Robson John G, Saszik Shannon M, Ahmed Jameel, Frishman Laura J
College of Optometry, University of Houston, Houston, TX 77204-2020, USA.
J Physiol. 2003 Mar 1;547(Pt 2):509-30. doi: 10.1113/jphysiol.2002.030304. Epub 2003 Jan 24.
The electroretinogram (ERG) of anaesthetised dark-adapted macaque monkeys was recorded in response to ganzfeld stimulation and rod- and cone-driven receptoral and postreceptoral components were separated and modelled. The test stimuli were brief (< 4.1 ms) flashes. The cone-driven component was isolated by delivering the stimulus shortly after a rod-saturating background had been extinguished. The rod-driven component was derived by subtracting the cone-driven component from the mixed rod-cone ERG. The initial part of the leading edge of the rod-driven a-wave scaled linearly with stimulus energy when energy was sufficiently low and, for times less than about 12 ms after the stimulus, it was well described by a linear model incorporating a distributed delay and three cascaded low-pass filter elements. Addition of a simple static saturating non-linearity with a characteristic intermediate between a hyperbolic and an exponential function was sufficient to extend application of the model to most of the leading edge of the saturated responses to high energy stimuli. It was not necessary to assume involvement of any other non-linearity or that any significant low-pass filter followed the non-linear stage of the model. A negative inner-retinal component contributed to the later part of the rod-driven a-wave. After suppressing this component by blocking ionotropic glutamate receptors, the entire a-wave up to the time of the first zero-crossing scaled with stimulus energy and was well described by summing the response of the rod model with that of a model describing the leading edge of the rod-bipolar cell response. The negative inner-retinal component essentially cancelled the early part of the rod-bipolar cell component and, for stimuli of moderate energy, made it appear that the photoreceptor current was the only significant component of the leading edge of the a-wave. The leading edge of the cone-driven a-wave included a slow phase that continued up to the peak, and was reduced in amplitude either by a rod-suppressing background or by the glutamate analogue, cis-piperidine-2,3-dicarboxylic acid (PDA). Thus the slow phase represents a postreceptoral component present in addition to a fast component of the a-wave generated by the cones themselves. At high stimulus energies, it appeared less than 5 ms after the stimulus. The leading edge of the cone-driven a-wave was adequately modelled as the sum of the output of a cone photoreceptor model similar to that for rods and a postreceptoral signal obtained by a single integration of the cone output. In addition, the output of the static non-linear stage in the cone model was subject to a low-pass filter with a time constant of no more than 1 ms. In conclusion, postreceptoral components must be taken into account when interpreting the leading edge of the rod- and cone-driven a-waves of the dark-adapted ERG.
记录了麻醉状态下暗适应猕猴对全视野刺激的视网膜电图（ERG），并分离和模拟了视杆和视锥驱动的感受器及感受器后成分。测试刺激为短暂（<4.1毫秒）闪光。在视杆饱和背景熄灭后不久施加刺激，分离出视锥驱动成分。通过从混合的视杆 - 视锥ERG中减去视锥驱动成分得到视杆驱动成分。当能量足够低时，视杆驱动a波前沿的初始部分与刺激能量呈线性比例关系，并且在刺激后小于约12毫秒的时间内，它可以通过包含分布延迟和三个级联低通滤波器元件的线性模型很好地描述。添加一个简单的静态饱和非线性，其特性介于双曲线函数和指数函数之间，足以将模型的应用扩展到对高能量刺激的饱和反应的大部分前沿。无需假设任何其他非线性的参与，也无需假设在模型的非线性阶段之后有任何显著的低通滤波器。一个负的视网膜内成分对视杆驱动a波的后期部分有贡献。通过阻断离子型谷氨酸受体抑制该成分后，直到第一次过零时间的整个a波与刺激能量呈比例关系，并且通过将视杆模型的响应与描述视杆双极细胞反应前沿的模型的响应相加可以很好地描述。负的视网膜内成分基本上抵消了视杆双极细胞成分的早期部分，对于中等能量的刺激，使得看起来光感受器电流是a波前沿的唯一重要成分。视锥驱动a波的前沿包括一个持续到峰值的慢相，并且通过视杆抑制背景或谷氨酸类似物顺式哌啶 - 2,3 - 二羧酸（PDA）可使其幅度减小。因此，慢相代表了除视锥自身产生的a波的快相之外存在的一个感受器后成分。在高刺激能量下，它在刺激后不到5毫秒出现。视锥驱动a波的前沿可以充分地建模为类似于视杆模型的视锥光感受器模型的输出与通过对视锥输出进行单次积分获得的感受器后信号的总和。此外，视锥模型中静态非线性阶段的输出经过一个时间常数不超过1毫秒的低通滤波器。总之，在解释暗适应ERG中视杆和视锥驱动a波的前沿时，必须考虑感受器后成分。
