NEUROTOXIC DESTRUCTION OF DOPAMINERGIC CELLS IN THE CARP RETINA REVEALED BY A HISTOFLUORESCENCE STUDY

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A histofluorescence study was carried out with flat-mounts and cryosections of the carp (Cyprinus carpio) retina in order to explore morphological changes of dopaminergic (DA) cells following intravitreous injection of 6-hydroxydopamine (6-OHDA). The eyes were injected with a mixture of 6-OHDA, pargyline and ascorbic acid (10μg each to small-sized fish or 20μg each to large-sized fish) on two successive days, and enucleated at various survival intervals (2hr to 7 days) after the second injection. DA cells, taking up 6-OHDA and emitting a white-greenish fluorescence, were apparently normal in shape in 2 to 24hr after the injection, while they became yellowish and began to exhibit deformed cell bodies (swollen or shrunken) with tattered processes within 2 to 3 days after the injection. These cells lost uptake capability for noradrenaline given intravitreously. Such changes became severer in 4 to 7 days; faint yellowish cell bodies with no processes were collapsed or broken down into pieces and finally disappeared. These successive changes are reasonably assumed to represent the cytolytic destruction of DA cells induced by intravitreous 6-OHDA.