The NMDAR modulator NYX-2925 alleviates neuropathic pain via a Src-dependent mechanism in the mPFC.

Previous studies have shown that oral administration of the NMDAR modulator NYX-2925 alleviates pain in several animal models of neuropathic pain and this appears to be through mPFC, but not spinal, mediated mechanisms. While much is known about the impact of neuropathic pain on NMDAR-mediated signaling in the spinal cord, limited studies have focused on the brain. In the current study, we assess signaling changes associated with NMDAR-mediated plasticity in the mPFC and the impact of NYX-2925 administration on the normalization of these signaling changes.

Temporal and sex differences in the role of BDNF/TrkB signaling in hyperalgesic priming in mice and rats.

Brain-derived neurotrophic factor (BDNF) signaling through its cognate receptor, TrkB, is a well-known promoter of synaptic plasticity at nociceptive synapses in the dorsal horn of the spinal cord. Existing evidence suggests that BDNF/TrkB signaling in neuropathic pain is sex dependent. We tested the hypothesis that the effects of BDNF/TrkB signaling in hyperalgesic priming might also be sexually dimorphic.

Non-invasive dural stimulation in mice: A novel preclinical model of migraine.

Background: Migraine is characterized by a collection of neurological symptoms in the absence of injury or damage. However, several common preclinical migraine models require significant damage to the skull to stimulate the dura mater, the likely source of afferent signaling leading to head pain. The goal of this study was to determine whether dural stimulation can be performed in mice using an injection that does not cause injury or damage.

eIF4E Phosphorylation Influences mRNA Translation in Mouse Dorsal Root Ganglion Neurons.

Plasticity in dorsal root ganglion (DRG) neurons that promotes pain requires activity-dependent mRNA translation. Protein synthesis inhibitors block the ability of many pain-promoting molecules to enhance excitability in DRG neurons and attenuate behavioral signs of pain plasticity. In line with this, we have recently shown that phosphorylation of the 5' cap-binding protein, eIF4E, plays a pivotal role in plasticity of DRG nociceptors in models of hyperalgesic priming.

Pharmacological activation of AMPK inhibits incision-evoked mechanical hypersensitivity and the development of hyperalgesic priming in mice.

New therapeutics to manage post-surgical pain are needed to mitigate the liabilities of opioid and other analgesics. Our previous work shows that key modulators of excitability in peripheral nociceptors, such as extracellular signal-regulated kinases (ERK) are inhibited by activation of adenosine monophosphate activated protein kinase (AMPK). We hypothesized that AMPK activation would attenuate acute incision-evoked mechanical hypersensitivity and the development of hyperalgesic priming caused by surgery in mice.

The MNK-eIF4E Signaling Axis Contributes to Injury-Induced Nociceptive Plasticity and the Development of Chronic Pain.

Injury-induced sensitization of nociceptors contributes to pain states and the development of chronic pain. Inhibiting activity-dependent mRNA translation through mechanistic target of rapamycin and mitogen-activated protein kinase (MAPK) pathways blocks the development of nociceptor sensitization. These pathways convergently signal to the eukaryotic translation initiation factor (eIF) 4F complex to regulate the sensitization of nociceptors, but the details of this process are ill defined.

The AMPK Activator A769662 Blocks Voltage-Gated Sodium Channels: Discovery of a Novel Pharmacophore with Potential Utility for Analgesic Development.

Voltage-gated sodium channels (VGSC) regulate neuronal excitability by governing action potential (AP) generation and propagation. Recent studies have revealed that AMP-activated protein kinase (AMPK) activators decrease sensory neuron excitability, potentially by preventing sodium (Na+) channel phosphorylation by kinases such as ERK or via modulation of translation regulation pathways. The direct positive allosteric modulator A769662 displays substantially greater efficacy than other AMPK activators in decreasing sensory neuron excitability suggesting additional mechanisms of action.

Targeting AMPK for the Alleviation of Pathological Pain.

Chronic pain is a major clinical problem that is poorly treated with available therapeutics. Adenosine monophosphate-activated protein kinase (AMPK) has recently emerged as a novel target for the treatment of pain with the exciting potential for disease modification. AMPK activators inhibit signaling pathways that are known to promote changes in the function and phenotype of peripheral nociceptive neurons and promote chronic pain.

The potent, indirect adenosine monophosphate- activated protein kinase activator R419 attenuates mitogen-activated protein kinase signaling, inhibits nociceptor excitability, and reduces pain hypersensitivity in mice.

