MULLER CELLS IN THE RETINA OF THE CANE TOAD, BUFO-MARINUS, EXPRESS NEUROPEPTIDE Y-LIKE IMMUNOREACTIVITY

We have used light- and electron-microscopic immunohistochemistry to i dentify the presence of immunoreactivity to neuropeptide Y (NPY) withi n Muller cells in the retina of the cane toad, Bufo marinus. Muller ce lls containing NPY-like immunoreactivity (NPY-LI) were identified at t he light-microscopic level by the coexistence with immunoreactivity to glial fibrillary acidic protein (GFAP) and at the ultrastructural lev el by their characteristic relationship to neuron cell bodies and proc esses. At the light-microscopic level, those cells which contained bot h NPY-LI and GFAP-LI usually had small cell bodies in the inner nuclea r layer, while those cells which contained only NPY-LI were identified as large and small amacrine cells. The radially oriented primary proc esses in the inner plexiform layer and the vitreal end feet of GFAP-LI Muller cells also expressed NPY-LI. At the ultrastructural level, thi n lamellar processes of Muller cells with NPY-LI enclosed some amacrin e cell bodies in the inner nuclear layer and amacrine cell dendrites i n the inner plexiform layer. These observations suggest that NPY-LI is localized in Muller cells in addition to two types of amacrine cells previously identified in the Bufo retina. This study provides the firs t evidence that glial elements in the vertebrate retina express NPY-LI .