Identification of two related pentapeptides from the brain with potent opiate agonist activity

Organization of enkephalinergic neuronal system in the central nervous system of the gecko Hemidactylus frenatus

Enkephalins are endogenous opioid pentapeptides that play a role in neurotransmission and pain modulation in vertebrates. However, the distribution pattern of enkephalinergic neurons in the brains of reptiles has been understudied. This study reports the organization of the methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) neuronal systems in the central nervous system of the gecko Hemidactylus frenatus using an immunofluorescence labeling method. Although M-ENK and L-ENK-immunoreactive (ir) fibers extended throughout the pallial and subpallial subdivisions, including the olfactory bulbs, M-ENK and L-ENK-ir cells were found only in the dorsal septal nucleus. Enkephalinergic perikarya and fibers were highly concentrated in the periventricular and lateral preoptic areas, as well as in the anterior and lateral subdivisions of the hypothalamus, while enkephalinergic innervation was observed in the hypothalamic periventricular nucleus, infundibular recess nucleus and median eminence. The dense accumulation of enkephalinergic content was noticed in the pars distalis of the hypophysis. In the thalamus, the nucleus rotundus and the dorsolateral, medial, and medial posterior thalamic nuclei contained M-ENK and L-ENK-ir fibers, whereas clusters of M-ENK and L-ENK-ir neurons were observed in the pretectum, mesencephalon, and rhombencephalon. The enkephalinergic fibers were also seen in the area X around the central canal, as well as the dorsal and ventral horns. The widespread distribution of enkephalin-containing neurons within the central nervous system implies that enkephalins regulate a variety of functions in the gecko, including sensory, behavioral, hypophysiotropic, and neuroendocrine functions.

Raman Spectra of Amino Acids and Peptides from Machine Learning Polarizabilities

Raman spectroscopy is an important tool in the study of vibrational properties and composition of molecules, peptides, and even proteins. Raman spectra can be simulated based on the change of the electronic polarizability with vibrations, which can nowadays be efficiently obtained via machine learning models trained on first-principles data. However, the transferability of the models trained on small molecules to larger structures is unclear, and direct training on large structures is prohibitively expensive. In this work, we first train two machine learning models to predict the polarizabilities of all 20 amino acids. Both models are carefully benchmarked and compared to density functional theory (DFT) calculations, with the neural network method being found to offer better transferability. By combination of machine learning models with classical force field molecular dynamics, Raman spectra of all amino acids are also obtained and investigated, showing good agreement with experiments. The models are further extended to small peptides. We find that adding structures containing peptide bonds to the training set greatly improves predictions, even for peptides not included in training sets.

Fabrication and Optimization of a Molecularly Imprinted Carbon Fiber Microelectrode for Selective Detection of Met-enkephalin Using Fast-Scan Cyclic Voltammetry

Methionine-enkephalin (Met-Enk) is an endogenous opioid peptide that is involved in various physiological processes including memory. A technological gap in the understanding of Met-Enk's role in memory is the lack of rapid measurement tools to selectively quantify Met-Enk concentrations in situ. Here, we integrate molecularly imprinted polymers (MIPs) with carbon fiber microelectrodes (CFMs) to selectively detect Met-Enk by using fast-scan cyclic voltammetry (FSCV). We report two MIP conditions that yield 2-fold and 5-fold higher selectivity toward Met-Enk than the tyrosine-containing hexapeptide fragment angiotensin II (3-8). We demonstrate that MIP technology can be combined with FSCV at CFMs to create rapid and selective sensors for Met-Enk. This technology is a promising platform for creating selective sensors for other peptides and biomarkers.

Porous silicon and silica carriers for delivery of peptide therapeutics

Peptides have gained tremendous popularity as biological therapeutic agents in recent years due to their favourable specificity, diversity of targets, well-established screening methods, ease of production, and lower cost. However, their poor physiological and storage stability, pharmacokinetics, and fast clearance have limited their clinical translation. Novel nanocarrier-based strategies have shown promise in overcoming these issues. In this direction, porous silicon (pSi) and mesoporous silica nanoparticles (MSNs) have been widely explored as potential carriers for the delivery of peptide therapeutics. These materials possess several advantages, including large surface areas, tunable pore sizes, and adjustable pore architectures, which make them attractive carriers for peptide delivery systems. In this review, we cover pSi and MSNs as drug carriers focusing on their use in peptide delivery. The review provides a brief overview of their fabrication, surface modification, and interesting properties that make them ideal peptide drug carriers. The review provides a systematic account of various studies that have utilised these unique porous carriers for peptide delivery describing significant in vitro and in vivo results. We have also provided a critical comparison of the two carriers in terms of their physicochemical properties and short-term and long-term biocompatibility. Lastly, we have concluded the review with our opinion of this field and identified key areas for future research for clinical translation of pSi and MSN-based peptide therapeutic formulations.

Neuromarkers in addiction: definitions, development strategies, and recent advances

Substance use disorders (SUDs) are the most costly and prevalent psychiatric conditions. Recent calls emphasize a need for biomarkers-measurable, stable indicators of normal and abnormal processes and response to treatment or environmental agents-and, in particular, brain-based neuromarkers that will advance understanding of the neurobiological basis of SUDs and clinical practice. To develop neuromarkers, researchers must be grounded in evidence that a putative marker (i) is sensitive and specific to the psychological phenomenon of interest, (ii) constitutes a predictive model, and (iii) generalizes to novel observations (e.g., through internal cross-validation and external application to novel data). These neuromarkers may be used to index risk of developing SUDs (susceptibility), classify individuals with SUDs (diagnostic), assess risk for progression to more severe pathology (prognostic) or index current severity of pathology (monitoring), detect response to treatment (response), and predict individualized treatment outcomes (predictive). Here, we outline guidelines for developing and assessing neuromarkers, we then review recent advances toward neuromarkers in addiction neuroscience centering our discussion around neuromarkers of craving-a core feature of SUDs. In doing so, we specifically focus on the Neurobiological Craving Signature (NCS), which show great promise for meeting the demand of neuromarkers.

