Investigation of Basal Ganglia Function and Intrinsic Dopamine Release by Positron Emission Tomography

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To investigate the role of nigrostriatal dopamine system in performing a skilled complex motor task without leaning such as writing, we measured endogenous dopamine release in human brain with ^<13>C-raclopride (RAC) and PET.We studied six right-handed healthy volunteers (ages 22.0±1.7 years). After an intravenous injection of RAC, a 60 minites dynamic scan was performed. Each subject participated in RAC-PET twice on the same day (scan interval 145.0±35.2 minutes) under two different conditions ; during hand writing and at rest in balanced order. In the writing condition, the subjects was asked to dictate sentences as quick as possible on a computer-controlled writing pad with pen tool using their right hand. In resting condition, the subject was asked to watch the display without any movement. Endgeneous dopamine release was estimated indirectly based on the occupancy model, from the difference of the binding potential (BP) of PAC in two different conditions. The same subjects also participated in H_<2>^<15>O-PET with the same paradigm to evaluate the regional cerebral activation with the task in terms of regional cerebral blood flow change.The left striatum was activated significantly with H_<2>^<15>5O-PET study with writing task. In the same region, the binding potentials of RAC was significantly reduced by dictation task, thus, the intrinsic dopamine release was considered to be accelerated by the task. The activated region located in the ventro-caudal portion of the putamen which we previosly reported to be corresponding to hand area in the sometotopic organization in the basal ganglia. This result demonstrated the ability of indirect measurement method of intrinsic dopamine release by RAC-PET in physiological condition. Our results are the first report of activation of dopaminergic neurons by a skilled voluntary monements.