Long-term effects of pre-pubertal fluoxetine on behaviour and monoaminergic stress response in stress-sensitive rats

Effects of chronic fluoxetine treatment on anxiety- and depressive-like behaviors in adolescent rodents - systematic review and meta-analysis

Background

Drugs prescribed for psychiatric disorders in adolescence should be studied very extensively since they can affect developing and thus highly plastic brain differently than they affect the adult brain. Therefore, we aimed to summarize animal studies reporting the behavioral consequences of chronic exposure to the most widely prescribed antidepressant drug among adolescents i.e., fluoxetine.

Methods

Electronic databases (Medline via Pubmed, Web of Science Core Collection, ScienceDirect) were systematically searched until April 12, 2022, for published, peer-reviewed, controlled trials concerning the effects of chronic fluoxetine administration vs. vehicle on anxiety and depression measures in naïve and stress-exposed adolescent rodents. All of the relevant studies were selected and critically appraised, and a meta-analysis of eligible studies was performed.

Results

A total of 18 studies were included in the meta-analysis. In naïve animals, chronic adolescent fluoxetine administration showed dose-related anxiogenic-like effects, measured as a reduction in time spent in the open arms of the elevated plus maze. No significant effects of chronic adolescent fluoxetine on depression-like behavior were reported in naïve animals, while in stress-exposed rodents chronic adolescent fluoxetine significantly decreased immobility time in the forced swim test compared to vehicle.

Conclusions

These results suggest that although chronic fluoxetine treatment proves positive effects in animal models of depression, it may simultaneously increase anxiety in adolescent animals in a dose-related manner. Although the clinical implications of the data should be interpreted with extreme caution, adolescent patients under fluoxetine treatment should be closely monitored.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-022-00420-w.

Upregulation of miR-19b-3p exacerbates chronic stress-induced changes in synaptic plasticity and cognition by targeting Drebrin

Chronic stress is associate with impairment of synapse plasticity in hippocampus and cognitive dysfunction in rodent and human. Notably, corticosterone (CORT) is believed to take responsible for dendritic atrophy and reduction of spine number induced by chronic stress in hippocampus. But little is known about the molecular mechanisms underlying CORT induced abnormal synapse plasticity and cognitive dysfunction. Drebrin is an F-actin binding protein that modulates memory formation and maintenance by controlling the genesis and morphology of dendritic spines. In addition, miRNAs have been reported to participate in the negative regulation of protein-coding genes. In this study, five miRNAs capable of targeting Drebrin were selected by searching miRNA databases. One of these miRNAs, miR-19b-3p, was found to be upregulated in the hippocampal neurons of mice with chronic restraint stress (CRS). Luciferase reporter assay and Fluorescence in situ hybridization (FISH) were employed to identified the interaction between miR-19b-3p and Drebrin. In addition, silencing miR-19b-3p expression in vivo using an antagomir or in vitro using an inhibitor increased Drebrin expression, ameliorated the abnormal dendritic structure and upregulated the spine density in hippocampal CA1 pyramidal neurons of CRS mice and primary hippocampal neurons cultured under CORT stimulation, respectively. Electrophysiological analysis revealed that inhibition of miR-19b-3p rescued the limited synaptic transmission and synaptic plasticity in hippocampal neurons. Moreover, blocking miR-19b-3p drastically protected against cognitive deficits in CRS mice. These in vivo and in vitro findings indicate that the upregulation of miR-19b-3p exacerbates CRS-induced abnormal synaptic plasticity and cognitive impairment by targeting Drebrin.

The long-term bio-behavioural effects of juvenile sildenafil treatment in Sprague-Dawley versus flinders sensitive line rats

OBJECTIVE

To investigate the long-term effects of juvenile sub-chronic sildenafil (SIL) treatment on the depressive-like behaviour and hippocampal brain-derived neurotrophic factor (BDNF) levels of adult Sprague-Dawley (SD) versus Flinders Sensitive Line (FSL) rats.

