In Vitro and In Vivo Pharmacological Profiles of LENART01, a Dermorphin-Ranatensin Hybrid Peptide.

Diverse chemical and pharmacological strategies are currently being explored to minimize the unwanted side effects of currently used opioid analgesics while achieving effective pain relief. The use of multitarget ligands with activity at more than one receptor represents a promising therapeutic approach. We recently reported a bifunctional peptide-based hybrid LENART01 combining dermorphin and ranatensin pharmacophores, which displays activity to the mu-opioid receptor (MOR) and dopamine D2 receptor (D2R) in rat brains and spinal cords. In this study, we investigated the in vitro binding and functional activities to the human MOR and the in vivo pharmacology of LENART01 in mice after subcutaneous administration. In vitro binding assays showed LENART01 to bind and be selective to the human MOR over the other opioid receptor subtypes and delta, kappa and nociceptin receptors. In the [35S]GTPγS binding assay, LENART01 acted as a potent and full agonist to the human MOR. In mice, LENART01 produced dose-dependent antinociceptive effects in formalin-induced inflammatory pain, with increased potency than morphine. Antinociceptive effects were reversed by naloxone, indicating MOR activation in vivo. Behavioral studies also demonstrated LENART01's properties to induce less adverse effects without locomotor dysfunction and withdrawal syndrome compared to conventional opioid analgesics, such as morphine. LENART01 is the first peptide-based MOR-D2R ligand known to date and the first dual MOR-dopamine D2R ligand for which in vivo pharmacology is reported with antinociceptive efficacy and reduced opioid-related side effects. Our current findings may pave the way to new pain therapeutics with limited side effects in acute and chronic use.

Genetic background and sex influence somatosensory sensitivity and oxycodone analgesia in the Hybrid Rat Diversity Panel.

Opioid use disorder (OUD) is an ongoing public health concern in the United States, and relatively little work has addressed how genetic background contributes to OUD. Understanding the genetic contributions to oxycodone-induced analgesia could provide insight into the early stages of OUD development. Here, we present findings from a behavioral phenotyping protocol using several inbred strains from the Hybrid Rat Diversity Panel. Our behavioral protocol included a modified "up-down" von Frey procedure to measure inherent strain differences in the sensitivity to a mechanical stimulus on the hindpaw. We also performed the tail immersion assay, which measures the latency to display tail withdrawal in response to a hot water bath. Initial withdrawal thresholds were taken in drug-naïve animals to record baseline thermal sensitivity across the strains. Oxycodone-induced analgesia was measured after administration of oxycodone over the course of 2 h. Both mechanical and thermal sensitivity are shaped by genetic factors and display moderate heritability (h2 = 0.23-0.40). All strains displayed oxycodone-induced analgesia that peaked at 15-30 min and returned to baseline by 2 h. There were significant differences between the strains in the magnitude and duration of their analgesic response to oxycodone, although the heritability estimates were quite modest (h2 = 0.10-0.15). These data demonstrate that genetic background confers differences in mechanical sensitivity, thermal sensitivity, and oxycodone-induced analgesia.

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.

The Role of Opioid Receptor Antagonists in Regulation of Blood Pressure and T-Cell Activation in Mice Selected for High Analgesia Induced by Swim Stress.

Opioid peptides and their G protein-coupled receptors are important regulators within the cardiovascular system, implicated in the modulation of both heart and vascular functions. It is known that naloxone-an opioid antagonist-may exert a hypertensive effect. Recent experimental and clinical evidence supports the important role of inflammatory mechanisms in hypertension. Since opioids may play a role in the regulation of both blood pressure and immune response, we studied these two processes in our model. We aimed to evaluate the effect of selective and non-selective opioid receptor antagonists on blood pressure and T-cell activation in a mouse model of high swim stress-induced analgesia. Blood pressure was measured before and during the infusion of opioid receptor antagonists using a non-invasive tail-cuff measurement system. To assess the activation of T-cells, flow cytometry was used. We discovered that the non-selective antagonism of the opioid system by naloxone caused a significant elevation of blood pressure. The selective antagonism of µ and κ but not δ opioid receptors significantly increased systolic blood pressure. Subsequently, a brief characterization of T-cell subsets was performed. We found that the blockade of µ and δ receptors is associated with the increased expression of CD69 on CD4 T-cells. Moreover, we observed an increase in the central memory CD4 and central memory CD8 T-cell populations after the δ opioid receptor blockade. The antagonism of the µ opioid receptor increased the CD8 effector and central memory T-cell populations.

