Serotonin inhibition of tumor necrosis factor-alpha synthesis by human monocytes

Diminazene aceturate attenuates systemic inflammation via microbiota gut-5-HT brain-spleen sympathetic axis in male mice

The sympathetic arm of the inflammatory reflex is the efferent pathway through which the central nervous system (CNS) can control peripheral immune responses. Diminazene aceturate (DIZE) is an antiparasitic drug that has been reported to exert protective effects on various experimental models of inflammation. However, the pathways by which DIZE promotes a protective immunomodulatory effects still need to be well established, and no studies demonstrate the capacity of DIZE to modulate a neural reflex to control inflammation. C57BL/6 male mice received intraperitoneal administration of DIZE (2 mg/Kg) followed by lipopolysaccharide (LPS, 5 mg/Kg, i.p.). Endotoxemic animals showed hyperresponsiveness to inflammatory signals, while those treated with DIZE promoted the activation of the inflammatory reflex to attenuate the inflammatory response during endotoxemia. The unilateral cervical vagotomy did not affect the anti-inflammatory effect of DIZE in the spleen and serum. At the same time, splenic denervation attenuated tumor necrosis factor (TNF) synthesis in the spleen and serum. Using broad-spectrum antibiotics for two weeks showed that LPS modulated the microbiota to induce a pro-inflammatory profile in the intestine and reduced the serum concentration of tryptophan and serotonin (5-HT), while DIZE restored serum tryptophan and increased the hypothalamic 5-HT levels. Furthermore, the treatment with 4-Chloro-DL-phenylalanine (pcpa, an inhibitor of 5-HT synthesis) abolished the anti-inflammatory effects of the DIZE in the spleen. Our results indicate that DIZE promotes microbiota modulation to increase central 5-HT levels and activates the efferent sympathetic arm of the inflammatory reflex to control splenic TNF production in endotoxemic mice.

Deciphering psilocybin: Cytotoxicity, anti-inflammatory effects, and mechanistic insights

A decade of clinical research has indicated psilocybin's effectiveness in treating various neuropsychiatric disorders, such as depression and substance abuse. The correlation between increased pro-inflammatory cytokines and the severity of neuropsychiatric symptoms, along with the known anti-inflammatory potential of some psychedelics, suggests an immunomodulatory role for psilocybin. This study aims to understand the mechanism of action of psilocybin by investigating the cytotoxic and immunomodulatory effects of psilocybin and psilocin on both resting and LPS-activated RAW 264.7 murine macrophages. The study evaluated the cytotoxicity of psilocybin and psilocin using an LDH assay across various doses and assessed their impact on cytokine production in RAW 264.7 cells, measuring cytokine expression via ELISA. Different doses, including those above and below the LC50, were used in both pre-treatment and post-treatment approaches. The LDH assay revealed that psilocybin is almost twice as cytotoxic as psilocin, with an LC50 of 12 ng/ml and 28 ng/ml, respectively. In resting macrophages, both psilocybin and psilocin triggered significant release of TNF- α after 4 h, with the lowest doses inducing higher levels of the cytokine than the highest doses. IL-10 expression in resting cells was only triggered by the highest dose of psilocin in the 4-hour incubation group. In LPS-stimulated cells, psilocin reduced TNF- α levels more than psilocybin in pre-treatment and post-treatment, with no significant effects on IL-10 in pre-treatment. Psilocin, but not psilocybin, induced a significant increase of IL-10 in post-treatment, leading to the conclusion that psilocin, but not psilocybin, exerts anti-inflammatory effects on classically activated macrophages.

Role of Serotonergic System in Regulating Brain Tumor-Associated Neuroinflammatory Responses

Serotonin signaling regulates wide arrays of both neural and extra-neural functions. Serotonin is also found to affect cancer progression directly as well as indirectly by modulating the immune cells. In the brain, serotonin plays a key role in regulating various functions; disturbance of the normal activities of serotonin leads to various mental illnesses, including the neuroinflammatory response in the central nervous system (CNS). The neuroinflammatory response can be initiated in various psychological illnesses and brain cancer. Serotonergic signaling can impact the functions of both glial as well as the immune cells. It can also affect the tumor immune microenvironment and the inflammatory response associated with brain cancers. Apart from this, many drugs used for treatment of psychological illness are known to modulate serotonergic system and can cross the blood-brain barrier. Understanding the role of serotonergic pathways in regulating neuroinflammatory response and brain cancer will provide a new paradigm in modulating the serotonergic components in treating brain cancer and associated inflammation-induced brain damages.

The effect of antidepressants on the severity of COVID-19 in hospitalized patients: A systematic review and meta-analysis

INTRODUCTION

Clinical Depression and the subsequent low immunity is a comorbidity that can act as a risk factor for the severity of COVID-19 cases. Antidepressants such as Selective serotonin reuptake inhibitor and Serotonin-norepinephrine reuptake inhibitors are associated with immune-modulatory effects, which dismiss inflammatory responses and reduce lung tissue damage. The current systematic review and meta-analysis aims to evaluate the effect of antidepressant drugs on the prognosis and severity of COVID-19 in hospitalized patients.

METHODS

A systematic search was carried out in PubMed/Medline, EMBASE, and Scopus up to June 14, 2022. The following keywords were used: "COVID-19", "SARS-CoV-2", "2019-nCoV", "SSRI", "SNRI", "TCA", "MAOI", and "Antidepressant". A fixed or random-effect model assessed the pooled risk ratio (RR) with 95% CI. We considered P < 0.05 as statistically significant for publication bias. Data were analyzed by Comprehensive Meta-Analysis software, Version 2.0 (Biostat, Englewood, NJ).

RESULTS

Fourteen studies were included in our systematic review. Five of them were experimental with 2350, and nine of them were observational with 290,950 participants. Eight out of fourteen articles revealed the effect of antidepressants on reducing the severity of COVID-19. Selective serotonin reuptake inhibitors drugs, including Fluvoxamine, Escitalopram, Fluoxetine, and Paroxetine, and among the Serotonin-norepinephrine inhibitors medications Venlafaxine, are reasonably associated with reduced risk of intubation or death. Five studies showed no significant effect, and only one high risk of bias article showed the negative effect of antidepressants on the prognosis of Covid-19. The meta-analysis of clinical trials showed that fluvoxamine could significantly decrease the severity outcomes of COVID-19 (RR: 0.763; 95% CI: 0.602-0.966, I2: 0.0).

FINDINGS

Most evidence supports that the use of antidepressant medications, mainly Fluvoxamine, may decrease the severity and improve the outcome in hospitalized patients with SARS-CoV-2. Some studies showed contradictory findings regarding the effects of antidepressants on the severity of COVID-19. Further clinical trials should be conducted to clarify the effects of antidepressants on the severity of COVID-19.

