Recovery of Fibre Numbers and Diameters in the Regeneration of Peripheral Nerves

Axotomy-induced changes in rabbit hindlimb nerves and the effects of chronic electrical stimulation

“…7, 8). These results confirm and extend our earlier electrophysiological studies of axotomized cat nerves (Davis et al, 1978) and show further that the shift from a normal bimodal to a unimodal distribution of fiber diameters (Gutmann and Sanders, 1943;Aitken and Thomas, 1962;Carlson et al, 1979;Dyck et al, 198 1;Gillespie and Stein, 1983;Risling et al, 1983) occurs very rapidly after axotomy. They also show that the rapid decrease in CAP amplitude and increase in latency is concomitant with the loss of the larger peak of the bimodal distribution of nerve fibers.…”

“…7). As first described by Gutmann and Sanders (1943), the bimodal distributions become unimodal as the numbers of large fibers decline ( Figure 7). The extent of atrophy and the progression with time are readily apparent when the distributions are plotted as cumulative frequency histograms and compared to the normal fiber distribution plotted as circles in Figure 7B.…”

“…Sample areas were photographed and printed at magnification of 1200-2000 x for digitization of the outer perimeter of the myelinated axons. Total fiber numbers in the CP nerve were calculated by counting fibers in four to eight sample photographs of the nerve cross section at the same magnification and by multiplying the average count by the ratio of the area of the whole nerve to the area of the sample counted (Table 1; see also Gutmann and Sanders, 1943). Samples of between 700 (15% of the total) and 5094 (100% of the total) nerve fibers were examined from randomly selected areas of the nerve cross section for representation of the fiber size distribution.…”

“…Morphological changes in the cell body, the chromatolytic changes, include decentralization of the nucleolus and dissolution of Nissl substance (Nissl, 1892;Liebermann, 197 1). Axotomized nerve fiber caliber decreases (Gutmann and Sanders, 1943;Kreutzberg and Schubert, 197 1;Carlson et al, 1979;Risling et al, 1983) concurrent with a decline in conduction velocity (Cragg and Thomas, 196 1;Milner et al, 198 1;Gillespie and Stein, 1983). Molecular studies have more recently provided direct evidence for a switch in gene expression after axotomy: levels of messenger RNA and expression of neurotransmitters, rate limiting enzymes for transmitter synthesis and neurofilament (NF) protein decline following axotomy (Grafstein and McQuarrie, 1978;Gordon, 1983;Hoffman et al, 1984;Woolf et al, 1984;Tetzlaff et al, 1988a); other proteins associated with slow axonal transport, actin and tubulin, are upregulated (Hall et al, 1978;Hoffman and Lasek, 1980;Neumann et al, 1983;Sinicropi and McIlwain, 1983;Tetzlaff et al, 1988a), and the axotomized neurons express novel growth-associated proteins (Heacock and Agranoff, 1976;Skene and Willard, 198 1;Kalil and Skene, 1986;Tetzlaff et al, 1988aHoffman, 1989; for review, see Skene, 1989).…”

Is Standardization of Nerve Graft Groups Necessary for Experimental Studies?

“…Fol lo wing im me di a te ne u rorr haphy or ner ve graf ting, axons re en ter the dis tal stump and re gene ra te down the pe ri ne u ri al and en do ne u ri al tubes, 19 but the in comp le te re turn in fi ber di a me ter se en may com pro mi se sub se qu ent con duc ti ve 20 and func ti o nal 21 pro per ti es. We do cu men ted he re that in dis tant ner ve graft gro up, the dis tri bu ti on of fiber di a me ter was cle arly uni mo dal and fre qu ency was much hig her (43.4%) for small di a me ter fi bers (bet we en 2 and 3 μm) com pa red to tho se ob ser ved in ort ho to pic and in ver ted nerve graft gro ups.…”