Effect of antidepressant drugs on dopamine D1 and D2 receptor expression and dopamine release in the nucleus accumbens of the rat

PM2.5 exposure contributes to anxiety and depression-like behaviors via phenyl-containing compounds interfering with dopamine receptor

As a global problem, fine particulate matter (PM2.5) really needs local fixes. Considering the increasing epidemiological relevance to anxiety and depression but inconsistent toxicological results, the most important question is to clarify whether and how PM2.5 causally contributes to these mental disorders and which components are the most dangerous for crucial mitigation in a particular place. In the present study, we chronically subjected male mice to a real-world PM2.5 exposure system throughout the winter heating period in a coal combustion area and revealed that PM2.5 caused anxiety and depression-like behaviors in adults such as restricted activity, diminished exploratory interest, enhanced repetitive stereotypy, and elevated acquired immobility, through behavioral tests including open field, elevated plus maze, marble-burying, and forced swimming tests. Importantly, we found that dopamine signaling was perturbed using mRNA transcriptional profile and bioinformatics analysis, with Drd1 as a potential target. Subsequently, we developed the Drd1 expression-directed multifraction isolating and nontarget identifying framework and identified a total of 209 compounds in PM2.5 organic extracts capable of reducing Drd1 expression. Furthermore, by applying hierarchical characteristic fragment analysis and molecular docking and dynamics simulation, we clarified that phenyl-containing compounds competitively bound to DRD1 and interfered with dopamine signaling, thereby contributing to mental disorders. Taken together, this work provides experimental evidence for researchers and clinicians to identify hazardous factors in PM2.5 and prevent adverse health outcomes and for local governments and municipalities to control source emissions for diminishing specific disease burdens.

D1 receptor-expressing neurons in ventral tegmental area alleviate mouse anxiety-like behaviors via glutamatergic projection to lateral septum

Dopamine (DA) acts as a key regulator in controlling emotion, and dysfunction of DA signal has been implicated in the pathophysiology of some psychiatric disorders, including anxiety. Ventral tegmental area (VTA) is one of main regions with DA-producing neurons. VTA DAergic projections in mesolimbic brain regions play a crucial role in regulating anxiety-like behaviors, however, the function of DA signal within VTA in regulating emotion remains unclear. Here, we observe that pharmacological activation/inhibition of VTA D1 receptors will alleviate/aggravate mouse anxiety-like behaviors, and knockdown of VTA D1 receptor expression also exerts anxiogenic effect. With fluorescence in situ hybridization and electrophysiological recording, we find that D1 receptors are functionally expressed in VTA neurons. Silencing/activating VTA D1 neurons bidirectionally modulate mouse anxiety-like behaviors. Furthermore, knocking down D1 receptors in VTA DA and glutamate neurons elevates anxiety-like state, but in GABA neurons has the opposite effect. In addition, we identify the glutamatergic projection from VTA D1 neurons to lateral septum is mainly responsible for the anxiolytic effect induced by activating VTA D1 neurons. Thus, our study not only characterizes the functional expression of D1 receptors in VTA neurons, but also uncovers the pivotal role of DA signal within VTA in mediating anxiety-like behaviors.

Review and meta-analysis of add-on tranylcypromine with antipsychotic drugs for the treatment of schizophrenia with predominant negative symptoms: a restoration of evidence

BACKGROUND

Treatment using add-on antidepressants with antipsychotic drugs in negative symptoms of schizophrenia has been reviewed recently in comprehensive meta-analyses. Tranylcypromine (TCP), an irreversible monoamine oxidase (MAO)-A/B inhibitor applied in treatment resistant depression, was not included because of strict requirements for quality of study design. To get a clear picture of available evidence for this resource in the treatment of schizophrenia, we conducted a review and meta-analysis of add-on TCP in the treatment of predominant negative symptoms of schizophrenia (negative schizophrenia).

METHODS

Seven controlled studies of add-on TCP in schizophrenia with predominant negative symptoms were found in a search of multiple databases. A subset of four studies of the prospective and parallel comparison of add-on TCP with antipsychotic drugs vs. antipsychotic drug monotherapy and meeting minimum quality criteria formed the primary meta-analysis. The effect size was calculated as the natural logarithm of the odds ratio (logOR) of responders and non-responders.

RESULTS

In the primary meta-analysis, a pooled logOR = 1.092 with 95%CI 0.410-1.774 (I² = 43.4%, moderate heterogeneity) was calculated according to a fixed-effect model. Heterogeneity was reduced for three double-blind studies of add-on TCP with trifluoperazine (TFP) vs. TFP-monotherapy and resulted a pooled logOR = 0.916 with 95%CI 0.216-1.616 (I² negative, no heterogeneity). A significant logOR = 1.558 with 95%CI 0.340-2.776 was found for TCP/TFP compared to placebo in one study. In a meta-analysis of extrapyramidal adverse effects, studies were very heterogeneous and revealed no significant differences between treatments. The risk of exacerbation of positive symptoms with add-on TCP was found to be very low for a duration of treatment of 12-16 weeks. No cases of hypertensive crisis were reported. The main methodical limitations were insufficient description of randomization or matching of patients without randomization. The main clinical limitation is a gap of data for add-on TCP with second-generation antipsychotics.

CONCLUSION

New studies are needed for add-on TCP with antipsychotic drugs in schizophrenia with predominant negative symptoms. Trials of this treatment may be possible in rare and selected cases. The therapeutic effect of add-on TCP may be explained by a strong dopaminergic activity.

β-Carbolines found in cigarette smoke elevate intracranial self-stimulation thresholds in rats

Identifying novel constituents that contribute to tobacco addiction is essential for developing more effective treatments and informing FDA regulation of tobacco products. While preclinical data indicate that monoamine oxidase (MAO) inhibitors can have abuse liability or potentiate the addiction-related effects of nicotine, most of these studies have used clinical MAO inhibitors (e.g., tranylcypromine) that are not present in cigarette smoke. The primary goal of this study was to evaluate the abuse potential of the β-carbolines harmane, norharmane, and harmine - MAO inhibitors that are found in cigarette smoke - in an intracranial self-simulation (ICSS) model in rats. A secondary goal was to evaluate the ability of norharmane to influence nicotine's acute effects on ICSS. None of the β-carbolines lowered ICSS thresholds at any dose studied when administered alone, suggesting a lack of abuse liability. Rather, all three β-carbolines produced dose-dependent elevations in ICSS thresholds, indicating aversive/anhedonic effects. Harmane and harmine also elevated ICSS response latencies, suggesting a disruption of motor function, albeit with reduced potency compared to their ICSS threshold-elevating effects. Norharmane (2.5 mg/kg) modestly attenuated the effects of nicotine on ICSS thresholds. Our findings indicate that these β-carbolines produced only aversive/anhedonic effects in an ICSS model when administered alone, and that norharmane unexpectedly attenuated nicotines acute effects on ICSS. Future work evaluating the addiction-related effects of nicotine combined with these and other MAO inhibitors present in smoke may be useful for understanding the role of MAO inhibition in tobacco addiction and informing FDA tobacco regulation.

Antidepressant Withdrawal and Rebound Phenomena

BACKGROUND

Antidepressants are among the most commonly prescribed drugs worldwide. They are often discontinued, frequently without the knowledge of the prescribing physician. It is, therefore, important for physicians to be aware of the withdrawal and rebound phenomena that may arise, in order to prevent these phenomena, treat them when necessary, and counsel patients appropriately.

