Tracheal parasympathetic neurons of rat, mouse and guinea pig: partial expression of noradrenergic phenotype and lack of innervation from noradrenergic nerve fibres

Autonomic neural control of intrathoracic airways

Autonomic neural control of the intrathoracic airways aids in optimizing air flow and gas exchange. In addition, and perhaps more importantly, the autonomic nervous system contributes to host defense of the respiratory tract. These functions are accomplished by tightly regulating airway caliber, blood flow, and secretions. Although both the sympathetic and parasympathetic branches of the autonomic nervous system innervate the airways, it is the later that dominates, especially with respect to control of airway smooth muscle and secretions. Parasympathetic tone in the airways is regulated by reflex activity often initiated by activation of airway stretch receptors and polymodal nociceptors. This review discusses the preganglionic, ganglionic, and postganglionic mechanisms of airway autonomic innervation. Additionally, it provides a brief overview of how dysregulation of the airway autonomic nervous system may contribute to respiratory diseases.

Innervation of tracheal parasympathetic ganglia by esophageal cholinergic neurons: evidence from anatomic and functional studies in guinea pigs

In the present study, we describe a subset of nerve fibers, characterized by their immunoreactivity for the calcium-binding protein calretinin, that are densely and selectively associated with cholinergic postganglionic neurons in the guinea pig tracheal ganglia. Retrograde neuronal tracing with cholera toxin B, combined with immunohistochemical analyses, showed that these nerve fibers do not originate from sensory neurons in the nodose, jugular, or dorsal root ganglia or from motor neurons in the nucleus ambiguus, dorsal motor nucleus of the vagus nerve, spinal cord, stellate ganglia, or superior cervical ganglia. Calretinin-immunoreactive nerve fibers disappeared from tracheal segments after 48 h in organotypic culture, indicating that the fibers were of extrinsic origin. However, calretinin-positive nerve fibers persisted in tracheal ganglia when tracheae were cocultured with the adjacent esophagus intact. Immunohistochemical analysis of the esophagus revealed a population of cholinergic neurons in the esophageal myenteric plexus that coexpressed calretinin. In functional studies, electrical stimulation of the esophagus in vitro evoked measurable contractions of the trachea. These contractions were not altered by prior organotypic culture of the trachea and esophagus to remove the extrinsic innervation to the airways but were significantly (P < 0.05) inhibited by the ganglionic blocker hexamethonium or by physical disruption of the tissue connecting the trachea and esophagus. These data suggest that a subset of esophageal neurons, characterized by the expression of calretinin and acetylcholine, provide a previously unrecognized excitatory input to tracheal cholinergic ganglia in guinea pigs.

The study of volume density of tracheal ganglions in vitro in new born babies with respiratory distress syndrome

Volume density of respiratory organs was studied in vitro in newborn babies at different age of gestation (abort, immature, premature and mature) using stereometric method. The total of 23 cases was subject to this study. The respiratory organs (trachea, lungs) were taken from autopsies of newborn babies exited from different causes. For this purpose the tissues were fixed in formalin (10%) solution, cut serially in 7micro and 10micro slabs. Volume density of the respiratory system was assessed stereometricaly using Universal testing system Weibel M 42. We observed that volume density of epithelia, musculature and glands were proportionally present in the tracheal tissue. Cellular interstitial tissue is consistently increasing and corresponds to the developmental stages of the newborn babies. The density of tracheal ganglions is greater in premature ages of immature and premature newborns (p<0,05). Decreased number of ganglion cells is observed in mature ages (p<0,05). This is caused by intensive ramification of ganglions from serosa to deeper layers of trachea right to epithelium. Medium diameter of tracheal ganglions is greater in mature newborn babies and corresponds to developmental ages of babies.