Inhibition of spinal BRD4 alleviates pyroptosis and M1 microglia polarization via STING-IRF3 pathway in morphine-tolerant rats.

BACKGROUND: Morphine tolerance has been a challenging medical issue. Neuroinflammation is considered as a critical mechanism for the development of morphine tolerance. Bromodomain-containing protein 4 (BRD4), a key regulator in cell damage and inflammation, participates in the development of chronic pain. However, whether BRD4 is involved in morphine tolerance and the underlying mechanisms remain unknown. METHODS: The morphine-tolerant rat model was established by intrathecal administration of morphine twice daily for 7 days. Behavior test was assessed by a tail-flick latency test. The roles of BRD4, pyroptosis, microglia polarization and related signaling pathways in morphine tolerance were elucidated by Western blot, real-time quantitative polymerase chain reaction, and immunofluorescence. RESULTS: Repeated morphine administration upregulated BRD4 level, induced pyroptosis, and promoted microglia M1-polarization in spinal cord, accompanied by the release of proinflammatory cytokines, such as TNF-α and IL-1ß. JQ-1, a BRD4 antagonist, alleviated the development of morphine tolerance, diminished pyroptosis and induced the switch of microglia from M1 to M2 phenotype. Mechanistically, stimulator of interferon gene (STING)- interferon regulatory factor 3 (IRF3) pathway was activated and the protective effect of JQ-1 against morphine tolerance was at least partially mediated by inhibition of STING-IRF3 pathway. CONCLUSION: This study demonstrated for the first time that spinal BRD4 contributes to pyroptosis and switch of microglia polarization via STING-IRF3 signaling pathway during the development of morphine tolerance, which extend the understanding of the neuroinflammation mechanism of morphine tolerance and provide an alternative strategy for the precaution against of this medical condition.

The impact of chronic fentanyl administration on the cerebral cortex in mice: Molecular and histological effects.

PURPOSE: Fentanyl, a fully synthetic opioid, is widely used for severe pain management and has a huge abuse potential for its psychostimulant effects. Unlike other opioids, the neurotoxic effects of chronic fentanyl administration are still unclear. In particular, little is known about its effect on the cerebral cortex. The current study aims to test the chronic toxicity of fentanyl in the mice model. METHODS: Adult male Balb/c mice were chronically treated with low (0.05 mg/kg, i.p) and high (0.1 mg/kg, i.p) doses of fentanyl for 5 consecutive weeks, and various neurotoxic parameters, including apoptosis, oxidative stress, and neuroinflammatory response were assessed in the cortex. Potential histological as well as neurochemical changes were also evaluated. RESULTS: The results of this study show that chronic fentanyl administration induced intense levels of apoptosis, oxidative stress, and neuroinflammation in the cerebral cortex. These findings were found to be correlated with histopathological characteristics of neural degeneration and white matter injury. Moreover, fentanyl administration was found to reduce the expression of both NMDA receptor subunits and dopamine receptors and elevate the level of epidermal growth factor (EGF). CONCLUSION: Fentanyl administration induced neurotoxic effects in the mouse cerebral cortex that could be primarily mediated by the evoked oxidative-inflammatory response. The altered expression of NMDA receptors, dopamine receptors, and EGF suggests the pernicious effects of fentanyl addiction that may end in the development of toxic psychosis.