Effect of sumatriptan on acetic acid-induced experimental colitis in rats: a possible role for the 5-HT1B/1D receptors

Mucosal inflammation in colitis is associated with changes in the intestinal serotonin (5-HT) level. Sumatriptan, a 5-HT_1B/1D receptor agonist, has demonstrated anti-inflammatory characteristics. The purpose of this study was to determine the effects of sumatriptan in a rat model of acute experimental colitis and to elucidate the probable participation of presynaptic 5-HT_1B/1D receptors. To induce colitis, acetic acid (4%) was injected intrarectally. Treatments were given intraperitoneally (IP) once daily over 3 consecutive days starting 1-h post-induction. Sumatriptan was given at 0.5, 1, 2, and 5 mg/kg. GR-127935, a 5-HT_1B/1D receptor antagonist, was injected (0.1 and 0.3 mg/kg) 30 min prior to the most effective dose of sumatriptan (1 mg/kg). On day 4, the colon samples were isolated. Significant enhancements of the tissue tumor necrosis factor-alpha (TNF-α), myeloperoxidase (MPO), microscopic and macroscopic damages, body weight losses, and also reductions in tissue superoxide dismutase (SOD) and 5-HT were observed in colitis rats. On the other hand, sumatriptan at doses 0.5, 1, and 2 mg/kg could diminish pathologic changes in the measured biomarkers, histopathologic damages, and body weight losses. Although GR-127935 at dose 0.3 mg/kg could markedly improve the pathologic indexes, its sub-effective dose (0.1 mg/kg) reversed the protective effect of sumatriptan (1 mg/kg). Moreover, sumatriptan (1 and 5 mg/kg) and GR-127935 (0.3 mg/kg) increased the serotonin level. Post-treatment with low-dose sumatriptan demonstrated a protective impact on this peripheral inflammatory condition. Notably, this protective effect may be mediated, at least in part, through 5-HT_1B/1D receptors, as well as anti-inflammatory and anti-oxidative characteristics.

Psychedelics and Anti-inflammatory Activity in Animal Models

The serotonin (5-hydroxytryptamine, 5-HT) 2A receptor is most well known as the common target for classic psychedelic compounds. Interestingly, the 5-HT_2A receptor is the most widely expressed mammalian serotonin receptor and is found in nearly every examined tissue type including neural, endocrine, endothelial, immune, and muscle, suggesting it could be a novel and pharmacological target for several types of disorders. Despite this, the bulk of research on the 5-HT_2A receptor is focused on its role in the central nervous system (CNS). Recently, activation of 5-HT_2A receptors has emerged as a new anti-inflammatory strategy. This review will describe recent findings regarding psychedelics as anti-inflammatory compounds, as well as parse out differences in functional selectivity and immune regulation that exist between a number of well-known hallucinogenic compounds.

The Bezold-Jarisch Reflex and The Inflammatory Response Modulation in Unanesthetized Endotoxemic Rats

Evidence indicates that the activation of the parasympathetic branch of the autonomic nervous system may be effective in treating inflammatory diseases. Previously, we have described that baroreflex activation displays anti-inflammatory properties. Analogous to the baroreflex, the Bezold-Jarisch reflex also promotes parasympathetic activation with simultaneous inhibition of the sympathetic system. Thus, the present study aimed to evaluate whether the activation of the Bezold-Jarisch reflex would also have the ability to reduce inflammation in unanesthetized rats. We used lipopolysaccharide (LPS) injection (5mg/kg, i.p.) to induce systemic inflammation in male Wistar Hannover rats and phenylbiguanide (PBG) administration (5μg/kg, i.v.) to activate the Bezold-Jarisch reflex. Spleen, heart, hypothalamus, and blood samples were collected to determine the levels of cytokines. Compared to baseline, PBG reduced the arterial pressure (115±2 vs. 88±5mmHg) and heart rate (380±7 vs. 114±26bpm), immediately after its administration, confirming the activation of the parasympathetic system and inhibition of the sympathetic system. From the immunological point of view, the activation of the Bezold-Jarisch reflex decreased the plasma levels of TNF (LPS: 775±209 vs. PBG + LPS: 248±30pg/ml) and IL-6 levels in the spleen (LPS: 39±6 vs. PBG + LPS: 24±4pg/mg of tissue). However, it did not change the other cytokines in the plasma or the other tissues evaluated. These findings confirm that the activation of the Bezold-Jarisch reflex can modulate inflammation and support the understanding that the cardiovascular reflexes regulate the immune system.

New insights into neuropeptides regulation of immune system and hemopoiesis: effects on hematologic malignancies

Several neurotransmitters and neuropeptides were reported to join to or to cooperate with different cells of the immune system, bone marrow, and peripheral cells and numerous data support that neuroactive molecules might control immune system activity and hemopoiesis operating on lymphoid organs, and the primary hematopoietic unit, the hematopoietic niche. Furthermore, many compounds seem to be able to take part to the leukemogenesis and lymphomagenesis process, and in the onset of multiple myeloma. In this review, we will assess the possibility that neurotransmitters and neuropeptides may have a role in the onset of haematological neoplasms, may affect the response to treatment or may represent a useful starting point for a new therapeutic approach. More in vivo investigations are needed to evaluate neuropeptide's role in haematological malignancies and the possible utilization as an antitumor therapeutic target. Comprehending the effect of the pharmacological administration of neuropeptide modulators on hematologic malignancies opens up new possibilities in curing clonal hematologic diseases to achieve more satisfactory outcomes.

Elevated serotonin alters whole-blood expression of serotonin receptor and metabolism genes in the lactating dairy cow

Serotonin's role as a hormone has been demonstrated through modulating calcium metabolism, energy homeostasis, and immune function in the preweaned and lactating bovine. Recently, manipulation of the serotonergic axis in calves via administration of 5-hydroxy-l-tryptophan (5-HTP), the serotonin precursor, elicited immunomodulatory effects and regulated serotonin transport and metabolism genes in leukocytes. However, serotonin's ability to modulate whole-blood gene expression in lactating dairy cows is unknown. Our objective was to explore the effect of infusing 5-HTP on whole-blood expression of genes regulating serotonin transport (reuptake transporter), signaling (receptors), metabolism (synthesis and degradation), and cytokines in dairy cows. Twelve lactating multiparous Holstein dairy cows were blocked by parity, milk production, and days in milk in a randomized complete block design and randomly assigned to intravenous infusion of either 1 L of 1.5 mg/kg 5-HTP dissolved in saline (n = 6) or 1 L of saline solution (n = 6) for 3 consecutive days. Whole blood was collected at 48, 56, and 72 h relative to termination of first infusion to analyze whole-blood gene expression. Infusion of 5-HTP increased whole-blood mRNA expression of monoamine oxidase-A and serotonin receptor 7 across the experimental period. Forty-eight hours from termination of first infusion, the mRNA of monoamine oxidase-A, serotonin reuptake transporter, and serotonin receptor 7 were increased in blood relative to the control. Interleukin-8 concentrations and mRNA were unchanged in response to 5-HTP infusion. Collectively, these data suggest that infusion of 5-HTP may alter mRNA of serotonin metabolism, transport, and signaling genes in whole blood of lactating dairy cows.

Drug repurposing of selective serotonin reuptake inhibitors: Could these drugs help fight COVID-19 and save lives?

