Photomicrographs of coronal sections showing SNAP-25 immunoreactivity in CA1, CA3 and DG subregions of hippocampus of rats from Hypo, T4, DON, T4+DON and C groups (n=10–12). Distinct punctate spots of reaction product were observed in every layer of CA1, CA3 and DG subregions; note that the staining for SNAP-25 was more intense in CA3-SO, CA3-SR and in all layers of CA1 and DG of Hypo and DON groups, and the overall staining intensity was equal in CA3-SL of five groups; magnification, ×400; scale bar: 50 μm. C, control group, Hypo, hypothyroid group; DON, hypothyroid rats treated with 0.005% (w/v) donepezil; T4, hypothyroid rats treated with 6 μg T4/100 g body weight; T4+DON, hypothyroid rats treated with 6 μg T4/100 g body weight beside adding 0.005% (w/v) donepezil to the drinking water. Syt-1, synaptotagmin-1; T4, thyroxine; SNAP-25, synaptosomal-associated protein of 25 kDa; DON, donepezil; DG, dentate gyrus; SO, stratum oriens; SR, stratum radiatum; SLM, stratum lacunosum-moleculare; SL, stratum lucidum; ML, molecular layer; PL, polymorphic layer; w/v, weight/volume.