Different Types Of Nerve Fibers Research Articles

Small nerve fiber dysfunction in diabetic neuropathy.

Sensory and autonomic small nerve fiber function was studied in 142 type I diabetics and 45 control subjects. Thermal sensitivity (TS), hot pain sensitivity, and the activity of sweat glands (SGs) were quantitated on the dorsum of the hand and the foot. TS was abnormal in 86% of patients in the foot and 66% in the hand. TS was more sensitive than the hot pain threshold, the number of pilocarpine activated SGs, or the amount of sweat secreted, all of which were abnormal in about 50% of patients for the foot and less than 25% in the hand. Thermal and sweating tests correlated significantly with the scores of abnormal temperature and pinprick sensation obtained by physical examination but not with the duration of the diabetes. TS was also correlated with motor and sensory nerve conduction parameters, but SG number was not. The results indicate that diabetic neuropathy has a variable presentation in different types of nerve fibers.

Fine structure of the ganglion of Cephalodiscus gracilis (Pterobranchia, Hemichordata).

The ganglion of Cephalodiscus gracilis M'Intosh 1882 is entirely intraepithelial and located in the dorsal epidermis immediately behind the tentacular apparatus that is formed by the mesosome (collar). A characteristic feature of the ganglion is a well-developed neuropile in which different types of nerve fibres can be discerned, many of which contain small granules with electron-dense contents. There are no glia-like cells in association with these fibres. Only slender basal processes of epidermal epithelial cells traverse the neuropile. In the depth of the epithelium the neuropile borders the epidermal basal lamina; apically it is covered by a layer of cell bodies, the majority of which belong to what appear to be ordinary ciliated epidermal cells. Besides these epidermal cells the perikarya of two additional types of cells, which are considered to be neurons, can be discerned. One type is characterised by many rough endoplasmic reticulum cisterns and mitochondria, the other by abundant small, electron-dense granules. The nuclei of these cells are comparatively pale and contain a prominent nucleolus. The neuron cell bodies do not form a distinct layer; but they are loosely distributed somewhat deeper than those of the ordinary epidermal cells. They probably send off an apical process to the epidermal surface and a basally directed one into the neuropile. The ganglion has been compared to the nervous systems in cnidarians, some spiralians, and especially other hemichordates, echinoderms, and chordates; it is found to be of primitive rather than degenerate nature. Furthermore, the possible functional significance of its close connection to the food-capturing tentacular apparatus is discussed.

Nerves containing substance P, vasoactive intestinal polypeptide, enkephalin or somatostatin in the guinea-pig taenia coli. Distribution, ultrastructure and possible functions.

The guinea-pig taenia coli is rich in peptide-containing nerves. Nerve fibres containing substance P (SP), vasoactive intestinal peptide (VIP), or enkephalin, were numerous in the smooth muscle while somatostatin fibres were very few. Nerve fibres displaying SP or VIP immunoreactivity were numerous in the myenteric plexus. Enkephalin nerve fibres were fairly numerous in the plexus while somatostatin nerve fibres were sparse. Nerve cell bodies containing immunoreactive SP or VIP were regularly seen in the plexus. Delicate varicose elements of the different types of nerve fibres were found to ramify around nerve cell bodies in a manner suggestive of innervation. In the electron microscope the various peptide-storing nerve fibres (i.e., elements containing SP, VIP or enkephalin) were found to contain a varying number of fairly large, electron-opaque vesicles in the varicose swellings. These vesicles represent the storage site of the neuropeptides. The isolated taenia coli responded to electrical nerve stimulation with a contraction. After cholinergic and adrenergic blockade the contractile response was replaced by a relaxation followed by a contraction upon cessation of stimulation. SP contracted the taenia while VIP caused a relaxation. The enkephalins raised the resting tension slightly while somatostatin had no effect. These observations are compatible with a role for SP as an excitatory neurotransmitter and for VIP as an inhibitory one, and with the view that both SP neurones and VIP neurones act as motor neurones. In preparations contracted by SP the electrically induced contractions were reduced in amplitude while the electrically induced relaxations seen after adrenergic and cholinergic blockade were enhanced in amplitude. In preparations relaxed by VIP there was an increased contractile response to electrical stimulation, while in the atropine + guanethidine-treated preparation the electrically induce relaxations were reduced in amplitude. The enkephalins reduced the contractile response to electrical stimulation, while somatostatin induced a very small reduction in the amplitude of such responses. These observations suggest that SP neurones and VIP neurones may play additional roles as interneurones. Somatostatin neurones probably act as interneurones. Enkephalin-containing fibres may serve to modify the release of transmitter from other nerves in the smooth muscle, perhaps through axo-axonal arrangements. Alternatively, the enkephalin nerve fibres in the smooth muscle are afferent elements involved in mediating sensory impulses to the myenteric plexus.

