Microtubule-associated protein 1A (MAP 1A) is a ganglion cell marker in adult rat retina

We have used antibodies raised against a cytoskeletal protein, microtubule-associated protein 1A (MAP 1A), to stain adult rat retina. In cryostat and polyethylene glycol-embedded radial sections, the fiber layer, ganglion cell layer, and inner plexiform layer were highly immunoreactive, a finding that suggested that the ganglion cell somata, axons, and dendrites were recognized by these antibodies. Retrograde labeling of retinal cell somata from the superior colliculus and dorso-lateral geniculate nucleus to identify ganglion cells showed colocalization of the tracer and immunoreactive cells. Double labeling with nuclear stains revealed that many cells in the ganglion cell layer, which are likely displaced amacrine cells, were not recognized by these antibodies. Furthermore, transection of ganglion cell axons, a procedure that causes retrograde degeneration of many of the axotomized ganglion cells, led to a decrease in the number of anti-MAP 1A immunoreactive cells in retinal wholemounts. Thus, MAP 1A antibodies preferentially stain ganglion cell somata and dendrites but not amacrine cells. These antibodies should be useful ganglion cell markers.