The opioid peptide leucine enkephalin modulates hypothalamic-hypophysial axis in the cichlid fish Oreochromis mossambicus

In vertebrates, opioid peptides are thought to be involved in the regulation of reproduction; however, the significance of enkephalins in testicular function remains unclear. We examined the influence of δ-opioid receptor agonist leucine enkephalin (L-ENK) on the hypophysial-testicular axis of the cichlid fish Oreochromis mossambicus. Treatment with a low dose of L-ENK (60 µg) caused a significant increase in the numbers of primary and secondary spermatocytes and early and late spermatids, concomitant with intense immunolabelling of testicular androgen receptors, but did not significantly alter serum luteinizing hormone (LH) and 11-ketotestosterone (11-KT) levels compared to those of controls. Nevertheless, treatment with a high dose of L-ENK (200 µg) caused a significant reduction in the numbers of secondary spermatocytes as well as late spermatids associated with marginal immunolabelling of androgen receptors and significantly lower concentrations of serum 11-KT and LH compared to controls. In addition, the serum cortisol level was not affected in low-dose L-ENK-treated fish, but its level was significantly increased in the high-dose L-ENK-treated group. Together, these findings indicate that a low dose of L-ENK stimulates the germ cells at the meiosis stage and promotes further stages of spermatogenesis, whereas a high concentration of L-ENK inhibits spermatogenesis at the advanced stages. This effect appears to be mediated through the suppression of testicular steroidogenesis and the reduction of LH release in the pituitary gland of tilapia. The findings also suggest that elevated L-ENK levels in teleosts may exert their inhibitory influence on the hypophysial-testicular axis via glucocorticoids.

Analgesic Peptides: From Natural Diversity to Rational Design

Pain affects one-third of the global population and is a significant public health issue. The use of opioid drugs, which are the strongest painkillers, is associated with several side effects, such as tolerance, addiction, overdose, and even death. An increasing demand for novel, safer analgesic agents is a driving force for exploring natural sources of bioactive peptides with antinociceptive activity. Since the G protein-coupled receptors (GPCRs) play a crucial role in pain modulation, the discovery of new peptide ligands for GPCRs is a significant challenge for novel drug development. The aim of this review is to present peptides of human and animal origin with antinociceptive potential and to show the possibilities of their modification, as well as the design of novel structures. The study presents the current knowledge on structure-activity relationship in the design of peptide-based biomimetic compounds, the modification strategies directed at increasing the antinociceptive activity, and improvement of metabolic stability and pharmacodynamic profile. The procedures employed in prolonged drug delivery of emerging compounds are also discussed. The work summarizes the conditions leading to the development of potential morphine replacements.

Applications of biaryl cyclization in the synthesis of cyclic enkephalin analogs with a highly restricted flexibility

A series of 10 cyclic, biaryl analogs of enkephalin, with Tyr or Phe residues at positions 1 and 4, were synthesized according to the Miyaura borylation and Suzuki coupling methodology. Biaryl bridges formed by side chains of the two aromatic amino acid residues are of the meta-meta, meta-para, para-meta, and para-para configuration. Conformational properties of the peptides were studied by CD and NMR. CD studies allowed only to compare conformations of individual peptides while NMR investigations followed by XPLOR calculations provided detailed information on their conformation. Reliability of the XPLOR calculations was confirmed by quantum chemical ones performed for one of the analogs. No intramolecular hydrogen bonds were found in all the peptides. They are folded and adopt the type IV β-turn conformation. Due to a large steric strain, the aromatic carbon atoms forming the biaryl bond are distinctly pyramidalized. Seven of the peptides were tested in vitro for their affinity for the µ-opioid receptor.

A Balancing Act: Learning from the Past to Build a Future-Focused Opioid Strategy

The harmful side effects of opioid drugs such as respiratory depression, tolerance, dependence, and abuse potential have limited the therapeutic utility of opioids for their entire clinical history. However, no previous attempt to develop effective pain drugs that substantially ameliorate these effects has succeeded, and the current opioid epidemic affirms that they are a greater hindrance to the field of pain management than ever. Recent attempts at new opioid development have sought to reduce these side effects by minimizing engagement of the regulatory protein arrestin-3 at the mu-opioid receptor, but there is significant controversy around this approach. Here, we discuss the ongoing effort to develop safer opioids and its relevant historical context. We propose a new model that reconciles results previously assumed to be in direct conflict to explain how different signaling profiles at the mu-opioid receptor contribute to opioid tolerance and dependence. Our goal is for this framework to inform the search for a new generation of lower liability opioid analgesics.

A Novel Leu-Enkephalin Prodrug Produces Pain-Relieving and Antidepressant Effects

Persistent pain is a significant healthcare problem with limited treatment options. The high incidence of comorbid chronic pain and depression significantly reduces life quality and complicates the treatment of both conditions. Antidepressants are less effective for pain and depression than for depression alone and they induce severe side effects. Opioids are highly efficacious analgesics, but rapid development of tolerance, dependence, and debilitating side effects limit their efficacy and safe use. Leucine-enkephalin (Leu-ENK), the endogenous delta opioid receptor agonist, controls pain and mood and produces potent analgesia with reduced adverse effects compared to conventional opioids. High proteolytic instability, however, makes Leu-ENK ineffective after systemic administration and limits its clinical usefulness. KK-103, a Leu-ENK prodrug, was developed to overcome these limitations of Leu-ENK via markedly increased plasma stability in mice. We showed rapid and substantially increased systemic adsorption and blood plasma exposure of KK-103 compared to Leu-ENK. We also observed brain uptake of radiolabeled KK-103 after systemic administration, indicating a central effect of KK-103. We then established KK-103's prolonged antinociceptive efficacy in the ramped hot plate and formalin test. In both models, KK-103 produced a comparable dose to the maximum antinociceptive-effect relationship. The pain-alleviating effect of KK-103 primarily resulted from activating the delta opioid receptor after the likely conversion of KK-103 to Leu-ENK in vivo. Finally, KK-103 produced an antidepressant-like activity comparable to the antidepressant desipramine, but with minimal gastrointestinal inhibition and no incidence of sedation.

Interactions Between Endogenous Opioids and the Immune System

The endogenous opioid system, which consists of opioid receptors and their ligands, is widely expressed in the nervous system and also found in the immune system. As a part of the body's defense machinery, the immune system is heavily regulated by endogenous opioid peptides. Many types of immune cells, including macrophages, dendritic cells, neutrophils, and lymphocytes are influenced by endogenous opioids, which affect cell activation, differentiation, proliferation, apoptosis, phagocytosis, and cytokine production. Additionally, immune cells also synthesize and secrete endogenous opioid peptides and participate peripheral analgesia. This chapter is structured into two sections. Part one focuses on immunoregulatory functions of central endogenous opioids; and part two describes how opioid peptide-containing immune cells participate in local analgesia.

