Electron probe x-ray microanalysis: A tool for elucidating the role of ions in neuronal physiology and pathophysiology

Electron probe x-ray microanalysis (EPMA) is a quantitative electron microscope technique that measures both water content (percentage water) and total (free plus bound) concentrations of biological elements in selected morphological compartments. Unlike other methods for determination of ion/element concentrations, EPMA permits simultaneous quantitation of several elements (Na, P, S, Cl, K, Ca, and Mg) and allows optical differentiation of nervous tissue cell types (i.e, neurons, glia) with subsequent analysis of respective submembrane regions or organelles (e.g, axoplasm, mitochondria, nuclei). EPMA, therefore, represents a powerful tool for extending our current understanding of elements/ions in neurophysiological processes. In addition, it is presumed that neuropathic injury disrupts normal intraneuronal Na⁺, K⁺, and Ca²⁺ distribution and that the structural and functional consequences are mediated by ion translocation. However, little specific information is available regarding how translocated ions distribute among subcellular anatomical compartments after injury. EPMA quantification of ion/element changes associated with various nervous tissue injury models has helped to elucidate corresponding pathophysiological mechanisms. In this review, we will discuss EPMA and the realized, as well as potential, contributions of this technique to deciphering the role of ions in neuronal physiology and pathophysiology. Our recent studies of axon degeneration during acrylamide intoxication will be described to illustrate the utility of EPMA.