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PubMed2006

Surgical anatomy of the innervation of pylorus in human and Suncus murinus, in relation to surgical technique for pylorus-preserving pancreaticoduodenectomy.

AIM: To clarify the innervation of the antro-pyloric region in humans from a clinico-anatomical perspective. METHODS: The stomach, duodenum and surrounding structures were dissected in 10 cadavers, and immersed in a 10mg/L solution of alizarin red S in ethanol to stain the peripheral nerves. The distribution details were studied to confirm innervations in the above areas using a binocular microscope. Similarly, innervations in 10 Suncus murinus were examined using the method of whole-mount immunohistochemistry. RESULTS: The innervation of the pyloric region in humans involved three routes: One arose from the anterior hepatic plexus via the route of the suprapyloric/supraduodenal branch of the right gastric artery; the second arose from the anterior and posterior gastric divisions, and the third originated from the posterior-lower region of the pyloric region, which passed via the infrapyloric artery or retroduodenal branches and was related to the gastroduodenal artery and right gastroepiploic artery. For Suncus murinus, results similar to those in humans were observed. CONCLUSION: There are three routes of innervation of the pyloric region in humans, wherein the route of the right gastric artery is most important for preserving pyloric region innervation. Function will be preserved by more than 80% by preserving the artery in pylorus-preserving pancreaticoduodenectomy (PPPD). However, the route of the infrapyloric artery should not be disregarded. This route is related to several arteries (the right gastroepiploic and gastroduodenal arteries), and the preserving of these arteries is advantageous for preserving pyloric innervation in PPPD. Concurrently, the nerves of Latarjet also play an important role in maintaining innervation of the antro-pyloric region in PPPD. This is why pyloric function is not damaged in some patients when the right gastric artery is dissected or damaged in PPPD.

Aged↗
PubMed2000

Development of peripheral hindlimb and central spinal cord innervation by subpopulations of dorsal root ganglion cells in the embryonic rat.

The development of rat peripheral hindlimb and lumbar dorsal horn innervation by different subpopulations of dorsal root ganglion cells was investigated from embryonic day (E)13 to birth by using immunostaining. Antibodies to protein gene product (PGP) 9.5, growth associated protein (GAP) 43, and peripherin were used as pan-neuronal markers, RT97 for A fibres; calcitonin gene-related peptide (CGRP), trkA, and the lectin IB4 for small A and C fibres. Size frequency analysis showed that RT97 is a selective marker for large A cells at E18. Although both A and C fibres enter the hindlimb at E13-14, A fibres are the first to innervate the skin and dominate over small fibre innervation until later fetal life. CGRP expression in sensory axons appears at E19 and in all regions simultaneously, suggesting expression in existing fibres. All sensory terminals grow transiently to the skin surface before retracting subepidermally at late embryonic stages. The development of peripheral and central innervation by the same subpopulations of sensory neurons was compared. The entry of A fibre terminals into the lumbar dorsal horn at E14 coincided with hindlimb skin innervation. In contrast, C fibres were not detected in the dorsal horn until E18, 4 days after peripheral innervation. CGRP expression appears in both spinal cord and hindlimb targets at E19. IB4 binding in the central terminals began at E18 but was never observed in embryonic peripheral axons. These results demonstrate that in fetal skin, A fibre innervation dominates over C fibres. In addition, alathough peripheral and central innervation by A fibres coincide, this is not true for C fibres, suggesting that central target factors may control C fibre terminal growth within the dorsal horn.

Animals↗
PubMed1984

Regional innervation of rabbit ciliary ganglion cells by the terminals of preganglionic axons.

In the rabbit, ciliary ganglion neurons with dendrites maintain inputs from several different axons during the period of synaptic rearrangement that occurs in early postnatal life. Neurons without dendrites, on the other hand, lose the majority of their initial inputs and are innervated in maturity by the terminals of only one or two axons (Purves, D., and R.I. Hume (1981) J. Neurosci. 1: 441-452; Hume, R.I., and D. Purves (1981) Nature 293: 469-471). We have explored the basis of this phenomenon by individually marking preganglionic axons and the neurons they innervate with horseradish peroxidase. In general, the innervation of geometrically complex (multiply innervated) neurons by individual preganglionic axons is regional. That is, the synaptic contacts made by an axon on these neurons are limited to a portion of the postsynaptic surface that includes some, but not all, of the dendrites. This regional innervation of target neurons is consistent with the view that dendrites allow multiple innervation to persist by providing relatively separate postsynaptic domains for individual preganglionic axons. Such regional innervation may mitigate competitive interactions between the several axons which initially innervate the same neuron.

