ALZ-50 RECOGNIZES EPITOPES IN PRIMARY SENSORY FIBERS AND IN NEURONS OF THE SUBSTANTIA-GELATINOSA OF THE SPINAL-CORD - AN ULTRASTRUCTURAL-STUDY IN THE RAT

The monoclonal antibody Alz-50 has been proposed as a marker for cellu lar pathological changes in Alzheimer's disease. However, it has been reported that this antibody also reacts with specific epitopes in norm al individuals. Furthermore, intense Alz-50 immunoreactivity has been recently described in the hypothalamus and spinal cord of rat and monk ey. In the present study, we analysed the distribution pattern of Alz- 50 immunostaining in the spinal cord of the adult rat. Using light mic roscopy, immunostained fibres and varicosities were detected mainly in laminae I-II, although some immunostaining could be detected in deepe r laminae. At the ultrastructural level, immunostained axonal varicosi ties could be detected in lamina I and the outer two thirds of lamina II. The varicosities appeared either scalloped or dome-shaped and cont ained numerous agranular synaptic vesicles and a few dense-core vesicl es. Most varicosities were presynaptic to dendrites. A few immunostain ed cell bodies and dendrites were also observed, but glial cells were never immunostained. Some ultrathin sections were processed for postem bedding immunogold detection of calcitonin gene-related peptide and GA BA immunoreactivities. Most of the varicosities which were immunoreact ive for Alz-50 also showed calcitonin gene-related peptide immunoreact ivity. In contrast, GABA immunoreactivity was never co-localized with Alz-50 immunoreactivity. These results indicate that, in the superfici al dorsal hem, the epitope recognized by the Alz-50 antibody is locate d mainly, but not exclusively, in primary sensory fibres.