Protective effects of mirtazapine in mice lacking the Mbnl2 gene in forebrain glutamatergic neurons: Relevance for myotonic dystrophy 1

Mirtazapine attenuates the cocaine-induced locomotor sensitization in male and female C57BL/6J and BALBA/cJ mouse

BACKGROUND

Clinical studies have described the efficacy of various therapeutic approaches. Results are inconsistent and clinical application is limited. Clinical trials have suggested that individual variability in the response to pharmacological therapies and sex affects the efficacy of some antidepressant drugs. Mouse strain-dependent variability influenced the response to antidepressant drugs. Some mouse strains respond faster and better to antidepressants than other mouse strains. We recently reported a series of preclinical studies that showed that dosing of mirtazapine, a noradrenergic and serotonergic antidepressant, in male and female Wistar rats decreased cocaine-induced locomotor activity and attenuated the induction and expression of cocaine-induced locomotor sensitization. Therefore, the aim of this study was to evaluate the mirtazapine effects, on cocaine-induced locomotor activity and cocaine-induced locomotor sensitization in male and female mice of the C57BL/6J and BALB/cJ strains, which differ in sensitivity to the cocaine motor effects and response to antidepressant drugs.

METHODS

Male and female BALB/cJ and C57BL/6J inbred mice (20-25 g) were daily dosed with 10 mg/kg of cocaine during the induction and expression of locomotor sensitization. During drug withdrawal, cocaine was withdrawn, and the groups received daily mirtazapine (30 mg/kg, i.p.) or saline. Mirtazapine was administered 30 min before cocaine. After each administration, locomotor activity for each animal was recorded for 30 min in transparent Plexiglass activity chambers.

RESULTS

Cocaine-induced locomotor activity were greater in C57BL/6J strain mice than BALB/cJ strain mice during the induction and expression phase of locomotor sensitization. The female mice of both strains showed a higher cocaine locomotor response than males and mirtazapine significantly decreased cocaine-induced locomotor activity, as well as the induction and expression of locomotor sensitization, regardless of mouse strain or sex.

CONCLUSION

The results suggest mirtazapine may be considered an effective therapeutic option to treat cocaine use disorder in men and women with very diverse genetic backgrounds.

Electrical stimulus combined with venlafaxine and mirtazapine improves brain Ca2+ activity, pre-pulse inhibition, and immobility time in a model of major depressive disorder in schizophrenia

BACKGROUND

The prevalence of major depressive disorder in patients with schizophrenia (SZ-MDD) has been reported to be about 32.6 %, but it varies considerably depending on the stage (early or chronic) and state (acute or post-psychotic) of schizophrenia. The exploration of ideal strategies for the treatment of major depressive disorder in the context of schizophrenia is urgently needed. Thus, the present study was conducted to investigate the treatment effects of clozapine, electrical stimulation (ECS; the mouse model equivalent of electroconvulsive therapy for humans), venlafaxine, and mirtazapine for SZ-MDD.

METHODS

A mouse model of SZ-MDD was established with MK801 administration and chronic unpredictable mild stress exposure. Clozapine and ECS, alone and with mirtazapine and/or venlafaxine, were used as treatment strategies. In-vivo two-photon imaging was performed to visualize Ca²⁺ neural activity in the prefrontal cortex (PFC). Mouse performance on behavioral assays was taken to reflect acute treatment effects.

RESULTS

ECS + venlafaxine + mirtazapine performed significantly better than other treatments in alleviating major depressive disorder, as reflected by PFC Ca²⁺ activity and behavioral assay performance. Clozapine + venlafaxine + mirtazapine did not have an ideal treatment effect. Brain Ca²⁺ activity alterations did not correlate with behavioral expression in any treatment group.

CONCLUSIONS

In this mouse model of SZ-MDD, ECS + venlafaxine + mirtazapine improved brain Ca2+ activity, pre-pulse inhibition, and immobility time. These findings provide useful information for the further exploration of treatment methods for patients with SZ-MDD, although the mechanisms underlying this comorbidity needed to be investigated further.

Investigating the potential of mirtazapine to induce drug-seeking behavior in free-choice drinking mouse model

