Borg-Graham L J, Monier C, Frégnac Y
Equipe Cognisciences, Institut Alfred Fessard, CNRS, Gif sur Yvette, France.
Nature. 1998 May 28;393(6683):369-73. doi: 10.1038/30735.
The function and nature of inhibition of neurons in the visual cortex have been the focus of both experimental and theoretical investigations. There are two ways in which inhibition can suppress synaptic excitation. In hyperpolarizing inhibition, negative and positive currents sum linearly to produce a net change in membrane potential. In contrast, shunting inhibition acts nonlinearly by causing an increase in membrane conductance; this divides the amplitude of the excitatory response. Visually evoked changes in membrane conductance have been reported to be nonsignificant or weak, supporting the hyperpolarization mode of inhibition. Here we present a new approach to studying inhibition that is based on in vivo whole-cell voltage clamping. This technique allows the continuous measurement of conductance dynamics during visual activation. We show, in neurons of cat primary visual cortex, that the response to optimally orientated flashed bars can increase the somatic input conductance to more than three times that of the resting state. The short latency of the visually evoked peak of conductance, and its apparent reversal potential suggest a dominant contribution from gamma-aminobutyric acid ((GABA)A) receptor-mediated synapses. We propose that nonlinear shunting inhibition may act during the initial stage of visual cortical processing, setting the balance between opponent 'On' and 'Off' responses in different locations of the visual receptive field.
视觉皮层中神经元抑制的功能和性质一直是实验研究和理论研究的焦点。抑制作用可通过两种方式抑制突触兴奋。在超极化抑制中，负电流和正电流线性叠加，从而产生膜电位的净变化。相比之下，分流抑制通过增加膜电导以非线性方式起作用；这会使兴奋性反应的幅度减小。据报道，视觉诱发的膜电导变化不显著或很微弱，这支持了超极化抑制模式。在此，我们提出一种基于体内全细胞电压钳制的研究抑制作用的新方法。该技术能够在视觉激活过程中持续测量电导动态变化。我们发现，在猫的初级视觉皮层神经元中，对最佳定向闪光条的反应可使体细胞输入电导增加至静息状态时的三倍以上。视觉诱发的电导峰值潜伏期较短，且其明显的反转电位表明γ-氨基丁酸（GABA）A受体介导的突触起主要作用。我们提出，非线性分流抑制可能在视觉皮层处理的初始阶段起作用，在视觉感受野的不同位置设定对抗性“开”和“关”反应之间的平衡。
