The serotonin-dopamine interaction is critical for fast-onset action of antidepressant treatment: in vivo studies in an animal model of depression

Memory impairments in rodent depression models: A link with depression theories

More than 80% of depressed patients struggle with learning new tasks, remembering positive events, or concentrating on a single topic. These neurocognitive deficits accompanying depression may be linked to functional and structural changes in the prefrontal cortex and hippocampus. However, their mechanisms are not yet completely understood. We conducted a narrative review of articles regarding animal studies to assess the state of knowledge. First, we argue the contribution of changes in neurotransmitters and hormone levels in the pathomechanism of cognitive dysfunction in animal depression models. Then, we used numerous neuroinflammation studies to explore its possible implication in cognitive decline. Encouragingly, we also observed a positive correlation between increased oxidative stress and a depressive-like state with concomitant memory deficits. Finally, we discuss the undeniable role of neurotrophin deficits in developing cognitive decline in animal models of depression. This review reveals the complexity of depression-related memory impairments and highlights the potential clinical importance of gathered findings for developing more reliable animal models and designing novel antidepressants with procognitive properties.

Optogenetic Stimulation of Midbrain Dopamine Neurons Produces Striatal Serotonin Release

Targeting neurons with light-driven opsins is widely used to investigate cell-specific responses. We transfected midbrain dopamine neurons with the excitatory opsin Chrimson. Extracellular basal and stimulated neurotransmitter levels in the dorsal striatum were measured by microdialysis in awake mice. Optical activation of dopamine cell bodies evoked terminal dopamine release in the striatum. Multiplexed analysis of dialysate samples revealed that the evoked dopamine was accompanied by temporally coupled increases in striatal 3-methoxytyramine, an extracellular dopamine metabolite, and in serotonin. We investigated a mechanism for dopamine-serotonin interactions involving striatal dopamine receptors. However, the evoked serotonin associated with optical stimulation of dopamine neurons was not abolished by striatal D1- or D2-like receptor inhibition. Although the mechanisms underlying the coupling of striatal dopamine and serotonin remain unclear, these findings illustrate advantages of multiplexed measurements for uncovering functional interactions between neurotransmitter systems. Furthermore, they suggest that the output of optogenetic manipulations may extend beyond opsin-expressing neuronal populations.

Trophic factors as potential therapies for treatment of major mental disorders

Notwithstanding major advances in psychotherapeutics, their efficacy and specificity remain limited. The slow onset of beneficial outcomes and numerous adverse effects of widely used medications remain of chief concern, warranting in-depth studies. The majority of frontline therapies are thought to enhance the endogenous monoaminergic drive, to initiate a cascade of molecular events leading to lasting functional and structural plasticity. They also involve alterations in trophic factor signalling, including brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), glial cell-derived neurotrophic factor (GDNF), and others. In several major mental disorders, emerging data suggest protective and restorative effects of trophic factors in preclinical models, when applied on their own. Antidepressant outcomes of VGF and FGF2, for instance, were shown in experimental animals, while BDNF and GDNF prove useful in the treatment of addiction, schizophrenia, and autism spectrum disorders. The main challenge with the effective translation of these and other findings in the clinic is the knowledge gap in action mechanisms with potential risks, as well as the lack of effective platforms for validation under clinical settings. Herein, we review the state-of-the-art and advances in the therapeutic use of trophic factors in several major neuropsychiatric disorders.

3D fuzzy graphene microelectrode array for dopamine sensing at sub-cellular spatial resolution

The development of a high sensitivity real-time sensor for multi-site detection of dopamine (DA) with high spatial and temporal resolution is of fundamental importance to study the complex spatial and temporal pattern of DA dynamics in the brain, thus improving the understanding and treatments of neurological and neuropsychiatric disorders. In response to this need, here we present high surface area out-of-plane grown three-dimensional (3D) fuzzy graphene (3DFG) microelectrode arrays (MEAs) for highly selective, sensitive, and stable DA electrochemical sensing. 3DFG microelectrodes present a remarkable sensitivity to DA (2.12 ± 0.05 nA/nM, with LOD of 364.44 ± 8.65 pM), the highest reported for nanocarbon MEAs using Fast Scan Cyclic Voltammetry (FSCV). The high surface area of 3DFG allows for miniaturization of electrode down to 2 × 2 μm², without compromising the electrochemical performance. Moreover, 3DFG MEAs are electrochemically stable under 7.2 million scans of continuous FSCV cycling, present exceptional selectivity over the most common interferents in vitro with minimum fouling by electrochemical byproducts and can discriminate DA and serotonin (5-HT) in response to the injection of their 50:50 mixture. These results highlight the potential of 3DFG MEAs as a promising platform for FSCV based multi-site detection of DA with high sensitivity, selectivity, and spatial resolution.

Discovering the Lost Reward: Critical Locations for Endocannabinoid Modulation of the Cortico-Striatal Loop That Are Implicated in Major Depression

Depression, the most prevalent psychiatric disorder in the Western world, is characterized by increased negative affect (i.e., depressed mood, cost value increase) and reduced positive affect (i.e., anhedonia, reward value decrease), fatigue, loss of appetite, and reduced psychomotor activity except for cases of agitative depression. Some forms, such as post-partum depression, have a high risk for suicidal attempts. Recent studies in humans and in animal models relate major depression occurrence and reoccurrence to alterations in dopaminergic activity, in addition to other neurotransmitter systems. Imaging studies detected decreased activity in the brain reward circuits in major depression. Therefore, the location of dopamine receptors in these circuits is relevant for understanding major depression. Interestingly, in cortico-striatal-dopaminergic pathways within the reward and cost circuits, the expression of dopamine and its contribution to reward are modulated by endocannabinoid receptors. These receptors are enriched in the striosomal compartment of striatum that selectively projects to dopaminergic neurons of substantia nigra compacta and is vulnerable to stress. This review aims to show the crosstalk between endocannabinoid and dopamine receptors and their vulnerability to stress in the reward circuits, especially in corticostriatal regions. The implications for novel treatments of major depression are discussed.

