DIFFERENTIAL DISTRIBUTION OF N-ACETYLASPARTYLGLUTAMATE AND N-ACETYLASPARTATE IMMUNOREACTIVITIES IN RAT FOREBRAIN

Contradictory immunohistochemical data have been reported on the local ization of N-acetylaspartylglutamate in the rat forebrain, using diffe rent carbodiimide fixation protocols and antibody purification methods . In one case, N-acetylaspartylglutamate immunoreactivity was observed in apparent interneurons throughout all allocortical and isocortical regions, suggesting possible colocalization with GABA. In another case , strong immunoreactivity was observed in numerous pyramidal cells in neocortex and hippocampus, suggesting colocalization with glutamate or aspartate. Reconciling these disparate findings is crucial to underst anding the role of N-acetylaspartylglutamate in nervous system functio n. Antibodies to N-acetylaspartylglutamate and a structurally related molecule, N-acetylaspartate, were purified in stages, and their crossr eactivities with protein conjugates of N-acetylaspartylglutamate and N -acetylaspartate were monitored at each stage by solid-phase immunoass ay. Reduction of the cross-reactivity of the anti-N-acetylaspartylglut amate antibodies to N-acetylaspartateprotein conjugates to about 1% el iminated significant staining of most pyramidal neurons in the rat for ebrain. Utilizing highly purified antibodies, the distributions of N-a cetylaspartylglutamate and N-acetylaspartate were examined in several major telencephalic and diencephalic regions of the rat, and were foun d to be distinct. N-acetylaspartylglutamate-immunoreactivity was obser ved in specific neuronal populations, including many groups thought to use GABA as a neurotransmitter. Among these were the globus pallidus, ventral pallidum, ent.opeducular nucleus, thalamic reticular nucleus, and scattered nonpyramidal neurons in all layers of isocortex and all ocortex. N-acetylaspartate-immunoreactivity was more broadly distribut ed than N-acetylaspartylglutamate-immunoreactivity in the rat forebrai n, appearing strongest in many pyramidal neurons. Although N-acetylasp artate-immunoreactivity was found in most neurons, it exhibited a grea t range of intensities between different neuronal types.