depress cardiac efficiency by a nitric oxide-dependent mechanism

Proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma; Cytomix) depress myocardial contractile work partially by stimulating expression of inducible nitric oxide (NO) synthase (iNOS). Because NO and peroxynitrite inhibit myocardial O2 consumption (MVO2), we examined whether this mechanism contributes to reduced cardiac work. In control isolated working rat hearts, cardiac work was stable for 60 min, followed by a decline from 60 to 120 min, without change in MVO2. Cardiac efficiency (work/MVO2) was therefore reduced from 60 to 120 min. Cytomix shortened the onset (within 20-40 min) and enhanced the depression in cardiac work and efficiency and inhibited MVO2 after 80 min. Mercaptoethylguanidine (MEG), an iNOS inhibitor and peroxynitrite scavenger, or the glucocorticoid dexamethasone (Dex) abolished the effects of Cytomix. iNOS expression was increased 10-fold by Cytomix and abolished by Dex but not MEG. That cytokine-induced depression in cardiac work precedes the reduction in MVO2 suggests, at least in the early response, that NO and/or peroxynitrite may not impair heart function by inhibiting mitochondrial respiration but reduce the heart's ability to utilize ATP for contractile work.

The vagal origin of preganglionic fibers containing nitric oxide synthase in the guinea-pig heart

The origin of nerve fibers projecting to the guinea pig heart that contain nitric oxide synthase (NOS) were studied by unilateral cervical vagotomy. Three kinds of NOS-immunoreactive (NOS-ir) nerve fibers are distributed in the control guinea pig heart: the sparse network covering the right atrium, the basket-like endings around intracardiac neuronal cell bodies in the small ganglia located in the left atrium and the interatrial septum, and the axons situated in the septal region. The sparse network in the right atrium did not change after vagotomy of right or left side. In the whole mount preparations of right atrium, we often traced labeled axons from the somata to join the network covering the right atrium. Therefore, most of this network of labeled fibers must be of intrinsic origin. Because the basket-like endings around neuronal cell bodies in the ganglia in the left atrium and the septum disappeared completely after vagotomy of left side, we conclude that they are parasympathetic preganglionic fibers originating from the left vagus nerve. NOS-ir cell bodies and the positive fibers in the atrioventricular nodal region survived after vagotomy. All of such nerve fibers were unmyelinated axons. Therefore, they seem to be the postganglionic fibers arising from the ganglia located in the left atrium or the septum.

Nonuniformity of endothelial constitutive nitric oxide synthase distribution in cardiac endothelium

Endocardial endothelium and endothelium of coronary vessels produce NO. Histochemical methods have suggested that coronary arterial endothelial cells contain more endothelial constitutive NO synthase (ecNOS) than does coronary venous endothelium. We have further investigated the distribution of ecNOS in cardiac endothelium using immunofluorescence and en face confocal microscopy of rat heart. In endocardial endothelium, confocal microscopy revealed distinct ecNOS labeling of peripheral cell borders, cytoplasmic labeling, and labeling of the Golgi complexes. Labeling of the cell borders and of the Golgi complexes was confirmed by double staining for ecNOS and for platelet and endothelial cell adhesion molecule or Golgi 58k protein, respectively. Cytoplasmic labeling was strongest in coronary arterial endothelium. The size of the ecNOS-labeled Golgi complexes decreased from coronary arterial endothelial cells (8.63 +/- 0.39 microm2, mean +/- SE of 5 rats) to endocardial endothelium (7.07 +/- 0.61 microm2) and to coronary venous endothelium (3.65 +/- 0.20 microm2). In addition, pixel intensity of ecNOS labeling was higher in arterial endothelial cells than in venous endothelial cells. Endothelium of myocardial capillaries also contained small ecNOS-labeled Golgi complexes. No correlation was observed between endothelial cell surface area and Golgi complex size. Caveolin-1 labeling was strongest in capillaries and did not coincide completely with ecNOS labeling in endocardial and venous endothelium. These results suggest that endocardial and coronary arterial endothelium in the rat have a higher synthetic activity and might express more ecNOS than is expressed by cardiac venous and capillary endothelium. The observed heterogeneity in ecNOS distribution might be related to the specific mechanochemical environment and function of each endothelial compartment.