The current 2019 novel coronavirus disease (COVID-19), an emerging infectious disease, is undoubtedly the most challenging pandemic in the 21st century. A total of 92,977,768 confirmed cases of COVID-19 and 1,991,289 deaths were reported globally up to January 14, 2021. COVID-19 also affects people's mental health and quality of life. At present, there is no effective therapeutic strategy for the management of this disease. Therefore, in the absence of a specific vaccine or curative treatment, it is an urgent need to identify safe, effective and globally available drugs for reducing COVID-19 morbidity and fatalities. In this review, we focus on selective serotonin reuptake inhibitors (SSRIs: a class of antidepressant drugs with widespread availability and an optimal tolerability profile) that can potentially be repurposed for COVID-19 and are currently being tested in clinical trials. We also summarize the existing literature on what is known about the link between serotonin (5-HT) and the immune system. From the evidence reviewed here, we propose fluoxetine as an adjuvant therapeutic agent for COVID-19 based on its known immunomodulatory, anti-inflammatory and antiviral properties. Fluoxetine may potentially reduce pro-inflammatory chemokine/cytokines levels (such as CCL-2, IL-6, and TNF-α) in COVID-19 patients. Furthermore, fluoxetine may help to attenuate neurological complications of COVID-19.

Serotonin and dopamine receptors profile on peripheral immune cells from patients with temporal lobe epilepsy

The role of inflammation and immune cells has been demonstrated in neurological diseases, including epilepsy. Leukocytes, as well as inflammatory mediators, contribute to abnormal processes that lead to a reduction in seizure threshold and synaptic reorganization. In this sense, identifying different phenotypes of circulating immune cells is essential to understanding the role of these cells in epilepsy. Immune cells can express a variety of surface markers, including neurotransmitter receptors, such as serotonin and dopamine. Alteration in these receptors expression patterns may affect the level of inflammatory mediators and the pathophysiology of epilepsy. Therefore, in the current study, we evaluated the expression of dopamine and serotonin receptors on white blood cells from patients with temporal lobe epilepsy with hippocampal sclerosis (TLE-HS). Blood samples from 17 patients with TLE-HS and 21 controls were collected. PBMC were isolated and stained ex vivo for flow cytometry. We evaluated the expression of serotonin (5-HT_1A, 5-HT_1B, 5-HT₂, 5-HT_2B, 5-HT_2C, 5-HT₃, 5-HT₄), and dopamine receptors (D₁, D₂, D₃, D₄, and D₅) on the cell surface of lymphocytes and innate immune cells (monocytes and granulocytes). Our results demonstrated that innate cells and lymphocytes from patients with TLE-HS showed high mean fluorescent intensity (MFI) for 5-HT_1A, 5-HT_1B, 5-HT_2A, and 5-HT₄ compared to controls. No difference was observed for 5-HT_2B. For dopamine receptors, the expression of D₁, D₂, D_4, and D₅ receptors was higher on innate cells from patients with TLE-HS when compared to controls for the MFI. Regarding lymphocytes population, D₂ expression was increased in patients with TLE-HS. In conclusion, there are alterations in the expression of serotonin and dopamine receptors on immune blood cells of patients with TLE-HS. Although the biological significance of these findings still needs to be further investigated, these changes may contribute to the understanding of TLE-HS pathophysiology.

Sumatriptan reduces severity of status epilepticus induced by lithium-pilocarpine through nitrergic transmission and 5-HT1B/D receptors in rats: A pharmacological-based evidence

Status epilepticus (SE) is a life-threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti-inflammatory property of the anti-migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole-induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium-pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5-hydroxytryptamin 1B/1D (5-HT_1B/1D ) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001-1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5-HT_1B/1D antagonist GR-127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor-α (TNF-α) and NO levels were markedly elevated in the rats' brain tissues post-SE induction, pre-treatment with sumatriptan significantly reduced both TNF-α (P < 0.05) and NO (P < 0.001) levels. Combined GR-127935 and sumatriptan treatment inhibited these anti-inflammatory effects of sumatriptan, whereas combined non-specific NOS (L-NAME) or selective neuronal NOS (7-nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5-HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.

Monocyte mobilisation, microbiota & mental illness

The gastrointestinal microbiome has emerged as a key player in regulating brain and behaviour. This has led to the strategy of targeting the gut microbiota to ameliorate disorders of the central nervous system. Understanding the underlying signalling pathways in which the microbiota impacts these disorders is crucial for the development of future therapeutics for improving CNS functionality. One of the major pathways through which the microbiota influences the brain is the immune system, where there is an increasing appreciation for the role of monocyte trafficking in regulating brain homeostasis. In this review, we will shed light on the role of monocyte trafficking as a relay of microbiota signals in conditions where the central nervous system is in disorder, such as stress, peripheral inflammation, ageing, traumatic brain injury, stroke, multiple sclerosis, Alzheimer's disease and Parkinson's disease. We also cover how the gastrointestinal microbiota is implicated in these mental illnesses. In addition, we aim to discuss how the monocyte system can be modulated by the gut microbiota to mitigate disorders of the central nervous system, which will lead to novel microbiota-targeted strategies.

The effect of Toxoplasma gondii on plasma serotonin concentration in sheep

Background and Aim

Toxoplasma gondii is an intracellular parasite that commonly infects warm-blooded animals, including humans. Virtually all species can be infected, but a species-specific variability is evident, in terms of both type and severity of the symptoms encountered. As serotonin (5-hydroxytryptamine [5-HT]) plays an important regulatory role in both physiological and immune responses, the aim of this research was to assess whether toxoplasmosis disease could affect plasma 5-HT concentration and/or hematochemical parameters in a particularly susceptible species to infection as sheep.

Materials and Methods

5-HT plasma levels were analyzed in platelet-poor plasma fraction by enzyme-linked immunosorbent assay. Blood count and hematochemical parameters were evaluated. Total proteins (TPs), glucose (Glu), and lactate dehydrogenase were determined by a spectrophotometer.

Results

Results showed significantly higher levels in plasma 5-HT, monocytes, and TP and significantly lower levels of Glu, in infected sheep compared to the control group.

Conclusion

Results could support the hypothesis of an effect of toxoplasmosis infection on plasma 5-HT concentrations in sheep. More research is needed to assess the function of 5-HT in the regulation of infected sheep's immune responses.

Psychedelics as anti-inflammatory agents

Serotonin (5-hydroxytryptamine, 5-HT)_2A receptor agonists have recently emerged as promising new treatment options for a variety of disorders. The recent success of these agonists, also known as psychedelics, like psilocybin for the treatment of anxiety, depression, obsessive-compulsive disorder (OCD), and addiction, has ushered in a renaissance in the way these compounds are perceived in the medical community and populace at large. One emerging therapeutic area that holds significant promise is their use as anti-inflammatory agents. Activation of 5-HT_2A receptors produces potent anti-inflammatory effects in animal models of human inflammatory disorders at sub-behavioural levels. This review discusses the role of the 5-HT_2A receptor in the inflammatory response, as well as highlight studies using the 5-HT_2A agonist (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] to treat inflammation in cellular and animal models. It also examines potential mechanisms by which 5-HT_2A agonists produce their therapeutic effects. Overall, psychedelics regulate inflammatory pathways via novel mechanisms, and may represent a new and exciting treatment strategy for several inflammatory disorders.

