ABSTRACT
ObjectiveTo investigate the role of proinflammatory cytokines tumor necrosis factor alpha （TNFα） and interleukin-1β （IL-1β） in rostral ventromedial medulla （RVM） in chronic postsurgical pain （CPSP） induced by skin/muscle incision and retraction （SMIR）. MethodsSD rats were randomly divided into 5 groups： ① Sham group； ② SMIR group； ③ SMIR+TNFα/IL-1β neutralizing antibody group； ④ SMIR+TNFα/IL-1β group and ⑤ SMIR+vehicle group. 50% paw mechanical withdrawal threshold （MWT） was measured by the up-down method， immunofluroscence was used to detect the TNFα and IL-1β expression and ELISA for the 5-Hydroxytryptamine （5-HT） level. ResultsSMIR elicited persistent nociceptive sensitization， upregulated TNFα and IL-1β expression in RVM neurons and astrocytes. Microinjection of TNFα or IL-1β neutralizing antibody into RVM inhibited the development of nociceptive sensitization and decreased the level of 5-HT in both RVM and spinal dorsal horn. While microinjection of recombinant TNFα or IL-1β into RVM enhanced the development of nociceptive sensitization and increased the level of 5-HT in both RVM and spinal dorsal horn. ConclusionUp-regulation of proinflammatory cytokines in RVM may contribute to SMIR induced CPSP by promoting 5-HT release.
ABSTRACT
The rostral ventromedial medulla is one of the key structures in descending pain modulation system. It receives inputs from the thalamus, the periaqueductal gray, and parabrachial nucleus, and sends descending projections through the dorsolateral funiculus and ventrolateral funiculus to the spinal dorsal horns. The rostral ventromedial medulla is thought to be the final relay in descending modulation of pain. The neurons in this region can be classified into On-cells, Off-cells and Neutral cells according to the changes in the firing activity before tail flick. This review mainly focuses on pain modulation functions and potential analgesia mechanisms of On-cells and Off-cells.
ABSTRACT
Descending nociceptive modulation from the supraspinal structures plays an important role in cancer-induced bone pain (CIBP).Rostral ventromedial medulla (RVM) is a critical component of descending nociceptive facilitation circuitry,but so far the mechanisms are poorly known.In this study,we investigated the role of RVM glial activation in the descending nociceptive facilitation circuitry in a CIBP rat model.CIBP rats showed significant activation of microglia and astrocytes,and also up-regulation of phosphorylated p38 mitogen-activated protein kinase (p38 MAPK) and pro-inflammatory mediators released by glial cells (IL-1β,IL-6,TNF-a and brain-derived neurotrophic factor) in the RVM.Stereotaxic microinjection of the glial inhibitors (minocycline and fluorocitrate) into CIBP rats' RVM could reverse the glial activation and significantly attenuate mechanical allodynia in a time-dependent manner.RVM microinjection of p38 MAPK inhibitor (SB203580) abolished the activation of microglia,reversed the associated up-regulation of pro-inflammatory mediators and significantly attenuated mechanical allodynia.Taken together,these results suggest that RVM glial activation is involved in the pathogenesis of CIBP.RVM microglial p38 MAPK signaling pathway is activated and leads to the release of downstream pro-inflammatory mediators,which contribute to the descending facilitation of CIBP.