Aspirin attenuates tramadol-induced conditioned place preference: involvement of cytokines, antioxidant enzymes, and apoptosis.

Tramadol is widely prescribed for moderate to severe pain, but prolonged use carries a high risk of opioid dependence. Inflammation, oxidative stress, and apoptosis are key mechanisms implicated in the neurobiological responses to chronic opioid exposure. Aspirin, due to its anti-inflammatory and antioxidant properties, may offer protective benefits against these negative outcomes. This study investigated whether aspirin attenuates tramadol-induced reinforcement and associated molecular alterations. Adult male rats were divided into four groups: (1) Control (vehicle only), (2) TRA-saline (tramadol 75 mg/kg, i.p., every other day for 8 days), (3) TRA-ASP (aspirin 37.5 mg/kg, p.o., administered 45 min before each tramadol injection), and (4) ASP-saline (aspirin 37.5 mg/kg, p.o.), only. All groups underwent conditioned place preference testing, followed by biochemical analysis of the prefrontal cortex. Expression of cytokines (Il1b, Il6, Il4, Tgfb1, and Tnf), oxidative stress markers, including antioxidant enzyme activities (catalase (CAT) and superoxide dismutase (SOD)) and lipid peroxidation marker (malondialdehyde (MDA)), and Caspase3 activity were evaluated. Tramadol treatment significantly increased mRNA expression of Il1b (p < 0.0001), Il6 (p = 0.0035), Tgfb1 (p < 0.0001), and Tnf (p < 0.0001) compared to control. Tramadol also elevated antioxidant enzyme activities, including CAT (p = 0.0010) and SOD (p < 0.0001), and increased lipid peroxidation (MDA, p = 0.0131). Pretreatment with aspirin significantly attenuated all these molecular changes (Il1b p < 0.0001, Il6 p = 0.0035, Tgfb1 p < 0.0001, Tnf p < 0.0001; CAT p = 0.0010, SOD p < 0.0001, MDA p = 0.0131). Caspase 3 activity was increased by tramadol (p < 0.0001) and normalized by aspirin treatment. These findings suggest that aspirin may be protective against tramadol-seeking behavior, likely through modulation of neuroinflammatory, oxidative, and apoptotic pathways.