Involvement of the cholinergic system of CA1 on harmane-induced amnesia in the step-down passive avoidance test.

β-carboline alkaloids such as harmane (HA) are naturally present in the human food chain. They are derived from the plant Peganum harmala and have many cognitive effects. In the present study, effects of the nicotinic system of the dorsal hippocampus (CA1) on HA-induced amnesia and exploratory behaviors were examined. One-trial step-down and hole-board paradigms were used to assess memory retention and exploratory behaviors in adult male mice. Pre-training (15 mg/kg) but not pre-testing intraperitoneal (i.p.) administration of HA decreased memory formation but did not alter exploratory behaviors. Moreover, pre-testing administration of nicotine (0.5 µg/mouse, intra-CA1) decreased memory retrieval, but induced anxiogenic-like behaviors. On the other hand, pre-test intra-CA1 injection of ineffective doses of nicotine (0.1 and 0.25 µg/mouse) fully reversed HA-induced impairment of memory after pre-training injection of HA (15 mg/kg, i.p.) which did not alter exploratory behaviors. Furthermore, pre-testing administration of mecamylamine (0.5, 1 and 2 µg/mouse, intra-CA1) did not alter memory retrieval but fully reversed HA-induced impairment of memory after pre-training injection of HA (15 mg/kg, i.p.) which had no effect on exploratory behaviors. In conclusion, the present findings suggest the involvement of the nicotinic cholinergic system in the HA-induced impairment of memory formation.