Exercise and CGRP in the spinal cord do Nascimento PS et al. CLINICS 2012;67(9):1087-1091 Figure 3 - Digitized images of transverse sections of spinal cord in the C, D and TD animals revealing the CGRP-ir in the dorsal horn of the spinal cord. Note the decreased CGRP-ir in the D group. In the image from the TD animal, note that the CGRP-ir is similar to that of the C animal. The scale bar indicates 100 mm. group took only 34.7% more time to deflect the tail than the C group (p.0.05; Figure 1). Optical densitometry of CGRP-ir The OD analysis of the dorsal horn of the spinal cord revealed that CGRP-ir was lower in the D (0.056¡0.004) group than in the C (0.098¡0.003; p,0.001) and TD (0.096¡0.01; p,0.05) groups. There was no difference between the C and TD groups (p.0.05; Figure 2). Representative images are presented in Figure 3. DISCUSSION In the present study, we have demonstrated that treadmill training alone, with no pharmacological intervention, can prevent the nociceptive loss caused by the hyperglycemic state in rats with STZ-induced diabetes. This beneficial effect was associated with changes in the CGRP-ir in the dorsal horn of the spinal cord. As expected, diabetic rats display lower body weights and higher blood glucose levels than non-diabetic rats (8,10). Treadmill training did not alter the body weight or blood glucose levels in rats (8,10,18) or in type 1 diabetic patients (19). STZ induces an insulin-deficient state similar to type 1 diabetes in humans, which is not typically improved by exercise interventions (20), in contrast to type 2 diabetes, which is an insulin-resistant state (21). In the analysis of nociceptive sensitivity, measured using the tail-flick test, the diabetic rats demonstrated an increase in the latency to deflect the tail from the apparatus, which indicates an STZ-induced loss of sensitivity. These data are in accordance with those of previous studies, which found deficits in motor and sensory nerve conduction (22,23) and thermal (23,24) and nociceptive hypoalgesia (24) in animals. Our findings are also in agreement with clinical data indicating that diabetes in humans can cause nociceptive hypoalgesia (25-27), which is an important determinant of lower limb ulcers and amputations. However, diabetic rats that were subjected to treadmill training displayed a latency to deflect the tail from the apparatus similar to that of the non-diabetic animals, indicating that training is able to prevent alterations in the sensitivity behavior of diabetic animals. These data have not previously been reported in the literature. We also examined the effects of training on the CGRP-ir in the dorsal horn of the spinal cord, and the data reveal that physical exercise can maintain the content of this peptide in the spinal cord at levels similar to those of control animals. Diabetes is well known to cause a reduction in the content of CGRP in peripheral nerves (2,3,28), the neurons of the dorsal root ganglia and the dorsal horn of the spinal cord (29). Although physical training has been considered in the treatment of diabetic patients for some time, it was not 1090 known, until now, whether training was able to prevent alterations in nociceptive signaling and CGRP content in the spinal cord. The benefits of treadmill training in these parameters could arise from the effects of nerve growth factor (NGF) and neurotrophin-3 (NT-3). These neuro- trophic factors promote neuronal survival and differentia- tion by activating phosphatidylinositol 3-kinase signaling (PI3-K). Moreover, there are various studies demonstrating that treadmill training increases the level of NGF in the sensory neurons (30) and in the hippocampus (31,32) of NT- 3 in the spinal cord (33) and of NGF and NT-3 in the soleus muscle (34,35). In conclusion, treadmill training is able to alleviate the nociceptive hypoalgesia caused by diabetes and this improvement is related to the content of CGRP in the dorsal horn of the spinal cord. ACKNOWLEDGMENTS We thank Silvia Barbosa for her technical assistance. This study was supported by grants from CNPq and CAPES. do Nascimento PS was supported by a Ph.D. scholarship from CNPq. Achaval M, Schaan BD and Xavier LL are CNPq investigators. We are indebted to Roche, which donated the test strips. AUTHOR CONTRIBUTIONS do Nascimento PS is the primary author of this manuscript, who organized the research protocol and participated in the research and article preparation. Lovatel GA, Ilha J and Xavier LL participated in the research protocol. Schaan BD participated in the article preparation. Achaval M is responsible for the research and participated in the article preparation. REFERENCES 1. Boulton AJ. Lowering the risk of neuropathy, foot ulcers and amputa- tions. Diabet Med. 1998;15(Suppl 4):S57-9, http://dx.doi.org/10.1002/ (SICI)1096-9136(1998120)15:4+,S57::AID-DIA741.3.3.CO;2-4. 2. Diemel LT, Stevens EJ, Willars GB, Tomlinson DR. Depletion of substance P and calcitonin gene-related peptide in sciatic nerve of rats with experimental diabetes; effects of insulin and aldose reductase inhibition. Neurosci Lett. 1992;137(2):253-6, http://dx.doi.org/10.1016/ 0304-3940(92)90416-5. 3. Brewster WJ, Diemel LT, Leach RM, Tomlinson DR. Reduced sciatic nerve substance P and calcitonin gene-related peptide in rats with short- term diabetes or central hypoxaemia co-exist with normal messenger RNA levels in the lumbar dorsal root ganglia. Neuroscience. 1994;58(2):323-30, http://dx.doi.org/10.1016/0306-4522(94)90038-8. 4. Schmidt Y, Unger JW, Bartke I, Reiter R. Effect of nerve growth factor on peptide neurons in dorsal root ganglia after taxol or cisplatin treatment and in diabetic (db/db) mice. Exp Neurol. 1995;132(1):16-23, http:// dx.doi.org/10.1016/0014-4886(95)90054-3. 5. F u¨rst S. Transmitters involved in antinociception. Brain Res Bull. 1999;15;48(2):129-41, http://dx.doi.org/10.1016/S0361-9230(98)00159-2. 6. Costentin J. Pain and its main transmitters. Ann Pharm Fr. 2000; 58:77-83. 7. van Dijk JW, Manders RJ, Tummers K, Bonomi AG, Stehouwer CD, Hartgens F, et al. Both resistance- and endurance-type exercise reduce the prevalence of hyperglycaemia in individuals with impaired glucose tolerance and in insulin-treated and non-insulin-treated type 2 diabetic