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Targeted expression of μ-opioid receptors in a subset of striatal direct-pathway neurons restores opiate reward.

Cui Y, Ostlund SB, James AS, Park CS, Ge W, Roberts KW, Mittal N, Murphy NP, Cepeda C, Kieffer BL, Levine MS, Jentsch JD, Walwyn WM, Sun YE, Evans CJ, Maidment NT, Yang XW - Nat. Neurosci. (2014)

Bottom Line: μ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive.We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward.Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

View Article: PubMed Central - PubMed

Affiliation: 1] Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, California, USA. [2] Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, California, USA. [3] Brain Research Institute, University of California, Los Angeles, Los Angeles, California, USA. [4] David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA.

ABSTRACT
μ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive. Here we devised a new conditional bacterial artificial chromosome rescue strategy to show, in mice, that targeted MOR expression in a subpopulation of striatal direct-pathway neurons enriched in the striosome and nucleus accumbens, in an otherwise MOR- background, restores opiate reward and opiate-induced striatal dopamine release and partially restores motivation to self administer an opiate. However, these mice lack opiate analgesia or withdrawal. We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward. Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

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Selective MOR expression in striosome and NAc direct-pathway MSNs partially rescues opiate self-administration. (a) WT and Rescue mice, but not MOR-KO mice, self-administered remifentanil (0.10 mg/kg i.v.) under the FR1 reinforcement schedule. Repeated-measures ANOVA analysis revealed a significant day x genotype interaction F(18, 17)=2.974, p = 0.015. WT mice self-administered more drug across days than MOR-KO mice (genotype x day: F(9,11)=21.873, p < 0.001) and rescue mice (F(9,13)=3.485, p = 0.021), and rescue mice self-administered more than MOR-KO mice (F(9,10.072) = 4.920, p = 0.010. (b) The cumulative number of infusions earned during the 2-hour session, averaged over the last three days of FR1, show that not only did WT and Rescue mice earn more infusions than MOR-KO mice, WT mice also earned these infusions earlier time points within the session than Rescue mice (WT vs MOR-KO, F(24,264) = 10.367, p < 0.001; Rescue vs MOR-KO, F(24,240) = 2.506, p < 0.001; WT vs Rescue, F(12,156) = 2.660, p < 0.01, Repeated-measures ANOVA). (c)The number of inactive lever presses across the 10 days of FR1 did not differ (genotype x day: F(18,17)=17.000=1.578, p = 0.176), showing that WT, MOR-KO and Rescue mice are not significantly different with respect to non-drug-directed responding. Data from WT (n=8) and MOR-KO (n=5) and Rescue (n=7) mice were analyzed in (a, b) and (c). (d) FR3 reinforcement schedule responding demonstrated that the WT mice obtained more remifentanil infusions than Rescue mice (WT vs Rescue, F(1,7) = 5.672, p = 0.049; Repeated-measures two way ANOVA, n=5, WT; n=4, Rescue). (e) PR reinforcement schedules demonstrated that the WT mice obtained more infusions than Rescue mice before reaching breakpoint (WT vs Rescue, F(1,6) = 7.107, p = 0.037, Repeated-measures two way ANOVA, n=4, WT; n=4, Rescue). The data shown and analyzed are the last 3 days at FR3 (d) and PR (e), when stable responding was achieved). Values are mean ± SEM.
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Figure 3: Selective MOR expression in striosome and NAc direct-pathway MSNs partially rescues opiate self-administration. (a) WT and Rescue mice, but not MOR-KO mice, self-administered remifentanil (0.10 mg/kg i.v.) under the FR1 reinforcement schedule. Repeated-measures ANOVA analysis revealed a significant day x genotype interaction F(18, 17)=2.974, p = 0.015. WT mice self-administered more drug across days than MOR-KO mice (genotype x day: F(9,11)=21.873, p < 0.001) and rescue mice (F(9,13)=3.485, p = 0.021), and rescue mice self-administered more than MOR-KO mice (F(9,10.072) = 4.920, p = 0.010. (b) The cumulative number of infusions earned during the 2-hour session, averaged over the last three days of FR1, show that not only did WT and Rescue mice earn more infusions than MOR-KO mice, WT mice also earned these infusions earlier time points within the session than Rescue mice (WT vs MOR-KO, F(24,264) = 10.367, p < 0.001; Rescue vs MOR-KO, F(24,240) = 2.506, p < 0.001; WT vs Rescue, F(12,156) = 2.660, p < 0.01, Repeated-measures ANOVA). (c)The number of inactive lever presses across the 10 days of FR1 did not differ (genotype x day: F(18,17)=17.000=1.578, p = 0.176), showing that WT, MOR-KO and Rescue mice are not significantly different with respect to non-drug-directed responding. Data from WT (n=8) and MOR-KO (n=5) and Rescue (n=7) mice were analyzed in (a, b) and (c). (d) FR3 reinforcement schedule responding demonstrated that the WT mice obtained more remifentanil infusions than Rescue mice (WT vs Rescue, F(1,7) = 5.672, p = 0.049; Repeated-measures two way ANOVA, n=5, WT; n=4, Rescue). (e) PR reinforcement schedules demonstrated that the WT mice obtained more infusions than Rescue mice before reaching breakpoint (WT vs Rescue, F(1,6) = 7.107, p = 0.037, Repeated-measures two way ANOVA, n=4, WT; n=4, Rescue). The data shown and analyzed are the last 3 days at FR3 (d) and PR (e), when stable responding was achieved). Values are mean ± SEM.

