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Abstract: Potassium channels regulate many neuronal functions, including neuronal excitability and synaptic plasticity, contributing, by these means, to mnemonic processes. In particular, A-type K+ currents (I A) play a key role in hippocampal synaptic plasticity. Therefore, we evaluated the effect of the peptidic toxin Tx3-1, a selective blocker of I A currents, extracted from the venom of the spider Phoneutria nigriventer, on memory of mice. Administration of Tx3-1 (i.c.v., 300 pmol/site) enhanced both short- and long-term memory consolidation of mice tested in the novel object recognition task. In comparison, 4-aminopyridine (4-AP; i.c.v., 30–300 pmol/site), a non-selective K+ channel blocker did not alter long-term memory and caused toxic side effects such as circling, freezing and tonic–clonic seizures. Moreover, Tx3-1 (i.c.v., 10–100 pmol/site) restored memory of Aβ25-35-injected mice, and exhibited a higher potency to improve memory of Aβ25-35-injected mice when compared to control group. These results show the effect of the selective blocker of I A currents Tx3-1 in both short- and long-term memory retention and in memory impairment caused by Aβ25-35, reinforcing the role of I A in physiological and pathological memory processes. [Copyright &y& Elsevier]