METHODS

This review is based on a comprehensive, structured literature search on antidepressant withdrawal phenomena that we carried out in the CENTRAL, PubMed (Medline), and Embase databases. We classified the relevant publications and reports by their methodological quality.

RESULTS

Out of a total of 2287 hits, there were 40 controlled trials, 38 cohort studies and retrospective analyses, and 271 case reports that met the inclusion criteria. Withdrawal manifestations are usually mild and self-limiting; common ones include dizziness, headache, sleep disturbances, and mood swings. More serious or pro- longed manifestations rarely arise. There is an increased risk with MAO inhibitors, tricyclic antidepressants, venlafaxine, and paroxetine; on the other hand, for agome- latine and fluoxetine, abrupt discontinuation seems to be unproblematic. There is also some evidence of rebound phenomena, i.e., of higher relapse rates or especially severe relapses of depression after the discontinuation of an anti- depressant.

CONCLUSION

A robust evidence base now indicates that there can be acute with- drawal phenomena when antidepressants are discontinued. Putative rebound phenomena have not been adequately studied to date. It is recommended that antidepressants should be tapered off over a period of more than four weeks.

The D2 dopamine receptor (DRD2) gene is associated with co-morbid depression, anxiety and social dysfunction in untreated veterans with post-traumatic stress disorder

Objective.

To identify clusters of patients with post-traumatic stress disorder (PTSD) according to symptom profile and to examine the association of the A1 allele of the D2 dopamine receptor (DRD2) gene with these clusters.

Method.

Fifty-seven untreated Caucasian Vietnam veterans with PTSD were administered the General Health Questionnaire-28 (GHQ) and the Mississippi Scale for combat-related PTSD. DRD2 allelic status was determined by PCR.

Results.

Subjects with the DRD2 Al allele compared to those without this allele had significantly higher scores on GHQ 2 (anxiety/insomnia), GHQ 3 (social dysfunction) and GHQ 4 (depression). Cluster analysis of the GHQ data identified two primary groups. A high psychopathology cluster (cluster 3), featured by high co-morbid levels of somatic concerns, anxiety/insomnia, social dysfunction and depression, and a low psychopathology cluster (cluster 1), manifested by the reverse pattern. Scores in each of the four GHQ groups were significantly higher in cluster 3 than cluster 1, as was Mississippi Scale PTSD score. DRD2 A1 allele veterans compared to those without this allele were significantly more likely to be found in the high than the low psychopathology cluster group.

Conclusions.

DRD2 variants are associated with severe co-morbid psychopathology in PTSD subjects.

Neuropsychiatric Disorders in Parkinson's Disease: What Do We Know About the Role of Dopaminergic and Non-dopaminergic Systems?

Besides the hallmark motor symptoms (rest tremor, hypokinesia, rigidity, and postural instability), patients with Parkinson’s disease (PD) have non-motor symptoms, namely neuropsychiatric disorders. They are frequent and may influence the other symptoms of the disease. They have also a negative impact on the quality of life of patients and their caregivers. In this article, we will describe the clinical manifestations of the main PD-related behavioral disorders (depression, anxiety disorders, apathy, psychosis, and impulse control disorders). We will also provide an overview of the clinical and preclinical literature regarding the underlying mechanisms with a focus on the role of the dopaminergic and non-dopaminergic systems.

Dopaminergic impact of cART and anti-depressants on HIV neuropathogenesis in older adults

The success of combination antiretroviral therapy (cART) has transformed HIV infection into a chronic condition, resulting in an increase in the number of older, cART-treated adults living with HIV. This has increased the incidence of age-related, non-AIDS comorbidities in this population. One of the most common comorbidities is depression, which is also associated with cognitive impairment and a number of neuropathologies. In older people living with HIV, treating these overlapping disorders is complex, often creating pill burden or adverse drug-drug interactions that can exacerbate these neurologic disorders. Depression, NeuroHIV and many of the neuropsychiatric therapeutics used to treat them impact the dopaminergic system, suggesting that dopaminergic dysfunction may be a common factor in the development of these disorders. Further, changes in dopamine can influence the development of inflammation and the regulation of immune function, which are also implicated in the progression of NeuroHIV and depression. Little is known about the optimal clinical management of drug-drug interactions between cART drugs and antidepressants, particularly in regard to dopamine in older people living with HIV. This review will discuss those interactions, first examining the etiology of NeuroHIV and depression in older adults, then discussing the interrelated effects of dopamine and inflammation on these disorders, and finally reviewing the activity and interactions of cART drugs and antidepressants on each of these factors. Developing better strategies to manage these comorbidities is critical to the health of the aging, HIV-infected population, as the older population may be particularly vulnerable to drug-drug interactions affecting dopamine.

Voluntary Wheel Running Reverses Deficits in Social Behavior Induced by Chronic Social Defeat Stress in Mice: Involvement of the Dopamine System

Voluntary exercise has been reported to have a therapeutic effect on many psychiatric disorders and social stress is known to impair social interaction. However, whether voluntary exercise could reverse deficits in social behaviors induced by chronic social defeat stress (CSDS) and the underlying mechanism remain unclear. The present study shows CSDS impaired social preference and induced social interaction deficiency in susceptible mice. Voluntary wheel running (VWR) reversed these effects. In addition, CSDS decreased the levels of tyrosine hydroxylase in the ventral tegmental area and the D2 receptor (D2R) in the nucleus accumbens (NAc) shell. These changes can be recovered by VWR. Furthermore, the recovery effect of VWR on deficits in social behaviors in CSDS mice was blocked by the microinjection of D2R antagonist raclopride into the NAc shell. Thus, these results suggest that the mechanism underlying CSDS-induced social interaction disorder might be caused by an alteration of the dopamine system. VWR may be a novel means to treat CSDS-induced deficits in social behaviors via modifying the dopamine system.

Error-related Brain Activity as a Treatment Moderator and Index of Symptom Change during Cognitive-Behavioral Therapy or Selective Serotonin Reuptake Inhibitors

Increased neural error monitoring, as measured by the error-related negativity (ERN), is a transdiagnostic neurobiological marker of anxiety. To date, little is known about whether the ERN can inform the choice between first-line anxiety disorder treatments and whether the ERN changes following treatment completion. The aim of the study was to therefore assess whether the ERN is a treatment moderator and index of symptom change during cognitive-behavioral therapy (CBT) or selective serotonin reuptake inhibitors (SSRIs). Participants included adult volunteers (M age=25.8±8.5; 67% female) with principal anxiety disorders (n=60) or no lifetime history of Axis I psychopathology (ie, healthy controls; n=26). A flanker task was used to elicit the ERN at baseline and 12 weeks later, following either CBT or SSRIs in the patient sample. Results indicated that baseline ERN was a significant treatment moderator such that a more enhanced baseline ERN was associated with greater reduction in anxiety symptoms within individuals who received CBT but not SSRIs. Results also revealed that the ERN increased pre- to post-treatment among patients randomized to SSRIs, but remained stable among patients randomized to CBT and healthy controls. Together, these novel findings highlight that ERN may help guide treatment decisions regarding engagement in CBT or SSRIs, especially among individuals with an enhanced ERN. The findings also suggest that SSRIs have the capacity to alter individual differences in the ERN, providing evidence that the ERN is not entirely static in patients with anxiety disorders.

