The aim of the present study was to investigate whether and by which mechanism; histamine can induce state-dependent retrieval of passive avoidance task. The pre-training or pre-test intracerebroventricular (i.c.v.) injection of histamine (20μg/mouse) impaired retrieval, when it was tested 24 h later. In the animals, which retrieval was impaired due to histamine pre-training administration, pre-test administration of histamine, with the same dose, restored retrieval. The H1 blocker, pyrilamine (20 μg/mouse, i.c.v.), but not the H2 blocker; ranitidine prevented the restoration of retrieval by pre-test histamine. A pre-test administration of histamine H3 receptor antagonist, clobenprobit, also reversed hitamine-induced impairment of memory retention. In conclusion, histamine can induce state-dependent retrieval through the H1 receptor H1 mechanism.
