Distinct Effects of Escitalopram and Vortioxetine on Astroglial L-Glutamate Release Associated with Connexin43.

It has been established that enhancement of serotonergic transmission contributes to improvement of major depression; however, several post-mortem studies and experimental depression rodent models suggest that functional abnormalities of astrocytes play important roles in the pathomechanisms/pathophysiology of mood disorders. Direct effects of serotonin (5-HT) transporter inhibiting antidepressants on astroglial transmission systems has never been assessed in this context. Therefore, to explore the effects of antidepressants on transmission associated with astrocytes, the present study determined the effects of the selective 5-HT transporter inhibitor, escitalopram, and the 5-HT partial agonist reuptake inhibitor, vortioxetine, on astroglial L-glutamate release through activated hemichannels, and the expression of connexin43 (Cx43), type 1A (5-HT1AR) and type 7 (5-HT7R) 5-HT receptor subtypes, and extracellular signal-regulated kinase (ERK) in astrocytes using primary cultured rat cortical astrocytes in a 5-HT-free environment. Both escitalopram and 5-HT1AR antagonist (WAY100635) did not affect basal astroglial L-glutamate release or L-glutamate release through activated hemichannels. Subchronic (for seven days) administrations of vortioxetine and the 5-HT7R inverse agonist (SB269970) suppressed both basal L-glutamate release and L-glutamate release through activated hemichannels, whereas 5-HT1AR agonist (BP554) inhibited L-glutamate release through activated hemichannels, but did not affect basal L-glutamate release. In particular, WAY100635 did not affect the inhibitory effects of vortioxetine on L-glutamate release. Subchronic administration of vortioxetine, BP554 and SB269970 downregulated 5-HT1AR, 5-HT7R and phosphorylated ERK in the plasma membrane fraction, but escitalopram and WAY100635 did not affect them. Subchronic administration of SB269970 decreased Cx43 expression in the plasma membrane but did not affect the cytosol; however, subchronic administration of BP554 increased Cx43 expression in the cytosol but did not affect the plasma membrane. Subchronic vortioxetine administration increased Cx43 expression in the cytosol and decreased it in the plasma membrane. WAY100635 prevented an increased Cx43 expression in the cytosol induced by vortioxetine without affecting the reduced Cx43 expression in the plasma membrane. These results suggest that 5-HT1AR downregulation probably increases Cx43 synthesis, but 5-HT7R downregulation suppresses Cx43 trafficking to the plasma membrane. These results also suggest that the subchronic administration of therapeutic-relevant concentrations of vortioxetine inhibits both astroglial L-glutamate and Cx43 expression in the plasma membrane via 5-HT7R downregulation but enhances Cx43 synthesis in the cytosol via 5-HT1AR downregulation. This combination of the downregulation of 5-HT1AR, 5-HT7R and Cx43 in the astroglial plasma membrane induced by subchronic vortioxetine administration suggest that astrocytes is possibly involved in the pathophysiology of depression.

Central 5-HT neurotransmission modulates weight loss following gastric bypass surgery in obese individuals.

The cerebral serotonin (5-HT) system shows distinct differences in obesity compared with the lean state. Here, it was investigated whether serotonergic neurotransmission in obesity is a stable trait or changes in association with weight loss induced by Roux-in-Y gastric bypass (RYGB) surgery. In vivo cerebral 5-HT2A receptor and 5-HT transporter binding was determined by positron emission tomography in 21 obese [four men; body mass index (BMI), 40.1 ± 4.1 kg/m(2)] and 10 lean (three men; BMI, 24.6 ± 1.5 kg/m(2)) individuals. Fourteen obese individuals were re-examined after RYGB surgery. First, it was confirmed that obese individuals have higher cerebral 5-HT2A receptor binding than lean individuals. Importantly, we found that higher presurgical 5-HT2A receptor binding predicted greater weight loss after RYGB and that the change in 5-HT2A receptor and 5-HT transporter binding correlated with weight loss after RYGB. The changes in the 5-HT neurotransmission before and after RYGB are in accordance with a model wherein the cerebral extracellular 5-HT level modulates the regulation of body weight. Our findings support that the cerebral 5-HT system contributes both to establish the obese condition and to regulate the body weight in response to RYGB.

Mice with compromised 5-HTT function lack phosphotyrosine-mediated inhibitory control over prefrontal 5-HT responses.