Hippocampal monoamine changes in the Flinders sensitive line rat: A case for the possible use of selective α2C-AR-antagonists in stress and anxiety disorders in companion animals

Non-selective α₂-adrenoreceptor (AR) stimulation delivers favourable sedative, analgesic, muscle relaxant and anxiolytic actions in companion animals, but is associated with cardiovascular and respiratory side effects. Anxiety conditions underscore monoamine disturbances amenable to α₂-AR modulation. We investigated sub-chronic (14 day s.c.) treatment with the selective α_2C-AR antagonist, ORM-10921 (0.03, 0.1, 0.3 mg/kg/d) on hippocampal noradrenaline (NA), dopamine (DA), serotonin (5-HT) and their turnover levels in stress sensitive Flinders Sensitive Line (FSL) rats versus Flinders Resistant Line (FRL) controls, using high performance liquid chromatography. The effects of ORM-10921 were compared to the non-selective α₂-AR antagonist, idazoxan (IDAZ; 3 mg/kg/d), and to imipramine (IMI; 15 mg/kg/d), a reference antidepressant in this model. FSL rats displayed significantly reduced 5-HT (p = 0.03) and DA (p = 0.02) levels vs. FRL controls, while NA levels showed a similar trend. ORM-10921 significantly increased NA (all doses p ≤ 0.02), 5-HT (0.1 and 0.3 mg/kg p ≤ 0.03) and DA levels (all doses p ≤ 0.03), which correlated with decreased monoamine turnover. In contrast, IDAZ significantly elevated NA (p < 0.005) and DA (p < 0.004) but not 5-HT levels. IMI also significantly increased 5-HT (p < 0.009), with a tendency to increase NA (p = 0.09) but not DA. ORM-10921 exerts similar albeit broader effects on hippocampal monoamines than IDAZ, explaining earlier established efficacy associated with α_2C-AR antagonism in animal models of depression and cognitive dysfunction. These and the current studies encourage application of ORM-10921 in depression in humans, as well as raise the intriguing possibility that selective α_2C-AR antagonists may be beneficial in anxiety and stress-related disorders in companion animals. Both warrant further study.

An Overview of the Heterogeneity of Major Depressive Disorder: Current Knowledge and Future Prospective

Major depressive disorder (MDD) is estimated to impose maximum debilitating effects on the society by 2030, with its critical effects on health, functioning, quality of life and concomitant high levels of morbidity and mortality. Yet, the disease is inadequately understood, diagnosed and treated. Moreover, with the recent drastic rise in the pace of life, stress has materialized as one of the most potent environmental factors for depression. In this scenario, it is important to understand the modern pathogenetic hypotheses and mechanisms, and possibly try to shift from the traditional approaches in depression therapy. These include the elaboration of pathophysiological changes in heterogeneous systems such as genetic, epigenetic, serotonergic, noradrenergic, gamma-aminobutyric acid, glutamatergic and endocannabinoid systems, neurotrophic factors, HPA axis, immune system as well as cellular stress mechanisms. These components interact with each other in a complex matrix and further elucidation of their mechanism and cascade pathways are needed. This might aid in the identification of MDD subtypes as well as the development of sophisticated biomarkers. Further, characterization might also aid in developing multitargeted therapies that hold much promise as compared to the conventional monoamine based treatment. New candidate pharmacons, refined psychotherapeutic modalities, advanced neuro-surgical and imaging techniques as well as the implementation of pharmacokinetic, pharmacogenetic prescribing guidelines constitute the emerging expanses of MDD treatment.

The Response of Ventral Tegmental Area Dopaminergic Neurons to Bupropion: Excitation or Inhibition?

Introduction:

Antidepressants can modulate brain monoamines by acting on pre-synaptic and postsynaptic receptors. Autoreceptors can reduce the monoamines effect on the somatodendritic or pre-synaptic regions despite its postsynaptic counter effects. The direct effect of some antidepressants is related to its temporal and spatial bioavailability in the vicinity of these receptors (still a matter of controversies). This research evaluated the direct effect of acute bupropion on the Ventral Tegmental Area (VTA) dopaminergic neuronal firing rate.

Methods:

Male Wistar rats were divided into intracerebroventricular and microiontophoretic groups with 14 subgroups (n=5 in each subgroup). Amounts of 1, 0.5, 0.1, 0.01, 0.001, and 0.0001 mol of bupropion (5 μL/3 min) were microinfused to the first group and then the ejected amounts of bupropion at -500, -300, -150, -50 nA of electrical currents (1 mol, pH=4.5, 5 min) were applied to the second group. The control and sham subgroups were studied in each group, too. The units with stable firing rates were extracted, and the effect of bupropion was evaluated statistically with a P value less than 0.05 as the level of significance.

Results:

The highest amount of bupropion in the intracerebroventricular application could excite 42% of the neurons and inhibit 56% of them, but the highest amount of microiontophoretic application of bupropion could inhibit 97.5% of the neurons. The neuronal response to bupropion was dose-dependent in all treated groups.

Conclusion:

The dual effects of intracerebroventricular bupropion on the VTA dopaminergic neurons but solo inhibitory effect of its microiontophoretic application reflect the intra-VTA and extra-VTA heterogenic cellular and molecular control over the dopaminergic outflow that can be mediated by different receptors. The dopamine autoreceptors on the VTA dopaminergic neurons have complex modulatory effects on the dopaminergic response.

