Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) Reveals Functional Connectivity Associated with Learning
Date Issued
2007
Date
2007
Author(s)
Chen, Ke-Hsin
DOI
zh-TW
Abstract
Manganese (Mn2+) is used as a contrast agent because it enhances the signal of T1-weighted images in magnetic resonance imaging (MRI). It shares with calcium (Ca2+) certain biochemical properties, and could be taken up by excitable neurons through the calcium channel. No metabolic mechanism washes out Mn2+ accumulated within a neuron, it thus can be transported along the axons, released at the terminal, and taken up by the postsynaptic neuron during excitation. These properties allow Mn2+ to trace fiber track and code the neuronal activity history in the so-called “manganese-enhanced magnetic resonance imaging (MEMRI)”. The present study was aimed to test the hypothesis that the learning-related neuronal activity alters the absorption and transportation rate of Mn2+ in comparison with those without learning, and the difference could be detected by T1-weighted images of MRMRI. The first experiment used the substantia nigra as a testing site for stereotaxic micro-infusion and showed that the optimal dose is 63 nl of 60 mM MnCl2. The second experiment used polyethylene catheters filled with different concentration of manganese inserted into the rat brain as phantom. The signal intensity of those in T1-weighted images was recorded as the concentration varied between 50 to 1000 μM. In the third experiment, male Sprague-Dawley rats received stereotaxic micro-infusion of Mn2+ (60 mM, 63 nl) into the amygdala and hippocampus. After recovery from the anesthesia, the shocked group was subjected to a step-through inhibitory avoidance task with 5 footshocks (1 mA, 1 s). In contrast, the control group was exposed to the same task apparatus but received no footshocks. On the next day, the T1-weighted images were acquired on the Bruker BioSpect 3 T MRI system. The results showed that the manganese infused into hippocampus was transported to the lateral septal nuclei through fornix, and that in amygdala was to bed nucleus of stria terminalis (BNST) and substantia nigra. Only the signal intensity of BNST in the shocked group was significantly lower than the control. After cutting the stria terminalis, manganese was infused into the amygdala in the fourth experiment. The result showed the manganese accumulated in amygdala was transported to BNST through stria ternimalis. The present study proved that Mn2+ could be used as neuronal activity marker in an animal model of learning and memory. However, for this method to be better applied in the future, spatial resolution of images and the analyzing method remain to be improved.
Subjects
杏仁核
海馬
終紋床核
側膈核
神經活動標記
抑制型逃避學習作業
amygdala
hippocampus
bed nucleus of stria terminalis
lateral septal nuclei
neuronal activity history marker
inhibitory avoidance task
Type
other
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