The interaction effects between opioidergic and D1-like dopamine receptors in the nucleus accumbens on pain-related behaviors in the animal model of acute pain

The opioidergic and dopaminergic systems play an essential role in processing pain information in the nucleus accumbens (NAc). The present work examined the hypothesis that interaction between opioidergic and D1-like dopamine receptors in the NAc area may influence acute pain-related behaviors. One hundred sixty adult male Wistar rats unilaterally received different doses of the drug solution or vehicle. First, separate groups of animals received different doses of morphine (5, 10, and 25 mmol/0.5 μL) and various doses of SKF38393 (1.5, 3, 6, and 12 mmol/0.5 μL) as opioid and D1-like receptor agonists in the NAc region, respectively. In the second set of experiments, animals got different amounts (1.5, 3, 6, and 12 mmol/0.5 μL) of SCH23390, a D1-like receptor antagonist, before an effective dose of morphine (10 mmol/0.5 μL). In the last experiment, the animals were given naloxone (1.5, 5, and 15 mmol/0.5 μL) before they were given an effective dose of SKF38393 (3 mmol/0.5 μL). The tail-flick test was then used to measure their acute pain threshold. The main findings showed that intra-NAc injection of morphine and SKF38393 alone causes antinociceptive responses. However, the intra-accumbal injection of SCH23390 significantly reduced the antinociceptive responses elicited by intra-NAc morphine. Additionally, intra-NAc naloxone significantly reduced the antinociceptive effects elicited by intra-NAc SKF38393. Interestingly, SCH23390 was more effective in reversing the analgesic effects of morphine (η2 = 0.61) than naloxone in reversing the analgesic effects of SKF38393 (η2 = 0.49). The findings suggest that the opioidergic and dopamine systems in the NAc collaborate to produce pain-relieving effects. This insight could potentially enhance the effectiveness of lower doses of opioids for pain management, ultimately reducing their usage in clinical settings in the future.