Role of glucocorticoid- and monoamine-metabolizing enzymes in stress-related psychopathological processes

Glucocorticoid signaling is fundamental in healthy stress coping and in the pathophysiology of stress-related diseases, such as post-traumatic stress disorder (PTSD). Glucocorticoids are metabolized by cytochrome P450 (CYP) as well as 11-β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and 2 (11βHSD2). Acute stress-induced increase in glucocorticoid concentrations stimulates the expression of several CYP sub-types. CYP is primarily responsible for glucocorticoid metabolism and its increased activity can result in decreased circulating glucocorticoids in response to repeated stress stimuli. In addition, repeated stress-induced glucocorticoid release can promote 11βHSD1 activation and 11βHSD2 inhibition, and the 11βHSD2 suppression can lead to apparent mineralocorticoid excess. The activation of CYP and 11βHSD1 and the suppression of 11βHSD2 may at least partly contribute to development of the blunted glucocorticoid response to stressors characteristic in high trait anxiety, PTSD, and other stress-related disorders. Glucocorticoids and glucocorticoid-metabolizing enzymes interact closely with other biomolecules such as inflammatory cytokines, monoamines, and some monoamine-metabolizing enzymes, namely the monoamine oxidase type A (MAO-A) and B (MAO-B). Glucocorticoids boost MAO activity and this decreases monoamine levels and induces oxidative tissue damage which then activates inflammatory cytokines. The inflammatory cytokines suppress CYP expression and activity. This dynamic cross-talk between glucocorticoids, monoamines, and their metabolizing enzymes could be a critical factor in the pathophysiology of stress-related disorders.Lay summaryGlucocorticoids, which are produced and released under the control by brain regulatory centers, are fundamental in the stress response. This review emphasizes the importance of glucocorticoid metabolism and particularly the interaction between the brain and the liver as the major metabolic organ in the body. The activity of enzymes involved in glucocorticoid metabolism is proposed to play not only an important role in positive, healthy glucocorticoid effects, but also to contribute to the development and course of stress-related diseases.

[The time course of changes in the state of monoaminergic systems in the brain of mice under the acute hypoxia with hypercapnia]

In socially isolated male outbred albino mice, the changes of monoaminergic systems under acute hypoxia with hypercapnia were studied. In cerebral cortex, hippocampus and striatum of the right and left sides of the brain, the concentrations of norepinephrine, dopamine, serotonin and their metabolites - dihydroxyphenylacetic, homovanillic and 5-hydroxyindoleacetic acids were investigated using the HPLC method. In isolated mice, which were not subjected to hypoxia with hypercapnia, higher levels of dopamine and serotonin in the left cortex were found. There was no asymmetry in monoamines and their metabolites in other studied brain structures. 10 min after the onset of exposure, acute hypoxia with hypercapnia resulted in a right-sided increase in norepinephrine levels and a decrease in dopamine levels in the striatum and serotonin levels in the hippocampus. In the cerebral cortex, 10 min after of hypoxic exposure beginning, there was a left-sided decrease in the dopamine content, while the original asymmetry found in the cortex of intact animals disappeared. In isolated mice perished of hypoxia with hypercapnia, almost all parameters returned to the control level. The exception was the ratio of serotonin metabolite level to the neurotransmitter, which in the right cortex became lower than in control animals. In white outbred mice, the brain monoaminergic systems are suggested to be relatively resistant to the negative consequences of hypoxia and hypercapnia, and corresponding shifts resulting in the reflex brain response to changes in the gas composition of the respiratory air.

[Central monoaminergic systems sensitivity to acute hypoxia with hypercapnia changes after the maintenance under the long-term social isolation]

The experiments were performed in male albino outbred mice kept in a group and under the conditions of long-term social isolation. The changes in the monoaminergic systems of the left and right hemispheres of the brain after acute hypoxia with hypercapnia have been studied. The levels of dopamine (DA), serotonin (5-HT) and their metabolites - dioxyphenylacetic (DOPAC), homovanillic (HVA), and 5-hydroxyindoleacetic (5-HIAA) acids - were determined by HPLC in the cerebral cortex, hippocampus and striatum of the right and left sides of the brain. In the control mice kept both in the group and under the conditions of social isolation, a higher content of DA in the cortex of the left hemisphere has been found. In the other brain structures the monoamine content was symmetric. In the cerebral cortex of the mice in the group, acute hypoxia with hypercapnia led to a right-sided increase in the DA and 5HT levels. At the same time, the DOPAC content decreased in the left cortex. In mice in the group, under the hypoxia with hypercapnia conditions, the DA level in the left hippocampus increased. In the striatum, the content of monoamines and their metabolites did not change significantly. In animals kept for a long time under the conditions of social isolation, hypoxia with hypercapnia no statistically significant changes in the monoamines and their metabolites levels were found. It has been concluded that the preliminary maintenance under the conditions of prolonged social isolation changes the reaction of central monoaminergic systems to acute hypoxia with hypercapnia.

Integrating Preclinical and Clinical Models of Negative Urgency

Overwhelming evidence suggests that negative urgency is robustly associated with rash, ill-advised behavior, and this trait may hamper attempts to treat patients with substance use disorder. Research applying negative urgency to clinical treatment settings has been limited, in part, due to the absence of an objective, behavioral, and translational model of negative urgency. We suggest that development of such a model will allow for determination of prime neurological and physiological treatment targets, the testing of treatment effectiveness in the preclinical and the clinical laboratory, and, ultimately, improvement in negative-urgency-related treatment response and effectiveness. In the current paper, we review the literature on measurement of negative urgency and discuss limitations of current attempts to assess this trait in human models. Then, we review the limited research on animal models of negative urgency and make suggestions for some promising models that could lead to a translational measurement model. Finally, we discuss the importance of applying objective, behavioral, and translational models of negative urgency, especially those that are easily administered in both animals and humans, to treatment development and testing and make suggestions on necessary future work in this field. Given that negative urgency is a transdiagnostic risk factor that impedes treatment success, the impact of this work could be large in reducing client suffering and societal costs.

