Gender differences in genetic mouse models evaluated for depressive-like and antidepressant behavior

Investigating the potential effects of α-synuclein aggregation on susceptibility to chronic stress in a mouse Parkinson's disease model

BACKGROUND

Parkinson's disease (PD) is a motor disorder characterized by the degeneration of dopaminergic neurons, putatively due to the accumulation of α-synuclein (α-syn) in Lewy bodies (LBs) in Substantia Nigra. PD is also associated with the formation of LBs in brain areas responsible for emotional and cognitive regulation such as the amygdala and prefrontal cortex, and concurrent depression prevalence in PD patients. The exact link between dopaminergic cell loss, α-syn aggregation, depression, and stress, a major depression risk factor, is unclear. Therefore, we aimed to explore the interplay between sensitivity to chronic stress and α-syn aggregation.

METHODS

Bilateral injections of α-syn preformed fibrils (PFFs) into the striatum of C57Bl/6 J mice were used to induce α-syn aggregation. Three months after injections, animals were exposed to chronic social defeat stress.

RESULTS

α-syn aggregation did not affect stress susceptibility but independently caused increased locomotor activity in the open field test, reduced anxiety in the light-dark box test, and increased active time in the tail suspension test. Ex vivo analysis revealed modest dopaminergic neuron loss in the substantia nigra and reduced dopaminergic innervation in the dorsal striatum in PFFs injected groups. α-Syn aggregates were prominent in the amygdala, prefrontal cortex, and substantia nigra, with minimal α-syn aggregation in the raphe nuclei and locus coeruleus.

CONCLUSIONS

Progressive bilateral α-syn aggregation might lead to compensatory activity increase and alterations in emotionally regulated behavior, without affecting stress susceptibility. Understanding how α-syn aggregation and degeneration in specific brain structures contribute to depression and anxiety in PD patients requires further investigation.

CNS genomic profiling in the mouse chronic social stress model implicates a novel category of candidate genes integrating affective pathogenesis

Despite high prevalence, medical impact and societal burden, anxiety, depression and other affective disorders remain poorly understood and treated. Clinical complexity and polygenic nature complicate their analyses, often revealing genetic overlap and cross-disorder heritability. However, the interplay or overlaps between disordered phenotypes can also be based on shared molecular pathways and 'crosstalk' mechanisms, which themselves may be genetically determined. We have earlier predicted (Kalueff et al., 2014) a new class of 'interlinking' brain genes that do not affect the disordered phenotypes per se, but can instead specifically determine their interrelatedness. To test this hypothesis experimentally, here we applied a well-established rodent chronic social defeat stress model, known to progress in C57BL/6J mice from the Anxiety-like stage on Day 10 to Depression-like stage on Day 20. The present study analyzed mouse whole-genome expression in the prefrontal cortex and hippocampus during the Day 10, the Transitional (Day 15) and Day 20 stages in this model. Our main question here was whether a putative the Transitional stage (Day 15) would reveal distinct characteristic genomic responses from Days 10 and 20 of the model, thus reflecting unique molecular events underlining the transformation or switch from anxiety to depression pathogenesis. Overall, while in the Day 10 (Anxiety) group both brain regions showed major genomic alterations in various neurotransmitter signaling pathways, the Day 15 (Transitional) group revealed uniquely downregulated astrocyte-related genes, and the Day 20 (Depression) group demonstrated multiple downregulated genes of cell adhesion, inflammation and ion transport pathways. Together, these results reveal a complex temporal dynamics of mouse affective phenotypes as they develop. Our genomic profiling findings provide first experimental support to the idea that novel brain genes (activated here only during the Transitional stage) may uniquely integrate anxiety and depression pathogenesis and, hence, determine the progression from one pathological state to another. This concept can potentially be extended to other brain conditions as well. This preclinical study also further implicates cilial and astrocytal mechanisms in the pathogenesis of affective disorders.

