Pain-sensing Neurons Research Articles

Lidocaine reduces the transition to slow inactivation in Nav1.7 voltage‐gated sodium channels

The primary use of local anaesthetics is to prevent or relieve pain by reversibly preventing action potential propagation through the inhibition of voltage-gated sodium channels. The tetrodotoxin-sensitive voltage-gated sodium channel subtype Na(v)1.7, abundantly expressed in pain-sensing neurons, plays a crucial role in perception and transmission of painful stimuli and in inherited chronic pain syndromes. Understanding the interaction of lidocaine with Na(v)1.7 channels could provide valuable insight into the drug's action in alleviating pain in distinct patient populations. The aim of this study was to determine how lidocaine interacts with multiple inactivated conformations of Na(v)1.7 channels. We investigated the interactions of lidocaine with wild-type Na(v)1.7 channels and a paroxysmal extreme pain disorder mutation (I1461T) that destabilizes fast inactivation. Whole cell patch clamp recordings were used to examine the activity of channels expressed in human embryonic kidney 293 cells. Depolarizing pulses that increased slow inactivation of Na(v)1.7 channels also reduced lidocaine inhibition. Lidocaine enhanced recovery of Na(v)1.7 channels from prolonged depolarizing pulses by decreasing slow inactivation. A paroxysmal extreme pain disorder mutation that destabilizes fast inactivation of Na(v)1.7 channels decreased lidocaine inhibition. Lidocaine decreased the transition of Na(v)1.7 channels to the slow inactivated state. The fast inactivation gate (domain III-IV linker) is important for potentiating the interaction of lidocaine with the Na(v)1.7 channel.

Activity-dependent targeting of TRPV1 with a pore-permeating capsaicin analog

The capsaicin receptor TRPV1 is the principal transduction channel for nociception. Excessive TRPV1 activation causes pathological pain. Ideal pain mangement requires selective inhibition of hyperactive pain-sensing neurons, but sparing normal nociception. We sought to determine whether it is possible to use activity-dependent TRPV1 agonists to identify nerves with excessive TRPV1 activity, as well as exploit the TRPV1 pore to deliver charged anesthetics for neuronal silencing. We synthesized a series of permanently charged capsaicinoids and found that one, cap-ET, efficaciously evoked TRPV1-dependent entry of Ca(2+) or the large cationic dye YO-PRO-1 comparably to capsaicin, but far smaller electrical currents. Cap-ET-induced YO-PRO-1 transport required permeation of both the agonist and the dye through the TRPV1 pore and could be enhanced by kinase activation or oxidative covalent modification. Moreover, cap-ET reduced capsaicin-induced currents by a voltage-dependent block of the pore. A low dose of cap-ET elicited entry of permanently charged Na(+) channel blockers to effectively suppress Na(+) currents in sensory neurons presensitized with oxidative chemicals. These results implicate therapeutic potential of these unique TRPV1 agonists exhibiting activity-dependent ion transport but of minimal pain-producing risks.

Targeting Ion Channel Trafficking Mechanisms for Novel Analgesics

ISSN 1758-1869 10.2217/PMT.11.23 © 2011 Future Medicine Ltd Pain Manage. (2011) 1(3), 199–201 In February of this year, the New York Times reported on the increasing number of brazen robberies occurring at pharmacies throughout the USA. One thief in Rockland (ME, USA) brandished a machete and leapt over the pharmacy counter to grab oxycodone. He gulped down some of it even before he fled. In Florida, thousands of doses of oxycodone pills are dispensed in pain clinics, resulting in some calling the highway that leads into Florida, I-75, the ‘Oxy Express’. In 2008, Ohio pharmacists dispensed 4.8 million prescriptions for hydrocodone medications, one for every 2.5 people in the state [101]. Although we have been treating pain effectively for millennia, the need for efficacious, safe but especially nonaddictive analgesics remains strong. We require analgesics that can specifically act on peripheral pain-sensing neurons and not centrally to avert addiction. In this article, I argue that the future of pain research must include the development of compounds that directly target the ion channel trafficking machinery of nociceptors. Analgesics act by reducing the firing properties of neurons within the pain pathway. For treatment of mild pain, nonsteroidal antiflammatory drugs (NSAIDs) are recommended. These agents reduce algogenic substances, such as prostaglandins, which directly affect the firing properties of nociceptive neurons. NSAID use is widespread; however, gastrointestinal and renal toxicities associated with these agents are prevalent, with an estimated 10–20% of NSAID patients experiencing dyspepsia [1]. The development of cyclooxygenase-2 selective inhibitors, which minimize gastro intestinal effects, seemed promising, but their severe cardiovascular toxicities have dramatically restricted their use. Vioxx, the most famous of the cyclooxygenase-2 inhibitor drug class, had to be removed from the market owing to its toxic effects. For moderate-to-severe pain, moderate opioid agonists, such as hydrocodone, strong opioid agonists, such as oxycodone, or even morphine are used. These agents act on opioid receptors in the CNS, especially on descending pathways originating from the periaqueductal gray matter, to block pain transmission in the dorsal horn of the spinal cord. They can also act presynaptically by inhibiting neurotransmitter release from the central terminations of nociceptors in the spinal cord. Opioids do so via μ-receptors, ultimately affecting potassium and calcium conductances. As

