Alz-50 recognizes epitopes in primary sensory fibres 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 cellular pathological changes in Alzheimer's disease. However, it has been reported that this antibody also reacts with specific epitopes in normal individuals. Furthermore, intense Alz-50 immunoreactivity has been recently described in the hypothalamus and spinal cord of rat and monkey. In the present study, we analysed the distribution pattern of Alz-50 immunostaining in the spinal cord of the adult rat. Using light microscopy, immunostained fibres and varicosities were detected mainly in laminae I-II, although some immunostaining lamina I and the outer two thirds of lamina II. The varicosities appeared either scalloped or dome-shaped and contained numerous agranular synaptic vesicles and a few dense-core vesicles. Most varicosities were presynaptic to dendrites. A few immunostained cell bodies and dendrites were also observed, but glial cells were never immunostained. Some ultrathin sections were processed for postembedding immunogold detection of calcitonin gene-related peptide and GABA immunoreactivities. Most of the varicosities which were immunoreactive for Alz-50 also showed calcitonin gene-related peptide immunoreactivity. In contrast, GABA immunoreactivity was never co-localized with Alz-50 immunoreactivity. These results indicate that, in the superficial dorsal horn, the epitope recognized by the Alz-50 antibody is located mainly, but not exclusively, in primary sensory fibres.