S-ketamine reduces marble burying behaviour: Involvement of ventromedial orbitofrontal cortex and AMPA receptors

Sex-dependent effects of chronic intermittent hypoxia: implication for obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) affects 10-26% of adults in the United States with known sex differences in prevalence and severity. OSA is characterized by elevated inflammation, oxidative stress (OS), and cognitive dysfunction. However, there is a paucity of data regarding the role of sex in the OSA phenotype. Prior findings suggest women exhibit different OSA phenotypes than men, which could result in under-reported OSA prevalence in women. To examine the relationship between OSA and sex, we used chronic intermittent hypoxia (CIH) to model OSA in rats. We hypothesized that CIH would produce sex-dependent phenotypes of inflammation, OS, and cognitive dysfunction, and these sex differences would be dependent on mitochondrial oxidative stress (mtOS).

METHODS

Adult male and female Sprague Dawley rats were exposed to CIH or normoxia for 14 days to examine the impact of sex on CIH-associated circulating inflammation (IL-1β, IL-6, IL-10, TNF-α), circulating steroid hormones, circulating OS, and behavior (recollective and spatial memory; gross and fine motor function; anxiety-like behaviors; and compulsive behaviors). Rats were implanted with osmotic minipumps containing either a mitochondria-targeting antioxidant (MitoTEMPOL) or saline vehicle 1 week prior to CIH initiation to examine how inhibiting mtOS would affect the CIH phenotype.

RESULTS

Sex-specific differences in CIH-induced inflammation, OS, motor function, and compulsive behavior were observed. In female rats, CIH increased inflammation (plasma IL-6 and IL-6/IL-10 ratio) and impaired fine motor function. Conversely, CIH elevated circulating OS and compulsivity in males. These sex-dependent effects of CIH were blocked by inhibiting mtOS. Interestingly, CIH impaired recollective memory in both sexes but these effects were not mediated by mtOS. No effects of CIH were observed on spatial memory, gross motor function, or anxiety-like behavior, regardless of sex.

CONCLUSIONS

Our results indicate that the impact of CIH is dependent on sex, such as an inflammatory response and OS response in females and males, respectively, that are mediated by mtOS. Interestingly, there was no effect of sex or mtOS in CIH-induced impairment of recollective memory. These results indicate that mtOS is involved in the sex differences observed in CIH, but a different mechanism underlies CIH-induced memory impairments.

Sex differences in the anticompulsive-like effect of memantine: Involvement of nitric oxide pathway but not AMPA receptors

Memantine, an N-Methyl-D-Aspartate (NMDA) antagonist, has been examined as a potential treatment for Obsessive-Compulsive Disorder (OCD). Yet, there is limited knowledge regarding how it works to reduce compulsive behaviour and whether it has different effects on individuals based on their sex. Herein, we investigated if there are sex differences in the anticompulsive-like effect of memantine in adult Swiss mice. Additionally, we explored whether the nitric oxide (NO) pathway and α-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) receptors play a role in memantine's effects. To start, we assessed the impact of a single intraperitoneal dose of memantine (at 3, 5, and 10 mg/kg) on behaviours exhibited in the open field test (OFT) and the marble-burying test (MBT), the latter being a predictive test for anticompulsive effects. All doses of memantine reduced marble-burying behaviour in both male and female mice without affecting their locomotor activity in the OFT. This anticompulsive-like effect was also confirmed in another predictive test, the nest-building test, with the highest memantine dose (10 mg/kg) reducing nest-building behaviour without significant differences between male and female mice. We observed that pre-treatment with L-arginine, a NO precursor, mitigated the anticompulsive-like effect of memantine in male mice but had no effect in female mice in the MBT. Finally, NBQX, an AMPA receptor antagonist, did not block the anticompulsive-like effect of memantine. In summary, our study suggests that the anticompulsive-like effect of memantine does not appear to be sex-specific, does not depend on AMPA receptors, and involves the NO pathway primarily in male mice.

