Mechanical effects of compression of peripheral nerves

Effects of graded compression on nerve function were analyzed in order to evaluate the relative importance of pressure level and duration of compression for functional deterioration. The pressure was applied by means of a small inflatable cuff. The effects of two pressure levels, i.e., 80 mm Hg applied for 2 hr or 400 mm Hg applied for 15 min, were studied in rabbit tibial nerves. The lower pressure tested, which is known to induce ischemia of the compressed nerve segment, also causes some degree of mechanical deformation of the nerve trunk, which leads to incomplete recovery following pressure release. The duration of compression is of importance for the degree of nerve injury even at the higher pressure level tested.     

Serotonin uptake inhibitors and the prejunctional effects of serotonin on peripheral sympathetic nerves

The experiments were designed to study whether the inhibitors of the uptake of serotonin (5-HT) potentiated the prejunctional effects of 5-HT on peripheral sympathetic nerves. The effect of two selective 5-HT uptake inhibitors, citalopram and fluoxetine, were studied on the presynaptic actions of 5-HT in the cat isolated nictitating membrane and in the guinea-pig isolated atria. Frequency-effect curves to nerve stimulation and concentration-response curves to noradrenaline (NA) were performed in both preparations. The facilitation that 0.1 microM 5-HT causes on the contractile responses to nerve stimulation of the nictitating membrane of the cat was not potentiated but entirely prevented by both 0.01 microM citalopram and 1.0 microM fluoxetine. On the other hand the diminution that 1.0 microM 5-HT evokes on the chronotropic responses to nerve stimulation of guinea-pig isolated atria was not modified at all by 0.1 and 1.0 microM fluoxetine and only partially prevented by 10.0 microM fluoxetine and by 0.001 microM, 0.01 microM and 0.1 microM citalopram. This latter effect of citalopram was unrelated to the concentration employed. The 5-HT uptake inhibitors did not modify per se either the responses to nerve stimulation or the sensitivity to exogenous NA in both tissues studied. In addition, the 5-HT uptake inhibitors did not interfere with the contractile responses caused by 5-HT in the cat isolated nictitating membrane. Taken together, these observations might indicate a pharmacological rather than a physiological role for the effects of 5-HT in guinea-pig isolated atria and cat nictitating membranes. It is concluded that the 5-HT uptake inhibitors do not potentiate but even antagonize the presynaptic effects of 5-HT. Our results also show that 5-HT uptake inhibitors are more effective to interfere with the facilitation rather than with the inhibition that 5-HT causes on sympathetic responses.     

Fluorescent histochemical studies on the effects of 6-hydroxydopamine on adrenaline-containing nerves in the toad

Summary Fluorescence histochemistry has been used to study the effects of 6-hydroxydopamine (6-OHDA) (100 mg/kg injected into the dorsal lymph sac) on adrenaline-containing nerves in the large intestine, mesentery, lung, bladder and heart atria of the toad Bufo marinus. A gradual decrease both in fluorescence intensity and in number of detectable fibres during the first 4 hours after 6-OHDA was accompanied by a build-up of fluorescence in the nonterminal regions. These phenomena have been discussed in relation to the time course of the degeneration produced by 6-OHDA in noradrenergic nerves of higher vertebrates. Almost complete chemical sympathectomy was seen after one day, and it was not till 13 days that regenerating nerve fibres were seen in any organ. In the large intestine, however, re-innervation was slower, being first noted after 39 days. The time course of regeneration has been compared with that following sympathectomy in various mammalian organs.     

Effect of neuropeptides released from sensory nerves on blood flow in the rat airway microcirculation.

