Proteins that were significantly decreased in content in the nerves from old mice were primarily structural proteins reflecting the extensive changes in axonal structure seen in Fig. 1 (highlighted in blue), a number of proteins showing an increased content have previously been identified as up regulated in brain during aging and in neurodegenerative diseases [34], including Apolipoproteins D and E, Cathepsin B and D and Galectin 3 (highlighted in orange). Here, CTSB is linked to neurodegenerative disease.