Search PubMed⌕ Search

Biomedical subjects

N Danielsen

Publications and source records attributed to N Danielsen.

At least 55 records · Page 3Linked to original sources
PubMed1994

Tubular repair of the median nerve in the human forearm. Preliminary findings.

Transected median nerves in the forearm of two male patients, 12 and 21 years of age, were treated with a chamber technique leaving a 3 to 5 mm gap between the nerve ends. The nerve ends were enclosed in a silicone tube of such a dimension that would not cause compression of the nerve. Post-operative examination including sensory evaluation and assessment of muscle contraction force was carried out after 3 years. In both cases there was excellent motor recovery of the thenar muscles. Outgrowth of sensory fibres was remarkably fast, resulting ultimately in functional sensibility allowing almost normal hand function. 2PD was < or = 6 mm (12-year-old patient) and 8 to 10 mm (21-year-old patient) respectively. In one case the silicone tube was re-explored because of minor local discomfort 2 years after the repair. The former gap was bridged by a smooth continuous nerve-like structure of the same diameter as the adjacent nerve trunk and with no signs of neuroma formation or compression of the nerve.

Adult↗
PubMed1994

Can sensory and motor collateral sprouting be induced from intact peripheral nerve by end-to-side anastomosis?

The possibility that collateral sprouting could occur from intact axons in an undamaged sciatic nerve was studied in the rat by suturing either a 7-day predegenerated or a fresh nerve segment in an end-to-side fashion to the sciatic nerve proper. Following a 14- or 35-day recovery period, the pinch reflex test was performed on the transplanted segment to demonstrate the presence of sensory axons. The majority of cases, using a predegenerated nerve segment but not a fresh segment, responded positively. Neurofilament staining and histological examination confirmed the presence of axons in the attached nerve segment. In another series of experiments, the proximal peroneal fascicle was ligated and cut. Following a 7-day predegeneration period the distal stump was sutured end-to-side to the ipsilateral tibial fascicle. After 90 days, stimulation of the tibial nerve proximal to the attached site induced substantial contraction in both the native gastrocnemius muscle and the foreign tibialis anterior muscle. These findings suggest that collateral sprouting may occur from intact axons, perhaps induced by factors emanating from the attached nerve segment, and subsequently make functional peripheral connections.

Anastomosis, Surgical↗
PubMed1994

Trophism, tropism, and specificity in nerve regeneration.

Target-derived neurotrophic factors are of basic importance for survival of neurons. In the normal state, such neurotrophic factors, synthesized by the target tissues, are taken up by nerve terminals and transported by retrograde axonal transport in axons to the nerve-cell bodies to maintain their viability. After nerve injury, neurotrophic factors are synthesized by non-neuronal cells (Schwann cells and fibroblasts) in the nerve trunk, thereby supporting the outgrowth of axons. Neurite-outgrowth-promoting factors on cell surfaces (cell adhesion molecules, "recognition molecules") or in the extracellular matrix promote extension of the axons by providing an appropriate "adhesiveness" in the substrate. Both neurotrophic and neurite-outgrowth-promoting factors are essential for axonal growth after injury. Specificity in end-organ reinnervation is a complex phenomenon which may be based on physical factors at the zone of injury, as well as on molecular interaction between axons and substrate cells along the pathways and at the target level. Such processes may include molecular recognition of appropriate axons and maintenance of such axons by trophic mechanisms, as well as the pruning of inappropriate axons. The ultimate errors in target reinnervation are reflected in a cortical re-organization in the somatosensory cortex. The capacity of the brain to "reprogram" itself and adapt to this functional re-organization is critical for the ultimate recovery of functional sensory/motor function after nerve injuries.

Animals↗
PubMed1993

The influence of predegeneration on regeneration through peripheral nerve grafts in the rat.

