Immunocytochemical localisation of neuropeptide Y and 5-hydroxytryptamine in a subpopulation of amine-handling intracardiac neurones that do not contain dopamine beta-hydroxylase in tissue culture

Role of Cholinergic Innervation and RGS2 in Atrial Arrhythmia

The heart receives sympathetic and parasympathetic efferent innervation as well as the ability to process information internally via an intrinsic cardiac autonomic nervous system (ICANS). For over a century, the role of the parasympathetics via vagal acetylcholine release was related to controlling primarily heart rate. Although in the late 1800s shown to play a role in atrial arrhythmia, the myocardium took precedence from the mid-1950s until in the last decade a resurgence of interest in the autonomics along with signaling cascades, regulators, and ion channels. Originally ignored as being benign and thus untreated, recent emphasis has focused on atrial arrhythmia as atrial fibrillation (AF) is the most common arrhythmia seen by the general practitioner. It is now recognized to have significant mortality and morbidity due to resultant stroke and heart failure. With the aging population, there will be an unprecedented increased burden on health care resources. Although it has been known for more than half a century that cholinergic stimulation can initiate AF, the classical concept focused on the M2 receptor and its signaling cascade including RGS4, as these had been shown to have predominant effects on nodal function (heart rate and conduction block) as well as contractility. However, recent evidence suggests that the M3 receptor may also playa role in initiation and perpetuation of AF and thus RGS2, a putative regulator of the M3 receptor, may be a target for therapeutic intervention. Mice lacking RGS2 (RGS2^−/−), were found to have significantly altered electrophysiological atrial responses and were more susceptible to electrically induced AF. Vagally induced or programmed stimulation-induced AF could be blocked by the selective M3R antagonist, darifenacin. These results suggest a potential surgical target (ICANS) and pharmacological targets (M3R, RGS2) for the management of AF.

Evidence for enhanced M3 muscarinic receptor function and sensitivity to atrial arrhythmia in the RGS2-deficient mouse

Atrial fibrillation (AF) is the most common arrhythmia seen in general practice. Muscarinic ACh receptors (M2R, M3R) are involved in vagally induced AF. M2R and M3R activate the heterotrimeric G proteins, G(i) and G(q), respectively, by promoting GTP binding, and these in turn activate distinct K(+) channels. Signaling is terminated by GTP hydrolysis, a process accelerated by regulator of G protein signaling (RGS) proteins. RGS2 is selective for G(q) and thus may regulate atrial M3R signaling. We hypothesized that knockout of RGS2 (RGS2(-/-)) would render the atria more susceptible to electrically induced AF. One-month-old male RGS2(-/-) and C57BL/6 wild-type (WT) mice were instrumented for intracardiac electrophysiology. Atrial effective refractory periods (AERPs) were also determined in the absence and presence of carbachol, atropine, and/or the selective M3R antagonist darifenacin. Susceptibility to electrically induced AF used burst pacing and programmed electrical stimulation with one extrastimulus. Real-time RT-PCR measured atrial and ventricular content of RGS2, RGS4, M2R, M3R, and M4R mRNA. AERP was lower in RGS2(-/-) compared with WT mice in both the high right atrium (HRA) (30 +/- 1 vs. 34 +/- 1 ms, P < 0.05) and mid right atrium (MRA) (21 +/- 1 vs. 24 +/- 1 ms, P < 0.05). Darifenacin eliminated this difference (HRA: 37 +/- 2 vs. 39 +/- 2 ms, and MRA: 30 +/- 2 vs. 30 +/- 1, P > 0.4). RGS2(-/-) were more susceptible than WT mice to atrial tachycardia/fibrillation (AT/F) induction (11/22 vs. 1/25, respectively, P < 0.05). Muscarinic receptor expression did not differ between strains, whereas M2R expression was 70-fold higher than M3R (P < 0.01). These results suggest that RGS2 is an important cholinergic regulator in the atrium and that RGS2(-/-) mice have enhanced susceptibility to AT/F via enhanced M3 muscarinic receptor activity.

Potentiation by neuropeptide Y of 5HT2A receptor-mediated contraction in porcine coronary artery

Potentiation by neuropeptide Y of serotonin (5-HT)-induced vasoconstriction was investigated in porcine coronary artery. 5-HT caused concentration-dependent contraction through 5-HT2A receptors. Neuropeptide Y (30 nM) significantly increased the 5HT-induced contraction by 16+/-5% in arteries with intact endothelium. Removal of the endothelium abolished the potentiation. A neuropeptide Y1 antagonist, BIBP3226, blocked this neuropeptide Y-induced potentiation. In vessels with intact endothelium, the potentiation by neuropeptide Y was inhibited by in the presence of a cyclo-oxygenase inhibitor, indomethacin (30 microM), but not by the presence of ETA or ETB endothelin receptor antagonists or an NO synthase inhibitor, NG-nitro-L-arginine (L-NNA) (1 mM) at all. A thromboxane A2 (TXA2) synthase inhibitor, ozagrel, and prostanoid TP receptor antagonists, seratrodast and ONO-3708, also inhibited the neuropeptide Y-induced potentiation. In the endothelium-denuded arteries, a prostanoid TP receptor agonist, U-46619 (0.01-0.1 nM), potentiated 5-HT-induced contraction. These results indicate that neuropeptide Y potentiates the 5-HT-induced contraction, due to release of TXA2 from the endothelium via neuropeptide Y1 receptors, in porcine coronary artery.

