Transmitter-specific retrograde tracing of pathways?

Publisher Summary Transmitter specificity in neuronal pathways may be detected morphologically by means of retrograde perikaryal labeling after application of a transmitter in the terminal area. This chapter discusses this hypothesis. This hypothesis originated from observations made in the connection between the subtectal nucleus isthmi pars parvocellularis (Ipc) and the tectum after injection of [ 3 H]glycine into the pigeon optic tectum. In this Ipc-tectal pathway, a retrograde axonal migration of soluble labeled material was found. This pathway is likely to be glycinergic. The hypothesis of transmitter-specific retrograde labeling of pathways was further tested in some rat central connections with known transmitter. After nigral injection of [ 3 H]GABA, perikaryal labeling was observed in the striatum, whereas injection of [ 3 H]serotonin resulted in labeled cell bodies in the nucleus raphe dorsalis. After striatal injections of [ 3 H]dopamine or [ 3 H]serotonin, perikaryal labeling was obtained in the substantia nigra, the dopaminergic groups A8 and A10, and in the nucleus raphe dorsalis.