Gilbert M E, Mack C M
Neurotoxicology Division, US Environmental Protection Agency, Research Triangle Park, North Carolina, USA.
Hippocampus. 1999;9(3):277-87. doi: 10.1002/(SICI)1098-1063(1999)9:3<277::AID-HIPO7>3.0.CO;2-H.
Urethane is a standard anesthetic utilized for in vivo recordings in the hippocampus. In studies of long-term potentiation (LTP), the measure of interest is the response amplitude minutes to hours following train delivery. In the absence of experimental treatment, we have consistently observed upward drift in the amplitude of the population spike (PS) and EPSP slope of the dentate gyrus (DG) evoked field response in acute surgical preparations performed in the urethanized rat. The present study systematically monitored PS amplitude and EPSP slope in the DG every 30 minutes for 6 hours following optimal positioning of Teflon-coated bipolar stainless steel electrodes under urethane anesthesia. At maximal stimulus intensities, large time-dependent increases in PS amplitude (70-80%) were observed over the first 2-4 hours, an effect that was exaggerated at lower stimulus intensities. Increases in the EPSP slope were smaller in magnitude (20-30%) and stabilized within a shorter period of time (1-2 hours). Animals were warmed on a heating pad and body and brain temperature remained constant over the recording session. Reducing stimulating electrode size and recording with glass micropipettes did not alleviate the upward drift in response amplitude. Similar increases were also seen under pentobarbital anesthesia. To dissociate anesthetic from surgical effects, recordings were obtained from animals previously prepared with indwelling electrodes and injected with urethane. Although slight declines (10-15%) in EPSP slope occurred over time, no significant alterations in PS amplitude were seen in the chronic preparation at high stimulus intensities. Low stimulus intensities yielded a more variable response pattern and, in direct contrast to the acute preparation, time-dependent declines, not increases, were noted in both parameters. These data suggest that generalized surgical trauma contributes to the upward drift in response amplitude and indicate that long stabilization periods are required in acute surgical preparations for accurate field potential recordings.
乌拉坦是用于海马体内记录的一种标准麻醉剂。在长时程增强（LTP）研究中，关注的指标是在给予刺激串后数分钟至数小时的反应幅度。在没有实验处理的情况下，我们在乌拉坦麻醉的大鼠所进行的急性手术准备中，持续观察到在齿状回（DG）诱发场反应中群体峰电位（PS）的幅度和兴奋性突触后电位（EPSP）斜率出现向上漂移。本研究在乌拉坦麻醉下，将涂有特氟龙的双极不锈钢电极最佳定位后，每30分钟系统监测DG中的PS幅度和EPSP斜率，持续6小时。在最大刺激强度下，在最初的2 - 4小时内观察到PS幅度有较大的时间依赖性增加（70 - 80%），在较低刺激强度下这种效应更为明显。EPSP斜率的增加幅度较小（20 - 30%），且在较短时间内（1 - 2小时）趋于稳定。动物置于加热垫上保暖，在记录过程中身体和大脑温度保持恒定。减小刺激电极尺寸并用玻璃微电极记录并不能减轻反应幅度的向上漂移。在戊巴比妥麻醉下也观察到类似的增加。为了区分麻醉和手术效应，从预先植入电极并注射乌拉坦的动物身上进行记录。尽管随着时间推移EPSP斜率略有下降（10 - 15%），但在慢性准备中，在高刺激强度下PS幅度没有明显变化。低刺激强度产生的反应模式更具变异性，与急性准备直接相反，在这两个参数中均观察到时间依赖性下降而非增加。这些数据表明，全身性手术创伤导致反应幅度向上漂移，并表明在急性手术准备中需要较长的稳定期才能进行准确的场电位记录。
