Retrograde labeling of corticospinal motor neurons from early postnatal rodents.

Immunopanning of viable neurons requires availability of an antibody directed against a neuronal surface epitope that is specific for a neuron type of interest (e.g., corticospinal motor neurons [CSMNs]) and that is able to immobilize only neurons of interest from a dissociated brain suspension on a culture dish. However, few, if any, neuron type-specific monoclonal antibodies have been developed. Panning antibodies have not been characterized for CSMNs. To circumvent this issue, we developed a method to retrograde label CSMNs with a cholera toxin B subunit (CTB) tracer that localizes to the plasma membrane only of labeled CSMNs. The main objective of this procedure is to provide CSMNs with a surface marker that can be used to immunopan only the labeled CSMNs by using a CTB-specific antibody.