Somatic Nerve Fibers Research Articles

Excitatory and inhibitory A- and C-reflexes in pelvic parasympathetic efferent nerves elicited by single shock to A and C afferent fibers of perineal and limb somatic nerves in anesthetized rats

The effects of single electrical shocks to myelinated A and unmyelinated C afferent fibers of perineal and limb somatic nerves on the reflex discharges in pelvic parasympathetic (L6/S1) efferent nerves to the bladder were examined in anesthetized central nervous system (CNS)-intact and acute spinal rats. When the bladder was empty, stimulation of perineal somatic inputs to the L6 and S1 segments from the perineo-femoral branch of a pudendal nerve produced excitatory A- and C-reflex discharge components in postganglionic parasympathetic efferent nerve branches on the bladder surface. When the bladder was expanded and pelvic efferent neurons were rhythmically active, additional inhibitory A- and C-reflex components could be seen. After acute spinal transection, the same stimuli elicited excitatory A- and C-reflex discharges of similar latency as those observed before the spinal transection, but were of larger amplitude and longer duration; resting activity in the pelvic nerve was low, and no evoked inhibitory reflex components could be observed. Electrical stimulation of afferents in the tibial nerve had no effect when the bladder pressure was low, but when the bladder was distended, early and late components of reflex inhibition and excitation of parasympathetic activity were visible in CNS-intact rats; these reflex responses were abolished following spinalization.

Effects of afferent neural stimulation on critical oxygen delivery: a hemodynamic explanation

Injury and activation of somatic afferent nerve fibers may alter critical oxygen delivery (DO2C), the point at which oxygen consumption becomes dependent upon delivery, and hence reduce tolerance to hypovolemia. The present study investigated the mechanism of this. Anesthetized mongrel dogs were divided into two groups: control (n = 6) and those subject to brachial nerve stimulation (BNS; n = 5). Whole body oxygen delivery (DO2I) and consumption were initially similar in both groups. DO2I was reduced by cardiac tamponade to determine DO2C. DO2C was significantly higher in BNS compared with control (11.5: 11.0-16.7 vs. 7.5: 6.9-9.5 ml.min-1.kg-1; median: Q1 - Q3), whereas critical oxygen extraction ratios were lower (54.8: 39.7-61.2 vs. 78.3: 53.5-92.4%). At approximately DO2C, normalized femoral blood flow was lower than renal flow in control (renal-femoral difference 17.4: 8.7-40.0%) but not in BNS (-7.8: -14.8 to +11.8%). These results indicate that activation of somatic afferent nerve fibers elevates DO2C. This could be due to an impairment in peripheral oxygen extraction as a consequence of a redistribution of blood flow away from metabolically active vital organs toward relatively inactive skeletal muscle.

Acupuncture — from empiricism to science: Functional background to acupuncture effects in pain and disease Pain and disease

Acupuncture is part of Traditional Chinese Medicine, a system with an empirical basis which has been used in the treatment and prevention of disease for centuries. A lack of scientific studies to prove or disprove its claimed effects led to rejection by many of the western scientific community. Now that the mechanisms can be partly explained in terms of endogenous pain inhibitory systems, the integration of acupuncture with conventional medicine may be possible. Its use for pain relief has been supported by clinical trials and this has facilitated its acceptance in pain clinics in most countries. Acupuncture effects must devolve from physiological and/or psychological mechanisms with biological foundations, and needle stimulation could represent the artificial activation of systems obtained by natural biological effects in functional situations. Acupuncture and some other forms of sensory stimulation elicit similar effects in man and other mammals, suggesting that they bring about fundamental physiological changes. Acupuncture excites receptors or nerve fibres in the stimulated tissue which are also physiologically activated by strong muscle contractions and the effects on certain organ functions are similar to those obtained by protracted exercise. Both exercise and acupuncture produce rhythmic discharges in nerve fibres, and cause the release of endogenous opioids and oxytocin essential to the induction of functional changes in different organ systems. Beta-endorphin levels, important in pain control as well as in the regulation of blood pressure and body temperature, have been observed to rise in the brain tissue of animals after both acupuncture and strong exercise. Experimental and clinical evidence suggest that acupuncture may affect the sympathetic system via mechanisms at the hypothalamic and brainstem levels, and that the hypothalamic beta-endorphinergic system has inhibitory effects on the vasomotorcenter, VMC. Post-stimulatory sympathetic inhibition which proceeds to a maximum after a few hours and can be sustained for more than 12 hours, has been demonstrated in both man and animals. Experimental and clinical studies suggest that afferent input in somatic nerve fibres has a significant effect on autonomic functions. Hypothetically, the physiological counterpart lies in physical exercise, and the effect can be artificially reproduced via various types of electrical or manual stimulation of certain nerve fibres.

