Characterization of chemically defined neurons and their cellular relationships by combined immunocytochemistry and radioautographic localization of transmitter uptake sites

Radioautography and immunocytochemistry may be combined at the light and electron microscopic levels for simultaneously localizing uptake sites for exogenous transmitter molecules [such as (³H)monoamines or (³H)amino acids] and endogenous transmitter-related antigens (classical transmitters and their synthesizing enzymes as well as neuropeptides) in the central nervous system. Silver grain accumulations indicative of transmitter uptake sites are readily distinguishable from immunocytochemical labels of the peroxidase-antiperoxidase (PAP), avitin-biotin, or colloidal gold methods. The combination of uptake radioautography and immunocytochemistry may be applied to the investigation of (1) the chemical identity of (³H) transmitter-accumulating elements, (2) the coexistence of different neurotransmitters within the same neurons, and (3) the cellular basis of interactions between certain neurotransmitters, in particular monoamines, GABA, and neuropeptides. This article describes and evaluates the method and reviews the available experimental data derived from its application.