A quantitative study of the effects of some muscarinic antagonists on the guinea-pig olfactory cortex slice.
1. Muscarinic depression of the electrically-evoked surface-negative field potential (N-wave) was measured in guinea-pig olfactory cortex slices maintained in vitro. 2. The effects of three muscarinic receptor antagonists, pirenzepine, atropine and gallamine on this muscarinic response were analysed in detail. 3. Pirenzepine was a potent competitive antagonist of carbachol (CCh)-evoked responses. Schild plot analysis yielded a pA2 value of 7.9 (Schild slope constrained to unity). A similar analysis for atropine versus CCh responses gave a pA2 of 8.9. 4. Combination experiments using pirenzepine and atropine produced dose-ratio shifts close to those expected for two antagonists competing for a similar receptor site. 5. Gallamine was only a weak antagonist of responses to CCh. 6. Oxotremorine behaved as a competitive antagonist at this muscarinic receptor (pA2 = 6.1). 7. It is concluded that the presynaptic muscarinic receptor mediating depression of the N-wave in the olfactory cortex slice is of the M1-subtype.
Williams
S H
SH
M.R.C. Neuropharmacology Research Group, Dept. of Pharmacology, School of Pharmacy, London.
Constanti
A
A
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects*; D004347:Drug Interactions; D005071:Evoked Potentials / Q000187:drug effects; D005703:Gallamine Triethiodide / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D010095:Oxotremorine / Q000494:pharmacology; D010277:Parasympathomimetics / Q000494:pharmacology*; D010890:Pirenzepine / Q000494:pharmacology
D010277:Parasympathomimetics; D010890:Pirenzepine; D010095:Oxotremorine; D001285:Atropine; D002217:Carbachol; D005703:Gallamine Triethiodide