The autonomic innervation of the vasa nervorum

S1 Brain Connectivity in Carpal Tunnel Syndrome Underlies Median Nerve and Functional Improvement Following Electro-Acupuncture

Carpal Tunnel Syndrome (CTS) is a median nerve entrapment neuropathy that alters primary somatosensory cortex (S1) organization. While electro-acupuncture (EA), a form of peripheral neuromodulation, has been shown to improve clinical and neurophysiological CTS outcomes, the role of EA-evoked brain response during therapy (within and beyond S1) for improved outcomes is unknown. We investigated S1-associated whole brain fMRI connectivity during both a resting and sustained EA stimulation state in age-matched healthy controls (N = 28) and CTS patients (N = 64), at baseline and after 8 weeks of acupuncture therapy (local, distal, or sham EA). Compared to healthy controls, CTS patients at baseline showed decreased resting state functional connectivity between S1 and thalamic pulvinar nucleus. Increases in S1/pulvinar connectivity strength following verum EA therapy (combined local and distal) were correlated with improvements in median nerve velocity (r = 0.38, p = 0.035). During sustained local EA, compared to healthy controls, CTS patients demonstrated increased functional connectivity between S1 and anterior hippocampus (aHipp). Following 8 weeks of local EA therapy, S1/aHipp connectivity significantly decreased and greater decrease was associated with improvement in patients' functional status (r = 0.64, p = 0.01) and increased median nerve velocity (r = -0.62, p = 0.013). Thus, connectivity between S1 and other brain areas is also disrupted in CTS patients and may be improved following EA therapy. Furthermore, stimulus-evoked fMRI connectivity adds therapy-specific, mechanistic insight to more common resting state connectivity approaches. Specifically, local EA modulates S1 connectivity to sensory and affective processing regions, linked to patient function and median nerve health.

Effects of Lumbar Acupuncture Stimulation on Blood Flow to the Sciatic Nerve Trunk - An Exploratory Study

Introduction

Acupuncture may have a role in the treatment of intermittent claudication of the cauda equina due to lumbar spinal canal stenosis. The aim of this study was to explore the possible physiological mechanisms.

Methods

In a laboratory experiment, manual acupuncture was performed at a point adjacent to the sixth lumbar vertebra of 13 animals and its effect on sciatic nerve blood flow was measured using a laser Doppler flowmetry. Simultaneously, changes in blood pressure and cardiac rate were observed. Each animal was stimulated four to eight times, making a total of 58 experiments.

Results

Acupuncture stimulation did not produce consistent changes in sciatic nerve blood flow, with increased and decreased blood flow as well as no change in blood flow observed. Among the 58 individual experiments, sciatic nerve blood flow was increased in 33, reduced in 12, and unchanged in 13. Approximately half of the stimulations showed a correlation between blood flow and blood pressure change.

Conclusion

Our results indicate that lumbar acupuncture stimulation can have an influence on sciatic nerve blood flow. The effect is dependent not only on blood pressure but also other factors, for example vasodilator and vasoconstrictor nerve activity. This mechanism may contribute to a clinical effect on intermittent claudication of the cauda equina.

The contribution of muscarinic-receptor-mediated responses to epineurial vascular diameter at the sciatic nerve

This study used an anaesthetized rat model to directly observe changes in diameter of the vessels supplying the sciatic nerve in response to acetylcholine (10^-4 M), a muscarinic receptor agonist, and atropine (10^-5 M), a muscarinic receptor antagonist. Topical application of acetylcholine resulted in increases in vessel diameter (baseline: 22.0 ± 2.5 μm, acetylcholine: 28.8 ± 3.3 μm), while topical application of atropine resulted in a decrease in diameter (baseline: 26.6 ± 3.2 μm, atropine: 15.5 ± 3.6 μm) of the epineurial vessels. Mean arterial pressure was not affected by either acetylcholine (baseline: 103.8 ± 1.8 mm Hg, acetylcholine: 102.8 ± 3.2 mm Hg) or atropine (baseline: 104.0 ± 1.9 mm Hg, atropine: 105.2 ± 2.2 mm Hg). These data suggest that muscarinic-receptor-mediated responses can affect the diameter of the epineurial vessels at the sciatic nerve. In addition, muscarinic-receptor-mediated responses appear to contribute to baseline diameter of epineurial vessels at the sciatic nerve.

