Maria Smirnova

Role of DRD3 in morphine-induced conditioned place preference using drd3-knockout mice.

The dopamine D3 receptor (DRD3) mediates expression of conditioned effects of psychostimulants, but conflicting results have been obtained with opiates. In a conditioned place preference (CPP) procedure, morphine increased the time spent in a compartment previously paired with drug injection. CPP was obtained at morphine doses of 16 and 32u2009mg/kg in wild-type (drd3+/+) mice and 8, 16 and 32u2009mg/kg in DRD3-knockout (drd3−/−) mice. BP897, a DRD3-selective partial agonist, inhibited the expression of morphine-CPP in drd3+/+, but not drd3−/− mice. BPu2009897 reduced brain regional activation, measured by c-fos imaging after the CPP test session, in the somatosensory cortex of drd3+/+, but not drd3−/− mice. These results confirm the role of DRD3 in the expression of conditioned effects of morphine and the participation of the somatosensory cortex in these effects.

ABCG2- and ABCG4-Mediated Efflux of Amyloid-β Peptide 1-40 at the Mouse Blood-Brain Barrier

The accumulation of amyloid-β peptide (Aβ) in the brain is a critical hallmark of Alzheimers disease. This high cerebral Aβ concentration may be partly caused by impaired clearance of Aβ across the blood-brain barrier (BBB). The low-density lipoprotein receptor-related protein-1 (LRP-1) and the ATP-binding cassette (ABC) protein ABCB1 (P-glycoprotein) are involved in the efflux of Aβ across the BBB. We hypothesized that other ABC proteins, such as members of the G subfamily, are also involved in the BBB clearance of Aβ. We therefore investigated the roles of ABCG2 (BCRP) and ABCG4 in the efflux of [3H] Aβ1-40 from HEK293 cells stably transfected with human ABCG2 or mouse abcg4. We showed that ABCG2 and Abcg4 mediate the cellular efflux of [3H] Aβ1-40. In addition, probucol fully inhibited the efflux of [3H] Aβ1-40 from HEK293-abcg4 cells. Using the in situ brain perfusion technique, we showed that GF120918 (dual inhibitor of Abcb1 and Abcg2) strongly enhanced the uptake (Clup, μl/g/s) of [3H] Aβ1-40 by the brains of Abcb1-deficient mice, but not by the brains of Abcb1/Abcg2-deficient mice, suggesting that Abcg2 is involved in the transport of Aβ at the mouse BBB. Perfusing the brains of Abcb1/Abcg2- and Abca1-deficient mice with [3H] Aβ1-40 plus probucol significantly increased the Clup of Aβ. This suggests that a probucol-sensitive transporter that is different from Abca1, Abcb1, and Abcg2 is involved in the brain efflux of Aβ. We suggest that this probucol-sensitive transporter is Abcg4. We conclude that Abcg4 acts in concert with Abcg2 to efflux Aβ from the brain across the BBB.

Respiratory toxicity of buprenorphine results from the blockage of P-glycoprotein-mediated efflux of norbuprenorphine at the blood-brain barrier in mice.

Objectives:Deaths due to asphyxia as well as following acute poisoning with severe respiratory depression have been attributed to buprenorphine in opioid abusers. However, in human and animal studies, buprenorphine exhibited ceiling respiratory effects, whereas its metabolite, norbuprenorphine, was assessed as being a potent respiratory depressor in rodents. Recently, norbuprenorphine, in contrast to buprenorphine, was shown in vitro to be a substrate of human P-glycoprotein, a drug-transporter involved in all steps of pharmacokinetics including transport at the blood–brain barrier. Our objectives were to assess P-glycoprotein involvement in norbuprenorphine transport in vivo and study its role in the modulation of buprenorphine-related respiratory effects in mice. Setting:University-affiliated research laboratory, INSERM U705, Paris, France. Subjects:Wild-type and P-glycoprotein knockout female Friend virus B-type mice. Interventions:Respiratory effects were studied using plethysmography and the P-glycoprotein role at the blood–brain barrier using in situ brain perfusion. Measurements and Main Results:Norbuprenorphine(≥1 mg/kg) and to a lesser extent buprenorphine (≥10 mg/kg) were responsible for dose-dependent respiratory depression combining increased inspiratory (TI) and expiratory times (TE). PSC833, a powerful P-glycoprotein inhibitor, significantly enhanced buprenorphine-related effects on TI (p < .01) and TE (p < .05) and norbuprenorphine-related effects on minute volume (VE, p < .05), TI, and TE (p < .001). In P-glycoprotein-knockout mice, buprenorphine-related effects on VE (p < .01), TE (p < .001), and TI (p < .05) and norbuprenorphine-related effects on VE (p < .05) and TI (p < .001) were significantly enhanced. Plasma norbuprenorphine concentrations were significantly increased in PSC833-treated mice (p < .001), supporting a P-glycoprotein role in norbuprenorphine pharmacokinetics. Brain norbuprenorphine efflux was significantly reduced in PSC833-treated and P-glycoprotein-knockout mice (p < .001), supporting P-glycoprotein-mediated norbuprenorphine transport at the blood–brain barrier. Conclusions:P-glycoprotein plays a key-protective role in buprenorphine-related respiratory effects, by allowing norbuprenorphine efflux at the blood–brain barrier. Our findings suggest a major role for drug–drug interactions that lead to P-glycoprotein inhibition in buprenorphine-associated fatalities and respiratory depression.

