The rat sciatic nerve was crushed at the level of the mid-thigh (testing lesion), and the rate of outgrowth of the regenerating adrenergic axons was examined in the nerve. Two methods were used: (1) counts of axons containing norepinephrine demonstrable by histofluorescence; (2) measurement of the specific uptake of [3H]d,l-norepinephrine in vitro. In order to determine whether a prior nerve lesion had any effect on the outgrowth rate, all of the animals were subjected, two weeks prior to the testing lesion, to either a transection of the tibial branch of the sciatic nerve at the level of the ankle (conditioning lesion) or a sham operation. Counts of fluorescent axons made 3 days after the testing lesion showed that at 1.40 mm proximal to the lesion, the numbers of axons in both the conditioning-lesion group and the sham-operated group were not significantly different from non-lesioned animals. At a level 0.35 mm proximal to the testing lesion, counts in both groups were about 75% greater than at 1.40 mm, indicating that axonal sprouting had occurred. At 1.40 mm distal to the testing lesion, the numbers of axons had decreased by 9% in the sham-operated group, and by 24% in the group that had been subjected to a conditioning lesion (P < 0.05). Farther distally, axon counts in both groups showed an approximately exponential decrease with distance from the testing lesion, with the animals subjected to a conditioning lesion showing consistently lower values. These results suggest that the conditioning lesion caused some impairment in axonal outgrowth of adrenergic neurons. The specific uptake of [3H]d,l-norepinephrine was measured 3 and 7 days after the testing lesion. The axonal component of uptake showed an approximately exponential decay with distance from the testing lesion; the leading edge of axonal uptake advanced at a rate of 3.9 ± 0.5 mm/day (S.E.) in the sham-operated group compared to 1.8 ± 0.6 mm/day (S.E.) in the conditioning-lesion group (P < 0.001). These results are also consistent with the conclusion that a conditioning lesion impairs the outgrowth of regenerating adrenergic axons.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Clinical Neurology
- Developmental Biology