BACKGROUND: Proteomic analysis was performed in post-nuclear supernatant (PNS) and Percoll-purified membranes (PM) prepared from fore brain cortex of rats exposed to increasing doses of morphine (10-50 mg/kg) for 10 days. RESULTS: In PNS, the 10 up (↑)- or down (↓)-regulated proteins exhibiting the largest morphine-induced change were selected, excised manually from the gel and identified by MALDI-TOF MS/MS: 1-(gi|148747414, Guanine deaminase), ↑2.5×; 2-(gi|17105370, Vacuolar-type proton ATP subunit B, brain isoform), ↑2.6×; 3-(gi|1352384, Protein disulfide-isomerase A3), ↑3.4×; 4-(gi|40254595, Dihydropyrimidinase-related protein 2), ↑3.6×; 5-(gi|149054470, N-ethylmaleimide sensitive fusion protein, isoform CRAa), ↑2.0×; 6-(gi|42476181, Malate dehydrogenase, mitochondrial precursor), ↑1.4×; 7-(gi|62653546, Glyceraldehyde-3-phosphate dehydrogenase), ↑1.6×; 8-(gi|202837, Aldolase A), ↑1.3×; 9-(gi|31542401, Creatine kinase B-type), ↓0.86×; 10-(gi|40538860, Aconitate hydratase, mitochondrial precursor), ↑1.3×. The identified proteins were of cytoplasmic (1, 4, 5, 7, 9), cell membrane (2), endoplasmic reticulum (3) and mitochondrial (6, 8, 10) origin and 9 of them were significantly increased, 1.3-3.6×. The 4 out of 9 up-regulated proteins (4, 6, 7, 10) were described as functionally related to oxidative stress; the 2 proteins participate in genesis of apoptotic cell death.In PM, the 18 up (↑)- or down (↓)-regulated proteins were identified by LC-MS/MS and were of plasma membrane [Brain acid soluble protein, ↓2.1×; trimeric Gβ subunit, ↓2.0x], myelin membrane [MBP, ↓2.5×], cytoplasmic [Internexin, ↑5.2×; DPYL2, ↑4.9×; Ubiquitin hydrolase, ↓2.0×; 60S ribosomal protein, ↑2.7×; KCRB, ↓2.6×; Sirtuin-2, ↑2.5×; Peroxiredoxin-2, ↑2.2×; Septin-11, ↑2.2×; TERA, ↑2.1×; SYUA, ↑2.0×; Coronin-1A, ↓5.4×] and mitochondrial [Glutamate dehydrogenase 1, ↑2.7×; SCOT1, ↑2.2×; Prohibitin, ↑2.2×; Aspartate aminotransferase, ↓2.2×] origin. Surprisingly, the immunoblot analysis of the same PM resolved by 2D-ELFO indicated that the "active", morphine-induced pool of Gβ subunits represented just a minor fraction of the total signal of Gβ which was decreased 1.2x only. The dominant signal of Gβ was unchanged. CONCLUSION: Brain cortex of rats exposed to increasing doses of morphine is far from being adapted. Significant up-regulation of proteins functionally related to oxidative stress and apoptosis suggests a major change of energy metabolism resulting in the state of severe brain cell "discomfort" or even death.

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