Stimulation of sensory nerves in the airway mucosa causes local release of the neuropeptides substance P and calcitonin gene-related peptide (CGRP). In this study we used a modification of the reference-sample microsphere technique to measure changes in regional blood flow and cardiac output distribution produced in the rat by substance P, CGRP, and capsaicin (a drug that releases endogenous neuropeptides from sensory nerves). Three sets of microspheres labeled with different radionuclides were injected into the left ventricle of anesthetized F344 rats before, immediately after, and 5 min after left ventricular injections of capsaicin, substance P, or CGRP. The reference blood sample was withdrawn from the abdominal aorta and was simultaneously replaced with 0.9% NaCl at 37 degrees C. We found that stimulation of sensory nerves with a low dose of capsaicin causes a large and selective increase in microvascular blood flow in the extrapulmonary airways. The effect of capsaicin is mimicked by systemic injection of substance P but not by CGRP, suggesting that substance P is the main agent of neurogenic vasodilation in rat airways.     

Comparative studies of purinergic nerves.

Purinergic nerves supply the gastrointestinal tract of vertebrates, including fish, amphibians, reptiles and birds, as well as mammals. Their cell bodies are located in Auerbach's plexus and their axons extend in an anal direction before innervating mainly the circular muscle coat. In the stomach they are controlled by preganglionic cholinergic fibres of parasympathetic origin. They are involved in "receptive relaxation" of the stomach, "descending inhibition" in peristalsis and reflex relaxation of oesophageal and internal anal sphincters. The terminal varicosities of purinergic nerves are characterised by a predominance of "large opaque vesicles," which can be distinguished from the "large granular vesicles" found in small numbers in both adrenergic and cholinergic nerves. Stimulation of purinergic nerves with single pulses produces hyperpolarisations of up to 25 mV (inhibitory junction potentials) in smooth muscle cells. These potentials are unaffected by atropine, adrenergic neuron blocking agents or sympathetic denervation, but are abolished by tetrodotoxin. The "rebound contraction" which characteristically follows cessation of purinergic nerve stimulation is probably due to prostaglandin. Evidence that ATP is the transmitter released from purinergic nerves includes: (1) synthesis and storage of ATP in nerves; (2) release of ATP from the nerves when they are stimulated; (3) exogenously applied ATP mimicking the action of nerve-released transmitter, both producing a specific increase in K+ conductance; (4) the presence of Mg-activated ATPase, 5'-nucleotidase and adenosine deaminase, enzymes which inactivate ATP; (5) drugs (including quinidine, some 2-substituted imidazolines, 2-2'pyridylisatogen and dipyridamole) which produce similar blocking or potentiating effects on the response to exogenously applied ATP and nerve stimulation. Speculations are made about the evolution and development of the nervous system, including the possibility that purinergic nerves are a primitive nerve type.     

Morphometric studies of peripheral nerves and spinal ganglion cells in streptozotocin diabetic rats

Morphometric studies of sural nerves and dorsal root ganglia cells L5 were performed in 8 diabetic rats 35 or 44d after the administration of streptozotocin and in 8 controls. Morphometry of photographed semithin sections was realized after whole body glutaraldehyde perfusion with semiautomatic MOP AM 02 and MOP Videoplan. The peripheral nerve showed no decrease of the total nerve area, number of nerve fibres or of myelinated area. Parameters area of fibres decreased in diabetic animals caused by reduction of myelin sheath thickness. There were no changes of mean neuron volume and maximal cell diameter in the dorsal root ganglia. Whereas in experimental short-term diabetes the peripheral nerves demonstrate morphologic changes correlating to biochemical abnormalities, no such correlations can be observed in the perikarya. It is suggested, that primary SCHWANN cell lesion is responsible for the observed myelin thickness reduction.     

The effects of ultrasonic energy on peripheral nerves: implications for ultrasound-assisted liposuction

The integration of ultrasound-assisted liposuction with traditional suction-assisted lipoplasty has extended the role of liposuction in body contouring. Although there are ample data regarding the effects of ultrasound on peripheral nerves from studies with the Cavitron ultrasound surgical aspirator, there is little information concerning the effects of modern ultrasound body contouring equipment on neural tissue. This study was designed to evaluate the functional and histologic effects of ultrasound energy on rat peripheral nerves (sciatic nerves) using a commonly-used ultrasound-assisted liposuction generator. After the application of ultrasound to exposed rat sciatic nerves, operative magnification was used to assess any visible injury. The sciatic function index was serially measured to quantify immediate and long-term functional effects on the nerves. Our results showed immediate visible injury using low amplitude settings (level 6), but no functional evidence of injury until much higher settings were used (level 9). All animals in the groups with initial functional impairment had returned to normal or near-normal function at completion of the study (51 days). Histologic examination revealed no evidence of damage in the low amplitude groups. Histologic analysis of the high amplitude groups displayed diffuse infiltration of the nerve, with foamy histiocytes and an increased number of mast cells, consistent with remote neural injury followed by myelin breakdown and repair.     

