Monoclonal antibody anti-type I and anti-zebrin II labelling in siluriform fishes: the role of shared lineage versus shared function in polypeptide co-distributions.

Two monoclonal antibodies (mabs), the newly generated mab anti-type I and the previously described mab anti-zebrin II, were reacted with brainstem sections of two ostariophysan siluriforms, the gymnotoid Rhamphichthys rostratus and the siluroid Ictalurus punctatus. Mab anti-type I recognizes a 47 kDa polypeptide present in the dendrites and soma of projection neurons. Mab anti-zebrin II recognizes a 36 kDa polypeptide present throughout the neuronal cytoplasm, including the axon. Strongly type I immunopositive cells include: all cerebellar Purkinje cells; pyramidal cells of the nucleus medialis, electrosensory lateral line lobe and tectum; pacemaker relay cells; Mauthner neurons; lateral line ganglion cells; cells of the inferior olive; and large neurons of the reticular formation and lateral reticular nucleus. Weakly reactive type I cells include: neurons in the torus semicircularis, medial and efferent octavolateralis nuclei, the magnocellular and lateral tegmental nuclei; and the motor neurons of the Vth, VIIth and Xth cranial nerves. Most type I positive cells are brainstem projection neurons. Zebrin II expression is restricted to subsets of two cell types which also express the type I antigen - Purkinje cells and acousticolateralis pyramidal cells. Both of these neuronal types develop from the region of the rhombic lip. While the mutual expression of the type I antigen can be explained by the shared function of projection neurons, the common expression of the zebrin II antigen is most likely due to a shared embryological and/or phylogenetic lineage.