Hirsch J A, Gilbert C D
Laboratory of Neurobiology, Rockefeller University, New York, New York 10021.
J Neurosci. 1991 Jun;11(6):1800-9. doi: 10.1523/JNEUROSCI.11-06-01800.1991.
Horizontal connections are a principal component of intrinsic cortical circuitry. They arise mainly from pyramidal cells and course parallel to the brain's surface for distances as long as 8 mm, linking columns with shared orientation preference and allowing cells to integrate visual information from outside their receptive fields. We examined the synaptic physiology of the horizontal pathway in slices of the cat's striate cortex and found that activating lateral fibers produced both excitation and inhibition. We recorded the postsynaptic responses of identified pyramidal cells in layer 2 + 3 of area 17 to electrical shocks applied at three sites: in the home column of the impaled neuron either in layer 2 + 3 or 4, or at a lateral distance of 0.9-3 mm in layer 2 + 3. Within the home column, suprathreshold stimuli produced compound EPSPs with action potentials, followed by fast, GABAAergic IPSPs and a slower, GABABergic IPSP. For the distant stimulating site, the threshold response was an EPSP. Stronger shocks frequently evoked a disynaptic, GABAAergic IPSP that truncated the EPSP and could dominate the postsynaptic response. At the resting potential, the horizontally evoked EPSP was too small to elicit spikes. With depolarization of the membrane, however, it grew several hundred-fold. This amplification was blocked by N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium bromide (QX-314), but not by 2-amino-5-phosphonovalerate (APV), indicating that it was mediated by Na+ channels, rather than by NMDA receptors. We propose that the horizontal connections provide the means for stimuli outside the receptive field to modulate activity elicited within its confines. The voltage-dependent enhancement of the laterally evoked EPSP may explain why stimulating the surround by itself fails to drive cells but can facilitate their response to stimuli within the receptive field. The ability to initiate disynaptic inhibition from lateral sites shows that recruiting appropriate groups of horizontal fibers can also have a suppressive effect. Thus, the effect of horizontal input is state dependent, with the size and sign of the laterally evoked response changing according to the balance of converging inputs.
水平连接是大脑皮质固有回路的主要组成部分。它们主要起源于锥体细胞，沿着与脑表面平行的方向延伸长达8毫米，连接具有共同方向偏好的柱体，使细胞能够整合来自其感受野之外的视觉信息。我们研究了猫纹状皮质切片中水平通路的突触生理学，发现激活外侧纤维会产生兴奋和抑制作用。我们记录了17区第2 + 3层中已识别的锥体细胞对在三个部位施加电刺激的突触后反应：在被刺穿神经元的本柱内，即在第2 + 3层或第4层，或在第2 + 3层中距离为0.9 - 3毫米的外侧部位。在本柱内，阈上刺激产生带有动作电位的复合兴奋性突触后电位（EPSP），随后是快速的GABAA能抑制性突触后电位（IPSP）和较慢的GABAB能IPSP。对于远处的刺激部位，阈反应是一个EPSP。更强的电刺激经常诱发一个双突触的GABAA能IPSP，它截断EPSP并可能主导突触后反应。在静息电位时，水平诱发的EPSP太小以至于无法引发动作电位。然而，随着膜的去极化，它增大了数百倍。这种放大被N - (2,6 - 二甲基苯基氨基甲酰甲基)三乙铵溴化物（QX - 314）阻断，但不被2 - 氨基 - 5 - 磷酸戊酸（APV）阻断，这表明它是由Na + 通道介导的，而不是由NMDA受体介导的。我们提出水平连接为感受野之外的刺激提供了调节其范围内所引发活动的方式。外侧诱发EPSP的电压依赖性增强可能解释了为什么单独刺激周边区域无法驱动细胞，但却能促进它们对感受野内刺激的反应。从外侧部位启动双突触抑制的能力表明，募集适当的水平纤维群也可能具有抑制作用。因此，水平输入的效应取决于状态，外侧诱发反应的大小和符号会根据汇聚输入的平衡而变化。