Stochastic behavior of atrial and ventricular intrinsic cardiac neurons

To quantify the concurrent transduction capabilities of spatially distributed intrinsic cardiac neurons, the activities generated by atrial vs. ventricular intrinsic cardiac neurons were recorded simultaneously in 12 anesthetized dogs at baseline and during alterations in the cardiac milieu. Few (3%) identified atrial and ventricular neurons (2 of 72 characterized neurons) responded solely to regional mechanical deformation, doing so in a tightly coupled fashion (cross-correlation coefficient r = 0.63). The remaining (97%) atrial and ventricular neurons transduced multimodal stimuli to display stochastic behavior. Specifically, ventricular chemosensory inputs modified these populations such that they generated no short-term coherence among their activities (cross-correlation coefficient r = 0.21 +/- 0.07). Regional ventricular ischemia activated most atrial and ventricular neurons in a noncoupled fashion. Nicotinic activation of atrial neurons enhanced ventricular neuronal activity. Acute decentralization of the intrinsic cardiac nervous system obtunded its neuron responsiveness to cardiac sensory stimuli. Most atrial and ventricular intrinsic cardiac neurons generate concurrent stochastic activity that is predicated primarily upon their cardiac chemotransduction. As a consequence, they display relative independent short-term (beat-to-beat) control over regional cardiac indexes. Over longer time scales, their functional interdependence is manifest as the result of interganglionic interconnections and descending inputs.

Neuropeptide Y selectively potentiates alpha1-adrenoceptor-mediated contraction through Y1 receptor subtype in rat femoral artery

The aim of this study was to investigate the synergism between neuropeptide Y and other vasoconstrictors (phenylephrine and serotonin) and which neuropeptide Y receptor subtype is responsible for the neuropeptide Y-induced potentiation. Exogenous neuropeptide Y (10 nM) potentiated alpha1-adrenoceptor-mediated (PE-induced) contraction in rat femoral artery permissively without its direct action, but not in the thoracic aorta. In contrast, neuropeptide Y produced no change in serotonin-induced contraction in both arteries. Increasing concentrations of neuropeptide Y caused dose-dependent potentiation of the phenylephrine-induced contraction in the femoral artery. This potentiation was blocked by a selective neuropeptide Y-Y1 receptor antagonist, BIBP3226 [(R)-N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-argininamide] (1 microM). Semiquantitative reverse transcriptase polymerase chain reaction showed the selective expression of neuropeptide Y-Y1 receptor mRNA in the femoral artery. These findings indicated that the neuropeptide Y-induced selective potentiation of alpha1-adrenoceptor-mediated contraction is mediated through neuropeptide Y-Y1 receptor in rat femoral artery.

Localisation and quantitation of autonomic innervation in the porcine heart II: endocardium, myocardium and epicardium

The immunological problems of pig hearts supporting life in human recipients have potentially been solved by transgenic technology. Nevertheless, other problems still remain. Autonomic innervation is important for the control of cardiac dynamics and there is evidence suggesting that some neurons remain intact after transplantation. Previous studies in the human heart have established regional differences in both general autonomic innervation and in its component neural subpopulations. Such studies are lacking in the pig heart. Quantitative immunohistochemical and histochemical techniques were used to demonstrate the pattern of innervation in pig hearts (Sus scrofa). Gradients of immunoreactivity for the general neural marker protein gene product 9.5 were observed both within and between the endocardial, myocardial and epicardial plexuses throughout the 4 cardiac chambers. An extensive ganglionated plexus was observed in the epicardial tissues and, to a lesser extent, in the myocardial tissues. The predominant neural subpopulation displayed acetylcholinesterase activity, throughout the endocardium, myocardium and epicardium. These nerves showed a right to left gradient in density in the endocardial plexus, which was not observed in either the myocardial or epicardial plexuses. A large proportion of nerves in the ganglionated plexus of the atrial epicardial tissues displayed AChE activity, together with their cell bodies. Tyrosine hydroxylase (TH)-immunoreactive nerves were the next most prominent subpopulation throughout the heart. TH-immunoreactive cell bodies were observed in the atrial ganglionated plexuses. Endocardial TH- and NPY-immunoreactive nerves also displayed a right to left gradient in density, whereas in the epicardial tissues they showed a ventricular to atrial gradient. Calcitonin gene-related peptide (CGRP)-immunoreactive nerves were the most abundant peptide-containing subpopulation after those possessing NPY immunoreactivity. They were most abundant in the epicardial tissues of the ventricles. Several important differences were observed between the innervation of the pig heart compared with the human heart. These differences may have implications for the function of donor transgenic pig hearts within human recipients.