Paecilomyces tenuipes extract prevents depression-like behaviors in chronic unpredictable mild stress-induced rat model via modulation of neurotransmitters

The medicinal fungus Paecilomyces tenuipes exhibits a variety of pharmacological effects, including antidepressive effects. The chronic unpredictable mild stress (CUMS)‑induced rat model has served an important role in studies involving antidepressants screening. The aim of the present study was to evaluate the antidepressant‑like activity of P. tenuipes N45 aqueous extract (PTNE) in a CUMS‑induced rat model of behavioral despair depression. Following 4 weeks of PTNE treatment, behavioral tests were conducted to investigate the antidepressant‑like activities, and the levels of neurotransmitters and hormones in blood and hypothalamus were measured. The results demonstrated that PTNE treatment significantly increased movement in the forced running test, whereas the immobility time was reduced in the hotplate test and the forced swim test in depression‑model rats. PTNE treatment was able to normalize the levels of hormones and neurotransmitters in serum and hypothalamus of CUMS rats. The data demonstrated that PTNE treatment may be a potential pharmaceutical agent in treatment‑resistant depression, and the effects of PTNE may be partly mediated through normalizing the levels of neurotransmitters.

Dysregulation of Striatal Dopamine Receptor Binding in Suicide

Inconsistent evidence implicates disruptions of striatal dopaminergic indices in suicide and major depression. To determine whether there are alterations in the striatal dopamine system in suicide, we conducted a quantitative autoradiographic survey of dopamine transporter (DAT; [³H]mazindol), D1 receptor ([³H]SCH23390), and D2 receptor ([³H]sulpiride) binding in the dorsal striatum postmortem from matched suicides and controls. Axis I and axis II psychiatric diagnosis, recent treatment history, and early life adversity (ELA) were determined by psychological autopsy. Mean DAT, D2, and D1 receptor binding did not differ in suicide. However, there was a positive correlation between D1 and D2 receptor binding in the dorsal striatum of control subjects (R²=0.31, p<0.05) that was not present in suicides (R²=0.00, p=0.97). In suicides and controls with reported ELA, there was no correlation between striatal DAT and D1 receptor binding (R²=0.07, p=0.33), although DAT and D1 receptor binding was positively correlated in subjects with no report of ELA (R²=0.32, p<0.05). After controlling for age, there were no significant ELA-related mean differences. Binding of D1 receptors and DAT throughout the striatum correlated negatively with age (D1 receptor: R²=0.12, p<0.05; DAT: R²=0.36, p<0.001). There appears to be an imbalance in dopaminergic receptor and transporter expression related to suicide that differs from that associated with ELA or age.

Investigation of the antidepressant effects of exopolysaccharides obtained from Marasmius androsaceus fermentation in a mouse model

Marasmius androsaceus, a well‑known medical fungus, possesses antihypertensive, analgesic and antioxidant effects. Exopolysaccharide (EPS), produced by microorganism secretion, exerts various types of biological activities. The present study aimed to investigate the antidepressant‑like effect of the EPS produced during Marasmius androsaceus submerge fermentation (MEPS). Based on the assessment of acute toxicity and behavior, a forced swimming test (FST), tail suspension test (TST), 5‑hydroxytryptophan‑induced head‑twitch assessment and reserpine‑induced hypothermia assessment were performed. The administration of MEPS for 7 days enhanced mouse locomotor and balance ability in the mice. Similar to the results following treatment with fluoxetine, which was used as positive control drug, MEPS significantly decreased the duration of immobility in the FST and TST, increased head twitches in the 5‑HTP‑induced head‑twitch test and enhanced rectal temperature in resperpine‑induced hypothermia. MEPS altered the abnormal concentrations of 5‑hydroxytryptamine, 5‑hydroxyindoleacetic acid, dopamine and norepinephrine in the hypothalamus in the resperine‑induced mouse model. Additionally, an increase in the expression of tyrosine hydroxylase and a reduction in the level of dopamine transporter in the hypothalamus were noted following 7 days of MEPS administration. Taken together, the EPS produced during MEPS exhibited antidepressant‑like effects, which may be associated with its regulation on the dopaminergic system. The results of the present study provide experimental evidence supporting the clinical use of MEPS as an effective agent against depression.

Effects of palatable cafeteria diet on cognitive and noncognitive behaviors and brain neurotrophins' levels in mice

The consumption of palatable high-fat and high-sugar foods have increased dramatically over the past years. Overconsumption of calorically dense food contributes to increasing rates of overweight and obesity that are associated with psychiatry disorders, in particular mood and anxiety disorders. This study evaluated the impact of palatable cafeteria diet (CAF) intake on cognitive and noncognitive behaviors, as well as identified factors related to these behaviors through an evaluation of brain neurotrophic factor (BDNF, NGF, and GDNF) levels in hippocampus of mice. Male Swiss mice received two different diets during 13 weeks: standard chow (STA) and highly CAF. Posteriorly, forced swimming test (FST), tail suspension test (TST), plus-maze test (PMT), open-field tests (OFT), and object recognition task (ORT) were utilized as behavioral tests. In addition, brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and nerve growth factor (NGF) neurotrophins' levels were evaluated in hippocampus of mice. The results demonstrated that mice from the CAF group showed a decrease in the immobility time in the FST and TST. Besides, mice in the CAF group spent more time in the open arms of the PMT. No significant differences were observed in the cognitive behaviors, which were evaluated in the OFT and ORT. In addition, the CAF group showed that BDNF and NGF protein levels increased in the hippocampus of mice. In conclusion, our data suggest that the consumption of palatable high-fat and high-sugar foods induces antidepressant- and anxiolytic-like behaviors, which can be related with BDNF and NGF expression increases in hippocampus of mice in the CAF group.

Reinforcement learning in depression: A review of computational research

Despite being considered primarily a mood disorder, major depressive disorder (MDD) is characterized by cognitive and decision making deficits. Recent research has employed computational models of reinforcement learning (RL) to address these deficits. The computational approach has the advantage in making explicit predictions about learning and behavior, specifying the process parameters of RL, differentiating between model-free and model-based RL, and the computational model-based functional magnetic resonance imaging and electroencephalography. With these merits there has been an emerging field of computational psychiatry and here we review specific studies that focused on MDD. Considerable evidence suggests that MDD is associated with impaired brain signals of reward prediction error and expected value ('wanting'), decreased reward sensitivity ('liking') and/or learning (be it model-free or model-based), etc., although the causality remains unclear. These parameters may serve as valuable intermediate phenotypes of MDD, linking general clinical symptoms to underlying molecular dysfunctions. We believe future computational research at clinical, systems, and cellular/molecular/genetic levels will propel us toward a better understanding of the disease.

Dopamine receptor D3 deficiency results in chronic depression and anxiety

Over the last decade accumulating evidence suggests that brain dopamine (DA) has a role in depression, particularly given the high comorbidity of depression with Parkinson's Disease (PD) and the antidepressant effects of the DA receptor subtype 3 (D3R) agonist pramipexole. The present study assesses the role of D3R in depression. Here we hypothesized that D3R mediates the antidepressant effects of DA. Thus, genetic deficiency of D3R in D3R knockout (D3RKO) mice would yield animals with chronic depressive symptoms. Whereas D3R deficient mice did not show significant alterations in locomotion when tested in the openfield, these animals showed anxiety-like symptoms measured as a significant increase in thigmotaxis at the openfield and a significantly lower time spent in the lit compartment at the light/dark exploration test. D3RKO animals also showed depressive-like symptoms as measured by increased immobility time in the Porsolt forced swim test and the tail suspension test, as well as anhedonia measured in the non-motor dependent sucrose test. In conclusion, D3R deficiency results in anxiety-like and depressive-like symptoms that cannot be attributed to motor dysfunction.