The Roles of Endogenous Opioids in Placebo and Nocebo Effects: From Pain to Performance to Prozac

Placebo and nocebo effects have been well documented for nearly two centuries. However, research has only relatively recently begun to explicate the neurobiological underpinnings of these phenomena. Similarly, research on the broader social implications of placebo/nocebo effects, especially within healthcare delivery settings, is in a nascent stage. Biological and psychosocial outcomes of placebo/nocebo effects are of equal relevance. A common pathway for such outcomes is the endogenous opioid system. This chapter describes the history of placebo/nocebo in medicine; delineates the current state of the literature related to placebo/nocebo in relation to pain modulation; summarizes research findings related to human performance in sports and exercise; discusses the implications of placebo/nocebo effects among diverse patient populations; and describes placebo/nocebo influences in research related to psychopharmacology, including the relevance of endogenous opioids to new lines of research on antidepressant pharmacotherapies.

Untapped Potential: Real-Time Measurements of Opioid Exocytosis at Single Cells

The endogenous opioid system is commonly targeted in pain treatment, but the fundamental nature of neuropeptide release remains poorly understood due to a lack of methods for direct detection of specific opioid neuropeptides in situ. These peptides are concentrated in, and released from, large dense-core vesicles in chromaffin cells. Although catecholamine release from these neuroendocrine cells is well characterized, the direct quantification of opioid peptide exocytosis events has not previously been achieved. In this work, a planar carbon-fiber microelectrode served as a "postsynaptic" sensor for probing catecholamine and neuropeptide release dynamics via amperometric monitoring. A constant potential of 500 mV was employed for quantification of catecholamine release, and a higher potential of 1000 mV was used to drive oxidation of tyrosine, the N-terminal amino acid in the opioid neuropeptides released from chromaffin cells. By discriminating the results collected at the two potentials, the data reveal unique kinetics for these two neurochemical classes at the single-vesicle level. The amplitude of the peptidergic signals decreased with repeat stimulation, as the halfwidth of these signals simultaneously increased. By contrast, the amplitude of catecholamine release events increased with repeat stimulation, but the halfwidth of each event did not vary. The chromogranin dense core was identified as an important mechanistic handle by which separate classes of transmitter can be kinetically modulated when released from the same population of vesicles. Overall, the data provide unprecedented insight into key differences between catecholamine and opioid neuropeptide release from isolated chromaffin cells.

Modification and Delivery of Enkephalins for Pain Modulation

Chronic pain negatively affects patient's quality of life and poses a significant economic burden. First line pharmaceutical treatment of chronic pain, including NSAIDs or antidepressants, is often inefficient to reduce pain, or produces intolerable adverse effects. In such cases, opioids are frequently prescribed for their potent analgesia, but chronic opioid use is also frequently associated with debilitating side effects that may offset analgesic benefits. Nonetheless, opioids continue to be widely utilized due to the lack of effective alternative analgesics. Since their discovery in 1975, a class of endogenous opioids called enkephalins (ENKs) have been investigated for their ability to relieve pain with significantly reduced adverse effects compared to conventional opioids. Their low metabolic stability and inability to cross biological membranes, however, make ENKs ineffective analgesics. Over past decades, much effort has been invested to overcome these limitations and develop ENK-based pain therapies. This review summarizes and describes chemical modifications and ENK delivery technologies utilizing ENK conjugates, nanoparticles and ENK gene delivery approaches and discusses valid lessons, challenges, and future directions of this evolving field.

Fifty years of pain research and clinical advances: highlights and key trends

ABSTRACT

This article highlights advances in basic science preclinical pain research, clinical research, and psychological research occurring over the 50 years since the International Association for the Study of Pain was founded. It presents important findings and key trends in these 3 areas of pain science: basic science preclinical research, clinical research, and psychological research.

The influence of the opioid pentapeptide methionine-enkephalin on seasonal and FSH-induced ovarian recrudescence in the gecko Hemidactylus frenatus

Although methionine-enkephalin (M-ENK) is implicated in the regulation of reproductive functions in vertebrates, its function in reptiles is little understood. This study aims to elucidate the role of M-ENK on seasonal and follicle stimulating hormone (FSH)-induced ovarian recrudescence in the gecko Hemidactylus frenatus. In the first experiment, administration of 5 µg M-ENK did not affect germinal bed activity or follicular developmental stages I, II, and III (previtellogenic) and IV (vitellogenic), but there were no stage V (vitellogenic) follicles in the ovary. However, there was a significant decrease in the mean numbers of oogonia and primary oocytes in the germinal bed associated with the complete absence of stage IV and V follicles in 25 µg M-ENK-treated lizards in contrast to experimental controls. Furthermore, there was a significant decrease in gonadotropin-releasing hormone - immunoreactive (GnRH-ir) content in the median eminence (ME) and pars distalis (PD) of the pituitary gland and sparse labelling of hypothalamic GnRH-ir neurons in 25 µg M-ENK-treated lizards. In the second experiment, treatment with FSH during the regression phase of the ovarian cycle resulted in the appearance of stage IV and V follicles, in contrast to their absence in the initial controls and treatment controls. However, treatment with 25 µg M-ENK + FSH did not result in the appearance of these follicles, indicating the inhibitory effect of M-ENK on FSH-induced ovarian recrudescence. These findings suggest that M-ENK inhibits the germinal bed and vitellogenic follicular growth in a dose-dependent manner, possibly mediated through the suppression of GnRH release in the ME and PD. In addition, M-ENK may also act at the level of the ovary in the gecko.

The opioid peptide leucine-enkephalin disrupts seasonal and gonadotropin-induced ovarian recrudescence in the gecko Hemidactylus frenatus

The enkephalins are known to regulate many physiological functions, including reproduction in vertebrates. However, the role of leucine-enkephalin (L-ENK) in the ovarian recrudescence activity of reptiles is not known. In the present study, we studied the influence of L-ENK on seasonal and FSH-induced ovarian recrudescence during the breeding and non-breeding phases of the cycle in the tropical and subtropical gecko Hemidactylus frenatus. In the first experiment, treatment with 5 and 25 μg L-ENK resulted in a dose-dependent inhibitory effect on the hypothalamic gonadotropin-releasing hormone (GnRH) neurons and ovary, as indicated by a significantly decreased percent area of GnRH-immunoreactive (GnRH-ir) fibres in the median eminence and pars distalis of the pituitary gland, concomitant with complete absence of stage V (late vitellogenic) follicles in the ovary compared to those of experimental controls. In the second experiment, administration of FSH to lizards in the regression phase stimulated the recruitment of stage IV and V (vitellogenic) follicles in contrast to their absence in initial controls or treatment controls. However, similar treatment of FSH in combination with 25 μg L-ENK did not result in the development of stage IV or V follicles. Together, these results suggest for the first time that treatment with 5 and 25 μg L-ENK exerts a dose-dependent inhibitory effect on the hypothalamic GnRH release into the median eminence and pituitary gland, leading to the blockade of ovarian recrudescence. These results also suggest a possible direct inhibitory effect of L-ENK at the level of the ovary in the gecko.