Noradrenaline-induced cation currents in isolated rat paratracheal ganglion neurons

The actions of noradrenaline (NA) on the neurons acutely isolated from paratracheal ganglia of rats and the ionic mechanisms involved were studied with nystatin-perforated patch recording configuration. Under current-clamp conditions, application of 10 microM NA produced membrane depolarization followed by repetitive action potentials. NA evoked an inward cationic current under voltage-clamp conditions at a holding potential of -60 mV. Transient tail inward ('hump') current was also induced by washout of NA. The NA-induced current was reduced by extracellular Ca(2+) and Mg(2+), with half-maximal concentrations of 0.7 and 2.6 mM for Ca(2+) and Mg(2+), respectively. Phenylephrine, an alpha(1)-adrenoceptor agonist, mimicked the NA-induced current, but the 'hump' current did not occur upon washout of phenylephrine. The NA-induced current was inhibited by prazosin and WB-4101, alpha(1)-adrenoceptor antagonists. In contrast, in the presence of yohimbine, an alpha(2)-adrenoceptor antagonist, the NA-induced current was potentiated and the washout of NA failed to evoke the 'hump' current. The pretreatment of paratracheal neurons with pertussis toxin also potentiated the NA-induced current. The NA-induced inward current was inhibited by pretreatment with U73122, a phospholipase C inhibitor, and xestospongin-C, a membrane-permeable IP(3) receptor antagonist. On the other hand, thapsigargin, BAPTA-AM and calmidazolium had no effect on the NA-induced current, suggesting that release of Ca(2+) from intracellular Ca(2+) stores via IP(3) receptors is not involved in the NA action. The cationic channels activated by NA play an important physiological role in neuronal membrane depolarization in rat paratracheal ganglia.

Intrinsic neurons in the duck choroid are contacted by CGRP-immunoreactive nerve fibres: evidence for a local pre-central reflex arc in the eye

Intrinsic choroidal neurons represent peripherally displaced autonomic nerve cells supposed to work as a local integrative network similar to the enteric nervous system, to control choroidal vasculature and stromal smooth muscle. A typical feature of such intramural neuronal networks is the innervation by primary afferent collaterals expressing peptides, e.g. CGRP. The present study was aimed at determining primary afferent contacts on nitrergic intrinsic choroidal neurons (ICN) in the duck eye. In addition, a sympathetic innervation of ICN was assessed. Choroids were immunohistochemically processed for the following markers: neuronal nitric oxide synthase (nNOS), galanin (GAL), calcitonin gene-related peptide (CGRP), and tyrosine hydroxylase (TH). For evaluation, fluorescence as well as confocal laser scanning microscopy were used. For electron microscopy, immunoperoxidase staining for CGRP in combination with NADPH-diaphorase histochemistry was applied. ICN immunoreactive for nNOS or GAL spread over the entire choroid, although they were concentrated in an equatorial zone passing obliquely from naso-cranial to temporo-caudal. About 40% of ICN showed close relationships with CGRP-immunoreactive nerve fibres, originating most likely in the trigeminal ganglion, as seen in the fluorescence and confocal laserscanning microscope. These appositions could be ultrastructurally defined as both synapses and close contacts without synaptic specialization. Some ICN endowed with CGRP-positive fibres also received TH-immunoreactive boutons. CGRP-immunoreactive profiles were also detected in close relationship to choroidal non-vascular smooth muscle cells and collagen fibres connected to them. In many instances, they were intercalated between smooth muscle cells and processes of ICN forming triads. These results suggest that ICN, similar to other intramural autonomic systems integrate signals from trigeminal primary afferent collaterals. The 'sensory' terminals of these primary afferents may be located in the anterior eye segment but also within the smooth muscle stroma of the choroid itself. Thus, ocular homeostasis may be regulated via intraocular pre-central reflexes which are probably subject to sympathetic modulation.

Morphology and electrophysiology of guinea-pig paratracheal neurones

BACKGROUND

Although guinea-pig tracheal preparations are used as models of asthma, the morphological and electrophysiological characteristics of its associated ganglion neurones (paratracheal neurones) have not been characterized.

