Methylenendioxyamphetamine produces serotonin nerve terminal loss and diminished behavioural and neurochemical responses to the antidepressant fluoxetine

Effects of acute or repeated paroxetine and fluoxetine treatment on affective behavior in male and female adolescent rats

RATIONALE

The SSRI antidepressant fluoxetine is one of the few drugs that is effective at treating depression in adolescent humans. In contrast, the SSRI paroxetine has limited efficacy and is more at risk for inducing suicidal behavior.

OBJECTIVE

The purpose of the present study was to more fully characterize the differential actions of paroxetine and fluoxetine.

METHODS

In experiment 1, male and female rats were injected with paroxetine (2.5 or 10 mg/kg), fluoxetine (10 mg/kg), or vehicle for 10 days starting on postnatal day (PD) 35, and affective behaviors were assessed using sucrose preference and elevated plus maze tasks. A separate set of rats were used to examine monoamine levels. In experiment 2, rats were injected with paroxetine (2.5, 5, or 10 mg/kg), fluoxetine (5, 10, or 20 mg/kg), or vehicle during the same time frame as experiment 1, and anxiety-like behaviors were measured using elevated plus maze, light/dark box, and acoustic startle.

RESULTS

Repeated SSRI treatment failed to alter sucrose preference, although both paroxetine and fluoxetine reduced time spent in the open arms of the elevated plus maze and light compartment of the light/dark box. Paroxetine, but not fluoxetine, enhanced acoustic startle and interfered with habituation. Serotonin turnover was decreased by both acute and repeated fluoxetine treatment but unaltered by paroxetine administration.

DISCUSSION

These results show that repeated treatment with paroxetine and fluoxetine has dissociable actions in adolescent rats. In particular, paroxetine, but not fluoxetine, increases acoustic startle at low doses and may increase sensitivity to environmental stressors.

Neuropeptide Y administration reverses tricyclic antidepressant treatment-resistant depression induced by ACTH in mice

Depression is one of the most common mental disorders and a primary cause of disability. To better treat patients suffering this illness, elucidation of the underlying psychopathological and neurobiological mechanisms is urgently needed. Based on the above-mentioned evidence, we sought to investigate the effects of neuropeptide Y (NPY) treatment in tricyclic antidepressant treatment-resistant depression induced by adrenocorticotropic hormone (ACTH) administration. Mice were treated with NPY (5.84, 11.7 or 23.4mmol/μl) intracerebroventricularly (i.c.v.) for one or five days. The levels of serum corticosterone, tryptophan (TRP), kynurenine (KYN), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and indoleamine 2,3-dioxygenase (IDO) activity in the hippocampus were analyzed. The behavioral parameters (depressive-like and locomotor activity) were also verified. This study demonstrated that ACTH administration increased serum corticosterone levels, KYN, 5-HIAA levels, IDO activity (hippocampus), immobility in the forced swimming test (FST) and the latency to feed in the novelty suppressed feeding test (NSFT). In addition, ACTH administration decreased the BDNF and NGF levels in the hippocampus of mice. NPY treatment was effective in preventing these hormonal, neurochemical and behavioral alterations. It is suggested that the main target of NPY is the modulation of corticosterone and neuronal plasticity protein levels, which may be closely linked with pharmacological action in a model of tricyclic antidepressant treatment-resistant depression. Thus, this study demonstrated a protective effect of NPY on the alterations induced by ACTH administration in mice, indicating that it could be useful as a therapy for the treatment of tricyclic antidepressant treatment-resistant depression.