Nitric oxide synthases and cardiac muscle. Autocrine and paracrine influences

The different cell types comprising cardiac muscle express one or more of the three isoforms (neuronal NOS, or nNOS; inducible NOS, or iNOS; and endothelial NOS, or eNOS) of nitric oxide synthase (NOS). nNOS is expressed in orthosympathetic nerve terminals and regulates the release of catecholamines in the heart. eNOS constitutively expressed in endothelial cells inhibits contractile tone and the proliferation of underlying vascular smooth muscle cells, inhibits platelet aggregation and monocyte adhesion, promotes diastolic relaxation, and decreases O2 consumption in cardiac muscle through paracrinally produced NO. eNOS is also constitutively expressed in cardiac myocytes from rodent and human species, where it autocrinally opposes the inotropic action of catecholamines after muscarinic cholinergic and beta-adrenergic receptor stimulation. iNOS gene transcription and protein expression are induced in all cell types after exposure to a variety of inflammatory cytokines. Aside from participating in the immune defense against intracellular microorganisms and viruses, the large amounts of NO produced autocrinally or paracrinally mediate the vasoplegia and myocardial depression characteristic of systemic immune stimulation and promote cell death through apoptosis. In cardiac myocytes, NO may regulate L-type calcium current and contraction through activation of cGMP-dependent protein kinase and cGMP-modulated phosphodiesterases. Other mechanisms independent of cGMP elevations may operate through interaction of NO with heme proteins, non-heme iron, or free thiol residues on target signaling proteins, enzymes, or ion channels. Given the multiplicity of NOS isoforms expressed in cardiac muscle and of the potential molecular targets for the NO produced, tight molecular regulation of NOS expression and activity at the transcriptional and posttranscriptional level appear to be needed to coordinate the many roles of NO in heart function in health and disease.

Distribution of nitric oxide in the nasal mucosa of the rat: a histochemical study

We evaluated the distribution of nitric oxide (NO) in the rat nasal mucosa using nicotineamide adenosine dinucleotide phosphate (NADPH)-diaphorase histochemistry. The NADPH-diaphorase positive nerve fibers in the nasal mucosa were observed around blood vessels and submucosal glands and in sphenopalatine ganglions. Strong positive reactions for NADPH-diaphorase were observed in ganglions as compared with the other tissues. In septal and turbinate mucosa, positive reactions for NADPH-diaphorase were mainly seen in the anterior portion, and a few positive reactions were observed in the posterior portion. No positive reactions for NADPH-diaphorase were demonstrated in the sinus mucosa. These results suggest that NO may be related to regulation of blood flow, glandular secretion and neurotransmission, and also that NO may play an important role in the defense mechanism of the upper airway system against external environments.

Heme oxygenase-2 and nitric oxide synthase in guinea-pig intracardiac neurones

There is increasing evidence that carbon monoxide (CO), like nitric oxide (NO), may be a neuronal messenger molecule. This study investigated the expression of heme oxygenase-2 (HO-2), the enzyme responsible for the synthesis of CO, by intracardiac neurones. Many, if not all newborn guinea-pig intracardiac neurones in culture were HO-2-immunoreactive. Furthermore, double labelling showed that a relatively small subpopulation of these neurones also expressed NO synthase/nicotinamide dinucleotide phosphate (NADPH)-diaphorase (NOS/NADPH-d) activity. These findings suggest that intracardiac neurones can synthesize CO and that CO may be fundamental to their function. Comparison of the proportions of intracardiac neurones that contain HO-2 with those that express NOS/NADPH-d activity also indicates that CO may be more important than NO in the intrinsic neuronal control of the heart.

