Interaction of reelin and stress on immobility in the forced swim test but not dopamine-mediated locomotor hyperactivity or prepulse inhibition disruption: Relevance to psychotic and mood disorders

Emotional behaviors as well as the hippocampal reelin expression in C57BL/6N male mice chronically treated with corticosterone

Depression is a common psychiatric disorder affecting around 300 million people worldwide. Serum cortisol and glucocorticoid levels in humans are reportedly higher in patients with depression compared to controls. Furthermore, rodents repeatedly treated with exogenous corticosterone (CORT), a glucocorticoid in rodents, exhibit deficits in emotional behaviors. To confirm the availability of mice with chronic CORT treatment as an animal model of depression, we investigated the effect of chronic CORT treatment on depression-like behavioral and neuropathological phenotypes in C57BL/6N male mice. Behavioral studies showed depression- and anxiety-like behaviors in mice treated with CORT compared with control mice in the forced-swim and elevated-plus maze tests. Additionally, treated mice represented anhedonia and social behavior impairments in the sucrose preference and social interaction tests, respectively. Brains of depression patients have altered expression of reelin, an extracellular matrix protein involved in neuronal development and function. Likewise, in the present study, mice with chronic CORT treatment also exhibited reelin downregulation in cells of the hippocampus. Hence, we investigated therapeutic effects of reelin supplementation on CORT-induced behavioral abnormalities in mice. Microinjections of recombinant reelin protein into the hippocampus did not rescue behavioral deficits in mice with chronic CORT treatment. These results suggest that C57BL/6N male mice chronically treated with CORT are a suitable animal depression model, in which depressive behaviors may occur independently of the alternation of hippocampal Reelin expression.

Reelin Alterations, Behavioral Phenotypes, and Brain Anomalies in Schizophrenia: A Systematic Review of Insights From Rodent Models

Reelin is an extracellular matrix glycoprotein reduced in brain regions (the prefrontal cortex and the hippocampus) of patients with schizophrenia. There are diverse rodent models of schizophrenia that mimic patient symptoms based on various causal theories; however, likely shared reelin alterations have not yet been systematically assessed in those models. A systematic review of the literature was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) model. Articles focused on psychotic disorders or schizophrenia and their relationship with reelin in rodent models were selected. Data (first author, publication year, results, both open field and prepulse inhibition test results, and type of reelin alteration) were extracted in duplicate by two independent reviewers. The 37 reviewed articles reported about various schizophrenia models and their reelin alterations, brain morphology, and behavioral defects. We conclude that reelin is an altered preclinical biomarker common to all models included, mainly prenatal or genetic models, and a key protein in schizophrenia disease, making the reelin signaling pathway in prenatal stages a target of special interest for future preclinical and clinical studies. All models presented at least one of the four described reelin alteration types.

Systematic Review Registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021210568], identifier [CRD42021210568].

Sex Differences in Psychosis: Focus on Animal Models

Most psychiatric illnesses, such as schizophrenia, show profound sex differences in incidence, clinical presentation, course, and outcome. Fortunately, more recently the literature on sex differences and (to a lesser extent) effects of sex steroid hormones is expanding, and in this review we have focused on such studies in psychosis, both from a clinical/epidemiological and preclinical/animal model perspective. We begin by briefly describing the clinical evidence for sex differences in schizophrenia epidemiology, symptomatology, and pathophysiology. We then detail sex differences and sex hormone effects in behavioral animal models of psychosis, specifically psychotropic drug-induced locomotor hyperactivity and disruption of prepulse inhibition. We expand on the preclinical data to include developmental and genetic models of psychosis, such as the maternal immune activation model and neuregulin transgenic animals, respectively. Finally, we suggest several recommendations for future studies, in order to facilitate a better understanding of sex differences in the development of psychosis.

Selective Inactivation of Reelin in Inhibitory Interneurons Leads to Subtle Changes in the Dentate Gyrus But Leaves Cortical Layering and Behavior Unaffected

Reelin is an extracellular matrix protein, known for its dual role in neuronal migration during brain development and in synaptic plasticity at adult stages. During the perinatal phase, Reelin expression switches from Cajal-Retzius (CR) cells, its main source before birth, to inhibitory interneurons (IN), the main source of Reelin in the adult forebrain. IN-derived Reelin has been associated with schizophrenia and temporal lobe epilepsy; however, the functional role of Reelin from INs is presently unclear. In this study, we used conditional knockout mice, which lack Reelin expression specifically in inhibitory INs, leading to a substantial reduction in total Reelin expression in the neocortex and dentate gyrus. Our results show that IN-specific Reelin knockout mice exhibit normal neuronal layering and normal behavior, including spatial reference memory. Although INs are the major source of Reelin within the adult stem cell niche, Reelin from INs does not contribute substantially to normal adult neurogenesis. While a closer look at the dentate gyrus revealed some unexpected alterations at the cellular level, including an increase in the number of Reelin expressing CR cells, overall our data suggest that Reelin derived from INs is less critical for cortex development and function than Reelin expressed by CR cells.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

Severe life stress, mitochondrial dysfunction, and depressive behavior: A pathophysiological and therapeutic perspective

Mitochondria are responsible for providing our cells with energy, as well as regulating oxidative stress and apoptosis, and considerable evidence demonstrates that mitochondria-related alterations are prevalent during chronic stress and depression. Here, we discuss how chronic stress may induce depressive behavior by potentiating mitochondrial allostatic load, which ultimately decreases energy production, elevates the generation of harmful reactive oxygen species, damages mitochondrial DNA and increases membrane permeability and pro-apoptotic factor release. We also discuss how mitochondrial insults can exacerbate the immune response, contributing to depressive symptomology. Furthermore, we illustrate how depression symptoms are associated with specific mitochondrial defects, and how targeting of these defects with pharmacological agents may be a promising avenue for the development of novel, more efficacious antidepressants. In summary, this review supports the notion that severe psychosocial stress induces mitochondrial dysfunction, thereby increasing the vulnerability to developing depressive symptoms.