Examination of peripheral nerves with the scanning electron microscope.

The theoretical applications and advantages of the scanning microscope in peripheral nerve research are presented. The internal anatomy of the peripheral nerve can be distinctly examined, and long segments of axons can be examined without the necessity of tedious study of multiple sections. The SEM should make it possible to more readily study the migration of axon sprouts across a repair site. New concepts in teaching and research may develop from the use of this excellent tool.     

Cerebral and peripheral blood flow effects of TRH in the rat--a role of vagal nerves

The cardiovascular effects of the IV infusion of TRH were studied in the rat. TRH tended to increase the MAP and markedly increased the CBF(tot) in the control group, in vagotomized animals and in methylatropine-pretreated rats. A marked vasodilation was noted in the pancreas, gastric mucosa, duodenum and cardiac muscle. This effect was turned to vasoconstriction, the heart excluded, in vagotomized animals. Muscarinic blockade attenuated the vasodilating effect of TRH in the duodenum and gastric mucosa. The results indicate that TRH elicits cerebral vasodilation and a partly nonmuscarinic parasympathetically mediated vasodilation in several gastrointestinal organs in parallel with a vasoconstriction which is unmasked by vagotomy.     

Regeneration of peripheral nerves to supernumerary legs in cockroaches.

1. Clusters of legs were grown from metathoracic coxae of the cockroach. Legs of a cluster had different segmental origins, sizes, and orientations. 2. Regenerating metathoracic nerves tended to enter the nearest leg, and to a lesser extent of the largest leg, but showed no significant tendency to penetrate metathoracic rather than prothoracic legs, or normally oriented rather than abnormally oriented legs. 3. Movements of legs were evoked by nerve stimulation significantly more often in nearest, largest, and normally oriented legs, but were equally frequent in prothoracic and metathoracic legs. 4. Close proximity of peripheral nerves is not required for the differentiation of the legs, since nerves were visible in the legs only at the later stages of their development, and many of the legs were apparently nerve innervated.     

Micropinocytotic invaginations in the axolemma of peripheral nerves

Summary Coated invaginations of the axolemma in myelinated axons of the sciatic nerve of young mice are described. Such invaginations occur preferentially in the area of the inner Schwann cell lip. It is suggested that they may be involved in the transport of metabolites between Schwann cell and axon.Supported by Grants NB-07512-01, NB-02665 (NIH), and GY-108, GB-3128 (NSF). The author wishes to thank Prof. J. D. Robertson for his support of early parts of this work, which was carried out in part at the Dept. of Anatomy, University College London.     

Early effects of tobacco smoke exposure on vascular dynamics in the microcirculation.

The purpose of these studies is to examine the early effects of chronic tobacco smoke exposure on vascular dynamics in the mesenteric microcirculation. Female rats were exposed daily to tobacco smoke from five reference cigarettes for a period of 2 mo. At the end of this period the smoke-treated rats had gained 12 g less than sham-treated controls, and arterial blood pressure in the smoke-treated animals was slightly less than pressure in the sham-treated animals. These are characteristic effects of tobacco smoke exposure on rats. Following the treatment period, red blood cell (RBC) velocity in single mesenteric capillaries and microvascular pressures in arterioles and venules were measured in accordance to established methods. There was no significant difference in pressure distribution on the arterial side of the mesenteric vascular network, but pressure in the venules of the smoke-treated animals was significantly higher than that of the sham-treated group. In association with the higher venular pressure in the smoke-treated animals, capillary RBC velocity (an index of capillary flow) was significantly lower. The reduction in velocity was in proportion to the decrease in pressure drop (arteriole-venule) across the capillary network.