Abstract
Purpose :
Important information can be gathered from non-saturated system responses, such as those obtained from the retina with very dim flashes (i.e., below the rod Vmax) of the scotopic electroretinogram (ERG). This study focuses specifically on the oscillatory potentials (OPs) of these responses to assess how their synchronicity evolves with flash strength, in rats and mice.
Methods :
Scotopic ERGs (Intensity: -6.3 to 0.9 log cd.s.m-2; dark-adaptation: 12 h) were performed on 6-8 adult pigmented (C57BL/6; PM) and albino (Balb/c; AM) mice as well as pigmented (Long-Evans; PR) and albino (Sprague-Dawley; AR) rats. ERGs were band-passed filtered (zero-phase FIR filter; order: 150) in 3 frequency bands (65-90 Hz; 90-115 Hz; 115-140 Hz) and a Hilbert transform was performed on each time series leading to a harmonic signal modulated with a time varying envelop. A threshold on the envelopes was set to delimit OP burst segment. The total OP burst duration and mean peak time difference (PTD) between each frequency band envelope were measured.
Results :
The OP bursts duration behaved in opposite ways between pigmented and albino animals. In PM and PR the burst duration peaked between -3.9 and -2.7 log cd.s.m-2, while it was minimal in AM and AR. This difference between pigmented and albino animals was also seen when considering the synchronicity of the OP burst as measured with the PTD. Indeed, at -3.9 log cd.s.m-2, PM and PR had a large peak of PTD (38.2±11.7 ms and 27.1±13.4 ms, respectively), while AM and AR had very low PTDs, except for the dimmest flashes (Peak PTDs: AM = 21.4±15.2 ms at -5.1 log cd.s.m-2; AR = 15.6±0 ms at -6 log cd.s.m-2). Regardless of animal species and pigmentation, all animals had a minimal PTD at the 4 brightest flash intensities (PTD at 0.9 log cd.s.m-2: AM= 3.4±1.6 ms; PM= 3.5±0.8 ms; AR= 4.7±1.4 ms; PR= 5.9±0.8 ms).
Conclusions :
Our results suggest a clear distinction between the scotopic OP bursts of pigmented and albino animals. The synchronicity peak found in pigmented animals matched the peak in burst duration, suggesting that longer OP bursts seen at dimmer flashes are more disorganized in their frequency contributions than the shorter bursts seen in albino animals at the same intensities. The increased synchronization observed at the brightest intensities in all animal tested, could suggest an optimization of the retinal (neuronal) response.
This is a 2021 ARVO Annual Meeting abstract.