Biomedical subjects

B L Kieffer

Publications and source records attributed to B L Kieffer.

At least 19 recordsLinked to original sources

PubMed2006

Mu opioid receptor-effector coupling and trafficking in dorsal root ganglia neurons.

Morphine induces profound analgesic tolerance in vivo despite inducing little internalization of the mu opioid receptor (muOR). Previously proposed explanations suggest that this lack of internalization could either lead to prolonged signaling and associated compensatory changes in downstream signaling systems, or that the receptor is unable to recycle and resensitize and so loses efficacy, either mechanism resulting in tolerance. We therefore examined, in cultured neurons, the relationship between muOR internalization and desensitization in response to two agonists, D-Ala2, N-MePhe4, Gly5-ol-enkephalin (DAMGO) and morphine. In addition, we studied the chimeric mu/delta opioid receptor (mu/ partial differentialOR) which could affect internalization and desensitization in neurons. Dorsal root ganglia neurons from muOR knockout mice were transduced with an adenovirus expressing either receptor and their respective internalization, desensitization and trafficking profiles determined. Both receptors desensitized equally, measured by Ca2+ current inhibition, during the first 5 min of agonist exposure to DAMGO or morphine treatment, although the mu/partial differentialOR desensitized more extensively. Such rapid desensitization was unrelated to internalization as DAMGO, but not morphine, internalized both receptors after 20 min. In response to DAMGO the mu/partial differentialOR internalized more rapidly than the muOR and was trafficked through Rab4-positive endosomes and lysosomal-associated membrane protein-1-labeled lysosomes whereas the muOR was trafficked through Rab4 and Rab11-positive endosomes. Chronic desensitization of the Ca2+ current response, after 24 h of morphine or DAMGO incubation, was seen in the DAMGO, but not morphine-treated, muOR-expressing cells. Such persistence of signaling after chronic morphine treatment suggests that compensation of downstream signaling systems, rather than loss of efficacy due to poor receptor recycling, is a more likely mechanism of morphine tolerance in vivo. In contrast to the muOR, the mu/partial differentialOR showed equivalent desensitization whether morphine or DAMGO treated, but internalized further with DAMGO than morphine. Such ligand-independent desensitization could be a result of the observed higher rate of synthesis and degradation of this chimeric receptor.

Analgesics, Opioid↗

PubMed2005

Physiological control of emotion-related behaviors by endogenous enkephalins involves essentially the delta opioid receptors.

The endogenous pentapeptide enkephalins bind to the mu and delta opioid receptors, with a slightly higher affinity for the latter. It remains a controversy regarding the respective physiological role of mu and delta opioid receptors in the control of emotion and motivation. One of the difficulties to investigate this problem is the low tonic extracellular release of enkephalins in various brain structures. To overcome this problem the synaptic levels of these pentapeptides were enhanced by inhibition of enzymes involved in their catabolism with the selective inhibitor H3N-CH(CH2-CH2-S-CH3)-CH2-S-S-CH2-CH(CH2phi)-CONH-CH(CH2phi)-COOCH2phi (RB101). This compound was shown to increase the extracellular levels and lifetime of endogenous enkephalins. Similar responses were obtained in wild-type and mu opioid receptor knockout mice following RB 101 administration in behavioral tests measuring locomotor activity, anxiety (elevated O-maze), and motivation (forced swim test and conditioned suppression of motility). In contrast, RB 101 led to antinociceptive responses only in wild-type animals using hot plate and tail immersion tests. These results clearly demonstrate the critical role of delta opioid receptors activated by the endogenous opioid peptides, in the physiological control of emotion- and motivation-related behaviors. In contrast, antinociceptive modulation, at least with respect to thermal nociceptive stimuli, involves enkephalin-activated mu opioid receptors. These findings could open new perspectives in the treatment of mood disorders using either inhibitors of enkephalin catabolism or delta opioid agonists.

Analysis of Variance↗

PubMed2004

Inverse agonism and neutral antagonism at wild-type and constitutively active mutant delta opioid receptors.

