EFFECTS OF 5-HYDROXYTRYPTAMINE ON DISCHARGE OF VAGAL MUCOSAL AFFERENT-FIBERS FROM THE UPPER GASTROINTESTINAL-TRACT OF THE FERRET

This study was undertaken to determine the effects of 5-hydroxytryptam ine (5-HT) on vagal mucosal afferent endings and how this may relate t o their sensitivity to other stimuli. Single afferent fibres with rece ptive fields in the mucosa of the upper gastrointestinal tract were re corded from the cervical vagus of Urethane anaesthetized ferrets. The selection criteria included failure to respond to luminal distension ( i.e., vagal tension receptors were excluded). All fibres tested respon ded to mucosal stroking. The majority of these (28/32) also responded to close-intrarterially applied 5-HT (10 mug) with a brief burst (usua lly < 15 s) of action potentials, which in 6/6 cases was reduced or ab olished by the 5-HT3 receptor antagonist granisetron (0.1-0.5 mg/kg i. v.), as were four responses to cholecystokinin-octapeptide (100-400 pm ol close I.A.). The response to 5-HT was shown to be dose-dependent ov er the dose range 2-75 mug on six occasions. Responses to luminal stim uli, which included 150 mM HCl, 1 M NaCl, and mucosal stroking, were n ot blocked by granisetron although in three fibres, the resting discha rge was reduced by the antagonist, suggesting that resting discharge i n vagal mucosal afferents may be influenced by endogenously released 5 -HT.