Chen You-Yin, Shih Yen-Yu I, Lo Yu-Chun, Lu Pen-Li, Tsang Siny, Jaw Fu-Shan, Liu Ren-Shyan
Department of Electrical Engineering, National Chiao Tung University, Hsinchu, Taiwan, ROC.
Somatosens Mot Res. 2010;27(3):69-81. doi: 10.3109/08990220.2010.508222.
Small animal positron emission tomography (microPET) has been utilized in the investigation of nociception. However, a possible drawback from previous studies is the reduced activation pattern due to the application of anesthesia. The purpose of the present study was to demonstrate a potential means of avoiding anesthesia during stimulation, as well as minimizing the confounding anesthetic effect. Sodium pentobarbital and ketamine were first evaluated to determine their effect on microPET images in the current study. [(18)F]-Fluorodeoxyglucose ((18)F-FDG) was an appropriate radiotracer to reveal activated regions in rat brains. Pentobarbital anesthesia significantly reduced (18)F-FDG uptake in neural tissues, blurrier to lower contrast; therefore, ketamine was used to anesthetize animals during microPET. After the rats were anesthetized and secured in a laboratory-made stereotaxic frame, a simple, noninvasive stereotaxic technique was used to position their heads in the microPET scanner and to roughly conform the images in the stereotaxic atlas. For functional imaging, conscious rats were restrained in cages with minimal ambient noise; short repetitive thermal stimuli were applied to each rat's tail subsequently. The rats were adequately anesthetized with ketamine following 30 min of scanning without stimulation. An activation index (AI) was calculated from microPET data to quantify the local metabolic activity changes according to the normalized (18)F-FDG dosage. The average AI indicated a side-to-side difference for all innocuous stimulations in the thalamus. However, such side-to-side difference was only observed for noxious heat and cold stimulations in primary somatosensory cortex (SI), secondary somatosensory cortex (SII), and agranular insular cortex (AIC). The present study demonstrated the feasibility of the microPET technique to image metabolic functions of the conscious rat brain, offering better rationale and protocol designs for future pain studies.
小动物正电子发射断层扫描（microPET）已被用于伤害感受的研究。然而，以往研究的一个可能缺点是由于使用麻醉而导致激活模式减弱。本研究的目的是展示一种在刺激过程中避免麻醉以及将麻醉的混杂效应降至最低的潜在方法。在本研究中，首先评估了戊巴比妥钠和氯胺酮对microPET图像的影响。[（18）F] - 氟脱氧葡萄糖（（18）F - FDG）是一种用于揭示大鼠脑内激活区域的合适放射性示踪剂。戊巴比妥麻醉显著降低了神经组织中（18）F - FDG的摄取，使对比度降低且图像更模糊；因此，在microPET检查期间使用氯胺酮麻醉动物。将大鼠麻醉并固定在实验室自制的立体定位框架中后，采用一种简单、无创的立体定位技术将其头部置于microPET扫描仪中，并使图像大致与立体定位图谱相符。对于功能成像，清醒的大鼠被限制在环境噪音最小的笼子里；随后对每只大鼠的尾巴施加短时间的重复性热刺激。在无刺激扫描30分钟后，用氯胺酮对大鼠进行充分麻醉。根据归一化的（18）F - FDG剂量，从microPET数据计算激活指数（AI）以量化局部代谢活性变化。平均AI表明，在丘脑中所有无害刺激均存在左右差异。然而，这种左右差异仅在初级体感皮层（SI）、次级体感皮层（SII）和无颗粒岛叶皮层（AIC）的有害热刺激和冷刺激中观察到。本研究证明了microPET技术对清醒大鼠脑代谢功能成像的可行性，为未来的疼痛研究提供了更好的理论依据和方案设计。
