Toda K, Bush R A, Humphries P, Sieving P A
Department of Ophthalmology, and Programs in Neuroscience and in Bioengineering, University of Michigan, Ann Arbor, USA.
Vis Neurosci. 1999 Mar-Apr;16(2):391-8. doi: 10.1017/s0952523899162187.
The electroretinogram (ERG) of the rhodopsin knockout (rho-/-) mouse of Humphries et al. (1997) (Humphries et al., 1997) was studied for evidence of light-evoked rod activity and to describe the cone function. The rho-/- retina develops normal numbers of rod and cone nuclei, but the rods have no outer segments, and no rhodopsin is found by immunohistochemistry. The dark-adapted ERG threshold was elevated 4.7 log units above wild-type (WT) control mice, indicating that any residual rod responses were reduced >50,000-fold, consistent with a complete functional knockout. The dark-adapted rho-/- ERG had a cone waveform, and the spectral sensitivity peaked near 510 nm for both dark-adapted and light-adapted conditions, without evidence of a Purkinje shift. The light-adapted ERG b-wave amplitude of young rho-/- mice was the same as WT. The amplitude remained steady up to postnatal day P47, but thereafter it declined to only 1-2% by P80 when no cone outer segments remained. Cone b-wave threshold of dark-adapted rho-/- mice was -1.07 +/- 0.39 log cd-s/m2 (n = 17), which is 1.27 log units more sensitive than light-adapted thresholds against a rod-suppressing Ganzfeld background of 1.61 log scotopic cd/m2. This indicates that dark-adapted WT responses to still dimmer stimuli are exclusively rod driven with minimal cone intrusion. Above this cone threshold intensity, the dark-adapted b-wave of WT will be a summation of rod and cone responses. Threshold versus intensity (TVI) studies gave no evidence of a rod influence on the mouse cone b-wave.
对Humphries等人（1997年）的视紫红质基因敲除（rho-/-）小鼠的视网膜电图（ERG）进行了研究，以寻找光诱发视杆细胞活动的证据并描述视锥细胞功能。rho-/-视网膜中视杆细胞核和视锥细胞核的数量发育正常，但视杆细胞没有外节，免疫组织化学检测未发现视紫红质。暗适应的ERG阈值比野生型（WT）对照小鼠高4.7个对数单位，这表明任何残留的视杆细胞反应都降低了>50000倍，这与完全功能性敲除一致。暗适应的rho-/- ERG具有视锥细胞波形，在暗适应和明适应条件下，光谱敏感度在510 nm附近达到峰值，没有浦肯野氏位移的证据。幼年rho-/-小鼠明适应的ERG b波振幅与WT相同。该振幅在出生后第47天之前保持稳定，但此后在出生后第80天下降到仅1%-2%，此时视锥细胞外节已不存在。暗适应的rho-/-小鼠视锥细胞b波阈值为-1.07±0.39 log cd-s/m2（n = 17），在1.61 log scotopic cd/m2的抑制视杆细胞的全视野背景下，比明适应阈值敏感1.27个对数单位。这表明暗适应的WT对更暗淡刺激的反应完全由视杆细胞驱动，视锥细胞的干扰最小。高于该视锥细胞阈值强度时，暗适应的WT的b波将是视杆细胞和视锥细胞反应的总和。阈值与强度（TVI）研究未发现视杆细胞对小鼠视锥细胞b波有影响。