Involvement of ATP in the non-adrenergic non-cholinergic inhibitory neurotransmission of lamb isolated coronary small arteries

1. The involvement of non-adrenergic non-cholinergic (NANC) transmitters, such as nitric oxide (NO) and adenosine 5'-triphosphate (ATP), in the neurogenic relaxation of lamb coronary small arteries was investigated in vessel segments with an internal lumen diameter of 200-550 microns, isolated from the left ventricle of the heart, and suspended for isometric tension recording in microvascular myographs. 2. In both endothelium-intact and -denuded coronary small arteries treated with phentolamine (3 x 10(-6) M), propranolol (3 x 10(-6) M), and atropine (10(-6) M) and contracted to 3 x 10(-7) M of the thromboxane analogue U46619, electrical field stimulation (EFS) evoked frequency-dependent relaxations, which were markedly reduced in the presence of tetrodotoxin (10(-6) M). 3. Exogenous NO added as acidified sodium nitrite (10(-6)-10(-3) M) and L-nitrosocysteine induced potent relaxations of lamb coronary small arteries. However, both inhibition of NO synthase with NG- nitro-L-arginine (L-NOARG, 3 x 10(-5) M), and mechanical endothelial cell removal increased rather than inhibited relaxations to EFS. In small arteries processed for NADPH-diaphorase histochemistry, activity was only observed within endothelial cells. 4. In arteries contracted to U46619, exogenously added ATP caused concentration-dependent relaxations with pD2 and maximum responses of 4.72 +/- 0.12 and 89.6 +/- 3.8% (n = 12), respectively. ADP and the P2Y-agonist, 2-methylthio-ATP, induced relaxations equipotent to ATP, while the P2x-agonist, alpha, beta-methylene ATP (10(-9)-10(-4) M), and the P2U-agonist, UTP (10(-9)-10(-4) M) only caused small transient relaxations at the highest concentrations (10(-4) and 10(-3) M). 5. ATP and EFS-induced relaxations were unchanged in the presence of the P1-purinoceptor antagonist, 8-phenyltheophylline (10(-5) M), while this antagonist inhibited the concentration-dependent relaxations to adenosine. In contrast, the P2-purinoceptor antagonist, suramin (3 x 10(-5) M), markedly reduced the relaxations to EFS. 6. After desensitization of P2x-purinoceptors with alpha, beta-methylene ATP (2 x 10(-5) M), the relaxations to exogenous added ATP were enhanced, but this procedure did not influence the relaxations to EFS. In contrast, the P2y-purinoceptor antagonist, basilen blue E-3G (3 x 10(-5) M, earlier named reactive blue 2) significantly inhibited the concentration-relaxation curves to ATP and almost abolished the EFS-induced relaxations. 7. Mechanical removal of the endothelium significantly inhibited ATP-induced maximal relaxations without affecting sensitivity, pD2 and maximum relaxations being 4.72 +/- 0.12 and 89.7 +/- 3.8% (n = 10), and 5.45 +/- 0.38 and 48.0 +/- 8.6% (P < 0.05, paired t test, n = 10) in endothelium-intact and -denuded coronary small arteries, respectively. However, incubation with L-NOARG did not change relaxations elicited by ATP. 8. The present study suggests that in NANC conditions neurogenic relaxations of coronary small arteries are mediated by ATP, which relaxes coronary small arteries through P2Y-purinoceptors. A prejunctional modulation of these relaxations by endothelial-derived NO cannot be excluded.

Morphological study of neurons in the nerve plexus on heart base of rats and guinea pigs

The paper describes the morphological pattern of neurons in the nerve plexus on the heart base of rats and guinea pigs. The nerve plexus, containing the investigated neurons, lies beneath the pulmonary arteries on the myocardium of the left atrium. This plexus is not covered by the epicardium. Therefore, contrary to the subepicardiac nerve plexus the investigated plexus was termed the nerve plexus of the cardiac hilum (NPCH). The morphology of neurons in the NPCH was revealed by ionophoretic injection of Lucifer Yellow via an intracellular microelectrode in vitro. A total of 139 neurons in 31 rats and 15 guinea pigs were labeled with dye and examined without chemical fixation with a fluorescent microscope. In the NPCH of both species, two types of neuron were revealed: unipolar and multipolar. The unipolar predominated (61.2% of the labeled nerve cells), whereas the multipolar were encountered less frequently (38.8% of the sampled neurons). Morphometrically, both types were similar and there was no significant difference in their length or width. The dyed neurons of both types were divided into separate groups according to indentations on the surface of their soma. Most of the unipolar nerve cells were encompassed into a group of "smooth' neurons because the surface of their soma was without noticeable prominences or grooves. The rest of the unipolar neurons were distinguished from the 'smooth' by various types of unevenness of the surface of their body, such as spine-like sprouts and grooves of different depth. The latter were attached to another group, the 'unsmooths', which made up 22.4% of all the labeled cells. The multipolar neurons were subdivided into two groups according to the number of long processes. The first group included neurons with a single long process, whereas the other group encompassed the nerve cells with two or more processes. The latter groups made up 31.6% and 7.2%, respectively, of the total number of labeled nerve cells. The obtained data have shown that the neurons in the NPCH of the rats and guinea pigs are morphologically different, and therefore it is proposed that the function of the neurons in the diverse groups may also be different.