Serotonin drives the acquisition of a profibrotic and anti-inflammatory gene profile through the 5-HT7R-PKA signaling axis

Peripheral serotonin (5-hydroxytryptamine, 5-HT) regulates cell growth and differentiation in numerous cell types through engagement of seven types of cell surface receptors (HTR1-7). Deregulated 5-HT/HTR levels contribute to pathology in chronic inflammatory diseases, with macrophages being relevant targets for the physio-pathological effects of 5-HT. In fact, 5-HT skews human macrophage polarization through engagement of 5-HT2BR and 5-HT7R receptors. We now report that 5-HT primes macrophages for reduced pro-inflammatory cytokine production and IFN type I-mediated signaling, and promotes an anti-inflammatory and pro-fibrotic gene signature in human macrophages. The acquisition of the 5-HT-dependent gene profile primarily depends on the 5-HT7R receptor and 5-HT7R-initiated PKA-dependent signaling. In line with the transcriptional results, 5-HT upregulates TGFβ1 production by human macrophages in an HTR7- and PKA-dependent manner, whereas the absence of Htr7 in vivo results in diminished macrophage infiltration and collagen deposition in a mouse model of skin fibrosis. Our results indicate that the anti-inflammatory and pro-fibrotic activity of 5-HT is primarily mediated through the 5-HT7R-PKA axis, and that 5-HT7R contributes to pathology in fibrotic diseases.

The Effects of Serotonin in Immune Cells

Serotonin [5-hydroxytryptamine (5-HT)] plays an important role in many organs as a peripheral hormone. Most of the body’s serotonin is circulating in the bloodstream, transported by blood platelets and is released upon activation. The functions of serotonin are mediated by members of the 7 known mammalian serotonin receptor subtype classes (15 known subtypes), the serotonin transporter (SERT), and by covalent binding of serotonin to different effector proteins. Almost all immune cells express at least one serotonin component. In recent years, a number of immunoregulatory functions have been ascribed to serotonin. In monocytes/macrophages, for example, serotonin modulates cytokine secretion. Serotonin can also suppress the release of tumor necrosis factor-α and interleukin-1β by activating serotonin receptors. Furthermore, neutrophil recruitment and T-cell activation can both be mediated by serotonin. These are only a few of the known immunomodulatory roles of serotonin that we will review here.

Serotonin and histamine mediate gastroprotective effect of fluoxetine against experimentally-induced ulcers in rats

Research in the treatment of gastric ulcer has involved the investigation of new alternatives, such as anti-depressant drugs. The present study was designed to investigate the gastroprotective effects of fluoxetine against indomethacin and alcohol induced gastric ulcers in rats and the potential mechanisms of that effect. Fluoxetine (20 mg/kg) was administered IP for 14 days. For comparative purposes, other rats were treated with ranitidine (30 mg/kg). Thereafter, after 24 h of fasting, INDO (100 mg/kg) or absolute alcohol (5 ml/kg) was administered to all rats (saline was administered to naïve controls) and rats in each group were sacrificed 5 h (for INDO rats) or 1 h (for alcohol rats) later. Macroscopic examination revealed that both fluoxetine and ranitidine decreased ulcer scores in variable ratios, which was supported by microscopic histopathological examination. Biochemical analysis of fluoxetine- or ranitidine-pre-treated host tissues demonstrated reductions in tumor necrosis factor (TNF)-α and myeloperoxidase (MPO) levels and concomitant increases in gastric pH, nitric oxide (NO) and reduced glutathione (GSH) contents. Fluoxetine, more than ranitidine, also resulted in serotonin and histamine levels nearest to control values. Moreover, immuno-histochemical analysis showed that fluoxetine markedly enhanced expression of cyclo-oxygenases COX-1 and COX-2 in both models; in comparison, ranitidine did not affect COX-1 expression in either ulcer model but caused moderate increases in COX-2 expression in INDO-induced hosts and high expression in alcohol-induced hosts. The results here indicated fluoxetine exhibited better gastroprotective effects than ranitidine and this could be due to anti-secretory, anti-oxidant, anti-inflammatory and anti-histaminic effects of the drug, as well as a stabilization of gastric serotonin levels.

Immune functions of platelets

This review collects evidence about immune and inflammatory functions of platelets from a clinician's point of view. A focus on clinically relevant immune functions aims at stimulating further research, because the complexity of platelet immunity is incompletely understood and not yet translated into patient care. Platelets promote chronic inflammatory reactions (e.g. in atherosclerosis), modulate acute inflammatory disorders such as sepsis and other infections (participating in the host defense against pathogens), and contribute to exacerbations of autoimmune conditions (like asthma or arthritis). It would hence be obsolete to restrict a description of platelet functions to thrombosis and haemostasis--platelets clearly are the most abundant cells with immune functions in the circulation.

Genetic variation in the serotonin receptor gene affects immune responses in rheumatoid arthritis

Many genetic variants associate with the risk of developing rheumatoid arthritis (RA); however, their functional roles are largely unknown. Here, we aimed to investigate whether the RA-associated serotonin receptor 2A (HTR2A) haplotype affects T-cell and monocyte functions. Patients with established RA (n=379) were genotyped for two single-nucleotide polymorphisms (SNPs) in the HTR2A locus, rs6314 and rs1328674, to define presence of the risk haplotype for each individual. Patients with and without the RA-associated TC haplotype were selected and T-cell and monocyte function was monitored following in vitro stimulations with staphylococcal enterotoxin B and lipopolysaccharide (LPS) using multiparameter flow cytometry. Within the cohort, 44 patients were heterozygous for the TC haplotype (11.6%) while none were homozygous. Upon stimulation, T cells from TC-carrier patients produced more proinflammatory cytokines (tumor necrosis factor alpha (TNF-α), interleukin-17 (IL-17) and interferon gamma (IFN-γ)) and monocytes produced higher levels of TNF-α compared with patients carrying the non-TC haplotype (P<0.05 and 0.01, respectively). Such cytokine production could be inhibited in the presence of the selective 5-HT2 receptor agonist (2,5-Dimethoxy-4-iodoamphetamine, DOI); interestingly, this effect was more pronounced in TC carriers. Our data demonstrate that association of RA with a distinct serotonin receptor haplotype has functional impact by affecting the immunological phenotype of T cells and monocytes.

