Arrangement of sympathetic fibers within the human common peroneal nerve: implications for microneurography.

Recently, interest has grown in the firing patterns of individual or multiunit action potential firing patterns in human muscle sympathetic nerve recordings using microneurography. Little is known, however, about sympathetic fiber distribution in human lower limb nerves that will affect the multiunit recordings. Therefore, the purpose of this study was to examine the sympathetic fiber distribution within the human common peroneal nerve using immunohistochemical techniques (tyrosine hydroxylase, avidin-biotin complex technique). Five-micrometer transverse and 10-µm longitudinal sections, fixed in formaldehyde, were obtained from the peroneal nerve that had been harvested from three human cadavers (83 ± 11 yr) within 24 h of death. Samples of rat adrenal gland and brain served as controls. Sympathetic fiber arrangement varied between left and right nerves of the same donor, and between donors. However, in general, sympathetic fibers were dispersed throughout ∼25-38 fascicles of the peroneal nerve. The fibers were grouped in bundles of ∼2-44 axons or expressed individually throughout the fascicles, and the distribution was skewed toward smaller bundles with median and interquartile ratio values of 5 and 1 axons/bundle, respectively. These findings confirm the bundled organization of sympathetic axons within the peroneal nerve and provide the anatomical basis for outcomes in microneurographic studies.

Choline acetyltransferase activity in collateral sprouting of peripheral nerve after surgical intervention: experimental study in rats.

The purpose of this study was to establish an assay of choline acetyltransferase (ChAT) activity to investigate the regeneration of injured peripheral nerve, repaired by end-to-end or end-to-side neurorrhaphy. Murine sciatic and peroneal nerves were exposed, and the peroneal nerve was transected at a site 5 mm from its ramification. For end-to-side neurorrhaphy, an epineurotomy producing a 5-x5-mm window was carried out on the tibial nerve, just above the level of gastrocnemius muscle ramification. The peroneal nerve stump was then sutured end-to-side to the tibial nerve window. For end-to-end neurorrhaphy, the peroneal stump was directly sutured end-to-end. ChAT activity was measured at a site distal to the peroneal stump at 1 to 3 months postoperatively, and the results were compared among four groups: 1) end-to-end neurorrhaphy group; 2) end-to-side neurorrhaphy group; 3) unrepaired group; and 4) positive controls. ChAT activity in the end-to-side neurorrhaphy yielded approximately two-thirds the value of the end-to-end neurorrhaphy, and more than half the value of positive controls at 3 months postoperatively. Histologic sections of the end-to-side and end-to-end sutured peroneal nerve demonstrated large numbers of myelinated axons and Schwann cells at the third postoperative month. All the results demonstrated that end-to-side neurorrhaphy is comparable to well-performed end-to-end neurorrhaphy, thus providing another option for surgical treatment of avulsion nerve injury and massive nerve defect.

Soma size and oxidative enzyme activity in normal and chronically stimulated motoneurones of the cat's spinal cord.

In normal adult cats we measured the density of staining for the activity of succinate dehydrogenase (SDH staining) in ventral horn cells of different sizes. The measurements were restricted to that part of the lumbar ventral horn (L6-L7) which is known to contain motoneurones of the peroneal nerve. A statistically significant tendency was found for the SDH staining to be denser in smaller than in larger neurones within the size range of a motoneurones (soma diameter greater than 40 microns). These results are consistent with recently published evidence for ventral horn cells of rats and qualitatively similar relationships between size and SDH staining have also been observed among skeletal muscle fibres (confirmed for mixed muscle of cat in present study). In hindlimb muscles, size as well as SDH staining are known to be markedly activity-dependent. We tested whether this is the case for peroneal motoneurones as well by analyzing the effects of chronic nerve stimulation on the properties of neurones within the appropriate region of the ventral horn. Prior to the final acute experiment, these cats had been subjected to a left-side dorsal rhizotomy and hemispinalization. By aid of a portable mini-stimulator, the left-side common peroneal nerve was activated by repetitive pulses during 50% of total time per day (intra-activity rate: 10, 20 or 40 Hz). After 8 weeks of such treatment, cell sizes as well as the densities of SDH staining showed hardly any differences between peroneal ventral horn cells of the experimental and control sides of the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraoperative nerve fascicle identification using choline acetyltransferase: a preliminary report.

One reason for failure of nerve recovery after suture or nerve grafting is the inappropriate matching of motor and sensory fibers. Methods used in attempting to solve this problem have either been unprecise, too time consuming, or unpleasant to the patient. Both experimentally and on cadaver samples, the level of choline acetylase activity is eight times higher in motor nerve fascicles than in sensory fascicles. In experimentally cut nerves, the ChAC activity remained high even after a period of 45 days. Thus it was possible to identify both ends of the motor and sensory fascicles in fresh injuries, and the proximal parts in old injuries. We have since used this method of intraoperative nerve identification in three patients. It has proved to be a rapid (70-80 minutes), viable technique for the immediate differentiation between proximal parts of motor and sensory nerve fascicles in cases of old nerve injuries. In contrast to our animal studies we found that the ChAC activity in the distal segment was still different for the various fascicles five months after transection. Presumably the present need for distal exploration to identify the "target organ" can be avoided.