The Interaction of Selective A1 and A2A Adenosine Receptor Antagonists with Magnesium and Zinc Ions in Mice: Behavioural, Biochemical and Molecular Studies

The purpose of the study was to investigate whether the co-administration of Mg²⁺ and Zn²⁺ with selective A1 and A2A receptor antagonists might be an interesting antidepressant strategy. Forced swim, tail suspension, and spontaneous locomotor motility tests in mice were performed. Further, biochemical and molecular studies were conducted. The obtained results indicate the interaction of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ manifested in an antidepressant-like effect. The reduction of the BDNF serum level after co-administration of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ was noted. Additionally, Mg²⁺ or Zn²⁺, both alone and in combination with DPCPX or istradefylline, causes changes in Adora1 expression, DPCPX or istradefylline co-administered with Zn²⁺ increases Slc6a15 expression as compared to a single-drug treatment, co-administration of tested agents does not have a more favourable effect on Comt expression. Moreover, the changes obtained in Ogg1, MsrA, Nrf2 expression show that DPCPX-Mg²⁺, DPCPX-Zn²⁺, istradefylline-Mg²⁺ and istradefylline-Zn²⁺ co-treatment may have greater antioxidant capacity benefits than administration of DPCPX and istradefylline alone. It seems plausible that a combination of selective A1 as well as an A2A receptor antagonist and magnesium or zinc may be a new antidepressant therapeutic strategy.

Time-restricted feeding prevents depressive-like and anxiety-like behaviors in male rats exposed to an experimental model of shift-work

Individuals who regularly shift their sleep timing, like night and/or shift-workers suffer from circadian desynchrony and are at risk of developing cardiometabolic diseases and cancer. Also, shift-work is are suggested to be a risk factor for the development of mood disorders such as the burn out syndrome, anxiety, and depression. Experimental and clinical studies provide evidence that food intake restricted to the normal activity phase is a potent synchronizer for the circadian system and can prevent the detrimental health effects associated with circadian disruption. Here, we explored whether adult male Wistar rats exposed to an experimental model of shift-work (W-AL) developed depressive and/or anxiety-like behaviors and whether this was associated with neuroinflammation in brain areas involved with mood regulation. We also tested whether time-restricted feeding (TRF) to the active phase could ameliorate circadian disruption and therefore would prevent depressive and anxiety-like behaviors as well as neuroinflammation. In male Wistar rats, W-AL induced depressive-like behavior characterized by hypoactivity and anhedonia and induced increased anxiety-like behavior in the open field test. This was associated with increased number of glial fibrillary acidic protein and IBA-1-positive cells in the prefrontal cortex and basolateral amygdala. Moreover W-AL caused morphological changes in the microglia in the CA3 area of the hippocampus indicating microglial activation. Importantly, TRF prevented behavioral changes and decreased neuroinflammation markers in the brain. Present results add up evidence about the importance that TRF in synchrony with the light-dark cycle can prevent neuroinflammation leading to healthy mood states in spite of circadian disruptive conditions.

Genetic Background and Sex: Impact on Generalizability of Research Findings in Pharmacology Studies

Animal models consisting of inbred laboratory rodent strains have been a powerful tool for decades, helping to unravel the underpinnings of biological problems and employed to evaluate potential therapeutic treatments in drug discovery. While inbred strains demonstrate relatively reliable and predictable responses, using a single inbred strain alone or as a background to a mutation is analogous to running a clinical trial in a single individual and their identical twins. Indeed, complex etiologies drive the most common human diseases, and a single inbred strain that is a surrogate of a single genome, or data generated from a single sex, is not representative of the genetically diverse patient populations. Further, pharmacological and toxicology data generated in otherwise healthy animals may not translate to disease states where physiology, metabolism, and general health are compromised. The purpose of this chapter is to provide guidance for improving generalizability of preclinical studies by providing insight into necessary considerations for introducing systematic variation within the study design, such as genetic diversity, the use of both sexes, and selection of appropriate age and disease model. The outcome of implementing these considerations should be that reproducibility and generalizability of significant results are significantly enhanced leading to improved clinical translation.