beta 2-adrenoreceptor immunoreactivity in cardiac ganglia of the guinea pig

Previous pharmacological studies in co-culture systems have indicated the presence of beta-adrenoreceptors on intrinsic cardiac neurons of the guinea pig (Horackova et al., 1993) but radioligand binding studies on tissue sections failed to provide a definite answer as to the presence of such receptors on cardiac neurons in situ, due to the iodine-binding properties of cardiac nerve bundles and ganglia (Molenaar et al., 1992). We therefore addressed this question by immunohistochemistry, using antisera raised against synthetic peptides of the beta 2-adrenoreceptor. For comparison, cholinergic and catecholaminergic neurons were identified immunohistochemically by means of antibodies against the enzymes involved in the synthesis of acetylcholine (choline acetyltransferase), and of catecholamines (tyrosine hydroxylase). Virtually all intrinsic cardiac neurons contained both beta 2-adrenoreceptor- and choline acetyltransferase-immunoreactivities. In addition, some nerve fibre bundles exhibited beta 2-adrenoreceptor-immunoreactivity. Several ganglia were innervated by tyrosine hydroxylase-immunoreactive axons, but the majority of ganglia did not receive tyrosine hydroxylase-immunoreactive nerve terminals, and additional intraganglionic sources of catecholamine synthesis could not be identified. Thus, the results are in favour of beta-adrenergic modulation of guinea pig cardiac ganglia by humorally and, partially, by locally released catecholamines.

Distribution of nitric oxide synthase-containing ganglionic neuronal somata and postganglionic fibers in the rat kidney

Nitric oxide synthase (NOS)-immunoreactive neurons were identified in the rat kidney by using an antibody against type Ia NOS and the avidin-biotin complex immunoperoxidase method in whole kidneys examined in 100 microns serial sections. The histochemical method for demonstration of the nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) was also used to characterize NOS-containing neurons. All somata showing NOS immunoreactivity also displayed NADPH-d activity. The greatest number of neuronal somata were observed in groups at the wall of the renal pelvis and in the angular space formed by the pole of the renal parenchyma and renal pelvic wall. They were also seen at the renal hilus close to the renal artery and along the interlobar vasculature. The size of the neuronal somata in the 35-day-old rat ranged from 13.6 to 34.8 microns, with a mean size of 21.52 +/- 4.81 microns. Seventy percent, however, ranged in size from 17.8 to 26.8 microns. The shape of the neuronal somata also varied, with the majority having an ovoid or round shape. The distribution of the postganglionic fibers was investigated by means of the camera lucida. Postganglionic fibers projected into the wall of the renal pelvis and/or to the interlobar arteries extending to the arcuate arteries and to the beginning of the afferent arterioles. The NOS-immunoreactive neurons may have a vasodilator and relaxing function on the renal pelvic wall and vasculature. In addition, the presence of NOS-containing nerve fibers in nerve bundles, which are known to have predominantly vasomotor and sensory fibers, suggest that they may have a possible modulatory role on renal neural function.