Antidepressant-like activity of Tagetes lucida Cav. is mediated by 5-HT(1A) and 5-HT(2A) receptors

It has been demonstrated that the aqueous extract of Tagetes lucida Cav. shows an antidepressant-like effect on the forced swimming test (FST) in rats. The aim of this study was to analyze the participation of the serotoninergic system in the antidepressant-like effect of the aqueous extract of T. lucida. Different doses of the extract of T. lucida were administered at 72, 48, 24, 18 and 1 h before FST. The animals were pretreated with a 5-HT1A receptor antagonist (WAY-100635, 0.5 mg/kg), a 5-HT2A receptor antagonist (ketanserin, 5 mg/kg), a β-noradrenergic receptor antagonist (propranolol, 200 mg/kg), and with a α2-noradrenergic receptor antagonist (yohimbine, 1 mg/kg) alone or combined with the extract and pretreated with a serotonin synthesis inhibitor (PCPA) before treatment with 8-OH-DPAT + the extract of T. lucida. In addition, suboptimal doses of the 5-HT1A agonist (8-OH-DPAT) + non-effective dose of extract was analyzed in the FST. To determine the presence of flavonoids, the aqueous extract of T. lucida (20 µl, 4 mg/ml) was injected in HPLC; however, a quercetin concentration of 7.72 mg/g of extract weight was detected. A suboptimal dose of 8-OH-DPAT + extract of T. lucida decreased immobility and increased swimming and climbing. An antidepressant-like effect with the aqueous extract of T. lucida at doses of 100 and 200 mg/kg was observed on the FST with decreased immobility behavior and increased swimming; however, this effect was blocked by WAY-100635, ketanserin and PCPA but not by yohimbine and propranolol, suggesting that the extract of T. lucida could be modulating the release/reuptake of serotonin.

Antidepressant-like effects of lycii radicis cortex and betaine in the forced swimming test in rats

The purpose of the present study was to examine the effect of Lycii Radicis Cortex (LRC) and betaine (BT) on immobility and neurochemical change in the forced swimming test (FST) in the rat. LRC, BT or fluoxentine was administered intraperitoneally to Sprague-Dawley rats three times (1, 5 and 23.5 h) before the FST. To investigate antidepressant-like effect, serotonin (5-HT) and norepinephrine (NE) were examined in the hippocampus and hypothalamus of rats. LRC (100 mg/kg) and BT (30, 100 mg/kg) significantly decreased the immobility time in the FST. LRC (100 mg/kg) significantly increased both 5-HT and NE levels in the hypothalamus of rats exposed to FST. BT (100 mg/kg) significantly increased 5-HT levels in the hypothalamus and hippocampus of rats. Taken together, these results demonstrated that improvement in the behavioral changes after LRC and BT administration may be mediated by elevation of 5-HT level in the hypothalamus and hippocampus, indicating a possible antidepressant-like activity. The present results suggest that the efficacy of LRC and BT in an animal model of depression may provide anti-depressant effects in human, which remains to be determined.

Poly I:C-induced activation of the immune response is accompanied by depression and anxiety-like behaviours, kynurenine pathway activation and reduced BDNF expression

In this study we characterised the ability of the viral mimetic poly I:C to induce a neuroinflammatory response and induce symptoms of depression and anxiety in rats. Furthermore, the ability of poly I:C to deplete central tryptophan and serotonin via induction of indolamine 2,3 dioxygenase (IDO), and also the ability of poly I:C to impact upon expression of the neurotrophin BDNF and its receptor TrkB were examined as potential mechanisms to link inflammation to depression. Poly I:C induced a neuroinflammatory response characterised by increased expression of IL-1β, IL-6, TNF-α and CD11b in frontal cortex and hippocampus. In the first 24h following poly I:C administration rats displayed sickness behaviour characterised by reduced locomotor activity and weight gain. Anhedonia measured using the saccharin preference test was used as an indicator of depressive behaviour, and poly I:C induced depressive behaviour that persisted for up to 72h following administration. Anxiety was measured using the open field test and anxious behaviour was observed 24h following poly I:C, a time-point when sickness behaviour had resolved. These behavioural changes were accompanied by decreased expression of BDNF and TrkB in hippocampus and frontal cortex. In addition, poly I:C increased central IDO expression and increased concentrations of tryptophan, and its metabolite kynurenine. However this activation of the kynurenine pathway did not result in reduced central serotonin concentrations. These findings suggest that depressive and anxiety-like behaviours elicited by poly I:C are associated with a reduction in BDNF signalling, and activation of the kynurenine pathway, but not a reduction in serotonin.

