“…Therefore, we could suggest that endomorphins produce their antidepressant-like effect by the activation of the m-opioid receptors. This observation is in good agreement with the previous studies, showing that a wide variety of the m-opioid receptor agonists, including b-endorphin and buprenorphine, possess antidepressant-like behavioral effects (Mansour et al, 1988;Darko et al, 1992;Bodkin et al, 1995;Tejedor-Real et al, 1995;Besson et al, 1996;Stoll and Rueter, 1999;Vilpoux et al, 2002) and that morphine, an alkaloid opiate with substantial affinity to the m-opioid receptors, produces a significant antidepressant effect in the forced-swimming test after subcutaneous injections (Eschalier et al, 1987). Endomorphins and the m-opioid receptors are localized in the brain regions involved in the physiopathology of depression, such as the limbic system (septum, nucleus accumbens, amygdala), thalamic nuclei, locus coeruleus, and some regions of brain stem (Schreff et al, 1998;MartinSchild et al, 1999;Zadina, 2002).…”