Degeneration of Serotonin Neurons Triggers Spasticity in Amyotrophic Lateral Sclerosis

Spasticity occurs in a wide range of neurological diseases, including neurodegenerative diseases, after trauma, and after stroke, and is characterized by increased reflexes leading to muscle hypertonia. Spasticity is a painful symptom and can severely restrict everyday life, but might also participate in maintaining a low level of motor function in severely impaired patients. Constitutive activity of the serotonin receptors 5‐HT2B/C is required for the development of spasticity after spinal cord injury and during amyotrophic lateral sclerosis (ALS). We sought here to provide direct evidence for a role of brainstem serotonin neurons in spasticity.