A monoclonal antibody raised against the Mauthner cell also recognizes some reticular neurons

A monoclonal antibody was raised against dissected Mauthner cells of goldfish, Carassius auratus. The immunoglobulin (mAb 222C2) recognized in this neuron a determinant that was localized on the soma of the Mauthner cell in front of the axon hillock and on the dorsomedial portion of the initial third of its ventral dendrite. When observed with electron microscopy, the staining was associated with polyribosomes and with the reticulum, close to the Golgi cisternae. The antibody also labelled other large neurons (10-40 microns) of the nuclei reticularis superior, medialis and inferior. In these cells, patchy immunolabelled elements could be detected, dispersed within cytoplasm. They did not exhibit the characteristic topological distribution observed in the Mauthner cell. On the basis of their size and location, this group of neurons may send axons to the spinal cord. No staining was observed in other areas of the brainstem, or in other structures such as the cerebellum or the optic tectum. The expression of this antigenic molecule in Mauthner and reticular cells suggests that these two sets of neurons are functionally and/or ontogenetically related. Although the molecular and functional characteristics of the antigenic molecule have not been determined, this antibody should be a useful marker for further developmental studies.