Mohammad Hassan Karimfar; Shervin Gholizadeh; Amir Peyman Hajrasouliha; Kaveh Tabrizian; Kian Azami; Mohammad Abdollahi; Mohammad Sharifzadeh; Abdol Hossain Miri. Low Dose Morphine Enhances Morphine Antinociception Effectsin the Animals Pretreated With Selective and Non-Selective Phosphodiestrase Inhibitors: Effects of Phosphodiesterase Inhibitors on Morphine Antinociception. Iran J Pharm Sci 2009, 5, 73-81.