The antidepressant fluoxetine acts on energy balance and leptin sensitivity via BDNF

Mechanisms Involved in the Link between Depression, Antidepressant Treatment, and Associated Weight Change

Major depressive disorder is a severe mood disorder associated with a marked decrease in quality of life and social functioning, accompanied by a risk of suicidal behavior. Therefore, seeking out and adhering to effective treatment is of great personal and society-wide importance. Weight changes associated with antidepressant therapy are often cited as the reason for treatment withdrawal and thus are an important topic of interest. There indeed exists a significant mechanistic overlap between depression, antidepressant treatment, and the regulation of appetite and body weight. The suggested pathomechanisms include the abnormal functioning of the homeostatic (mostly humoral) and hedonic (mostly dopaminergic) circuits of appetite regulation, as well as causing neuromorphological and neurophysiological changes underlying the development of depressive disorder. However, this issue is still extensively discussed. This review aims to summarize mechanisms linked to depression and antidepressant therapy in the context of weight change.

Endothelial nitric oxide synthase (eNOS) S1176 phosphorylation status governs atherosclerotic lesion formation

Objective

We have previously demonstrated the in vivo importance of the Akt-eNOS substrate-kinase relationship, as defective postnatal angiogenesis characteristic of global Akt1-null mice is rescued when bred to 'gain-of-function' eNOS S1176D mutant mice. While multiple studies support the vascular protective role of endothelial NO generation, the causal role of Akt1-dependent eNOS S1176 phosphorylation during atherosclerotic plaque formation is not yet clear.

Approach and results

We herein bred congenic 'loss-of-function' eNOS S1176A and 'gain-of-function' eNOS S1176D mutant mice to the exacerbated atherogenic Akt1-/-; ApoE-/- double knockout mice to definitively test the importance of Akt-mediated eNOS S1176 phosphorylation during atherogenesis. We find that a single amino acid substitution at the eNOS S1176 phosphorylation site yields divergent effects on atherosclerotic plaque formation, as an eNOS phospho-mimic aspartate (D) substitution at S1176 leads to favorable lipid profiles and decreased indices of atherosclerosis, even when on a proatherogenic Akt1 global deletion background. Conversely, mice harboring an unphosphorylatable mutation to alanine (S1176A) result in increased plasma lipids, increased lesion formation and cellular apoptosis, phenocopying the physiological consequence of eNOS deletion and/or impaired enzyme function. Furthermore, gene expression analyses of whole aortas indicate a combinatorial detriment from NO deficiency and Western Diet challenge, as 'loss-of-function' eNOS S1176A mice on a Western Diet present a unique expression pattern indicative of augmented T-cell activity when compared to eNOS S1176D mice.

Conclusions

By using genetic epistasis approaches, we conclusively demonstrate that Akt-mediated eNOS S1176 phosphorylation and subsequent eNOS activation remains to be the most physiologically relevant method of NO production to promote athero-protective effects.

Azepine-Indole Alkaloids From Psychotria nemorosa Modulate 5-HT2A Receptors and Prevent in vivo Protein Toxicity in Transgenic Caenorhabditis elegans

Nemorosine A (1) and fargesine (2), the main azepine-indole alkaloids of Psychotria nemorosa, were explored for their pharmacological profile on neurodegenerative disorders (NDs) applying a combined in silico–in vitro–in vivo approach. By using 1 and 2 as queries for similarity-based searches of the ChEMBL database, structurally related compounds were identified to modulate the 5-HT_2A receptor; in vitro experiments confirmed an agonistic effect for 1 and 2 (24 and 36% at 10 μM, respectively), which might be linked to cognition-enhancing properties. This and the previously reported target profile of 1 and 2, which also includes BuChE and MAO-A inhibition, prompted the evaluation of these compounds in several Caenorhabditis elegans models linked to 5-HT modulation and proteotoxicity. On C. elegans transgenic strain CL4659, which expresses amyloid beta (Aβ) in muscle cells leading to a phenotypic paralysis, 1 and 2 reduced Aβ proteotoxicity by reducing the percentage of paralyzed worms to 51%. Treatment of the NL5901 strain, in which α-synuclein is yellow fluorescent protein (YFP)-tagged, with 1 and 2 (10 μM) significantly reduced the α-synuclein expression. Both alkaloids were further able to significantly extend the time of metallothionein induction, which is associated with reduced neurodegeneration of aged brain tissue. These results add to the multitarget profiles of 1 and 2 and corroborate their potential in the treatment of NDs.

