Significant changes in mitochondrial distribution in different pain models of mice.

Mitochondria play an important role in pathophysiology of inflammatory and neuropathic pain but the mechanism is unclear. So far no comprehensive study exists that evaluates the changes of mitochondrial dynamics following the pain. In this study, we detected the mitochondrial distribution and subcellular morphology by using intrathecal injection of mitochondrial marker, Mitotracker Red® CM-H2XRox (Mito-Red) and confocal microscopic analysis in models of formalin-induced acute inflammatory pain, Complete Freund's Adjuvant (CFA)-induced persistent pain and spared nerve injury (SNI)-induced neuropathic pain. The results demonstrated that subcutaneous formalin injection did not affect the number of Mito-Red cells within the spinal dorsal horn at both acute and tonic phases, but significantly increased the number of cluster type mitochondria in superficial spinal dorsal horn (laminas I-II) at tonic phase. Differently, the number of Mito-Red cells significantly increased in superficial and deep spinal dorsal horn (laminas III-V) following persistent CFA and SNI neuropathic pain. Moreover, both CFA and SNI remarkably increased the number of cluster type mitochondria and decreased the number of granule type mitochondria, in both superficial and deep spinal dorsal horn. So we concluded that abnormal mitochondrial distribution contributes to neuropathic and some forms of inflammatory pain.