Nerve regeneration through predegenerated (PNG) or fresh (FNG) autografts in either fresh or delayed recipient nerve beds were studied in the rat sciatic nerve. Grafts 10 mm in length were excised either immediately or following a 7-day period of predegeneration. They were sutured into gaps on the contralateral side which were either freshly made or had been made 7 days previously. The early recovery (10 days at 2-day intervals) was evaluated by the sensory pinch test to measure the rate of regeneration and the delay period. The PNG group had an improvement in axonal regeneration as evidenced by a reduced delay period, a reduced number of regeneration failures, and less variability in regeneration distances compared to the FNG group. Conditioning the host site blocked some of the delay reduction in the PNG group, but had no effect on regeneration rate or delay in the FNG group. The presence of axons in the graft was confirmed by immunocytochemistry for neurofilament protein and by electron microscopy. The results suggest that proliferated cells, primarily Schwann cells, promote regeneration through the suture line and graft into the distal segment.

Animals↗
PubMed1993

Inflammatory cells and mediators in the silicone chamber model for nerve regeneration.

In the present study the inflammatory response was quantitatively evaluated during peripheral nerve regeneration. The fluid from silicone nerve regeneration chambers, inserted in rats, was collected during the early period of regeneration of transected sciatic nerves (6 h-7 d) and analysed with respect to inflammatory cells and mediators (leukotriene B4, LTB4, and interleukin-1 alpha, IL-1 alpha). Leucocytes were detected during the entire period (up to 7 d after implantation). The highest concentration was detected after 24 h. PMNG (polymorphonuclear granulocyte) was the predominant cell type in the chamber fluid during the initial 5d of regeneration. Analysis of the concentration of LTB4 demonstrated two peaks (at 24 h and 5 d). The IL-1 alpha concentration displayed an early and relatively smaller peak after 24 h and a second and much larger peak after 7 d, concomitant with an increase of the number of mononuclear cells.

Animals↗
PubMed1993

A mathematical model for regeneration rate and initial delay following surgical repair of peripheral nerves.

A mathematical model is presented by which the regeneration rate and initial delay for peripheral nerve regeneration can be calculated from sensory pinch test data following surgical repair of peripheral nerves. The model is based on the assumption that experimental variations in regeneration distances between animals is due to the initial delay period--the time period before the regenerating fibers cross the suture line whereas the rate of regeneration is constant. This model which accounts for all observed data including 'regenerating failures' showed that nerve fibers in the rat sciatic nerve repaired with a fresh nerve graft regenerated at a rate of 1.5 mm/day after an initial delay of 3.6 days.

Animals↗
PubMed1993

Glial and neuronal marker proteins in the silicone chamber model for nerve regeneration.

In the present study, neuronal and Schwann cell marker proteins were used to biochemically characterize the spatiotemporal progress of degeneration/regeneration in the silicone chamber model for nerve regeneration. Rat sciatic nerves were transected and the proximal and distal stumps were inserted into a bridging silicone chamber with a 10-mm interstump gap. Using dot immunobinding assays, S-100 protein and neuronal intermediate filament polypeptides were measured in different parts of the nerve 0-30 days after transection. In the most proximal nerve segment, all the measured proteins were transiently increased. In the proximal and distal stumps adjacent to the transection, the studied proteins were decreased indicating degeneration of the nerve. Within the silicone chamber, the regenerating nerve expressed the Schwann cell S-100 protein already at 7 days, whereas the neurofilament polypeptides appeared later. These observations are corroborated by previous morphological studies. The biochemical method described provides a new and fast approach to the study of nerve regeneration.

Animals↗
PubMed1991

Effects of chondroitinase ABC on intrathecal and peripheral nerve tissue. An in vivo experimental study on rabbits.

