Chronic pain: Central role of the claustrum in pain processing

Nociceptive stimuli are processed by the brain into an unpleasant sensation. Two new studies highlight an important role of the claustrum in the processing of pain-related information.

A next generation peripherally restricted Cavα2δ-1 ligand with inhibitory action on Cav2.2 channels and utility in neuropathic pain

The Voltage-Gated Calcium Channel (VGCC) auxiliary subunit Cavα2δ-1 (CACNA2D1) is the target/receptor of gabapentinoids which are known therapeutics in epilepsy and neuropathic pain. Following damage to the peripheral sensory nervous system, Cavα2δ-1 is upregulated in dorsal root ganglion (DRG) neurons in several animal models of chronic neuropathic pain. Gabapentinoids, such as gabapentin and pregabalin, engage with Cavα2δ-1 via binding an arginine residue (R241) within an RRR motif located at the N-terminus of human Cavα2δ-1. A novel, next generation gabapentinoid, engineered not to penetrate the brain, was able to generate a strong analgesic response in Chronic Constriction Injury animal model of chronic neuropathic pain and showed binding specificity for Cavα2δ-1 versus the Cavα2δ-2 subunit. This novel non-brain penetrant gabapentinoid, binds to R241 and a novel binding site on Cavα2δ-1, which is located within the VGCC_α2 domain, identified as a lysine residue within an IKAK amino acid motif (K634). The overall whole cell current amplitudes were diminished by the compound, with these inhibitory effects being diminished in R241A mutant Cavα2δ-1 subunits. The functional effects occurred at lower concentrations than those needed for inhibition by gabapentin or pregabalin, which apparently bound the Cavα2δ-1 subunit only on the R241 and not on the K634 residue. Our work sets the stage for the identification and characterisation of novel compounds with therapeutic properties in neuropathic pain and possibly in other disorders and conditions which require engagement of the Cavα2δ-1 target.

Prunin from Poncirus trifoliata (L.) Rafin Inhibits Aldose Reductase and Glucose-Fructose-Mediated Protein Glycation and Oxidation of Human Serum Albumin

Diabetes complications are associated with aldose reductase (AR) and advanced glycation end products (AGEs). Using bioassay-guided isolation by column chromatography, 10 flavonoids and one coumarin were isolated from Poncirus trifoliata Rafin and tested in vitro for an inhibitory effect against human recombinant AR (HRAR) and rat lens AR (RLAR). Prunin, narirutin, and naringin inhibited RLAR (IC50 0.48-2.84 μM) and HRAR (IC50 0.68-4.88 μM). Docking simulations predicted negative binding energies and interactions with the RLAR and HRAR binding pocket residues. Prunin (0.1 and 12.5 μM) prevented the formation of fluorescent AGEs and nonfluorescent Nε-(carboxymethyl) lysine (CML), as well as the fructose-glucose-mediated protein glycation and oxidation of human serum albumin (HSA). Prunin suppressed the formation of the β-cross-amyloid structure of HSA. These results indicate that prunin inhibits oxidation-dependent protein damage, AGE formation, and AR, which may help prevent diabetes complications.

Voltage-gated Calcium Channels as Potential Therapeutic Targets in Migraine

Migraine is a complex and highly incapacitating neurological disorder that affects around 15% of the general population with greater incidence in women, often at the most productive age of life. Migraine physiopathology is still not fully understood, but it involves multiple mediators and events in the trigeminovascular system and the central nervous system. The identification of calcitonin gene-related peptide as a key mediator in migraine physiopathology has led to the development of effective and highly selective antimigraine therapies. However, this treatment is neither accessible nor effective for all migraine sufferers. Thus, a better understanding of migraine mechanisms and the identification of potential targets are still clearly warranted. Voltage-gated calcium channels (VGCCs) are widely distributed in the trigeminovascular system, and there is accumulating evidence of their contribution to the mechanisms associated with headache pain. Several drugs used in migraine abortive or prophylactic treatment target VGCCs, which probably contributes to their analgesic effect. This review aims to summarize the current evidence of VGGC contribution to migraine physiopathology and to discuss how current pharmacological options for migraine treatment interfere with VGGC function. PERSPECTIVE: Calcitonin gene-related peptide (CGRP) represents a major migraine mediator, but few studies have investigated the relationship between CGRP and VGCCs. CGRP release is calcium channel-dependent and VGGCs are key players in familial migraine. Further studies are needed to determine whether VGCCs are suitable molecular targets for treating migraine.

Effect of ABT-639 on Cav3.2 channel activity and its analgesic actions in mouse models of inflammatory and neuropathic pain

Cav3.2 T-type calcium channels are important targets for pain relief in rodent models of inflammatory and neuropathic pain. Even though many T-type channel blockers have been tested in mice, only one molecule, ABT-639, has been tested in phase II clinical studies and did not produce analgesic effects over placebo. Here we examined the effects of ABT-639 on Cav3.2 channel activity in tsA-201 cells and dorsal root ganglion (DRG) neurons, in comparison with another established Cav3.2 inhibitor Z944. These experiments revealed that Z944 mediated ∼100-fold more potent inhibition of Cav3.2 currents than ABT-639, with the latter blocking channel activity by less than 15 percent when applied at a concentration of 30 μM. A slight increase in ABT-639 potency was observed at more depolarized holding potentials, suggesting that this compound may act preferentially on inactivated channels. We tested the effects of both compounds in the Complete Freund's Adjuvant (CFA) model of chronic inflammatory pain, and in partial sciatic nerve injury model of neuropathic pain in mice. In the neuropathic pain model, both Z944 and ABT-639 reversed mechanical hypersensitivity to similar degrees when delivered systemically, but remarkably, when delivered intrathecally, only Z944 was effective. In the CFA model, both compounds reversed thermal hyperalgesia upon systemic delivery, but only Z944 mediated pain relief upon intrathecal delivery, indicating that ABT-639 acts primarily at peripheral sites. ABT-639 lost its analgesic effects in CFA treated Cav3.2 null mice, indicating that these channels are essential for ABT-639-mediated pain relief despite its poor inhibition of Cav3.2 currents.

Opening the KV3.1 gates: A therapeutic strategy for progressive myoclonus epilepsy type 7?

Progressive myoclonus epilepsy type 7, a debilitating neurological disorder, is caused by a loss-of-function mutation in the KV3.1 channel. Exciting work by Feng et al.1 utilizes a new knockin mouse model to identify a potential therapeutic intervention.