Sex-dependent effects of chronic intermittent hypoxia: Implication for obstructive sleep apnea

Background Obstructive sleep apnea (OSA) affects 10-26% of adults in the United States with known sex differences in prevalence and severity. OSA is characterized by elevated inflammation, oxidative stress (OS), and cognitive dysfunction. However, there is a paucity of data regarding the role of sex in the OSA phenotype. Prior findings suggest women exhibit different OSA phenotypes than men, which could result in under-reported OSA prevalence in women. To examine the relationship between OSA and sex, we used chronic intermittent hypoxia (CIH) to model OSA in rats. We hypothesized that CIH would produce sex-dependent phenotypes of inflammation, OS, and cognitive dysfunction, and these sex differences would be dependent on mitochondrial oxidative stress (mtOS). Methods Adult male and female Sprague Dawley rats were exposed to CIH or normoxia for 14 days to examine the impact of sex on CIH-associated circulating inflammation (IL-1β, IL-4, IL-6, IL-10, TNF-α), circulating OS, and behavior (recollective and spatial memory; gross and fine motor function; anxiety-like behaviors; and compulsive behaviors). A subset of rats was implanted with osmotic minipumps containing either a mitochondria-targeting antioxidant (MitoTEMPOL) or saline vehicle 1 week prior to CIH initiation to examine how inhibiting mtOS would affect the CIH phenotype. Results Sex-specific differences in CIH-induced inflammation, OS, motor function, and compulsive behavior were observed. In female rats, CIH increased inflammation (plasma IL-6 and IL-6/IL-10 ratio) and impaired fine motor function. Conversely, CIH elevated circulating OS and compulsivity in males. These sex-dependent effects of CIH were blocked by inhibiting mtOS. Interestingly, CIH impaired recollective memory in both sexes but these effects were not mediated by mtOS. No effects of CIH were observed on spatial memory, gross motor function, or anxiety-like behavior, regardless of sex. Conclusions Our results indicate that the impact of CIH is dependent on sex, such as an inflammatory response and OS response in females and males, respectively, that are mediated by mtOS. Interestingly, there was no effect of sex or mtOS in CIH-induced impairment of recollective memory. These results indicate that mtOS is involved in the sex differences observed in CIH, but a different mechanism underlies CIH-induced memory impairments.

Methodological approach: using a within-subjects design in the marble burying assay

In 2016, the National Institutes of Health mandated the use of both male and female mice in funded research. The use of both sexes is an important variable to consider; however, it comes with negative consequences such as increased animal expenses. One way to combat these negatives is to explore the option of using a within-subjects design (repeated measures) in behavioral assays that historically use a between-subjects design. Our study aimed to determine if a within-subjects design can be utilized in the marble burying assay. The marble burying assay is used as a tool for screening putative anxiolytic compounds as the assay is thought to measure obsessive-compulsive disorder- or anxiety-like behaviors. First, we compared the effects of sex and digging medium (corn cob or Sani Chip) on the number of marbles buried using CD-1 mice. Second, we determined if mice would continue to bury marbles after repeated exposures to the test arena. Lastly, we tested three positive controls (buspirone, ketamine, and fluoxetine). We found that mice buried significantly more marbles within Sani Chip digging medium, and no sex differences were observed. Next, the number of marbles buried and locomotor activity remained consistent across four test sessions. The positive controls buspirone (3.2-10 mg/kg) ketamine (32 mg/kg), and fluoxetine (10 mg/kg) decreased the number of marbles buried using the within-subjects design. These data suggest that a within-subjects design is optimal for the marble burying assay as it will reduce the number of animals and increase statistical power.

Antidepressant effects of repeated s-ketamine administration as NMDAR Antagonist: Involvement of CaMKIIα and mTOR signaling in the hippocampus of CUMS mice

With the approval of s-ketamine nasal spray as a novel antidepressant, its robust antidepressant effects have been intensively examined in clinical trials. However, the therapeutic efficacy and mechanisms of repeated intermittent drug administration remain unclear. In the present study, we applied a classic chronic unpredictable mild stress (CUMS) model to induce depressive-like behaviors of mice and evaluated the role of repeated s-ketamine administration (10 mg/kg, 7 consecutive days) in ameliorating depressive-like behaviors and modulating related molecular pathways. A battery of behavioral tests were performed to assess CUMS-induced depression. The protein expressions of GluN1, GluN2A, GluN2B, GluR1, CaMKIIα, phosphorylated CaMKIIα (p-CaMKIIα), BDNF, TrkB, phosphorylated TrkB (p-TrkB), mTOR, and phosphorylated mTOR (p-mTOR) as well as modification of synaptic ultrastructure was identified in hippocampal tissues. It turned out that s-ketamine manifested evident antidepressant effects with improved synaptic plasticity. Meanwhile, the results suggested that s-ketamine could differentially modulate glutamate receptors with upregulated GluN1 and GluR1 levels and downregulated GluN2B levels. CUMS-induced elevation of CaMKIIα phosphorylation and decline of BDNF, TrkB phosphorylation and mTOR could also be reversed through s-ketamine treatment. Together, our study provided evidence that selectively modulated glutamate receptors as well as CaMKIIα and mTOR signaling were involved in repeated s-ketamine administration.