Myelinated and unmyelinated endoneurial axon quantitation and clinical correlation

INTRODUCTION

Different disease patterns result from loss of myelinated and unmyelinated axons, but quantitation to define their loss has been difficult.

METHODS

We measured large and small endoneurial axons in axonal neuropathies by staining them with peripherin and comparing their area to that of nonmyelinating Schwann cells stained with neural cell adhesion molecule (NCAM).

RESULTS

Loss of myelinated and unmyelinated axons was typically proportional, with predominant myelinated or unmyelinated axon loss in a few patients. Myelinated axon loss was associated with loss of distal vibration sense and sensory potentials (P < 0.0001) and was selective in patients with bariatric and bowel resection surgery (P < 0.001). Unmyelinated axon measurements correlated with skin (ankle P = 0.01; thigh P = 0.02) and vascular (nerve P < 0.0001; muscle P = 0.01) innervation.

CONCLUSIONS

Myelinated and unmyelinated axons can be quantitated by comparing areas of axons and nonmyelinating Schwann cells. Clinical features correlate with myelinated axon loss, and unmyelinated axon loss correlates with skin and vascular denervation.

Transient intrapulmonary shunting in a patient treated with β₂-adrenergic agonists for status asthmaticus

Intrapulmonary arteriovenous anastomoses (IPAVs) are large-diameter pathways that directly connect the arterial and venous networks, bypassing the pulmonary capillaries. Ubiquitously present in healthy humans, these pathways are recruited in experimental conditions by exercise, hypoxia, and catecholamines and have been previously shown to be closed by hyperoxia. Whether they play a role in pulmonary pathophysiology is unknown. Here, we describe IPAV recruitment associated with hypoxemia and right-to-left shunt in a patient with status asthmaticus, treated with agonists of the B2-adrenergic pathway. Our observation of IPAVs in a pediatric patient, mechanically ventilated with 100% O₂, suggests that these pathways are recruited in clinically important circumstances and challenges the notion that IPAVs are always closed by alveolar hyperoxia.

Neurovascular proximity in the diaphragm muscle of adult mice

OBJECTIVE

Regional blood flow to the diaphragm muscle varies with the workload of inspiration. To provide anatomical insight into coupling between muscle fiber recruitment and oxygen supply, we tested whether arterioles are physically associated with motor nerve branches of the diaphragm.

METHODS

Following vascular casting, intact diaphragm muscles of C57BL/6 and CD-1 mice were stained for motor innervation. Arteriolar networks and nerve networks were mapped (~2 μm resolution) to evaluate their physical proximity.

RESULTS

Neurovascular proximity was similar between muscle regions and mouse strains. Of total mapped nerve lengths (C57BL/6, 70 ± 15 mm; CD-1, 87 ± 13 mm), 80 ± 14% and 67 ± 10% were ≤250 μm from the nearest arteriole and associated predominantly with arterioles ≤45 μm in diameter. Distances to the nearest arteriole encompassing 50% of total nerve length (D(50)) were consistently within 200 μm. With nerve networks repositioned randomly within muscle borders, D(50) values nearly doubled (p < 0.05). Reference lines within anatomical boundaries reduced proximity to arterioles (p < 0.05) as they deviated from the original location of motor nerves.

CONCLUSION

Across two strains of mice, motor nerves and arterioles of the diaphragm muscle are more closely associated than can be explained by chance. We hypothesize that neurovascular proximity facilitates local perfusion upon muscle fiber recruitment.

