Inhibitory effects of GABA, L-glutamic acid and nicotine on the potassium-evoked release of substance P in substantia nigra slices of the rat.
Rat substantia nigra slices were superfused with a physiological medium containing a diluted substance P (SP) antiserum, bacitracin and serum albumin to measure SP released in superfusates. As shown by measuring the degradation of a SP-labelled derivative incubated with cerebellar slices, this medium prevented the enzymatic inactivation of SP. Potassium (K+, 50 mM) and veratridine (5 X 10(-5) M) stimulated SP release and these effects were respectively prevented in absence of calcium and in presence of tetrodotoxin (5 X 10(-7) M). GABA (5 X 10(-5) M), nicotine (10(-6) M) and L-glutamic acid (5 X 10(-5) M) reduced the K+ (50 mM)-evoked release of SP. In contrast, glycine (5 X 10(-5) M), oxotremorine (5 X 10(-5) M), D-glutamic acid (5 X 10(-5) M) and serotonin (5 X 10(-5) M) were without effect. Pempidine (10(-5) M) prevented the inhibitory effect of nicotine (10(-6) M) on the K+-evoked release of SP. Glutamic acid diethyl ester (10(-4) M) completely abolished the L-glutamic acid-induced inhibition of the K+-evoked release of SP. Picrotoxin (5 X 10(-5) M) did not influence the L-glutamic acid inhibitory effect excluding the intervention of GABAergic mechanisms.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D007106:Immune Sera / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009538:Nicotine / Q000494:pharmacology*; D010852:Picrotoxin / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects; D013373:Substance P / Q000378:metabolism*; D013378:Substantia Nigra / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D002118:Calcium; D005971:Glutamates; D007106:Immune Sera; D009538:Nicotine; D010852:Picrotoxin; D011188:Potassium; D011978:Receptors, Nicotinic; D013373:Substance P; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid