Abstract
Abstract: :
Purpose: To detect and monitor functional development of the visual (parvo– and magnocellular) pathways in rats using the pattern electroretinogram (PERG). Methods: Sixteen Lewis rat puppies were raised in a normal laboratory environment under diurnal conditions. Rats were individually identified. PERG responses were recorded from both eyes at ages 5, 7, 11, 14 and 18 weeks. Stimulus was a series of 5 shifting (6.1 Hz) checkerboard patterns of decreasing spatial frequency (0.368–0.023 cycles per degree, cpd), projected directly on the animals’ fundus using a specially–modified direct ophthalmoscope. Results: PERG amplitudes increased progressively from age 5 to 11 weeks in response to all stimulus patterns. The mean PERG responses to 0.092, 0.046 and 0.023 cpd patterns increased during these 6 weeks by 355% (to 10.9 µV), 238% (to 13.1 µV) and 225% (to 13.3 µV), respectively (Fig 1). These responses to large patterns originate in the magnocellular pathways. The responses to finer patterns, representing parvocellular responses, showed an increase of similar magnitude, though the peak response was lower. By 11 weeks, responses to patterns of 0.368 and 0.184 cpd increased by 194% (to 6.6 µV) and 219% (to 9.0 µV), respectively (Fig 1). After peaking at 11 weeks, the PERG responses declined progressively. By 18 weeks of age, mean PERG responses decreased an average of 138% (Fig 1). Conclusion: We used the PERG to monitor functional development of the rat visual pathways. Varying the stimulus size allowed us to track functional maturation and ageing of both the parvo– and magnocellular pathways. These findings contribute to our understanding of the maturation and development of the visual system, as well as the decline in visual function in the elderly.
Keywords: visual development • electroretinography: non–clinical • retinal development