Serotonin: a review

N(ε)-Carboxymethyllysine (CML), a Maillard reaction product, stimulates serotonin release and activates the receptor for advanced glycation end products (RAGE) in SH-SY5Y cells

Maillard reaction products, which are formed in highly thermally treated foods, are commonly consumed in a Western diet. In this study, we investigated the impact of N(ε)-carboxymethyllysine (CML), a well-characterized product of the Maillard reaction, on the gene regulation of the human neuroblastoma cell line SH-SY5Y. Pathway analysis of data generated from customized DNA microarrays revealed 3 h incubation with 50 μM and 500 μM CML to affect serotonin receptor expression. Further experiments employing qRT-PCR showed an up-regulation of serotonin receptors 2A, 1A and 1B after 0.25 h and 3 h. In addition, 500 μM CML increased serotonin release, thus showing effects of CML not only at a genetic, but also at a functional level. Intracellular calcium mobilization, which mediates serotonin release, was increased by CML at concentrations of 0.05-500 μM. Since calcium mobilization has been linked to the activation of the receptor for advanced glycation end products (RAGE), we further investigated the effects of CML on RAGE expression. RAGE was found to be up-regulated after incubation with 500 μM CML for 0.25 h. Co-incubation with the calcium blocker neomycin for 0.25 h blocked the up-regulation of RAGE and the serotonin receptors 2A, 1A and 1B. These results indicate a possible link between a CML-induced calcium-mediated serotonin release and RAGE.

Looking beyond the DNA sequence: the relevance of DNA methylation processes for the stress-diathesis model of depression

The functioning of the hypothalamic-pituitary-adrenal (HPA) axis and serotonergic (5-HT) system are known to be intertwined with mood. Alterations in these systems are often associated with depression. However, neither are sufficient to cause depression in and of themselves. It is now becoming increasingly clear that the environment plays a crucial role, particularly, the perinatal environment. In this review, we posit that early environmental stress triggers a series of epigenetic mechanisms that adapt the genome and programme the HPA axis and 5-HT system for survival in a harsh environment. We focus on DNA methylation as it is the most stable epigenetic mark. Given that DNA methylation patterns are in large part set within the perinatal period, long-term gene expression programming by DNA methylation is especially vulnerable to environmental insults during this period. We discuss specific examples of genes in the 5-HT system (serotonin transporter) and HPA axis (glucocorticoid receptor and arginine vasopressin enhancer) whose DNA methylation state is associated with early life experience and may potentially lead to depression vulnerability. We conclude with a discussion on the relevance of studying epigenetic mechanisms in peripheral tissue as a proxy for those occurring in the human brain and suggest avenues for future research.

Serotonin promotes the proliferation of serum-deprived hepatocellular carcinoma cells via upregulation of FOXO3a

Background

Peripheral serotonin is involved in tumorigenesis and induces a pro-proliferative effect in hepatocellular carcinoma (HCC) cells; however, the intracellular mechanisms by which serotonin exerts a mitogenic effect remain unclear. In this research, we examined whether FOXO3a, a transcription factor at the interface of crucial cellular processes, plays a role downstream of serotonin in HCC cells.

Results

The cell viability and expression of FOXO3a was assessed in three HCC cell lines (Huh7, HepG2 and Hep3B) during serum deprivation in the presence or absence of serotonin. Serum free media significantly inhibited HCC proliferation and led to reduced expression and nuclear accumulation of FOXO3a. Knockdown of FOXO3a enhanced the ability of serum deprivation to inhibit HCC cells proliferation. And overexpression of non-phosphorylated FOXO3a in HCC cells reversed serum-deprivation-induced growth inhibition. Serotonin reversed the serum-deprivation-induced inhibition of cell proliferation and upregulated FOXO3a in Huh7 cells; however, serotonin had no effect on the proliferation of serum-deprived HepG2 or Hep3B cells. In addition to proliferation, serotonin also induced phosphorylation of AKT and FOXO3a in serum-deprived Huh7 cells but not in HepG2 and Hep3B cells. However, the phosphorylation of FOXO3a induced by serotonin did not export FOXO3a from nucleus to cytoplasm in serum-deprived Huh7 cells. Consequently, we demonstrated that serotonin promoted the proliferation of Huh7 cells by increasing the expression of FOXO3a. We also provide preliminary evidence that different expression levels of the 5-HT2B receptor (5-HT_2BR) may contribute to the distinct effects of serotonin in different serum-deprived HCC cells.

