Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “innervation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed2005

Identification of motoneurons supplying multiply- or singly-innervated extraocular muscle fibers in the rat.

In mammals, the extraocular muscle fibers can be categorized in singly-innervated and multiply-innervated muscle fibers. In the monkey oculomotor, trochlear and abducens nucleus the motoneurons of multiply-innervated muscle fibers lie separated from those innervating singly-innervated muscle fibers and show different histochemical properties. In order to discover, if this organization is a general feature of the oculomotor system, we investigated the location of singly-innervated muscle fiber and multiply-innervated muscle fiber motoneurons in the rat using combined tract-tracing and immunohistochemical techniques. The singly-innervated muscle fiber and multiply-innervated muscle fiber motoneurons of the medial and lateral rectus muscle were identified by retrograde tracer injections into the muscle belly or the distal myotendinous junction. The belly injections labeled the medial rectus muscle subgroup of the oculomotor nucleus or the greatest part of abducens nucleus, including some cells outside the medial border of abducens nucleus. In contrast, the distal injections labeled only a subset of the medial rectus muscle motoneurons and exclusively cells outside the medial border of abducens nucleus. The tracer detection was combined with immunolabeling using antibodies for perineuronal nets (chondroitin sulfate proteoglycan) and non-phosphorylated neurofilaments. In monkeys both antibodies permit a distinction between singly-innervated muscle fiber and multiply-innervated muscle fiber motoneurons. The experiments revealed that neurons labeled from a distal injection lack both markers and are assumed to represent multiply-innervated muscle fiber motoneurons, whereas those labeled from a belly injection are chondroitin sulfate proteoglycan- and non-phosphorylated neurofilament-immunopositive and assumed to represent singly-innervated muscle fiber motoneurons. The overall identification of multiply-innervated muscle fiber and singly-innervated muscle fiber motoneurons within the rat oculomotor nucleus, trochlear nucleus, and abducens nucleus revealed that the smaller multiply-innervated muscle fiber motoneurons tend to lie separate from the larger diameter singly-innervated muscle fiber motoneurons. Our data provide evidence that rat extraocular muscles are innervated by two sets of motoneurons that differ in their molecular, morphological, and anatomical properties.

Abducens Nerve↗
PubMed1996

Innervation of the chick cornea analyzed in vitro.

PURPOSE: During the early stages (embryonic day 3 [E3]) of avian corneal development, nerve fibers extend from the trigeminal ganglion to the corneal limbus. On E11, these nerve fibers enter the cornea and extend through the secondary stroma to begin innervation of the epithelium on E13. This process of innervation is concomitant with the cornea's dehydration and transition from opacity to transparency; thus, suggesting a link between innervation and the attainment of corneal function. This investigation attempts to ascertain whether the developing cornea can support its innervation in vitro and whether there is a possible developmental interrelationship between corneal innervation and dehydration, with the associated transition from opacity to transparency. METHODS: Isolated corneas from either E8 or E14 chicks were co-cultured with E8 dorsal root ganglia. After 4 days of culture, innervation was visualized by silver staining and immunohistochemistry. Changes in corneal composition and organization associated with this innervation in vitro were analyzed by measuring changes in specific hydration, thickness and compaction, and incorporation of [35S]sulfate into glycosaminoglycans during co-culture. RESULTS: The E8 and E14 corneas support extensive innervation in vitro. Developing nerve fibers extend through the secondary stroma to innervate the epithelium. In vitro innervation of E8, but not E14, corneas was associated with a decrease in corneal specific hydration, whereas control corneas (without dorsal root ganglia) failed to show any such changes. E8 corneas also showed a significant increase in compaction when innervated in vitro. Corneal innervation in vitro did not significantly change the overall incorporation of [35S]sulfate into glycosaminoglycans. Furthermore, incorporation of [35S]sulfate into corneal sulfated glycosaminoglycans (sGAG) is not influenced by either the number of nerve fibers innervating the cornea or nerve growth factor (NGF). In addition, the distribution of staining of the corneal glycosaminoglycans, chondroitin sulfate and keratan sulfate, and peanut agglutinin-binding epitopes, suggests that these molecules are not associated with inhibition of axonal development. CONCLUSIONS: The in vitro system described here is a useful model to understand the process of corneal development. Co-culture has shown that corneal innervation promotes the process of dehydration, which is dependent on the age of the cornea. However, other functionally related refinements necessary for transparency-notably proteoglycan synthesis-may not be linked to innervation or NGF production. The authors conclude that the development of transparency is dependent on corneal innervation, though not exclusively, and that other controlling factors also are required.