Reinnervation of frog sympathetic ganglia with somatic nerve fibres

The formation of synapses in the last two ganglia of the sympathetic chain of the frog Rana esculenta was investigated after anastomosing the 6th spinal nerve to the denervated ganglia in order to evaluate the reinnervation of deafferented sympathetic neurons with somatic cholinergic axons. The same ganglia were examined both electrophysiologically and morphologically from 25 to 280 days after the operation. In response to electrical stimulations of the anastomosed spinal nerve, synaptic transmission was analysed with intracellular microelectrodes placed into B or C sympathetic neurons. Synaptic density was quantified using electron microscopy by a synaptic index defined as the ratio of the number of synapses encountered to the number of perykarya examined. After ganglionic deafferentation, post-synaptic membrane differentiations persisted without any pre-synaptic element and an index of the ‘vacated’ post-synaptic differentiations was calculated. Although somatic axons were growing into all ganglia studied, no sign of neuronal reinnervation was detected in ganglia of 8 of the 31 frogs (26%) taken from 29 to 210 days after the anastomosis. Moreover, in 18 out of 31 frogs (58%) analysed at different times after the operation, the ganglia were reinnervated with regenerating preganglionic axons in spite of care taken to avoid it. However, even after 3 months, certain neurons of these ganglia were not reinnervated and the synaptic index approximated the value of normal ganglia only in the 8th ganglion. In addition, post-synaptic membrane differentiations could still persist and coexist with normal synapses. It was only beyond three months after the anastomosis that the ganglia of 5 of the 31 frogs (16%) were reinnervated with regenerating somatic axons. Reinnervated B and C neurons were polyinnervated. But in 3 out of these 5 frogs the ganglia were also reinnervated with preganglionic axons and several B and C neurons received a double reinnervation. The synaptic indices were far from the value of normal ganglia except for the 8th ganglion of one frog reinnervated by both types of axons and the indices of vacated differentiations were close to that of ganglia with no reinnervated neurons. Contrary to mammals, frog somatic axons are, therefore, relatively ineffective at reinnervating sympathetic neurons, probably because in amphibian ganglia, synapses between the pre- and post-synaptic elements require higher specificity.

Idiopathic autonomic neuropathy: clinical, neurophysiologic, and follow-up studies on 27 patients.

We evaluated the natural history, electrophysiologic characteristics, spectrum of autonomic involvement, pathology, and laboratory features in 27 patients with idiopathic autonomic neuropathy who were followed up for a mean of 32 months. The typical features of idiopathic autonomic neuropathy include the absence of an associated disease, frequent history of preceding infection, and acute or subacute onset with a monophasic course. The spectrum of autonomic involvement ranges from panautonomic to selective adrenergic or cholinergic failure. There is infrequent involvement of somatic nerve fibers as assessed by routine nerve conduction studies. Pathologic features include the presence of a small inflammatory mononuclear cell infiltrate in the epineurium. Recovery tends to be gradual and frequently incomplete. The acute onset, frequent antecedent viral infection, selectivity of involvement by fiber type and autonomic level, and presence of perivascular mononuclear cell infiltration suggest that the underlying mechanism is likely to be immune-mediated. These observations may justify plasma exchange or other immunosuppressive modalities as early therapeutic intervention in patients with progressive disability.

