Diminished responses to monoaminergic antidepressants but not ketamine in a mouse model for neuropsychiatric lupus.

BACKGROUND: A significant proportion of patients suffering from major depression fail to remit following treatment and develop treatment-resistant depression. Developing novel treatments requires animal models with good predictive validity. MRL/lpr mice, an established model of systemic lupus erythematosus, show depression-like behavior. AIMS: We evaluated responses to classical antidepressants, and associated immunological and biochemical changes in MRL/lpr mice. METHODS AND RESULTS: MRL/lpr mice showed increased immobility in the forced swim test, decreased wheel running and sucrose preference when compared with the controls, MRL/MpJ mice. In MRL/lpr mice, acute fluoxetine (30 mg/kg, intraperitoneally (i.p.)), imipramine (10 mg/kg, i.p.) or duloxetine (10 mg/kg, i.p.) did not decrease the immobility time in the Forced Swim Test. Interestingly, acute administration of combinations of olanzapine (0.03 mg/kg, subcutaneously)+fluoxetine (30 mg/kg, i.p.) or bupropion (10 mg/kg, i.p.)+fluoxetine (30 mg/kg, i.p.) retained efficacy. A single dose of ketamine but not three weeks of imipramine (10 mg/kg, i.p.) or escitalopram (5 mg/kg, i.p.) treatment in MRL/lpr mice restored sucrose preference. Further, we evaluated inflammatory, immune-mediated and neuronal mechanisms. In MRL/lpr mice, there was an increase in autoantibodies' titers, [3H]PK11195 binding and immune complex deposition. There was a significant infiltration of the brain by macrophages, neutrophils and T-lymphocytes. p11 mRNA expression was decreased in the prefrontal cortex. Further, there was an increase in the 5-HT2aR expression, plasma corticosterone and indoleamine 2,3-dioxygenase activity. CONCLUSION: In summary, the MRL/lpr mice could be a useful model for Treatment Resistant Depression associated with immune dysfunction with potential to expedite antidepressant drug discovery.

Characterization of the adrenocorticotrophic hormone - induced mouse model of resistance to antidepressant drug treatment.

Approximately 30-60% of patients treated with existing antidepressants fail to achieve remission of depressive symptoms leading to Treatment Resistant Depression (TRD). There is an urgent need to develop novel medications, which is highly limited by the non-availability of relevant animal models with good predictive validity. ACTH administration has been shown to result in the resistance to acute and chronic effects of imipramine. However, the pharmacology of the model and the mechanisms contributing to the resistance are not completely understood. Furthermore, it is not known whether the ACTH administered animals show signs of depression-like behavior. Accordingly, we characterized the behavioral profile and sensitivity to antidepressants in BALB/c mice treated with ACTH and to evaluate some of the mechanisms responsible for the behavioral effects. Daily treatment with ACTH for 14, 21 or 28days failed to produce a depression-like phenotype in the sucrose preference test, voluntary wheel running or FST. In contrast, the acute antidepressant response in the FST was no longer observed in ACTH mice treated with fluoxetine, imipramine, duloxetine or bupropion. Interestingly, the combination of fluoxetine and a low dose of olanzapine, or the combination of fluoxetine and bupropion was efficacious in ACTH treated mice. Further, the sensitivity to a GluN2B receptor antagonist, radiprodil was retained in the ACTH model. To understand the mechanism responsible for the diminished response in these mice, we evaluated p11 (S100A10) mRNA expression and 5-HT2A protein expression. p11 expression was decreased and 5-HT2A protein content increased in ACTH treated mice. In summary, this model may have utility for the identification of novel treatments for TRD.