METHODS

SD and FSL rats were divided into pre-pubertal and pubertal groups, whereafter 14-day saline or SIL treatment was initiated. Pre-pubertal and pubertal rats were treated from postnatal day 21 (PND21) and PND35, respectively. The open field and forced swim tests (FST) were performed on PND60, followed by hippocampal BDNF level analysis 1 day later.

RESULTS

FSL rats displayed greater immobility in the FST compared to SD rats (p < 0.0001), which was reduced by SIL (p < 0.0001), regardless of treatment period. Hippocampal BDNF levels were unaltered by SIL in all treatment groups (p > 0.05).

CONCLUSION

Juvenile sub-chronic SIL treatment reduces the risk of depressive-like behaviour manifesting during young adulthood in genetically susceptible rats.

Animal Models of Depression: What Can They Teach Us about the Human Disease?

Depression is apparently the most common psychiatric disease among the mood disorders affecting about 10% of the adult population. The etiology and pathogenesis of depression are still poorly understood. Hence, as for most human diseases, animal models can help us understand the pathogenesis of depression and, more importantly, may facilitate the search for therapy. In this review we first describe the more common tests used for the evaluation of depressive-like symptoms in rodents. Then we describe different models of depression and discuss their strengths and weaknesses. These models can be divided into several categories: genetic models, models induced by mental acute and chronic stressful situations caused by environmental manipulations (i.e., learned helplessness in rats/mice), models induced by changes in brain neuro-transmitters or by specific brain injuries and models induced by pharmacological tools. In spite of the fact that none of the models completely resembles human depression, most animal models are relevant since they mimic many of the features observed in the human situation and may serve as a powerful tool for the study of the etiology, pathogenesis and treatment of depression, especially since only few patients respond to acute treatment. Relevance increases by the fact that human depression also has different facets and many possible etiologies and therapies.

GPR39 protects against corticosterone-induced neuronal injury in hippocampal cells through the CREB-BDNF signaling pathway

BACKGROUND

The release of zinc from glutamatergic terminals in the hippocampal CA3 region can activate postsynaptic GPR39 receptors and regulate cognition and depression. However, the role and mechanism of GPR39 in the stress-induced depression is still poorly understood.

METHODS

In this study, hippocampal cells (HT-22) were treated with corticosterone (CORT). Then the effects of stress on the activity, mitochondrial function and apoptosis of HT-22 cells were observed. The effects of GPR39 on CORT-induced stress injury were analyzed by both siRNA and agonist (TC-G-1008).

RESULTS

Compared with the 500 nM CORT group, the cell viability, apoptosis, mitochondrial membrane potential, and expression levels of BCL-2, CREB and BDNF mRNA were significantly decreased in the GPR39 siRNA+500 nM CORT group, while the expression levels of caspase3, caspase9, AIF and BAX mRNA were significantly increased in the GPR39 siRNA+500 nM CORT group. Compared with the 1 μM CORTgroup, the cell viability, apoptosis, mitochondrial membrane potential, and expression levels of BCL-2, CREB and BDNF were significantly increased in the GPR39 agonist+1 μΜ CORT group, while the expression levels of caspase3, caspase9, AIF and BAX mRNA were significantly decreased in the GPR39 siRNA+500 nM CORT group. Compared with the control group, the mRNA and protein levels of GPR39, CREB and BDNF were significantly increased, and the mRNA and protein levels of CREB and BDNF were significantly decreased after 50 μM zinc sulfate treatment for 6 h.

CONCLUSIONS

GPR39 may play a neuroprotective role in CORT-induced cell injury via the improvement of CREB-BDNF expression, by inhibiting pro-apoptotic proteins and by upregulating anti-apoptotic proteins.

