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B A Todd - One of the best experts on this subject based on the ideXlab platform.
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Ionic permeability of the frog sciatic nerve Perineurium: Parallel studies of potassium and lanthanum penetration using electrophysiological and electron microscopic techniques
Journal of Neurocytology, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:The isolated sciatic nerve of the frog Rana temporaria was used for a parallel electrophysiological and electron microscopic examination of the ionic permeability of the Perineurium, one component of the blood-nerve barrier. Nerves mounted in a grease-gap chamber for electrophysiological recording showed negligible changes in DC potential (ΔDC) or compound action potential on challenge with 100 mM K^+ Ringer, evidence that the Perineurium was tight to K^+. In preparations then fixed and exposed to 5 mM lanthanum in the fixative, and examined in the electron microscope, electron-dense lanthanum deposits were seen between perineurial lamellae, but lanthanum was not detectable within the endoneurium, confirming that the Perineurium was also tight to lanthanum. Absence of lanthanum penetration was confirmed by X-ray analysis of electron microscopic sections. In nerves exposed to 2 mM sodium deoxycholate (DOC) in the recording chamber, then challenged with high [K^+], a moderate increase in perineurial K^+ permeability ( P _ K ) was observed, but lanthanum was still excluded. Exposure of nerves to 4 mM DOC caused a greater increase in perineurial potassium permeability, and the two nerves with the greatest permeability ( P _ K > 1 × 10^−5 cm.sec^−1) also showed detectable lanthanum within the endoneurium. The results indicate that DOC causes a dose-dependent increase in tight junctional permeability in the Perineurium, and that the electrophysiological monitoring of K^+ penetration is a more sensitive measure of small ion permeability than electron microscopical analysis using lanthanum as tracer. Vesicular profiles observed in perineurial lamellae did not form open channels for ion flux across the Perineurium in control nerves, or in those exposed to DOC. In preparations where lanthanum reached the endoneurium, lanthanum was observed in dense deposits in the extracellular spaces around nodes of Ranvier, and in the outer mesaxon cleft, but did not penetrate the internodal periaxonal space, the myelin intraperiod line, or the Schmidt-Lanterman incisures, in contrast to observations in mammalian nerves. The apparent differences in accessibility of the internodal periaxonal space in frog and mammalian axons are discussed in relation to axonal physiology. The study illustrates the value of parallel electrophysiological and electron microscopic examination in elucidating the properties of extracellular ionic pathways and their role in neural function.
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ionic permeability of the opossum sciatic nerve Perineurium examined using electrophysiological and electron microscopic techniques
Brain Research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:Abstract A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica . The electrophysiological method was used to monitor permeability to K + , followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a ‘grease gap’ chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since a change in DC potential (ΔDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K + challenge ( n =71 nerves) indicating negligible K + permeability under control conditions. The inflammatory mediators histamine 0.1–40 mg/ml (1.3–130 mM), bradykinin (0.1–4.7 mM) and 5HT (serotonin) 0.1–5.0 mg/ml (0.5–23.5 mM) caused no measurable ΔDC on subsequent challenge with 100 mM [K + ] Ringer, indicating no effect on perineurial K + permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K + Ringer caused a dose-dependent ΔDC in the range 10–100 mM [K + ] (1.67±0.17 mV in 100 mM [K + ], n =20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined ( n =51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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Ionic permeability of the opossum sciatic nerve Perineurium, examined using electrophysiological and electron microscopic techniques.
