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Effects of dorsal hippocampal orexin-2 receptor antagonism on the acquisition, expression, and extinction of morphine-induced place preference in rats

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Abstract

Rationale

Orexinergic system is involved in reward processing and drug addiction.

Objectives

Here, we investigated the effect of intrahippocampal CA1 administration of orexin-2 receptor (OX2r) antagonist on the acquisition, expression, and extinction of morphine-induced place preference in rats.

Methods

Conditioned place preference (CPP) was induced by subcutaneous injection of morphine (5 mg/kg) during a 3-day conditioning phase. Three experimental plots were designed; TCS OX2 29 as a selective antagonist of orexin-2 receptors (OX2rs) was dissolved in DMSO, prepared in solutions with different concentrations (1, 3, 10, and 30 nM), and was bilaterally microinjected into the CA1 and some neighboring regions (0.5 μl/side). Conditioning scores and locomotor activities were recorded during the test.

Results

Results demonstrate that intra-CA1 administration of the OX2r antagonist attenuates the induction of morphine CPP during the acquisition and expression phases. Effect of TCS OX2 29 on reduction of morphine CPP was dose-dependent and was more pronounced during the acquisition than the expression. Furthermore, higher concentrations of TCS OX2 29 facilitated the extinction of morphine-induced CPP and reduced extinction latency period. Nevertheless, administration of TCS OX2 29 solutions did not have any influence on locomotor activity of all phases.

Conclusions

Our findings suggest that OX2rs in the CA1 region of hippocampus are involved in the development of the acquisition and expression of morphine CPP. Moreover, blockade of OX2rs could facilitate extinction and may abrogate or extinguish the ability of drug-related cues, implying that the antagonist might be considered as a propitious therapeutic agent in suppressing drug-seeking behavior.

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Acknowledgments

This work was supported by the grant (88-1039-A) from the Neuroscience Research Center of Shahid Beheshti University of Medical Sciences, Tehran, Iran.

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Correspondence to Abbas Haghparast.

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The authors declare that they have no conflict of interest.

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Sadeghi, B., Ezzatpanah, S. & Haghparast, A. Effects of dorsal hippocampal orexin-2 receptor antagonism on the acquisition, expression, and extinction of morphine-induced place preference in rats. Psychopharmacology 233, 2329–2341 (2016). https://doi.org/10.1007/s00213-016-4280-3

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  • DOI: https://doi.org/10.1007/s00213-016-4280-3

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