Quinpirole attenuates striatal c-fos induction by 5-HT, opioid and muscarinic receptor agonists.

Pretreatment with the dopamine D2 receptor agonist quinpirole (0.025-2.5 mg/kg) produced a marked, dose-dependent, attenuation of the striatal Fos expression induced by the serotonin (5-Hydroxytryptamine, 5-HT) releasing agent fenfluramine (25 mg/kg). Quinpirole (2.5 mg/kg) was also able to drastically attenuate the striatal Fos response produced by injections of the direct 5-HT1/2 receptor agonist N-(3-trifluoromethylphenyl)piperazine hydrochloride (TFMPP) (5 mg/kg), the selective 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (6.64 mg/kg), the 5-HT1A/1B receptor agonist RU-24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)1H-indole) (5 mg/kg), the mu-opioid receptor agonist morphine (5 mg/kg) and the muscarinic cholinergic receptor agonist pilocarpine (50 mg/kg). These results are in marked contrast to the previously reported ability of quinpirole to potentiate the response to D1 dopamine receptor agonists and demonstrate that stimulation of D2-like receptors can have differential effects on the Fos responses induced by various drugs.