Monoamine oxidase-A-positive retinal ganglion cells projecting to the superior colliculus and dorsolateral geniculate nucleus of the rat brain

Detailed morphology and distribution of monoamine oxidase type A (MAO-A) positive retinal ganglion cells, and their synaptic terminals in the superior colliculus and the lateral geniculate nucleus, were investigated by light and electron microscopy. In addition, the differences in various retinal ganglion cells with respect to the projection site were examined by the injection of colloidal gold into the superior colliculus and the lateral geniculate nucleus. The effects of unilateral enucleation were also examined. In the retina, small, medium and large sized MAO-A-positive ganglion cells were observed; the large sized cells were distributed evenly throughout the retina, while the small and medium sized cells were most numerous in a ring surrounding the central retina and decreased in density near the optic disc and the peripheral retina. The MAO-A-positive terminals in the superior colliculus were smaller in size than those in the lateral geniculate nucleus. From colloidal gold injections, it was apparent that the MAO-A-positive ganglion cells projecting to the superior colliculus were generally smaller in size than those projecting to the lateral geniculate nucleus. Fourteen days after unilateral enucleation, the MAO-A-positive terminals in the superior colliculus and lateral geniculate nucleus contralateral to the enucleated eye had almost disappeared, whereas those in the ipsilateral regions remained unaffected. These findings demonstrate the distribution and projections of the MAO-A-positive ganglion cells. (C) 1998 Academic Press Limited.