The Plasma Levels of 3-Hydroxybutyrate, Dityrosine, and Other Markers of Oxidative Stress and Energy Metabolism in Major Depressive Disorder

Major depressive disorder (MDD) is a serious mental disease with a pathophysiology that is not yet fully clarified. An increasing number of studies show an association of MDD with energy metabolism alteration and the presence of oxidative stress. We aimed to evaluate plasma levels of 3-hydroxybutyrate (3HB), NADH, myeloperoxidase, and dityrosine (di-Tyr) in adolescent and adult patients with MDD, compare them with healthy age-matched controls, and assess the effect of antidepressant treatment during hospitalisation on these levels. In our study, plasmatic levels of 3HB were elevated in both adolescents (by 55%; p = 0.0004) and adults (by 88%; p < 0.0001) with MDD compared to controls. Levels of dityrosine were increased in MDD adults (by 19%; p = 0.0092) but not adolescents. We have not found any significant effect of antidepressants on the selected parameters during the short observation period. Our study supports the findings suggesting altered energy metabolism in MDD and demonstrates its presence independently of the age of the patients.

Change of hypothalamic adult neurogenesis in mice by chronic treatment of fluoxetine

OBJECTIVE

More than half of patients with depression display eating disorders, such as bulimia nervosa and anorexia nervosa. Feeding centers are located in the hypothalamus, and hypothalamic adult neurogenesis has an important role in feeding and energy balance. Antidepressants, which can regulate adult neurogenesis in the hippocampus, olfactory bulb, and neocortex, are used for eating disorders, but it is unclear whether antidepressants change hypothalamic adult neurogenesis. In this study, we used immunohistological analysis to assess effects of the antidepressant fluoxetine (FLX) on hypothalamic adult neurogenesis of adult mice.

RESULTS

Expressions of the proliferating cell marker, Ki67, and the neural stem cell marker, nestin, were significantly decreased in the hypothalamus by FLX. As regard to postmitotic cells, the number of the neural marker, NeuN, positive cells was significantly upregulated by FLX, but that of the astrocytic marker, S100B, positive cells was significantly reduced by FLX. The number of the oligodendrocyte marker, Olig2, positive cells was not changed by FLX. Interestingly, FLX treatment did not affect the total number of newly generated cells in the hypothalamus, comparing that in controls. These results suggest that FLX treatment influence hypothalamic adult neurogenesis and shift the balance between the numbers of neurons and astrocytes under studied conditions.

Leptin, the brain and energy homeostasis: From an apparently simple to a highly complex neuronal system

Leptin, produced and secreted by white adipose tissue in tight relationship with adipose mass, informs the brain about the status of the energy stores serving as the main peripheral signal for energy balance regulation through interaction with a multitude of highly interconnected neuronal populations. Most obese patients display resistance to the anorectic effect of the hormone. The present review unravels the multiple levels of complexity that trigger hypothalamic response to leptin with the objective of highlighting those critical hubs that, mainly in the hypothalamic arcuate nucleus, may undergo obesity-induced alterations and create an obstacle to leptin action. Several mechanisms underlying leptin resistance have been proposed, possibly representing useful targets to empower leptin effects. Among these, a special focus is herein dedicated to detail how leptin gains access into the brain and how neuronal plasticity may interfere with leptin function.

The role of leptin in indirectly mediating "somatic anxiety" symptoms in major depressive disorder

BACKGROUND

Leptin is a multifunctional hormone secreted from adipose tissue, which plays a core role in regulating energy intake and expenditure. Evidence has demonstrated that leptin receptors are located in brain areas involved in emotional processing, and major depressive disorder (MDD) is characterized by dysfunction of emotional processing. Taken together, these features suggest that leptin may play a potential role in the pathophysiology of MDD. However, the precise roles of leptin in modulating depressive symptoms in MDD remain unclear.