Psychotropic and neurological medication effects on mitochondrial complex I and IV in rodent models

Mitochondrial complex I (NADH-dehydrogenase) and complex IV (cytochrome-c-oxidase) are reported to be affected by drugs used to treat psychiatric or neurodegenerative diseases, including antidepressants, antipsychotics, anxiolytics, mood stabilizers, stimulants, antidementia, and antiparkinsonian drugs. We conducted meta-analyses examining the effects of each drug category on complex I and IV. The electronic databases Pubmed, EMBASE, CENTRAL, and Google Scholar were searched for studies published between 1970 and 2018. Of 3105 screened studies, 68 articles covering 53 drugs were included in the meta-analyses. All studies assessed complex I and IV in rodent brain at the level of enzyme activity. Results revealed that selected antidepressants increase or decrease complex I and IV, antipsychotics and stimulants decrease complex I but increase complex IV, whereas anxiolytics, mood stabilizers, antidementia, and antiparkinsonian drugs preserve or even enhance both complex I and IV. Potential contributions to the drug effects were found to be related to the drugs' neurotransmitter receptor profiles with adrenergic (α1B), dopaminergic (D1/2), glutaminergic (NMDA1,3), histaminergic (H1), muscarinic (M1,3), opioid (OP1-3), serotonergic (5-HT_2A, 5-HT_2C, 5-HT_3A) and sigma (σ1) receptors having the greatest effects. The findings are discussed in relation to pharmacological mechanisms of action that might have relevance for clinical and research applications.

Selective Depletion of CREB in Serotonergic Neurons Affects the Upregulation of Brain-Derived Neurotrophic Factor Evoked by Chronic Fluoxetine Treatment

Neurotrophic factors are regarded as crucial regulatory components in neuronal plasticity and are postulated to play an important role in depression pathology. The abundant expression of brain-derived neurotrophic factor (BDNF) in various brain structures seems to be of particular interest in this context, as downregulation of BDNF is postulated to be correlated with depression and its upregulation is often observed after chronic treatment with common antidepressants. It is well-known that BDNF expression is regulated by cyclic AMP response element-binding protein (CREB). In our previous study using mice lacking CREB in serotonergic neurons (Creb1^TPH2CreERT2 mice), we showed that selective CREB ablation in these particular neuronal populations is crucial for drug-resistant phenotypes in the tail suspension test observed after fluoxetine administration in Creb1^TPH2CreERT2 mice. The aim of this study was to investigate the molecular changes in the expression of neurotrophins in Creb1^TPH2CreERT2 mice after chronic fluoxetine treatment, restricted to the brain structures implicated in depression pathology with profound serotonergic innervation including the prefrontal cortex (PFC) and hippocampus. Here, we show for the first time that BDNF upregulation observed after fluoxetine in the hippocampus or PFC might be dependent on the transcription factor CREB residing, not within these particular structures targeted by serotonergic projections, but exclusively in serotonergic neurons. This observation may shed new light on the neurotrophic hypothesis of depression, where the effects of BDNF observed after antidepressants in the hippocampus and other brain structures were rather thought to be regulated by CREB residing within the same brain structures. Overall, these results provide further evidence for the pivotal role of CREB in serotonergic neurons in maintaining mechanisms of antidepressant drug action by regulation of BDNF levels.

Transgenic mice lacking CREB and CREM in noradrenergic and serotonergic neurons respond differently to common antidepressants on tail suspension test

Evidence exists that chronic antidepressant therapy enhances CREB levels and activity. Nevertheless, the data are not conclusive, as previous analysis of transgenic mouse models has suggested that CREB inactivation in fact contributes to antidepressant-like behavior. The aim of this study was to evaluate the role of CREB in this context by exploiting novel transgenic mouse models, characterized by selective ablation of CREB restricted to noradrenergic (Creb1^DBHCre/Crem−/−) or serotonergic (Creb1^TPH2CreERT2/Crem−/−) neurons in a CREM-deficient background to avoid possible compensatory effects of CREM. Selective and functional ablation of CREB affected antidepressant-like behavior in a tail suspension test (TST) after antidepressant treatment. Contrary to single Creb1^DBHCre mutants, Creb1^DBHCre/Crem−/− mice did not respond to acute desipramine administration (20 mg/kg) on the TST. On the other hand, single Creb1^TPH2CreERT2 mutants displayed reduced responses to fluoxetine (10 mg/kg) on the TST, while the effects in Creb1^TPH2CreERT2/Crem−/− mice differed by gender. Our results provide further evidence for the important role of CREM as a compensatory factor. Additionally, the results indicate that new models based on the functional ablation of CREB in select neuronal populations may represent a valuable tool for investigating the role of CREB in the mechanism of antidepressant therapy.

