Potentiation by serotonergic inhibition of yawning induced by dopamine receptor agonists in rats.
Low doses of the dopamine D2-receptor agonist, B-HT 920 (25 micrograms/kg, SC), and the dopamine D1/D2-receptor agonists, apomorphine (50 micrograms/kg, SC) and piribedil (1 mg/kg, SC), evoked yawning. However, the dopamine D1-receptor agonist, SK&F 38393 (2 mg/kg, SC), failed to induce yawning. The yawning responses induced by B-HT 920, apomorphine or piribedil were markedly increased without eliciting stereotypy by pretreatment with reserpine (5 mg/kg, IP, 24 hr). These yawning responses were also enhanced by p-chlorophenylalanine (PCPA) (300 mg/kg, IP, 72 hr), but not by alpha-methyl-p-tyrosine (300 mg/kg, IP, 6 hr). The yawning induced by B-HT 920 given alone and in combination with reserpine or PCPA was inhibited by spiperone (0.5 mg/kg, IP) or scopolamine (0.5 mg/kg, IP), but not by SCH 23390 (0.5 mg/kg, IP). The present results suggest that yawning is evoked by stimulation of dopamine D2-receptors having a high affinity and consequent muscarinic activation, and that the yawning induced by dopamine receptor agonists is potentiated by decreases in serotonergic neuron activity.
Matsumoto
S
S
Department of Pharmacology, School of Medicine, Fukuoka University, Japan.
Yamada
K
K
Nagashima
M
M
Matsuo
N
N
Shirakawa
K
K
Furukawa
T
T
D000818:Animals; D001381:Azepines / Q000494:pharmacology; D010134:Fenclonine / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D017448:Receptors, Dopamine D2; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000502:physiology*; D015000:Yawning / Q000187:drug effects*
D001381:Azepines; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D012701:Serotonin; C024763:talipexole; D012110:Reserpine; D010134:Fenclonine