Animals↗
PubMed1996

[Functional motor innervation of brachial plexus roots: an intraoperative electrophysiological study].

The electrophysiological properties of normal brachial plexus and functional motor innervation during the operation of contralateral healthy side C7 transfer were studied different roots of brachial plexus were stimulated and maximum amplitudes were recorded. The results showed functional motor innervation of brachial plexus roots are (1)C5 mainly forms the axillary nerve which innervates deltoid muscle; (2)C5 constructs most of the musculocutaneous nerve fibers which innervate biceps muscle; (3)main component of the radial nerve comes from C7, which innervates triceps muscle; (4)Medial nerve mainly comes from C8, which innervates flexor digitorum muscle; (5)T1 forms most of the ulnar nerve which innervates intrinsic muscle. Based on the relationship between brachial plexus roots and their functional distribution, the particular aspects of functional innervation of C7 as well as the possibility of utilization of other cervical roots were discussed.

Adolescent↗
PubMed2024

Neuronal innervation regulates the secretion of neurotrophic myokines and exosomes from skeletal muscle.

Myokines and exosomes, originating from skeletal muscle, are shown to play a significant role in maintaining brain homeostasis. While exercise has been reported to promote muscle secretion, little is known about the effects of neuronal innervation and activity on the yield and molecular composition of biologically active molecules from muscle. As neuromuscular diseases and disabilities associated with denervation impact muscle metabolism, we hypothesize that neuronal innervation and firing may play a pivotal role in regulating secretion activities of skeletal muscles. We examined this hypothesis using an engineered neuromuscular tissue model consisting of skeletal muscles innervated by motor neurons. The innervated muscles displayed elevated expression of mRNAs encoding neurotrophic myokines, such as interleukin-6, brain-derived neurotrophic factor, and FDNC5, as well as the mRNA of peroxisome-proliferator-activated receptor γ coactivator 1α, a key regulator of muscle metabolism. Upon glutamate stimulation, the innervated muscles secreted higher levels of irisin and exosomes containing more diverse neurotrophic microRNAs than neuron-free muscles. Consequently, biological factors secreted by innervated muscles enhanced branching, axonal transport, and, ultimately, spontaneous network activities of primary hippocampal neurons in vitro. Overall, these results reveal the importance of neuronal innervation in modulating muscle-derived factors that promote neuronal function and suggest that the engineered neuromuscular tissue model holds significant promise as a platform for producing neurotrophic molecules.

Exosomes↗
PubMed1989

The autonomic innervation in the pharynx. A study by the horseradish peroxidase tracer method.

Autonomic innervation of the mucosa in the pharynx was investigated by the horseradish peroxidase retrograde tracer method. The pharynx was divided into three regions, the epipharynx, mesopharynx, and hypopharynx. The epipharynx was sympathetically innervated by the fibers originating in the ipsilateral superior cervical ganglion and parasympathetically innervated by the fibers originating in the bilateral pterygopalatine ganglia. The mesopharynx and hypopharynx were sympathetically innervated by the fibers originating in the superior cervical, middle cervical, and stellate ganglia but not innervated by the pterygopalatine ganglion. The sympathetic innervation of the mesopharynx and hypopharynx was considered bilateral and predominant in the ipsilateral side. Comparing these two regions, the hypopharynx showed a tendency to be more innervated by the middle cervical and stellate ganglia.

Animals↗
PubMed1998

Sympathetic and sensory innervation of the extracerebral vasculature: roles for p75NTR neuronal expression and nerve growth factor.

