title: The mode of action of bromocriptine following pretreatment with reserpine and alpha-methyl-p-tyrosine in rats.
abstract: The ability of bromocriptine (BRC), a selective dopamine D-2 receptor agonist, to induce yawning responses was studied in rats pretreated with reserpine and alpha-methyl-p-tyrosine (alpha-MPT). BRC (1 20 mg/kg IP) evoked yawning responses, which were pronounced at 2.5 mg/kg and characterized by the head moving downward. Higher doses of BRC (5 20 mg/kg) dose-dependently delayed the onset and peak time of yawning. A low dose of the selective D-1 dopamine receptor agonist SK&F38393 did not induce yawning but enhanced the BRC-induced response. Pretreatment with reserpine (1 and 5 mg/kg SC), alpha-MPT (100 and 300 mg/kg IP) and reserpine (1 mg/kg) plus alpha-MPT (100 mg/kg) was able to significantly reduce BRC-induced yawning. The inhibitory effects were prevented by a low dose of SK&F38393 (0.5 mg/kg IP). In particular, combined treatment with reserpine (5 mg/kg) and BRC (10 and 20 mg/kg) elicited upright fighting and jumping behaviors which were inhibited by haloperidol (1 mg/kg IP), a non-selective D-1 and D-2 receptor antagonist, SCH23390 (0.05 mg/kg SC). a selective D-1 receptor antagonist, or sulpiride (20 mg/kg IP), a potent D-2 receptor antagonist, and were potentiated by SK&F38393 (0.5 mg/kg). SCH23390 (0.05 mg/kg) decreased BRC-induced yawning and the apomorphine (low doses)-induced potentiation of BRC yawning, and prevented the apomorphine (high doses)-induced reduction of BRC yawning. SCH23390 also inhibited apomorphine-induced stereotypy and BRC-induced potentiation of apomorphine stereotypy.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D001971:Bromocriptine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D012110:Reserpine / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D015000:Yawning / Q000187:drug effects; D019805:alpha-Methyltyrosine
chemical_list: D001552:Benzazepines; D008781:Methyltyrosines; D011954:Receptors, Dopamine; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D001971:Bromocriptine; D019805:alpha-Methyltyrosine; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D012110:Reserpine; D014446:Tyrosine 3-Monooxygenase