α-氯醛醣麻醉劑量對功能性磁振造影相關參數之影響

Abstract

在探究大腦活動的時候，功能性磁振造影是一個有用的工具，而在動物的功能性磁振造影實驗中，一個有效且穩定的麻醉是很重要的。本實驗主要是決定使用α－氯醛醣來麻醉動物時，所需的最佳麻醉劑量，另外使用此最佳劑量來探討，嗎啡對於疼痛相關反應的影響。20隻Long-Evans大鼠 (220 ~ 320 克)分為4組，分別給予不同的α－氯醛醣劑量：高劑量 (60 毫克/公斤/小時) 、低劑量 (30 毫克/公斤/小時)或對照組。在5小時的監測時間中，持續觀察動物的血壓、心跳、血液氧氣分壓、血液二氧化碳分壓，並且在後腳掌給予電刺激 (2 mA, 0.5 ms, 0.3 Hz)，紀錄刺激所引發的體感覺誘發電位 (EEG) 及屈肌反射 (EMG)等生理參數。在低劑量的α－氯醛醣麻醉下，動物的生理狀態可以維持穩定達5個小時，並且在fMRI的實驗中得到清楚的BOLD反應，但是對照組以及高劑量的老鼠，在這樣長時間的麻醉中，生理及麻醉狀況無法維持穩定。另外在嗎啡的實驗中，與疼痛相關的反應區域都會被嗎啡所抑制，在經過3小時的恢復時間後，體感覺皮質的反應會回復，但是前扣帶迴皮質、運動皮質區及扣帶迴皮質的反應，仍然被抑制。在本實驗中，我們測試並達到了穩定的α－氯醛醣麻醉，而這個方法將可以應用在其他相關的實驗上。

Functional magnetic resonance imaging (fMRI) is an important tool for exploring brain activities. A stable anesthetized animal preparation is critically important for fMRI applications. The present study intended to determine the optimal infusion rate of α-chloralose anesthesia, the most popular anesthetics used in animal fMRI. In addition, the analgesia effect of morphine was tested by giving morphine before electrical stimulation. Long-Evans female rats (220 ~ 320 g) were used. After halothane induction, α-chloralose was given in an intravenous bolus injection (80 mg/kg). Subsequently, 3 different maintenance dosages were compared. These were administrated through intravenous infusion：high (60 mg/kg/hr), low (30 mg/kg/hr) or vehicle. During the 5 hours of recording period, blood pressure, heart rate, O2 and CO2 concentration in arterial blood were monitored. In addition, somatosensory evoked potentials (EEG) and flexor reflex activities (EMG) after hind paw electrical stimulation (2 mA, 0.5 ms, 0.3 Hz) were recorded every half hour. Under suitable infusion rate (30 mg/kg/hr), the physiological conditions remained stable for 5 hr, while the results suggested that the high dose and vehicle were not appropriate dosages for a stable anesthesia. Also, fMRI activations of the contralateral primary somatosensory cortex (SI) were readily observed under low dosage of α-chloralose infusion. In the morphine effect study, activations of anterior cingulate cortex (ACC), motor area/cingulate cortex (CC) and SI were attenuated after morphine administration. However, BOLD signals of SI were recovered after 3 hours, while the responses in ACC, motor area/CC remained suppressed. This study demonstrates that a steady α-chloralose anesthesia can be achieved for fMRI study, which can be utilized in the study of drug, lesion or other brain experiments.