The T-type calcium channelosome

T-type calcium channels perform crucial physiological roles across a wide spectrum of tissues, spanning both neuronal and non-neuronal system. For instance, they serve as pivotal regulators of neuronal excitability, contribute to cardiac pacemaking, and mediate the secretion of hormones. These functions significantly hinge upon the intricate interplay of T-type channels with interacting proteins that modulate their expression and function at the plasma membrane. In this review, we offer a panoramic exploration of the current knowledge surrounding these T-type channel interactors, and spotlight certain aspects of their potential for drug-based therapeutic intervention.

Caveolin-1 forms a complex with P2X7 receptor and tunes P2X7-mediated ATP signaling in mouse bone marrow-derived macrophages

The ionotropic purinergic P2X7 receptor responds to extracellular ATP and can trigger proinflammatory immune signaling in macrophages. Caveolin-1 (Cav-1) is known to modulate functions of macrophages and innate immunity. However, it is unknown how Cav-1 modulates P2X7 receptor activity in macrophages. We herein examined P2X7 receptor activity and macrophage functions using bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cav-1 knockout (KO) mice. ATP (1 mM) application caused biphasic increase in cytosolic [Ca2+] and sustained decrease in cytosolic [K+]. A specific P2X7 receptor blocker, A-740003, inhibited the maintained cytosolic [Ca2+] increase and cytosolic [K+] decrease. Total internal reflection fluorescent imaging and proximity ligation assays revealed a novel molecular complex formation between P2X7 receptors and Cav-1 in WT BMDMs that were stimulated with lipopolysaccharides. This molecular coupling was increased by ATP application. Specifically, the ATP-induced Ca2+ influx and K+ efflux through P2X7 receptors were increased in Cav-1 KO BMDMs, even though the total and surface protein levels of P2X7 receptors in WT and Cav-1 KO BMDMs were unchanged. Cell-impermeable dye (TO-PRO3) uptake analysis revealed that macropore formation of P2X7 receptors was enhanced in Cav-1 KO BMDMs. Cav-1 KO BMDMs increased ATP-induced IL-1β secretion, reactive oxygen species production, Gasdermin D (GSDMD) cleavage, and lactate dehydrogenase release indicating pyroptosis. A-740003 completely prevented ATP-induced pyroptosis. In combination, these datasets show that Cav-1 has a negative effect on P2X7 receptor activity in BMDMs and that Cav-1 in macrophages may contribute to finely tuned immune responses by preventing excessive IL-1β secretion and pyroptosis.NEW & NOTEWORTHY In bone marrow-derived macrophages, Cav-1 suppresses the macropore formation of P2X7 receptors through their direct or indirect interactions, resulting in reduced membrane permeability of cations (Ca2+ and K+) and large cell-impermeable dye (TO-PRO3) induced by ATP. Cav-1 also inhibits ATP-induced IL-1β secretion, ROS production, GSDMD cleavage, and pyroptosis. Cav-1 contributes to the maintenance of proper immune responses by finely tuning IL-1β secretion and cell death in macrophages.

Electrophysiological characterization of a Cav3.2 calcium channel missense variant associated with epilepsy and hearing loss

T-type calcium channelopathies encompass a group of human disorders either caused or exacerbated by mutations in the genes encoding different T-type calcium channels. Recently, a new heterozygous missense mutation in the CACNA1H gene that encodes the Cav3.2 T-type calcium channel was reported in a patient presenting with epilepsy and hearing loss-apparently the first CACNA1H mutation to be associated with a sensorineural hearing condition. This mutation leads to the substitution of an arginine at position 132 with a histidine (R132H) in the proximal extracellular end of the second transmembrane helix of Cav3.2. In this study, we report the electrophysiological characterization of this new variant using whole-cell patch clamp recordings in tsA-201 cells. Our data reveal minor gating alterations of the channel evidenced by a mild increase of the T-type current density and slower recovery from inactivation, as well as an enhanced sensitivity of the channel to external pH change. To what extend these biophysical changes and pH sensitivity alterations induced by the R132H mutation contribute to the observed pathogenicity remains an open question that will necessitate the analysis of additional CACNA1H variants associated with the same pathologies.

Inhibitory insula-ACC projections modulate affective but not sensory aspects of neuropathic pain

The insula and anterior cingulate cortex (ACC) are brain regions that undergo structural and functional reorganization in neuropathic pain states. Here, we aimed to study inhibitory parvalbumin positive (PV+) posterior insula (pIC) to posterior ACC (pACC) projections, and to evaluate the effects of direct optogenetic manipulation of such projections on mechanical nociception and spontaneous ongoing pain in mice with Spared Nerve Injury (SNI). CTB488 tract-tracing in male PVCrexAi9 mice revealed a small proportion of PV+ projections from the pIC to the pACC. Electrophysiological analysis confirmed the existence of synaptic inputs into the pACC by pIC GABAergic cells. Optogenetic stimulation of these pathways did not change mechanical nociception, but induced conditioned place preference behavior responses. Our results suggest the presence of inhibitory projections between the pIC and the pACC which are able to selectively modulate affective aspects of neuropathic pain.

Antihyperalgesic effect of joint mobilization requires Cav3.2 calcium channels

The present study was undertaken to explore the relative contributions of Cav3.2 T-type channels to mediating the antihyperalgesic activity of joint manipulation (JM) therapy. We used the chronic constriction injury model (CCI) to induce peripheral neuropathy and chronic pain in male mice, followed by JM. We demonstrate that JM produces long-lasting mechanical anti-hyperalgesia that is abolished in Cav3.2 null mice. Moreover, we found that JM displays a similar analgesic profile as the fatty acid amide hydrolase inhibitor URB597, suggesting a possible converging mechanism of action involving endocannabinoids. Overall, our findings advance our understanding of the mechanisms through which JM produces analgesia.

Analgesia by intrathecal delta-9-tetrahydrocannabinol is dependent on Cav3.2 calcium channels

Delta-9-tetrahydrocannabinol (Δ⁹-THC) is known to produce systemic analgesia that involves CB₁ and CB₂ cannabinoid receptors. However, there is compelling evidence that Δ⁹-THC can potently inhibit Cav3.2T-type calcium channels which are highly expressed in dorsal root ganglion neurons and in the dorsal horn of the spinal cord. Here, we investigated whether spinal analgesia produced by Δ⁹-THC involves Cav3.2 channels vis a vis cannabinoid receptors. We show that spinally delivered Δ⁹-THC produced dose-dependent and long-lasting mechanical anti-hyperalgesia in neuropathic mice, and showed potent analgesic effects in models of inflammatory pain induced by formalin or Complete Freund's Adjuvant (CFA) injection into the hind paw, with the latter showing no overt sex differences. The Δ⁹-THC mediated reversal of thermal hyperalgesia in the CFA model was abolished in Cav3.2 null mice, but was unaltered in CB₁ and CB₂ null animals. Hence, the analgesic effects of spinally delivered Δ⁹-THC are due to an action on T-type calcium channels, rather than activation of spinal cannabinoid receptors.