Activation of various G-protein coupled receptors modulates Ca2+ channel currents via PTX-sensitive and voltage-dependent pathways in rat intracardiac neurons

In the present study, we examined the ability of several putative neurotransmitters and neuromodulators to modulate voltage-dependent Ca2+ channel currents in adult rat intracardiac neurons. Of 17 compounds tested, acetylcholine (Ach), neuropeptide Y (NPY), norepinephrine (NE), and met-enkephalin (met-Enk) were effective modulators of the Ca2+ currents. The neurotransmitter-induced current inhibition was associated with slow activation kinetics and relief by a strong depolarizing prepulse. Overnight pretreatment of neurons with pertussis toxin (PTX, 500 ng/ml) significantly attenuated the neurotransmitter-induced current inhibition. Heterologous expression of transducin, a known chelator of G-protein betagamma subunits, almost completely abolished the neurotransmitter-induced current inhibition. Taken together, our data suggest that four different neurotransmitters inhibit the Ca2+ channel currents in adult rat intracardiac neurons via a pathway that is voltage-dependent, membrane-delimited, and utilizes betagamma subunits released from PTX-sensitive G-proteins. The Ca2+ channel inhibition by non-cholinergic neurotransmitters may play important roles in regulation of neuronal excitability and Ach release at synapses in intracardiac ganglia, thereby contributing to cholinergic control of cardiac functions.

Monoamine- and histamine-synthesizing enzymes and neurotransmitters within neurons of adult human cardiac ganglia

BACKGROUND

Cardiac ganglia were originally thought to contain only cholinergic neurons relaying parasympathetic information from preganglionic brain stem neurons to the heart. Accumulating evidence, however, suggests that cardiac ganglia contain a heterogeneous population of neurons that synthesize or respond to several different neurotransmitters and neuropeptides. Reports regarding monoamine and histamine synthesis and neurotransmission within cardiac ganglia, however, present conflicting information or are limited in number. Furthermore, very few studies have examined the neurochemistry of adult human cardiac ganglia. The purpose of this study was, therefore, to determine whether monoamine- and histamine-synthesizing enzymes and neurotransmitters exist within neurons of adult human cardiac ganglia.

METHODS AND RESULTS

Human heart tissue containing cardiac ganglia was obtained during autopsies of patients without cardiovascular pathology. Avidin-biotin complex immunohistochemistry was used to demonstrate tyrosine hydroxylase, L-dopa decarboxylase, dopamine beta-hydroxylase, phenylethanolamine-N-methyltransferase, tryptophan hydroxylase, and histidine decarboxylase immunoreactivity within neurons of cardiac ganglia. Dopamine, norepinephrine, serotonin, and histamine immunoreactivity was also found in ganglionic neurons. Omission or preadsorption of primary antibodies from the antisera and subsequent incubation with cardiac ganglia abolished specific staining in all cases examined.

CONCLUSIONS

Our results suggest that neurons within cardiac ganglia contain enzymes involved in the synthesis of monoamines and histamine and that they contain dopamine, norepinephrine, serotonin, and histamine immunoreactivity. Our findings suggest a putative role for monoamine and histamine neurotransmission within adult human cardiac ganglia. Additional, functional evidence will be necessary to evaluate what the physiological role of monoamines and histamine may be in neural control of the adult human heart.

Distribution of peptide-containing neurons in the developing rat right atrium, studied using immunofluorescence and confocal laser scanning

The developmental pattern and distribution of peptide-containing neurons in the rat heart right atrium has been studied by indirect immunofluorescence. Antibodies against neuropeptide Y (NPY), substance P (SP), and vasoactive intestinal polypeptide (VIP) were applied to whole-mount stretch preparations of the right atria from hearts of newborn to 40 day-old animals. NPY-like immunoreactivity (L1) was compared with the synaptic vesicle marker SV2 in double immunoincubation studies. The distribution of immunofluorescence was studied by confocal laser scanning microscopy. NPY-L1 and SP-L1 were present throughout the atria already at birth, in contrast to VIP-L1 that was observed at day 10. The postnatal changes of innervation were basically quantitative, with an increase in density of nerve fibres and number of varicosities, while the basic pattern of innervation was essentially established during the first 1-10 days. NPY- and SP-positive bundles of fibres appeared to enter the right atrium along the superior caval vein, having extrinsic origins. Nerve fibres with NPY-L1 colocalized in most nerve terminals with SV2-L1, and showed a developmental pattern similar to that observed for adrenergic neurons earlier. These NPY/SV2 positive fibres probably represent the extrinsic NPY innervation. In addition, NPY-L1 was identified in large intrinsic nerve cells bodies located near the atrioventricular (AV) region. Most of the VIP-L1 was observed in short nerve fibres originating in intrinsic VIP-positive cell bodies, but a few apparently extrinsic VIP-positive fibres were found, probably representing preganglionic parasympathetic neurons. SP in the atria was probably of extrinsic (sensory) origin and no nerve cell bodies with SP-L1 were detected. The results show that the peptidergic innervation in the developing rat right atrium involves both extrinsic and intrinsic peptidergic neurons which may participate in the regulation of neurotransmission in local neuronal circuits.