The delta opioid receptor modulates nociceptive and emotional behaviors. This receptor has been shown to exhibit measurable spontaneous activity. Progress in understanding the biological relevance of this activity has been slow, partly due to limited characterization of compounds with intrinsic negative activity. Here, we have used constitutively active mutant (CAM) delta receptors in two different functional assays, guanosine 5'-O-(3-thio)triphosphate binding and a reporter gene assay, to test potential inverse agonism of 15 delta opioid compounds, originally described as antagonists. These include the classical antagonists naloxone, naltrindole, 7-benzylidene-naltrexone, and naltriben, a new set of naltrindole derivatives, H-Tyr-Tic-Phe-Phe-OH (TIPP) and H-Tyr-TicPsi[CH2N]Cha-Phe-OH [TICP(Psi)], as well as three 2',6'-dimethyltyrosine-1,2,3,4-tetrahydroquinoline-3-carboxylate (Dmt-Tic) peptides. A reference agonist, SNC 80 [(+)-4-[(alphaR)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide], and inverse agonist, ICI 174864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu), were also included. In a screen using wild-type and CAM M262T delta receptors, naltrindole (NTI) and close derivatives were mostly inactive, and TIPP behaved as an agonist, whereas Dmt-Tic-OH and N,N(CH3)2-Dmt-Tic-NH2 showed inverse agonism. The two latter compounds showed negative activity across 27 CAM receptors, suggesting that this activity was independent from the activation mechanism. These two compounds also exhibited nanomolar potencies in dose-response experiments performed on wild-type, M262T, Y308H, and C328R CAM receptors. TICP(Psi) exhibited strong inverse agonism at the Y308H receptor. We conclude that the stable N,N(CH3)2-Dmt-Tic-NH2 compound represents a useful tool to explore the spontaneous activity of delta receptors, and NTI and novel derivatives behave as neutral antagonists.

Alkaline Phosphatase↗

PubMed2004

Neurofilament proteins and cAMP pathway in brains of mu-, delta- or kappa-opioid receptor gene knock-out mice: effects of chronic morphine administration.

Opiate addiction is associated with abnormalities of neurofilament (NF) proteins and upregulation of cAMP signaling in the brain, which may modulate neuronal plasticity. This study investigated, using gene-targeted mice lacking mu-, delta- or kappa-opioid receptors, the role of these receptors in modulating the basal activity and the chronic effects of morphine on both intracellular targets. In WT mice, chronic treatment (5 days) with morphine (20-100 mg/kg) resulted in decreases in the immunodensity of neurofilament (NF)-L in the cerebral cortex (14-23%). In contrast, chronic morphine did not decrease NF-L in cortices of mu-, delta-, and kappa-KO mice, suggesting the involvement of the three types of opioid receptors in this effect of morphine. Also, the marked increase in phosphorylated NF-H induced by chronic morphine in WT mice (two-fold) was abolished in mu -KO mice. In cortex and/or striatum of mu-, delta- and kappa-KO mice, the basal immunodensities of Galphai1/2 proteins, the catalytic isoform (Calpha) of protein kinase A (PKA) and the total content of cAMP response element-binding protein (CREB, the nuclear target of PKA) were not different from those of WT mice. In contrast, phosphorylated CREB (the active form of this transcription factor) was reduced in cortex and/or striatum (23-26%) of mu- and delta-KO mice, but not in kappa-KO animals. These results suggest that the endogenous opioid tone acting on mu-/delta-receptors tonically stimulate CREB activation in the brain. In cortex and/or striatum of WT mice, chronic morphine did not induce upregulation of the main components of the cAMP signaling pathway. In contrast, chronic morphine treatment in mu-KO mice, but not in delta- or kappa-KO, resulted in a paradoxical upregulation of Galphai1/2 (12-19%), PKA (19-21%,) and phosphorylated CREB (21-73%), but not total CREB, in cortex and/or striatum. The induction of heterologous receptor adaptations in mu-KO mice may explain this paradoxical effect of morphine.

Animals↗

PubMed2004

Functional coupling, desensitization and internalization of virally expressed mu opioid receptors in cultured dorsal root ganglion neurons from mu opioid receptor knockout mice.