Icariside II, a Prenyl-Flavonol, Alleviates Inflammatory and Neuropathic Pain by Inhibiting T-Type Calcium Channels and USP5-Cav3.2 Interactions

Cav3.2 channels play an important role in the afferent nociceptive pathway, which is responsible for both physiological and pathological pain transmission. Cav3.2 channels are upregulated during neuropathic pain or peripheral inflammation in part due to an increased association with the deubiquitinase USP5. In this study, we investigated nine naturally occurring flavonoid derivatives which we tested for their abilities to inhibit transiently expressed Cav3.2 channels and their interactions with USP5. Icariside II (ICA-II), one of the flavonols studied, inhibited the biochemical interactions between USP5 and Cav3.2 and concomitantly and effectively blocked Cav3.2 channels. Molecular docking analysis predicts that ICA-II binds to the cUBP domain and the Cav3.2 interaction region. In addition, ICA-II was predicted to interact with residues in close proximity to the Cav3.2 channel's fenestrations, thus accounting for the observed blocking activity. In mice with inflammatory and neuropathic pain, ICA-II inhibited both phases of the formalin-induced nocifensive responses and abolished thermal hyperalgesia induced by injection of complete Freund's adjuvant (CFA) into the hind paw. Furthermore, ICA-II produced significant and long-lasting thermal anti-hyperalgesia in female mice, whereas Cav3.2 null mice were resistant to the action of ICA-II. Altogether, our data show that ICA-II has analgesic activity via an action on Cav3.2 channels.

Electrophysiological characterization of a CaV3.1 calcium channel mutation linked to trigeminal neuralgia

Trigeminal neuralgia is a rare and debilitating disorder that affects one or more branches of the trigeminal nerve, leading to severe pain attacks and a poor quality of life. It has been reported that the Ca_V3.1 T-type calcium channel may play an important role in trigeminal pain and a recent study identified a new missense mutation in the CACNA1G gene that encodes the pore forming α1 subunit of the Ca_V3.1 calcium channel. The mutation leads to a substitution of an Arginine (R) by a Glutamine (Q) at position 706 in the I-II linker region of the channel. Here, we used whole-cell voltage-clamp recordings to evaluate the biophysical properties of Ca_V3.1 wild-type and R706Q mutant channels expressed in tsA-201 cells. Our data indicate an increase in current density in the R706Q mutant, leading to a gain-of-function effect, without changes in the voltage for half activation. Moreover, voltage clamp using an action potential waveform protocol revealed an increase in the tail current at the repolarization phase in the R706Q mutant. No changes were observed in the voltage-dependence of inactivation. However, the R706Q mutant displayed a faster recovery from inactivation. Hence, the gain-of-function effects in the R706Q Ca_V3.1 mutant have the propensity to impact pain transmission in the trigeminal system, consistent with a contribution to trigeminal neuralgia pathophysiology.

Ursonic acid from Artemisia montana exerts anti-diabetic effects through anti-glycating properties, and by inhibiting PTP1B and activating the PI3K/Akt signaling pathway in insulin-resistant C2C12 cells

Artemisia is one of the largest genera in the plant family Asteraceae and has long been used in traditional medicine for its antitussive, analgesic, antihypertensive, antitoxic, antiviral, antimalarial, and anti-inflammatory properties. However, the anti-diabetic activity of Artemisia montana has not been broadly studied. The goal of this study was to determine whether extracts of the aerial parts of A. montana and its main constituents inhibit protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase activities. We isolated nine compounds from A. montana including ursonic acid (UNA) and ursolic acid (ULA), which significantly inhibited PTP1B with IC₅₀ values of 11.68 and 8.73 μM, respectively. In addition, UNA showed potent inhibitory activity against α-glucosidase (IC₅₀ = 61.85 μM). Kinetic analysis of PTP1B and α-glucosidase inhibition revealed that UNA was a non-competitive inhibitor of both enzymes. Docking simulations of UNA demonstrated negative binding energies and close proximity to residues in the binding pockets of PTP1B and α-glucosidase. Molecular docking simulations between UNA and human serum albumin (HSA) revealed that UNA binds tightly to all three domains of HSA. Furthermore, UNA significantly inhibited fluorescent AGE formation (IC₅₀ = 4.16 μM) in a glucose-fructose-induced HSA glycation model over the course of four weeks. Additionally, we investigated the molecular mechanisms underlying the anti-diabetic effects of UNA in insulin-resistant C2C12 skeletal muscle cells and discovered that UNA significantly increased glucose uptake and decreased PTP1B expression. Further, UNA increased GLUT-4 expression level by activating the IRS-1/PI3K/Akt/GSK-3 signaling pathway. These findings clearly demonstrate that UNA from A. montana shows great potential for treatment of diabetes and its complications.

Differential regulation of Cav 3.2 and Cav 2.2 calcium channels by CB1 receptors and cannabidiol

BACKGROUND AND PURPOSE

Cannabinoids are a promising therapeutic avenue for chronic pain. However, clinical trials often fail to report analgesic efficacy of cannabinoids. Inhibition of voltage gate calcium (Ca_v ) channels is one mechanism through which cannabinoids may produce analgesia. We hypothesized that cannabinoids and cannabinoid receptor agonists target different types of Ca_v channels through distinct mechanisms.

EXPERIMENTAL APPROACH

Electrophysiological recordings from tsA-201 cells expressing either Ca_v 3.2 or Ca_v 2.2 were used to assess inhibition by HU-210 or cannabidiol (CBD) in the absence and presence of the CB₁ receptor. Homology modelling assessed potential interaction sites for CBD in both Ca_v 2.2 and Ca_v 3.2. Analgesic effects of CBD were assessed in mouse models of inflammatory and neuropathic pain.

KEY RESULTS

HU-210 (1 μM) inhibited Ca_v 2.2 function in the presence of CB₁ receptor but had no effect on Ca_v 3.2 regardless of co-expression of CB₁ receptor. By contrast, CBD (3 μM) produced no inhibition of Ca_v 2.2 and instead inhibited Ca_v 3.2 independently of CB₁ receptors. Homology modelling supported these findings, indicating that CBD binds to and occludes the pore of Ca_v 3.2, but not Ca_v 2.2. Intrathecal CBD alleviated thermal and mechanical hypersensitivity in both male and female mice, and this effect was absent in Ca_v 3.2 null mice.

