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N Danielsen

Publications and source records attributed to N Danielsen.

67 records · Page 4Linked to original sources
PubMed1987

Exogenous matrix precursors promote functional nerve regeneration across a 15-mm gap within a silicone chamber in the rat.

When silicone regeneration chambers are implanted empty, axonal regeneration fails if the interstump gap length is greater than 10 mm. Previous experiments using the 10-mm gap model demonstrated that regeneration success correlated with the dimension and/or consistency of the naturally formed acellular fibrin matrix. Both spatial and temporal parameters of regeneration could be stimulated through modifications of the fibrin matrix by prefilling the chambers at the time of implantation either with phosphate-buffered saline or plasma dialyzed against phosphate-buffered saline. In the present experiments, similar modification of matrix formation was found to promote successful regeneration across 15-mm and 20-mm interstump gap lengths. In addition, prefilling 15-mm-gap chambers with dialyzed plasma resulted in a 3.5-fold increase in the incidence of functional restitution detected at 8 weeks after implantation over the outcome with chambers prefilled with phosphate-buffered saline.

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PubMed1987

Effects of epidural and intrathecal application of collagenase in the lumbar spine: an experimental study in rabbits.

An experimental model is described in which collagenase in different concentrations and volumes were applied epidurally or intrathecally in the rabbit lumbar spine. This made it possible to study the tissue effects in a situation similar to that of collagenase leaking from a disc or accidental epidural or intrathecal injection at chemonucleolysis. Epidurally applied collagenase, in higher concentration, caused a local thinning of the dura. This effect was reduced at lower concentrations and volumes. Intrathecally injected collagenase, even in small amounts, caused intrathecal hemorrhage and acute paraplegia in the hind limbs. Therefore, in the clinical situation, intrathecal injection of collagenase must be avoided.

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PubMed1987

Intraneural edema following exposure to vibration.

Peripheral neuropathy represents a well-known complication from long-term exposure to vibration. In the present study an experimental model is presented with the purpose of analyzing the formation of intraneural edema following vibration exposure. Vibration (82 Hz, peak-to-peak amplitude 0.21 mm) was induced in the hind limb of rats by the use of vibrating electric motors during 4 h/d for 5 d. Tracer techniques (with albumin Evans blue and horseradish peroxidase) were used to study the permeability of intraneural microvessels after the vibration exposure on day 5. It was found that the vibration trauma in this model induced epineurial edema in the sciatic nerve. It is hypothesized that the formation of intraneural edema may be an important pathophysiological factor in the occurrence of vibration-induced neuropathy.

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PubMed1986

Nerve repair and axonal transport: outgrowth delay and regeneration rate after transection and repair of rabbit hypoglossal nerve.

The axonal transport and distribution of the fast phase of [3H]leucine-labeled proteins were used to monitor the outgrowth delay and regeneration rate in rabbit hypoglossal nerves 5-21 days after crush or transection. The transected nerves were repaired with mesothelial chambers or epineurial sutures. Radiolabeled proteins were transported into regenerating axons in the distal nerve segment after an initial delay of 2.5 days for crushed nerves and after a delay (initial and scar delays) of 4.8 and 5.7 days for sutured and mesothelial chamber-reconnected nerves, respectively. Regeneration rate was 3.5 mm/day after a crush and 2 mm/day after a transection with either type of repair. Total radioactivity was greater in both crushed and repaired nerves than in their contralateral controls. Transported radioactivity accumulated at the site of the lesions. This accumulation was greater and persisted longer in repaired nerves than in crushed ones. The difference in regenerative response after different types of trauma with respect to changes in axonal transport is emphasized.

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PubMed1986

Experimental hyperthyroidism stimulates axonal growth in mesothelial chambers.

An experimental model is presented for studying axonal growth after experimental hyperthyroidism and hypothyroidism. The left sciatic nerve of the rat was transected and transposed to the back. The proximal nerve stump was inserted into a 50-mm-long mesothelial chamber leaving the distal end of the chamber open. Different groups of young adult rats were given daily injections of thyroxine (10 micrograms/100 g body weight) or the goitrogen, thiamazol, in the drinking water (0.125 g/liter) for 12 weeks. Thyroxine treatment increased significantly the extent of axonal outgrowth from the proximal nerve stump compared with untreated rats. Experimental hypothyroidism (thiamazol treatment), evidenced by a retarded body growth, did not affect the extent of axonal outgrowth. In other experiments the left proximal nerve stump was cross-anastomosed with the right distal nerve stump. The two nerve stumps were bridged with a mesothelial chamber leaving a 15-mm gap. This gap distance is known from our previous studies to inhibit axonal overgrowth to the distal nerve stump. As evidenced by histological evaluation, in three of six thyroxine-treated rats, axons had bridged the 15-mm gap. We conclude that experimentally induced hyperthyroidism enhances axonal growth in mesothelial chambers.

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PubMed1986

Nerve repair and axonal transport. Distribution of axonally transported proteins during maturation period in regenerating rabbit hypoglossal nerve.

