Quantitative autoradiography of adenosine receptors and NBTI-sensitive adenosine transporters in the brains and spinal cords of mice deficient in the mu-opioid receptor gene

The relationship between sleep and opioids in chronic pain patients

BACKGROUND

Sleep problems are common among chronic pain patients who take opioids. There are documented effects of opioids on sleep architecture; however, the long-term effects of opioids on sleep remain unknown. This study examined whether opioid-naïve participants have better sleep quality than current and previous chronic users of opioids. We also explored whether sleep differed between methadone and buprenorphine users, and whether amount of time since abstaining from opioids was associated with sleep quality.

METHOD

Participants were 120 people with chronic pain (84.2% Caucasian, M_age = 42.0 years, SD = 11.44). They were in one of four groups of 30 participants each: (1) current users of methadone for opioid use disorder (OUD); (2) current users of buprenorphine for OUD; (3) a history of medication-assisted therapy for OUD but currently opioid-abstinent for at least 6 months; (4) those who have less than one month of cumulative lifetime opioids (opioid-naïve group). Only participants in group 1 and group 2 were taking opioids during the time of the study. Participants completed the Pittsburgh Sleep Quality Index and the SF-36.

RESULTS

A MANCOVA revealed that all three groups with current or previous opioid use (i.e., groups 1-3) differed significantly from the opioid-naïve group (group 4) on sleep quality, sleep duration, sleep disturbances, and daytime dysfunction after controlling for sleep medications (all p < .05). For group 1 (methadone users), 2 (buprenorphine users), and 3 (prolonged abstinence), there were no statistically significant differences between each group. There was also a significant relationship between opioid-abstinent weeks and sleep disturbances in the opioid-abstinent group (r = - 0.604, p < .001).

DISCUSSION

The results of this study suggest that opioids interfere with sleep quality, even after months of abstention. Further research into the long-term effects of opioids is warranted and may contribute further to the importance of addressing sleep problems in this population.

Of adenosine and the blues: The adenosinergic system in the pathophysiology and treatment of major depressive disorder

Major depressive disorder (MDD) is the foremost cause of global disability, being responsible for enormous personal, societal, and economical costs. Importantly, existing pharmacological treatments for MDD are partially or totally ineffective in a large segment of patients. As such, the search for novel antidepressant drug targets, anchored on a clear understanding of the etiological and pathophysiological mechanisms underpinning MDD, becomes of the utmost importance. The adenosinergic system, a highly conserved neuromodulatory system, appears as a promising novel target, given both its regulatory actions over many MDD-affected systems and processes. With this goal in mind, we herein review the evidence concerning the role of adenosine as a potential player in pathophysiology and treatment of MDD, combining data from both human and animal studies. Altogether, evidence supports the assertions that the adenosinergic system is altered in both MDD patients and animal models, and that drugs targeting this system have considerable potential as putative antidepressants. Furthermore, evidence also suggests that modifications in adenosine signaling may have a key role in the effects of several pharmacological and non-pharmacological antidepressant treatments with demonstrated efficacy, such as electroconvulsive shock, sleep deprivation, and deep brain stimulation. Lastly, it becomes clear from the available literature that there is yet much to study regarding the role of the adenosinergic system in the pathophysiology and treatment of MDD, and we suggest several avenues of research that are likely to prove fruitful.

Adenosine deaminase activity modulation by some street drug: molecular docking simulation and experimental investigation

BACKGROUND

Adenosine deaminase (ADA) is an enzyme that plays important roles in proliferation, maturation, function and development of the immune system. ADA activity may be altered by variety of substances including synthetic or natural products. Morphine, cocaine and their analogs exert immune suppressive activities by decreasing immune system function. The purpose of this study is to confirm that this possible effect may be modulated by interaction of these substances with ADA activity by experimental and computational method.

METHODS

The structural changes in ADA have been studied in presence of cocaine, ethylmorphine, homatropine, morphine and thebaine by determination of ADA hydrolytic activity, circular dichroism and fluorescence spectroscopy in different concentrations. Docking study was performed to evaluate interaction method of test compound with ADA active site using AutoDock4 software.