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.

Cardiac neurones of autonomic ganglia

The properties of the postganglionic sympathetic neurones supplying the heart and arising in the stellate and adjacent paravertebral ganglia of various species are discussed with respect to their location, morphology, synaptic input and membrane characteristics. Results from our laboratory on the morphology of rat stellate neurones projecting to the heart were obtained either by intracellular injection of hexammine cobaltic (III) chloride or by retrograde labelling of cells using cobalt-lysine complex. Intracellular recordings were made from cells using electrodes filled either with potassium chloride plus hexammine cobaltic chloride or potassium acetate. Neurones which projected axons into cardiac nerve branches arising from the stellate ganglion were termed putative cardiac neurones, because of the possibility that some supply pulmonary targets. Putative cardiac neurones had unbranched axons and were ovoid or polygonal in shape, but showed considerable variation in soma size and in the complexity of dendritic trees. The mean two-dimensional surface area was 463 microns2 and the mean number of primary dendrites was seven. Other studies have found that the morphology of rat stellate ganglion neurones is similar to that of superior cervical ganglion cells. However, in strains of rat displaying spontaneous hypertension, dendritic length may be increased. Histochemical studies do not, as yet, seem to have demonstrated a distinctive neurochemical profile for stellate cardiac neurones, but various types of peptide-containing intraganglionic nerve fibres have been identified in the guinea pig. In our electrophysiological studies, putative cardiac neurones were found to receive a complex presynaptic input arising from the caudal sympathetic trunk and from T1 and T2 thoracic rami. In addition, 16% of cardiac neurones received a synaptic input from the cardiac nerve. The properties of postganglionic parasympathetic neurones distributed in the cardiac plexus and termed intrinsic cardiac neurones are discussed, including the results of studies on cultures of these neurones.

Morphological and immunohistochemical properties of primary long-term cultures of adult guinea-pig ventricular cardiomyocytes with peripheral cardiac neurons

Long-term (2-12 weeks) cultures of adult guinea-pig ventricular myocytes, cocultured with neurons derived from stellate or intrinsic cardiac ganglia, retain their functional properties (Horackova et al., 1993, 1994, 1995). The present study was designed to investigate the morphological and immunochemical properties of such neurons and their associated cardiomyocytes. Cultured myocytes studied by means of phalloidin-rhodamine (for F-actin) and an antibody raised against myomes revealed parallel myofibrils with striations typical of rod-shaped cardiomyocytes, even while myocytes changed from cylindrical to flattened form as they established intercellular contacts. Microtubular networks, identified by alpha-tubulin DM1A antibody, were arrayed longitudinally in myofibrils, being especially prominent during the formation of intercellular contacts between myocytes. Histochemically identified adult peripheral autonomic neurons cultured alone or with myocytes displayed a variety of shapes. alpha-Tubulin staining was associated with the somata and neurites of various-shaped neurons whether cultured alone or with myocytes. Cultured neurons derived from stellate and intrinsic cardiac ganglia also exhibited staining for the general neuronal marker PGP 9.5 (protein gene product 9.5), and for specific markers of the following neurochemicals: tyrosine hydroxylase, acetylcholinesterase, choline acetyltransferase, neuropeptide Y, vasoactive intestinal peptide, calcitonin gene-related peptide, bradykinin, oxytocin, and NADPH-diaphorase. These data indicate that: (a) adult ventricular myocytes cocultured with intrathoracic neurons retain the structural properties of adult myocytes found in vivo; (b) intrinsic cardiac and extrinsic intrathoracic neurons cultured alone or with cardiomyocytes display morphological characteristics similar to those of neurons studied in situ; (c) intrinsic cardiac and intrathoracic extracardiac neurons cultured alone or with cardiomyocytes display a variety of morphologies (unipolar, bipolar, and multipolar), larger and more multipolar neurons being present in cultures derived from stellate versus intrinsic cardiac ganglia; (d) such cultured neurons are associated with a number of neurochemicals, more than one chemical being associated with each neuron. This model presents an excellent opportunity to study the morphology of individual peripheral extracardiac and intracardiac neurons as well as their potential to produce various neurochemicals that are known to be involved in the neuromodulation of cardiomyocyte function.

