Microglia-mediated BLA glutamatergic neuronal hyperactivity in the BLA-ACC pathway contributes to stress-induced visceral hypersensitivity and anxiety in rats.

backgroundVisceral hypersensitivity and anxiety are frequently present as comorbidities in patients with irritable bowel syndrome (IBS). We previously found that both the basolateral amygdala (BLA) and the anterior cingulate cortex (ACC) are involved in stress-related IBS, but the underlying mechanisms remain incompletely understood. In this study, we aimed to determine the role of microglia in the BLA and the BLA-ACC pathway in modulating stress-induced visceral hypersensitivity and anxiety.

methodsA rat model of chronic stress was established by water avoidance stress (WAS). The abdominal electromyogram was applied to measure visceral sensitivity. The open field test and elevated plus maze test were used to assess anxiety-like behaviors. Minocycline or lipopolysaccharide (LPS) was administrated to inhibit or activate microglia in the BLA. Microglial morphology and neuronal activity were analyzed by immunofluorescence. The expression level of inflammatory mediators in the BLA was determined by quantitative real-time PCR. Chemogenetic approaches were used to manipulate neuronal activity.

resultsWAS induced activation of microglia and secretion of pro-inflammatory mediators in the BLA. Inhibition of microglia in the BLA with minocycline pretreatment prevented the development of visceral hypersensitivity and anxiety-like behaviors induced by WAS. Treatment with LPS could mimic WAS-induced microglia activation in the BLA and result in visceral hypersensitivity and anxiety-like behaviors. Both WAS and LPS significantly enhanced BLA neuronal excitability, whereas inhibition of microglia in the BLA prevented WAS-induced glutamatergic neuron hyperactivity. Inhibition of BLA glutamatergic neurons alleviated both visceral hypersensitivity and anxiety-like behaviors in rats experiencing WAS. Activation of BLA glutamatergic neurons could mimic WAS-induced changes. Selective manipulation of the BLA-ACC glutamatergic pathway bilaterally modulated both visceral hypersensitivity and anxiety-like behaviors. Furthermore, inhibition of BLA microglial activity in WAS rats followed by activation of the BLA-ACC glutamatergic pathway induced visceral hypersensitivity and anxiety-like behaviors.

conclusionsOverall, our findings reveal that the development of visceral hypersensitivity and anxiety induced by stress is associated with activation of microglia and secretion of pro-inflammatory mediators in the BLA, as well as the hyperactivity of BLA-ACC glutamatergic pathway, thus highlighting the BLA-ACC neurocircuitry as a potential therapeutic target for treating the comorbidities of visceral pain and anxiety.