Elsevier

Neuroscience

Volume 117, Issue 2, 21 March 2003, Pages 383-389
Neuroscience

Research paper
Differential regulation of β-arrestin 1 and β-arrestin 2 gene expression in rat brain by morphine

https://doi.org/10.1016/S0306-4522(02)00930-2Get rights and content

Abstract

β-Arrestins are a family of regulatory and scaffold proteins functioning in signal transduction of G protein-coupled receptors including opioid receptors. Upon agonist stimulation, β-arrestins bind to opioid receptors phosphorylated by G protein-coupled receptor kinases and promote receptor internalization and desensitization. Studies indicated that β-arrestins are required in the development of morphine tolerance in mice. In the current study, we investigated the potential regulatory effects of morphine administration on β-arrestin 1 and β-arrestin 2 mRNA levels in different brain regions in rat using in situ hybridization method. Our results showed that the acute morphine administration (10 mg/kg) resulted in approximately 30% reduction in both β-arrestin 1 and β-arrestin 2 mRNA levels in hippocampus while the chronic morphine treatment (10 mg/kg, b.i.d., for 9 days) caused no significant change in level of either β-arrestin mRNA. In locus coeruleus, both acute and chronic morphine treatments resulted in significant decreases (over 50%) in β-arrestin 1 mRNA level but failed to induce any change in the level of β-arrestin 2 gene expression. The acute morphine administration had no significant effect on β-arrestin 1 or β-arrestin 2 mRNA level in periaqueductal gray and cerebral cortex. However, after chronic morphine treatment, β-arrestin 2 mRNA level decreased by 40% in periaqueductal gray and increased by 25% in cerebral cortex, in strong contrast to the unchanged β-arrestin 1 mRNA level in these two brain regions. Furthermore, spontaneous or naloxone-precipitated withdrawal of morphine that did not affect the level of β-arrestin 1 mRNA resulted in an aberrant increase (100% over control) in β-arrestin 2 mRNA level in hippocampus. Our results thus demonstrated for the first time that opiate administration regulates level of β-arrestin mRNAs in brain and the expression of β-arrestin 1 and β-arrestin 2 subtypes is differentially regulated in locus coeruleus, periaqueductal gray, and cerebral cortex by morphine. These data suggest that β-arrestin 1 and β-arrestin 2 may play different roles in the development of opioid tolerance and dependence.

Section snippets

Animals

Male Sprague–Dawlay rats (160–200 g, Shanghai Experimental Animal Center, Chinese Academy Sciences) were housed at 20–25 °C on a 12-h light/dark cycle with food and water freely accessible. All animal experiments were carried out in accordance with the National Institutes of Health Guideline for the Care and Use of Laboratory Animals and all efforts were made to minimize the number of animals used and their suffering.

Morphine treatments

In chronic experiment, rats received twice daily for 9 days s.c. injections of

Similar expression patterns of β-arr1 and β-arr2 in various brain regions

The results of in situ hybridization with β-arr isoform-specific probes revealed that β-arr1 and β-arr2 were expressed in the most regions of rat brain. Similar patterns of β-arr1 and β-arr2 gene expression were observed. As shown in Fig. 1, β-arr1- and β-arr2-positive cells with high staining intensity were present in pyramidal cell layers of cingulate cortex, motor cortex, somatosensory cortex and CA1–CA3 fields and in the granular layer of dentate gyrus of hippocampus. β-arr1- and

Discussion

β-arr1 and β-arr2 share high degree of homology (Krupnick and Benovic, 1998) and both express widely in brain. Several studies suggested there are potential functional differences between the two subtypes of β-arr in brain. β-arr2 appears to be more abundant than β-arr1 in the CNS (Attramadal et al., 1992). β-arr2 binds to the β2AR, m2 muscarinic cholinergic receptor, clathrin, and AP-2 at affinities different from those of β-arr1 Gurevich et al 1995, Laporte et al 1999, Goodman et al 1996.

Acknowledgements

We thank Dr. Lin Lu, Yan Liu, Shiduo Lu and T. M. Wang for technical help and discussion. This work was supported in part by grants from the National Natural Science Foundation of China (39825110, 30230130, and 30000050), the Ministry of Science and Technology (G1999054003), the Ministry of Education, and Shanghai Municipal Commissions for Science and Technology and for Education.

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    X. L. Fan and J. S. Zhang contributed equally to this work.

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