Abstract
Abstract: :
Purpose: To compare the structural organization and electroretinographic (ERG) response of the retina of the sugar glider (Petaurus Breviceps), a nocturnal marsupial, to those of the WT C57BL/6 mouse. Methods: ERGs were recorded in response to monochromatic and broadband light stimuli during night– and daytime from anesthetized sugar gliders (n=3) and mice (n=5). Retinas of sugar gliders (n=4) and mice (n=5) were also examined by histological and immunocytochemical methods using a panel of antibodies. Results: (1) Hematoxylin–eosin staining revealed that the sugar glider retina is about half as thick as the mouse retina. WGA staining showed that the distribution and number of rods per 100 µm is roughly the same for the two species. For the sugar glider, PNA labeling indicated the presence of a few single and double cones and cones containing oil droplets. The identity of cone pigment(s) could not be established by immunocytochemistry using the cone–specific antibodies available in our laboratory. Besides this, the mouse and sugar glider displayed marked differences in staining pattern for CRALBP and brain creatine kinase. (2) At night, a "white" flash delivering ≥ 300,000 photons µm–2 at the cornea elicited saturating a–wave amplitudes of 140–180 µV from the sugar glider and 400–500 µV from the mouse. During the day, the same flash elicited a–wave amplitudes of 12 – 80 µV while mouse response amplitudes remained in the range of 400–500 µV. (3) A background producing ∼ 7000 R* s–1 rod–1 isolated the mouse cone response at all times, whether day or night. In the sugar glider, this background suppressed all ERG responses at night; however, during the day, it isolated a cone–driven b–wave response. (4) A double–flash ERG technique was used to derive the time course of the rod photoreceptor response. The conditioning flash (CF) produced ∼ 400 R* and the test flash ∼ 70,000 R* in a mouse rod. For the mouse, the derived rod response peaked at ∼ 35 ms and attained 50% recovery at ∼ 700 ms. For the sugar glider, these times were ∼ 45 ms and ∼ 750 ms, respectively. Conclusions: The rod density in the sugar glider and mouse retina is roughly the same. The rod photoreceptor kinetics are also reasonably similar. The difference in saturating a–wave response is large and may result from differences in retinal thickness and/or effects of circadian rhythms on sugar glider photoreceptor function.
Keywords: electroretinography: non–clinical • retina • photoreceptors