Presynaptic inhibition of excitatory synaptic transmission from the calcitonin gene-related peptide-containing parabrachial neurons to the central amygdala in mice - unexpected influence of systemic inflammation thereon.

The monosynaptic connection from the lateral parabrachial nucleus (LPB) to the central amygdala (CeA) serves as a fundamental pathway for transmitting nociceptive signals to the brain. The LPB receives nociceptive information from the dorsal horn and spinal trigeminal nucleus and sends it to the "nociceptive" CeA, which modulates pain-associated emotions and nociceptive sensitivity. To elucidate the role of densely expressed mu-opioid receptors (MORs) within this pathway, we investigated the effects of exogenously applied opioids on LPB-CeA synaptic transmission, employing optogenetics in mice expressing channelrhodopsin-2 in LPB neurons with calcitonin gene-related peptide (CGRP). A MOR agonist ([D-Ala2,N-Me-Phe4,Glycinol5]-enkephalin, DAMGO) significantly reduced the amplitude of light-evoked excitatory postsynaptic currents (leEPSCs), in a manner negatively correlated with an increase in the paired-pulse ratio. An antagonist of MORs significantly attenuated these effects. Notably, this antagonist significantly increased leEPSC amplitude when applied alone, an effect further amplified in mice subjected to lipopolysaccharide injection 2 h before brain isolation, yet not observed at the 24-h mark. We conclude that opioids could shut off the ascending nociceptive signal at the LPB-CeA synapse through presynaptic mechanisms. Moreover, this gating process might be modulated by endogenous opioids, and the innate immune system influences this modulation.

Pharmacologic Characterization of Substituted Nitazenes at µ, κ, and Δ Opioid Receptors Suggests High Potential for Toxicity.

The benzimidazole opioids (substituted nitazenes) are highly potent µ opiod receptor (MOR) agonists with heroin- or fentanyl-like effects. These compounds have caused hospitalizations and fatal overdoses. We characterized the in vitro pharmacology and structure-activity relationships of 19 nitazenes with substitutions at three positions of the benzimidazole core. Affinities were assessed using agonist radioligand binding assays at human µ, κ, and Δ opioid receptors (MOR, KOR, and DOR, respectively) heterologously expressed in CHO cells. Notably, for MOR binding, nine substituted nitazenes had significantly higher affinities than fentanyl including N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, and N-desethyl isotonitazene; 13 had subnanomolar affinities. Only metodesnitazene and flunitazene had significantly lower affinities than fentanyl. Affinities for the substituted nitazenes at KOR and DOR relative to MOR were 46- to 2580-fold and 180- to 1280-fold lower, respectively. Functional activities were assessed using [35S]GTPγS binding assays. Four nitazenes had subnanomolar potencies at MOR: N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, N-pyrrilidino protonitazene and N-desethyl isotonitazene. Ten substituted nitazenes had significantly higher potencies than fentanyl. All tested nitazenes were full MOR agonists. Potencies at KOR and DOR relative to MOR were 7.3- to 7920-fold and 24- to 9400-fold lower, respectively. Thus, many of these compounds are high affinity/high potency MOR agonists with elevated potential to elicit toxicity and overdose at low doses. SIGNIFICANCE STATEMENT: Substituted nitazenes are a growing public health threat. Although the 19 nitazenes tested vary in their opioid receptor pharmacology, a number are very high affinity, high potency, and high efficacy compounds- higher than fentanyl. Their pharmacology suggests high potential for harm.

Evaluation of the analgesic effects of diclofenac as a premedication drug in dogs undergoing ovariohysterectomy.