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

OBJECTIVE

Although prescription rates of antidepressants for children and adolescents have increased, concerns have been raised regarding effects on neurodevelopment and long-term outcome. Using a genetic animal model of depression, this study investigated the long-term effects of pre-pubertal administration of fluoxetine (FLX) on depressive-like behaviour in early adulthood, as well as on central monoaminergic response to an acute stressor. We postulated that pre-pubertal FLX will have lasting effects on animal behaviour and monoaminergic stress responses in early adulthood.

METHODS

Flinders sensitive line (FSL) rats received 10 mg/kg/day FLX subcutaneously from postnatal day 21 (PnD21) to PnD34 (pre-pubertal). Thereafter, following normal housing, rats were either subjected to locomotor testing and the forced swim test (FST) on PnD60 (early adulthood), or underwent surgery for microdialysis, followed on PnD60 by exposure to acute swim stress and measurement of stressor-induced changes in plasma corticosterone and pre-frontal cortical monoamine concentrations.

RESULTS

Pre-pubertal FLX did not induce a late emergent effect on immobility in FSL rats on PnD60, whereas locomotor activity was significantly decreased. Acute swim stress on PnD60 significantly increased plasma corticosterone levels, and increased pre-frontal cortical norepinephrine (NE) and 5-hydroxyindole-3-acetic acid (5-HIAA) concentrations. Pre-pubertal FLX significantly blunted the pre-frontal cortical NE and 5-HIAA response following swim stress on PnD60. Baseline dopamine levels were significantly enhanced by pre-pubertal FLX, but no further changes were induced by swim stress.

CONCLUSION

Pre-pubertal FLX did not have lasting antidepressant-like behavioural effects in genetically susceptible, stress-sensitive FSL rats. However, such treatment reduced locomotor activity, abrogated noradrenergic and serotonergic stressor responses and elevated dopaminergic baseline levels in adulthood.

Effect of Physical Exercise and Acute Escitalopram on the Excitability of Brain Monoamine Neurons: In Vivo Electrophysiological Study in Rats

Background

The antidepressant effect of physical exercise has been reported in several clinical and animal studies. Since serotonin, norepinephrine, and dopamine play a central role in depression, it is possible that the beneficial effects of physical exercise are mediated via monoamine pathways. This study investigates the effects of voluntary wheel running on the excitability of monoamine neurons.

Materials and Methods

Male Sprague-Dawley rats were used in the study. Voluntary wheel running (VWR) rats were housed in individual cages with free access to a running wheel, while control animals were housed in standard laboratory cages. After three weeks, the rats were anesthetized, and in vivo electrophysiological recordings were taken from dorsal raphe nucleus serotonin neurons, locus coeruleus norepinephrine neurons, and ventral tegmental dopamine neurons.

Results

VWR stimulated activity in serotonin, but not in norepinephrine or dopamine neurons. Subsequently, acute administration of the selective serotonin reuptake inhibitor escitalopram in control rats led to complete suppression of serotonin neurons; this suppression was reversed by subsequent administration of selective antagonist of serotonin-1A receptors, WAY100135. Escitalopram induced only partial inhibition of serotonin neurons in the VWR rats while WAY100135 increased the firing activity of serotonin neurons above the baseline value.

Conclusions

The beneficial effect of physical exercise on mood is mediated, at least in part, via activation of serotonin neurons. Physical exercise can potentiate the response to selective serotonin reuptake inhibitors by increasing the basal firing activity and diminishing selective serotonin reuptake inhibitor-induced inhibition of serotonin neurons.

Levo-Tetrahydroberberrubine Produces Anxiolytic-Like Effects in Mice through the 5-HT1A Receptor

Tetrahydroprotoberberines (THPBs) are isoquinoline alkaloids isolated from the Chinese herb Corydalis yanhusuo. In the present study, we performed competitive binding assays to examine the binding of l-THBr to neurotransmitter receptors known to be involved in sedation, hypnosis and anxiety. Our results show that l-THBr does not interact with GABAergic receptors but has binding affinities for dopamine and serotonin receptors. In addition, cAMP and [³⁵S]GTPγS assays were used to determine the agonist or antagonist properties of l-THBr at dopamine (D₁, D₂) or serotonin (5-HT) receptors. Our results show that l-THBr displays D₁ and D₂ antagonist and 5-HT_1A agonist properties. Moreover, l-THBr-treated rodents exhibit anxiolytic-like effects in the light/dark box and elevated plus-maze tests, and the anxiolytic effect of l-THBr can be reduced by WAY-100635, a selective 5-HT_1A receptor antagonist. Our results suggest that l-THBr may produce potent anxiolytic-like effects mainly through serotonin receptors.

5-HT2C receptors in psychiatric disorders: A review

5-HT2Rs have a different genomic organization from other 5-HT2Rs. 5HT2CR undergoes post-transcriptional pre-mRNA editing generating diversity among RNA transcripts. Selective post-transcriptional editing could be involved in the pathophysiology of psychiatric disorders through impairment in G-protein interactions. Moreover, it may influence the therapeutic response to agents such as atypical antipsychotic drugs. Additionally, 5-HT2CR exhibits alternative splicing. Central serotonergic and dopaminergic systems interact to modulate normal and abnormal behaviors. Thus, 5HT2CR plays a crucial role in psychiatric disorders. 5HT2CR could be a relevant pharmacological target in the treatment of neuropsychiatric disorders. The development of drugs that specifically target 5-HT2C receptors will allow for better understanding of their involvement in the pathophysiology of psychiatric disorders including schizophrenia, anxiety, and depression. Among therapeutic means currently available, most drugs used to treat highly morbid psychiatric diseases interact at least partly with 5-HT2CRs. Pharmacologically, 5HT2CRs, have the ability to generate differentially distinct response signal transduction pathways depending on the type of 5HT2CR agonist. Although this receptor property has been clearly demonstrated, in vitro, the eventual beneficial impact of this property opens new perspectives in the development of agonists that could activate signal transduction pathways leading to better therapeutic efficiency with fewer adverse effects.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

