Antagonistic action of baclofen on substance P-induced depolarization in the isolated spinal cord of the frog

Abstract

1. 1. The depolarization induced by substance P (2 × 10 −8 mol) on the ventral root of the isolated frog spinal cord was not affected by baclofen (10 −4 M) in the normal medium, whereas the depolarization in the tetrodotoxin-treated or Ca 2+-free, 1.8 mM Mg 2+ medium-perfused preparation was significantly reduced by baclofen. 2. 2. The depolarization induced by l-glutamate (2 × 10 −7 mol) was not affected by baclofen in normal and also in TTX- or Ca 2+-free, 1.8 mM Mg 2+-treated preparation. 3. 3. The results suggest that baclofen specifically antagonizes the depolarization induced by substance P at postsynaptic membrane.