Peripheral calcium-permeable AMPA receptors regulate chronic inflammatory pain in mice

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type (AMPA-type) glutamate receptors (AMPARs) play an important role in plasticity at central synapses. Although there is anatomical evidence for AMPAR expression in the peripheral nervous system, the functional role of such receptors in vivo is not clear. To address this issue, we generated mice specifically lacking either of the key AMPAR subunits, GluA1 or GluA2, in peripheral, pain-sensing neurons (nociceptors), while preserving expression of these subunits in the central nervous system. Nociceptor-specific deletion of GluA1 led to disruption of calcium permeability and reduced capsaicin-evoked activation of nociceptors. Deletion of GluA1, but not GluA2, led to reduced mechanical hypersensitivity and sensitization in models of chronic inflammatory pain and arthritis. Further analysis revealed that GluA1-containing AMPARs regulated the responses of nociceptors to painful stimuli in inflamed tissues and controlled the excitatory drive from the periphery into the spinal cord. Consequently, peripherally applied AMPAR antagonists alleviated inflammatory pain by specifically blocking calcium-permeable AMPARs, without affecting physiological pain or eliciting central side effects. These findings indicate an important pathophysiological role for calcium-permeable AMPARs in nociceptors and may have therapeutic implications for the treatment chronic inflammatory pain states.

Emerging Roles for Ectonucleotidases in Pain-Sensing Neurons

Nociceptive neurons located in the dorsal root ganglia detect painful stimuli and can be sensitized following inflammation or nerve injury. Many analgesics have ‘antinociceptive’ effects, which mean these drugs can reduce noxious thermal and mechanical sensitization—two symptoms that are associated with chronic pain. One drug that has been studied for its antinociceptive effects in rodents and humans is adenosine (Sawynok and Liu, 2003). Adenosine exerts its antinociceptive effects by activating the adenosine A1 receptor (A1R). A1R is expressed by nociceptive neurons and many other cells of the body, suggesting localized activation of this receptor in nociceptive neurons might inhibit pain without producing cardiovascular and other effects that are associated with systemic A1R activation. Recently, several new studies found that A1R can be activated locally near nociceptive neurons or their axons by ectonucleotidases—a class of enzymes that hydrolyze extracellular adenine nucleotides to adenosine. Moreover, this localized A1R activation was sufficient to inhibit chronic pain in animal models.

Dural afferents express acid-sensing ion channels: A role for decreased meningeal pH in migraine headache

Migraine headache is one of the most common neurological disorders. The pathological conditions that directly initiate afferent pain signaling are poorly understood. In trigeminal neurons retrogradely labeled from the cranial meninges, we have recorded pH-evoked currents using whole-cell patch-clamp electrophysiology. Approximately 80% of dural-afferent neurons responded to a pH 6.0 application with a rapidly activating and rapidly desensitizing ASIC-like current that often exceeded 20nA in amplitude. Inward currents were observed in response to a wide range of pH values and 30% of the neurons exhibited inward currents at pH 7.1. These currents led to action potentials in 53%, 30% and 7% of the dural afferents at pH 6.8, 6.9 and 7.0, respectively. Small decreases in extracellular pH were also able to generate sustained window currents and sustained membrane depolarizations. Amiloride, a non-specific blocker of ASIC channels, inhibited the peak currents evoked upon application of decreased pH while no inhibition was observed upon application of TRPV1 antagonists. The desensitization time constant of pH 6.0-evoked currents in the majority of dural afferents was less than 500ms which is consistent with that reported for ASIC3 homomeric or heteromeric channels. Finally, application of pH 5.0 synthetic-interstitial fluid to the dura produced significant decreases in facial and hind-paw withdrawal threshold, an effect blocked by amiloride but not TRPV1 antagonists, suggesting that ASIC activation produces migraine-related behavior in vivo. These data provide a cellular mechanism by which decreased pH in the meninges following ischemic or inflammatory events directly excites afferent pain-sensing neurons potentially contributing to migraine headache.

