Physiological studies of the dying-back phenomenon. Muscle stretch afferents in acrylamide neuropathy

(1) The responses of 1,001 medial gastrocnemius afferents with conduction velocities of 24-126 m/sec have been studied in cats with experimental acrylamide neuropathy. (2) Many units which conducted at velocities indicating that they innervated muscle stretch receptors failed to discharge during muscle stretch or contraction. In animals with mild neuropathy 10 per cent of 366 units were non-responsive. In animals with moderate or severe neuropathy the proportion of non-responsive units was 68 per cent of 315 fibres and 89 per cent of 320 fibres respectively. Group I fibres were involved to a greater extent than Group II fibres. (3) The distributions of identified functioning units with respect to conduction velocity were normal, indicating that acrylamide did not produce conduction slowing before failure of function. (4) Electrophysiological and histological findings indicate that acrylamide initially produces failure of impluse conduction and subsequent fibre breakdown in the terminal axon while normal impulse conduction is preserved more proximally.