RESULTS

According to in-vitro studies all compounds inhibited ADA with different potencies, however thebaine activated it at concentration below 50 μM, ethylmorphine inhibited ADA at 35 μM. Moreover, fluorescence spectra patterns were differed from compounds based on structural resemblance which were very considerable for cocaine and homatropine.

CONCLUSION

The results of this study confirms that opioids and some other stimulant drugs such as cocaine can alter immune function in illegal drug abusers. These findings may lead other investigators to develop a new class of ADA activators or inhibitors in the near future.

Extracellular ADP prevents neuronal apoptosis via activation of cell antioxidant enzymes and protection of mitochondrial ANT-1

Apoptosis in neuronal tissue is an efficient mechanism which contributes to both normal cell development and pathological cell death. The present study explores the effects of extracellular ADP on low [K(+)]-induced apoptosis in rat cerebellar granule cells. ADP, released into the extracellular space in brain by multiple mechanisms, can interact with its receptor or be converted, through the actions of ectoenzymes, to adenosine. The findings reported in this paper demonstrate that ADP inhibits the proapoptotic stimulus supposedly via: i) inhibition of ROS production during early stages of apoptosis, an effect mediated by its interaction with cell receptor/s. This conclusion is validated by the increase in SOD and catalase activities as well as by the GSSG/GSH ratio value decrease, in conjunction with the drop of ROS level and the prevention of the ADP protective effect by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), a novel functionally selective antagonist of purine receptor; ii) safeguard of the functionality of the mitochondrial adenine nucleotide-1 translocator (ANT-1), which is early impaired during apoptosis. This effect is mediated by its plausible internalization into cell occurring as such or after its hydrolysis, by means of plasma membrane nucleotide metabolizing enzymes, and resynthesis into the cell. Moreover, the findings that ADP also protects ANT-1 from the toxic action of the two Alzheimer's disease peptides, i.e. Aβ1-42 and NH2htau, which are known to be produced in apoptotic cerebellar neurons, further corroborate the molecular mechanism of neuroprotection by ADP, herein proposed.

Chronic methamphetamine treatment induces oxytocin receptor up-regulation in the amygdala and hypothalamus via an adenosine A2A receptor-independent mechanism

There is mounting evidence that the neuropeptide oxytocin is a possible candidate for the treatment of drug addiction. Oxytocin was shown to reduce methamphetamine self-administration, conditioned place-preference, hyperactivity and reinstatement in rodents, highlighting its potential for the management of methamphetamine addiction. Thus, we hypothesised that the central endogenous oxytocinergic system is dysregulated following chronic methamphetamine administration. We tested this hypothesis by examining the effect of chronic methamphetamine administration on oxytocin receptor density in mice brains with the use of quantitative receptor autoradiographic binding. Saline (4ml/kg/day, i.p.) or methamphetamine (1mg/kg/day, i.p.) was administered daily for 10 days to male, CD1 mice. Quantitative autoradiographic mapping of oxytocin receptors was carried out with the use of [(125)I]-vasotocin in brain sections of these animals. Chronic methamphetamine administration induced a region specific upregulation of oxytocin receptor density in the amygdala and hypothalamus, but not in the nucleus accumbens and caudate putamen. As there is evidence suggesting an involvement of central adenosine A2A receptors on central endogenous oxytocinergic function, we investigated whether these methamphetamine-induced oxytocinergic neuroadaptations are mediated via an A2A receptor-dependent mechanism. To test this hypothesis, autoradiographic oxytocin receptor binding was carried out in brain sections of male CD1 mice lacking A2A receptors which were chronically treated with methamphetamine (1mg/kg/day, i.p. for 10 days) or saline. Similar to wild-type animals, chronic methamphetamine administration induced a region-specific upregulation of oxytocin receptor binding in the amygdala and hypothalamus of A2A receptor knockout mice and no genotype effect was observed. These results indicate that chronic methamphetamine use can induce profound neuroadaptations of the oxytocinergic receptor system in brain regions associated with stress, emotionality and social bonding and that these neuroadaptations are independent on the presence of A2A receptors. These results may at least partly explain some of the behavioural consequences of chronic methamphetamine use.

