A new electrophysiological non-invasive method to assess retinocortical conduction time in the Dark Agouti rat through the simultaneous recording of electroretinogram and visual evoked potential.

PURPOSE

To develop a non-invasive method exploiting simultaneous recording of epidermal visual evoked potential (VEP) and epicorneal electroretinogram (ERG) to study retinocortical function and to evaluate its reliability and repeatability over time.

METHODS

Female wild-type DA rats were anesthetized with ketamine/xylazine (40/5 mg/kg). Epidermal VEP (Ag/AgCl cup electrode on scalp) and epicorneal ERG (gold ring electrode on eye surface) were recorded simultaneously in response to flash stimulation.

RESULTS

ANOVA for repeated measures showed that peak times of ERG b-wave and of VEP N1 and P2 were stable across 6 weekly time-points, as well as the corresponding amplitudes. Mean retinocortical time from b-wave to N1 (RCT1) was 7.6 ms and remained comparable across the 6 time-points. Mean retinocortical time from b-wave to P2 (RCT2) was 28.7 ms and did not show significant variations over time. Coefficient of variation (CoV%) and CoV% adjusted for sample size, namely relative standard error (RSE%), were calculated as indexes of repeatability. Good RSE% over time was obtained (< 5% for b-wave, N1 and P2 peak times; < 20% and < 7% for RCT1 and RCT2, respectively).

CONCLUSIONS

Simultaneous recording of ERG and VEP has been previously achieved through invasive methods requiring surgery. Here, we present a new non-invasive method, which allowed to obtain peak and retinocortical times that were constant across a long period and had a good repeatability over time. This method will ensure not only a gain in animal welfare, but will also avoid stress and eye or brain lesions which can interfere with experimental variables.