METHODS

Intracellular staining and electrophysiological recording techniques have been applied to guinea-pig paratracheal neurones in isolated preparations.

RESULTS

Most (32/35) neurones were multipolar, with many short (< 70 microns), finely tapering processes and one or more long processes; the latter, which were traced for up to 400 microns, travelled along the interconnecting nerve trunks, often in pairs, or over smooth muscle bundles. About 20% (6/32) of neurones had conspicuous somal extensions that gave rise to 3-8 processes. The soma morphology of neurones of the intrinsic ganglionated plexus close to the trachealis muscle were usually more complex than those in or associated with recurrent or vagal nerve trunks. Two types of neurone were identified electrophysiologically; neurones with fast excitatory synaptic potentials were found only in ganglia located very close to the smooth muscle, whereas > 90% of neurones lacking synaptic inputs were associated with recurrent nerve trunks. Transmural or focal electrical stimulation failed to evoke either slow inhibitory or slow excitatory (cholinergic or non-cholinergic) synaptic potentials in either electrophysiological type.

CONCLUSIONS

It is tentatively concluded that the neurones of the intrinsic ganglionated plexus receiving synaptic input probably provided the para-sympathetic innervation to effector cells (such as trachealis muscle). Both these and the spiking neurones located in or near nerve trunks showed little potential for synaptic modulation of their excitability.

Tyrosine-hydroxylase-containing vagal afferent neurons in the rat nodose ganglion are independent from neuropeptide-Y-containing populations and project to esophagus and stomach

Immunoreactivity to the rate limiting enzyme of catecholamine synthesis, tyrosine hydroxylase, has been described in the inferior sensory (= nodose) ganglion of the vagal nerve in the rat. The aim of the present study was to characterize further this neuronal population. The neurons do not represent displaced autonomic efferent neurons, since they do not receive synaptic input, as indicated by the absence of synaptophysin-immunoreactive terminals. In addition to the immunoreactivity to tyrosine hydroxylase, a tyrosine hydroxylase cRNA probe hybridizes with nodose ganglion neurons as demonstrated by in situ hybridization and Northern blotting. Many but not all of the tyrosine hydroxylase-immunoreactive neurons are also immunoreactive to the dopamine synthesizing enzyme, aromatic-L-amino-acid-decarboxylase, but lack the noradrenaline-synthesizing enzyme, dopamine-beta-hydroxylase, thus favoring synthesis of dopamine. Neuropeptide Y, which is often colocalized with catecholamines, is also present in a subset of nodose ganglion neurons, as indicated by immunohistochemistry, in situ hybridization and Northern blotting. However, double-labeling immunofluorescence has revealed that these two antigens are localized in different cell populations. Retrograde neuronal tracing utilizing fluorescent dyes (Fast blue, Fluoro-gold) combined with tyrosine hydroxylase immunohistochemistry has demonstrated that the esophagus and stomach are peripheral targets of tyrosine-hydroxylase-containing vagal viscero-afferent neurons.

Distribution of catecholamine-containing nerves on blood vessels of the rat trachea

This study was performed to determine the distribution of catecholamine-containing sympathetic nerves on blood vessels of the rat trachea. The glyoxylic acid method was used to visualize catecholamine-containing axons in tracheal whole mounts, and silicone vascular casts were used to elucidate the architecture of the vasculature. We also examined the relationship of these axons to the trachea's plexus of cholinergic nerves and ganglia, using tracheal whole mounts stained for acetylcholinesterase activity. We found that most catecholamine-containing axons were associated with arterioles located between cartilaginous rings or in the posterior membrane. In both regions, catecholamine-containing nerves were most abundant at the origin of terminal arterioles, which supplied the airway mucosa and smooth muscle. At the origin of these vessels, the fluorescent axons changed their orientation from longitudinal to circumferential. Few fluorescent axons were present beyond this region of the terminal arterioles, and none was found on capillaries or venules or on smooth muscle cells of the posterior membrane. Fluorescent axons were present in some tracheal ganglia but non enveloped neuronal cell bodies or had varicosities, and no ganglion cells had glyoxylic acid-induced fluorescence. Catecholamine-fluorescence was also present in clusters of small intensely fluorescent (SIF) cells, which were located in the adventitia of the posterior membrane and in the longitudinal nerve trunks which ran the length of the trachea. Pargyline pretreatment increased the fluorescence of axons and SIF cells but did not reveal a different distribution of these structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of noradrenaline on rat paratracheal neurones and localization of an endogenous source of noradrenaline