The enzyme chondroitinase ABC has recently been suggested for use in chemonucleolysis. The effects of 200 U ml of chondroitinase ABC were studied on intrathecal and peripheral nerve tissue in rabbits. After the intrathecal (subarachnoid) application of 0.2 ml of either the diluent in the control group (N = 2) or chondroitinase in the study group (N = 4), no neurologic deficit was detected. Compared with the control group, no morphologic changes at the light microscopic level were induced in the spinal cord by chondroitinase. No neurophysiologic differences were detected between tibial nerves after exposure to 1 ml of the diluent (control, N = 8) or chondroitinase (the other leg) for 4 weeks, nor did the study group, compared with the control group, show any morphologic changes in the tibial nerves. Because the concentration of chondroitinase ABC tested was approximately 40 times higher than might be used clinically for chemonucleolysis, the present study indicates a wide margin of safety for unwanted side effects on nerve tissue.

Animals↗
PubMed1991

Ulnar nerve repair by the silicone chamber technique. Case report.

The ulnar nerve of a 21-year old man was repaired at the wrist by a silicone chamber technique 10 days after a traumatic transection. A 3 mm gap was left between the nerve ends inside the chamber. At follow-up three years later, motor and sensory recovery was excellent. At exploration at that time a macroscopically normal nerve was found in the tube.

Adult↗
PubMed1990

Effects of sympathetic stimulation on C-fibre response after peripheral nerve compression: an experimental study in the rabbit common peroneal nerve.

Non-myelinated C-fibre responses during sympathetic trunk stimulation were studied in rabbit common peroneal nerve 2 weeks after the nerve had been subjected to compression at 400 mmHg for 30 min. Our previous studies have demonstrated that during sympathetic trunk stimulation the compound action potential of uninjured somatic C-fibres is characterized by a reduced amplitude and an increased latency. In the present study, nerve compression changed the C-fibre response to sympathetic stimulation. Three out of eight nerves reacted to nerve compression by increased C-fibre compound action potential amplitude in response to sympathetic stimulation. In three other rabbits with compressed nerves the C-fibre action potential amplitude was unchanged, and in the remaining two rabbits the action potential amplitude was decreased during sympathetic stimulation. The action potential latency increased in all tested compressed C-fibres. The phenomenon of increased C-fibre amplitude during sympathetic activation has not been observed in uninjured nerves. As in uninjured nerves, noradrenaline infusion produced an increased C-fibre action potential amplitude and latency in six animals. Sympathetic stimulation did not affect the A-fibre response. These results indicate that sympathetic activity influences the conduction properties in C-fibres of somatic origin and that the response can be changed after a nerve injury. The findings may be of importance for the understanding of pain aggravation in different types of nerve injuries during increased sympathetic activity.

Action Potentials↗
PubMed1990

Microvascular effects of chondroitinase ABC and chymopapain. An in vivo experimental study on hamsters and rabbits.

Immediate and long-term microvascular effects of chondroitinase ABC, 200 unit/ml, were analyzed in ten hamsters. The immediate effects on the microcirculation were studied by vital microscopy following local injection in the cheek pouch. There were no detectable effects on the microvascular blood flow during the 60 minutes of observation for chondroitinase ABC or the control. A therapeutic concentration (2000 pKat/ml) of chymopapain stopped the microcirculation in the injected area immediately, with numerous microbleedings at the border zone. Long-term effects were studied after subcutaneous injections in the ears of six rabbits. Chondroitinase ABC and the control did not cause any macroscopic or microangiographic effects. However, light microscopy showed a moderate inflammatory reaction in the subcutaneous layer for both chondroitinase ABC and the control. Chymopapain induced severe effects on the cartilage and surrounding tissues. Microangiography revealed a vessel-free zone at the injection site. Since 200 units/ml of chondroitinase ABC is four to eight times higher than the concentration that might be used for chemonucleolysis, i.e., dissolution of intervertebral discs by local enzyme injection, the present investigation suggests a wide margin of safety regarding the potential effects on blood vessels in tissues surrounding the disc.

Animals↗
PubMed1989

Effects of nerve compression or ischaemia on conduction properties of myelinated and non-myelinated nerve fibres. An experimental study in the rabbit common peroneal nerve.

