LIFU Alleviates Neuropathic Pain by Improving the KCC2 Expression and Inhibiting the CaMKIV–KCC2 Pathway in the L4–L5 Section of the Spinal Cord

Abstract

Effective treatment remains lacking for neuropathic pain (NP), a type of intractable pain. Low-intensity focused ultrasound (LIFU), a noninvasive, cutting-edge neuromodulation technique, can effectively enhance inhibition of the central nervous system (CNS) and reduce neuronal excitability. We investigated the effect of LIFU on NP and on the expression of potassium chloride cotransporter 2 (KCC2) in the spinal cords of rats with peripheral nerve injury (PNI) in the lumbar 4–lumbar 5 (L4–L5) section. In this study, rats received PNI surgery on their right lower legs followed by LIFU stimulation of the L4–L5 section of the spinal cord for 4 weeks, starting 3 days after surgery. We used the 50% paw withdraw threshold (PWT50) to evaluate mechanical allodynia. Western blotting (WB) and immunofluorescence (IF) were used to calculate the expression of phosphorylated extracellular signal–regulated kinase 1/2 (p-ERK1/2), calcium/calmodulin-dependent protein kinase type IV (CaMKIV), phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB), and KCC2 in the L4–L5 portion of the spinal cord after the last behavioral tests. We found that PWT50 decreased ( P < 0.05 ) 3 days post-PNI surgery in the LIFU− and LIFU+ groups and increased ( P < 0.05 ) after 4 weeks of LIFU stimulation. The expression of p-CREB and CaMKIV decreased ( P < 0.05 ) and that of KCC2 increased ( P < 0.05 ) after 4 weeks of LIFU stimulation, but that of p-ERK1/2 ( P > 0.05 ) was unaffected. Our study showed that LIFU could effectively alleviate NP behavior in rats with PNI by increasing the expression of KCC2 on spinal dorsal corner neurons. A possible explanation is that LIFU could inhibit the activation of the CaMKIV–KCC2 pathway.

Low-Intensity Focused Ultrasound Alleviates Spasticity and Increases Expression of the Neuronal K-Cl Cotransporter in the L4–L5 Sections of Rats Following Spinal Cord Injury

“…Both cellular and animal experiments have confirmed that LIFU not only affects the activation and depolarization of Ca 2+ and Na + ion channels on the cell membrane (Kubanek et al, 2016 ) but also upregulates the expression of brain-derived neurotrophic factor (BDNF) following central nerve injury (Yang et al, 2015 ; Ni et al, 2017 ; Blackmore et al, 2019 ). In a previous study, our team also confirmed that LIFU stimulation can activate the spinal cord neurocircuits (Liao et al, 2021a ) and increase the expression of KCC 2 of the spinal cords of neuropathic pain rats effectively (Liao et al, 2021b ). However, whether LIFU can activate the spinal cord neurocircuits, upregulate the expression of KCC 2 , and then alleviate spasticity post-SCI spasm is still not completely clear.…”

“…LIFU stimulation of the spinal cord was performed as described previously (Liao et al, 2021a , b ). Briefly, before LIFU treatment, the hair around the ultrasonic irradiation site on the back of each rat was shaved off.…”

Effects of Noninvasive Low-Intensity Focus Ultrasound Neuromodulation on Spinal Cord Neurocircuits In Vivo

“…The LIFU stimulation procedure was performed as follows [ 29 ]: after anesthesia, the rats were fixed on a table, and the hair on their backs was removed using a depilating cream to expose the L4–L5 segments of the spinal cord. An ultrasound probe was fixed to the back of the L4–L5 spinal cord segment with a clapper.…”

The cannabinoid dehydroxylcannabidiol suppresses neuropathic pain by upregulating a spinal glycine receptor-mediated compensation mechanism

“…It is noteworthy that the evidence of other studies may give some hints. For example, several previous reports have reported that activation of the CaMKII/IV-CREB pathway in the SCDH contributes to NP through increasing the level of brain-derived neurotrophic factor, neuropeptides, and NMDA receptor or decreasing GABAergic transmission in SCDH ( 33 , 34 , 52 , 53 , 54 ). In addition, i.t.…”