Accepted

There is strong evidence that spinoparabrachial neurons in the superficial dorsal horn contribute to persistent pain states, and that the lateral parabrachial complex (PB) conveys relevant nociceptive information to higher structures. The role of PB itself in hyperalgesia and how it recruits descending facilitation has nevertheless received significantly less attention. The current study is a first step towards delineating the functional dynamics of PB and its link to descending control in acute and persistent inflammatory pain. In lightly anesthetized rats, we recorded behavioral withdrawal evoked by mechanical stimulation of the hindpaw, and simultaneously, activity of identified pain-modulating neurons, "ON-cells" and "OFF-cells," in the rostral ventromedial medulla (RVM). This was done before and after inactivation of PB, or to an inflamed paw (1 h, 1 d, or 5-6 d after intraplantar injection of Complete Freund's adjuvant, CFA). Inactivation of but not PB interfered with nociceptive input to RVM under basal conditions, as well as in acute inflammation. By contrast, blocking , but not , PB in established inflammation interfered with behavioral hyperalgesia and ON- and OFF-cell responses. Lesion of PB prior to CFA injection prevented this recruitment of PB in persistent inflammation. These experiments show that PB is required to initiate hyperalgesia, which is then maintained by PB, most likely in both cases via engagement of pain-modulating neurons of the RVM.The lateral parabrachial complex (PB) relays nociceptive information to brain circuits important for transmission and modulation of pain, but its specific role in persistent pain and engagement of descending control mechanisms has received relatively little attention. We show here that PB and to an inflammatory insult demonstrate different functions as inflammation persists, likely by engaging pain-facilitating neurons of the rostral ventromedial medulla. While the PB, the target of the major spinoparabrachial pathway, relays acute nociceptive information, the PB is recruited or unmasked in persistent inflammation to maintain hyperalgesia. These data point to plasticity in the PB itself or its direct and indirect connections with pain-modulating systems as central to development and maintenance of persistent pain.

Dysfunctions of genes transcription and translation in the nociceptive pathways play the critical role in development and maintenance of chronic pain. Circular RNAs (circRNAs) are emerging as new players in regulation of gene expression, but whether and how circRNAs are involved in chronic pain remains elusive. We showed here that complete Freund's adjuvant (CFA)-induced chronic inflammation pain significantly increased circRNA-Filip1l (filamin A interacting protein 1-like) expression in spinal neurons of mice. Blockage of this increase attenuated CFA-induced nociceptive behaviors, and overexpression of spinal circRNA-Filip1l in naïve mice mimicked the nociceptive behaviors as evidenced by decreased thermal and mechanical nociceptive threshold. Furthermore, we found that mature circRNA-Filip1l expression was negatively regulated by miRNA-1224 via binding and splicing of precursor of circRNA-Filip1l (pre-circRNA-Filip1l) in the Argonaute-2 (Ago2)-dependent manner. Increase of spinal circRNA-Filip1l expression resulted from the decrease of miRNA-1224 expression under chronic inflammation pain state. MiRNA-1224 knockdown or Ago2 overexpression induced nociceptive behaviors in naïve mice, which was prevented by the knockdown of spinal circRNA-Filip1l. Finally, we demonstrated that an ubiquitin protein ligase E3 component n-recognin 5 (Ubr5), validated as a target of circRNA-Filip1l, plays a pivotal role in regulation of nociception by spinal circRNA-Filip1l. These data suggest that miRNA-1224-mediated and Ago2-dependent modulation of spinal circRNA-Filip1l expression regulates nociception via targeting Ubr5, revealing a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.CircRNAs are emerging as new players in regulation of gene expression. Here, we found that the increase of circRNA-Filip1l mediated by miRNA-1224 in Ago2-dependent way in the spinal cord is involved in regulation of nociception via targeting Ubr5. Our study reveals a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.

Sensory neurons perceive environmental cues and are important of organismal survival. Peripheral sensory neurons interact intimately with glial cells. While the function of axonal ensheathment by glia is well studied, less is known about the functional significance of glial interaction with the somatodendritic compartment of neurons. Herein, we show that three distinct glia cell types differentially wrap around the axonal and somatodendritic surface of the polymodal dendritic arborization (da) neuron of the peripheral nervous system for detection of thermal, mechanical, and light stimuli. We find that glial cell-specific loss of the chromatin modifier gene dATRX in the subperineurial glial layer leads to selective elimination of somatodendritic glial ensheathment, thus allowing us to investigate the function of such ensheathment. We find that somatodendritic glial ensheathment regulates the morphology of the dendritic arbor, as well as the activity of the sensory neuron, in response to sensory stimuli. Additionally, glial ensheathment of the neuronal soma influences dendritic regeneration after injury.

The transient receptor potential vanilloid-1 (TRPV1) ion channel is essential for sensation of thermal and chemical pain. TRPV1 activation is accompanied by Ca-dependent desensitization; acute desensitization reflects rapid reduction in channel activity during stimulation, whereas tachyphylaxis denotes the diminution in TRPV1 responses to repetitive stimulation. Acute desensitization has been attributed to conformational changes of the TRPV1 channel; however, the mechanisms underlying the establishment of tachyphylaxis remain to be defined. Here, we report that the degree of whole-cell TRPV1 tachyphylaxis is regulated by the strength of inducing stimulation. Using light-sheet microscopy and pH-sensitive sensor pHluorin to follow TRPV1 endocytosis and exocytosis trafficking, we provide real-time information that tachyphylaxis of different degrees concurs with TRPV1 recycling to the plasma membrane in a proportional manner. This process controls TRPV1 surface expression level thereby the whole-cell nociceptive response. We further show that activity-gated TRPV1 trafficking associates with intracellular Ca signals of distinct kinetics, and recruits recycling routes mediated by synaptotagmin 1 and 7, respectively. These results suggest that activity-dependent TRPV1 recycling contributes to the establishment of tachyphylaxis.