Retrograde changes in the nerve fibers of the dorsal spinocerebellar and spinocervical tracts in the cat

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Abstract
The potential retrograde changes that occur in the proximal segment of transected nerve fibers found in the region of the spinocervical tract (SCT) and in the region of the dorsal spinocerebellar tract (DSCT) after unilateral dorsolateral column (DLC) lesions were studied in kittens and adult cats. Nerve fibers in the region of the SCT and DSCT in the spinal segments caudal to the lesion were studied in transverse sections of Epon embedded material that had been fixed by vascular perfusion with a 4% buffered paraformaldehyde solution, post‐fixed in osmium tetroxide, and stained with Azur II‐methylene blue. T8 level DLC lesions in the 10‐week old kitten resulted in a 14 to 25% decrease in mean fiber diameter in the SCT fibers (≥ 5 μ) of the T13 level. Retrograde fiber degeneration occurred in the small and large caliber fibers of the DSCT. A 15 to 30% decrease in mean fiber diameter occurred in the DSCT fibers (≥ 5 μ). The fiber density of the DSCT decreased by 20 to 30% and this could be correlated with a 20% loss of class C neurons (Loewy, '70) and a severe atrophy affecting the remaining 80% of the surviving class C neurons in the L3 segment. Mid‐cervical DLC lesions in the 10‐week old kitten resulted in a 10% decrease in mean fiber diameter in the SCT fibers (≥ 5 μ), a 15% decrease in mean fiber diameter in the DSCT fibers (≥ 5 μ), and no change in fiber density could be determined despite the finding that these lesions produced about a 10% loss of class C neurons. A T1 level lesion in a 20‐week old kitten produced no change in the SCT fibers suggesting that the changes seen in the 10‐week old kitten after midcervical lesions were probably age‐dependent changes. A 20% decrease in mean fiber diameter (≥ 5 μ) and a 6% decrease in fiber density was detected in the DSCT. T13‐L1 level DLC lesions in the adult cats resulted in degeneration of some of the large and medium size fibers in the DSCT which was most noticeable at 20 to 25 days after surgery. DLC lesions did not cause degenerative changes in the SCT fibers 5 to 25 days after surgery.