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Thiago Costa, Claudia Ammann, Gabriela Ioshimoto, Agnès Gruart, José Delgado-García, Dora Ventura, Javier Márquez-Ruiz; The Awake Rabbit as a Model For Studies of Transcranial Direct Current Stimulation of The Visual Cortex. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3410.
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© ARVO (1962-2015); The Authors (2016-present)
Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulatory technique with increasing popularity in the field of rehabilitation research. As the mechanisms behind tDCS effects are roughly understood, non-anesthetized animal models are urgent. Contemporary literature does not provide examples of such models for visual system / tDCS studies. Here we propose to study the conscious rabbit as a model to investigate the underlying mechanisms of tDCS effects on the visual system.
Three male New Zealand white rabbits were tested awake and restrained. Sessions consisted of 30 min baseline recordings of visual evoked potentials (VEPs), 20 min of tDCS (no recording) and 60 min of post tDCS recordings. Anodal and cathodal tDCS (2mA) were delivered in separate sessions (one week interval). tDCS was applied simultaneously through 4 silver ball electrodes (Ø1mm) implanted over the skull equidistantly 2mm from the left primary visual cortex (AP 10mm / L7mm) with a saline-soaked sponge (35 cm2 surface area) fixated to the left ear serving as a counterelectrode. VEPs were recorded with the same silver ball electrodes. Monocular stimulation with trains of 20 flashes at 1Hz was presented every 2 minutes by a photostimulator (Grass PS33+) placed 12cm from the right eye. Peak-to-baseline analyses of main components (C1 and C2) were done for each block of flashes before and after anodal and cathodal tDCS application.
Repeated measures ANOVA revealed that anodal tDCS had no significant after-effects on VEP amplitudes or latencies (all p>0,37). Interestingly, cathodal tDCS increased the amplitude of the P1 component, an effect that seemed to last for at least one hour after tDCS (p<0,001). In addition, cathodal tDCS delayed the latencies of the C1 and C2 components (p<0,001). These changes were observed in all the animals.
Amplitude increase of positive VEP components by cathodal tDCS in rabbit confirms earlier reports in humans, reinforcing the adequacy of these procedures on animal model for tDCS/visual system investigations. In addition, the experimental design used here is compatible with the simultaneous recording of cortical neurons during tDCS application allowing for future investigations of underlying mechanisms of tDCS effects on vision.
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