Conclusions

This study demonstrates that FOXO3a functions as a growth factor in serum-deprived HCC cells and serotonin promotes the proliferation of serum-deprived HCC cells via upregulation of FOXO3a, in the presence of sufficient levels of the serotonin receptor 5-HT_2BR. Drugs targeting the serotonin-5-HT_2BR-FOXO3a pathway may provide a novel target for anticancer therapy.

Retrospective evaluation of toxicosis from selective serotonin reuptake inhibitor antidepressants: 313 dogs (2005-2010)

OBJECTIVE

To evaluate a clinical population of dogs exposed to selective serotonin reuptake inhibitor (SSRI) antidepressant medications and describe the clinical findings, epidemiological characteristics, outcome, and prognosis.

DESIGN

Retrospective study (February 1, 2005-August 31, 2010).

SETTING

Animal poison control helpline.

ANIMALS

Three hundred thirteen dogs with presumed SSRI toxicosis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Dogs with presumptive SSRI medication toxicosis identified by a review of the electronic database of Pet Poison Helpline, an animal poison control center, were evaluated. No clinical signs were reported in 76.3% (239/313) of cases. The remaining 23.6% (74/313) of cases demonstrated the following clinical signs: neurological 79.7% (59/74), gastrointestinal 25.6% (19/74), cardiovascular 9.5% (7/74), respiratory 8.2% (6/74), and thermoregulatory 6.7% (5/74). Of the dogs exhibiting neurological signs, 62.7% (37/59) showed depression, 37.2% (22/59) showed hyperactivity, 10.1% (6/59) exhibited ataxia, and 1.7% (1/59) showed other miscellaneous signs (eg, hyperesthesia). There was a significant difference between the dose ingested by symptomatic and asymptomatic dogs for fluoxetine (P = 0.0039), but not with any other SSRI. Ninety-four patients were confirmed to have received veterinary care. In cases where duration of veterinary care was determined (55/313), 67.2% (37/55) of dogs were hospitalized and 32.7% (18/55) treated as outpatients. The average duration of hospitalization was 18.5 hours, excluding outpatient visits. Of those patients that had complete follow-up information available (136/313), overall survival was 100%.

CONCLUSIONS

The overall prognosis for animals with SSRI toxicosis is excellent with veterinary attention. Central nervous system depression was the most common clinical sign associated with SSRI toxicosis.

The Use of IV Lipid Emulsion for Lipophilic Drug Toxicities

IV lipid emulsion (ILE) therapy is emerging as a potential antidote for lipophilic drug toxicities in both human and veterinary medicine. ILE has already gained acceptance in human medicine as a treatment of local anesthetic systemic toxicity, but its mechanism of action, safety margins, and standardized dosing information remains undetermined at this time. Experimental and anecdotal use of ILE in the human and veterinary literature, theorized mechanisms of action, current dosing recommendations, potential adverse effects, and indications for use in human and veterinary emergency medicine are reviewed herein.