The interaction of adenosine and morphine on pentylenetetrazole-induced seizure threshold in mice

Adenosine agonists or low doses of morphine exert anti-convulsant effects in different models of seizures. On the other hand, a tight interaction has been reported between morphine and adenosine in various paradigms. This study investigated the effect of the interaction of adenosine and morphine on seizure susceptibility in the intravenous mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. The researchers used acute systemic administration of morphine, N(6)-cyclohexyladenosine (CHA) (a selective A1 receptor agonist), naltrexone (an opioid receptor antagonist) and 8-Cyclopentyl-1,3-dimethylxanthine (8-CPT) (a selective A1 receptor antagonist). Acute administration of morphine (0.25, 0.5 and 1 mg/kg) or CHA (0.25, 0.5, 1, 2 and 4 mg/kg) raised the threshold of seizures induced by PTZ. Non-effective dose of 8-CPT (2 mg/kg) inhibited the anticonvulsant effects of CHA (0.5 and 1 mg/kg). Combination of sub-effective doses of morphine (0.125 mg/kg) and CHA (0.125 mg/kg) increased clonic seizure latency showing the additive effect of morphine and CHA. The enhanced latency induced by combination of low doses of morphine and CHA completely reversed by 8-CPT (2 mg/kg) or naltrexone (1 mg/kg). Moreover, 8-CPT (2 mg/kg) inhibited anticonvulsant effects of morphine (0.25 and 0.5 mg/kg) and naltrexone (1 mg/kg) inhibited anticonvulsant effects of CHA (0.25, 0.5 and 1 mg/kg). Combination of low doses of 8-CPT (1 mg/kg) and naltrexone (0.5 mg/kg) inhibited the anticonvulsant effect of CHA (0.5 and 1 mg/kg). In conclusion, adenosine and morphine exhibit an additive effect on the enhancement of the pentylenetetrazole-induced seizure threshold in mice, probably through A1 or μ receptors.

Opioid-induced decreases in rat brain adenosine levels are reversed by inhibiting adenosine deaminase

BACKGROUND

Opioids disrupt sleep and adenosine promotes sleep, but no studies have characterized the effects of opioids on adenosine levels in brain regions known to regulate states of arousal. Delivering opioids to the pontine reticular formation (PRF) and substantia innominata (SI) region of the basal forebrain disrupts sleep. In contrast, administering adenosine agonists to the PRF or SI increases sleep. These findings encouraged the current study testing the hypothesis that microdialysis delivery of opioids to the PRF or SI decreases adenosine levels in the PRF or SI, respectively.

METHODS

A microdialysis probe was placed in the PRF of isoflurane anesthetized rats and perfused with Ringer's solution (control) followed by Ringer's solution containing morphine (0, 10, 30, 100, or 300 microm), fentanyl (100 microm), morphine (100 microm) and the adenosine deaminase inhibitor EHNA (100 microm), or naloxone (10 microm) and morphine (100 microm). Additional experiments measured adenosine levels in the SI before and during microdialysis delivery of morphine, fentanyl, and morphine plus EHNA.

RESULTS

Morphine caused a significant (P < 0.05) concentration-dependent decrease in PRF adenosine levels. The significant decrease (-20%) in adenosine caused by 100 microm morphine was blocked by coadministration of naloxone. Fentanyl also significantly decreased (-13.3%) PRF adenosine. SI adenosine levels were decreased by morphine (-26.8%) and fentanyl (-27.4%). In both PRF and SI, coadministration of morphine and EHNA prevented the significant decrease in adenosine levels caused by morphine alone.

CONCLUSIONS

These data support the interpretation that decreased adenosine levels in sleep-regulating brain regions may be one of the mechanisms by which opioids disrupt sleep.

