K E Y W O R D S . Scanning electron microscopy (SEM), resin histology, transmission electron microscopy (TEM), small intestine, frozen hydrated, mouse, cryomicroscopy, ice crystal damage. S U M M A R YEtched frozen hydrated specimens of mouse small intestine have been examined with low temperature scanning electron microscopy as a preliminary to X-ray microanalysis. Recognizable images have been obtained of most of the known histological features of the gut. Nuclear and cytoplasmic details were often seen. Ice crystal damage was evident, although the degree of artefact depended on the cell type being examined and also varied from cell to cell or within cells.The same specimens were later examined with resin light microscopy and transmission electron microscopy. These two techniques confirmed that preservation was adequate for identification of cells and tissues, although cavities were seen, representing ice crystal damage.These preliminary results indicate that SEM of etched, frozen, hydrated specimens provides adequate identification of cellular detail to allow further work using X-ray microanalysis to be carried out.

The pathology of Alzheimer’s disease can ultimately be traced to the increased aggregation stability of Aβ42 peptides which possess two extra residues (Ile 41 & Ala 42) that the non-pathological strain (Aβ40) lacks. We have found Aβ42 fibrils to exhibit stronger energies in inter-chain interactions and we have also identified the cause for this increase to be the result of different Ramachandran angle values in certain residues of the Aβ42 strain compared to Aβ40. These unique angle configurations result in the peptide planes in the fibril structures to be more vertical along the fibril axis for Aβ42 which thus reduces the inter-atomic distance between interacting atoms on vicinal peptide chains thereby increasing the electrostatic interaction energies. We lastly postulate that these different Ramachandran angle values could possibly be traced to the unique conformational folding avenues sampled by the Aβ42 peptide owing to the presence of its two extra residues.