Chronic fluoxetine selectively upregulates dopamine D₁-like receptors in the hippocampus

The dentate gyrus of the hippocampus has been implicated in mechanisms of action of selective serotonin reuptake inhibitors (SSRIs). We have recently demonstrated that the SSRI fluoxetine can reverse the state of maturation of the adult dentate granule cells and enhances serotonin 5-HT₄ receptor-mediated synaptic potentiation at the synapses formed by their mossy fiber axons. Here, we show that fluoxetine can induce long-lasting enhancement of dopaminergic modulation at the mossy fiber synapse. Synaptic responses arising from the mossy fiber-CA3 pyramidal cell synapse were recorded using acute mouse hippocampal slices. Dopamine potentiates mossy fiber synaptic transmission by activating D₁-like receptors. Chronic fluoxetine treatment induced a prominent increase in the magnitude of dopamine-induced synaptic potentiation, and this effect was maintained at least up to 1 month after withdrawal of fluoxetine. Quantitative autoradiography revealed that binding of the D₁-like receptor ligand [³H]SCH23390 was selectively increased in the dentate gyrus and along the mossy fiber in fluoxetine-treated mice. However, binding of the 5-HT₄ receptor ligand [³H]GR113808 was not significantly changed. These results suggest that chronic fluoxetine enhanced the dopaminergic modulation at least in part by upregulating expression of D₁-like receptors, while the enhanced serotonergic modulation may be mediated by modifications of downstream signaling pathways. These enhanced monoaminergic modulations would greatly increase excitatory drive to the hippocampal circuit through the dentate gyrus. The highly localized upregulation of D₁-like receptors further supports the importance of the dentate gyrus in the mechanism of action of SSRIs.

Receptor targets for antidepressant therapy in bipolar disorder: an overview

The treatment of bipolar depression is one of the most challenging issues in contemporary psychiatry. Currently only quetiapine and the olanzapine-fluoxetine combination are officially approved by the FDA against this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain relatively elusive. We performed a complete and systematic review to identify agents with definite positive or negative results concerning efficacy followed by a second systematic review to identify the pharmacodynamic properties of these agents. The comparison of properties suggests that the stronger predictors for antidepressant efficacy in bipolar depression were norepinephrine alpha-1, dopamine D1 and histamine antagonism, followed by 5-HT2A, muscarinic and dopamine D2 and D3 antagonism and eventually by norepinephrine reuptake inhibition and 5HT-1A agonism. Serotonin reuptake which constitutes the cornerstone in unipolar depression treatment does not seem to play a significant role for bipolar depression. Our exhaustive review is compatible with a complex model with multiple levels of interaction between the major neurotransmitter systems without a single target being either necessary or sufficient to elicit the antidepressant effect in bipolar depression.

Triple monoamine inhibitor tesofensine decreases food intake, body weight, and striatal dopamine D2/D3 receptor availability in diet-induced obese rats

The novel triple monoamine inhibitor tesofensine blocks dopamine, serotonin and norepinephrine re-uptake and is a promising candidate for the treatment of obesity. Obesity is associated with lower striatal dopamine D2 receptor availability, which may be related to disturbed regulation of food intake. This study assesses the effects of chronic tesofensine treatment on food intake and body weight in association with changes in striatal dopamine D2/D3 receptor (D2/3R) availability of diet-induced obese (DIO) rats. Four groups of 15 DIO rats were randomized to one of the following treatments for 28 days: 1. tesofensine (2.0 mg/kg), 2. vehicle, 3. vehicle+restricted diet isocaloric to caloric intake of group 1, and 4. tesofensine (2.0 mg/kg)+ a treatment-free period of 28 days. Caloric intake and weight gain decreased significantly more in the tesofensine-treated rats compared to vehicle-treated rats, which confirms previous findings. After treatment discontinuation, caloric intake and body weight gain gradually increased again. Tesofensine-treated rats showed significantly lower D2/3R availability in nucleus accumbens and dorsal striatum than both vehicle-treated rats and vehicle-treated rats on restricted isocaloric diet. No correlations were observed between food intake or body weight and D2/3R availability. Thus, chronic tesofensine treatment leads to decreased food intake and weight gain. However, this appears not to be directly related to the decreased striatal D2/3R availability, which is mainly a pharmacological effect.

Role for monoaminergic systems in the antidepressant-like effect of ethanol extracts from Hemerocallis citrina

ETHNOPHARMACOLOGICAL RELEVANCE

Hemerocallis citrina, a traditional herbal medicine, has been used for the improvement of emotions in Eastern-Asia countries.

AIM OF THE STUDY

Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the ethanol extracts from Hemerocallis citrina (HCE).

MATERIALS AND METHODS

Effect of HCE (90, 180 and 360 mg/kg, p.o.) on the immobility time was assessed in the mouse forced swim test (FST) and tail suspension test (TST), and locomotor activity was evaluated in the open-field test (OFT). Additionally, the monoamine neurotransmitters serotonin (5-HT), noradrenaline (NA) and dopamine (DA) levels involved in the antidepressant-like effect of HCE were also measured in the mice brain regions of frontal cortex and hippocampus.

RESULTS

HCE (90, 180 and 360 mg/kg, p.o.) administration significantly reduced the immobility time in both the FST and TST without accompanying changes in locomotor activity in the OFT. The pretreatment of mice with WAY 100635 (0.1 mg/kg, s.c., a 5-HT(1A) receptor antagonist), cyproheptadine (3 mg/kg, i.p., a 5-HT(2) receptor antagonist), prazosin (62.5 μg/kg, i.p., an α(1)-adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α(2)-adrenoceptor antagonist), propranolol (5 mg/kg, i.p., a β-adrenoceptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D(2) receptor antagonist), but not SCH23390 (0.05 mg/kg, s.c., a dopamine D(1) receptor antagonist) prevented the antidepressant-like effect of HCE (360 mg/kg, p.o.) in the TST. In addition, HCE enhanced 5-HT and NA levels in the frontal cortex and hippocampus as well as elevated DA levels in the frontal cortex.

CONCLUSION

The results indicate that the antidepressant-like effect of HCE is dependent on the serotonergic (5-HT(1A) and 5-HT(2) receptors), noradrenergic (α(1)-, α(2)- and β-adrenoceptors) and dopaminergic (D(2) receptor) systems as well as the elevation of 5-HT, NA and DA levels in the mouse brain.

Expression of the dopaminergic D1 and D2 receptors in the anterior cingulate cortex in a model of neuropathic pain

BACKGROUND

The anterior cingulate cortex (ACC) has been related to the affective component of pain. Dopaminergic mesocortical circuits, including the ACC, are able to inhibit neuropathic nociception measured as autotomy behaviour. We determined the changes in dopamine D1 and D2 (D1R and D2R) receptor expression in the ACC (cg1 and cg2) in an animal model of neuropathic pain. The neuropathic group had noxious heat applied in the right hind paw followed 30 min. later by right sciatic denervation. Autotomy score (AS) was recorded for eight days and subsequently classified in low, medium and high AS groups. The control consisted of naïve animals.A semiquantitative RT-PCR procedure was done to determine mRNA levels for D1R and D2R in cg1 and cg2, and protein levels were measured by Western Blot.

