Mancilla J G, Fowler M, Ulinski P S
Department of Psychology, University of Chicago, IL 60637, USA.
Vis Neurosci. 1998 Sep-Oct;15(5):979-93. doi: 10.1017/s0952523898155190.
Sharp electrodes were used to record light-evoked postsynaptic potentials (PSPs) from neurons in turtle visual cortex in an in vitro preparation of the geniculocortical pathway. Neurons were placed into four groups based on the firing patterns produced by intracellular current injections: regular spiking (RS), fast spiking (FS), intrinsic bursting (IB), and chattering (CH) cells. RS cells have been shown to be pyramidal cells while FS cells are typically interneurons. Light stimuli were diffuse, 1-s flashes of 640-nm light with intensities (I) varying from 0 to 10(4) photons microm(-2) s(-1). The response (R) in each case was the maximal amplitude of the light-evoked depolarizing PSP. Cells of all four types showed sigmoidal intensity-response (IR) functions with a linear rising phase for stimuli above the intensity threshold followed by saturation at high light intensities. Responses at high intensities were variable and some cells showed indications of supersaturation. Light-evoked PSPs had longer latencies and times-to-peak response in RS cells than they did in FS cells. RS cells fired action potentials as much as 200 ms later than did FS cells. Since responses recorded in RS cells at light intensities just above threshold are unlikely to involve contributions from other pyramidal cells, these data indicate that the geniculocortical or feedforward pathway to pyramidal cells has a high gain. The fact that FS cells fire well before RS cells suggests that feedforward inhibition plays a role in controlling the gain of the geniculocortical pathway.
在膝状体皮质通路的体外制备中，使用尖锐电极记录乌龟视皮质中神经元的光诱发突触后电位（PSP）。根据细胞内电流注入产生的放电模式，将神经元分为四组：规则发放（RS）、快速发放（FS）、内在爆发（IB）和喋喋不休（CH）细胞。已证明RS细胞是锥体细胞，而FS细胞通常是中间神经元。光刺激为漫射的640 nm光的1秒闪光，强度（I）从0变化到10⁴ 光子·微米⁻²·秒⁻¹。每种情况下的反应（R）是光诱发去极化PSP的最大幅度。所有四种类型的细胞都表现出S形强度-反应（IR）函数，对于高于强度阈值的刺激，有一个线性上升阶段，随后在高光强度下达到饱和。高强度下的反应是可变的，一些细胞显示出过饱和的迹象。与FS细胞相比，光诱发的PSP在RS细胞中的潜伏期和峰值反应时间更长。RS细胞产生动作电位的时间比FS细胞晚多达200毫秒。由于在略高于阈值的光强度下在RS细胞中记录的反应不太可能涉及其他锥体细胞的贡献，这些数据表明到锥体细胞的膝状体皮质或前馈通路具有高增益。FS细胞比RS细胞更早放电这一事实表明前馈抑制在控制膝状体皮质通路的增益中起作用。
