Serotonin excitation of facial motoneurons: receptor subtype characterization.
The receptor subtype(s) mediating the enhancement of facial motoneuron excitability by serotonin (5-HT) was evaluated by means of single-cell recording in vivo (in the anesthetized rat) and in vitro in brain slices. In vivo, microiontophoretic application of the broad-spectrum 5-HT1 agonist 5-carboxamidotryptamine (5-CT), the 5-HT2/5-HT1C agonist 1-[2,5-dimethoxy-4-methylphenyl]-2-aminopropane (DOM), but not the selective 5-HT1A agonist 8-OH-2[di-n-propylamino]tetralin (8-OH-DPAT), produced a 5-HT-like enhancement of facial motoneuron excitability. Intravenous administration of the 5-HT2/5-HT1C antagonists ritanserin and LY 53857 in vivo blocked the facilitatory effects of 5-HT and DOM, but not norepinephrine (NE). Similarly, in brain slices, bath application of ritanserin blocked the effects of 5-HT, DOM, and 5-CT, but not NE on facial motoneurons. Intracellular recordings showed that DOM induced a slow depolarization and an increase in evoked spikes, but these effects were of lesser magnitude and longer duration than those produced by 5-HT. Taken together, these results indicate a role for 5-HT2 and/or 5-HT1C but not 5-HT1A receptors in serotonergic enhancement of facial motoneuron excitability since 5-HT's effect was 1) at least partially mimicked by the selective 5-HT2/5-HT1C agonist DOM, 2) mimicked by the broad-spectrum 5-HT1 agonist 5-CT but not the selective 5-HT1A agonist 8-OH-DPAT, and 3) blocked by the 5-HT2/5-HT1C antagonists ritanserin and LY 53857.
Rasmussen
K
K
Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut.
Aghajanian
G K
GK
D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000662:Amphetamines / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology; D005154:Facial Nerve / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology*
D000662:Amphetamines; D011985:Receptors, Serotonin; D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine; D012701:Serotonin; C047087:5-carboxamidotryptamine