Deficit of inhibitory glycine receptors in spinal cord from Peruvian Pasos: evidence for an equine form of inherited myoclonus.

Inherited myoclonus in Poll Hereford calves and spasticity in the spastic mouse (spa/spa) are characterized by myoclonic jerks of the skeletal musculature which occur spontaneously and in response to sensory stimuli, symptoms resembling those in subconvulsive strychnine poisoning. The primary, biochemical defect in these myoclonic animals is a deficit of inhibitory glycine receptors in the central nervous system. We now report the occurrence of similar stimulus-induced myoclonus in individual, pure-bred Peruvian Paso horses and an associated, specific deficiency in the density of [3H]strychnine binding to inhibitory glycine receptors sites in spinal cord of these animals. Specificity of the deficit was confirmed by a demonstrated lack of change in the density of several other receptor types in affected spinal cord, including muscarinic receptors and GABAA/benzodiazepine receptors. In light of the existence of genetically-inherited myoclonus in other species, these results suggest the occurrence of an equine form of the disorder.