Although mu opioid receptors desensitize in various cell lines in vitro, the relationship of this change in signaling efficacy to the development of tolerance in vivo remains uncertain. It is clear that a system is needed in which functional mu opioid receptor expression is obtained in appropriate neurons so that desensitization can be measured, manipulated, and mutated receptors expressed in this environment. We have developed a recombinant system in which expression of a flag-tagged mu opioid receptor is returned to dorsal root ganglia neurons from mu opioid receptor knockout mice in vitro. Flow cytometry analysis showed that adenoviral-mediated expression of the amino-terminal flag-tagged mu opioid receptor in neurons resulted in approximately 1.3x10(6) receptors/cell. Many mu opioid receptor cell lines express a similar density of receptors but this is approximately 7x greater than the number of endogenous receptors expressed by matched wild-type neurons. Inhibition of the high voltage-activated calcium currents in dorsal root ganglia neurons by the mu agonist, D-Ala(2), N-MePhe(4), Gly(5)-ol-enkephalin (DAMGO), was not different between the endogenous and flag-tagged receptor at several concentrations of DAMGO used. Both receptors desensitized equally over the first 6 h of DAMGO pre-incubation, but after 24 h the response of the endogenous receptor to DAMGO had desensitized further than the flag- tagged receptor (71+/-3 vs 29+/-7% respectively; P<0.002), indicating less desensitization in neurons expressing a higher density of receptor. Using flow cytometry to quantify the percentage of receptors remaining on the neuronal cell surface, the flag-tagged receptor internalized by 17+/-1% after 20 min and 55+/-2% after 24 h of DAMGO. These data indicate that this return of function model in neurons recapitulates many of the characteristics of endogenous mu opioid receptor function previously identified in non-neuronal cell lines.

Animals↗

PubMed2004

Contrasting effects of mu opioid receptor and delta opioid receptor deletion upon the behavioral and neurochemical effects of cocaine.

Conventional brain microdialysis was used to assess basal and cocaine-induced dopamine (DA) levels in the nucleus accumbens of wildtype (WT) C57BL/6J mice and mice with constitutive deletion of ether mu- or delta-opioid receptors (MOR or DOR knockout [KO], respectively). Locomotor activity was assessed in these same animals. Basal locomotor activity of DOR KO was elevated relative to MOR KO, but did not differ from that of WT mice. DOR mice, but not WT or MOR KO, exhibited a significant increase in activity in response to an injection of saline. The acute administration of cocaine produced a dose-related increase in locomotor activity in the three genotypes. The locomotor activating effects of a low dose (10 mg/kg) of cocaine were enhanced in DOR KO mice whereas the locomotor activating effects of both a low and higher (20 mg/kg) dose of cocaine were reduced in MOR KO animals. Microdialysis studies revealed no difference between genotypes in basal DA levels. Acute administration of cocaine, but not saline, increased DA levels in WT and KO animals. Paradoxically, however, the magnitude of this effect was smaller in DOR KO as compared with that in either WT or MOR KO. These data indicate that constitutive deletion of either MOR or DOR results in contrasting effects upon responsiveness to cocaine, which is consistent with the distinct phenotypes previously described for these mutants.

Animals↗

PubMed2003

Differential involvement of the mu and kappa opioid receptors in spatial learning.

In order to test the role of mu and kappa opioid receptors (Mu opioid receptor (MOR) and Kappa opioid receptor (KOR)) in hippocampal-dependent spatial learning, we analyzed genetically engineered null mutant mice missing the functional MOR or KOR gene. Compared to wild-type mice, the homozygous MOR null mutants exhibited an impairment in the ultimate level of spatial learning as shown in two distinct tasks, the 8-arm radial-maze and the Morris water-maze. Control behaviors were normal. The learning impairment could be associated with the impairment we found in the maintenance of long-term potentiation in mossy fibers in CA3. In comparison, there was no impairment in spatial learning in our KOR mutants or in mossy fibers (mf) in CA3 region long-term potentiation (LTP). Our work suggests that the MOR may play a positive role in learning and memory by increasing LTP in CA3 neurons.

Animals↗

PubMed2003

Comparison of morphine-6-glucuronide and morphine on respiratory depressant and antinociceptive responses in wild type and mu-opioid receptor deficient mice.