Animals↗
PubMed1980

Innervation of sympathetic neurones in the guinea-pig thoracic chain.

We have investigated the organization of the guinea-pig thoracic chain by studying the innervation of the stellate and fifth thoracic sympathetic ganglia with intracellular recording. 1. These ganglia receive preganglionic innervation from different but overlapping sets of spinal cord segments: the stellate ganglion is innervated by preganglionic axons from spinal segments more rostral than those supplying the fifth thoracic ganglion, but somewhat more caudal than those innervating the superior cervical ganglion. 2. Individual thoracic ganglion cells are innervated by only some of the spinal segments that supply each ganglion as a whole. In general, the subset of spinal segments innervating a ganglion cell is contiguous; one of these segments provides the strongest innervation, with progressively weaker innervation arising from spinal levels adjacent to the dominant one. This selective pattern of innervation is similar to that in the superior cervical ganglion (Njå & Purves, 1977 a). 3. Preganglionic axons frequently innervate neurones in more than one ganglion. 4. Although neurones innervated by the same spinal cord segments are found in both the stellate and the fifth thoracic ganglion, as well as in the superior cervical, the number of ganglion cells receiving innervation from particular spinal segments is different in each ganglion. Moreover, neurones dominated by the same segment but located in different ganglia receive somewhat different average innervation from adjacent segments as a function of the ganglion in which they reside. 5. These results indicate that neurones in the thoracic chain ganglia, as those in the superior cervical ganglion, are selectively innervated by particular spinal cord segments. We suggest that the different average innervation of sympathetic ganglia reflects at least two related factors: the selective qualities of their constituent neurones, and the availability of different preganglionic axons to each ganglion.

Animals↗
PubMed1991

Sensory innervation of the canine esophagus, stomach, and duodenum.

The sensory innervation of the postpharyngeal foregut was investigated by injecting the enzyme horseradish peroxidase (HRP) into the walls of the esophagus, stomach, or duodenum. The transported HRP was identified histochemically, labeled neurons in the spinal and vagal ganglia were counted, and the results were plotted using an SAS statistical program. The spinal sensory fields of each viscus were defined using three determinations: craniocaudal extent, principal innervation field, and peak innervation field. The data revealed that innervation fields are craniocaudally extensive, the sensory field of each viscus overlaps significantly with its neighbor, yet each viscus can be characterized by a field of peak innervation density. Craniocaudal innervation of the esophagus spans as many as 22-23 paired spinal ganglia (C1-L2). There are two peak innervation fields for the cervical (C2-C6 and T2-T4) and for the thoracic (T2-T4 and T8-T12) sectors of the esophagus. The sensory innervation of the stomach extends craniocaudally over as many as 25 paired spinal ganglia (C2-L5). The peak innervation field of the stomach spans a large area comprising the cranial, middle, and the immediately adjoining caudal thoracic ganglia (T2-T10). The duodenum is innervated craniocaudally by as many as 15 paired thoracolumbar ganglia (T2-L3). Peak innervation originates in the middle and caudal thoracic ganglia and cranial lumbar (T6-L1) ganglia. There is a recognizable viscerotopic organization in the sensory innervation of the postpharyngeal foregut; successively more caudal sectors of this region of the alimentary canal are supplied with sensory fibers from successively more caudal spinal dorsal root ganglia. Vagal afferent innervation of the esophagus, stomach, and duodenum is bilateral and originates predominantly, but not exclusively, from vast numbers of neurons in the nodose (distal) ganglia. The esophagus is innervated bilaterally and more abundantly by jugular (proximal) ganglia neurons than is either the stomach or duodenum. The physiological significance of the findings are discussed in relation to the phenomena of visceral pain and referred pain.

