Raffaele d'Isa1, Valerio Castoldi1,2, Silvia Marenna1,2, Roberto Santangelo1,2, Giancarlo Comi1,2, Letizia Leocani3,4. 1. Institute of Experimental Neurology (INSPE), San Raffaele Scientific Institute, IRCCS-San Raffaele Hospital, Via Olgettina 60, 20132, Milan, Italy. 2. Vita-Salute San Raffaele University, Via Olgettina 58, 20132, Milan, Italy. 3. Institute of Experimental Neurology (INSPE), San Raffaele Scientific Institute, IRCCS-San Raffaele Hospital, Via Olgettina 60, 20132, Milan, Italy. letizia.leocani@hsr.it. 4. Vita-Salute San Raffaele University, Via Olgettina 58, 20132, Milan, Italy. letizia.leocani@hsr.it.
Abstract
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.
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.