BACKGROUND: Morphine-6-glucuronide (M6G) is a metabolite of morphine with potent analgesic properties. The influence of M6G on respiratory and antinociceptive responses was investigated in mice lacking the micro -opioid receptor (MOR) and compared with morphine. METHODS: Experiments were performed in mice lacking exon 2 of the MOR (n=18) and their wild type (WT) littermates (n=20). The influence of M6G and morphine on respiration was measured using whole body plethysmography during three elevations of inspired carbon dioxide. Antinociception was assessed using tail flick and hotplate tests. RESULTS: In WT but not null mutant mice, a dose-dependent depression of the slope of the ventilatory carbon dioxide response was observed after M6G and morphine. Similarly, both opioids were devoid of antinociceptive effects in null mutant mice, but showed potent dose-dependent analgesia in WT animals. Potency differences between M6G and morphine in WT mice were of the same order of magnitude for analgesia and respiration. CONCLUSIONS: The data indicate that the desired (antinociceptive) and undesired (respiratory depression) effects of M6G and morphine are linked to the same gene product; that is the MOR. Other opioid- and non-opioid-receptor systems may play a minor role in the actions of M6Gs and morphine. The clinical implications of our findings are that any agent acting at the MOR will invariably cause (potent) analgesia in combination with (variable) respiratory depression.

Analgesics, Opioid↗

PubMed2001

Analysis of [3H]bremazocine binding in single and combinatorial opioid receptor knockout mice.

Despite ample pharmacological evidence for the existence of multiple mu-, delta- and kappa-opioid receptor subtypes, only three genes encoding mu-(MOR), delta-(DOR) and kappa-(KOR) opioid receptor have been cloned. The KOR gene encodes kappa(1)-sites, which specifically bind arylacetamide compounds, and the possible existence of kappa-opioid receptor subtypes derived from another kappa-opioid-receptor gene, yet to be characterized, remains a very contentious issue. kappa(2)-Opioid receptors are described as binding sites typically labelled by the non-selective benzomorphan ligand [3H]bremazocine in the presence of mu-, delta- and kappa(1)-opioid receptor blocking ligands. To investigate the genetic origin of kappa(2)-opioid receptors, we have carried out homogenate binding experiments with [3H]bremazocine in brains of single MOR-, DOR-, KOR- and double MOR/DOR-deficient mice. Scatchard analysis showed that 68+/-12% of the binding sites arise from the MOR gene, 27+/-1% from the DOR gene and 14.5+/-0.2% from the KOR gene, indicating that the three known genes account for total [3H]bremazocine binding. Experiments in the presence of mu-, delta- and kappa(1)-opioid receptor suppressor ligands further showed that non-kappa(1)-opioid receptor labelling can be accounted for by binding to both the mu- and delta-opioid receptors. Finally, [3H]bremazocine binding experiments performed on brain membranes from the triple MOR/DOR/KOR-deficient mice revealed a complete absence of binding sites, confirming definitively that no additional gene is required to explain the total population of [3H]bremazocine binding sites. Altogether the data show that the putative kappa(2)-opioid receptors are in fact a mixed population of KOR, DOR and predominantly MOR gene products.

Analgesics↗

PubMed2001

Murine inter-strain polymorphisms alter gene targeting frequencies at the mu opioid receptor locus in embryonic stem cells.

Chromosomal regions near the mu opioid receptor gene are implicated in morphine preference by quantitative trait loci studies. Differences in expression of the mu opioid receptor are expected to contribute to differences in inter-individual (humans) or strain-specific (mice) responses to painful stimuli, opiate drugs, and addictive behaviors. The search for relevant genetic elements is hindered by a lack of inter-strain (or inter-individual) genomic sequence information. This work describes 9.3 kb of DNA sequence surrounding exons 2 and 3 of the murine mu opioid receptor gene from both 129/Sv and C57BL/6 strains. While the exons are perfectly conserved, intronic sequences demonstrate approximately a 2.5% divergence between the strains. Polymorphism within these intronic regions may effect either primary transcript stability or C-terminal splicing. Homologous recombination frequencies of targeting vectors harboring mu opioid receptor gene sequences have also been compared in embryonic stem cells derived from these strains. Non-isogenic targeting reduces homologous recombination in both 129/Sv and C57BL/6 embryonic stem cells by greater than 15-fold. These findings are the first to examine C57BL/6 embryonic stem cells for non-isogenic targeting frequencies and to define polymorphisms that exist between these mouse strains which might contribute to opioid behaviors.

