Pores in synthetic nerve conduits are beneficial to regeneration.

Current opinion holds that pores in synthetic nerve guides facilitate nerve regeneration. Solid factual support for this opinion, however, is absent; most of the relevant studies assessed only morphological parameters and results have been contradictory. To evaluate the effect of pores, the rat sciatic nerve was either autografted or grafted with nonporous, macroporous (10-230 mum), and microporous (1-10 microm) biodegradable epsilon-caprolactone grafts. Twelve weeks later, the grafted nerves were resected, and the electrophysiological properties were determined in vitro. Subsequently midgraft-level sections were inspected, and peroneal nerve sections were evaluated morphometrically. Finally, the gastrocnemic and tibial muscle morphometrical properties were quantified. The microporous nerve graft performed much better than the nonporous and macroporous grafts with respect to most parameters: it was bridged by a free floating bundle that contained myelinated nerve fibers, there were more nerve fibers present distal to the graft, the electrophysiological response rate was higher, and the decrease in muscle cross-sectional area was markedly smaller. Hence, the present study demonstrates the beneficial effect of synthetic nerve guide pores on nerve regeneration, although with the caveat that not pores per se, but only small (1-10 microm) pores were effective.

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 Aalpha-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 Aalpha-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.

Morphometry of human superficial dorsal and dorsolateral column fibres: significance to spinal cord stimulation.

In spinal cord stimulation (SCS) large diameter cutaneous (Abeta) fibres in the dorsal columns (DCs) are activated and have an inhibiting effect on the transmission of pain signals by Adelta and C fibres from the corresponding dermatome(s). The largest Abeta fibres can be activated up to a maximum depth of about 0.25 mm in the DCs. No data are available on the distribution of the large fibres in this superficial human DC layer at the common SCS levels Th(10-11). Such data are indispensable to improve the predictive capability of a computer model of SCS. The whole myelinated fibre population in the superficial 300 microm of the dorsal column (DC(0-300)) at Th(10-11 )of two human subjects was morphometrically analysed. Some data was obtained from a third subject. The superficial dorsolateral column (DLC(0-300)) was included in this analysis because it was hypothesized that large dorsal spinocerebellar tract fibres could also be activated by SCS. Only very few fibres larger than 10.7 microm were found: a mean of 68 (0.5%) in DC(0-300) and 114 (2%) in DLC(0-300). Considering that the effect of SCS is primarily attributed to activation of these largest fibres, it is concluded that a surprisingly small average amount of 2.4 fibres per running 0.1 mm width and 6 fibres per segmental division of the DC is involved. Distinct mediolateral heterogeneity in fibre composition was found in both DC(0-300) and DLC(0-300). In the DC(0-300), the mean diameter of fibres > or =7.1 microm increases significantly by 5% from medial to lateral. Density (i.e. number of fibres per 1000 microm(2)) and frequency (i.e. percentage of a fibre size group compared to its parent population) of the large fibres increase significantly from medial to lateral in the DC(0-300). For fibres > or =10.7 microm, these parameters increase by 200 and 269%, respectively. It is concluded that the difference in stimulation threshold of large Abeta fibres in the median and lateral DC can be mainly attributed to the absence and presence, respectively, of collaterals at the stimulation site. Marked differences were found between DC(0-300) and DLC(0-300). The largest DLC(0-300) fibres (> or =10.7 microm) have a 320% higher frequency and a 473% higher density. Their mean diameter is, however, only 2% larger. The largest DLC(0-300) fibres are not likely to be recruited by SCS, since they are not larger than their DC(0-300) counterparts, they lack collaterals (which would reduce the threshold stimulus substantially) and they are more remote from the stimulation electrode.