Changes in axonal transport during regeneration of feline ventral roots

Effects of cochlear ablation on choline acetyltransferase activity in the rat cochlear nucleus and superior olive

Using microdissection and quantitative microassay, choline acetyltransferase (ChAT) activity was mapped in the cochlear nucleus (CN) and in the source nuclei of the olivocochlear bundle, the lateral superior olive and ventral nucleus of the trapezoid body. In control rats, gradients of ChAT activity were found within the major subdivisions of the CN and in the lateral superior olive. These gradients correlated with the known tonotopic organizations, with higher activities corresponding to locations representing higher sound frequencies. No gradient was found in the ventral nucleus of the trapezoid body. In rats surviving 7 days or 1 or 2 months after cochlear ablation, ChAT activity was increased 1 month after ablation in the anteroventral CN by 30-50% in most parts of the lesion-side and by 40% in the contralateral ventromedial part. ChAT activity in the lesion-side posteroventral CN was increased by approximately 40-50% at all survival times. Little change was found in the dorsal CN. Decreases of ChAT activity were also found ipsilaterally in the lateral superior olive and bilaterally in the ventral nucleus of the trapezoid body. Our results suggest that cholinergic neurons are involved in plasticity within the CN and superior olive following cochlear lesions.

Ciliary muscle choline acetyltransferase and acetylcholinesterase after ciliary ganglionectomy

Choline acetyltransferase (ChAT; EC 2.3.1.6) and acetylcholinesterase (AChE; EC 3.1.1.7) activities were measured in cynomolgus monkey ciliary muscle 1 month and 6 or more months after ciliary ganglionectomy (CG) or post-ganglionic ciliary neurectomy (PCN). ChAT activity was undetectable and AChE activity was elevated 1 month after CG or PCN, while both averaged about 30% of normal levels 6 or more months after denervation. Four out of six eyes reinnervated by functional criteria 6-12 months after CG or PCN. In one of the two remaining eyes permanently denervated, ChAT was absent from the ciliary muscle. In the other, ChAT activity was about 50% of normal, similar to the reinnervated eyes, but the regenerated cholinergic nerves were not approximated to the ciliary muscle fibers.

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.

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.

Peripheral nerve grafts: the relationship of axonal growth cone and biomechanical properties

Cat sciatic nerves containing 2 and 4 cm nerve grafts were subjected to tensile testing with the finding that a significant decrease in force at failure occurs at the distal suture line at a time after surgery that is graft length dependent. Tritiated labeling of regenerating axons and qualitative electromyography demonstrated that this effect was unrelated to the leading edge of the axonal growth cone, but temporally related to the functional reinnervation of denervated muscle.

Choline acetyltransferase and acetylcholinesterase in centrifugal labyrinthine bundles of rats

Activities of choline acetyltransferase and acetylcholinesterase were measured for the acetylcholinesterase-positive fiber bundles containing axons projecting from the brainstem to the labyrinth of the rat. These activities were compared to those of a well-established cholinergic tract: the facial motor root. The choline acetyltransferase activities were roughly similar between the tracts, consistent with a conclusion that the centrifugal labyrinthine fibers are all cholinergic. The acetylcholinesterase activities were much higher in the centrifugal labyrinthine bundle than in the facial motor root, probably relating to the smaller diameters of the labyrinthine fibers. Transection of the centrifugal labyrinthine bundle led to virtually total loss of its choline acetyltransferase activity lateral to the cut, consistent with a centrifugal direction of all the fibers, but loss of only half its acetylcholinesterase activity, even after 34 days. These results agree with those for well-established cholinergic pathways, including the facial motor root in the present study, and with previous suggestions that a component of the acetylcholinesterase in cholinergic tracts might be synthesized by cells other than the neurons in the tract.

Rapid axonal transport of glycerophospholipids in regenerating hypoglossal nerve of the rabbit