Pre-emptive analgesia consists of administering drugs such as opioids and nonsteroid anti-inflammatory drugs. This study aims to evaluate the intraoperative antinociceptive effects of diclofenac administered alone in premedication or combined with morphine along with its potential influence on recovery of dogs undergoing ovariohysterectomy. A total of 34 dogs (ASA I or II) admitted for ovariohysterectomy were randomly allocated into three groups according to the drugs given in premedication: Diclofenac (D) (n = 11), Morphine (M) (n = 13) and Diclofenac-Morphine (DM) (n = 10) groups. Induction and maintenance of anesthesia were standardized in all dogs. To assess intraoperative nociception, the heart rate (HR) and mean arterial pressure (MAP) were recorded during the surgery and at predefined time points: St (steady-state), Cut (cutaneous incision), P1 (first ovarian manipulation), P2 (second ovarian manipulation) and Cerv (cervical manipulation). The dynamic variation of HR (ΔHR) and MAP (ΔMAP) over 2 min was calculated at each time point. After extubation, early quality of recovery was assessed. Compared to St, a significant increase in HR and MAP at P1, P2 and Cerv was shown in all groups. MAP in the M group was lower at St than in the other groups. The dynamic variation of HR (ΔHR) and MAP (ΔMAP) was significantly less important at P2 and Cerv compared to P1 only in the DM group. Also, a better quality of recovery was shown in the D group compared to the M and DM groups. Diclofenac may be considered a suitable premedication drug and a part of a multimodal anesthetic approach in dogs.

Food preference-based screening method for identification of effectors of substance use disorders using Caenorhabditis elegans.

Substance use disorder (SUD) affects over 48 million Americans aged 12 and over. Thus, identifying novel chemicals contributing to SUD will be critical for developing efficient prevention and mitigation strategies. Considering the complexity of the actions and effects of these substances on human behavior, a high-throughput platform using a living organism is ideal. We developed a quick and easy screening assay using Caenorhabditis elegans. C. elegans prefers high-quality food (Escherichia coli HB101) over low-quality food (Bacillus megaterium), with a food preference index of approximately 0.2, defined as the difference in the number of worms at E. coli HB101 and B. megaterium over the total worm number. The food preference index was significantly increased by loperamide, a µ-opioid receptor (MOPR) agonist, and decreased by naloxone, a MOPR antagonist. These changes depended on npr-17, a C. elegans homolog of opioid receptors. In addition, the food preference index was significantly increased by arachidonyl-2'-chloroethylamide, a cannabinoid 1 receptor (CB1R) agonist, and decreased by rimonabant, a CB1R inverse agonist. These changes depended on npr-19, a homolog of CB1R. These results suggest that the conserved opioid and endocannabinoid systems modulate the food preference behaviors of C. elegans. Finally, the humanoid C. elegans strains where npr-17 was replaced with human MOPR and where npr-19 was replaced with human CB1R phenocopied the changes in food preference by the drug treatment. Together, the current results show that this method can be used to rapidly screen the potential effectors of MOPR and CB1R to yield results highly translatable to humans.

Guanidine-to-piperidine switch affords high affinity small molecule NPFF ligands with preference for NPFF1-R and NPFF2-R subtypes.

The Neuropeptide FF (NPFF) receptor system is known to modulate opioid actions and has been shown to mediate opioid-induced hyperalgesia and tolerance. The lack of subtype selective small molecule compounds has hampered further exploration of the pharmacology of this receptor system. The vast majority of available NPFF ligands possess a highly basic guanidine group, including our lead small molecule, MES304. Despite providing strong receptor binding, the guanidine group presents a potential pharmacokinetic liability for in vivo pharmacological tool development. Through structure-activity relationship exploration, we were able to modify our lead molecule MES304 to arrive at guanidine-free NPFF ligands. The novel piperidine analogues 8b and 16a are among the few non-guanidine based NPFF ligands known in literature. Both compounds displayed nanomolar NPFF-R binding affinity approaching that of the parent molecule. Moreover, while MES304 was non-subtype selective, these two analogues presented new starting points for subtype selective scaffolds, whereby 8b displayed a 15-fold preference for NPFF1-R, and 16a demonstrated an 8-fold preference for NPFF2-R. Both analogues showed no agonist activity on either receptor subtype in the in vitro functional activity assay, while 8b displayed antagonistic properties at NPFF1-R. The calculated physicochemical properties of 8b and 16a were also shown to be more favorable for in vivo tool design. These results indicate the possibility of developing potent, subtype selective NPFF ligands devoid of a guanidine functionality.

