Opiate Interaction Research Articles

A central role for glial CCR5 in directing the neuropathological interactions of HIV-1 Tat and opiates

BackgroundThe collective cognitive and motor deficits known as HIV-associated neurocognitive disorders (HAND) remain high even among HIV+ individuals whose antiretroviral therapy is optimized. HAND is worsened in the context of opiate abuse. The mechanism of exacerbation remains unclear but likely involves chronic immune activation of glial cells resulting from persistent, low-level exposure to the virus and viral proteins. We tested whether signaling through C-C chemokine receptor type 5 (CCR5) contributes to neurotoxic interactions between HIV-1 transactivator of transcription (Tat) and opiates and explored potential mechanisms.MethodsNeuronal survival was tracked in neuronal and glial co-cultures over 72 h of treatment with HIV-1 Tat ± morphine using cells from CCR5-deficient and wild-type mice exposed to the CCR5 antagonist maraviroc or exogenously-added BDNF (analyzed by repeated measures ANOVA). Intracellular calcium changes in response to Tat ± morphine ± maraviroc were assessed by ratiometric Fura-2 imaging (analyzed by repeated measures ANOVA). Release of brain-derived neurotrophic factor (BDNF) and its precursor proBDNF from CCR5-deficient and wild-type glia was measured by ELISA (analyzed by two-way ANOVA). Levels of CCR5 and μ-opioid receptor (MOR) were measured by immunoblotting (analyzed by Student’s t test).ResultsHIV-1 Tat induces neurotoxicity, which is greatly exacerbated by morphine in wild-type cultures expressing CCR5. Loss of CCR5 from glia (but not neurons) eliminated neurotoxicity due to Tat and morphine interactions. Unexpectedly, when CCR5 was lost from glia, morphine appeared to entirely protect neurons from Tat-induced toxicity. Maraviroc pre-treatment similarly eliminated neurotoxicity and attenuated neuronal increases in [Ca2+]i caused by Tat ± morphine. proBDNF/BDNF ratios were increased in conditioned media from Tat ± morphine-treated wild-type glia compared to CCR5-deficient glia. Exogenous BDNF treatments mimicked the pro-survival effect of glial CCR5 deficiency against Tat ± morphine.ConclusionsOur results suggest a critical role for glial CCR5 in mediating neurotoxic effects of HIV-1 Tat and morphine interactions on neurons. A shift in the proBDNF/BDNF ratio that favors neurotrophic support may occur when glial CCR5 signaling is blocked. Some neuroprotection occurred only in the presence of morphine, suggesting that loss of CCR5 may fundamentally change signaling through the MOR in glia.

Productive infection of human neural progenitor cells by R5 tropic HIV-1: opiate co-exposure heightens infectivity and functional vulnerability.

HIV type-1 (HIV-1) causes a spectrum of central nervous system (CNS) complications; many are worsened by opiate co-exposure. Human neural progenitor cells (hNPCs) give rise to all CNS neurons and macroglia. We tested the hypothesis that hNPC maturation and fate are altered by HIV and opiates, contributing to HIV-1-related neuropathology. Reports of hNPC infection remain controversial. We rigorously examined this question, testing whether hNPCs propogated infection, and whether HIV affected hNPCs absent their infection. Primary hNPCs were characterized over multiple passages. Following R5 HIV-1BaL exposure, p24, Nef, and tat assays monitored infection; a serial dilution approach tested infection transfer to naive hNPCs. Bromodeoxyuridine uptake, population doubling time, and immunostaining assessed proliferation and differentiation. Morphine co-exposure assessed opiate interactions. Supernatant from HIV-1BaL-infected PBMCs (HIVsup), HIV-1BaL, and ultraviolet light-inactivated HIVsup were compared to test effects of inflammatory milieu versus virus or infection per se. The hNPCs (CD4/CD8/Iba/CXC3CL1/CD11b) were infectable and could transfer infection to naive hNPCs. Infection was partly blocked by maraviroc, implicating CCR5. HIVsup reduced hNPC proliferation and caused premature differentiation into neurons/astroglia. Effects on proliferation were due to soluble factors/viral proteins, not infection per se. Morphine co-exposure exacerbated certain functional consequences of HIVsup, and sustained the infection of hNPCs. hNPCs can be infected and propagate virus in vitro. hNPCs or their progeny may represent an underappreciated viral reservoir. Factors from infected cells alter hNPC proliferation and neural cell maturation, which likely compromises CNS structure and function. Morphine-HIV interactions may worsen dysfunction and sustain infection.

