BACKGROUND: The phenotype of large diameter sensory afferent neurons changes in several models of neuropathic pain. We asked if similar changes also occur in "functional" pain syndromes. METHODOLOGY/PRINCIPAL FINDINGS: Acidic saline (AS. pH 4. https://www.roneverhart.com/Tc-Electronics-M350-Multi-Effects-and-Reverb-Processor-M350-p36058/