Donner K, Copenhagen D R, Reuter T
Department of Zoology, University of Helsinki, Finland.
J Gen Physiol. 1990 Apr;95(4):733-53. doi: 10.1085/jgp.95.4.733.
Responses to flashes and steps of light were recorded intracellularly from rods and horizontal cells, and extracellularly from ganglion cells, in toad eyecups which were either dark adapted or exposed to various levels of background light. The average background intensities needed to depress the dark-adapted flash sensitivity by half in the three cell types, determined under identical conditions, were 0.9 Rhs-1 (rods), 0.8 Rhs-1 (horizontal cells), and 0.17 Rhs-1 (ganglion cells), where Rh denotes one isomerization per rod. Thus, there is a range (approximately 0.7 log units) of weak backgrounds where the sensitivity (response amplitude/Rh*) of rods is not significantly affected, but where that of ganglion cells (1/threshold) is substantially reduced, which implies that the gain of the transmission from rods to the ganglion cell output is decreased. In this range, the ganglion cell threshold rises approximately as the square root of background intensity (i.e. in proportion to the quantal noise from the background), while the maintained rate of discharge stays constant. The threshold response of the cell will then signal light deviations (from a mean level) of constant statistical significance. We propose that this type of ganglion cell desensitization under dim backgrounds is due to a post-receptoral gain control driven by quantal fluctuations, and term it noise adaptation in contrast to the Weber adaptation (desensitization proportional to the mean background intensity) of rods, horizontal cells, and ganglion cells at higher background intensities.
在暗适应或暴露于不同背景光水平的蟾蜍眼杯中，从视杆细胞和水平细胞进行细胞内记录，从神经节细胞进行细胞外记录对闪光和光阶跃的反应。在相同条件下测定，使三种细胞类型的暗适应闪光敏感度降低一半所需的平均背景强度分别为：0.9 Rhs-1（视杆细胞）、0.8 Rhs-1（水平细胞）和0.17 Rhs-1（神经节细胞），其中Rh表示每个视杆细胞一次异构化。因此，在一个弱背景范围（约0.7对数单位）内，视杆细胞的敏感度（反应幅度/Rh*）没有受到显著影响，但神经节细胞的敏感度（1/阈值）却大幅降低，这意味着从视杆细胞到神经节细胞输出的传递增益降低。在此范围内，神经节细胞的阈值大约随背景强度的平方根升高（即与背景的量子噪声成比例），而持续放电率保持恒定。细胞的阈值反应将发出具有恒定统计显著性的光偏差（相对于平均水平）信号。我们提出，这种在暗光背景下神经节细胞的脱敏是由于量子涨落驱动的感受器后增益控制，与视杆细胞、水平细胞和神经节细胞在较高背景强度下的韦伯适应（脱敏与平均背景强度成比例）相比，我们将其称为噪声适应。
