Vortioxetine restores reversal learning impaired by 5-HT depletion or chronic intermittent cold stress in rats.

Ashley Wallace,Connie Sánchez,David A Morilak,Alan L Pehrson

doi:10.1017/s1461145714000571

Abstract

Current treatments for depression, including serotonin-specific reuptake inhibitors (SSRIs), are only partially effective, with a high incidence of residual symptoms, relapse, and treatment resistance. Loss of cognitive flexibility, a component of depression, is associated with dysregulation of the prefrontal cortex. Reversal learning, a form of cognitive flexibility, is impaired by chronic stress, a risk factor for depression, and the stress-induced impairment in reversal learning is sensitive to chronic SSRI treatment, and is mimicked by serotonin (5-HT) depletion. Vortioxetine, a novel, multimodal-acting antidepressant, is a 5-HT3, 5-HT7 and 5-HT1D receptor antagonist, a 5-HT1B receptor partial agonist, a 5-HT1A receptor agonist, and inhibits the 5-HT transporter. Using adult male rats, we first investigated the direct effects of vortioxetine, acting at post-synaptic 5-HT receptors, on reversal learning that was compromised by 5-HT depletion using 4-chloro-DL-phenylalanine methyl ester hydrochloride (PCPA), effectively eliminating any contribution of 5-HT reuptake blockade. PCPA induced a reversal learning impairment that was alleviated by acute or sub-chronic vortioxetine administration, suggesting that post-synaptic 5-HT receptor activation contributes to the effects of vortioxetine. We then investigated the effects of chronic dietary administration of vortioxetine on reversal learning that had been compromised in intact animals exposed to chronic intermittent cold (CIC) stress, to assess vortioxetine's total pharmacological effect. CIC stress impaired reversal learning, and chronic vortioxetine administration prevented the reversal-learning deficit. Together, these results suggest that the direct effect of vortioxetine at 5-HT receptors may contribute to positive effects on cognitive flexibility deficits, and may enhance the effect of 5-HT reuptake blockade.

Highlights

Executive functions involving the prefrontal cortex (PFC) are disrupted in patients with depression (Merriam et al, 1999; Jaeger et al, 2006; Herrera-Guzmán et al, 2010)
In previous studies using the attentional set-shifting test (AST) to measure cognitive flexibility in rats (Birrell and Brown, 2000), we have shown that serotonergic neurotransmission in the orbitofrontal cortex (OFC) modulates reversal learning, one form of cognitive flexibility measured by the AST (Lapiz-Bluhm et al, 2009; Lapiz-Bluhm and Morilak, 2010; Furr et al, 2012)
We investigated the effects of vortioxetine, a novel antidepressant drug with multimodal action, on impairments in reversal learning mediated in the OFC

Summary

Introduction

Executive functions involving the prefrontal cortex (PFC) are disrupted in patients with depression (Merriam et al, 1999; Jaeger et al, 2006; Herrera-Guzmán et al, 2010). One such executive process is cognitive flexibility, the ability to modify previously learned associations and behavioral patterns in response to a changing environment (Kehagia et al, 2010). In previous studies using the attentional set-shifting test (AST) to measure cognitive flexibility in rats (Birrell and Brown, 2000), we have shown that serotonergic neurotransmission in the orbitofrontal cortex (OFC) modulates reversal learning, one form of cognitive flexibility measured by the AST (Lapiz-Bluhm et al, 2009; Lapiz-Bluhm and Morilak, 2010; Furr et al, 2012). Chronic intermittent cold (CIC) stress induces a selective deficit in reversal learning that is sensitive to chronic treatment with an SSRI (Lapiz-Bluhm et al, 2009; Lapiz-Bluhm and Morilak, 2010)

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Results

Conclusion