Association of the 5-HTT gene-linked promoter region (5-HTTLPR) polymorphism with psychiatric disorders: review of psychopathology and pharmacotherapy

Serotonin (5-HT) regulates important biological and psychological processes including mood, and may be associated with the development of several psychiatric disorders. An association between psychopathology and genes that regulate 5-HT neurotransmission is a robust area of research. Identification of the genes responsible for the predisposition, development, and pharmacological response of various psychiatric disorders is crucial to the advancement of our understanding of their underlying neurobiology. This review highlights research investigating 5-HT transporter (5-HTTLPR) polymorphism, because studies investigating the impact of the 5-HTTLPR polymorphism have demonstrated significant associations with many psychiatric disorders. Decreased transcriptional activity of the S allele ("risk allele") may be associated with a heightened amygdala response leading to anxiety-related personality traits, major depressive disorder, suicide attempts, and bipolar disorder. By contrast, increased transcriptional activity of the L allele is considered protective for depression but is also associated with completed suicide, nicotine dependence, and attention deficit hyperactivity disorder. For some disorders, such as post-traumatic stress disorder and major depressive disorder, the research suggests that treatment response may vary by allele (such as an enhanced response to serotonin specific reuptake inhibitors in patients with major depressive disorder and post-traumatic stress disorder with L alleles), and for alcohol dependence, the association and treatment for S or L alleles may vary with alcoholic subtype. While some studies suggest that 5-HTTLPR polymorphism can moderate the response to pharmacotherapy, the association between 5-HTTLPR alleles and therapeutic outcomes is inconsistent. The discovery of triallelic 5-HTTLPR alleles (L(A)/L(G)/S) may help to explain some of the conflicting results of many past association studies, while concurrently providing more meaningful data in the future. Studies assessing 5-HTTLPR as the solitary genetic factor contributing to the etiology of psychiatric disorders continue to face the challenges of statistically small effect sizes and limited replication.

The neuronal influence on tumor progression

Nerve fibers accompany blood and lymphatic vessels all over the body. An extensive amount of knowledge has been obtained with regard to tumor angiogenesis and tumor lymphangiogenesis, yet little is known about the potential biological effects of "neoneurogenesis". Cancer cells can exploit the advantage of the factors released by the nerve fibers to generate a positive microenvironment for cell survival and proliferation. At the same time, they can stimulate the formation of neurites by secreting neurotrophic factors and axon guidance molecules. The neuronal influence on the biology of a neoplasm was initially described several decades ago. Since then, an increasing amount of experimental evidence strongly suggests the existence of reciprocal interactions between cancer cells and nerves in humans. Moreover, researchers have been able to demonstrate a crosstalk between cancer cells and nerve fibers as a strategy for survival. Despite all these evidence, a lot remains to be done in order to clarify the role of neurotransmitters, neuropeptides, and their associated receptor-initiated signaling pathways in the development and progression of cancer, and response to therapy. A global-wide characterization of the neurotransmitters or neuropeptides present in the tumor microenvironment would provide insights into the real biological influences of the neuronal tissue on tumor progression. This review is intended to discuss our current understanding of neurosignaling in cancer and its potential implications on cancer prevention and therapy. The review will focus on the soluble factors released by cancer cells and nerve endings, their biological effects and their potential relevance in the treatment of cancer.

Association of the A-1438G polymorphism in serotonin 2A receptor in migraine with aura among Japanese patients

We investigated the possible association of serotonin (5-HT) 2A receptor gene A-1438G polymorphism in Japanese patients with migraine. Genotyping of 5-HT(2A) A-1438G polymorphism was performed by polymerase chain reaction-restriction fragment length polymorphism in patients with migraine (male 17 : 3 with aura and 14 without aura, female 65 : 17 with aura and 48 without aura) and controls (male 31, female 84). The distribution of 5-HT(2A) A-1438G genotype frequency between migraine patients and controls did not differ. These results suggest that the A-1438G polymorphism of the 5-HT(2A) receptor gene is not a direct risk factor for migraine; however, the incidence of the A/A genotype between migraine with aura (MA) and without aura (MO) was significantly different. The 5-HT(2A) A-1438G polymorphism may be involved in determining the subtypes of migraine in Japanese.