Roles of lncLingo2 and its derived miR-876-5p in the acquisition of opioid reinforcement.

Recent studies found that non-coding RNAs (ncRNAs) played crucial roles in drug addiction through epigenetic regulation of gene expression and underlying drug-induced neuroadaptations. In this study, we characterized lncRNA transcriptome profiles in the nucleus accumbens (NAc) of mice exhibiting morphine-conditioned place preference (CPP) and explored the prospective roles of novel differentially expressed lncRNA, lncLingo2 and its derived miR-876-5p in the acquisition of opioids-associated behaviours. We found that the lncLingo2 was downregulated within the NAc core (NAcC) but not in the NAc shell (NAcS). This downregulation was found to be associated with the development of morphine CPP and heroin intravenous self-administration (IVSA). As Mfold software revealed that the secondary structures of lncLingo2 contained the sequence of pre-miR-876, transfection of LV-lncLingo2 into HEK293 cells significantly upregulated miR-876 expression and the changes of mature miR-876 are positively correlated with lncLingo2 expression in NAcC of morphine CPP trained mice. Delivering miR-876-5p mimics into NAcC also inhibited the acquisition of morphine CPP. Furthermore, bioinformatics analysis and dual-luciferase assay confirmed that miR-876-5p binds to its target gene, Kcnn3, selectively and regulates morphine CPP training-induced alteration of Kcnn3 expression. Lastly, the electrophysiological analysis indicated that the currents of small conductance calcium-activated potassium (SK) channel was increased, which led to low neuronal excitability in NAcC after CPP training, and these changes were reversed by lncLingo2 overexpression. Collectively, lncLingo2 may function as a precursor of miR-876-5p in NAcC, hence modulating the development of opioid-associated behaviours in mice, which may serve as an underlying biomarker and therapeutic target of opioid addiction.

The blockade of neuropeptide FF receptor 1 and 2 differentially contributed to the modulating effects on fentanyl-induced analgesia and hyperalgesia in mice.

Neuropeptide FF (NPFF) plays a critical role in various physiological processes through the activation of neuropeptide FF receptor 1 and 2 (NPFFR1 and NPFFR2). Numerous evidence has indicated that NPFF exhibits opposite opioid-modulating effects on opioid-induced analgesia after supraspinal and spinal administrations, while the detailed role of NPFFR1 and NPFFR2 remains unclear. In this study, we employed pharmacological and genetic inhibition of NPFFR to investigate the modulating roles of central NPFFR1 and NPFFR2 in opioid-induced analgesia and hyperalgesia, using a male mouse model of acute fentanyl-induced analgesia and secondary hyperalgesia. Our findings revealed that intrathecal (i.t.) injection of the nonselective NPFFR antagonist RF9 significantly enhanced fentanyl-induced analgesia, whereas intracerebroventricular (i.c.v.) injection did not show the same effect. Moreover, NPFFR2 deficient (npffr2-/-) mice exhibited stronger analgesic responses to fentanyl compared to wild type (WT) or NPFFR1 knockout (npffr1-/-) mice. Intrathecal injection of RF9 in npffr1-/- mice also significantly enhanced fentanyl-induced analgesia. These results indicate a crucial role of spinal NPFFR2 in the enhancement of opioid analgesia. Contrastingly, hyperalgesia induced by fentanyl was markedly reversed in npffr1-/- mice but remained unaffected in npffr2-/- mice. Similarly, i.c.v. injection of the selective NPFFR1 antagonist RF3286 effectively prevented fentanyl-induced hyperalgesia in WT or npffr2-/- mice. Notably, co-administration of i.c.v. RF3286 and i.t. RF9 augmented fentanyl-induced analgesia while reducing hyperalgesia. Collectively, these findings highlight the modulating effects of blocking spinal NPFFR2 and supraspinal NPFFR1 on fentanyl-induced analgesia and hyperalgesia, respectively, which shed a light on understanding the pharmacological function of NPFF system in future studies.

Danavorexton (TAK-925): an orexin receptor 2 agonist as a new 'arousal' agent.

A preclinical study in animals has further characterised a new 'arousal' agent. Danavorexton (TAK-925) is an agonist for orexin receptor 2 where it promotes recovery from inhalational and i.v. anaesthesia and opioid sedation. Although danavorexton reverses opioid sedation, it does not compromise analgesia. This could be a useful addition to the postoperative drug cupboard.

Morphinan Evolution: The Impact of Advances in Biochemistry and Molecular Biology.

Morphinan-based opioids, derived from natural alkaloids like morphine, codeine and thebaine, have long been pivotal in managing severe pain. However, their clinical utility is marred by significant side effects and high addiction potential. This review traces the evolution of the morphinan scaffold in light of advancements in biochemistry and molecular biology, which have expanded our understanding of opioid receptor pharmacology. We explore the development of semi-synthetic and synthetic morphinans, their receptor selectivity and the emergence of biased agonism as a strategy to dissociate analgesic properties from undesirable effects. By examining the molecular intricacies of opioid receptors and their signaling pathways, we highlight how receptor-type selectivity and signaling bias have informed the design of novel analgesics. This synthesis of historical and contemporary perspectives provides an overview of the morphinan landscape, underscoring the ongoing efforts to mitigate the problems facing opioids through smarter drug design. We also highlight that most morphinan derivatives show a preference for the G protein pathway, although detailed experimental comparisons are still necessary. This fact underscores the utility of the morphinan skeleton in future opioid drug discovery.

Enantiomeric contributions to methamphetamine's bidirectional effects on basal and fentanyl-depressed respiration in mice.

RATIONALE: Fentanyl remains the primary cause of fatal overdoses, and its co-use with methamphetamine (METH) is a growing concern. We previously demonstrated that racemic METH can either enhance or mitigate opioid-induced respiratory depression (OIRD) dependent upon whether a low or high dose is administered. The optical isomers of METH, dextromethamphetamine (d-METH) and levomethamphetamine (l-METH), differ substantially in their selectivity and potency to activate various monoamine (MA) receptors, and these pharmacological differences may underlie the bidirectional effects of the racemate. Since it is unknown which of METH's MA receptor mechanisms mediate these respiratory effects, examination of METH's pharmacologically distinct enantiomers may provide insight into treatment targets for OIRD. METHODS: The two optical isomers of METH, d-METH and l-METH, were tested in adult male mice to determine their effects on basal and fentanyl-depressed respiratory frequency, tidal volume, and minute ventilation (MVb; i.e., respiratory frequency x tidal volume) using whole-body plethysmography. RESULTS: When tested at dose ranges of 1.0-10 mg/kg, d-METH elevated MVb and l-METH decreased basal MVb. A dose of 30 mg/kg l-METH increased basal MVb. Under fentanyl-depressed conditions, the bidirectional effects of racemic METH were observed with d-METH treatment while l-METH significantly exacerbated OIRD at 1.0 and 3.0 mg/kg. CONCLUSIONS: d-METH and l-METH differentially contribute to the bidirectional respiratory modulation observed by the racemate, with d-METH exhibiting predominantly stimulatory effects and l-METH exhibiting primarily depressant effects depending on dose.

Opioid modulation of prefrontal cortex cells and circuits.

Several neurochemical systems converge in the prefrontal cortex (PFC) to regulate cognitive and motivated behaviors. A rich network of endogenous opioid peptides and receptors spans multiple PFC cell types and circuits, and this extensive opioid system has emerged as a key substrate underlying reward, motivation, affective behaviors, and adaptations to stress. Here, we review the current evidence for dysregulated cortical opioid signaling in the pathogenesis of psychiatric disorders. We begin by providing an introduction to the basic anatomy and function of the cortical opioid system, followed by a discussion of endogenous and exogenous opioid modulation of PFC function at the behavioral, cellular, and synaptic level. Finally, we highlight the therapeutic potential of endogenous opioid targets in the treatment of psychiatric disorders, synthesizing clinical reports of altered opioid peptide and receptor expression and activity in human patients and summarizing new developments in opioid-based medications. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

The impact of multifunctional enkephalin analogs and morphine on the protein changes in crude membrane fractions isolated from the rat brain cortex and hippocampus.

Endogenous opioid peptides serve as potent analgesics through the opioid receptor (OR) activation. However, they often suffer from poor metabolic stability, low lipophilicity, and low blood-brain barrier permeability. Researchers have developed many strategies to overcome the drawbacks of current pain medications and unwanted biological effects produced by the interaction with opioid receptors. Here, we tested multifunctional enkephalin analogs LYS739 (MOR/DOR agonist and KOR partial antagonist) and LYS744 (MOR/DOR agonist and KOR full antagonist) under in vivo conditions in comparison with MOR agonist, morphine. We applied 2D electrophoretic resolution to investigate differences in proteome profiles of crude membrane (CM) fractions isolated from the rat brain cortex and hippocampus exposed to the drugs (10 mg/kg, seven days). Our results have shown that treatment with analog LYS739 induced the most protein changes in cortical and hippocampal samples. The identified proteins were mainly associated with energy metabolism, cell shape and movement, apoptosis, protein folding, regulation of redox homeostasis, and signal transduction. Among these, the isoform of mitochondrial ATP synthase subunit beta (ATP5F1B) was the only protein upregulation in the hippocampus but not in the brain cortex. Contrarily, the administration of analog LYS744 caused a small number of protein alterations in both brain parts. Our results indicate that the KOR full antagonism, together with MOR/DOR agonism of multifunctional opioid ligands, can be beneficial in treating chronic pain states by reducing changes in protein expression levels but retaining analgesic efficacy.

Morphine exposure modulates dimensional bias and set formation in anthropoids.

Humans demonstrate significant behavioural advantages with particular perceptual dimensions (such as colour or shape) and when the relevant dimension is repeated in consecutive trials. These dimension-related behavioural modulations are significantly altered in neuropsychological and addiction disorders; however, their underlying mechanisms remain unclear. Here, we studied whether these behavioural modulations exist in other trichromatic primate species and whether repeated exposure to opioids influences them. In a target detection task where the target-defining dimension (colour or shape) changed trial by trial, humans exhibited shorter response time (RT) and smaller event-related electrodermal activity with colour dimension; however, macaque monkeys had shorter RT with shape dimension. Although the dimensional biases were in the opposite directions, both species were faster when the relevant dimension was repeated, compared with conditions when it changed, across consecutive trials. These indicate that both species formed dimensional sets and that resulted in a significant 'switch cost'. Scheduled and repeated exposures to morphine, which is analogous to its clinical and recreational use, significantly augmented the dimensional bias in monkeys and also changed the switch cost depending on the relevant dimension. These cognitive effects occurred when monkeys were in abstinence periods (not under acute morphine effects) but expressing significant morphine-induced conditioned place preference. These findings indicate that significant dimensional biases and set formation are evolutionarily preserved in humans' and monkeys' cognition and that repeated exposure to morphine interacts with their manifestation. Shared neural mechanisms might be involved in the long-lasting effects of morphine and expression of dimensional biases and set formation in anthropoids.