Afferent Pathways↗
PubMed1986

Noradrenergic and serotoninergic innervation of cortical, thalamic, and tectal visual structures in Old and New World monkeys.

Antisera directed against human dopamine-beta-hydroxylase and against serotonin were used to characterize the noradrenergic (NA) and serotoninergic (5-HT) innervation of several cortical and subcortical visual areas in squirrel monkey (Saimiri sciureus) and cynomolgus monkey (Macaca fascicularis). Few species differences were observed for either monoamine. Cortical areas 17 and 18, as well as visual areas in the temporal and parietal lobe were found to exhibit regional specialization of both 5-HT and NA innervation. Precisely at the border between areas 17 and 18, the laminar innervation patterns and density characteristic of NA fibers in area 17 (Morrison et al., '82a; Kosofsky et al., '84) shift so that layer IV of area 18 contains more fibers than layer IV of area 17, and the overall density of fibers in area 18 is higher. For 5-HT, the highly laminated patterns characteristic of area 17 (Morrison et al., '82a; Kosofsky et al., '84) also observe this cytoarchitectonic boundary. Fibers in area 18 are more evenly distributed across laminae, and the overall density of fibers decreases. The visual region of the inferotemporal cortex was found to be very lightly innervated by NA fibers and very densely innervated by 5-HT fibers. Area 7 of the parietal lobule was more densely innervated by NA fibers, and less densely innervated by 5-HT fibers, than any other visual cortical region examined. The visual thalamic nuclei exhibited even greater regional differences in the density of NA innervation. The lateral geniculate nucleus was found to be virtually devoid of NA fibers, while the pulvinar-lateral posterior complex was densely innervated. The density of 5-HT fibers was more uniform across thalamic visual nuclei. The lateral geniculate, pulvinar, and lateral posterior nuclei all exhibit a moderate to high density of immunoreactive fibers. In the mesencephalon, the superficial layers of the superior colliculus were found to be densely innervated by NA fibers, whereas 5-HT fibers were most dense in the intermediate layers. These patterns of innervation indicate that, in these primate species, functionally related visual regions share common and distinguishable densities of NA innervation. Specifically, tecto-pulvinar-juxtastriate structures are more densely innervated than geniculo-striate and inferotemporal structures. These relationships suggest that, within the visual system, NA fibers preferentially innervate the regions involved in spatial analysis and visuomotor response rather than those involved in feature extraction and pattern analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Innervation of regenerated spindles in muscle grafts of the rat.

