Time dependent antinociceptive effects of morphine and tramadol in the hot plate test: using different methods of drug administration in female rats

Morphine and tramadol which have analgesic effects can be administered acutely or chronically. This study tried to investigate the effect of these drugs at various times by using different methods of administration (intraperitoneal, oral, acute and chronic). Sixty adult female rats were divided into six groups. They received saline, morphine or tramadol (20 to 125 mg/Kg) daily for 15 days. A hot plate test was performed for the rats at the 1(st), 8(th) and 15(th) days. After drug withdrawal, the hot plate test was repeated at the 17(th), 19(th), and 22(nd) days. There was a significant correlation between the day, drug, group, and their interaction (P