POWER OF DUAL-WAVELENGTH APPROACHES IN STUDYING PHYSIOLOGICAL AND FUNCTIONAL CHANGES OF INTACT HEART AND IN VIVO BRAIN

Since the dual-wavelength spectrophotometer was developed,it has been widely used for studying biological samples and applied to extensive investigations of the electron transport in respiration and redox cofactors,redox state,metabolic control,and the generation of reactive oxygen species in mitochondria.Here,we discuss some extension of dual-wavelength approaches in our research to study the physiological and functional changes in intact hearts and in vivo brain.Specifically,we aimed at(1)making nonratiometricfluorescent indicator become ratiometricfluorescence function for investigation of Ca^(2+) dynamics in live tissue;(2)eliminating the effects of physiological changes on measurement of intracellular calcium;(3)permitting simultaneous imaging of multiple physiological parameters.The animal models of the perfused heart and transiently ischemic insult of brain are used to validate these approaches for physiological applications.

DETECTION OF Ca^(2+)-DEPENDENT NEURONAL ACTIVITY SIMULTANEOUSLY WITH DYNAMIC CHANGES IN CEREBRAL BLOOD VOLUME AND TISSUE OXYGENATION FROM THE LIVE RAT BRAIN

We present a catheter-based optical diffusion and fluorescence(ODF)probe to study the functional changes of the brain in vivo.This ODF probe enables the simultaneous detection ofthe multi-wavelength absorbance and fluorescence emission from the living rat brain.Our previous studies,including a transient stroke experiment of the rat brain as well as the brainresponse to cocaine,have established the feasibility of simultaneously determining changes incerebral blood volume(CBV),tissue oxygenation(StO2)and intracellular calcium([Ca^(2+)]i,using the fluorescence indicator Rhod2).Here,we present our preliminary results of somatosensory response to electrical forepaw stimulation obtained from the rat cortical brain by using theODF probe,which indicate that the probe could track brain activation by directly detecting[Ca^(2+)]i along with separately distinguishing CBV and StO2 in real time.The changes of CBV,StO2 and[Ca^(2+)]i are comparable with the blood-oxygen-level-dependent(BOLD)response tothe stimulation obtained using functional magnetic resonance imaging(fMRI).However,thehigh temporal resolution of the optical methodology is advanced,thus providing a new modalityfor brain functional studies to understand the hemodynamic changes that underlie the neuronalactivity.