Selective recognition of 5-hydroxytryptamine and dopamine on a multi-walled carbon nanotube-chitosan hybrid film-modified microelectrode array

It is difficult to determine dopamine (DA) and 5-hydroxytryptamine (5-HT) accurately because of the interference of ascorbic acid (AA) in vitro, which has a high concentration and can be oxidized at a potential close to DA and 5-HT at a conventional electrode, combined with the overlapping voltammetric signal of DA and 5-HT at a bare electrode. Herein, chitosan (CS) was used as a stabilizing matrix by electrochemical reaction, and multi-walled carbon nanotubes (MWCNTs) were modified onto the microelectrode array (MEA). The CS-MWCNT hybrid film-modified MEA was quite effective at simultaneously recognizing these species in a mixture and resolved the overlapping anodic peaks of AA, DA and 5-HT into three well-defined oxidation peaks in differential pulse voltammetry (DPV) at −80 mV, 105 mV and 300 mV (versus Ag|AgCl), respectively. The linear responses were obtained in the range of 5 × 10⁻⁶ M to 2 × 10⁻⁴ M for DA (r = 0.996) and in the range of 1 × 10⁻⁵ M to 3 × 10⁻⁴ M for 5-HT (r = 0.999) using the DPV under the presence of a single substance. While DA coexisted with 5-HT in the interference of 3 × 10⁻⁴ M AA, the linear responses were obtained in the range of 1 × 10⁻⁵ M to 3 × 10⁻⁴ M for selective molecular recognition of DA (r = 0.997) and 5-HT (r = 0.997) using the DPV. Therefore, this proposed MEA was successfully used for selective molecular recognition and determination of DA and 5-HT using the DPV, which has a potential application for real-time determination in vitro experiments.

Evidence for the involvement of 5-HT1A receptor in the acute antidepressant-like effect of creatine in mice

Creatine was previously shown to produce an antidepressant-like effect in the tail suspension test through a modulation of the dopaminergic system. In this study, the mechanisms underlying its antidepressant-like effect were further evaluated by investigating the involvement of the serotonergic system in its effect. The anti-immobility effect of creatine (1mg/kg) was prevented by the pretreatment of mice with p-chlorophenylalanine methyl ester (PCPA; 100mg/kg, i.p., for 4 consecutive days, an inhibitor of serotonin (5-HT) synthesis). Creatine (0.01 mg/kg, sub-effective dose) in combination with sub-effective doses of WAY100635 (0.1mg/kg, s.c., a 5-HT1A receptor antagonist), 8-OH-DPAT (0.1mg/kg, i.p., a 5-HT1A receptor agonist) or selective serotonin reuptake inhibitors fluoxetine (5mg/kg, p.o.), paroxetine (0.1mg/kg, p.o.), citalopram (0.1mg/kg, p.o.) and sertraline (3mg/kg, p.o.) reduced the immobility time in the tail suspension test as compared with either drug alone. These results indicate that the antidepressant-like effect of creatine is likely mediated by an interaction with 5-HT1A receptors. Of note, the present results also indicate that creatine improves the effectiveness of the selective serotonin reuptake inhibitors, a finding that may have therapeutic implications for the treatment of depressive disorders.

Abnormality of VTA local field potential in an animal model of depression was restored by patterned DBS treatment

Depressive disorders affect approximately 5% of the population in any given year. Deep brain stimulation (DBS) was previously shown to have a long-lasting normalizing effect on the ventral tegmental area (VTA) firing pattern in Flinders-Sensitive-Line (FSL) rats, an animal model for depression. In the current study, we aimed to find a possible electrophysiological mechanism that underlies this adaptation. Local-field-potential (LFP) time-series were recorded in the VTA of conscious, freely-moving FSL (depressive-like) and control Sprague-Dawley (SD) rats. We found that 42% of recordings both from FSL and SD rats showed clear peaks between 1-8Hz. Within these recordings, SD rats mostly demonstrated a single, uniform peak at frequencies of 1-3Hz. However, FSL rats demonstrated a significantly higher amount of recordings with double or triple peaks, at frequencies of 1-8Hz. In addition to the power spectrum, autocorrelation calculation of LFP recordings also showed significant differences between groups. We examined acute DBS of the VTA as a novel method for ameliorating these electrophysiological aberrations, in addition to attenuation of depressive-like behavior. The pattern of stimulation was fashioned to mimic the firing pattern of VTA neurons in control rats, as shown in previous work. The results suggest that treatment with programmed acute electrical stimulation of the VTA substantially restores VTA LFP in FSL rats to normal activity levels, parallel to alleviation of depressive-like behavior, for an extended period of time.

Selectively bred rodents as models of depression and anxiety

Stress related diseases such as depression and anxiety have a high degree of co morbidity, and represent one of the greatest therapeutic challenges for the twenty-first century. The present chapter will summarize existing rodent models for research in psychiatry, mimicking depression- and anxiety-related diseases. In particular we will highlight the use of selective breeding of rodents for extremes in stress-related behavior. We will summarize major behavioral, neuroendocrine and neuronal parameters, and pharmacological interventions, assessed in great detail in two rat model systems: The Flinders Sensitive and Flinders Resistant Line rats (FSL/FRL model), and rats selectively bred for high (HAB) or low (LAB) anxiety related behavior (HAB/LAB model). Selectively bred rodents also provide an excellent tool in order to study gene and environment interactions. Although it is generally accepted that genes and environmental factors determine the etiology of mental disorders, precise information is limited: How rigid is the genetic disposition? How do genetic, prenatal and postnatal influences interact to shape adult disease? Does the genetic predisposition determine the vulnerability to prenatal and postnatal or adult stressors? In combination with modern neurobiological methods, these models are important to elucidate the etiology and pathophysiology of anxiety and affective disorders, and to assist in the development of new treatment paradigms.

