Functional anatomy of L-5-hydroxytryptophan-induced myoclonus in the guinea pig

Myoclonus was induced in guinea pigs in a dose-dependent manner by intraperitoneal injection of L-5-hydroxytryptophan (L-5-HTP). At a dosage of 400 mg per kilogram, all animals developed myoclonus. Autoradiographic analysis, using the [14C]-deoxyglucose method, showed increased glucose utilization in the ventral and ventral anterior thalamic nuclei and decreased glucose utilization in the cortex and molecular layer of the hippocampus. These changes were dose-dependent and occurred to a lesser extent in both myoclonic and non-myoclonic guinea pigs given an ED50 of L-5-HTP, demonstrating that the autoradiographic changes are not dependent on the presence of myoclonus. We believe that the thalamus is the final common pathway for the expression of myoclonus induced by L-5-HTP.