RESULTS

The results of D1R mRNA in cg1 showed a decrease in all groups. D2R mRNA levels in cg1 decreased in low AS and increased in medium and high AS. Regarding D1R in cg2, there was an increase in all groups. D2R expression levels in cg2 decreased in all groups. In cg1, the D2R mRNA correlated positively with autotomy behaviour. Protein levels of D2R in cg1 increased in all groups but to a higher degree in low AS. In cg2 D2R protein only decreased discretely. D1R protein was not found in either ACC region.

CONCLUSIONS

This is the first evidence of an increase of inhibitory dopaminergic receptor (D2R) mRNA and protein in cg1 in correlation with nociceptive behaviour in a neuropathic model of pain in the rat.

Effects of antidepressant drug treatment and psychotherapy on striatal and thalamic dopamine D2/3 receptors in major depressive disorder studied with [11C]raclopride PET

Antidepressant drug treatment and psychotherapy are both effective in treating major depression, but there are no published studies comparing the effects of these two treatments on the dopaminergic neurotransmitter system in major depression. We conducted a randomized comparative study on the effects of fluoxetine medication and short-term psychodynamic psychotherapy on striatal and thalamic dopamine D(2/3) receptors in patients with major depression. Duration of the treatment was 4 months, and dopamine D(2/3) receptor binding was quantified before and after treatment as the binding potential (BP (ND)) using [(11)C]raclopride and 3D positron emission tomography. Both treatments were clinically effective in treating major depression, as shown by substantial decreases in symptom ratings. Yet, there were no effects on D(2/3) receptor availability in the ventral striatum or other subdivisions of the striatum. Fluoxetine but not psychotherapy increased [(11)C]raclopride BP (ND) in lateral thalamus (+7.74%, p = 0.002) but this increase was not correlated with clinical improvement. In conclusion, this preliminary study does not support the involvement of ventral dopaminergic neurotransmission in the antidepressant effects of fluoxetine or psychodynamic psychotherapy. The effects of fluoxetine on thalamic dopamine systems need to be further explored.

Evidence of involvement of the human Par-4 (PAWR) gene in major depressive disorder

QBJECTIVES: The aim of the study was to examine the associations between genetic variations in the human PAWR gene and major depressive disorder (MDD) as well as the response to antidepressant treatment.

METHODS

Six-hundred and two patients with MDD and 543 controls were included in the study; among the MDD patients, 268 were followed-up for a further 8 weeks in order to assess their response to treatment with selective serotonin reuptake inhibitors (SSRIs). Six polymorphisms (rs17005769, rs4842318, rs7305141, rs2307223, rs8176874 and rs2307220) of the PAWR gene were investigated with regard to their association with MDD and antidepressant treatment efficacy.

RESULTS

One polymorphism, rs8176874, was in genotypic (uncorrected P=0.005) and allelic (uncorrected P=0.0015) association with MDD. Several haplotypes spanning rs7305141-rs2307223-rs8176874 were also significantly associated with MDD after correction for multiple testing (corrected P<0.05). However, neither single-marker nor haplotype-based analyses suggested an association between the studied markers and SSRI treatment response.

CONCLUSIONS

Genetic variations in the PAWR gene are related to susceptibility to MDD but not to SSRI treatment response.

Neurochemistry of the nucleus accumbens and its relevance to depression and antidepressant action in rodents

There is accumulating evidence that the nucleus accumbens (NAc) plays an important role in the pathophysiology of depression. Given that clinical depression is marked by anhedonia (diminished interest or pleasure), dysfunction of the brain reward pathway has been suggested as contributing to the pathophysiology of depression.Since the NAc is the center of reward and learning, it is hypothesized that anhedonia might be produced by hampering the function of the NAc. Indeed, it has been reported that stress, drug exposure and drug withdrawal, all of which produce a depressive-phenotype, alter various functions within the NAc, leading to inhibited dopaminergic activity in the NAc.In this review, we describe various factors as possible candidates within the NAc for the initiation of depressive symptoms. First, we discuss the roles of several neurotransmitters and neuropeptides in the functioning of the NAc, including dopamine, glutamate, gamma-aminobutyric acid (GABA), acetylcholine, serotonin, dynorphin, enkephaline, brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein (CREB), melanin-concentrating hormone (MCH) and cocaine- and amphetamine-regulated transcript (CART). Second, based on previous studies, we propose hypothetical relationships among these substances and the shell and core subregions of the NAc.

Dopaminergic challenges in social anxiety disorder: evidence for dopamine D3 desensitisation following successful treatment with serotonergic antidepressants

Serotonergic antidepressants (SSRIs) are first-line treatments for social anxiety disorder [SAnD], though there is evidence of dopaminergic system dysfunction. Twenty subjects with DSM-IV SAnD, untreated (n = 10) and SSRI-remitted DSM-IV SAnD (n = 10), were administered a single dose of 1) a dopamine agonist (pramipexole 0.5 mg) and 2) a dopamine antagonist (sulpiride 400 mg), followed by anxiogenic challenges (verbal tasks and autobiographical scripts) in a double-blind crossover design, the two test days being one week apart. Anxiety symptoms were measured by self-reported changes in Visual Analogue Scales, specific SAnD scales and anxiety questionnaires. Plasma levels of prolactin were obtained. Untreated SAnD subjects experienced significant increases in anxiety symptoms following behavioural challenges after either sulpiride or pramipexole. Following remission with SSRIs, the socially anxiogenic effect of behavioural provocation was significantly attenuated under pramipexole, whereas under sulpiride effects remained significantly elevated. There appears to be instability of the dopamine system under behavioural stress in social anxiety subjects that is only partly rectified by successful treatment with an SSRI, which may induce a desensitisation of postsynaptic dopamine D(3) receptors.

Chronic treatment with fluoxetine decreases cerebral metabolic responses to the 5-HT1A agonist 8-hydroxy-2(di-N-propylamino)tetralin and increases those to the 5-HT2A/2C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and to the dopaminergic agonist apomorphine

Fluoxetine is a selective serotonin (5-HT) reuptake inhibitor that, when given chronically, alters different neurotransmitter systems. To assess functional changes occurring in the 5-HT and dopaminergic systems, we investigated the effects of 5-HT(1A) agonist 8-hydroxy-2(di-N-propylamino)tetralin (8-OH-DPAT), of the 5-HT(2A/2C) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and of the dopamine D(1/2) agonist apomorphine (APO) on behavior and on regional cerebral metabolic rates for glucose (rCMRglc) in rats pretreated for 3weeks with saline or fluoxetine (8mg/kg/day). Behavioral effects were assessed for 8-OH-DPAT by scoring the 5-HT syndrome, for DOI by counting head shakes and for APO with an activity monitor. rCMRglc were measured with quantitative autoradiographic [(14)C]2-deoxyglucose technique in 60 brain regions at 10min after acute administration of 8-OH-DPAT 1mg/kg, at 30min after DOI 5mg/kg or at 10min after APO 1mg/kg. Chronic fluoxetine did not alter the 5-HT syndrome by 8-OH-DPAT, decreased head shakes by DOI and enhanced hyperlocomotion by APO. 8-OH-DPAT produced rCMRglc increases in sensorimotor regions that were unaffected by fluoxetine pretreatment and diffuse metabolic decrements that were attenuated by fluoxetine in limbic and raphe areas (17% and 4% mean decreases, respectively, in saline control and fluoxetine-pretreated rats). DOI produced widespread rCMRglc declines that were intensified by fluoxetine (14% and 20% decreases, in control and fluoxetine rats). APO caused rCMRglc increases in 22 brain regions that were potentiated by fluoxetine in dopaminergic motor areas (10% and 25% increases, in control and fluoxetine rats). In conclusion, fluoxetine enhances 5-HT neurotransmission by blunting responsivity of 5-HT(1A) autoreceptors and increasing that of 5-HT(2A/2C) postsynaptic receptors and enhances dopaminergic D(1/2) receptor neurotransmission.