Sciatic nerve of diabetic rat treated with epoetin delta: effects on C-fibers and blood vessels including pericytes

In diabetes mellitus (DM) reduced motor and sensory properties of peripheral nerves are linked with the dysfunction of neural vasculature. We investigated C-fibers and microvessels of sciatic nerve of normal, DM, and DM + epoetin delta-treated rats. C-fibers immunoreactive for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH), epoetin receptor (EpoR), and common beta receptor subunit of the interleukin 3 receptor (IL-3Rbeta) were present in all rats, whereas in DM and epoetin-treated rats C-fibers also showed neuronal (nNOS) and inducible (iNOS) nitric oxide synthases. The cross-sectional area of CGRP-positive C-fibers was decreased in DM, but it recovered after epoetin treatment. In all conditions, vascular endothelium showed scarce immunolabeling for endothelial nitric oxide synthase (eNOS); the profound immunoreactivity for eNOS, EpoR, and IL-3Rbeta was in pericytes. Some perivascular autonomic nerves were damaged and IL-3Rbeta positive. Findings are discussed in terms of declined sensory conduction velocity in DM, its improvement after epoetin treatment, and the possible vascular contribution to these phenomena.

Developmental changes of mast cell populations in the cerebral meninges of the rat

It is known that both the dura and the pia mater attract and support the differentiation of mast cells. The present study shows that unevenly distributed mast cells in the cerebral meninges of the rat can be found in perivascular sites and vessel ramification points, but can also be unrelated to the meningeal vasculature. It also documents changes in the number, localization and staining preferences of the mast cells in the two meninges of the developing and mature rat brain. Quantitative examination of all types of histochemically differentiated meningeal mast cells reveals no major (although some exist) differences between right and left side subpopulations, but strongly suggests a different origin and fate of the dural and the pial mast cells. The number of dural mast cells, already high from postnatal day 0, although declining from postnatal day 21 onwards, remains conspicuous up to postnatal day 180. In contrast, pial mast cells are comparatively very few in the first day of the postnatal life, and despite a transient significant increase in the following two weeks, they reach almost zero levels from postnatal day 21.

Blood flow in the sciatic nerve is regulated by vasoconstrictive and vasodilative nerve fibers originating from the ventral and dorsal roots of the spinal nerves

Anesthetized rats were subjected to repetitive electrical stimulation of either the ventral or dorsal root of the spinal nerves between the 11th thoracic and 2nd sacral spinal segments. The response of nerve blood flow (NBF) in the sciatic nerve was examined using laser Doppler flowmetry. For all nerve fibers stimulation was for a 10-30-s period at a supramaximal intensity. (1) Stimulation of the T11-L1 ventral roots produced an increase in mean arterial pressure (MAP) and a biphasic NBF response was comprised of an initial increase and a subsequent decrease. The initial increase was a passive vasodilation due to the increase in MAP, while the following decrease in NBF resulted from active vasoconstriction of the vasa nervorum due to the activation of sympathetic nerves innervating the sciatic vasa nervorum. (2) Stimulation of the ventral root of the L6 segment produced an increase in NBF, even though MAP decreased. This increase in NBF was apparently mediated by activation of parasympathetic cholinergic vasodilators, because the response was abolished by i.v. injection of atropine, a muscarinic cholinergic receptor antagonist. (3) Stimulation of the dorsal roots between the L3 and S1 segments produced an increase in NBF, independent of changes in MAP. This increase in NBF appeared to be mediated by activation of a calcitonin gene-related peptide (CGRP) containing afferent fibers innervating the vasa nervorum, because the response was abolished by topical application of hCGRP (8-37), a CGRP receptor antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effect of the Ca2+ antagonist, nimodipine, on existing diabetic neuropathy in the BB/Wor rat

