Astrocytes enhance the synaptic transmission between VTA GABASST and DA neurins to induce depression in chronic neuropathic pain
Background: As pain persists, it is often accompanied by the development of negative emotional states, such as depression. Approximately 50%-85% of patients with chronic pain experience depressive symptoms. Ventral tegmental area (VTA) ?--aminobutyric acid (GABA) neurons play a crucial role in regulating emotions. VTA GABA neurons can be mainly classified into those expressing somatostatin (SST) and parvalbumin (PV) neurons. The subtypes of VTA GABA neurons exhibit significant heterogeneity, but it remains unclear whether these subtypes mediate different functions in the development of chronic pain and depression. Inward rectifying potassium channel 4.1 (Kir4.1) is an important potassium channel mainly expressed in astrocytes and plays an important role in regulating neural activity. In lipopolysaccharide (LPS)-induced depression, Kir4.1 in lateral habenula (LHb) was upregulated. Lys05 (an inhibitor of Kir4.1) reversed the Kir4.1-driven depression-like phenotype. However, there was no study has reported the changes of Kir4.1 in chronic pain-induced depression or verified the therapeutic effects of Lys05 on it. Methods: We established chronic constriction injury (CCI) model to induce chronic pain in mice, and used the sugar preference test (SPT), tail suspension test (TST), and open field test (OFT) to detect depressive behavior in mice. Lys05 was injected to investigate the effect of Kir4.1 inhibitors on depression caused by chronic neuropathic pain. The adeno-associated virus (AAV) was designed to knockdown or overexpress the expression of Kir4.1 in VTA astrocytes.  Using optogenetic manipulations and transgenic mice, specific activation of VTA GABASST neurons or VTA GABAPV neurons was used to explore which types of VTA GABA neurons Kir4.1 has effects on.  Patch-clamp recording was applied to explore the effects of Kir4.1 on the excitability of different types of VTA neurons. Results: Lys05 could reverse the depressive behaviors induced by LPS. In detail, mice treated with 10 mg/kg Lys05 showed increased sucrose preference, decreased immobility durations in TST and increased percent center time in OFT. However, Lys05 didn't show any specific response to depression behavior in CCI-induced depression mice. Then we found Kir4.1 expression decreased in VTA and LHb of CCI-induced depression mice. Next, we found knockdown of Kir4.1 in the VTA resulted mice became depression but with no hyperalgesia. Correspondingly, overexpress Kir4.1 in VTA astrocytes could reverse the chronic pain-induced depression like states. In the patch clamp, when knocked down Kir4.1 in VTA astrocytes, the excitability of dopamine neurons decreased, GABASST neurons increased, but GABAPV neurons did not change significantly. Specifically excitable VTA GABASST neurons could cause depression in mice, while excitable GABAPV neurons did not. Conclusion: Chronic pain decreases the expression of Kir4.1 in VTA astrocytes, which activates GABASST neurons and in turns inhibits DA neurons, then leads depression. Overall design: The VTA of wide type and chronic neuropathic pain adult mice were analyzed by single-nucleus RNA sequencing.