Contribution of Opioid and Nitrergic Systems to m-Trifluoromethyl diphenyl Diselenide Attenuates Morphine-Induced Tolerance in Mice

m-Trifluoromethyl diphenyl diselenide (TFDD) has antinociceptive and antidepressant-like properties and attenuates morphine withdrawal signs in mice. This study investigated if TFDD affects the development of morphine tolerance to its antinociceptiveand antidepressant-like effects in mice. We also investigated whether TFDD modulates signaling pathways related to morphine tolerance, including the opioid receptors and some parameters of the nitrergic system. Male adult Swiss mice received morphine alone (5 mg/kg, subcutaneous) and in combination with TFDD (10 mg/kg, intragastric) for 7 days.Mice were subjected to hot plate and forced swim tests on days 1, 3, 5, and 7 of theexperimental protocol. Repeated TFDD administrations avoided tolerance developmentmediated by morphine, including its antinociceptive and antidepressant-like effects. A singlemorphine dose increased MOR and NOx but decreasediNOS contents in the mousecerebral cortex. In turn, single morphine and TFDD co-administration restored the MORandiNOS protein levels. On the other hand, morphine repeated doses enhanced DOR and reduced MOR and NOx contents, whereas the morphine and TFDD association re established DOR and NOx levels in the mouse cerebral cortex. In conclusion, some opioid and nitrergic system parameters might contribute to TFDD attenuation of antinociceptive and antidepressant-like tolerance induced by morphine in mice.