Rat mitochondrion-neuron focused microarray (rMNChip) and bioinformatics tools for rapid identification of differential pathways in brain tissues

Mitochondrial function is of particular importance in brain because of its high demand for energy (ATP) and efficient removal of reactive oxygen species (ROS). We developed rat mitochondrion-neuron focused microarray (rMNChip) and integrated bioinformatics tools for rapid identification of differential pathways in brain tissues. rMNChip contains 1,500 genes involved in mitochondrial functions, stress response, circadian rhythms and signal transduction. The bioinformatics tool includes an algorithm for computing of differentially expressed genes, and a database for straightforward and intuitive interpretation for microarray results. Our application of these tools to RNA samples derived from rat frontal cortex (FC), hippocampus (HC) and hypothalamus (HT) led to the identification of differentially-expressed signal-transduction-bioenergenesis and neurotransmitter-synthesis pathways with a dominant number of genes (FC/HC = 55/6; FC/HT = 55/4) having significantly (p<0.05, FDR<10.70%) higher (≥1.25 fold) RNA levels in the frontal cortex than the others, strongly suggesting active generation of ATP and neurotransmitters and efficient removal of ROS. Thus, these tools for rapid and efficient identification of differential pathways in brain regions will greatly facilitate our systems-biological study and understanding of molecular mechanisms underlying complex and multifactorial neurodegenerative diseases.

Absence of bioactivity of lipid derivatives of serotonin

BACKGROUND

Serotonin (5-HT) and its receptors are present in central, the brain stem, and peripheral, the carotid body, tissues controlling the ventilatory responses to hypoxia. The exact action of serotonin and its nature are, however, unsettled. We hypothesized that the discrepant results on the ventilatory action of serotonin could be caused by the inability of serotonin to penetrate into the brain or the plasma membrane lipid bilayers, the target site of signal transduction cascades, after its exogenous administration.

OBJECTIVE

To study the penetrability of novel lipid derivatives of serotonin of varying fatty acid chain length and number of saturated/unsaturated bonds, the oleic, caprylic, and caprolic amides of 5-HT, into the brain, and their functional effects on the hypoxic ventilatory response in awake rats after systemic administration.

MATERIAL AND METHODS

Adult Wistar rats were used for the experiments. In the biochemical part of the study, the presence and stability of the compounds tested, after i.p. injection, was assessed in brain extracts using spectrophotometry and thin-layered chromatography. In the functional part, the ventilatory responses to 8 and 12% hypoxia were compared before and 1 h after the compound administration using a whole body plethysmography.

RESULTS

The "lipidized" serotonin compounds turned out to be stable in brain extracts in vitro for up to 3 h of the test. However, we could not substantiate the presence of any of the compounds in the brain, with either method used, after i.p. administration. Likewise, none of the compounds had any appreciable effect on the profile of the stimulatory hypoxic ventilatory response.

CONCLUSIONS

Synthetically attaching lipophilic groups to the serotonin molecule does not make it penetrate into the brain. The lack of serotonin penetrability likely depends on the planarity of its molecule, as it does not seem to depend on the size, number of carbons or bond saturation of the "lipidized" molecules. Such molecules do not directly interfere with the carotid chemoreceptor-mediated hypoxic ventilatory response. The study failed to substantiate the bioactive potential of the lipid derivatives of serotonin.

Multiple cellular responses to serotonin contribute to epithelial homeostasis

Epithelial homeostasis incorporates the paradoxical concept of internal change (epithelial turnover) enabling the maintenance of anatomical status quo. Epithelial cell differentiation and cell loss (cell shedding and apoptosis) form important components of epithelial turnover. Although the mechanisms of cell loss are being uncovered the crucial triggers that modulate epithelial turnover through regulation of cell loss remain undetermined. Serotonin is emerging as a common autocrine-paracine regulator in epithelia of multiple organs, including the breast. Here we address whether serotonin affects epithelial turnover. Specifically, serotonin's roles in regulating cell shedding, apoptosis and barrier function of the epithelium. Using in vivo studies in mouse and a robust model of differentiated human mammary duct epithelium (MCF10A), we show that serotonin induces mammary epithelial cell shedding and disrupts tight junctions in a reversible manner. However, upon sustained exposure, serotonin induces apoptosis in the replenishing cell population, causing irreversible changes to the epithelial membrane. The staggered nature of these events induced by serotonin slowly shifts the balance in the epithelium from reversible to irreversible. These finding have very important implications towards our ability to control epithelial regeneration and thus address pathologies of aberrant epithelial turnover, which range from degenerative disorders (e.g.; pancreatitis and thyrioditis) to proliferative disorders (e.g.; mastitis, ductal ectasia, cholangiopathies and epithelial cancers).

