Pharmacological characterization of 5-hydroxytryptamine-induced excitation of afferent cervical vagus nerve in anaesthetized rats.
1. An excitatory response to 5-hydroxytryptamine (5-HT) was measured from the afferent vagus nerve of anaesthetized rats. Measurements were determined by an extracellular recording from the whole nerve. 2. Intravenous bolus injection of 5-HT (1.56-100 micrograms kg-1) evoked a dose-dependent excitation of afferent vagus nerve activity. This response was blocked not only by a selective 5-HT3 receptor antagonist, GR38032F (10 and 100 micrograms kg-1), but also by a 5-HT2 receptor antagonist, ketanserin (10 and 100 micrograms kg-1). 3. Both a 5-HT3 receptor agonist, 2-methyl-5-HT (3.12-100 micrograms kg-1), and a 5-HT2 receptor agonist, alpha-methyl-5-HT (3.12-50 micrograms kg-1), produced a dose-dependent excitation of afferent vagus nerve activity. These excitatory effects were antagonized by GR38032F (10 micrograms kg-1) and ketanserin (10 micrograms kg-1), respectively. 4. A 5-HT1 like receptor agonist, 5-carboxamidotryptamine (50 micrograms kg-1), and a putative 5-HT4 receptor agonist, 5-methoxytryptamine (100 micrograms kg-1), failed to produce excitatory effects on the afferent vagus nerve. 5. These results suggest that the 5-HT-induced excitatory response of the afferent vagus nerve might be mediated not only via 5-HT3 receptors but also via 5-HT2 receptors in anaesthetized rats. It is unlikely, however, that either 5-HT1-like or putative 5-HT4 receptors are involved in the excitatory response of the afferent vagus nerve to 5-HT.
Yoshioka
M
M
First Department of Pharmacology, Hokkaido University School of Medicine, Sapporo, Japan.
Ikeda
T
T
Abe
M
M
Togashi
H
H
Minami
M
M
Saito
H
H
D000818:Animals; D007093:Imidazoles / Q000494:pharmacology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects; D017294:Ondansetron; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists; D014630:Vagus Nerve / Q000187:drug effects*
D007093:Imidazoles; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D017294:Ondansetron; D007650:Ketanserin