Brain research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica. The electrophysiological method was used to monitor permeability to K(+), followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a 'grease gap' chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K(+)] Ringer was used to assess the K(+) permeability of the Perineurium, since a change in DC potential (DeltaDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K(+) challenge (n=71 nerves) indicating negligible K(+) permeability under control conditions. The inflammatory mediators histamine 0.1-40 mg/ml (1. 3-130 mM), bradykinin (0.1-4.7 mM) and 5HT (serotonin) 0.1-5.0 mg/ml (0.5-23.5 mM) caused no measurable DeltaDC on subsequent challenge with 100 mM [K(+)] Ringer, indicating no effect on perineurial K(+) permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K(+) Ringer caused a dose-dependent DeltaDC in the range 10-100 mM [K(+)] (1.67+/-0.17 mV in 100 mM [K(+)], n=20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined (n=51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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effects of the bile salt sodium deoxycholate protamine and inflammatory mediators on the potassium permeability of the frog nerve Perineurium
Brain Research, 1997Co-Authors: B A Todd, E M Sedgwick, Joan N AbbottAbstract:Abstract An electrophysiological method was used to measure the potassium permeability ( P K ) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens . Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (ΔDC) in response to challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating ΔDC to bathing [K + ] in desheathed nerves of Abbott et al. (1997). In the control condition, P K was −6 cm·s −1 . The bile salt sodium deoxycholate (DOC, 1–4 mM) caused a dose-dependent increase in P K , which reached a maximum of 1.7×10 −5 cm·s −1 after 2-min exposure to 4 mM DOC, but access of K + to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1–5 mg/ml equals 0.125–6.25 mM) had no effect on P K . Neither histamine (0.4–40 mg/ml), bradykinin (0.1–5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1–5 mg/ml) affected P K . The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood–nerve barrier and the blood–brain barrier.
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Effects of the bile salt sodium deoxycholate, protamine, and inflammatory mediators on the potassium permeability of the frog nerve Perineurium.
Brain research, 1997Co-Authors: B A Todd, E M Sedgwick, N J AbbottAbstract:An electrophysiological method was used to measure the potassium permeability (PK) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens. Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (delta DC) in response to challenge with 100 mM [K+] Ringer was used to assess the K+ permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating delta DC to bathing [K+] in desheathed nerves of Abbott et al. (1997). In the control condition, PK was < 1.1 x 10(-6) cm.s-1. The bile salt sodium deoxycholate (DOC, 1-4 mM) caused a dose-dependent increase in PK, which reached a maximum of 1.7 x 10(-5) cm.s-1 after 2-min exposure to 4 mM DOC, but access of K+ to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1-5 mg/ml equals 0.125-6.25 mM) had no effect on PK. Neither histamine (0.4-40 mg/ml), bradykinin (0.1-5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1-5 mg/ml) affected PK. The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood-nerve barrier and the blood-brain barrier.
N J Abbott - One of the best experts on this subject based on the ideXlab platform.
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Ionic permeability of the frog sciatic nerve Perineurium: Parallel studies of potassium and lanthanum penetration using electrophysiological and electron microscopic techniques
Journal of Neurocytology, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:The isolated sciatic nerve of the frog Rana temporaria was used for a parallel electrophysiological and electron microscopic examination of the ionic permeability of the Perineurium, one component of the blood-nerve barrier. Nerves mounted in a grease-gap chamber for electrophysiological recording showed negligible changes in DC potential (ΔDC) or compound action potential on challenge with 100 mM K^+ Ringer, evidence that the Perineurium was tight to K^+. In preparations then fixed and exposed to 5 mM lanthanum in the fixative, and examined in the electron microscope, electron-dense lanthanum deposits were seen between perineurial lamellae, but lanthanum was not detectable within the endoneurium, confirming that the Perineurium was also tight to lanthanum. Absence of lanthanum penetration was confirmed by X-ray analysis of electron microscopic sections. In nerves exposed to 2 mM sodium deoxycholate (DOC) in the recording chamber, then challenged with high [K^+], a moderate increase in perineurial K^+ permeability ( P _ K ) was observed, but lanthanum was still excluded. Exposure of nerves to 4 mM DOC caused a greater increase in perineurial potassium permeability, and the two nerves with the greatest permeability ( P _ K > 1 × 10^−5 cm.sec^−1) also showed detectable lanthanum within the endoneurium. The results indicate that DOC causes a dose-dependent increase in tight junctional permeability in the Perineurium, and that the electrophysiological monitoring of K^+ penetration is a more sensitive measure of small ion permeability than electron microscopical analysis using lanthanum as tracer. Vesicular profiles observed in perineurial lamellae did not form open channels for ion flux across the Perineurium in control nerves, or in those exposed to DOC. In preparations where lanthanum reached the endoneurium, lanthanum was observed in dense deposits in the extracellular spaces around nodes of Ranvier, and in the outer mesaxon cleft, but did not penetrate the internodal periaxonal space, the myelin intraperiod line, or the Schmidt-Lanterman incisures, in contrast to observations in mammalian nerves. The apparent differences in accessibility of the internodal periaxonal space in frog and mammalian axons are discussed in relation to axonal physiology. The study illustrates the value of parallel electrophysiological and electron microscopic examination in elucidating the properties of extracellular ionic pathways and their role in neural function.