Pharmacological evidence for the involvement of the opioid system in the antidepressant-like effect of adenosine in the mouse forced swimming test

This study investigated the involvement of the opioid system in the antidepressant-like effect of adenosine in the forced swimming test. The effect of adenosine (10 mg/kg, i.p.) was prevented by the pretreatment of mice with naloxone (1 mg/kg, i.p., a nonselective opioid receptor antagonist), naltrindole (3 mg/kg, i.p., a selective delta-opioid receptor antagonist), clocinnamox (1 mg/kg, i.p., an irreversible mu-opioid receptor antagonist), and 2-(3,4-dichlorophenyl)-Nmethyl-N-[(1S)-1-(3-isothiocyanatophenyl)-2-(1-pyrrolidinyl)ethyl]acetamide (DIPPA; 1 mg/kg, i.p., a selective kappa-opioid receptor antagonist), but not with naloxone methiodide (1 mg/kg, s.c., a nonselective opioid receptor antagonist that does not cross the blood-brain barrier). Naloxone also prevented the anti-immobility effect of cyclohexyladenosine (CHA, 0.1 mg/kg, i.p., a selective adenosine A(1) receptor agonist) and N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl]adenosine (DPMA, 1 mg/kg, i.p., a selective adenosine A(2A) receptor agonist). The administration of DIPPA (0.1 mg/kg, i.p.) or morphine (1 mg/kg, s.c., a nonselective opioid receptor agonist), but not naltrindole (0.3 mg/kg, i.p.) and clocinnamox (0.1 mg/kg, i.p.) potentiated the effect of a subeffective dose of adenosine (1 mg/kg, i.p.) in the forced swimming test, without affecting the locomotor activity. No additive effect in the immobility time was observed when mice were treated with morphine (5 mg/kg, s.c.) plus adenosine (10 mg/kg, i.p.). These results indicate that the anti-immobility effect of adenosine in the forced swimming test, via adenosine A(1) and A(2A) receptors, is mediated by an interaction with the opioid system, likely dependent on an activation of mu- and delta-opioid receptors and an inhibition of kappa-opioid receptors.

Modulation of paracetamol antinociception by caffeine and by selective adenosine A2 receptor antagonists in mice

This study investigated the involvement of adenosine receptors in the interaction between paracetamol and caffeine in mice, using the adenosine A2A receptor antagonist 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261) and the adenosine A2B receptor antagonist 1-propyl-8-p-sulfophenylxanthine (PSB1115), in the tail immersion and hot-plate tests. Paracetamol (10-200 mg/kg) was antinociceptive in both tests, but, in contrast to previous studies, caffeine (10 mg/kg) was pronociceptive in the tail immersion test, and reduced the effects of paracetamol in both tests. SCH58261 (3 mg/kg) was antinociceptive in both tests and in its presence paracetamol (50 mg/kg) had no further effect. PSB1115 (10 mg/kg) had little effect alone but potentiated the effect of paracetamol (50 mg/kg) in the hot-plate test and abolished it in the tail immersion test. These results suggest that adenosine A2B receptors may be involved in the action of paracetamol in a pathway-dependent manner, and also support the existence of pronociceptive adenosine A2A receptors.

Opioid-induced preconditioning: recent advances and future perspectives

Opioids, named by Acheson for compounds with morphine-like actions despite chemically distinct structures, have received much research interest, particularly for their central nervous system (CNS) actions involved in pain management, resulting in thousands of scientific papers focusing on their effects on the CNS and other organ systems. A more recent area which may have great clinical importance concerns the role of opioids, either endogenous or exogenous compounds, in limiting the pathogenesis of ischemia-reperfusion injury in heart and brain. The role of endogenous opioids in hibernation provides tantalizing evidence for the protective potential of opioids against ischemia or hypoxia. Mammalian hibernation, a distinct energy-conserving state, is associated with depletion of energy stores, intracellular acidosis and hypoxia, similar to those which occur during ischemia. However, despite the potentially detrimental cellular state induced with hibernation, the myocardium remains resilient for many months. What accounts for the hypoxia-tolerant state is of great interest. During hibernation, circulating levels of opioid peptides are increased dramatically, and indeed, are considered a "trigger" of hibernation. Furthermore, administration of opioid antagonists can effectively reverse hibernation in mammals. Therefore, it is not surprising that activation of opioid receptors has been demonstrated to preserve cellular status following a hypoxic insult, such as ischemia-reperfusion in many model systems including the intestine [Zhang, Y., Wu, Y.X., Hao, Y.B., Dun, Y. Yang, S.P., 2001. Role of endogenous opioid peptides in protection of ischemic preconditioning in rat small intestine. Life Sci. 68, 1013-1019], skeletal muscle [Addison, P.D., Neligan, P.C., Ashrafpour, H., Khan, A., Zhong, A., Moses, M., Forrest, C.R., Pang, C.Y., 2003. Noninvasive remote ischemic preconditioning for global protection of skeletal muscle against infarction. Am. J. Physiol. Heart Circ. Physiol. 285, H1435-H1443], the CNS [Borlongan, C.V., Wang, Y., Su, T.P., 2005. Delta opioid peptide (d-ala 2, d-leu 5) enkephalin: linking hiberation and neuroprotection. Front Biosci. 9, 3392-3398] and the myocardium [Romano, M.A., Seymour, E.M., Berry, J.A., McNish, R.A., Bolling, S.F., 2004. Relative contribution of endogenous opioids to myocardial ischemic tolerance. J Surg Res. 118, 32-37; Peart, J.N., Gross, G.J., 2004a. Exogenous activation of delta- and kappa-opioid receptors affords cardioprotection in isolated murine heart. Basic Res Cardiol. 99(1), 29-37]. For the purpose of this review, we will focus primarily on the protective effects of opioids against post-reperfusion myocardial stunning and infarction.