Mentions: To address the role of MORs in striosomal and NAc direct-pathway MSNs in opiate-induced reinforcement, Rescue, MOR-KO and WT mice were trained to self-administer remifentanil, a potent short-acting synthetic opioid with a half-life of about 4 minutes19. In contrast to MOR-KO mice which lacked any motivation to self-administer remifentanil, both WT and Rescue mice obtained a stable level of remifentanil self-administration across the last 3 days at the fixed-ratio 1 (FR1) reinforcement schedule (one lever press results in one infusion; Fig. 3a). Further within-session analysis of the rate of infusions earned showed that both WT and Rescue mice obtained more infusions than MOR-KO during the 2-hour session once stable self-administration at FR1 had been obtained (Fig. 3b). Moreover, there was no effect of genotype on inactive lever responding (Fig. 3c). This demonstrates that the Rescue mice, unlike MOR-KO mice, can acquire opioid self-administration. However, further analyses revealed that the motivation to obtain remifentanil is only partially restored in these mice. Firstly, Rescue mice earned infusions at a slower pace during FR1 testing (Fig. 3a and 3b) and gained fewer infusions overall during FR3 testing (Fig. 3d) than the WT mice. In addition, Rescue mice exhibited lower infusion “break points” during a progressive ratio (PR) task, indicating that they were willing to exert less effort than WT mice to obtain the opiate drug (Fig. 3e). These results demonstrate that MOR re-expression in the subpopulation of striatal direct-pathway MSNs partially restores opioid-seeking and taking behaviors that are lacking in the MOR-KO mice. Moreover, our results also suggest that full restoration of opiate reinforcement behavior may require MOR expression in other opiate-sensitive neuronal populations beyond the subpopulation of striatal direct-pathway MSNs.


Targeted expression of μ-opioid receptors in a subset of striatal direct-pathway neurons restores opiate reward.

Cui Y, Ostlund SB, James AS, Park CS, Ge W, Roberts KW, Mittal N, Murphy NP, Cepeda C, Kieffer BL, Levine MS, Jentsch JD, Walwyn WM, Sun YE, Evans CJ, Maidment NT, Yang XW - Nat. Neurosci. (2014)

