Development Of Analgesic Drugs Research Articles

Is Acid Painful or not?

Acid (or proton) is an effective algogen to excite primary afferent nociceptors and evoke pain. Pain associated with tissue acidosis occurs where there is/are tissue injury, inflammation, ischemia, fatiguing exercise, or tumors. However, a recent study in mice has virtually changed our view regarding the significance of acid signaling in nociception. In the study, an acid-induced muscle pain model was used to probe the endogenous antinociceptive signaling pathway. Surprisingly, instead of acid-induced pain, the authors discovered that acid could also elicit an antinociceptive effect on mice, when specific acid sensors of muscle nociceptors, such as ASIC3 and TRPV1, were blocked. The acid-mediated antinociceptive pathway might act via a subset of acid-sensitive muscle afferent neurons to release substance P (SP), which would act on neurokinin 1 (NK1) receptors to reduce acid-induced depolarization via activation of an M-type potassium channel. The newly uncovered antinociceptive role for acid has largely changed our concept of pain biology and brought new insight for the analgesic drug development.

Carvacrol Reduces Cancer Pain by GABAergic System

The aim of this study was to evaluate the effect of carvacrol (CARV), a monoterpene present in oregano oil, on nociception induced by Sarcoma 180 (S180) in mice. Mice were treated (s.c.) after tumor induction (106 cells/25 mL, s.c.) with vehicle, CARV (12.5‐50 mg/kg, s.c.) or morphine (15 mg/kg) daily for 15 days. Mechanical hyperalgesia was evaluated by von Frey and marcation for Fos protein in lumbar spinal cord by imunofluorescence. All protocols were approved for the UFS Ethic Committee (CEPA: 71/10). Molecular docking studies also were performed to evaluate possible intermolecular interactions of the CARV and muscimol, as ligands of GABAA receptors. CARV (50 mg/kg) was able to increase (p < 0.05) the paw withdrawal threshold in 9 (0.37 ± 0.50 g), 11 (0.85 ± 0.65 g), 13 (1.48 ± 0.65 g) and 15 (1.63 ± 0.62 g) days compared to vehicle (2.50 ± 0.34 g, 3.87 ± 0.46 g, 3.82 ± 0.69 g, 4.24 ± 0.60 g, respectively). CARV also decrease number of positively marked neurons in spinal cord (p < 0.001). Docking studies showed favorable interaction overlay of the CARV with GABAA. These results demonstrate that CARV may be an interesting candidate for the development of new analgesic drugs for the management of cancer pain.

1-Heteroaryl-3-phenoxypropan-2-ones as inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: Effect of the replacement of the ether oxygen with sulfur and nitrogen moieties on enzyme inhibition and metabolic stability

Cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are enzymes, which have emerged as attractive targets for the development of analgesic and anti-inflammatory drugs. We recently reported that certain 3-phenoxy-substituted 1-heteroarylpropan-2-ones are inhibitors of cPLA2α and/or FAAH. Starting from 1-[2-oxo-3-(4-phenoxyphenoxy)propyl]indole-5-carboxylic acid (3) and 1-(1H-benzotriazol-1-yl)-3-(4-phenoxyphenoxy)propan-2-one (4), the effect of the replacement of the oxygen in position 3 of the propan-2-one scaffold by sulfur and nitrogen containing moieties on inhibition of cPLA2α and fatty acid amide hydrolase as well as on metabolic stability in rat liver S9 fractions was investigated. As a result of these structure–activity relationship studies it was found that the ether oxygen is of great importance for enzyme inhibitory potency. Replacement by sulfur led to an about 100-fold decrease of enzyme inhibition, nitrogen and substituted nitrogen atoms at this position even resulted in inactivity of the compounds. The effect of the structural variations performed on metabolic stability of the important ketone pharmacophore was partly different in the two series of compounds. While introduction of SO and SO2 significantly increased stability of the ketone against reduction in case of the indole-5-carboxylic acid 3, it had no effect in case of the benzotriazole 4. Further analysis of the metabolism of 3 and 4 in rat liver S9 fractions revealed that the major metabolite of 3 was the alcohol 53 formed by reduction of the keto group. In contrast, in case of 4 beside keto reduction an excessive hydroxylation of the terminal phenoxy group occurred leading to the dihydroxy compound 50. Experiments with enzyme inhibitors showed that the phenylhydroxylation of 4 was catalyzed by tranylcypromine sensitive cytochrome P450 isoforms, while the reduction of the ketone function of 3 and 4 was mainly caused by cytosolic short chain dehydrogenases/reductases (cSDR).

