Purpose: Chronic inflammatory pain is a common condition in the clinic, and the underlying mechanism is not being completely understood. Various studies have demonstrated that central and peripheral sensitization and synaptic plasticity could play crucial functions in chronic inflammatory pain. Moreover, families of monocarboxylate transporters (MCTs) are closely related to cellular metabolism and synaptic plasticity, and it is also reported that MCTs participate in chronic inflammatory pain. Nevertheless, there is a probability of the engaging role of MCT 1 is in chronic inflammatory pain, but its specific cellular level mechanism is yet to be investigated. In our study, we hypothesized that MCT 1 in the spinal dorsal horn plays an important part in chronic inflammatory pain.
Methods: In experiment A, rats were gone through nociceptive behavioral testing at 1 d day before and 1 d, 3 d, and 7 d after completing complete Freund’s adjuvant (CFA) injection. The specimens collected for detecting MCT 1 by Western blotting. In experiment B, rats were randomly divided into four groups. Intrathecal injection of MCT 1 inhibitor and nociceptive behavioral tests were performed 1 d day before and 1 d, 3 d, 7 d, 14 d, and 21 d after CFA injection. MCT 1 and p-ERK levels in spinal dorsal horn were measured by Western blotting, and GFAP in spinal dorsal horn was detected by immunofluorescence.
Results: The expression of MCT 1 in the spinal dorsal horn was increased during chronic inflammatory pain in rats. The intrathecal injection of an MCT 1 inhibitor evidently diminished the expression of MCT 1 and GFAP in the spinal dorsal horn, and the behavioral nociceptive responses were also attenuated. Meanwhile, the expression of p-ERK was also decreased by the intrathecal injection of an MCT 1 inhibitor.
Conclusion: Our results indicate that MCT 1 very likely play a critical role in regulating chronic inflammatory pain and may influence the regulation of synaptic plasticity via ERK in the spinal dorsal horn of rats.
Keywords: chronic inflammatory pain, monocarboxylate transporter 1, spinal dorsal horn, astrocyte, synaptic plasticity