Journal of Neuroscience, Vol 7, 2639-2650, Copyright © 1987 by Society for Neuroscience
Monoclonal antibodies specific for fixative-modified aspartate: immunocytochemical localization in the rat CNS
JE Madl, AJ Beitz, RL Johnson and AA Larson
Aspartate is a putative excitatory amino acid neurotransmitter that is
widely distributed in the CNS. To study its distribution, monoclonal
antibodies were produced against beta-L-aspartyl-L-aspartate (beta-Asp-
Asp) conjugated to keyhole limpet hemocyanin (KLH) using glutaraldehyde-
borohydride. Three monoclonal antibodies, Asp1-3, were obtained with high
degrees of selectivity for aldehyde-fixed aspartate. The immunocytochemical
staining pattern of rat CNS was found to be similar for all 3 antibodies
but differed in some regions from staining patterns produced by Glu1, a
monoclonal antibody with high selectivity for a form of amide-linked
glutamate. Tissue staining produced by Asp1- 3 could be inhibited using
aspartate conjugated to carrier proteins. Staining by Asp1 and Asp2 was
also inhibited by free small molecules containing aspartate. Specificity of
the 3 antibodies was evaluated by enzyme-linked immunoassay (ELISA) as
follows: (1) reactivity of antibodies for conjugates of small molecules
coated on ELISA plates; (2) ability of free small molecules to inhibit
reactivity of antibodies for beta-Asp-Asp/KLH coated on ELISA plates; and
(3) ability of conjugates to inhibit reactivity of antibodies for
beta-Asp-Asp/KLH coated on ELISA plates. In all 3 types of assays, Asp1 and
Asp2 displayed strong reactivity for small molecules and conjugates
containing aspartate and little reactivity for small molecules and
conjugates containing glutamate or GABA. Asp3 was highly reactive with
conjugates containing aspartate using both directed and inhibition ELISA
assays. For all 3 antibodies the precise staining pattern varied with the
fixative used. Following glutaraldehyde fixation, dense immunocytochemical
staining was observed in cerebral cortical neurons, some cerebellar granule
cells, hippocampal pyramidal cells, and neurons of the inferior olivary
nucleus. In addition, some putative GABAergic neurons, e.g., cerebellar
basket and stellate cells, appeared to be stained. In general, acrolein
fixation resulted in a more selective staining pattern in the CNS. For
example, putative GABAergic neurons were no longer immunoreactive nor were
hippocampal pyramidal cells.