Impaired Nociception in the Diabetic Ins2 Mouse

The mechanisms responsible for painful and insensate diabetic neuropathy are not completely understood. Here, we have investigated sensory neuropathy in the Ins2 mouse, a hereditary model of diabetes. Akita mice become diabetic soon after weaning, and we show that this is accompanied by an impaired mechanical and thermal nociception and a significant loss of intraepidermal nerve fibers. Electrophysiological investigations of skin-nerve preparations identified a reduced rate of action potential discharge in Ins2 mechanonociceptors compared with wild-type littermates, whereas the function of low-threshold A-fibers was essentially intact. Studies of isolated sensory neurons demonstrated a markedly reduced heat responsiveness in Ins2 dorsal root ganglion (DRG) neurons, but a mostly unchanged function of cold-sensitive neurons. Restoration of normal glucose control by islet transplantation produced a rapid recovery of nociception, which occurred before normoglycemia had been achieved. Islet transplantation also restored Ins2 intraepidermal nerve fiber density to the same level as wild-type mice, indicating that restored insulin production can reverse both sensory and anatomical abnormalities of diabetic neuropathy in mice. The reduced rate of action potential discharge in nociceptive fibers and the impaired heat responsiveness of Ins2 DRG neurons suggest that ionic sensory transduction and transmission mechanisms are modified by diabetes.