Photopic ERGs in Selected Animal Species: Evidence for a Possible Contribution of the Tapetum Lucidum

Abstract

Abstract: : Purpose: We previously reported the ERGs of two dogs affected with unilateral absence of the Tapetum Lucidum (TL) where the ERG from the TL–free eye did not include the post b–wave negativity recorded in normal eyes. In order to further document the possible role of the TL, we compared the photopic ERGs in selected animal species with a TL such as carnivores (dogs and cats) with animal species devoid of a TL such as pigs and monkeys. Methods: Binocular, full field photopic ERGs were recorded from fully anaethetised yound adult dogs of various breeds (n=23), 16 young adult domestic cats, 21 young adult Göttingen minipigs and 17 young adult cynomolgus monkeys. ERGs analysis included: a– and b– waves amplitude measurements as well as that of the post–b–wave negative response (NR), and the datas were reported as b–wave/a–wave amplitude ratio and NR/b–wave amplitude ratio. Results: The b/a amplitude ratios were: 2.62 +/– 0.83; 3.28 +/– 0.76; 2.81 +/– 0.27 and 2.39 +/– 0.34 for dogs, cats, minipigs and monkeys respectively. The NR/b–wave amplitude ratios were 1.30 +/– 0.09; 1.42 +/– 0.13; 0.27 +/– 0.06 and 0.42 +/– 0.07 for dogs, cats, minipigs and monkeys respectively. Conclusions: While the b/a amplitude ratios did not demonstrate significant inter–species differences, the NR/b–wave amplitude ratio was found to be significantly (p<0.001) larger in cats and dogs compared to minipigs and monkeys. It is of interest to note that the latter two species are devoid of a TL, a finding that further confirms our claim that the TL contributes to the ERG NR component. It should be noted that this NR component is most probably different from the photopic negative response since it can also be visualized in scotopic ERGs as well.

Keywords: electrophysiology: non-clinical • electroretinography: non-clinical • comparative anatomy