17β-Estradiol Rapidly Enhances Bradykinin Signaling in Primary Sensory Neurons In Vitro and In Vivo

Many studies have demonstrated that premenopausal women are at increased risk for various pain disorders. Pain-sensing neurons, termed "nociceptors," in the trigeminal ganglia (TG) and dorsal root ganglia (DRG) express receptors for inflammatory mediators and noxious physical stimuli and transmit signals for central processing of pain sensation. Estrogen receptors (ERs) are also expressed on nociceptors in the TG and DRG, and there is ample literature to suggest that activation of ERs can influence pain mechanisms. However, the mechanism for ER modulation of nociceptor activity is incompletely understood. The aim of this study was to characterize the effect of 17β-estradiol (17β-E(2)) on signaling of the inflammatory mediator bradykinin (BK) in primary cultures of rat sensory neurons and a behavioral model of thermal allodynia in rats. Here, we show that exposure to 17β-E(2) rapidly (within 15 min) enhanced responses to BK in vitro and in vivo. The 17β-E(2)-mediated enhancement of BK signaling was not blocked by the transcription inhibitor anisomycin and was mediated by a membrane-associated ER. The effect of 17β-E(2) to enhance BK responses required activation of β1-containing, RGD-binding integrins. These data show that 17β-E(2) rapidly enhances inflammatory mediator responses both in vitro and in vivo and suggest that 17β-E(2) acting at primary sensory pain neurons may participate in regulating the sensitivity of women to painful stimuli.

Congenital insensitivity to pain: novel SCN9A missense and in-frame deletion mutations.

SCN9A encodes the voltage-gated sodium channel Nav1.7, a protein highly expressed in pain-sensing neurons. Mutations in SCN9A cause three human pain disorders: bi-allelic loss of function mutations result in Channelopathy-associated Insensitivity to Pain (CIP), whereas activating mutations cause severe episodic pain in Paroxysmal Extreme Pain Disorder (PEPD) and Primary Erythermalgia (PE). To date, all mutations in SCN9A that cause a complete inability to experience pain are protein truncating and presumably lead to no protein being produced. Here, we describe the identification and functional characterization of two novel non-truncating mutations in families with CIP: a homozygously-inherited missense mutation found in a consanguineous Israeli Bedouin family (Nav1.7-R896Q) and a five amino acid in-frame deletion found in a sporadic compound heterozygote (Nav1.7-ΔR1370-L1374). Both of these mutations map to the pore region of the Nav1.7 sodium channel. Using transient transfection of PC12 cells we found a significant reduction in membrane localization of the mutant protein compared to the wild type. Furthermore, voltage clamp experiments of mutant-transfected HEK293 cells show a complete loss of function of the sodium channel, consistent with the absence of pain phenotype. In summary, this study has identified critical amino acids needed for the normal subcellular localization and function of Nav1.7. © 2010 Wiley-Liss, Inc.

The M-Channel Blocker Linopirdine Is an Agonist of the Capsaicin Receptor TRPV1

Linopirdine is a well known blocker of voltage-gated potassium channels from the Kv7 (or KCNQ) family that generate the so called M current in mammalian neurons. Kv7 subunits are also expressed in pain-sensing neurons in dorsal root ganglia, in which they modulate neuronal excitability. In this study we demonstrate that linopirdine acts as an agonist of TRPV1 (transient receptor potential vanilloid type 1), another ion channel expressed in nociceptors and involved in pain signaling. Linopirdine induces increases in intracellular calcium concentration in human embryonic kidney 293 (HEK293) cells expressing TRPV1, but not TRPA1 and TRPM8 or in wild-type HEK293 cells. Linopirdine also activates an inward current in TRPV1-expressing HEK293 cells that is almost completely blocked by the selective TRPV1 antagonist capsazepine. At low concentrations linopirdine sensitizes both recombinant and native TRPV1 channels to heat, in a manner that is not prevented by the Kv7-channel opener flupirtine. Taken together, these results indicate that linopirdine exerts an excitatory action on mammalian nociceptors not only through inhibition of the M current but also through activation of the capsaicin receptor TRPV1.

