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Physical properties of the body fluids and the cell membrane
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
Measurement of these fluid volumes can be achieved by using “tracer materials” that have the unique property of remaining in specific fluid compartments. The fluid volume of a specific compartment can then be found by adding a known mass of a tracer to a specific compartment and, after an appropriate period of time for dispersal, measuring the concentration (mass/volume) of the tracer in the fluid compartment. The compartment volume is then given by the ratio of the tracer mass that was added and the measured tracer concentration, i.e., mass/(mass/volume) = volume.
Fatigue: Is it all neurochemistry?
Published in European Journal of Sport Science, 2018
One big advantage of animal research is the ability to use in vivo brain microdialysis. This technique is based on the kinetic dialysis principle. A small microdialysis catheter or probe is inserted in the area of interest. This probe functions as a blood capillary and is connected to inlet and outlet tubing. Its membrane, permeable to water and small solutes, separates two fluid compartments. The membrane is continuously being flushed on one side (inlet) with a solution that lacks the substances of interest, whereas the other side (outlet) is in contact with the extracellular space. This creates a concentration gradient which in turn causes passive diffusion to take place. Brain microdialysis allows to have direct analysis of extracellular neurotransmitters and metabolites from the brain of resting or active animals with only limited tissue trauma (Meeusen & De Meirleir, 1995; Meeusen et al., 2006). Two studies by Hattori, Li, Matsui, and Nishino (1993) and Hattori, Naoi, and Nishino (1994) – using in vivo brain microdialysis – showed that only 20 min of running on a treadmill significantly increased DA concentration in the rat striatum. Hasegawa, Yazawa, Yasumatsu, Otokawa, and Aihara (2000) measured the neurotransmitter concentrations in the preoptic area and anterior hypothalamus (PO/AH) – the thermoregulatory centre of the brain – in exercising rats, using an in vivo microdialysis technique. They reported that the extracellular level of DOPAC and HVA, both DA metabolites, in the PO/AH increased during treadmill exercise, whereas the levels of serotonin and 5-HIAA were left unchanged. Hasegawa et al. (2000) concluded that DA is the prime candidate for thermoregulatory substances working in the PO/AH.