Highlights d Dopamine projections from the VTA innervate the mPFC d Dopamine release in the mPFC reverses mechanical hypersensitivity in SNI mice d Dopamine release induces conditioned place preference in SNI mice d Dopamine inputs increase activity of mPFC neurons projecting to the vlPAG

We recently reported that nerve injury or peripheral inflammation triggers an upregulation of the deubiquitinase, USP5 in mouse dorsal root ganglion and spinal dorsal horn. This leads to dysregulated ubiquitination of Cav3.2 T-type calcium channels, thus increasing Cav3.2 channel plasma membrane expression and nociceptive signaling in the primary afferent pain pathway. This phenomenon could be recapitulated by noninvasive, optogenetic activation of transient receptor potential vanilloid-1–expressing nociceptors, indicating that neuronal activity is a key player in this process. Given the relevance of the pro-inflammatory cytokine interleukin-1 beta in many forms of pathological pain, we hypothesized that interleukin-1 beta may be a critical cofactor required to drive upregulation of interactions between USP5 and Cav3.2 channels. Here, we report that gene expression, as well as protein levels for interleukin-1 beta and the endogenous interleukin-1 receptor-I antagonist, IL-1Ra are unaltered following conditioning stimulation of optogenetically targeted cutaneous nociceptors, indicating that neuronal activity is not a driver of interleukin-1 beta signaling. In contrast, co-immunoprecipitation experiments revealed that intrathecal administration of interleukin-1 beta in wild-type mice led to an increase in the interaction between USP5 and Cav3.2 in the spinal dorsal horn. Moreover, disruption of the interaction between USP5 and Cav3.2 with TAT peptides suppressed acute nocifensive responses produced by interleukin-1 beta, which was similar to that achieved by elimination of T-type channel activity with the channel blockers, mibefradil, or TTA-A2. Finally, this upregulation could be maintained in dorsal root ganglion neuron cultures exposed overnight to interleukin-1 beta, while the copresence of interleukin-1 receptor antagonist or the dampening of neuronal cell activity with tetrodotoxin attenuated this response. Altogether, our findings identify interleukin-1 beta as an upstream trigger for the upregulation of interactions between USP5 and Cav3.2 channels in the pain pathway, presumably by triggering increased firing activity in afferent fibers.

Many patients with visceral inflammation develop pain and psychiatric comorbidities such as major depressive disorder, worsening the quality of life and increasing the risk of suicide. Here we show that neuroimmune activation in mice with dextran sodium sulfate-induced colitis is accompanied by the development of pain and depressive behaviors. Importantly, treatment with the flavonoid luteolin prevented both neuroimmune responses and behavioral abnormalities, suggesting a new potential therapeutic approach for patients with inflammatory bowel diseases.

In humans, spinal cord lesions induce not only major motor and neurovegetative deficits but also severe neuropathic pain which is mostly resistant to classical analgesics. Better treatments can be expected from precise characterization of underlying physiopathological mechanisms. This led us to thoroughly investigate (i) mechanical and thermal sensory alterations, (ii) responses to acute treatments with drugs having patent or potential anti-allodynic properties and (iii) the spinal/ganglion expression of transcripts encoding markers of neuronal injury, microglia and astrocyte activation in rats that underwent complete spinal cord transection (SCT). SCT was performed at thoracic T8–T9 level under deep isoflurane anaesthesia, and SCT rats were examined for up to two months post surgery. SCT induced a marked hyper-reflexia at hindpaws and strong mechanical and cold allodynia in a limited (6 cm2) cutaneous territory just rostral to the lesion site. At this level, pressure threshold value to trigger nocifensive reactions to locally applied von Frey filaments was 100-fold lower in SCT- versus sham-operated rats. A marked up-regulation of mRNAs encoding ATF3 (neuronal injury) and glial activation markers (OX-42, GFAP, P2×4, P2×7, TLR4) was observed in spinal cord and/or dorsal root ganglia at T6-T11 levels from day 2 up to day 60 post surgery. Transcripts encoding the proinflammatory cytokines IL-1β, IL-6 and TNF-α were also markedly but differentially up-regulated at T6–T11 levels in SCT rats. Acute treatment with ketamine (50 mg/kg i.p.), morphine (3–10 mg/kg s.c.) and tapentadol (10–20 mg/kg i.p.) significantly increased pressure threshold to trigger nocifensive reaction in the von Frey filaments test, whereas amitriptyline, pregabalin, gabapentin and clonazepam were ineffective. Because all SCT rats developed long lasting, reproducible and stable allodynia, which could be alleviated by drugs effective in humans, thoracic cord transection might be a reliable model for testing innovative therapies aimed at reducing spinal cord lesion-induced central neuropathic pain.