The activity of the prefrontal cortex is essential for normal emotional processing and is strongly modulated by serotonin (5-HT). Yet, little is known about the regulatory mechanisms that control the activity of the prefrontal 5-HT receptors. Here, we found and characterized a deregulation of prefrontal 5-HT receptor electrophysiological signaling in mouse models of disrupted serotonin transporter (5-HTT) function, a risk factor for emotional and cognitive disturbances. We identified a novel tyrosine kinase-dependent mechanism that regulates 5-HT-mediated inhibition of prefrontal pyramidal neurons. We report that mice with compromised 5-HTT, resulting from either genetic deletion or brief treatment with selective serotonin reuptake inhibitors during development, have amplified 5-HT1A receptor-mediated currents in adulthood. These greater inhibitory effects of 5-HT are accompanied by enhanced downstream coupling to Kir3 channels. Notably, in normal wild-type mice, we found that these larger 5-HT1A responses can be mimicked through inhibition of Src family tyrosine kinases. By comparison, in our 5-HTT mouse models, the larger 5-HT1A responses were rapidly reduced through inhibition of tyrosine phosphatases. Our findings implicate tyrosine phosphorylation in regulating the electrophysiological effects of prefrontal 5-HT1A receptors with implications for neuropsychiatric diseases associated with emotional dysfunction, such as anxiety and depressive disorders.

On the role of 5-HT(1A) receptor gene in behavioral effect of brain-derived neurotrophic factor.

Experiments were made on a congenic AKR.CBA-D13Mit76C (76C) mouse strain created by transferring a chromosome 13 fragment containing the 5-HT1A receptor gene from a CBA strain to an AKR background. It was shown that 76C mice differed from AKR mice by decreased 5-HT1A receptor and tryptophan hydroxylase-2 (tph-2) genes expression in the midbrain. Functional activity of 5-HT2A receptors and 5-HT(2A) receptor mRNA levels in the midbrain and hippocampus of 76C mice were decreased compared with AKR mice. Central brain-derived neurotrophic factor (BDNF) administration (300 ng i.c.v.) reduced 5-HT1A and 5-HT(2A) receptor mRNA levels in the frontal cortex and tph-2 mRNA level in the midbrain of AKR mice. However, BDNF failed to produce any effect on the expression of 5-HT(1A) , 5-HT(2A) , and tph-2 genes in 76C mice but decreased functional activity of 5-HT(2A) receptors in 76C mice and increased it in AKR mice. BDNF restored social deficiency in 76C mice but produced asocial behavior (aggressive attacks towards young mice) in AKR mice. The data indicate that a small genetic variation altered the response to BDNF and show an important role of 5-HT(1A) receptor gene in the 5-HT system response to BDNF treatment and in behavioral effects of BDNF.

Synthesis and evaluation of novel 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives as potential antidepressants.

A series of 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives were synthesized and the target compounds were evaluated for their binding affinities at the 5-HT1A receptor and serotonin transporter. Antidepressant-like activities of the compounds were screened using the tail suspension and forced swim tests in mice. Preliminary results indicated that the target compounds exhibited high binding affinities at the 5-HT1A receptor and serotonin transporter, and produced marked antidepressant-like effects. The best example from this study, compound 5, exhibited high binding affinities for the 5-HT1A receptor (Ki = 96 nM) and serotonin transporter (Ki = 9.8 nM). The intrinsic activity of compound 5 showed agonistic property to the 5-HT1A receptor and inhibition of the 5-HT transporter. Furthermore, compound 5 exhibited greater antidepressant efficacy than fluoxetine and showed acceptable pharmacokinetic properties.

Alterations in the brain serotonin system and serotonin-regulated behavior during aging in zebrafish males and females.