Nrg1 deficiency modulates the behavioural effects of prenatal stress in mice

Little is known about the exact genes that confer vulnerability or resilience to environmental stressors during early neurodevelopment. Partial genetic deletion of neuregulin 1 (Nrg1) moderates the neurobehavioural effects of stressors applied in adolescence and adulthood, however, no study has yet examined its impact on prenatal stress. Here we examined whether Nrg1 deficiency in mice modulated the impact of prenatal stress on various behaviours in adulthood. Male heterozygous Nrg1 mice were mated with wild-type female mice who then underwent daily restraint stress from days 13 to 19 of gestation. Surprisingly, prenatal stress had overall beneficial effects by facilitating sensorimotor gating, increasing sociability, decreasing depressive-like behaviour, and improving spatial memory in adulthood. Such benefits were not due to any increase in maternal care, as prenatal stress decreased nurturing of the offspring. Nrg1 deficiency negated the beneficial behavioural effects of prenatal stress on all measures except sociability. However, Nrg1 deficiency interacted with prenatal stress to trigger locomotor hyperactivity. Nrg1 deficiency, prenatal stress or their combination failed to alter acute stress-induced plasma corticosterone concentrations. Collectively these results demonstrate that Nrg1 deficiency moderates the effects of prenatal stress on adult behaviour, but it does so in a complex, domain-specific fashion.

Sex-Dependent Effects of Environmental Enrichment on Spatial Memory and Brain-Derived Neurotrophic Factor (BDNF) Signaling in a Developmental "Two-Hit" Mouse Model Combining BDNF Haploinsufficiency and Chronic Glucocorticoid Stimulation

Neurodevelopmental disorders are thought to be caused by a combination of adverse genetic and environmental insults. The "two-hit" hypothesis suggests that an early first "hit" primes the developing brain to be vulnerable to a second "hit" during adolescence which triggers behavioral dysfunction. We have previously modeled this scenario in mice and found that the combined effect of a genetic hapolinsuffuciency in the brain-derived neurotrophic factor (BDNF) gene (1st hit) and chronic corticosterone (CORT) treatment during adolescence (2nd hit), caused spatial memory impairments in adulthood. Environmental enrichment (EE) protocols are designed to stimulate experience-dependent plasticity and have shown therapeutic actions. This study investigated whether EE can reverse these spatial memory impairments. Wild-type (WT) and BDNF heterozygous (HET) mice were treated with corticosterone (CORT) in their drinking water (50 mg/L) from weeks 6 to 8 and exposed to EE from 7 to 9 weeks. Enriched housing included open top cages with additional toys, tunnels, housing, and platforms. Y-maze novel preference testing, to assess short-term spatial memory, was performed at 10 weeks of age. At week 16 dorsal hippocampus tissue was obtained for Western blot analysis of expression levels of BDNF, the BDNF receptor TrkB, and NMDA receptor subunits, GluNR1, 2A and 2B. As in our previous studies, spatial memory was impaired in our two-hit (BDNF HET + CORT) mice. Simultaneous EE prevented these impairments. However, EE appeared to worsen spatial memory performance in WT mice, particularly those exposed to CORT. While BDNF levels were lower in BDNF HET mice as expected, there were no further effects of CORT or EE in males but a close to significant female CORT × EE × genotype interaction which qualitatively corresponded with Y-maze performance. However, EE caused both sex- and genotype-specific effects on phosphorylated TrkB residues and GluNR expression within the dorsal hippocampus, with GluNR2B levels in males changing in parallel with spatial memory performance. In conclusion, beneficial effects of EE on spatial memory emerge only following two developmental disruptions. The mechanisms by which EE exerts its effects are likely via regulation of multiple activity-dependent pathways, including TrkB and NMDA receptor signaling.

Reelin Haploinsufficiency and Late-Adolescent Corticosterone Treatment Induce Long-Lasting and Female-Specific Molecular Changes in the Dorsal Hippocampus

Reelin depletion and stress seem to affect similar pathways including GABAergic and glutamatergic signaling and both are implicated in psychiatric disorders in late adolescence/early adulthood. The interaction between reelin depletion and stress, however, remains unclear. To investigate this, male and female heterozygous reelin mice (HRM) and wildtype (WT) controls were treated with the stress hormone, corticosterone (CORT), during late adolescence to simulate chronic stress. Glucocorticoid receptors (GR), N-methyl-d-aspartate receptor (NMDAr) subunits, glutamic acid decarboxylase (GAD₆₇) and parvalbumin (PV) were measured in the hippocampus and the prefrontal cortex (PFC) in adulthood. While no changes were seen in male mice, female HRM showed a significant reduction in GR expression in the dorsal hippocampus. In addition, CORT reduced GR levels as well as GluN2B and GluN2C subunits of NMDAr in the dorsal hippocampus in female mice only. CORT furthermore reduced GluN1 levels in the PFC of female mice. The combined effect of HRM and CORT treatment appeared to be additive in terms of GR expression in the dorsal hippocampus. Female-specific CORT-induced changes were associated with overall higher circulating CORT levels in female compared to male mice. This study shows differential effects of reelin depletion and CORT treatment on GR and NMDAr protein expression in male and female mice, suggesting that females are more susceptible to reelin haploinsufficiency as well as late-adolescent stress. These findings shed more light on female-specific vulnerability to stress and have implications for stress-associated mental illnesses with a female bias including anxiety and major depression.