Highlights d Toll-like receptors are upregulated during CFA-induced inflammatory pain d TLR2/6 receptor activation triggers acute pain via NLRP3dependent upregulation of IL-33 d IL-33 primes pain responses via neuroimmune crosstalk d Blocking IL-33 receptors mediates analgesia during inflammatory pain states

Numerous reported data support the idea that Brain Derived Neurotrophic Factor (BDNF) is critically involved in both depression and comorbid pain. The possible direct effect of BDNF on pain mechanisms was assessed here and compared with behavioral/neurobiological features of neuropathic pain caused by chronic constriction injury to the sciatic nerve (CCI-SN). Sprague-Dawley male rats were either injected intrathecally with BDNF (3.0 ng i.t.) or subjected to unilateral CCI-SN. Their respective responses to anti-hyperalgesic drugs were assessed using the Randall-Selitto test and both immunohistochemical and RT-qPCR approaches were used to investigate molecular/cellular mechanisms underlying hyperalgesia in both models. Long lasting hyperalgesia and allodynia were induced by i.t. BDNF in intact healthy rats like those found after CCI-SN. Acute treatment with the BDNF-TrkB receptor antagonist cyclotraxin B completely prevented i.t. BDNF-induced hyperalgesia and partially reversed this symptom in both BDNF-pretreated and CCI-SN lesioned rats. Acute administration of the anticonvulsant pregabalin, the NMDA receptor antagonist ketamine, the opioid analgesics morphine and tapentadol or the antidepressant agomelatine also transiently reversed hyperalgesia in both i.t. BDNF injected- and CCI-SN lesioned-rats. Marked induction of microglia activation markers (OX42, Iba1, P-p38), proinflammatory cytokine IL-6, NMDA receptor subunit NR2B and BDNF was found in spinal cord and/or dorsal root ganglia of CCI-SN rats. A long lasting spinal BDNF overexpression was also observed in BDNF i.t. rats, indicating an autocrine self-induction, with downstream long lasting TrkB-mediated neuropathic-like pain. Accordingly, TrkB blockade appeared as a relevant approach to alleviate not only i.t. BDNF- but also nerve lesion-evoked neuropathic pain.

No abstract

Peripheral nerve injury and tissue inflammation result in upregulation of the deubiquitinase USP5, thus causing a dysregulation of T-type calcium channel activity and increased pain sensitivity. Here, we have explored the role of afferent fiber activity in this process. Conditioning stimulation of optogenetically targeted cutaneous TRPV1 expressing nociceptors, but not that of non-nociceptive fibers, resulted in enhanced expression of USP5 in mouse dorsal root ganglia and spinal dorsal horn, along with decreased withdrawal thresholds for thermal and mechanical stimuli that abated after 24 hr. This sensitization was drastically reduced by an interfering peptide that prevented USP5-Cav3.2 association. Sensitization was relieved by pharmacological block of TRPV1 afferents, but not of myelinated neurons. In spinal cord slice recordings, we could optogenetically trigger an activity-dependent potentiation of presynaptic neurotransmission in the spinal dorsal horn that relied on Cav3.2 channel activity. This neuronal-activity-induced USP5 upregulation may underlie a protective, transient sensitization of the pain pathway.