METHODS

Participants [18 drug-naïve MDD patients, 15 unaffected first-degree relatives of MDD patients (FDR-MDD), and 40 healthy controls] completed clinical assessments and provided blood samples for measurement of leptin levels. We evaluated the effect of leptin on clinical status (MDD or FDR-MDD) and symptomatic dimensionalities of MDD using mediation analysis.

RESULTS

We found that leptin was increased in MDD patients and this only predicted "somatic anxiety" symptoms. Furthermore, leptin was a significant and indirect mediator of the association between clinical status (MDD or FDR-MDD) and "somatic anxiety" symptoms.

CONCLUSION

Our finding that leptin was a significant and indirect mediator of clinical status (MDD or FDR-MDD) and "somatic anxiety" symptoms suggests that leptin may indirectly affect somatic depressive symptoms in MDD. Our findings may provide a theoretical basis for novel clinical interventions in MDD.

Fluoxetine ameliorates high-fat diet-induced metabolic abnormalities partially via reduced adipose triglyceride lipase-mediated adipocyte lipolysis

Patients with type 2 diabetes mellitus have more risk to develop depression. Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), is drug for mood and anxiety disorders. Previous studies showed that FLX could induce weight loss in non-depressed clinically overweight individuals. Although the anti-appetite effect of FLX is well-documented, its potential effects on metabolic abnormalities have not been investigated. In this study, we want to investigate whether FLX could be a therapeutic drug against high fat diet (HFD)-induced metabolic disorder. We generated metabolic disorders and depressed mouse model by feeding HFD for 12 weeks at the age of 8 weeks. Then, mice were intraperitoneally injected once daily with FLX (10 mg/kg or 20 mg/kg) for four weeks. Our results showed that FLX alleviated the HFD-induced metabolic dysfunctions and depressive phenotypes in mice. FLX improved systemic glucose homeostasis, at least in part, by improving visceral white adipose tissue (vWAT) insulin signaling. Moreover, FLX reduced circulating plasma leptin level, and decreased the expression of adipose triglyceride lipase (ATGL) and peroxisome proliferator-activated receptor gamma (PPARγ) in vWAT. Our data revealed that FLX also reduced the triglyceride (TG) accumulation in vWAT. Therefore, these findings suggest that FLX exhibits significant potential on comorbidity of metabolic disorder and depression in mice.

Comparison of Brain-derived Neurotrophic Factor Level in Depressed Patients Treated with Fluoxetine and Sertraline

Background: The Brain-Derived NeurotrophicFactor (BDNF) is the main neuronal growth factor in the brain that regulates neurogenesis, neuronal maturity, synaptic formation and plasticity. Studies showed BDNF level decreased in depression and the administration of anti depressant drugs increased BDNF level. In this study, we used fluoxetine and sertraline, which are Selective Serotonin Reuptake Inhibitor (SSRI) but had a different mechanism in influencing the BDNF levels. The purpose of this study was to compare the effect of fluoxetine and sertraline administration tothe BDNF level in depressed subjects. This study was conducted at Wahidin Sudirohusodo Hospital, Makassar, Indonesia and its affiliates from January to February 2019. Twenty outpatient subjects were diagnosed with depression based on DSM-V. The subjects were either antidepressant naïve, or dropping out of antidepressant therapy for at least 3 months since the last administration. Blood samples from each subject were taken by consecutive sampling, and BDNF levels were analyzed before and after administration of fluoxetine and sertraline for six weeks. Also, Hamilton Depression Rating Scale (HDRS) scores are measured before and after administration. The BDNF serum was significantly increased by 100.6% (p<0,001) from the baseline level in the fluoxetine group and 75.4% in the sertraline group. HDRS score was decreased by39.5%  (p<0,001) in the fluoxetine group and 30.1% in the sertraline group after six weeks of administration. This study suggests that fluoxetine was superior to sertraline in increasing the BDNF level in depression.