Nitric oxide signalling and antidepressant action revisited

Studies about the pathogenesis of mood disorders have consistently shown that multiple factors, including genetic and environmental, play a crucial role on their development and neurobiology. Multiple pathological theories have been proposed, of which several ultimately affects or is a consequence of dysfunction in brain neuroplasticity and homeostatic mechanisms. However, current clinical available pharmacological intervention, which is predominantly monoamine-based, suffers from a partial and lacking response even after weeks of continuous treatment. These issues raise the need for better understanding of aetiologies and brain abnormalities in depression, as well as developing novel treatment strategies. Nitric oxide (NO) is a gaseous unconventional neurotransmitter, which regulates and governs several important physiological functions in the central nervous system, including processes, which can be associated with the development of mood disorders. This review will present general aspects of the NO system in depression, highlighting potential targets that may be utilized and further explored as novel therapeutic targets in the future pharmacotherapy of depression. In particular, the review will link the importance of neuroplasticity mechanisms governed by NO to a possible molecular basis for the antidepressant effects.

Transgenerational hypocortisolism and behavioral disruption are induced by the antidepressant fluoxetine in male zebrafish Danio rerio

The global prevalence of depression is high during childbearing. Due to the associated risks to the mother and baby, the selective serotonin reuptake inhibitor fluoxetine (FLX) is often the first line of treatment. Given that FLX readily crosses the placenta, a fetus may be susceptible to the disruptive effects of FLX during this highly plastic stage of development. Here, we demonstrate that a 6-day FLX exposure to a fetus-relevant concentration at a critical developmental stage suppresses cortisol levels in the adult zebrafish (F₀). This effect persists for three consecutive generations in the unexposed descendants (F₁ to F₃) without diminution and is more pronounced in males. We also show that the in vivo cortisol response of the interrenal (fish "adrenal") to an i.p. injection of adrenocorticotropic hormone was also reduced in the males from the F₀ and F₃ FLX lineages. Transcriptomic profiling of the whole kidney containing the interrenal cells revealed that early FLX exposure significantly modified numerous pathways closely associated with cortisol synthesis in the male adults from the F₀ and F₃ generations. We also show that the low cortisol levels are linked to significantly reduced exploratory behaviors in adult males from the F₀ to F₂ FLX lineages. This may be a cause for concern given the high prescription rates of FLX to pregnant women and the potential long-term negative impacts on humans exposed to these therapeutic drugs.

Long-lasting effects of fluoxetine and/or exercise augmentation on bio-behavioural markers of depression in pre-pubertal stress sensitive rats

Juvenile depression is of great concern with only limited treatment currently approved. Delayed onset of action, low remission and high relapse rates, and potential long-lasting consequences further complicates treatment and highlights the need for new treatment options. Studies reporting on long-lasting effects of early-life treatment have reported conflicting results, with the pre-adolescent period mostly overlooked. The anti-depressive effect of exercise, as a possible treatment option or augmentation strategy, is dependent on age and exercise intensity. We investigated the immediate (i.e. postnatal day 35 (PND35)) and lasting (PND60 to PND61) effects of pre-pubertal (PND21 to PND34) fluoxetine and/or exercise on bio-behavioural markers of depression and oxidative stress in stress sensitive Flinders Sensitive Line rats. Low, but not moderate, intensity exercise or 5, but not 10, mg/kg/day fluoxetine displayed anti-depressant-like properties at PND35. Pre-pubertal treatment with 5mg/kg/day fluoxetine or low intensity exercise exerted lasting anti-depressive-like effects into adulthood, whereas the combination of these two treatments did not. Furthermore, the combination of fluoxetine plus exercise reduced hippocampal BDNF levels as compared to exercise alone, which may explain the latter findings. In all treatment groups hippocampal SOD activity was significantly increased at PND61, suggesting an increased anti-oxidant capacity in adulthood. In conclusion, the data confirm the anti-depressant-like properties of both early-life fluoxetine and exercise in a genetic animal model of depression. However, optimal lasting effects of early-life interventions may require adjustment of antidepressant dose and/or exercise intensity to developmental age, and that a combination of antidepressant and exercise may not necessarily be augmentative.