1. Neuropathy is a frequently diagnosed complication of diabetes mellitus. Effective pharmacotherapy is not available. 2. The spontaneously diabetic BB/Wor rats develop secondary complications like neuropathy as do human diabetic patients. 3. BB/Wor rats treated with insulin via a subcutaneous implant show a significant impairment of sensory and motor nerve conduction velocity 6 weeks after the onset of diabetes mellitus. 4. Intraperitoneal treatment of diabetic BB/Wor rats with the Ca2+ antagonist, nimodipine (20 mg kg-1), from week 6 onwards every 48 h for a period of 6 weeks resulted in a significant increase of sensory and motor nerve conduction velocity. 5. Twelve weeks after the onset of diabetes mellitus BB/Wor rats show a 40% impairment of sciatic nerve blood flow as compared to the non-diabetic age-matched controls. Treatment with nimodipine (20 mg kg-1) from week 6 onwards significantly increased the sciatic nerve blood flow as compared to placebo-treated diabetic BB/Wor rats. 6. The adrenergic responsiveness of the vasa nervorum of the sciatic nerve to tyramine and phenylephrine was investigated as a parameter for autonomic neuropathy. 7. The fact that nimodipine treatment restored the reduced response to tyramine independently of the reduced postsynaptic phenylephrine responsiveness indicates that nimodipine improves adrenergic responsiveness mainly at the presynaptic level.

Innervation of normal human sural and optic nerves by noradrenaline- and peptide-containing nervi vasorum and nervorum: effect of diabetes and alcoholism

Histochemical, immunohistochemical and neurochemical techniques were used to examine the innervation of epineurial nerve sheaths and fascicular nerve bundles of human sural and optic nerves from controls and patients with peripheral neuropathy due to diabetes or alcoholism. The normal distribution of autonomic nerves in both nerve trunk sheaths consisted of a dense innervation by noradrenaline (NA)-containing nerves of the vasa nervorum, together with some fibres in the nervi nervorum. Intrafascicular NA-containing nerves were only present in the sural nerve. Vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing nerves also innervated the vasa nervorum and nervi nervorum of the nerve sheaths, although their density was considerably less. Substance P (SP)-containing nerves were sparse and primarily intrafascicular. Neurochemical assays for NA, VIP, NPY and SP in fascicular and epineurial preparations from the sural and optic nerves confirmed the light microscopical observations. Post mortem delay significantly affected the NA levels in the sural nerve but not in the optic nerve while the NA fascicular/epineurial ratio for the sural nerve was independent of this factor. Age, sex and the presence of alcohol at time of death had no effect on transmitter levels in normal sural nerves. In the optic nerve fascicles NA levels were higher in females than in males. In patients with peripheral neuropathy there was a significant reduction in the SP fascicular/epineurial ratio in both the optic nerve, which was histologically normal, and in the sural nerve, where there was evidence of neuropathy. The NA fascicular/epineurial ratio was also significantly reduced in the sural nerve from patients with peripheral neuropathy with a possible greater effect in diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential vulnerability of neuropeptides in nerves of the vasa nervorum to streptozotocin-induced diabetes

Neuropeptides in perivascular nerves of vasa nervorum supplying blood to rat optic, sciatic, vagus and sympathetic chain nerve trunks are differentially vulnerable to streptozotocin (STZ)-induced diabetes. Immunohistochemical analysis of epineurial/perineurial nerve sheaths showed that 8 weeks after induction of diabetes, the density of neuropeptide Y (NPY)-immunoreactive nerve fibres in optic nerve sheaths was increased, while it was decreased in sciatic, vagus and sympathetic nerve sheaths. Vasoactive intestinal polypeptide (VIP)-immunoreactivity was increased in vasa and nervi nervorum of optic, sciatic, vagus and sympathetic chain nerve sheaths. Immunoassay of NPY confirmed increased levels in optic nerve sheaths and showed that substance P and calcitonin gene-related peptide levels increased in sciatic but not optic nerve sheaths. Neuropeptide levels in the intrafascicular nerve fibres were unaffected. This provides further evidence for a disturbance in the autonomic control of blood flow to peripheral and cranial nerve trunks via vasa nervorum in STZ-induced diabetes, which may lead to ischaemic changes, alter local axon reflexes and contribute to the pathogenesis of the disease.

