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Effect of chronic exposure to morphine on the rat blood–brain barrier: focus on the P‐glycoprotein
Author(s) -
Yousif Salah,
Saubaméa Bruno,
Cisternino Salvatore,
MarieClaire Cynthia,
Dauchy Sandrine,
Scherrmann JeanMichel,
Declèves Xavier
Publication year - 2008
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.2008.05647.x
Subject(s) - morphine , occludin , blood–brain barrier , in situ hybridization , chemistry , p glycoprotein , gene expression , isolated brain , receptor , cerebral cortex , pharmacology , medicine , microbiology and biotechnology , biology , central nervous system , endocrinology , tight junction , biochemistry , gene , antibiotics , multiple drug resistance
Morphine may affect the properties of the blood–brain barrier (BBB) by modifying the expression of certain BBB markers. We have determined the effect of chronic morphine treatment on the expression and function of some BBB markers in the rat. The mRNAs of 19 selected genes encoding caveolins, endothelial transporters, receptors and tight junctions proteins in the total RNA of isolated cortex microvessels were assayed by quantitative RT‐PCR (qRT‐PCR). The expression of genes Mdr1a, Mrp1, Bcrp, Glut‐1 and Occludin , was slightly increased, while that of Flk‐1 was decreased in microvessels from morphine‐treated rats. The expression of the Mrd1a and Mdr1b genes encoding the P‐glycoprotein (P‐gp) also increased in the whole hippocampus and cortex of morphine‐treated rats. The Mdr1a gene induction (1.38‐fold) observed by qRT‐PCR was also confirmed using in situ hybridization technique (1.40‐fold). Immunoblotting revealed an increase in P‐gp expression in the hippocampus (1.8‐fold) and cortex (1.36‐fold) of morphine‐treated rats, but no effect in isolated microvessels. In contrast, morphine treatment increased by 1.48‐fold the expression of P‐gp in a large vessel‐enriched fraction. The integrity of the BBB, measured by in situ brain perfusion of [ 14 C]‐sucrose, and the activity of P‐gp at the BBB, measured with the P‐gp substrate [ 3 H]‐colchicine, were not modified by morphine. Immunohistofluorescence experiments revealed that P‐gp expression is restricted to large vessels and microvessels in control rats and that morphine treatment did not induce the expression of P‐gp in the brain parenchyma (astrocytes or neurons). Taken together, our results showed that chronic morphine treatment does not significantly alter BBB integrity or P‐gp activity. The impact of morphine‐mediated P‐gp induction observed in large vessels remains to be determined in terms of brain disposition of drugs that are P‐gp substrates.