Identification of bipolar cell subtypes by protein kinase C-like immunoreactivity in the goldfish retina

Subtypes of bipolar cells were identified by protein kinase C (PKC)-like immunoreactivity in the goldfish retina. The PKC-like immunoreactivity was visualized by either the avidin/biotin peroxidase method or immunofluorescence method. In frozen cross sections and in wholemounts, the monoclonal antibody against alpha species of PKC reacted with ON-type bipolar cells, identified by the location of axon terminals in sublamina b of the inner plexiform layer. OFF-type bipolar cells (identified by the location of the axon terminal in sublamina a of the inner plexiform layer) were not immunoreactive. The immunoreactive cells consisted of two subtypes; the rod-dominant ON-type with a large soma and a large bulbous axon terminal, and the cone-dominant ON-type with a small soma and small axon terminal. Antibodies against beta and gamma species of PKC did not react with any bipolar cells. Of the isolated bipolar cells, enzymatically dissociated from the goldfish retina, 59% were immunoreactive to the monoclonal antibody against alpha species of PKC. The immunoreactive isolated cells also consisted of two morphological types. Each of them had a morphology typical either to rod-dominant ON-type or to cone-dominant ON-type.