An electron microscopic study on the retina of rodless mutant mice (ddN/Nagoya).

Abstract

The fine structure of the retina in rodless mutant mice (ddN/Nagoya) was studied electron-microscopically. Photoreceptor cells of the retina in these mice degenerated and entirely disappeared in the course of postnatal development. Consequently in the adult mice the inner nuclear layer was contiguous with the outer limiting membrane. Small triangular plexiform areas (remnant of the outer plexiform layer) intervened between the outer limiting membrane and the outermost row of the bipolar cells. These plexiform areas were occupied by the processes and terminals classified into four types; neurotubular processes, neurofilamentous processes, terminals containing spherical vesicles and terminals containing cored vesicles. A few synaptic contacts made by these structures were observed. A small part of the neurotubular processes was assigned to be the bipolar cell dendrites, while the other profiles could not be identified in this study.In the inner plexiform layer of the retina in normal mice, large bipolar terminals which were characterized by the presence of ribbons and closely packed vesicles made diad synaptic contacts, whereas in the rodless retina of the mutant mice, the diad synaptic contacts between smaller terminals were observed packed less closely with vesicles and containing ribbons. In the inner plexiform layer of the rodless retina the ganglion dendrites, the amacrine terminals and their synaptic contacts were well preserved, though the size of components forming synapses seemed to be somewhat reduced.