CONCLUSION AND IMPLICATIONS

Our findings reveal differential modulation of Ca_v 2.2 and Ca_v 3.2 channels by CB₁ receptors and CBD. This advances our understanding of how different cannabinoids produce analgesia through action at different voltage-gated calcium channels and could influence the development of novel cannabinoid-based therapeutics for treatment of chronic pain.

Regulation of N-type calcium channels by nociceptin receptors and its possible role in neurological disorders

Activation of nociceptin opioid peptide receptors (NOP, a.k.a. opioid-like receptor-1, ORL-1) by the ligand nociceptin/orphanin FQ, leads to G protein-dependent regulation of Cav2.2 (N-type) voltage-gated calcium channels (VGCCs). This typically causes a reduction in calcium currents, triggering changes in presynaptic calcium levels and thus neurotransmission. Because of the widespread expression patterns of NOP and VGCCs across multiple brain regions, the dorsal horn of the spinal cord, and the dorsal root ganglia, this results in the alteration of numerous neurophysiological features. Here we review the regulation of N-type calcium channels by the NOP-nociceptin system in the context of neurological conditions such as anxiety, addiction, and pain.

Electrophysiological and computational analysis of Cav3.2 channel variants associated with familial trigeminal neuralgia

Trigeminal neuralgia (TN) is a rare form of chronic neuropathic pain characterized by spontaneous or elicited paroxysms of electric shock-like or stabbing pain in a region of the face. While most cases occur in a sporadic manner and are accompanied by intracranial vascular compression of the trigeminal nerve root, alteration of ion channels has emerged as a potential exacerbating factor. Recently, whole exome sequencing analysis of familial TN patients identified 19 rare variants in the gene CACNA1H encoding for Ca_v3.2T-type calcium channels. An initial analysis of 4 of these variants pointed to a pathogenic role. In this study, we assessed the electrophysiological properties of 13 additional TN-associated Ca_v3.2 variants expressed in tsA-201 cells. Our data indicate that 6 out of the 13 variants analyzed display alteration of their gating properties as evidenced by a hyperpolarizing shift of their voltage dependence of activation and/or inactivation resulting in an enhanced window current supported by Ca_v3.2 channels. An additional variant enhanced the recovery from inactivation. Simulation of neuronal electrical membrane potential using a computational model of reticular thalamic neuron suggests that TN-associated Ca_v3.2 variants could enhance neuronal excitability. Altogether, the present study adds to the notion that ion channel polymorphisms could contribute to the etiology of some cases of TN and further support a role for Ca_v3.2 channels.

The road to the brain in Timothy syndrome is paved with enhanced CaV1.2 activation gating

Specific gating effects of Timothy syndrome CaV1.2 channel mutations determine cardiovascular versus nervous system deficits.

The natural product argentatin C attenuates postoperative pain via inhibition of voltage-gated sodium and T-type voltage-gated calcium channels

BACKGROUND AND PURPOSE

Postoperative pain occurs in as many as 70% of surgeries performed worldwide. Postoperative pain management still relies on opioids despite their negative consequences, resulting in a public health crisis. Therefore, it is important to develop alternative therapies to treat chronic pain. Natural products derived from medicinal plants are potential sources of novel biologically active compounds for development of safe analgesics. In this study, we screened a library of natural products to identify small molecules that target the activity of voltage-gated sodium and calcium channels that have important roles in nociceptive sensory processing.

EXPERIMENTAL APPROACH

Fractions derived from the Native American medicinal plant, Parthenium incanum, were assessed using depolarization-evoked calcium influx in rat dorsal root ganglion (DRG) neurons. Further separation of these fractions yielded a cycloartane-type triterpene identified as argentatin C, which was additionally evaluated using whole-cell voltage and current-clamp electrophysiology, and behavioural analysis in a mouse model of postsurgical pain.

KEY RESULTS

Argentatin C blocked the activity of both voltage-gated sodium and low-voltage-activated (LVA) calcium channels in calcium imaging assays. Docking analysis predicted that argentatin C may bind to Na_V 1.7-1.9 and Ca_V 3.1-3.3 channels. Furthermore, argentatin C decreased Na⁺ and T-type Ca²⁺ currents as well as excitability in rat and macaque DRG neurons, and reversed mechanical allodynia in a mouse model of postsurgical pain.

CONCLUSION AND IMPLICATIONS

These results suggest that the dual effect of argentatin C on voltage-gated sodium and calcium channels supports its potential as a novel treatment for painful conditions.

Copper ions, prion protein and Aβ modulate Ca levels in central nervous system myelin in an NMDA receptor-dependent manner

As in neurons, CNS myelin expresses N-Methyl-D-Aspartate Receptors (NMDARs) that subserve physiological roles, but have the potential to induce injury to this vital element. Using 2-photon imaging of myelinic Ca in live ex vivo mouse optic nerves, we show that Cu ions potently modulate Ca levels in an NMDAR-dependent manner. Chelating Cu in the perfusate induced a substantial increase in Ca levels, and also caused significant axo-myelinic injury. Myelinic NMDARs are shown to be regulated by cellular prion protein; only in prion protein KO optic nerves does application of NMDA + D-serine induce a large Ca increase, consistent with strong desensitization of these receptors in the presence of prion protein limiting Ca overload. Aβ_1-42 peptide induced a large Ca increase that was also Cu-dependent, and was blocked by NMDAR antagonism. Our results indicate that like in neurons, myelinic NMDARs permeate potentially injurious amounts of Ca, and are also potently regulated by micromolar Cu and activated by Aβ_1-42 peptides. These findings shed mechanistic light on the important primary white matter injury frequently observed in Alzheimer's brain.

The calcium channel terminator: hasta la vista pain

Chronic pain remains a major burden and is difficult to treat. N-type calcium channels may be a suitable therapeutic target for analgesics, and a new study from Colecraft and colleagues utilizes a clever new way to modulate their expression to achieve therapeutic benefits in preclinical models of neuropathic pain.

The neuronal tyrosine kinase receptor ligand ALKAL2 mediates persistent pain

The anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase known for its oncogenic potential that is involved in the development of the peripheral and central nervous system. ALK receptor ligands ALKAL1 and ALKAL2 were recently found to promote neuronal differentiation and survival. Here, we show that inflammation or injury enhanced ALKAL2 expression in a subset of TRPV1⁺ sensory neurons. Notably, ALKAL2 was particularly enriched in both mouse and human peptidergic nociceptors, yet weakly expressed in nonpeptidergic, large-diameter myelinated neurons or in the brain. Using a coculture expression system, we found that nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn of the spinal cord. Finally, depletion of ALKAL2 in dorsal root ganglia or blocking ALK with clinically available compounds crizotinib or lorlatinib reversed thermal hyperalgesia and mechanical allodynia induced by inflammation or nerve injury, respectively. Overall, our work uncovers the ALKAL2/ALK signaling axis as a central regulator of nociceptor-induced sensitization. We propose that clinically approved ALK inhibitors used for non–small cell lung cancer and neuroblastomas could be repurposed to treat persistent pain conditions.

