Norepinephrine-deficient mice lack responses to antidepressant drugs, including selective serotonin reuptake inhibitors.
ABSTRACT: Mice unable to synthesize norepinephrine (NE) and epinephrine due to targeted disruption of the dopamine beta-hydroxylase gene, Dbh, were used to critically test roles for NE in mediating acute behavioral changes elicited by different classes of antidepressants. To this end, we used the tail suspension test, one of the most widely used paradigms for assessing antidepressant activity and depression-related behaviors in normal and genetically modified mice. Dbh(-/-) mice failed to respond to the behavioral effects of various antidepressants, including the NE reuptake inhibitors desipramine and reboxetine, the monoamine oxidase inhibitor pargyline, and the atypical antidepressant bupropion, even though they did not differ in baseline immobility from Dbh(+/-) mice, which have normal levels of NE. Surprisingly, the effects of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, sertraline, and paroxetine were also absent or severely attenuated in the Dbh(-/-) mice. In contrast, citalopram (the most selective SSRI) was equally effective at reducing immobility in mice with and without NE. Restoration of NE by using L-threo-3,4-dihydroxyphenylserine reinstated the behavioral effects of both desipramine and paroxetine in Dbh(-/-) mice, thus demonstrating that the reduced sensitivity to antidepressants is related to NE function, as opposed to developmental abnormalities resulting from chronic NE deficiency. Microdialysis studies demonstrated that the ability of fluoxetine to increase hippocampal serotonin was blocked in Dbh(-/-) mice, whereas citalopram's effect was only partially attenuated. These data show that NE plays an important role in mediating acute behavioral and neurochemical actions of many antidepressants, including most SSRIs.
Project description:Deficits in neuronal inhibition via gamma-aminobutyric acid (GABA) type A receptors (GABAA-Rs) are implicated in the pathophysiology of major depressive disorder and the therapeutic effects of current antidepressant treatments, however, the relevant GABAA-R subtype as defined by its alpha subunit is still unknown. We previously reported anxiety- and depressive-like behavior in alpha2+/- and alpha2-/- mice, respectively (Vollenweider, 2011). We sought to determine whether this phenotype could be reversed by chronic antidepressant treatment. Adult male mice received 4 or 8mg/kg fluoxetine or 53mg/kg desipramine in their drinking water for four weeks before undergoing behavioral testing. In the novelty suppressed feeding test, desipramine had anxiolytic-like effects reducing the latencies to bite and to eat the pellet in both wild-type and alpha2+/- mice. Surprisingly, 4mg/kg fluoxetine had anxiogenic-like effects in alpha2+/- mice increasing latency to bite and to eat while 8mg/kg fluoxetine increased the latency to eat in both wild-type and alpha2+/- mice. In the forced swim and tail suspension tests, chronic desipramine treatment increased latency to immobility in wild-type and alpha2-/- mice. In contrast, chronic fluoxetine treatment increased immobility in alpha2-/- mice in both tasks while generally having no effect in wild-type mice. These findings suggest that in preclinical paradigms of anxiety and behavioral despair the antidepressant-like effects of desipramine are independent of alpha2-containing GABAA-Rs, while a reduction in alpha2 expression leads to an increased sensitivity to anxiogenic- and prodepressant-like effects with chronic fluoxetine treatment, pointing to a potential role of alpha2-containing GABAA-Rs in the response to serotonin-selective antidepressants.
Project description:Selective serotonin reuptake inhibitors (SSRIs) bind 5-HT transporters, leading to the accumulation of 5-HT and amelioration of depression. Although different mouse strains show varying sensitivity to SSRIs in mouse models of depression, the underlying mechanism of these strain differences remains unclear. Here, the SSRI citalopram dose-dependently reduced immobility time in both the FST and TST in DBA/2J mice but not C57BL/6J mice, whereas fluoxetine showed the opposite results. Paroxetine similarly reduced immobility time in both strains. The affinity of citalopram for the 5-HT transporter was 700-fold higher in DBA/2J mice than in C57BL/6J mice, whereas the affinity of fluoxetine was 100-fold higher in C57BL/6J mice than in DBA/2J mice. Furthermore, high citalopram concentrations were required for [3H]5-HT uptake in C57BL/6J but not in DBA/2J mouse cortical synaptosomes, whereas fluoxetine showed the opposite results. The effects of paroxetine on 5-HT transporter binding and synaptosomal 5-HT uptake were similar in the two strains. These results suggest that immobility duration depends on 5-HT transporter binding levels, which lead to apparent strain differences in immobility time in the FST and TST. Furthermore, differences in 5-HT transporter binding may cause variations in SSRI effects on behaviors.
