Tracing of neuronal connections with cholera toxin subunit B: light and electron microscopic immunohistochemistry using monoclonal antibodies.

Subunit B of cholera toxin was used as a tracer substance in the central nervous system after being injected into various brain regions, mainly somatosensory relay structures. The tracer was localized with an immunoperoxidase technique, using monoclonal antibodies raised in mouse hybridomas. This method, which is applicable in both light and electron microscopic studies, is characterized by high contrast between specific labeling and unspecific background activity. It yields excellent retrograde labeling of the dendritic tree and is thus suitable for studying the neuronal cytoarchitecture and, on the ultrastructural level, the synaptic organization of identified projection neurons.