title: Effects of various direct or indirect dopamine agonists on the latency of the acoustic startle response in rats.
abstract: The effects of dopamine agonists were investigated on the latency of the acoustic startle response in male Wistar rats. Four indirect dopamine agonist were tested: GBR 12783 (5-20 mg/kg), BTCP (5-20 mg/kg), dexamphetamine (3-6 mg/kg) and L-DOPA 100 mg/kg associated with benserazide 25 mg/kg; they induced an increase in startle latency. Apomorphine at a dose (50 micrograms/kg) known to decrease dopaminergic transmissions, was ineffective on the startle response. On the contrary, at 0.6 or 2 mg/kg, apomorphine induced an increase in the startle latency. A similar effect was observed with bromocriptine at 10 mg/kg from the 10th min up to at least the 9th hour after treatment. The specific agonist of D2 receptors Ru 24926 (0.45 mg/kg) enhanced the startle latency as well as the specific agonist of D1 receptors SKF 38393 (10 mg/kg). The association of these drugs resulted in an apparent additivity of their individual effects. The effect of apomorphine (0.6 mg/kg) was only partially reduced by a high dose of the specific D2 antagonist amisulpride (80 mg/kg) and more clearly antagonized by the specific D1 antagonist SCH 23390 (50 micrograms/kg). It is concluded that D2 and D1 receptors contribute to the increase in startle latency elicited by direct or indirect dopamine agonists.
authors.affiliation: Unité de Neuropsychopharmacologie expérimentale, U.R.A. C.N.R.S., Faculté de Médecine et de Pharmacie de Rouen, St. Etienne Rouvray, France.
authors.forename: B
authors.initials: B
authors.lastname: Naudin
authors.forename: S
authors.initials: S
authors.lastname: Canu
authors.forename: J
authors.initials: J
authors.lastname: Costentin
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D015259:Dopamine Agents / Q000494:pharmacology*; D018492:Dopamine Antagonists; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D013216:Reflex, Startle / Q000187:drug effects*
chemical_list: D015259:Dopamine Agents; D018492:Dopamine Antagonists; D001058:Apomorphine