MEDIATION OF SEROTONIN-INDUCED HYPERVENTILATION VIA 5-HT3-RECEPTOR INEUROPEAN EEL ANGUILLA-ANGUILLA

The effects of serotonin (5-hydroxytryptamine) on ventilation were inv estigated by continuous measurements of intrabuccal pressure in unrest rained eel. Intravenous administration of 5-hydroxytryptamine (30 mu g . kg(-1)) caused a large increase in ventilatory frequency( +100%) an d amplitude( +140%). The 5-hydroxytryptamine-induced hyperventilation was blocked by the 5-HT3-receptor antagonists metoclopramide (1.0 mg . kg(-1)) or MDL72222 (1.0 mg . kg(-1)), and was insensitive to the 5-H T1/2-receptor antagonist methysergide (3.0 mg . kg(-1)) and to the 5-H T4-receptor antagonist DAU 6285 CL (3.0 mg . kg(-1)). The hyperventila tory response to 5-hydroxytryptamine could be mimicked by the 5-HT3 re ceptor agonist l-phenylbiguanide (300 mu g . kg(-1)). These results st rongly implicate the 5-HT3-receptor as the mediator of the 5-hydroxytr yptamine-induced hyperventilation in eel.