The role of nitric oxide (NO) modulators in obsessive-compulsive disorder (OCD)

Obsessive-compulsive disorder (OCD) is as serious devastating anxiety disorder. Selective serotonin reuptake inhibitors (SSRIs) are largely used for the treatment of this mental disease. This pharmacological approach presents consistent limitations including modest efficacy and important side effects. There is pressing need, therefore, to develop new molecules with higher efficacy and safety. Nitric oxide (NO) is an intra-and inter-cellular messenger in the brain. Its involvement in the pathogenesis of OCD has been proposed. In a series of preclinical studies, the anxiolytic profile of NO modulators has been emerged. In the present review I intended to critically evaluate advances in research of these molecules as potential novel agents for the treatment of OCD, comment their advantages over currently used pharmacological therapy as well remaining challenges. Up to now, few preclinical studies have been carried out to this end. Nonetheless, experimental evidence proposes a role for NO and its modulators in OCD. Additional research is mandatory aiming to definitively determine a role for NO modulators for the treatment of OCD. A note of caution, however, is needed on account of potential neurotoxicity and narrow therapeutic window of NO compounds.

Fast antidepressant action of ketamine in mouse models requires normal VGLUT1 levels from prefrontal cortex neurons

The NMDA antagonist ketamine demonstrated a fast antidepressant activity in treatment-resistant depression. Pre-clinical studies suggest that de novo synthesis of the brain-derived neurotrophic factor (BDNF) in the PFC might be involved in the rapid antidepressant action of ketamine. Applying a genetic model of impaired glutamate release, this study aims to further identify the molecular mechanisms that could modulate antidepressant action and resistance to treatment. To that end, mice knocked-down for the vesicular glutamate transporter 1 (VGLUT1+/-) were used. We analyzed anhedonia and helpless behavior as well as the expression of the proteins linked to glutamate transmission in the PFC of mice treated with ketamine or the reference antidepressant reboxetine. Moreover, we analyzed the acute effects of ketamine in VGLUT1+/- mice pretreated with chronic reboxetine or those that received a PFC rescue expression of VGLUT1. Chronic reboxetine rescued the depressive-like phenotype of the VGLUT1+/- mice. In addition, it enhanced the expression of the proteins linked to the AMPA signaling pathway as well as the immature form of BDNF (pro-BDNF). Unlike WT mice, ketamine had no effect on anhedonia or pro-BDNF expression in VGLUT1+/- mice; it also failed to decrease phosphorylated eukaryote elongation factor 2 (p-eEF2). Nevertheless, we found that reboxetine administered as pretreatment or PFC overexpression of VGLUT1 did rescue the antidepressant-like activity of acute ketamine in the mice. Our results strongly suggest that not only do PFC VGLUT1 levels modulate the rapid-antidepressant action of ketamine, but also highlight a possible mechanism for antidepressant resistance in some patients.

The use of esketamine in comorbid treatment resistant depression and obsessive compulsive disorder following extensive pharmacogenomic testing: a case report

BACKGROUND

Major depressive disorder (MDD) patients not responding to two or more different antidepressant treatments are currently considered to suffer from treatment resistant depression (TRD). Recently, intranasal esketamine has been approved by both the American Food and Drug Administration and European Medicines Agency for TRD and, more recently, in moderate to severe episode of MDD, as acute short-term treatment for the rapid reduction of depressive symptoms, which, according to clinical judgement, constitute a psychiatric emergency. There is currently no indication for obsessive-compulsive disorder (OCD) although recently published studies have already shown a rapid and significant reduction of OCD-like symptoms following ketamine administration. The etiology of OCD has not yet been fully elucidated but there is a growing evidence that glutamate signaling dysfunction in the cortico-striatal-thalamo-cortical circuitry plays an essential role. This case report exemplifies possible clinical effects of esketamine on both depressive and OCD symptoms.

CASE PRESENTATION

We present the case of a 39-year-old man suffering from TRD. During the first evaluation at our clinic, he also reported the presence of OCD spectrum symptoms, causing him to perform time-consuming mental rituals due to pathological doubts regarding the relationship with his wife as well as intrusive thoughts regarding his mental conditions. He underwent psychometric evaluations, therapeutic drug monitoring analysis, and pharmacogenomic tests. The overall results helped to explain patient's treatment-resistance. Moreover, we observed a significant reduction in both depressive and OCD symptoms after administration of esketamine.

