Retinal Function in P23H rats assessed by full-field ERGRetinal Function in P23H rats assessed by full-field ERG

Abstract

Purpose: Longitudinal study in a rod-dominated animal model with slow retinal degeneration.

Methods: Ten P23H rats were evaluated at different time points after birth starting from postnatal day 40 (PN40). ERG protocol included scotopic and photopic responses to single flashes followed by flicker series in light adapted state with frequencies of 5, 10, 15, 20 and 30 Hz.<br /> The ERG was recorded and stored for offline analysis with an Espion® system (Diagnosys LLC, Littleton, MA). The recorded signal was filtered on-line with a band-pass filter from 0,625 Hz to 300 Hz. Eyes were stimulated using a Ganzfeld stimulator (Color Dome; Diagnosys LLC, Littleton, MA).

Results: ERG amplitudes and implicit times show different courses of decay of rod and cone functionality. Dim single flash responses indicate that rod function is already abolished between PN150 and PN200. In contrast we observed reduced but maintained cone specific responses up to PN300. In the cone flicker response at all frequencies we consistently find some surprising signs of transient recovery of the function between PN150 and PN250. Different decay rates of cone and rod function allowed to model these results by a functional inhibition of rod pathways onto cone function. This model was tested in the flicker series and indicates that even relatively small remnants of rod function can substantially inhibit the cone response.

Conclusions: Evaluation of flicker series in retinal degeneration can offer new insights in terms of functional interaction of rods and cones during the course of retinal degeneration. Here we present first promising results in a small number of P23H rats that may trigger further similar investigations also in other animal models with retinal degeneration.