Comparative effects of endothelin and neurotensin on intrinsic cardiac neurons in situ

Studies were performed on anesthetized dogs to determine whether the peptides endothelin and neurotensin influence intrinsic cardiac neurons in situ and, if so, whether intrinsic cardiac neurons sensitive to these peptides are involved in cardiac regulation. Endothelin-1 (0.1 ml, 100 nM), which has high affinity for ETA endothelin receptors, when administered to a population of right atrial neurons via their regional arterial blood supply increased neuronal activity (+173%), heart rate (+18%), as well as right (62%) and left ventricular (14%) intramyocardial systolic pressures in 12 dogs so tested. When the selective ETB endothelin receptor agonist BQ-3020 (0.1 ml, 100 nM) was applied to these neurons their activity increased (+119%) in 10 of 12 dogs tested, as did right (56%) and left (12%) ventricular intramyocardial systolic pressures. Neuronal and cardiac responses were induced by BQ-3020, but not by endothelin-1, in the presence of a selective ETA receptor antagonist (BQ-610). When a greater dose of endothelin-1 (0.1 ml. 10 microM) was administered to right atrial neurons in tour separate dogs, alterations in neuronal activity were accompanied by ventricular arrhythmias that progressed to ventricular fibrillation. In contrast, when neurotensin (0.1 ml, 10 microM) was administered into their regional arterial blood supply intrinsic cardiac neurons were excited without cardiac variables being affected. These data indicate that: 1) mammalian intrinsic cardiac neurons are sensitive to endothelin and neurotensin; 2) endothelin-sensitive intrinsic cardiac neurons possess ETA and ETB receptors; 3) cardiac indices are enhanced when intrinsic cardiac neurons sensitive to endothelin, not neurotensin, become activated.

Innervation of the human cardiac conduction system. A quantitative immunohistochemical and histochemical study

BACKGROUND

Cardiac conduction is influenced by peptidergic mechanisms as well as classic neurotransmitters. The distribution of peptide-containing nerves has not been well defined.

METHODS AND RESULTS

Immunofluorescence and histochemical techniques were used to visualize the innervation of the human conduction system and to distinguish nerve subpopulations according to their peptide and enzyme content. Nerve fibers and fascicles displaying immunoreactivity for protein gene product 9.5 (PGP 9.5) were more numerous in the sinus and atrioventricular nodes than in the penetrating bundle, bundle branches, and adjacent myocardium. The relative density of innervation was greater in the central region of the sinus node than in the peripheral regions. Nerve densities were also higher in the transitional region of the atrioventricular node compared with its compact region. Acetylcholinesterase (AChE)-positive nerves were the main subtype identified in the sinus and atrioventricular nodes, representing half to two thirds of the stained area occupied by PGP 9.5-immunoreactive nerves. Neuropeptide Y-immunoreactive nerves represented the main peptide-containing subpopulation and occurred throughout the conduction system, displaying a similar pattern of distribution and relative density to those demonstrating tyrosine hydroxylase immunoreactivity. Nerve fibers showing immunoreactivity for vasoactive intestinal polypeptide, somatostatin, substance P, or calcitonin gene-related peptide exhibited distinct patterns of distribution and comprised a relatively minor component of the innervation, the percentage of stained area being 10- to 40-fold lower than that occupied by neuropeptide Y- and PGP 9.5-immunoreactive nerves, respectively.

CONCLUSIONS

The innervation of human conduction tissues exhibits significant regional variation and comprises putative parasympathetic nerves and intrinsic neurons (AChE positive), sympathetic efferent nerves (neuropeptide Y- and tyrosine hydroxylase-immunoreactive nerves), and other peptide-containing nerves, some of which (substance P and calcitonin gene-related peptide containing) are considered to represent afferent nerves. Locally released peptides may be involved in the neural modulation of the human conduction system.

Peptidergic modulation of in situ canine intrinsic cardiac neurons

In order to determine which peptides are involved in modulating intrinsic cardiac neurons, angiotensin II, atrial natriuretic peptide, bradykinin, calcitonin gene-related peptide, enkephalin, neuropeptide Y, oxytocin, substance P, and vasoactive intestinal peptide dissolved in saline were administered individually by microinjection adjacent to spontaneously active canine intrinsic cardiac neurons. No neuronal or cardiac responses were elicited when saline was administered into active loci or when peptides were administered into loci with no spontaneous activity. Each peptide elicited neuronal responses when administered into active loci in most animals, bradykinin eliciting neuronal responses in every active locus studied. Concomitant cardiovascular responses were elicited in many cases when every peptide except atriopeptin was studied. After cardiac decentralization, neuronal and cardiovascular responses to repeat doses of peptides occurred with less frequency than before decentralization, implying that connections with central and other intrathoracic neurons can influence the function of peptide-sensitive intrinsic cardiac neurons. After atropine and timolol administration, cardiovascular, but not neuronal, responses to peptides were eliminated, indicating that cardiovascular responses were dependent upon efferent parasympathetic and sympathetic neurons. It is concluded that a number of neuropeptides may be involved in regulation of cardiac function by intrinsic cardiac neurons.

