Effect of 5-hydroxytryptamine on external carotid nerve activity and its blockade by GR38032F in anesthetized rats.

Excitatory response to 5-hydroxytryptamine was recorded from the external carotid nerve, a branch of the superior cervical ganglia, in anesthetized rats using an electrophysiological technique. Bolus intravenous injection of 5-HT (1.5625-50 micrograms/kg) evoked a rapid and dose-dependent excitation of external carotid nerve activity. This response was blocked by a selective 5-HT3-receptor antagonist, GR38032F (10 micrograms/kg). A 5-HT3 receptor agonist, 2-methyl-5-HT (3.125-50 micrograms/kg), also produced a rapid and dose-dependent excitation of external carotid nerve activity. GR38032F (10 micrograms/kg) caused a significant rightward shift in the 2-methyl-5-HT dose-response curve. These results suggest that the 5-HT-induced excitatory response of ECNA might be mediated via a 5-HT3 receptor.