Intrinsic innervation of the urinary bladder

The intrinsic innervation of the urinary bladder of the cat was studied with the aid of total extrinsic denervation (L7, S1, S2, S3 and the first coccygeal spinal nerves were transected and the hypogastric ganglia were extirpated on both sides); the materials were studied by electron microscopy. Several synapses could be observed between nerve processes and perikarya and between two adjacent nerve processes. The terminals could be classified into four groups according to the existence of a dense core and according to the size of the synaptic vesicles; the first group is made up of small clear vesicles; the second group of terminals contains some large granulated vesicles in addition to a few small clear vesicles; the third group of terminals contains small granulated vesicles and in the fourth type of terminals, large, 150- to 250-nm 'peptiderg' vesicles could be observed. The latter type of terminals was always observed in postsynaptic situation. Spine synapses could also be found in the ureterovesical ganglia. Several desmosome-liek attachments also could be observed between the nerve processes and perikaraya and between two nerve fibers. Up to three different types of nerve fibers have been observed on the same neuron. These morphological results suggest that the ureterovesical junction should be considered a single functional unit which plays an important role in coordinating the function of the bladder; further local circuits might exist in the urinary bladder wall.

Ultrastructure of the nerve cells and fibres in the urinary bladder wall of the cat

The nerve elements in the urinary bladder of the cat were studied by electron microscopy. According to their ultrastructure, nerve cell somata can be classified into three types: the large cells with a cytoplasm rich in organelles, several processes and numerous synaptic contacts on their surface; the cytoplasm contained 80- 120-nm granulated vesicles. The second type is poor in cytoplasmic organelles and has very few processes and virtually no synaptic contacts on the soma. The third type contains numerous large 160- to 220-nm 'neurosecretory' vesicles in the cytoplasm. According to the morphology of the vesicle population, four types of nerve processes could be distinguished: Type a, with a dominant population of small (40-60 nm) agranular vesicles. These are thought to be sacral parasympathetic fibres. Type b, with small (40-60 nm) granular vesicles, which may be the noradrenergic sympathetic fibres. Type c, with 80- to 120-nm granulated vesicles, probably of local origin. Typed d, with large 160- to 220-nm 'neurosecretory' vesicles also of local origin. Different types of nerve fibres are converging on the local nerve cells. This suggests that the local circuits can play an important role in coordinating the function of the bladder. Therefore, ganglia may be considered as an elementary functional unit.

Ultrastructure of the neurohypophysis of the teleost Poecilia latipinna in relation to neural control of the adenohypophysial cells

The structure of the neurohypophysis of Poecilia latipinna (green molly, sailfin molly) was studied with the electron microscope. Profile diameters of neurosecretory granules in the non-myelinated neurohypophysial nerve fibres were measured and mathematically corrected for error due to section thickness. Six different types of nerve fibres could be distinguished by statistical classification of their granules and by other ultrastructural features. One fibre-type (type B) contained granules with a mean diameter of 85 nm, and the other five types (types Ala, Alb, A2, A3 and A4) all contained granules with mean diameters greater than 100 nm. Synaptic contacts were observed between type B fibres and all the adenohypophysial cell-types, although in the case of the ACTH cells the synapses were separated from the cell membrane by a continuous double basement membrane. Type A fibres were observed to contact the cells of the proximal pars distalis and pars intermedia, but did not form synapses. However, synapses occurred between type A fibres and pituicytes, and between type A fibres and the pericapillary basement membrane in the interior of the neurohypophysis. The possible roles of the different types of nerve fibres in controlling the adenohypophysial cells are discussed in the context of evidence from other teleosts.

Inhibition of the action of bradykinin and acetylcholine on paravascular pain receptors by tetrodotoxin and procaine.

