Types Of Nerve Endings Research Articles

The Morphology of the Lorenzinian Ampullae of the Sturgeon Acipenser ruthenus (Pisces: Chondrostei)

Jørgensen, J. M. 1980. The morphology of the Lorenzinian ampullae of the sturgeon Acipenser ruthenus (Pisces: Chondrostei). (Zoological Laboratory, University of Aarhus, Denmark.) — Acta zool. (Stockh.) 61 (2): 87–92. The snout of a sturgeon, Acipenser ruthenus (Chondrostei, Osteichthyes) is provided with sensory pores. Light and electron microscopical examination of these reveals that the ampullary organs have a sensory epithelium very similar to what has been found in the Lorenzinian ampullae, which are electroreceptors previously examined at a fine structural level in elasmobranchs and the paddle-fish, Polyodon spathula. The sensory cells are pear-shaped with a very small apical part, in the centre of which there is a short cilium. Basally, the sensory cells make several contacts with button-shaped nerve-endings. The presumed synaptic area in the sensory cell is characterized by a presynaptic sheet surrounded by vesicles. Only one type of nerve ending, an afferent type, has been observed.

Cobalt iontophoresis of sensory nerves in the rat lung.

By iontophoretically introducing, first, cobalt and, subsequently, sulfide ions into the vagus nerve, it is possible to trace sensory nerves to their endings in the rat lung. Nerve fibers and terminals are found predominantly in the adventitia of the airways and blood vessels. Some nerves are found in the submucosa of the bronchi and bronchioles. Some are found in the cardiac muscle on the periphery of pulmonary veins, and a few nerves are seen to end among smooth muslces of the blood vessels and the airways. At least three types of nerve endings can be identified at the light microscopic level: (1) free nerve endings; (2) brush-like endings; (3) knob-like terminals.

Innervation of the carotid body, types of nerve endings and their possible significance

The nerve endings in the carotid body of normal cats are investigated by means of serial sections. Two types of endings not described previously are especially studied: the non-synaptic bouton and the meniscus with prolongations. The first is a small nerve ending with abundant mitochondria and glycogen which is devoid of synaptic vesicles. The second is a normal meniscus which presents prolongations containing the same cytological elements of the nonsynaptic boutons. It is proposed that some menisci are lateral endings of an afferent fiber. Relating these results with well-known functional characteristics of the carotid body, the existence of axonal reflexes is suggested. These views can explain apparently contradictory facts.

Partial separation of synaptosomes accumulating 4-aminobutyrate or glutamate by zonal centrifugation on a discontinuous sucrose gradient.

Rat cerebral cortex slices were incubated with 1muM [3H]4-aminobutyrate or [3H]L-glutamine. The subcellular distribution of the accumulated labelled substances were determined by fractionating the nuclei-free homogenates on a 5-step discontinuous sucrose density gradient in a B XIV zonal rotor. The gradient was designed to separate the synaptosomes into 3 subpopulations of increasing density. The patterns of distribution of [3H]4-aminobutyrate and [3H-a1L-glutamate in the three synaptosomal peaks were distinctly different. This indicates the presence of separate types of nerve ending accumulating these two potential neurotransmitters, which are known to be metabolically closely linked through the enzyme glutamate decarboxylase. Recentrifugation of the 3 synaptosomal peaks on flat step gradients in a swingout rotor did not result in any further enrichment in transmitter-specific synaptosomes.

