To evaluate the role of lactate-induced mitochondrial division of spinal cord neurons in diabetic neuropathic pain (DNP) in mice.

Thirty-six SPF-grade healthy adult male C57BL/6 mice, aged 2 months, weighing 20-25 g, were divided into 3 groups (n=12 each) using a random number table method: control group (CON group), DNP group, and DNP+ sodium oxalate group (OXA group). The diabetic model was established by intraperitoneal injection of streptozotocin 130 mg/kg. After the diabetic model was successfully established, sodium oxalate 750 mg/kg was intraperitoneally injected once a day for 4 consecutive weeks to inhibit lactate production in OXA group, while the equal volume of normal saline was given instead at the same time in C group and DNP group. The mechanical paw withdrawal threshold (MWT) of the left hindpaw was measured before developing the model and at 1, 2, 3 and 4 weeks after developing the model. After completing the last behavioral testing, the spinal cord tissue of the lumbar segment (L_4-6) was taken for determination of the levels of lactate in serum and spinal cord tissues (by the colorimetric method), expression of the mitochondrial membrane potential, reactive oxygen species (ROS) content (using JC-1 or DHE probes), expression of mitochondrial dynamin-related protein 1 (Drp1) and mitochondrial protein mitofusin 2 (Mfn2) (by Western blot), and co-expression of Drp1 and neuronal neuronal marker neuronal nuclear protein (NeuN) (by immunofluorescence double labeling) and for examination of the structure and the number of mitochondria (with a transmission electron microscope).

Compared with C group, the MWT was significantly decreased after developing the model, the levels of lactate in serum and spinal cord tissues and ROS content in the spinal cord were increased, the mitochondrial membrane potential was decreased, the Drp1 expression was up-regulated, the Mfn2 expression was down-regulated, the number of mitochondria was increased, the area was reduced (P<0.05), and the co-expression of Drp 1 and NeuN was increased in DNP group and OXA group. Compared with DNP group, the MWT was significantly increased after developing the model, the levels of lactate in serum and spinal cord tissues and ROS content in the spinal cord were decreased, the mitochondrial membrane potential was increased, the Drp1 expression was down-regulated, the Mfn2 expression was up-regulated, the number of mitochondria was decreased, the area was increased (P<0.05), and the co-expression of Drp 1 and NeuN was decreased in OXA group.

Lactate-induced excessive mitochondrial division of spinal cord neurons can lead to mitochondrial dysfunction, which may be involved in the maintenance mechanism of DNP in mice.

Diabetic neuropathies; Lactic acid; Mitochondria