Assessment of Central Dopamine Release by Exercise in Hunian in vivo.

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Assessment of central dopamine (DA) release in vivo in human using D_2 PET mapping is a novel technique for neuroscience. We applied this technique to assess DA release by enduring ergometer exercise. We hypothesized that failure of the previous studies to reveal DA release by exercise may be from technical problems. They measured D_2 receptor distribution after completion of exercise. By using a modified ergometer that allows bicycling while lying on PET couch, we carried out raclopride PET simultaneously during exercise. To minimize head movements due to bicycling, we used a plastic face mask for each subject developed for conformal radiotherapy. In addition head movements were mathematically corrected using an image alignment algorithm equipped in SPM5 (Functional Imaging Laboratory, London). Eight healthy male volunteers aged 21.4±2.0 (s.d.) years collaborated the study. They made an ergometer exercise of moderate intensity (VO2Max 35〜60%) for 50 minutes. [^<11>C]Raclopride was injected intravenously at 20 minutes after start of the exercise and then a sequential PET images were collected using 3D positron camera (Shimadzu 2400W) with scatter correction. ROIs were placed at the caudate, putamen, and cerebellum of each side. Choosing cerebellum as a reference tissue we calculated raclopride binding potential (BP) to D_2 receptors using the simplified reference tissue model (Lammersma and Gunn), Logan noninvasive model, and Ichise model. The BP in the striatum were significantly reduced at exercise (-12.9〜17.0%, P<0.01) when compared to a control condition (lying on PET couch only). The reductions were almost similar between the caudate and the putemen and between hemispheres. The results strongly support DA release at this ergometer exercise condition. Dopamine release in our brain may explain refreshing feeling after exercise and its habituations.