1. Intracellular recording techniques were used to study the actions of exogenous noradrenaline (NA) on rat paratracheal neurones in situ. The receptor subtypes underlying these actions were investigated by application of selective adrenoceptor antagonists. 2. Application of NA (0.1-10 microM) by superfusion evoked a membrane depolarization in 85% (52 out of 61) of all paratracheal neurones studied. The response consisted of a slow depolarization which was sometimes accompanied by action potential discharge. In 26 out of 31 cells the response was associated with a change in input resistance of the cell membrane. In 22 out of 26 cells there was a 30% increase, whilst in a further 4 cells there was a 15% decrease in input resistance. The amplitude of the NA depolarization was concentration-dependent. 3. The depolarization evoked by NA was reversibly antagonized by prazosin (1 microM) but unaffected by yohimbine (1 microM) or propranolol (1-10 microM). 4. High performance liquid chromatography with electrochemical detection (h.p.l.c.-e.c.d.) was used to assay for NA and dopamine in samples containing mainly paratracheal ganglia and in samples of tracheal smooth muscle with mucosa. NA was present in all samples assayed at a level of 1.6 micrograms NA g-1 and 0.5 microgram NA g-1 wet weight of the two sample types respectively. Dopamine was not detected in any samples of either ganglia or smooth muscle with mucosa. 5. It is concluded that NA-evoked depolarizations of rat paratracheal neurones result from stimulation of alpha 1-adrenoceptors, and that local levels of NA may be sufficiently high to activate these receptors directly.

The sensory and sympathetic innervation of guinea-pig lung and trachea as studied by retrograde neuronal tracing and double-labelling immunohistochemistry

The sympathetic and sensory innervation of guinea-pig trachea and lung were studied by means of retrograde neuronal tracing using fluorescent dyes, and double-labelling immunofluorescence. Sympathetic neurons supplying the lung were located in stellate ganglia and in thoracic sympathetic chain ganglia T2-T4; those supplying the trachea resided in the superior cervical and stellate ganglia. Retrogradely labelled sympathetic neurons were usually immunoreactive to tyrosine hydroxylase; the majority also contained neuropeptide Y immunoreactivity. However, a small number were non-catecholaminergic (i.e. tyrosine hydroxylase negative), but neuropeptide Y immunoreactive. Within the airways, tyrosine hydroxylase/neuropeptide Y-immunoreactive axons were found in the smooth muscle layer, around blood vessels including the pulmonary artery and vein, and to a lesser extent in the lamina propria. Periarterial axons contained in addition dynorphin immunoreactivity. Sensory neurons supplying the lung were located in jugular and nodose vagal ganglia as well as in upper thoracic dorsal root ganglia; those supplying the trachea were most frequently found bilaterally in the nodose ganglia and less frequently in the jugular ganglia. A spinal origin of tracheal sensory fibres could not be consistently demonstrated. With regard to their immunoreactivity to peptides, three types of sensory neurons projecting to the airways could be distinguished: (i) substance P/dynorphin immunoreactive; (ii) substance P immunoreactive but dynorphin negative; and (iii) negative to all peptides tested. Substance P-immunoreactive neurons innervating the airways invariably contained immunoreactivity to neurokinin A and calcitonin gene-related peptide. Retrogradely labelled neurons located in the nodose ganglia belonged almost exclusively (greater than or equal to 99%) to the peptide-negative group, whereas the three neuron types each represented about one-third of retrogradely labelled neurons in jugular and dorsal root ganglia. Within the airways, axons immunoreactive to substance P/neurokinin A and substance P/calcitonin gene-related peptide were distributed within the respiratory epithelium of trachea and large bronchi, in the lamina propria and smooth muscle from the trachea down to the smallest bronchioli (highest density at the bronchial level), in the alveolar walls, around systemic and pulmonary blood vessels, and within airway ganglia. Those axons also containing dynorphin immunoreactivity were restricted to the lamina propria and smooth muscle. The origin of nerve fibres immunoreactive for vasoactive intestinal polypeptide, of which a part were also neuropeptide Y immunoreactive, could not be determined by retrograde tracing experiments. Vasoactive intestinal polypeptide-immunoreactive fibres terminating within airway ganglia may be of preganglionic parasympathetic origin, whereas others (e.g. those found in smooth muscle) may arise from intrinsic ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Substance P-immunoreactive sensory axons in the rat respiratory tract: a quantitative study of their distribution and role in neurogenic inflammation