The extracerebral vasculature receives a postnatal innervation of noradrenergic sympathetic axons and nociceptive sensory axons. These axons are responsive to the neurotrophin nerve growth factor (NGF), in that they possess the transmembrane receptors p140proto-trkA and p75neurotrophin receptor (NTR) which bind NGF. p75NTR-deficient mice display reduced patterns of sympathetic innervation of the pineal gland and sensory innervation of the skin (Lee et al., 1992, 1994a). The goal of this investigation was to determine whether an absence of p75 expression likewise perturbs the sympathetic and sensory innervation of the extracerebral vessels of adult mice, and if so, whether increasing levels of NGF within the target field is capable of enhancing this perturbed axon growth. Four lines of mice were used: wild-type C57Bl/6 mice, transgenic mice overexpressing NGF in the brain, p75NTR-deficient mice, and hybrid mice which overexpress NGF in the brain but lack p75NTR expression. Sympathetic and sensory innervation of the meningeal arteries were severely perturbed in p75NTR-deficient mice. Wild-type and hybrid mice displayed comparable patterns of sympathetic and sensory axons along the dural arteries. Transgenic mice, however, possessed the greatest degree of arterial innervation. These data reveal that while p75NTR expression may be a critical factor for initiating axon growth along the extracerebral vasculature during postnatal development, the sympathetic and sensory nervous systems display a remarkable degree of NGF-induced axonal plasticity, such that increased levels of NGF can ameliorate perturbed patterns of arterial innervation in p75-deficient mice.

Animals↗
PubMed1995

Formation of new myotubes occurs exclusively at the multiple innervation zones of an embryonic large muscle.

This work examines the general principle of whether production of embryonic muscle fibres is invariably linked to sites of innervation, as we have previously reported in small rodent muscles (Duxson et al. [1989] Development 107:743-750). The experimental strategy has been to make a detailed electron microscopic analysis of the formation of new myotubes in a large muscle having multiple, discrete innervation zones. The particular model system is the guinea pig sternomastoid muscle, a strap-like, parallel-fibred muscle with four distinct endplate bands, both in the embryo and the adult. Primary myotubes in the developing muscle extended from tendon to tendon of the muscle and were innervated at each of the multiple endplate zones. Each point of innervation of the primary myotubes was a focus around which many new secondary myotubes formed, and each secondary myotube was approximately centred on one of the innervation sites of its supporting primary myotube. This confirms our previous report, in rat IVth lumbrical muscle, of an invariable association between sites of formation of new secondary myotubes and sites of innervation. We suggest that, in vivo, nerve terminals either directly induce the initial myoblast fusions which give rise to new secondary myotubes, or induce some precondition for fusion. An alternative hypothesis is that a common patterning influence in the muscle localizes both innervation and secondary myotube formation to the same zone. The pattern of secondary myotube production in the embryo has important implications for the size and final architecture of muscles in larger animals, and some of these are discussed.

Acetylcholinesterase↗
PubMed1991

Anatomic distribution of autonomic neural tissue in the developing dog heart: II. Nonadrenergic noncholinergic innervation by calcitonin gene-related peptide-immunoreactive tissue.

We used immunocytochemical localization of calcitonin gene-related peptide (CGRP) to trace the ontogenesis and anatomic distribution of this component of nonadrenergic noncholinergic (NANC) innervation in fetal, neonatal, and mature canine hearts and autonomic ganglia which control cardiac function. Rare varicose CGRP-immunoreactive nerve processes were present in the heart during late gestation. Abundant CGRP-immunoreactive neural tissue in the neonate suggested a burst of NANC innervation around birth. Neonatal, 1-, and 2-month-old animals all had many varicose individual nerve processes in addition to processes within bundles; however, the density of all CGRP-immunoreactive tissue appeared to decrease during this stage of development. Similarly, there were relatively more varicose stained nerve processes in the epicardial ganglia and numerous CGRP-immunoreactive cells and smooth nerve processes in the stellate ganglia of the neonate, as compared with older animals. In the mature animal CGRP-immunoreactive neural tissue in the heart was more sparse and largely confined to heterogeneous nerve bundles in the epicardium. The extramural coronary arteries were virtually the only site of innervation by individual nerve processes; CGRP-immunoreactive neural tissue was not found adjacent to working cardiac muscle fibers. At all developmental stages, the area of the sinoatrial node was the primary focus of CGRP innervation, although the atrioventricular nodal region was also preferentially innervated. In general, the atria contained more CGRP-immunoreactive tissue than the ventricles, which were only sparsely innervated. The perinatal peak in density of CGRP-immunoreactive neural tissue with subsequent decline to reach the adult pattern suggests a developmental role for NANC innervation in the dog heart.

