intracerebroventricular injection of histamine induces state-dependency through h1 receptors

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.