Enhanced sensitivity of the MRL/MpJ mouse to the neuroplastic and behavioral effects of acute and chronic antidepressant treatments

Complex epigenetic patterns in cerebellum generated after developmental exposure to trichloroethylene and/or high fat diet in autoimmune-prone mice

Trichloroethylene (TCE) is an environmental contaminant associated with immune-mediated inflammatory disorders and neurotoxicity. Based on known negative effects of developmental overnutrition on neurodevelopment, we hypothesized that developmental exposure to high fat diet (HFD) consisting of 40% kcal fat would enhance neurotoxicity of low-level (6 μg per kg per day) TCE exposure in offspring over either stressor alone. Male offspring were evaluated at ∼6 weeks of age after exposure beginning 4 weeks preconception in the dams until weaning. TCE, whether used as a single exposure or together with HFD, appeared to be more robust than HFD alone in altering one-carbon metabolites involved in glutathione redox homeostasis and methylation capacity. In contrast, opposing effects of expression of key enzymes related to DNA methylation related to HFD and TCE exposure were observed. The mice generated unique patterns of anti-brain antibodies detected by western blotting attributable to both TCE and HFD. Taken together, developmental exposure to TCE and/or HFD appear to act in complex ways to alter brain biomarkers in offspring.

Actions of Brain-Derived Neurotrophic Factor and Glucocorticoid Stress in Neurogenesis

Altered neurogenesis is suggested to be involved in the onset of brain diseases, including mental disorders and neurodegenerative diseases. Neurotrophic factors are well known for their positive effects on the proliferation/differentiation of both embryonic and adult neural stem/progenitor cells (NSCs/NPCs). Especially, brain-derived neurotrophic factor (BDNF) has been extensively investigated because of its roles in the differentiation/maturation of NSCs/NPCs. On the other hand, recent evidence indicates a negative impact of the stress hormone glucocorticoids (GCs) on the cell fate of NSCs/NPCs, which is also related to the pathophysiology of brain diseases, such as depression and autism spectrum disorder. Furthermore, studies including ours have demonstrated functional interactions between neurotrophic factors and GCs in neural events, including neurogenesis. In this review, we show and discuss relationships among the behaviors of NSCs/NPCs, BDNF, and GCs.

Effects of chronic fluoxetine treatment on neurogenesis and tryptophan hydroxylase expression in adolescent and adult rats

The antidepressant drug fluoxetine (Prozac) has been increasingly prescribed to children and adolescents with depressive disorders despite a lack of thorough understanding of its therapeutic effects in the paediatric population and of its putative neurodevelopmental effects. Within the framework of PRIOMEDCHILD ERA-NET, we investigated; a) effects of chronic fluoxetine treatment on adult hippocampal neurogenesis, a structural readout relevant for antidepressant action and hippocampal development; b) effects on tryptophan hydroxylase (TPH) expression, a measure of serotonin synthesis; c) whether treatment effects during adolescence differed from treatment at an adult age, and d) whether they were subregion-specific. Stereological quantification of the number of proliferating (Ki-67+) cells and of the number of young migratory neurons (doublecortin+), revealed a significant age-by-treatment interaction effect, indicating that fluoxetine affects both proliferation and neurogenesis in adolescent-treated rats differently than it does in adult-treated rats. In terms of subregional differences, fluoxetine enhanced proliferation mainly in the dorsal parts of the hippocampus, and neurogenesis in both the suprapyramidal and infrapyramidal blades of the dentate gyrus in adolescent-treated rats, while no such differences were seen in adult-treated rats. Fluoxetine exerted similar age-by-treatment interaction effects on TPH cells mainly in the ventral portion of the dorsal raphe nucleus. We conclude that fluoxetine exerts divergent effects on structural plasticity and serotonin synthesis in adolescent versus adult-treated rats. These preliminary data indicate a differential sensitivity of the adolescent brain to this drug and thus warrant further research into their behavioural and translational aspects. Together with recent related findings, they further call for caution in prescribing these drugs to the adolescent population.

Is neurogenesis relevant in depression and in the mechanism of antidepressant drug action? A critical review

OBJECTIVES

Major depression is a complex disorder that involves genetic, epigenetic and environmental factors in its aetiology. Recent research has suggested that hippocampal neurogenesis may play a role in antidepressant action. However, careful examination of the literature suggests that the complex biological and psychological changes associated with depression cannot be attributed to disturbance in hippocampal neurogenesis alone. While antidepressants may induce hippocampal neurogenesis in non-human primates, there is a paucity of evidence that such effects are sufficient for full therapeutic action in humans.