Differential Expression of BDNF and BIM in Streptozotocin-induced Diabetic Rat Retina After Fluoxetine Injection

BACKGROUND

Chronic diabetic retinopathy (DR) is a diabetic complication that causes blindness. Brain-derived neurotrophic factor (BDNF) expression is induced by fluoxetine. We observed the effects of fluoxetine on a streptozotocin (STZ)-induced diabetic rat model in this study.

MATERIALS AND METHODS

Rats were divided into three groups: Control, diabetic (65 mg/kg STZ injection), and diabetic with fluoxetine injection (20 mg/kg/week, six times). Western blotting was performed using anti-BDNF and anti-hexaribonucleotide-binding protein-3. Expression of BCL2 apoptosis regulator-like protein 11 (BIM) was analysed using a reverse transcription-polymerase chain reaction.

RESULTS

BDNF levels were significantly higher in the diabetic group treated with fluoxetine than in the untreated diabetic group. BIM expression was higher in the diabetic group than in the control group. BIM gene expression was lower in fluoxetine-treated diabetic group than in the untreated diabetic group.

CONCLUSION

Fluoxetine had an anti-apoptotic effect with upregulation of BDNF expression in retina of rats with STZ-induced diabetes.

How Antidepressant Drugs Affect the Antielectroshock Action of Antiseizure Drugs in Mice: A Critical Review

Depression coexists with epilepsy, worsening its course. Treatment of the two diseases enables the possibility of interactions between antidepressant and antiepileptic drugs. The aim of this review was to analyze such interactions in one animal seizure model-the maximal electroshock (MES) in mice. Although numerous antidepressants showed an anticonvulsant action, mianserin exhibited a proconvulsant effect against electroconvulsions. In most cases, antidepressants potentiated or remained ineffective in relation to the antielectroshock action of classical antiepileptic drugs. However, mianserin and trazodone reduced the action of valproate, phenytoin, and carbamazepine against the MES test. Antiseizure drug effects were potentiated by all groups of antidepressants independently of their mechanisms of action. Therefore, other factors, including brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) modulation, should be considered as the background for the effect of drug combinations.

TPH2 in the Dorsal Raphe Nuclei Regulates Energy Balance in a Sex-Dependent Manner

AbstractCentral 5-hydroxytryptamine (5-HT), which is primarily synthesized by tryptophan hydroxylase 2 (TPH2) in the dorsal Raphe nuclei (DRN), plays a pivotal role in the regulation of food intake and body weight. However, the physiological functions of TPH2 on energy balance have not been consistently demonstrated. Here we systematically investigated the effects of TPH2 on energy homeostasis in adult male and female mice. We found that the DRN harbors a similar amount of TPH2+ cells in control male and female mice. Adult-onset TPH2 deletion in the DRN promotes hyperphagia and body weight gain only in male mice, but not in female mice. Ablation of TPH2 reduces hypothalamic pro-opiomelanocortin (POMC) neuronal activity robustly in males, but only to a modest degree in females. Deprivation of estrogen by ovariectomy (OVX) causes comparable food intake and weight gain in female control and DRN-specific TPH2 knockout mice. Nevertheless, disruption of TPH2 blunts the anorexigenic effects of exogenous estradiol (E2) and abolishes E2-induced activation of POMC neurons in OVX female mice, indicating that TPH2 is indispensable for E2 to activate POMC neurons and to suppress appetite. Together, our study revealed that TPH2 in the DRN contributes to energy balance regulation in a sexually dimorphic manner.

Early life fluoxetine treatment causes long-term lean phenotype in skeletal muscle of rats exposed to maternal lard-based high-fat diet

