Pharmacological characterization of serotonin receptors in the facial motor nucleus: a microiontophoretic study.
The effects of 'peripheral' serotonin (5-HT) antagonists on the facilitation of facial motoneuron excitation by 5-HT were investigated in the present study. Microiontophoretic application (5--10 aA) or intravenous administration of methysergide (0.5--1.0 mg/kg), cyproheptadine (0.5--1.0 mg/kg), cinanserin (0.5--1.0 mg/kg), or metergoline (50--100 micrograms/kg) antagonized the facilitating effect of 5-HT but not that of norepinephrine (NE) on facial motoneurons. Blockade developed within 1--2 min of the intravenous administration of methysergide, cyproheptadine and cinanserin and continued up to 30 min. The antagonism produced by intravenous metergoline took 8--15 min to develop and lasted for at least 6 h. Chronic administration of metergoline resulted in supersensitivity to 5-HT and NE in the facial nucleus. The putative 5-HT antagonists chlorpromazine, propranolol, and methiothepin failed to block the facilitating effect of 5-HT; however, methiothepin did block NE. The results are discussed in relation to a two-component model of the 5-HT mediated motor syndrome consisting of : (1) patterned excitatory inputs to motor nuclei; (2) 5-HT facilitation of these excitatory inputs. The 'peripheral' 5-HT antagonists appear to directly block the latter component.
D000818:Animals; D002928:Cinanserin / Q000494:pharmacology; D003533:Cyproheptadine / Q000494:pharmacology; D005154:Facial Nerve / Q000187:drug effects*; D007478:Iontophoresis; D008297:Male; D008711:Metergoline / Q000494:pharmacology; D008719:Methiothepin / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D009046:Motor Neurons / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects*
D011985:Receptors, Serotonin; D008711:Metergoline; D003533:Cyproheptadine; D008719:Methiothepin; D011433:Propranolol; D002928:Cinanserin; D009638:Norepinephrine; D008784:Methysergide