Effects of Chronic Pain Following Unilateral Ureteral Obstruction on Hippocampal CA1 Pyramidal Neurons in Male Wistar Rats

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Background: Chronic pain can adversely affect cognitive functions such as learning, memory, and attention. However, the precise mechanisms underlying cognitive impairment in chronic pain remain elusive. Objectives: This study aims to investigate the impact of chronic pain induced by unilateral ureteral obstruction (UUO) on hippocampal neurons. Methods: In the current case-control study, 27 male Wistar rats (230 - 280 g) were randomly assigned to three groups: 1-sham, 2-UUO, and 3-UUO treated with naloxone (i.p.; 1 mg/kg for 5 days). Following transcardial perfusion, the rats' brains were removed, and histological studies were performed to count the number of neurons using an optical microscope. Concurrently, TNF-α and nerve growth factor (NGF) levels were measured in brain tissue homogenate. Results: The mean number of neurons in the CA1 region of the animals in the UUO group was 68.11 ± 1.34, which showed a significant decrease compared to the mean number of neurons in the sham-operated group (114.1 ± 1.77; P < 0.0001). In contrast, the mean number of neurons in the CA1 region of the UUO with naloxone group showed a significant increase compared to the animals in the UUO group (73.44 ± 1.37; P < 0.0001). TNF-α was 264.3 ± 2.6 pg/mL in the UUO animals and decreased significantly in the UUO animals treated with naloxone (P = 0.001). However, NGF was 115.2 ± 2.9 pg/mL in UUO animals and increased significantly in the UUO with naloxone group (P < 0.01). Conclusions: Unilateral ureteral obstruction, through inducing chronic pain and inflammation, resulted in neurodegeneration in the CA1 region of the hippocampus. The use of naloxone, an opioid antagonist, immediately after the surgery was able to provide neuronal protection and an anti-inflammatory effect.