CaVβ-subunit dependence of forward and reverse trafficking of CaV1.2 calcium channels

Auxiliary CaVβ subunits interact with the pore forming CaVα1 subunit to promote the plasma membrane expression of high voltage-activated calcium channels and to modulate the biophysical properties of Ca2+ currents. However, the effect of CaVβ subunits on channel trafficking to and from the plasma membrane is still controversial. Here, we have investigated the impact of CaVβ1b and CaVβ2a subunits on plasma membrane trafficking of CaV1.2 using a live-labeling strategy. We show that the CaVβ1b subunit is more potent in increasing CaV1.2 expression at the plasma membrane than the CaVβ2a subunit and that this effect is not related to modification of intracellular trafficking of the channel (i.e. neither forward trafficking, nor recycling, nor endocytosis). We conclude that the differential effect of CaVβ subunit subtypes on CaV1.2 surface expression is likely due to their differential ability to protect CaV1.2 from degradation.

Putative Synthetic Cannabinoids MEPIRAPIM, 5F-BEPIRAPIM (NNL-2), and Their Analogues Are T-Type Calcium Channel (CaV3) Inhibitors

Synthetic cannabinoid receptor agonists (SCRAs) are a large and growing class of new psychoactive substances (NPSs). Two recently identified compounds, MEPIRAPIM and 5F-BEPIRAPIM (NNL-2), have not been confirmed as agonists of either cannabinoid receptor subtype but share structural similarities with both SCRAs and a class of T-type calcium channel (Ca_V3) inhibitors under development as new treatments for epilepsy and pain. In this study, MEPIRAPIM and 5F-BEPIRAPIM and 10 systematic analogues were synthesized, analytically characterized, and pharmacologically evaluated using in vitro cannabinoid receptor and Ca_V3 assays. Several compounds showed micromolar affinities for CB₁ and/or CB₂, with several functioning as low potency agonists of CB₁ and CB₂ in a membrane potential assay. 5F-BEPIRAPIM and four other derivatives were identified as potential Ca_V3 inhibitors through a functional calcium flux assay (>70% inhibition), which was further confirmed using whole-cell patch-clamp electrophysiology. Additionally, MEPIRAPIM and 5F-BEPIRAPIM were evaluated in vivo using a cannabimimetic mouse model. Despite detections of MEPIRAPIM and 5F-BEPIRAPIM in the NPS market, only the highest MEPIRAPIM dose (30 mg/kg) elicited a mild hypothermic response in mice, with no hypothermia observed for 5F-BEPIRAPIM, suggesting minimal central CB₁ receptor activity.

Central and peripheral contributions of T-type calcium channels in pain

Chronic pain is a severely debilitating condition that reflects a long-term sensitization of signal transduction in the afferent pain pathway. Among the key players in this pathway are T-type calcium channels, in particular the Cav3.2 isoform. Because of their biophysical characteristics, these channels are ideally suited towards regulating neuronal excitability. Recent evidence suggests that T-type channels contribute to excitability of neurons all along the ascending and descending pain pathways, within primary afferent neurons, spinal dorsal horn neurons, and within pain-processing neurons in the midbrain and cortex. Here we review the contribution of T-type channels to neuronal excitability and function in each of these neuronal populations and how they are dysregulated in chronic pain conditions. Finally, we discuss their molecular pharmacology and the potential role of these channels as therapeutic targets for chronic pain.

Subcellular localization of hippocampal ryanodine receptor 2 and its role in neuronal excitability and memory

Ryanodine receptor 2 (RyR2) is abundantly expressed in the heart and brain. Mutations in RyR2 are associated with both cardiac arrhythmias and intellectual disability. While the mechanisms of RyR2-linked arrhythmias are well characterized, little is known about the mechanism underlying RyR2-associated intellectual disability. Here, we employed a mouse model expressing a green fluorescent protein (GFP)-tagged RyR2 and a specific GFP probe to determine the subcellular localization of RyR2 in hippocampus. GFP-RyR2 was predominantly detected in the soma and dendrites, but not the dendritic spines of CA1 pyramidal neurons or dentate gyrus granular neurons. GFP-RyR2 was also detected within the mossy fibers in the stratum lucidum of CA3, but not in the presynaptic terminals of CA1 neurons. An arrhythmogenic RyR2-R4496C^+/− mutation downregulated the A-type K⁺ current and increased membrane excitability, but had little effect on the afterhyperpolarization current or presynaptic facilitation of CA1 neurons. The RyR2-R4496C^+/− mutation also impaired hippocampal long-term potentiation, learning, and memory. These data reveal the precise subcellular distribution of hippocampal RyR2 and its important role in neuronal excitability, learning, and memory.

A mouse model containing a GFP-tagged ryanodine receptor 2 (RyR2) has shed light on the precise subcellular localization of hippocampal RyR2 and mechanisms underlying neuronal excitability, learning, and memory.

A52 GUT-INNERVATING TRPV1+ NEURONS DRIVE CHRONIC VISCERAL PAIN VIA MICROGLIAL P2Y12 RECEPTOR

Background

Long-lasting changes in neural pain circuits precipitate the transition from acute to chronic pain in patients living with inflammatory bowel diseases (IBDs). While significant improvement in IBD therapy has been made to reduce inflammation, a large subset of patients continues to suffer throughout quiescent phases of the disease. Peripheral and central mechanisms contribute to the transition from acute to chronic pain during active disease and clinical remission. Lower mechanical threshold and hyperexcitability of visceral afferents induce gliosis in central pain circuits, leading to persistent visceral hypersensitivity (VHS). In the spinal cord, microglia, the immune sentinels of the central nervous system, undergo activation in multiple models of VHS. Using the Dextran Sodium Sulfate (DSS) model of colitis, we found that microglial G-CSF was able to sensitize colonic nociceptors that express the pain receptor TRPV1. While TRPV1+ nociceptors have been implicated in peripheral sensitization, their contribution to central sensitization via microglia remains unknown.

Aims

Here we investigated the mechanisms of microglia activation to identify centrally acting analgesics for chronic IBD pain.

Methods

Using Designer Receptors Exclusively Activated by Designer Drugs (DREADD) expressed in TRPV1-expressing visceral neurons that sense colonic inflammation, we tested whether neuronal activity was indispensable to control microglia activation and VHS. We then investigated the neuron-microglia signaling system involved in visceral pain chronification.