Substance P is one of the peptides released from sensory nerves that mediate "neurogenic inflammation." Although substance P-immunoreactive (SP-IR) axons are known to be present within the mucosa of the respiratory tract, the relative extent of the innervation of various components of the mucosa is not known. Therefore, we determined the distribution and number of SP-IR axons in the rat trachea and bronchi, by using immunohistochemistry on tissue whole mounts. Specifically, we sought to learn whether these axons directly innervate the postcapillary venules involved in neurogenic plasma extravasation, the arterioles involved in neurogenic vasodilatation, and the airway smooth muscle involved in bronchoconstriction in pathogen-free, adult male F344 rats. We found that 90% of the SP-IR axons were single axons, usually having varicosities. Eighty-five percent of these were in the epithelium, 6% innervated arterioles, and the remainder elsewhere in the lamina propria. Only 10% of the mediator-sensitive postcapillary venules (i.e., venules labeled with Monastral blue pigment after challenge with capsaicin or substance P) were within 10 microns of SP-IR axons. SP-IR axons were more than 10 times as frequent in the smooth muscle of the distal bronchi as in the trachea. Capsaicin pretreatment (168 mg/kg over 7 days) reduced the number of SP-IR axons in the trachea by 96%, which is consistent with their being sensory. Unilateral vagotomy reduced the number of SP-IR axons bilaterally in the trachea and ipsilaterally in the main stem bronchus. Using an antibody to Protein Gene Product 9.5 as a nonspecific marker for all nerves in the trachea, we determined that SP-IR axons constituted 90% of the axons in the epithelium, 32% of the axons on arterioles, and only 4% of the axons in the smooth muscle. We conclude that most SP-IR nerves in the trachea are sensory axons and most of these axons end in the epithelium. SP-IR axons innervate mucosal arterioles, but few innervate postcapillary venules. Therefore, the mechanism by which sensory axons evoke plasma extravasation from these venules is likely to involve the diffusion of the peptide or a secondary mediator from the epithelium or from the arterioles upstream.

Expression of catecholamine-synthesizing enzymes in paraganglionic and ganglionic cells in the laryngeal nerves of the rat

The rat recurrent and superior laryngeal nerves with adjacent connective tissue were examined by immunohistochemical techniques for localization of the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase. Most of the cells in the paraganglia of the recurrent and superior laryngeal nerves showed an intense tyrosine hydroxylase-like immunoreactivity. A few paraganglionic cells exhibited dopamine-beta-hydroxylase-like immunoreactivity while none of the cells displayed phenylethanolamine-N-methyltransferase-like immunoreactivity. Some of the ganglionic cells in the recurrent and superior laryngeal nerves showed dopamine-beta-hydroxylase-like immunoreactivity whilst these cells never showed tyrosine hydroxylase- or phenylethanolamine-N-methyltransferase-like immunoreactivity. The arterioles were supplied with plexuses of nerve fibres showing tyrosine hydroxylase- and dopamine-beta-hydroxylase-like immunoreactivity. The results indicate that dopamine is the major catecholamine located in the laryngeal nerve paraganglia and show that ganglionic cells in the recurrent and superior laryngeal nerves show immunolabelling for one of the enzymes in the catecholamine synthetic pathway, dopamine-beta-hydroxylase.