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ionic permeability of the opossum sciatic nerve Perineurium examined using electrophysiological and electron microscopic techniques
Brain Research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:Abstract A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica . The electrophysiological method was used to monitor permeability to K + , followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a ‘grease gap’ chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since a change in DC potential (ΔDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K + challenge ( n =71 nerves) indicating negligible K + permeability under control conditions. The inflammatory mediators histamine 0.1–40 mg/ml (1.3–130 mM), bradykinin (0.1–4.7 mM) and 5HT (serotonin) 0.1–5.0 mg/ml (0.5–23.5 mM) caused no measurable ΔDC on subsequent challenge with 100 mM [K + ] Ringer, indicating no effect on perineurial K + permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K + Ringer caused a dose-dependent ΔDC in the range 10–100 mM [K + ] (1.67±0.17 mV in 100 mM [K + ], n =20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined ( n =51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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Ionic permeability of the opossum sciatic nerve Perineurium, examined using electrophysiological and electron microscopic techniques.
Brain research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica. The electrophysiological method was used to monitor permeability to K(+), followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a 'grease gap' chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K(+)] Ringer was used to assess the K(+) permeability of the Perineurium, since a change in DC potential (DeltaDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K(+) challenge (n=71 nerves) indicating negligible K(+) permeability under control conditions. The inflammatory mediators histamine 0.1-40 mg/ml (1. 3-130 mM), bradykinin (0.1-4.7 mM) and 5HT (serotonin) 0.1-5.0 mg/ml (0.5-23.5 mM) caused no measurable DeltaDC on subsequent challenge with 100 mM [K(+)] Ringer, indicating no effect on perineurial K(+) permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K(+) Ringer caused a dose-dependent DeltaDC in the range 10-100 mM [K(+)] (1.67+/-0.17 mV in 100 mM [K(+)], n=20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined (n=51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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An electrophysiological method for measuring the potassium permeability of the nerve Perineurium.
Brain research, 1997Co-Authors: N J Abbott, Gillian Mitchell, Kevin J Ward, Faruhana Abdullah, I C SmithAbstract:An electrophysiological method is described for measuring the potassium permeability (PK) of the Perineurium of the sciatic nerve of the frog. The method is based on the principle of grease-gap recording, in which an insulating compartment separates two surface recording electrodes. The sciatic nerves of frogs Rana temporaria and R. pipiens were isolated and mounted across a five compartment chamber, with Vaseline grease seals on the partitions between compartments. Compartments #1, #2 and #5 contained frog Ringer solution, #4 was filled with Vaseline and formed the grease gap, and #3 was the test compartment in which solutions could be changed. The nerve was stimulated via platinum electrodes in compartments #1 and #2, and DC potentials and compound action potentials (CAP) were recorded between Ag/AgCl electrodes connected through Ringer-agar bridges to compartments #3 and #5. In nerves with undamaged Perineurium, changing from normal Ringer to high [K+] Ringer (100 mM, KCl replacing NaCl) for 2 min caused negligible change in DC potential or CAP, indicating that raised [K+] was not reaching the axon surface, and hence that the Perineurium was exerting a diffusional restriction on K+ entry. In nerves damaged by stretching or drying, K+ pulses caused a depolarising change in DC potential (delta DC), and corresponding decline in CAP amplitude, consistent with a leaky Perineurium allowing K+ entry and axonal depolarisation. Ringer made hypertonic by the addition of 2.5 M sucrose or 5 M NaCl caused increased perineurial permeability to K+. The method was calibrated by measuring the delta DC in response to raised [K+] in the range 5-100 mM [K+] in desheathed nerves; from this calibration curve relating delta DC to endoneurial [K+] it was possible to calculate the change in endoneurial [K+] occurring in intact preparations. The calculations showed that the undamaged Perineurium had a PK of < 6.3 x 10(-7) cm.s-1, similar to the value calculated for in situ nerves using radioisotopic techniques, but less than the value reported for isolated perineurial cylinders. The method gives real-time information on the K+ permeability of the nerve Perineurium and its modulation by experimental treatments.