Aberrant mesolimbic dopamine–opiate interaction in obesity

Dopamine and opioid neurotransmitter systems share many functions such as regulation of reward and pleasure. μ-Opioid receptors (MOR) modulate the mesolimbic dopamine system in ventral tegmental area and striatum, key areas implicated in reward. We hypothesized that dopamine and opioid receptor availabilities correlate in vivo and that this correlation is altered in obesity, a disease with altered reward processing.Twenty lean females (mean BMI 22) and 25 non-binge eating morbidly obese females (mean BMI 41) underwent two positron emission tomography scans with [11C]carfentanil and [11C]raclopride to measure the MOR and dopamine D2 receptor (DRD2) availability, respectively.In lean subjects, the MOR and DRD2 availabilities were positively associated in the ventral striatum (r=0.62, p=0.003) and dorsal caudate nucleus (r=0.62, p=0.004). Moreover, DRD2 availability in the ventral striatum was associated with MOR availability in other regions of the reward circuitry, particularly in the ventral tegmental area. In morbidly obese subjects, this receptor interaction was significantly weaker in ventral striatum but unaltered in the caudate nucleus. Finally, the association between DRD2 availability in the ventral striatum and MOR availability in the ventral tegmental area was abolished in the morbidly obese.The study demonstrates a link between DRD2 and MOR availabilities in living human brain. This interaction is selectively disrupted in mesolimbic dopamine system in morbid obesity. We propose that interaction between the dopamine and opioid systems is a prerequisite for normal reward processing and that disrupted cross-talk may underlie altered reward processing in obesity.

Opiate Substitute Prescription and Interactions with Anti-HIV Drugs.

Introduction Injecting Drug use is a major risk factor for the acquisition and transmission of HIV and accounts for approximately 5-10% of HIV infections worldwide. Opiate Substitution Treatment using Methadone and Buprenorphine reduces the HIV risk for people who inject drugs by up to half. Therefore proper diagnosis and treatment of opiate dependence are essential. Both Methadone and Buprenorphine have been shown to interact with a lot of anti-retroviral medications. This may lead to potentially toxic drug interactions. This could also lead either to withdrawal symptoms or to morbidity/mortality by overdose if these medications are not prescribed carefully. Aims & Objectives Our objectives were to look for the relationship between substance abuse and HIV and to analyze the interactions and adverse reactions when combining Methadone/Buprenorphine and Antiretrovirals. Methodology Using MEDLINE, English literature was reviewed from 1990 to June 2014. The search strategy was 'Substance abuse” OR 'Drug abuse” OR Methadone OR Buprenorphine AND HIV OR AIDS OR HAART. Results Subjects who use drugs are more prone to acquire HIV because of increased risky behaviours. Substitute Opiate treatment may improve adhesion to the antiretroviral treatment and also leads to a reduction in risk-taking behaviours. In the poster, we will be presenting the interactions of each Anti-Retroviral agent with both Methadone and Buprenorphine. Conclusion Choosing the best therapeutic intervention in each case, particularly considering those drugs with least interactions and adverse effects is crucial for the success of Opiate substitution programme and also to combat the HIV infection.

Morphine enhances HIV-1SF162-mediated neuron death and delays recovery of injured neurites.