Alleles↗

PubMed2001

Autoradiographic mapping of the opioid receptor-like 1 (ORL1) receptor in the brains of mu-, delta- or kappa-opioid receptor knockout mice.

The opioid receptor-like 1 (ORL1) receptor shares a high degree of sequence homology with the classical mu-, delta- and kappa-opioid receptors and a functional mutual opposition between these receptors has been suggested. To further address this possible interaction we have used mu-, delta- and kappa-opioid receptor knockout mice to determine autoradiographically if there are any changes in the number or distribution of the ORL1 receptor, labelled with [(3)H]nociceptin, in the brains of mice deficient in each of the opioid receptors. An up-regulation of ORL1 expression was observed across all brain regions in delta-knockouts with cortical regions typically showing a 15-30% increase in binding that was most marked in heterozygous mice. In contrast, ORL1 receptor expression was down-regulated in virtually all brain structures in heterozygous kappa-knockouts although the magnitude of this change was not as great as for the delta-knockouts. No significant alterations in ORL1 receptor expression were observed across brain regions in mu-receptor knockout mice and there were no qualitative differences in ORL1 receptor expression in any groups. These data suggest there are interactions between the ORL1 system and the classical opioid receptors and that the interactions are receptor-specific. The greater differences observed in heterozygous mice suggest that these interactions might be most relevant when there is only partial loss of receptor function.

Animals↗

PubMed2001

Naloxone fails to produce conditioned place aversion in mu-opioid receptor knock-out mice.

There is growing evidence that tonic activity of the opioid system may be important in the modulation of affective state. Naloxone produces a conditioned place aversion in rodents, an effect that is centrally mediated. Previous pharmacological data using antagonists with preferential actions at mu-, delta-, and kappa-opioid receptors indicate the importance of the mu-opioid receptor in mediating this effect. We sought to test the mu-opioid receptor selectivity of naloxone aversion using mu-opioid receptor knock-out mice. mu-Opioid receptor knock-out and wild-type mice were tested for naloxone (10 mg/kg, s.c.) aversion using a place conditioning paradigm. As a positive control for associative learning, knock-out mice were tested for conditioned place aversion to a kappa agonist, U50,488H (2 mg/kg, s.c.). Naloxone produced a significant place aversion in wild-type mice, but failed to have any effect in mu-opioid receptor knock-out mice. On the other hand, both knock-out and wild-type mice treated with U50,488H spent significantly less time in the drug-paired chamber compared to their respective vehicle controls. We conclude that the mu-opioid receptor is crucial for the acquisition of naloxone-induced conditioned place aversion. Furthermore, in a separate experiment using C57BL/6 mice, the delta-selective antagonist naltrindole (10 or 30 mg/kg, s.c.) failed to produce conditioned place aversion.Taken together, these data further support the notion that naloxone produces aversion by antagonizing tonic opioid activity at the mu-opioid receptor.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2001

Orphanin FQ/nociceptin binds to functionally coupled ORL1 receptors on human immune cell lines and alters peripheral blood mononuclear cell proliferation.

Orphanin FQ/nociceptin (OFQ/N) has been shown to modulate nociception, responses to stress and anxiety. We investigated OFQ/N function in human immune cells. We find that monocytic U937, T lymphocytic CEM, and MOLT-4 cell lines express OFQ/N binding sites at levels comparable to that of human SH-SY5Y neuroblastoma cells. We show that OFQ/N receptors are functionally coupled to G proteins in these cells. Finally OFQ/N decreases proliferation of phytohemagglutinin-stimulated peripheral blood mononuclear cells in vitro at doses ranging from 10(-13) to 10(-8) M. Thus, our data suggest that OFQ/N and OFQ/N receptor may act as an immunomodulatory system.

Adult↗

PubMed2001

Activity of mu- and delta-opioid agonists in vas deferens from mice deficient in MOR gene.