Intra-arterial injection of the algogens bradykinin and acetylcholine into the isolated perfused rabbit ear connected to the body by its nerve only elicit a dose-dependent reflex fall in blood pressure. Procaine and tetrodotoxin were used to investigate whether bradykinin and acetylcholine exerted their algesic effect via different types of nerve fibers. Procaine reduced the effect of bradykinin and acetylcholine to a very similar degree. Tetrodotoxin reduced the effect of bradykinin slightly more than that of acetylcholine. It is assumed that on the whole bradykinin and acetylcholine act via the same nerve fibers but bradykinin seems to have some more affinity to fibers with a fewer number of sodium channels than acetylcholine.

Electron microscopic observations on synapse-like contacts between pituicytes and different types of nerve fibers in the anuran pars nervosa.

Pituicytes of Rana pipiens could be classified into two types, pale and dense, according to their relative densities of cytoplasm and the populations of free ribosomes and cell organelles. An intermediate type of pituicyte was also recognized.

Innervation of the corneal endothelium of the eye of the rabbit.

The cornea is known to be supplied by a complicated system of nonmedullated nerve fibers which originate in the ciliary plexus. These nerves enter the cornea from the limbus in the middle layers of the stroma. They lose their myelin sheaths soon after entering the stroma and divide into many branches as they run centrally and anteriorly toward Bowman's membrane, which they penetrate through the pores. The nerve fibrils form a plexus beneath the epithelium, send up branches between the epithelial cells, and end in round or pear-shaped endbulbs (Friedenwald 1 ). Histologic evidence for the existence of three different types of nerve fibers in the corneal stroma has been described elsewhere (Wolter 2 ). Surprisingly, however, the nervous system of the cornea is generally believed to be limited to the stroma, the subepithelium, and the epithelium. In the literature we find no histological reports indicating the existence of nerves and nerve

Paralysis of the ulnar nerve and management of its deformity.

p ARALYSIS Of the ulnar nerve has been more frequent and unfortunately the results of suture of this nerve have given less gratifying results than in any other peripheral nerve. Reasons for this are: (1) the ulnar is a mixed motor and sensory nerve carrying different types of nerve fibers, (~) distal innervation is to small highly specialized muscles for the finer movements of the hand, (3) another reason may be the poor blood supply of the nerve which may be further impaired by anterior transplantat ion of the nerve. The functional return of a useful hand should be the objective when confronted with an ulnar nerve paralysis. This may be obtained by neurorrhaphy or by a combination of primary nerve repair followed by tendon transfers for deficient regeneration. In either case we must preserve the parts of the hand that are essential for function. An innervated, but stiff hand is useless. Steps must be taken to preserve muscles, joints and soft tissues in a state of mobility. I t seems to the writer that mechanical splintage of paralyzed joints must follow more closely the anatomical and physiological characteristics of a part. The prevention of muscle stretching is important , but the joint structures on which the muscle acts must also be considered; namely, the ligaments, joint capsules and soft tissues. For example, t ight skin about a joint can vitiate completely normal nerve-muscle-joint mechanism. Paralysis of the ulnar nerve sparing the nerves to the flexor digitorum profundus muscle presents a deformity of the hand that is not seen when the lesion is above the elbow. Phylogenetically, the muscles innervated by the ulnar nerve arc oldest and more highly co-ordinated than those supplied by other peripheral nerves. This nerve is peculiar by supplying muscles at different levels in the extremity, but which co-ordinate for fine hand movement involving identical joints. An active flexor digitorum profundus muscle sets in motion the platform of origin of the lumbrical muscles. The latter, however, have their insertion upon the dorsal expansion of the metaearpophalangeal joint. Paralysis of the ulnar nerve above the elbow, producing a flail state of all the muscles supplied by this nerve, causes a minimal deformity of the hand. However, a lesion below the elbow sparing the innervation of the

ATROPHY IN SKELETAL MUSCLE

Mammalian skeletal muscle is served by a number of different types of nerve fibers. Some represent the central and others the autonomic nervous system. Diagrammatic representation of the component parts of skeletal muscle innervation has been attempted in figure 1. Probably only the motor nerve fibers, axons of the lower motor neuron, make functional connection with the muscle fibers. It is generally believed that these fibers, and these alone, are responsible for the control of the activity of the muscle fiber and are chiefly responsible for the trophic state of muscle tissue. Boeke 1 and others have claimed that muscle fibers are also innervated by autonomic nerve fibers. Such connections may exist, but there is no satisfactory evidence that the autonomic nervous system has any direct control over the activity of skeletal muscle fibers. Sympathetic and parasympathetic nerve fibers to blood vessels in muscle give the autonomic nervous system indirect