Analysis of the actions of 5-hydroxytryptamine on the rabbit isolated vagus nerve.
Depolarization and reduction in the C fibre compound action potential (C spike) in response to 5-HT were recorded simultaneously from rabbit isolated vagus nerve. 5-HT (0.1-100 mumol/l) was applied either as single concentrations or cumulatively and EC50 and IC50 values measured from individual concentration-response curves. The EC50 values for depolarization (cumulative curves: 2.33, 1.64-3.33 mumol/l, geometric means and 95% confidence limits, n = 31; non-cumulative curves: 3.99, 2.89-5.52 mumol/l, n = 9) were significantly higher than IC50 values for C spike reduction (cumulative curves: 1.25, 0.91-1.74 mumol/l, n = 30; non-cumulative curves: 1.41, 0.72-2.76 mumol/l, n = 8). Complex effects on the C spike were observed, suggesting a susceptible group of C fibres and a 5-HT-resistant component to the C fibre action potential. The motor nerve C fibres in the vagus nerve appear insensitive to 5-HT, whereas the sensory C fibres were sensitive to 5-HT. Phenylbiguanide had a similar selective effect on the C spike, while the depolarizing agents, 1,1-dimethyl-4-phenylpiperazinium (DMPP) and gamma-aminobutyric acid (GABA) did not. Cumulative concentration-response curves for depolarization and C spike reduction could be repeated reproducibly if an interval of 90 min was left between determinations. Up to 6 curves could be generated from one preparation. The 5-HT uptake inhibitor, citalopram (0.1 and 1 mumol/l), had no effect on cumulative concentration-response curves.(ABSTRACT TRUNCATED AT 250 WORDS)
Elliott
P
P
Department of Physiology, University of Wales College of Cardiff, UK.
Wallis
D I
DI
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001645:Biguanides / Q000494:pharmacology; D015283:Citalopram / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D017829:Granisetron; D007191:Indazoles / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008787:Metoclopramide / Q000494:pharmacology; D009046:Motor Neurons / Q000187:drug effects; D011817:Rabbits; D012701:Serotonin / Q000494:pharmacology*; D014630:Vagus Nerve / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D001645:Biguanides; D015283:Citalopram; D017829:Granisetron; D007191:Indazoles; D008787:Metoclopramide; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; C008846:phenyl biguanide