Therapeutic potential of adenosine A2A receptor antagonists in Parkinson's disease

In the pursuit of improved treatments for Parkinson's disease (PD), the adenosine A(2A) receptor has emerged as an attractive nondopaminergic target. Based on the compelling behavioral pharmacology and selective basal ganglia expression of this G-protein-coupled receptor, its antagonists are now crossing the threshold of clinical development as adjunctive symptomatic treatment for relatively advanced PD. The antiparkinsonian potential of A(2A) antagonism has been boosted further by recent preclinical evidence that A(2A) antagonists might favorably alter the course as well as the symptoms of the disease. Convergent epidemiological and laboratory data have suggested that A(2A) blockade may confer neuroprotection against the underlying dopaminergic neuron degeneration. In addition, rodent and nonhuman primate studies have raised the possibility that A(2A) receptor activation contributes to the pathophysiology of dyskinesias-problematic motor complications of standard PD therapy--and that A(2A) antagonism might help prevent them. Realistically, despite being targeted to basal ganglia pathophysiology, A(2A) antagonists may be expected to have other beneficial and adverse effects elsewhere in the central nervous system (e.g., on mood and sleep) and in the periphery (e.g., on immune and inflammatory processes). The thoughtful design of new clinical trials of A(2A) antagonists should take into consideration these counterbalancing hopes and concerns and may do well to shift toward a broader set of disease-modifying as well as symptomatic indications in early PD.

An investigation of binding sites for paracetamol in the mouse brain and spinal cord

Quantitative autoradiography has been used to assess whether [3H]paracetamol (3 microM) binds specifically to any area of the murine brain and spinal cord and to investigate whether paracetamol (1-100 microM) competes for binding to the nociceptin opioid peptide (NOP) receptor or to the nitrobenzylthioinosine (NBTI)-sensitive adenosine transporter in the brains of mice. [3H]paracetamol binding was homogenous and, although there was some indication of specific binding overall, this binding in most individual regions failed to reach statistical significance. However, thoracic segments of the spinal cord were found to have significantly higher specific binding than cervical and lumbar regions. Paracetamol did not significantly compete for binding to the NOP receptor or to the NBTI-sensitive adenosine transporter, showing that it does not mediate its effect via these sites. Although paracetamol did bind specifically to the murine brain and spinal cord, the binding was not region-specific, suggesting binding is not related to any particular neurotransmitter system.

Persistent upregulation of μ-opioid, but not adenosine, receptors in brains of long-term withdrawn escalating dose “binge” cocaine-treated rats