Tingenone, a pentacyclic triterpene, induces peripheral antinociception due to NO/cGMP and ATP-sensitive K+ channels pathway activation in mice

Substances derived from plants play an important role in the development of new analgesic drugs, among them, triterpenoids. The connection between the participation of L-arginine/NO/cGMP pathway and the activation of ATP-sensitive K+ channels (KATP) has been established on the peripheral antinociception induced by various drugs. The study assessed the involvement of L-arginine/NO/cGMP/KATP pathway in the antinociceptive effect induced by tingenone, from Maytenus imbricata, against the hyperalgesia evoked by prostaglandin E2 (PGE2) in peripheral pathway. The paw pressure test was used, with hyperalgesia induced by intraplantar injection of PGE2 (2μg). Tingenone (200µg/paw) administered into the right hind paw induced a local antinociceptive effect, that was antagonized by l-NOArg, nonselective nitric oxide synthase (NOS) inhibitor and by L-NPA, selective neuronal NOS (nNOS) inhibitor. The L-NIO, selective inhibitor of endothelial (eNOS), and the L-NIL, selective inhibitor of inducible (iNOS), did not alter the peripheral antinociceptive effect of the tingenone. The ODQ, selective soluble guanylyl cyclase inhibitor, prevented the antinociceptive effect of tingenone, and zaprinast, inhibitor of the phosphodiesterase that is cyclic guanosine monophosphate (cGMP) specific, intensified the peripheral antinociceptive effect of the smaller dose of tingenone. Glibenclamide, ATP-sensitive K+ channels (KATP) blocker, but not tetraethylammonium chloride, voltage-dependent K+ channel blocker; dequalinium dichloride, blocker of the small conductance Ca2+-activated K+ channel, and paxilline, a potent blocker of high-conductance Ca2+-activated K+ channels, respectively, prevented the peripheral antinociceptive effect of tingenone. The results demonstrate that tingenone induced a peripheral antinociceptive effect by L-arginine/NO/cGMP/KATP pathway activation, with potential for a new analgesic drug.

The Pore-Domain of TRPA1 Mediates the Inhibitory Effect of the Antagonist 6-Methyl-5-(2-(Trifluoromethyl)Phenyl)-1H-Indazole

The pore-domain of TRPA1 mediates the inhibitory effect of the antagonist 6-Methyl-5-(2-(trifluoromethyl)phenyl)-1H-indazole The ion channel TRPA1 gives to the organisms the ability to detect noxious chemicals to sensory neurons and as a result of this, mediates chemical nociception in vivo. Mouse TRPA1 is activated by electrophilic compounds such as mustard-oil (MO) and several physical stimuli such as cold temperature. Both stimuli are mechanistic linked to the N terminus of the channel. Due to its sensory function, the inhibition of TRPA1 activity might provide an effective treatment against chronic and inflammatory pain, for that reason, TRPA1 has become an important target for the development of new and better analgesic drugs. 6-Methyl-5-(2-(trifluoromethyl)phenyl)-1H-indazole (Compound 31) has been identified by a chemical screen and lead optimization as an inhibitor of chemical activation of TRPA1. However, the structures or domains of TRPA1 that mediate the inhibitory effect of Compound 31 are unknown. Here, we screened 12,000 random mutant clones of mouse TRPA1 for their sensitivity to mustard-oil and the ability of Compound 31 to inhibit chemical activation by MO. We identified five mutations located within the pore domain that cause loss of inhibition by Compound 31, one of them in the residue T877 placed in the TM5, important in the binding of menthol, a dose-dependent agonist/blocker. This result demonstrates that the pore-domain is a regulator of chemical activation and suggests that Compound 31 might be acting directly on the pore-domain.

