Abstract: BACKGROUND: Deep brain stimulation of the anterior cingulate cortex has emerged as a new surgical treatment for psychiatric disorders such as depression; however, the specific mechanisms underlying its therapeutic effects are still not well understood. It has been shown that damage to the anterior cingulate cortex improves depressive behavior in mice, leading to the hypothesis that deep brain stimulation may hold promise as a treatment for depression.
OBJECTIVE: To elucidate the neuroregulatory mechanisms of DBS of the anterior cingulate cortex and compares the effects of DBS and electroablation on depression-like behavior in mice using calcium imaging and fiber optic recording combined with C-fos immunohistochemistry.
METHODS: (1) Grouping and modeling: C57BL/6J mice were randomly divided into four groups: a control group, a model+sham stimulation group, a model+deep brain electrical stimulation group, and a model + electroablation group. Chronic restraint stress (3.5 weeks) was conducted to establish mouse models of depression in the latter three groups, and deep brain electrical stimulation electrodes were implanted in the anterior cingulate cortex in all four groups. (2) Intervention protocol: Mice in the deep brain stimulation group received daily 2-hour high-frequency electrical stimulation (130 Hz, 200 μA, 50 μs) for 1 week; mice in the model + sham stimulation group received electrode implantation without electrical stimulation; mice in the model + ablation group received a single 0.5-hour alternating current stimulation (130 Hz, 200 μA). (3) Behavioral assessment: Depression-like behavior was quantified using the forced swim test and tail suspension test. (4) Circuit mechanism analysis: Real-time neural activity was monitored by fiber photometry to assess the activation effect of deep brain stimulation on the anterior cingulate cortex-basolateral amygdala circuit. (5) Anxiety behavior analysis: Open field test was performed to assess anxiety-like behavior in mice after intervention. (6) Whole-brain activation map: C-fos immunohistochemical staining was used to quantify neuronal activity in the downstream brain regions of the anterior cingulate cortex. (7) The improvement in depression-like behavior in mice was verified using electroablation. 
RESULTS AND CONCLUSION: (1) Behavioral analysis: The forced swim test showed that the immobility time was significantly longer in the model + deep brain stimulation and model + sham stimulation groups than the control group (P < 0.05), but there was no significant difference between the model + deep brain stimulation and model + sham stimulation groups; the immobility time was significantly shorter in the model + electroablation group than that of the model + sham stimulation group (P < 0.01). In the tail suspension test, there was no significant difference in immobility time between the model + deep brain stimulation and model + sham stimulation groups. In the open field test, the central zone residence time and locomotor distance were significantly shorter in the deep brain stimulation group than the control group (P < 0.05), suggesting that deep brain stimulation may exacerbate anxiety-like behavior. (2) Neural mechanisms: Fiber optic recording confirmed that anterior cingulate cortex-deep brain stimulation specifically activated the anterior cingulate cortex-basolateral amygdala circuit. (3) C-fos staining showed that deep brain stimulation significantly enhanced neuronal activity in the downstream brain regions of the anterior cingulate cortex. These results suggest that although traditional high-frequency anterior cingulate cortex-deep brain stimulation effectively activates the target neural circuit, it fails to improve depression-like behavior and may exacerbate anxiety states by enhancing limbic system activity; conversely, functional inhibition of the anterior cingulate cortex by electroablation exhibits marked antidepressant effects, providing new directions for optimizing neuromodulation strategies. 

Key words: deep brain stimulation, depression, anterior cingulate cortex, electroablation, fiber photometry