Possible Involvement of Convergent Nociceptive Input to Medullary Dorsal Horn Neurons in Intraoral Hyperalgesia Following Peripheral Nerve Injury

Effects of Peripheral Nerve Injury on the Induction of c-Fos and Phosphorylated ERK in the Brainstem Trigeminal Sensory Nuclear Complex

Background

Sequential changes in brainstem and spinal cord neurons after traumatic injury to peripheral nerves are related to neuropathic pain symptoms.

Purpose

This study was conducted to elucidate the influence of nerve insult on stimulus-induced c-Fos expression and ERK phosphorylation by brainstem neurons.

Methods

The brainstem trigeminal sensory nuclear complex (BTSNC) was examined for neuronal profiles immunolabeled with c-Fos and phosphorylated ERK (p-ERK) antibodies elicited by stimulation of the tongue with capsaicin after lingual or inferior alveolar nerve (IAN) injury.

Results

Abundant neuronal profiles immunolabeled for c-Fos and p-ERK elicited by capsaicin were distributed in the spinal trigeminal nucleus caudalis (Vc) without nerve injury. The spinal trigeminal nucleus oralis (Vo) contained limited numbers of these neuronal profiles after stimulation of the tongue. A significant reduction of these neuronal profiles in the ipsilateral Vc was detected after lingual nerve injury. After IAN injury, an increased number of neuronal profiles immunolabeled for c-Fos elicited by capsaicin was noted, while that of p-ERK was left unchanged in the ipsilateral Vc. On the both sides of the Vo, an increased number of capsaicin-induced neuronal profiles immunolabeled for c-Fos and p-ERK was detected after lingual or IAN injury.

Conclusion

Differential effects of lingual or IAN injury on stimulus-induced c-Fos expression and ERK phosphorylation by Vo and Vc neurons may be involved in the complex nature of symptoms of trigeminal neuralgia.

Nrf2 and NF-κB modulation by Plumbagin attenuates functional, behavioural and biochemical deficits in rat model of neuropathic pain

BACKGROUND

Plumbagin is known to exhibit a broad range of biological activities including anti-cancer, antimicrobial and has been widely used traditionally. Nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) inhibitory and Nuclear factor (erythroid derived-2) like-2 (Nrf2) modulatory activities of Plumbagin have been reported already. In nerve injury model of neuropathy in rats, the role of NF-κB upregulation and declined antioxidant defence has been well recognized. So, we evaluated neuroprotective potential of Plumbagin in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in male Sprague-Dawley rats.

METHODS

Animals were tested for functional, behavioural and biochemical changes. Various markers associated with oxidative stress and inflammatory changes were assessed in the sciatic nerve and dorsal root ganglion (DRG) of the animals exposed to CCI mediated nerve injury.

RESULTS

CCI induced nerve injury led to long-lasting mechanical hyperalgesia, loss of hind limb function and abnormal pain sensation. Plumbagin treatment (10 and 20mg/kg, po) significantly and dose-dependently reversed mechanical hyperalgesia and other functional deficits. There was a marked increase in NF-κB and reduced Nrf2 levels in sciatic nerve and DRG following nerve injury. Plumbagin strengthened the antioxidant defence by improving Nrf2 levels and checked the neuroinflammation by decreasing NF-κB levels in sciatic nerve and DRG.

CONCLUSIONS

Together, these results suggested that Plumbagin alleviated CCI-induced neuropathic pain via antioxidant and anti-inflammatory mechanisms. Hence, the study suggests that Plumbagin may be useful for the management of trauma-induced neuropathic pain.