Brain Glycogen Decreases During Intense Exercise Without Hypoglycemia: The Possible Involvement of Serotonin

Abstract

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.

Effects of exercise on depressive behavior and striatal levels of norepinephrine, serotonin and their metabolites in sleep-deprived mice

“…In the present study, mice submitted to exercise showed higher levels of serotonin turnover. This is in agreement with a previous report showing an improvement of depressive symptoms and high striatal serotonin turnover after aerobic exercise [17,46]. Clinical study shows that unmedicated patients with major depression show higher serotonin turnover levels [47].…”

Visual evoked potentials in subgroups of migraine with aura patients

“…In the latter group, however, lactate levels were already elevated at baseline and remained consistently high during the visual stimulation [ 20 ]. Besides its role as energy substrate of the brain, lactate acts as a neuromodulator and interacts with glutamate [ 21 ], GABA [ 22 ], and monoamines [ 23 ], which suggest that it is important in regulating the activity of cortical neurons. Lactate may increase to attenuate the electrical activity of excessively active neurons as observed in experimental models [ 22 , 24 , 25 ] and in healthy humans during sustained visual stimulation [ 26 ].…”

The hypoglycemia associated autonomic failure triggered by exercise in the patients with “brittle” diabetes and the strategy for prevention

“…In contrast, Takashi et al suggested that serotonin (5-HT) turnover increased in the hippocampus and brainstem and was associated with a decrease in glycogen. As a result, they concluded that serotonergic neurons in the hippocampus and brainstem are likely to regulate the intense exercise-induced brain glycogenolysis [29].…”