Influence and interaction of genetic polymorphisms in catecholamine neurotransmitter systems and early life stress on antidepressant drug response

BACKGROUND

Catecholamine neurotransmission plays an important role in major depression. Variation in genes implicated in the synthesis and signal transduction of catecholamines (norepinephrine and dopamine) may interact with environmental factors to affect the outcome of antidepressant treatment. We aimed to determine how a range of polymorphisms in noradrenergic and dopaminergic genes influence this response to treatment and how they interact with childhood trauma and recent life stress in a Chinese sample.

METHODS

In a sample of 308 Chinese Han patients with major depressive disorder, 13 single nucleotide polymorphisms (SNPs) in coding regions of six genes (MAOA, SLC6A2, TH, COMT, DRD2, DRD3) with minor allele frequencies >5% were successfully genotyped from an initial series of 35 SNPs in 11 candidate genes associated with catecholamine neurotransmission. The responses to 6 weeks' treatment with antidepressant drugs was determined by changes in the 17-item Hamilton Depression Rating Scale (HAMD-17) score, and previous stressful events were evaluated by the Life Events Scale (LES) and Childhood Trauma Questionnaire-Short Form (CTQ-SF). Single SNP and haplotype associations with treatment response were analysed by UNPHASED 3.0.13, gene-gene interactions were analysed by generalized multifactor dimensionality reduction (GMDR) and gene-environment interactions by logistic regression.

RESULTS

A haplotype in MAOA (rs1137070 and rs6323) was significantly associated with antidepressant response in the total group, the nonSSRI subgroup and the female subgroup. Two haplotypes in COMT (involving rs4633, rs4818 and rs769224) were significantly associated with antidepressant response in the nonSSRI subgroup. The SLC6A2 SNPs interacted with childhood trauma to influence antidepressant response.

CONCLUSIONS

A haplotype in MAOA and two haplotypes in COMT are found to be associated with antidepressant treatment response in this sample. Stressors in early life may interact with polymorphisms in SLC6A2 to influence response to antidepressant treatment.

Genetic lotteries within families

Drawing on findings from the biomedical literature, this paper introduces the idea that specific exogenously inherited differences in the genetic code between full biological siblings can be used to test within-family estimators and potentially improve our understanding of economic relationships. These points are illustrated with an application to identify the causal impact of several poor health conditions on academic outcomes. We present evidence that family fixed effects estimators by themselves cannot fully account for the endogeneity of poor health when estimating education production functions. Further, our analysis elucidates the situations under which genetic markers can serve as instrumental variables for specific health conditions.

Role of serotonin in central dopamine dysfunction

The interaction between serotonin (5-HT) and dopamine (DA)-containing neurons in the brain is a research topic that has raised the interest of many scientists working in the field of neuroscience since the first demonstration of the presence of monoamine-containing neurons in the mid 1960. The bulk of neuroanatomical data available clearly indicate that DA-containing neurons in the brain receive a prominent innervation from serotonin (5-hydroxytryptamine, 5-HT) originating in the raphe nuclei of the brainstem. Compelling electrophysiological and neurochemical data show that 5-HT can exert complex effects on the activity of midbrain DA neurons mediated by its various receptor subtypes. The main control seems to be inhibitory, this effect being more marked in the mesocorticolimbic DA system as compared to the DA nigrostriatal system. In spite of a direct effect of 5-HT by its receptors located on DA cells, 5-HT can modulate their activity indirectly, modifying gamma-aminobutyric (GABA)-ergic and glutamatergic input to the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). Although 5-HT/DA interaction in the brain has been extensively studied, much work remains to be done to clarify this issue. The recent development of subtype-selective ligands for 5-HT receptors will not only allow a detailed understanding of this interaction but also will lead to the development of new treatment strategies, appropriate for those neuropsychiatric disorders in which an alteration of the 5-HT/DA balance is supposed.

Programmed acute electrical stimulation of ventral tegmental area alleviates depressive-like behavior

Depressive disorders affect approximately 5% of the population in any given year. Antidepressants may require several weeks to produce their clinical effects. Despite progress being made in this area there is still room and a need to explore additional therapeutic modes to increase treatment effectiveness and responsiveness. Herein, we examined a new method for intervention in depressive states based on deep brain stimulation of the ventral tegmental area (VTA) as a source of incentive motivation and hedonia, in comparison to chemical antidepressants. The pattern of stimulation was fashioned to mimic the firing pattern of VTA neurons in the normal rat. Behavioral manifestations of depression were then monitored weekly using a battery of behavioral tests. The results suggest that treatment with programmed acute electrical stimulation of the VTA substantially alleviates depressive behavior, as compared to chemical antidepressants or electroconvulsive therapy, both in onset time and longitudinal effect. These results were also highly correlated with increases in brain-derived neurotrophic factor mRNA levels in the prefrontal cortex.