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Effects of the bile salt sodium deoxycholate, protamine, and inflammatory mediators on the potassium permeability of the frog nerve Perineurium.
Brain research, 1997Co-Authors: B A Todd, E M Sedgwick, N J AbbottAbstract:An electrophysiological method was used to measure the potassium permeability (PK) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens. Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (delta DC) in response to challenge with 100 mM [K+] Ringer was used to assess the K+ permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating delta DC to bathing [K+] in desheathed nerves of Abbott et al. (1997). In the control condition, PK was < 1.1 x 10(-6) cm.s-1. The bile salt sodium deoxycholate (DOC, 1-4 mM) caused a dose-dependent increase in PK, which reached a maximum of 1.7 x 10(-5) cm.s-1 after 2-min exposure to 4 mM DOC, but access of K+ to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1-5 mg/ml equals 0.125-6.25 mM) had no effect on PK. Neither histamine (0.4-40 mg/ml), bradykinin (0.1-5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1-5 mg/ml) affected PK. The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood-nerve barrier and the blood-brain barrier.
M Roytta - One of the best experts on this subject based on the ideXlab platform.
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the Perineurium modifies the effects of phenol and glycerol in rat sciatic nerve
Acta Neuropathologica, 2004Co-Authors: Taina Westerlund, Ville Vuorinen, M RoyttaAbstract:Endoneurial cell response and type of nerve fibre damage were studied after perineural injections of 7% phenol-aqua and pure glycerol. Our previous studies have shown that phenol and glycerol induce different types of nerve fibre degeneration after intraneural injections: phenol dissolves axons and Schwann cells inside the basal lamina tubes but glycerol breaks them down into cellular flakes. The current study investigated whether the difference in type of endoneurial damage also appears after perineural application and how the Perineurium affects the effect of these neurolytic agents. Rat sciatic nerves were treated with perineural injections of 7% phenol-aqua or pure glycerol and were followed up to 6 months. The results support the previous findings that perineural phenol injection induces damage that covers almost the whole endoneurium, but glycerol injection results in minor subperineurial damage. An ultrastructural study showed that the endoneurial effects are much milder after perineural injection than after intraneural injections. Phenol-induced nerve fibre dissolving was only rarely seen and the nerve fibre damage appeared similar to that after regular Wallerian degeneration in both groups. Axonal regeneration began within 2 weeks of the injections. Endoneurial macrophages were numerous in the damaged area in many individual nerves even at 3–6 months in both groups, which may indicate impaired phagocytotic activity. Regenerating axonal sprouts were seen first at 1 week post injection and Schwann cells proliferated within 2 weeks in both groups. However, the number of axonal sprouts was higher (P=0.002) and the size of the sprouts appeared larger after glycerol injection at 4 weeks post injection. The present study shows that the effects of extraneurally applied neurolytic agents phenol and glycerol are modified by the Perineurium. Phenol readily penetrates the Perineurium, but glycerol causes only subperineurial damage. The type of damage is rather similar to regular Wallerian degeneration in both groups and the endoneurial effects differ from those seen after intraneural injections.