Involvement of the Opioid Peptide Family in Cancer Progression

Peptides mediate cancer progression favoring the mitogenesis, migration, and invasion of tumor cells, promoting metastasis and anti-apoptotic mechanisms, and facilitating angiogenesis/lymphangiogenesis. Tumor cells overexpress peptide receptors, crucial targets for developing specific treatments against cancer cells using peptide receptor antagonists and promoting apoptosis in tumor cells. Opioids exert an antitumoral effect, whereas others promote tumor growth and metastasis. This review updates the findings regarding the involvement of opioid peptides (enkephalins, endorphins, and dynorphins) in cancer development. Anticancer therapeutic strategies targeting the opioid peptidergic system and the main research lines to be developed regarding the topic reviewed are suggested. There is much to investigate about opioid peptides and cancer: basic information is scarce, incomplete, or absent in many tumors. This knowledge is crucial since promising anticancer strategies could be developed alone or in combination therapies with chemotherapy/radiotherapy.

Chemical tools for the opioids

The opioids are potent and widely used pain management medicines despite also possessing severe liabilities that have fueled the opioid crisis. The pharmacological properties of the opioids primarily derive from agonism or antagonism of the opioid receptors, but additional effects may arise from specific compounds, opioid receptors, or independent targets. The study of the opioids, their receptors, and the development of remediation strategies has benefitted from derivatization of the opioids as chemical tools. While these studies have primarily focused on the opioids in the context of the opioid receptors, these chemical tools may also play a role in delineating mechanisms that are independent of the opioid receptors. In this review, we describe recent advances in the development and applications of opioid derivatives as chemical tools and highlight opportunities for the future.

Energetics and mechanisms for decomposition of cationized amino acids and peptides explored using guided ion beam tandem mass spectrometry

Fragmentation studies of cationized amino acids and small peptides as studied using guided ion beam tandem mass spectrometry (GIBMS) are reviewed. After a brief examination of the key attributes of the GIBMS approach, results for a variety of systems are examined, compared, and contrasted. Cationization of amino acids, diglycine, and triglycine with alkali cations generally leads to dissociations in which the intact biomolecule is lost. Exceptions include most lithiated species as well as a few examples for sodiated and one example for potassiated species. Like the lithiated species, cationization by protons leads to numerous dissociation channels. Results for protonated glycine, cysteine, asparagine, diglycine, and a series of tripeptides are reviewed, along with the thermodynamic consequences that can be gleaned. Finally, the important physiological process of the deamidation of asparagine (Asn) residues is explored by the comparison of five dipeptides in which the C-terminal partner (AsnXxx) is altered. The GIBMS thermochemistry is shown to correlate well with kinetic results from solution phase studies.

Methionine enkephalin suppresses lung cancer metastasis by regulating the polarization of tumor-associated macrophages and the distribution of myeloid-derived suppressor cells in the tumor microenvironment and inhibiting epithelial-mesenchymal transition

Metastasis is one of the most difficult challenges for clinical lung cancer treatment. Epithelial-mesenchymal transition (EMT) is the crucial step of tumor metastasis. Immune cells in the tumor microenvironment (TME), such as tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs), promote cancer cell EMT. In this study, we explored the effect of methionine enkephalin (MENK) on the EMT process in vitro and in vivo, and its influence on TAMs, MDSCs, and associated cytokines in vivo. The results showed that MENK suppressed growth, migration, and invasion of lung cancer cells and inhibited the EMT process by interacting with opioid growth factor receptor. MENK reduced the number of M2 macrophages and MDSC infiltration, and downregulated the expression of interleukin-10 and transforming growth factor-β1 in both primary and metastatic tumors of nude mice. The present findings suggest that MENK is a potential target for suppressing metastasis in lung cancer treatment.

Efficacy of dual enkephalinase inhibition in a preclinical migraine model is mediated by activation of peripheral delta opioid receptors

OBJECTIVE

The aim of this study was to evaluate whether elevating levels of enkephalin by inhibiting their degradation can attenuate stress-induced migraine-like behaviors in mice.

BACKGROUND

Previous studies in animals have suggested the delta opioid receptor (DOR) as a novel migraine target. The primary endogenous ligands for DOR are enkephalins and their levels can be increased by pharmacological inhibition of enkephalinases; however, it is not clear whether enkephalinase inhibition can be efficacious in preclinical migraine models through activation of DOR or whether other opioid receptors might be involved. Further, it is not clear whether opioid receptors in the central nervous system are necessary for these effects.

METHODS

This study used a model of repetitive restraint stress in mice that induces periorbital hypersensitivity and priming to the nitric oxide donor sodium nitroprusside (SNP; 0.1 mg/kg). Von Frey filaments were used to measure periorbital mechanical thresholds and grimace scores were evaluated by observing mouse facial features. Animals were treated with the dual enkephalinase inhibitor (DENKI) PL37.

RESULTS

On day two post-stress, PL37 given to mice via either intravenous injection (10 mg/kg) or oral gavage (20 mg/kg) significantly attenuated stress-induced periorbital hypersensitivity and facial grimace responses. Additionally, both intravenous (10 mg/kg) and oral gavage (20 mg/kg) of PL37 prior to SNP (0.1 mg/kg) administration on day 14 post-stress significantly reduced SNP-induced facial hypersensitivity. Injection of the DOR antagonist naltrindole (0.1 mg/kg) but not the mu-opioid receptor antagonist CTAP (1 mg/kg) prior to PL37 treatment blocked the effects. Finally, pretreatment of mice with the peripherally restricted opioid receptor antagonist naloxone methiodide (5 mg/kg) blocked the effects of PL37.

CONCLUSIONS

These data demonstrate that inhibiting enkephalinases, and thus protecting enkephalins from degradation, attenuates stress-induced migraine-like behavior via activation of peripheral DOR. Peripheral targeting of endogenous opioid signaling may be an effective therapeutic strategy for migraine.