Tyrosine hydroxylase- and nitric oxide synthase-immunoreactive nerve fibers in mitral valve of young adult and aged Fischer 344 rats

Using confocal fluorescence microscopy we studied, in whole mounts of heart mitral valves of young adult and aged Fischer 344 rats, the distribution of nerves containing the catecholamine marker tyrosine hydroxylase (TH) or the synthetic enzyme marker for nitric oxide, nitric oxide synthase (NOS). TH-IR was localized in two separate nerve plexuses which do not intermingle. The 'major' plexus arose from the annulus region, traversed the basal zone of the valve, and ramified in the intermediate zone to form a dense network of fine fibers. The 'minor' plexus was restricted to the distal zone and originated from bundles that ascended the chordae tendineae to enter the valve cusp. A concentric zone located between the major and minor plexuses was devoid of TH-IR nerve fibers. Both plexuses demonstrated (i) nerves that contained numerous varicosities along the length of each fiber, (ii) many terminal axons and (iii) different shaped terminal axon endings. With age, the density of TH-IR innervation in the mitral valve was markedly reduced; and nerve fibers of the minor plexus were limited to the chordae tendinae, without extending into the valve cusp itself. NOS-IR fibers in the mitral valve formed a loose network that extended from the annulus to more than halfway down the cusp. The varicose beads of the terminal NOS-IR axons appeared to become progressively smaller and less intensely fluorescent until they disappeared at the terminal endings, which showed no specializations. No NOS-IR fibers were observed in the distal zone of the valve leaflet or in the chordae. In the aged mitral valve, the density of NOS-IR nerves was decreased, as compared with NOS-IR innervation in the young adult valve. The existence of TH and NOS as well as other signal molecule markers in heart valve nerves and the disparate patterns of their distribution and localization provide evidence supporting the theory that heart valve nerves form a complex reflexogenic control system in the mitral heart valve. In summary, two distinct neural architectures are described for TH-IR and NOS-IR valve nerves, respectively. The former are believed to be axons dedicated to sympathetic motor functions. The NOS-IR valve nerves may have sensory and/or postganglionic parasympathetic motor functions. An implication of these findings is that different, but perhaps related, valve functions may be mediated by separate, dedicated circuits.

Projections of intrinsic cardiac neurons to different targets in the guinea-pig heart

We set out to determine the projections of the major immunohistochemically-defined populations of intrinsic cardiac neurons to different target tissues within the guinea-pig heart. Ultrastructural studies, and immunoreactivity to the neuronal marker, neuron-specific enolase, suggested that the number of axons of intrinsic neurons in most regions of the heart was low when compared with the populations of axons projecting from extrinsic sensory and sympathetic ganglia. Multiple-labelling immunofluorescence was used to demonstrate the terminals of the major populations of peptide-containing intrinsic neurons. The intrinsic nature of peptide-containing axons was confirmed by long-term organotypic culture of cardiac tissue, which resulted in degeneration of axons of extrinsic neurons. The relative density and peptide content of intrinsic axons throughout the heart was not consistent with the relative proportions of peptide-containing intracardiac nerve cell bodies observed previously. The most commonly-encountered axons contained immunoreactivity (IR) to vasoactive intestinal peptide (VIP) alone, although nerve cell bodies with VIP constituted less than 5% of the total population of intrinsic neurons. Populations of axons containing IR to somatostatin alone, somatostatin and substance P, neuropeptide Y (NPY) alone, somatostatin and NPY, or VIP and NPY, also were observed. Intrinsic axons containing substance P-IR were very rare, much more so than would be predicted from the peptide content of intrinsic nerve cell bodies. The regions of the heart with the most dense innervation by axons of intrinsic neurons were the cardiac valves, the atrio-ventricular node and the sino-atrial node. Each of these targets was innervated by several populations of peptide-containing axons. Thus, each population of peptide-containing intrinsic neurons projected to a variety of target tissues within the heart. One possible interpretation of these results is that immunohistochemically-distinct populations of intrinsic neurons belong to different functional classes of neurons (sensory neurons, interneurons, final motor neurons), each of which innervates many regions of the heart.