Immune Quiescence of the Brain Is Set by Astroglial Connexin 43

In the normal brain, immune cell trafficking and immune responses are strictly controlled and limited. This unique homeostatic equilibrium, also called brain immune quiescence, is crucial to maintaining proper brain functions and is altered in various pathological processes, from chronic immunopathological disorders to cognitive and psychiatric impairments. To date, the precise nature of factors regulating the brain/immune system interrelationship is poorly understood. In the present study, we demonstrate that one of these regulating factors is Connexin 43 (Cx43), a gap junction protein highly expressed by astrocytes at the blood–brain barrier (BBB) interface. We show that, by setting the activated state of cerebral endothelium, astroglial Cx43 controls immune recruitment as well as antigen presentation mechanisms in the mouse brain. Consequently, in the absence of astroglial Cx43, recruited immune cells elaborate a specific humoral autoimmune response against the von Willebrand factor A domain-containing protein 5a, an extracellular matrix protein of the brain. Altogether, our results demonstrate that Cx43 is a new astroglial factor promoting the immune quiescence of the brain.

Carrier-Mediated Cocaine Transport at the Blood-Brain Barrier as a Putative Mechanism in Addiction Liability

Background: The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier. Methods: We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion. Results: Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter. Conclusions: Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms.

Coexistence of Passive and Proton Antiporter-Mediated Processes in Nicotine Transport at the Mouse Blood–Brain Barrier

Nicotine, the main tobacco alkaloid leading to smoking dependence, rapidly crosses the blood–brain barrier (BBB) to become concentrated in the brain. Recently, it has been shown that nicotine interacts with some organic cation transporters (OCT), but their influence at the BBB has not yet been assessed in vivo. In this study, we characterized the transport of nicotine at the mouse luminal BBB by in situ brain perfusion. Its influx was saturable and followed the Michaelis–Menten kinetics (Kmu2009=u20092.60xa0mM, Vmaxu2009=u200937.60xa0nmol/s/g at pHxa07.40). At its usual micromolar concentrations in the plasma, most (79%) of the net transport of nicotine at the BBB was carrier-mediated, while passive diffusion accounted for 21%. Studies on knockout mice showed that the OCT Oct1–3, P-gp, and Bcrp did not alter [3H]-nicotine transport at the BBB. Neither did inhibiting the transporters Mate1, Octn, or Pmat. The in vivo manipulation of intracellular and/or extracellular pH, the chemical inhibition profile, and the trans-stimulation experiments demonstrated that the nicotine transporter at the BBB shared the properties of the clonidine/proton antiporter. The molecular features of this proton-coupled antiporter have not yet been identified, but it also transports diphenhydramine and tramadol and helps nicotine cross the BBB at a faster rate and to a greater extent. The pharmacological inhibition of this nicotine/proton antiporter could represent a new strategy to reduce nicotine uptake by the brain and thus help curb addiction to smoking.

Transport of Biogenic Amine Neurotransmitters at the Mouse Blood–Retina and Blood–Brain Barriers by Uptake1 and Uptake2

Uptake1 and uptake2 transporters are involved in the extracellular clearance of biogenic amine neurotransmitters at synaptic clefts. We looked for them at the blood–brain barrier (BBB) and blood–retina barriers (BRB), where they could be involved in regulating the neurotransmitter concentration and modulate/terminate receptor-mediated effects within the neurovascular unit (NVU). Uptake2 (Oct1-3/Slc22a1-3, Pmat/Slc29a4) and Mate1/Slc47a1 transporters are also involved in the transport of xenobiotics. We used in situ carotid perfusion of prototypic substrates like [3H]-1-methyl-4-phenylpyridinium ([3H]-MPP+), [3H]-histamine, [3H]-serotonin, and [3H]-dopamine, changes in ionic composition and genetic deletion of Oct1-3 carriers to detect uptake1 and uptake2 at the BBB and BRB. We showed that uptake1 and uptake2 are involved in the transport of [3H]-dopamine and [3H]-MPP+ at the blood luminal BRB, but not at the BBB. These functional studies, together with quantitative RT-PCR and confocal imaging, suggest that the mouse BBB lacks uptake1 (Net/Slc6a2, Dat/Slc6a3, Sert/Slc6a4), uptake2, and Mate1 on both the luminal and abluminal sides. However, we found evidence for functional Net and Oct1 transporters at the luminal BRB. These heterogeneous transport properties of the brain and retina NVUs suggest that the BBB helps protect the brain against biogenic amine neurotransmitters in the plasma while the BRB has more of a metabolic/endocrine role.

