In vivo release of substance P in the cat substantia nigra.

Push-pull cannuale were implanted into the substantia nigra (SN) and the caudate nucleus (CN) of the cat to study the in vivo release of substance P (SP), using a radioimmunoassay and high pressure liquid chromatography (HPLC) analysis. The spontaneous release of SP could be detected in the SN and the CN. Potassium (50 mM) locally applied stimulated SP release in both structures. Furthermore an important evoked release of SP was observed in the SN during depolarization of striato-nigral SP fibers with potassium (50 mM) applied in the CN.