Aging↗
PubMed2002

Cholinergic innervation of the chick basilar papilla.

Antibodies directed against choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine (ACh) and a specific marker of cholinergic neurons, were used to label axons and nerve terminals of efferent fibers that innervate the chick basilar papilla (BP). Two morphologically distinct populations of cholinergic fibers were labeled and classified according to the region of the BP they innervated. The inferior efferent system was composed of thick fibers that coursed radially across the basilar membrane in small fascicles, gave off small branches that innervated short hair cells with large cup-like endings, and continued past the inferior edge of the BP to ramify extensively in the hyaline cell area. The superior efferent system was made up of a group of thin fibers that remained in the superior half of the epithelium and innervated tall hair cells with bouton endings. Both inferior and superior efferent fibers richly innervated the basal two thirds of the BP. However, the apical quarter of the chick BP was virtually devoid of efferent innervation except for a few fibers that gave off bouton endings around the peripheral edges. The distribution of ChAT-positive efferent endings appeared very similar to the population of efferent endings that labeled with synapsin antisera. Double labeling with ChAT and synapsin antibodies showed that the two markers colocalized in all nerve terminals that were identified in BP whole-mounts and frozen sections. These results strongly suggest that all of the efferent fibers that innervate the chick BP are cholinergic.

Animals↗
PubMed1984

An immunocytochemical study of the serotonergic innervation of the thalamus of the rat.

The serotonergic innervation of the rat thalamus was studied with an indirect immunocytochemical technique using an antiserum raised against a serotonin-hemocyanin conjugate in animals pretreated with L-tryptophan and a monoamine oxidase (MAO) inhibitor. When pretreatment was not used there was a decrease in the number of immunoreactive fibers observed in the thalamic region. Innervation was greatest in nucleus ventralis corporis geniculati lateralis, and in the following midline nuclei: nucleus periventricularis, nucleus rhomboideus, and nucleus reuniens. Also well labeled were nucleus anterior ventralis, the intralaminar nuclei, and nucleus lateralis dorsalis. Moderate innervation was found in nucleus reticularis, nucleus anterior dorsalis, nucleus ventralis medialis, nucleus lateralis pars posterior, the posterior complex, and in nucleus dorsalis corporis geniculati lateralis. Very few serotonergic fibers were observed in nucleus paratenialis, nucleus gelatinosus, nucleus anterior medialis, nucleus medialis dorsalis, nucleus ventralis, nucleus ventralis pars dorsomedialis, or in nucleus corporis geniculati medialis. Serotonin immunoreactivity was also noted in a number of fiber bundles in the thalamic region. These include the fasciculus retroflexus, the fasciculus mamillothalamicus, the stria medullaris, and the stria terminalis. These results differ from those of previous descriptions of the serotonergic innervation of thalamic nuclei most notably in the midline nuclei and in the posterior complex. In this study the midline nuclei, nucleus rhomboideus, and nucleus reuniens were more densely innervated than had been described, and in the posterior complex a moderate, rather than sparse, innervation was observed. The more densely innervated nuclei of the anterior and lateral nuclear groups, nucleus lateralis dorsalis and nucleus anterior ventralis, also contained a greater number of labeled fibers than had been indicated.

Animals↗
PubMed1989

Calcitonin-gene-related-peptide-immunoreactive innervation of the rat head with emphasis on specialized sensory structures.

