Weng Jun-Cheng, Chen Jyh-Horng, Yang Pai-Feng, Tseng Wen-Yih I
Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan.
Neuroimage. 2007 Jul 15;36(4):1179-88. doi: 10.1016/j.neuroimage.2007.04.010. Epub 2007 Apr 18.
Cortical whisker barrels in the primary somatosensory cortex are a well-known example of brain function in rodents. The well-defined relationship between barrels and whiskers makes this system a unique model to study neuronal function and plasticity. In this study, we sought to establish a feasible working protocol of applying manganese-enhanced MRI (MEMRI) to map the cortical barrels following whisker stimulation.
The protocol was based on the principle of activity-induced manganese-dependent (AIM) contrast. Rats were prepared by sodium pentobarbital anesthetization, intraperitoneal manganese-chloride injection, right common carotid mannitol injection and temperature maintenance. Left whiskers were connected to a speaker through a cotton thread and were stimulated by a series of rectangular pulses. MEMRI was acquired with a 3T scanner 3 h after whisker stimulation. Before MR scanning, Wistar rats were euthanized to avoid motion artifacts. To improve the signal-to-noise ratio (SNR) and detection sensitivity, image coregistration, pixel intensity normalization, statistical mapping, group averaging and subtraction were performed. The AIM enhancement of the cortical barrels was quantified using volume of interest analysis on the acquired T1WI and R1 mapping.
Both experimental and control groups showed greater enhancement in the right hemisphere, same side as mannitol injection. In the experimental group, however, activity-induced enhancement was more localized in the right barrel fields, whereas in the control group, the enhancement was uniform throughout the right cortex. In the right cortical barrels, the enhancement ratios and R1 values in the experimental group were significantly higher than those in the control group. In the left cortical barrels, there was no significant difference between the two groups. Subtracted images and voxel-based statistical t-value mapping between experimental and control groups showed additional enhancement concentrated in the right cortical barrels.
We have mapped rat whisker barrels using the AIM method and have shown a clear relationship between manganese-enhanced cortical regions and whisker tactile-sense-evoked activity. It is possible that, with sufficient SNR, the AIM method may reach whisker barrel discrimination, potentially useful to study plasticity in surgically or genetically manipulated rat brains.
初级体感皮层中的皮质胡须桶状结构是啮齿动物脑功能的一个著名例子。桶状结构与胡须之间明确的关系使这个系统成为研究神经元功能和可塑性的独特模型。在本研究中，我们试图建立一个可行的工作方案，应用锰增强磁共振成像（MEMRI）来绘制胡须刺激后的皮质桶状结构。
该方案基于活动诱导的锰依赖性（AIM）对比原理。通过戊巴比妥钠麻醉、腹腔注射氯化锰、右颈总动脉注射甘露醇和维持体温来制备大鼠。左胡须通过棉线连接到扬声器，并由一系列矩形脉冲刺激。在胡须刺激3小时后，用3T扫描仪采集MEMRI。在磁共振扫描前，对Wistar大鼠实施安乐死以避免运动伪影。为了提高信噪比（SNR）和检测灵敏度，进行了图像配准、像素强度归一化、统计映射、组平均和减法运算。使用采集的T1WI和R1映射上的感兴趣体积分析对皮质桶状结构的AIM增强进行量化。
实验组和对照组在右半球（与甘露醇注射同侧）均显示出更大的增强。然而，在实验组中，活动诱导的增强更局限于右侧桶状区，而在对照组中，增强在整个右侧皮质中是均匀的。在右侧皮质桶状结构中，实验组的增强率和R1值显著高于对照组。在左侧皮质桶状结构中，两组之间没有显著差异。实验组和对照组之间的减法图像和基于体素的统计t值映射显示，额外的增强集中在右侧皮质桶状结构中。
我们使用AIM方法绘制了大鼠胡须桶状结构，并显示了锰增强的皮质区域与胡须触觉诱发活动之间的明确关系。在有足够信噪比的情况下，AIM方法有可能实现对胡须桶状结构的辨别，这可能有助于研究手术或基因操作的大鼠大脑中的可塑性。