Dopamine D3 receptor ligands modulate the acquisition of morphine-conditioned place preference

RationaleThe dopamine D3 receptor has been shown to mediate conditioned effects of psychostimulants such as cocaine. The present work was aimed at determining whether drugs acting at D3 receptors alter acquisition of conditioned effects of opiates.MethodsWe have used the conditioned place preference (CPP) in mice, which permits the measurement of approach behaviour to environmental stimuli previously paired with drug effects. To assess the interaction of morphine and D3 receptor ligands during acquisition of CPP, we have used a particular procedure, in which the animals were given the choice between compartments associated with either morphine alone or the combination of morphine with the tested agent.ResultsD3 receptor agonists (7-OH-DPAT, quinelorane, BP 897) did not induce, alone, a significant CPP but, all of them, at the doses tested, and notably BP 897, a highly selective partial agonist, significantly enhanced acquisition of morphine-induced CPP when administered together with morphine at each conditioning session. PNU-99194A, a D3 receptor-preferring antagonist, induced a CPP itself at the dose of 10xa0mg/kg but not at 5 or 15xa0mg/kg and impaired significantly at 10 and 15xa0mg/kg the morphine-induced CPP. In contrast, BP 897 did not alter morphine-induced analgesia, an unconditioned effect of this drug.ConclusionsThese results suggest the stimulation of D3 receptors has no rewarding effect per se, but may synergize upon opiate-induced dopamine release with stimulation of other dopamine receptor subtypes to enhance approach behaviour to morphine-associated environment.

Impact of P-glycoprotein at the blood-brain barrier on the uptake of heroin and its main metabolites: behavioral effects and consequences on the transcriptional responses and reinforcing properties.

RationaleTransport across the BBB is a determinant of the rate and extent of drug distribution in the brain. Heroin exerts its effects through its principal metabolites 6-monoacetyl-morphine (6-MAM) and morphine. Morphine is a known substrate of P-glycoprotein (P-gp) at the blood-brain-barrier (BBB) however, little is known about the interaction of heroin and 6-MAM with P-gp.ObjectiveThe objective of this paper is to study the role of the P-gp-mediated efflux at the BBB in the behavioral and molecular effects of heroin and morphine.MethodsThe transport rates of heroin and its main metabolites, at the BBB, were measured in mice by in situ brain perfusion. We then examined the effect of inhibition ofxa0P-gp on the acute nociception, locomotor activity, and gene expression modulations induced by heroin and morphine. The effect of P-gp inhibition during the acquisition of morphine-induced place preference was also studied.ResultsInhibition of P-gp significantly increased the uptake of morphine but not that of heroin nor 6-MAM. Inhibition of P-gp significantly increased morphine-induced acute analgesia and locomotor activity but did not affect the behavioral effects of heroin; in addition, acute transcriptional responses to morphine were selectively modulated in the nucleus accumbens. Increasing morphine uptake by the brain significantly increased its reinforcing properties in the place preference paradigm.ConclusionsThe present study demonstrated that acute inhibition of P-gp not only modulates morphine-induced behavioral effects but also its transcriptional effects and reinforcing properties. This suggests that, in the case of morphine, transport across the BBB is critical for the development of dependence.

Gender and strain contributions to the variability of buprenorphine-related respiratory toxicity in mice.

While most deaths from asphyxia related to buprenorphine (BUP) overdose have been reported in males, higher plasma concentrations of BUP and its toxic metabolite norbuprenorphine (NBUP) have been observed in females. We previously demonstrated that P-glycoprotein (P-gp) modulation at the blood-brain barrier (BBB) contributes highly to BUP-related respiratory toxicity, by limiting NBUP entrance into the brain. In this work, we sought to investigate the role of P-gp-mediated transport at the BBB in gender and strain-related variability of BUP and NBUP-induced respiratory effects in mice. Ventilation was studied using plethysmography, P-gp expression using western blot, and transport at the BBB using in situ cerebral perfusion. In male Fvb and Swiss mice, BUP was responsible for ceiling respiratory effects. NBUP-related reduction in minute volume was dose-dependent but more marked in Fvb (p<0.01 at 1mg/kg NBUP and p<0.001 at 3 and 9mg/kg NBUP) than in Swiss mice (p<0.001 at 9mg/kg NBUP). Female Fvb mice were more susceptible to BUP than males with significantly increased inspiratory time (p<0.05) and to NBUP with significantly increased expiratory time (p<0.01). Following BUP administration, plasma BUP concentrations were significantly higher (p<0.01) and plasma NBUP concentrations significantly lower (p<0.001) in Fvb mice compared to Swiss mice. Plasma BUP concentrations were significantly higher (p<0.05) and plasma NBUP concentrations significantly lower (p<0.01) in male compared to female Fvb mice. In contrast, following NBUP administration, comparable plasma NBUP concentrations were observed in both genders and strains. No differences in P-gp expression or BUP and NBUP transport across the BBB were observed between male and female Fvb mice as well as between Swiss and Fvb mice. Our results suggest that P-gp-mediated transport across the BBB does not play a key-role in gender and strain-related variability in BUP and NBUP-induced respiratory toxicity in mice. Both gender- and strain-related differences in respiratory effects of BUP could be attributed to BUP itself rather than to its metabolite, NBUP.