Extracellular Loops 2 and 4 of GLYT2 Are Required for N-Arachidonylglycine Inhibition of Glycine Transport

Concentrations of extracellular glycine in the central nervous system are regulated by Na(+)/Cl(-)-dependent glycine transporters, GLYT1 and GLYT2. N-Arachidonylglycine (NAGly) is an endogenous inhibitor of GLYT2 with little or no effect on GLYT1 and is analgesic in rat models of neuropathic and inflammatory pain. Understanding the molecular basis of NAGly interactions with GLYT2 may allow for the development of novel therapeutics. In this study, chimeric transporters were used to determine the structural basis for differences in NAGly sensitivity between GLYT1 and GLYT2 and also the actions of a series of related N-arachidonyl amino acids. Extracellular loops 2 and 4 of GLYT2 are important in the selective inhibition of GLYT2 by NAGly and by the related compounds N-arachidonyl-gamma-aminobutyric acid and N-arachidonyl-d-alanine, whereas only the extracellular loop 4 of GLYT2 is required for N-arachidonyl-l-alanine inhibition of transport. These observations suggest that the structure of the head group of these compounds is important in determining how they interact with extracellular loops 2 and 4 of GLYT2. Site-directed mutagenesis of GLYT2 EL4 residues was used to identify the key residues Arg(531), Lys(532), and Ile(545) that contribute to the differences in NAGly sensitivity.

Sodium Metabisulfite Modulation of Potassium Channels in Pain-Sensing Dorsal Root Ganglion Neurons

The effects of sodium metabisulfite (SMB), a general food preservative, on potassium currents in rat dorsal root ganglion (DRG) neurons were investigated using the whole-cell patch-clamp technique. SMB increased the amplitudes of both transient outward potassium currents and delayed rectifier potassium current in concentration- and voltage-dependent manner. The transient outward potassium currents (TOCs) include a fast inactivating (A-current or IA) current and a slow inactivating (D-current or ID) current. SMB majorly increased IA, and ID was little affected. SMB did not affect the activation process of transient outward currents (TOCs), but the inactivation curve of TOCs was shifted to more positive potentials. The inactivation time constants of TOCs were also increased by SMB. For delayed rectifier potassium current (IK), SMB shifted the activation curve to hyperpolarizing direction. SMB differently affected TOCs and IK, its effects major on A-type K+ channels, which play a role in adjusting pain sensitivity in response to peripheral redox conditions. SMB did not increase TOCs and IK when adding DTT in pipette solution. These results suggested that SMB might oxidize potassium channels, which relate to adjusting pain sensitivity in pain-sensing DRG neurons.

Mu and Delta Opioid Receptors Diverge

Contrary to current models, Scherrer et al. (2009) provide evidence that mu and delta opioid receptors are not expressed by the same pain-sensing neurons. In mice, agonists for these receptors produce analgesia restricted to either noxious heat or mechanical stimuli, implying that the receptors act on distinct fibers to mediate completely different types of pain relief.

Translating nociceptor sensitivity: the role of axonal protein synthesis in nociceptor physiology

The increased sensitivity of peripheral pain-sensing neurons, or nociceptors, is a major cause of the sensation of pain that follows injury. This plasticity is thought to contribute to the maintenance of chronic pain states. Although we have a broad knowledge of the factors that stimulate changes in nociceptor sensitivity, the cellular mechanisms that underlie this plasticity are still poorly understood; however, they are likely to involve changes in gene expression required for the phenotypic and functional changes seen in nociceptive neurons after injury. While the regulation of gene expression at the transcriptional level has been studied extensively, the regulation of protein synthesis, which is also a tightly controlled process, has only recently received more attention. Despite the established role of protein synthesis in the plasticity of neuronal cell bodies and dendrites, little attention has been paid to the role of translation control in mature undamaged axons. In this regard, several recent studies have demonstrated that the control of protein synthesis within the axonal compartment is crucial for the normal function and regulation of sensitivity of nociceptors. Pathways and proteins regulating this process, such as the mammalian target of rapamycin signaling cascade and the fragile X mental retardation protein, have recently been identified. We review here recent evidence for the regulation of protein synthesis within a nociceptor's axonal compartment and its contribution to this neuron's plasticity. We believe that an increased understanding of this process will lead to the identification of novel targets for the treatment of chronic pain.