Depressive-like immobility behavior and genotype × stress interactions in male mice of selected strains

In this study, we investigated whether basal immobility time of C57BL/6J mice, which are commonly used in transgenesis, interferes with detection of depressive-like behavior in the tail suspension test (TST) after chronic restraint stress (CRS). We included in the study mice of the C57BL/6N strain, not previously compared with C57BL/6J for behavior in the TST, and contrasted both strains with NMRI mice which exhibit low basal immobility. NMRI, C57BL/6J, and C57BL/6N male mice (n = 20 per strain) were tested under basal conditions and after CRS (2 h daily for 14 d). NMRI and C57BL/6J mice were differentiated in the TST by low and high basal immobility times, respectively, while the C57BL/6N and NMRI mice showed similar levels of basal immobility. CRS extended the immobility time of NMRI mice in the TST, whereas both C57BL/6J and C57BL/6N mice were unaffected regardless of their initial phenotype. We explored whether detailed analysis of activity microstructure revealed effects of CRS in the TST, which are not apparent in the overall comparison of total immobility time. Interestingly, unlike C57BL/6J and/6N strains which showed no sensitivity to CRS, stressed NRMI mice displayed distinct activity microstructure. In contrast to behavioral differences, all stressed mice showed significant retardation in body weight gain, decreased thymus weight and increased adrenal cortex size. However, after CRS, enlargement of the adrenal medulla was observed in both C57BL/6J and C57BL/6N mice, suggesting similar sympatho-medullary activation and stress coping mechanism in these substrains.

Sex-Specific and Estrous Cycle-Dependent Antidepressant-Like Effects and Hippocampal Akt Signaling of Leptin

Sex differences in the incidence of depression and antidepressant treatment responses are well documented. Depression is twice as common in women as in men. Recent studies indicate that low levels of leptin, an adipocyte-derived hormone, are associated with increased symptoms of depression in women. Leptin has been shown to produce antidepressant-like effects in male rodents. In the present study, we examined sex differences and estrous cycle variations in antidepressant-like responses to leptin. Leptin administration significantly reduced immobility, a putative measure of behavioral despair, in the forced swim test in intact female mice in the proestrus phase but not in the diestrus phase of the estrous cycle. Moreover, leptin administration stimulated Akt phosphorylation in the hippocampus of female mice in proestrus but not in diestrus, in correlation with its differential behavioral effects in these two phases of the cycle. Leptin-induced behavioral responses and stimulation of hippocampal Akt phosphorylation in female mice were abolished by ovariectomy. By contrast, the antidepressant-like effect of leptin in male mice was not affected by gonadectomy (castration). Pretreatment with 17β-estradiol restored sensitivity to the effects of leptin on behavior and hippocampal Akt phosphorylation in ovariectomized female mice. These results suggest leptin regulates depression-like behavior and hippocampal Akt signaling in a sex-specific and estrous cycle-dependent manner.

Chronic selective serotonin reuptake inhibition modulates endothelial dysfunction and oxidative state in rat chronic mild stress model of depression