1. Mice lacking the mu-opioid receptor have been recently generated. Centrally mediated responses of mu-opioid agonists are suppressed whereas some of the delta-opioid responses are preserved in these mutant mice. 2. The vas deferens bioassay has been used in this study to investigate the functional activity at a peripheral level of mu- and delta-opioid agonists in mice lacking mu-opioid receptors. 3. The different mu-opioid agonists evaluated, morphine, DAMGO, dermorphin and [Lys(7)]-dermorphin produced an inhibitory response in vas deferens from wild-type mice but had no relevant activity on vas deferens from mutant mice. 4. The selective delta-opioid agonists DPDPE, BUBU, deltorphin I, deltorphin II and [D-Met(2)]-deltorphin induced inhibitory effects in vas deferens from both wild-type and mutant mice. However, the biological activities of these ligands were slightly reduced in preparations from mutant mice. The inhibitory responses of all these delta-opioid agonists were prevented by the administration of the selective delta-opioid antagonist naltrindole. 5. These data indicate that delta-opioid agonists, but not mu-opioid agonists, are biologically active in vas deferens from mice lacking mu-opioid receptors. The decreased response of delta-agonists in mutant mice suggests that some cooperativity may exist between mu- and delta-opioid receptors in these vas deferens preparations.

Analgesics, Opioid↗

PubMed2001

Respiratory function in adult mice lacking the mu-opioid receptor: role of delta-receptors.

Mice lacking the mu-opioid receptor (MOR) provide a unique model to determine whether opioid receptors are functionally interactive. Recent results have shown that respiratory depression produced by delta-opioid receptor agonists is suppressed in mice lacking the mu-opioid receptor. Here we investigated the involvement of mu- and delta-opioid receptors in the control of ventilation and mu/delta receptor interactions in brainstem rhythm-generating structures. Unrestrained MOR-/- and wild-type mice showed similar ventilatory patterns at rest and similar chemosensory responses to hyperoxia (100% O2), hypoxia (10% O2) or hypercapnia (5%CO2-95%O2). Blockade of delta-opioid receptors with naltrindole affected neither the ventilatory patterns nor the ventilatory responses to hypoxia in MOR-/- and wild-type mice. In-vitro, respiratory neurons were recorded in the pre-Bötzinger complex of thick brainstem slices of MOR-/- and wild-type young adult mice. Respiratory frequency was not significantly different between these two groups. The delta2 receptor agonist deltorphin II (0.1-1.0 microM) decreased respiratory frequency in both groups whereas doses of the delta1 receptor agonist enkephalin[D-Pen2,5] (0.1-1.0 microM) which were ineffective in wild-type mice significantly decreased respiratory frequency in MOR-/- mice. We conclude that deletion of the mu-opioid receptor gene has no significant effect on ensuing respiratory rhythm generation, ventilatory pattern, or chemosensory control. In MOR-/- mice, the loss of respiratory-depressant effects of delta2-opioid receptor agonists previously observed in vivo does not result from a blunted response of delta receptors in brainstem rhythm-generating structures. These structures show an unaltered response to delta2-receptor agonists and an augmented response to delta1-receptor agonists.

Analgesics, Opioid↗

PubMed2001

The involvement of the mu-opioid receptor in ketamine-induced respiratory depression and antinociception.

UNLABELLED: N-methyl-D-aspartate receptor antagonism probably accounts for most of ketamine's anesthetic effects; its analgesic properties are mediated partly via N-methyl-D-aspartate and partly via opioid receptors. We assessed the involvement of the mu-opioid receptor in S(+) ketamine-induced respiratory depression and antinociception by performing dose-response curves in exon 2 mu-opioid receptor knockout mice (MOR(-/-)) and their wild-type littermates (WT). The ventilatory response to increases in inspired CO(2) was measured with whole body plethysmography. Two antinociceptive assays were used: the tail-immersion test and the hotplate test. S(+) ketamine (0, 10, 100, and 200 mg/kg intraperitoneally) caused a dose-dependent respiratory depression in both genotypes, with greater depression observed in WT relative to MOR(-/-) mice. At 200 mg/kg, S(+) ketamine reduced the slope of the hypercapnic ventilatory response by 93% +/- 15% and 49% +/- 6% in WT and MOR(-/-) mice, respectively (P < 0.001). In both genotypes, S(+) ketamine produced a dose-dependent increase in latencies in the hotplate test, with latencies in MOR(-/-) mice smaller compared with those in WT animals (P < 0.05). In contrast to WT mice, MOR(-/-) mice displayed no ketamine-induced antinociception in the tail-immersion test. These results indicate that at supraspinal sites S(+) ketamine interacts with the mu-opioid system. This interaction contributes significantly to S(+) ketamine-induced respiratory depression and supraspinal antinociception. IMPLICATIONS: The involvement of the mu-opioid receptor system in S(+) ketamine-induced respiratory depression and spinal and supraspinal analgesia was demonstrated by performing experiments in mice lacking the mu-opioid receptor and in mice with intact mu-opioid receptors.