Compound action potentials of both myelinated (A) and non-myelinated (C) fibres in the common peroneal nerve of rabbits were studied during and after acute, graded compression of the nerve at 200 or 400 mmHg applied for 2 h or during ischaemia created by nitrogen inhalation or aortic occlusion. Compression of the nerve at 200 mmHg blocked the AI component (large myelinated fibres) after about 23 min, while compression at 400 mmHg shortened this time to 11 min. The A2 component (thinner myelinated fibres) had a lower conduction velocity and a higher resistance to compression. There was just a slight decrease in conduction velocity of the non-myelinated fibres when the nerves were compressed at 200 mmHg for 2 h. However, compression at 400 mmHg for 2 h induced a marked deterioration of amplitude and conduction velocity of the C-fibres. There was an incomplete restitution of function of A- and C-fibres during 2 h of recovery. The thinner myelinated fibres were more susceptible to deprivation of oxygen than the thicker ones, while non-myelinated fibres differed in response according to method of ischaemia induction. It is concluded that non-myelinated fibres are very resistant to compression and a very high pressure (greater than 400 mmHg) is needed to affect these fibres.

Animals↗
PubMed1988

Rat amnion membrane matrix as a substratum for regenerating axons from peripheral and central neurons: effects in a silicone chamber model.

An extracellular matrix preparation, the human amnion membrane matrix (hAMM) can serve as a neurite-promoting substratum for cultured peripheral and central neurons, and also as a support for axonal growth in experimentally injured adult brain in vivo. In the present study, we tested similar materials as bridges in a silicone chamber model for the regeneration of sciatic nerve in the adult rat. Since hAMM elicited an inflammatory response, we developed a rat amnion membrane matrix (rAMM), which proved to be an excellent neurite-promoting substratum for cultured ganglionic and spinal cord neurons. The rAMM was coiled and inserted in the 10 mm gap between the two nerve stumps from the silicone chambers. At 16 days after implantation, temporal progress of regeneration was grossly similar as in saline-prefilled control chambers. However, rAMM-prefilled chambers displayed significantly higher number of vessels and a markedly different geometry of the regenerate: an endoneurium, surrounded by a perineurial-like cell layer, was formed outside the largely preserved central portion of the rAMM coil. After longer regeneration times (28 days), a rAMM core was no longer detected, but some rAMM-like materials remained interspersed in the endoneurium. The overall organization of the regenerate and the number of myelinated axons at this time were similar to those of control chambers, although the endoneurial cross-sectional area was larger in the rAMM chambers. One specimen, however, displayed the very patterns for which the experiments were designed, namely an array of numerous, myelinated axons tracing the spiraling spaces between consecutive lamellae of the rAMM coil.

Amnion↗
PubMed1988

Fibroblast growth factor effects on peripheral nerve regeneration in a silicone chamber model.

We have developed a silicone nerve regeneration chamber that is partitioned into two compartments by a strip of nitrocellulose paper. The modified two-compartment chamber allows the investigation of the effects on rat sciatic nerve regeneration of trophic or growth factors that are initially bound to the nitrocellulose partition. In this study we compared the effects of untreated nitrocellulose, a siliconized nitrocellulose strip, and a strip that had been soaked in a basic fibroblast growth factor (FGF) solution. FGF is a known angiogenic factor and a mitogen for endothelial cells, fibroblasts, and Schwann cells. All of these cell types are present in the peripheral nerve. In vitro analyses, using 3T3 cells as test cells, showed that some of the bound FGF remained active on the nitrocellulose paper for at least 8-10 days. In vivo experiments, examined at 16 days post-implantation, revealed that spatial migration of all cellular elements (perineurial-like cells, vasculature, and Schwann cells) across the chamber gap was slower with untreated nitrocellulose strips than with siliconized strips but was most advanced with FGF-treated ones. Most striking was the well-developed vascular arborization of the regenerate within the FGF chambers. Histologic sections from the proximal one-half of the chamber revealed that the regenerate in untreated strip chambers consisted of fibrin matrix and erythrocytes, whereas a well-developed structure with all the cellular elements of a regenerating nerve was seen in several of the FGF strip chambers. We conclude that FGF stimulates peripheral nerve regeneration in this model.

