Electrophysiological studies with the spastic mutant mouse.

Electromyographic (EMG) studies were carried out with the genetically spastic mouse (spa, autosomal recessive), obtained from matings of B6C3a/a, spa/+ heterozygotes. Spastic homozygotes exhibited high amplitude repetitive EMG bursts during spontaneous activity. Following an electrical stimulus to hindlimb or forelimb, high amplitude stereotyped EMG bursts were recorded from contralateral limbs in spastic mice, but were not observed in phenotypically unaffected littermates or normal C57BL/6J mice. The timing and latency of this stereotyped response to an electrical stimulus was consistent with the participation of spinal cord neuronal pathways. In normal C57BL/6J mice the administration of strychnine (0.65 mg/kg), but not picrotoxinin (up to convulsant doses), reproduced all of the behavioral and EMG features observed in spastic homozygotes. We hypothesize that the symptoms in the spastic mutant may result from a deficiency of strychnine-sensitive (presumably glycinergic) inhibition in the spinal cord.