Intracellular zinc irritates TRPA1

Exposure to zinc can cause pain and inflammation and can be harmful to human health. New evidence suggests that activation of the irritant receptor, TRPA1, which is expressed on pain-sensing neurons, may be responsible for some of these symptoms of zinc toxicity.

Herpes virus-based recombinant herpes vectors: gene therapy for pain and molecular tool for pain science

This paper reviews work by Yeomans and Wilson in the area of herpes vector-mediated gene transfer to sensory neurons. Beginning in 1997, these researchers have published a number of papers describing and exploiting this technology in altering the phenotype of pain-sensing neurons (nociceptors). Their initial work, continuing to the present, inserted a transgene cassette encoding the human preproenkephalin gene into the thymidine kinase locus under control of a cytomegalovirus promoter. This vector induced enkephalin expression selectively in the nociceptors innervating the tissue onto which it was applied, producing a profound analgesic and antihyperalgesic in acute and chronic pain models in both rodents and non-human primates. An improved version of this vector is now in clinical trials. In addition to inducing the de novo expression of foreign transgenes, this group also investigated the utility of herpes vectors in altering the endogenous genome of nociceptors. Thus, they inserted antisense sequences for genes of interest in the physiology of these neurons and successfully and selectively knocked down expression of several proteins known or thought to be involved in various pain states, including calcitonin gene-related peptide and mu-opioid receptors. They also used similar techniques to investigate the involvement of acid-sensing ion channels and Nav1.7 sodium channel in different pain states. These experiments uniquely allowed for spatially and temporally selective investigations into the function of these proteins in pain, highly valuable information in target validation for therapy development.

Pore Dilation Occurs in TRPA1 but Not in TRPM8 Channels

Abundantly expressed in pain-sensing neurons, TRPV1, TRPA1 and TRPM8 are major cellular sensors of thermal, chemical and mechanical stimuli. The function of these ion channels has been attributed to their selective permeation of small cations (e.g., Ca2+, Na+ and K+), and the ion selectivity has been assumed to be an invariant fingerprint to a given channel. However, for TRPV1, the notion of invariant ion selectivity has been revised recently. When activated, TRPV1 undergoes time and agonist-dependent pore dilation, allowing permeation of large organic cations such as Yo-Pro and NMDG+. The pore dilation is of physiological importance, and has been exploited to specifically silence TRPV1-positive sensory neurons. It is unknown whether TRPA1 and TRPM8 undergo pore dilation. Here we show that TRPA1 activation by reactive or non-reactive agonists induces Yo-Pro uptake, which can be blocked by TRPA1 antagonists. In outside-out patch recordings using NMDG+ as the sole external cation and Na+ as the internal cation, TRPA1 activation results in dynamic changes in permeability to NMDG+. In contrast, TRPM8 activation does not produce either Yo-Pro uptake or significant change in ion selectivity. Hence, pore dilation occurs in TRPA1, but not in TRPM8 channels.

Subunit-specific modulation of glycine receptors by cannabinoids and N-arachidonyl-glycine

