Objective: Phospholipase A2 (PLA2) plays an important role in regulating the production of arachidonic acid and various eicosanoids. The aim of our study was to investigate the analgesic mechanisms of calcium-dependent cytosolic phospholipase A2 and calcium-independent PLA2 (iPLA2) inhibitors in the spinal cord in a rat model of neuropathic pain.
Methods: Lumbar 5 spinal nerve ligation was performed in male Sprague-Dawley rats to develop a peripheral neuropathic pain model. Paw withdrawal thresholds in response to von Frey filaments, brush, pressure, and pinch were measured. Lumbar wide dynamic range neuronal firing rates and iPLA2 subtype expression were measured by in vivo extracellular recording and double immunofluorescence staining, respectively.
Results: In our rat models, oral administration of prednisolone, a non-selective PLA2 inhibitor, and intrathecal injection of bromoenolactone, a iPLA2 inhibitor, significantly increased the ipsilateral hindpaw withdrawal thresholds in response to von Frey filament stimulation, but intrathecal injection of arachidonyl trifluoromethyl ketone, a selective cytosolic PLA2 inhibitor, did not show significant changes. In spinal dorsal horn neurons, bromoenolactone reduced neuronal firing rates in response to withdrawal stimulation and spontaneous firing rates in the ipsilateral side of the spinal dorsal horn. In addition, the expression of iPLA2 was co-localized with astrocytes and neurons on the ipsilateral side of the dorsal horn in rats that underwent spinal nerve ligation.
Discussion: These data suggest that selective iPLA2 inhibitor produce analgesia in neuropathic rats by reducing central sensitization in the dorsal horn.
Keywords: Bromoenolactone; calcium-independent cytosolic phospholipase a2; neuropathic pain; spinal nerve ligation; wide dynamic range.