β-Amyloid induced effects on cholinergic, serotonergic, and dopaminergic neurons is differentially counteracted by anti-inflammatory drugs

β-Amyloid (Aβ) is a small peptide that plays a potent role in synaptic plasticity as well as forms amyloid plaques in Alzheimer's disease (AD). Recent studies suggest that Aβ deposition is deleterious not only in AD, but also in Parkinson's disease (PD) and depression. This Aβ effect is associated with inflammatory processes. However, further evaluation is needed to understand how Aβ and inflammation interact and contribute to the regulation of the cholinergic, serotonergic, and dopaminergic neuronal populations. The aim of the present study was to investigate the effects of Aβ(1-42) on cholinergic neurons of the nucleus basalis of Meynert (which degenerate in AD), on serotonergic neurons of the dorsal raphe nucleus (which play a role in depression), and on dopaminergic neurons of the ventral mesencephalon (which degenerate in PD) in rat organotypic brain slices. Furthermore, we investigated whether anti-inflammatory drugs (celecoxib, citalopram, cyclooxygenase-2 inhibitor, ibuprofen, indomethacin, piclamilast) modulate or counteract Aβ-induced effects. Two-week-old organotypic brain slices of the nucleus basalis of Meynert, dorsal raphe nucleus, and ventral mesencephalon were incubated with 50 ng/ml Aβ(1-42) with or without anti-inflammatory agents for 3 days. Our results reveal that Aβ significantly decreased the number of choline acetyltransferase-positive cholinergic, tryptophan hydroxylase-positive serotonergic, and tyrosine hydroxylase-positive dopaminergic neurons and that anti-inflammatory drugs partially counteracted the Aβ-induced neuronal decline. This decline was not due to apoptotic processes (as evaluated by TUNEL, propidium iodide, caspase), oxidative stress (as measured by nitrite, catalase, or superoxide dismutase-2), or inflammation, but was most likely caused by a downregulation of these key enzymes.

Immunomodulatory effect of sertraline in a rat model of rheumatoid arthritis

OBJECTIVE

Previous studies suggest that selective serotonin reuptake inhibitors (SSRIs) modulate immune system functionality. SSRIs are the preferred treatment for major depressive disorder (MDD). A high rate of MDD is observed in rheumatoid arthritis (RA) patients. The aim of this study was to evaluate immunological effects of SSRIs in a rat model of RA.

METHODS

Adjuvant arthritis was induced in 8-week-old Lewis rats; in the first set of experiments following the induction, 15.3 or 30.6 mg/kg of sertraline was daily injected into the ankle joint of the left rear leg. Clinical disease activity was evaluated and the findings compared with the 3 untreated legs and with control groups given methotrexate (MTX) or vehicle only at the same site. In a second set of experiments, the effect of 5, 25 and 50 mg/kg daily oral sertraline was evaluated in the same rat model. Splenocyte viability and inflammatory mediators were evaluated.

RESULTS

The sertraline-treated rats showed a significant reduction in clinical arthritis compared to controls, at all doses given, accompanied by a significant increase in interleukin 10 and a decrease in tumor necrosis factor-α levels and cycloxygenase-2 production, without lymphotoxicity. There was no significant difference from MTX, the first-line treatment for RA patients. Oral sertraline had a significant anti-inflammatory effect at all doses. There was no treatment × time effect.

CONCLUSION

The beneficial effects of sertraline in this rat model of arthritis have clinical implications for its use in humans. Large-scale clinical efficacy trials are needed.

Beta-D-glucosidase-catalyzed deglucosidation of phenylpropanoid amides of 5-hydroxytryptamine glucoside in safflower seed extracts optimized by response surface methodology

Beta-D-glucosidase-catalyzed deglucosidation of phenylpropanoid amides of 5-hydroxytryptamine (PAHAs) glucoside in safflower (Carthamus tinctorius L.) seed extracts, including N-(p-coumaroyl)serotonin glucoside (CSG) and N-feruloylserotonin glucoside (FSG), was optimized by response surface methodology (RSM). The Box-Behken design (BBD) was employed to evaluate the interactive effects of independent variables on the deglucosidation rates of CSG and FSG. The variables involved were pH (5.6-6.2), temperature (45-55 degrees C), and enzyme load (2.0-3.0%, relative to the weight of the total substrate). The substrate concentration was fixed at 3.3 g/L on the basis of factorial experiments. The optimum conditions obtained via RSM at a fixed time of 2 h were as follows: pH, 5.9; temperature, 48 degrees C; and enzyme load, 3.0%. Under these conditions, the actual deglucosidation rates of CSG and FSG were 75.5 and 42.2%, respectively, which agree well with the predicted values (75.3 and 41.9%) by RSM. The final incubation time (10 h) was determined by the time course of the deglucosidation under the above-mentioned optimum conditions, which gave the deglucosidation rates of both CSG and FSG above 90%. Simultaneously, 2-hydroxyarctiin, a typical cathartic beta-glucoside, was also removed by 80.3%.

Oxidative stress parameters after combined fluoxetine and acetylsalicylic acid therapy in depressive patients

OBJECTIVE

There are numerous reports indicating disturbed equilibrium between oxidative processes and antioxidative defense in patients with depression. Moreover, depressive patients are characterized by the presence of elements of an inflammatory process, which is one of the sources of reactive oxygen species (ROS). In view of the above, it was decided to study both the effect of fluoxetine monotherapy and that of fluoxetine co-administered with acetylsalicylic acid on lipid peroxidation and antioxidative defense in patients with the first depressive episode in their life.

METHOD

Seventy seven patients with major depressive disorder (MDD), divided into two groups were included in the study. The first group, consisting of 52 patients, received fluoxetine 20 mg, and the second one, in addition to fluoxetine 20 mg, received 150 mg of acetylsalicylic acid. The activity of antioxidative enzymes, copper-zinc superoxide dismutase (CuZnSOD, SOD1), catalase (CAT), glutathione peroxidase (GPSH-x) and the concentration of malonyldialdehyde (MDA) was determined in erythrocytes, whereas the total antioxidant status (TAS) was determined in the plasma. All parameters were measured before and after three month therapy.

RESULTS

The obtained results indicate a significant decrease in the activity of SOD1, CAT and GSHP-x, as well as in MDA concentration after the combined therapy. Also a significant TAS increase was observed after the combined therapy. The study demonstrated that combined therapy with fluoxetine and ASA is characterized by the same efficacy and clinical safety as fluoxetine monotherapy, resulting additionally in improvement of oxidative stress parameters in the patients treated for depression.

