Axonal branching of ventral tegmental and raphe projections to the frontal cortex in the rat.

Axonal collateralization of neurons whose divergent branches innervate the medial prefrontal cortex (MFC) and the sulcal cortex was studied in the rat by using the retrograde double-labeling technique. Injections of bisbenzimide and propidium iodide into the MFC and sulcal cortex resulted in double-labeling of a small population of cells within the ventral tegmental area (VTA) and pars compacta of the substantia nigra (SNC). More extensive double-labeling was evident in the midbrain raphe nuclei. Collateralization++ therefore does not appear to be an important property of the dopamine innervation of the prefrontal cortex.