HIV-1 enters the CNS soon after initial systemic infection; within the CNS parenchyma infected and/or activated perivascular macrophages, microglia and astrocytes release viral and cellular toxins that drive secondary toxicity in neurons and other cell types. Our previous work has largely modeled HIV-neuropathology using the individual viral proteins Tat or gp120, with murine striatal neurons as targets. To model disease processes more closely, the current study uses supernatant from HIV-1-infected cells. Supernatant from HIV-1SF162-infected differentiated-U937 cells (HIV+ sup) was collected and p24 level was measured by ELISA to assess the infection. Injection drug abuse is a significant risk factor for HIV-infection, and opiate drug abusers show increased HIV-neuropathology, even with anti-retroviral treatments. We therefore assessed HIV+ sup effects on neuronal survival and neurite growth/pruning with or without concurrent exposure to morphine, an opiate that preferentially acts through µ-opioid receptors. Effects of HIV+ sup ± morphine were assessed on neuronal populations, and also by time-lapse imaging of individual cells. HIV+ sup caused dose-dependent toxicity over a range of p24 levels (10–500 pg/ml). Significant interactions occurred with morphine at lower p24 levels (10 and 25 pg/ml), and GSK3β was implicated as a point of convergence. In the presence of glia, selective neurotoxic measures were significantly enhanced and interactions with morphine were also augmented, perhaps related to a decreased level of BDNF. Importantly, the arrest of neurite growth that occurred with exposure to HIV+ sup was reversible unless neurons were continuously exposed to morphine. Thus, while reducing HIV-infection levels may be protective, ongoing exposure to opiates may limit recovery. Opiate interactions observed in this HIV-infective environment were similar, though not entirely concordant, with Tat/gp120 interactions reported previously, suggesting unique interactions with virions or other viral or cellular proteins released by infected and/or activated cells.

Morphine potentiates neurodegenerative effects of HIV-1 Tat through actions at -opioid receptor-expressing glia

Individuals infected with human immunodeficiency virus-1 who abuse opiates can have a higher incidence of virus-associated neuropathology. Human immunodeficiency virus does not infect neurons, but viral proteins such as transactivator of transcription and glycoprotein 120, originating from infected glia, are neurotoxic. Moreover, functional changes in glial cells that enhance inflammation and reduce trophic support are increasingly implicated in human immunodeficiency virus neuropathology. In previous studies, co-exposure with morphine enhanced transactivator of transcription neurotoxicity towards cultured striatal neurons. Since those cultures contained µ-opioid receptor-expressing astroglia and microglia, and since glia are the principal site of infection in the central nervous system, we hypothesized that morphine synergy might be glially mediated. A 60 hour, repeated measures paradigm and multiple co-culture models were used to investigate the cellular basis for opiate-enhanced human immunodeficiency virus neurotoxicity. Morphine co-exposure significantly enhanced transactivator of transcription-induced neuron death when glia were present. Synergistic effects of morphine on transactivator of transcription neurotoxicity were greatest with neuron-glia contact, but also occurred to a lesser extent with glial conditioned medium. Importantly, synergy was lost if glia, but not neurons, lacked µ-opioid receptors, indicating that opiate interactions with human immunodeficiency virus converge at the level of µ-opioid receptor-expressing glia. Morphine enhanced transactivator of transcription-induced inflammatory effectors released by glia, elevating reactive oxygen species, increasing 3-nitrotyrosine production by microglia, and reducing the ability of glia to buffer glutamate. But neuron survival was reduced even more with glial contact than with exposure to conditioned medium, suggesting that noxious elements associated with cell contact augment the toxicity due to soluble factors. Similar morphine-transactivator of transcription synergy was also observed in studies with the clade C sequence of HIV-1 transactivator of transcription, which did not cause neuron death unless morphine was present. Several paradoxical observations related to opiate effects were noted when µ-opioid receptors were specifically ablated from either glia or neurons. This suggests that µ-opioid receptor loss in isolated cell types can fundamentally distort cell-to-cell signalling, revealing opponent processes that may exist in individual cell types. Our findings show the critical role of glia in orchestrating neurotoxic interactions of morphine and transactivator of transcription, and support the emerging concept that combined exposure to opiates and human immunodeficiency virus drives enhanced pathology within the central nervous system.

