Dose–response effect of Aβ25–35 peptide in mice. The Aβ25–35 peptide (Aβ, 1, 3 or 9 nmol) or the scrambled Aβ25–35 peptide (Sc.Aβ, 9 nmol) was administered i.c.v. The spontaneous alternation behaviour was examined on day 7: (a) spontaneous alternation percentage; (b) total number of arm entries. The step-through passive avoidance training was carried out on day 8 and retention examined on day 9: (c) step-through latency; (d) escape latency. The number of animals per group was n=10. One-way ANOVA: F(3,36)=7.24, P<0.001 in (a), F(3,36)=2.06, P>0.05 in (b). Kruskal–Wallis ANOVA: H=9.96, P<0.05 in (c), H=12.91,P<0.01 in (d). *P<0.05, **P<0.01 vs Sc.Aβ-treated group, Dunnett's test in (a), Dunn's test in (c, d).