Forced-exercise delays neuropathic pain in experimental diabetes: effects on voltage-activated calcium channels

J Neurochem. 2011 Jul;118(2):224-36. doi: 10.1111/j.1471-4159.2011.07302.x. Epub 2011 Jun 2.

Abstract

Physical exercise produces a variety of psychophysical effects, including altered pain perception. Elevated levels of centrally produced endorphins or endocannabinoids are implicated as mediators of exercise-induced analgesia. The effect of exercise on the development and persistence of disease-associated acute/chronic pain remains unclear. In this study, we quantified the physiological consequence of forced-exercise on the development of diabetes-associated neuropathic pain. Euglycemic control or streptozotocin (STZ)-induced diabetic adult male rats were subdivided into sedentary or forced-exercised (2-10 weeks, treadmill) subgroups and assessed for changes in tactile responsiveness. Two weeks following STZ-treatment, sedentary rats developed a marked and sustained hypersensitivity to von Frey tactile stimulation. By comparison, STZ-treated diabetic rats undergoing forced-exercise exhibited a 4-week delay in the onset of tactile hypersensitivity that was independent of glucose control. Exercise-facilitated analgesia in diabetic rats was reversed, in a dose-dependent manner, by naloxone. Small-diameter (< 30 μm) DRG neurons harvested from STZ-treated tactile hypersensitive diabetic rats exhibited an enhanced (2.5-fold) rightward (depolarizing) shift in peak high-voltage activated (HVA) Ca(2+) current density with a concomitant appearance of a low-voltage activated (LVA) Ca(2+) current component. LVA Ca(2+) currents present in DRG neurons from hypersensitive diabetic rats exhibited a marked depolarizing shift in steady-state inactivation. Forced-exercise attenuated diabetes-associated changes in HVA Ca(2+) current density while preventing the depolarizing shift in steady-state inactivation of LVA Ca(2+) currents. Forced-exercise markedly delays the onset of diabetes-associated neuropathic pain, in part, by attenuating associated changes in HVA and LVA Ca(2+) channel function within small-diameter DRG neurons possibly by altering opioidergic tone.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Calcium Channels / metabolism*
  • Calcium Channels / physiology
  • Diabetes Mellitus, Experimental / complications
  • Diabetes Mellitus, Experimental / metabolism*
  • Diabetes Mellitus, Experimental / therapy*
  • Diabetic Neuropathies / etiology
  • Diabetic Neuropathies / metabolism*
  • Diabetic Neuropathies / prevention & control*
  • Exercise Therapy / methods*
  • Male
  • Neural Conduction / physiology
  • Physical Conditioning, Animal / methods
  • Random Allocation
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Calcium Channels