Characterization of 5-HT transporter and receptor system in HeLaS3 cells by [(3)H]8-OH-DPAT and other serotonergic ligands

[(3)H]8-OH-DPAT is a selective ligand for labeling 5-HT(1A) receptor sites. In competition binding experiments, we found that classic biogenic amine transporter inhibitors displaced [(3)H]8-OH-DPAT binding at its high-affinity binding sites in HeLaS3 cells. [(125)I]RTI-55 and [(3)H]paroxetine are known to specifically label amine transporter sites, and this was observed in our cells. Displacement studies showed that 8-OH-DPAT displayed affinity in a dose-dependent manner for the labeled amine transporter sites. These data suggest that [(3)H]8-OH-DPAT binds to amine uptake sites in HeLaS3 cells. A variety of drugs targeting different classes of receptors did not significantly affect [(3)H]8-OH-DPAT binding. Moreover, we determined the specific binding effects of various serotonergic ligands (i.e. [(125)I]cyanopindolol, [(3)H]ketanserin/[(3)H]mesulergine, [(3)H]GR-65630, [(3)H]GR-113808 and [(3)H]LSD) that specifically labeled 5-HT(1), 5-HT(2), 5-HT(3), 5-HT(4) and 5-HT(5-7) receptors, respectively. It is suggested that HeLaS3 cells contain distinct types of the related to 5-HT receptor recognition binding sites. These observations could help elucidate the relevant characteristics of different types of 5-HT receptors and 5-HT membrane transporters in tumor cells and their role in tumorigenesis.

Serotonin level and serotonin uptake in human platelets: a variable interrelation under marked physiological influences

BACKGROUND

Although it is known that platelet serotonin level (PSL) depends directly on platelet serotonin uptake (PSU) through the plasma membrane, reports on their interrelation are inconsistent. The aim of this study was to systematically explore the relationship between these two platelet serotonin parameters in large human population.

METHODS

PSL and full-kinetics of PSU were determined on 318 blood donors (276 males, 42 females; 20-67 years).

RESULTS

The overall correlation coefficient between PSL and maximal velocity of PSU was highly significant but unexpectedly low (r=0.269). Further analyses revealed lack of correlation among females, and variable association among males, depending on the subject age and season of measurements. Highly significant correlations were observed in spring-winter, while association was absent during summer-autumn. Lowering of PSL-PSU correlation with increased age was also demonstrated, showing modest interrelation among younger men and no interrelation in older population. By multiple regression analyses season was identified as the only independent predictor of PSL-PSU relationship.

CONCLUSIONS

The results show prominent influence of biological (sex, age) and, especially, environmental (seasons) physiology on the intraindividual relationship between PSL and PSU. Although serotonin transporter activity plays an important role in determining PSL, the observed correlations indicate that other factors may predominate.

A molecular mechanism for diacylglycerol-mediated promotion of negative caloric balance

AIMS

A substitution of diacylglycerol (DAG) oil for triacylglycerol (TAG) oil in diet has been reported to reduce body fat and body weight, possibly by increasing postprandial energy expenditure (EE). We have previously studied plasma serotonin, which increases EE and exists in the small intestine, in individuals who ingested TAG and DAG oil, and found that DAG ingestion elevates plasma serotonin levels by about 50% compared with TAG ingestion. We studied the molecular mechanisms for DAG-mediated increase in serotonin and EE.