The brain serotonin (5-HT) system performs a neurotrophic function and supports the plasticity of the nervous system, while its age-related changes can increase the risk of senile neurodegeneration. Zebrafish brain is highly resistant to damage and neurodegeneration due to its high regeneration potential and it is a promising model object in searching for molecular factors preventing age-related neurodegeneration. In the present study alterations in 5-HT-related behavior in the home tank and the novel tank diving test, as well as 5-HT, 5-HIAA levels, tryptophan hydroxylase (TPH), monoamine oxidase (MAO) activity and the expression of genes encoding TPH, MAO, 5-HT transporter and 5-HT receptors in the brain of 6, 12, 24 and 36 month old zebrafish males and females are investigated. Marked sexual dimorphism in the locomotor activity in the novel tank test is revealed: females of all ages move slower than males. No sexual dimorphism in 5-HT-related traits is observed. No changes in 5-HT and 5-HIAA levels in zebrafish brain during aging is observed. At the same time, the aging is accompanied by a decrease in the locomotor activity, TPH activity, tph2 and htr1aa genes expression as well as an increase in the MAO activity and slc6a4a gene expression in their brain. These results indicate that the brain 5-HT system in zebrafish is resistant to age-related alterations.

Butyrate acts as a positive allosteric modulator of the 5-HT transporter to decrease availability of 5-HT in the ileum.

BACKGROUND AND PURPOSE: Radiation therapy-induced gastrointestinal distress is partly associated with the elimination of gut microbiota. The effectiveness of 5-HT receptor antagonists to treat radiation therapy-induced emesis implies a pathophysiological role of 5-HT. Peripheral 5-HT is derived from intestinal epithelium. We have investigated the role of gut microbiota in regulating intestinal 5-HT availability. EXPERIMENTAL APPROACH: A radiation therapy murine model accompanied by faecal microbiota transplantation from donors fed different diets was investigated, and mouse ileal organoids were used for mechanistic studies. The clinical relevance was validated by a small-scale human study. KEY RESULTS: Short-term high-fat diet (HFD) induced gut bacteria to produce butyrate. Irradiated mice receiving HFD-induced microbiome had the lowest ileal levels of 5-HT, compared with other recipients. Treatment with butyrate increased 5-HT uptake in mouse ileal organoids, assayed by the real-time tracking of a fluorescent substrate for monoamine transporters. Silencing the 5-HT transporter (SERT) in the organoids abolished butyrate-stimulated 5-HT uptake. The competitive tests using different types of selective 5-HT reuptake inhibitors suggested that butyrate acted as a positive allosteric modulator of SERT. In human gut microbiota, butyrate production was associated with the interconversion between acetate and butyrate. Faecal contents of both acetate and butyrate were negatively associated with serum 5-HT, but only butyrate was positively correlated with body mass index in humans. CONCLUSION AND IMPLICATIONS: Short-term HFD may be beneficial for alleviating gastrointestinal reactions by increasing butyrate to suppress local 5-HT levels and providing energy to cancer patients given radiation therapy.

Effect of glial cell line-derived neurotrophic factor on behavior and key members of the brain serotonin system in mouse strains genetically predisposed to behavioral disorders.

The effect of glial cell line-derived neurotrophic factor (GDNF) on behavior and on the serotonin (5-HT) system of a mouse strain predisposed to depressive-like behavior, ASC/Icg (Antidepressant Sensitive Cataleptics), in comparison with the parental "nondepressive" CBA/Lac mice was studied. Within 7 days after acute administration, GDNF (800 ng, i.c.v.) decreased cataleptic immobility but increased depressive-like behavioral traits in both investigated mouse strains and produced anxiolytic effects in ASC mice. The expression of the gene encoding the key enzyme for 5-HT biosynthesis in the brain, tryptophan hydroxylase-2 (Tph-2), and 5-HT1A receptor gene in the midbrain as well as 5-HT2A receptor gene in the frontal cortex were increased in GDNF-treated ASC mice. At the same time, GDNF decreased 5-HT1A and 5-HT2A receptor gene expression in the hippocampus of ASC mice. GDNF failed to change Tph2, 5-HT1A , or 5-HT2A receptor mRNA levels in CBA mice as well as 5-HT transporter gene expression and 5-HT1A and 5-HT2A receptor functional activity in both investigated mouse strains. The results show 1) a GDNF-induced increase in the expression of key genes of the brain 5-HT system, Tph2, 5-HT1A , and 5-HT2A receptors, and 2) significant genotype-dependent differences in the 5-HT system response to GDNF treatment. The data suggest that genetically defined cross-talk between neurotrophic factors and the brain 5-HT system underlies the variability in behavioral response to GDNF.

[Correlation between curative effect and 5-HTTLPR polymorphism in treatment of diarrhea-predominant irritable bowel syndrome with acupuncture for regulating shen and strengthening spleen].