Features of the nerve supply and the encapsulated fibers of muscle spindles were assessed in grafted and normal extensor digitorum longus (EDL) muscles of rats by analysis of serial 10-microns frozen transverse sections stained for enzymes which delineated motor and sensory endings, oxidative capacity and muscle fiber type. The number of fibers was significantly more variable, and branched fibers were more frequently observed in regenerated spindles than in control spindles. Forty-eight percent of regenerated spindles received sensory innervation. Spindles reinnervated by afferents had a larger periaxial space than did spindles which were not reinnervated by afferents. Regenerated fibers innervated by afferents had small cross-sectional areas, equatorial regions with myofibrils restricted to the periphery of fibers, unpredictable patterns of nonuniform and nonreversible staining along the length of the fiber for 'myofibrillar' adenosine triphosphatase (mATPase) after acid and alkaline preincubation. In contrast, regenerated fibers devoid of sensory innervation resembled extrafusal fibers in that they usually exhibited myofibrils throughout the length of the fiber, no central aggregations of myonuclei, uniform staining for mATPase and a reversal of staining for mATPase after preincubation in an acid or alkaline medium. Approximately thirty percent of encapsulated fibers devoid of sensory innervation stained analogous to a type I extrafusal fiber, a pattern of staining never observed in intrafusal fibers of normal spindles. Groups of encapsulated fibers all exhibiting this pattern of staining reflect that either these fibers may have been innervated by collaterals of skeletomotor axons that originally innervated type I extrafusal fibers or that fibers innervated by only fusimotor neurons express patterns of staining for mATPase similar to extrafusal fibers in the absence of sensory innervation. Sensory innervation may also influence the reestablishment of multiple sites of motor endings on regenerated intrafusal fibers. Those regenerated fibers innervated by afferents had more motor endings than did regenerated fibers devoid of sensory innervation. Differences in size, morphology, and patterns of staining for mATPase and numbers of motor endings between fibers innervated by afferents and fibers devoid of sensory innervation reflect that afferents can influence the differentiation of muscle cells and the reestablishment of motor innervation other than during the late prenatal/early postnatal period when muscle spindles form and differentiate in rats.

Adenosine Triphosphatases↗
PubMed1986

The organization of the motoneurons innervating the axial musculature of vertebrates. I. Goldfish (Carassius auratus) and mudpuppies (Necturus maculosus).

The motoneurons innervating different regions of the myomeres in goldfish and mudpuppies were examined by applying HRP to the musculature or to branches of spinal nerves. In goldfish, the populations of motoneurons innervating epaxial or hypaxial muscle occupied similar positions in the motor column and had similar size distributions. There was no relationship between the size or location of a motoneuron in the motor column and the dorsoventral location of the muscle it innervated in the myomeres. Instead, different populations of motoneurons innervated the functionally different red and white musculature. The red muscle was innervated only by small motoneurons that occupied the ventral portion of the motor column. Their small axons passed lateral to the Mauthner axon in the cord, and most of them traveled in a separate branch of each spinal nerve that ran in the horizontal septum to the red muscle. The white muscle was innervated by a population of motoneurons that did not innervate red. They were large and they occupied a characteristic position in the extreme dorsal part of the motor column. Their large axons traveled medial to the Mauthner axon in the cord and entered branches of spinal nerves running deep in the epaxial or hypaxial muscle. The white muscle was probably also innervated by some smaller motoneurons similar to those innervating red; however, these may have been motoneurons whose axons ran through white muscle to reach other muscle. The large motoneurons innervating only white muscle are similar to the primary motoneurons identified in developmental studies in teleosts (Myers: Soc. Neurosci. Abstr. 9:848, '83); the smaller ones, innervating both red and white, are like secondary motoneurons. Therefore, in goldfish, motoneurons having different morphology and developmental history also innervate different regions in the myomeres. The motor column in mudpuppies was, in general respects, similar to the column in goldfish. There were large primary motoneurons and small secondary ones. Though there were slight differences in the locations of motoneurons filled from nerves entering epaxial and hypaxial muscle, their distributions in the cord overlapped substantially. The motor columns in these two anamniotes differ substantially from the motor columns in those amniotes that have been studied. In amniotes, the motoneurons innervating epaxial and hypaxial muscles are spatially segregated in the cord (Smith and Hollyday: J. Comp. Neurol. 220:16-28, '83; Fetcho: J. Comp. Neurol. 249:551-563, '86).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Serotoninergic innervation of the thalamus in the primate: an immunohistochemical study.

