Fluoxetine enhanced neurogenesis is not translated to functional outcome in stroke rats

Fluoxetine Protects Retinal Ischemic Damage in Mice

BACKGROUND

To evaluate the neuroprotective effect of the topical ocular administration of fluoxetine (FLX) in a mouse model of acute retinal damage.

METHODS

Ocular ischemia/reperfusion (I/R) injury in C57BL/6J mice was used to elicit retinal damage. Mice were divided into three groups: control group, I/R group, and I/R group treated with topical FLX. A pattern electroretinogram (PERG) was used as a sensitive measure of retinal ganglion cell (RGC) function. Finally, we analyzed the retinal mRNA expression of inflammatory markers (IL-6, TNF-α, Iba-1, IL-1β, and S100β) through Digital Droplet PCR.

RESULTS

PERG amplitude values were significantly (p < 0.05) higher in the I/R-FLX group compared to the I/R group, whereas PERG latency values were significantly (p < 0.05) reduced in I/R-FLX-treated mice compared to the I/R group. Retinal inflammatory markers increased significantly (p < 0.05) after I/R injury. FLX treatment was able to significantly (p < 0.05) attenuate the expression of inflammatory markers after I/R damage.

CONCLUSIONS

Topical treatment with FLX was effective in counteracting the damage of RGCs and preserving retinal function. Moreover, FLX treatment attenuates the production of pro-inflammatory molecules elicited by retinal I/R damage. Further studies need to be performed to support the use of FLX as neuroprotective agent in retinal degenerative diseases.

The effect of fluoxetine on morning blood pressure surge in patients with ischemic stroke: a prospective preliminary clinical study

OBJECTIVE

Our study aimed to evaluate the effect of fluoxetine on morning blood pressure surge (MBPS) in patients with ischemic stroke.

METHODS

A total of 30 patients with acute ischemic stroke, 15 in the control group and 15 in the treatment group, were enrolled. Two patients in the control group and one in the treatment group were lost during follow-up. The patients in the treatment group were treated with fluoxetine (20 mg per day for 3 months) based on the treatments in the control group. Baseline characteristics, Patient Health Questionnaire 9 (PHQ-9) items scale score, mean blood pressure and MBPS were evaluated before and after treatment, and the correlation between the improvements of PHQ-9 scale score and MBPS was also analyzed.

RESULTS

The mean SBP and the systolic and diastolic MBPS in the treatment group were significantly lower than that in the control group after 3 months of treatment (P = 0.024, P = 0.022, P = 0.001, respectively). Besides, the improvement of PHQ-9 scale score was significantly higher in the treatment group than in the control group (P = 0.049). There was no significant correlation between the improvement of systolic or diastolic MBPS and the improvement of PHQ-9 scale score in the treatment group (P = 0.289 and P = 0.206, respectively).

CONCLUSION

Fluoxetine might improve MBPS in patients with ischemic stroke.

Pro-neurogenic effect of fluoxetine in the olfactory bulb is concomitant to improvements in social memory and depressive-like behavior of socially isolated mice

Although loneliness is a human experience, it can be estimated in laboratory animals deprived from physical contact with conspecifics. Rodents under social isolation (SI) tend to develop emotional distress and cognitive impairment. However, it is still to be determined whether those conditions present a common neural mechanism. Here, we conducted a series of behavioral, morphological, and neurochemical analyses in adult mice that underwent to 1 week of SI. We observed that SI mice display a depressive-like state that can be prevented by enriched environment, and the antidepressants fluoxetine (FLX) and desipramine (DES). Interestingly, chronic administration of FLX, but not DES, was able to counteract the deleterious effect of SI on social memory. We also analyzed cell proliferation, neurogenesis, and astrogenesis after the treatment with antidepressants. Our results showed that the olfactory bulb (OB) was the neurogenic niche with the highest increase in neurogenesis after the treatment with FLX. Considering that after FLX treatment social memory was rescued and depressive-like behavior decreased, we propose neurogenesis in the OB as a possible mechanism to unify the FLX ability to counteract the deleterious effect of SI.