Electrophysiological properties of in vitro intrinsic cardiac neurons in the pig (Sus scrofa)

Physiological properties and synaptically mediated responses of 34 ganglionated plexus neurons from the right atrium of the pig heart were studied with in vitro intracellular recording techniques. Whole-cell input resistance of these neurons was lower, time constant was shorter, and threshold for directly evoked action potentials was higher than the same properties in extracardiac autonomic neurons. Long intracellular depolarizing current pulses (400-500 ms) failed to generate more than one or two action potentials. Nicotinic and non-nicotinic synapses were present on neurons in cardiac ganglia and neuronal properties could be modified by norepinephrine. Based on their physiological properties, cardiac ganglionated plexus neurons in the pig appear to represent a distinct population of autonomic neurons that may be capable of intracardiac integration of efferent information to the heart.

Pathogenesis of migraine

Endothelial cells are not just a semipermeable membrane that forms a barrier between the blood and the vascular smooth muscles. This cell system is a highly active metabolic endocrine organ. It not only produces a number of important substances in vascular and neural homeostasis but also inactivates vasoactive substances such as serotonin and bradykinin. In addition, it produces endothelin-1 and angiotensin II; more importantly in the context of migraine, endothelial cells produce the vasodilators prostacyclin and EDRF-NO, both of which are local (paracrine) hormones. The physiologic function of endothelial cells is affected by aspirin, which prevents prostacyclin formation but has little effect on normal blood pressure. From this information, one can infer that endothelial cell production of prostacyclin does not play an important part in normal cardiovascular control. On the other hand, the administration of Ng-monomethyl-L-arginine causes immediate increases in blood pressure. Because the administration of this substance inhibits the release of EDRF-NO, it appears that this paracrine endothelial hormone actively dilates the normal circulation. It is of cardinal importance that damage or flow perturbations of cell membranes of the endothelial lining of blood vessels cause an increased production of prostaglandins. However, smooth muscle cells underlying the endothelial lining also synthesize prostacyclin. This mechanism is thought to be held in reserve to reinforce local production of prostacyclin and vasodilatation when cell damage to the endothelial lining occurs and EDRF-No is not produced. Many theories for the causation of migraine have been proposed, and some have been reviewed. Those holding sway tend to ignore inconsistencies and cite supporting evidence in favor of their pet explanation only. I therefore have no hesitation to show that the best explanation at present, based on the most recent cellular evidence, explains all features of migraine and the response of migraineurs to therapy. The endothelial cell is the most likely site of the primary abnormality (Fig. 1). Although under physiologic circumstances perivascular innervation and endothelial systems closely interact in the control of vascular tone during pathologic conditions such as ischemia, the dominant role in protecting the circulation is endothelium-mediated. The biology of headache is so diverse and our ignorance sufficiently pervasive that the investigation of endothelial cell function may solve the mystery of migraine. To match the postulated crucial role of the endothelial cell in the pathogenesis of migraine, another cell would have to be ubiquitously present throughout the vasculature and not just confined to the central nervous system.(ABSTRACT TRUNCATED AT 400 WORDS)

Catecholamine-synthesizing enzymes and neuropeptides in rat heart epicardial ganglia; an immunohistochemical study

The subepicardial atrial ganglia of rat hearts were examined using immunohistochemical techniques and antibodies against the catecholamine-synthetic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), and the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and met-5-enkephalin (ENK). Some of the ganglion cells present in the ganglia exhibited DBH-like immunoreactivity (LI) and NPY-LI, whilst these cells never exhibited TH-, VIP-, CGRP-, SP- or ENK-LI. Groups of small cells exhibiting an intense TH-LI, corresponding to cells referred to as catecholamine-containing cells and sometimes small intensely fluorescent cells in the literature, were observed in the ganglia. A subpopulation of these cells exhibited immunoreactivity to one of the neuropeptides tested, namelyu SP. Only a few of the cells showing TH-LI displayed DBH-LI. Nerve fibres showing SP-, CGRP-, DBH- and TH-LI were present in the ganglia; some of these fibres being closely associated with the ganglion cells or with the cells showing TH-LI. The observation provide new information on the catecholamine-synthetic enzyme/neuropeptide expression of the ganglion and catecholamine-containing cells and of the associated nerve fibres of rat heart subepicardial ganglia.

The intracardiac neurones of the fetal human heart in culture

Dissociated cell culture preparations were employed to study intracardiac neurones of the atria from human fetal hearts at 9 to 21 weeks' gestation. Intracardiac neurones were not observed in cultures dissociated from the ventricles. Single neurones, as well as groups, could be identified by phase-contrast microscopy in all of the atrial cultures prepared from 14 to 21 weeks' gestation, and protein gene product 9.5-like immunoreactive neurones were detected in cultures from as early as 10 weeks' gestation. The neurones were mononucleate, with a prominent nucleolus or multiple nucleoli, and often had extensive neurites. Neurones tended to be bigger in cultures from later stages in gestation, and these cells appeared to be more mature with a complex pattern of neurite outgrowth. Many neurones from 15 to 20 weeks' gestation expressed somatostatin-like immunoreactivity in culture. A very low proportion of cultured neurones was immunoreactive for neuropeptide Y and its C-terminal flanking peptide. Neuropeptide Y-like immunoreactive neurones also contained 5-hydroxy-tryptamine-like immunoreactivity in culture, but dopamine beta-hydroxylase-like immunoreactive neurones were not detected. This study is the first description of human intracardiac neurones in culture and forms the essential baseline for further direct investigation of these cells.