Somatic nerve fibres impairment during hemodialysis

Somatic nerve fibres impairment during hemodialysis

Comparison of autonomic and somatic nerve fiber regeneration

Comparison of autonomic and somatic nerve fiber regeneration

Neuropharmacology of the Lower Urinary Tract in Women

One of the most common gynecologic complaints is urinary incontinence, which afflicts approximately one third of the female population. In urodynamic units, approximately 80 per cent of women with urinary incontinence have detrusor hyperreflexia as the sole reason for, or as a component of, their incontinence problem. Approximately 80 to 85 per cent of patients with detrusor hyperreflexia have a functional neuromuscular disturbance of their detrusor muscle. One to 2 per cent of the patients seen in our urodynamic unit have detrusor hyperreflexia caused by a neurogenic bladder. As our clinic's population ages, this type of functional neuromuscular disturbance--neurogenic bladder problem--will increase. The neuromuscular control of the lower urinary tract is complex and not fully understood, explaining why we are unable to treat the functional neuromuscular disturbance in some patients effectively and why we may have to try several drugs before finding one that is effective in other patients. Although patients may have the same symptoms and even the same urodynamic findings, the cause of the functional neuromuscular disturbance may be different. One patient may respond to drug A and not to drug B, and another patient with virtually the same symptoms and urodynamic findings responds to drug B and not to drug A. The main neurologic control of the lower urinary tract is through the sacral outflow of somatic and (mainly) parasympathetic nerve fibers. There appears to be an "on-off" control mechanism involving the urethrovesical unit wherein there is parasympathetic inhibition of the detrusor muscle and parasympathetic stimulation of the urethral smooth muscle and stimulation of somatic nerves to the urethral striated muscle at rest. Reverse action occurs when the patient voids. For this reason, cholinergic and anticholinergic drugs exert a powerful influence on the lower urinary tract. Adrenergic control through alpha 1- (and indirectly alpha 2-) and beta 2-receptors (with a preponderance of alpha-receptors in urethral smooth musculature and a preponderance of beta-receptors in the detrusor muscle) appears to modulate and modify parasympathetic action. This explains why adrenergic stimulant and blocker drugs, in most women, do not affect the lower urinary tract as much as parasympathomimetic-lytic drugs. However, adrenergic effect seems to be greater in some women than in others, explaining, for example, why some patients with detrusor hyperreflexia respond to beta 2-stimulatory drugs and not to anticholinergic drugs. Also inter-twined in the neuromuscular control of the lower urinary tract are the roles of prostaglandins and calcium-potassium channel changes.(ABSTRACT TRUNCATED AT 400 WORDS)

Nerve pathways between the pterygopalatine ganglion and eye in cats.

By dissection of thiocholine-stained orbital preparations, it has been determined that three different nerve pathways link the pterygopalatine ganglion and the eye in cats. 1) Nerves from the proximal half of the ganglion join a plexus of nerves and ganglion cells in the rete mirabile of the maxillary artery. Branches of the internal carotid nerve also supply this plexus. Fine nerves from the plexus travel to the optic nerve and then to the eye, accompanying both the nasociliary nerve that passes through the rete and the ciliary arteries that arise from the rete. 2) One or more nerves from the nerve of the pterygoid canal and from a prominent accessory ganglion near the orbital apex course to the inferior optic nerve surface at the optic foramen; these then run distally along the optic nerve to fuse with ciliary nerves or to accompany ciliary arteries entering the eye. 3) Other nerves from the pterygopalatine ganglion travel medially around the extraocular muscle cone to join the ethmoidal and infratrochlear branches of the nasociliary nerve; some nerves from the ganglion then take a retrograde course to the optic nerve, where they join ciliary nerves or arteries to the eye. All three pathways may transmit sympathetic, parasympathetic and somatic sensory nerve fibers.

Clinical Significance of Sacral and Pudendal Nerve Anatomy

The neuroanatomy and neurophysiology of the external urethral closure mechanisms still are under debate because the motor fibers that emanate from the sacral plexus and pudendal nerve to supply this segment have not been traced, nor has their functional interrelationship been established. Therefore, we dissected 3 male human cadavers (aged 31 to 69 years) by tracing the entire sacral plexus, particularly the pudendal nerve, from the cauda equina throughout the branching of the nerves to their final destination. The dissection demonstrated that the extrinsic urethral sphincter, formed by the rhabdosphincter around the membranous urethra as well as the levator ani muscle and pelvic floor (especially the transversus perinei muscle), is innervated by somatic nerve fibers that emanate primarily from sacral roots S2 and S3.In 5 patients with neurogenic lower urinary tract dysfunction electrostimulation of the sacral root and pudendal nerve markedly increased intraurethral closure pressures. Stimulation of the pudendal nerve or its transversus perinei branch alone resulted in an increase in intraurethral closure pressure to 60 to 70cm. water—an increase similar to that produced by stimulation of the sacral root without neurotomy. By means of neurotomy and/or neural blockade with lidocaine we were able to differentiate between the contributions of each muscular element to the external sphincteric mechanism. Almost 70 per cent of the closure pressure of the external urethral sphincter is induced by stimulation of the S3 ventral root, while the other 30 per cent derives from S2 and S4 neuronal impulses.

