The functionality of kappa- and delta-opioid receptors, might be less associated with relaxation and analgesic effects as kappa-OR often suppress activation of mu-opioid receptors, and delta-OR differ from mu-OR in its interaction with agonists and antagonists. Kappa-opioid receptors were implicated in perceptual mobilization seen in chronic anxiety whereas delta-opioid receptors were found to induce initiation of actions, impulsivity and behavioural mobilization. These differences led some researches to suggest that up- or down-regulations within three opioid receptors families are the basis of different dispositional emotionality seen in psychiatric disorders.