2009). of pain research to understand mechanisms involved in the transition between acute pain and chronic pain. The influence of emotional and cognitive inputs and feedbacks from different brain areas makes pain not only a perception but an experience (Zieglg?nsberger et al. in CNS Spectr 10:298C308, 2005; Trenkwaldner et al. Sleep Med 31:78C85, 2017). This review focuses on functional neuronal plasticity in spinal dorsal horn neurons as a major relay for nociceptive information. gene products that are expressed throughout the nervous and immune systems. These genes encode precursor proteins, from which the active peptide transmitter Rabbit polyclonal to EGR1 is subsequently cleaved. Neuropeptide-encoding messenger RNAs (mRNAs) can be found in neuronal processes beyond the perikaryon. SP is synthesized in small- and medium-sized neurons of DRG and stored in dense core vesicles and transported by fast axonal transport to both spinal and peripheral nerve terminals (Hoyer and Bartfai 2012). It binds to tachykinin receptors [neurokinin-1 receptor (NK1R), NK2R, NK3R] that belong, like most neuropeptide receptors, to the family of seven-transmembrane, G protein-coupled receptors. All tachykinins interact with all the three-receptor subtypes with SP preferring NK1, NKA preferring NK2 and NKB (encoded by the TAC3 gene in humans and by the tachykinin 2 (TAC2) gene in rodents) preferring NK3. This lack of specificity can be accounted for by the conformational flexibility of the short, linear peptides (Ganjiwale and Cowsik Abarelix Acetate 2013). Additionally, some of the multiple subtypes and splice variants of these receptors form heterodimers with other neuropeptides and regulate, e.g., trafficking and resensitization of receptors (Pfeiffer et al. 2003). Toxins such as saporin bind to NK receptors (NKRs) and kill, e.g., dorsal horn neurons after they have been internalized following activation (Wiley et al. 2007; Iadarola et al. 2017). Peripheral nerve injury and inflammation change the phenotype of neurons with regard to receptors and messengers (Weisshaar and Winkelstein 2014). SP released from primary afferent fibers during inflammation upregulates NK1 receptors in dorsal horn neurons. Peptidase inhibitors, which prevent SP breakdown, Abarelix Acetate enhance peptidergic transmission. NKR couples to phospholipase C generating intracellular messengers Abarelix Acetate whose downstream effects include depolarizing the membrane and facilitating the function of -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and NMDA receptors (see below). They, furthermore, control the expression of cytokines and chemokines as well as transcription factors such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) (Bekhbat et al. 2017) and members of the nuclear hormone family PPAR (Okine et al. 2018). NF-kB is a ubiquitous transcriptional activator of inflammatory mediators that increases the synthesis of pro-inflammatory factors such as cytokines, prostaglandins and nitric oxide that contribute to the development of hyperalgesia (Petho and Reeh 2012). Whereas NK1 receptors in the hippocampus are downregulated in rat models of pain and stress (Duric and McCarson 2005), they are upregulated in neurons of superficial laminae in the spinal cord (Bradesi et al. 2009). Inflammation and stimulation of nociceptors by capsaicin triggers NKR endocytosis in neurons in superficial laminae of the dorsal horn reflecting sustained release of SP (Kunde et al. 2013). Microglial cell activation plays a major role in the development of this nociceptive sensitization (Wieseler-Frank et al. 2004; Li et al. 2015) (see below). The half-life of the SP response is defined by the kinetics of degradation of the neuropeptide in the extracellular environment and by the dynamics of desensitization and cellular internalization Abarelix Acetate followed by recycling of the receptor. Noteworthy, ligand-induced internalization of NK1 receptors into neurons in the dorsal horn can be triggered also by non-noxious somatosensory stimulation (Honor et al. 1999). SP antagonists Many potent and selective non-peptide, low molecular tachykinin antagonists have been developed and proven effective in preclinical studies (Carvalho et al. 2018). Early experiments showed that antagonists selectively block nociceptive responses such as the slow, prolonged, excitatory postsynaptic potential that follows intense electrical stimuli to small high-threshold multimodal nociceptors (De Koninck and Henry 1991). Unfortunately, most of the knowledge obtained from preclinical studies on nociception has not yet been translated into new therapies. This failure could be due, at least to some extent, to a misconception of what characterizes pain as a chronic disease. Both preclinical.
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