Serotonin nerve terminals in adult rat neocortex

Axonal processes which take up and retain exogenous tritiated serotonin ([ 3H]5-HT) have been demonstrated in the fronto-parietal cortex of adult rats, by means of high resolution radioautography. Prolonged topical superfusion with relatively high concentrations of [ 3H]5-HT allowed detection of a maximal number of axonal reactions in the upper 3 layers of cortex. Comparison of results obtained from normal rats and animals pretreated with 6-hydroxydopamine or bearing midbrain raphe lesions established the specificity of this labeling. All reactive axons seemed to arise from the serotonin nerve cell bodies in groups B7 and B8 of Dahlström and Fuxe 15. In electron microscope radioautographs, the serotonin fibers appeared as tenuous, naked axonal processes (0.1–0.5 μm in diameter) exhibiting small enlargements (0.7 μm in mean diameter) spaced at frequent intervals (1–3 μm). These boutons contained occasional mitochondria, small, round, agranular ‘synaptic’ vesicles and large granular vesicles. Within axons, [ 3H]5-HT was concentrated in the boutons, and to a much lesser extent in connecting segments. This reactive pattern resembled that revealed by the fluorescence technique for endogenous serotonin. Preferential accumulations of the tracer by mitochondria and vesicular organelles indicated that these elements could sequester exogenous serotonin. Large granular vesicles were not necessarily visible in random thin sections of the labeled varicosities, and thus could not serve as the unique criterion for electron microscopic identification of 5-HT terminals. Moreover, these organelles are known to be present in other types of nerve endings. Topometric analysis of serial thin sections nevertheless demonstrated that large granular vesicles were potentially detectable in every 5-HT containing bouton, and also enabled extrapolation of their average number at 7 per varicosity. This low number makes it unlikely that large granular vesicles primarily represent storage sites. They could rather serve as a carrier for particle-bound enzymes essential to the local metabolism of serotonin or its precursors. A very small fraction of the serotonin varicosities exhibited the membrane differentiations of typical synaptic terminals. Extensive sampling in serial thin sections revealed junctional complexes in only 5% of labeled boutons, as opposed to 50% of unlabeled nerve endings in the sorrounding neuropil. The data do not preclude the possibility that other monoaminergic neurons also share similar characteristics. It is probable that endogenous serotonin can be liberated from all axonal varicosities including those lacking strictu senso synaptic relationships. The overall configuration and ultrastructural features of cortical serotonin fibers suggest intrinsic dynamic properties which could assume particular significance in terms of function, plasticity and regrowth.

Synaptosomes containing large agranular vesicles isolated from developing rat brain.

Using the subcellular fractionation technique the fine structure of the isolated nerve endings (synaptosomes) from the hemispheres and brain stem of the 1-day old and adult rat was examined. In the synaptosomal fractions of the brain of 1-day old rats we observed a new type of nerve endings containing predominantly large agranular vesicles about 1,000 A in diameter. After incubation with alpha-methylnoradrenaline or 5-hydroxydopamine these vesicles remained agranular. It is assumed that the new type of large vesicles represent developing synaptic vesicles.

New theory for receptor mechanism of carotid body chemoreceptors

EVER since De Castro1 first ascribed a chemosensory function to the carotid body (later confirmed by Heymans, et al.2), there has been much discussion and controversy over the precise mechanism whereby stimulation of the afferent fibres is achieved3,4. The controversy initially centred around the nature of the neurotransmitter released by the glomus cell, which was assumed to be highly sensitive to hypoxia and less sensitive to hypercapnia and acidaemia. Perhaps the most generally accepted theory was that the glomus cells respond to hypoxia by releasing a neurotransmitter that initiates an increase in firing rate of the nerve fibres terminating on the glomus cells. The afferent nature of these fibres was originally deduced by De Castro5 from light microscopic examination of the nerve fibres innervating the carotid body. The early ultrastructural studies, however, failed to show clear evidence of afferent types of nerve ending in synaptic contact with the glomus cells. On the contrary, these nerve endings were purported to be presynaptic and therefore efferent in function because they contain large numbers of agranular ‘synaptic’ vesicles6–8. This conclusion was further substantiated by Biscoe et al.9, who showed that intracranial decentralisation of the IXth cranial nerve caused degeneration of nerve endings on glomus cells. These findings led to an alternative theory of chemoreceptor action3. In this case the chemosensory function is attributed to numerous free nerve endings of small diameter, which are found in the carotid body tissue. The glomus cells and associated nerves are held to form part of an efferent inhibitory feedback system, in which release of biogenic amines, that are known to be present in large quantities in glomus cells, depresses chemoreceptor activity.

The ultrastructure and source of nerve endings in the carotid body.

The fine structure of nerve endings in the cat carotid body was analyzed by serial section electron microscopy. In the normal animal, three types of intralobular endings can be recognized. The first type consists of large, calyciform endings which surround glomus cells. The second type includes small calyciform endings which arise from a thin axon and also contact glomus cells. Interstitial enlargements enveloped by sustentacular cells having no direct contact with glomus cells constitute a third type of nerve ending. Intracranial section of the glossopharyngeal nerve caused no change in the number or appearance of intralobular endings, indicating that they are afferent terminals. Stromal axons in the connective tissue of the carotid body may be autonomicfibers as indicated by their degeneration following removal of the superior cervical ganglion.