Evidence for the involvement of descending pain-inhibitory mechanisms in the attenuation of cancer pain by carvacrol aided through a docking study

AimsThe present study evaluated the carvacrol (CARV) effect on hyperalgesia and nociception induced by sarcoma 180 (S180) in mice. Main methodsCarvacrol treatment (12.5–50mg/kgs.c.) once daily for 15days was started 24h after injection of the sarcoma cells in the hind paw (s.c.). Mice were evaluated for mechanical sensitivity (von Frey), spontaneous and palpation-induced nociception, limb use and tumor growth on alternate days. CARV effects on the central nervous system were evaluated through immunofluorescence for Fos protein. Molecular docking studies also were performed to evaluate intermolecular interactions of the carvacrol and muscimol, as ligands of interleukin-10 and GABAA receptors. Key findingsCARV was able to significantly reduce mechanical hyperalgesia and spontaneous and palpation-induced nociception, improve use paw, decrease the number of positively marked neurons in lumbar spinal cord and activate periaqueductal gray, nucleus raphe magnus and locus coeruleus. CARV also caused significant decreased tumor growth. Docking studies showed favorable interaction overlay of the CARV with IL-10 and GABAA. SignificanceTogether, these results demonstrated that CARV may be an interesting option for the development of new analgesic drugs for the management of cancer pain.

Assessment of mechanisms involved in antinociception produced by the alkaloid caulerpine.

In previous works we showed that oral administration of caulerpine, a bisindole alkaloid isolated from algae of the genus Caulerpa, produced antinociception when assessed in chemical and thermal models of nociception. In this study, we evaluated the possible mechanism of action of this alkaloid in mice, using the writhing test. The antinociceptive effect of caulerpine was not affected by intraperitoneal (i.p.) pretreatment of mice with naloxone, flumazenil, l-arginine or atropine, thus discounting the involvement of the opioid, GABAergic, l-arginine-nitric oxide and (muscarinic) cholinergic pathways, respectively. In contrast, i.p. pretreatment with yohimbine, an α2-adrenoceptor antagonist, or tropisetron, a 5-HT3 antagonist, significantly blocked caulerpine-induced antinociception. These results suggest that caulerpine exerts its antinociceptive effect in the writhing test via pathways involving α2-adrenoceptors and 5-HT3 receptors. In summary, this alkaloid could be of interest in the development of new dual-action analgesic drugs.

The pore-domain of TRPA1 mediates the inhibitory effect of the antagonist 6-methyl-5-(2-(trifluoromethyl)phenyl)-1H-indazole.

The transient receptor potential ion channel TRPA1 confers the ability to detect tissue damaging chemicals to sensory neurons and as a result mediates chemical nociception in vivo. Mouse TRPA1 is activated by electrophilic compounds such as mustard-oil and several physical stimuli such as cold temperature. Due to its sensory function inhibition of TRPA1 activity might provide an effective treatment against chronic and inflammatory pain. Therefore, TRPA1 has become a target for the development of analgesic drugs. 6-Methyl-5-(2-(trifluoromethyl)phenyl)-1H-indazole (Compound 31) has been identified by a chemical screen and lead optimization as an inhibitor of chemical activation of TRPA1. However, the structures or domains of TRPA1 that mediate the inhibitory effect of Compound 31 are unknown. Here, we screened 12,000 random mutant clones of mouse TRPA1 for their sensitivity to mustard-oil and the ability of Compound 31 to inhibit chemical activation by mustard-oil. In addition, we separately screened this mutant library while stimulating it with cold temperatures. We found that the single-point mutation I624N in the N-terminus of TRPA1 specifically affects the sensitivity to mustard-oil, but not to cold temperatures. This is evidence that sensitivity of TRPA1 to chemicals and cold temperatures is conveyed by separable mechanisms. We also identified five mutations located within the pore domain that cause loss of inhibition by Compound 31. This result demonstrates that the pore-domain is a regulator of chemical activation and suggests that Compound 31 might be acting directly on the pore-domain.

Antinociceptive effect of 3-(4-fluorophenyl)-5-trifluoromethyl-1H-1-tosylpyrazole. A Celecoxib structural analog in models of pathological pain

Pain is the most common complaint in the medical field and the identification of novel compounds that can effectively treat painful states without causing side effects remains a major challenge in biomedical research. The aim of the present study is to investigate the antinociceptive effect of 3-(4-fluorophenyl)-5-trifluoromethyl-1H-1-tosylpyrazole (FTosPz) in models of pathological pain in mice and compare these effects with those produced by Celecoxib. FTosPz (100–500μmol/kg) or Celecoxib (26–260μmol/kg) was administrated orally. The administration of either FTosPz or Celecoxib reduced the hyperalgesia but not the edema or leukocyte infiltration that was caused by Complete Freund's Adjuvant (CFA), used as an arthritis model. Oral administration of both FTosPz and Celecoxib also attenuated the postoperative hyperalgesia as well as the hyperalgesia caused by partial sciatic nerve ligation, used as a neuropathic pain model. FTosPz and Celecoxib produced antinociceptive effects without altering the locomotor activity of animals. Furthermore, FTosPz neither altered AST/ALT enzyme activity nor the urea/creatinine levels. Still, the FTosPz did not alter the COX-1 and COX-2 enzyme activities. Thus, FTosPz is an interesting prototype for the development of novel analgesic drugs.