Stimulation of lumbar sympathetic trunk produces vasoconstriction of the vasa nervorum in the sciatic nerve via alpha-adrenergic receptors in rats

The effects of repetitive electrical stimulation of a lumbar sympathetic trunk (LST) for 30 s at various frequencies and supramaximum intensity on the nerve blood flow in a sciatic nerve were studied by laser Doppler flowmetry in anesthetized Fischer-344 male rats. The response was biphasic; i.e. an initial increase and then a decrease. The maximum mean increase after 2 Hz stimulation was 22 +/- 8%, while the maximum mean decrease after 20-50 Hz stimulation was 79 +/- 3%, of the prestimulus control level. The initial increase, which was greater at lower frequencies and existed even after local sympathetic denervation, was passive, and was caused by the systemic pressor response to LST stimulation. The decrease, which was nearly abolished by an i.v. alpha-adrenergic blocker, phentolamine (10 mg/kg), resulted from vasoconstriction in the vasa nervorum, mainly via activation of alpha-adrenergic receptors.

Decreased density of beta-adrenergic and muscarinic cholinergic receptor sites in the vasa nervorum of aged rats

The pharmacological profile and the anatomical localization of beta-adrenergic and muscarinic cholinergic receptors of the vasa nervorum were studied in sections of sciatic nerve using radioreceptor binding and light microscope autoradiography techniques. Sprague-Dawley rats of 4 and 24 months of age were used. [3H]Dihydroalprenolol (DHA) and [3H]quinuclidinyl benzilate (QNB) were used to label beta-adrenergic and muscarinic cholinergic receptors, respectively. The ligands were bound to sections of rat sciatic nerve in a manner consistent with the labelling of beta-adrenergic or muscarinic cholinergic receptors in the 2 age groups investigated. The dissociation constant (Kd) values (about 1.37 nM for [3H]DHA and 0.75 nM for [3H]QNB) did not significantly change between 4- and 24-month-old rats. The maximum concentration of binding sites (Bmax) for [3H]DHA was decreased by about 35% in 24 in comparison with 4-month-old rats. The Bmax value for [3H]QNB was reduced by about 50% in the aged rats. Light microscope autoradiography revealed the development of specific silver grains in the medial layer of epineurial and perineurial arteries in sections of sciatic nerve exposed either to [3H]DHA or [3H]QNB. The number of silver grains developed in epineurial and perineurial arteries of rats of 24 months is significantly lower than in animals of 4 months. The above results suggest the occurrence of an age-dependent loss in the density of beta-adrenergic and muscarinic cholinergic receptors of vasa nervorum. Vasa nervorum are the blood vessels which supply peripheral nerve trunks. They are constituted by outer (epineurial) and inner (perineurial) arteries and veins as well as by a capillary (endoneurial) plexus. Vasa nervorum are innervated by both sympathetic and non-sympathetic nerves which probably play a role in the pathogenesis of some neuropathies. Several different neurotransmitter containing nerve fibres have been identified in the vasa nervorum perivascular plexuses. However, no information is so far available concerning the neurotransmitter receptors of vasa nervorum. Moreover, although the occurrence of age-dependent changes in peripheral nerve morphology and function is well documented, very few reports were centered on the age-dependent changes of the vasa nervorum. The aims of the present study were to characterize pharmacologically and to localize anatomically the beta-adrenergic and muscarinic cholinergic receptors in the rat vasa nervorum. Moreover, the effect of ageing on the density and pattern of these receptors was investigated.

