Differential regulation of beta-arrestin 1 and beta-arrestin 2 gene expression in rat brain by morphine
X L Fan1, J S Zhang, X Q Zhang
1National Laboratory of Medical Neurobiology, Fudan University Medical Center, 138 Yi Xue Yuan Road, Shanghai 200032, People's Republic of China.
Abstract:
Beta-arrestins are a family of regulatory and scaffold proteins functioning in signal transduction of G protein-coupled receptors including opioid receptors. Upon agonist stimulation, beta-arrestins bind to opioid receptors phosphorylated by G protein-coupled receptor kinases and promote receptor internalization and desensitization. Studies indicated that beta-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 beta-arrestin 1 and beta-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 beta-arrestin 1 and beta-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 beta-arrestin mRNA. In locus coeruleus, both acute and chronic morphine treatments resulted in significant decreases (over 50%) in beta-arrestin 1 mRNA level but failed to induce any change in the level of beta-arrestin 2 gene expression. The acute morphine administration had no significant effect on beta-arrestin 1 or beta-arrestin 2 mRNA level in periaqueductal gray and cerebral cortex. However, after chronic morphine treatment, beta-arrestin 2 mRNA level decreased by 40% in periaqueductal gray and increased by 25% in cerebral cortex, in strong contrast to the unchanged beta-arrestin 1 mRNA level in these two brain regions. Furthermore, spontaneous or naloxone-precipitated withdrawal of morphine that did not affect the level of beta-arrestin 1 mRNA resulted in an aberrant increase (100% over control) in beta-arrestin 2 mRNA level in hippocampus. Our results thus demonstrated for the first time that opiate administration regulates level of beta-arrestin mRNAs in brain and the expression of beta-arrestin 1 and beta-arrestin 2 subtypes is differentially regulated in locus coeruleus, periaqueductal gray, and cerebral cortex by morphine. These data suggest that beta-arrestin 1 and beta-arrestin 2 may play different roles in the development of opioid tolerance and dependence.
Insights
Morphine alters beta-arrestin (a protein family) mRNA levels in rat brains, with acute doses reducing levels in the hippocampus. Chronic morphine and withdrawal show differential regulation of beta-arrestin 1 and beta-arrestin 2, suggesting distinct roles in opioid tolerance.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- Beta-arrestins are crucial scaffold proteins in G protein-coupled receptor signaling, particularly for opioid receptors.
- They mediate receptor internalization and desensitization, and are implicated in morphine tolerance.
- Understanding beta-arrestin regulation by opioids is key to deciphering tolerance and dependence mechanisms.
Purpose of the Study:
- To investigate the regulatory effects of morphine on beta-arrestin 1 and beta-arrestin 2 mRNA levels in specific rat brain regions.
- To determine if acute and chronic morphine administration differentially affect beta-arrestin mRNA expression.
- To explore the role of beta-arrestins in morphine withdrawal.
Main Methods:
- In situ hybridization was employed to quantify beta-arrestin 1 and beta-arrestin 2 mRNA levels.
- Rats were administered acute (10 mg/kg) or chronic (10 mg/kg, b.i.d., for 9 days) morphine.
- mRNA levels were analyzed in hippocampus, locus coeruleus, periaqueductal gray, and cerebral cortex, including during withdrawal.
Main Results:
- Acute morphine reduced beta-arrestin 1 and 2 mRNA in the hippocampus by ~30%.
- Chronic morphine decreased beta-arrestin 1 mRNA in the locus coeruleus (>50%) but increased beta-arrestin 2 mRNA in the cerebral cortex (+25%) and decreased it in the periaqueductal gray (-40%).
- Morphine withdrawal significantly increased beta-arrestin 2 mRNA in the hippocampus (+100%).
Conclusions:
- Opiate administration differentially regulates beta-arrestin 1 and beta-arrestin 2 mRNA levels across brain regions.
- These findings highlight distinct roles for beta-arrestin 1 and beta-arrestin 2 in mediating the effects of morphine, including tolerance and withdrawal.
- The differential regulation suggests specific involvement in opioid dependence pathways.