There is a concern about early life exposure to Selective Serotonin Reuptake Inhibitors (SSRI) in child development and motor system maturation. Little is known, however, about the interaction of environmental factors, such as maternal nutrition, associated with early exposure to SSRI. The increased maternal consumption of high-fat diets is worrisome and affects serotonin system development with repercussions in body phenotype. This study aimed to assess the short- and long-term effects of neonatal fluoxetine treatment on the body and skeletal muscle phenotype of rats exposed to a maternal lard-based high-fat (H) diet during the perinatal period. A maternal lard-based high-fat diet causes reduced birth weight, a short-term reduction in type IIA fibers in the soleus muscle, and in type IIB fibers in the Extensor Digitorum Longus (EDL) muscle, reducing Lactate Dehydrogenase (LDH) activity in both muscles. In the long-term, the soleus showed reduced muscle weight, smaller area and perimeter of muscle fibers, while the EDL muscle showed reduced Citrate Synthase (CS) activity in offspring from the rats on the maternal lard-based high-fat diet. Early-life exposure to fluoxetine reduced body weight and growth and reduced soleus weight and enzymatic activity in young rats. Exposure to neonatal fluoxetine in adult rats caused a decreased body mass index, less food intake, and reduced muscle weight with reduced CS and LDH activity. Neonatal fluoxetine in young rats exposed to a maternal lard-based high-fat diet caused reduced body weight and growth, reduced soleus weight as well as area and perimeter of type I muscle fibers. In adulthood, there was a reduction in food intake, increased proportion of IIA type fibers, reduced area and perimeter of type IIB, and reduction in levels of CS activity in EDL muscle. Neonatal fluoxetine treatment in rats exposed to a maternal lard-based, high-fat diet induces a reduction in muscle weight, an increase in the proportion of oxidative fibers and greater oxidative enzymatic activity in adulthood.

Excess body weight as a predictor of response to treatment with antidepressants in patients with depressive disorder

BACKGROUND

Depression and obesity are debilitating conditions representing an enormous health and economic burden worldwide. Depression is common among patients with excess weight, but more importantly, these patients may be at risk for poor response when treated with antidepressant medications (AD).

METHODS

We conducted a comprehensive scoping review to summarize the evidence regarding the difference in response to treatment of depression with AD among patients with excess weight as compared to normal weight patients and to identify knowledge gaps.

RESULTS

The search of the Medline and PsycINFO (2004-2019) identified twelve relevant studies. Tabulation and frequency analysis of the charted data along with a narrative synthesis were performed. Nine studies (75%) reported clinically relevant negative association between patients' high BMI or obesity and treatment response to either nortriptyline, fluoxetine, or various AD; one study (8.3%) reported no difference in response to various AD combinations between BMI groups. One study showed benefits of bupropion and escitalopram combination in patients with morbid obesity (BMI > 35 kg/m²) as compared with escitalopram monotherapy. Another study reported benefits when using venlafaxine-XR in patients with morbid obesity. We also acknowledge the possible role of sex and genetic factors predicting AD treatment response.

LIMITATIONS

The search was restricted to two most relevant sources, publications in four languages and adult population.

CONCLUSION

The synthesized data may be useful to physicians in their decision regarding the choice of AD in patients with excess weight. Researchers need to address causality of association between obesity and treatment response to individual AD types.

Evaluating Prevalence and Patterns of Prescribing Medications for Depression for Patients With Obesity Using Large Primary Care Data (Canadian Primary Care Sentinel Surveillance Network)

Introduction: Depression is a serious disorder that brings a tremendous health and economic burden. Many antidepressants (AD) have obesogenic effects, increasing the population of obese patients at increased risk for a more severe disease course and poor treatment response. In addition, obese patients with depression may not be receiving the recommended standard of care due to "obesity bias." It is important to evaluate prescribing pharmacological treatment of depression in patients with obesity. Objectives: To describe the prevalence and patterns of AD prescribing for patients with depression and comorbid obesity compared with normal weight patients, and to examine the association of prescribing prevalence with obesity class. Methods: Study sample of adult patients (>18 years old) with depression was extracted from the national Canadian Primary Care Sentinel Surveillance Network (CPCSSN) Electronic Medical Records database for 2011-2016. Measures were prescribing of at least one AD (outcome) and body mass index (BMI) to categorize patients into weight categories (exposure). Data were analyzed cross-sectionally using descriptive statistics and mixed effects logistic regression model with clustering on CPCSSN networks and adjusting for age, sex, and the comorbidities. Results: Of 120,381 patients with depression, 63,830 patients had complete data on studied variables (complete cases analysis). Compared with normal weight patients, obese patients were more likely to receive an AD prescription (adjusted Odds Ratio [aOR] = 1.17; 95% Confidence Interval [CI]: 1.12-1.22). Patients with obesity classes II and III were 8% (95% CI: 1.00, 1.16) and 6% (95% CI: 0.98, 1.16) more likely, respectively, to receive AD. After imputing missing data using Multiple Imputations by Chained Equations, the results remained unchanged. The prevalence of prescribing >3 AD types was higher in obese category (7.27%, [95% CI: 6.84, 7.73]) than in normal weight category (5.6%; [95% CI: 5.24, 5.99]). Conclusion: The association between obesity and high prevalence of AD prescribing and prescribing high number of different AD to obese patients, consistent across geographical regions, raises a public health concern. Study results warrant qualitative studies to explore reasons behind the difference in prescribing, and quantitative longitudinal studies evaluating the association of AD prescribing patterns for obese patients with health outcomes.