THE FINE STRUCTURE OF THE PARS INTERMEDIA OF THE PITUITARY BODY IN THE MONKEY, MACACUS EUSCATUS

The pars intermedia of the pituitary body in the adult male monkey (Macacus f uscatus) was investigated by means of electron microscope. The pars intermedia contains glandular cells, agranular cells, and a great number of unmyelinated nerve fibers. The glandular cells are further composed of three types of cells : Type I contains numerous large secretory granules (about 2500 - 4000 A in diameter) with variable electron density, and are most dominant in number. Type II possesses smaller dense secretory granules (about 2000 - 2200 A) and the well-developed rough-surfaced endoplasmic reticulum. Type III contains the smallest dense secretory granules (about 1300- 1500 A). Both types, II and III, are quite small in number. Agranular cells have no granules suggestive of secretion, and may serve as the supporting cell. In the monkey pars intermedia, three types of nerve endings can be distinguished ; (I) nerve endings only containing synaptic vesicles of about 500 A, (II) nerve endings with synaptic vesicles and large dense-cored vesicles (large granular vesicles), about 900 A, and (III) nerve endings containing synaptic vesicles and elementary granules of neurosecretory substance, about 1500 A. The results may indicate that the pays intermedia of the adult male monkey is still active in secretory function.

Comparative aspect on the innervation of submandibular glands in cat and rabbit: an electron microscopic study.

The innervation of the submandibular glands of cat and rabbit was studied by electron microscopy. The acini of the submandibular glands of both species were composed of myoepithelial cells and two types of secretory cell; namely, acinar and demilunar cells in the cat, and neck and acinar cells in the rabbit. In the peri-acinar connective tissue there were both adrenergic and cholinergic nerve endings which were differentiated by their contents of synaptic vesicles, especially of small granular vesicles. These nerve endings were surrounded partly or completely by Schwann. cell cytoplasm. On the other hand, only one type of nerve ending (cholinergic) was observed within the acini. These intra-acinar nerve endings were devoid of Schwann cell sheath, contacted directly with the plasma membranes of the myoepithelial cells and of the one type of secretory cell that was close to the intercalated duct; namely, the acinar cells in the cat and the neck cells in the rabbit. The occurrence of the nerve endings within the acini was seen more frequently in young cats but somewhat less in adult cats. The functional significance of the intra-acinar nerve endings is discussed.

Electron microscopic studies on the pars intermedia in normal and in mice with hereditary nephrogenic diabetes insipidus.

The ultrastructure of the pars intermedia (PI) of the normal VII +/+ and hereditary nephrogenic diabetes inspidus DI Os/+ mice has been studied with particular reference to the morphology of the glandular cells and their innervation. Four types of cells were observed in both the genotypes of mice, 1) the light glandular cell, 2) the dark cell, 3) a type of cell similar to ependymal cells and 4) a small percentage of typical ACTH cells, observed mostly on the PI border of the cleft and rarely in the centre of PI. The predominant light glandular cells contain mainly two types of membrane bound granules: 1) electron dense core granules, which measure 1500–2500 A and 2) electron lucent vesicles, which measure 3000–4000 A in diameter. Granules of intermediate size with various density are also present in both types of mice. The electron dense core granules are predominant in DI Os/+ mice, whereas, electron lucent vesicles are predominant in the normal VII +/+ mice. Similar uniform size membrane bound electron dense granules have been observed in ACTH cells of PI and pars distalis. From earlier experimental evidences and the present observations, it is concluded that the dense core granules in PI may be synthesizing ACTH or ACTH-like substance. It is also discussed that these dense core granules may further mature and give rise to MSH in the form of electron lucent vesicles. If it is so, PI light glandular cells may have dual functions, of producing MSH and ACTH. One of the functions of ependymal-like cells, may be the transport of PI secretion. Three types of nerve endings are observed throughout the PI, making synaptic contact with the predominant cell type. The innervation is more in DI Os/+ mice than in normal mice. The classification of these nerves is according to Bargmann and co-workers 1) peptidergic neurosecretory fibers, contain mainly membrane bound dense core granules, measuring 1200 to 1800 A, and are the classic neurosecretory granules; 2) adrenergic fibers, measuring 700–900 A; 3) cholinergic fibers, measuring 300–400 A. Adrenergic and cholinergic fibers are more towards the hypophysial cleft. The increased innervation, the synaptic contact, the extremely hypertrophied PI and the greater activity of its light glandular cells in the DI Os/+ mice show the PI is under the influence of the nervous system.