232: Transport of opiates by P-glycoprotein expressed in preparations of human placental inside-out vesicles

The use of methadone (MT) or buprenorphine (BUP) for treatment of the pregnant opiate-dependent patient improves maternal and neonatal outcome. However, both medications are associated with development of neonatal abstinence syndrome (NAS). The incidence and intensity of NAS should correlate with the concentration of the opiate in the fetal circulation which is regulated by the placenta. The function of human placental P-glycoprotein (P-gp) is the extrusion of its substrates from the feto-placental unit to the maternal circulation. Previously, we demonstrated that MT, BUP, and morphine (MR) inhibit P-gp transport of its prototypic substrate paclitaxel indicating opiate/P-gp interactions. The goal of this investigation was to determine the transport kinetics of [3H]-MT, [3H]-BUP, and [3H]-MR by placental P-gp. Opiate interaction with P-gp was determined by their stimulation of ATP hydrolysis by human P-gp expressing membranes. ATP-dependent transport of [3H]-MT, [3H]-BUP, and [3H]-MR was determined by inside-out brush border membrane vesicles prepared from human placental tissue (n = 60). Specific transport of each opiate was calculated from the difference in its transfer in presence and absence of 600 μM verapamil. The three opiates stimulated ATP hydrolysis by P-gp expressing membranes. The transport of MT and MR by placental P-gp was saturable and revealed the following kinetics parameters: [3H]-MT Kt: 300 ± 100 nM and Vmax 4.3 ± 0.6 pmol/mg protein min; [3H]-MR Kt: 226 ± 200 nM, and Vmax: 3.6 ± 2.4 pmol/mg proteinmin. Verapamil did not inhibit the uptake of [3H]-BUP by inside-out vesicles, indicating that it is not transported by P-gp. The data demonstrate that placental P-gp is involved in regulating the maternal-to-fetal transfer of MT and MR.

Alteration of lymphocyte opioid receptors in methadone maintenance subjects

Methadone maintenance therapy is the most widely used treatment in patients with heroin addiction. Multiple studies have suggested that both current and former heroin addicts entering a methadone maintenance treatment program have altered immune function. Our previous study indicated that heroin addicts have depressed mitogen-stimulated lymphocyte proliferation and a decrease in the modulation of lymphocyte surface markers. This immunosuppression may be mediated via the direct interaction of opiates with lymphocyte opioid receptors. In order to test this hypothesis, the levels of opioid receptors on immune cells obtained from heroin users were determined using saturation binding, and it was found that former heroin addicts on methadone maintenance treatment had a significantly reduced maximum number ( B max) of [ 3H]naloxone binding. The B max values were 51.3 ± 7.6 fmol/mg protein for the non-addicted group and 25.3 ± 3.1 fmol/mg protein for the methadone maintenance group. Opioid receptor gene expression on the immune cell was determined using a semi-quantitative reverse-transcription polymerase chain reaction technique with specific pairs of primers to amplify mu- and delta-opioid receptor mRNAs. Both types of mRNAs were significantly decreased in lymphocytes obtained from the former heroin addicts on methadone maintenance subjects. Similarly, in an in vitro study, 100 μM methadone significantly down-regulated both mu- and delta-opioid receptor mRNA expressions in cultured lymphocytes obtained from naïve subjects. This effect was prevented by including 100 μM naloxone or pretreating with 50 ng/ml pertussis toxin. The data presented indicate that chronic opiate exposure was associated with down-regulation of G-protein-coupled opioid receptor gene expression in human lymphocytes.

