The Role Of The Parabrachial Nucleus In Allodynia In Chronic Neuropathic Pain Mice

Objective: The parabrachial nucleus(PB),which is located in the pons and is dissected by one of the major cerebellar output tracks,is known to relay sensory information(visceral malaise,taste,temperature,pain,itch)to forebrain structures including the thalamus,hypothalamus,and extended amygdala.Since the PB is closely related to amygdala and anterior cingulate cortex and these two nuclei are known to play important roles in chronic neuropathic pain,so this study mainly observed the role of the PB in chronic neuropathic pain.Methods: We chose partial sciatic nerve ligation(PSNL)as the chronic neuropathic pain model.The experimental group(PSNL)and the control group(Sham)were established.We investigated the expression of c-Fos in PB region of mice in PSNL group and Sham group after Von-Frey hairs stimulation and the behavioral experiments,including the open field test,the high-plus maze test,and the tail suspension test,were used to detect the effects of chronic neuropathic pain on pain-related behaviors in mice.Then we investigated the effect of the PB activity on mechanical pain threshold and Pain-related negative emotion in PSNL mice using chemo genetic “designer receptors exclusively activated by designer drugs”(DREADDs)approach.Results: 1 The mechanical pain threshold in PSNL mice was significant lower than the Sham mice and this may last long for more than 35days;2 The c-Fos expression of the PB region in PSNL mice increased compared to the Sham mice(?PSNL group 67.17 ± 5.268,Sham group 23.25 ± 3.707,P=0.000009);3 The data of the behavior test after PSNL in PSNL group and Sham group:(1)The central distance of the open field test(124.8 ± 13.17 in the PSNL group,235.5 ± 11.21 in the Sham group,P=0.000017)and the time spent in central area(18.07±2.895 in the PSNL group,33.29±3.945 in the Sham group,P=0.0077)of the PSNL group was lower than the Sham group without affecting the total distance of movement;(2)The PSNL group had lower duration(PSBL group25.25 ± 8.488,Sham group56.53 ±5.166,P=0.0071)and entries(PSBL group 2.25±0.45,Sham group 5.63±0.94,P=0.0061)of the open arm than those of Sham group;(3)There was no difference between the PSNL group and the Sham group in immobility time(PSLEN group 129.9 ± 11.66,Sham group 143.2 ± 9.725,P=0.3942);(4)Inhibition of the PB activity in chronic neuropathic pain mice had no effect on mechanical pain threshold and anxiety-like behavioral.Conclusion: The touch-induced pain can activate the parabrachial nucleus(PB)in PSNL-mice and induced the anxiety-like behaviors in PSNL mice,but the inhibition of the PB cannot alleviate the allodynia and anxiety-like behavior of chronic neuropathic pain.