Retinal dopamine sensitivity to MPP+ toxicity: electrophysiological and biochemical evaluation

This study concerns the effect of intravitreal injection of 1-methyl-4-phenylpyridinium ion (MPP+) on the electroretinograms (ERG) and on the levels of retinal dopamine (DA) in rabbits. The right eye was injected intravitreously with MPP+ while the other received only the vehicle and served as control. The administration of 7, 40, 70 or 700 micrograms MPP+ resulted in a dose-related decrease of the amplitude of the a and b-waves as well as the oscillatory potentials (OPs) of the ERG, down to extinction. In contrast, the retinal DA content was decreased only with the 700 micrograms MPP+ dose. Fluorescein angiography demonstrated abnormalities in the retinal circulation of all MPP+-treated eyes. These observations indicate that MPP+ causes lesions to the retinal vessels at doses non-toxic to the retinal dopaminergic neurons. These data suggest that intravitreal injection of MPP+ cannot be used to study the physiological role of retinal DA.