Proteasome activation by insulin-like growth factor-1/nuclear factor erythroid 2-related factor 2 signaling promotes exercise-induced neurogenesis

Physical exercise-induced enhancement of learning and memory and alleviation of age-related cognitive decline in humans have been widely acknowledged. However, the mechanistic relationship between exercise and cognitive improvement remains largely unknown. In this study, we found that exercise-elicited cognitive benefits were accompanied by adaptive hippocampal proteasome activation. Voluntary wheel running increased hippocampal proteasome activity in adult and middle-aged mice, contributing to an acceleration of neurogenesis that could be reversed by intrahippocampal injection of the proteasome inhibitor MG132. We further found that increased levels of insulin-like growth factor-1 (IGF-1) in both serum and hippocampus may be essential for exercise-induced proteasome activation. Our in vitro study demonstrated that IGF-1 stimulated proteasome activity in cultured adult neural progenitor cells (NPCs) by promoting nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2), followed by elevated expressions of proteasome subunits such as PSMB5. In contrast, pretreating adult mice with the selective IGF-1R inhibitor picropodophyllin diminished exercise-induced neurogenesis, concurrent with reduced Nrf2 nuclear translocation and proteasome activity. Likewise, lowering Nrf2 expression by RNA interference with bilateral intrahippocampal injections of recombinant adeno-associated viral particles significantly suppressed exercise-induced proteasome activation and attenuated cognitive function. Collectively, our work demonstrates that proteasome activation in hippocampus through IGF-1/Nrf2 signaling is a key adaptive mechanism underlying exercise-related neurogenesis, which may serve as a potential targetable pathway in neurodegeneration.

Fluoxetine reverses brain radiation and temozolomide-induced anxiety and spatial learning and memory defect in mice

Radiation therapy and concomitant temozolomide chemotherapy are commonly used in treatment of brain tumors, but they may also result in behavioral impairments such as anxiety and cognitive deficit. The present study sought to investigate the effect of fluoxetine on the behavioral impairments caused by radiation and temozolomide treatment. C57BL/6J mice were subjected to a single cranial radiation followed by 6-wk cyclic temozolomide administration and were then treated with chronic administration of fluoxetine. Behavioral tests were carried out to determine the anxiety-like behavior and cognition function of these animals. Long-term potentiation (LTP) in the hippocampus was measured by electrophysiology, and neurogenesis in the dentate gyrus was evaluated by immunohistochemistry. Mice treated with radiation and temozolomide showed increased anxiety-like behavior and cognitive impairment, along with LTP impairment and neurogenesis deficit. Chronic fluoxetine administration could reverse the behavioral dysfunction, enhance LTP, and increase neurogenesis in the hippocampus. NEW & NOTEWORTHY Mice treated with radiation and temozolomide showed increased anxiety-like behavior and cognitive impairment. Chronic fluoxetine administration could reverse the behavioral dysfunction. The effect of fluoxetine might be via rescuing the neurogenesis deficit caused by radiation and temozolomide treatment.

Neuroplasticity and behavioral effects of fluoxetine after experimental stroke

The brain can undergo self-repair and has the ability to compensate for functions lost after a stroke. The plasticity of the ischemic brain is influenced by several factors including aging and pharmacotherapy. Fluoxetine is an antidepressant which enhances serotonergic neurotransmission through selective inhibition of neuronal reuptake of serotonin. In clinical practice, fluoxetine alleviates the symptoms of post-stroke depression (PSD), helps motor recovery in stroke patients. In animal experiments, chronic administration of fluoxetine induces increased excitability of mature granule cells (GCs), enhancing axonal and dendritic reorganization, as well as promoting neurogenesis or angiogenesis in the dentate gurus (DG), but the effect of fluoxetine in the subventricular zone (SVZ) remains controversial. Meanwhile, chronic treatment with fluoxetine did not reverse age-dependent suppression of proliferation cells in the DG. Interestingly, although fluoxetine has been found to enhance neurogenesis in the DG in stroke rats, this property is not consistent with the behavioral recovery. More studies into this issue will be required to reveal how to translate enhanced neuronal plasticity into behavioral benefits. This review provides an update of the current knowledge about the neurogenesis and the fate of the newly generated cells after the use of fluoxetine, as well as its ability to promote a behavioral recovery after stroke in clinical and experimental results and attempts to define the therapeutic properties of fluoxetine in regenerative neuroscience.