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the endoneurial response to microsurgically removed epi and Perineurium
Journal of The Peripheral Nervous System, 2002Co-Authors: Perttu Terho, Ville Vuorinen, M RoyttaAbstract:The purpose of the study was to examine the response of the endoneurium of the rat sciatic nerve after removal of the epi- and Perineurium. For this purpose, segments (4–5 mm long) of the whole epi- and Perineurium around the rat sciatic nerve were microsurgically removed (the peel-off area) and the endoneurium was left intact. The postoperative changes were followed up to 5 weeks post-operatively (PO) by histo- and immunohistochemical studies. Additionally, neuromorphometric analyses considering the number of Schwann cells, axons, macrophages and endothelial cells were examined in the peel-off area. The results showed that at the operative area the central part of the endoneurium (65% of the total area of the endoneurium) remained morphologically intact, but the outer part of the endoneurium (35% of the total area) reacted strongly and showed Wallerian type of degeneration. The number of axons and Schwann cells decreased 3 days PO. However, after 2 weeks the number of Schwann cells increased markedly and the highest number was noted 5 weeks PO. A great number of capillaries were observed in the outer part 1 week PO. A rapid invasion of macrophages was noted at the outer part of the endoneurium immediately after the operation. During the regeneration the endoneurial fibroblasts in the peripheral zone started to form minifascicle-like formations, which resulted in a distinct dense outer part of the endoneurium. This dense outer zone was preserved up to 5 weeks PO and participated in the formation of a new Perineurium-like structure, but no distinct new Perineurium was formed. At the border zone, areas beside the normal epi- and Perineurium proliferation of preserved perineurial cells were noted, which fused to the outer part of the dense endoneurium. On focal areas, an attachment of the operated area to the adjoining muscle was observed. This study shows for the first time that despite the microsurgical removal of epi- and Perineurium, the inner part of the endoneurium stays intact, but in the outer part of the endoneurium marked reactive changes ensue, probably to protect the injured peripheral nerve.
E M Sedgwick - One of the best experts on this subject based on the ideXlab platform.
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Ionic permeability of the frog sciatic nerve Perineurium: Parallel studies of potassium and lanthanum penetration using electrophysiological and electron microscopic techniques
Journal of Neurocytology, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:The isolated sciatic nerve of the frog Rana temporaria was used for a parallel electrophysiological and electron microscopic examination of the ionic permeability of the Perineurium, one component of the blood-nerve barrier. Nerves mounted in a grease-gap chamber for electrophysiological recording showed negligible changes in DC potential (ΔDC) or compound action potential on challenge with 100 mM K^+ Ringer, evidence that the Perineurium was tight to K^+. In preparations then fixed and exposed to 5 mM lanthanum in the fixative, and examined in the electron microscope, electron-dense lanthanum deposits were seen between perineurial lamellae, but lanthanum was not detectable within the endoneurium, confirming that the Perineurium was also tight to lanthanum. Absence of lanthanum penetration was confirmed by X-ray analysis of electron microscopic sections. In nerves exposed to 2 mM sodium deoxycholate (DOC) in the recording chamber, then challenged with high [K^+], a moderate increase in perineurial K^+ permeability ( P _ K ) was observed, but lanthanum was still excluded. Exposure of nerves to 4 mM DOC caused a greater increase in perineurial potassium permeability, and the two nerves with the greatest permeability ( P _ K > 1 × 10^−5 cm.sec^−1) also showed detectable lanthanum within the endoneurium. The results indicate that DOC causes a dose-dependent increase in tight junctional permeability in the Perineurium, and that the electrophysiological monitoring of K^+ penetration is a more sensitive measure of small ion permeability than electron microscopical analysis using lanthanum as tracer. Vesicular profiles observed in perineurial lamellae did not form open channels for ion flux across the Perineurium in control nerves, or in those exposed to DOC. In preparations where lanthanum reached the endoneurium, lanthanum was observed in dense deposits in the extracellular spaces around nodes of Ranvier, and in the outer mesaxon cleft, but did not penetrate the internodal periaxonal space, the myelin intraperiod line, or the Schmidt-Lanterman incisures, in contrast to observations in mammalian nerves. The apparent differences in accessibility of the internodal periaxonal space in frog and mammalian axons are discussed in relation to axonal physiology. The study illustrates the value of parallel electrophysiological and electron microscopic examination in elucidating the properties of extracellular ionic pathways and their role in neural function.
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ionic permeability of the opossum sciatic nerve Perineurium examined using electrophysiological and electron microscopic techniques
Brain Research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:Abstract A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica . The electrophysiological method was used to monitor permeability to K + , followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a ‘grease gap’ chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since a change in DC potential (ΔDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K + challenge ( n =71 nerves) indicating negligible K + permeability under control conditions. The inflammatory mediators histamine 0.1–40 mg/ml (1.3–130 mM), bradykinin (0.1–4.7 mM) and 5HT (serotonin) 0.1–5.0 mg/ml (0.5–23.5 mM) caused no measurable ΔDC on subsequent challenge with 100 mM [K + ] Ringer, indicating no effect on perineurial K + permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K + Ringer caused a dose-dependent ΔDC in the range 10–100 mM [K + ] (1.67±0.17 mV in 100 mM [K + ], n =20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined ( n =51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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Ionic permeability of the opossum sciatic nerve Perineurium, examined using electrophysiological and electron microscopic techniques.
