Neurofilament phosphorylation in the axonless horizontal cells of rat retina

Axonless horizontal cells in the outer plexiform layer of rat retina were studied with 19 monoclonal antibodies reacting with phosphorylated and non-phosphorylated epitopes of the two high molecular weight neurofilament proteins (NF 150K and NF 200K). With 6 antibodies, immunoreactivity was confined to the nerve fiber layer on the inner surface of the retina. Horizontal cells were not stained. Four antibodies in this group were axon-specific, while the remaining two stained motor and sensory neuron perikarya in rat spinal cord and dorsal root ganglia, respectively. Of the 13 antibodies which stained horizontal cells, 11 reacted with phosphorylated epitopes and failed to decorate motor neuron perikarya in the spinal cord, while in dorsal root ganglia, they stained a subpopulation of sensory neurons.