Characterization of the Therapeutic Profile of Albiflorin for the Metabolic Syndrome

Albiflorin (AF) is a small molecule (MW 481) isolated from Paeoniae radix, a plant used as a remedy for various conditions with pathogenesis shared by metabolic diseases. Reported here is our characterization of its therapeutic profiles in three mouse models with distinctive pathological features of metabolic syndrome (MetS). Our results firstly showed that AF alleviated high fat (HF) induced obesity and associated glucose intolerance, suggesting its therapeutic efficacy for MetS. In the type 2 diabetes (T2D) model induced by a combination of HF and low doses of streptozotocin, AF lowered hyperglycaemia and improved insulin-stimulated glucose disposal. In the non-alcoholic steatohepatitis-like model resulting from a HF and high cholesterol (HF-HC) diet, AF reversed the increased liver triglyceride and cholesterol, plasma aspartate aminotransferase, and liver TNFα mRNA levels. Consistent with its effect in promoting glucose disposal in HF-fed mice, AF stimulated glucose uptake and GLUT4 translocation to the plasma membrane in L6 myotubes. However, these effects were unlikely to be associated with activation of insulin, AMPK, ER, or cellular stress signalling cascades. Further studies revealed that AF increased the whole-body energy expenditure and physical activity. Taken together, our findings indicate that AF exerts a therapeutic potential for MetS and related diseases possibly by promoting physical activity associated whole-body energy expenditure and glucose uptake in muscle. These effects are possibly mediated by a new mechanism distinct from other therapeutics derived from Chinese medicine.

Plasma levels of leptin and adiponectin and depressive symptoms in young adults

Circulating levels of adipokines are known to be associated with depression. This study aimed to investigate a possible association between leptin, adiponectin and dimensional measures of depressive symptoms in young adults with and without psychiatric illness. Total plasma adiponectin and leptin levels were measured in 194 young adults seeking psychiatric ambulatory care and 57 healthy controls. Depressive symptoms were assessed using the Montgomery-Åsberg Depression Self-Rating Scale (MADRS-S). Analysis was performed on men and women separately. P-leptin levels were significantly elevated in patients compared with controls and correlated with total MADRS-S scores in the women. Women with P-leptin in the highest quartile reached a significantly higher MADRS-S score than women in the lowest quartile, but this difference disappeared after adjusting for body mass index (BMI) and antidepressant use. MADRS-S score was associated with P-leptin in female patients without antidepressant use, independently of BMI. There was no association between P-leptin levels and current major depression. P-adiponectin levels were not associated with depressive symptoms or current major depression. The findings indicate that P-leptin levels are associated with depressive symptom severity in young women; however, the association is linked to other factors, which challenges its usefulness as a biomarker for depression in clinical psychiatry.