On the kinetics and maximal capacity of the system for rapid axonal transport in mammalian neurones.

1. Rabbit peroneal nerves were incubated in vitro in two-compartment chambers. Step-gradients of temperature were established so that the proximal part of each nerve was slightly warmer than the distal part. After incubation, the distribution of dopamine-beta-hydroxylase (DBH) activity along the nerves was examined as an indication of the behaviour of rapid transport in adrenergic axons. 2. With temperature gradients of 5 and 8 degrees C, transport velocity in the proximal regions was expected from previous work to be, respectively, 1.5 and 2 times faster than in the distal regions. Exposing nerves to these gradients induced a significant increment in the concentration of DBH activity, beginning at the boundary between regions. This increment was up to 50% of the normal activity and it propagated distally at the velocity expected for transport at the local temperature. 3. A temperature gradient of 13 degrees C was expected to produce a threefold difference in transport velocity between proximal and distal regions. This gradient produced a slightly larger increment of DBH activity propagating distally, again at the expected velocity. However there was also a disproportionate accumulation of enzyme activity at the boundary between regions. Further increases in the temperature gradient did not enhance the size of the propagating increment but only the rate at which enzyme accumulated at the temperature boundary. 4. It was concluded that adrenergic nerves can transport between two and three times as much material per unit time as they normally do. The ability to increase the flux of material appeared to depend on increases in the concentration of material in motion. There was no indication that such increases led to significant changes in the velocity of transport.

Rapid orthograde and retrograde axonal transport of acetylcholinesterase as characterized by the stop-flow technique.

1. In rabbit peroneal nerves incubated in vitro at 37 degrees C, acetylcholinesterase (AChE) activity accumulated at both borders of a short region cooled to 5 degrees C. Accumulation was unaffected by concentrations of cycloheximide that inhibited 86% of local protein synthesis, as measured by the incorporation of [3H]leucine. It is probable that the local changes in enzyme activity during incubation reflected redistribution of the enzyme by axonal transport. 2. AChE activity accumulated almost three times faster at the proximal than at the distal border of cooled regions. This suggests that three times more enzyme is normally exported from nerve cell bodies than is returned to them, as though most of the transported AChE were degraded or secreted from distal parts of the neurones. The rates of accumulation of enzyme activity were consistent with average velocities of transport of 24 mm/day in the distal (orthograde) direction and 8.6 mm/day in the proximal (retrograde) direction. 3. When nerves that had been locally cooled for 3 hr were rewarmed to 37 degrees C, the accumulated AChE activity moved rapidly away from the cooled region. More than half of the activity appeared in a wave moving distally with a maximum velocity of 400 +/- 35 mm/day. A smaller wave moved proximally with a maximum velocity of 288 mm/day. 4. The observed behaviour of AChE is direct evidence that a small amount of this enzyme, probably less than 10% of the axonal content, is normally transported away from cell bodies as rapidly as any substance known. A still smaller amount of the enzyme is subject to an almost equally rapid retrograde transport. However, 85% of the AChE in peripheral nerve appears to be stationary, which probably explains why the average velocity of transport of this enzyme is so low.

On the origin and fate of external acetylcholinesterase in peripheral nerve.

1. Rabbit peroneal nerves were exposed to echothiophate, a quaternary ammonium inhibitor of acetylcholinesterase (AChE), and 217-AO, its tertiary analogue, in an attempt to characterize the localization of the enzyme. Although 217-AO readily inhibited AChE throughout the nerves, echothiophate spared significant amounts unless the tissues had first been homogenized. Notably, doses of echothiophate inhibiting 84% of the total AChE inhibited only 30% of the rapidly transported enzyme, suggesting that AChE was distributed between compartments differing greatly in their accessibility to this drug. 2. Since charged molecules penetrate cells poorly, it seemed likely that the more accessible compartment of AChE was external, perhaps consisting mainly of enzyme incorporated into the outer surface of the axolemma. If one assumes that the inhibition of the transported enzyme accurately reflected the inhibition throughout the inaccessible compartment, it can be calculated that external AChE comprised about 80% of the total. 3. The quasi-irreversible inhibition of AChE by echothiophate was used to probe the dynamics of the external enzyme. Locally exposing nerves to this drug in vivo markedly inhibited the AChE in a short region, which subsequently recovered with a half-time of about 5 days. Recovery appeared to reflect delivery of new enzyme into the inhibited region rather than spontaneous reactivation or local synthesis of AChE. Surprisingly, the zone of inhibition neither broadened nor moved noticeably for at least 8 days. This implies that external AChE is largely fixed in place and must be renewed locally, presumably by incorporation of rapidly transported enzyme from the internal compartment.