Brain research, 2000Co-Authors: B A Todd, C Inman, E M Sedgwick, N J AbbottAbstract:A parallel electrophysiological and electron microscopic study was used to assess the ionic permeability of the sciatic nerve Perineurium of the opossum Monodelphis domestica. The electrophysiological method was used to monitor permeability to K(+), followed by combined electron microscopy and X-ray probe analysis to monitor permeability to the electron-dense tracer lanthanum. Isolated but intact nerves were mounted in a 'grease gap' chamber for extracellular measurement of DC potential and compound action potential (CAP). Challenge with 100 mM [K(+)] Ringer was used to assess the K(+) permeability of the Perineurium, since a change in DC potential (DeltaDC) under these conditions reflected changes in the axonal resting membrane potential. There was no detectable change in DC potential or CAP to the first K(+) challenge (n=71 nerves) indicating negligible K(+) permeability under control conditions. The inflammatory mediators histamine 0.1-40 mg/ml (1. 3-130 mM), bradykinin (0.1-4.7 mM) and 5HT (serotonin) 0.1-5.0 mg/ml (0.5-23.5 mM) caused no measurable DeltaDC on subsequent challenge with 100 mM [K(+)] Ringer, indicating no effect on perineurial K(+) permeability. In nerves exposed to the bile salt sodium deoxycholate (DOC, 6 min, 4 mM), challenge with elevated K(+) Ringer caused a dose-dependent DeltaDC in the range 10-100 mM [K(+)] (1.67+/-0.17 mV in 100 mM [K(+)], n=20), indicating increased perineurial permeability caused by DOC, but the response was smaller than that previously reported for the frog Perineurium. Lanthanum was observed in the outer layers of the Perineurium, but was not seen to penetrate the endoneurium in any of the nerves examined (n=51), even after DOC application. This study shows that the combined electrophysiological and electron microscopic technique for monitoring ionic permeability can be applied to mammalian nerve, and suggests that the opossum Perineurium is more resistant to tight junction opening by chemical modulators than is the frog Perineurium.
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effects of the bile salt sodium deoxycholate protamine and inflammatory mediators on the potassium permeability of the frog nerve Perineurium
Brain Research, 1997Co-Authors: B A Todd, E M Sedgwick, Joan N AbbottAbstract:Abstract An electrophysiological method was used to measure the potassium permeability ( P K ) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens . Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (ΔDC) in response to challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating ΔDC to bathing [K + ] in desheathed nerves of Abbott et al. (1997). In the control condition, P K was −6 cm·s −1 . The bile salt sodium deoxycholate (DOC, 1–4 mM) caused a dose-dependent increase in P K , which reached a maximum of 1.7×10 −5 cm·s −1 after 2-min exposure to 4 mM DOC, but access of K + to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1–5 mg/ml equals 0.125–6.25 mM) had no effect on P K . Neither histamine (0.4–40 mg/ml), bradykinin (0.1–5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1–5 mg/ml) affected P K . The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood–nerve barrier and the blood–brain barrier.
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Effects of the bile salt sodium deoxycholate, protamine, and inflammatory mediators on the potassium permeability of the frog nerve Perineurium.
Brain research, 1997Co-Authors: B A Todd, E M Sedgwick, N J AbbottAbstract:An electrophysiological method was used to measure the potassium permeability (PK) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens. Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (delta DC) in response to challenge with 100 mM [K+] Ringer was used to assess the K+ permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating delta DC to bathing [K+] in desheathed nerves of Abbott et al. (1997). In the control condition, PK was < 1.1 x 10(-6) cm.s-1. The bile salt sodium deoxycholate (DOC, 1-4 mM) caused a dose-dependent increase in PK, which reached a maximum of 1.7 x 10(-5) cm.s-1 after 2-min exposure to 4 mM DOC, but access of K+ to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1-5 mg/ml equals 0.125-6.25 mM) had no effect on PK. Neither histamine (0.4-40 mg/ml), bradykinin (0.1-5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1-5 mg/ml) affected PK. The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood-nerve barrier and the blood-brain barrier.
