Influence of Effort-based Reward Training on Neuroadaptive Cognitive Responses: Implications for Preclinical Behavioral Approaches for Depressive Symptoms

Despite the presence of multiple pharmacotherapeutic options, incidence rates for depressive disorders continue to rise. Nonpharmacological approaches (e.g., cognitive and behavioral therapies) exhibit encouraging efficacy rates; however, a lack of preclinical models has prevented progress in the identification of relevant neurobiological mechanisms of these approaches. Accordingly, the effort-based reward (EBR) preclinical model exposes rats to response-outcome (R-O) contingencies and provides an opportunity to investigate behavioral clinical approaches. In the current study, male and female rats were assigned to either an EBR contingent- or noncontingent-trained group and exposed to 7 weeks of training. Neuroadaptive cognitive responses were assessed in a cognitive uncertainty task (UT) and an object pattern separation task (OPST). Although no significant effects of EBR were observed in the UT, EBR contingent-trained rats approached the novel panel in the most difficult trial of the OPST faster than the noncontingent-trained group. Additionally, female EBR contingent-trained rats exhibited increased engagement with the novel stimulus panel across all trials. Examination of brain-derived neurotrophic factor (BDNF) in the lateral habenula (LHb), a putative neurobiological target for depressive symptoms, revealed lower BDNF immunoreactivity in EBR contingent-trained rats. Females in both training groups exhibited higher dehydroepiandrosterone/cortisol (DHEA/CORT) ratios, suggesting, along with the increased engagement with novel stimulus panels, that female rats may be more responsive to EBR contingency training than males. Together, these results suggest that EBR contingency training offers promise as a preclinical rat model for behavioral therapeutic interventions for depressive symptoms leading to a clearer understanding of putative neurobiological mechanisms.