Identification of transcriptional regulators of neuropeptide FF gene expression

Neuropeptide FF (NPFF) is an RF-amide peptide with pleiotropic functions in the mammalian central nervous system, including pain modulation, opiate interactions, cardiovascular regulation and neuroendocrine effects. To gain insights into the transcriptional mechanisms that regulate NPFF gene expression, we cloned and sequenced 9.8 and 1.5 kb of the mouse and rat NPFF 5′-flanking region, respectively. Regions with high sequence homology between mouse, rat and human were expected to have high probability to interact with regulatory proteins and were studied further. Electromobility shift assays revealed one region that may interact with the homeobox proteins Oct-1, PDX1, Pit-1 and MEIS and two consensus DRE sites that bind a nuclear protein, which was identified as the downstream regulatory element antagonistic modulator DREAM by supershift assays. The distribution of NPFF gene expression was examined in the mouse using in situ hybridization and RT-PCR. NPFF expression was also evident during mouse embryogenesis. A fixed transcription initiation site for the mouse NPFF gene was found. A novel splice variant with a retained intron of the NPFF gene was characterized. Chimeric luciferase reporter gene constructs for the mouse NPFF gene revealed a minimal promoter region and a region with transcriptional suppressor features. An NGF responsive area was found using mouse NPFF reporter gene constructs. We postulate that Oct-1, PDX1, Pit-1, MEIS and DREAM are likely transcriptional regulators of NPFF gene expression.

Opioid receptor-mediated hyperalgesia and antinociceptive tolerance induced by sustained opiate delivery

Opiates are commonly used to treat moderate to severe pain and can be used over prolonged periods in states of chronic pain such as those associated with cancer. In addition, to analgesic actions, studies show that opiate administration can paradoxically induce hyperalgesia. At the pre-clinical level, such hyperalgesia is associated with numerous pronociceptive neuroplastic changes within the primary afferent fibers and the spinal cord. In rodents, sustained opiate administration also induces antinociceptive tolerance. The mechanisms by which prolonged opiate exposure induces hyperalgesia and the relationship of this state to antinociceptive tolerance remain unclear. The present study was aimed at determining whether sustained opiate-induced hyperalgesia, associated neuroplasticity and antinociceptive tolerance are the result of specific opiate interaction at opiate receptors. Enantiomers of oxymorphone, a mu opioid receptor agonist, were administered to rats by spinal infusion across 7 days. Sustained spinal administration of (−)-oxymorphone, but not its inactive enantiomer (+)-oxymorphone or vehicle, upregulated spinal dynorphin content, produced thermal and tactile hypersensitivity, and produced antinociceptive tolerance. These results indicate that these pronociceptive actions of sustained opiate administration require specific interaction with opiate receptors and are unlikely to be the result of accumulation of potentially excitatory metabolic products. While the precise mechanisms, which may account for these pronociceptive changes remain to be unraveled, the present data point to plasticity initiated by opiate receptor interaction.

Colloquium C01: Mechanisms of HIV‐induced neuropathology: a critical role for astroglia, microglia, and HIV–opiate interactions

Colloquium C01: Mechanisms of HIV‐induced neuropathology: a critical role for astroglia, microglia, and HIV–opiate interactions

Pain- and morphine-associated transcriptional regulation of neuropeptide FF and the G-protein-coupled NPFF2 receptor gene

Neuropeptide FF (NPFF) is involved in pain modulation, especially plasticity during inflammatory and neuropathic pain, and opiate interactions. Its nociceptive functions may be mediated by the NPFF2 receptor. To elucidate the role of the NPFF system in plasticity associated with pathologic pain, we studied the changes of NPFF mRNA and NPFF2 receptor mRNA in rat models of acute colonic inflammation, inflammatory pain, and neuropathic pain. Furthermore, we studied the mRNA levels of both NPFF and NPFF2 receptor in morphine-tolerant rats and after acute morphine injections. We found an activation of spinal NPFF and NPFF2 receptor during early inflammatory pain. Supraspinally, we found an up-regulation of NPFF2 receptor mRNA during acute colonic inflammation and neuropathic pain. Acute, but not chronic, morphine activated the genes supraspinally. The results give further evidence for the involvement of the NPFF system in pain modulation and may provide new therapeutic opportunities for pathologic pain.

