Mouse Models for Studying Depression-Like States and Antidepressant Drugs

Novel mouse model of alternating hemiplegia of childhood exhibits prominent motor and seizure phenotypes

Pathogenic variants in ATP1A3 encoding the neuronal Na/K-ATPase cause a spectrum of neurodevelopmental disorders including alternating hemiplegia of childhood (AHC). Three recurrent ATP1A3 variants are associated with approximately half of known AHC cases and mouse models of two of these variants (p.D801N, p.E815K) replicated key features of the human disorder, which include paroxysmal hemiplegia, dystonia and seizures. Epilepsy occurs in 40-50 % of individuals affected with AHC, but detailed investigations of seizure phenotypes were limited in the previously reported mouse models. Using gene editing, we generated a novel AHC mouse expressing the third most recurrent ATP1A3 variant (p.G947R) to model neurological phenotypes of the disorder. Heterozygous Atp1a3-G947R (Atp1a3G947R) mice on a pure C57BL/6J background were born at a significantly lower frequency than wildtype (WT) littermates, but in vitro fertilization or outcrossing to a different strain (C3HeB/FeJ) generated offspring at near-Mendelian genotype ratios, suggesting a defect in reproductive fitness rather than embryonic lethality. Heterozygous mutant mice were noticeably smaller and exhibited premature lethality, hyperactivity, anxiety-like behaviors, severe motor dysfunction including low grip strength, impaired coordination with abnormal gait and balance, reduced REM sleep, and cooling-induced hemiplegia and dystonia. We also observed a prominent seizure phenotype with lower thresholds to chemically (flurothyl, kainic acid) and electrically induced seizures, post-handling seizures, sudden death following seizures, and abnormal EEG activity. Together, our findings support face validity of a novel AHC mouse model with quantifiable traits including co-morbid epilepsy that will be useful as an in vivo platform for investigating pathophysiology and testing new therapeutic strategies for this rare neurodevelopmental disorder.

Astroglial Connexins Inactivation Increases Relapse of Depressive-like Phenotype after Antidepressant Withdrawal

Studies suggest that astrocytic connexins (Cx) have an important role in the regulation of high brain functions through their ability to establish fine-tuned communication with neurons within the tripartite synapse. In light of these properties, growing evidence suggests a role of Cx in psychiatric disorders such as major depression but also in the therapeutic activity of antidepressant drugs. However, the real impact of Cx on treatment response and the underlying neurobiological mechanisms remain yet to be clarified. On this ground, the present study was designed to evaluate the functional activity of Cx in a mouse model of depression based on chronic corticosterone exposure and to determine to which extent their pharmacological inactivation influences the antidepressant-like activity of venlafaxine (VENLA). On the one hand, our results indicate that depressed mice have impaired Cx-based gap-junction and hemichannel activities. On the other hand, while VENLA exerts robust antidepressant-like activity in depressed mice; this effect is abolished by the pharmacological inhibition of Cx with carbenoxolone (CBX). Interestingly, the combination of VENLA and CBX is also associated with a higher rate of relapse after treatment withdrawal. To our knowledge, this study is one of the first to develop a model of relapse, and our results reveal that Cx-mediated dynamic neuroglial interactions play a critical role in the efficacy of monoaminergic antidepressant drugs, thus providing new targets for the treatment of depression.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Evidence of an antidepressant-like effect of xylopic acid mediated by serotonergic mechanisms

BACKGROUND

Depression causes significant debilitating symptoms and economic burden. Current management is challenged by slow onset of action and modest efficacies of antidepressants; thus, the search for newer antidepressants remains relevant. We evaluated the antidepressant effects of a kaurene diterpene, xylopic acid (XA), in zebrafish and mouse models.

METHODS

The chronic unpredictable stress (CUS) protocol in zebrafish and the tail suspension test (TST), forced swim test (FST), lipopolysaccharide-induced depression-like behaviour test (LID) and repeated open space swimming test (OSST) in mice were used. We further examined the impact of depleting monoamines on XA's antidepressant effects. The contribution of glutamatergic and nitrergic pathways on the antidepressant effect of XA in mice and XA's effects on 5-HT receptors and monoamine oxidase (MAO) enzymes were also evaluated. Finally, XA's influence on neuroprotection was evaluated by measuring BDNF and oxidative stress enzymes in whole brain. XA doses (1-10 μM) in zebrafish and (10, 30, 100 mg kg-1) in mice exerted potent antidepressant-like potential in FST, TST, LID and showed fast-onset antidepressant-like property in the OSST.

RESULTS

The antidepressant-like properties in mice were reversed by blocking synthesis/release of serotonin but not noradrenaline using p-chlorophenylalanine and α-methyl-p-tyrosine, respectively. This antidepressant-like effect was potentiated by D-cycloserine and Nω-Nitro-L-arginine methyl ester (L-NAME) but not by D-serine and L-arginine. XA also evoked partial agonist-like effects on 5-hydroxytrptamine receptors on the rat fundus but it did not have MAO inhibition effect. It also increased BDNF, glutathione and antioxidant enzymes.

CONCLUSION

Therefore, xylopic acid possesses antidepressant-like effects largely mediated by serotonergic and neuroprotective mechanisms.

UV irradiation to mouse skin decreases hippocampal neurogenesis and synaptic protein expression via HPA axis activation

The skin senses external environment, including ultraviolet light (UV). Hippocampus is a brain region that is responsible for memory and emotion. However, changes in hippocampus by UV irradiation to the skin have not been studied. In this study, after 2 weeks of UV irradiation to the mouse skin, we examined molecular changes related to cognitive functions in the hippocampus and activation of the hypothalamic-pituitary-adrenal (HPA) axis. UV exposure to the skin decreased doublecortin-positive immature neurons and synaptic proteins, including N-methyl-D-aspartate receptor 2 A and postsynaptic density protein-95, in the hippocampus. Moreover, we observed that UV irradiation to the skin down-regulated brain-derived neurotrophic factor expression and ERK signaling in the hippocampus, which are known to modulate neurogenesis and synaptic plasticity. The cutaneous and central HPA axes were activated by UV, which resulted in significant increases in serum levels of corticosterone. Subsequently, UV irradiation to the skin activated the glucocorticoid-signaling pathway in the hippocampal dentate gyrus. Interestingly, after 6 weeks of UV irradiation, mice showed depression-like behavior in the tail suspension test. Taken together, our data suggest that repeated UV exposure through the skin may negatively affect hippocampal neurogenesis and synaptic plasticity along with HPA axis activation.

Structural Features and Potent Antidepressant Effects of Total Sterols and β-sitosterol Extracted from Sargassum horneri

The purified total sterols and β-sitosterol extracted from Sargassum horneri were evaluated for their antidepressant-like activity using the forced swim test (FST) and tail suspension test (TST) in mice. Total sterols and β-sitosterol significantly reduced the immobility time in the FST and TST. Total sterols were administered orally for 7 days at doses of 50, 100, and 200 mg/kg, and β-sitosterol was administered intraperitoneally at doses of 10, 20, and 30 mg/kg. β-sitosterol had no effect on locomotor activity in the open field test. In addition, total sterols and β-sitosterol significantly increased NE, 5-HT, and the metabolite 5-HIAA in the mouse brain, suggesting that the antidepressant-like activity may be mediated through these neurotransmitters.