Antidromic discharges in dorsal roots of decerebrate cats - I. Studies at rest and during fictive locomotion

Spontaneous rhythmic antidromic discharges have previously been recorded in proximal stumps of cut dorsal roots during locomotion (real and fictive). The goals of the present study were to elucidate (1) whether both orthodrom ic and antidromic discharges occur in the same dorsal root filament and (2) whether orthodromic discharges have an influence upon antidromic discharge s of units in the same filament. Unitary activity was recorded in 70 uncut dorsal root filaments (L6-S1) in 15 decerebrate cats using bipolar Ag/AgCl electrodes. Spikes with similar wave shapes were considered to represent th e activity of single units. Spike-triggered averaging (STA), local anaesthe sia and transection of filaments were used to determine the direction of pr opagation of spikes. Spikes with different initial electrical polarities we re found in most of the filaments and shown to propagate in opposite direct ions at rest and during fictive locomotion. On average, there were 38% +/- S.D. 23% antidromically discharging units per filament and their mean condu ction velocity was 55 m/s +/- S.D. 25 m/s. After blocking orthodromic activ ity of the whole filament by a transection or local anesthesia applied dist ally to the recording site, changes were seen in the antidromic discharges of some units suggesting that spontaneous orthodromic discharges normally s een in the filament may influence the antidromic discharges of some units. Moreover, out of 27 antidromic units recorded during fictive locomotion, 12 were rhythmically modulated with peak discharges occurring in various part s of the locomotor cycle. We conclude that, in uncut dorsal soots, there is a normal coexistence of spontaneous orthodromic and antidromic discharges revealed by STA and that there is an interaction between spontaneous orthod romic and antidromic discharges. (C) 1999 Elsevier Science B.V. All rights reserved.