Phenelzine–Opiate–Induced Delirium Complicated by Phenelzine Withdrawal

Objective: To report a case of delirium involving a drug interaction of the antidepressant phenelzine in combination with an opiate and to discuss the exacerbation of delirium secondary to a withdrawal syndrome caused by the abrupt discontinuation of phenelzine. Case Summary: A 67-year-old white woman with a history of major depression and chronic anxiety developed delirium shortly after the postsurgical administration of opioid analgesics. In addition, she was taking the antidepressant phenelzine and had been maintained on this medication for approximately 20 years. Her presenting symptoms included combativeness, auditory and visual hallucinations, and persecutory delusions. After development of the delirium, the patient's phenelzine medication was abruptly discontinued, introducing a withdrawal syndrome that further aggravated her condition. Discussion: This case emphasizes the importance of the potentially fatal drug interaction involving phenelzine and opiates and addresses the adverse consequences of abruptly discontinuing phenelzine during phenelzine–opiate–induced delirium. Phenelzine–opiate interactions and phenelzine withdrawal should be considered as possible etiologies of delirium in patients with a history of phenelzine use. Conclusions: Less widely prescribed antidepressants such as phenelzine may be unfamiliar to contemporary clinicians, resulting in adverse consequences for patients, such as phenelzine–opiate drug interactions and phenelzine withdrawal.

Interactions between the endothelium-derived relaxing factor/nitric oxide system and the endogenous opiate system in the modulation of cerebral and spinal vascular CO2 responsiveness.

The role of the L-arginine-nitric oxide (NO) system, the role of the endogenous morphine-like substances (endorphins), and the possible interaction between these two systems in the modulation of regional cerebral and spinal CO2 responsiveness was investigated in anesthetized, ventilated, normotensive, normoxic cats. Regional cerebral blood flow was measured with radiolabeled microspheres in hypocapnic, normocapnic, and hypercapnic conditions in nine individual cerebral and spinal cord regions. General opiate receptor blockade by 1 mg/kg naloxone intravenously alone or NO synthase blockade by 3 mg/kg N(omega)-nitro-L-arginine-methyl ester (L-NAME) intravenously alone caused no changes in regional CO2 responsiveness. Combined administration of these two blocking agents in the very same doses, however, resulted in a strong potentiation, with a statistically significant reduction of the CO2 responsiveness observed. Separation of the blood flow response to hypercapnia and hypocapnia indicates that this reduction occurs only during hypercapnia. Specific mu and delta opiate receptors were blocked by 0.5 mg kg(-1) IV beta-funaltrexamine and 0.4 mg kg(-1) IV naltrindole, respectively. The role of specific mu and delta opiate receptors in the NO-opiate interaction was found to be negligible because neither mu nor delta receptor blockade along with simultaneous NO blockade were able to decrease CO2 responsiveness. The current findings suggest a previously unknown interaction between the endothelium-derived relaxing factor/nitric oxide (EDRF/NO) system and the endogenous opiate system in the cerebrovascular bed during hypercapnic stimulation, with the phenomenon not mediated by mu or delta opiate receptors.

Dopamine–opiate interaction in the regulation of neostriatal and pallidal neuronal activity as assessed by opioid precursor peptides and glutamate decarboxylase messenger RNA expression

