Optical imaging of neural activity in transient ischemia and plasticity in cortex

用光学记录技术，借助电压敏感染料(RH-795)，研究了哺乳动物听皮层声诱发神经活动的时空模式。将该方法应用于观察短暂性脑缺血时皮层活动的变化。用12×12光电二极管阵列记录在不同频率和压力水平下620 nm处诱发声的光强度变化。反应的幅度被显示为连续的二维图像。在听皮质的多个区域均可见声门组织。然而，通过功能组织的频率表征是短暂的。从主场开始的震源活动沿等频带向背部传播。在大鼠听皮层，声音诱导的光信号在脑缺血后1min消失。在缺血30min内，未观察到任何反应成分。再循环后，144个测点的反应再次出现。然而，短暂性脑缺血后的反应模式与对照组明显不同。尤其是后组分未恢复到缺血前水平。虽然出现了功能组织，但在组织内发现了视反应没有恢复到对照的脆弱区域。我们的结果表明，听皮质的功能变化先于这些脑区的神经元死亡。在豚鼠中，有一些病例显示大脑皮质的光学反应因短暂性脑缺血而增加。光学记录方法具有实时成像二维大脑皮层活动的优点，具有广阔的应用前景。

The spatio-temporal pattern of sound-evoked neural activity in the mammalian auditory cortex was studied by optical recording with aid of voltage-sensitive dye (RH 795). This method was applied to observation of transient ischemic changes in the cortical activity. Changes in light intensity at 620 nm induced sounds at various frequency and pressure levels were recorded with a 12 x 12 array of photodiodes. The amplitude of the responses were displayed as sequential two-dimensional images. Tonotopical organization was found in the multi-fields of the auditory cortex. However, frequency representation through the functional organization was transient. The focal activity that began in the primary field propagated dorsally along the iso-frequency bands. In the rats auditory cortex, the optical signals induced by sounds were disappeared by 1 min after induction of ischemia. During the 30 min of ischemia, no components of the responses were observed. After recirculation the responses from 144 sites appeared again. However the pattern of the responses after the transient ischemia was significantly different from the control. Especially the later component did not recover to the preischemic level. Although functional organization appeared, but vulnerable regions were found within the organization where the optical responses ded not return to the control Our results suggest that the functional changes in the auditory cortex precede the post-ischemic neuronal death in those cerebral regions. In guinea pigs, there were some cases which showed an increase in the magnitude of optical responses from the cortex by transient ischemia. The optical recording method has the advantage of real-time imaging of two-dimensional cortical activity and will be used widely in the future.