Serotonin modulates the cytokine network in the lung: involvement of prostaglandin E2

Serotonin, well known for its role in depression, has been shown to modulate immune responses. Interestingly, the plasma level of serotonin is increased in symptomatic asthmatic patients and the use of anti-depressants, known to reduce serotonin levels, provokes a decrease in asthma symptoms and an increase in pulmonary function. Thus, we tested the hypothesis that serotonin affects alveolar macrophage (AM) cytokine production, altering the cytokine network in the lung and contributing to asthma pathogenesis. AMs were treated with different concentrations of serotonin (10(-11)-10(-9) M) or 5-HT(1) and 5-HT(2) receptor agonists for 2 h prior stimulation. T helper 1 (Th1) and Th2 cytokines, prostaglandin-E(2) (PGE(2)) and nitric oxide (NO) were measured in cell-free supernatants. Serotonin significantly inhibited the production of tumour necrosis factor (TNF) and interleukin (IL)-12, whereas IL-10, NO and PGE(2) production were increased. These immunomodulatory effects of serotonin were mimicked by 5-HT(2) receptor agonist but were not abrogated by 5-HT(2) receptor antagonist, suggesting the implication of other 5-HT receptors. Inhibitors of cyclooxygenase and antibody to PGE(2) abrogated the inhibitory and stimulatory effect of serotonin on TNF and IL-10 production, respectively, whereas NO synthase inhibitor eliminated serotonin-stimulated IL-10 increase. Furthermore, PGE(2) significantly increased AM IL-10 and NO production. These results suggest that serotonin alters the cytokine network in the lung through the production of PGE(2). The reduction of Th1-type cytokine by serotonin may contribute to asthma pathogenesis.

Effect of serotonin on the differentiation of human monocytes into dendritic cells

The local cytokine environment and presence of stimulatory signals determine whether monocytes acquire dendritic cell (DC) or macrophage characteristics and functions. Because enhanced platelet activation is reported in patients with many allergic disorders, such as atopic dermatitis, platelet-derived factors may influence monocytic differentiation into DC. In this study we examined the effect of serotonin, a prototypic mediator of allergic inflammation released mainly by activated platelets at the inflammatory site, on the granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4-driven differentiation of monocytes into monocyte-derived DC. Monocytes from healthy adult donors were cultured with GM-CSF and IL-4 in the presence or absence of serotonin, and the phenotypes and function of these cells were analysed. In the presence of serotonin, monocytes differentiated into DC with reduced expression of co-stimulatory molecules and CD1a, whereas expression of CD14 was increased. These serotonin-treated DC exhibited significantly reduced stimulatory activity toward allogeneic T cells. However, these cells showed enhanced cytokine-producing capacity, including IL-10 but not IL-12. There was no significant difference between both types of DC in phagocytic activity. Experiments using agonists and antagonists indicated that serotonin 5-hydroxytryptamine (5-HT) induced the alteration of their phenotype and reduction in antigen-presenting capacity were mediated via 5-HTR(1/7). It is therefore suggested that serotonin-driven DC may have a regulatory function in the inflammatory process.

The negative immunoregulatory effects of fluoxetine in relation to the cAMP-dependent PKA pathway

Recently, we have shown that various types of antidepressants, including selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, have negative immunoregulatory effects. These antidepressants suppress the interferon-gamma (IFN-gamma)/interleukin-10 (IL-10) production ratio, which is of critical importance for the determination of the capacity of immunocytes to inhibit or activate monocytic/lymphocytic functions. Since cyclic adenosine monophosphate (cAMP) production is stimulated by some antidepressants, and since cAMP inhibits IFN-gamma and stimulates IL-10 production, we postulate that the negative immunoregulatory effects of antidepressants result from their effects on the cAMP-dependent protein kinase A (PKA) pathway. The aim of the present study was to determine whether the negative immunoregulatory effects of fluoxetine may be blocked by antagonists of the cAMP-dependent PKA pathway, such as, e.g., SQ 22536, an adenylate cyclase inhibitor, and Rp-8-Br-cAMPs (Rp-isomer of 8-bromo-adenosine-3',5'-monophosphorothioate), a PKA antagonist. To this end, diluted whole blood collected from 17 normal volunteers was incubated with fluoxetine (10(-6) and 10(-5) M), with or without SQ 22536 (10(-6) and 10(-4) M) and Rp-8-Br-cAMPs (10(-6) and 10(-4) M), afterwards, IFN-gamma, IL-10 and the tumor necrosis factor alpha (TNF-alpha) were determined. Fluoxetine, 10(-6) and 10(-5) M, significantly reduced the production of IFN-gamma and TNF-alpha, and significantly decreased the IFN-gamma/IL-10 production ratio. SQ 22536 and Rp-8-Br-cAMPs were unable to block the suppressant effects of fluoxetine on the IFN-gamma/IL-10 ratio. Rp-8-Br-cAMPs, 10(-4), but not 10(-6) M, normalized the fluoxetine-induced suppression of TNF-alpha production. It is concluded that the suppressant effect of fluoxetine on the IFN-gamma/IL-10 production ratio is probably not related to the induction of the cAMP-dependent PKA pathway, whereas the suppressant effect on TNF-alpha may be related to the induction of PKA. The obtained results suggest that increased activation of the PKA-dependent pathway may constitute an important molecular basis for some (suppression of TNF-alpha production), but not all (suppression of IFN-gamma production), negative immunoregulatory effects of fluoxetine.

Effects of serotonin and serotonergic agonists and antagonists on the production of tumor necrosis factor alpha and interleukin-6

Serotonin (5-HT) is a neurotransmitter and immune modulator. The effect of 5-HT on the production of cytokines by human macrophages and lymphocytes is poorly recognized. In the present article we examine the role of 5-HT in modulating the production of two pro-inflammatory cytokines, i.e. interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFalpha), as well as the role of 5-HT(1A) and 5-HT(2) receptors in this process. The specific aims were to examine the effects of 5-HT, p-chlorophenylalanine (PCPA), a 5-HT depleting agent, flesinoxan, a 5-HT(1A) agonist, m-chlorophenylpiperazine (mCPP), a 5-HT(2B/2C) agonist, and ritanserin, a 5-HT(2A/2C) antagonist, on the production of the above cytokines. We found that: (1) 5-HT, 15 microg/ml, significantly decreased IL-6 and TNFalpha production; (2) pCPA, 5 microM, significantly suppressed the production of IL-6 and TNFalpha; and (3) mCPP, 2.7 microg/ml, significantly increased the production of IL-6 and TNFalpha. It is concluded that intracellular 5-HT is necessary for optimal synthesis of IL-6 and TNFalpha; 5-HT in physiological concentrations may increase IL-6 and TNFalpha production by stimulating 5-HT(2) receptors; and extracellular 5-HT concentrations above the baseline physiological levels may suppress the production of the above cytokines.

Chronic administration of tianeptine balances lipopolysaccharide-induced expression of cytokines in the spleen and hypothalamus of rats

The antidepressant tianeptine has been shown to protect the hippocampus against the deleterious consequences of stress and to attenuate the behavioral and neuroendocrine effects of the cytokine inducer lipopolysaccharide (LPS). Since sickness symptoms are linked to peripheral and brain production of cytokines and pro-inflammatory cytokines can promote neurotoxicity, the present study was undertaken to test the possibility that tianeptine attenuates production of pro-inflammatory cytokines. This hypothesis has been tested by studying the effects of a chronic intraperitoneal (i.p.) administration of tianeptine (10 mg/kg twice a day for 21 days) to rats on the induction by LPS (250 microg/kg, i.p.) of the production of pro- and anti-inflammatory cytokines, at the periphery (spleen, pituitary) and in the brain (hypothalamus, hippocampus). The expression of mRNAs coding for IL-1 beta, TNF-alpha, IL-6 or IL-10 (RT-PCR) and plasma levels of IL-1 beta, TNF-alpha and IL-10 (ELISA) were measured at various time intervals following LPS. Chronic tianeptine treatment attenuated LPS-induced expression of TNF-alpha in the spleen as well as plasma levels of this cytokine and altered the central balance between pro- and anti-inflammatory cytokines (IL-1 beta/IL-10). These results open new vistas in the pharmacological activity of tianeptine and provide further insights on the possible mechanisms of action involved in its neuroprotective properties.