The intraaxonal transport of phospholipids in regenerating hypoglossal nerve of the rabbit was investigated by administration of labeled lipid precursors into the medulla oblongata. At various time intervals after crushing the left hypoglossal nerve at the level of the digastric muscle, a mixture of 60 mu Ci of [2-3H]glycerol and 15 mu Ci of [1-14C]palmitate, dissolved in 15% bovine serum albumin, was injected into the calamus scriptorius of the fourth ventricle. The amount and the pattern of labeling of glycerophospholipids synthesized in the motor neurons were determined. Three days after nerve crush there was an accumulation of labeled glycerophospholipids immediately proximal to the injury site. Seven days after crushing, the regenerating nerve incorporated rapidly transported labeled lipids in greater amounts than the contralateral normal nerve; the incorporation was elevated along the entire length of the nerve containing both regenerating axons and the post-crush sprouting terminals. The difference between the two sides increased up to 14 days, but disappeared as regeneration proceeded (21-45 days). The "pool" of radioactive lipids remaining in the cell bodies of hypoglossal nuclei, in the segments of nerve, both proximal and distal to the crush site, and in all the segments of uncrushed nerve was similar 6-12 h after labeling. Among the phospholipids, the highest 3H and 14C radioactivity was observed in phosphatidylcholine and phosphatidylethanolamine. These results support the hypothesis than an increase in the amount of glycerophospholipids, conveyed by rapid axonal transport, takes place in the first 2 weeks during nerve regeneration. The increased transport of lipids presumably reflects an augmented demand for membrane precursors during the sprouting process.

Regeneration of motor axons in the rat sciatic nerve studied by labeling with axonally transported radioactive proteins

Labeling regenerating axons with axonally transported radioactive proteins provides information about the location of the entire range of axons from the fastest growing ones to those which are trapped in the scar. We have used this technique to study the regeneration of motor axons in the rat sciatic nerve after a crush lesion. From 2 to 14 days after the crush the lumbar spinal cord was exposed by laminectomy and multiple injections of [3H]proline were made stereotactically in the ventral horn. Twenty-four hours later the nerves were removed and the distribution of radioactivity along the nerve was measured by liquid scintillation counting. There was a peak of radioactivity in the regenerating axons distal to the crush due to an accumulation of label in the tips of these axons. After a delay of 3.2 +/- 0.2 (S.E.) days, this peak advanced down the nerve at a rate of 3.0 +/- 0.1 (S.E.) mm/day. The leading edge of this peak, which marks the location of the endings of the most rapidly growing labeled fibers, moved down the nerve at a rate of 4.4 +/- 0.2 mm/day after a delay of 2.1 +/- 0.2 days; this is the same time course as that of the most rapidly regenerating sensory axons in the rat sciatic nerve, measured by the pinch test. Another peak of radioactivity at the crush site, presumed to represent the ends of unregenerated axons or misdirected sprouts, declined rapidly during the first week, and more slowly thereafter.

Fast axonal transport in motor nerve regeneration

This report describes the fast transport of [3H]-leucine-labeled proteins in regenerating rat sciatic motor nerves. A normal rate of fast transport (383 +/- 33 mm/day) was present in the regenerating sprouts, as well as in the central stumps. The rapidly transported proteins passed the level of axotomy without impediment, and accumulated in the endings of the regenerating sprouts, as shown by electron microscope autoradiography. In addition, transported proteins accumulated in terminal neuromas. The relative amount of protein-incorporated radioactivity in the crest of transport in the regenerating nerves was increased compared to control nerves. These results are interpreted to suggest that the mechanism of fast transport is the same in regenerating nerves was increased compared to control nerves. These results are interpreted to suggest that the mechanism of fast transport is the same in regenerating sprouts as in normal axons; during regeneration fast transport appears to add newly synthesized materials to the growing tip.

Transport of choline acetyltransferase and acetylcholinesterase in the central stump and isolated segments of a peripheral nerve

Axonal transport of choline acetyltransferase (ChAc, E.E.:2.3.1.6) and acetyl cholinesterase (AChE, E.C.:3.1.1.7) was studied in the peroneal fascicles of rabbit sciatic nerves. The accumulation of ChAc in the central nerve stump proceeded 5 times more slowly than that of AChE and occurred at a distanct of 2-4 mm proximally from the end, whereas AChE accumulated in the last 2 mm of the stump. In double-ligated segments of the nerve in situ the activity of ChAc decreased at the proximal and increased at the distal end; the activity of AChE rose at both ends, The increase of ChAc activity did not cease until 22 h, whereas that of AChE stopped before 10 h. The intensity of ChAc transport is considerably diminished in the part of axon separated from the nerve cell body. Differences between the behavior of ChAc and AChE are interpreted by the assumption that the axonal transport of ChAc is slow, unidirectional, concerns all of the enzyme in the nerve, and that most of the transported enzyme is not associated with intraaxonal organelles. In contrast to ChAc, the transport of AChE is fast, bidirectional, and concerns a minor proportion of enzyme in the nerve; the transported enzyme is associated with organelles. The rate of proximodistal transport of ChAc is estimated at 4 mm/day (based on the assumption that 100% of the enzyme moves proximo-distally) and that of AChE at 480 mm/day (based on the extimate that 5% of enzyme moved proximo-distally in the present experiments).