Pharmacological approaches promoting stem cell-based therapy following ischemic stroke insults

Stroke can lead to long-term neurological deficits. Adult neurogenesis, the continuous generation of newborn neurons in distinct regions of the brain throughout life, has been considered as one of the appoaches to restore the neurological function following ischemic stroke. However, ischemia-induced spontaneous neurogenesis is not suffcient, thus cell-based therapy, including infusing exogenous stem cells or stimulating endogenous stem cells to help repair of injured brain, has been studied in numerous animal experiments and some pilot clinical trials. While the effects of cell-based therapy on neurological function during recovery remains unproven in randomized controlled trials, pharmacological agents have been administrated to assist the cell-based therapy. In this review, we summarized the limitations of ischemia-induced neurogenesis and stem-cell transplantation, as well as the potential proneuroregenerative effects of drugs that may enhance efficacy of cell-based therapies. Specifically, we discussed drugs that enhance proliferation, migration, differentiation, survival and function connectivity of newborn neurons, which may restore neurobehavioral function and improve outcomes in stroke patients.

Effects of Fluoxetine on Hippocampal Neurogenesis and Neuroprotection in the Model of Global Cerebral Ischemia in Rats

A selective serotonin reuptake inhibitor, fluoxetine, has recently attracted a significant interest as a neuroprotective therapeutic agent. There is substantial evidence of improved neurogenesis under fluoxetine treatment of brain ischemia in animal stroke models. We studied long-term effects of fluoxetine treatment on hippocampal neurogenesis, neuronal loss, inflammation, and functional recovery in a new model of global cerebral ischemia (GCI). Brain ischemia was induced in adult Wistar male rats by transient occlusion of three main vessels originating from the aortic arch and providing brain blood supply. Fluoxetine was injected intraperitoneally in a dose of 20 mg/kg for 10 days after surgery. To evaluate hippocampal neurogenesis at time points 10 and 30 days, 5-Bromo-2′-deoxyuridine was injected at days 8–10 after GCI. According to our results, 10-day fluoxetine injections decreased neuronal loss and inflammation, improved survival and functional recovery of animals, enhanced neurogenesis, and prevented an early pathological increase in neural stem cell recruitment in the subgranular zone (SGZ) of the hippocampus without reducing the number of mature neurons at day 30 after GCI. In summary, this study suggests that fluoxetine may provide a promising therapy in cerebral ischemia due to its neuroprotective, anti-inflammatory, and neurorestorative effect.

Neuroimmunological interactions in stroke

INTRODUCTION

Stroke is one of the leading causes of death in the world; its incidence is increasing due to increased life expectancy. However, treatment options for these patients are limited since no clinically effective drugs have been developed to date.

DEVELOPMENT

According to clinical evidence, a number of neurochemical changes take place after stroke, including energy depletion, increased free radical synthesis, calcium accumulation, neurotransmitter imbalance, excitotoxicity, and, at a later stage, immune system activation leading to inflammation. Immune response has been shown to be a major factor in disease progression. The release of proinflammatory cytokines such as TNF increase brain damage secondary to excitotoxicity and calcium accumulation, and promote free radical synthesis and cell death through various mechanisms. On the other hand, certain anti-inflammatory cytokines, such as IL-10 and IL-4, have been shown to have a neuroprotective effect and even promote neurogenesis and synapse remodeling, which makes immune modulation a promising treatment approach.

