Microglia in the rostral ventromedial medulla mediate synaptic pruning via the C1q/C3-CR3 signaling pathway – a mechanism for the chronic orofacial pain
The mechanism of chronic orofacial pain was investigated by examining the interaction between activated microglia, C1q and neurons in RVM of rats with orofacial pain caused by temporomandibular joint injection of CFA. The results demonstrated that the pain threshold in CFA group exhibited a continuous decline, reaching its lowest point on the third day. During the modeling process, administered daily stereotactic injections of ANX-005 and minocycline into the RVM, which resulted in a notable recovery in the rats' pain threshold and a significant increase in C1q/C3 and microglia in RVM of CFA rat. The application of ANX-005 or minocycline resulted in a reduction in the expression of C1q/C3 and microglia. Notably, the expression of excitatory presynaptic membrane markers reduced and the length and density of dendritic spines decreased on neurons in RVM. Additionally, C1q was abundantly localized on excitatory presynaptic membranes and expressed in microglial lysosomes. Treatment with ANX-005 or minocycline resulted in a reduced number of immunofluorescence colocalizations and an elevated dendritic spine density. These findings indicate that initial orofacial pain induced by CFA, microglia in RVM are involved in the pruning of excitatory presynaptic membranes through the complement C1q/C3-CR3 signaling pathway. This process results in a reduction in the proportion of excitatory synapses and a disruption in the physiological balance between RVM descending facilitation and descending inhibition. This leads to the predominance of descending facilitation in pain transmission in the RVM, which in turn facilitates the chronification of orofacial pain. Overall design: RNA sequencing analysis in RVM of CON rats and CFA rats on the third day.