OBJECTIVE: To compare the curative effect on diarrhea-predominant irritable bowel syndrome (IBS-D) between acupuncture for regulating shen and strengthening spleen and pinaverium bromide, and explore the relevant mechanism of curative effect of acupuncture in view of polymorphism of 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR). METHODS: A total of 231 patients with IBS-D were randomized into an acupuncture group (154 cases) and a western medication group (77 cases) at the ratio of 2 to 1. In the acupuncture group, acupuncture was applied to acupoint regimen for regulating shen and strengthening spleen, i.e. Baihui (GV 20), Yintang (GV 29), Tianshu (ST 25), Shangjuxu (ST 37) and Zusanli (ST 36), etc. The treatment was given once every 2 days, 3 times a week. In the western medication group, pinaverium bromide was prescribed for oral administration, 50 mg each time, 3 times daily. The duration of treatment was 6 weeks in each group. Separately, before treatment, after treatment and in 3-month follow-up, the IBS symptom severity scale (IBS-SSS) and IBS quality of life scale (IBS-QOL) scores were adopted in assessment. After treatment, the curative effect and safety were compared between the two groups. Before treatment, 5-HTTLPR genotypes were determined in the patients. RESULTS: After treatment and in follow-up, the total scores of IBS-SSS in the patients of the two groups were all reduced as compared with those before treatment (P<0.01) and the scores in the acupuncture group were lower than those in the western medication group (P<0.01). After treatment and in follow-up, the total scores of IBS-QOL in the two groups were all increased as compared with those before treatment (P<0.01) and the score in the acupuncture group was higher than the western medication group in follow-up (P<0.01). The total effective rate was 79.2% (122/154) in the acupuncture group, higher than 58.4% (45/77) in the western medication group (P<0.01). There was no severe adverse reaction found in the two groups. The difference in the total score of IBS-SSS before and after treatment in the patients with LS and SS genotypes was greater than that in the patients with LL in the acupuncture group (P<0.01). The difference in the total score of ISB-SSS before and after treatment in the patients with SS genotype was greater than that in the patients with LL in the western medication group (P<0.01). The difference in the total score of IBS-SSS before and after treatment in the patients with LS and SS genotypes in the acupuncture group was greater than that in the patients with the same genotypes in the western medication group (P<0.01). CONCLUSION: Acupuncture for regulating shen and strengthening spleen achieves the more curative effect on IBS-D as compared with pinaverium bromide. The acupuncture regimen effectively relieves the clinical symptoms and improves the quality of life in patients as well as presents a satisfactory long-term effect and safety. The clinical curative effect of acupuncture is correlated with 5-HTTLPR polymorphism, in which, the curative effect of acupuncture may be more effective in the patients with LS and SS genotypes.

Examination of associations between personality traits, and polymorphisms of MAO-A and 5-HTT with the severity of menopausal symptoms and depression levels.

The aim of the present study was to investigate the association between different personality traits with monoamine oxidase A (MAO-A) and serotonin transporter (5-HTT), and to examine their effects on the severity of menopause symptoms as well as the levels of depression in menopausal women. The study was designed as an analytical cross-sectional study, performed on 132 healthy post-menopausal women in Iran. Personality was assessed using the Revised Edition of the NEO Personality Index (Neuroticism-Extroversion-Openness-Five Factor Inventory). The symptoms score sheet, used for measuring menopausal symptoms, was used to classify the participants according to their menopausal symptoms. Furthermore, Beck Depression Inventory short version was also used to assess depressive symptoms. Examination of blood samples taken from all participants was to identify DNA polymorphisms of 5-HTT using PCR. The results of the present study showed that a high level of neuroticism (P<0.0001), low levels of extroversion (P<0.002), an openness to experience (P=0.039) and conscientiousness (P=0.001) were all positively associated with the severity of menopausal symptoms. In addition, a high level of neuroticism (P<0.0001), low levels of extroversion (P<0.0001), and a low level of agreeableness (P<0.024) and conscientiousness (P<0.0001) were all positively associated with depressive symptoms. There was no statistically significant association between MAO-A and 5-HTT polymorphisms with menopause and depression scores. Based on these results, there appears to be a significant association between personality traits with both depression and menopausal symptoms. Identification of homogeneous groups of women who are predisposed to depression and severe menopausal symptoms may allow for the implementation of early prevention programs.

Smoking moderates association of 5-HTTLPR and in vivo availability of serotonin transporters.