Major depression is known to be associated with cardiovascular abnormalities, and oxidative stress has been suggested to play a role. We tested the hypothesis that antidepressant treatment reduces oxidative stress and endothelial dysfunctions in the chronic mild stress (CMS) model of depression in rats. Rats with >30% reduction in sucrose intake after 4 wk of CMS were defined in the study as CMS-susceptible and compared with unstressed controls. Sixteen CMS-susceptible and eight unstressed rats were treated during weeks 5 to 8 of the CMS protocol with escitalopram. Escitalopram-treated rats with >20% recovery in the sucrose consumption during the last 2 wk of treatment were defined as escitalopram responders. Rats that did not reach these criteria were defined as escitalopram nonresponders. In the open field test, escitalopram responders demonstrated anxiolytic effect of treatment. In mesenteric small arteries, escitalopram affected neither NO nor cyclooxygenase-1 (COX-1)-mediated vasodilation. Escitalopram potentiated endothelium-dependent hyperpolarization-like response, which was suppressed in the vehicle-treated CMS-susceptible rats and reduced COX-2-dependent relaxation, which was elevated in the vehicle-treated CMS-susceptible rats. Escitalopram did not affect blood pressure and heart rate, which were elevated in the vehicle-treated CMS-susceptible rats. Oxidative stress markers were changed in association with CMS in liver, heart, and brain. Escitalopram normalized oxidative stress markers in the majority of tissues. This study demonstrates that the antidepressant effect of escitalopram is associated with partial improvement of endothelial function in small arteries affecting COX-2 and endothelium-dependent hyperpolarization-like pathways.

Disruption of glucocorticoid receptors in the noradrenergic system leads to BDNF up-regulation and altered serotonergic transmission associated with a depressive-like phenotype in female GR(DBHCre) mice

Recently, we have demonstrated that conditional inactivation of glucocorticoid receptors (GRs) in the noradrenergic system, may evoke depressive-like behavior in female but not male mutant mice (GR(DBHCre) mice). The aim of the current study was to dissect how selective ablation of glucocorticoid signaling in the noradrenergic system influences the previously reported depressive-like phenotype and whether it might be linked to neurotrophic alterations or secondary changes in the serotonergic system. We demonstrated that selective depletion of GRs enhances brain derived neurotrophic factor (BDNF) expression in female but not male GR(DBHCre) mice on both the mRNA and protein levels. The possible impact of the mutation on brain noradrenergic and serotonergic systems was addressed by investigating the tissue neurotransmitter levels under basal conditions and after acute restraint stress. The findings indicated a stress-provoked differential response in tissue noradrenaline content in the GR(DBHCre) female but not male mutant mice. An analogous gender-specific effect was identified in the diminished content of 5-hydroxyindoleacetic acid, the main metabolite of serotonin, in the prefrontal cortex, which suggests down-regulation of this monoamine system in female GR(DBHCre) mice. The lack of GR also resulted in an up-regulation of alpha2-adrenergic receptor (α2-AR) density in the female but not male mutants in the locus coeruleus. We have also confirmed the utility of the investigated model in pharmacological studies, which demonstrates that the depressive-like phenotype of GR(DBHCre) female mice can be reversed by antidepressant treatment with desipramine or fluoxetine, with the latter drug evoking more pronounced effects. Overall, our study validates the use of female GR(DBHCre) mice as an interesting and novel genetic tool for the investigation of the cross-connected mechanisms of depression that is not only based on behavioral phenotypes.

Pathogenesis of depression: Insights from human and rodent studies

Major depressive disorder (MDD) will affect one out of every five people in their lifetime and is the leading cause of disability worldwide. Nevertheless, mechanisms associated with the pathogenesis of MDD have yet to be completely understood and current treatments remain ineffective in a large subset of patients. In this review, we summarize the most recent discoveries and insights for which parallel findings have been obtained in human depressed subjects and rodent models of mood disorders in order to examine the potential etiology of depression. These mechanisms range from synaptic plasticity mechanisms to epigenetics and the immune system where there is strong evidence to support a functional role in the development of specific depression symptomology. Ultimately we conclude by discussing how novel therapeutic strategies targeting central and peripheral processes might ultimately aid in the development of effective new treatments for MDD and related stress disorders.

Investigating the mechanism(s) underlying switching between states in bipolar disorder