Analgesia↗

PubMed2001

Anesthetic potency and influence of morphine and sevoflurane on respiration in mu-opioid receptor knockout mice.

BACKGROUND: The involvement of the mu-opioid receptor (muOR) system in the control of breathing, anesthetic potency, and morphine- and anesthesia-induced respiratory depression was investigated in mice lacking the muOR. METHODS: Experiments were performed in mice lacking exon 2 of the muOR gene (muOR-/-) and their wild-type littermates (muOR+/+). The influence of saline, morphine, naloxone, and sevoflurane on respiration was measured using a whole body plethysmographic method during air breathing and elevations in inspired carbon dioxide concentration. The influence of morphine and naloxone on anesthetic potency of sevoflurane was determined by tail clamp test. RESULTS: Relative to wild-type mice, muOR-deficient mice displayed approximately 15% higher resting breathing frequencies resulting in greater resting ventilation levels. The slope of the ventilation-carbon dioxide response did not differ between genotypes. In muOR+/+ but not muOR-/- mice, a reduction in resting ventilation and slope, relative to placebo, was observed after 100 mg/kg morphine. Naloxone increased resting ventilation and slope in both genotypes. Sevoflurane at 1% inspired concentration induced similar reductions in resting ventilation and slope in the two genotypes. Anesthetic potency was 20% lower in mutant relevant to wild-type mice. Naloxone and morphine caused an increase and decrease, respectively, in anesthetic potency in muOR+/+ mice only. CONCLUSIONS: The data indicate the importance of the endogenous opioid system in the physiology of the control of breathing with only a minor role for the muOR. The muOR gene is the molecular site of action of the respiratory effects of morphine. Anesthetic potency is modulated by the endogenous mu-opioid system but not by the kappa- and delta-opioid systems.

Analgesics, Opioid↗

PubMed2001

Lack of dependence and rewarding effects of deltorphin II in mu-opioid receptor-deficient mice.

We have previously shown that the antinociceptive effects produced by the delta opioid-selective agonist deltorphin II are preserved in mu-opioid receptor (MOR)-deficient mice. We have now investigated rewarding effects and physical dependence produced by deltorphin II in these animals. Wild-type and MOR-deficient mice were implanted with a cannula into the third ventricle and deltorphin II was administered centrally. The rewarding effects induced by deltorphin II were then investigated using the place preference paradigm. Wild-type mice showed place preference for the compartment previously associated with deltorphin II and this effect was not observed in MOR-deficient mice. In a second experiment, mice received a chronic perfusion of deltorphin II over 6 days, via an Alzet minipump connected to the intraventricular cannula, and withdrawal was precipitated by naloxone administration. Wild-type animals showed a moderate but significant incidence of several somatic signs of withdrawal. This withdrawal response was suppressed in MOR-deficient mice. Analysis of the immunoreactivity levels of PKC-alpha, PKC-beta (I and II) and PKC-gamma isozymes in the cerebral cortex of mice infused chronically with deltorphin II showed a significant up-regulation of all these isozymes in the soluble fraction in wild-type but not in MOR-deficient mice. In conclusion, mu-opioid receptors, which are not involved in deltorphin II antinociception, appear to mediate the effects of chronic deltorphin II on rewarding responses, physical dependence and adaptive changes to PKC.

Animals↗