Effect of H1-antagonists on spatial memory deficit evaluated by 8-arm radial maze in rats.

To evaluate effects of certain H1-antagonists on spatial memory with 8-arm radial maze performance of rats. Eight-arm radial maze performance was used to measure spatial memory in rats. Chronic treatments of classical H1-antagonists, diphenhydramine (5 mg/kg) and pyrilamine (20 mg/kg) impaired acquisition memory process regarding both parameters of radial maze performance. In addition, the memory retrieval process was also impaired significantly by a single administration of diphenhydramine (5, 10 mg/kg) and pyrilamine (50 mg/kg). However, the newly developed H1-antagonist, epinastine caused no appreciable effect on both acquisition and retrieval memory even at a high dose of 50 mg/kg. The memory deficit induced by diphenhydramine (10 mg/kg) or pyrilamine (50 mg/kg) was reversed by tacrine (1 mg/kg). Histamine H(1)-receptors plays a certain role in spatial cognition, and its action may be due to both histaminergic and cholinergic neurons.