Neostriatal GABAergic neurons projecting to the globus pallidus synthesize the opioid peptide enkephalin, while those innervating the substantia nigra pars reticulata and the entopeduncular nucleus synthesize dynorphin. The differential control exerted by dopamine on the activity of these two efferent projections concerns also the biosynthesis of these opioid peptides. Using in situ hybridization histochemistry, we investigated the role of opioid co-transmission in the regulation of neostriatal and pallidal activity. The expression of the messenger RNAs encoding glutamate decarboxylase—the biosynthetic enzyme of GABA—and the precursor peptides of enkephalin (preproenkephalin) and dynorphin (preprodynorphin) were measured in rats after a sustained blockade of opioid receptors by naloxone (s.c. implanted osmotic minipump, eight days, 3 mg/kg per h), and/or a subchronic blockade of D 2 dopamine receptors by haloperidol (one week, 1.25 mg/kg s.c. twice a day). The density of μ opioid receptors in the neostriatum and globus pallidus was determined by autoradiography. Naloxone treatment resulted in a strong up-regulation of neostriatal and pallidal μ opioid receptors that was not affected by the concurrent administration of haloperidol. Haloperidol alone produced a moderate down-regulation of neostriatal and pallidal μ opioid receptors. Haloperidol strongly stimulated the expression of neostriatal preproenkephalin and preprodynorphin messenger RNAs. This effect was partially attenuated by naloxone, which alone produced moderate increases in preproenkephalin and preprodynorphin messenger RNA levels. In the neostriatum, naloxone did not affect either basal or haloperidol-stimulated glutamate decarboxylase messenger RNA expression. A strong reduction of glutamate decarboxylase messenger RNA expression was detected over pallidal neurons following either naloxone or haloperidol treatment, but concurrent administration of the two antagonists did not result in a further decrease. The amplitude of the variations of μ opioid receptor density and of preproenkephalin and preprodynorphin messenger RNA levels suggests that the regulation of neostriatal and pallidal μ opioid receptors is more susceptible to a direct opioid antagonism, while the biosynthesis of opioid peptides in the neostriatum is more dependent on the dopaminergic transmission. The down-regulation of μ opioid receptors following haloperidol represents probably an adaptive change to increased enkephalin biosynthesis and release. The haloperidol-induced increase in neostriatal preprodynorphin messenger RNA expression might result from an indirect, intermittent stimulation of neostriatal D 1 receptors. The haloperidol-induced decrease of pallidal glutamate decarboxylase messenger RNA expression suggests, in keeping with the current functional model of the basal ganglia, that the activation of the striatopallidal projection produced by the interruption of neostriatal dopaminergic transmission reduces the GABAergic output of the globus pallidus. The reduction of pallidal glutamate decarboxylase messenger RNA expression following opioid receptor blockade indicates an indirect, excitatory influence of enkephalin upon globus pallidus neurons and, consequently, a functional antagonism between the two neuroactive substances (GABA and enkephalin) of the striatopallidal projection in the control of globus pallidus output. Through this antagonism enkephalin could partly attenuate the GABA-mediated effects of a dopaminergic denervation on pallidal neuronal activity.

Pharmacological Interaction of Opiates with Various Classes of Centrally Acting Dopaminergic Drugs

The comparative analgesic and sedative (narcosis potentiating) efficacy of mu and kappa opioids was studied as a function of time in rats and mice. The mu agonists, morphine and fentanyl, produced antinociceptive actions against both heat and chemical noxious agents, but the half-lives of their ED50s were longer in the writhing than in the hot plate test. The kappa agonist drugs, bremazocine, ethylketocyclazocine and pentazocine, proved to be inactive against heat nociception, and produced a potent, long-lasting analgesia in the acetic acid writhing test, similar to mu agonists. The combination of two mu agonists resulted in a synergistic interaction and a remarkable prolongation of antinociceptive action. When the kappa-drug bremazocine was coadministered with morphine, there was a significant prolongation of the duration of analgesic action, without any influence on the potency. The interactions of mu and kappa opioids with agonists and antagonists at dopamine receptors were also studied in narcosis. The time course of the naloxone-morphine antagonism in analgesiometric assays revealed similarities, when apparent pA2 values were estimated at the peak of agonist and antagonist activity, but it was different in the writhing test when the pA2 was determined 84 minutes after morphine administration (EDt1/2, half-life belonging to the ED50) while naloxone was given at its peak effect.

