Furthermore, preliminary fluorescent labelling experiments in rat brain slices were undertaken. Carbamate 17 successfully blocked ChE activity, as determined by the modified Koelle-Karnovsky 48,66 histochemical method (Figure ). Unfortunately, further click reaction derivatisations for labelling with the fluorophore 26 were not successful. The observed strong background fluorescence points to non-specific binding of the lipophilic fluorophore. Therefore, careful selection of the fluorophore moiety and additional optimisation are needed before this method can be applied for histochemical determination of ChEs.