Although preclinical studies clearly indicate an effect of 5-HTTLPR genotype on 5-HT transporter (5-HTT) expression, studies in humans provided inconclusive results, hypothetically due to environmental factors and differences in individual behavior. For example, nicotine and other constituents of tobacco smoke elevate serotonin (5-HT) levels in the brain and may thereby cause homeostatic adaptations in 5-HTT availability that moderate effects of 5-HTTLPR genotype. To test whether 5-HTT availability in the midbrain is affected by smoking status and 5-HTTLPR genotype, we pooled data from prior studies on in vivo 5-HTT availability (BPND) measured with positron emission tomography (PET) and [11C]DASB. In total, we reanalyzed 5-HTT availability in 116 subjects using ANCOVA statistics. ROI analysis revealed that current smokers and non-smokers do not differ in midbrain BPND. Interestingly, smoking status significantly interacted with 5-HTTLPR genotype: active smoking was associated with reduced 5-HTT availability only in LL subjects but not in carriers of the S-allele. From the perspective of genotype effects, non-smokers showed the expected association with 5-HTTLPR, i.e. higher 5-HTT availability in LL subjects compared to carriers of the S-allele, whereas this pattern was actually reversed for active smokers. Our study indicates that smoking status moderates the association of 5-HTTLPR genotype and 5-HTT expression, which may help to explain inconsistent findings in previous studies. Regarding the mechanism, we suggest that smoking may induce epigenetic processes such as methylation of SLC6A4, which can differ depending on its genetic constitution.

In vitro pharmacology of ambroxol: Potential serotonergic sites of action.

AIMS: Ambroxol is a muco-active agent with multiple, clinically relevant effects in the airway. Despite its widespread use and well documented clinical efficacy, there are few data on its mechanism of action and receptor pharmacology beyond sodium channel blockade and inhibition of guanylate cyclase. Accordingly, in vitro studies were conducted to determine its overall receptor pharmacology and possible sites of action. MATERIALS AND METHODS: In vitro radioligand binding/enzyme inhibition studies were conducted at 62 receptors, ion channels and enzymes using standard techniques. Additional in vitro studies were conducted to establish the potency of ambroxol at selected sites. KEY FINDINGS: These studies indicate that ambroxol has affinity for the 5-HT3 serotonin receptor, as well as affinity for the 5-HT serotonin transporter (SERT), with IC50 values of 17,600 nM and 19,500 nM respectively. In vitro functional studies in isolated guinea pig colon indicate that ambroxol is a 5-HT3 serotonin receptor antagonist with an IC50 value of 36,000 nM. SIGNIFICANCE: Together, these studies indicate that ambroxol may exert its beneficial properties via antagonism of the 5-HT3 serotonin receptor and/or inhibition of serotonin uptake (5-HT transport: SERT), in addition to its reported effects at the sodium channel and guanylate cyclase.

Interplay between the key proteins of serotonin system in SSRI antidepressants efficacy.

INTRODUCTION: Selective serotonin reuptake inhibitors (SSRIs) are the most effective and most used antidepressant drugs. Acting by inhibiting serotonin (5-HT) transporter, SSRIs display a typical 3-4-week delay in their therapeutic effects, with nearly 40% of depressed patients remaining treatment-resistant. Recent evidence suggests complex interplay between 5-HT receptors and key proteins of 5-HT metabolism in molecular mechanisms of such delay and resistance to SSRIs. Area covered: This paper concentrates on the interplay between 5-HT receptors in the delay of therapeutic effect of SSRIs, and the interaction between tryptophan hydroxylase 2 and 5-HT transporter in the SSRI resistance. Specifically, it discusses: (1) the data on the association between antidepressant drug efficacy and genetically defined characteristics of key proteins in the 5-HT signaling (TPH2, MAOA, SERT and 5-HT1A receptor), (2) the effect of dimerization of 5-HT7 and 5-HT1A receptors on the internalization and functioning of 5-HT1A presynaptic receptors, (3) the role of Tph2 deficiency in the resistance to SSRIs treatment. We shift the emphasis from individual proteins to their interactions in explaining antidepressant action of SSRI. Expert opinion: These interactions should be considered when developing more effective antidepressant drugs as well as for predicting and improving the efficacy of antidepressant therapies.

Tryptophan supplementation and serotonin function: genetic variations in behavioural effects.

