[I-123]IBZM SPET analysis of dopamine D-2 receptor occupancy in narcoleptic patients in the course of treatment

Elevated levels of central D-2 dopamine receptors were found on postmortem examination in cases of human narcolepsy, In vivo investigations using positron emission tomography (PET) and single photon emission tomography (SPET) found no changes of D-2 binding in the striatal structures. To investigate whether the elevated D-2 receptors in postmortem investigations are due to long-term treatment effects, we applied I-123-labeled (S)-2-hydroxy-3-iodo-6-methoxy-([1-ethyl-2-pyrrolidinyl]methyl) benzamide (IBZM) ([I-123]IBZM, a highly selective CNS D2 dopamine receptor ligand) and SPET in narcoleptic patients in the course of treatment with stimulants and/or antidepressants. Before treatment we found no changes in D-2 binding in 10 patients (in comparison to 10 normal controls). After treatment (performed in five patients for 3 months) we found changes in D-2 binding in four of them, indicating that the results of the postmortem studies could have been influenced by long-term medications. Human narcolepsy seems not to be related to a striatal O-2 dopaminergic disturbance.