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Ingestive Behavior and Neurosciences

Iron-Deficiency Sensitizes Mice to Acute Pain Stimuli and Formalin-Induced Nociception^1,2

Department of Clinical Neurophysiology, Georg-August-University Göttingen, 37075 Göttingen, Germany

Iron deficiency has been described as a risk factor in secondary restless legs syndrome (RLS), although it has not been investigated whether iron deficiency induces sensory symptoms in RLS patients. In this study, we established a mouse model of iron deficiency by administering a purified iron-deficient (ID) diet (<8 mg/kg iron) or nonpurified standard diet [normal diet (ND)] (<179 mg/kg iron) to male C57Bl/6 mice from postnatal d 28 for 1, 4, or 15 wk. The level of iron deficiency was assessed by the plasma iron concentration. After varying durations of iron deficiency, both acute and chronic sensory components of pain were measured using hot-plate and formalin tests, which preferentially assess A- and C-fibers, respectively. Based on hot-plate reaction time, ID mice had a lower acute pain threshold than the ND mice after 4 and 15 wk but not after 1 wk. In addition, ID mice had an increased chronic pain response compared with the ND mice only in the late phase of the formalin-test after 1, 4, and 15 wk of iron deficiency. This increased pain response was accompanied by an elevated expression of c-Fos immunoreactive cells at the ipsilateral dorsal horn, suggesting that iron deficiency indirectly increases cell activity at the spinal cord level. These results demonstrate that iron deficiency increases acute and chronic pain responses in mice and may cause similar alterations to the acute pain threshold and sensitivity to C-fiber–mediated chronic pain in ID RLS patients.

^* To whom correspondence should be addressed. E-mail: david.liebetanz{at}medizin.uni-goettingen.de.

Manuscript received 7 July 2009. Initial review completed 6 August 2009. Revision accepted 26 August 2009.

Published online 23 September 2009.