Project description:Depression is a complex, heterogeneous mental disorder. Currently available antidepressants are only effective in about one-third to one-half of all patients. The mechanisms underlying antidepressant response and treatment resistance are poorly understood. Recent clinical evidence implicates the involvement of leptin in treatment response to antidepressants. In this study, we determined the functional role of the leptin receptor (LepRb) in behavioral responses to the selective serotonergic antidepressant fluoxetine and the noradrenergic antidepressant desipramine. While acute and chronic treatment with fluoxetine or desipramine in wild-type mice elicited antidepressant-like effects in the forced swim test, mice null for LepRb (db/db) displayed resistance to treatment with either fluoxetine or desipramine. Fluoxetine stimulated phosphorylation of Akt(Thr308) and GSK-3β(Ser9) in the hippocampus and prefrontal cortex (PFC) of wild-type mice but not in db/db mice. Desipramine failed to induce measurable changes in Akt, GSK-3β or ERK1/2 phosphorylation in the hippocampus and PFC, as well as hypothalamus of either genotype of mice. Deletion of LepRb specifically from hippocampal and cortical neurons resulted in fluoxetine insensitivity in the forced swim test and tail suspension test while leaving the response to desipramine intact. These results suggest that functional LepRb is critically involved in regulating the antidepressant-like behavioral effects of both fluoxetine and desipramine. The antidepressant effects of fluoxetine but not desipramine are dependent on the presence of functional LepRb in the hippocampus and cortex.
Project description:The forced swim test in rodents allows rapid detection of substances with antidepressant-like activity, evidenced as a decreased duration of immobility that is produced by the majority of clinically used antidepressants. Antidepressants also increase the latency to immobility, and this additional measure reportedly can increase the sensitivity of the forced swim test in mice. Extending these findings, the present study examined the effects of desipramine and fluvoxamine in a forced swim test in C57BL/6J mice, a strain commonly used as background for genetic modifications, analyzing results with a method (i.e. survival analysis) that can model the skewed distribution of latencies and that can deal with censored data (i.e. when immobility does not occur during the test), in comparison with the more traditional Student's t-test. Desipramine increased the latency to immobility at 32?mg/kg, but not at lower doses. Fluvoxamine also did not affect latency at lower doses, but in contrast to desipramine, fluvoxamine decreased the latency to immobility at the highest dose (i.e. 32?mg/kg). At doses affecting latency to immobility, neither desipramine nor fluvoxamine significantly affected duration of immobility. Together, these results are generally consistent with the suggestion that inclusion of the latency measure can increase the sensitivity of the forced swim test to detect antidepressant-like effects in mice.
Project description:1. The present study was undertaken to characterise the relationship between in vivo brain serotonin transporter (SERT) binding, plasma concentration and pharmacological effect of selective serotonin reuptake inhibitors (SSRIs) in mice. Oral administration of fluvoxamine, fluoxetine, paroxetine and sertraline at pharmacologically relevant doses exerted dose- and time-dependent binding activity of brain SERT as revealed by significant increases in KD for specific [3H]paroxetine binding, and the in vivo SERT-binding potency was in the order of paroxetine>>fluoxetine, sertraline>fluvoxamine. 2. The time courses of brain SERT binding by SSRIs in mice were mostly in parallel to those of their plasma concentrations. Also, norfluoxetine (active metabolite) has been suggested to contribute largely to the long-lasting binding activity of brain SERT after the fluoxetine administration. 3. Oral administration of each SSRI suppressed significantly the marble-burying behaviour with no change in locomotor activity in mice, and the extent and time course of suppression agreed well with those of brain SERT binding. Thus, the pharmacological potencies of SSRIs in the attenuation of marble-burying behaviour correlated significantly with their brain SERT binding activities. 4. In conclusion, the present study has provided the first in vivo evidences to support that fluvoxamine, fluoxetine, paroxetine and sertraline orally administered bind to the pharmacologically relevant brain SERT in mice and that their SERT-binding characteristics is closely associated with the pharmacokinetics and inhibition of marble-burying behaviour.