Results

We found that chemogenetic inhibition of TRPV1+ visceral afferents prevents microglial activation in the spinal cord and subsequent VHS in colitis mice. In contrast, chemogenetic activation, in the absence of colitis, enhanced microglial activation associated with VHS. We identified a purinergic signaling mechanism mediated by neuronal ATP and microglial P2RY12 receptor, triggering VHS in colitis. Inhibition of P2RY12 prevented microglial reactivity and chronic VHS post-colitis.

Conclusions

Overall, these data provide novel insights into the central mechanisms of chronic visceral pain and suggest that targeting microglial P2RY12 signaling could be harnessed to relieve pain in IBD patients who are in remission.

Funding Agencies

CCC

A Synthetically Accessible Small-Molecule Inhibitor of USP5-Cav3.2 Calcium Channel Interactions with Analgesic Properties

Cav3.2 calcium channels are important mediators of nociceptive signaling in the primary afferent pain pathway, and their expression is increased in various rodent models of chronic pain. Previous work from our laboratory has shown that this is in part mediated by an aberrant expression of deubiquitinase USP5, which associates with these channels and increases their stability. Here, we report on a novel bioactive rhodanine compound (II-1), which was identified in compound library screens. II-1 inhibits biochemical interactions between USP5 and the Cav3.2 domain III-IV linker in a dose-dependent manner, without affecting the enzymatic activity of USP5. Molecular docking analysis reveals two potential binding pockets at the USP5-Cav3.2 interface that are distinct from the binding site of the deubiquitinase inhibitor WP1130 (a.k.a. degrasyn). With an understanding of the ability of some rhodanines to produce false positives in high-throughput screening, we have conducted several orthogonal assays to confirm the validity of this hit, including in vivo experiments. Intrathecal delivery of II-1 inhibited both phases of formalin-induced nocifensive behaviors in mice, as well as abolished thermal hyperalgesia induced by the delivery of complete Freund's adjuvant (CFA) to the hind paw. The latter effects were abolished in Cav3.2 null mice, thus confirming that Cav3.2 is required for the action of II-1. II-1 also mediated a robust inhibition of mechanical allodynia induced by injury to the sciatic nerve. Altogether, our data uncover a novel class of analgesics─well suited to rapid structure-activity relationship studies─that target the Cav3.2/USP5 interface.

Trigeminal neuropathic pain causes changes in affective processing of pain in rats

Trigeminal neuropathic pain has been modeled in rodents through the constriction of the infraorbital nerve (CCI-ION). Sensory alterations, including spontaneous pain, and thermal and mechanical hyperalgesia are well characterized, but there is a notable lack of evidence about the affective pain component in this model. Evaluation of the emotional component of pain in rats has been proposed as a way to optimize potential translational value of non-clinical studies. In rats, 22 and 50 kHz ultrasonic vocalizations (USVs) are considered well-established measures of negative and positive emotional states, respectively. Thus, this study tested the hypothesis that trigeminal neuropathic pain would result, in addition to the sensory alterations, in a decrease of 50 kHz USV, which may be related to altered function of brain areas involved in emotional pain processing. CCI-ION surgery was performed on 60-day-old male Wistar rats. 15 days after surgery, von Frey filaments were applied to detect mechanical hyperalgesia, and USV was recorded. At the same timepoint, systemic treatment with d,l-amphetamine (1 mg/kg) allowed investigation of the involvement of the dopaminergic system in USV emission. Finally, brain tissue was collected to assess the change in tyrosine hydroxylase (TH) expression in the nucleus accumbens (NAc) and c-Fos expression in brain areas involved in emotional pain processing, including the prefrontal cortex (PFC), amygdala, and NAc. The results showed that CCI-ION rats presented mechanical hyperalgesia and a significant reduction of environmental-induced 50 kHz USV. Amphetamine caused a marked increase in 50 kHz USV emission in CCI-ION rats. In addition, TH expression was lower in constricted animals and c-Fos analysis revealed an increase in neuronal activation. Taken together, these data indicate that CCI-ION causes a reduction in the emission of environmental-induced appetitive calls concomitantly with facial mechanical hyperalgesia and that both changes may be related to a reduction in the mesolimbic dopaminergic activity.

Gut-innervating TRPV1+ Neurons Drive Chronic Visceral Pain via Microglial P2Y12 Receptor

BACKGROUND & AIMS

Chronic abdominal pain is a common symptom of inflammatory bowel diseases (IBDs). Peripheral and central mechanisms contribute to the transition from acute to chronic pain during active disease and clinical remission. Lower mechanical threshold and hyperexcitability of visceral afferents induce gliosis in central pain circuits, leading to persistent visceral hypersensitivity (VHS). In the spinal cord, microglia, the immune sentinels of the central nervous system, undergo activation in multiple models of VHS. Here, we investigated the mechanisms of microglia activation to identify centrally acting analgesics for chronic IBD pain.

METHODS

Using Designer Receptors Exclusively Activated by Designer Drugs (DREADD) expressed in transient receptor potential vanilloid member 1-expressing visceral neurons that sense colonic inflammation, we tested whether neuronal activity was indispensable to control microglia activation and VHS. We then investigated the neuron-microglia signaling system involved in visceral pain chronification.

RESULTS

We found that chemogenetic inhibition of transient receptor potential vanilloid member 1⁺ visceral afferents prevents microglial activation in the spinal cord and subsequent VHS in colitis mice. In contrast, chemogenetic activation, in the absence of colitis, enhanced microglial activation associated with VHS. We identified a purinergic signaling mechanism mediated by neuronal adenosine triphosphate (ATP) and microglial P2Y12 receptor, triggering VHS in colitis. Inhibition of P2RY12 prevented microglial reactivity and chronic VHS post-colitis.

CONCLUSIONS

Overall, these data provide novel insights into the central mechanisms of chronic visceral pain and suggest that targeting microglial P2RY12 signaling could be harnessed to relieve pain in patients with IBD who are in remission.

