Opioid system modulation of cognitive affective bias: implications for the treatment of mood disorders

A significant number of patients (30%) do not adequately respond to commonly prescribed antidepressants (e.g. SSRIs, SNRIs, and TCAs). Opioid receptors and their endogenous peptides have demonstrated a clear role in the regulation of mood in animal models and may offer an alternative approach to augment existing therapies. Nevertheless, there is an urgent need to find better ways to predict a patient's response to drug treatment, to improve overall drug responding, and to reduce the time to symptom remission using novel diagnostic and efficacy biomarkers. Cognitive processes, such as perception, attention, memory, and learning, are impaired in patients with mood disorders. These processes can be altered by emotions, a phenomenon called cognitive affective bias. Negative affective biases are a key feature of major depressive disorder (MDD) and may present concurrently with other cognitive deficits. Importantly, a significant percentage of patients report residual cognitive impairments even after effective drug treatment. This approach offers a new opportunity to predict patient treatment responses, potentially improving residual cognitive symptoms and patient outcomes. This review will (1) describe the underlying neurocircuitry of affective cognition and propose how negative biases may occur, (2) outline the role of opioid receptors in affective cognition, executive function, and MDD, and (3) present evidence from the published literature supporting a modulatory role for opioid drugs on negative affective bias, with a focus on kappa-opioid receptor antagonists, currently in development for clinical use for treatment-resistant MDD.