Neonatal Maternal Deprivation Followed by Adult Stress Enhances Adrenergic Signaling to Advance Visceral Hypersensitivity

The pathophysiology of visceral pain in patients with irritable bowel syndrome remains largely unknown.Our previous study showed that neonatal maternal deprivation(NMD) does not induce visceral hypersensitivity at the age of 6 weeks in rats. The aim of this study was to determine whether NMD followed by adult stress at the age of 6 weeks induces visceral pain in rats and to investigate the roles of adrenergic signaling in visceral pain. Here we showed that NMD rats exhibited visceral hypersensitivity 6 h and 24 h after the termination of adult multiple stressors(AMSs). The plasma level of norepinephrine was significantly increased in NMD rats after AMSs. Whole-cell patch-clamp recording showed that the excitability of dorsal root ganglion(DRG) neurons from NMD rats with AMSs was remarkably increased. The expression of β_2 adrenergic receptors at the protein and mRNA levels was markedly higher in NMD rats with AMSs than in rats with NMD alone. Inhibition of β_2 adrenergic receptors with propranolol or butoxamine enhanced the colorectal distention threshold and application of butoxamine also reversed the enhanced hypersensitivity of DRG neurons. Overall,our data demonstrate that AMS induces visceral hypersensitivity in NMD rats, in part due to enhanced NE-β_2 adrenergic signaling in DRGs.

Adult Stress Promotes Purinergic Signaling to Induce Visceral Pain in Rats with Neonatal Maternal Deprivation

Chronic visceral pain is one of the primary symptoms of patients with irritable bowel syndrome(IBS),which affects up to 15%of the population world-wide.The detailed mechanisms of visceral pain remain largely unclear.Our previous studies have shown that neonatal maternal deprivation(NMD)followed by adult multiple stress(AMS)advances the occurrence of visceral pain,likely due to enhanced norepinephrine(NE)-β2 adrenergic signaling.This study was designed to explore the roles of P2X3 receptors(P2X3Rs)in the chronic visceral pain induced by combined stress.Here,we showed that P2X3 Rs were co-expressed inβ2 adrenergic receptor(β2-AR)-positive dorsal root ganglion neurons and that NE significantly enhanced ATP-induced Ca2+signals.NMD and AMS not only significantly increased the protein expression of P2X3Rs,but also greatly enhanced the ATP-evoked current density,number of action potentials,and intracellular Ca2+concentration of colon-related DRG neurons.Intrathecal injection of the P2X3R inhibitor A317491 greatly attenuated the visceral pain and the ATP-induced Ca2+signals in NMD and AMS rats.Furthermore,theβ2-AR antagonist butoxamine significantly reversed the expression of P2X3Rs,the ATP-induced current density,and the number of action potentials of DRG neurons.Overall,our data demonstrate that NMD followed by AMS leads to P2X3R activation,which is most likely mediated by upregulation ofβ2 adrenergic signaling in primary sensory neurons,thus contributing to visceral hypersensitivity.

Mechanosensitive Ion Channel TMEM63A Gangs Up with Local Macrophages to Modulate Chronic Post-amputation Pain

Post-amputation pain causes great sufering to amputees,but still no efective drugs are available due to its elusive mechanisms.Our previous clinical studies found that surgical removal or radiofrequency treatment of the neuroma at the axotomized nerve stump efectively relieves the phantom pain aficting patients after amputation.This indicated an essential role of the residual nerve stump in the formation of chronic post-amputation pain(CPAP).However,the molecular mechanism by which the residual nerve stump or neuroma is involved and regulates CPAP is still a mystery.In this study,we found that nociceptors expressed the mechanosensitive ion channel TMEM63A and macrophages infltrated into the dorsal root ganglion(DRG)neurons worked synergistically to promote CPAP.Histology and qRT-PCR showed that TMEM63A was mainly expressed in mechanical pain-producing non-peptidergic nociceptors in the DRG,and the expression of TMEM63A increased signifcantly both in the neuroma from amputated patients and the DRG in a mouse model of tibial nerve transfer(TNT).Behavioral tests showed that the mechanical,heat,and cold sensitivity were not afected in the Tmem63a-/-mice in the naïve state,suggesting the basal pain was not afected.In the infammatory and post-amputation state,the mechanical allodynia but not the heat hyperalgesia or cold allodynia was signifcantly decreased in Tmem63a-/-mice.Further study showed that there was severe neuronal injury and macrophage infltration in the DRG,tibial nerve,residual stump,and the neuromalike structure of the TNT mouse model,Consistent with this,expression of the pro-infammatory cytokines TNFα,IL-6,and IL-1βall increased dramatically in the DRG.Interestingly,the deletion of Tmem63a signifcantly reduced the macrophage infltration in the DRG but not in the tibial nerve stump.Furthermore,the ablation of macrophages signifcantly reduced both the expression of Tmem63a and the mechanical allodynia in the TNT mouse model,indicating an interaction between nociceptors and macrophages,and that these two factors gang up together to regulate the formation of CPAP.This provides a new insight into the mechanisms underlying CPAP and potential drug targets its treatment.

Sympathetic Nerve Mediated Spinal Glia Activation Underlies Itch in a Cutaneous T-Cell Lymphoma Model

Dear Editor,Cancer-associated itch can be described as pruritus associated with malignancy.Although intractable itch associated with specific types of cancer afflicts patients badly,few effective treatments are available due to limited knowledge about the mechanisms of such itch.Globally,cancer-associated itch is an uncommon symptomin malignancy.