OPRD1 and major depressive disorder: A number of DOR selective agonists were subsequently developed, demonstrating promising effects in rodents, reducing immobility in the FST (Broom et al., 2002b, Jutkiewicz et al., 2005), and attenuating the hyperemotional responses found in olfactory bulbectomized rats (Saitoh et al., 2008) (this rodent model exhibits behavioural abnormalities that may mimic the anxiety, aggression, and irritability seen in depression).