IDENTIFICATION OF A 140 KDA PROTEIN OF RAT PRESYNAPTIC TERMINAL MEMBRANES ENCOMPASSING THE ACTIVE ZONES

A polyclonal antiserum raised against the carboxy-terminal 17 amino ac ids of the rat p185(c-neu) (anct) reacted with a 140 kDa polypeptide i n membranes of synaptosome fractions from neocortex and hippocampus of Ii-day-old and adult rats. The same antiserum reacted with a 185 kDa polypeptide in microsome membranes from rat pheochromocytoma cells (PC 12). By light microscopic immunocytochemistry, the anct antibodies aga inst the 140 kDa protein were localized in the neuropile of brain, cer ebellum and spinal cord of Ii-day-old and adult rats. Especially promi nent staining was obtained in the CA2-CA3 zones of the hippocampus, an d in the substantia gelatinosa in the spinal cord. The finely granular and diffuse pattern of the immunostain was consistent with synaptic l ocalizations. Interestingly, antibodies against the entire endodomain of p185(c-neu) (a-Bacneu) were localized in granular structures, proba bly representing axe-somatic and axo-dendritic synapses, on a subset o f pyramidal neurons of the CA3 zone. By immunoelectron microscopy, con ducted in the hippocampus of adult rats, the anct antibodies were loca lized at the cytoplasmic site of presynaptic terminals in the giant me ssy fiber type in the CA3 and CA4 regions. The immunolocalization of t he anct antibodies was restricted in segments of the presynaptic membr ane facing the synaptic cleft which include the active zone. The ident ity and function of the 140 kDa membrane protein of rat brain presynap tic terminals, detected by the anct antibodies, is unknown. The 140 kD a protein may be related to p185(c-neu), a tyrosine kinase, or to othe r known or unknown kinases.