On The Hemodynamic Response Of Neuronal Activity And Ischemia In Rat Cortex By Optical Imaging

The brain is critically dependent on a continuous supply of blood to function. The cerebral vasculature is endowed with neurovascular control mechanisms that assure that the blood supply of the brain is commensurate to the needs of energy and oxygen. In the normal state of brain, this neurovascular coupling regulation mechanism (functional hyperemia) is the basis for several modern imaging techniques that have revolutionized the study of human brain activity. However, in several brain pathologies, such as the cerebral ischemia, the control of cerebral blood flow (CBF) is influenced and disrupted, and the resulting homeostatic unbalance may contribute to brain dysfunction and even irreversible massive damage. To study this evolution and essential mechanism of the regulation of CBF in brain normal and ischemic state is benefit to promote understanding of neurophysiological basis of the detected signals in neuroimaging techniques, to determine the standard of the diagnosis of the ischemic penumbra tissue and seek a therapeutic target for ischemia. Optical intrinsic signal imaging (OISI) and laser speckle imaging (LSI), which can simultaneously provide high temporal and spatial resolution, have been extensively applied into the studies focusing on cortical hemodynamic response , and bring on fresh insight, validation and relavant supplement to the conventional brain functional imaging studies.In this dissertation, OIIS combined with LSI was applied into our study to monitor the dynamic changes of cerebral blood volume (CBV) in primary somatosensory cortex evoked by peripheral noxious stimuli, the distribution of CBF associated with cortical mini-ischemia/reperfusion, and to elucidate the relationship between the regional heterogeneity of ischemia induced spontaneous spreading depression (SD) and the local CBF level. The main results and conclusion are listed as following:1) Although the dimensions of peak response defined in the spatial domain (CBV increase) in the S1 cortex presented no significant difference under non-/noxious stimuli, its early response component revealed by OISI technique was suggested to differentiate the loci of activated cortical region due to different stimulation in this study. The magnitude and duration of the optical intrinsic signal (OIS) response was found increasing with the varying stimulus intensity. Regions activated by the delivery of a noxious stimulus were surrounded by a ring of inverted optical intrinsic signal, the amplitude of that was inversely proportional to the strength of the optical signal attributable to activation. The selective hypoalgesic effect of fentanyl could suppress the magnitude of OIS and evoke different response pattern while suffering from the same nociceptive stimuli. These results indicated that the contralateral S1 cortex acts a role in the perception of nociception.2) A new mini-ischemia/reperfusion stroke model was developed by sharing feathers from previous mini-stroke model and cortical compression model. Our results showed that a distinct CBF gradient from ischemic core, penumbra zone to normal tissue immediately after cortical ischemia was clearly presented in the imaged cortex. This model could facilicate vascular recannulation, while confining the collateral flow and draining veins to localize the infarct into a special cortical area.3) In the early phase of ischemia, the maximum increase in OIS related the saoteneous SD was inversive propational to the rCBF, whereas the maximum decrease in OIS has an opposite tendency. The spontenous SD originated from the penumbra zone and bypassed the severe ischemic core, and presented four types of OIS through the propagation of the imaged cortex: SD could not invade the ischemic core, and dominated with significant increase of optical reflectance in the mild ischemic region distal to infarct core. In the normal tissue with fully perfusion, the OIS was represented as the typical four-phase fluctuation. In the oligemic tissue abuts on the fully perfused region, the increase and decrease phases in the OIS were equivalent in amplitude and prominence. This comparison suggests that the OIS characteristics could reflect the severity of ischemia and collateral flow, beside for the regional CBF level.