Transforming the Concept of “State of the Art” Into “Real Pain Relief” for Patients after Cardiac Surgery – A Combined Nursing-Anesthesia Initiative

Several publications have shown that adequate postsurgical pain control after cardiac surgery has been difficult to obtain. Hospital services have been admonished to develop appropriate organizations of care that will facilitate the use of existing expertise rather than focusing on the development of new analgesic drugs. In this article the authors discuss the multidisciplinary collaboration that enabled the creation and implementation, in a busy cardiac surgery service, of a structure that has forged significant improvement in the treatment of pain after cardiac surgery. This nurse-run program promotes the use of a “low-tech, highly personalized” approach to pain management where the daily clinical work is supported by the concept of the “Patient Pyramid of Care”.

Peripheral Pain-Sensing Neurons: from Molecular Diversity to Functional Specialization

Recent work in Cell Reports by Minett et al. and Yang et al. highlights the complexity of pain pathways and points to new ways of thinking about chronic and disease-related pain.

Drug Repositioning: Playing Dirty to Kill Pain

The number of approved new molecular entity drugs has been decreasing as the pharmaceutical company investment in research and development is increasing. As we face this painful crisis, called an innovation gap, there is increasing awareness that development of new uses of existing drugs may be a powerful tool to help overcome this obstacle because it takes too long, costs too much and can be risky to release drugs developed de novo. Consequently, drug repositioning is emerging in different therapeutic areas, including the pain research area. Worldwide, pain is the main reason for seeking healthcare, and pain relief represents an unmet global clinical need. Therefore, development of analgesics with better efficacy, safety and cost effectiveness is of paramount importance. Despite the remarkable advancement in research on cellular and molecular mechanisms underlying pain pathophysiology over the past three decades, target-based therapeutic opportunities have not been pursued to the same extent. Phenotypic screening remains a more powerful tool for drug development than target-based screening so far. It sounds somewhat heretical, but some multi-action drugs, rather than very selective ones, have been developed intentionally. In the present review, we first critically discuss the utility of drug repositioning for analgesic drug development and then show examples of 'old' drugs that have been successfully repositioned or that are under investigation for their analgesic actions. We conclude that drug repositioning should be more strongly encouraged to help build a bridge between basic research and pain relief worldwide.

Resiniferatoxin (RTX) Causes a Uniquely Protracted Musculoskeletal Hyperalgesia in Mice by Activation of TRPV1 Receptors

Inactivation of transient receptor potential vanilloid-1 (TRPV1) receptors is one approach to analgesic drug development. However, TRPV1 receptors exert different effects on each modality of pain. Because muscle pain is clinically important, we compared the effect of TRPV1 ligands on musculoskeletal nociception to that on thermal and tactile nociception. Injected parenterally, capsaicin had no effect on von Frey fiber responses (tactile) but induced a transient hypothermia and hyperalgesia in both the tail flick (thermal) and grip force (musculoskeletal) assays, presumably by its agonistic action at TRPV1 sites. In contrast, resiniferatoxin (RTX) produced a chronic (>58 days) thermal antinociception, consistent with its reported ability to desensitize TRPV1 sites. In the same mice, RTX produced a transient hypothermia (7 hours) and a protracted (28-day) musculoskeletal hyperalgesia in spite of a 35.5% reduction in TRPV1 receptor immunoreactivity in muscle afferents. Once musculoskeletal hyperalgesia subsided, mice were tolerant to the hyperalgesic effects of either capsaicin or RTX whereas tolerance to hypothermia did not develop until after 3 injections. Musculoskeletal hyperalgesia was prevented but not reversed by SB-366791, a TRPV1 antagonist, indicating that TRPV1 receptors initiate but do not maintain hyperalgesia. Injected intrathecally, RTX produced only a brief musculoskeletal hyperalgesia (2 days), after which mice were tolerant to this effect. PerspectiveThe effect of TRPV1 receptors varies depending on modality and tissue type, such that RTX causes thermal antinociception, musculoskeletal hyperalgesia, and no effect on tactile nociception in healthy mice. Spinal TRPV1 receptors are a potential target for pain relief as they induce only a short musculoskeletal hyperalgesia followed by desensitization.