Nitric oxide modulates signaling between cultured adult peripheral cardiac neurons and cardiomyocytes

To determine whether nitric oxide (NO) modifies cardiomyocytes directly or indirectly via peripheral autonomic neurons, the effects of NO were studied in long-term (3-6 wk) cultures of adult guinea pig ventricular myocytes alone as well as in cocultures with adult extracardiac (stellate ganglion) or intrinsic cardiac neurons. NADPH diaphorase was associated histochemically with cultured intrinsic cardiac and, to a lesser extent, stellate ganglion neurons. The beating frequency of ventricular myocytes cocultured with intrinsic cardiac neurons (M-intrinsic) or stellate ganglion neurons (M-stellate) increased by 20-30% (P < 0.001) after administration of the NO donor S-nitroso-N-acetylpenicillamine (SNAP); this effect was abolished by the guanylate cyclase inhibitor LY-83583. The beating frequency of noninnervated myocyte cultures was not affected by SNAP. The precursor of NO, L-arginine, also increased the beating rate (approximately 20%; P < 0.05) of M-intrinsic cocultures, not affecting that of M-stellate cocultures or noninnervated myocyte cultures. Augmentor effects induced by SNAP were no longer elicited in the presence of tetrodotoxin and were unaffected by beta-adrenergic or muscarinic receptor blockade. It is concluded that 1) NO-sensitive neurons are present in stellate and intrinsic cardiac ganglia, and these neurons increase the beating rate of cardiomyocytes in the presence of NO; 2) more NO-synthesizing neurons are present in M-intrinsic than M-stellate cocultures, since L-arginine increased the beating frequency of myocytes significantly only in M-intrinsic cocultures; and 3) the beating rate of noninnervated myocyte cultures is not directly affected by NO.

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves associated with coronary blood vessels of rat and guinea-pig

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves closely associated with blood vessels in rat and guinea-pig hearts revealed many labelled nerve fibres in the walls of the main branches of the coronary arteries, and in arterioles, capillaries and post-capillary venules. The number of nitric oxide synthase-containing nerve fibres associated with different vessels, even those of the same calibre, varied. Terminal regions of nitric oxide synthase-immunoreactive fibres were observed in the endocardium and myocardium. Nitric oxide synthase-labelled fibres displayed electron-dense immunoproduct in both varicose and intervaricose regions. Immunoreactive axonal varicosities contained both small and large synaptic vesicles. The characteristics of the nitric oxide synthase-immunoreactive nerve fibres observed in the heart and the possibility that these fibres represent the processes of intracardiac neurones and/or sensory neurones of extrinsic origin are discussed.

Nitric oxide synthase containing nerves in the atrioventricular node of the guinea pig heart

Immunoelectron microscopy was performed to localize immunoreactivity for nitric oxide synthase (NOS) in the guinea-pig atrioventricular node. Many small ganglia were found in the interatrial septum near the atrioventricular node. A small number of neurons in these ganglia were immunoreactive. NOS immunoreactive axons were observed in nerve bundles near or within the node. Very thick immunoreactive axons, 8-10 microns in diameter, were found between the conductive tissue and the ordinary cardiac muscles. Electron-microscopic examination confirmed that these axons were unmyelinated. Nerve bundles in this region contained both myelinated and unmyelinated axons; however, immunoreactivity was detected exclusively in unmyelinated axons. Fine NOS-immunoreactive nerve fibers with terminal varicosities were often seen in the atrioventricular node. Close contact between NOS-immunoreactive axon varicosity and specialized cardiac muscle cell was observed. Intranodal ganglia were observed among the specialized cardiac muscles. They were surrounded by numerous axons, some of them were immunoreactive. Direct axo-somatic synapses from NOS-immunoreactive terminals to the intranodal ganglion cells were observed. The present results indicate a possibility that nitric oxide plays a role in the neural control of the conductive tissue in the heart through direct neuromuscular contact.

Nitric oxide synthase containing neurons in the carotid body and sinus of the guinea pig

The morphology and function of the carotid sinus and carotid body have been extensively studied, but our knowledge of their transmitter(s) is still incomplete. Nitric oxide (NO) recently has been identified as a novel messenger molecule in a number of neuronal and non-neuronal tissues. Nitric oxide synthase (NOS) has been demonstrated in many neurons of the autonomic nervous system. The present study examines the distribution of NOS in the carotid sinus and body. The carotid sinus and body of newborn guinea pigs were removed for histochemical examination of NOS using the NADPH-diaphorase method. In the carotid body, many nerve fibers enveloping the glomus cells were positive for NOS. In addition, some glomus cells were positive for NOS. In the carotid sinus, NADPH-d positive fibers were distributed unevenly in the adventitia and media. These results indicate the possibility that nitric oxide plays a role in both arterial chemoreception and baroreception.