The distribution of calcitonin-gene-related peptide-like immunoreactivity (CGRP-IR) was studied in sections of decalcified rat head and selected whole-mount preparations in order to address the complex peptidergic innervation patterns in peripheral cephalic specialized zones and to examine neuronal ganglia in situ. Labeled neuron somata in trigeminal, glossopharyngeal, and vagal ganglia comprised a large proportion of small to medium size type B ganglion cells. Parasympathetic ganglia (ciliary, otic, sphenopalatine, submandibular) revealed a small population of labeled somata and numerous perisomatic IR axons, whereas sympathetic ganglion cells (superior cervical) were devoid of label though richly innervated by perisomatic IR axons. The gustatory geniculate ganglion contained only a few labeled neurons and axons. Coarse peripheral CGRP-IR axons were traced to skeletal muscle motor end plates (e.g., lingual, tensor tympani, etc.), and thin sensory axons most densely innervated the cornea, iris, general integument, all mucosal epithelia lining the tympanic, nasal, sinus and oropharyngeal cavities, and the cerebral meninges. Blood vessels, glands, ducts, and their orifices were often heavily innervated, and specific specializations and exceptions are discussed. Distinctive patterns of IR innervation characterized the various specialized sensory systems, including 1) cochlear and vestibular hair cells; 2) lingual, palatal, oropharyngeal, and laryngoepiglottal taste buds; 3) main olfactory epithelium and axons projecting to glomeruli in specific sectors of main olfactory bulb; 4) septal-olfactory organ; 5) vomeronasal organ; and 6) the nervus terminalis system. Secretory epithelia (ciliary body, choroid plexus, and stria vascularis) were notably lacking in CGRP-IR. Despite the multiplicity of functionally distinct CGRP neuronal and axonal populations, certain generalizations merit consideration. The extensive innervation of chemosensory nasal and oral epithelia may contribute to specific chemical sensitivities (e.g., relating to olfactory and gustatory senses) as well as evoking "nociceptive" responses to chemical irritants as part of a "common chemical sense." An efferent role for some of these peptidergic afferent axons may also be inferred from their specific distributions. Sites involved in regulating access to and sensitivity of sense organs to external stimuli (e.g., cochlear and vestibular hair cells, taste bud orifices, and main olfactory epithelium) are heavily innervated. Other IR axons are in position to exert control over airflow through nasal turbinates, glandular secretion, blood circulation, and duct transport systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1994

Peripheral innervation patterns of vestibular nerve afferents in the bullfrog utriculus.

Vestibular nerve afferents innervating the bullfrog utriculus differ in their response dynamics and sensitivity to natural stimulation. They also supply hair cells that differ markedly in hair bundle morphology. To examine the peripheral innervation patterns of individual utricular afferents more closely, afferent fibers were labeled by the extracellular injection of horseradish peroxidase (HRP) into the vestibular nerve after sectioning the vestibular nerve medial to Scarpa's ganglion to allow the degeneration of sympathetic and efferent fibers. The peripheral arborizations of individual afferents were then correlated with the diameters of their parent axons, the regions of the macula they innervate, and the number and type of hair cells they supply. The utriculus is divided by the striola, a narrow zone of distinctive morphology, into medial and lateral parts. Utricular afferents were classified as striolar or extrastriolar according to the epithelial entrance of their parent axons and the location of their terminal fields. In general, striolar afferents had thicker parent axons, fewer subepithelial bifurcations, larger terminal fields, and more synaptic endings than afferents in extrastriolar regions. Afferents in a juxtastriolar zone, immediately adjacent to the medial striola, had innervation patterns transitional between those in the striola and more peripheral parts of the medial extrastriola. Most afferents innervated only a single macular zone. The terminal fields of striolar afferents, with the notable exception of a few afferents with thin parent axons, were generally confined to one side of the striola. Hair cells in the bullfrog utriculus have previously been classified into four types based on hair bundle morphology (Lewis and Li: Brain Res. 83:35-50, 1975). Afferents in the extrastriolar and juxtastriolar zones largely or exclusively innervated Type B hair cells, the predominant hair cell type in the utricular macula. Striolar afferents supplied a mixture of four hair cell types, but largely contacted Type B and Type C hair cells, particularly on the outer rows of the medial striola. Afferents supplying more central striolar regions innervated fewer Type B and large numbers of Type E and Type F hair cells. Striolar afferents with thin parent axons largely supplied Type E hair cells with bulbed kinocilia in the innermost striolar rows.

Animals↗
PubMed1994

Immunocytochemical characterization of the synaptic innervation of a single spinal neuron, the electric catfish electromotoneuron.