No pain, more gain

A new study shows that a specific mutation in SCN11A, which encodes the Nav1.9 voltage-gated sodium channel, underlies a human disorder characterized by insensitivity to pain. This finding provides fresh insights into human pain perception and suggests a new avenue for the development of analgesic drugs.

Mechanism underlying anti-hyperalgesic and anti-allodynic properties of anomalin in both acute and chronic inflammatory pain models in mice through inhibition of NF-κB, MAPKs and CREB signaling cascades

The numerous mediators of pain and inflammation are products of injury-induced gene expression that lead to changes in the nervous system and immune responses. These multiple molecules and mechanisms suggest novel strategies that could be used for analgesic drug development. The present study investigated the possible anti-hyperalgesic effects of anomalin in complete Freund′s adjuvant (CFA)-induced acute and chronic inflammatory pain models. Acute pretreatment of mice with anomalin (10 and 50mg/kg, i.p.) produced a significant anti-nociceptive effect against CFA- and carrageenan-induced mechanical hyperalgesia and allodynia. In a chronic pain model, administration of anomalin inhibited CFA-induced hyperalgesia, and it did not cause any apparent toxicity. Another set of experiments observed that anomalin inhibited CFA- and carrageenan-induced paw edema in acute and chronic models. To elucidate the molecular mechanism underlying the anti-nociceptive effect of anomalin, the various pain signaling pathways [NF-κB, cAMP response element-binding protein (CREB), and mitogen activated protein kinase (MAPKs)/AP-1] that are involved were examined. Intraperitoneal (i.p.) pretreatment of anomalin exhibited potent inhibitory effects on direct mediators of hyperalgesia (iNOS and COX-2). The release of CFA-induced plasma nitrite and paw tissue hyperalgesic cytokine (TNF-α) was reduced remarkably. In addition, the adenosine 5'-triphosphate (ATP) in plasma and substance P (SP) in paw tissue were markedly suppressed by anomalin. These results demonstrate that anomalin exhibits an analgesic effect in a consistent manner and that its mechanisms involve the inhibition of the NF-κB, CREB, and MAPKs/AP-1 signaling pathways.

Expression and treatment of pain-related behavioral depression

Pain is often associated with clinically relevant depression of behavior and mood, and relief of pain-related depression is a common goal of treatment in both human and veterinary medicine. In the development of pharmacological compounds to treat pain and related depression, preclinical studies may be used to evaluate the analgesic potential of new drugs. Such studies require reliable, accurate assays of pain-related behavioral depression in animals. Intracranial self-stimulation (ICSS) is a type of operant conditioning procedure that produces stable baseline behavioral response rates. The author reviews recent research on the use of ICSS to evaluate the expression and pharmacological modulation of pain-related behavioral depression in rats. Results suggest that assays of pain-depressed behavior using ICSS may serve as a useful new tool to improve the translation of preclinical findings to clinical results in analgesic drug development.

The K + channel GIRK2 is both necessary and sufficient for peripheral opioid‐mediated analgesia

The use of opioid agonists acting outside the central nervous system (CNS) is a promising therapeutic strategy for pain control that avoids deleterious central side effects such as apnea and addiction. In human clinical trials and rat models of inflammatory pain, peripherally restricted opioids have repeatedly shown powerful analgesic effects; in some mouse models however, their actions remain unclear. Here, we investigated opioid receptor coupling to K+ channels as a mechanism to explain such discrepancies. We found that GIRK channels, major effectors for opioid signalling in the CNS, are absent from mouse peripheral sensory neurons but present in human and rat. In vivo transgenic expression of GIRK channels in mouse nociceptors established peripheral opioid signalling and local analgesia. We further identified a regulatory element in the rat GIRK2 gene that accounts for differential expression in rodents. Thus, GIRK channels are indispensable for peripheral opioid analgesia, and their absence in mice has profound consequences for GPCR signalling in peripheral sensory neurons.GIRK channels are indispensable for peripheral opioid analgesia. The absence of GIRK channels from mouse dorsal root ganglion neurons questions the predictive validity of mice as a model organism for investigating peripheral GPCRmediated analgesia.

Analgesic drug development: time to break the mould

Success in the introduction of novel, effective and safe analgesics has been notably limited over the past ten years even though existing treatments have low responder rates and a high side effect burden. The pipeline of compounds acting on novel targets is very restricted and there have been many disappointments with drugs that appeared promising in preclinical studies, failing repeatedly in clinical trials. We have to recognize that something is fundamentally wrong with the industry standard approach to the selection of targets, identification of hits, validation of leads and proof of concept clinical studies. A radically alternative strategy is required, one that is driven by the patient and focused on disease phenotype. I will discuss what such an approach may look like and how it may contribute to new therapeutics.

