Journal of Neuroscience, Vol 9, 2697-2709, Copyright © 1989 by Society for Neuroscience
A nerve terminal protein with a selective distribution in spinal cord and brain
TC Ritchie, MA Thomas and JD Coulter
Department of Anatomy, College of Medicine, University of Iowa, Iowa City 52242.
A monoclonal antibody, designated S-7B8, recognizes a protein antigen
localized to highly selected populations of nerve terminals in spinal cord
and brain. The antibody produces dense immunocytochemical staining of
primary afferent endings that synapse in superficial laminae of the spinal
cord dorsal horn. Electron microscopy shows staining to be localized in
nerve terminals where reaction product is associated primarily with
spherical vesicles. In brain, S-7B8 immunoreactivity occurs in nerve
terminals in sensory relay nuclei, most thalamic nuclei, and other selected
areas, including the cerebellar molecular layer, the substantia nigra, the
globus pallidus, and certain synaptic layers of the hippocampus and dentate
gyrus. Endocrine glands and other tissues do not exhibit S-7B8
immunoreactivity. Although the antibody localizes to certain populations of
nerve terminals that may use excitatory amino acid neurotransmitters, the
distribution of S-7B8 immunoreactivity in the CNS does not correspond to
that of any previously identified nerve terminal protein. Experiments to
characterize the S-7B8 antigen indicate it may be an integral membrane
component since extraction of synaptosomes with alkaline pH or high ionic
strength does not release the antigen from the membranes. To identify the
molecular weight of the S-7B8 antigen, synaptosomal membranes were
solubilized in CHAPS and sequentially chromatographed on hydroxylapatite
and then on DEAE anion-exchange resin to produce enriched fractions. When
enriched fractions were separated on SDS-PAGE and Western blotted, the
S-7B8 antibody specifically stained a protein migrating at 75,000 Da. This
protein has been designated NT75. Preliminary studies of developing
pathways show that the appearance of S-7B8 immunoreactivity in growing
nerve endings corresponds closely to the time when synaptic connections are
formed. Thus, the NT75 protein recognized by the S-7B8 antibody may have a
role in the development and maintenance of specific synaptic endings.