Psychomotor slowing, negative symptoms and dopamine receptor availability - An IBZM SPECT study in neuroleptic-treated and drug-free schizophrenic patients

Anhedonia and psychomotor slowing in schizophrenia have been attributed to a dysfunction of dopaminergic neurotransmission. To differentiate between disease and drug-induced negative symptoms, we examined eight drug-free and eight neuroleptic-treated schizophrenic patients. Positive and negative symptoms and extrapyramidal side effects were assessed using standardized rating scales (PSAS, AMDP, SANS). 'Reaction time' and 'motor speed' were measured using a computer-aided system and striatal dopamine D₂/D₃ receptor availability was assessed using [I-123]IBZM SPECT. Psychomotor reaction time, parkinsonism, affective flattening and avolition were increased in treated patients relative to the untreated cohort and were negatively correlated with dopamine D₂/D₃ receptor availability. Significant positive correlations were found between parkinsonism and affective flattening and between psychomotor slowing and avolition. Positive symptoms were not significantly associated with striatal IBZM binding. These findings support the hypothesis that neuroleptic-induced dopamine D₂/D₃ blockade in the striatum can mimic certain negative symptoms, such as affective flattening and avolition, and indicates that psychomotor testing may be helpful in differentiating between disease and drug-induced negative symptoms.