Acute Exercise Releases Endogenous Dopamine In The Human Hippocampus

Physical exercise has beneficial effects on the brain function including hippocampus-dependent function (e.g. memory). However, mechanistic understanding of how physical exercise stimulates the hippocampus is elusive in humans. In particular, neuromodulation induced by physical exercise has not been determined yet. Here, we tested the hypothesis that acute exercise releases endogenous dopamine (DA) in the human hippocampus, which potentially contributes to improvements in the hippocampus-dependent function. PURPOSE: The purpose of this study was to investigate whether acute exercise releases endogenous DA in the hippocampus using positron emission tomography (PET) with [11C]raclopride. METHODS: Sixteen male participants (age: 22.3 ± 0.7 yrs, height: 1.73 ± 0.06 m, mass: 62.5 ± 6.3 kg, peak oxygen uptake: 42.1 ± 5.3 mL/kg/min) completed the Exercise and Control conditions in a randomized order. In the Exercise condition, the participants cycled in a supine position at 35% peak oxygen uptake (61 ± 14 W) for 40 minutes. In the Control condition, they remained a supine position. Parametric images of DA D2 receptor binding potential (BPND) were generated from the averaged emission images (summation of images obtained between 6 and 90 min). BPND values were obtained for the bilateral hippocampus in each condition. Endogenous DA release in response to acute exercise was evaluated by the differences between the conditions. RESULTS: We observed that BPND was greater in the Control condition as compared with the Exercise condition (Control: 0.269 ± 0.083 vs. Exercise: 0.232 ± 0.073, p = 0.009). Reductions in BPND in the Exercise condition indicate that endogenous DA was released by acute exercise. CONCLUSION: The present findings suggest that acute exercise releases endogenous DA in the human hippocampus. Our novel findings extend our mechanistic understanding of neuromodulation in the hippocampus and emphasize the importance of the DA systems for the hippocampal function. Supported by: This study was supported by the Japan Society for the Promotion of Science KAKENHI (16H03230 & 22H03493) and Supply Platform of Short-lived Radioisotopes, supported by JSPS Grant-in-Aid for Scientific Research on Innovative Areas, Grant Number 16H06278.