Addiction to various drugs and chemicals is a significant public health concern worldwide. Addiction to prescription medications has increased due to the psychoactive effects of these medications, their availability, low price, and the lack of legal consequences for abusers. One of such prescription medication is mirtazapine (MIRT). MIRT is an antidepressant that has recently been reported to be abused and could induce withdrawal symptoms in different case studies. No previous study has investigated its abuse potential in animal models of drug addiction. Here, we conducted a free-choice drinking paradigm to investigate voluntary drinking of MIRT at two different concentrations. Male BALB/c mice were given unlimited access to two water bottles for five days before being divided into three groups: the first group had free access to two water bottles. The second group (MIRT10) and the third group (MIRT20) was allowed unlimited choice to one bottle of water and one bottle of MIRT at concentrations of 0.03 and 0.06 mg/mL, respectively. The average daily MIRT intake in the MIRT20 group was significantly higher on all tested days than that in the MIRT10 group. Moreover, mice in the MIRT20 group preferred to self-administer MIRT over water, indicating that MIRT can induce drug-seeking behavior. To further investigate the addictive potential of MIRT and its possible deterioration of memory and recognition, as reported with several known drugs of abuse, animals underwent a novel object recognition test. Mice in the MIRT20 group demonstrated significant deterioration in memory and recognition, indicating its effects on different brain regions involved in recognition, similar to other known drugs of abuse. The forced swimming test and tail suspension test were used to test MIRT-induced withdrawal symptoms after forced abstinence. After eight days of abstinence, mice in the MIRT20 group demonstrated significant depression-like symptoms in both the TST and FST, manifested by a significant increase in immobility time. MIRT was shown to induce drug-seeking behavior, deteriorate recognition, and cause withdrawal symptoms. This might confirm that MIRT has the potential to induce drug dependence and further studies are warranted to explore the neurobiological basis of MIRT-induced drug-seeking behavior.

Effects of norepinephrine on microglial neuroinflammation and neuropathic pain

Norepinephrine (NE) is an important neurotransmitter in the central nervous system. NE is released from locus coeruleus neurons and is involved in a variety of physiological and pathological processes. Neuroinflammation is a common manifestation of many kinds of neurological diseases. The activation of microglia directly affects the status of neuroinflammation. Several kinds of adrenergic receptors, which anchor on microglia and can be regulated by NE, affect the activation of microglia and neuroinflammation. NE influences chronic pain, anxiety, and depression by regulating the activation of microglia.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3'-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

Defined D-hexapeptides bind CUG repeats and rescue phenotypes of myotonic dystrophy myotubes in a Drosophila model of the disease

In Myotonic Dystrophy type 1 (DM1), a non-coding CTG repeats rare expansion disease; toxic double-stranded RNA hairpins sequester the RNA-binding proteins Muscleblind-like 1 and 2 (MBNL1 and 2) and trigger other DM1-related pathogenesis pathway defects. In this paper, we characterize four d-amino acid hexapeptides identified together with abp1, a peptide previously shown to stabilize CUG RNA in its single-stranded conformation. With the generalized sequence cpy(a/t)(q/w)e, these related peptides improved three MBNL-regulated exon inclusions in DM1-derived cells. Subsequent experiments showed that these compounds generally increased the relative expression of MBNL1 and its nuclear-cytoplasmic distribution, reduced hyperactivated autophagy, and increased the percentage of differentiated (Desmin-positive) cells in vitro. All peptides rescued atrophy of indirect flight muscles in a Drosophila model of the disease, and partially rescued muscle function according to climbing and flight tests. Investigation of their mechanism of action supports that all four compounds can bind to CUG repeats with slightly different association constant, but binding did not strongly influence the secondary structure of the toxic RNA in contrast to abp1. Finally, molecular modeling suggests a detailed view of the interactions of peptide-CUG RNA complexes useful in the chemical optimization of compounds.

Effect of trazodone on cognitive decline in people with dementia: Cohort study using UK routinely collected data

OBJECTIVES

Evidence in mouse models has found that the antidepressant trazodone may be protective against neurodegeneration. We therefore aimed to compare cognitive decline of people with dementia taking trazodone with those taking other antidepressants.

METHODS

Three identical naturalistic cohort studies using UK clinical registers. We included all people with dementia assessed during 2008-16 who were recorded taking trazodone, citalopram or mirtazapine for at least 6 weeks. Linear mixed models examined age, time and sex-adjusted Mini-mental state examination (MMSE) change in people with all-cause dementia taking trazodone compared with those taking citalopram and mirtazapine. In secondary analyses, we examined those with non-vascular dementia; mild dementia; and adjusted results for neuropsychiatric symptoms. We combined results from the three study sites using random-effects meta-analysis.

RESULTS

We included 2,199 people with dementia, including 406 taking trazodone, with mean 2.2 years follow-up. There was no difference in adjusted cognitive decline in people with all-cause or non-vascular dementia taking trazodone, citalopram or mirtazapine in any of the three study sites. When data from the three sites were combined in meta-analysis, we found greater mean MMSE decline in people with all-cause dementia taking trazodone compared to those taking citalopram (0·26 points per successive MMSE measurement, 95% CI 0·03-0·49; p = 0·03). Results in sensitivity analyses were consistent with primary analyses.

CONCLUSIONS

There was no evidence of cognitive benefit from trazodone compared to other antidepressants in people with dementia in three naturalistic cohort studies. Despite preclinical evidence, trazodone should not be advocated for cognition in dementia.