The electric catfish, Malapterurus electricus, possesses electric organs that are innervated by a pair of identifiable electromotoneurons located within the cervical spinal cord. The pattern of synaptic innervation of the electromotoneurons can be revealed by an antibody against the synaptic vesicle protein SV2. Both somata and proximal dendrites are densely innervated. Several transmitters contribute to this innervation. Glutamate, the neurotransmitter of the dorsal root sensory fibers, reveals a weak punctuate immunoreactivity. The previously described electrical synapses of the electromotoneurons were visualized by an antibody against a gap-junctional protein. In contrast to the electromotoneurons of other electric fish, the electric catfish electromotoneurons possess many inhibitory synapses. With antibodies against glycine and against the glycine receptor, a dense immunoreactivity of the surface of the somata and proximal dendrites can be revealed. The glycine receptor-like immunoreactivity exhibits a patch-like distribution similar to that revealed by the anti-SV2 antibody. gamma-Aminobutyric acid (GABA)-immunopositive terminals contribute to the inhibitory electromotoneuron innervations to a lesser degree. The chemical characteristics of the electromotoneuron innervations of Malapterurus resemble those of other spinal motoneurons rather than spinal electromotoneurons of other electric fish. Thus our immunocytochemical study supports the view that the pattern of electromotoneuron innervations in Malapterurus reveals little specialization. The capacity for information processing required for the control of the electric organ discharge appears to be achieved by the increased integrational capacity of the newly evolved multiple dendrites and not by an additional parallel channel specific for the electromotor system.

Animals↗
PubMed1995

Dopaminergic innervation of the telencephalon of the pigeon (Columba livia): a study with antibodies against tyrosine hydroxylase and dopamine.

The dopaminergic structures in the telencephalon of the pigeon were investigated with antisera against glutaraldehyde-conjugated dopamine (DA) and tyrosine hydroxylase (TH). Our goal was to describe the morphological patterns of the labelled axons and to provide a detailed map of the density and regional distribution of the dopaminergic innervation in relation to cytoarchitectonic areas. DA- and TH-like fibers reached their highest density in the paleostriatum augmentatum and the lobus parolfactorius of the basal ganglia. The paleostriatum primitivum was characterized by a dichotomous DA-positive innervation with a diffuse fiber network contacting enpassant granular cells and a more specific input that completely wrapped up large cells, which probably represent relay neurons. Two distinct DA-positive pathways could be followed back from the forebrain leading to the dopaminergic cell groups of the nucleus tegmenti pedunuculopontinus pars lateralis and the area ventralis tegmentalis. The primary sensory areas of the visual, auditory, somatosensory, and trigeminal systems within the forebrain of the pigeon were virtually devoid of DA-like fibers and demonstrated only TH-positive axons, probably of a noradrenergic nature. Among the limbic structures, the neostriatum caudolaterale (a possible equivalent of the mammalian prefrontal cortex), the septum, the nucleus accumbens, and parts of the archistriatum were heavily labelled by DA-like axons. A highly characteristic morphological feature of the catecholaminergic innervation was the presence of "baskets," which are constituted by TH- and DA-positive fibers coiled up around large perikarya, so that the surrounded somata were virtually visible by the presence of labelled axons. The density of basket and nonbasket type innervations seemed to be independently regulated, so that each forebrain structure could be characterized by a mixture consisting of the individual degrees of these two features. Our results demonstrate that the dopaminergic innervation of the forebrain of the pigeon is widespread but shows important regional variations. Similar to mammals, associative and motor structures are heavily innervated by dopaminergic fibers, whereas sensory areas are dominated by their noradrenergic input. The basket and nonbasket type innervations observed in virtually all of these subdivisions of the telencephalon may indicate the presence of two main classes of catecholaminergic afferents with different mechanisms of modulation of forebrain activity patterns.

Animals↗
PubMed1988

Adrenergic innervation of the large arteries and veins of the semiarboreal rat snake Elaphe obsoleta.

