Maximal regeneration distance. How far can a peripheral axon regenerate?

Peripheral nerves of the fore- and hindlimbs of 20 rats were induced to regenerate over double and triple of their original lengths through consecutive orthograde and retrograde (zigzag) anastomoses along parallel nerves of the same limb. Morphological changes were followed on longitudinal sections of the whole-mount composite nerves by several histological techniques. Regeneration regularly took place along this pathway. The regenerated axonal segments were intensively remyelinated, demonstrating the capacity of the spinal neurons to produce and maintain disproportionately long axonal processes. These observations may be relevant for reconstructive neurosurgery when very long peripheral nerve gaps have to be bridged.

The geomagnetic field: a factor in cellular interactions? I. Magnetism and Schwann cell-axon interaction in the peripheral nerves of the newborn rat.

Axonal ensheathment and myelination, one form of axon-sheath cell interaction, was studied under normal earth magnetism, in the absence of terrestrial magnetic field, and under a 5 G (0.0005 T) magnetic field. Results indicate that the geomagnetic field is necessary for the fundamental biological activity of axonal ensheathment and myelination. The exact mechanism of action remains obscure.

Structural and regenerative changes in deafferented and deefferented ulnar nerves.

Both brachial plexuses of Wistar rats were deafferented or deefferented by disrupting their dorsal or ventral roots. At the same time, the ulnar nerves were transected and sutured. A sham group and another group in which the upper (C-5) and lower (T-1) spinal nerves were transected on both sides were included as control groups. Clear differences in the ulnar nerve regeneration rate were found between the deafferented and the deefferented animals. Ultrastructural studies disclosed signs of transient axonopathy in the nontransected fibers of the proximal segment of the ulnar nerve. The possible role of bioelectricity in the genesis of these changes is discussed.

Polarization of nerve regeneration (electrotaxis).

Regeneration of both median nerves was studied in the rat in three different experimental models of centrocentral anastomosis through an interposed segment of pre-degenerated tibial nerve after denervation by spinal root transection. Different patterns of regeneration were observed in the anastomoses. These patterns suggest a bio-electrical polarity related to neuronal function. The present experimental model appears to offer a new opportunity to study neuronal regeneration under the influence of defined bioelectrical conditions.

Nerve regeneration in synthetic and autogenous interfascicular grafts. II. Morphometric analysis.

Cross-sectional areas at different levels, number of axons, maximal diameters, and number and maximal diameters of vessels were measured comparing autologous transplants with synthetic implants and nonlesion controls in a rat nerve regeneration model. The corresponding electrophysiologic data have been reported earlier in this journal. Although similar in many aspects, transplants led to the overall more reliable and slightly superior results, still lacking a substantial percentage of numerical qualities found in normal nerve, at least within the 3-month regeneration in this study.

Evoked muscle action potentials from regenerated rat tibial and peroneal nerves: synthetic versus autologous interfascicular grafts.

To compare peripheral nerve regeneration across bridging synthetic tubular implants with ordinary autologous transplantation, we recorded evoked muscle action potentials 3 months after transection, following direct stimulation of rat tibial and peroneal nerves. Significantly, with autologous transplantation we were able to evoke compound muscle action potentials in all but one case (this having a 15-mm gap). Pooling the groups together, compound action potentials could be recorded in 15 of 45 cases that had regenerated through 13- to 16-mm gaps. Potentials in the synthetic implant-treated group tended to show more temporal "scattering" in the late phases of the EMG response. No differences were found in compound muscle action potential amplitudes and duration, or terminal motor conduction velocity, between both experimental groups, between different artificial tubuli, between different gap lengths, or between the peroneal and tibial nerves. The overall values were remarkably lower than in nontransected controls, about 25% of the compound muscle action potential normal amplitude voltage and 60% of the terminal motor conduction velocity.

Factors predicting pituitary adenoma invasiveness in acromegalic patients.

Forty-four adult acromegalic patients carrying growth hormone-producing pituitary macroadenomas were investigated with neuroradiological and endocrinological techniques. Plasma growth hormone and somatomedin-C levels were repeatedly measured before surgical removal of tumors and during the follow-up period. Twenty-five patients presented preoperatively with an invasive adenoma that involved the cavernous sinus (CS). Diagnosis of tumor invasivity was made according to distinct neuroradiological criteria and was confirmed or rejected during surgery Significantly higher basal growth hormone levels were found in patients with CS invasion than in cases without tumor growth in the CS. Evidence is presented that plasma growth hormone level in acromegalics is a more sensitive indicator for predicting tumor invasiveness than somatomedin-C. Growth hormone basal values before surgery and the extent of their decrease after removal of tumor correlate with adenoma growth in the parasellar compartments and should be used as a prognostic factor to aid in planing adjuvant tumor treatment.