Exofocal dopaminergic degeneration as antidepressant target in mouse model of poststroke depression

BACKGROUND

Although poststroke depression (PSD) is a frequent chronic complication of stroke with high relevance for outcome and survival, underlying pathomechanisms remain inadequately understood. This may be because suitable animal models are largely lacking and existing models are poorly characterized.

METHODS

Male 129/SV mice were subjected to 30-min middle cerebral artery occlusion (MCAo)/reperfusion and serial magnetic resonance imaging scans. A subset of animals received selective serotonin reuptake inhibitor citalopram starting 7 days after MCAo. Behavioral assessment was performed at 14 weeks. To identify biological correlates of PSD, we quantified corticosterone levels in serum and brain-derived neurotrophic factor levels in brain. The integrity of the mesolimbic dopaminergic system was assessed using tyrosine hydroxylase and dynorphin in situ hybridizations as well as dopamine transporter autoradiography.

RESULTS

Left, but not right, MCAo, elicited anhedonia and increased anxiety and despair. This depression-like syndrome was associated with alterations in the mesolimbic reward system. MCAo resulted in delayed degeneration of dopaminergic neurons in ipsilateral midbrain, which was accompanied by reduced dopamine concentrations and decreased levels of dopamine transporter density along with increased brain-derived neurotrophic factor protein levels in ischemic striatum and increased dynorphin messenger RNA expression in nucleus accumbens. Chronic antidepressant treatment initiated as late as 7 days after stroke reversed the behavioral phenotype, prevented degeneration of dopaminergic midbrain neurons, and attenuated striatal atrophy at 4 months.

CONCLUSIONS

Our results highlight the importance of the dopaminergic system for the development of PSD. Prevention of secondary neurodegeneration by antidepressants may provide a novel target for subacute stroke therapy.

Reduced efficacy of fluoxetine following MDMA ("Ecstasy")-induced serotonin loss in rats

Long-term serotonin (5-HT) neuronal loss is currently a major cause of concern associated with recreational use of the substituted amphetamine 3,4 methylenedioxymethamphetamine (MDMA; "Ecstasy"). Such loss may be problematic considering that psychiatric disorders such as depression and anxiety and responses to first line treatments for these disorders are associated with 5-HT. In this study the effects of prior exposure to MDMA on behavioural and central neurochemical changes induced by the serotonin (5-HT) re-uptake inhibitor and antidepressant fluoxetine were examined in rats. Animals were administered MDMA (10 mg/kg. i.p.) four times daily for two consecutive days. One week later the animals were subjected to treatment with fluoxetine (10 mg/kg, i.p.). Fluoxetine treatment groups received either acute (saline injections for 20 days followed by 3 fluoxetine treatments over 24 h) or chronic (once daily fluoxetine for 21 days) drug administration. Prior exposure to MDMA resulted in an attenuation of fluoxetine-induced swimming behaviour in the modified forced swimming test (FST); a behavioural test of antidepressant action. In parallel MDMA treatment resulted in significant regional depletions of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) accompanied by a reduction in cortical [3H] paroxetine binding to nerve terminal 5-HT transporters. MDMA-induced 5-HT loss was enhanced in animals following chronic fluoxetine administration. Elimination of fluoxetine and its metabolite norfluoxetine from the brain abolished this interaction between MDMA and fluoxetine treatment. Fluoxetine administration reduced both 5-HIAA and the 5-HIAA:5-HT metabolism ratio, which was attenuated in animals pre-treated with MDMA. Overall the results show that MDMA induces long-term 5-HT loss in the rodent brain and consequently diminishes behaviour and reductions in 5-HT metabolism induced by the antidepressant fluoxetine. These results have potential clinical relevance, suggesting that 5-HT re-uptake inhibitors such as fluoxetine may be less effective at treating depression in chronic abusers of MDMA.

Depletion of serotonin and catecholamines block the acute behavioral response to different classes of antidepressant drugs in the mouse tail suspension test

RATIONALE

Few studies have investigated whether the behavioral effects elicited by different types of antidepressant drugs are mediated by either serotonin (5-HT) or the catecholamines norepinephrine (NE) and dopamine (DA).