There is a great need for new therapeutics for the treatment of pain. A possible avenue to development of such therapeutics is to interfere with signaling pathways engaged in peripheral nociceptors that cause these neurons to become hyperexcitable. There is strong evidence that mitogen activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K) / mechanistic target of rapamycin (mTOR) signaling pathways are key modulators of nociceptor excitability and .

Neuroligin 2 regulates spinal GABAergic plasticity in hyperalgesic priming, a model of the transition from acute to chronic pain.

Plasticity in inhibitory receptors, neurotransmission, and networks is an important mechanism for nociceptive signal amplification in the spinal dorsal horn. We studied potential changes in GABAergic pharmacology and its underlying mechanisms in hyperalgesic priming, a model of the transition from acute to chronic pain. We find that while GABAA agonists and positive allosteric modulators reduce mechanical hypersensitivity to an acute insult, they fail to do so during the maintenance phase of hyperalgesic priming.

The novel PAR2 ligand C391 blocks multiple PAR2 signalling pathways in vitro and in vivo.

Background And Purpose: Proteinase-activated receptor-2 (PAR2) is a GPCR linked to diverse pathologies, including acute and chronic pain. PAR2 is one of the four PARs that are activated by proteolytic cleavage of the extracellular amino terminus, resulting in an exposed, tethered peptide agonist. Several peptide and peptidomimetic agonists, with high potency and efficacy, have been developed to probe the functions of PAR2, in vitro and in vivo.

Meningeal norepinephrine produces headache behaviors in rats via actions both on dural afferents and fibroblasts.

Background: Stress is commonly reported to contribute to migraine although mechanisms by which this may occur are not fully known. The purpose of these studies was to examine whether norepinephrine (NE), the primary sympathetic efferent transmitter, acts on processes in the meninges that may contribute to the pain of migraine.

Methods: NE was applied to rat dura using a behavioral model of headache.

Local translation and retrograde axonal transport of CREB regulates IL-6-induced nociceptive plasticity.

Transcriptional regulation of genes by cyclic AMP response element binding protein (CREB) is essential for the maintenance of long-term memory. Moreover, retrograde axonal trafficking of CREB in response to nerve growth factor (NGF) is critical for the survival of developing primary sensory neurons. We have previously demonstrated that hindpaw injection of interleukin-6 (IL-6) induces mechanical hypersensitivity and hyperalgesic priming that is prevented by the local injection of protein synthesis inhibitors.

Development and evaluation of small peptidomimetic ligands to protease-activated receptor-2 (PAR2) through the use of lipid tethering.

Protease-activated receptor-2 (PAR2) is a G-Protein Coupled Receptor (GPCR) activated by proteolytic cleavage to expose an attached, tethered ligand (SLIGRL). We evaluated the ability for lipid-tethered-peptidomimetics to activate PAR2 with in vitro physiological and Ca2+ signaling assays to determine minimal components necessary for potent, specific and full PAR2 activation. A known PAR2 activating compound containing a hexadecyl (Hdc) lipid via three polyethylene glycol (PEG) linkers (2at-LIGRL-PEG3-Hdc) provided a potent agonist starting point (physiological EC50 = 1.

Inhibition of carbonic anhydrase augments GABAA receptor-mediated analgesia via a spinal mechanism of action.

Unlabelled: Peripheral nerve injury (PNI) negatively influences spinal gamma-aminobutyric acid (GABA)ergic networks via a reduction in the neuron-specific potassium-chloride (K(+)-Cl(-)) cotransporter (KCC2). This process has been linked to the emergence of neuropathic allodynia. In vivo pharmacologic and modeling studies show that a loss of KCC2 function results in a decrease in the efficacy of GABAA-mediated spinal inhibition.

mTORC1 inhibition induces pain via IRS-1-dependent feedback activation of ERK.

Mammalian target of rapamycin complex 1 (mTORC1) inhibitors are extensively used as immunosuppressants to prevent transplant rejection and in treatment of certain cancers. In patients, chronic treatment with rapamycin or its analogues (rapalogues) has been reported to lead to sensory hypersensitivity and pain conditions via an unknown mechanism. Here, we show that pharmacological or genetic inhibition of mTORC1 activates the extracellular signal-regulated kinase (ERK) pathway in sensory neurons via suppression of S6K1 to insulin receptor substrate 1 negative feedback loop.

BDNF regulates atypical PKC at spinal synapses to initiate and maintain a centralized chronic pain state.