Little is known of the serotoninergic innervation of the thalamus in primates; therefore, we undertook a detailed study of the distribution of 5-hydroxytryptamine (5-HT)-immunoreactive neuronal profiles in the thalamus of the squirrel monkey (Saimiri sciureus) with a specific antibody directly raised against 5-HT. All thalamic nuclei in the squirrel monkey displayed 5-HT-immunoreactive fibers, but none contained immunopositive cell bodies. The 5-HT innervation of the thalamus derived from extrinsic fibers arising mostly from the midbrain raphe nuclei and forming the transtegmental system. Most of the fibers destined to the thalamus collected into a major bundle that swept dorsoventrally within the midbrain tegmentum and coursed beneath the thalamus along its entire caudorostral extent. Several fiber fascicles broke off from this main bundle at different levels and ascended dorsally to innervate the various thalamic nuclei. Overall, the 5-HT innervation of the thalamus in the squirrel monkey was more massive than would have been expected from earlier studies in nonprimate species. Marked differences in the regional density of innervation were noted both between the various nuclei and within single nuclei. The most densely innervated nuclei were those delineating the principal subdivisions of the thalamic mass, that is, the midline, rostral intralaminar, limitans, and reticular nuclei, where very dense fields of isolated axonal varicosities occurred. In contrast to the rostral intralaminar nuclei, which were rather uniformly innervated, the centre médian/parafascicular complex contained immunoreactive fibers and isolated varicosities distributed according to a mediolateral gradient. The habenula and the ventral anterior nucleus were among the most weakly innervated nuclei. In the latter nucleus, as well as in more densely innervated nuclei, thin varicose fibers formed numerous pericellular contacts on cell bodies and proximal dendrites of thalamic neurons. The 5-HT innervation of the lateral nuclear group as well as that of the medial and lateral geniculate nuclei ranged from very weak to dense. The mediodorsal nucleus displayed a highly heterogeneous 5-HT innervation that varied from weak in its central portion to moderate or dense in its medial and lateral borders. A moderate 5-HT innervation was observed in the anterior nuclear group. The surprisingly dense and heterogeneous 5-HT innervation of the thalamus noted in the present study suggests that serotonin may be involved in several specific functions of the thalamus in primates.

Animals↗
PubMed1992

Distribution and innervation of lateral line organs in the axolotl.

The lateral line system in axolotls consists of three types of receptors and the cranial nerves that innervate them. Superficial neuromasts, which are mechanoreceptors, are distributed in lines on both the head and trunk. Eight cephalic and three trunk lines can be distinguished on the basis of their innervation and differences in the orientation of the major axes of their neuromasts. A combination of histological techniques reveals that five separate pairs of cranial nerves innervate the neuromasts: anterodorsal lateral line nerves innervate cephalic supraorbital and infraorbital lines; anteroventral lateral line nerves innervate cephalic angular, oral, jugal, and preoperculomandibular lines of the cheek and lower jaw; middle and supratemporal lateral line nerves innervate the cephalic postotic lines; and posterior lateral line nerves innervate the trunk lines. In addition to lines of neuromasts, a second class of mechanoreceptive lateral line organs, pit organs, also occur on the head. Pit organs are smaller than neuromasts but are innervated in a manner identical to that of neuromasts: the sensory hair cells of a single pit organ are innervated by two afferent fibers and a single efferent fiber. Although they occur in localized clusters rather than lines, the four distinct pit organ clusters occurring in axolotls are referred to as the anterior, middle, middle cheek, and gular pit lines as they appear to be homologous to the similarly named pit lines in fishes on the basis of their topography and innervation. In addition to neuromasts and pit organs, ampullary organs comprise a third class of lateral line receptors and are restricted to the head. These electroreceptors occur singly or in small clusters adjacent to the neuromast lines and along the base of the external gills. The ampullary organs adjacent to the supraorbital and infraorbital lines are innervated by the anterodorsal lateral line nerves, whereas all other ampullary organs of the head are innervated by the anteroventral lateral line nerves. Thus postotic ampullary organs and neuromasts of the head are innervated by different lateral line nerves. Examination of the sensory ganglia of the lateral line nerves with respect to the ganglia of the other cranial nerves indicates varying levels of fusion. The ganglia of the anterodorsal lateral line and profundal-trigeminal nerves are totally separate throughout their rostrocaudal extent. The ganglia of the anteroventral lateral line and facial nerves form a fused ganglionic complex with the larger pigmented cells of the anteroventral nerve occupying the dorsal portion of the ganglionic complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma mexicanum↗
PubMed1991

Influence of innervation on molecular forms of acetylcholinesterase in regenerating fast and slow skeletal muscles.

