Intracellular recordings were made from facial motoneurons of anesthetized rats during systemic administration of 5-methoxy-N,-N-dimethyltryptamine (5-MeODMT) and p-chloroamphetamine (PCA), drugs which elicit the behavioral serotonin syndrome. Both drugs caused a slow depolarization, increased input resistance, and increased excitability of facial motoneurons. These changes are identical to...