Role of expression of protein kinase C in spinal dorsal horn in metabotropic glutamate receptor 5's participation in development of morphine tolerance in rats

Abstract

Objective To evaluate the role of the expression of protein kinase Cγ and Cα in spinal dorsal horn in the metabotropic glutamate receptor subtype 5 (mGluR5)'s participation in the development of morphine tolerance in rats. Methods Thirty-two male SD rats in which the intrathecal (IT) catheter was successfully placed were randomly divided into 4 groups (n = 8 each): control group (group C), morphine tolerance group (group M), antisense oligodeoxynucleotide (ODN) plus morphine group (group ANT) and mismatch ODN plus morphine group (group MIS). Rats in group M received 0.9% normal saline (NS) 5 μl twice a day for 8 days, and IT morphine 15 μg was injected simultaneously at 6, 7 and 8 days twice a day. Rats in group ANT and MIS received IT antisense and mismatch ODN 30 nmol (in 0.9% NS 5 μl) twice a day for 8 days respectively and IT morphine 15 μg was injected simultaneously at 6, 7 and 8 days twice a day. Rats in group C received NS instead twice a day for 8 days. Paw-withdrawl threshold (PWT) to thermal and mechanical stimulation was measured at 6, 7 and 8 days after ODN injection (T1-3). The animals were killed on 9th day (T4) and the lumbar segment of the spinal cord was removed for determination of the expression of mGluR5, PKCα and PKCγ mRNA (by RT-PCR), PKCαand PKCγ ( by Western blot). Results PWT to thermal and mechanical stimulation was significantly higher at T1.2in group M and MIS and at T1.3 in group ANT, the expression of mGluR5 mRNA, PKCα and PKCγ was significantly higher at T4 in group M and MIS, and mGluR5 mRNA expression was significantly lower at T4 in group ANT than in group C ( P ＜ 0.05). PWT to thermal and mechanical stimulation was significantly higher at T2.3, while the expression of mGluR5 mRNA, PKCα and PKCγ lower at T4 in group ANT than in group M ( P ＜ 0.05). Conclusion The expression of protein kinase C in spinal dorsal horn plays an important role in the mGluR5's participation in the development of morphine tolerance in rats. Key words: Protein kinase C; Receptors,glutamate; Morphine; Drug tolerance; Spinal cord