Fluorescence histochemistry was used to study the adrenergic innervation of the large arteries and veins at six points along the body of the semiarboreal rat snake Elaphe obsoleta. Apart from the vessels adjacent to the heart, there was a marked contrast in the density of adrenergic innervation of anterior and posterior systemic arteries and veins. The anterior arteries and veins have little adrenergic innervation in contrast to the extremely dense innervation of the arteries and veins posterior to the heart. The innervation pattern is consistent with known physiological adjustments to gravity and suggests a mechanism for regulating dependent blood flow via sympathetic nerves. In comparison to the posterior systemic arteries, parallel segments of pulmonary artery taken from the same body position of Elaphe contained a much sparser innervation by adrenergic nerves. The sparser innervation can be correlated with less gravitational disturbance in the pulmonary artery, which is relatively short in this and in other arboreal snakes.

Animals↗
PubMed1993

Distribution and morphology of motoneurons innervating different muscle fiber types in an amphibian muscle complex.

The distribution and morphology of motoneurons innervating specific types of muscle fibers in the levator scapulae superior (LSS) muscle complex of the bullfrog (Rana catesbeiana) and tiger salamander (Ambystoma tigrinum) were studied by retrograde labelling with cholera toxin-conjugated horseradish peroxidase (CT-HRP). The LSS muscle complex in both of these amphibians has a segregated pattern of muscle-fiber types (tonic; fast oxidative-glycolytic twitch [FOG]; fast glycolytic twitch [FG]) along an anteroposterior axis. The entire motor pool was labelled by injection of CT-HRP into the whole LSS muscle complex. The motoneurons innervating specific fiber types were labelled by injection of CT-HRP into certain muscle regions. The organization of the motoneuron pool of the LSS complex of both species was arranged in two columns--one ventrolateral and one medial. In bullfrogs, the ventrolateral column contains motoneurons innervating FG and tonic fiber types and the medial column contains motoneurons innervating FOG fiber types. In tiger salamanders, the ventrolateral column contains motoneurons innervating FG fiber types and the medial column contains motoneurons innervating FOG and tonic fiber types. The different motoneuron types also have different soma sizes and patterns of dendritic arborization. In both species, FG motoneurons are the largest, whereas FOG motoneurons are intermediate in size and tonic motoneurons are the smallest. In bullfrogs, the main dendrites of FG motoneurons extend into the dorsolateral and the ventrolateral gray matter of the spinal cord, whereas the dendrites of FOG motoneurons extend into the ventral and medial cord. In the tiger salamander, dendrites of FG motoneurons extend into the ventrolateral spinal cord and dendrites of the FOG motoneurons extend more generally into the ventral cord. Dendrites of tonic motoneurons in both amphibians were small and short, and difficult to observe. These results establish that motoneurons innervating different types of muscle fibers in the LSS muscle complex are segregated spatially and display consistent morphological differences.

Ambystoma↗
PubMed2004

Pruning of motor neuron branches establishes the DLM innervation pattern in Drosophila.

During the Drosophila life-cycle two sets of neuromuscular junctions are generated: the embryonic/larval NMJs develop during the first half, followed by the period of metamorphosis during which the adult counterpart is generated. Development of the adult innervation pattern is preceded by a withdrawal of larval NMJs, which occurs at the onset of metamorphosis, and is followed by adult-specific motor neuron outgrowth to innervate the newly developing adult fibers. Establishment of the adult innervation pattern occurs in the context of a broader restructuring of the nervous system, which results in the development of neural circuits that are necessary to carry out behaviors specific to the adult. In this article, we follow development of the dorsal longitudinal muscle (DLM) innervation pattern through metamorphosis. We find that the initial period of motor neuron elaboration is followed by a phase of extensive pruning resulting in a threefold reduction of neuromuscular contacts. This event establishes the adult pattern of second order branching. Subsequent higher order branching from the second order "contact" points generates the characteristic multiterminal innervation pattern of the DLMs. Boutons begin to appear after the pruning phase, and are much smaller than their larval counterparts. Additionally, we demonstrate that the DLM innervation is altered in the hyperexcitable double mutant, ether a go-go Shaker, and that the phenotype is suppressed by the hypoexcitable mutant, nap(ts1). Our results demonstrate that electrical activity regulates the patterning of DLM innervation during metamorphosis.

Animals↗