Possible involvement of sigma-1 receptors in the anti-immobility action of bupropion, a dopamine reuptake inhibitor

Sigma receptors particularly, sigma-1 subtype is known to modulate the release of catecholamines in the brain and may participate in the mechanism of action of various antidepressants. The present study investigated the possible involvement of sigma receptors in modulating the anti-immobility-like effect of bupropion (a dopamine reuptake inhibitor) using the forced swim test (FST) in mice. Bupropion produced dose-dependent (10-40 mg/kg, i.p.) reduction in immobility period and the ED(50) value was found to be 18.5 (7.34-46.6) mg/kg, i.p. (+)-Pentazocine (2.5 mg/kg, i.p.), a high-affinity sigma-1 receptor agonist, produced synergistic response when it was co-administered with a subeffective dose of bupropion (10 mg/kg, i.p.). On the contrary, pretreatment with progesterone (10 mg/kg, s.c.), a sigma-1 receptor antagonist neurosteroid, rimcazole (5 mg/kg, i.p.), another sigma-1 receptor antagonist, or BD 1047 (1 mg/kg, i.p.), a novel sigma-1 receptor antagonist, reversed the anti-immobility effects of bupropion (20 mg/kg, i.p.). The various modulators used in the study did not show any effect per se on locomotor activity except bupropion which at a higher dose (15-40 mg/kg, i.p.) significantly increased the locomotor activity. The results for the first time demonstrated the involvement of sigma-1 receptors in the anti-immobility effects of bupropion.

Increased sensitivity to antidepressants of D3 dopamine receptor-deficient mice in the forced swim test (FST)

Evidence exists for a dopaminergic system dysregulation in mood disorders. In particular, depression may be accompanied by a relative fall of brain dopamine (DA) availability, while the increase of dopamine D2/D3 receptors (D2R/D3R) binding may reflect a compensatory change following primary reduction of mesolimbic DA levels. It is well established that D3Rs, acting as autoreceptors, inhibit DA synthesis and release, although lack of selective compounds have limited the progress in understanding D3Rs role in mood disorders. Aim of this study was to assess the behavioral responses of D3R-deficient (D3(-/-)) mice tested in the forced swim test (FST) and to evaluate their sensitivity to the treatment with different antidepressant drugs. Different groups of mice received one injection of the tricyclic compound, clomipramine (1, 5 and 10 mg/kg) or of one the selective serotonin reuptake inhibitors (SSRIs), paroxetine, sertraline or citalopram (1, 4 and 16 mg/kg), 30 min prior the behavioral test. Vehicle-injected wild type (WT) mice and D3(-/-) animals were used as controls and submitted to the same experimental procedure. In a preliminary experiment, vehicle-injected D3(-/-) mice, but not their littermates, failed to show an increased immobility time in FST as compared to intact controls, suggesting an increased resistance to injection-induced stress in the former. Clomipramine 1 mg/kg failed to affect behavioral responses of both D3(-/-) mice and WT animals. After the 5 mg/kg dose, D3(-/-) and WT mice showed a better performance in FST than vehicle-injected controls, with a lower immobility time exhibited by D3(-/-) mice than that shown by WT animals. No difference was found between WT mice treated with the highest dose of clomipramine (10 mg/kg) and the respective controls, although D3(-/-) mice exhibited a decreased immobility time as compared to vehicle-injected controls. In contrast to WT animals, when treated with 1 mg/kg sertraline and the 4 mg/kg dose of every SSRI D3(-/-) mice exhibited a decreased immobility time in FST in comparison to vehicle-injected controls. Furthermore, 16 mg/kg doses of citalopram, paroxetine or sertraline induced a greater reduction of immobility time in D3(-/-) mice than in WT-treated animals as compared to their respective controls. These data suggest that D3(-/-) mice, as being more resistant to stressful procedure than WT littermates, are more sensitive to antidepressants in FST paradigm than the former. Although the present data do not allow any conclusion on the neurochemical base of this difference, it might be possible that the greater sensitivity to antidepressants depends on a higher DA levels in mesolimbic pathways following the lack of D3Rs.

Dopamine receptor gene expression in human amygdaloid nuclei: elevated D4 receptor mRNA in major depression

Previous findings from this laboratory demonstrating changes in dopamine (DA) transporter and D2 receptors in the amygdaloid complex of subjects with major depression indicate that disruption of dopamine neurotransmission to the amygdala may contribute to behavioral symptoms associated with depression. Quantitative real-time RT-PCR was used to investigate the regional distribution of gene expression of DA receptors in the human amygdala. In addition, relative levels of mRNA of DA receptors in the basal amygdaloid nucleus were measured postmortem in subjects with major depression and normal control subjects. All five subtypes of DA receptor mRNA were detected in all amygdaloid subnuclei, although D1, D2, and D4 receptor mRNAs were more abundant than D3 and D5 mRNAs by an order of magnitude. The highest level of D1 mRNA was found in the central nucleus, whereas D2 mRNA was the most abundant in the basal nucleus. Levels of D4 mRNA were highest in the basal and central nuclei. In the basal nucleus, amounts of D4, but not D1 or D2, mRNAs were significantly higher in subjects with major depression as compared to control subjects. These findings demonstrate that the D1, D2 and D4 receptors are the major subtypes of DA receptors in the human amygdala. Elevated DA receptor gene expression in depressive subjects further implicates altered dopaminergic transmission in the amygdala in depression.

Involvement of dopamine (DA)/serotonin (5-HT)/sigma (σ) receptor modulation in mediating the antidepressant action of ropinirole hydrochloride, a D2/D3 dopamine receptor agonist

