Effects of varying degrees of ligation in a neuropathic pain model induced by chronic constriction injury.

AIM: Ligature tightness of chronic constriction injury (CCI) model remains inconsistent and controversial, presenting barriers for researchers. METHODS: We summarized the different ligation criteria in literature and attempted to clarify their effects. To assess constriction under different criteria, we calculated the radial strain (εR) of ligated nerves from digital photographs. The mechanical withdrawal thresholds (MWT), thermal withdrawal latency (TWL) and sciatic functional index (SFI) were observed in rats of different groups to assess the state of model. Changes of myelin sheath were detected by pathological staining and immunohistochemistry. RESULTS: The median εR values in the Loose, Medium and Tight groups were 13.6%, 15.2% and 21.7%, respectively. Ligated groups had lower MWT than Sham group and the TWL of rats in the Loose approached to rats with sham operation, while that of the Tight group was higher than Medium group 14 days after surgery. Medium and Tight groups showed more abnormal in SFI, compared with the other two groups 14 days. Pathological staining revealed demyelination in three CCI groups, especially in the sciatic nerves. Myelin protein zero levels decreased in the sciatic nerves as the degree of constriction increased, but myelin basic protein of the Medium group was lowest abundant in the spinal cords of all rats. CONCLUSIONS: Our study demonstrated that the surrounding muscles briefly twitched when the diameter of the sciatic nerves was constricted by approximately 14-15%, which may provide a reference for other researchers for establishing CCI models.

Zerumbone Modulates α2A-Adrenergic, TRPV1, and NMDA NR2B Receptors Plasticity in CCI-Induced Neuropathic Pain In Vivo and LPS-Induced SH-SY5Y Neuroblastoma In Vitro Models.

Zerumbone has shown great potential in various pathophysiological models of diseases, particularly in neuropathic pain conditions. Further understanding the mechanisms of action is important to develop zerumbone as a potential anti-nociceptive agent. Numerous receptors and pathways function to inhibit and modulate transmission of pain signals. Previously, we demonstrated involvement of the serotonergic system in zerumbone's anti-neuropathic effects. The present study was conducted to determine zerumbone's modulatory potential involving noradrenergic, transient receptor potential vanilloid type 1 (TRPV1) and N-methyl-D-aspartate (NMDA) receptors in chronic constriction injury (CCI)-induced in vitro and lipopolysaccharide (LPS)-induced SH-SY5Y in vitro neuroinflammatory models. von Frey filament and Hargreaves plantar tests were used to assess allodynia and hyperalgesia in the chronic constriction injury-induced neuropathic pain mouse model. Involvement of specific adrenoceptors were investigated using antagonists- prazosin (α1-adrenoceptor antagonist), idazoxan (α2-adrenoceptor antagonist), metoprolol (ß1-adrenoceptor antagonist), ICI 118,551 (ß2-adrenoceptor antagonist), and SR 59230 A (ß3-adrenoceptor antagonist), co-administered with zerumbone (10 mg/kg). Involvement of excitatory receptors; TRPV and NMDA were conducted using antagonists capsazepine (TRPV1 antagonist) and memantine (NMDA antagonist). Western blot was conducted to investigate the effect of zerumbone on the expression of α2A-adrenoceptor, TRPV1 and NMDA NR2B receptors in CCI-induced whole brain samples of mice as well as in LPS-induced SH-SY5Y neuroblastoma cells. Pre-treatment with α1- and α2-adrenoceptor antagonists significantly attenuated both anti-allodynic and anti-hyperalgesic effects of zerumbone. For ß-adrenoceptors, only ß2-adrenoceptor antagonist significantly reversed the anti-allodynic and anti-hyperalgesic effects of zerumbone. ß1-adrenoceptor antagonist only reversed the anti-allodynic effect of zerumbone. The anti-allodynic and anti-hyperalgesic effects of zerumbone were both absent when TRPV1 and NMDA receptors were antagonized in both nociceptive assays. Zerumbone treatment markedly decreased the expression of α2A-adrenoceptor, while an up-regulation was observed of NMDA NR2B receptors. Expression of TRPV1 receptors however did not significantly change. The in vitro study, representing a peripheral model, demonstrated the reduction of both NMDA NR2B and TRPV1 receptors while significantly increasing α2A-adrenoceptor expression in contrast to the brain samples. Our current findings suggest that the α1-, α2-, ß1- and ß2-adrenoceptors, TRPV1 and NMDA NR2B are essential for the anti-allodynic and antihyperalgesic effects of zerumbone. Alternatively, we demonstrated the plasticity of these receptors through their response to zerumbone's administration.

Persistent, comorbid pain and anxiety can be uncoupled in a mouse model.

Clinically, pain and anxiety frequently coexist; however, these two conditions' interaction is limited and contradictory in animal studies. In this study, we combined social defeat (SD) stress with Freund's adjuvant (CFA)-induced persistent inflammatory pain to investigate the reciprocal relationship between anxiety-like and nociceptive behaviors in two mouse strains. C57BL/6J mice subjected to the 10-day period of SD stress by repeated CD-1 mice aggression exhibited significant social interaction avoidance behaviors in the social interaction (SI) test, which is believed to represent the symptoms of anxiety. These mice also displayed anxiety-like behaviors in elevated plus maze (EPM) and open field (OF) tests. Compared to C57BL/6J mice, FVB/NJNju mice showed less basal social contact, but their behavioral responses to 10-day SD stress were more resilient. CFA-inflammatory mice showed robust mechanical allodynia and thermal hyperalgesia in both strains, but did not develop obvious social avoidance and anxiety-like behaviors 10 days after CFA-inflammation. Interestingly, CFA-inflammatory mice exposed to SD stress were not accompanied by a worsening of pain and anxiety-like behaviors in most tests. In contrast, the SD stress-induced social avoidance was significantly antagonized by combining with CFA-inflammatory pain. These findings suggest that persistent inflammatory pain and SD stress-induced anxiety may not necessarily exacerbate one another in animal models of comorbidity.