There is evidence showing that the opioid and adenosine systems play an important role in cocaine addiction; fewer studies have examined their roles in cocaine withdrawal. To determine whether cocaine and/or chronic withdrawal from cocaine alters the specific components of the opioid and adenosine systems, we carried out quantitative autoradiographic mapping of mu-opioid, A1 and A2A adenosine receptors in the brains of rats treated with an escalating dose "binge" cocaine administration paradigm and of rats chronically withdrawn from cocaine. Male Fischer rats were injected with saline or cocaine (15 x 3 mg/kg/day for 4 days, 20 x 3 mg/kg/day for 4 days, 25 x 3 mg/kg/day for 4 days and 30 x 3 mg/kg/day for 2 days) at 1-h intervals for 14 days. Similarly treated rats were withdrawn from that paradigm for 14 days. A significant increase in [(3)H]DAMGO binding to mu-receptors was detected in the frontal and cingulate cortex, as well as in the caudate putamen, of long-term withdrawn rats after an escalating dose "binge" cocaine administration paradigm and in chronic cocaine-treated rats. No significant cocaine-induced change was found in A1 or A2A receptor binding in any region analyzed. These results reconfirm that mu-opioid (MOP) receptors undergo upregulation in response to chronic escalating dose "binge" cocaine administration. This upregulation was shown for the first time to persist at least 14 days into withdrawal after escalating "binge" cocaine.

Quantitative autoradiography of adenosine receptors and NBTI-sensitive adenosine transporters in the brains of mice deficient in the preproenkephalin gene

There is a large body of evidence indicating important interactions between the adenosine and the opioid systems in regulating pain, opioid dependence and withdrawal. Mice lacking the proenkephalin gene and therefore lacking the endogenous enkephalin peptides have been successfully developed and exhibit decreased locomotor activity, are hyperalgesic and show enhanced anxiety and aggression. In addition, an upregulation of mu and delta receptors was also observed in the brains of knockout mice. To investigate if there are any compensatory alterations in adenosine systems in the brains of mutant mice, we have carried out quantitative autoradiographic mapping of A(1) and A(2A) adenosine receptors and nitrobenzylthioinosine (NBTI)-sensitive adenosine transporters in the brains of wild-type and homozygous enkephalin knockout mice. Adjacent coronal brain sections were cut from brains of +/+ and -/- mice for the determination of binding of [(3)H]1,3-dipropyl-8-cyclopentylxanthine ([(3)H]DPCPX), [(3)H]2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine ([(3)H]CGS21680) or [(3)H]NBTI to A(1) and A(2A) adenosine receptors and NBTI-sensitive adenosine transporters, respectively. A small but significant increase in [(3)H]DPCPX and [(3)H]NBTI binding but no significant change in [(3)H]CGS21680 binding was detected in enkephalin knockout brains. The results provide further evidence of functional interactions in the brain between opioid receptors and A(1) adenosine receptors as well as NBTI-sensitive adenosine transporters but not A(2A) receptors.

The adenosine transporter, mENT1, is a target for adenosine receptor signaling and protein kinase Cepsilon in hypoxic and pharmacological preconditioning in the mouse cardiomyocyte cell line, HL-1

Brief exposure of the heart to hypoxia results in less cellular damage after subsequent hypoxia, an effect known as preconditioning (PC). PC has been widely studied but is still not fully understood. Adenosine (Ado), adenosine receptors, and protein kinase C (PKC) have been implicated as integral components of PC. Adenosine (nucleoside) transporters (NTs) facilitate flux of Ado across cell membranes, but their role in PC is unknown. Therefore, we used the murine cardiomyocyte cell line, HL-1, and asked if there was feedback regulation of NTs by Ado, Ado receptors, and PKC following either hypoxic or pharmacological PC. Activation (by specific agonists) of A1 or A3 Ado receptors or PKC resulted in PC in HL-1. The A1 (but not A3) receptor is coupled to PKCepsilon, and activation of PKCepsilon (by specific peptide agonist) resulted in PC. Moreover, PKCepsilon stimulates Ado uptake via the predominant NT in HL-1, mouse equilibrative nucleoside transporter 1 (mENT1). Studies in primary neonatal mouse cardiomyocytes confirmed our observations in HL-1 cells. Hypoxic challenge led to a rapid increase in, and efflux of, intracellular Ado from cells, which was blocked by NT inhibitors (dipyridamole/nitrobenzylthioinosine). Moreover, NT inhibition during hypoxia or PC was highly protective, suggesting that Ado loss contributes to decreased cell viability. Our data suggest that hypoxic challenge causes an efflux of Ado via ENTs, activation of A1 and/or A3 receptors, signaling through PKCepsilon, and activation of ENT1. Since Ado is required for ATP synthesis on reperfusion, this feedback regulation of mENT1 would promote reuptake of Ado.

