The i.c.v. injection of 4-AP had no effect SB431542 mw on memory, but induced shaking, circling and tonic–clonic seizures at the higher doses tested. In fact, clinical trials have shown that although 4-AP improves cognitive functions in AD patients, the incidence of adverse-effects has hindered its clinical use (Davidson et al., 1988 and Wiseman and Jarvik, 1991). Interestingly, the analysis of amino acid sequence of Tx3-1 shows no relation to other K+ channel blockers (Cordeiro et al., 1993).

The lack of homology with other known blockers of K+ channels could explain the selective pattern of toxin against IA currents, and thus a possible better therapeutic profile when compared to the non-selective Kv blocker 4-AP. In vitro experiments shed light on the involvement of IA currents in AD’s cognitive decline ( Kerrigan et al., 2008, Pan et al., 2004 and Plant et al., 2006). The Aβ peptide, which accumulates in the brain of AD patients ( Fraser et al., 1997; Prince et al., 2009), alters synaptic plasticity ( Holscher RG7204 in vitro et al., 2007 and Cheng et al., 2009), and ion channel function, such as potassium (K+) channels ( Furukawa et al., 1996). Moreover, current evidences suggest a role for Aβ peptides in IA K+ currents regulation ( Kerrigan et al., 2008, Pan

et al., 2004 and Plant et al., 2006). Therefore, we evaluated whether Tx3-1 alter Aβ25-35-induced memory deficits in mice. Administration of Tx3-1, immediately after training session, reversed the Aβ25-35-induced memory impairment. Interestingly, Tx3-1 proved to be more potent in Aβ25-35-treated mice when compared to the control group. One of the causes of this better effect could be attributed to the enhanced expression of cortical and hippocampal IA K+ channels induced by Aβ25-35 ( Pan et al., 2004). The higher potency of Tx3-1 in AD-like conditions makes this toxin a potential prototype for the emergence of more effective therapies

for AD-related cognitive decline. In line with this view, Tx3-1 has been produced through bacterial expression system ( Carneiro et al., 2002). This molecular biological technique is useful to produce not only the recombinant toxin but also to generate mutated versions of the native peptide. Here we reported the memory enhancing effect of Tx3-1, a selective IA blocker, in physiological Farnesyltransferase and AD-like conditions in mice. Despite the data showed here, more experiments, such as electrophysiological techniques, are needed to better elucidate the effect of Tx3-1 on neuronal mechanisms involved in memory storage. This study was supported by Conselho Nacional de Desenvolvimento Científico (CNPq, Brazil – 306164/2010-8, 481664/2010-6, 476551/2009-9), Toxinologia – Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes 2865/2010, 1444/2011), Instituto Nacional de Ciência e Tecnologia (INCT) em Medicina Molecular (MCT/CNPq) and FAPEMIG. We thank CNPq, CAPES and FAPEMIG for the fellowship support.