1. Department of Physiology, Faculty of Health Sciences, University of Pretoria, Arcadia 0007, South Africa
2. Microscopy and Microanalysis Unit, University of Pretoria, Arcadia 0007, South Africa
3. Department of Neurology Faculty of Health Sciences, University of Pretoria, Arcadia 0007, South Africa
4. School of Chemistry and The Manchester Institute of Biotechnology, The University of Manchester, Manchester M1 7DN, Lancs, UK