OBJECTIVES

By depleting 5-HT, or NE and DA, the present study investigated the contributions of these monoamines to the acute behavioral effects of selective serotonin reuptake inhibitors (SSRIs; fluoxetine and citalopram) and norepinephrine reuptake inhibitors (NRIs; desipramine and reboxetine) in the mouse tail suspension test (TST).

RESULTS

Depletion of 5-HT tissue content by para-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, completely blocked reductions of immobility by the SSRIs in the TST. In contrast, PCPA did not alter the behavioral effects of the NRIs. Inhibition of catecholamine synthesis by alpha-methyl-para-tyrosine (AMPT) reduced brain NE and DA tissue content, whereas disruption of vesicular storage with reserpine decreased brain NE, DA and 5-HT tissue content. However, neither treatment completely prevented responses to desipramine, fluoxetine, or citalopram in the TST. Depleting both newly synthesized and vesicular components of NE and DA transmission with a combination of reserpine and AMPT completely prevented the behavioral effects of desipramine, reboxetine, and fluoxetine and attenuated those of citalopram. Although PCPA did not alter baseline immobility, AMPT and reserpine increased baseline values in the TST.

CONCLUSIONS

These studies demonstrated that endogenous 5-HT synthesis mediates the behavioral effects of SSRIs, but not NRIs, in the TST. In contrast, disruption of the behavioral effects of NRI and SSRI antidepressants required disruption of both catecholamine synthesis and vesicular storage and release mechanisms.

Caffeine promotes hyperthermia and serotonergic loss following co-administration of the substituted amphetamines, MDMA (“Ecstasy”) and MDA (“Love”)

The present study determined the effect of caffeine co-administration on the core body temperature response and long-term serotonin (5-HT) loss induced by methylenedioxymethamphetamine (MDMA; "Ecstasy") and its metabolite methylenedioxyamphetamine (MDA; "Love") to rats. In group-housed animals, caffeine (10 mg/kg) enhanced the acute toxicity of MDMA (15 mg/kg) and MDA (7.5 mg/kg), resulting in an exaggerated hyperthermic response (+2 degrees C for 5 h following MDMA and +1.5 degrees C for 3 h following MDA) when compared to MDMA (+1 degree C for 3 h) and MDA (+1 degree C for 1 h) alone. Co-administration of caffeine with MDMA or MDA was also associated with increased lethality. To reduce the risk of lethality, doses of MDMA and MDA were reduced in further experiments and the animals were housed individually. To examine the effects of repeated administration, animals received MDMA (10 mg/kg) or MDA (5 mg/kg) with or without caffeine (10 mg/kg) twice daily for 4 consecutive days. MDMA and MDA alone induced hypothermia (fall of 1 to 2 degrees C) over the 4 treatment days. Co-administration of caffeine with MDMA or MDA resulted in hyperthermia (increase of up to 2.5 degrees C) following acute administration compared to animals treated with caffeine or MDMA/MDA alone. This hyperthermic response to caffeine and MDMA was not observed with repeated administration, unlike caffeine + MDA, where hyperthermia was obtained over the 4 day treatment period. In addition, 4 weeks after the last treatment, co-administration of caffeine with MDA (but not MDMA) induced a reduction in 5-HT and 5-hydroxyindole acetic acid (5-HIAA) concentrations in frontal cortex (to 61% and 58% of control, respectively), hippocampus (48% and 60%), striatum (79% and 64%) and amygdala (63% and 37%). However, when caffeine (10 mg/kg) and MDMA (2.5 mg/kg) were co-administered four times daily for 2 days to group-housed animals, both hyperthermia and hippocampal 5-HT loss were observed (reduced to 68% of control). Neither MDMA nor MDA alone induced a significant reduction in regional 5-HT or 5-HIAA concentrations following repeated administration. In conclusion, caffeine promotes the acute and long-term toxicity associated with MDMA and MDA. This is a serious drug interaction, which could have important acute and long-term health consequences for recreational drug users.