BDNF mediates the protective effects of scopolamine in reserpine-induced depression-like behaviors via up-regulation of 5-HTT and TPH1

Reserpine treatment in rodents has been shown to induce depression-like behaviors that mimic monoamine dysfunction implicated in the development of depression. Herein, we aimed to demonstrate the antidepressant-like activities of scopolamine, the muscarinic receptor antagonist, in a reserpine-induced mouse model. Mice were injected with 1.5 mg/kg (i.p.) of reserpine for 10 days, and the depression-like state was confirmed via the open field test (OFT) and forced swimming test (FST). Then, the mice were treated with scopolamine (25 µg/kg, i.p.) or saline for 3 days. Ten days of reserpine treatment resulted in a significant decrease in locomotor activity and an increase in immobility time in the OFT and FST, respectively, indicating that ten days of reserpine administration significantly induced depression-like behaviors in mice. However, scopolamine rapidly ameliorated the increase in immobility time in the FST and had no effect on locomotor activity in the OFT. In addition, the reserpine-induced decreases in serotonin transporter (5-HTT), brain-derived neurotrophic factor (BDNF) and tryptophan hydroxylase 1 (TPH1) in mouse hippocampus and prefrontal cortex (PFC) were significantly reversed by scopolamine. Our study provides evidence that scopolamine rapidly attenuates reserpine-induced depression in mice partially by regulating 5-HTT, BDNF and TPH1 in the hippocampus and PFC of mice.

Fluoxetine exposure in adolescent and adult female mice decreases cocaine and sucrose preference later in life

BACKGROUND

Preclinical evidence from male subjects indicates that exposure to psychotropic medications, during early development, results in long-lasting altered responses to reward-related stimuli. However, it is not known if exposure to the antidepressant fluoxetine, in female subjects specifically, changes sensitivity to natural and drug rewards, later in life.

AIMS

The aim of this work was to investigate if exposure to fluoxetine mediates enduring changes in sensitivity to the rewarding properties of cocaine and sucrose, using female mice as a model system.

METHODS

We exposed C57BL/6 female mice to fluoxetine (250 mg/L in their drinking water) for 15 consecutive days, either during adolescence (postnatal day 35-49) or adulthood (postnatal day 70-84). Twenty-one days later, mice were examined on their behavioral reactivity to cocaine (0, 2.5, 5, 7.5 mg/kg) using the conditioned place preference paradigm, or assessed on the two-bottle sucrose (1%) test.

RESULTS

We found that regardless of age of antidepressant exposure, female mice pre-exposed to fluoxetine displayed reliable conditioning to the cocaine-paired compartment. However, when compared to respective age-matched controls, antidepressant pre-exposure decreased the magnitude of conditioning at the 5 and 7.5 mg/kg cocaine doses. Furthermore, fluoxetine pre-exposure reduced sucrose preference without altering total liquid intake.

CONCLUSIONS

The data suggest that pre-exposure to fluoxetine, during adolescence or adulthood, results in a prolonged decrease in sensitivity to the rewarding properties of both natural and drug rewards in female C57BL/6 mice.

Fluoxetine Modulates the Activity of Hypothalamic POMC Neurons via mTOR Signaling

Hypothalamic proopiomelanocortin (POMC) neurons are important players in the regulation of energy homeostasis; we previously demonstrated that environmental stimulation excites arcuate nucleus circuits to undergo plastic remodeling, leading to altered ratio between excitatory and inhibitory synaptic contacts on these neurons. The widely used selective serotonin reuptake inhibitor fluoxetine (FLX) is known to affect body weight. On the other hand, FLX administration mimics the effects of environmental stimulation on synaptic plasticity in the hippocampus and cortex. The mammalian target of rapamycin (mTOR) pathway is instrumental in these phenomena. Thus, we aimed at investigating whether and how FLX affects POMC neurons activity and hypothalamic mTOR function. Adult mice expressing green fluorescent protein (GFP) under the POMC promoter were treated with FLX for 3 weeks resulting in diminished body weight. Patch clamp recordings performed on POMC neurons indicate that FLX increases their firing rate and the excitatory AMPA-mediated transmission, and reduces the inhibitory GABAergic currents at presynaptic level. Immunofluorescence studies indicate that FLX increases the ratio between excitatory and inhibitory synaptic contacts on POMC neurons. These changes are associated with an increased activity of the hypothalamic mTOR pathway. Use of the mTOR inhibitor rapamycin blunts the effects of FLX on body weight and on functional and structural plasticity of POMC neurons. Our findings indicate that FLX is able to remodel POMC neurons, and that this may be partly mediated by the mTOR signaling pathway.