Altered spinal motoneurons in dogs with experimental hind-lamb rigidity.

Abstract

Lumbosacral motoneurons in dogs with hind-limb rigidity, produced by temporary lumbosacral ischemia 10 or more days earlier, exhibited altered excitability characteristics when subjected to several procedures under acute experimental conditions. The greater excitability was reflected by the smaller subliminal fringe fraction in motoneuron populations of such preparations, as compared to normal ones. The slower decay and different course of post-tetanic potentiation of the mono-synaptic reflex indicated altered characteristics also of the subliminal fringe population. Low frequency depression was either absent or reduced in such preparations. The extent, as well as decay rate, of augmentation of presynaptic discharges after an afferent tetanus was the same in the rigid as in the normal animal. Such augmented discharges, however, overcame the subnormality of many motoneurons of rigid animals during post-tetanic potentiation but not of normal ones. The minor fraction of the motoneuron population which can be anti-dromically inhibited, with or without post-tetanic potentiation, on the other hand, was not further reduced in the rigid animal.