Desensitization properties of P2X3 receptors shaping pain signaling

ATP-gated P2X3 receptors are mostly expressed by nociceptive sensory neurons and participate in transduction of pain signals. P2X3 receptors show a combination of fast desensitization onset and slow recovery. Moreover, even low nanomolar agonist concentrations unable to evoke a response, can induce desensitization via a phenomenon called “high affinity desensitization.” We have also observed that recovery from desensitization is agonist-specific and can range from seconds to minutes. The recovery process displays unusually high temperature dependence. Likewise, recycling of P2X3 receptors in peri-membrane regions shows unexpectedly large temperature sensitivity. By applying kinetic modeling, we have previously shown that desensitization characteristics of P2X3 receptor are best explained with a cyclic model of receptor operation involving three agonist molecules binding a single receptor and that desensitization is primarily developing from the open receptor state. Mutagenesis experiments suggested that desensitization depends on a certain conformation of the ATP binding pocket and on the structure of the transmembrane domains forming the ion pore. Further molecular determinants of desensitization have been identified by mutating the intracellular N- and C-termini of P2X3 receptor. Unlike other P2X receptors, the P2X3 subtype is facilitated by extracellular calcium that acts via specific sites in the ectodomain neighboring the ATP binding pocket. Thus, substitution of serine275 in this region (called “left flipper”) converts the natural facilitation induced by extracellular calcium to receptor inhibition. Given their strategic location in nociceptive neurons and unique desensitization properties, P2X3 receptors represent an attractive target for development of new analgesic drugs via promotion of desensitization aimed at suppressing chronic pain.

Neuromuscular electrostimulation techniques: historical aspects and current possibilities in treatment of pain and muscle waisting

Application of electricity for pain treatment dates back to thousands of years BC. The Ancient Egyptians and later the Greeks and Romans recognized that electrical fishes are capable of generating electric shocks for relief of pain. In the 18th and 19th centuries these natural producers of electricity were replaced by man-made electrical devices. This happened in following phases. The first was the application of static electrical currents (called Franklinism), which was produced by a friction generator. Christian Kratzenstein was the first to apply it medically, followed shortly by Benjamin Franklin. The second phase was Galvanism. This method applied a direct electrical current to the skin by chemical means, applied a direct and pulsed electrical current to the skin. In the third phase the electrical current was induced intermittently and in alternate directions (called Faradism). The fourth stage was the use of high frequency currents (called d'Arsonvalisation). The 19th century was the "golden age" of electrotherapy. It was used for countless dental, neurological, psychiatric and gynecological disturbances. However, at beginning of the 20th century electrotherapy fell from grace. It was dismissed as lacking a scientific basis and being used also by quacks and charlatans for unserious aims. Furthermore, the development of effective analgesic drugs decreased the interest in electricity. In the second half of the 20th century electrotherapy underwent a revival. Based on animal experiments and clinical investigations, its neurophysiological mechanisms were elucidated in more details. The pain relieving action of electricity was explained in particular by two main mechanisms: first, segmental inhibition of pain signals to the brain in the dorsal horn of the spinal cord and second, activation of the descending inhibitory pathway with enhanced release of endogenous opioids and other neurochemical compounds (serotonin, noradrenaline, gamma aminobutyric acid (GABA), acetylcholine and adenosine). The modern electrotherapy of neuromusculo- skeletal pain is based in particular on the following types: transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS or electro-acupuncture) and spinal cord stimulation (SCS). In mild to moderate pain, TENS and PENS are effective methods, whereas SCS is very useful for therapy of refractory neuropathic or ischemic pain. In 2005, high tone external muscle stimulation (HTEMS) was introduced. In diabetic peripheral neuropathy, its analgesic action was more pronounced than TENS application. HTEMS appeared also to have value in the therapy of symptomatic peripheral neuropathy in end-stage renal disease (ESRD). Besides its pain-relieving effect, electrical stimulation is of major importance for prevention or treatment of muscle dysfunction and sarcopenia. In controlled clinical studies electrical myostimulation (EMS) has been shown to be effective against the sarcopenia of patients with chronic congestive heart disease, diabetes, chronic obstructive pulmonary disease and ESRD.