Role of histamine H receptor in caffeine induced locomotor sensitization.

The present study elucidated the role of histamine H receptor in the caffeine induced locomotor sensitization. Intermittent administration of caffeine (15 mg/kg, i.p.) on alternate days (induction phase) i.e. 1, 3, 5, 7, 9, 11 and 13 resulted in the development of locomotor sensitization. In addition, challenge with sub-stimulant dose of caffeine (10 mg/kg, i.p.) directly on 17 day to induction group animals resulted in expression to locomotor sensitization to caffeine. I.c.v. injection of histaminergic agents concomitantly with caffeine during induction phase i.e. histamine H receptor agonist, FMPH (6.5 μg/mouse) significantly potentiated while H receptor antagonist, cetirizine (0.1 μg/mouse) attenuated the locomotor sensitization induced by caffeine (15 mg/kg, i.p.). In addition, challenge with caffeine (10 mg/kg, i.p.) on the expression day (17) to the induction group mice on FMPH + caffeine treatment showed enhanced, while those on cetirizine + caffeine treatment exhibited lesser expression to locomotor sensitization. Therefore, a possible contributory role of the central histaminergic system via H receptor stimulation or up-regulation in the caffeine-induced locomotor sensitizing effect is proposed.