Role of the cardiopulmonary blood volume in changes in left ventricular output during stimulation of somatic afferent nerve fibers

The effect of cytochalasin D (CD), an agent specifically destroying actin cytoskeleton, on DNA replication of cultured mouse embryonic fibroblasts (MEF) and BALB/3T3 strain cells was studied. Incubation of normal cells with CD resulted in progressive inhibition of DNA synthesis: in the first 16-20 h the percentage of cells pulse-labelled with 3H-thymidine was similar to that in control cultures, on day 8 the percentage of labelled cells was 7-8 times lower than in the control. The transfer of cells into fresh medium upon 8-day incubation in the presence of CD resulted in the recovery of DNA synthesis. Similar curves of DNA synthesis inhibition in the presence of CD and of DNA synthesis recovery in fresh medium were observed both in mononuclear and binuclear cells. Thus, CD-induced reorganization of actin cytoskeleton can have an abrupt but reversible disturbing effect on normal cell cycle.

Two distinct projection areas from tongue nerves in the frontal operculum of macaque monkeys as revealed with evoked potential mapping

Projection areas in the cerebral cortex from tongue nerves were investigated in anesthetized macaque monkeys ( Macaca fuscata). Three tongue nerves (lingual nerve, chorda tympani, and a lingual branch of the glossopharyngeal nerve) were electrically stimulated and thereby evoked mass field potentials were recorded with microelectrodes roving through the exposed and buried frontal operculum. Two distinct tongue nerve projection areas were thus located; one in the lower part of the precentral gyrus ventral to the inferior precentral sulcus, and the other in the medial part of the buried frontal operculum. The former corresponds to the “cortical masticatory area”, previously defined in macaque monkeys as involved in somatic sensation as well as mastication. However, the prominent projection from the chorda tympani and glossopharyngeal nerve branch, containing taste fibers, to this area suggests its involvement in taste sensation. The latter corresponds to the “pure gustatory area” defined in squirrel monkeys in both location and cytoarchitecture. However, projection to this area from the lingual nerve, which contains only somatic nerve fibers, suggests its involvement in somatic sensation, as well.

Distribution of somatic and visceral primary afferent fibres within the thoracic spinal cord of the cat.

Transport of horseradish peroxidase (HRP) through somatic and visceral nerve fibres was used to study the patterns of termination of somatic and visceral primary afferent fibres within the lower thoracic segments of the cat's spinal cord. A concentrated solution of HRP was applied for at least 5 hours to the central end of the righ greater splanchnic nerve and of the left T9 intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport times (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Somatic afferent fibres and varicosities (presumed terminals) were found in laminae I, II, III, IV, and V of the ipsilateral dorsal horn and in the ipsilateral Clarke's column. The density of the somatic projection was particularly high in the superficial dorsal horn. In parasagittal sections of the cord, bundles of somatic fibres were seen joining the dorsal horn from the dorsal roots via the dorsal columns and Lissauer's tract. A medio-lateral somatotopic arrangement of somatic afferent terminations was observed, with afferent fibres from the ventral parts of the dermatome ending in the medial dorsal horn and afferent fibres from the dorsal parts of the dermatome ending in the lateral dorsal horn. The total rostro-caudal extent of the somatic projection through a single spinal nerve was found to be of 2 and 2/3 segments, including the segment of entry, the entire segment rostral to it and two-thirds of the segment caudal to it. A lateral to medial shift in the position of the somatic projection was observed in the rostro-caudal axis of the cord. Visceral afferent fibres and varicosities (presumed terminals) were seen in laminae I and V of the ipsilateral dorsal horn. The density of the visceral projection to the dorsal horn was substantially lower than that of the somatic projection. Visceral afferent fibres reached the dorsal horn via Lissauer's tract and joined a lateral bundle of fine fibres that run along the lateral edge of the dorsal horn. The substantia gelatinosa (lamina II) appeared free of visceral afferent fibres. These results are discussed in relation to the mechanisms of viscero-somatic convergence onto sensory pathways in the thoracic spinal cord.

Dichotomizing somatic nerve fibers exist in rats but they are rare

Electrophysiological methods that resolve problems of current spread were used to reinvestigate recent claims that over 40% of myelinated afferent neurons in rats have dichotomizing axons in which branches are maintained in two separate hindlimb nerves. Out of a sample of about 6400 axons recorded in rat hindlimb nerves including 3641 myelinated afferents, 14 axons were found to have a branch in both the sciatic nerve and a second somatic nerve. Examples were found of dichotomizing myelinated afferents, myelinated efferents and unmyelinated afferents.

