Microglial-derived nitric oxide regulates amygdala synaptic plasticity to drive chronic pain and depression induced by lumbar disc herniation.

Lumbar disc herniation (LDH) is a major driver of chronic low back pain often accompanied by depression-like behaviors, yet the supraspinal mechanisms that link nociception to affective disturbance remain unclear. Here, we investigated the potential mechanisms by which microglia-derived nitric oxide (NO) modulates synaptic plasticity in the amygdala of a rat model of LDH. Behavioral assessments confirmed the presence of mechanical hyperalgesia and depression-like behaviors in LDH rats. Multi-omics profiling revealed increased L-arginine in CSF and enrichment of cGMP-PKG and glutamatergic, long-term potentiation pathways in the amygdala. Protein-level validation confirmed upregulation of iNOS, NO, cGMP, and PRKG2 in the amygdala. Concurrently, increased levels of IL-1β and TNF-α in both the amygdala and CSF, along with Iba1 and iNOS co-localization in microglia, confirmed a neuroinflammatory microenvironment. Enhanced expression of GRIA1, p-GRIA1, GRIN2B, and p-CaMKII indicated potentiation of excitatory synaptic transmission in the amygdala. In a microglia-neuron co-culture system, conditioned medium from CSF-activated BV2 cells upregulated PRKG2, cGMP, and synaptic plasticity markers in PC12 cells. These effects were abolished by the iNOS inhibitor 1400W and mimicked by the NO donor DETA-NONOate, confirming a mechanistic link between microglial NO and neuronal plasticity. These findings suggested that LDH-induced neuroinflammation activates microglial iNOS in the amygdala, leading to NO elevations that engage the cGMP/PRKG2 pathway and drive pathological excitatory synaptic plasticity. Targeting this neuroimmune pathway may offer novel therapeutic strategies for chronic pain and related depression induced by LDH.