Rationale: A glutamate-dopamine interaction has been implicated in the psychosis-like effects of glutamate N-methyl- D-aspartate (NMDA) receptor antagonists, such as phencyclidine and ketamine. However, recent imaging studies addressing striatal glutamate-dopamine interaction directly in vivo in man have been controversial.
Objectives: To examine whether the NMDA receptor antagonist ketamine in high subanesthetic concentrations decreases striatal [(11)C]raclopride binding potential in man. To further evaluate whether changes in striatal [(11)C]raclopride binding are associated with ketamine-induced behavioral effects.
Methods: The effect of computer-driven subanesthetic ketamine infusion on striatal dopamine release was studied in healthy male subjects using a controlled study design. Dopamine release was studied using positron emission tomography and the [(11)C]raclopride displacement paradigm. A conventional region of interest-based analysis and voxel-based analysis were applied to the positron emission tomography data.
Results: The average plasma ketamine concentration was 293+/-29 ng/ml. Ketamine did not alter striatal [(11)C]raclopride binding. Ketamine induced typical behavioral effects, such as hallucinations but there was no correlation between these effects and displacement of [(11)C]raclopride binding.
Conclusions: This controlled study indicates that ketamine does not decrease striatal [(11)C]raclopride binding. Striatal dopamine release is of minor importance in the psychosis-like effects of ketamine.