Dexmedetomidine attenuates haemorrhage-induced thalamic pain by inhibiting the TLR4/NF-κB/ERK1/2 pathway in mice

Background Thalamic pain, a neuropathic pain syndrome, frequently occurs after stroke. This research aimed to investigate the effect of dexmedetomidine (DEX) on thalamic pain. Methods The cellular localization of the TLR4 protein was determined by immunostaining. The expression of Iba1, GFAP and protein associated with the TLR4/NF-κB/ERK1/2 pathway was measured by Western blotting. Continuous pain hypersensitivity was evaluated by behavioural tests. The results were analysed by one-way ANOVA, two-way ANOVA and Tukey’s post hoc test. Results The results demonstrated that DEX obviously alleviated thalamic pain induced by haemorrhage on the ipsilateral side and delayed the development of pain hypersensitivity. Furthermore, the expression levels of Iba1, GFAP and proteins associated with the TLR4/NF-κB/ERK1/2 signalling pathway were greatly increased in mice with thalamic pain, but these effects were reversed by DEX. Conclusion Our findings suggest that DEX alleviates the inflammatory response during thalamic pain through the TLR4/NF-κB/ERK1/2 signalling pathway and might be a potential therapeutic agent for thalamic pain.

FTO (Fat-Mass and Obesity-Associated Protein) Participates in Hemorrhage-Induced Thalamic Pain by Stabilizing Toll-Like Receptor 4 Expression in Thalamic Neurons

Background and Purpose: Hemorrhage-caused gene changes in the thalamus likely contribute to thalamic pain genesis. RNA N 6 -methyladenosine modification is an additional layer of gene regulation. Whether FTO (fat-mass and obesity-associated protein), an N 6 -methyladenosine demethylase, participates in hemorrhage-induced thalamic pain is unknown. Methods: Expression of Fto mRNA and protein was assessed in mouse thalamus after hemorrhage caused by microinjection of Coll IV (type IV collagenase) into unilateral thalamus. Effect of intraperitoneal administration of meclofenamic acid (a FTO inhibitor) or microinjection of adeno-associated virus 5 (AAV5) expressing Cre into the thalamus of Fto fl/fl mice on the Coll IV microinjection–induced TLR4 (Toll-like receptor 4) upregulation and nociceptive hypersensitivity was examined. Effect of thalamic microinjection of AAV5 expressing Fto (AAV5- Fto ) on basal thalamic TLR4 expression and nociceptive thresholds was also analyzed. Additionally, level of N 6 -methyladenosine in Tlr4 mRNA and its binding to FTO or YTHDF2 (YTH N 6 -methyladenosine RNA binding protein 2) were observed. Results: FTO was detected in neuronal nuclei of thalamus. Level of FTO protein, but not mRNA, was time-dependently increased in the ipsilateral thalamus on days 1 to 14 after Coll IV microinjection. Intraperitoneal injection of meclofenamic acid or adeno-associated virus-5 expressing Cre microinjection into Fto fl/fl mouse thalamus attenuated the Coll IV microinjection–induced TLR4 upregulation and tissue damage in the ipsilateral thalamus and development and maintenance of nociceptive hypersensitivities on the contralateral side. Thalamic microinjection of AAV5- Fto increased TLR4 expression and elicited hypersensitivities to mechanical, heat and cold stimuli. Mechanistically, Coll IV microinjection produced an increase in FTO binding to Tlr4 mRNA, an FTO-dependent loss of N 6 -methyladenosine sites in Tlr4 mRNA and a reduction in the binding of YTHDF2 to Tlr4 mRNA in the ipsilateral thalamus. Conclusions: Our findings suggest that FTO participates in hemorrhage-induced thalamic pain by stabilizing TLR4 upregulation in thalamic neurons. FTO may be a potential target for the treatment of this disorder.