Serotonin transporter in substance P (neurokinin 1) receptor knock-out mice

We recently demonstrated that mice lacking the gene for substance P (neurokinin 1) receptors (NK1-/-) show improved cortical dialysate serotonin (5-HT) responses to paroxetine [J. Neurosci. 21 (2001) 8188]. To test for changes that may involve the 5-HT transporter (5-HTT) in these mutant mice, in vivo/in vitro studies were performed. Autoradiographic quantification of 5-HTT was performed: [3H]citalopram binding did not reveal any modification of 5-HT binding sites in the dorsal raphe nucleus (DRN) of wild-type NK1+/+ control and mutant NK1-/- mice. These results were further confirmed by 5-HTT mRNA quantification using competitive reverse transcription and polymerase chain reaction (RT-PCR) assay, which showed similar messenger levels in the DRN of both mice genotypes. The functional status of 5-HTT in vivo was tested by using the zero net flux method of quantitative microdialysis in two serotonergic nerve terminal regions, the frontal cortex and ventral hippocampus, of wild-type NK1+/+ and NK1-/- mice. Neither basal extracellular 5-HT levels nor the 5-HT extraction fraction of the probe (Ed an index of 5-HT uptake in vivo) differed between wild-type and mutant mice in the two brain regions studied. These results suggest that no compensatory response to the constitutive deletion of the tachykinin NK1 receptor involving changes in the activity of the selective 5-HT transporter occurred in the DRN, frontal cortex and ventral hippocampus in mice.

Inhibition of glucose uptake in murine cardiomyocyte cell line HL-1 by cardioprotective drugs dilazep and dipyridamole

Inhibition of adenosine reuptake by nucleoside transport inhibitors, such as dipyridamole and dilazep, is proposed to increase extracellular levels of adenosine and thereby potentiate adenosine receptor-dependent pathways that promote cardiovascular health. Thus adenosine can act as a paracrine and/or autocrine hormone, which has been shown to regulate glucose uptake in some cell types. However, the role of adenosine in modulating glucose transport in cardiomyocytes is not clear. Therefore, we investigated whether exogenously applied adenosine or inhibition of adenosine transport by S-(4-nitrobenzyl)-6-thioinosine (NBTI), dipyridamole, or dilazep modulated basal and insulin-stimulated glucose uptake in the murine cardiomyocyte cell line HL-1. HL-1 cell lysates were subjected to SDS-PAGE and immunoblotting to determine which GLUT isoforms are present. Glucose uptake was measured in the presence of dipyridamole (3-300 microM), dilazep (1-100 microM), NBTI (10-500 nM), and adenosine (50-250 microM) or the nonmetabolizable adenosine analog 2-chloro-adenosine (250 microM). Our results demonstrated that HL-1 cells possess GLUT1 and GLUT4, the isoforms typically present in cardiomyocytes. We found no evidence for adenosine-dependent regulation of basal or insulin-stimulated glucose transport in HL-1 cardiomyocytes. However, we did observe a dose-dependent inhibition of glucose transport by dipyridamole (basal, IC(50) = 12.2 microM, insulin stimulated, IC(50) = 13.09 microM) and dilazep (basal, IC(50) = 5.7 microM, insulin stimulated, IC(50) = 19 microM) but not NBTI. Thus our data suggest that dipyridamole and dilazep, which are widely used to specifically inhibit nucleoside transport, have a broader spectrum of transport inhibition than previously described. Moreover, these data may explain previous observations, in which dipyridamole was noted to be proischemic at high doses.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Adenosine and opioid receptor-mediated cardioprotection in the rat: evidence for cross-talk between receptors