Adrenergic innervation of blood vessels in rat tibial nerve during Wallerian degeneration

Adrenergic innervation of blood vessels in rat tibial nerve during Wallerian degeneration was examined, using the formaldehyde-induced histo-fluorescence method. The left sciatic nerve was transected at the level of the sciatic notch, whereas the right sciatic nerve was left intact and used as control. At 1, 3, 7, 14, 42, 56 or 84 days after transection, the tibial nerves of the transected and contralateral sides were exposed. Pieces of each nerve were used for light microscopy or for examination of adrenergic innervation with the fluorescence microscope. One day after transection, no adrenergic nerve fiber was observed in the endoneurium of the transected nerve. After 3 days, adrenergic innervation of small- and medium-sized arterioles in the epi-perineurium was absent, and after 7 days no fibers were visible around large arterioles. Fluorescent fibers were not detected even at 84 days post-surgery. It is concluded that adrenergic innervation of blood vessels in the rat tibial nerve is irreversibly lost after permanent axotomy, and that adrenergic regulation of nerve blood flow may also be lost.

Adrenergic innervation of the vasa nervorum in the cranial nerves and spinal roots in the subarachnoid space

Fluorescence microscopy revealed that the innervation of the vasa nervorum of both cranial and spinal nerve roots in the subarachnoid space in the monkey is adrenergic in nature. The endoneurium of the cranial nerve roots contained free adrenergic nerve fibers which were not related to the vessel wall.

The noradrenergic innervation of the vasa nervorum in old rats: a fluorescence histochemical study

The effect of ageing on the density and pattern of noradrenergic nerves in the perivascular nerve plexus supplying the vasa nervorum of the rat sciatic nerve was studied using combined catecholamine histofluorescence and quantitative image analysis techniques. The density of noradrenergic fibres around arteries and arterioles of the rat sciatic nerve vasa nervorum increased in the old animals. In contrast, no changes in perivascular nerve fibres supplying the veins and venules were found in the vasa nervorum of old rats. The increase in old age of noradrenergic innervation of arteries and arterioles of the vasa nervorum may be related to the pathogenesis of some peripheral nerve diseases.

Adrenergic innervation of vasa and nervi nervorum of optic, sciatic, vagus and sympathetic nerve trunks in normal and streptozotocin-diabetic rats

Adrenergic nerves were studied in nervi nervorum and perivascular nerve plexus of vasa nervorum in whole-mount nerve sheath preparations of optic, sciatic and vagus nerves and in the paravertebral sympathetic chain in normal and streptozotocin-treated diabetic rats. A substantial or complete loss of fluorescent adrenergic fibres around blood vessels in the optic nerves was observed 8 weeks after induction of diabetes. This was in marked contrast to the increase in perivascular adrenergic fibres in the sciatic, vagus and sympathetic chain nerve trunks of the same animals at the same time. Assays of noradrenaline levels in whole nerve segments also showed that they were not biochemically detectable in the optic nerves but were significantly higher in the vagus of diabetic animals (P less than 0.05). There was also an increase in numbers of mast cells in the vicinity of vasa nervorum of diabetic nerves.

The adrenergic innervation of rat uterine tubes in old age: a fluorescence histochemical study

The effect of ageing on the density and pattern of adrenergic innervation of rat uterine tubes was studied using combined glyoxylic acid induced fluorescence and quantitative image analysis techniques. With age a reduction in the number of nerve fibers of the circular muscle layer of the isthmic portion was observed. No significant differences in the density of innervation were found at the level of blood vessels associated with uterine tubes.

Image analysis of FITC-immunofluorescence histochemistry in perivascular substance P-positive nerves

The ability of image analysis to quantify nerves labelled by FITC-immunofluorescence histochemistry has been tested on whole-mount stretch preparations of perivascular substance P-positive nerves. It has been shown that image analysis can make consistent measurements of nerves demonstrated by immunohistochemistry despite the fading of FITC-fluorescence which occurs during storage and on exposure to ultraviolet light.