NEURONAL AND GLIAL LOCALIZATION OF HOMOCYSTEATE-LIKE IMMUNOREACTIVITYIN THE RAT RETINA

To study the distribution of L-homocysteate in the rat retina, specifi c polyclonal and monoclonal anti-homocysteate antibodies have been use d in combination with a highly sensitive postembedding method for ligh t microscopic immunocytochemistry. In central and peripheral retina, t he most strongly immunoreactive cell bodies lay in the inner nuclear l ayer. They represented about 17% of the total neuronal cell population of the layer and were identified as bipolar cells (19-20% of cells in the outer half of the inner nuclear layer) and amacrine cells (15% of cells in the inner half of the inner nuclear layer). A third cell typ e showing heavy homocysteate-like immunoreactivity was identified as M uller glial cells. Characteristically, their descending processes form ed three immunoreactive bands in the inner plexiform layer. Furthermor e, the outer and inner limiting membranes as well as glia around and b etween ganglion cell axons and in the vicinity of blood vessels were l abelled intensely. Photoreceptors and their terminals, and ganglion ce lls, were not immunostained. These findings indicate the presence of h omocysteate in some bipolar and amacrine cells of the inner nuclear la yer and support a role for this sulphur-containing excitatory amino ac id as a neurotransmitter candidate in the retina.