Reduced stress-sensitivity or increased reward experience: the psychological mechanism of response to antidepressant medication

Depression has often been associated with increased negative affect reactivity to stress (Stress-Sensitivity) and reduced capacity to experience pleasure or positive affect (Reward Experience). To date, no studies have prospectively examined changes in Stress-Sensitivity and Reward Experience following antidepressant treatment. The sample included 83 depressed patients and 22 healthy controls. A randomized controlled trial was carried out with patients receiving either imipramine or placebo for 6 weeks. At baseline and 6 weeks, patients and controls participated in an Experience Sampling procedure, prospectively measuring ecologically valid daily life appraisals of activities and mood states. The course of depression was assessed with the Hamilton Depression Rating Scale (HDRS). Multilevel linear regression analyses showed that patients had higher negative and lower positive appraisals of activities than controls. In addition, patients showed increased Stress-Sensitivity (negative affect reactivity to negatively appraised activities). Treatment with imipramine decreased Stress-Sensitivity and increased Reward Experience (positive affect reactivity to positively appraised activities). Changes in Stress-Sensitivity and Reward Experience were in part reducible to changes in the process of activity appraisal itself. However, increase in Reward Experience, but not decrease in Stress-Sensitivity, discriminated between patients who responded and those who did not, independent of changes in the process of activity appraisal itself. Response to treatment in depression may be conditional on restoration of hedonic capacity, the cerebral substrate of which requires further study in relation to antidepressant response. A search for (synergistic) antidepressant therapies specifically targeting ability to experience reward may be warranted.

The catechol-O-methyltransferase Val(108/158)Met polymorphism affects antidepressant response to paroxetine in a naturalistic setting

RATIONALE

The noradrenergic and dopaminergic systems are targets for antidepressants and are stimulated by serotonergic antidepressant drugs. The COMT enzyme inactivates catecholamines, and the COMT Val(108/158)Met polymorphism (rs4680) influences the enzyme activity. Clinical studies on the effect of rs4680 on antidepressant response gave contrasting results.

OBJECTIVES

We studied the effect of rs4680 on response to paroxetine antidepressant monotherapy at doses administered upon clinical need.

MATERIALS AND METHODS

Fifty-five consecutively referred outpatients affected by a major depressive episode without psychotic features in course of major depressive disorder were administered paroxetine at a mean daily dose of 31.64 mg for 1 month. Changes in severity of depression were assessed with weekly Hamilton depression ratings and analyzed with repeated measures analysis of variance in the context of general linear model, taking into account potential confounding variables (age, sex, number of previous illness episodes, duration of current episode and paroxetine daily dose).

RESULTS

rs4680 significantly interacted with time in affecting antidepressant response to paroxetine, with outcome being inversely proportional to the enzyme activity: better effects in Met/Met homozygotes, worse effects in Val/Val homozygotes and intermediate effects in heterozygotes. The effect became significant at the third week of treatment. Paroxetine daily dose was proportional to baseline severity, but did not influence outcome.

CONCLUSIONS

This is the first study that reports a positive effect of rs4680 on response to selective serotonin reuptake inhibitors monotherapy in a Caucasian sample. Our findings support the hypothesis that factors affecting catecholaminergic neurotransmission might contribute to shape the individual response to antidepressants.

Sustained administration of pramipexole modifies the spontaneous firing of dopamine, norepinephrine, and serotonin neurons in the rat brain

Pramipexole (PPX) is a D(2)/D(3) receptor agonist that has been shown to be effective in the treatment of depression. Serotonin (5-HT), norepinephrine (NE) and dopamine (DA) systems are known to be involved in the pathophysiology and treatment of depression. Due to reciprocal interactions between these neuronal systems, drugs selectively targeting one system-specific receptor can indirectly modify the firing activity of neurons that contribute to firing patterns in systems that operate via different neurotransmitters. It was thus hypothesized that PPX would alter the firing rate of DA, NE and 5-HT neurons. To test this hypothesis, electrophysiological experiments were carried out in anesthetized rats. Subcutaneously implanted osmotic minipumps delivered PPX at a dose of 1 mg/kg per day for 2 or 14 days. After a 2-day treatment with PPX the spontaneous neuronal firing of DA neurons was decreased by 40%, NE neuronal firing by 33% and the firing rate of 5-HT neurons remained unaltered. After 14 days of PPX treatment, the firing rate of DA had recovered as well as that of NE, whereas the firing rate of 5-HT neurons was increased by 38%. It was also observed that sustained PPX administration produced desensitization of D(2)/D(3) and 5-HT(1A) cell body autoreceptors, as well as a decrease in sensitivity of alpha(2)-adrenergic cell body autoreceptors. These adaptive changes are implicated in long-term firing rate adaptations of DA, NE and 5-HT neurons after prolonged PPX administration. In conclusion, the therapeutic action of PPX in depression might be attributed to increased DA and 5-HT neurotransmission.

DHEA lessens depressive-like behavior via GABA-ergic modulation of the mesolimbic system

Alterations in the levels of dehydroepiandrosterone (DHEA) in the brain can allosterically modulate gamma-aminobutyric-acid-type-A (GABA(A)R), N-methyl-D-aspartate (NMDAR), and Sigma-1 (sigma 1R) receptors. In humans, DHEA has antidepressive effects; however, the mechanism is unknown. We examined whether alterations in DHEA also occur in an animal model of depression, the Flinders-sensitive-line (FSL) rats, with the intention of determining the brain site of DHEA action and its antidepressant mechanism. We discovered that DHEA levels were lower in some brain regions involved with depression of FSL rats compared to Sprague-Dawley (SD) controls. Moreover, DHEA (1 mg/kg IP for 14 days)-treated FSL rats were more mobile in the forced swim test than FSL controls. In the NAc and VTA, significant changes were observed in the levels of the delta-subunit of GABA(A), but not of sigma 1R mRNA, in FSL rats compared to SD rats. The delta-subunit controls the sensitivity of the GABA(A)R to the neurosteroid. Indeed, treatment (14 days) of FSL rats with the GABA(A) agonist muscimol (0.5 mg/kg), together with DHEA (a negative modulator of GABA(A)), reversed the effect of DHEA on immobility in the swim test. Perfusion of DHEA sulfate (DHEAS) (3 nM and 30 nM for 14 days) into the VTA and NAc of FSL rats improved their performance in the swim test for at least 3 weeks post-treatment. Our results imply that alterations in DHEA are involved in the pathophysiology of depression and that the antidepressant action of DHEA is mediated via GABA(A)Rs in the NAc and VTA.

