Transcranial Direct Current Stimulation Attenuates Visceral Hypersensitivity Via Suppression Of P2X3 Receptor Expression In Rat Insular Cortex

Background and Aims: Chronic visceral pain is a common clinical disease.It’s pathogenesis is not clear,and treatment options are very limited.Recently,it has been reported that the insular cortex(IC)is involved in the development of chronic visceral pain,but the detailed molecular mechanism remains unknown.The peripheral purinergic receptors have been thought to be involved in the development of chronic pain,therefore,the first part of this present study focuses on the role and mechanism of the purinergic receptors in the IC brain region in chronic visceral pain.Transcranial direct current stimulation(tDCS)has the characteristics of painless,convenient and quick relief for chronic pain.It has become a popular treatment method,but the mechanism of its analgesic effect is rarely reported.Therefore,the second part of this study focuses on whether tDCS can alleviate chronic visceral pain by suppressing the sensitization of purinergic receptors.The present and future studies might provide a theoretical basis for clinical treatment for chronic visceral pain hypersensitivity.Methods:1.The rat model of chronic visceral pain was established by the neonatal maternal deprivation(NMD)in neonatal rats.2.The visceral pain sensitivity of adult rats was measured by detecting the threshold of colorectal distention(CRD).3.TDCS stimulation was performed by a direct current stimulation device connected with a stimulus isolator.4.Western blotting and immunofluorescence techniques were used to detect the expression and distribution of P2X3 receptors.5.The excitability and synaptic transmission characteristics of neurons in the insular cortex were recorded by the patch clamp technology.Results:1.The expression of P2X3 receptors was significantly increased in NMD rats.P2X3 receptors were co-localized with Neu N but not with markers of astrocytes and glial cells.2.P2X3 receptors antagonist A317491 significantly reversed the CRD threshold of NMD rats and significantly decreased the frequency of s EPSC and m EPSC in NMD rats IC neurons.There was no effect on the amplitude change.3.P2X3 receptors agonists α,β-ATP significantly increased the frequency of s EPSC and m EPSC in normal rats IC neurons and there was no effect on the amplitude change.4.TDCS significantly increased the threshold of CRD in NMD rats.5.TDCS significantly reduced the IC neurons excitability,the frequency of s EPSC and m EPSC in NMD rats and there was no effect on the amplitude change.6.TDCS significantly reduced the expression of P2X3 receptors in the IC region of NMD rats.Conclusions:Our results suggested that IC region P2X3 receptors involved in NMD rats visceral hyperalgesia and that tDCS reduced the frequency of s EPSC and m EPSC in neurons of the island cortex by down-regulating the expression of P2X3 receptors,thereby relieving the visceral hypersensitivity of NMD rats.