Several studies indicate that 17b-estradiol (E2) protects against amyloid b-peptide (Ab)-induced cell death and activates factors associated with learning and memory, a function involving the hippocampal somatostatinergic system. As alterations in somatostatin have been demonstrated in Alzheimer 0 s disease, we examined whether E2 prevents changes in the hippocampal somatostatinergic system induced by Ab25-35 and cell death, as well as the possible involvement of leptin and insulin-like growth factor (IGF)-I signaling. We also measured the levels of Ab proteases neprilysin and insulin-degrading-enzyme. Co-administration of E2 with Ab25-35 reduced both its levels and cell death, in addition to preventing the Ab-induced depletion of some somatostatinergic parameters. Activation of leptin and IGF-I pathways increased after E2 co-administration, and this correlated with changes in the somatostatinergic system. Changes in some components of this system were inversely related with Ab levels and cell death. Moreover, neprilysin levels were increased only in Ab plus E2-treated rats and E2 prevented the Ab-induced insulin-degradingenzyme reduction. Our results suggest that the E2-induced E2, 17b-estradiol; ER, estradiol receptor; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; Gi proteins, guanine nucleotide-binding inhibitory proteins; GSK3b, glycogen synthase kinase-3b; HRP, horseradish peroxidase; IDE, insulin-degrading-enzyme; IGF-I, insulin-like growth factor-I; IGF-IR, IGF-I receptor; IRS1, insulin receptor substrate 1; NeuN, neuronal nuclei; Ovx, ovariectomized; SOCS3, suppressor of cytokine signaling 3; SRIF, somatostatin; sst, somatostatin receptor subtype; STAT, signal transducer and activator of transcription; TTBS, Tris-Tween buffered saline; TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling.