Dexamethasone-induced selective inhibition of the central mu opioid receptor: functional in vivo and in vitro evidence in rodents

Evaluation of Analgesia Using Perineural Dexamethasone Compound in Interscalene Brachial Plexus Block After Shoulder Surgery

Background

The objective of this study was to examine analgesia when using perineural dexamethasone compound in an interscalene brachial plexus block following shoulder surgery.

Methods

This study was designed as a randomized, double-blind clinical trial. Patients meeting the specified criteria were randomly divided into two groups: The experimental group and the control group, each comprising 30 individuals. Age and gender were matched between the groups. The control group received lidocaine along with 2 cc of 0.5% bupivacaine (20 milligrams) and 2 cc of normal saline; however, the experimental group received lidocaine, along with 2 cc of 0.5% bupivacaine and 2 cc of dexamethasone. Pain levels were assessed using the Visual Analog Scale (VAS), and covariance analysis was applied for data analysis.

Results

The results demonstrated that pain intensity was notably lower in the experimental (dexamethasone) group than in the control group at both the 12-hour group (P < 0.001) and 24-hour (P < 0.001) postoperative marks. Dexamethasone significantly reduced pain among the patients.

Conclusions

In conclusion, administering dexamethasone to potential candidates for shoulder surgery could lead to prolonged analgesia for up to 24 hours after the surgery. Consequently, this medication can serve as an efficacious analgesic option for pain management in these patients.

Shared Mechanisms of GABAergic and Opioidergic Transmission Regulate Corticolimbic Reward Systems and Cognitive Aspects of Motivational Behaviors

The functional interplay between the corticolimbic GABAergic and opioidergic systems plays a crucial role in regulating the reward system and cognitive aspects of motivational behaviors leading to the development of addictive behaviors and disorders. This review provides a summary of the shared mechanisms of GABAergic and opioidergic transmission, which modulate the activity of dopaminergic neurons located in the ventral tegmental area (VTA), the central hub of the reward mechanisms. This review comprehensively covers the neuroanatomical and neurobiological aspects of corticolimbic inhibitory neurons that express opioid receptors, which act as modulators of corticolimbic GABAergic transmission. The presence of opioid and GABA receptors on the same neurons allows for the modulation of the activity of dopaminergic neurons in the ventral tegmental area, which plays a key role in the reward mechanisms of the brain. This colocalization of receptors and their immunochemical markers can provide a comprehensive understanding for clinicians and researchers, revealing the neuronal circuits that contribute to the reward system. Moreover, this review highlights the importance of GABAergic transmission-induced neuroplasticity under the modulation of opioid receptors. It discusses their interactive role in reinforcement learning, network oscillation, aversive behaviors, and local feedback or feedforward inhibitions in reward mechanisms. Understanding the shared mechanisms of these systems may lead to the development of new therapeutic approaches for addiction, reward-related disorders, and drug-induced cognitive impairment.

Opioid Receptor-Mediated Regulation of Neurotransmission in the Brain

Opioids mediate their effects via opioid receptors: mu, delta, and kappa. At the neuronal level, opioid receptors are generally inhibitory, presynaptically reducing neurotransmitter release and postsynaptically hyperpolarizing neurons. However, opioid receptor-mediated regulation of neuronal function and synaptic transmission is not uniform in expression pattern and mechanism across the brain. The localization of receptors within specific cell types and neurocircuits determine the effects that endogenous and exogenous opioids have on brain function. In this review we will explore the similarities and differences in opioid receptor-mediated regulation of neurotransmission across different brain regions. We discuss how future studies can consider potential cell-type, regional, and neural pathway-specific effects of opioid receptors in order to better understand how opioid receptors modulate brain function.

Callous unemotional trait-like mice and their stressed dams

The co-occurrence of excess rates of aggression, general violation of societal norms and callous-unemotional trait confers specific risk for adult psychopathy. With the aim to address experimentally a model of conduct disorder, we investigated the male offspring of individual mouse dams characterized by high basal plasma corticosterone concentration (HC trait). Notably, classification indices correlated selectively in these females with quite poor maternal care devoted to their offspring. Contrary to their HC mothers, adult male offspring exhibited an integrated profile of dampened physiological reactivity to external stressors co-occurring poor sociability/emotional contagion, impaired punishment-induced memory, and exacerbated aggression. A significant reduction of glucocorticoid and opioid mu receptors' expression in frontal cortex of model HC offspring was also evidenced. Moreover, in the absence of changes in oxytocin receptor in behaviorally-relevant neural areas, we showed that intranasal oxytocin administration (0 or 20.0 µg/kg) selectively modulated specific components of the behavioral phenotype. Ultimately, current data support the notion that maternally-inoculated environmental stress early in development may represent a critical risk factor in disturbances characterised by abnormal aggression and excess callousness.

Modulation of Opioid Transport at the Blood-Brain Barrier by Altered ATP-Binding Cassette (ABC) Transporter Expression and Activity

Opioids are highly effective analgesics that have a serious potential for adverse drug reactions and for development of addiction and tolerance. Since the use of opioids has escalated in recent years, it is increasingly important to understand biological mechanisms that can increase the probability of opioid-associated adverse events occurring in patient populations. This is emphasized by the current opioid epidemic in the United States where opioid analgesics are frequently abused and misused. It has been established that the effectiveness of opioids is maximized when these drugs readily access opioid receptors in the central nervous system (CNS). Indeed, opioid delivery to the brain is significantly influenced by the blood-brain barrier (BBB). In particular, ATP-binding cassette (ABC) transporters that are endogenously expressed at the BBB are critical determinants of CNS opioid penetration. In this review, we will discuss current knowledge on the transport of opioid analgesic drugs by ABC transporters at the BBB. We will also examine how expression and trafficking of ABC transporters can be modified by pain and/or opioid pharmacotherapy, a novel mechanism that can promote opioid-associated adverse drug events and development of addiction and tolerance.

The long-term impact of early life pain on adult responses to anxiety and stress: Historical perspectives and empirical evidence

Approximately 1 in 6 infants are born prematurely each year. Typically, these infants spend 25 days in the Neonatal Intensive Care Unit (NICU) where they experience 10-18 painful and inflammatory procedures each day. Remarkably, pre-emptive analgesics and/or anesthesia are administered less than 25% of the time. Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and high rates of neuropsychiatric disorders. To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of insult, remains unclear. Work in our lab using a rodent model of early life pain suggests that inflammatory pain experienced on the day of birth blunts adult responses to stress- and pain-provoking stimuli, and dysregulates the hypothalamic pituitary adrenal (HPA) axis in part through a permanent upregulation in central endogenous opioid tone. This review focuses on the long-term impact of neonatal inflammatory pain on adult anxiety- and stress-related responses, and underlying neuroanatomical changes in the context of endogenous pain control and the HPA axis. These two systems are in a state of exaggerated developmental plasticity early in postnatal life, and work in concert to respond to noxious or aversive stimuli. We present empirical evidence from animal and clinical studies, and discuss historical perspectives underlying the lack of analgesia/anesthetic use for early life pain in the modern NICU.

Enhanced brain performance in mice following postnatal stress

The double postnatal stress model (brief maternal separation plus sham injection daily applied from birth to weaning) induces metabolic alterations similar to type 2 diabetes in young-adult male mice. We verify whether 1) the stress also induces brain metabolic-functional alterations connected to diabetes and 2) different alterations are modulated selectively by two stress-damaged endogenous systems (opioid- and/or ACTH-corticosteroid-linked). Here, diabetes-like metabolic plus neurophysiologic-neurometabolic parameters are studied in adult mice following postnatal stress and drug treatment. Surprisingly, together with 'classic' diabetes-like alterations, the stress model induces in young-adult mice significantly enhanced brain neurometabolic-neurophysiologic performances, consisting of decreased latency to flash-visual evoked potentials (- ~8%); increased level (+ ~40%) and reduced latency (- ~30%) of NAD(P)H autofluorescence postsynaptic signals following electric stimuli; enhanced passive avoidance learning (+ ~135% latency); and enhanced brain-derived neurotrophic factor level (+ ~70%). Postnatal treatment with the opioid receptor antagonist naloxone prevents some alterations, moreover the treatment with antisense (AS; AS vs proopiomelanocortin mRNA) draws all parameters to control levels, thus showing that some alterations are bound to endogenous opioid-system hyper-functioning, while others depend on ACTH-corticosterone system hyper-functioning. Our stress model induces diabetes-like metabolic alterations coupled to enhanced brain neurometabolic-neurophysiologic performances. Taken all together, these findings are compatible with an 'enduring acute-stress' reaction, which puts mice in favorable survival situations vs controls. However, prolonged hormonal-metabolic imbalances are expected to also produce diabetes-like complications at later ages in stressed mice.

Targeting blood-brain barrier changes during inflammatory pain: an opportunity for optimizing CNS drug delivery

The blood-brain barrier (BBB) is the most significant obstacle to effective CNS drug delivery. It possesses structural and biochemical features (i.e., tight-junction protein complexes and, influx and efflux transporters) that restrict xenobiotic permeation. Pathophysiological stressors (i.e., peripheral inflammatory pain) can alter BBB tight junctions and transporters, which leads to drug-permeation changes. This is especially critical for opioids, which require precise CNS concentrations to be safe and effective analgesics. Recent studies have identified molecular targets (i.e., endogenous transporters and intracellular signaling systems) that can be exploited for optimization of CNS drug delivery. This article summarizes current knowledge in this area and emphasizes those targets that present the greatest opportunity for controlling drug permeation and/or drug transport across the BBB in an effort to achieve optimal CNS opioid delivery.

Post-natal stress-induced endocrine and metabolic alterations in mice at adulthood involve different pro-opiomelanocortin-derived peptides

In previous investigations we added a physical stress (mild pain) to the "classical" post-natal psychological stress in male mice, and we found that this combination produced a series of dysmetabolic signs very similar to mild human type-2 diabetes. Here, for the first time we demonstrate that within this diabetes model at least two groups of signs depend on the unbalance of two different endogenous systems. Newborn male mice were daily exposed to stressful procedures for 21 days (brief mother separation plus sham injection). Other groups underwent the same procedure, and also received naloxone (Na) to block μ-δ endogenous receptors, or a phosphorothioate antisense oligonucleotide (AS) directed against pro-opiomelanocortin (POMC)-mRNA [to block adrenocorticotropin (ACTH)- and POMC-derived opioid peptides]. Adult mice which received only post-natal stress increased body weight (+7.5%), abdominal overweight (+74%), fasting glycemia (+43%), plasma corticosterone (+110%), plasma (+169%) and pituitary (+153%) ACTH levels. Conversely, hypothalamic ACTH and corticotropin-releasing hormone (CRH) were reduced (-70% and -75%, respectively). Neonatal AS administration reverted all parameters to control values. Neonatal naloxone had little or no influence on glucose, corticosterone, ACTH, CRH levels, whereas it prevented body overweight and abdominal overweight. We conclude that, within this type-2 diabetes model in male mice at least two endocrino-neurohumoral systems are damaged, one concerning the opioid system, and the other concerning HPA hormones. The use of the two drugs was of primary importance to demonstrate this statement, and to demonstrate that these two groups of signs could be defined as "separate entities" following our complex post-natal stress model.

Spinal mu-opioid receptor expression and hyperalgesia with dexamethasone in chronic adjuvant-induced arthritis in rats

1. It is known that inflammation influences peripheral and central mu-opioid receptor expression. Previous studies have indicated that glucocorticoids may influence the density of mu-opioid receptors. In the present study, we investigated the fluctuations of spinal mu-opioid receptor expression and hyperalgesia induced by complete Freund's adjuvant (CFA) under long-term administration of dexamethasone. 2. Adjuvant arthritis (AA) was induced by subcutaneous injection of CFA in the right hindpaw of male Wistar rats. Spinal mu-opioid receptor expression was detected by semiquantitative reverse transcription-polymerase chain reaction on Days 6 and 21 following AA induction. Dexamethasone (0.1 mg/kg) was administered intraperitoneally for 21 days. Variations in thermal hyperalgesia were checked by radiant heat on the same days as mu-opioid receptor expression was determined. 3. The results indicated a significant increase in spinal mu-opioid receptor expression on Days 6 and 21 after AA induction compared with the control group. Spinal mu-opioid receptor expression decreased significantly only on Day 21 in the AA + dexamethasone group compared with the AA alone group. Thermal hyperalgesia on Day 6 after AA induction showed a significant increase compared with the control group. Hyperalgesia decreased significantly on Day 21 after AA compared with Day 6. The AA + dexamethasone group showed a significant decrease in hyperalgesia on Day 6 compared with the AA group, but hyperalgesia increased significantly on Day 21 in the AA + dexamethasone group compared with the AA group. 4. The effects of long-term dexamethasone on both spinal mu-opioid receptor expression and hyperalgesia during persistent AA inflammation are time dependent. In addition, the effect of long-term dexamethasone administration on hyperalgesia during persistent arthritis inflammation needs to be investigated further.

Effects of environmental enrichment on sensitivity to mu, kappa, and mixed-action opioids in female rats

Several studies report that environmental enrichment enhances sensitivity to opioid receptor agonists in male rats. Very few studies have examined the effects of enrichment in female rats, and thus it is not clear whether females are similarly sensitive to these effects. Consequently, the purpose of the present study was to examine the effects of environmental enrichment on sensitivity to representative mu, kappa, and mixed-action opioids in female rats. Following a protocol established in males, females were obtained at weaning and randomly assigned to two groups immediately upon arrival: isolated rats were housed individually with no visual or tactile contact with other rats; enriched rats were housed in groups of four in large cages and given various novel objects on a regular basis. After 6 weeks under these conditions, the antinociceptive effects of mu (morphine, levorphanol), kappa (spiradoline, U69,593), and mixed-action (buprenorphine, butorphanol) opioids were examined in a warm-water, tail-withdrawal procedure. All the opioids examined produced dose-dependent increases in antinociception; however, no differences in opioid sensitivity were observed between the two groups. To determine whether these findings were consistent across behavioral endpoints, the antidiuretic effects of representative mu opioids, and the diuretic effects of representative kappa opioids, were examined in female rats reared under isolated or enriched conditions for 10 weeks. Similar to that seen in the antinociceptive experiment, no significant differences in opioid sensitivity were observed between groups. These data indicate that environmental enrichment does not alter sensitivity to the effects of opioid receptor agonists in female rats, and suggest that females may respond differently to environmental enrichment than males.

Tramadol enhances hepatic insulin sensitivity via enhancing insulin signaling cascade in the cerebral cortex and hypothalamus of 90% pancreatectomized rats

Clinical observation found that tramadol, mu opioid receptor (MOR) agonist and serotonin (5-HT) reuptake inhibitor, has a hypoglycemic effect in type 2 diabetes patients. The mechanism of its hypoglycemic effect has not been fully defined. This study showed that tramadol activated a neuronal insulin signaling cascade by increasing the induction of insulin receptor substrate-2 expression in primary cultured neuronal cells while this activation was suppressed by naloxone (MOR inhibitor) and dexamethasone (non-specific inhibitor of MOR and 5-HT receptor, DEX). Glucose utilization of the cerebral cortex and hypothalamus was enhanced by a 4-week-tramadol administration in 90% pancreatectomized rats, in vivo, as assessed by measurement of glucokinase expression and glycogen deposition via activating insulin signaling cascade such as neuronal cells in vitro. This improvement was almost completely suppressed by naloxone as well as DEX. Tramadol decreased fasted serum glucose levels, favored an increase in the glucose infusion rate and reduced endogeneous hepatic glucose production after 4 weeks of treatment. However, tramadol did not modulate hepatic glucose output directly, as exhibited by liver perfusion, suggesting tramadol altered hepatic glucose utilization through the effect of organs other than the liver, possibly the central nervous system. The data suggest that tramadol ameliorates peripheral glucose metabolism through central activation of MOR, and that central and peripheral glucose metabolism are therefore likely to be interrelated.

Glucocorticoid Hormone Regulates the Circadian Coordination of μ-Opioid Receptor Expression in Mouse Brainstem

The 24-h variation in glucocorticoid secretion from the adrenal cortex is observed not only in nocturnally active rodents but also in diurnally active humans. Although the cyclic change in circulating glucocorticoid levels is thought to influence the efficacy and/or toxicity of many drugs, the mechanism underlying the influence remains poorly understood. In this study, we demonstrate that the 24-h variation in circulating glucocorticoid levels modulates the analgesic effect of morphine by regulating the expression of the mu-opioid receptor. Significant time-dependent variations in the mRNA levels of the mu-opioid receptor and its binding capacity were observed in mouse brainstem. The analgesic effect of morphine was enhanced by administering the drug when mu-opioid receptor levels were increased. However, corticotrophin-releasing hormone (CRH)-deficient mice, disrupting the 24-h rhythm of glucocorticoid secretion, showed no significant time-dependent variation in the expression of the mu-opioid receptor. As a consequence, there was no significant dosing time-dependent difference in the analgesic effect of morphine in CRH-deficient mice. A single administration of corticosterone significantly induced the expression of the mu-opioid receptor in the CRH-deficient mouse brainstem and also enhanced the analgesic effect of morphine. These findings suggest a mechanism underlying the time-dependent variation in mu-opioid receptor function and provide clues to select the most appropriate time of day for administration of morphine.

Taurine administration during lactation modifies hippocampal CA1 neurotransmission and behavioural programming in adult male mice

Taurine plays a role in neuronal development. In this study, we examined whether postnatal taurine administration influences the long-term consequences induced by mild neonatal stressors (10 min maternal deprivation plus sham injection, applied daily to neonatal mice up to 21 days). At 30 days of age stressed mice showed higher pain threshold both in the tail-flick--which measures mostly the spinal mechanisms of pain--and in the hot-plate test--which reflects mainly the supraspinal mechanisms of pain. The latter effect was prevented completely by neonatal taurine administration, while the tail-flick test was not affected, thus suggesting that spinal pain is not sensitive to taurine treatment. At 140 days of age, mice which were stressed during the neonatal period showed consistent decrease in immobility time in forced swimming test, and taurine did not influence this parameter. At the same age, the fear/anxiety axis, measured with elevated plus maze test, did not show any consistent changes. Electrophysiological experiments in brain slices obtained from adult mice showed that input-output curves in hippocampal CA1 were increased by taurine administration in lactation. Hence, neonatal administration of taurine might permanently modify the functioning of hippocampus, a brain area which is known to be crucial for learning and memory.

Stimulus-dependent specificity for annexin 1 inhibition of the inflammatory nociceptive response: the involvement of the receptor for formylated peptides

In this study we investigated how the peptides derived from the glucocorticoid-inducible protein annexin 1 are able to alter the nociceptive threshold of mice. The effects of the annexin1 fragment 2-26 (Anxa1(2-26)) on nociceptive threshold were studied using both chemical (formalin test) and thermal (hot plate and tail flick test) nociceptive stimuli on mice. Subcutaneous administration of Anxa1(2-26) into the dorsal surface of the mouse's hind paw was able to selectively reduce formalin-induced nociceptive behavior in the last phase of the test. The same effect was observed after intracerebroventricular administration, however, this was not the case when performing the hot plate or tail flick tests. Of the shortest Anxa1(2-26)-derived peptides, Anxa1(2-12) reduced the nociceptive response to formalin, however, the Anxa1(2-6) did not. The possible involvement of the receptors for formylated peptide in the anti-nociceptive action of Anxa1(-26) and Anxa1(2-12) was studied, choosing the formalin test. We found that the formyl peptide receptor agonist formyl-MLF (fMLF) induced anti-nociceptive effects in the formalin test both after the peripheral and central administration. The formyl peptide receptor antagonist N-t-butoxycarbonyl-MLP did not alter the response to formalin, but it was able to block the anti-nociceptive effects of Anxa1(2-26,) Anxa1(2-12) and fMLF after peripheral or central administration. These results indicate that exogenously administered Anxa1 can peripherally and centrally inhibit the nociceptive transmission associated with inflammatory processes through a mechanism that involves formyl peptide receptors.

Vas deferens response to selective opioid receptor agonists in adult mice is impaired following postnatal repeated mild stress

Mild stress repeatedly applied to neonatal rodents induces alterations of central nervous system functions, persisting up to the adult age. Most alterations may be mediated through hormones and neuromediators active on the autonomic nervous system, therefore we tested the efficacy of selective opioid receptor agonists on the vas deferens of adult mice that, as neonates, had undergone daily mild stress until weaning (brief isolation and solvent injection). We found in the adult mouse (90 days old) decreased sensitivity of vas deferens to selective mu-, delta- and kappa-opioid receptor agonist drugs. The neonatal administration of an antisense oligodeoxynucleotide adrenocorticotropin-synthesis-inhibitor partly prevented these effects.

Dexamethasone reduces morphine-induced Straub reaction in mice

This study examined the effect of dexamethasone on morphine-induced straub reaction in mice. When morphine was administered in doses of 7.5, 15 and 30 mg kg(-1) intraperitoneally, a dose-dependent straub reaction was produced. Dexamethasone per-se (0.1-10 mg kg(-1) i.p.) did not modify the tail of control mice. Pre-treatment with dexamethasone 120 min before morphine injection caused a dose-dependent reduction of straub reaction. Cycloheximide (15 mg kg(-1) i.p.) administered 2 h before morphine did not change morphine-induced straub reaction, but was able to prevent the effects of dexamethasone on morphine-induced straub reaction. The glucocorticoid receptor antagonist RU-38486 (15 mg kg(-1) i.p.) did not affect morphine-induced straub reaction, whereas it was able to block the effects of dexamethasone on morphine-induced straub reaction. Results of this study indicate that dexamethasone reduced morphine-mediated straub reaction in mice, indicating a further important functional interaction between dexamethasone and the opioid system. The ability of cycloheximide and RU-38486 to block dexamethasone's effects indicates that the steroid's interference with morphine-mediated straub reaction involves a protein-synthesis-dependent mechanism via glucocorticoid receptors.

Naloxone prevents cell-mediated immune alterations in adult mice following repeated mild stress in the neonatal period

1. Mild stress plus mild pain (solvent injection) applied daily to neonatal mice induces hormonal, behavioural and metabolic changes perduring in the adult life. 2. We investigated whether daily mild stress to neonatal mice induces also long-term defined changes of immune response, and whether immune changes are prevented through repeated administration of the opioid antagonist naloxone. 3. Mild stress plus solvent injection administered from birth to the 21st postnatal day causes not only behavioural and metabolic changes, but also long-term (up to 110 days of life) splenocytes modifications, consisting in: increased release of the Th-1 type cytokines interleukin-2 (IL-2) (from an average of 346 to 788 pg ml(-1)), interferon-gamma (from 1770 to 3942) and tumour necrosis factor-alpha (from 760 to 1241); decreased release of the Th-2 type cytokines IL-4 (from 49.1 to 28.4) and IL-10 (from 1508 to 877). Moreover, enhanced natural killer-cell activity; enhanced proliferative splenocytes properties in resting conditions and following phytohemoagglutinin and concanavalin-A stimulation are observed. Immunological, behavioural and metabolic changes are prevented by the opioid antagonist (-)naloxone (1 mg kg(-1) per day s.c., administered instead of solvent) but not by the biologically inactive enantiomorph (+)naloxone. 4. In conclusion, endogenous opioid systems sensitive to naloxone are involved in long-lasting enhancement of the Th-1 type cytokines and cell-mediated immunological response caused by repeated mild stress administered postnatally.

Studies on the antinociceptive effect of [Nphe1]nociceptin(1-13)NH2 in mice

Nociceptin/orphanin FQ (NC) and its receptor (OP(4)) have been implicated in the regulation of various functions including nociception. [Nphe(1)]NC(1-13)NH(2) (Nphe) is a selective OP(4) antagonist which prevents the pronociceptive effects of supraspinal NC and causes per se a naloxone-insensitive antinociceptive effect. In the present study, we tested Nphe in wild type (WT) and OP(4) receptor knock out mice and found that a clear antinociceptive effect of the antagonist was evident only in WT mice. Moreover, we evaluated, over 5 days of treatment, the antinociceptive effects of Nphe in comparison with those of DAMGO and found that tolerance develops to the effects of the opioid receptor agonist but not to Nphe. These data demonstrate that the antinociceptive action of Nphe is due to the block of OP(4) receptors and that no tolerance develops to this kind of antinociception.

Dexamethasone modulates hypotension induced by opioids in anaesthetised rats

The effect of dexamethasone on hypotension induced by mu-, kappa- and delta-opioid receptor agonists was investigated in pentobarbital-anaesthetised rats. Morphine (nonselective opioid receptor agonist), DAGO (D-Ala2-N-methyl-[Phe4-Gly5-ol]enkephalin; mu-opioid receptor-selective agonist), U50-488H (trans(+/-)-3,4-dichloro-N-methyl-N-(2[1pyrrolidynyl]cyclohexyl)-benzeneacetamide; kappa-opioid receptor-selective agonist) and deltorphin II (delta-opioid receptor-selective agonist), given intravenously, 5 micromol/kg, induced hypotension in rats. This hypotension was characterised by a fall in mean arterial blood pressure in 1-2 min that recovered in 30 min for morphine and U50-488H and in 5 or 20 min for DAGO and deltorphin II, respectively. Dexamethasone per se at a dose of 7.5 micromol/kg, i.v. did not significantly modify the mean arterial blood pressure of animals. Dexamethasone administration 90 min, but not 30 or 60 min, before the opioid agonists injection, prevented the hypotension induced by morphine or U50-488H, but not that induced by DAGO or deltorphin II. Pretreatment with RU-38486 (mifepristone; 7.5 micromol/kg, i.v.), a glucocorticoid receptor antagonist, 15 min before the steroid, prevented dexamethasone inhibition of hypotension induced by morphine and U50-488H. Furthermore, pretreatment with cycloheximide, a protein synthesis inhibitor (3.5 micromol/kg, i.v.), was also able to abolish the effects of dexamethasone on morphine- and U50-488H-induced hypotension. Results of the present study indicate that dexamethasone inhibited kappa-opioid receptor-mediated hypotension in rats, indicating a further important functional interaction between corticosteroids and the opioid system at kappa receptors. The ability of cycloheximide and RU-38486 to block dexamethasone effects indicates that steroid interference with kappa-opioid receptor-mediated hypotension involves a protein synthesis-dependent mechanism via glucocorticoid receptors.

Difficulties in diagnosing neuropsychiatric complications of corticosteroids in advanced cancer patients: two case reports

Because of their variety of uses, corticosteroids are frequently prescribed in advanced cancer patients. Two patients who developed neuropsychiatric complications on corticosteroids and their subsequent management are described. The first patient, who had a known history of steroid-induced psychotic depression, required corticosteroids to treat recurrent brain edema from a malignant meningioma. The patient was managed by using low-dose corticosteroids and concomitant haloperidol. The second patient was prescribed corticosteroids for a constellation of symptoms, including pain and nausea from a possible bowel obstruction, and developed a severe delirium that required discontinuation of the corticosteroids. The difficulties of diagnosing steroid-related cognitive and mood changes in advanced cancer patients who often have multisystem disease are discussed, as well as strategies for minimizing the effects of corticosteroids' neuropsychological complications.

Antinociceptive activity of a 3(2H)-pyridazinone derivative in mice

The antinociceptive activity of a 3(2H)-pyridazinone derivative (18a) was investigated in mice. 18a administered at doses which did not change either motor coordination or locomotor activity was able to induce antinociceptive effects in four nociceptive tests, the hot plate test, the tail flick test, the writhing test, and the formalin test. In the hot plate and tail flick test, 18a-induced antinociception was observed both after intraperitoneal administration and after intracerebroventricular injection thus indicating 18a has a central site of action. The pretreatment with the opioid antagonist naloxone, the alpha2-antagonist yohimbine or the GABA(B) antagonist CGP 35348 did not change 18a-induced antinociception in the hot plate test and in the tail flick test. Pretreatment with nicotinic antagonist mecamylamine did not change 18a effects either. A reversion of the 18a effects was observed after pretreatment with the muscarinic antagonists atropine and pirenzepine. Binding experiments revealed that 18a binds to muscarinic receptors, suggesting that 18a antinociception is mediated by central muscarinic receptors. The above findings together with the lack of parasympathomimetic cholinergic side effects indicate useful clinical application for this compound.

Further studies on the involvement of the arachidonic acid cascade in the acute dependence produced by mu, kappa and delta opioid agonists in isolated tissues

The effects of phospholipase A2, cyclooxygenase-1, cyclooxygenase-2, and 5-lipoxygenase inhibitors on acute opiate withdrawal induced by selective mu, kappa and delta receptor agonists was investigated in vitro. After a 4 min in vitro exposure to D-Ala2-N-methyl-Phe-Gly5-ol)enkephalin (DAMGO; a highly selective mu agonist) and trans(+/-)-3,4-dichloro-N-methyl-N-(2(1pyrrolidynyl)-cyclohexyl)-+ ++benzeneacetamid (U50-488H; a highly selective K agonist) a strong contraction of the guinea pig isolated ileum was observed after the addition of naloxone. This effect was also observed when rabbit isolated jejunum was pretreated with deltorphin (a highly selective delta agonist). Mepacrine (a phospholipase A2 inhibitor), tolmetin (a selective cyclooxygenase-1 inhibitor) and meloxicam (a selective cyclooxygenase-2 inhibitor) treatment before or after DAMGO or U50-488H were able to both prevent and reverse the naloxone-induced contraction after exposure to the opioid agonists, in a concentration-dependent fashion. In addition, nordihydroguaiaretic acid (a 5-lipooxygenase inhibitor) was able to block the naloxone-induced contraction following exposure to DAMGO or U50-488H if injected either before or after the opioid agonist. In contrast, mepacrine, tolmetin, meloxicam and nordihydroguaiaretic acid did not affect the naloxone-induced contraction after exposure to deltorphin. The results of the present study confirm and extend a previous study performed with morphine indicating that arachidonic acid and its metabolites (prostaglandins and leukotrienes) are involved in the development of opioid withdrawal induced by selective mu and kappa opioid agonists whereas no effects were observed on withdrawal induced by the selective delta opioid agonist deltorphin.

Opiate binding sites in the cellular immune system: expression and regulation

The direct actions of opiates on the mammalian immune system depend on the existence of ligand binding sites either on the surface of the affected cell or in the interior of the cell. With the cloning of various opiate receptors from neuronal tissue, numerous researchers have screened leukocyte cDNA libraries for the expression of these receptors with some positive results. However, the pattern of expression of neuronal opiate receptors in the cellular immune system does not completely explain the biological action of opiates there. Several possibilities could account for this non-congruence including differential expression of the receptors as determined by such factors as cell population or prior history of the cells; the existence of sequence modified versions of the neuronal receptors such that the amplification methods miss their presence; or the opiates act by a different, non-receptor mechanism in the cellular immune system.

Characterization of the in vitro antiepileptic activity of new and old anticonvulsant drugs

1. The in vitro antiepileptiform effects of some old and new anticonvulsants in the experimental model of the "epileptiform" hippocampal slice have been reviewed. 2. On the basis of their influence on in vitro epileptogenesis and basal neuronal excitability, anticonvulsants can be classified into three main categories: (1) anticonvulsants (prototypical drug phenytoin) affecting basal neuronal excitability but not epileptogenesis; (2) anticonvulsants (prototypical drugs barbiturates) affecting basal neuronal excitability and epileptogenesis; (3) anticonvulsants (prototypical drug felbamate) affecting epileptogenesis but not basal neuronal excitability. 3. It is concluded that the model of the "epileptiform" hippocampal slices can be considered a previsional test for the study and the screening of new anticonvulsant drugs.

Dexamethasone modifies the behavioral effects induced by clonidine in mice

The present study examines the influence of dexamethasone on behavioral effects induced by clonidine in mice. 2. The behavior elements considered were locomoter activity, rota rod, catalepsy and stereotyped behavior (rearing, grooming, social response test, crossing, smelling, washing face, scratching and bar holding). 3. Clonidine (0.1-0.5-1.0 mg/kg, IP) induced a significant reduction of all behavioral elements studied when compared to the saline treated group: the behavioral reduction was significant 10 min after administration and lasted for the entire recording period (120 min). 4. Dexamethasone (0.1-0.5-1.0 mg/kg, IP) per se did not induce significant changes in the behavior elements recorded. 5. Dexamethasone (0.1-0.5 mg/kg, IP) dod not affect behavioral effects induced by the 3 doses of clonidine, whereas the high dose (1 mg/kg) of the steroid significantly reduced its behavioral inhibition. 6. The results of the present study suggest that dexamethasone induces significant effects on clonidine-induced behavioral effects and that this may be related to an interference with the monoaminergic system.

Dexamethasone reduced clonidine-induced hypoactivity in mice

Reduced clonidine anti-nociception in mice given low doses of dexamethasone has encouraged us to investigate the effects of dexamethasone pretreatment on locomotor hypoactivity, another example of clonidine-induced behaviour in mice. Dexamethasone administered intraperitoneally (0.1, 1.0, 10 mg kg-1) 30 min before clonidine reduced clonidine-induced locomotor hypoactivity in the activity cage to an extent which was dose-dependent. Dexamethasone administered centrally (10 ng/mouse) 30 min before clonidine was also able to reduce clonidine-induced locomotor hypoactivity. Cycloheximide administered at a dose of 10 mg kg-1 2 h before clonidine did not change the effects of clonidine but was able to prevent the effects of dexamethasone on clonidine-induced hypoactivity. The glucocorticoid receptor antagonist RU38486 administered centrally at the dose of 1 ng/mouse did not change the effects of clonidine, whereas it was able to block the effects of dexamethasone on clonidine-induced locomotor hypoactivity. These results suggest that the effects of dexamethasone on clonidine-induced locomotor hypoactivity depend on the stimulating effects that dexamethasone exerts on the protein synthesis via the glucocorticoid receptor in the brain.

Actinomycin D blocks the reducing effect of dexamethasone on amphetamine and cocaine hypermotility in mice

1. The present study examined a time-course effect of dexamethasone (DEX) on amphetamine and cocaine-induced hypermotility in mice and the influence of actinomycin D (dactinomycin), a protein synthesis inhibitor, on DEX effects. 2. Amphetamine (5 mg/kg IP) and cocaine (10 mg/kg IP) increased markedly the locomotor activity of mice, whereas DEX alone (0.1-1.0-10 mg/kg IP) did not modify the activity of control mice. 3. DEX pretreatment 0, 15, 30, 60 and 120 min before amphetamine or cocaine strongly decreased both amphetamine and cocaine effects, but no dose-related effect was observed. 4. The time-course study performed with DEX revealed differences in its reducing effect on cocaine and amphetamine hypermotility when the groups of animals treated with the steroid immediately before the cocaine (or amphetamine) injection were compared to those treated with the steroid later (15, 30, 60 and 120 min). 5. Furthermore, actinomycin D was able to block the reducing effect of DEX on both amphetamine and cocaine hypermotility. 6. Therefore, considering that the administration time of the steroid seems to be an important factor for reducing both cocaine and amphetamine hypermotility, and actinomycin D was able to block the reducing effect of the steroid, our study suggests that DEX exerts its reducing effect through a genomic activation.

Selective opposite modulation of dentate granule cells excitability by mu and kappa opioids in rat hippocampal slices

The effects of opioids having affinity for kappa (U50,488H and U54,494A) and mu receptors (DAMGO and methadone) were tested on the excitability of the dentate and CA1 neurons in rat hippocampal slices. Slice perfusion with 25 microM U50,488H or with 12 microM U54,494A produced within 60 min a significant (P < 0.05) decrease in the amplitude of the primary dentate population spike (PS). A similar decrease occurred on the CA1 PS amplitude only at concentrations higher than 100 microM of U50,488H or 50 microM of U54,494A. Slice perfusion with 0.5 microM DAMGO, or 100 microM methadone produced an increase in the amplitude of the primary dentate and CA1 PS and the appearance of secondary PSs. Slice perfusion with 12 microM U50,488H or with 25 microM of methadone significantly (P < 0.05) decreased or increased, respectively, the rate of appearance of the dentate posttetanic potentiation (PTP) and long-term potentiation (LTP) after a 100 Hz tetanic stimulation of the perforant path. The same concentration of U50,488H or methadone did not affect the rate of appearance of the CA1 PTP and LTP after a 100 Hz tetanic stimulation of the Schaffer collaterals. The data, providing evidence for a selective opposite modulation by mu and kappa opioids on the basal and stimulated dentate neuronal excitability, indicate the dentate area as a target within the hippocampus for an opposite influence between mu and kappa opioids on neuronal excitability.

Time-related antiepileptic effects of the synthetic glucocorticoid dexamethasone in rat hippocampal slices

The in vitro antiepileptic activity of the synthetic glucocorticoid dexamethasone (DEX) was tested in rat hippocampal slices on the CA1 epileptiform activity induced by sodium penicillin (PEN). Slice perfusion with 1 mM PEN produced within 60 min the development of a CA1 epileptiform bursting made up of an increase of the primary CA1 population spike followed by the appearance of secondary epileptiform population spikes. Slice perfusion with 100 microM DEX together with PEN (1 mM) partially prevented but did not block the expression of the CA1 epileptiform bursting as evidenced by a significant (P < 0.05) reduction of the duration of the bursting due to the epileptogenic agent. Slice perfusion with 50 microM DEX together with PEN (1 mM) failed to prevent or block the expression of the CA1 penicillin-induced epileptiform bursting. A 60 min slice pretreatment with 50-100 microM DEX followed by a slice perfusion with 50-100 microM DEX together with PEN (1 mM) prevented the expression of the CA1 epileptiform bursting. Cycloheximide (1 microM), a protein synthesis inhibitor, perfused together with DEX reverted the inhibitory effects of dexamethasone on the expression of the penicillin-induced CA1 epileptiform bursting. The results indicate that the synthetic glucocorticoid DEX presents concentration- and time-related in vitro antiepileptic effects. In addition, the data suggest that this inhibitory effect occurs via a protein synthesis-dependent mechanism.

Endogenous opiates: 1994

This article is the 17th installment of our annual review of research concerning the opiate system. It includes papers published during 1994 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics covered this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.