Bipolar disorder (BD) is a unique disorder that transcends domains of function since the same patient can exhibit depression or mania, states with polar opposite mood symptoms. During depression, people feel helplessness, reduced energy, and risk aversion, while with mania behaviors include grandiosity, increased energy, less sleep, and risk preference. The neural mechanism(s) underlying each state are gaining clarity, with catecholaminergic disruption seen during mania, and cholinergic dysfunction during depression. The fact that the same patient cycles/switches between these states is the defining characteristic of BD however. Of greater importance therefore, is the mechanism(s) underlying cycling from one state - and its associated neural changes - to another, considered the 'holy grail' of BD research. Herein, we review studies investigating triggers that induce switching to these states. By identifying such triggers, researchers can study neural mechanisms underlying each state and importantly how such mechanistic changes can occur in the same subject. Current animal models of this switch are also discussed, from submissive- and dominant-behaviors to kindling effects. Focus however, is placed on how seasonal changes can induce manic and depressive states in BD sufferers. Importantly, changing photoperiod lengths can induce local switches in neurotransmitter expression in normal animals, from increased catecholaminergic expression during periods of high activity, to increased somatostatin and corticotrophin releasing factor during periods of low activity. Identifying susceptibilities to this switch would enable the development of targeted animal models. From animal models, targeted treatments could be developed and tested that would minimize the likelihood of switching.

Behavioural changes in mothers and maternally sensitised female mice

The maternal motivation and depression-like behaviour of primiparous mother and maternally sensitised virgin female mice were investigated. During a 1-h test period, dams and sensitised female mice spent significantly more time in pup-associated than in control cages when they could freely choose between them, while virgin control and ovariectomised females had no such preference. In the forced swim test, the time spent in active (swimming and struggling) and passive (floating) behaviours was measured for 6 min. Mother mice spent more time engaged in active behaviours than virgin and sensitised female mice, while the latter two groups did not differ from each other in the forced swim test. The results suggest that maternal motivation is increased in postpartum mothers and maternally sensitised female mice. We also provide the first demonstration that postpartum mother mice display anti-depression-like behaviours in the forced swim test, while maternally sensitised females do not show such emotional changes.

New trends in the neurobiology and pharmacology of affective disorders

Although depression is a common disorder that is often resistant to pharmacotherapy, its pathophysiology has remained elusive. Since the early 1950s, when the first antidepressants were introduced, i.e., the non-selective MAO inhibitors and tricyclic drugs, a number of hypotheses describing ethiopathogenesis of depression and antidepressant drug action have been formulated. The Institute of Pharmacology, the Polish Academy of Sciences has performed experimental and clinical research focused on the pathophysiology of depression and the mechanisms of action of antidepressant drugs for over 40 years. Our results from this period have significantly contributed to understanding the complex mechanisms of antidepressant drug actions and new pathways that underpin the pathophysiology of depression. Most of these theories are based on the finding that the chronic administration of antidepressants leads to adaptive changes in pre- and post-synaptic monoaminergic and glutamatergic neurotransmission as well as to alterations in gene transcription and immune-inflammatory and neurotrophic factors, resulting in neuroplastic changes in the brain. Taking into account the functional interdependence of the neuronal, hormonal and immunologic systems, we propose neurodevelopmental and neuroimmune theories for affective disorders. Moreover, commonalities have been documented for the pathomechanisms of depression and neurodegenerative and metabolic disorders as well as drug dependence. The aim of this special issue is to briefly present the major research contributions and the new research directions of the Institute of Pharmacology, the Polish Academy of Sciences with respect to the neurobiology of affective disorders and the mechanisms of action of marketed and new putative antidepressant drugs.

Mechanisms underlying the antidepressant response and treatment resistance

Depression is a complex and heterogeneous disorder affecting millions of Americans. There are several different medications and other treatments that are available and effective for many patients with depression. However, a substantial percentage of patients fail to achieve remission with these currently available interventions, and relapse rates are high. Therefore, it is necessary to determine both the mechanisms underlying the antidepressant response and the differences between responders and non-responders to treatment. Delineation of these mechanisms largely relies on experiments that utilize animal models. Therefore, this review provides an overview of the various mouse models that are currently used to assess the antidepressant response, such as chronic mild stress, social defeat, and chronic corticosterone. We discuss how these mouse models can be used to advance our understanding of the differences between responders and non-responders to antidepressant treatment. We also provide an overview of experimental treatment modalities that are used for treatment-resistant depression, such as deep brain stimulation and ketamine administration. We will then review the various genetic polymorphisms and transgenic mice that display resistance to antidepressant treatment. Finally, we synthesize the published data to describe a potential neural circuit underlying the antidepressant response and treatment resistance.