Multiple lines of investigation have explored the role of dopaminergic systems in mental depression. Chronic treatment with antidepressant drugs has been reported to alter dopaminergic neurotransmission, most notably a sensitization of behavioural responses to agonists acting at D2/D3 dopamine receptors within the nucleus accumbens. Recent clinical evidences have shown that ropinirole, a D2/D3 dopamine receptor agonist, augments the action of various standard antidepressant drugs in treatment-resistant depression. The present study was undertaken to elucidate the possible mechanism of antidepressant action of ropinirole employing various behavioral paradigms of despair supported by the measurements of neurochemical changes in the tissue contents of dopamine (DA) and serotonin (5-HT) in the whole brain using high-performance-liquid chromatography (HPLC) with electrochemical detectors (ECD). In the mouse forced swim test (FST) or tail-suspension test (TST), ropinirole (1-10 mg/kg, i.p.) produced S-shaped dose-response curve in the percentage decrease in immobility period. Compared with vehicle, ropinirole (10 mg/kg., i.p.) had a significant anti-immobility effect without affecting locomotor activity. The reduction in the immobility period elicited by ropinirole (10 mg/kg, i.p.) in the FST was reversed by dopaminergic and sigma receptor antagonist, haloperidol (0.5 mg/kg, i.p.), and specific D2 dopamine receptor antagonist sulpiride (5 mg/kg i.p.), but not by SCH 23390 (0.5 mg/kg i.p), a D1 dopamine receptor antagonist. Rimcazole (5 mg/kg i.p.) (a sigma receptor antagonist), progesterone (10 mg/kg i.p.) (a sigma receptor antagonistic neurosteroid), BD 1047 (1 mg/kg i.p.) (a novel sigma receptor antagonist with preferential affinity for sigma-1 sites) also reversed the anti-immobility effect of ropinirole (10 mg/kg i.p.). The neurochemical studies of whole brain revealed that ropinirole at 10 mg/kg i.p. did not affect the tissue levels of dopamine but significantly increased serotonin levels. The study indicated that ropinirole possessed anti-immobility activity in FST by altering dopaminergic, serotonergic or sigma receptor function.

Extrastriatal D2 and striatal D2 receptors in depressive illness: pilot PET studies using [11C]FLB 457 and [11C]raclopride

BACKGROUND

Reduced dopaminergic function may occur in depressive disorders. In this paper the results of two pilot studies examining different aspects of the dopamine system in depression are presented. First, the binding of [(11)C]FLB 457 to extrastriatal D(2) receptors was measured in a group of depressed patients. Second, the hypothesis that selective serotonin reuptake inhibiting (SSRI) antidepressants affect the striatal binding of [(11)C]raclopride was tested.

METHODS

In the first study the binding of [(11)C]FLB 457 was compared between 7 people with depression and 7 healthy controls. In the second study the binding of [(11)C]raclopride to striatal D(2/3) receptors was compared between 8 people taking SSRI antidepressant medication and 8 healthy controls.

RESULTS

There was no difference in the binding of [(11)C]FLB 457 between the two groups. [(11)C]raclopride binding was reduced in the dorsal striatum of people taking antidepressants suggesting either that D(2/3) expression was reduced, or that dopamine release was increased, compared to untreated controls.

LIMITATIONS

The depressed patients were not severely depressed and were not matched for gender with controls. In the raclopride group the patients and controls were not matched by gender and were taking different SSRI antidepressants.

CONCLUSION

We found no support for the hypothesis that dopamine D(2) receptor expression is altered in extrastriatal brain regions in depression. SSRI antidepressants were associated with reduced [(11)C]raclopride binding in the dorsal striatum supporting the hypothesis that therapeutic effects of such drugs may, in part, be due to changes in the dopamine system.

Lesions of dopaminergic neurons in the substantia nigra pars compacta and in the ventral tegmental area enhance depressive-like behavior in rats

Depression is the most common psychiatric complication in Parkinson's disease (PD). The pathophysiological events leading to PD-associated depression, however, remain largely unknown. The present study tested the differential implication of dopaminergic systems in depressive-like behavior in rats and its response to l-Dopa and the selective serotonin reuptake inhibitor citalopram. The learned helplessness model was used as a behavioral paradigm. Rats were lesioned in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) and assigned to subgroups with respect to the stereologically verified extent of the nigral and/or VTA degeneration. Both lesions increased depressive-like behavior in rats, which was reduced by both citalopram and l-Dopa treatment. We conclude that dopaminergic lesions of either the SNc or the VTA contribute to the manifestation of depressive-like behavior in rats. The effects of citalopram administration on depressive behavior induced by lesions of dopaminergic brain regions furthermore suggest an involvement of serotonergic pathways in dopaminergic cell loss-induced depression.

Involvement of nitric oxide (NO) signaling pathway in the antidepressant action of bupropion, a dopamine reuptake inhibitor

The present study was undertaken to elucidate the alterations in various behavioral and neurochemical basis of antidepressant action of bupropion [(+/-)-alpha-t-butylamino-3-chloropropiophenone], a dopamine reuptake inhibitor and to elucidate the possible mechanism of its action. The involvement of L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway in the antidepressant action of bupropion was investigated besides its actions on various brain transmitters like norepinephrine, dopamine and homovanillic acid. Bupropion (10, 15, 20 and 40 mg/kg., i.p.) dose dependently inhibited the immobility period in mice in both forced swim test and tail suspension test. ED(50) values of bupropion in reducing the immobility period was found to be 18.5 and 18 mg/kg i.p., in forced swim test and tail suspension test, respectively. Bupropion (10, 20 and 40 mg/kg., i.p.) reversed the reserpine-induced behavioral despair also. When different doses (10, 15, 20 and 40 mg/kg., i.p.) of bupropion were tested for locomotor activity, it (15, 20 and 40 mg/kg., i.p.) increased locomotor activity. At 20 and 40 mg/kg doses the drug showed hypothermia. The neurochemical analysis of brain samples revealed that bupropion dose dependently (10-40 mg/kg., i.p.) increased the brain contents of dopamine and homovanillic acid in the mouse whole brain. The levels of norepinephrine were also increased at 20 mg/kg dose. The antidepressant-like effect of bupropion (20 mg/kg., i.p.) was prevented by pretreatment with L-arginine (750 mg/kg., i.p.) [substrate for nitric oxide synthase (NOS)]. Pretreatment of mice with 7-nitroindazole (25 mg/kg., i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] produced potentiation of the action of subeffective dose of bupropion (10 mg/kg i.p.). In addition, treatment of mice with methylene blue (10 mg/kg., i.p.) [direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] potentiated the effect of bupropion (10 mg/kg., i.p.) in the forced swim test. Furthermore, the reduction in the immobility period elicited by bupropion (20 mg/kg., i.p.) was also inhibited by pretreatment with sildenafil (5 mg/kg., i.p.) [phosphodiesterase 5 inhibitor]. The study indicated that bupropion possesses antidepressant activities in different animal models of depression through its dopaminergic and/or by modulating the L-arginine-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling pathway.

Fluvoxamine treatment and D2 receptors: a pet study on OCD drug-naïve patients

Changes in D(2) receptors during antidepressant therapy have been reported in patients with major depressive disorder using PET/SPET. The aim of this study was to evaluate modifications in D(2) receptors that might occur in patients affected by obsessive-compulsive disorder (OCD) during serotonin reuptake sites inhibitors (SSRIs). To this purpose, we measured the in vivo binding of [(11)C]raclopride ([(11)C]Rac)in the brain of a group of OCD naïve patients before and after the repeated administration of the inhibitor SSRI fluvoxamine. Eight patients with a Diagnostic and Statistical Manual of Mental Disorders IVth edition diagnosis of OCD completed the study undergoing a PET scan and a complete clinical evaluation before and during treatment with fluvoxamine. Patients have been compared also with a group of nine age-matched normal volunteers. Fluvoxamine treatment significantly improved clinical symptoms and increased [(11)C]Rac binding potential (BP) in the basal ganglia of OCD patients (7.5+/-5.2, 6.9+/-6.9, and 9.9+/-9.3% in dorsal caudate, dorsal putamen, and ventral basal ganglia, respectively; p<0.01) to values closer to those observed in the group of normal subjects. Chronic treatment with fluvoxamine induces a slight but significant increase in striatal [(11)C]Rac BP of previously drug-naïve OCD patients. The modifications in D(2) receptor availability might be secondary to fluvoxamine effects on serotoninergic activity.