Studies on colocalization of neuropeptide Y, vasoactive intestinal polypeptide, catecholamine-synthesizing enzymes and acetylcholinesterase in the larynx of the rat

In the present immunohistochemical study, the distribution of nerve fibers containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) in the larynx was examined and compared with that of fibers containing tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH), and with that of acetylcholinesterase (AChE)-positive nerve fibers, in intact and vagotomized rats and in rats subjected to removal of the superior cervical ganglion (SCG). Fibers showing TH/DBH-like immunoreactivity (LI) were only found in the walls of arteries and arterioles, whereas AChE-positive nerve fibers were located close to the acini and ducts of the glands, in blood vessel walls, in the perichondrium and in the lamina propria. NPY-LI and VIP-LI coexisted in local AChE-positive ganglionic cells and in a subpopulation of the AChE-positive fibers, NPY-LI also being present in some periarterial fibers showing TH/DBH-LI. Unilateral removal of the SCG eliminated the TH/DBH-innervation in the upper but not the lower parts of the larynx ipsilaterally, whereas the NPY-innervation of the arteries in the upper parts only partly disappeared and the NPY-innervation of the other structures remained unchanged. The distribution of VIP-innervation was unchanged after vagotomy and removal of the SCG. The results suggest that VIP is present in the postganglionic parasympathetic innervation, whereas NPY is present in both the postganglionic parasympathetic and sympathetic innervation of the rat larynx.

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.

Catecholamines and catecholamine-synthesizing enzymes in guinea-pig sensory ganglia

Cranial and spinal sensory ganglia of the guinea-pig were investigated by means of histochemistry and biochemistry for the presence of catecholamines and catecholamine-synthesizing enzymes. Sensory neurons exhibiting immunoreactivity to the rate-limiting enzyme of catecholamine synthesis, tyrosine hydroxylase (TH), were detected by immunohistochemistry in lumbo-sacral dorsal root ganglia, the nodose ganglion and the petrosal/jugular ganglion complex. The carotid body was identified as a target of TH-like-immunoreactive (TH-LI) neurons by the use of combined retrograde tracing and immunohistochemistry. Double-labelling immunofluorescence revealed that most TH-LI neurons also contained somatostatin-LI, but TH-LI did not coexist with either calcitonin gene-related peptide- or substance P-LI. TH-LI neurons did not react with antibodies to other enzymes involved in catecholamine synthesis, i.e., aromatic amino acid decarboxylase (AADC), dopamine-beta-hydroxylase (D beta H), and phenylethanolamine-N-methyl-transferase (PNMT). Petrosal neurons as well as their endings in the carotid body lacked dopamine- and L-DOPA-LI. Sensory neurons did not display glyoxylic acid-induced catecholamine fluorescence. Ganglia containing TH-LI neurons were kept in short-term organ culture after crushing their roots and the exiting nerve in order to enrich intra-axonal transmitter content at the ganglionic side of the crush. However, even under these conditions, catecholamine fluorescence was not detected in axons projecting peripherally or centrally from the ganglia. Sympathetic noradrenergic nerves entered the ganglia and terminated within them. Accordingly, biochemical analyses of guinea-pig sensory ganglia revealed noradrenaline but no dopamine. In conclusion, catecholamines within guinea-pig sensory ganglia are confined to sympathetic nerves, which fulfill presently unknown functions. The TH-LI neurons themselves, however, lack any additional sign of catecholamine synthesis, and the presence of enzymatically active TH within these neurons is questionable.