The terpenes camphene and alpha-bisabolol inhibit inflammatory and neuropathic pain via Cav3.2 T-type calcium channels

T-type calcium channels are known molecular targets of certain phytocannabinoids and endocannabinoids. Here we explored the modulation of Cav3.2 T-type calcium channels by terpenes derived from cannabis plants. A screen of eight commercially available terpenes revealed that camphene and alpha-bisabolol mediated partial, but significant inhibition of Cav3.2 channels expressed in tsA-201 cells, as well as native T-type channels in mouse dorsal root ganglion neurons. Both compounds inhibited peak current amplitude with IC50s in the low micromolar range, and mediated an additional small hyperpolarizing shift in half-inactivation voltage. When delivered intrathecally, both terpenes inhibited nocifensive responses in mice that had received an intraplantar injection of formalin, with alpha-bisabolol showing greater efficacy. Both terpenes reduced thermal hyperalgesia in mice injected with Complete Freund's adjuvant. This effect was independent of sex, and absent in Cav3.2 null mice, indicating that these compounds mediate their analgesic properties by acting on Cav3.2 channels. Both compounds also inhibited mechanical hypersensitivity in a mouse model of neuropathic pain. Hence, camphene and alpha-bisabolol have a wide spectrum of analgesic action by virtue of inhibiting Cav3.2 T-type calcium channels.

Splice-variant specific effects of a CACNA1H mutation associated with writer's cramp

The CACNA1H gene encodes the α1 subunit of the low voltage-activated Ca_v3.2 T-type calcium channel, an important regulator of neuronal excitability. Alternative mRNA splicing can generate multiple channel variants with distinct biophysical properties and expression patterns. Two major splice variants, containing or lacking exon 26 (± 26) have been found in different human tissues. In this study, we report splice variant specific effects of a Ca_v3.2 mutation found in patients with autosomal dominant writer’s cramp, a specific type of focal dystonia. We had previously reported that the R481C missense mutation caused a gain of function effect when expressed in Ca_v3.2 (+ 26) by accelerating its recovery from inactivation. Here, we show that when the mutation is expressed in the short variant of the channel (− 26), we observe a significant increase in current density when compared to wild-type Ca_v3.2 (− 26) but the effect on the recovery from inactivation is lost. Our data add to growing evidence that the functional expression of calcium channel mutations depends on which splice variant is being examined.

Hyperactivity of Innate Immunity Triggers Pain via TLR2-IL-33-Mediated Neuroimmune Crosstalk

The innate immune system responds to infections that give rise to pain. How the innate immune system interacts with the sensory nervous system and contributes to pain is poorly understood. Here we report that hyperactivity of innate immunity primes and initiates pain states via the TLR2-interleukin-33 (IL-33) axis. Toll-like receptors (TLRs) are upregulated in the complete Freund's adjuvant (CFA) pain model, and knockout of TLR2 abolishes CFA-induced pain. Selective activation of TLR2/6 triggers acute pain via upregulation of IL-33 in the hindpaw, dorsal root ganglia (DRG), and spinal cord in an NLRP3-dependent manner. The IL-33 increase further initiates priming of nociceptive neurons and pain states. Finally, blocking IL-33 receptors at the spinal level mediates analgesia during acute and chronic inflammatory pain, underscoring an important function of IL-33 in pain signaling. Collectively, our data reveal a critical role of the TLR2-IL-33 axis in innate immune activation for pain initiation and maintenance.

Structural optimization, synthesis and in vitro synergistic anticancer activities of combinations of new N3-substituted dihydropyrimidine calcium channel blockers with cisplatin and etoposide

T-type calcium channels are considered potential drug targets to combat cancer. Combining T-type calcium channel blockers with conventional chemotherapy drugs represents a promising strategy towards successful cancer treatment. From this perspective, we report in this study the design and synthesis of a novel series of N3-sustituted dihydropyrimidines (DHPMs) as anticancer adjuvants to cisplatin (Cis) and etoposide (Eto). Full spectral characterization of the new compounds was done using FT-IR, ¹H NMR, ¹³C NMR, and HRMS. Structure elucidation was confirmed by 2D NMR ¹H-H COSY, HSQC and NOESY experiments. Novel derivatives were tested for their Ca²⁺ channel blocking activity by employing the whole cell patch-clamp technique. Results demonstrated that most compounds were potential T-type calcium channel blockers with the triazole-based C12 and C13 being the most selective agents against Ca_V3.2 channel. Further electrophysiological studies demonstrated that C12 and C13 inhibited Ca_V3.2 currents with respective affinity of 2.26 and 1.27 µM, and induced 5 mV hyperpolarizing shifts in the half-inactivation potential. Subsequently, C12 and C13 were evaluated for their anticancer activities alone and in combination with Cis and Eto against A549 and MDA-MB 231 cancer cells. Interestingly, both compounds exhibited potential anticancer effects with IC₅₀ values < 5 µM. Combination studies revealed that both compounds had synergistic effects (combination index CI < 1) on Cis and Eto through induction of apoptosis (p53 activation and up-regulation of BAX and p21 gene expression). Importantly, in silico physicochemical and ADMET assessment of both compounds revealed their potential drug-like properties with decreased risk of cardiac toxicity. Hence, C12 and C13 are promising anticancer adjuvants through inhibition of Ca_V3.2 T-type calcium channels, thereby serving as eminent leads for further modification.

De novo SCN8A and inherited rare CACNA1H variants associated with severe developmental and epileptic encephalopathy

Developmental and epileptic encephalopathies (DEEs) are a group of severe epilepsies that are characterized by seizures and developmental delay. DEEs are primarily attributed to genetic causes and an increasing number of cases have been correlated with variants in ion channel genes. In this study, we report a child with an early severe DEE. Whole exome sequencing showed a de novo heterozygous variant (c.4873–4881 duplication) in the SCN8A gene and an inherited heterozygous variant (c.952G > A) in the CACNA1H gene encoding for Na_v1.6 voltage-gated sodium and Ca_v3.2 voltage-gated calcium channels, respectively. In vitro functional analysis of human Na_v1.6 and Ca_v3.2 channel variants revealed mild but significant alterations of their gating properties that were in general consistent with a gain- and loss-of-channel function, respectively. Although additional studies will be required to confirm the actual pathogenic involvement of SCN8A and CACNA1H, these findings add to the notion that rare ion channel variants may contribute to the etiology of DEEs.

Protocol for detecting plastic changes in defined neuronal populations in neuropathic mice

Characterization of synaptic plasticity changes via optogenetic manipulation between defined neuronal populations is important for mapping neural circuits involved in normal brain functions and disorders such as neuropathic pain. However, determining the strength of synaptic transmission based on optogenetic manipulation is challenging due to variability in opsin expression. This protocol describes the use of slice electrophysiology combined with optogenetics to examine synaptic transmission in genetically defined neuronal populations from neuropathic mice. We detail surgical procedures of spared nerve injury for inducing neuropathy.