The neurotransmitter serotonin has a role in affective disorders such as depression and anxiety, as well as sleep, cognitive function and appetite. This review examines the evidence that serotonin-related genotypes may moderate the behavioural effects of supplementation with the serotonin precursor amino acid l-tryptophan (TRP), on which synthesis of serotonin (or 5-hydroxytryptamine; 5-HT) depends. However, 95 % of serotonin is synthesised and used in the periphery, and TRP is also metabolised via non-5-HT routes such as the kynurenine pathway. Moreover, understanding of genotypes involved in regulation of serotonin raises questions over the generalisability of TRP effects on behaviour across individuals with varied serotonergic genotypes. To date, only differences between variants of the 5-HT transporter-linked promoter region (5-HTTLPR) have been investigated in relation to behavioural effects of TRP supplementation. Effects of 5-HTTLPR genotypes are usually compared between the alleles that are either high (L/L') or low (S/S') expressing of mRNA for the 5-HT transporter receptor. Yet, another key genetic variable is sex: in women, the S/S' genotype predicts sensitivity to improved mood and reduced cortisol by TRP supplementation, during stressful challenges, whereas the L/L' genotype protects against stress-induced mood deterioration. In men, the L/L' genotype may confer risk of stress-induced increases in negative affect; there are insufficient data to assess effects on male S/S' genotypes. However, better-powered studies to detect sex by genotype by stress by TRP interactions, as well as consideration of more genotypes, are needed before strong conclusions and recommendations for behavioural effects of TRP treatment can be reached.

Identification of novel serotonin reuptake inhibitors targeting central and allosteric binding sites: A virtual screening and molecular dynamics simulations study.

The serotonin (5-hydroxytryptamine, 5HT) transporter (SERT) is a member of neurotransmitter sodium symporter (NSS) family, which maintains neurotransmitter by reuptaking 5HT into synapses. Decrease in serotonin concentrations in synaptic clefts have been reported to cause psychological and neurological disorders. Therefore, inhibition of SERT is a potent strategy for the treatment of related diseases such as depression. In this study, approximately 260,000 small molecules from an available chemical database have been virtually screened both at central and allosteric binding sites of SERT to identify potent novel candidate SERT inhibitors. A set of docking algorithms were used to predict binding modes and energies of compounds. Screening analyses led three top-ranked hit compounds (160234, Otava ID: 7118020138; 159166, Otava ID: 7117171303; and 69419, Otava ID: 118671819) for central binding site (S1) and one compound (93507, Otava ID: 6248262) for allosteric binding site (S2). These promising compounds are then subjected to long multiple molecular dynamics (MD) simulations to elucidate their structural and dynamical profiles at the binding cavities of SERT. Higher predicted binding affinities of identified compounds were also confirmed with binding free energy calculations (MM/GBSA) in comparison with the reference central and allosteric binding site inhibitors, paroxetine (8PR) and escitalopram (68P), respectively. To the best of our knowledge, the present work is the first structure-based high throughput virtual screening study reported using recently revealed crystal structure of SERT for screening inhibitors from chemical databases on S1 and S2 binding sites. Small molecule library screening study yielded candidate compounds both at central and allosteric binding site of SERT, and further experimentation may pave the way for developing novel strong inhibitors.

Adaptive Control of Dorsal Raphe by 5-HT4 in the Prefrontal Cortex Prevents Persistent Hypophagia following Stress.

Transient reduced food intake (hypophagia) following high stress could have beneficial effects on longevity, but paradoxically, hypophagia can persist and become anorexia-like behavior. The neural underpinnings of stress-induced hypophagia and the mechanisms by which the brain prevents the transition from transient to persistent hypophagia remain undetermined. In this study, we report the involvement of a network governing goal-directed behavior (decision). This network consists of the ascending serotonergic inputs from the dorsal raphe nucleus (DR) to the medial prefrontal cortex (mPFC). Specifically, adult restoration of serotonin 4 receptor (5-HT4R) expression in the mPFC rescues hypophagia and specific molecular changes related to depression resistance in the DR (5-HT release elevation, 5-HT1A receptor, and 5-HT transporter reductions) of stressed 5-HT4R knockout mice. The adult mPFC-5-HT4R knockdown mimics the null phenotypes. When mPFC-5-HT4Rs are overexpressed and DR-5-HT1ARs are blocked in the DR, hypophagia following stress persists, suggesting an antidepressant action of early anorexia.

