Sex differences in the rapid and the sustained antidepressant-like effects of ketamine in stress-naïve and “depressed” mice exposed to chronic mild stress

Highlights

• Female C57BL/6J mice are more sensitive to the rapid and sustained antidepressant effects of ketamine in the FST.

• Ketamine affected the levels of excitatory amino acids in a brain region-selective and sex-dependent manner.

• Ketamine treatment induced sex-differentiated behavioral effects in mice subjected to the CMS model of depression.

Abstract

During the past decade, one of the most striking discoveries in the treatment of major depression was the clinical finding that a single infusion of a sub-anesthetic dose of the N-methyl-d-aspartate receptor antagonist ketamine produces a rapid (i.e. within a few hours) and long-lasting (i.e. up to two weeks) antidepressant effect in both treatment-resistant depressed patients and in animal models of depression. Notably, converging clinical and preclinical evidence support that responsiveness to antidepressant drugs is sex-differentiated. Strikingly, research regarding the antidepressant-like effects of ketamine has focused almost exclusively on the male sex. Herein we report that female C57BL/6J stress-naïve mice are more sensitive to the rapid and the sustained antidepressant-like effects of ketamine in the forced swim test (FST). In particular, female mice responded to lower doses of ketamine (i.e. 3 mg/kg at 30 min and 5 mg/kg at 24 h post-injection), doses that were not effective in their male counterparts. Moreover, tissue levels of the excitatory amino acids glutamate and aspartate, as well as serotonergic activity, were affected in a sex-dependent manner in the prefrontal cortex and the hippocampus, at the same time-points. Most importantly, a single injection of ketamine (10 mg/kg) induced sex-dependent behavioral effects in mice subjected to the chronic mild stress (CMS) model of depression. Intriguingly, female mice were more reactive to the earlier effects of ketamine, as assessed in the open field and the FST (at 30 min and 24 h post-treatment, respectively) but the antidepressant potential of the drug proved to be longer lasting in males, as assessed in the splash test and the FST (days 5 and 7 post-treatment, respectively). Taken together, present data revealed that ketamine treatment induces sex-dependent rapid and sustained neurochemical and behavioral antidepressant-like effects in stress-naïve and CMS-exposed C57BL/6J mice.

Introduction

According to the World Health Organization (WHO), by 2020 major depression is expected to rise to become the number two contributor to the global burden of disease (Collins et al., 2011). Current treatments for depressive disorders are only partly effective and patients who suffer from treatment-resistant depression require innovative pharmacological agents with novel mechanisms of action. Of note, women experience major depression at roughly twice the rate of men (Holden, 2005, Marcus et al., 2005, Grigoriadis and Robinson, 2007) and respond differentially to different types of antidepressant treatment (Young et al., 2009). The neurobiological mechanisms underlying these differences remain a largely neglected area of research and current treatments are based almost exclusively on research in male subjects (Beery and Zucker, 2011).

During the past decade, one of the most striking discoveries in the treatment of major depression was the clinical finding that a single infusion of a sub-anesthetic dose of the N-methyl-d-aspartate receptor (NMDAR) antagonist ketamine produces a rapid (i.e. within a few hours) and sustained (i.e. lasting from one day up to two weeks) antidepressant effect in both treatment-resistant depressed patients and in animal models of depression (Skolnick et al., 2009). In this context, administration of a single dose of ketamine in rodents has been shown to induce effects in antidepressant-predictive behavioral tasks including the forced swim test (FST) and the chronic mild stress (CMS) model of depression (Garcia et al., 2008, Maeng et al., 2008, Engin et al., 2009, Li et al., 2010, Autry et al., 2011, Bechtholt-Gompf et al., 2011, Li et al., 2011). Of note, the CMS is an ideal paradigm with which to screen the antidepressant-like effects of novel pharmacotherapeutic agents in rodents and possibly the most valid method for the preclinical investigation of the antidepressant-like effects of ketamine (Browne and Lucki, 2013, Franceschelli et al., 2014). Indeed, the discovery of ketamine’s antidepressant-like effects has reshaped and revolutionized antidepressant drug discovery (Browne and Lucki, 2013, Duman, 2014) and the behavioral and neurobiological mechanisms underlying its rapid and sustained antidepressant-like effects are under intensive investigation.

Converging clinical and experimental evidence from our group and others support that responsiveness to antidepressant drugs is sex-differentiated (Sloan and Kornstein, 2003, Marcus et al., 2005, Pitychoutis et al., 2010, Dalla et al., 2011, Pitychoutis et al., 2011, Pitychoutis et al., 2012). Strikingly, research regarding the antidepressant-like effects of ketamine has focused almost exclusively on the male sex. Recently, Carrier and Kabbaj (2013) provided first evidence that female Sprague-Dawley rats are more sensitive to the rapid antidepressant-like effects of a single injection of ketamine in the FST, as they respond to a lower dose (i.e. 2.5 mg/kg), a dose that does not induce antidepressant-like effects in male rats. C57BL/6J is the most widely used inbred mouse strain and has been widely used in preclinical ketamine research (Autry et al., 2011, Browne and Lucki, 2013). To our knowledge, sex differences in response to ketamine have never been reported in this strain.

Despite the fact that both the glutamatergic and the serotonergic systems have been implicated in ketamine’s mechanism of action (Gigliucci et al., 2013, Nishitani et al., 2014, Yamanaka et al., 2014), the intricate neurochemical mechanisms underlying its effects remain elusive. For instance, elegant microdialysis studies report that antidepressant-relevant doses of ketamine increase extracellular levels of the excitatory amino acid glutamate in the prefrontal cortex (PFC) due to a possible local disinhibition of γ-aminobutyric acid (GABA)-ergic interneurons (Lorrain et al., 2003, Duman, 2014). However, whether this effect is restricted to certain brain regions is not known. Notably, chronic treatment with conventional antidepressants has been shown to affect the serotonergic system and the levels of excitatory amino acids, glutamate and aspartate, in the PFC and the hippocampus (HIPP) in a sex-dependent manner (Kokras et al., 2009, Pitychoutis et al., 2011, Pitychoutis et al., 2012). However, putative sex differences in the neurochemical effects of ketamine have never been investigated.

In the present study we sought to investigate whether administration of a single dose of ketamine would induce sex-dependent behavioral and neurochemical effects in C57BL/6J mice. Our results show that female stress-naïve mice are more sensitive to both the rapid (i.e. at 30 min) and the sustained (i.e. at 24 h) antidepressant-like effects of ketamine in the FST. Moreover, ketamine treatment (10 mg/kg) induced region-dependent and sex-differentiated neurochemical effects in the PFC and the HIPP. Most importantly, a single injection of ketamine (10 mg/kg) induced intriguing sex-dependent behavioral effects in mice subjected to CMS for five weeks. Specifically, female CMS-exposed mice were more reactive to the earlier effects of ketamine, but the antidepressant potential of the drug proved to last longer in males.