Nerve-intact muscle regenerates were prepared by ischemic-toxic injury of slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles of the rat. Rapid innervation of regenerating myotubes modified intrinsic patterns of AChE molecular forms, revealed by velocity sedimentation in linear sucrose gradients. Regarding their onset, the effects of innervation can be classified as early and late. The earliest changes in the SOL regenerates appeared a few days after innervation by their motoneurons: the activity of the 13 S AChE form (A 8) increased significantly in comparison to non-innervated regenerates. The pattern of AChE molecular forms became similar to that in the normal SOL muscle during the 2nd week after injury. In contrast, no major differences were observed between 8 day-old innervated and non-innervated EDL regenerates. Their patterns of AChE molecular forms resembled that in the normal EDL. However, the predominance of the 10 S AChE form (G 4) characteristic for the 2-week old non-innervated regenerates was prevented by innervation. Early effect of innervation observed in the SOL regenerates but not in the EDL may be due to intrinsically different response of the regenerating SOL myotubes to innervation. Rather high extrajunctional activity of the asymmetric 16 S (A 12) molecular form of AChE in early regenerates was reduced to adult level in about 3 weeks in the SOL, and nearly completely suppressed in 5 weeks after innervation in the EDL regenerates. This reduction is assumed to be a late effect of innervation, as well as a decrease of the activity of the 4 S AChE form (G 1) in the SOL regenerates. A suppressive mechanism is activated in the extra-junctional regions of the innervated muscle regenerates during their maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1998

The catecholaminergic innervation of the rat amygdala.

The present study is the first to demonstrate conclusively and to analyze systematically synaptic contacts of all three types of catecholaminergic afferent fibers in different nuclei of the rat amygdala and to relate the catecholaminergic innervation to neurochemically identified target neurons. 4.1.1 Central Nucleus: The central nucleus is the amygdaloid nucleus receiving the most dense catecholaminergic innervation. In the medial central nucleus, dopaminergic, noradrenergic and adrenergic terminal plexus overlap, in the central lateral central nucleus mainly dopaminergic plexus are found. The lateral capsular central nucleus is generally scarcely innervated, but individual neurons of this subnucleus possess a dense dopaminergic innervation. Colocalization of neurotensin in dopaminergic afferents is rare, the majority of the dense neurotensin-ir terminal plexus consist of non-dopaminergic fibers. The catecholaminergic innervation of the medial central nucleus is directed preferentially at peripheral neuronal structures, and has thus presumably modulatory functions. Dopaminergic terminals form predominantly symmetric, noradrenergic and adrenergic terminals from preferentially asymmetric synapses. A characteristic feature of the dopaminergic innervation is the dense perisomatic innervation of selected neurons. Adrenergic and the majority of noradrenergic afferent fibers to the medial central nucleus originate from cell groups in the medulla oblongata and contain high levels of NPY. GAD mRNA-detection suggests that most target neurons of catecholaminergic afferent fibers are capable of synthesizing GABA in the medial central nucleus. In its dorsal part, GABA is possibly colocalized with somatostatin, and many neurons express the dopamine-1-receptor subtype mRNA. In the posteroventral medial central nucleus, on the other hand, enkephalin mRNA-r and dopamine-2-receptor subtype mRNA-reactive neurons show a similar distribution as the GAD mRNA-reactive ones. Contacts could be shown between dopaminergic, noradrenergic and adrenergic axons and NPY- and somatostatin-immunoreactive neurons which are supposedly among the brainstem projection neurons of the medial central nucleus. The dopaminergic innervation of the central lateral central nucleus resembles that of the neighboring striatum in many respects. The synaptic density is high. As in the medial subnucleus, distal neuronal elements are the preferential target structures, indicating a modulatory function possibly regulating the selectivity of the target neurons for stimuli transmitted by other afferent fibers. Besides, individual neurons possess a dense perisomatic, presumably non-selective dopaminergic innervation. The innervation does not appear to be targeted at one specific neurochemical type of neuron in the central lateral central nucleus, but rather contacts somatostatin- and neurotensin-immunoreactive neurons (which are possibly also GABAergic), in addition to GABA/enkephalin-synthesizing and other (e.g., CHAT-immunoreactive) neurons. Individual neurons of the central lateral central nucleus express the dopamine-2-receptor subtype mRNA. The dopaminergic fiber baskets of the lateral capsular central nucleus are found surrounding enkephalin mRNA-reactive neurons. Codistribution studies suggest that they express the dopamine-2-receptor subtype mRNA. 4.1.2 Basal Complex: The basal complex receives dopaminergic and noradrenergic innervation, the latter mainly originating in the locus coeruleus. Some of the dopaminergic afferents contain neurotensin, and in contrast to the central nucleus, all neurotensin-immunoreactive afferent fibers are dopaminergic. In the noradrenergic afferent fibers NPY is not detectable. These results and the innervation pattern displaying mostly peripheral neuronal target structures resemble dopaminergic and noradrenergic innervation patterns documented in cortical areas. (ABSTRACT TRUNCATED)