CONCLUSION

This case underlines the importance of pharmacogenomic tests in profiling TRD patients and confirms the possible use of esketamine in the treatment of comorbid OCD.

Short or moderate-time exposure to the inhalational anesthetics isoflurane and sevoflurane does not alter the marble-burying behavior in mice

Several studies suggest the involvement of glutamatergic neurotransmission in obsessive-compulsive disorder (OCD). Some NMDA glutamatergic receptor antagonists, such as the general anesthetic ketamine, have shown anti-OCD effects in preclinical and clinical studies. Therefore, we investigated whether the inhalational anesthetics isoflurane and sevoflurane, which are general anesthetics acting as NMDA receptor antagonists, would induce the same effects. To test our hypothesis, adult male Swiss mice were exposed to different concentrations of isoflurane (0.5, 1.5 or 3 %) or sevoflurane (0.8, 2.5 or 4 %) for 20 min (short-time exposure) or 1 h (moderate-time exposure) and submitted to the open field test (OFT) and the marble-burying test (MBT) in the same day (acute effect) or 7 days (long-lasting effect) after anesthetics administration. We found that single short or moderate-time exposure to isoflurane or sevoflurane, at sub-anesthetic or anesthetic concentrations, did not affect marble-burying behavior acutely or even 7 days after their administration. The same treatment schedules with isoflurane or sevoflurane did not impair total distance travelled in the OFT. A single moderate-time exposure to isoflurane (3 %) reduced, acutely, the central exploration of the open field, suggesting an anxiogenic-like effect of isoflurane in mice. Our results suggest that isoflurane and sevoflurane may not be promising anti-compulsive drugs.

mGlu2/3 receptor as a novel target for rapid acting antidepressants

Given that ketamine, a noncompetitive N-methyl-d-aspartate receptor antagonist that exerts rapid antidepressant effects in patients with treatment-resistant depression, also has undesirable adverse effects, agents that can be used as alternatives to ketamine have been actively pursued. Group II metabotropic glutamate (mGlu) receptors, consisting of mGlu2 and mGlu3 receptors, have emerged as one of the most promising targets in the development of ketamine-like antidepressants. Indeed, mGlu2/3 receptor antagonists have been demonstrated to exert rapid antidepressant effects in animal models and to be efficacious in animal models refractory to conventional antidepressants. Moreover, there are striking similarities between mGlu2/3 receptor antagonists and ketamine in terms of not only their antidepressant profiles, but also the underlying mechanisms of their antidepressant effects. Nonetheless, studies in rodents have shown that mGlu2/3 receptor antagonists do not cause ketamine-like adverse events, such as psychotomimetic-like behavior, abuse potential or neurotoxicity, supporting the usefulness of mGlu2/3 receptor antagonists as alternatives to ketamine. In this chapter, the past and recent research on the antidepressant effects of mGlu2/3 receptor antagonists will be reviewed. In particular, the potential of mGlu2/3 receptor antagonists as novel ketamine-like antidepressants will be emphasized.

Redistribution of Monocarboxylate 1 and 4 in Hippocampus and Spatial Memory Impairment Induced by Long-term Ketamine Administration

The monocarboxylate transporters (MCTs) MCT1, MCT2, and MCT4 are essential components of the astrocyte-neuron lactate shuttle (ANLS), which is a fundamental element of brain energetics. Decreased expression of MCTs can induce cognitive dysfunction of the brain. In the present study, we established a mouse model of long-term ketamine administration by subjecting mice to a 6-month course of a daily intraperitoneal injection of ketamine. These mice demonstrated learning and memory deficits and a significant decline in MCT1 and MCT4 proteins in the hippocampal membrane fraction, while cytoplasmic MCT1 and MCT4 protein levels were significantly increased. In contrast, the levels of global MCT2 protein were significantly increased. Analysis of mRNA levels found no changes in MCT1/4 transcripts, although the expression of MCT2 mRNA was significantly increased. We suggest that redistribution of hippocampal MCT1 and MCT4, but not MCT2 up-regulation, may be related to learning and memory deficits induced by long-term ketamine administration.

Impaired emotional response to stress in mice lacking galectin-1 or galectin-3

Galectin-1 (Gal-1) and galectin-3 (Gal-3) are multifunctional glycan-binding proteins, expressed in the brain and in its limbic structures that are involved in behavioral control. Gal-1 induces the expression of the brain-derived neurotrophic factor (BDNF) and promotes adult neural stem cells proliferation, biological events impaired in stress-related psychiatric disorders, such as depression and anxiety. Despite that, there is no evidence regarding galectin involvement in emotional control during stressful situations. Thus, we analyzed the behavioral phenotype of Gal-1 or Gal-3 knock-out mice (Gal-1 KO or Gal-3 KO) in different experimental models predictive of depressive and compulsive-like behaviors.

