Plumbagin attenuates neuropathic pain via inhibition of spinal astrogliosis and modulation of hippocampal CA1 opioidergic receptors

• Chronic constriction injury (CCI) of the sciatic nerve activates and elevates spinal astrocytes and induces nociception. • Intra-hippocampal naloxone produces hyperalgesia in CCI rats. • Intra-hippocampal naloxone reverses the anti-nociception produce by Plumbagin (PL). • PL reduces increased spinal astrocytes after CCI, modulates hippocampal opioid receptors, and exhibits biphasic antinociceptive effect. • In silico interactions of PL and morphine with mu, kappa, and delta opioid receptors revealed aggregable binding affinity. Plumbagin (PL), a natural phytochemical obtained from Plumbago zeylanica roots, known as Bai Hua Dan in traditional Chinese medicine, has become a thriving area of research. Emerging evidence suggests that PL exhibits analgesic effects in various rodent pain models. Therefore, exploring the mechanisms underlying PL's central antinociceptive effect is interesting. Despite extensive research into alternative therapies, chronic neuropathic pain (NP) remains a persistent clinical challenge. We investigated the role of spinal astrogliosis and hippocampal opioid receptors in the antinociceptive action of PL in rats with chronic constriction injury (CCI) of sciatic nerve-induced NP. A CCI of the sciatic nerve was performed to induce NP in rats. PL (1-8 µg/rat, intracerebroventricular-4V) and opioid antagonist naloxone (1-8 µg/rat, intra-hippocampal cornu ammonis-1 (CA 1 ) were administered per se or in combination, followed by a thermal-mechanical-cold sensitivity test. Using a molecular docking study, the affinity of PL at opioidergic receptors was investigated. Immunohistochemistry of glial-fibrillary acidic protein (GFAP) was used to evaluate the effect of PL on astrogliosis in the spinal dorsal horn (SDH). Treatment with PL showed a dose-dependent antinociceptive effect. Interestingly, pretreatment with naloxone attenuated the antinociceptive effect of PL. Furthermore, PL reduced the NP-triggered integrated density of GFAP+ve astrocytes in the SDH. The in-silico binding revealed a potent binding of PL to kappa, delta-, and mu-opioid receptors in the order of binding, comparable to morphine. Our findings suggest that PL possibly ameliorates NP by suppressing astroglial activation in the SDH and inhibiting nociceptive processing in the hippocampal CA 1 region via opioid receptors.