(R)-ketamine restores anterior insular cortex activity and cognitive deficits in social isolation-reared mice.

Chronic social isolation increases the risk of mental health problems, including cognitive impairments and depression. While subanesthetic ketamine is considered effective for cognitive impairments in patients with depression, the neural mechanisms underlying its effects are not well understood. Here we identified unique activation of the anterior insular cortex (aIC) as a characteristic feature in brain-wide regions of mice reared in social isolation and treated with (R)-ketamine, a ketamine enantiomer. Using fiber photometry recording on freely moving mice, we found that social isolation attenuates aIC neuronal activation upon social contact and that (R)-ketamine, but not (S)-ketamine, is able to counteracts this reduction. (R)-ketamine facilitated social cognition in social isolation-reared mice during the social memory test. aIC inactivation offset the effect of (R)-ketamine on social memory. Our results suggest that (R)-ketamine has promising potential as an effective intervention for social cognitive deficits by restoring aIC function.

Long-lasting anti-despair and anti-anhedonia effects of (S)-norketamine in social isolation-reared mice.

Alternatives to ketamine without psychotomimetic properties for the treatment of depression have attracted much attention. Here, we examined the anti-despair and anti-anhedonia effects of the ketamine metabolites (S)-norketamine ((S)-NK), (R)-NK, (2S,6S)-hydroxynorketamine, and (2R,6R)-hydroxynorketamine in a mouse model of depression induced by social isolation. All ketamine metabolites examined had acute (30 min after administration) anti-despair-like effects in the forced swim test, but only (S)-NK showed a long-lasting (1 week) effect. Additionally, only (S)-NK improved reduced motivation both 30 min and 24 h after injection in the female encounter test. These results suggest that (S)-NK has potent and long-lasting antidepressant-like effects.

Roles of the monoaminergic system in the antidepressant effects of ketamine and its metabolites.

While the molecular target of (R,S)-ketamine (ketamine) is thought to be the NMDA receptor, subanesthetic doses of ketamine have been known to modulate monoaminergic neurotransmission in the central nervous system. Although the involvement of the serotonergic system in the antidepressant effects of ketamine has been reported in most studies of this topic, some recent studies have reported that the dopaminergic system plays a key role in the effects of ketamine. Additionally, several lines of evidence suggest that the antidepressant-like effects of (R)-ketamine might be independent of the monoaminergic system. Ketamine metabolites also differ considerably in their ability to regulate monoamine neurotransmitters relative to (S)-ketamine and (R)-ketamine, while (2R,6R)-hydroxynorketamine might share common serotonergic signaling mechanisms with ketamine. In the current review, we summarize the effects of ketamine and its metabolites on monoamine neurotransmission in the brain and discuss the potential roles of the monoaminergic system in the mechanism of action of ketamine.

Claustrum mediates bidirectional and reversible control of stress-induced anxiety responses.

The processing of stress responses involves brain-wide communication among cortical and subcortical regions; however, the underlying mechanisms remain elusive. Here, we show that the claustrum (CLA) is crucial for the control of stress-induced anxiety-related behaviors. A combined approach using brain activation mapping and machine learning showed that the CLA activation serves as a reliable marker of exposure to acute stressors. In TRAP2 mice, which allow activity-dependent genetic labeling, chemogenetic activation of the CLA neuronal ensemble tagged by acute social defeat stress (DS) elicited anxiety-related behaviors, whereas silencing of the CLA ensemble attenuated DS-induced anxiety-related behaviors. Moreover, the CLA received strong input from DS-activated basolateral amygdala neurons, and its circuit-selective optogenetic photostimulation temporarily elicited anxiety-related behaviors. Last, silencing of the CLA ensemble during stress exposure increased resistance to chronic DS. The CLA thus bidirectionally controls stress-induced emotional responses, and its inactivation can serve as a preventative strategy to increase stress resilience.

Structure-activity relationship and mechanistic study on guggulsterone derivatives; Discovery of new anti-pancreatic cancer candidate.

Pancreatic cancer is one of the deadliest types of malignancies. A new intervention aiming to combat pancreatic cancer is targeting its extra-ordinary ability to tolerate nutrition starvation, a phenomenon known as "Austerity". As a part of a research program aiming to develop a new-generation of anticancer agents, known as "anti-austerity agents", guggulsterone derivatives (GSDs) were identified as unique anti-austerity agents in terms of potency and selectivity. These agents are able to exert preferential cytotoxic activity only under nutrient-deprived conditions with little or no toxicity under normal conditions. In the present study, a library of 14 GSDs was synthesized and screened against PANC-1 human pancreatic cells. Among tested compounds, GSD-11 showed the most potent activity with PC50 a value of 0.72 µM. It also inhibited pancreatic cancer cell migration and colony formation in a concentration-dependent manner. A mechanistic study revealed that this compound can inhibit the activation of the Akt/mTOR signaling pathway. Therefore, GSD-11 could be a promising lead compound for the anticancer drug discovery against pancreatic cancer.

Altered Functional Connectivity of the Orbital Cortex and Striatum Associated with Catalepsy Induced by Dopamine D1 and D2 Antagonists.

