Two-photon microscopy and its applications in (micro) vascular research

Currently many thermoregulatory models incorporate cutaneous perfusion, as it plays a major role in heat transport. The magnitude of perfusion is generally described as a function of temperature. Some physiological models, such as formulated by Stolwijk, Tanabe and Fiala, incorporate central tonus and local sensitivity explicitly. However, used perfusion control parameters have been estimated and are not based on physiological measurements. Therefore, their applicability might not be justified. In this research a method is proposed to measure central sympathetic vasoconstrictor tone and local cutaneous vasoconstrictor sensitivity. Together, the protocol was performed on males and females, young adults (18-28yr) and elderly (68-78yr) and on both glabrous and non-glabrous skin. Local cutaneous perfusion is measured by laser-Doppler flowmetry. Through iontophoresis of Bretylium tosylate (10mM) sympathetic nerve terminals are blocked, such that local endogenous release of sympathetic neurotransmitters is abolished. Afterwards a superphysiological dose noradrenaline (2.5mM) is administered through iontophoresis. The reduction in perfusion is used as a measure for vasoconstrictor sensitivity at maximal vasoconstrictor tone. This is repeated over a range of local temperatures. Then the whole body is cooled and the decrease in perfusion at a non-bretylium site is measured. Combining perfusion and local sensitivity, vasoconstrictor tone is described as a function of temperature.