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an electrophysiological method for measuring the potassium permeability of the nerve Perineurium
Brain Research, 1997Co-Authors: Joan N Abbott, Gillian Mitchell, Kevin J Ward, Faruhana Abdullah, Christopher I H SmithAbstract:Abstract An electrophysiological method is described for measuring the potassium permeability ( P K ) of the Perineurium of the sciatic nerve of the frog. The method is based on the principle of grease-gap recording, in which an insulating compartment separates two surface recording electrodes. The sciatic nerves of frogs Rana temporaria and R. pipiens were isolated and mounted across a five compartment chamber, with Vaseline grease seals on the partitions between compartments. Compartments #1, #2 and #5 contained frog Ringer solution, #4 was filled with Vaseline and formed the grease gap, and #3 was the test compartment in which solutions could be changed. The nerve was stimulated via platinum electrodes in compartments #1 and #2, and DC potentials and compound action potentials (CAP) were recorded between Ag/AgCl electrodes connected through Ringer-agar bridges to compartments #3 and #5. In nerves with undamaged Perineurium, changing from normal Ringer to high [K + ] Ringer (100 mM, KCl replacing NaCl) for 2 min caused negligible change in DC potential or CAP, indicating that raised [K + ] was not reaching the axon surface, and hence that the Perineurium was exerting a diffusional restriction on K + entry. In nerves damaged by stretching or drying, K + pulses caused a depolarising change in DC potential (ΔDC), and corresponding decline in CAP amplitude, consistent with a leaky Perineurium allowing K + entry and axonal depolarisation. Ringer made hypertonic by the addition of 2.5 M sucrose or 5 M NaCl caused increased perineurial permeability to K + . The method was calibrated by measuring the ΔDC in response to raised [K + ] in the range 5–100 mM [K + ] in desheathed nerves; from this calibration curve relating ΔDC to endoneurial [K + ] it was possible to calculate the change in endoneurial [K + ] occurring in intact preparations. The calculations showed that the undamaged Perineurium had a P K of −7 cm·s −1 , similar to the value calculated for in situ nerves using radioisotopic techniques, but less than the value reported for isolated perineurial cylinders. The method gives real-time information on the K + permeability of the nerve Perineurium and its modulation by experimental treatments.
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effects of the bile salt sodium deoxycholate protamine and inflammatory mediators on the potassium permeability of the frog nerve Perineurium
Brain Research, 1997Co-Authors: B A Todd, E M Sedgwick, Joan N AbbottAbstract:Abstract An electrophysiological method was used to measure the potassium permeability ( P K ) of the Perineurium of the sciatic nerve of frogs Rana temporaria and R. pipiens . Isolated but intact nerves were mounted in a grease-gap chamber, and compound action potential and DC potential monitored. Change in the DC potential (ΔDC) in response to challenge with 100 mM [K + ] Ringer was used to assess the K + permeability of the Perineurium, since change in DC potential under these conditions reflected changes in the axonal resting potential. The permeability of the Perineurium was calculated from the published calibration curve relating ΔDC to bathing [K + ] in desheathed nerves of Abbott et al. (1997). In the control condition, P K was −6 cm·s −1 . The bile salt sodium deoxycholate (DOC, 1–4 mM) caused a dose-dependent increase in P K , which reached a maximum of 1.7×10 −5 cm·s −1 after 2-min exposure to 4 mM DOC, but access of K + to the endoneurial compartment was more restricted after DOC than after desheathing. Protamine phosphate (1 mM) and protamine sulphate (0.1–5 mg/ml equals 0.125–6.25 mM) had no effect on P K . Neither histamine (0.4–40 mg/ml), bradykinin (0.1–5 mg/ml) nor serotonin (5-hydroxytryptamine, 0.1–5 mg/ml) affected P K . The frog nerve Perineurium appears to be relatively insensitive to chemical agents and inflammatory mediators, in contrast to the endothelial cells forming the endoneurial blood–nerve barrier and the blood–brain barrier.