Nitric oxide modulates sympathetic neurotransmission at the prejunctional level

In spite of accumulating evidence for a modulation of sympathetic neurotransmission by endogenously produced nitric oxide (NO), it remains unclear in which parts of the vascular system and at what level this interaction takes place. The aim of the present study was to investigate the distribution of endothelial and neuronal NO synthase (NOS) along the vascular tree of the heart at the light and electron microscopic level using NADPH-diaphorase (NADPH-d) staining as a marker for NOS. In addition, the functional effects of exogenous NO on coronary vascular resistance and cardiac adrenergic nerves was studied using the isolated perfused rat heart as a model. The intraaxonal catecholamine content of adrenergic nerve fibers was visualised and morphometrically assessed by applying glyoxylic acid-induced histofluorescence. The expression of endothelial NOS in the heart was found to depend on the diameter of the blood vessel. Arteries > 100 microns always showed intense staining, whereas staining in smaller arteries and veins was considerably weaker. Smooth-muscle free vessels were essentially devoid of NADPH-d activity. In atrial and ventricular myocardium, neuronal NOS localised in autonomic nerve fibers along the entire vascular tree. Ultrastructurally, NADPH-d staining revealed adjacent localisation of NOS-positive and -negative axons, suggesting and interaxonal modulation of adjacent autonomic nerve fibers by NO. In isolated perfused rat hearts, the intracoronary application of 10(-8) M NO produced a marked decrease of coronary perfusion pressure, which was accompanied by a distinct increase in intraaxonal catecholamine levels of intramural adrenergic nerve fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of age-related changes in NADPH-diaphorase activity in pancreatic neurons

The distribution of NADPH-diaphorase activity in the pancreatic neurons of neonatal, adult and aging rats was investigated using histochemistry. In the neonates, only 40% of the neuronal population showed NADPH-diaphorase labelling, and there was variation in the intensity of labelling ranging from light to heavy staining. In the young and mature adults, 95% of the neurons were labelled for NADPH-diaphorase activity, with most of the neurons being heavily labelled for the enzyme in the older animals. Immediately after birth, the pancreatic neurons found were small clusters of smaller sized cells compared with those observed in the mature adults. Their number reached the adult level by the third month after birth; this was maintained throughout the mature adult phase and subsequently decreased in the aging rats.

Distribution of NADPH-diaphorase positive nerve fibers in the rat nasal mucosa

Nasal mucosa was investigated by NADPH-diaphorase histochemistry. Positive fibers were distributed around blood vessels, seromucous glands and in the subepithelial layer. The pterygopalatine, trigeminal and superior cervical ganglia were also studied to examine the origin of these fibers. Many neurons in the pterygopalatine ganglion were labeled, and a few neurons were stained in the trigeminal ganglion. No perikarya were labeled in the superior cervical ganglion. Therefore, most of the labeled fibers must be originating from the pterygopalatine ganglion, and the rest of them may originate from the trigeminal ganglion. These results suggest that nitric oxide may have some role in the nervous control of the nasal mucosa.

Direct synaptic contacts of nitric oxide synthase-immunoreactive nerve terminals on the neurons of the intracardiac ganglia of the guinea pig

Immunoelectron microscopy was performed to localize immunoreactivity for nitric oxide synthase (NOS) in guinea pig atria. Many round intracardiac ganglia, close to the openings of the pulmonary veins, contained NOS-immunoreactive neurons. A small number of neurons were immunoreactive, but most of the non-immunoreactive neurons were surrounded by immunoreactive axons. Direct axo-somatic or -spinic synapses from NOS-immunoreactive axon varicosities to intracardiac ganglionic neurons were observed. The present results raise the possibility that nitric oxide plays a role in the neural control of the heart through synapses in the cardiac ganglia.