Hippocampus anatomy and hippocampal demyelination of the MS samples. Hippocampus tissue from controls, AD and MS patients were immunohistochemically stained for anti-proteolipid protein and revealed a as expected, no sign of demyelination in any of the control hippocampus samples. Cornu Ammonis subfields of the hippocampus (CA4, CA3-2, CA1), as well as the fimbria, are indicated. b None of the AD hippocampus samples showed any demyelination, (c) while 12 out of 15 MS patients showed demyelinated lesions. Black arrows indicate demyelination in CA4, CA3-2 and CA1. The white arrow indicates a small preserved area of normal myelination in CA1. d 3 out of 15 MS hippocampi were not affected by demyelination

Reduced ChAT activity and ChAT protein expression in MS hippocampus. a Statistically significant differences among the three different groups were found regarding the hippocampal choline acetyltransferase (ChAT) activity (Kruskal–Wallis: p = 0.026). In MS hippocampus compared to control hippocampus, a mean reduction in ChAT activity of 43% was found (after Dunn’s correction: p < 0.05). In AD hippocampus compared to control hippocampus, a mean reduction of 45% was found in ChAT activity (after Dunn’s correction: not significant). Non-neurological control hippocampus immunohistochemically stained with anti-ChAT, revealed ChAT immunopositive neurites (arrowsin the insets) in CA4 (b), CA3-2 (c) and CA1 (d). In all MS hippocampal subfields (e CA4, f CA3-2, g CA1), ChAT immunopositivity was clearly decreased as compared to control tissue, although bead-like varicosities were occasionally observed (arrows in the insets). In AD hippocampus, a decrease of ChAT immunopositivity was also found in CA4 (h), CA3-2 (i) and CA1 (j), with occasional immunopositive bead-like varicosities (arrows in the insets). Quantification of ChAT immunostainings revealed reductions of the amount of staining in MS and AD hippocampus in (k) CA4 (Con vs. MS: p < 0.05; Con vs. AD: p < 0.01), (l) CA3-2 (Con vs. MS: not significant; Con vs. AD: p < 0.01) and (m) CA4 (Con vs. MS: p < 0.05; Con vs. AD: p < 0.01). Original magnifications: (b-j) ×200 and ×630 (insets). Error bars indicate SEM. *p < 0.05, **p < 0.01, ns not significant

Unchanged AChE activity and protein expression in MS hippocampus. The activity of AChE as reflected by the amount of reaction product formed was equal in a non-neurological control hippocampus and b MS hippocampus in all hippocampal subfields. In contrast, in c AD hippocampus, the formed reaction product was clearly decreased in CA4 (asterisk) and CA1 (hash), but not in CA3-2 (dagger), indicating a decreased activity of AChE in these areas. Quantification of the reaction product formed by AChE in the (d) CA4 hippocampal subfield indicated differences among the three groups (ANOVA: p = 0.003, Dunnet correction revealed Con vs. AD and MS vs. AD: p < 0.01; Con vs. MS: no significant difference). For the CA3-2 subfield (e), no differences were found between the three groups (Kruskal–Wallis: p = 0.175). For the CA1 subfield (f) differences among the three groups were found (ANOVA: p = 0.013, Dunnet correction revealed Con vs. AD and MS vs. AD: p < 0.05; Con vs. MS: no significant difference). g Representative western blot of 3 control, 3 MS and 3 AD samples indicated decreased protein expression of AChE in AD hippocampus, but not in MS hippocampus tissue. h Quantification of protein expression levels of AChE of all samples included indicated significant differences among the three different groups (ANOVA: p = 0.015, Dunnet correction revealed Con vs. AD and MS vs. AD: p < 0.05; Con vs. MS: no significant difference). Error bars indicate SEM. *p < 0.05, **p < 0.01, ns not significant