Relation between yawning behavior and central serotonergic neuronal system in rats.
Subcutaneously (s.c.) administered apomorphine (0.0125-0.4 mg/kg) or physostigmine (0.025-0.4 mg/kg) to rats elicited yawning. The dose-response curves were bell-shaped. The peak effects of apomorphine and physostigmine were observed with a dose of 0.1 mg/kg of each drug. Yawning elicited by apomorphine (0.1 mg/kg) or physostigmine (0.1 mg/kg) was reduced by intraperitoneally (i.p.) administered 5-hydroxytryptophan (5-HTP, 50-200 mg/kg, given 30 min before). Yawning elicited by apomorphine but not by physostigmine was enhanced by p-chlorophenylalanine (p-CPA, 25-400 mg/kg i.p., given 24 h before). Apomorphine elicited but not physostigmine-elicited yawning was enhanced by pretreatment with 5,7-dihydroxytryptamine (5,7-DHT, 8 micrograms/rat, given 14 days before into the dorsal raphe). This treatment led to a 35% depletion of serotonin (5-HT) in the striatum. 5-HTP, p-CPA or 5,7-DHT given alone did not elicit yawning. Bilateral, intrastriatal microinjection of apomorphine (1.5-50 micrograms/site) but not physostigmine (5-50 micrograms/site) elicited yawning. The dose-response curve was also bell-shaped. These results indicate that central serotonergic pathways play an important role in modulating drug-elicited yawning in rats.
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D006916:5-Hydroxytryptophan / Q000494:pharmacology; D000818:Animals; D001058:Apomorphine / Q000008:administration & dosage / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D010134:Fenclonine / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D010830:Physostigmine / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*; D015000:Yawning / Q000187:drug effects*
D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D010830:Physostigmine; D006916:5-Hydroxytryptophan; D001058:Apomorphine; D010134:Fenclonine