The relative roles of free-radical production, mitochondrial ATP-sensitive K+ (mitoKATP) channels and possible receptor cross-talk in both opioid and adenosine A1 receptor (A1AR) mediated protection were assessed in a rat model of myocardial infarction. Sprague-Dawley rats were subjected to 30 min of occlusion and 90 min of reperfusion. The untreated rats exhibited an infarct of 58.8 +/- 2.9% [infarct size (IS)/area at risk (AAR), %] at the end of reperfusion. Pretreatment with either the nonselective opioid receptor agonist morphine or the selective A1AR agonist 2-chloro-cyclopentyladenosine (CCPA) dramatically reduced IS/AAR to 41.1 +/- 2.2% and 37.9 +/- 5.5%, respectively (P < 0.05). Protection afforded by either morphine or CCPA was abolished by the reactive oxygen species scavenger N-(2-mercaptopropionyl)glycine or the mitoKATP channel blocker 5-hydroxydecanoate. Both morphine- and CCPA-mediated protection were attenuated by the selective A1AR antagonist 1,3-dipropyl-8-cyclopentylxanthine and the selective delta1-opioid receptor (DOR) antagonist 7-benzylidenealtrexone. Simultaneous administration of morphine and CCPA failed to enhance the infarct-sparing effect of either agonist alone. These data suggest that both DOR and A1AR-mediated cardioprotection are mitoKATP and reactive oxygen species dependent. Furthermore, these data suggest that there are converging pathways and/or receptor cross-talk between A1AR- and DOR-mediated cardioprotection.

Quantitative autoradiography of adenosine receptors in brains of chronic naltrexone-treated mice

1. Manipulation of micro opioid receptor expression either by chronic morphine treatment or by deletion of the gene encoding micro opioid receptors leads to changes in adenosine receptor expression. Chronic administration of the opioid receptor antagonist naltrexone leads to upregulation of micro receptor binding in the brain. 2. To investigate if there are any compensatory alterations in adenosine systems in the brains of chronic naltrexone-treated mice, we carried out quantitative autoradiographic mapping of A(1) and A(2A) adenosine receptors in the brains of mice treated for 1 week with naltrexone (8 mg(-1) kg(-1) day(-1)), administered subcutaneously via osmotic minipump. 3. Adjacent coronal brain sections were cut from chronic saline- and naltrexone-treated mice for the determination of binding of [(3)H] D-Ala(2)-MePhe(4)-Gly-ol(5) enkephalin ([(3)H] DAMGO), [(3)H]1,3-dipropyl-8-cyclopentylxanthine ([(3)H] DPCPX) or [(3)H] 2-[p-(2-carbonylethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine ([(3)H] CGS21680) to micro, A(1) and A(2A) receptors, respectively. 4. A significant increase in micro and A(1) receptor binding was detected in chronic naltrexone-treated brains. The changes in micro receptors were significant in several regions, but changes in A(1) were relatively smaller but showed significant upregulation collectively. No significant change in A(2A) receptor binding was detected in chronic naltrexone-treated brains. 5. The results show that blockade of opioid receptors causes upregulation of A(1) receptors, but not A(2A) receptors, by as yet undefined mechanisms.

Changes in spinal delta and kappa opioid systems in mice deficient in the A2A receptor gene

A large body of evidence indicates important interactions between the adenosine and opioid systems in regulating pain at both the spinal and supraspinal level. Mice lacking the A(2A) receptor gene have been developed successfully, and these animals were shown to be hypoalgesic. To investigate whether there are any compensatory alterations in opioid systems in mutant animals, we have performed quantitative autoradiographic mapping of mu, delta, kappa, and opioid receptor-like (ORL1) opioid receptors in the brains and spinal cords of wild-type and homozygous A(2A) receptor knock-out mice. In addition, mu-, delta-, and kappa-mediated antinociception using the tail immersion test was tested in wild-type and homozygous A(2A) receptor knock-out mice. A significant reduction in [3H]deltorphin-I binding to delta receptors and a significant increase in [3H]CI-977 binding to kappa receptors was detected in the spinal cords but not in the brains of the knock-out mice. Mu and ORL1 receptor expression were not altered significantly. Moreover, a significant reduction in delta-mediated antinociception and a significant increase in kappa-mediated antinociception were detected in mutant mice, whereas mu-mediated antinociception was unaffected. Comparison of basal nociceptive latencies showed a significant hypoalgesia in knock-out mice when tested at 55 degrees C but not at 52 degrees C. The results suggest a functional interaction between the spinal delta and kappa opioid and the peripheral adenosine system in the control of pain pathways.