The distribution of fast migrating [3H]leucine-labelled proteins was studied in transected and repaired rabbit hypoglossal nerves. The nerves were repaired 90 days earlier with mesothelial chamber or epineurial suture technique. Fast migrating radiolabelled proteins were transported into the distal nerve segment and neurophysiological recordings from the tongue as well as the presence of myelinated axons in the distal nerve segment verified successful regeneration. The total amount of radioactivity was increased in repaired nerves as compared to contralateral nerves. In both groups there was a significant accumulation of radiolabelled proteins at the site of lesion. Nerves repaired with mesothelial chambers showed significantly more radioactivity in the distal nerve segment as compared to sutured nerves. The present study indicates long-standing effects on axonal transport system after both types of nerve repair. It is our opinion that axonal transport studies are a valuable complement when evaluating experimental nerve repair.

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PubMed1986

Absence of ongoing activity in fibres arising from proximal nerve ends regenerating into mesothelial chambers.

Morphological studies have indicated that proximal nerve ends of transected rat sciatic nerves regenerating into preformed mesothelial chambers show a different organization as compared to neuromas developed in contact with a muscle fascia. We have studied the physiological properties of nerve fibres arising from these types of preparations with reference to ongoing activity, response to mechanical stimulation and noradrenaline sensitivity. The study included also fibres arising from ligated and encapsulated neuromas. Fibres with ongoing activity arising from the neuroma could be found from neuromas in contact with a muscle fascia and also from ligated and encapsulated neuromas. This ongoing activity was enhanced by mechanical stimulation and i.v. infusion of noradrenaline. In contrast, fibres arising from proximal nerve ends in mesothelial chambers did not show ongoing activity. These silent fibres responded dynamically to light mechanical stimulation. Noradrenaline did not induce ongoing activity in these fibres.

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PubMed1986

Evidence indicating trophic importance of IGF-I in regenerating peripheral nerves.

The mechanisms influencing regeneration of peripheral nerves are incompletely known, but growth factors are supposed to play a key role. In the present study, we demonstrate, with the aid of immunohistochemical methods, that somatomedin C (Sm-C/insulin-like growth factor I/IGF-I) rapidly increased from low to high concentrations, reaching peak values in 2 weeks, in regenerating sciatic nerves of adult rats. In addition, IGF-I was demonstrated extracellularly, never observed in the control nerves. Reactive Schwann cells appeared to be the major source for IGF-synthesis. Higher concentrations were seen in tubulated nerves as compared to sutured ones. It is proposed that IGF-I exerts important growth supporting effects on regenerating peripheral nerves.

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PubMed1986

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.

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PubMed1986

Tissue specificity in nerve regeneration.

In 1944 Weiss & Taylor presented experimental evidence against "neurotropism" in nerve regeneration. We used a silicone Y-chamber system to repeat some of those experiments. The proximal stump of transected rat sciatic nerve was introduced into the proximal inlet of the Y. One of the distal outlets was left empty, plugged or occupied by a tendon graft, the other outlet being occupied by a nerve graft. Analysis after 4 and 12 weeks showed in all cases a preferential or exclusive axonal growth towards the nerve piece. The results, indicating the existence of "tissue specificity", are contradictory to the results reported by Weiss & Taylor (30). The findings are discussed with respect to possible influence of humoral, cellular and molecular factors associated with the distal nerve stump as well as the matrix, formed between both nerve segments.

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PubMed1983

Axonal growth in mesothelial chambers. The role of the distal nerve segment.

An experimental model is presented for studying nerve regeneration over gaps of various lengths between the both ends of a severed nerve. After transferring left and right sciatic nerves of rat to the back, the gap between the two nerve ends could be bridged by a preformed, tube-shaped mesothelial chamber of a desired length. When the gap length was 10 mm or less, a well developed nerve structure was generated in the chamber between the nerve ends, and axons from the left sciatic nerve reinnervated muscles in the right limb via the right sciatic nerve. When the gap length was extended to 15 mm or more no such regeneration occurred. When no distal nerve end was introduced into the chamber, there was a limited growth into this chamber over only 5-6 mm. This "limited growth phenomenon" is discussed with respect to a lack of "trophic" or cellular support from a distal nerve segment. It is also proposed that the termination of growth, seen under these circumstances, may suggest a new principle for avoiding the development of neuromas after nerve transections.

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PubMed1982

Nerve regeneration across an extended gap: a neurobiological view of nerve repair and the possible involvement of neuronotrophic factors.

We have compared the anatomic and functional regeneration of a transected sciatic nerve following regrowth from its proximal stump through either preformed empty mesothelial chambers or autologous nerve grafts bridging a 10 mm gap. Within the mesothelial chambers an organized multifascicular nerve trunk forms between the proximal and distal stumps. After 3 months, distal segment cross sections from the mesothelial chamber and nerve graft groups did not differ with respect to axonal density or distribution of axonal diameters. Mean conduction velocities across the gaps were also similar, although the nerve graft group had a wider distribution of velocities. Little or no regeneration was evident when the gap between the nerve stumps was left empty. These results suggest that if the regrowing proximal stump is in an appropriate environment, it can form a well organized and oriented nerve trunk. In the mesothelial chambers, the regenerating nerve is surrounded by a loose cellular stroma and a small amount of interstitial fluid, which was found to contain trophic activity for cultured rodent sensory neurons. Such factors may also support nerve regeneration in vivo.

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