The life and times of endogenous opioid peptides: Updated understanding of synthesis, spatiotemporal dynamics, and the clinical impact in alcohol use disorder

The opioid G-protein coupled receptors (GPCRs) strongly modulate many of the central nervous system structures that contribute to neurological and psychiatric disorders including pain, major depressive disorder, and substance use disorders. To better treat these and related diseases, it is essential to understand the signaling of their endogenous ligands. In this review, we focus on what is known and unknown about the regulation of the over two dozen endogenous peptides with high affinity for one or more of the opioid receptors. We briefly describe which peptides are produced, with a particular focus on the recently proposed possible synthesis pathways for the endomorphins. Next, we describe examples of endogenous opioid peptide expression organization in several neural circuits and how they appear to be released from specific neural compartments that vary across brain regions. We discuss current knowledge regarding the strength of neural activity required to drive endogenous opioid peptide release, clues about how far peptides diffuse from release sites, and their extracellular lifetime after release. Finally, as a translational example, we discuss the mechanisms of action of naltrexone (NTX), which is used clinically to treat alcohol use disorder. NTX is a synthetic morphine analog that non-specifically antagonizes the action of most endogenous opioid peptides developed in the 1960s and FDA approved in the 1980s. We review recent studies clarifying the precise endogenous activity that NTX prevents. Together, the works described here highlight the challenges and opportunities the complex opioid system presents as a therapeutic target.

EFFICACY AND SAFETY OF ORIGINAL DRUG BASED ON HEXAPEPTIDE SUCCINATE IN COMPLEX COVID-19 THERAPY IN ADULTS HOSPITALIZED PATIENTS

Currently, there are data that that make it possible to speak about a high clinical efficacy of the use of succinic salt of tyrosyl-D-alanyl-glycyl-phenylalanyl-leucyl-arginine (hexapeptide succinate) for the COVID-19 treatment. This article is devoted to the results of clinical trials of the original Russian drug based on it.

The aim of the study was to evaluate a clinical efficacy, safety and tolerability of intramuscular and inhalation use of hexapeptide succinate in complex therapy in comparison with standard therapy in patients with moderate COVID-19.

Materials and methods. The research was conducted from February 28, 2022 to November 22, 2022 based on 10 research centers in the Russian Federation. The study included hospitalized patients (n=312) over 18 years of age with moderate COVID-19 who had undergone a screening procedure and were randomized into 3 groups: group 1 received standard therapy in accordance with the Interim Guidelines in force at the time of the study, within 10 days; group 2 received hexapeptide succinate (Ambervin® Pulmo) intramuscularly at the dose of 1 mg once a day for 10 days; group 3 received hexapeptide succinate (Ambervin® Pulmo) 10 mg once a day by inhalation for 10 days.

Results. According to the results of the study, therapy with the drug hexapeptide succinate, both intramuscular and inhaled, provided an acceleration of recovery up to the complete absence of the disease signs in more than 80% of hospitalized COVID-19 patients. By the end of the therapy course with the drug, more than 60% of patients had met the criteria for discharge from hospital and could continue the treatment on an outpatient basis. About 70% of patients in the inhalation group and 80% in the intramuscular hexapeptide succinate injection group had concomitant diseases (hypertension – 28%, obesity – 14%), which indicates the effectiveness of this drug use in comorbid patients. The use of the drug contributed to the restoration of damaged lung tissues, normalization of oxygenation, the disappearance of shortness of breath and a decrease in the duration of the disease symptoms compared with standard therapy. As a result of a comparative analysis of adverse events in terms of their presence, severity, causal relationship with the therapy and outcome, there were no statistically significant differences between the treatment groups.

Conclusion. Thus, the results of the clinical study of the succinate hexapeptide efficacy and safety showed the feasibility of using the drug in pathogenetic therapy COVID-19 regimens.

Neurosurgical Treatment of Pain

The aim of this review is to draw attention to neurosurgical approaches for treating chronic and opioid-resistant pain. In a first chapter, an up-to-date overview of the main pathophysiological mechanisms of pain has been carried out, with special emphasis on the details in which the surgical treatment is based. In a second part, the principal indications and results of different surgical approaches are reviewed. Cordotomy, Myelotomy, DREZ lesions, Trigeminal Nucleotomy, Mesencephalotomy, and Cingulotomy are revisited. Ablative procedures have a limited role in the management of chronic non-cancer pain, but they continues to help patients with refractory cancer-related pain. Another ablation lesion has been named and excluded, due to lack of current relevance. Peripheral Nerve, Spine Cord, and the principal possibilities of Deep Brain and Motor Cortex Stimulation are also revisited. Regarding electrical neuromodulation, patient selection remains a challenge.

Release of an anti-anxiety peptide in casein hydrolysate with Aspergillus oryzae protease

Food protein-derived peptides with agonistic effects on receptors have great potential for treating anxiety, hypertension, and stress. In the present study, opioid peptides with agonistic activities for δ-receptor-expressing HEK293 cells were screened from casein hydrolysates prepared with five types of food grade proteolytic enzymes, among which casein hydrolysate with Aspergillus oryzae protease ASD showed the highest opioid activity. Eluted fractions showing potent opioid activity were further purified for active peptides by reverse phase-HPLC. The peptide in the active fraction was identified as YPFPGPIPNS, a member of β-casomorphin (CM-10) (β-casein 60-69). Various CM-10 derivative peptides were synthesized and their characteristic features for specificities towards δ- and μ-receptors were determined. Peptides 5 to 12 amino acids long showed relatively higher opioid activities for δ- and μ-receptors. CM-10 was docked into the optimized δ-receptor model. The CDOCKER energies of the CM-10 derivatives were consistent with their opioid activities. In the elevated plus-maze study, CM-10 showed a significant anti-anxiety effect in BALB/c mice at a dose of 10 mg per kg body weight when administered orally, but not via intravenous injection. Furthermore, intravital imaging revealed that Ca²⁺ signaling was induced in the small intestinal villi of a Yellow Cameleon 3.60 (YC3.60)-expressing mouse upon injection with CM-10. However, this decreased in the presence of δ- or μ-receptor antagonists. These results suggest that the opioid peptide CM-10 prepared from casein with ASD has an anti-anxiety effect through interaction with gut δ- and/or μ-opioid receptors in the mouse gut.

Opioidergic pathways and kisspeptin in the regulation of female reproduction in mammals

Endogenous opioid peptides have attracted attention as critical neuropeptides in the central mechanism regulating female reproduction ever since the discovery that arcuate dynorphin neurons that coexpress kisspeptin and neurokinin B (NKB), which are also known as kisspeptin/neurokinin B/dynorphin (KNDy) neurons, play a role as a master regulator of pulsatile gonadotropin-releasing hormone (GnRH) release in mammals. In this study, we first focus on the role of dynorphin released by KNDy neurons in the GnRH pulse generation. Second, we provide a historical overview of studies on endogenous opioid peptides. Third, we discuss how endogenous opioid peptides modulate tonic GnRH/gonadotropin release in female mammals as a mediator of inhibitory internal and external cues, such as ovarian steroids, nutritional status, or stress, on reproduction. Then, we discuss the role of endogenous opioid peptides in GnRH surge generation in female mammals.

