Pei X, Vidyasagar T R, Volgushev M, Creutzfeldt O D
Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
J Neurosci. 1994 Nov;14(11 Pt 2):7130-40. doi: 10.1523/JNEUROSCI.14-11-07130.1994.
Postsynaptic potentials (PSPs) were recorded from cat striate cortical cells by the whole-cell in vivo recording technique using patch-clamp electrodes. EPSPs and IPSPs evoked by flashing bars on the receptive field at different positions and orientations revealed the spatial structure of the excitatory and inhibitory inputs. The elongation of the excitatory input field (length:width ratio) was found to be minimal (mean ratio of 1.7) and much lower than those reported for spike discharges. Two-dimensional receptive field response profiles of early PSPs were recorded by flashing a small spot of light over a square matrix covering the receptive field. These recordings also showed only mild degrees of elongations of the receptive field. Such elongations could be the result of either an excitatory input from the geniculate that is already biased for orientation or an excitatory convergence from a limited number of LGN fields arranged in a row. In most first-order cells, we found that inhibition was contributing significantly to orientation selectivity. Often prominent IPSPs could be evoked by stimuli of nonoptimum orientations. Presence of inhibition could also be inferred by the way that EPSPs were sharply cut off by inhibition. When the amplitude of an EPSP was measured at different latencies after its onset, the EPSP was found to be very broadly tuned to orientation at the beginning, but showing increasing orientation selectivity with time. It is proposed that this progressive development of orientation selectivity is due to (1) inhibitory inputs arriving after the first wave of excitation, (2) intracortical excitatory inputs from other cells tuned to similar orientations, and (3) voltage-sensitive mechanisms such as NMDA channels.
使用膜片钳电极，通过全细胞膜片钳体内记录技术，从猫的纹状皮层细胞记录突触后电位（PSP）。在感受野的不同位置和方向上，由闪烁光条诱发的兴奋性突触后电位（EPSP）和抑制性突触后电位（IPSP）揭示了兴奋性和抑制性输入的空间结构。发现兴奋性输入场的伸长率（长：宽比）最小（平均比率为1.7），远低于尖峰放电所报告的比率。通过在覆盖感受野的方形矩阵上闪烁一个小光点，记录早期PSP的二维感受野响应轮廓。这些记录也仅显示出感受野有轻微的伸长。这种伸长可能是由于来自外侧膝状体的已经对方向有偏向的兴奋性输入，或者是由排成一排的有限数量的外侧膝状体场的兴奋性汇聚造成的。在大多数一级细胞中，我们发现抑制对方向选择性有显著贡献。通常，非最佳方向的刺激可以诱发明显的IPSP。通过EPSP被抑制急剧切断的方式也可以推断出抑制的存在。当在EPSP开始后的不同潜伏期测量其幅度时，发现EPSP在开始时对方向的调谐非常宽泛，但随着时间的推移显示出越来越高的方向选择性。有人提出，方向选择性的这种渐进发展是由于：（1）在第一波兴奋之后到达的抑制性输入；（2）来自其他调谐到相似方向的细胞的皮质内兴奋性输入；以及（3）诸如NMDA通道等电压敏感机制。