METHODS

C57BL-6 Gal-1 KO, Gal-3 KO, and wild-type mice (WT) were analyzed under the open field test (OFT) and, 6 h later, under the forced swim test (FST). Additionally, independent groups of male mice, lacking galectins or not, were exposed to the tail suspension test (TST) or to the marble burying test (MBT). The hippocampus and prefrontal cortex (PFC) of the mice submitted to MBT were dissected to access BDNF levels.

RESULTS

Both Gal-1 and Gal-3 KO mice showed increased time of immobility in the FST and in the TST compared to WT animals, thus reflecting an impaired stress-coping behavior. Additionally, Gal-1 and Gal-3 KO female mice presented increased compulsive-like behavior in the MBT, without significant changes in the locomotor activity. BDNF levels were found to be decreased in the PFC of Gal-1 KO mice.

DISCUSSION

Our results demonstrate that the absence of either endogenous Gal-1 and Gal-3 impairs stress-coping and increases compulsive-like behavior, suggesting that Gal-1 and Gal-3 are involved in the neurobiology of depression and obsessive-compulsive-like disorder.

Ketamine induces immediate and delayed alterations of OCD-like behavior

RATIONALE

Obsessive-compulsive disorder (OCD) is a psychiatric disorder characterized by intrusive obsessive thoughts and/or compulsive behaviors. Currently, serotonin reuptake inhibitors (SRIs) provide the only pharmacological monotherapy for OCD, but response rates are insufficient. Ketamine, a noncompetitive NMDA receptor antagonist, was reported to have rapid, sustained therapeutic effects in OCD patients. However, the mechanisms remain unknown.

OBJECTIVES

Here, we aimed to provide a platform for investigating mechanisms underlying anti-OCD effects of ketamine treatment by assessing whether ketamine pretreatment could alleviate 5-HT1B receptor (5-HT1BR)-induced OCD-like behavior in mice.

METHODS

We assessed whether acute ketamine (0, 3, 10, 30 mg/kg), administered at two pretreatment time points (30 min, 24 h), would modulate 5-HT1BR-induced OCD-like behavior in mice. Behavioral measures were perseverative hyperlocomotion in the open field and deficits in prepulse inhibition (PPI) induced by acute pharmacological 5-HT1BR challenge.

RESULTS

Three milligrams per kilogram of ketamine reduced 5-HT1BR-induced perseverative hyperlocomotion, but not PPI deficits, 24 h postinjection. In contrast, higher doses of ketamine were either ineffective (10 mg/kg) or exacerbated (30 mg/kg) 5-HT1BR-induced perseverative hyperlocomotion 30 min postinjection. At 24 h postinjection, 30 mg/kg ketamine reduced perseverative hyperlocomotion across all groups.

CONCLUSIONS

Our results suggest that the 5-HT1BR-induced model of OCD-like behavior is sensitive to a low dose of ketamine, a potential fast-acting anti-OCD treatment, and may provide a tool for studying mechanisms underlying the rapid therapeutic effects of ketamine in OCD patients.

mGlu2/3 receptor antagonists

Abnormalities of glutamatergic transmission are implicated in neuropsychiatric disorders. Among the glutamate receptors, metabotropic (mGlu) 2/3 receptors have recently gained much attention as molecular targets for the treatment of several neuropsychiatric disorders including depression and anxiety. Both orthosteric and allosteric antagonists of mGlu2/3 receptors have been synthesized, and their therapeutic potential has been examined. These research activities have demonstrated the promise of mGlu2/3 receptor antagonists as potential treatment agents for the above-mentioned neuropsychiatric disorders. In particular, it has been considered that the antidepressant effects of mGlu2/3 receptor antagonists are worthy of pursuing, since the antidepressant profiles as well as synaptic/neural mechanisms involved in the actions of mGlu2/3 receptor antagonists are similar to those of ketamine, which has been demonstrated to show potent, rapid and sustained efficacy in patients with depression, even those resistant to the conventionally prescribed antidepressants. In this chapter, the general pharmacology of mGlu2/3 receptor antagonists and their therapeutic potential are reviewed. In particular, I focus on the usefulness of mGlu2/3 receptor antagonists as novel antidepressants, in comparison with ketamine.