The dopamine system plays an important role in regulating many brain functions, including the motor function. The blockade of dopamine receptors results in a serious motor dysfunction, such as catalepsy and Parkinsonism. However, the neuronal mechanism underlying the drug-induced motor dysfunction is not well understood. Here, we examine brain-wide activation patterns in Fos-enhanced green fluorescent protein reporter mice that exhibit cataleptic behavior induced by SCH39166, a dopamine D1-like receptor antagonist, and raclopride, a dopamine D2-like receptor antagonist. Support vector classifications showed that the orbital cortex (ORB) and striatum including the caudoputamen (CP) and nucleus accumbens (ACB), prominently contribute to the discrimination between brains of the vehicle-treated and both SCH39166- and raclopride-treated mice. Interregional correlations indicated that the increased functional connectivity of functional networks, including the ORB, CP, and ACB, is the common mechanism underlying SCH39166- and raclopride-induced cataleptic behavior. Moreover, the distinct mechanisms in the SCH39166- and raclopride-induced cataleptic behaviors are the decreased functional connectivity between three areas above and the cortical amygdala, and between three areas above and the anterior cingulate cortex, respectively. Thus, the alterations of functional connectivity in diverse brain regions, including the ORB, provide new insights on the mechanism underlying drug-induced movement disorders.

Synthesis of guggulsterone derivatives as potential anti-austerity agents against PANC-1 human pancreatic cancer cells.

E- and Z-guggulsterones and nine guggulsterone derivatives (GSDs) were synthesized and evaluated for their preferential cytotoxicity against human PANC-1 cell in nutrient deprived medium utilizing antiausterity strategy. Among the synthesized compounds, GSD-1 and GSD-7 showed potent cytotoxicity against PANC-1 cells under nutrient-deprived conditions in a concentration dependent manner, with a PC50 value of 1.6 µM and 3.2 µM, respectively. The effect of GSD-1 and GSD-7 was further evaluated in a real time using live cell imaging. Both of these compounds altered PANC-1 cell morphology, leading to cell death at sub micromolar concentration range. GSD-1 and GSD-7 also inhibited PANC-1 cell colony formation in a concentration-dependent manner. GSD-1 and GSD-7 are lead structure for the anti-austerity drug development.

(S)-norketamine and (2S,6S)-hydroxynorketamine exert potent antidepressant-like effects in a chronic corticosterone-induced mouse model of depression.

Clinical and preclinical studies have shown that the N-methyl-d-aspartate receptor antagonist ketamine exerts rapid and long-lasting antidepressant effects. Although ketamine metabolites might also have potential antidepressant properties, controversial results have been reported for (2R,6R)-hydroxynorketamine ((2R,6R)-HNK) in particular, and there is little information regarding the effects of other ketamine metabolites. Here we aimed to compare the effects of (R)-norketamine ((R)-NK), (S)-NK, (2R,6R)-HNK, and (2S,6S)-HNK in a mouse model of depression induced by chronic corticosterone (CORT) injection. None of the ketamine metabolites at doses up to 20 mg/kg showed antidepressant-like activity in naïve male C57BL6/J mice. Chronic CORT treatment increased immobility in the forced swim test and caused anhedonic-like behaviors in the female encounter test. A single administration of (S)-NK and (2S,6S)-HNK dose-dependently reduced the enhanced immobility at 30 min after injection in chronic CORT-treated mice, while (R)-NK or (2R,6R)-HNK did not. Additionally, (S)-NK and (2S,6S)-HNK, but not (R)-NK or (2R,6R)-HNK, improved chronic CORT-induced anhedonia at 24 h after the injection. These results suggest that (S)-ketamine metabolites (S)-NK and (2S,6S)-HNK have potent acute and sustained antidepressant effects in rodents.

(R)-Ketamine Induces a Greater Increase in Prefrontal 5-HT Release Than (S)-Ketamine and Ketamine Metabolites via an AMPA Receptor-Independent Mechanism.

BACKGROUND: Although recent studies provide insight into the molecular mechanisms of the effects of ketamine, the antidepressant mechanism of ketamine enantiomers and their metabolites is not fully understood. In view of the involvement of mechanisms other than the N-methyl-D-aspartate receptor in ketamine's action, we investigated the effects of (R)-ketamine, (S)-ketamine, (R)-norketamine [(R)-NK], (S)-NK, (2R,6R)-hydroxynorketamine [(2R,6R)-HNK], and (2S,6S)-HNK on monoaminergic neurotransmission in the prefrontal cortex of mice. METHODS: The extracellular monoamine levels in the prefrontal cortex were measured by in vivo microdialysis. RESULTS: (R)-Ketamine and (S)-ketamine acutely increased serotonin release in a dose-dependent manner, and the effect of (R)-ketamine was greater than that of (S)-ketamine. In contrast, (S)-ketamine caused a robust increase in dopamine release compared with (R)-ketamine. Both ketamine enantiomers increased noradrenaline release, but these effects did not differ. (2R,6R)-HNK caused a slight but significant increase in serotonin and noradrenaline but not dopamine release. (S)-NK increased dopamine and noradrenaline but not serotonin release. Differential effects between (R)-ketamine and (S)-ketamine were also observed in a lipopolysaccharide-induced model of depression. An α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor antagonist, 2,3-dioxo-6-nitro-1,2,3,4- tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX), attenuated (S)-ketamine-induced, but not (R)-ketamine-induced serotonin release, whereas NBQX blocked dopamine release induced by both enantiomers. Local application of (R)-ketamine into the prefrontal cortex caused a greater increase in prefrontal serotonin release than that of (S)-ketamine. CONCLUSIONS: (R)-Ketamine strongly activates the prefrontal serotonergic system through an AMPA receptor-independent mechanism. (S)-Ketamine-induced serotonin and dopamine release was AMPA receptor-dependent. These findings provide a neurochemical basis for the underlying pharmacological differences between ketamine enantiomers and their metabolites.