H.K.P. Feirabend

Antigenic compartmentation of the cerebellar cortex in the chicken (Gallus domesticus)

The chick is a well‐understood developmental model of cerebellar pattern formation,but we know much less about the patterning of the adult chicken cerebellum. Therefore an expression study of two Purkinje cell stripe antigens—zebrin II/aldolase C and phospholipase Cβ4 (PLCβ4)—has been carried out in the adult chicken (Gallus domesticus). The mammalian cerebellar cortex is built around transverse expression domains (“transverse zones”), each of which is further subdivided into parasagittally oriented stripes. The results from the adult chicken reveal a similar pattern. Five distinct transverse domains were identified. In the anterior lobe a uniformly zebrin II‐immunopositive/PLCβ4‐immunonegative lingular zone (LZ; lobule I) and a striped anterior zone (AZ; lobules II–VIa) were distinguished. A central zone (CZ; ∼lobules VIa–VIIIa,b) and a posterior zone (PZ; ∼lobules VIIIa,b–IXc,d) were distinguished in the posterior lobe. Finally, the nodular zone (NZ; lobule X) is uniformly zebrin II‐immunoreactive and is innervated by vestibular mossy fibers. Lobule IXc,d is considered as a transitional region between the PZ and the NZ, because the vestibular mossy fiber projection extends into these lobules and because they receive optokinetic mossy and climbing fiber input. It is proposed that the zebrin II‐immunonegative P3‐ stripe corresponds to the lateral vermal B zone of the mammalian cerebellum and that the border between the avian homologs of the mammalian vermis and hemispheres is located immediately lateral to P3−. Thus, there seem to be transverse zones in chicken that are plausible homologs of those identified in mammals, together with an LZ that is characteristic of birds. J. Comp. Neurol. 518:2221–2239, 2010.

Type grouping in skeletal muscles after experimental reinnervation: another explanation

Type grouping signifies clustering of muscle fibres of the same metabolic type, and is a frequent finding in reinnervated muscles. To elucidate the mechanism behind it, the rat sciatic nerve was either autografted or grafted with hollow synthetic nerve grafts. Twelve weeks later the number and fibre area of the type I and type II muscle fibres in the gastrocnemic and anterior tibial muscles were determined after ATP‐ase staining. The number and diameter of peroneal nerve fibres distal to the grafts were measured, and the number of Aα‐nerve fibres was derived. Nearly all nerve and muscle morphometrical parameters changed equally in both experimental groups. However, type grouping occurred frequently only after autografting, whereas the number of nerve fibres and the number of Aα‐nerve fibres increased in this group. Hence type grouping cannot be explained by increased intramuscular sprouting subsequent to a decrease in the number of innervating nerve fibres, as previously presumed. Regenerating axons branch along their course through the peripheral nerve. We propose that the probability of the occurrence of type grouping is related to the dispersion of sibling branches in the nerve. In the autograft, emerging branches are kept together by Schwann cell basal lamina scaffolds, in contrast to the hollow synthetic nerve grafts where the emerging branches become dispersed. Thus, in muscles reinnervated after autografting, the probability that nerve branches that arrive at a specific muscle territory are sibling branches is greater than after hollow tube grafting. Consequently, the probability that type grouping will occur is greater.

Electrophysiology and morphometry of the Aα- and Aβ-fiber populations in the normal and regenerating rat sciatic nerve

We studied electrophysiological and morphological properties of the Aa- and Ah-fibers in the regenerating sciatic nerve to establish whether these fiber types regenerate in numerical proportion and whether and how the electrophysiological properties of these fiber types are adjusted during regeneration. Compound action potentials were evoked from isolated sciatic nerves 12 weeks after autografting. Nerve fibers were gradually recruited either by increasing the stimulus voltage from subthreshold to supramaximal levels or by increasing the interval between two supramaximal stimuli to obtain the cumulative distribution of the extracellular firing thresholds and refractory periods, respectively. Thus, the mean conduction velocity (MCV), the maximal charge displaced during the compound action potential (Qmax), the mean firing threshold (V50), and the mean refractory period (t50) were determined. The number of myelinated nerve fibers and their fiber diameter frequency distributions were determined in the peroneal nerve. Mathematical modeling applied to fiber recruitment and diameter distributions allowed discrimination of the Aa- and Ah-fiber populations. In regenerating nerves, the number of Aa-fibers increased fourfold while the number of Ah-fibers did not change. In regenerating Aa- and Ah-fibers, the fiber diameter decreased and V50 and t50 increased. The regenerating Aa-fibers’ contribution to Qmax decreased considerably while that of the Ah-fibers remained the same. Correlation of the electrophysiological data to the morphological data provided indications that the ion channel composition of both the Aa- and Ah-fibers are altered during regeneration. This demonstrates that combining morphometric and electrophysiological analysis provides better insight in the changes that occur during regeneration.

Effect of nerve graft porosity on the refractory period of regenerating nerve fibers

OBJECT In the present study the authors consider the influence of the porosity of synthetic nerve grafts on peripheral nerve regeneration. METHODS Microporous (1-13 microm) and nonporous nerve grafts made of a copolymer of trimethylene carbonate and epsilon-caprolactone were tested in an animal model. Twelve weeks after surgery, nerve and muscle morphological and electrophysiological results of regenerated nerves that had grown through the synthetic nerve grafts were compared with autografted and untreated (control) sciatic nerves. Based on the observed changes in the number and diameter of the nerve fibers, the predicted values of the electrophysiological parameters were calculated. RESULTS The values of the morphometric parameters of the peroneal nerves and the gastrocnemius and anterior tibial muscles were similar if not equal in the rats receiving synthetic nerve grafts. The refractory periods, however, were shorter in porous compared with nonporous grafted nerves, and thus were closer to control values. CONCLUSIONS A shorter refractory period enables the axon to follow the firing frequency of the neuron more effectively and allows a more adequate target organ stimulation. Therefore, porous are preferred over nonporous nerve grafts.

White matter of the cerebellum of the chicken (Gallus domesticus): a quantitative light and electron microscopic analysis of myelinated fibers and fiber compartments.

Low magnification light microscopic examination of the white matter in appropriately stained avian and mammalian cerebellum reveals a mediolateral succession in which areas of large, heavily myelinated fibers alternate with areas containing nearly exclusively small fibers. A large fiber accumulation (LFA) and its medially adjoining small fiber area (SFA) form a fiber compartment, which, with related parts of cortex and central nuclei, constitutes a so‐called cerebellar module.