Neuronal circuitry dissected by immunocytochemistry combined with retrograde tracing and electrophysiology

Several substances, once injected in a given central structure, are taken up by axon terminals and transported retrogradely over long distances, to the cell bodies of neurons projecting to the injection area. They are then visualized by means of histochemical (or immunohistochemical) reactions, making it possible to trace neural pathways . Here we describe a method to label retrogradely neocortical pyramidal neurons in a Golgi-like fashion. This method allows reconstructing the entire dendritic tree of retrogradely labeled cells and can be easily combined with immunohistochemical techniques. Methods suitable to establish relationships between morphological and functional features of projecting neurons are also discussed.