METHODS

This review examines the literature on neurogenesis and discusses the stress-induced cortisol neurotoxicity and antidepressant-induced neurogenesis rescue model of depression. The disparity between a simple antidepressant-induced neurogenesis rescue model in the hippocampus and the complexity of clinical depression is analyzed through critical evaluation of recent research data.

RESULTS AND CONCLUSIONS

Major depression is a complex brain disorder with multiple symptoms and disturbances reflecting dysfunction in more than one single brain area. Initial research suggesting a model of hippocampal degeneration as basis of depression, and reversal by antidepressants through neurogenesis seems to be over-simplified given the emergence of new data. Synaptogenesis and re-organization or re-integration of new neurons rather than simple addition of new neurons may underlie the role of antidepressant drugs in the reversal of some but not all symptoms in depression. The importance of the neurogenesis hypothesis of depression and antidepressant action lies in stimulating further research into the possible roles played by the new neurons and synapses generated.

Optimal dosages of fluoxetine in the treatment of hypoxic brain injury induced by 3-nitropropionic acid: implications for the adjunctive treatment of patients after acute ischemic stroke

AIM

The serotonin selective reuptake inhibitor fluoxetine (Flx) has tried to treat patients suffered acute ischemic stroke because of its possible neuroprotective actions. However, besides the neuroprotective effect, Flx at high concentration also induces some actions in contradiction to neuroprotection in the brain. The purpose of this study was to investigate whether Flx presents neuroprotective effect against 3-nitropropionic acid (3-NP)-induced hypoxic brain injury, and what is the most suitable dosage of Flx.

METHODS

Mouse model was established by subacute systemic administration of 3-NP. Rotarod and pole tests were used to evaluate motor deficit. The oxidative stress and oxidative DNA damage were assessed respectively by measuring malondialdehyde and 8-hydroxydeoxyguanosine content in brain homogenates.

RESULTS

According to measurements in the rotarod test, 7 days pretreatment plus 5 days treatment of Flx at low (2.5 mg/kg/day) and, to a lesser degree, medium (5 mg/kg/day) doses exerted a rapid and strong protection against the neurotoxicity induced by 3-NP, whereas Flx at high dose (10mg/kg/day) showed a much late and light effect. Similarly, in the pole test, Flx at 2.5 mg/kg/day had the strongest protective effects. Again, only Flx administration at 2.5 mg/kg/day canceled out the enhancement of malondialdehyde and 8-hydroxydeoxyguanosine in striatum following 3-NP neurotoxication.

CONCLUSIONS

Flx attenuated the motor deficits induced by 3-NP in a dose-dependent manner. In contrary to the high dose, Flx at the lower doses had a more remarkable effect against 3-NP insult, similar to acute ischemic stroke.

Fluoxetine treatment induces dose dependent alterations in depression associated behavior and neural plasticity in female mice

Antidepressant-induced increases in neurogenesis and neurotrophin mobilization in rodents and primates are proposed to be necessary for behavioral efficacy. The current study examines the relationship between the effects of fluoxetine treatment on behavior, cell proliferation and the neurotrophin BDNF in females. Female MRL/MpJ mice were treated acutely (5 and 10mg/kg) or chronically (2.5, 5 and 10mg/kg b.i.d.) with fluoxetine and tested in the tail suspension test (TST) and or novelty-induced hypophagia test (NIH), respectively. Mice treated chronically with fluoxetine received 4 (100mg/kg) injections of 5-bromo-2'-deoxyuridine (BrdU) on the last 4 days of treatment to measure DNA synthesis. The other half of the hippocampus and the frontal cortex was removed and examined for BDNF levels. Fluoxetine treatment decreased immobility in the TST and latency to eat in the NIH test, but only the highest dose of fluoxetine significantly altered behavior in both tests. Chronic treatment with 5 and 10mg/kg of fluoxetine significantly increased cell proliferation and BDNF levels in the hippocampus. Only chronic treatment with the highest of fluoxetine increased BDNF levels in the frontal cortex. Behavioral measures in the NIH test correlated with BDNF levels in the frontal cortex but not in the hippocampus or with cell proliferation in the hippocampus. These data suggest that females require high doses of fluoxetine for behavioral efficacy regardless of elevations of neurogenesis and BDNF mobilization in the hippocampus. Elevations in BDNF levels in the frontal cortex are related to the behavioral efficacy of fluoxetine.