Resolution of symptoms in idiopathic thalamic pain syndrome after implantation of a cervical and thoracic percutaneous spinal cord stimulator

Background: Thalamic pain syndrome is classically described as chronic pain after an infarct of the thalamus. It leads to a decrease in the quality of life, especially for patients with inadequate treatment. Supportive imaging, such as a thalamic lesion or infarct, is widely accepted as necessary to diagnose this condition. Case Description: In this case report, we describe the case of a patient who developed allodynia and hyperesthesia with a hemibody distribution characteristic of thalamic pain syndrome, despite having no clear inciting event or identifiable thalamic lesion. This patient was successfully treated with cervical and thoracic spinal cord stimulation (SCS). Conclusion: We suggest that this patient may have presented with a non-lesional thalamic pain syndrome, supported by the classic hemibody allodynia and hyperesthesia and the response to SCS. Further, we demonstrate that SCS was an effective method to control this central pain disorder.

Treatment of Déjerine–Roussy syndrome pain with scrambler therapy

Aim: Déjerine–Roussy syndrome or central thalamic pain can be devastating, and treatment with drugs and even deep brain stimulation can be unsatisfactory. Scrambler therapy is a form of neuromodulation that uses external skin electrodes to send a ‘non-pain’ signal to the brain, with some success in difficult-to-treat syndromes such as neuromyelitis optica spectrum disorder. We used scrambler therapy to treat a patient with 6 years of disabling Déjerine–Roussy syndrome pain. Methods: A 56-year-old man received multiple daily then monthly treatments with electrode pairs placed just above the area of distal pain. Each treatment was for 40 min. Results: His allodynia and hyperalgesia resolved within 10 min, and his pain score fell to almost zero after 30 min. Months later, he resumed normal activity and is off all his pain medications. No side effects were noted. Conclusion: Scrambler therapy appeared to reverse 6 years of disabling pain safely and economically, and continues to be effective. Further multi-institutional trials are warranted for this rare syndrome.

A New Rat Model of Thalamic Pain Produced by Administration of Cobra Venom to the Unilateral Ventral Posterolateral Nucleus

Background: Thalamic pain is a neuropathic pain syndrome that occurs as a result of thalamic damage. It is difficult to develop therapeutic interventions for thalamic pain because its mechanism is unclear. To better understand the pathophysiological basis of thalamic pain, we developed and characterized a new rat model of thalamic pain using a technique of microinjecting cobra venom into the ventral posterolateral nucleus (VPL) of the thalamus. Objectives: This study will establish a new thalamic pain rat model produced by administration of cobra venom to the unilateral ventral posterolateral nucleus. Study Design: This study used an experimental design in rats. Setting: The research took place in the laboratory at the Aviation General Hospital of China Medical University and Beijing Institute of Translational Medicine. Methods: Male Sprague-Dawley rats were subjected to the administration of cobra venom or saline into the left VPL. The development of mechanical hyperalgesia and changes in pain-related behaviors and motor function were measured after intrathalamic cobra venom microinjection using the von Frey test, video recording, and cylinder test, respectively. On postoperative days 7 to 35, both electroacupuncture and pregabalin (PGB) were administered to verify that the model reproduced the findings in humans. Moreover, the organizational and structural alterations of the thalamus were examined via transmission electron microscopy (TEM). Results: The threshold for mechanical stimuli in the left facial skin was significantly decreased on day 3 after thalamic pain modeling as compared with pre-venom treatment. Furthermore, the ultrastructural alterations of neurons such as indented neuronal nuclei, damaged mitochondria and endoplasmic reticulum, and dissolved surrounding tissues were observed under TEM. Moreover, electroacupuncture treatment ameliorated mechanical hyperalgesia, pain-like behaviors, and motor dysfunction, as well as restore normal structures of neurons in the thalamic pain rat model. However, no such beneficial effects were noted when PGB was administered. Limitations: The pathophysiological features were different from the present model and the patients in clinical practice (in most cases strokes, either ischemic or hemorrhagic). Conclusion: The cobra venom model may provide a reasonable model for investigating the mechanism of thalamic pain and for testing therapies targeting recovery and pain after thalamic lesions.