Establishment of a rat model of type II diabetic neuropathic pain.
OBJECTIVE
To establish a rat model of type II diabetic neuropathic pain.


METHODS
Sixty Sprague Dawley rats were randomly divided into two groups: group A (N = 10) was fed a normal diet, and group B (N = 50) was fed a high-fat and high-sugar diet. After 8 weeks, the body weight of all rats was recorded, and rats in both groups had their fasting plasma glucose, insulin concentration, and insulin sensitivity index measured and calculated. Subsequently, the rats in group B were randomly divided into three subgroups that were each given different doses of streptozotocin (STZ) by a single intraperitoneal injection (subgroup B1 received 30 mg/kg, subgroup B2 received 35 mg/kg, and subgroup B3 40 mg/kg). Two weeks after the STZ injection, the four groups of rats had their insulin sensitivity index, mechanical withdrawal threshold, and thermal withdrawal latency assessed, allowing us to establish a rat model of type II diabetic neuropathic pain and to determine the optimum dose of STZ. Four weeks after STZ injection (2 weeks after the model was established), the pain threshold was measured in the rats in group A and the group treated with the most effective STZ dose. We also measured the expression of phosphorylated extracellular signal-regulated kinase (p-ERK), phosphorylated cyclic AMP response element-binding protein (p-CREB), and phosphorylated N-methyl d-aspartate receptor subtype B (p-NR2B) in the dorsal root ganglion (DRG) and spinal cord dorsal horn regions, which are closely related to neuropathic pain, and also recorded the TTX-R sodium currents in the acutely isolated DRG neurons.


RESULTS
After 8 weeks of a high-fat, high-sugar diet, the body weight of the rats in group B was significantly increased. Although the fasting blood glucose levels did not change significantly, the fasting insulin levels were slightly elevated, and the insulin sensitivity index was significantly reduced. Two weeks after STZ injection, the blood glucose levels of the rats in subgroup B1 were elevated but did not remain so for a prolonged period. In contrast, the rats in subgroup B3 had elevated blood glucose that was accompanied by a high mortality rate, while the blood glucose levels of the rats in subgroup B2 were moderately elevated and relatively stable. In addition, the pain threshold was significantly decreased (P < 0.05), and the mortality was low in this group. Because of this, the dose of STZ that was used in group B2 was considered the most effective dose of STZ for induction of diabetes. Four weeks after STZ injection, the pain threshold in the rats of group B2 was still significantly decreased, and the expression of p-ERK, p-CREB, and p-NR2B in the dorsal root ganglion (DRG) and spinal cord dorsal horn was significantly increased. The tetrodotoxin-resistant sodium current density in DRG neurons was also significantly elevated (P < 0.05).


CONCLUSIONS
A rat model of type II diabetic neuropathic pain can be established by feeding rats a high-fat, high-sugar diet for 8 weeks, in combination with intraperitoneal injection of 35 mg/kg STZ. This model can be stably maintained for at least 2 weeks.
Department of Anesthesiology, Second Affiliated Hospital of Wenzhou Medical College, Wenzhou, Zhejiang, China.
Jiang-Kun
JK
Dang
Yan
Y
Wu
Hong
H
Cao
Bo
B
Meng
Cong-Cong
CC
Huang
Guo
G
Chen
Jun
J
Li
Xue-Jun
XJ
Song
Qing-Quan
QQ
Lian
D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000150:complications / Q000378:metabolism / Q000503:physiopathology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000378:metabolism / Q000503:physiopathology*; D003929:Diabetic Neuropathies / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology*; D004195:Disease Models, Animal; D005727:Ganglia, Spinal / Q000378:metabolism / Q000503:physiopathology*; D008297:Male; D017288:Pain Threshold / Q000502:physiology; D018408:Patch-Clamp Techniques; D011897:Random Allocation; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000378:metabolism / Q000503:physiopathology*; D013311:Streptozocin
D013311:Streptozocin
Neuropathic Pain; Rats; Streptozotocin; Type II Diabetes