An atlas of a rare neuronal surface antigen in the rat central nervous system

The mature nervous system contains functional synaptic networks composed of neuronal sets and subsets whose identity and maintenance may rely on external surface molecules specific for these neuronal subdivisions. Such molecules may reside permanently on specific neurons, serving to identify those neurons within a complex population. From a collection of monoclonal antibodies made to the Torpedo cholinergic synaptosome preparation, we have identified several antibodies that bind the surface of some, but not all, neurons of the mature rat brain (Kushner and Stephenson, 1983; Kushner, 1984). In the present study we catalog which neurons of the entire rat brain and spinal cord are immunopositive for one of these antibodies, Tor 23. The atlas we have compiled can be used (1) on a practical level to guide affinity purifications and neuronal cell sorting, and (2) more esoterically to address whether surface antigenic sets of neurons share or define a common functional property. In the forebrain, Tor 23-positive neurons predominate as a rare cell type of the inner cortical laminae. In the midbrain, few cells stain. In the hindbrain, labeled neurons are dispersed among several nuclei. The exceptions to these observations, areas that almost exclusively contain Tor 23-immunopositive neurons, are the spinal cord ventral horn, the deep cerebellar nuclei, some cerebellar-related nuclei, selected auditory nuclei, the supraoptic and paraventricular nuclei of the hypothalamus, and the CA2 pyramidal neurons of the hippocampus. The neurons that bind Tor 23 are related biochemically by virtue of that shared epitope alone. Whether they are related in a functional manner is a separate issue. Tor 23 demarks many motor-related structures, specifically, the ventral horn motor lamina, the orofacial motor nuclei 5 and 7, the ambiguus nucleus, the deep cerebellar nuclei, the pontine reticulotegmental nucleus, the lateral reticular nucleus, the gigantocellular reticular nucleus, the red nucleus, and neurons within the motor and somatosensory cortices. The overlap of Tor 23 with motor structures suggests that Tor 23 is a motor system marker.