IMMUNOLOCALIZATION OF THE RECEPTOR TYROSINE KINASE EPHA4, IN THE ADULT-RAT CENTRAL-NERVOUS-SYSTEM

EphA4 is a receptor tyrosine kinase of the Eph family previously desig nated Cek8 in chicken, Tyrol in rat, and Sek1 in mouse, which is prefe rentially expressed in the embryonic and adult nervous system. We have mapped the distribution of EphA4 in the adult rat brain and spinal co rd using a polyclonal antibody raised against a synthetic carboxy-term inal peptide. Immunoblotting experiments revealed that EphA4 is widely distributed in various regions of the adult rat brain. At the light m icroscopic level, intense immunoreactivity was apparent in the cerebra l cortex, hippocampus, matrix compartment of the neostriatum, choliner gic neurons in the basal forebrain, cerebellar Purkinje cells, and sub stantia gelatinosa of the spinal cord. Among white matter tracts, EphA 4 expression was detected in the corpus callosum, fornix, and posterio r portion of the anterior commissure, but not in the lateral olfactory tract, mammillothalamic tract, or optic chiasm. Interestingly, expres sion in the optic chiasm is high at postnatal day 6, but decreases wit h the maturation of this structure. While in some regions of the neuro pil neuronal cell bodies were prominently labeled, in others EphA4 imm unoreactivity was detected in a punctate pattern. This punctuate stain ing did not coincide with synaptophysin localization. At the electron microscopic level, EphA4 immunoreactivity was observed in dendrites in the gray matter, particularly associated with dendritic spines, and i n myelinated axons, but not their myelin sheaths in the white matter. The widespread distribution and diverse subcellular compartmentalizati on of EphA4 suggest that this receptor is important for the maintenanc e of multiple structures in the adult nervous system. (C) 1997 Elsevie r Science B.V.