Project description:Selective serotonin reuptake inhibitors (SSRIs) are a major class of antidepressants that act by blocking inward transport of serotonin (5-HT) into presynaptic neurons mediated by the serotonin transporter (SERT). Both reuptake and ongoing synthesis are essential in supporting intraneuronal serotonin concentrations in serotonergic neurons. A rare mutation in tryptophan hydroxylase 2 (Tph2), the rate limiting enzyme for 5-HT synthesis, was identified in several patients with major depression, and knock-in mice expressing the analogous mutation (R439H Tph2 KI) show 80% reduction in 5-HT synthesis and tissue levels. Chronic treatment with SSRIs (fluoxetine and paroxetine) resulted in a dramatic further depletion of 5-HT tissue levels in R439H Tph2 KI mice (down to 1-3% of wild type levels) while having little effects in wild-type controls. Treatment with the 5-HT precursor 5-hydroxytryptophan (5-HTP) restored 5-HT tissue content in mutant mice, and cotreatment with 5-HTP and fluoxetine essentially prevented the depleting effect of a chronic SSRI. These data demonstrate that chronic SSRI treatment could further exacerbate the 5-HT deficiency in Tph2 mutation carriers, and this can be prevented by 5-HTP supplementation.
Project description:Anhedonia, or diminished interest or pleasure in rewarding activities, characterizes depression and reflects deficits in brain reward circuitries. Social stress induces anhedonia and increases risk of depression, although the effect of social stress on brain reward function is incompletely understood.This study assessed the following: 1) brain reward function in rats (using the intracranial self-stimulation procedure) and protein levels of brain-derived neurotrophic factor and related signaling molecules in response to chronic social defeat, 2) brain reward function during social defeat and long-term treatment with the antidepressants fluoxetine (5 mg/kg/day) and desipramine (10 mg/kg/day), and 3) forced swim test behavior after social defeat and fluoxetine treatment.Social defeat profoundly and persistently decreased brain reward function, reflecting an enduring anhedonic response, in susceptible rats, whereas resilient rats showed no long-term brain reward deficits. In the ventral tegmental area, social defeat, regardless of susceptibility or resilience, decreased brain-derived neurotrophic factor and increased phosphorylated AKT, whereas only susceptibility was associated with increased phosphorylated mammalian target of rapamycin. Fluoxetine and desipramine reversed lower, but not higher, stress-induced brain reward deficits in susceptible rats. Fluoxetine decreased immobility in the forced swim test, as did social defeat.These results suggest that the differential persistent anhedonic response to psychosocial stress may be mediated by ventral tegmental area signaling molecules independent of brain-derived neurotrophic factor and indicate that greater stress-induced anhedonia is associated with resistance to antidepressant treatment. Consideration of these behavioral and neurobiological factors associated with resistance to stress and antidepressant action may promote the discovery of novel targets to treat stress-related mood disorders.
Project description:Selective serotonin reuptake inhibitor (SSRI) antidepressants are the mainstay treatment for the 10-20% of pregnant and postpartum women who suffer major depression, but the effects of SSRIs on their children’s developing brain and later emotional health are poorly understood. SSRI use during pregnancy can elicit antidepressant withdrawal in newborns and increase toddlers’ anxiety and social avoidance. In rodents, perinatal SSRI exposure increases adult depression- and anxiety-like behavior, although certain individuals are more vulnerable to these effects than others. Our study establishes a rodent model of individual differences in susceptibility to perinatal SSRI exposure, utilizing selectively-bred Low Responder (LR) and High Responder (HR) rats that were previously bred for high versus low behavioral response to novelty. Pregnant HR/LR females were chronically treated with the SSRI paroxetine (10 mg/kg/day p.o.) to examine its effects on offspring’s emotional behavior and gene expression in the developing brain. Paroxetine treatment had minimal effect on HR/LR dams’ pregnancy outcomes or maternal behavior. We found that LR offspring, naturally prone to an inhibited/anxious temperament, were susceptible to behavioral abnormalities associated with perinatal SSRI exposure (which exacerbated their Forced Swim Test immobility), while high risk-taking HR offspring were resistant. Microarray studies revealed robust perinatal SSRI-induced gene expression changes in the developing LR hippocampus and amygdala (postnatal days 7-21), including transcripts involved in neurogenesis, synaptic vesicle components, and energy metabolism. These results highlight the LR/HR model as a useful tool to explore the neurobiology of individual differences in susceptibility to perinatal SSRI exposure. Overall design: 78 samples from 2 brain regions (hippocampus and amygdala) across four developmental timepoints (postnatal days (P)7, 14, 21, 75) following perinatal exposure paroxetine (or normal drinking water).
