Potassium evoked in vivo release of substance P in rat caudate nucleus measured using a new technique of brain dialysis and an improved substance P-radioimmunoassay.

Semipermeable tubules were implanted in rat caudate nucleus in vivo. The tubules were perfused with artificial cerebrospinal fluid and the dialysates collected in fractions which were analysed for substance P content by a sensitive radioimmunoassay (detection limit: 0.1 fmol SP per sample). During controls periods no or comparatively small amounts of SP could be detected in the dialysates. An increase of the potassium concentration in the perfusion fluid to 100 mM or 200 mM induced a release of SP which tended to be concentration dependent. The present results demonstrate a new method to measure in vivo release of SP in rat brain.