Some parasympathetic neurons in the guinea-pig heart express aspects of the catecholaminergic phenotype in vivo

In a histochemical study of intrinsic cardiac ganglia of the guinea-pig in whole-mount preparations, it was found that some 70-80% of the neurons express aspects of the catecholaminergic phenotype. These neurons have an uptake mechanism for L-DOPA, and contain the enzymes for converting L-DOPA (but not D-DOPA) to dopamine and noradrenaline, i.e. aromatic L-aminoacid decarboxylase and dopamine beta-hydroxylase. Monoamine oxidase is also present within some of the neurons. In these respects, the neurons resemble noradrenergic neurons of sympathetic ganglia, so we refer to them as intrinsic cardiac amine-handling neurons. However, these neurons do not contain tyrosine hydroxylase and show little or no histochemically detectable uptake of alpha-methyldopa, dopamine or noradrenaline, even after depletion of endogenous stores of amines by pre-treatment with reserpine. Noradrenergic fibres from the sympathetic chain form pericellular baskets around nerve cell bodies. The uptake of L-DOPA into nerve cell bodies is not prevented by treatment with 6-hydroxydopamine sufficient to cause transmitter-depletion or degeneration of the extrinsic noradrenergic fibres. Such degeneration experiments suggest that axons of the amine-handling neurons project to cardiac muscle, blood vessels and other intrinsic neurons. The cardiac neurons do not show any immunohistochemically detectable serotonergic characteristics; there is no evidence for uptake of the precursors L-tryptophan and 5-hydroxytryptophan or 5-HT itself, whereas the extrinsic noradrenergic nerve fibres within the ganglia can take up 5-HT when it is applied in high concentrations.

Innervation of the serotonin-immunoreactive cells distributed in the wall of the common carotid artery and its branches in the chicken

In the chicken, serotonin-immunoreactive cells were widely distributed not only in the carotid body but also in the wall of the common carotid artery and around each artery arising from the common carotid artery. Almost all of the serotonin cells in the wall of the common carotid artery were intensely immunoreactive to the neuropeptide Y, met- and leu-enkephalin antisera, whereas in the carotid body only a few cells were immunoreactive to these antisera. Innervation of the serotonin cells in and around arteries of chickens was investigated by immunohistochemistry and electron microscopy, in comparison with that of the carotid body. The serotonin cell groups in and around arteries, as well as the carotid body, received numerous peptidergic nerve fibers. Calcitonin gene-related peptide (CGRP)- and substance P-immunoreactive varicose nerve fibers were densely distributed, and somatostatin-immunoreactive fibers were moderately distributed in the serotonin cell groups. Galanin- and vasoactive intestinal peptide (VIP)-immunoreactive fibers were sparsely distributed in the cell groups. By electron microscopy, the serotonin cells in and around arteries were characterized by the presence of numerous dense-cored vesicles, 70-220 nm in diameter. The granule-containing cells were in close association with numerous axons. Naked axons regarded axon terminals were frequently apposed on the granular cells. The axon terminals were usually long and often partly invested the granular cells. Numerous synaptic junctions were detected along the contact between the granular cells and axon terminals. Most of the synaptic junctions showed afferent morphology; the secretory granules were accumulated near and attached to the asymmetrical membrane thickenings. Thus, the serotonin cells in and around arteries, like the carotid body, constitute chemoreceptive tissue.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Some intrinsic neurons of the guinea-pig heart contain substance P

Whole-mount preparations of the posterior wall of the atria of the guinea pig heart containing intrinsic ganglion cells and nerve plexuses were stained for substance P-like immunoreactivity by the peroxidase-antiperoxidase method. Substance P-like nerve fibres are present as pericellular baskets around most, but not all, of the neuronal cell bodies, and are also found in the connecting nerve bundles, as perivascular nerve plexuses and in the myocardium and pericardium. The majority of ganglion cell bodies are negative for substance P, as reported previously, but we describe for the first time, a small subpopulation of intrinsic neuronal cell bodies which show immunoreactivity for substance P. Therefore, not all cardiac substance P nerves are extrinsic afferent fibres. At present, the physiological role of intrinsic substance P neurones is not clear.