For complete details on the use and execution of this protocol, please refer to Huang et al. (2019) and Huang et al. (2021)

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Surgical procedures for virus injection and spared nerve injury neuropathy

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Patch clamp electrophysiology in acute brain slice of mice using optogenetic targeting

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Determination of monosynaptic transmission in genetically defined neuron populations

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Detection of synaptic strength and E/I balance in defined circuits of neuropathic mice

Mutation of copper binding sites on cellular prion protein abolishes its inhibitory action on NMDA receptors in mouse hippocampal neurons

We have previously reported that cellular prion protein (PrPC) can down-regulate NMDA receptor activity and in a copper dependent manner. Here, we employed AAV9 to introduce murine cellular prion protein into mouse hippocampal neurons in primary cultures from PrP null mice to determine the role of the six copper binding motifs located within the N-terminal domain of PrPC. The results demonstrate that viral expression of wild type PrPC lowers NMDAR activity in PrP null mouse hippocampal neurons by reducing the magnitude of non-desensitizing currents. Elimination of the last two copper binding sites alone, or in combination with the remaining four attenuates this protective effect. Thus our data suggest that copper ion interactions with specific binding sites on PrPC are critical for PrPC dependent modulation of NMDA receptor function.

Modeling temperature- and Cav3 subtype-dependent alterations in T-type calcium channel mediated burst firing

T-type calcium channels are important regulators of neuronal excitability. The mammalian brain expresses three T-type channel isoforms (Cav3.1, Cav3.2 and Cav3.3) with distinct biophysical properties that are critically regulated by temperature. Here, we test the effects of how temperature affects spike output in a reduced firing neuron model expressing specific Cav3 channel isoforms. The modeling data revealed only a minimal effect on baseline spontaneous firing near rest, but a dramatic increase in rebound burst discharge frequency for Cav3.1 compared to Cav3.2 or Cav3.3 due to differences in window current or activation/recovery time constants. The reduced response by Cav3.2 could optimize its activity where it is expressed in peripheral tissues more subject to temperature variations than Cav3.1 or Cav3.3 channels expressed prominently in the brain. These tests thus reveal that aspects of neuronal firing behavior are critically dependent on both temperature and T-type calcium channel subtype.

SUMO wrestling in the cellular dohyō: crosstalk between phosphorylation and SUMOylation of PKCδ regulates oxidative cell damage

The novel PKCδ isoform has been shown to mediate a pro-apoptotic function in response to oxidative stressors. Siman Gao and colleagues performed an in-depth biochemical and molecular analysis of factors that regulate PKCδ function. They demonstrated convincingly that PKCδ is regulated by an interplay between SUMOylation and phosphorylation. They also showed that these events are critical for hydrogen peroxide induced apoptosis, thus identifying potentially novel mechanisms that may be harnessed for cell protection.

Opioid Receptor Regulation of Neuronal Voltage-Gated Calcium Channels

Neuronal voltage-gated calcium channels play a pivotal role in the conversion of electrical signals into calcium entry into nerve endings that is required for the release of neurotransmitters. They are under the control of a number of cellular signaling pathways that serve to fine tune synaptic activities, including G-protein coupled receptors (GPCRs) and the opioid system. Besides modulating channel activity via activation of second messengers, GPCRs also physically associate with calcium channels to regulate their function and expression at the plasma membrane. In this mini review, we discuss the mechanisms by which calcium channels are regulated by classical opioid and nociceptin receptors. We highlight the importance of this regulation in the control of neuronal functions and their implication in the development of disease conditions. Finally, we present recent literature concerning the use of novel μ-opioid receptor/nociceptin receptor modulators and discuss their use as potential drug candidates for the treatment of pain.

Dopamine Inputs from the Ventral Tegmental Area into the Medial Prefrontal Cortex Modulate Neuropathic Pain-Associated Behaviors in Mice

The medial prefrontal cortex (mPFC) is a brain region involved in the affective components of pain and undergoes plasticity during the development of chronic pain. Dopamine (DA) is a key neuromodulator in the mesocortical circuit and modulates working memory and aversion. Although DA inputs into the mPFC are known to modulate plasticity, whether and how these inputs affect pain remains incompletely understood. By using optogenetics, we find that phasic activation of DA inputs from the ventral tegmental area (VTA) into the mPFC reduce mechanical hypersensitivity during neuropathic pain states. Mice with neuropathic pain exhibit a preference for contexts paired with photostimulation of DA terminals in the mPFC. Fiber photometry-based calcium imaging reveals that DA increases the activity of mPFC neurons projecting to the ventrolateral periaqueductal gray (vlPAG). Together, our findings indicate an important role of mPFC DA signaling in pain modulation.

Synthesis and Biological Evaluation of Novel Benzhydrylpiperazine-Coupled Nitrobenzenesulfonamide Hybrids

A series of novel benzhydryl piperazine-coupled nitrobenzenesulfonamide hybrids were synthesized with good to excellent yields. They were tested for in vitro inhibition of mycobacterial activity against the Mycobacterium tuberculosis H37Rv strain, in vitro cytotoxicity MTT (RAW 264.7cells) assay, nutrient starvation (H37Rv strain), and ability to block Cav3.2 T-type calcium channels. Novel hybrids did not inhibit T-type calcium channels, whereas they showed excellent antituberculosis (TB) activity and low cytotoxicity with a selectivity index of >30. A direct impact of the amino acid linker was not observed. Studied hybrids exhibited good inhibition activities, and the 2,4-dinitrobenzenesulfonamide group emerged as a promising scaffold for further drug design by hybridization approaches for anti-TB therapy.

An orbitofrontal cortex to midbrain projection modulates hypersensitivity after peripheral nerve injury

Neuropathic pain is a debilitating condition that is often refractory to treatment. The network of neural substrates for pain transmission and control within the brain is complex and remains poorly understood. Through a combination of neuronal tracing, optogenetics, chemogenetics, electrophysiological recordings, and behavioral assessment, we demonstrate that activation of layer 5 pyramidal neurons in the ventrolateral orbitofrontal cortex (vlOFC) attenuates mechanical and thermal hypersensitivity and cold allodynia in mice with neuropathic pain induced by spared nerve injury (SNI). These vlOFC output neurons project to the posterior ventrolateral periaqueductal gray (vlPAG) region and receive inputs from the ventromedial thalamus (VM). Specific optogenetic and chemogenetic activation of the vlOFC-vlPAG and the VM-vlOFC circuits inhibits hypersensitivity associated with neuropathy. Thus, we reveal a modulatory role of the vlOFC and its projections to the vlPAG circuit in the processing of hypersensitive nociception.

Pain: Integration of Sensory and Affective Aspects of Pain

Painful stimuli are detected by peripheral nociceptors, and the brain processes this nociceptive input into an unpleasant sensation. A new study identifies a brain circuit that integrates sensory and affective aspects of inflammatory and neuropathic pain.