NGF and memory impairment: Indeed, several studies reported that GUO causes memory impairment (Roesler et al., 2000; Vinadé et al., 2003, 2004) but, at the same time and sinergistically with NGF, it promotes neurite outgrowth in PC12 cells via activation of heme-oxygenase and cGMP formation (Gysbers and Rathbone, 1996; Bau et al., 2005; Tomaselli et al., 2005).