Brain Glycogen Decreases During Intense Exercise Without Hypoglycemia: The Possible Involvement of Serotonin
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Brain glycogen stored in astrocytes, a source of lactate as a neuronal energy source, decreases during prolonged exercise with hypoglycemia. However, brain glycogen dynamics during exercise without hypoglycemia remain unknown. Since intense exercise increases brain noradrenaline and serotonin as known inducers for brain glycogenolysis, we hypothesized that brain glycogen decreases with intense exercise not accompanied by hypoglycemia. To test this hypothesis, we employed a well-established acute intense exercise model of swimming in rats. Rats swam for fourteen 20 s bouts with a weight equal to 8 % of their body mass and were sacrificed using high-power (10 kW) microwave irradiation to inactivate brain enzymes for accurate detection of brain glycogen and monoamines. Intense exercise did not alter blood glucose, but did increase blood lactate levels. Immediately after exercise, brain glycogen decreased and brain lactate increased in the hippocampus, cerebellum, cortex, and brainstem. Simultaneously, serotonin turnover in the hippocampus and brainstem mutually increased and were associated with decreased brain glycogen. Intense swimming exercise that does not induce hypoglycemia decreases brain glycogen associated with increased brain lactate, implying an importance of glycogen in brain energetics during intense exercise even without hypoglycemia. Activated serotonergic regulation is a possible underlying mechanism for intense exercise-induced glycogenolysis at least in the hippocampus and brainstem.
KeywordsIntense exercise Brain glycogen Lactate Serotonin Blood glucose
The authors gratefully acknowledge Yukio Ichitani (University of Tsukuba) for his technical assistance for the microwave irradiation. This study was supported, in part, by a Grant-in-Aid for Challenging Exploratory Research of the Japan Society for the Promotion of Science (JSPS); a Grant-in-Aid for JSPS Fellows and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) for the Body and Mind Integrated Sports Sciences (BAMIS) Project (2010–2013); and the Human High Performance (HHP) project (2014). T.M. was supported as a JSPS Research Fellow-SPD (2012–2014).
Conflict of interest
The authors declare no conflicts of interest.