| Summary: | 碩士 === 國立臺灣大學 === 動物學研究所 === 100 === Functional magnetic resonance imaging (fMRI) provides an excellent tool for the examination of brain function, especially for revealing the global spatial activation pattern in the brain. For rodent fMRI, to prevent the undesired stress and motion artifacts, suitable anesthesia is needed. Alpha-chloralose is the most commonly used anesthetic in rodent fMRI, since it preserve well the neurovascular coupling response in the brain. However, α-chloralose is very harmful to the animal, and is not recommended for longitudinal study.
Recently, a noninvasive rat fMRI protocol using the A2-adrenoreceptor agonist medetomidine as sedative has been proposed, and the peripheral evoked BOLD response was observed reproducibly over 5 days. In the current study, we further combine this protocol with chronic implantation of MRI compatible stimulation electrode, and seek to longitudinally trace the thalamocortical circuit in the rat brain.
By using medetomidine anesthesia, we were able to repetitively scan direct ventroposterior (VP) thalamus electrical stimulation over weeks. We found reproducible stimulus frequency and amplitude dependent BOLD response within ipsilateral S1, with highly conserved in amplitude (the correlation coefficient between two sessions = 0.8677, P < 0.001), area size (the second session was 92.41-96.99% to the first session) and location (61.3-80.02% overlapping). The pattern of the response was comparable to that under α-chloralose anesthesia, but the response amplitude was weaker.
We also found stimulus amplitude dependent change of glucose consumption (CMRglu) in S1 by Positron Emission Tomography (PET). The change of CMRglu was highly correlated with the amplitude of BOLD response in S1, with the correlation coefficient of 0.9001 (P < 0.001). Thus this new protocol will enable us to study long-term plasticity of specific circuitry of the brain in normal function and in disease states by rodent fMRI and PET.
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