Figure 3: Melatonin treatment alleviates pathological changes in Aβ1–42-induced AD rats. (A) Neuronal damage in the different brain regions (Nissl staining). (B) Representative images of hematoxylin-eosin staining. The black arrows point to darkly stained cells in A and pyknotic nuclei in B. After treatment with melatonin, cells were less darkly stained and nuclear pyknosis was decreased. Normal neurons had regular cell morphology and round nuclei. In contrast, damaged cells had irregular neuronal cell bodies, shrunken and hyperchromatic nuclei, and scant cytoplasm with vacuoles. A + M: AD + melatonin group; AD: Alzheimer’s disease; Aβ: AD group; Aβ1–42: amyloid-beta 1–42; CA1: cornu ammonis 1; CA3: cornu ammonis 3; CX: cortex; DG: dentate gyrus; M: melatonin group; Sham: sham group. Original magnification 200×; scale bars: 100 µm.