Glycine receptors (GlyRs) mediate inhibitory neurotransmission in spinal cord motor and pain sensory neurons. Recent studies demonstrated apparently contradictory (potentiating versus inhibitory) effects of the endocannabinoid anandamide on these receptors. The present study characterised the effects of cannabinoid agonists on α1, α1β, α2 and α3 GlyRs recombinantly expressed in HEK293 cells with the aims of reconciling effects of cannabinoids on these receptor subtypes and to establish the potential of different GlyR isoforms as novel physiological or analgesic targets for cannabinoids. The compounds investigated were anandamide, HU-210, HU-308, WIN55,212-2 and the endogenous non-cannabinoid, N-arachidonyl-glycine. The latter compound was chosen due to the structural similarity with anandamide and known analgesic actions in the spinal cord. Recombinant α1 and α1β GlyRs were potentiated by anandamide and HU-210 at submicromolar concentrations, whereas WIN55,212-2 had no effect and HU-308 produced only weak inhibition. By contrast, N-arachidonyl-glycine exerted complex effects including both potentiation and inhibition. Anandamide had no effect at α2 or α3 GlyRs although the other cannabinoids produced potent inhibition. On α2 GlyRs, the inhibitory potency sequence was HU-210 = WIN55,212-2 > HU-308 > N-arachidonyl-glycine but on α3 GlyRs it was HU-210 = WIN55212 = HU-308 > N-arachidonyl-glycine. These results suggest that α1, α2 and α3 containing GlyRs exhibit distinct pharmacological profiles for cannabinoids. We conclude that cannabinoid agonists may be useful as pharmacological tools for selectively inhibiting α2 and α3 GlyRs. Our results also establish GlyRs as potential novel targets for endogenous and exogenous cannabinoids.

Differential Block of Sensory Neuronal Voltage-Gated Sodium Channels by Lacosamide [(2R)-2-(Acetylamino)-N-benzyl-3-methoxypropanamide], Lidocaine, and Carbamazepine

Voltage-gated sodium channels play a critical role in excitability of nociceptors (pain-sensing neurons). Several different sodium channels are thought to be potential targets for pain therapeutics, including Na(v)1.7, which is highly expressed in nociceptors and plays crucial roles in human pain and hereditary painful neuropathies, Na(v)1.3, which is up-regulated in sensory neurons following chronic inflammation and nerve injury, and Na(v)1.8, which has been implicated in inflammatory and neuropathic pain mechanisms. We compared the effects of lacosamide [(2R)-2-(acetylamino)-N-benzyl-3-methoxypropanamide], a new pain therapeutic, with those of lidocaine and carbamazepine on recombinant Na(v)1.7 and Na(v)1.3 currents and neuronal tetrodotoxin-resistant (Na(v)1.8-type) sodium currents using whole-cell patch-clamp electrophysiology. Lacosamide is able to substantially reduce all three current types. However, in contrast to lidocaine and carbamazepine, 1 mM lacosamide did not alter steady-state fast inactivation. Inhibition by lacosamide exhibited substantially slower kinetics, consistent with the proposal that lacosamide interacts with slow-inactivated sodium channels. The estimated IC(50) values for inhibition by lacosamide of Na(v)1.7-, Na(v)1.3-, and Na(v)1.8-type channels following prolonged inactivation were 182, 415, and 16 microM, respectively. Na(v)1.7-, Na(v)1.3-, and Na(v)1.8-type channels in the resting state were 221-, 123-, and 257-fold less sensitive, respectively, to lacosamide than inactivated channels. Interestingly, the ratios of resting to inactivated IC(50)s for carbamazepine and lidocaine were much smaller (ranging from 3 to 16). This suggests that lacosamide should be more effective than carbamazepine and lidocaine at selectively blocking the electrical activity of neurons that are chronically depolarized compared with those at more normal resting potentials.

A Better Local and Regional Anesthetic

Anesthetics used for local and regional anesthesia block pain signals from pain-sensing (nociceptive) neurons. However, they also affect the function

A local route to pain relief

Local anaesthetics stop pain, but block all other sensations too. In rats, one molecular delivery vehicle makes an unusual local anaesthetic specific for pain — provided a little spice is added to the mix first. The snag with most local anaesthetics is their lack of specificity. They are lipophilic, so can enter virtually any neuron, where they indiscriminately block sodium channels in the membrane. A way of blocking the activity of specific pain-sensing neurons without affecting other sensory or motor neurons could be used to create a more targeted form of local anaesthesia, and that is the prospect held out by Binshtok et al. in this issue. They report that the lidocaine derivative QX-314 can be targeted to pain-sensing neurons. Normally QX-314 can't cross the cell membrane. But antipain specificity is ensured by allowing it to enter via the TRPV1 channel, a capsaicin receptor found only in pain-sensing neurons. Co-application of QX-314 and capsaicin in rats blocked mechanical and thermal pain, inducing local anaesthesia, without the paralysis seen in 'normal' lidocaine anaesthesia.