[The relationship between autophagy activation in spinal cord and type 2 diabetic neuropathic pain in rats]

To investigate the relationship between autophagy function in spinal cord and type 2 diabetic neuropathic pain in rats.

Forty-two male Sprague-Dawley rats were fed with a high-sugar, high-fat diet for 8 weeks to induce the insulin resistance, and then received a single intraperitoneal streptozocin (STZ) injection to establish type 2 diabetes rat model. Two weeks after STZ injection, mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of rats were detected, the rats with MWT and TWL decreasing to below 80% compared to baseline were chosen as type 2 diabetic neuropathic pain rats (group DNP, n=24), the rest of the rats were chosen as type 2 diabetic non-neuropathic pain rats (group DA, n=18). And another 18 normal rats randomly selected from the total were classified as control group (group C) and fed with common forage for 8 weeks. The MWT and TWL were measured again on the 3rd, 7th and 14th day after determining the grouping of DA and DNP, and then, the lumbar segments 4~6 of the spinal cord were removed from the executed rats for determination of the expressions of microtubule-associated protein light chain 3 (LC3)、Beclin-1and P62 by Western blot. The co-expressions of P62 with GFAP or OX-42 or NeuN in spinal dorsal horn were detected in another 6 lumbar segments of diabetic neuropathic pain (DNP) rats on the 7th day by immunofluorescence double dye method.

Compared with group C, the insulin level was increased and ISI decreased in SD rats fed with high-sugar, high-fat diet, that meant the rats in insulin-resistance. After STZ injection, blood glucose rose to the standard of type 2 diabetes mellitus, i.e. ≥ 16.7 mmol/L. Compared with group C and group DA, MWT was significantly decreased, TWL shortened and the expression of LC3-Ⅱ and Beclin-1 in the spinal dorsal horn up-regulated, P62 expression down-regulated on the 3rd, 7th and 14th day in group DNP (P<0.05). P62 was mainly localized in spinal dorsal horn and coexisted with neurons, and spots of P62 immunoreactivity could be detected in a few microglia but not observed in astrocyte.

The changes in expression of LC3-Ⅱ、Beclin-1 and P62 in spinal cord of type 2 diabetes neuropathic pain rats means autophagy activation of spinal, up-regulated autophagy of neurons in spinal dorsal horn mainly involves in the formation and development of type 2 diabetic neuropathic pain in rats.