Ablation of IB4 non-peptidergic afferents in the rat facet joint prevents injury-induced pain and thalamic hyperexcitability via supraspinal glutamate transporters

ALPK1 Expressed in IB4-Positive Neurons of Mice Trigeminal Ganglions Promotes MIA-Induced TMJ pain

Pain is one of the main reasons for patients with temporomandibular joint (TMJ) disorders seeking medical care. However, there is no effective treatment yet as its mechanism remains unclear. Herein, we found that the injection of monoiodoacetate (MIA) into mice TMJs can induce typical joint pain as early as 3 days, accompanied by an increased percentage of calcitonin gene-related peptide positive (CGRP+) neurons and isolectin B4 positive (IB4+) in the trigeminal ganglions (TGs). Our previous study has discovered that alpha-kinase 1 (ALPK1) may be involved in joint pain. Here, we detected the expression of ALPK1 in neurons of TGs in wild-type (WT) mice, and it was upregulated after intra-TMJ injection of MIA. Meanwhile, the increased percentage of neurons in TGs expressing ALPK1 and CGRP or ALPK1 and IB4 was also demonstrated by the immunofluorescent double staining. Furthermore, after the MIA injection, ALPK1-/- mice exhibited attenuated pain behavior, as well as a remarkably decreased percentage of IB4+ neurons and an unchanged percentage of CGRP+ neurons, as compared with WT mice. In vitro assay showed that the value of calcium intensity was weakened in Dil+ neurons from ALPK1-/- mice of TMJ pain induced by the MIA injection, in relation to those from WT mice, while it was significantly enhanced with the incubation of recombinant human ALPK1 (rhA). Taken together, these results suggest that ALPK1 promotes mice TMJ pain induced by MIA through upregulation of the sensitization of IB4+ neurons in TGs. This study will provide a new potential therapeutic target for the treatment of TMJ pain.

Dissecting the neurovascular unit in physiology and Alzheimer's disease: Functions, imaging tools and genetic mouse models

The neurovascular unit (NVU) plays an essential role in regulating neurovascular coupling, which refers to the communication between neurons, glia, and vascular cells to control the supply of oxygen and nutrients in response to neural activity. Cellular elements of the NVU coordinate to establish an anatomical barrier to separate the central nervous system from the milieu of the periphery system, restricting the free movement of substances from the blood to the brain parenchyma and maintaining central nervous system homeostasis. In Alzheimer's disease, amyloid-β deposition impairs the normal functions of NVU cellular elements, thus accelerating the disease progression. Here, we aim to describe the current knowledge of the NVU cellular elements, including endothelial cells, pericytes, astrocytes, and microglia, in regulating the blood-brain barrier integrity and functions in physiology as well as alterations encountered in Alzheimer's disease. Furthermore, the NVU functions as a whole, therefore specific labeling and targeting NVU components in vivo enable us to understand the mechanism mediating cellular communication. We review approaches including commonly used fluorescent dyes, genetic mouse models, and adeno-associated virus vectors for imaging and targeting NVU cellular elements in vivo.

Regional Hyperexcitability and Chronic Neuropathic Pain Following Spinal Cord Injury

Spinal cord injury (SCI) causes maladaptive changes to nociceptive synaptic circuits within the injured spinal cord. Changes also occur at remote regions including the brain stem, limbic system, cortex, and dorsal root ganglia. These maladaptive nociceptive synaptic circuits frequently cause neuronal hyperexcitability in the entire nervous system and enhance nociceptive transmission, resulting in chronic central neuropathic pain following SCI. The underlying mechanism of chronic neuropathic pain depends on the neuroanatomical structures and electrochemical communication between pre- and postsynaptic neuronal membranes, and propagation of synaptic transmission in the ascending pain pathways. In the nervous system, neurons are the only cell type that transmits nociceptive signals from peripheral receptors to supraspinal systems due to their neuroanatomical and electrophysiological properties. However, the entire range of nociceptive signaling is not mediated by any single neuron. Current literature describes regional studies of electrophysiological or neurochemical mechanisms for enhanced nociceptive transmission post-SCI, but few studies report the electrophysiological, neurochemical, and neuroanatomical changes across the entire nervous system following a regional SCI. We, along with others, have continuously described the enhanced nociceptive transmission in the spinal dorsal horn, brain stem, thalamus, and cortex in SCI-induced chronic central neuropathic pain condition, respectively. Thus, this review summarizes the current understanding of SCI-induced neuronal hyperexcitability and maladaptive nociceptive transmission in the entire nervous system that contributes to chronic central neuropathic pain.

Impaired mechanical, heat, and cold nociception in a murine model of genetic TACE/ADAM17 knockdown

TNF-α-converting enzyme, a member of the ADAM (A disintegrin and metalloproteinase) protease family and also known as ADAM17, regulates inflammation and regeneration in health and disease. ADAM17 targets are involved in pain development and hypersensitivity in animal models of inflammatory and neuropathic pain. However, the role of ADAM17 in the pain pathway is largely unknown. Therefore, we used the hypomorphic ADAM17 (ADAM17^ex/ex) mouse model to investigate the importance of ADAM17 in nociceptive behavior, morphology, and function of primary afferent nociceptors. ADAM17^ex/ex mice were hyposensitive to noxious stimulation, showing elevated mechanical thresholds as well as impaired heat and cold sensitivity. Despite these differences, skin thickness and innervation were comparable to controls. Although dorsal root ganglia of ADAM17^ex/ex mice exhibited normal morphology of peptidergic and nonpeptidergic neurons, a small but significant reduction in the number of isolectin β-4–positive neurons was observed. Functional electrical properties of unmyelinated nociceptors showed differences in resting membrane potential, afterhyperpolarization, and firing patterns in specific subpopulations of sensory neurons in ADAM17^ex/ex mice. However, spinal cord morphology and microglia activity in ADAM17^ex/ex mice were not altered. Our data suggest that ADAM17 contributes to the processing of painful stimuli, with a complex mode of action orchestrating the function of neurons along the pain pathway.—Quarta, S., Mitrić, M., Kalpachidou, T., Mair, N., Schiefermeier-Mach, N., Andratsch, M., Qi, Y., Langeslag, M., Malsch, P., Rose-John, S., Kress, M. Impaired mechanical, heat, and cold nociception in a murine model of genetic TACE/ADAM17 knockdown.