The Clash of Two Epidemics: the Relationship Between Opioids and Glucose Metabolism

PURPOSE OF REVIEW

We are currently in the midst of a global opioid epidemic. Opioids affect many physiological processes, but one side effect that is not often taken into consideration is the opioid-induced alteration in blood glucose levels.

RECENT FINDINGS

This review shows that the vast majority of studies report that opioid stimulation increases blood glucose levels. In addition, plasma levels of the endogenous opioid β-endorphin rise in response to low blood glucose. In contrast, in hyperglycaemic baseline conditions such as in patients with type 2 diabetes mellitus (T2DM), opioid stimulation lowers blood glucose levels. Furthermore, obesity itself alters sensitivity to opioids, changes opioid receptor expression and increases plasma β-endorphin levels. Thus, opioid stimulation can have various side effects on glycaemia that should be taken into consideration upon prescribing opioid-based medication, and more research is needed to unravel the interaction between obesity, glycaemia and opioid use.

Neuropeptide System Regulation of Prefrontal Cortex Circuitry: Implications for Neuropsychiatric Disorders

Neuropeptides, a diverse class of signaling molecules in the nervous system, modulate various biological effects including membrane excitability, synaptic transmission and synaptogenesis, gene expression, and glial cell architecture and function. To date, most of what is known about neuropeptide action is limited to subcortical brain structures and tissue outside of the central nervous system. Thus, there is a knowledge gap in our understanding of neuropeptide function within cortical circuits. In this review, we provide a comprehensive overview of various families of neuropeptides and their cognate receptors that are expressed in the prefrontal cortex (PFC). Specifically, we highlight dynorphin, enkephalin, corticotropin-releasing factor, cholecystokinin, somatostatin, neuropeptide Y, and vasoactive intestinal peptide. Further, we review the implication of neuropeptide signaling in prefrontal cortical circuit function and use as potential therapeutic targets. Together, this review summarizes established knowledge and highlights unknowns of neuropeptide modulation of neural function underlying various biological effects while offering insights for future research. An increased emphasis in this area of study is necessary to elucidate basic principles of the diverse signaling molecules used in cortical circuits beyond fast excitatory and inhibitory transmitters as well as consider components of neuropeptide action in the PFC as a potential therapeutic target for neurological disorders. Therefore, this review not only sheds light on the importance of cortical neuropeptide studies, but also provides a comprehensive overview of neuropeptide action in the PFC to serve as a roadmap for future studies in this field.

Methionine enkephalin inhibited cervical carcinoma via apoptosis promotion and reduction of myeloid derived suppressor cell infiltrated in tumor

Immunotherapy for cervical carcinoma is becoming increasingly important recently. In these studies methionine enkephalin (menk) is shown to inhibit cervical tumor cell proliferation in vitro in association with an increase in the expression of apoptosis markers and mediators, including an increase in fas, caspase 8, and caspase 3 expression and intrinsic expression of the signaling pathway mediator bax. In vivo, tumor growth was restrained in mice xenotransplant model with typical pathological features of apoptosis. Furthermore, myeloid derived suppressor cells (MDSCs) had a significant decrease in circulation and in tumor site. In brief, these findings showed menk could inhibit tumor growth in vitro and in vivo, providing direction of further research and clinical application prospect.

Challenges and new opportunities for detecting endogenous opioid peptides in reward

The endogenous opioid peptide system, comprised of enkephalins, endorphins, dynorphins, and nociceptin, is a highly complex neurobiological system. Opioid peptides are derived from four precursor molecules and undergo several processing events yielding over 20 unique opioid peptides. This diversity together with low in vivo concentration and complex processing and release dynamics has challenged research into each peptide's unique function. Despite the subsequent challenges in detecting and quantifying opioid peptides in vivo, researchers have pioneered several techniques to directly or indirectly assay the roles of opioid peptides during behavioral manipulations. In this review, we describe the limitations of the traditional techniques used to study the role of endogenous opioid peptides in food and drug reward and bring focus to the wealth of new techniques to measure endogenous opioid peptides in reward processing.

Functional Characterization and Molecular Marker Development of the Proenkephalin as Biomarker of Food Addiction in Food Habit Domestication of Mandarin Fish (Siniperca Chuatsi)

Proenkephalin (PENK), as the precursor of endogenous opioid enkephalin (ENK), is widely present in the nervous system and plays an important role in animal food addiction and rewarding behavior. In our study, we intend to study the functional characterization and molecular marker development of the penk gene related to food habit domestication of mandarin fish. We found that the penk gene of mandarin fish had three types of endogenous opioid peptide sequences. Compared with other tissues, penk mRNA was highly expressed in the whole brain. Intracerebroventricular (ICV) injection of lysine or methionine significantly increased the expression of penk mRNA. The expression of penk mRNA in the brain of mandarin fish that could be easily domesticated from eating live prey fish to artificial diets was significantly higher than those that could not. After feeding with high-carbohydrate artificial diets, the expression of penk mRNA showed no significant difference between mandarin fish with hypophagia and those that still ate normally. A total of four single nucleotide polymorphisms (SNP) loci related to easy domestication toward eating artificial diets were screened from the mandarin fish population. Additionally, the TT genotype at one of the loci was significantly correlated with the food habit domestication of mandarin fish.

Is Chronic Pain a Disease?

It was not until the twentieth century that pain was considered a disease. Before that it was managed medically as a symptom. The motivations for declaring chronic pain a disease, whether of the body or of the brain, include increasing its legitimacy as clinical problem and research focus worthy of attention from healthcare and research organizations alike. But 1 problem with disease concepts is that having a disease favors medical solutions and tends to reduce patient participation. We argue that chronic pain, particularly chronic primary pain (recently designated a first tier pain diagnosis in International Diagnostic Codes 11), is a learned state that is not intransigent even if it has biological correlates. Chronic pain is sometimes a symptom, and may sometimes be its own disease. But here we question the value of a disease focus for much of chronic pain for which patient involvement is essential, and which may need a much broader societal approach than is suggested by the disease designation. PERSPECTIVE: This article examines whether designating chronic pain a disease of the body or brain is helpful or harmful to patients. Can the disease designation help advance treatment, and is it needed to achieve future therapeutic breakthrough? Or does it make patients over-reliant on medical intervention and reduce their engagement in the process of recovery?

