Gly5 ol enkephalin

DAMGO: [D-Ala², N-Me-Phe⁴, Gly⁵-ol]-enkephalin, a μ receptor selective agonist, and DPDPE [D-Pen², D-Pen⁵]-enkephalin, a δ receptor selective agonist, were purchased from Sigma-Aldrich Company, USA. Naloxone, a non-selective opioid receptor antagonist, was purchased from Beijing Sihuan Pharmaceutical Technology Co., Ltd., China. Oxybuprocaine (Benoxil) was purchased from Santen Pharmaceutical Co, Ltd. (Osaka, Japan).

All the drugs used in the present study, including morphine, D-Ala², MePhe⁴, Gly⁵-ol enkephalin (DAMGO), naloxone, Gö6983, dopamine and phenylephrine (PE) were purchased from Sigma-Aldrich. For acute drug treatment, cells were seeded onto six-well plates for 24 h at densities of 5×10⁵ cells/well (CHO/μ cells and HEK 293 cells) or 1×10⁶ cells/well (SH-SY5Y cells), and were serum-starved overnight upon reaching 80% confluence prior to stimulation by different concentration of drugs or vehicles. For morphine chronic treatment, cells were seeded onto six-well plates for 12 h prior to treatment, at densities of 2×10⁵ cells/well (CHO/μ cells) or 5×10⁵ cells/well (SH-SY5Y cells), and then treated with morphine or vehicle for 36 h.