Background: Chronic pain is an important medical problem affecting hundreds of millions of people worldwide. Mechanisms underlying the maintenance of chronic pain states are poorly understood but the elucidation of such mechanisms have the potential to reveal novel therapeutics capable of reversing a chronic pain state. We have recently shown that the maintenance of a chronic pain state is dependent on an atypical PKC, PKMζ, but the mechanisms involved in controlling PKMζ in chronic pain are completely unknown.

Development of highly potent protease-activated receptor 2 agonists via synthetic lipid tethering.

Protease-activated receptor-2 (PAR₂) is a G-protein coupled receptor (GPCR) associated with a variety of pathologies. However, the therapeutic potential of PAR₂ is limited by a lack of potent and specific ligands. Following proteolytic cleavage, PAR₂ is activated through a tethered ligand.

Modulation of spinal GABAergic analgesia by inhibition of chloride extrusion capacity in mice.

Unlabelled: Spinal gamma-aminobutyric acid receptor type A (GABA(A)) receptor modulation with agonists and allosteric modulators evokes analgesia and antinociception. Changes in K(+)-Cl(-) cotransporter isoform 2 (KCC2) expression or function that occur after peripheral nerve injury can result in an impairment in the Cl(-) extrusion capacity of spinal dorsal horn neurons. This, in turn, alters Cl(-)-mediated hyperpolarization via GABA(A) receptor activation, contributing to allodynia or hypersensitivity associated with nerve injury or inflammation.

Resveratrol engages AMPK to attenuate ERK and mTOR signaling in sensory neurons and inhibits incision-induced acute and chronic pain.

Background: Despite advances in our understanding of basic mechanisms driving post-surgical pain, treating incision-induced pain remains a major clinical challenge. Moreover, surgery has been implicated as a major cause of chronic pain conditions. Hence, more efficacious treatments are needed to inhibit incision-induced pain and prevent the transition to chronic pain following surgery.

Targeting adenosine monophosphate-activated protein kinase (AMPK) in preclinical models reveals a potential mechanism for the treatment of neuropathic pain.

Neuropathic pain is a debilitating clinical condition with few efficacious treatments, warranting development of novel therapeutics. We hypothesized that dysregulated translation regulation pathways may underlie neuropathic pain. Peripheral nerve injury induced reorganization of translation machinery in the peripheral nervous system of rats and mice, including enhanced mTOR and ERK activity, increased phosphorylation of mTOR and ERK downstream targets, augmented eIF4F complex formation and enhanced nascent protein synthesis.

Spinal protein kinase M ζ underlies the maintenance mechanism of persistent nociceptive sensitization.

Sensitization of the pain pathway is believed to promote clinical pain disorders. We hypothesized that the persistence of a sensitized state in the spinal dorsal horn might depend on the activity of protein kinase M ζ (PKMζ), an essential mechanism of late long-term potentiation (LTP). To test this hypothesis, we used intraplantar injections of interleukin-6 (IL-6) in mice to elicit a transient allodynic state that endured ∼3 d.

The protease-activated receptor-2-specific agonists 2-aminothiazol-4-yl-LIGRL-NH2 and 6-aminonicotinyl-LIGRL-NH2 stimulate multiple signaling pathways to induce physiological responses in vitro and in vivo.

Protease-activated receptor-2 (PAR(2)) is one of four protease-activated G-protein-coupled receptors. PAR(2) is expressed on multiple cell types where it contributes to cellular responses to endogenous and exogenous proteases. Proteolytic cleavage of PAR(2) reveals a tethered ligand that activates PAR(2) and two major downstream signaling pathways: mitogen-activated protein kinase (MAPK) and intracellular Ca(2+) signaling.

IL-6- and NGF-induced rapid control of protein synthesis and nociceptive plasticity via convergent signaling to the eIF4F complex.

Despite the emergence of translational control pathways as mediators of nociceptive sensitization, effector molecules and mechanisms responsible for modulating activity in these pathways in pain conditions are largely unknown. We demonstrate that two major algogens, the cytokine interleukin 6 (IL-6) and the neurotrophin nerve growth factor (NGF), which are intimately linked to nociceptive plasticity across preclinical models and human pain conditions, signal primarily through two distinct pathways to enhance translation in sensory neurons by converging onto the eukaryotic initiation factor (eIF) eIF4F complex. We directly demonstrate that the net result of IL-6 and NGF signaling is an enhancement of eIF4F complex formation and an induction of nascent protein synthesis in primary afferent neurons and their axons.