Role of serotonin (5-HT) in the antidepressant-like properties of neuropeptide Y (NPY) in the mouse forced swim test

Neuropeptide Y (NPY) is thought to be implicated in depressive disorders. The mouse forced swim test (FST) is an animal model widely used as a predictor of the efficacy of antidepressant drugs. The present study was undertaken to explore the possible contribution of endogenous serotonin (5-HT) systems in the behavioral effects elicited by NPY in this model. The selective serotonin re-uptake inhibitor (SSRI), fluoxetine, was also tested for comparison. 5-HT was depleted prior to testing by the administration of the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA; 300 mg/kg, i.p., each day for 3 days; control mice received saline-vehicle over the same period). On the fourth day, mice received NPY (3 nmol, I.C.V.), fluoxetine (16 mg/kg, i.p.) or saline injections before testing in the FST. Both NPY and fluoxetine significantly reduced immobility time in saline-treated control animals. Pre-treatment with PCPA significantly blocked the effects of fluoxetine in the FST, confirming the role of endogenous 5-HT. Similarly, pre-treatment with PCPA also significantly attenuated the anti-immobility effects of NPY, thus suggesting a role for 5-HT in the effects of NPY in the FST. Quantitative receptor autoradiography revealed increases in specific [125I][Leu31, Pro34]PYY sites that were sensitive to BIBP3226 (Y1-like sites) in various brain regions. Specific [125I]GR231118 and [125I]PYY(3-36) binding levels were not changed following PCPA treatment, suggesting that depletion of endogenous 5-HT resulted in an apparent increase in the level of Y1 sites in their high-affinity state. Taken together, these results suggest a role for 5-HT-related systems in the antidepressant-like properties of NPY.

Methylenedioxymethamphetamine (MDMA, 'Ecstasy'): a stressor on the immune system

Drug abuse is a global problem of considerable concern to health. One such health concern stems from the fact that many drugs of abuse have immunosuppressive actions and consequently have the potential to increase susceptibility to infectious disease. This article is focused on the impact of the amphetamine derivative, methylenedioxymethamphetamine (MDMA; 'Ecstasy') on immunity. Research conducted over the last 5 years, in both laboratory animals and humans, has demonstrated that MDMA has immunosuppressive actions. Specifically, MDMA suppresses neutrophil phagocytosis, suppresses production of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta, and increases production of the endogenous immunosuppressive cytokine (IL-10), thereby promoting an immunosuppressive cytokine phenotype. MDMA also suppresses circulating lymphocyte numbers, with CD4+ T cells being particularly affected, and alters T-cell function as indicated by reduced mitogen-stimulated T-cell proliferation, and a skewing of T-cell cytokine production in a T helper 2 (Th2) direction. For the most part, the aforementioned effects of MDMA are not the result of a direct action of the drug on immune cells, but rather caused by the release of endogenous immunomodulatory substances. Consequently, the physiological mechanisms that are thought to underlie the immunosuppressive effects of MDMA will be discussed. As many of the physiological changes elicited by MDMA closely resemble those induced by acute stress, it is suggested that exposure to MDMA could be regarded as a 'chemical stressor' on the immune system. Finally, the potential of MDMA-induced immunosuppression to translate into significant health risks for abusers of the drug will be discussed.

Long-term imipramine withdrawal induces a depressive-like behaviour in the forced swimming test

Chronic antidepressant treatments enhance dopaminergic neurotransmission in the mesolimbic dopamine system. We suggested that this potentiation might underlie both the antidepressant therapeutic effect and the antidepressant-induced switch from depression to mania. In a recent study we have shown a reversal of the imipramine-induced dopaminergic supersensitivity after 40 days of chronic imipramine withdrawal. We interpreted this result suggesting that the mood-switches observed in bipolar patients following antidepressant treatment and subsequent withdrawal, i.e. mania followed by rebound depression, might depend upon parallel changes in the mesolimbic dopamine system sensitivity. On this basis, one might predict a depressive-like behaviour after long-term interruption of a chronic treatment with imipramine. To test this hypothesis we examined the behaviour of rats treated with chronic imipramine 40 days after treatment interruption in an animal model of depression, the forced swimming test. The results show that animals treated with chronic imipramine, 40 days after treatment interruption, display a depressive-like behaviour in the forced swimming test, as indicated by their increased immobility with respect to the control group.