Depression, anhedonia, and psychomotor symptoms: the role of dopaminergic neurocircuitry

The heterogeneity of major depression suggests that multiple neurocircuits and neurochemicals are involved in its pathogenesis. Anhedonia and psychomotor symptoms are, however, particularly characteristic features of major depression and may provide insights into its underlying psychobiology. Importantly, these symptoms appear to be mediated by dopaminergic mesolimbic and mesostriatal projections, the function of which is, in turn, influenced by key gene variants and environment stressors. Indeed, there is growing evidence of the way in which the dopaminergic system is associated with cognitive-affective disturbances in depression, and provides a useful target for therapeutic interventions. At the same time, a range of other systems are likely to contribute to the psychobiology of this condition.

Dehydroepiandrosterone and monoamines in the limbic system of a genetic animal model of childhood depression

Monoamines and dehydroepiandrosterone (DHEA) levels were measured in a genetic animal model for childhood depression in four subcortical structures: nucleus accumbens (Nac), ventral tegmental area (VTA), amygdala and hypothalamus. The "depressive-like" strain was the Flinders Sensitive Line (FSL), compared to their controls, Sprague-Dawley (SD) rats. Prepubertal FSL rats showed abnormal levels of only a few monoamines and their metabolites in these brain regions. This is in contrast to former studies, in which adult FSL rats exhibited significantly higher levels of all the monoamines and their metabolites measured. These different abnormal monoamine patterns between the "depressed" prepubertal rats and their adults, may help to explain why depressed children and adolescents fail to respond to antidepressant treatment as well as adults do. On the other hand, FSL prepubertal rats exhibited the same pattern of abnormal DHEA basal levels as was found in adults in previous experiments. The results from the current study may imply that treatment with DHEA could be a promising novel therapeutic option for depressed children and adolescents that fail to respond to common (monoaminergic) antidepressant treatments.

Association of the COMT val158met variant with antidepressant treatment response in major depression

In several previous biochemical, pharmacological, and genetic studies, the catechol-O-methyltransferase (COMT) has been suggested to be involved in the pathogenesis as well as the pharmacological treatment of affective disorders. In the present study, 256 patients with major depression (DSM-IV) of Caucasian descent were genotyped for the functional COMT val158met polymorphism and characterized for clinical response to antidepressive pharmacological treatment as measured by intra-individual changes of Hamilton Depression (HAM-D-21) scores over 6 weeks. The COMT 158val/val genotype conferred a significant risk of worse response after 4-6 weeks of antidepressant treatment in patients with major depression (week 4: p=0.003; week 5: p<0.0001; week 6: p<0.0001) after Bonferroni correction for multiple comparisons. The present results strongly point toward a negative influence of the higher activity COMT 158val/val genotype on antidepressant treatment response during the first 6 weeks of pharmacological treatment in major depression, possibly conferred by consecutively decreased dopamine availability. This finding suggests a potentially beneficial effect of an antidepressive add-on therapy with substances increasing dopamine availability individually tailored according to COMT val158met genotype.

The reward system and maternal behavior in an animal model of depression: a microdialysis study

RATIONALE AND OBJECTIVES

Flinders sensitive line (FSL) rats, an animal model of depression, display a different pattern of maternal behavior compared to Sprague-Dawley (SD) controls. In this study, we examined the rewarding value of mother-infant interaction for FSL dams.

MATERIALS AND METHODS

In the main study, we measured monoamine levels in the nucleus accumbens (NAc) of early postpartum FSL and SD dams during an interaction with pups, using the microdialysis technique. In addition, we compared the preference patterns of FSL and SD rats using the conditioned place preference paradigm, with pups as the unconditioned stimuli.

RESULTS

Dopamine (DA) levels in dialysates from the NAc of SD dams but not FSL dams were elevated while interacting with pups but the metabolism of DA to dihydroxyphenylacetic acid was greater in FSL than in SD dams. While SD dams showed a conditioned preference for a region that was associated with SD pups, FSL dams did not show a preference for regions associated either with SD or FSL pups, but water deprived FSL rats demonstrated a preference to a region associated with water, eliminating an alternative explanation of learning deficit in FSL rats.

CONCLUSIONS

Taken together, these results suggest that FSL dams are less rewarded by pups, compared to control dams.

VTA dopamine neuron bursting is altered in an animal model of depression and corrected by desipramine

Ventral tegmental area (VTA) neuronal activity plays an important role in reward-related learning and motivation. Tracing the bursting signal is important for understanding neural state and understanding communication between individual neurons. The dopaminergic system, which projects from the VTA to other regions in the mesolimbic system, is involved in hedonia and motivation. However, the role of this system in the pathophysiology of depression and its manipulation for treatment of depression has received little attention. Inter-spike interval time series were recorded from the VTA of control Sprague-Dawley and Flinders sensitive line (FSL) rats with or without 14 days of desipramine (5 mg/kg) treatment. Comparison of the firing modes of control and desipramine-treated FSL rats reveals dissimilar patterns. Desipramine treatment normalized depressive-like behavior and elevated the dopaminergic mesolimbic activity, although not to control levels. Mesolimbic neuronal activity is known to occur either in burst or in single-spike firing mode. Herein, we suggest a third mode that is characterized as a "cluster" formed from burst and post-burst activity. A significant reduction in the activity of both bursts and cluster was detected in FSL rats, which was restored by desipramine treatment.