Endoneurial fluid pressure in wallerian degeneration.

Endoneurial fluid pressure (EFP) was recorded by an active, servo-null pressure system after a glass micropipette was inserted into rat sciatic nerve undergoing wallerian degeneration. The lesions were produced by crushing the left sciatic nerve of the anesthetized animal at its point of entry into the thigh. Eighty-four animals were employed in this experiment, in which EFP was recorded from sham-operated rats and other controls as well as from rats with wallerian degeneration. The experiment was designed so that EFP could be recorded from 2 or more experimental animals at daily intervals starting at day 0 and concluding on day 28. Pressure progressively increased during the first week, reaching a peak elevation four to five times normal. The subsequent decline in EFP was more gradual, with values approaching normal during the third week after injury. Linear regression analysis showed the progressive increase in EFP to be statistically significant (p less than or equal to 0.01). To determine the time at which EFP was maximum, we used the Marquardt computer algorithm for lease-squares estimation of nonlinear variables. By this procedure the peak value for EFP occurred at six days. These biophysical observations were correlated with subsequent microscopic examination of 1 mu thick sections of Araldite-embedded sciatic nerve. Microscopy confirmed the presence of wallerian degeneration associated with edema, which was observed in every instance of elevated EFP.