Multiple mechanisms involved in the inhibition of proinflammatory cytokine production from human monocytes by N-(p-coumaroyl)serotonin and its derivatives

We have reported that N-(p-coumaroyl)serotonin(CS) isolated from safflower oil cake (Carthamus tinctorius L.) inhibits the production of proinflammatory cytokines by endotoxin (LPS)- stimulated human monocytes. In this study, the effects of CS and its three derivatives, N-(trans-cinnamoyl)serotonin (Cin.S), N-(trans-cinnamoyl)tryptamine (Cin.T), and N-(p-coumaroyl)tryptamine (CT) on the production of proinflammatory cytokines were compared. Cin.S possessed radical scavenging activity at a comparable level to CS, while CT and Cin.T exhibited lower activity, suggesting that hydroxyl group in serotonin is essential for the antioxidative activity. CS and CT strongly inhibited the production of proinflammatory cytokines (IL-1alpha, IL-1beta, IL-6, IL-8, and TNF-alpha) from LPS-stimulated human monocytes. However, Cin.S inhibited the production of only IL-1alpha and IL-1beta, and Cin.T inhibited none of these cytokines production. CS and CT markedly inhibited the protein synthesis in monocytes, the inhibitory effect of Cin.S was moderate, and that of Cin.T was quite weak. These results indicate that CS and its derivatives inhibit the production of proinflammatory cytokines through multiple mechanisms.

The relation of aggression, hostility, and anger to lipopolysaccharide-stimulated tumor necrosis factor (TNF)-alpha by blood monocytes from normal men

Aggression, hostility, and anger significantly predict morbidity and mortality from atherosclerotic cardiovascular disease (ACVD). ACVD is believed to be an inflammatory disease characterized by increased expression of a number of proinflammatory cytokines, such as tumor necrosis factor (TNF)-alpha. This study examined the relation of aggression, hostility, and anger to monocyte-associated TNF-alpha expression following lipopolysaccharide (LPS) stimulation. Participants were 62 healthy, non-smoking men (aged 18-45 years). Hostility, anger, verbal, and physical aggression were assessed using the Buss-Perry aggression questionnaire (BPAQ). LPS-stimulated TNF-alpha expression was determined using dual-color flow cytometry gating for CD14(+) cells. After controlling for age, race, education, and alcohol use, scores on the hostility (p=.013), physical aggression (p=.010), and verbal aggression (p=.034) subscales, and the total score (p=.007) on the BPAQ were positively associated with LPS-stimulated TNF-alpha expression. The results suggest that hostility and aggression are associated with an increased expression of TNF-alpha, a cytokine implicated in ACVD.

Increased splenocyte proliferative response and cytokine production in beta-endorphin-deficient mice

We used beta-endorphin-deficient mice as a novel approach to confirm the physiological role that opioid peptides play in the development or regulation of the immune system. We found that mice lacking beta-endorphin possessed an enhanced immune response, measured in terms of splenocyte proliferation and interleukin (IL)-2 mRNA levels, in vitro production of the splenic macrophage inflammatory cytokines IL-6 and Tumor Necrosis Factor (TNF)-alpha and plasma IL-6 following lipopolysaccharide (LPS) administration. beta-Endorphin-deficient mice had attenuated increases of plasma ACTH and corticosterone levels in response to LPS. These results are consistent with a postulated inhibitory role of endogenous beta-endorphin on the immune system at multiple levels.

Role of central 5-HT(2) receptors in fluoxetine-induced decreases in T lymphocyte activity

Previous studies have demonstrated that fluoxetine administration decreases mitogen-induced T lymphocyte proliferation. The present studies were carried out to determine which receptor subtype(s) was involved and whether these effects on lymphocyte responses were centrally or peripherally mediated. Two hours following administration of the 5-HT(1A) agonist 8-OH-DPAT (1 mg/kg), there was no change in lymphocyte proliferation responses, whereas the 5-HT(2) agonist DOI (2.5 mg/kg) significantly decreased (80%) proliferation. Similarly, pretreatment with the 5-HT(2) antagonists ritanserin (5 mg/kg, 30 min) or ketanserin (5 mg/kg, 1 h) was found to completely antagonize the effects of fluoxetine on lymphocyte proliferation. Consistent with central 5-HT(2) receptor involvement, microinjection of DOI (50 microg) resulted in a decrease in lymphocyte proliferation similar to that observed following systemic administration. Furthermore, central administration of ketanserin (20 microg) prevented the suppressive effects of systemic fluoxetine. Collectively, these results suggest that decreases in mitogen-induced lymphocyte proliferation following acute fluoxetine administration was due to indirect effects of fluoxetine following the activation of central 5-HT(2) receptors.

The proliferation of human T lymphoblastic cells induced by 5-HT1B receptors activation is regulated by 5-HT-moduline

Serotonin (5-hydroxytryptamine, 5-HT) is a well-known neurotransmitter and immunomodulator, which has been reported to affect the function of cells in the immune system. The purpose of the herein reported experiments was to investigate whether serotonin could regulate the proliferation of a human T lymphoblastic leukemia cell line (CCRF-CEM cells) and to characterize the 5-HT receptor(s) involved in this phenomenon using a pharmacological approach. The herein presented results show that serotonin alone stimulated the proliferation of CCRF-CEM cells and that this effect could be mimicked by two 5-HT1B/1D receptor agonists (L-694,247 and GR 46611). Serotonin- or L-694,247-induced increase in cell proliferation was inhibited by a selective 5-HT1B receptor antagonist, SB-224289. A recently identified endogenous tetrapeptide, 5-HT-moduline (Leu-Ser-Ala-Leu, LSAL), which specifically antagonizes 5-HT1B/1D receptor activity, was also shown to reverse the stimulating action of L-694,247 on T cell proliferation. Taken together, these results establish the existence of a direct serotonergic control of the T cell proliferation mediated through h5-HT1B receptors. In addition, these results are in favour of an immunomodulatory role of 5-HT-moduline.

