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.

Role of sirtuin1 in impairments of emotion-related behaviors in mice with chronic mild unpredictable stress during adolescence.

Long-term exposure to physical and/or psychosocial stress during early life and/or adolescence increases the risk of psychiatric disorders such as major depressive disorder and anxiety disorders. However, the molecular mechanisms underlying early stress-induced brain dysfunction are poorly understood. In the present study, mice at 4 weeks old were subjected to chronic mild unpredictable stress (CMUS) for 4 weeks, and subsequently to assays of emotion-related behaviors. Thereafter, they were sacrificed and their brains were collected for real-time quantitative polymerase chain reaction (RT-qPCR). Mice with CMUS during adolescence showed despair behavior, anxiety-like behavior, social behavior deficits, and anhedonia in forced-swim, marble-burying, social interaction, and sucrose preference tests, respectively. Additionally, RT-qPCR revealed that the expression levels of sirtuin1 (SIRT1), a NAD+-dependent deacetylase that mediates stress responses, were down-regulated in the prefrontal cortex and hippocampus of mice with CMUS compared with control mice. Next, to investigate the pathophysiological role of decreased Sirt1 expression levels in stress-induced behavioral deficits, we assessed the effects of resveratrol, a pharmacological activator of SIRT1, in mice exposed to CMUS. Chronic treatment with resveratrol prevented CMUS-induced social behavior deficits and depression-like behaviors. These results suggest that CMUS during adolescence decreases Sirt1 expression in the brain, leading to deficits in emotional behavior. Accordingly, SIRT1 activators, such as resveratrol, may be preventive agents against abnormalities in emotional behavior following stress during an immature period.

Preventive Effect of Betaine Against Cognitive Impairments in Amyloid ß Peptide-Injected Mice Through Sirtuin1 in Hippocampus.

In the pathophysiology of Alzheimer's disease, the deposition of amyloid ß peptide (Aß) is associated with oxidative stress, leading to cognitive impairment and neurodegeneration. We have already reported that betaine (glycine betaine), an osmolyte and methyl donor in cells, prevents the development of cognitive impairment in mice with intracerebroventricular injection of Aß25-35, an active fragment of Aß, associated with oxidative stress in the hippocampus, but molecular mechanisms of betaine remain to be determined. Here, to investigate a key molecule underlying the preventive effect of betaine against cognitive impairments in Aß25-35-injected mice, cognitive tests and qPCR assays were performed in Aß25-35-injected mice with continuous betaine intake, in which intake was started a day before Aß25-35 injection, and then continued for 8 days. The Aß25-35 injection impaired short-term and object recognition memories in the Y-maze and object recognition tests, respectively. PCR assays revealed the down-regulation of Sirtuin1 (SIRT1), a NAD+-dependent deacetylase that mediates metabolic responses, in the hippocampus of Aß25-35-injected mice, whereas betaine intake prevented memory deficits as well as the decrease of hippocampal SIRT1 expression in Aß25-35-injected mice. Further, sirtinol, an inhibitor of the Sirtuin family, blocked the preventive effect of betaine against memory deficits. On the other hand, resveratrol, the potent compound that activates SIRT1, also prevented memory impairments in Aß25-35-injected mice, suggesting that SIRT1 plays a causative role in the preventive effect of betaine against memory deficits caused by Aß exposure.

Reelin Supplementation Into the Hippocampus Rescues Abnormal Behavior in a Mouse Model of Neurodevelopmental Disorders.

In the majority of schizophrenia patients, chronic atypical antipsychotic administration produces a significant reduction in or even complete remission of psychotic symptoms such as hallucinations and delusions. However, these drugs are not effective in improving cognitive and emotional deficits in patients with schizophrenia. Atypical antipsychotic drugs have a high affinity for the dopamine D2 receptor, and a modest affinity for the serotonin 5-HT2A receptor. The cognitive and emotional deficits in schizophrenia are thought to involve neural networks beyond the classical dopaminergic mesolimbic pathway, however, including serotonergic systems. For example, mutations in the RELN gene, which encodes Reelin, an extracellular matrix protein involved in neural development and synaptic plasticity, are associated with neurodevelopmental disorders such as schizophrenia and autism spectrum disorder. Furthermore, hippocampal Reelin levels are down-regulated in the brains of both schizophrenic patients and in rodent models of schizophrenia. In the present study, we investigated the effect of Reelin microinjection into the mouse hippocampus on behavioral phenotypes to evaluate the role of Reelin in neurodevelopmental disorders and to test a therapeutic approach that extends beyond classical monoamine targets. To model the cognitive and emotional deficits, as well as histological decreases in Reelin-positive cell numbers and hippocampal synaptoporin distribution, a synaptic vesicle protein, offspring that were prenatally exposed to maternal immune activation were used. Microinjections of recombinant Reelin protein into the hippocampus rescued impairments in object memory and anxiety-like behavior and recruited synaptoporin in the hippocampus in offspring exposed to antenatal inflammation. These results suggest that Reelin supplementation has the potential to treat cognitive and emotional impairments, as well as synaptic disturbances, in patients with neurodevelopmental disorders such as schizophrenia.

Paternal valproic acid exposure in mice triggers behavioral alterations in offspring.

Sodium valproate (VPA) is the most widely used antiepileptic drug and is increasingly also being used for several non-epileptic indications including migraines and bipolar disorder. It is known that maternal VPA exposure during pregnancy increases the risk of autism spectrum disorder (ASD) in children. Animal model studies have shown that maternal treatment with VPA in rodents conveys an increased risk for ASD-like phenotypes at the molecular, cellular, and behavioral levels. In contrast, the effect of paternal VPA exposure on behaviors in offspring is unknown. This study seeks to investigate whether paternal VPA exposure in rodents triggers behavioral and epigenetic alterations in offspring. The results show that paternal VPA exposure impairs object cognitive memory, suppresses the hyperactivity evoked by an NMDA receptor antagonist in male and female offspring, and disturbs sensorimotor gating in only females. In addition, since VPA is well known as an inhibitor of histone deacetylases, we examined the levels of acetylated histone H3 in the frontal cortex and hippocampus in the offspring of VPA-exposed sires. Interestingly, paternal VPA exposure down-regulates the levels of acetylated histone H3 in the brain in offspring even though VPA exposure increased acetylated histone H3 levels in the testes of sires. Collectively, these findings suggest that paternal VPA exposure may disturb the histone acetylation balance in the brain of offspring through changes in the germline epigenome, leading to behavioral alterations in offspring.