Effects of forskolin and phosphodiesterase inhibitors on spinal antinociception by morphine

The effect of intrathecal pretreatment with forskolin and the phosphodiesterase inhibitors Ro 20-1724, rolipram and 3-isobutyl-1-methylxanthine (IBMX) on the antinociceptive action of morphine administered intrathecally was examined using the rat tail-flick test to determine whether inhibition of adenylate cyclase contributed to spinal antinociception. Intrathecal pretreatment with forskolin (10 μg), Ro 20-1724 (15μg) and IBMX (10 μg) inhibited the action of morphine in the tail-flick test. However, pretreatment with Ro 20-1724 (30 μg), rolipram (10 and 30 μg) and IBMX (30 μg) increased the action of morphine. These agents were devoid of intrinsic antinociceptive activity. Inhibition of spinal antinociception by morphine with agents which increase cyclic AMP levels in biochemical experiments is consistent with the hypothesis that some opiate actions are due to inhibition of adenylate cyclase. However, in view of the consistent increase in the effect of morphine with phosphodiesterase inhibitors at higher doses, this hypothesis may be insufficient to account for opiate interactions with the adenylate cyclase system in the spinal cord. some effects on spinal antinociception also may be due to additional pharmacological actions of the agents used.

The local monoaminergic dependency of spinal ketamine

The effects of s.c. doses of naloxone, methysergide and phentolamine on ketamine-induced spinal analgesia were assessed to determine the involvement of opiate, serotonergic and noradrenergic components mediating ketamine's antinociceptive action. Ketamine administered intrathecally (i.t.) produced a significant elevation in tail-flick latency in rats. The spinal antinociceptive effects of ketamine were dose dependently reversed by methysergide (ID 50 = 0.008 mg/kg s.c), phentolamine (ID 50 = 0.88 mg/kg s.c.) and naloxone (ID 50 = 3.0 mg/kg s.c). Unlike morphine, which remains analgesic and depedent on opiate interaction following bilateral lesions of the dorsolateral funiculus (DLF), ketamine analgesia was absent following DLF lesions. Thus, ketamine appears to produce an antinociceptive response which is dependent upon the neuronal activity of the descending pain-inhibitory pathways. The monoaminergic components comprising the descending pathways appear to be more prominent in the action of ketamine than they are in the spinal action of morphine. Furthermore, the spinal opioid receptors involved in ketamine's effect may be different from the μ subtype preferred by morphine.

Investigation of opiate interaction with the sympathetic nervous system in the human forearm

Investigation of opiate interaction with the sympathetic nervous system in the human forearm

Pharmacology of drug self-administration

Limited access to drugs provides a reliable model for their acute-reinforcing effects and a means by which to explore neuropharmacological mechanisms involved in these effects. In limited access situations intravenous self-administration rates of opiates and psychomotor stimulants is inversely related to dose, and competitive antagonists at low doses increase the number of injections self-administered. Competitive agonists decrease drug self-administration. However noncompetitive antagonists tend to produce decreases in self-administration and the specificity of these results are difficult to interpret. A limited access procedure of ethanol (10% v/v) self-administration using a sucrose or saccharin fade out procedure resulted in reliable and stable ethanol (10% v/v) and water self-administration in a concurrent choice situation using nondeprived unselected Wistar and alcohol preferring P-rats. As observed by others, the opiate antagonist naloxone decreased fluid intake in both strain of rats. However, contrary to earlier results naloxone did not produce a selective decrease in ethanol preference. The serotonin antagonist methysergide had no significant effect on fluid intake or ethanol preference. However, the long-acting dopamine agonist bromocriptine decreased ethanol intake and increased water intake producing a significant decrease in ethanol preference. The results with naloxone suggest that opiate interactions with ethanol may reflect a more general effect on consummatory behavior and the results with bromocriptine suggest that the reinforcing effects of low doses of ethanol may involve a dopaminergic component. Future studies should explore further the interactions of ethanol with competitive antagonists (if possible), and fluid intake or ethanol preference with limbic-extrapyramidal circuitry involved in mediating the reinforcing actions of other drugs of abuse.