Dopamine D3 receptor antisense oligodeoxynucleotide potentiates imipramine-induced dopaminergic behavioural supersensitivity

Chronic antidepressant treatments result in the potentiation of dopaminergic transmission in the mesolimbic dopamine system revealed as an increased motor response to dopamine D2-like agonists. On the basis of the involvement of this system in the control of motivation and reward-related behaviour, which are impaired in depression, it has been suggested that such supersensitivity might play an important role in the mechanism of action of these drugs. Several studies have provided evidence suggesting a role of dopamine D3 receptors in mediating antidepressant-induced increased motor response to dopamine agonists. To test this hypothesis, we studied the effect of the intracerebroventricular infusion of a dopamine D3 receptor antisense oligodeoxynucleotide (10 microg/3 microl, 2-3 daily injections) on the expression of imipramine-induced supersensitivity (20 mg/kg daily intraperitoneal injections for 21 days) to the motor effect of the dopamine D2-like receptor agonist quinpirole (a single 0.3 mg/kg subcutaneous injection 24-48 h after imipramine withdrawal). The results show that a treatment previously shown to reduce the synthesis of dopamine D3 receptors, rather than resulting in an inhibitory effect, potentiated the ability of imipramine to induce dopaminergic motor supersensitivity. The present results suggest that increased dopamine D3 receptor expression following antidepressant treatments is not involved in the mechanism of dopaminergic supersensitivity, and are consistent with evidence supporting an inhibitory role for dopamine D3 receptors in motor activity, both in normal and in sensitized subjects.

Effects of amantadine and budipine on antidepressant drug-evoked changes in extracellular dopamine in the frontal cortex of freely moving rats

NMDA receptors play a role in the aetiology of depression with non-competitive NMDA receptor antagonists such as amantadine showing synergy with conventional antidepressants. To advance a neurochemical rational for these findings, we have studied the effects of administration of amantadine and budipine with the antidepressants reboxetine (REB), paroxetine (PAROX) and clomipramine (CLOM) on extracellular DA in rats using microdialysis. Acutely, amantadine (40 mg/kg) or budipine (10 mg/kg) did not significantly alter extracellular DA. REB (10 mg/kg), PAROX (10 mg/kg) both increased cortical DA while CLOM (10 mg/kg) produced a decrease. When amantadine or budipine was administered 30 min before the antidepressants, DA increases were markedly greater than following the antidepressants alone. Chronically drug effects were studied at 4, 7, 14 and 21 days. Amantadine and budipine did not significantly alter extracellular DA at any time. The three antidepressants elicited a gradual increase in DA which became significant after 7 days and tended to plateau thereafter. When amantadine (20 mg/kg) or budipine (5 mg/kg) was co-administered with the three antidepressants, two differences were seen compared with the antidepressants alone. Firstly, the time required for significant increases in cortical DA was reduced with elevated levels now being observed by 4 days. Secondly, the increase in extracellular DA was greater in these rats throughout the experiment. If increased extracellular DA represents a step in the mechanism of action of antidepressants, these data suggest that combined treatment with clinically tolerated NMDA antagonists such as amantadine could reduce the delay in therapeutic onset of antidepressants and possibly enhance their efficacy.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Acute and repeated administration of fluoxetine, citalopram, and paroxetine significantly alters the activity of midbrain dopamine neurons in rats: An in vivo electrophysiological study

We examined the effect of the administration of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, citalopram, and paroxetine on the activity of spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA) in anesthetized adult male Sprague-Dawley rats. This was accomplished using the technique of in vivo extracellular recording. A single injection of 2.5 mg/kg (i.p.) of fluoxetine significantly increased the number of spontaneously active SNC and VTA DA neurons. In contrast, a single injection of either 1 mg/kg (i.p.) of paroxetine or 5 mg/kg of fluoxetine significantly increased the number of spontaneously active VTA DA neurons. The repeated administration (one injection per day for 21 days) of all of the SSRIs produced a significant increase in the number of spontaneously active VTA DA neurons. Overall, our results indicate that the systemic administration of SSRI alters the activity of midbrain DA neurons with differential effects on VTA compared with SNC DA neurons.

Antidepressant-like effect of D(2/3) receptor-, but not D(4) receptor-activation in the rat forced swim test

Dopamine plays a role in the pathophysiology of depression and therapeutic effects of antidepressants but the contribution of individual D(2)-like receptor subtypes (D(2), D(3), D(4)) to depression is not known. We present evidence that activation of D(2)/D(3), but not D(4) receptors, can affect the outcome in the rat forced swim test (FST). Nomifensine, a dopamine uptake inhibitor (7, 14, and 28 micromol/kg); quinpirole, a D(2)-like receptor and agonist (0.4, 1.0, and 2.0 micromol/kg); PD 12,8907, a preferential D(3) receptor agonist (0.17, 0.35, and 0.7 micromol/kg); PD 168077 (0.1, 0.3, and 1.0 micromol/kg) and CP 226269 (0.3, 1.0, and 3.0 micromol/kg), both selective D(4) receptor agonists, were administered s.c. 24, 5, and 0.5/1 h before testing. Nomifensine, quinpirole at all doses and PD 128907 at the highest dose decreased immobility time in FST. PD 168077 and CP 226269 had no effect on the model. To further clarify what type of dopamine receptors were involved in the anti-immobility effect of quinpirole, we tested different antagonists. Haloperidol, a D(2)-like receptor antagonist (0.27 micromol/kg), completely blocked the effect of quinpirole; A-437203 (LU-201640), a selective D(3) receptor antagonist (17.46 micromol/kg), showed a nonsignificant trend to attenuate the effect of the low dose of quinpirole, and L-745,870, a selective D(4) receptor antagonist (1.15 micromol/kg), had no effect. The pharmacological selectivity of the compounds tested suggests that the antidepressant-like effects of quinpirole are most likely mediated mainly by D(2) and to a lesser extent by D(3) but not D(4) receptors.

Evidence for increased expression of the vesicular glutamate transporter, VGLUT1, by a course of antidepressant treatment

The therapeutic effect of a course of antidepressant treatment is believed to involve a cascade of neuroadaptive changes in gene expression leading to increased neural plasticity. Because glutamate is linked to mechanisms of neural plasticity, this transmitter may play a role in these changes. This study investigated the effect of antidepressant treatment on expression of the vesicular glutamate transporters, VGLUT1-3 in brain regions of the rat. Repeated treatment with fluoxetine, paroxetine or desipramine increased VGLUT1 mRNA abundance in frontal, orbital, cingulate and parietal cortices, and regions of the hippocampus. Immunoautoradiography analysis showed that repeated antidepressant drug treatment increased VGLUT1 protein expression. Repeated electroconvulsive shock (ECS) also increased VGLUT1 mRNA abundance in regions of the cortex and hippocampus compared to sham controls. The antidepressant drugs and ECS did not alter VGLUT1 mRNA abundance after acute administration, and no change was detected after repeated treatment with the antipsychotic agents, haloperidol and chlorpromazine. In contrast to VGLUT1, the different antidepressant treatments did not commonly increase the expression of VGLUT2 or VGLUT3 mRNA. These data suggest that a course of antidepressant drug or ECS treatment increases expression of VGLUT1, a key gene involved in the regulation of glutamate secretion.