Autoradiographic localization of muscarinic receptors on cultured, peptide-containing neurones from newborn rat superior cervical ganglion

In order to identify subpopulations of cultured rat superior cervical ganglion (SCG) neurones which express muscarinic receptors, a combination of immunocytochemistry and autoradiography was performed on these cultures. Antibodies to vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY) were used to immunostain cultures that had previously been labelled with the irreversible muscarinic antagonist, [3H]propylbenzylylcholine mustard (PrBCM). Binding sites for [3H]PrBCM were observed on a large subpopulation of 65-85% of the ganglionic neuronal cell bodies. Specific labelling was not associated with non-neuronal cells found in these cultures. Approximately 60% of the SCG neurones were NPY-like immunoreactive (NPY-LI), a high proportion of which expressed muscarinic receptors. Five to 10% of the SCG neurones were VIP-LI, a small subpopulation of which displayed [3H]PrBCM binding sites. Receptor distribution on cell bodies was usually uniform, but occasionally, regions of high receptor density were seen. Dense networks of both varicose and non-varicose NPY-LI fibres were seen throughout the culture, a subpopulation of which expressed muscarinic receptors. Occasional VIP-LI fibres were also labelled with silver grains for [3H]PrBCM, but in less abundance than those for NPY-LI fibres. Conversely, neurones expressing muscarinic receptors were often immunonegative for either VIP or NPY: therefore, the identity of some of the neurones which express muscarinic receptors remains to be determined.

Biosynthesis, development, and regulation of neuropeptide Y in superior cervical ganglion culture

The biosynthesis of neuropeptide Y (NPY) and norepinephrine (NE) has been examined in dissociated neuronal cultures from newborn rat superior cervical ganglion (SCG). NPY synthetic rate was measured by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis after incubation in medium containing a labeled amino acid. The authenticity of the NPY was confirmed by reverse-phase HPLC analyses of tryptic peptides. The NPY synthetic rate in cultures grown in complete serum free medium increased 30-fold after plating, in parallel to catecholamine synthesis; both NPY and the catecholamines reached the rate for adult SCG neurons. This development in culture is seen without spinal cord input, target organs, or significant numbers of glial cells. NPY synthesis was maintained in the face of a major decrease in the rate of NE production after cholinergic induction.

The use of cell and tissue culture techniques in the study of regulatory peptides

Cell and tissue culture preparations have a number of general advantages for the study of biological processes: cells are more accessible for study, diffusion delays and barriers to applied substances are minimised, the humoral and cellular components of the culture environment can be controlled and progressive changes in intracellular and intercellular events can be directly monitored. These significant advantages mean that culture preparations can provide unique opportunities for investigation of the properties and functions of regulatory peptides. Culture preparations also have disadvantages and not all cultures are suitable for use in all types of experiments; therefore, the choice of preparation must be made accordingly. Here we describe different types of culture preparation and give examples where cultures have been used to examine peptide synthesis, storage, secretion and receptor localisation, as well as the short-term and trophic actions of regulatory peptides.

Potentiation by neuropeptide Y of vasoconstriction in rat resistance arteries

1. The effects of neuropeptide Y (NPY) on resistance arteries were investigated on 3rd generation mesenteric arterioles of the rat. 2. Contractions were elicited by noradrenaline (NA), 5-hydroxytryptamine (5-HT), prostaglandin F2 alpha (PGF2 alpha), depolarization (KCl substituted for NaCl) and by the calcium agonist Bay K 8644, in the absence and in the presence of NPY (100 nM), a concentration which by itself did not induce vasoconstriction. 3. NPY produced a leftward shift of the concentration-response curves to the agonists and to KCl, without any alteration of maximal contractions. 4. NPY also potentiated contractions elicited by addition of CaCl2 to KCl-depolarized vessels, but its effect on calcium-induced contractions decreased with increasing KCl concentrations (from 20 to 100 mM). 5. Calcium-induced contractions were inhibited by the calcium channel blocker nitrendipine, both in the presence and absence of NPY (100 nM). NPY increased slightly (but significantly) the sensitivity to nitrendipine (the apparent KB increased from 2.9 x 10(-10) M to 1.6 x 10(-10) M). 6. The KCl concentration necessary for the maximal effect of Bay K 8644 was decreased in the presence of NPY, and the sensitivity to the calcium channel agonist was increased. 7. Elevating the KCl concentration in the bath from 5 to 20 mM (which gives the same displacement to the left of the KCl concentration-effect curve seen in the presence of NPY) induced a parallel leftward shift of NA and 5-HT concentration-response curves. This shift was identical to the one induced by NPY on 5-HT-evoked contractions, but it was significantly smaller (P less than 0.001) than the shift of the NA concentration-response curve observed in the presence of NPY. In the latter case, NPY enhanced more markedly the contractions induced by low NA concentrations (between 10(-9) and 3 x 10(-8 M) than those induced by high concentrations (up to 3 x 10(-7) M), thus giving a shallow concentration-response curve. 8. The results strongly suggest that NPY partially depolarizes the arterioles and induces an increase in calcium entry through voltage-dependent channels, thus enhancing contractions elicited by agonists or by KCl-depolarization. In addition, they support the view that another mechanism also plays a part in the potentiation by NPY of the effects of low concentrations of NA.