Animals↗
PubMed1988

A two-compartment modification of the silicone chamber model for nerve regeneration.

In the nerve regeneration silicone chamber model, the regenerate which forms across a 10-mm gap between proximal and distal nerve stumps is a monofascicular structure with an outer perineurial-like cell sheath. Recent work has provided indications that the geometry of the regenerate within a silicone chamber can be altered by experimental modifications of the chamber matrix. In the present study we modified the standard silicone chamber into a two-compartment chamber by inserting a 6- or 10-mm-long siliconized nitrocellulose strip in order to obtain two separate regenerates. Light microscopy 16 days after implantation revealed that two separate nerve structures had formed, one on each side of the nitrocellulose partition and adjacent to it, and each with its own perineurial-like cell sheath. In chambers with 6-mm-long strips a monofascicular regenerate started from the proximal stump and divided into two separate structures as it approached the proximal end of the strip: the two fascicles joined again into a monofascicular structure in the distal portion of the chambers. The new two-compartment silicone chamber model appears suitable for future examinations of experimental fasciculation. In addition, the nitrocellulose partition should allow one to study specific effects of growth factors on axonal regeneration in vivo, as growth factors bind strongly to untreated nitrocellulose while retaining their biological activity.

Animals↗
PubMed1988

Axonal growth in mesothelial chambers: effects of a proximal preconditioning lesion and/or predegeneration of the distal nerve stump.

Preformed, autologous mesothelial chambers were utilized to study axonal growth following selective predegeneration of the distal nerve stump and/or preconditioning of the proximal nerve stump. The left and/or right sciatic nerve of rats was exposed and transected in the thigh. Two weeks after transection, the left proximal nerve stump was cross-anastomosed with the right distal nerve stump by using a mesothelial chamber leaving a 15-mm gap between the two nerve stumps. Previous studies have shown that axonal overgrowth normally does not occur over this gap distance to the distal stump. Three months after cross-anastomosing, regeneration across the 15-mm gap was evaluated by muscle action potential recordings and light microscopical examination. In experiments in which a distal nerve stump was selectively degenerated and the proximal segment was freshly cut, axons had bridged the 15-mm gap in six of seven rats. When a proximal preconditioned nerve stump was matched with a freshly cut distal stump, axonal overgrowth occurred in only 4 of 10 experiments. In experiments including a proximal preconditioned nerve stump and a distal predegenerated stump, axons bridged the gap in 6 of 8 experiments. We concluded that a priming lesion, including manipulation with proximal and/or distal stump, enhances axonal growth in mesothelial chambers.

Animals↗
PubMed1988

Peripheral nerve regeneration in Gore-tex chambers.

Gore-tex chambers were used to bridge a 6 mm gap between the proximal and distal nerve stumps of a rat sciatic nerve. The wall structure of these chambers is characterized by "nodes" interconnected by smaller fibrils. Chambers with internodal distances of 5, 10 and 30 microns were used. Some 30 microns chambers were coated from the outside with Gore-tex (0.2 micron internodal distance) and others were coated from the inside. Regeneration after 12 weeks, as evidenced by muscle action potential recordings and light microscopy, was successful regardless of what type of chamber had been used. The organization of the nerve structure varied among different chamber types. A well organized coaxial nerve structure with myelinated axons was observed if inner-coated chambers were used. In chambers that were not coated or in outer-coated chambers tissue completely filled the chambers, and myelinated axons were arranged in mini-fascicles surrounded by loose connective tissue.

Animals↗