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Quantitative effects of some muscarinic agonists on evoked surface‐negative field potentials recorded from the guinea‐pig olfactory cortex slice
Author(s) -
Williams S.H.,
Constanti A.
Publication year - 1988
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1988.tb11471.x
Subject(s) - neuroscience , guinea pig , muscarinic acetylcholine receptor , olfactory system , electrophysiology , chemistry , biology , medicine , endocrinology , receptor
1 The effects of muscarinic receptor agonists on the electrically‐evoked surface‐negative field potential (N‐wave) were measured in the guinea‐pig olfactory cortex slice maintained in vitro.2 Bath‐superfusion of (±)‐muscarine, acetylcholine (ACh), carbachol (CCh), or methacholine (MCh) (10–200 μ m ) produced reversible, dose‐dependent depressions of the N‐wave (ACh and MCh effects were observed in the presence of 10 μ m neostigmine). The order of potencies (based on agonist dose causing 50% field depression: IC 50 ) was: ACh ≥ muscarine > CCh > MCh. All four agonists depressed the field potential by 100% at doses greater than 500 μ m . 3 Pilocarpine and bethanechol were weak agonists and only produced measurable effects at high doses (1–2 m m ). Neither agonist evoked a maximum response at doses up to 10 m m . 4 The muscarinic ganglion stimulant, McN‐A‐343 yielded inconsistent results, depressing the field potential in some slices, but having no effect in others. Pre‐application of a conditioning dose (100 μ m ) of McN‐A‐343 reduced subsequent responses to CCh, suggesting possible partial agonist properties. 5 Oxotremorine (up to 100 μ m ) did not depress the field potential, but it reversibly antagonized the effects of CCh. 6 It is concluded that reproducible, quantifiable responses to muscarinic agonists can be evoked in the olfactory cortex slice. We suggest this preparation may be useful for conducting pharmacological studies of ‘intact’ central muscarinic receptors.