The structure and function of the lateral line system in larval Xenopus laevis.

AbstractEach lateral line organ in Xenopus laevis larvae contains about two dozen receptor cells. These are divided into two classes on the basis of the orientation of the cilia in their sensory‐hair‐bundles. The fine structure of the lateral line organs is similar to the adult pattern and that found in other species of amphibia and fish. However apparently degenerating receptor cells are found in normal tadpoles. Two types of nerve ending, considered to be afferent and efferent, contact the bases of receptor cells. Each organ has two physiologically distinct sensory units which are sensitive to mechanical deflection of the organ's sensory hairs. The organs have a plane of maximum sensitivity to stimulation and respond in a phasic‐tonic manner to vibrational stimuli and water currents. Efferent activity in unmyelinated fibres in the larval lateral line nerves is associated with tadpole movement; heavy efferent activity occurs throughout locomotory tail flexions and periodic bursting activity coincides with branchial respiratory movement. These patterns of activity are modified at metamorphosis when the mode of locomotion and breathing change. The larvae can detect differential stimulation of the system by small jets of water and turn to face the source although the lateral line system is not essential for the orientation of tadpoles in a flowing water mass. Adult toads subjected to a similar stimulus exhibit feeding behaviour.

The fine structure of the monkey submandibular gland with a special reference to intra-acinar nerve endings.

AbstractThe secretory terminations of monkey submandibular gland were studied by electron microscopy. The acini are composed of two types of secretory cells which are presumably serous and mucous in type. Myoepithelial cells are present also in the acini. The peri‐acinar connective tissue contains many unmyelinated nerve fibers. In some portions, the axons contain many synaptic vesicles of various types. These nerve endings partially lose their Schwann cell investment and reach the acinar basement membrane. In peri‐acinar connective tissue two types of nerve endings may be recognized. They are thought to be adrenergic and cholinergic in type. On the other hand, only one type of nerve ending (cholinergic) is observed within the acini. The intra‐acinar nerve endings are not surrounded by Schwann cell cytoplasm and make direct contact with plasma membranes of the myoepithelial and mucous cells, with a space about 200 Å wide intervening between the nerve and terminal cell. No nerve endings occur in the interspaces between the serous cells. Also, the ultrastructure of the secretory and myoepithelial cells is described.

Distribution and Ultrastructure of Epidermal Sensory Cells in the Freshwater Snails Lymnaea Stagnalis and Biomphalaria Pfeifferi

The epidermal receptor cells and their distribution throughout the body surface of Lymnaea stagnalis and Biomphalaria pfeifferi were studied by means of light and electron microscopic techniques. The investigations reveal general agreement between the two species. The receptor cells are primary sensory nerve cells with the cell bodies lying below the epidermis. The subepithelial cell bodies are frequently grouped together forming small ganglia, particularly in rich sensory regions, such as the lips and the tentacles. Dendrites extend from these sensory cell bodies between the epidermal cells and form free nerve endings at the surface of the epidermis. Six different types of free nerve endings are distinguished on the basis of the number of cilia present and on the length and structure of the cilia roots. A survey of the distribution of the sensory cells revealed that they are restricted primarily to the tentacles, lips, front edge of the foot, pneumostome and mantle edge, although they are also present in the dorsal and lateral surface of the foot. No free nerve endings were found in the dorsal head epidermis. Only one type of nerve ending was found to have a specific localization, whereas the other types have a general distribution. Although it is difficult to determine the function of the different types of free nerve endings in an ultrastructural study, some suggestions are made on the basis of morphological comparisons with receptor cells in other species and also on the basis of behavioral and physiological experiments which have been performed on L. stagnalis.

On different types of nerve endings in the frog median eminence after fixation with permanganate and glutaraldehyde-osmium.