Project description:Hepatotoxicity may be a concern when prescribing antidepressants. Nevertheless, this risk remains poorly understood for serotonin and noradrenaline reuptake inhibitors (SNRIs: venlafaxine, milnacipran, duloxetine) and 'other antidepressants' (mianserin, mirtazapine, tianeptine and agomelatine), particularly in comparison with selective serotonin reuptake inhibitors (SSRIs: fluoxetine, citalopram, paroxetine, sertraline, fluvoxamine, escitalopram), which are by far the most commonly prescribed antidepressants.We quantified the risk of serious liver injury associated with new use of SNRIs and 'other antidepressants' compared with SSRIs in real-life practice.Based on the French national health insurance database, this cohort study included 4,966,825 individuals aged 25 years and older with a first reimbursement of SSRIs, SNRIs or 'other antidepressants' between January 2010 and June 2015. We compared the risk of serious liver injury within the 6 months following antidepressant initiation according to antidepressant class, with SSRIs as the reference, using an inverse probability-of-treatment-weighted Cox proportional hazard model adjusted for demographic characteristics and risk factors of liver injury.We identified 382 serious liver injuries overall (none for milnacipran initiators). Age and gender standardized incidence rates per 100,000 person-years were 19.2 for SSRIs, 22.2 for venlafaxine, 12.6 for duloxetine, 21.5 for mianserin, 32.8 for mirtazapine, 31.6 for tianeptine and 24.6 for agomelatine initiators. Initiation of antidepressants of interest versus SSRIs was not associated with an increased risk of serious liver injury [adjusted hazard ratios (95% confidence interval): venlafaxine 1.17 (0.83-1.64), duloxetine 0.54 (0.28-1.02), mianserin 0.90 (0.58-1.41), mirtazapine 1.17 (0.67-2.02), tianeptine 1.35 (0.82-2.23) and agomelatine 1.07 (0.51-2.23)]. This finding was confirmed by the results of an additional study using a case-time-control design.These results do not provide evidence of an increased risk of serious liver injury following initiation of SNRIs or 'other antidepressants' compared with SSRIs in real-life practice. This could reflect an inherent lack of difference in risk between the drug classes, or the fact that individuals with higher susceptibility to drug-induced liver injury are not prescribed drugs considered to be more hepatotoxic.
Project description:The Dutch guideline for the treatment of depression in young people recommends initiating antidepressant treatment with fluoxetine, as the evidence for its efficacy is strongest and the risk of suicidality may be lower than with other antidepressants. Furthermore, low starting doses are recommended. We aimed to determine whether antidepressant prescriptions are in accord with guidelines. A cohort of young people aged between 6 and 17 at the time of antidepressant initiation was selected from IABD, a Dutch pharmacy prescription database. The percentage of prescriptions for each antidepressant was determined. Starting and maintenance doses were determined and compared with recommendations for citalopram, fluoxetine, fluvoxamine, and sertraline. During the study period, 2942 patients initiated antidepressant treatment. The proportion of these young people who were prescribed fluoxetine increased from 10.1 % in 1994-2003 to 19.7 % in 2010-2014. However, the most commonly prescribed antidepressants were paroxetine in 1994-2003 and citalopram in 2004-2014. The median starting and maintenance doses were ?0.5 DDD/day for tricyclic antidepressants and 0.5-1 DDD/day for SSRIs and other antidepressants. Starting doses were guideline-concordant 58 % of the time for children, 31 % for preteens, and 16 % for teens. Sixty percent of teens were prescribed an adult starting dose. In conclusion, guideline adherence was poor. Physicians preferred citalopram over fluoxetine, in contrast to the recommendations. Furthermore, although children were prescribed a low starting dose relatively frequently, teens were often prescribed an adult starting dose. These results suggest that dedicated effort may be necessary to improve guideline adherence.