Brain activity and fatigue during prolonged exercise in the heat

The published version of this article can be viewed at the link below.We hypothesized that fatigue due to hyperthermia during prolonged exercise in the heat is in part related to alterations in frontal cortical brain activity. The electroencephalographic activity (EEG) of the frontal cortex of the brain was measured in seven cyclists [maximal O2 uptake ([(V)\dot]O2maxVO2max ) 4.8-0.1 (SE) l min-1] cycling at 60% [(V)\dot]O2maxVO2max in a hot (H, 42°C) and a cool (C, 19°C) environment. Fast Fourier transformation of the EEG was used to obtain power spectrum areas in the ! (8-13 Hz) and # (13-30 Hz) frequencies. The ratio !/# was calculated as an index of arousal level; an elevated !/# index reflects suppressed arousal. In H, subjects fatigued after 34.4-1.4 min coinciding with an oesophageal temperature (Toes) of 39.8-0.1°C, an almost maximal heart rate (HR 192-3 beats·min-1), a rating of perceived exertion (RPE) of 19.0-0.8 and significantly elevated !/# index (188-71% of the value after 2 min of exercise; P<0.05). In C, subjects cycled for a similar period while Toes was below 38°C, HR and RPE were low, and the !/# index was not significantly elevated (59-27% of 2 min value; P=NS). Increases in the !/# index were strongly correlated to increases in Toes (r2=0.98; P=0.0001).This study belongs to a series of studies that were supported by grants from Team Denmark

Na⁺/K⁺-pump and neurotransmitter membrane receptors

Na+/K+-pump is an electrogenic transmembrane ATPase located in the outer plasma membrane of cells. The Na+/K+-ATPase pumps 3 sodium ions out of cells while pumping 2 potassium ions into cells. Both cations move against their concentration gradients. This enzyme’s electrogenic nature means that it has a chronic role in stabilizing the resting membrane potential of the cell, in regulating the cell volume and in the signal transduction of the cell. This review will mainly consider the role of the Na+/K+-pump in neurons, with an emphasis on its role in modulating neurotransmitter receptor. Most of the literature on the modulation of neurotransmitter receptors refers to the situation in the mammalian nervous system, but the position is likely to be similar in most, if not all, invertebrate nervous systems.</p