Bulbocavernosus reflex in benign hypertrophy of the prostate.

Electrically induced bulbocavernosus (BC) reflexes were investigated in 47 patients with benign prostatic hypertrophy and the possible harmful effects of prostatectomy on the pudendal nerve branches were followed up in 30 of the patients using the same method. BC reflex obtained by electrical stimulation of the glans penis did not differ significantly from the normal value in bulbocavernosus and external urethral sphincter muscles whether or not patients had been operated on. It was concluded that there is no reason to believe in the existence of somatic involvement of the pudendal nerve branches in prostatic hypertrophy, or that suprapubic prostatectomy could harmfully affect such somatic nerve fibers.

Effect of colchicine-induced disturbance of axoplasmic transport on mediator liberation in myoneural synapses of the frog sartorius muscle

Application of colchicine to the nerve innervating the sartorius muscle in frogs reduces differences in the functional state of the myoneural synapses of the muscle as reflected in the quantum composition of the end-plate potential (EPP) and the dynamics of EPP amplitudes during high-frequency stimulation. Meanwhile the frequency of the miniature EPP and its amplitude are reduced, the latter evidently as a result of a decrease in the effective resistance of the postsynaptic membrane. Changes in evoked and spontaneous secretion of mediator are connected with a disturbance of axoplasmic transport in somatic nerve fibers.

Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves

(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord ded not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.

Electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion.

An electron-microscopic analysis of the mouse facial nerve near the geniculate ganglion shows that there are, on the everage, 603 more nerve fibers in the portion of the nerve distal to the geniculate ganglion than there are in the part proximal to the ganglion. The average distal increase in the number of unmyelinated fibers is 444 and that in the myelinated fibers is 165. The somatic motor nerve fibers and the parasympathetic fibers in the mouse facial nerve may not contribute to the distal excess. It is possible that the increase in the number of unmyelinated fibers distal to the geniculate ganglion is mainly due to the presence of postganglionic sympathetic fibers in the facial trunk distal to the geniculate ganglion and the greater petrosal nerve. The distal increase in the number of myelinated fibers may be mainly contributed by the sensory fibers.

Ultrastructure and degeneration analysis of the nerve fibres of the tooth pulp in the cat

An attempt was made to distinguish somatic sensory nerve fibres from autonomic postganglionic sympathetic nerves in tooth pulp by secondary degeneration. Pulps were compared after transection of the inferior alveolar nerve, after extirpation of the superior cervical sympathetic ganglion and after both operations performed at the same time (total neural isolation). About 15 per cent of the nerves in normal feline pulps were myelinated and about 85 per cent unmyelinated. Only 1.5 per cent contained granular vesicles 30–50 nm or 80–120 nm in diameter. After transection of the alveolar nerve, all myelinated as well as some unmyelinated fibres degenerated. Degenerated fibres contained no vesicles. After extirpation of the ganglion, only a few degenerating unmyelinated fibres were observed; some contained 80–100 nm diameter granular vesicles. Two months after total neural isolation, the pulp contained no nerve fibres.

Reflexes to sacral parasympathetic neurones concerned with micturition in the cat.

1. Reflexes to sacral parasympathetic neurones were studied by electrophysiological techniques in decerebrate, in chloralose-anaesthetized, and in chronic spinal cats.2. Excitatory reflexes from pelvic nerve and sacral somatic afferent nerve fibres were present before and after chronic transection of the spinal cord, but the latencies differed markedly. It was concluded that the long-latency reflexes observed when the spinal cord was intact involved long-loop reflexes to the brain-stem. The weak, short-latency reflexes in the chronic spinal cat were never observed when the spinal cord was intact and could be due to reorganized spinal connexions. The short-latency reflexes are probably unimportant in normal micturition.3. Stimulation of afferent fibres in the pelvic or sacral somatic nerves produced short-latency inhibitory post-synaptic potentials (IPSPs) and inhibition of discharges in parasympathetic neurones. This inhibition was due to a spinal reflex.4. A local reflex was demonstrated in the pelvic plexus. This was probably a cholinergic axon reflex, but the remote possibility that it was a local cholinergic reflex involving sensory neurones in the bladder wall has not been excluded.