Comparison of Activated Cortical Area Between Light and Electrical Stimulation in the Photoreceptor Degeneration Rabbit Model by Positron Emission Tomography

Abstract

Purpose: : The previous study of our group showed increased metabolism of the same cortical area on light and electrical stimulation of the rabbit retina on positron emission tomography (PET). In this study, the cortical areas activated by light and electrical stimuli were evaluated in photoreceptor degeneration rabbit model.

Methods: : Photoreceptors of the retinae were destructed by intravenous injection of sodium iodate (50mg/kg) in four New Zealand white rabbits weighing 3.0 kg. Photoreceptor dysfunction was certified by the flattened electroretinogram one week after the injection. Static PET scan was started 30 minutes after intravenous injection of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) through the ear vein. Three consecutive, 10 minute-scan data were averaged. The resting PET studies were done without stimuli. For the light stimulation PET studies, repetitive flash light stimulation of whole visual field (10^3.6cd, 1 Hz, 6 min total) was applied on one eye 1 min prior to ¹⁸F-FDG injection. For the electrical stimulation PET studies, repetitive electrical retinal stimulation (250µA, 1 Hz, 6 min total) was applied on the same eye with light stimulation using a suprachoroidally-implanted polyimide electrode array placed under the visual streak. Each study was performed after washing-out of the ¹⁸F-FDG of the prior study. Stimulation studies were registered on the resting PET study. The quantitative change of cerebral glucose metabolism was determined from the difference between the resting and stimulation state.

Results: : The histological examination was correlated with the electroretinogram finding concerning the annihilation of the photoreceptor after systemic sodium iodate injection. The glucose metabolism of the visual cortex was not increased by light stimulation, however, it was increased by electrical retinal stimulation. The activated cortical area was coincided with the area activated by the light and electrical retinal stimulation of the previous study which was done with the normal rabbit.

Conclusions: : The PET study showed that the electrical retinal stimulation evokes the increase glucose metabolism at the specific cortical area in the normal and the photoreceptor degeneration rabbit model. By comparing the activated area in PET study, objective analysis of the cortical responses on the various retinal stimulations might be possible.

Keywords: retina • transplantation • visual cortex