Protein Kinases Alter the Allosteric Modulation of the Serotonin Transporter In Vivo and In Vitro.

AIM: Studies using S- and R-enantiomers of the SSRI citalopram have shown that R-citalopram exerts an antagonistic effect on the efficacy of the antidepressant S-citalopram (escitalopram) through an interaction at an allosteric modulator site on the serotonin transporter (SERT). Here, we show that protein kinase signaling systems are involved in the allosteric modulation of the SERT in vivo and in vitro. METHODS: We assessed the effects of nonspecific protein kinase inhibitor staurosporine in the action of escitalopram and/or R-citalopram using electrophysiological and behavioral assays in rats and cell surface SERT expression measures in serotoninergic cells. RESULTS: Acute administration of R-citalopram counteracted the escitalopram-induced suppression of the serotonin (5-HT) neuronal firing activity and increase of the head twitches number following L-5-hydroxytryptophan injection. Importantly, these counteracting effects of R-citalopram were abolished by prior systemic administration of staurosporine. Interestingly, the preventing effect of staurosporine on 5-HT neuronal firing activity was abolished by direct activation of protein kinase C with phorbol 12-myristate 13-acetate. Finally, in vitro, quantification of the amount of cell surface-expressed SERT molecules revealed that R-citalopram prevented escitalopram-induced SERT internalization that was completely altered by staurosporine. CONCLUSION: Taken together, these results highlight for the first time an involvement of protein kinases in the allosteric modulation of SERT function.

Genetic dysfunction of serotonin 2A receptor hampers response to antidepressant drugs: A translational approach.

Pharmacological studies have yielded valuable insights into the role of the serotonin 2A (5-HT2A) receptor in major depressive disorder (MDD) and antidepressant drugs (ADs) response. However, it is still unknown whether genetic variants in the HTR2A gene affect the therapeutic outcome of ADs and the mechanism underlying the regulation of such response remains poorly described. In this context, a translational human-mouse study offers a unique opportunity to address the possibility that variations in the HTR2A gene may represent a relevant marker to predict the efficacy of ADs. In a first part of this study, we investigated in depressed patients the effect of three HTR2A single nucleotide polymorphisms (SNPs), selected for their potential functional consequences on 5-HT2A receptor (rs6313, rs6314 and rs7333412), on response and remission rates after 3 months of antidepressant treatments. We also explored the consequences of the constitutive genetic inactivation of the 5-HT2A receptor (i.e. in 5-HT2A(-/-) mice) on the activity of acute and prolonged administration of SSRIs. Our clinical data indicate that GG patients for the rs7333412 SNP were less prone to respond to ADs than AA/AG patients. In the preclinical study, we demonstrated that the 5-HT2A receptor exerts an inhibitory influence on the neuronal activity of the serotonergic system after acute administration of SSRIs. However, while the chronic administration of the SSRIs escitalopram or fluoxetine elicited a progressive increased in the firing rate of 5-HT neurons in 5-HT2A(+/+) mice, it failed to do so in 5-HT2A(-/-) mutants. These electrophysiological impairments were associated with a decreased ability of the chronic administration of fluoxetine to stimulate hippocampal plasticity and to produce antidepressant-like activities. Genetic loss of the 5-HT2A receptor compromised the activity of chronic treatment with SSRIs, making this receptor a putative marker to predict ADs response.

Animal models of the serotonin syndrome: a systematic review.

The serotonin syndrome (SS) is a potentially life-threatening disorder in humans which is induced by ingestion of an overdose or by combination of two or more serotonin (5-HT)-enhancing drugs. In animals, acute administration of direct and indirect 5-HT agonists also leads to a set of behavioral and autonomic responses. In the current review, we provide an overview of the existing versions of the animal model of the SS. With a focus on studies in rats and mice, we analyze the frequency of behavioral and autonomic responses following administration of 5-HT-enhancing drugs and direct 5-HT agonists administered alone or in combination, and we briefly discuss the receptor mediation of these responses. Considering species differences, we identify a distinct set of behavioral and autonomic responses that are consistently observed following administration of direct and indirect 5-HT agonists. Finally, we discuss the importance of a standardized assessment of SS responses in rodents and the utility of animal models of the SS in translational studies, and provide suggestions for future research.