The substance P projections to the frontal cortex and the substantia nigra

In rats, brain substance P-like immunoreactivity (SPLI) was examined at different time intervals following hemisections. The SPLI of the frontal cortex ipsilateral to the cut disappeared following hemisections at anterior-posterior levels ranging from the level of the septum to the level of the interpeduncular nucleus. Hemisected brains examined after a 2–8 day survival period showed accumulation of SPLI in axons ascending in the medial forebrain bundle and in axons descending in the internal capsule. It was suggested that the cortical SP projection ascends in the medial forebrain bundle and that the striato-nigral projection descends in the internal capsule.