Selective MOR expression in striosome and NAc direct-pathway MSNs partially rescues opiate self-administration. (a) WT and Rescue mice, but not MOR-KO mice, self-administered remifentanil (0.10 mg/kg i.v.) under the FR1 reinforcement schedule. Repeated-measures ANOVA analysis revealed a significant day x genotype interaction F(18, 17)=2.974, p = 0.015. WT mice self-administered more drug across days than MOR-KO mice (genotype x day: F(9,11)=21.873, p < 0.001) and rescue mice (F(9,13)=3.485, p = 0.021), and rescue mice self-administered more than MOR-KO mice (F(9,10.072) = 4.920, p = 0.010. (b) The cumulative number of infusions earned during the 2-hour session, averaged over the last three days of FR1, show that not only did WT and Rescue mice earn more infusions than MOR-KO mice, WT mice also earned these infusions earlier time points within the session than Rescue mice (WT vs MOR-KO, F(24,264) = 10.367, p < 0.001; Rescue vs MOR-KO, F(24,240) = 2.506, p < 0.001; WT vs Rescue, F(12,156) = 2.660, p < 0.01, Repeated-measures ANOVA). (c)The number of inactive lever presses across the 10 days of FR1 did not differ (genotype x day: F(18,17)=17.000=1.578, p = 0.176), showing that WT, MOR-KO and Rescue mice are not significantly different with respect to non-drug-directed responding. Data from WT (n=8) and MOR-KO (n=5) and Rescue (n=7) mice were analyzed in (a, b) and (c). (d) FR3 reinforcement schedule responding demonstrated that the WT mice obtained more remifentanil infusions than Rescue mice (WT vs Rescue, F(1,7) = 5.672, p = 0.049; Repeated-measures two way ANOVA, n=5, WT; n=4, Rescue). (e) PR reinforcement schedules demonstrated that the WT mice obtained more infusions than Rescue mice before reaching breakpoint (WT vs Rescue, F(1,6) = 7.107, p = 0.037, Repeated-measures two way ANOVA, n=4, WT; n=4, Rescue). The data shown and analyzed are the last 3 days at FR3 (d) and PR (e), when stable responding was achieved). Values are mean ± SEM.
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Figure 3: Selective MOR expression in striosome and NAc direct-pathway MSNs partially rescues opiate self-administration. (a) WT and Rescue mice, but not MOR-KO mice, self-administered remifentanil (0.10 mg/kg i.v.) under the FR1 reinforcement schedule. Repeated-measures ANOVA analysis revealed a significant day x genotype interaction F(18, 17)=2.974, p = 0.015. WT mice self-administered more drug across days than MOR-KO mice (genotype x day: F(9,11)=21.873, p < 0.001) and rescue mice (F(9,13)=3.485, p = 0.021), and rescue mice self-administered more than MOR-KO mice (F(9,10.072) = 4.920, p = 0.010. (b) The cumulative number of infusions earned during the 2-hour session, averaged over the last three days of FR1, show that not only did WT and Rescue mice earn more infusions than MOR-KO mice, WT mice also earned these infusions earlier time points within the session than Rescue mice (WT vs MOR-KO, F(24,264) = 10.367, p < 0.001; Rescue vs MOR-KO, F(24,240) = 2.506, p < 0.001; WT vs Rescue, F(12,156) = 2.660, p < 0.01, Repeated-measures ANOVA). (c)The number of inactive lever presses across the 10 days of FR1 did not differ (genotype x day: F(18,17)=17.000=1.578, p = 0.176), showing that WT, MOR-KO and Rescue mice are not significantly different with respect to non-drug-directed responding. Data from WT (n=8) and MOR-KO (n=5) and Rescue (n=7) mice were analyzed in (a, b) and (c). (d) FR3 reinforcement schedule responding demonstrated that the WT mice obtained more remifentanil infusions than Rescue mice (WT vs Rescue, F(1,7) = 5.672, p = 0.049; Repeated-measures two way ANOVA, n=5, WT; n=4, Rescue). (e) PR reinforcement schedules demonstrated that the WT mice obtained more infusions than Rescue mice before reaching breakpoint (WT vs Rescue, F(1,6) = 7.107, p = 0.037, Repeated-measures two way ANOVA, n=4, WT; n=4, Rescue). The data shown and analyzed are the last 3 days at FR3 (d) and PR (e), when stable responding was achieved). Values are mean ± SEM.
Mentions: To address the role of MORs in striosomal and NAc direct-pathway MSNs in opiate-induced reinforcement, Rescue, MOR-KO and WT mice were trained to self-administer remifentanil, a potent short-acting synthetic opioid with a half-life of about 4 minutes19. In contrast to MOR-KO mice which lacked any motivation to self-administer remifentanil, both WT and Rescue mice obtained a stable level of remifentanil self-administration across the last 3 days at the fixed-ratio 1 (FR1) reinforcement schedule (one lever press results in one infusion; Fig. 3a). Further within-session analysis of the rate of infusions earned showed that both WT and Rescue mice obtained more infusions than MOR-KO during the 2-hour session once stable self-administration at FR1 had been obtained (Fig. 3b). Moreover, there was no effect of genotype on inactive lever responding (Fig. 3c). This demonstrates that the Rescue mice, unlike MOR-KO mice, can acquire opioid self-administration. However, further analyses revealed that the motivation to obtain remifentanil is only partially restored in these mice. Firstly, Rescue mice earned infusions at a slower pace during FR1 testing (Fig. 3a and 3b) and gained fewer infusions overall during FR3 testing (Fig. 3d) than the WT mice. In addition, Rescue mice exhibited lower infusion “break points” during a progressive ratio (PR) task, indicating that they were willing to exert less effort than WT mice to obtain the opiate drug (Fig. 3e). These results demonstrate that MOR re-expression in the subpopulation of striatal direct-pathway MSNs partially restores opioid-seeking and taking behaviors that are lacking in the MOR-KO mice. Moreover, our results also suggest that full restoration of opiate reinforcement behavior may require MOR expression in other opiate-sensitive neuronal populations beyond the subpopulation of striatal direct-pathway MSNs.

Bottom Line: μ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive.We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward.Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

View Article: PubMed Central - PubMed

Affiliation: 1] Center for Neurobehavioral Genetics, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, California, USA. [2] Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, Los Angeles, California, USA. [3] Brain Research Institute, University of California, Los Angeles, Los Angeles, California, USA. [4] David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA.

ABSTRACT
μ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive. Here we devised a new conditional bacterial artificial chromosome rescue strategy to show, in mice, that targeted MOR expression in a subpopulation of striatal direct-pathway neurons enriched in the striosome and nucleus accumbens, in an otherwise MOR- background, restores opiate reward and opiate-induced striatal dopamine release and partially restores motivation to self administer an opiate. However, these mice lack opiate analgesia or withdrawal. We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward. Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

Show MeSH
Related in: MedlinePlus