Psycho-Neuro-Endocrine-Immunological Basis of the Placebo Effect: Potential Applications beyond Pain Therapy

The placebo effect can be defined as the improvement of symptoms in a patient after the administration of an innocuous substance in a context that induces expectations regarding its effects. During recent years, it has been discovered that the placebo response not only has neurobiological functions on analgesia, but that it is also capable of generating effects on the immune and endocrine systems. The possible integration of changes in different systems of the organism could favor the well-being of the individuals and go hand in hand with conventional treatment for multiple diseases. In this sense, classic conditioning and setting expectations stand out as psychological mechanisms implicated in the placebo effect. Recent advances in neuroimaging studies suggest a relationship between the placebo response and the opioid, cannabinoid, and monoaminergic systems. Likewise, a possible immune response conditioned by the placebo effect has been reported. There is evidence of immune suppression conditioned through the insular cortex and the amygdala, with noradrenalin as the responsible neurotransmitter. Finally, a conditioned response in the secretion of different hormones has been determined in different studies; however, the molecular mechanisms involved are not entirely known. Beyond studies about its mechanism of action, the placebo effect has proved to be useful in the clinical setting with promising results in the management of neurological, psychiatric, and immunologic disorders. However, more research is needed to better characterize its potential use. This review integrates current knowledge about the psycho-neuro-endocrine-immune basis of the placebo effect and its possible clinical applications.

Endogenous Opioids and Their Role in Stem Cell Biology and Tissue Rescue

Opioids are considered the oldest drugs known by humans and have been used for sedation and pain relief for several centuries. Nowadays, endogenous opioid peptides are divided into four families: enkephalins, dynorphins, endorphins, and nociceptin/orphanin FQ. They exert their action through the opioid receptors (ORs), transmembrane proteins belonging to the super-family of G-protein-coupled receptors, and are expressed throughout the body; the receptors are the δ opioid receptor (DOR), μ opioid receptor (MOR), κ opioid receptor (KOR), and nociceptin/orphanin FQ receptor (NOP). Endogenous opioids are mainly studied in the central nervous system (CNS), but their role has been investigated in other organs, both in physiological and in pathological conditions. Here, we revise their role in stem cell (SC) biology, since these cells are a subject of great scientific interest due to their peculiar features and their involvement in cell-based therapies in regenerative medicine. In particular, we focus on endogenous opioids’ ability to modulate SC proliferation, stress response (to oxidative stress, starvation, or damage following ischemia–reperfusion), and differentiation towards different lineages, such as neurogenesis, vasculogenesis, and cardiogenesis.

The Role of the Endogenous Opioid System in the Vocal Behavior of Songbirds and Its Possible Role in Vocal Learning

The opioid system in the brain is responsible for processing affective states such as pain, pleasure, and reward. It consists of three main receptors, mu- (μ-ORs), delta- (δ-ORs), and kappa- (κ-ORs), and their ligands – the endogenous opioid peptides. Despite their involvement in the reward pathway, and a signaling mechanism operating in synergy with the dopaminergic system, fewer reports focus on the role of these receptors in higher cognitive processes. Whereas research on opioids is predominated by studies on their addictive properties and role in pain pathways, recent studies suggest that these receptors may be involved in learning. Rodents deficient in δ-ORs were poor at recognizing the location of novel objects in their surroundings. Furthermore, in chicken, learning to avoid beads coated with a bitter chemical from those without the coating was modulated by δ-ORs. Similarly, μ-ORs facilitate long term potentiation in hippocampal CA3 neurons in mammals, thereby having a positive impact on spatial learning. Whereas these studies have explored the role of opioid receptors on learning using reward/punishment-based paradigms, the role of these receptors in natural learning processes, such as vocal learning, are yet unexplored. In this review, we explore studies that have established the expression pattern of these receptors in different brain regions of birds, with an emphasis on songbirds which are model systems for vocal learning. We also review the role of opioid receptors in modulating the cognitive processes associated with vocalizations in birds. Finally, we discuss the role of these receptors in regulating the motivation to vocalize, and a possible role in modulating vocal learning.

Contributions of the International Narcotics Research Conference to Opioid Research Over the Past 50 years

The International Narcotics Research Conference (INRC), founded in 1969, has been a successful forum for research into the actions of opiates, with an annual conference since 1971. Every year, scientists from around the world have congregated to present the latest data on novel opiates, opiate receptors and endogenous ligands, mechanisms of analgesic activity and unwanted side effects, etc. All the important discoveries in the opiate field were discussed, often first, at the annual INRC meeting. With an apology to important events and participants not discussed, this review presents a short history of INRC with a discussion of groundbreaking discoveries in the opiate field and the researchers who presented from the first meeting up to the present.

Asymmetric Interaction of Neuropeptidase Activities between Cortico-Limbic Structures, Plasma and Cardiovascular Function after Unilateral Dopamine Depletions of the Nigrostriatal System

In emotional processing, dopamine (DA) plays an essential role, and its deterioration involves important consequences. Under physiological conditions, dopamine exhibits brain asymmetry and coexists with various neuropeptides that can coordinate the processing of brain functions. Brain asymmetry can extend into a broader concept of asymmetric neurovisceral integration, including behavior. The study of the activity of neuropeptide regulatory enzymes (neuropeptidases, NPs) is illustrative. We have observed that the left and right brain areas interact intra- and inter-hemispherically, as well as with peripheral tissues or with physiological parameters such as blood pressure or with behaviors such as turning preference. To obtain data that reflect this integrative behavior, we simultaneously analyzed the impact of left or right brain DA depletion on the activity of various NPs in corticolimbic regions of the left and right hemispheres, such as the medial prefrontal cortex, amygdala and hippocampus, as well as on the plasma activity of the same aminopeptidase activities (APs) and on systolic blood pressure (SBP). Intra- and inter-hemispheric interactions as well as the interactions of NPs from the left or right hemispheres were analyzed with the same plasma APs and the SBP obtained from sham and from left or right lesioned rats. The results demonstrate a complex profile depending on the hemisphere considered. They definitively confirm an asymmetric neurovisceral integration and reveal a higher level of inter-hemispheric corticolimbic interactions including with SBP after left dopamine depletion.

Safe use of opioids

Background: Opioids are effective analgesics for cancer pain and refractory non-cancer pain. Although they are essential medication, problematic issues on aberrant behavior and adverse events have rapidly emerged as social problems in Korea. This study aimed to describe the mechanisms, efficacy, and adverse events, especially how to deal with opioid dependency.Current Concepts: Opioid-induced aberrant behavior includes physical and psychological dependences (addiction), abuse, and diversion (giving prescribed opioids to another person). Most physicians are unfamiliar with how to handle patients presenting these problematic issues. Physical and psychological dependences develop through different pathophysiologic mechanisms, i.e., noradrenergic and dopaminergic pathways, respectively. Motivational enhancement therapy, psychosocial support, substitution therapy with buprenorphine, and adjunctive medications, including alpha-2 adrenergic agonist, antidepressants, and non-steroidal antiinflammatory drugs, are the mainstay of treatment for opioid dependency. Constipation, nausea/vomiting, drowsiness/sedation, delirium, itching sensation, voiding difficulty, dry mouth, opioid-induced hyperalgesia, and respiratory depression are well-known physical side effects of opioid consumption.Discussion and Conclusion: Research on the development history, epidemiology of opioid dependency, and its treatment are warranted to avoid an opioid crisis in Korea. Above all, thorough knowledge for physicians and patients is urgently needed.