Adrenergic Fibers↗
PubMed1987

Innervation of airway smooth muscle. Efferent mechanisms.

The classical view, with one excitatory (cholinergic) and one inhibitory (noradrenergic) component, of the innervation of airway smooth muscle is incomplete and at least two other, possibly peptidergic, types of innervation must be included when the innervation of airways is considered. A summary of these neuronal components is given in Fig. 1 and their possible origin is outlined. Besides the inhibitory noradrenergic innervation of the airways observed in some species, an inhibitory NANC (i-NANC) innervation has been demonstrated. The polypeptide, VIP, seems to be the most likely candidate for the neurotransmitter in the i-NANC innervation of the airways. The excitatory cholinergic innervation is present in the airways from the trachea down to the peripheral bronchi. In the guinea-pig bronchi an excitatory NANC (e-NANC) innervation has been demonstrated as well. The e-NANC nerves may correspond to chemosensitive primary afferent nerves with substance P or a related tachykinin as transmitter. When the innervation of airway smooth muscle of different mammalian species is compared it is evident that all nerve components except the cholinergic, show a considerable variability among species. The cholinergic innervation seems to be present in all mammalian species whereas the other components may be completely absent from some species. Distinct regional variations in the innervation of the airways may occur, which is exemplified by the distribution of the autonomic innervation in the guinea-pig tracheo-bronchial tree. Cholinergic neurotransmission in for example the guinea-pig and human airways can be modulated by NA via prejunctional inhibitory alpha 2-adrenoceptors. Furthermore, the e-NANC neurotransmission in the guinea-pig airways may be modulated by NA or by selective alpha 2-adrenoceptor agonists, acting via prejunctional inhibitory alpha 2-adrenoceptors. The clinical importance of the NANC innervation in relation to asthma is discussed. The i-NANC nerves may exert a modulating effect on bronchoconstriction, and a functional defect would presumably lead to an exaggerated response to constrictor stimuli. The e-NANC nerves in the airways may also be clinically relevant since the transmitter (tachykinins) from these nerves can produce bronchoconstriction and promote inflammation of the airway epithelium, either by direct mechanisms or indirectly by activation of mast cells, and thus contribute to the features of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