Cerebral blood flow (CBF) during dynamic exercise has never been examined quantitatively using positron emission tomography (PET). This study investigated changes in CBF that occur over the course of a moderate, steady-state cycling exercise. Global and regional CBF (gCBF and rCBF, respectively) were measured using oxygen-15-labeled water (H215O) and PET in 10 healthy human subjects at rest (Rest), at the onset of exercise (Ex1) and at a later phase in the exercise (Ex2). At Ex1, gCBF was significantly (P<0.01) higher (27.9%) than at Rest, and rCBF was significantly higher than at Rest in the sensorimotor cortex for the bilateral legs (M1Leg and S1Leg), supplementary motor area (SMA), cerebellar vermis, cerebellar hemispheres, and left insular cortex, with relative increases ranging from 37.6% to 70.5%. At Ex2, gCBF did not differ from Rest, and rCBF was significantly higher (25.9% to 39.7%) than at Rest in only the M1Leg, S1Leg, and vermis. The areas showing increased rCBF at Ex1 were consistent with the central command network and the anatomic pathway for interoceptive stimuli. Our results suggest that CBF increases at Ex1 in parallel with cardiovascular responses then recovers to the resting level as the steady-state exercise continues.

Dynamic exercise elicits fluctuations in blood pressure (BP) and cerebral blood flow (CBF). This study investigated responses in BP and CBF during cycling exercise and post-exercise hypotension (PEH) using positron emission tomography (PET). CBF was measured using oxygen-15-labeled water (HO) and PET in 11 human subjects at rest (Rest), at the onset of exercise (Ex1), later in the exercise (Ex2), and during PEH. Global CBF significantly increased by 13% at Ex1 compared with Rest, but was unchanged at Ex2 and during PEH. Compared with at Rest, regional CBF (rCBF) increased at Ex1 (20~42%) in the cerebellar vermis, sensorimotor cortex for the bilateral legs (M1 and S1), insular cortex and brain stem, but increased at Ex2 (28~31%) only in the vermis and M1 and S1. During PEH, rCBF decreased compared with Rest (8~13%) in the cerebellum, temporal gyrus, piriform lobe, thalamus and pons. The areas showing correlations between rCBF and mean BP during exercise and PEH were consistent with the central autonomic network, including the brain stem, cerebellum, and hypothalamus (R=0.25-0.64). The present study suggests that higher brain regions are coordinated through reflex centers in the brain stem in order to regulate the cardiovascular response to exercise.

( 11 C-ITMM) is a potential radioligand for mapping metabotropic glutamate receptor type 1 (mGluR1) in the brain by PET. The present study was performed to determine the safety, distribution, radiation dosimetry, and initial brain imaging of 11 C-ITMM in healthy human subjects. Methods: The multiorgan biodistribution and radiation dosimetry of 11 C-ITMM were assessed in 3 healthy human subjects, who underwent 2-h whole-body PET scans. Radiation dosimetry was estimated from the normalized number of disintegrations of source organs using the OLINDA/EXM program. Five healthy human subjects underwent 90-min dynamic 11 C-ITMM scans of brain regions with arterial blood sampling. For anatomic coregistration, T1-weighted MR imaging was performed. Metabolites in plasma and urine samples were analyzed by high-performance liquid chromatography. 11 C-ITMM uptake was assessed quantitatively using a 2-tissue-compartment model. Results: There were no serious adverse events in any of the subjects throughout the study period. 11 C-ITMM PET demonstrated high uptake in the urinary bladder and gallbladder, indicating both urinary and fecal excretion of radioactivity. The absorbed dose (mGy/MBq) was highest in the urinary bladder wall (13.2 6 3.5), small intestine (9.8 6 1.7), and liver (9.1 6 2.0). The estimated effective dose for 11 C-ITMM was 4.6 6 0.3 mSv/MBq. 11 C-ITMM showed a gradual increase of radioactivity in the cerebellar cortex. The total distribution volume in the brain regions ranged from 2.61 6 0.30 (cerebellar cortex) to 0.52 6 0.17 (pons), and the rank order of the corresponding total distribution volume of 11 C-ITMM was cerebellar cortex . thalamus . frontal cortex . striatum pons, which was consistent with the known distribution of mGluR1 in the primate brain. The rate of 11 C-ITMM metabolism in plasma was moderate: at 60 min after injection, 62.2% 6 8.2% of the radioactivity in plasma was intact parent compound. Conclusion: The initial findings of the present study indicated that 11 C-ITMM PET is feasible for imaging of mGluR1 in the brain. The low effective dose will permit serial examinations in the same subjects.