Comparison of basal oscillatory rhythm of retinal activities in rd1 and rd10 mice

Among the many animal models of retinitis pigmentosa (RP), the most extensively characterized animal is the rd1 mouse. Recent studies showed that the neurophysiological properties of rd1 retinas differ significantly from those of normal retina; the presence of an oscillatory rhythmic activity (∼10 Hz) both in retinal ganglion cell (RGC) spikes and field potentials (slow wave component, SWC). However, lesser studies have been done regarding electrical characteristics of rd10 retina, carrying the mutation of same rod-PDE gene and showing a later onset degeneration of photoreceptors. Therefore, in this study, we compared the oscillatory rhythm in RGC spike and SWC between rd1 and rd10 mice in different postnatal ages to understand neural code used by two diseased retinas to communicate with the brain. Extracellular action potentials are recorded by 8 × 8 MEA from the RGC in the in vitro whole mount retina. 4 and 8 weeks in rd1 mice and 4, 10, 15, and 20 weeks in rd10 mice were used (n=3 for each postnatal age). From the raw waveform of retinal recording, RGC Spikes and SWC were isolated by using 200 Hz high-pass filter and 20 Hz low-pass filter, respectively. Fourier transform was performed for detection of oscillatory rhythm in RGC spikes and SWC. In rd1 mice, there is no statistical difference between the frequency of SWC and spike in 4 weeks [p>0.05; spike 9.3 ± 0.9 Hz (n=40), SWC 9.3 ± 1.5 Hz (n=25)] and 8 weeks [p>0.05; spike 10.0 ± 1.3 Hz (n=87), SWC 10.9 ± 1.7 Hz (n=25)]. While in rd10 mice there is no statistical differences among the SWC through 4 ∼ 20 weeks, significant differences were observed between the frequency of RGC spike and SWC and also among RGC spikes [4 weeks (p<0.001): spike 5.5 ± 1.3 Hz (n=59), SWC 10.8 ± 3.1 Hz (n=14); 10 weeks (p<0.001): spike 6.8 ± 3.8 Hz (n=79), SWC - 0.3 ± 2.6 Hz (n=25); 15 weeks (p<0.05): spike 3.9 ± 0.7 Hz (n=33), SWC 9.9 ± 1.2 Hz (n=25); 20 weeks (p<0.05): spike 4.4 ± 1.2 Hz (n=53), SWC 9.8 ± 1.2 Hz (n=25)].