Abstract: BACKGROUND: Patients with lumbar disc herniation (LDH) often experience comorbid anxiety due to chronic pain and functional limitations, significantly affecting their quality of life. However, the mechanisms underlying the pain-anxiety comorbidity remain unclear.
OBJECTIVE: To investigate the neural regulatory mechanisms of the paraventricular nucleus in the hypothalamus in a mouse model of lumbar disc herniation with chronic pain-anxiety comorbidity.
METHODS: A total of 100 C57BL/6 mice were randomly divided into a normal group (24 mice) and a model group (76 mice). The lumbar disc herniation model was established in the model group using a needle puncture method. Seventy-two successfully modeled mice were randomly divided into the model group, oxytocin group, and oxytocin+Vasotocin group, with 24 mice in each group. Mice in the oxytocin group received a 200 nL injection of oxytocin (0.5 μg/μL) into the paraventricular nucleus of the hypothalamus. Mice in the oxytocin+Vasotocin group received a 200 nL injection of oxytocin into the paraventricular nucleus and a 20 μL intraperitoneal injection of Vasotocin (an oxytocin antagonist, 0.15 μg/μL). Anxiety-like behavioral changes were evaluated via the elevated plus maze and open field tests on day 20 after modeling. Mechanical paw withdrawal threshold and thermal paw withdrawal latency experiments were conducted for all groups before modeling and 21 days after modeling. On day 21 post-modeling, immunofluorescence staining was used to observe c-FOS expression in the paraventricular nucleus of the hypothalamus; q-PCR was employed to detect mRNA expression levels of inflammatory factors prostaglandin E2, tumor necrosis factor-α, and interleukin-1β; and western blot analysis was used to assess the protein expression levels of oxytocin receptors and p-ERK1/2. 
RESULTS AND CONCLUSION: (1) Compared with the normal group, the model group exhibited significantly reduced mechanical pain thresholds and thermal pain thresholds (P < 0.05), significantly decreased open arm duration and entries in the elevated plus maze (P < 0.05), and significantly reduced time spent and entries in the open area of the open field test (P < 0.05). Compared with the normal group, the mRNA expression levels of inflammatory factors prostaglandin E2, tumor necrosis factor-α, and interleukin-1β in the dorsal root ganglion tissue were significantly elevated (P < 0.05), c-FOS expression in the paraventricular nucleus of the hypothalamus was significantly increased (P < 0.05), the expression of oxytocin receptor protein in the paraventricular nucleus of the hypothalamus was significantly decreased, and p-ERK1/2 protein expression was significantly increased in the model group (P < 0.05). (2) Compared with the model group, the oxytocin group showed significantly increased mechanical pain thresholds and thermal pain thresholds (P < 0.05), significantly increased open arm duration and entries in the elevated plus maze (P < 0.05), and significantly increased time spent and entries in the open area of the open field test (P < 0.05). Compared with the model group, the mRNA expression levels of inflammatory factors prostaglandin E2, tumor necrosis factor-α, and interleukin-1β in the dorsal root ganglion tissue were significantly reduced (P < 0.05), c-FOS expression in the paraventricular nucleus of the hypothalamus was significantly decreased (P < 0.05), the expression of oxytocin receptor protein in the paraventricular nucleus of the hypothalamus was significantly increased, and p-ERK1/2 protein expression was significantly decreased in the oxytocin group (P < 0.05). (3) Compared with the oxytocin group, the oxytocin+Vasotocin group exhibited significantly reduced mechanical pain thresholds and thermal pain thresholds (P < 0.05), significantly decreased open arm duration and entries in the elevated plus maze (P < 0.05), and significantly reduced time spent and entries in the open area of the open field test (P < 0.05). Compared with the oxytocin group, the mRNA expression levels of inflammatory factors prostaglandin E2, tumor necrosis factor-α, and interleukin-1β in the dorsal root ganglion tissue were significantly increased (P < 0.05), c-FOS expression in the paraventricular nucleus of the hypothalamus was significantly elevated (P < 0.01), the expression of oxytocin receptor protein in the paraventricular nucleus of the hypothalamus was significantly decreased, and p-ERK1/2 protein expression was significantly increased in the oxytocin+Vasotocin group (P < 0.05). In conclusion, oxytocin can significantly alleviate chronic pain and anxiety-like behaviors in mice with lumbar disc herniation, and suppress inflammation in the dorsal root ganglion. Its mechanism may be related to the activation of the ERK signaling pathway in the paraventricular nucleus of the hypothalamus and the downregulation of inflammatory factor expression.

Key words: lumbar disc herniation, paraventricular nucleus of the hypothalamus, anxiety-like behavior, oxytocin receptor, chronic pain, neural regulatory mechanisms, molecular pathways, inflammatory factors