Imaging extrastriatal dopamine D2 receptor occupancy by endogenous dopamine in healthy humans

The effect of endogenous dopamine on in vivo measurement of dopamine D-2 receptors in extrastriatal regions (thalamus and temporal cortex) was evaluated with single photon emission computed tomography and the high affinity ligand [I-123]epidepride by comparing the binding potential before and after acute dopamine depletion. Dopamine depletion was achieved by per-oral administration of 5.5 g/70 kg body weight alpha-methyl-para-tyrosine given in 37 h. The alpha-methyl-pam tyrosine treatment increased the binding potential significantly in the temporal cortex (13 +/- 15%, P = 0.036) but not in the thalamus (2 +/- 9%). The increase of the binding potential in the temporal cortex correlated strongly with the increase of dysphoric mood evaluated by the Positive and Negative Symptom Scale (PANSS) (rho = 0.88, P = 0.004). These results imply that [I-123]epidepride, coupled with acute dopamine depletion might provide estimates of synaptic dopamine concentration. (C) 2000 Elsevier Science B.V. AU rights reserved.