Fundamentals of the Dynorphins/Kappa Opioid Receptor System: From Distribution to Signaling and Function

This chapter provides a general introduction to the dynorphins (DYNs)/kappa opioid receptor (KOR) system, including DYN peptides, neuroanatomy of the DYNs/KOR system, cellular signaling, and in vivo behavioral effects of KOR activation and inhibition. It is intended to serve as a primer for the book and to provide a basic background for the chapters in the book.

Engaging endogenous opioid circuits in pain affective processes

The pervasive use of opioid compounds for pain relief is rooted in their utility as one of the most effective therapeutic strategies for providing analgesia. While the detrimental side effects of these compounds have significantly contributed to the current opioid epidemic, opioids still provide millions of patients with reprieve from the relentless and agonizing experience of pain. The human experience of pain has long recognized the perceived unpleasantness entangled with a unique sensation that is immediate and identifiable from the first-person subjective vantage point as "painful." From this phenomenological perspective, how is it that opioids interfere with pain perception? Evidence from human lesion, neuroimaging, and preclinical functional neuroanatomy approaches is sculpting the view that opioids predominately alleviate the affective or inferential appraisal of nociceptive neural information. Thus, opioids weaken pain-associated unpleasantness rather than modulate perceived sensory qualities. Here, we discuss the historical theories of pain to demonstrate how modern neuroscience is revisiting these ideas to deconstruct the brain mechanisms driving the emergence of aversive pain perceptions. We further detail how targeting opioidergic signaling within affective or emotional brain circuits remains a strong avenue for developing targeted pharmacological and gene-therapy analgesic treatments that might reduce the dependence on current clinical opioid options.

Brain Asymmetry: Towards an Asymmetrical Neurovisceral Integration

Despite the ancestral evidence of an asymmetry in motor predominance, going through the inspiring discoveries of Broca and Wernicke on the localization of language processing, continuing with the subsequent noise coinciding with the study of brain function in commissurotomized patients—and the subsequent avalanche of data on the asymmetric distribution of multiple types of neurotransmitters in physiological and pathological conditions—even today, the functional significance of brain asymmetry is still unknown. Currently, multiple evidence suggests that functional asymmetries must have a neurochemical substrate and that brain asymmetry is not a static concept but rather a dynamic one, with intra- and inter-hemispheric interactions between its various processes, and that it is modifiable depending on changing endogenous and environmental conditions. Furthermore, based on the concept of neurovisceral integration in the overall functioning of an organism, some evidence has emerged suggesting that this integration could be organized asymmetrically, using the autonomic nervous system as a bidirectional communication pathway, whose performance would also be asymmetric. However, the functional significance of this distribution, as well as the evolutionary advantage of an asymmetric nervous organization, is still unknown.

The Opioid Receptor Antagonist Naloxone Enhances First-Order Fear Conditioning, Second-Order Fear Conditioning and Sensory Preconditioning in Rats

The opioid receptor antagonist naloxone enhances Pavlovian fear conditioning when rats are exposed to pairings of an initially neutral stimulus, such as a tone, and a painful foot shock unconditioned stimulus (US; so-called first-order fear conditioning; Pavlov, 1927). The present series of experiments examined whether naloxone has the same effect when conditioning occurs in the absence of US exposure. In Experiments 1a and 1b, rats were exposed to tone-shock pairings in stage 1 (one trial per day for 4 days) and then to pairings of an initially neutral light with the already conditioned tone in stage 2 (one trial per day for 4 days). Experiment 1a confirmed that this training results in second-order fear of the light; and Experiment 1b showed that naloxone enhances this conditioning: rats injected with naloxone in stage 2 froze more than vehicle-injected controls when tested with the light alone (drug-free). In Experiments 2a and 2b, rats were exposed to light-tone pairings in stage 1 (one trial per day for 4 days) and then to tone-shock pairings in stage 2 (one trial per day for 2 days). Experiment 2a confirmed that this training results in sensory preconditioned fear of the light; and Experiment 2b showed that naloxone enhances sensory preconditioning when injected prior to each of the light-tone pairings: rats injected with naloxone in stage 1 froze more than vehicle-injected controls when tested with the light alone (drug-free). These results were taken to mean that naloxone enhances fear conditioning independently of its effect on US processing; and more generally, that opioids regulate the error-correction mechanisms that underlie associative formation.

Taxonomy of Mitochondrial Cytochrome B Proteins of the Same Amino Acid Sequence Length

Prior to this study, we discovered a protein characterized by many different amino acid sequences with the same number of amino acid residues. This turned out to be a unique cytochrome b, in which 1048 molecules out of 1689 contain 379 amino acid residues. A detailed study of the occurrence of this protein in living organisms at different taxonomic levels (from biological domains to biological orders of animals) has been carried out in the work presented here. We found that the main part of all b cytochromes is present in eukaryotes (99.2%), in biological kingdoms (95.9% in animals), in biological phylums (97.5% in chordates), and in biological classes (79.7% in mammals). Withal, this protein, containing 379 amino acid residues and characterized by many different amino acid sequences, is found only in eukaryotes (100%), only in animals (100%) and mainly in mammals (81.1%). Thus, a representative that has cytochrome b with a corresponding number of amino acid residues has not yet been identified among archaea and prokaryotes, while it is common in representatives of different biological types, classes, and orders of animals. It is believed that the structural diversity of a given protein within the same length and its one function of participation in the process of electron transfer relate to the physicochemical features of the extra- and intramembrane fragments of the polypeptide chain of this protein.

Alternative Pre-mRNA Splicing of the Mu Opioid Receptor Gene, OPRM1: Insight into Complex Mu Opioid Actions

Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating multiple splice variants or isoforms via a variety of alternative splicing events. These OPRM1 splice variants can be categorized into three major types based on the receptor structure: (1) full-length 7 transmembrane (TM) C-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Increasing evidence suggests that these OPRM1 splice variants are pharmacologically important in mediating the distinct actions of various mu opioids. More importantly, the OPRM1 variants can be targeted for development of novel opioid analgesics that are potent against multiple types of pain, but devoid of many side-effects associated with traditional opiates. In this review, we provide an overview of OPRM1 alternative splicing and its functional relevance in opioid pharmacology.