扫描视觉诱发电位(SVEP)对成年野生型C57BL/6J小鼠客观视力评估的可靠性

The objective visual acuity in normal adult C57BL/6J mice : assessment with sweep visually evoked potential

目的评价扫描视觉诱发电位(sweep visual evoked potential,SVEP)对成年野生型C57BL/6J小鼠客观视力评估的可靠性。方法选取6只鼠龄32~33 d的正常野生型C57BL/6J小鼠,雌雄不限,麻醉小鼠将记录电极(2 mm直径的钨电极)放置在λ缝旁3 mm的左皮质(受刺激右眼的对侧),深度为皮层下400μm,额部的针状电极作为参考电极,尾部的针状电极作为接地电极,记录过程中遮盖左眼(未受刺激眼),屏幕放置在小鼠眼前20 cm处,视野范围为100°(水平)×82°(垂直),平均亮度为25 cd·m^(-2);采用垂直方向的正弦波光栅刺激,刺激对比度为100%,包括11个空间频率,时间频率为1 Hz;整个扫描过程需要12 s(11 s空间频率+1 s预适应),数据的误差值稳定后取其平均值。分别记录左右眼对应的视皮层VEP波形。不同刺激频率给予20次刺激,每眼重复测量3~4次,取其平均值,左右眼交替试验。以空间频率对数作为x轴,经离散傅里叶分析所得反应振幅为y轴建立坐标系,选取临近噪点的4个有效测定点行线性回归,回归曲线外推法至振幅为0处的空间频率即为推断的客观视力。结果空间频率为0.05 c·deg^(-1)时,SVEP提示N100波振幅达到峰值。随着逐步增加刺激空间频率,SVEP振幅降低﹑潜伏期延迟,空间频率为0.65 c·deg^(-1)时视皮层电反应几乎无法与噪点区分;6只小鼠右眼空间频率视力为(0.56±0.04)c·deg^(-1),左眼为(0.50±0.04)c·deg^(-1),两眼空间频率视力比较差异无统计学意义(P>0.05);12眼空间频率视力为(0.53±0.03)c·deg^(-1)。结论可以使用SVEP评估小鼠客观视力,此方法与行为方法测得的视力相近,但SVEP评估小鼠视力结果更为客观精确,所需时间更短。

Objective To evaluate the reliability of sweep visual evoked potential（ SVEP）for assessing the normal objective visual acuity in adult wild-type C57 BL/6 J mice. Methods A total of 6 wild C57 BL/6 J mice of either gender at 32-33 days of age were collected. After the mice were anesthetized,the recording electrode（ a 2-mm diameter tungsten electrode） was placed at 3 mm lateral to lambda over the left cortex（ contralateral to the stimulated right eyes）and advanced to 400 μm within the cortex,and the needle electrodes which placed in the forehead and tail served as the reference and the ground,accordingly. Left eyes（ unstimulated eyes）w ere covered during the recording. The screen（ mean luminance 25 cd·m-2） was placed 20 cm in front of the mice,thereby covering 100°（ horizontal） × 82°（ vertical） of the visual field.The mice were stimulated by vertically sinusoidal grating,which consisted of 11 spatial frequencies,stimulus contrast was 100%,and time frequency was 1 Hz; the entire sw eep took 12 seconds（ 11 spatial frequencies ＋ 1 s pre-adaptation）,and the values were averaged until the error bars for the data were stable. The VEP waveforms of visual cortex corresponding to the left and right eyes were recorded separately. At least 3-4 trials consisting of 20 events for different frequencies were averaged. Left and right eye were tested alternately. Then the coordinate system was established by using the spatial frequency logarithm as x-axis and the amplitude of the response obtained by the discrete Fourier analysis as y-axis,the objective visual acuity was obtained by extrapolation to zero amplitude of the linear regression through the 4 effective data points adjacent to noise. Results SVEP show ed that the amplitude of N100 wave was maximal at a spatial frequency of 0. 05 c·deg-1. W ith the increase of the stimulus spatial frequency progressively,SVEP decreased in amplitude and increased in latency. The cortical electrical signal could not be distinguished from noise at a spatial frequency of 0. 65 c·deg-1. The average acuity of 6 mice was（ 0. 56 ± 0. 04） c·deg-1 for right eyes and（ 0. 50 ± 0. 04） c·deg-1 for left eyes respectively. There was no significant difference betw een the two eyes（ P〈0. 05）; The visual evoked potential acuity of 12 eyes was（ 0. 53 ± 0. 03） c·deg-1. Conclusion SVEP could be used to estimate the mouse VEP acuity,which was closed to the behavioral visual acuity. How ever,the VEP acuity was more objective and accurate as well as time-saving.