Stress and inflammatory disease: widening roles for serotonin and substance P

Serotonin has been implicated in mediating the hypothalamo-pituitary-adrenal (HPA) axis response to stress and is an important therapeutic target for a number of psychiatric disorders including depression. The neurokinin substance P has been shown to inhibit stress-induced HPA axis activity and we have demonstrated that endogenous substance P is able to reduce the duration of the HPA axis response to stress suggesting an important role in the termination of the stress response. This may be important in controlling the transition from acute to chronic stress and substance P has recently attracted attention as a potential antidepressant.In addition to these central effects, serotonin and substance P are considered to be pro-inflammatory agents. Despite being implicated in mediating inflammation there have been few studies investigating the effects of manipulations of serotonergic or substance P systems on chronic inflammatory disease. Treatment of rats with adjuvant-induced arthritis(AA), a model of chronic inflammatory stress, with a substance P antagonist specific for the NK1 receptor subtype resulted in a reduction in hind paw inflammation suggesting substance P may influence inflammation. We have noted that depletion of whole body serotonin and selective central depletion of serotonin results in a decrease in the severity of inflammation in rats with adjuvant arthritis. Furthermore, treatment with a selective serotonin reuptake inhibitor results in an earlier onset and increased severity of inflammation in adjuvant arthritis, confirming a pro-inflammatory role for serotonin. Serotonin is also present in the immune tissues and concentrations in the spleen fall following the development of inflammation in adjuvant arthritis. Concentrations of serotonin are significantly higher in normal female spleen than in males, and this may underlie the greater predisposition of females to certain autoimmune diseases.There is increasing evidence of a role for transmitters such as serotonin and substance P,both centrally and peripherally, in mediating a wide variety of inflammatory and psychiatric disorders. A better understanding of the mechanisms of action of these transmitters and the development of suitable drugs targeting specific receptor subtypes has great potential to impact on clinical practice in the near future. The purpose of this review is to consider the separate roles of serotonin and substance P in relation to HPA axis stress responses, in the context of a model of chronic inflammatory disease, highlighting novel directions of current research for each of these transmitters.

Special feature for the Olympics: effects of exercise on the immune system: neuropeptides and their interaction with exercise and immune function

It is known today that the immune system is influenced by various types of psychological and physiological stressors, including physical activity. It is well known that physical activity can influence neuropeptide levels both in the central nervous system as well as in peripheral blood. The reported changes of immune function in response to exercise have been suggested to be partly regulated by the activation of different neuropeptides and the identification of receptors for neuropeptides and steroid hormones on cells of the immune system has created a new dimension in this endocrine-immune interaction. It has also been shown that immune cells are capable of producing neuropeptides, creating a bidirectional link between the nervous and immune systems. The most common neuropeptides mentioned in this context are the endogenous opioids. The activation of endogenous opioid peptides in response to physical exercise is well known in the literature, as well as the immunomodulation mediated by opioid peptides. The role of endogenous opioids in the exercise-induced modulation of immune function is less clear. The present paper will also discuss the role of other neuroendocrine factors, such as substance P, neuropeptide Y and vasoactive intestinal peptide, and pituitary hormones, including growth hormone, prolactin and adrenocorticotrophin, in exercise and their possible effects on immune function.

Special feature for the Olympics: effects of exercise on the immune system: neuropeptides and their interaction with exercise and immune function

It is known today that the immune system is influenced by various types of psychological and physiological stressors, including physical activity. It is well known that physical activity can influence neuropeptide levels both in the central nervous system as well as in peripheral blood. The reported changes of immune function in response to exercise have been suggested to be partly regulated by the activation of different neuropeptides and the identification of receptors for neuropeptides and steroid hormones on cells of the immune system has created a new dimension in this endocrine-immune interaction. It has also been shown that immune cells are capable of producing neuropeptides, creating a bidirectional link between the nervous and immune systems. The most common neuropeptides mentioned in this context are the endogenous opioids. The activation of endogenous opioid peptides in response to physical exercise is well known in the literature, as well as the immunomodulation mediated by opioid peptides. The role of endogenous opioids in the exercise-induced modulation of immune function is less clear. The present paper will also discuss the role of other neuroendocrine factors, such as substance P, neuropeptide Y and vasoactive intestinal peptide, and pituitary hormones, including growth hormone, prolactin and adrenocorticotrophin, in exercise and their possible effects on immune function.

Itch-associated response induced by intradermal serotonin through 5-HT2 receptors in mice

Serotonin (5-HT) is pruritogenic in humans and suggested to be involved in some pruritic diseases. Our experiments were carried out to determine whether an intradermal injection of 5-HT would elicit itch-associated response in mice and to elucidate the 5-HT receptor subtypes involved in this 5-HT action. 5-HT (14.1-235 nmol site(-1)) injected intradermally into the rostral back elicited scratching of the injected site, with bell-shaped dose-response relationship. The scratching induced by 5-HT (100 nmol site(-1), peak effective dose) was suppressed by capsaicin (repeated administration) and the opioid antagonist naloxone, features being similar to human itching. Scratching was also elicited by the 5-HT2 receptor agonist alpha-methylserotonin, but not by the 5-HT1A receptor agonist R(+)-8-hydroxy-N,N-dipropyl-2-aminotetralin nor the 5-HT3 receptor agonists 2-methylserotonin and 1-phenylbiganide. Scratching induced by 5-HT and alpha-methylserotonin was inhibited by peroral pretreatment with 5-HT1/2 receptor antagonists methysergide and cyproheptadine. 5-HT-induced scratching was also inhibited by intradermal injection of methysergide. Peroral pretreatment with 5-HT3 receptor antagonists ondansetron and 3-tropanyl-3, 5-dichrobenzoate did not significantly suppress 5-HT-induced scratching. The results suggest that scratching induced by intradermal injection of 5-HT is itch-associated response. The 5-HT action may be mediated at least partly by cutaneous 5-HT2 receptors.

The interaction of immunomodulatory muramyl dipeptide with peripheral 5-HT receptors: overview of the current state

Immunomodulator muramyl dipeptide (MDP) exerts also pronounced neuropharmacological activities which are probably mediated by an interaction with 5-HT receptors. Some of these effects are considered as undesirable by its clinical use. More precise information concerning MDP effects on 5-HT receptors with respect to their many subtypes could result from studies using isolated organs in vitro. Earlier conducted studies of this type provided data that are concisely overviewed and reinterpreted here from the view of current 5-HT receptor classification. Since new 5-HT receptor types have emerged recently, new studies are under way. The results might contribute to the development of novel immunomodulatory drugs devoid of adverse effects.

Serotonin 5-HT2A receptor activation inhibits cytokine-stimulated inducible nitric oxide synthase in C6 glioma cells

C6-glioma cells endogenously express both 5-HT2A receptors and inducible nitric oxide synthase (iNOS). iNOS can be induced by transcriptional activation to produce nitric oxide (NO) in response to a challenge with the pro-inflammatory cytokines TNF-alpha and IFN-gamma. Experiments were conducted to determine whether 5-HT2A receptor activation could modify the production of NO in response to the inducing agents. 1 muM DOI produced a dose-dependent inhibition of the cytokine-inducted nitrite levels of 40% which was inhibited by spiperone and ritanserin. In addition, the DOI-mediated decrease was prevented by the PKC inhibitor chelerythrine (100 nM). The effectiveness of DOI was lost when added more than two hours after the addition of inducing agent, suggesting that DOI was regulating iNOS at the level of transcription rather than post-translationally. We suggest that there is a link between the serotonergic system and NO-mediated immune responses in the brain.