CONCLUSIONS

Understanding the relationship between the immune system and the nervous system not only deepens our knowledge of stroke but also provides new diagnostic, prognostic, and therapeutic strategies that may increase the quality of life of stroke patients.

Duality of Antidepressants and Neuroprotectants

The co-morbidity of neuropsychiatric disorders, particularly major depressive disorder (MDD) with neurodegenerative diseases, in particular Parkinson's disease (PD) is now well recognized. Indeed, it is suggested that depressive disorders, especially in late life, may be an indication of latent neurodegeneration. Thus, it is not unreasonable to expect that deterrents of MDD may also deter the onset and/or progression of the neurodegenerative diseases including PD. In this review, examples of neuroprotective efficacy of established as well as prospective antidepressants are provided. Conversely, mood-regulating effects of some neuroprotective drugs are also presented. Thus, in addition to currently used antidepressants, ketamine, nicotine, curcumin, and resveratrol are discussed for their dual efficacy. In addition, potential neurobiological substrates for their actions are presented. It is concluded that pharmacological developments of mood-regulating or neuroprotective drugs can have cross benefit in co-morbid conditions of neuropsychiatric and neurodegenerative disorders and that inflammatory and neurotrophic factors play important roles in both conditions.

The role of adult neurogenesis in psychiatric and cognitive disorders

Neurogenesis in mammals occurs throughout life in two brain regions: the ventricular-subventricular zone (V-SVZ) and the subgranular zone (SGZ) of the hippocampal dentate gyrus. Development and regulation of the V-SVZ and SGZ is unique to each brain region, but with several similar characteristics. Alterations to the production of new neurons in neurogenic regions have been linked to psychiatric and neurodegenerative disorders. Decline in neurogenesis in the SGZ correlates with affective and psychiatric disorders, and can be reversed by antidepressant and antipsychotic drugs. Likewise, neurogenesis in the V-SVZ can also be enhanced by antidepressant drugs. The regulation of neurogenesis by neurotransmitters, particularly monoamines, in both regions suggests that aberrant neurotransmitter signaling observed in psychiatric disease may play a role in the pathology of these mental health disorders. Similarly, the cognitive deficits that accompany neurodegenerative disease may also be exacerbated by decreased neurogenesis. This review explores the regulation and function of neural stem cells in rodents and humans, and the involvement of factors that contribute to psychiatric and cognitive deficits. This article is part of a Special Issue entitled SI:StemsCellsinPsychiatry.

Fluoxetine Enhances Neurogenesis in Aged Rats with Cortical Infarcts, but This is not Reflected in a Behavioral Recovery

Age is associated with poor outcome and impaired functional recovery after stroke. Fluoxetine, which is widely used in clinical practice, can regulate hippocampal neurogenesis in young rodents. As the rate of neurogenesis is dramatically reduced during aging, we studied the effect of post-stroke fluoxetine treatment on neurogenesis in the subventricular zone (SVZ) and subgranular zone (SGZ) of dentate gyrus (DG) and whether this would be associated with any behavioral recovery after the cortical infarct in aged rats. Aged rats were randomly assigned to four groups: sham-operated rats, sham-operated rats treated with fluoxetine, rats subjected to cerebral ischemia, and rats with ischemia treated with fluoxetine. Focal cortical ischemia was induced by intracranial injection of vasoconstrictive peptide, endothelin-1 (ET-1). Fluoxetine was administered in the drinking water for 3 weeks starting 1 week after ischemia at a dose of 18 mg/kg/day. Behavioral recovery was evaluated on post-stroke days 29 to 31 after which the survival rate and fate of proliferating cells in the SVZ and DG were assessed by immunohistochemistry. Apoptosis was measured with the TUNEL assay. The results indicated that chronic fluoxetine treatment after stroke enhanced the proliferation of newborn neurons in the SVZ, but not in SGZ, and it suppressed perilesional apoptosis. Fluoxetine treatment did not affect the survival or differentiation of newly generated cells in the SVZ i.e., the enhanced neurogenesis was not translated into a behavioral outcome.