In the frog median eminence, fixed with glutaraldehyde and osmium tetroxide, four types of nerve endings can be generally distinguished. These endings are in contact with the pericapillary spaces of primary portal vessels and can be identified by the internal structure and the size of their granules and vesicles. Type 1 contains large granules (1500–2400 A in diameter) and small clear vesicles (300–500 A in diameter), type 2 intermediate granules (about 1100–1700 A in diameter) and small clear vesicles, type 3 small granules (about 600–1000 A in diameter) and small clear vesicles, type 4 only numerous small clear vesicles. The mixed types containing the large, intermediate and small dense granules in the same ending are infrequently found.

Neuromuscular and axoaxonal synapses of the crayfish opener muscle

Neuromuscular synapses of the opener muscles of the crayfish (Orconectes and Cambarus) have been studied by electrophysiological methods and by electron microscopy. Stimulation of the single inhibitory axon produced both pre- and postsynaptic inhibition. Presynaptic inhibition was more effective than post-synaptic inhibition at frequencies of stimulation below 40 Hz. Two types of nerve terminals were distinguished on the basis of a statistically demonstrable difference in size and shape of the synaptic vesicles in pairs of adjacent endings. Axoaxonal synapses were observed between the two types of nerve ending. The axoaxonal synapses were at least 10–20 times less frequent than neuromuscular synapses.

The neural lobe of the neurohypophysis of the rat: several types of nerve endings.

Se ha estudiado la zona pericapilar del proceso infundibular de la neurohipofisis de ratas de ambos sexos. El analisis del material al microscopio electronico revelo cuatro tipos de terminales nerviosas. Tipo I: con granulos que pertenecen al sistema peptidergico; Tipo II: con las caracteristicas de las terminales colinergicas; Tipo III: similares a las terminales de la eminencia media; Tipo IV: de igual ultraestructura que las terminales de los nervios adrenergicos.

Study of the nerve endings in the vas deferens and seminal vesicle of the guinea pig.

Abstract The characteristics of nerve endings present in the vas deferens and in the seminal vesicle of guinea pig have been studied by pharmacological techniques and by electron microscopy. From a pharmacological point of view it appears that cholinesterase inhibitors potentiated in both organs the contractions elicited by stimulation of the hypogastric nerve. This potentiation is present even in preparations obtained from animals pretreated with reserpine or α-methyltyrosine and is prevented or abolished by atropine. On the basis of the electron microscopic studies two types of nerve terminals, adrenergic and cholinergic, can be distinguished. The difference between the two types of nerve endings is still more evident in the organs of animals pretreated with iproniazid and DOPA. These results are interpreted as supporting the concept that the hypogastric nerve carries, to the vas deferens and to the seminal vesicle, fibers of adrenergic and cholinergic type.

Evidence for a doubly innervated secretory unit in the anuran pars intermedia: II. Electron microscopic studies

Two types of nerve endings were found in synaptic contact with secretory cells of the pars intermedia of Rana pipiens. One type contains relatively large granules 1000 to 1700 Å in diameter. The other type, more numerous and more broadly distributed, contains vesicles 600 to 1000 Å in diameter with a dark core. One example was found of a single secretory cell on which two synapses of the two types occurred in the same plane of section. Several examples were found of single nerve endings in presynaptic contact with a secretory cell and another neuron. This information is considered in relation to a hypothesis of opposed double innervation of the pars intermedia cell.

Fine structure of nerve endings in the human dental pulp

Thick sections of the peripheral coronal areas of the mature dental pulp were examined under light microscopy and thin sections prepared for electron microscopy after fixation in Palade's osmium tetroxide. The area examined corresponded to the “plexus of Raschkow” and myelinated nerve fibres 2–5 μ dia. and unmyelinated nerve fibres 2500–16,000 Å dia. were seen. Three types of nerve endings could be identified by the presence of vesicles and mitochondria within their structure. The first type, presumably derived from myelinated nerve fibres, displayed varicosities up to 4 μ dia. and constrictions of 1 μ diameter, and axonal swellings 5000–10,000 Å dia. The second type consisted of fine-diameter unmyelinated nerve fibres exposed freely in the ground substance, which presumably correspond to pain afferent terminals. The third type consisted of unmyelinated fibres related to blood vessels.