The atypical antipsychotic profile of NRA0045, a novel dopamine D 4 and 5‐hydroxytryptamine 2A receptor antagonist, in rats

• Published in: British journal of pharmacology 2009-02, Vol.121 (3), p.515-525
• Main Authors: Okuyama, Shigeru, Chaki, Shigeyuki, Kawashima, Naoya, Suzuki, Yoshiko, Ogawa, Shin‐ichi, Kumagai, Toshihito, Nakazato, Atsuro, Nagamine, Masashi, Yamaguchi, Kazumasa, Tomisawa, Kazuyuki
• Format: Article
• Language: English
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1038/sj.bjp.0701164

The atypical antipsychotic profile of ( R )‐(+)‐2‐amino‐4‐(4‐fluorophenyl)‐5‐[1‐[4‐(4‐fluorophenyl)‐4‐oxobutyl] pyrrolidin‐3‐yl] thiazole (NRA0045), a potent dopamine D 4 and 5‐hydroxytryptamine (5‐HT) 2A receptor antagonist, was examined in rats. Spontaneous locomotor activity was decreased dose‐dependently with i.p. administration of clozapine (ED 50 3.7 mg kg −1 ), haloperidol (ED 50 0.1 mg kg −1 ) and chlorpromazine (ED 50 0.9 mg kg −1 ), whereas inhibition of this type of behaviour induced by i.p. administration of NRA0045, at doses up to 10 mg kg −1 , did not exceed 50%. Locomotor hyperactivity induced by methamphetamine (MAP, 2 mg kg −1 , i.p.) in rats (a model of antipsychotic activity) was dose‐dependently antagonized by NRA0045 (ED 50 0.4 mg kg −1 , i.p., and 0.3 mg kg −1 , p.o., respectively), clozapine (ED 50 0.3 mg kg −1 , i.p. and 0.8 mg kg −1 , p.o., respectively), haloperidol (ED 50 0.02 mg kg −1 , i.p. and 0.1 mg kg −1 , p.o., respectively), chlorpromazine (ED 50 0.3 mg kg −1 , i.p. and 3.3 mg kg −1 , p.o., respectively). In contrast, the MAP (3 mg kg −1 , i.v.)‐induced stereotyped behaviour in rats (a model of extrapyramidal symptoms) was not affected by NRA0045 or clozapine, at the highest dose given (30 mg kg −1 , i.p.). Haloperidol (ED 50 0.3 mg kg −1 , i.p.) and chlorpromazine (ED 50 4.8 mg kg −1 , i.p.) strongly blocked the MAP‐induced stereotyped behaviour. NRA0045 and clozapine selectively blocked behaviour associated with activation of the mesolimbic/mesocortical dopamine neurones rather than nigrostriatal dopamine neurones. Extracellular single‐unit recording studies demonstrated that MAP (1 mg kg −1 , i.v.) decreased the firing rate in the substantia nigra (A9) and ventral tegmental area (A10) dopamine neurones in anaesthetized rats. NRA0045 completely reversed the inhibitory effects of MAP on A10 dopamine neurones (ED 50 0.1 mg kg −1 , i.v.), whereas the inhibitory effects of MAP on A9 dopamine neurones were not affected by NRA0045, in doses up to 1 mg kg −1 (i.v.). Clozapine completely reversed the inhibitory effects of MAP on A10 dopamine neurones (ED 50 1.9 mg kg −1 , i.v.) and on A9 dopamine neurones (ED 50 2.5 mg kg −1 , i.v.). Haloperidol completely reversed the inhibitory effects of MAP on A10 (ED 50 0.03 mg kg −1 , i.v.) and on A9 dopamine neurones (0.02 mg kg −1 , i.v.). NRA0045, like clozapine, was more potent in reversing the effects of MAP on A10 than A9 dopamine neurones. Prepulse inhibition (PPI) is impaired marke