The effects of dihydropyridine compounds in behavioural tests of dopaminergic activity.
1. The effects of the dihydropyridine calcium channel blocker nifedipine and the activator Bay K 8644 were investigated in different behavioural tests involving dopaminergic systems. These were the discriminative stimulus induced by amphetamine, rotational behaviour in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions and apomorphine-induced yawning in rats. 2. The yawning induced by apomorphine (40 micrograms kg-1 s.c.) was significantly potentiated by nifedipine (5-10 mgkg-1 i.p.). Bay K 8644 (0.05-0.5 mgkg-1 i.p.) dose-dependently inhibited yawning induced by apomorphine (80 micrograms kg-1 s.c.) and, at 0.4 mgkg-1, inhibited the nifedipine potentiation of apomorphine-induced yawning. In contrast to their effects on apomorphine-induced yawning, nifedipine and Bay K 8644 had no effect on apomorphine-induced penile erection. 3. Bay K 8644 (0.06-0.5 mgkg-1 i.p.) and nifedipine (5-20 mgkg-1 i.p.) had no dose-related effect on the discrimination performance of rats trained to discriminate amphetamine from saline. However, nifedipine dose-dependently reduced the response rate of amphetamine-treated rats. Bay K 8644 had no effect on this measure except at high doses that also caused disruption. 4. Neither nifedipine (5-10 mgkg-1 i.p.) nor Bay K 8644 (0.06-0.5 mgkg-1 i.p.) affected the turning behaviour induced by amphetamine (1 mgkg-1 i.p.) in rats with unilateral 6-OHDA lesion of the medial forebrain bundle, and did not induce turning themselves. 5. As the dihydropyridine compounds affected apomorphine-induced yawning but not penile erection, and did not affect amphetamine-induced rotation or drug discrimination, it seems unlikely that they are affecting dopamine release in vivo.
Bourson
A
A
Merrell Dow Research Institute, Strasbourg, France.
Gower
A J
AJ
Mir
A K
AK
Moser
P C
PC
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects*; D004095:Dihydropyridines / Q000494:pharmacology*; D004298:Dopamine / Q000502:physiology*; D005793:Generalization, Psychological / Q000187:drug effects; D007858:Learning / Q000187:drug effects; D008297:Male; D008474:Medial Forebrain Bundle / Q000502:physiology; D009043:Motor Activity / Q000187:drug effects; D010410:Penile Erection / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013563:Sympathectomy, Chemical; D015000:Yawning / Q000187:drug effects
D004095:Dihydropyridines; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000661:Amphetamine; D001058:Apomorphine; D004298:Dopamine