Antipsychotic Drug-Induced Muscle Rigidity and D2 Receptor Occupancy in the Basal Ganglia of the Rat

The relationship between tonic electromyographic (EMG) activity, an index of muscle rigidity, and D2 dopamine receptor occupancy is reported for a range of antipsychotic drugs. Raclopride, chlorpromazine and fluphenazine increased EMG when ~70% of striatal D2 receptors were occupied, whereas clozapine failed to increase EMG and had a maximum D2 occupancy of 54%. The findings for each drug are discussed in the context of their interactions with D2 and other neurotransmitter receptors.