METHODS

We studied effects of 1-monoacylglycerol and 2-monoacylglycerol, distinct digestive products of DAG and TAG, respectively, on serotonin release from the Caco-2 cells (the human intestinal cell line, n = 8). Further, we studied effects of 1- and 2-monoacylglycerol, and serotonin on expression of mRNA associated with β-oxidation, FA metabolism, and thermogenesis, in the Caco-2 cells (n = 5).

RESULTS

1-monoacylglycerol (100 μM 1-monooleyl glycerol [1-MOG]) significantly increased serotonin release from the Caco-2 cells compared with 2-monoacylglycerol (100 μM 2-MOG) by 36.6%. Expression of mRNA of acyl-CoA oxidase (ACO), fatty acid translocase (FAT), and uncoupling protein-2 (UCP-2) were significantly higher in 100 μM 1-MOG-treated Caco-2 cells than 100 μM 2-MOG-treated cells by 12.8%, 23.7%, and 35.1%, respectively. Further, expression of mRNA of ACO, medium-chain acyl-CoA dehydrogenase, FAT, and UCP-2 were significantly elevated in serotonin (400 nM)-treated Caco-2 cells compared with cells incubated without serotonin by 28.7%, 30.1%, and 39.2%, respectively.

CONCLUSIONS

Our study demonstrated that 1-monoacylglycerol, a digestive product of DAG, increases serotonin release from the Caco-2 cells, and enhances expression of genes associated with β-oxidation, FA metabolism, and thermogenesis, and that serotonin increases expression of these genes, proposing a novel molecular mechanism for DAG-mediated promotion of negative caloric balance.

Altered serotonin physiology in human breast cancers favors paradoxical growth and cell survival

Introduction

The breast microenvironment can either retard or accelerate the events associated with progression of latent cancers. However, the actions of local physiological mediators in the context of breast cancers are poorly understood. Serotonin (5-HT) is a critical local regulator of epithelial homeostasis in the breast and other organs. Herein, we report complex alterations in the intrinsic mammary gland serotonin system of human breast cancers.

Methods

Serotonin biosynthetic capacity was analyzed in human breast tumor tissue microarrays using immunohistochemistry for tryptophan hydroxylase 1 (TPH1). Serotonin receptors (5-HT1-7) were analyzed in human breast tumors using the Oncomine database. Serotonin receptor expression, signal transduction, and 5-HT effects on breast cancer cell phenotype were compared in non-transformed and transformed human breast cells.

Results

In the context of the normal mammary gland, 5-HT acts as a physiological regulator of lactation and involution, in part by favoring growth arrest and cell death. This tightly regulated 5-HT system is subverted in multiple ways in human breast cancers. Specifically, TPH1 expression undergoes a non-linear change during progression, with increased expression during malignant progression. Correspondingly, the tightly regulated pattern of 5-HT receptors becomes dysregulated in human breast cancer cells, resulting in both ectopic expression of some isoforms and suppression of others. The receptor expression change is accompanied by altered downstream signaling of 5-HT receptors in human breast cancer cells, resulting in resistance to 5-HT-induced apoptosis, and stimulated proliferation.

Conclusions

Our data constitutes the first report of direct involvement of 5-HT in human breast cancer. Increased 5-HT biosynthetic capacity accompanied by multiple changes in 5-HT receptor expression and signaling favor malignant progression of human breast cancer cells (for example, stimulated proliferation, inappropriate cell survival). This occurs through uncoupling of serotonin from the homeostatic regulatory mechanisms of the normal mammary epithelium. The findings open a new avenue for identification of diagnostic and prognostic markers, and valuable new therapeutic targets for managing breast cancer.

Irritable bowel syndrome is strongly associated with generalized anxiety disorder: a community study

BACKGROUND

No previous study has examined the comorbidity of Irritable Bowel Syndrome (IBS) and Generalized Anxiety Disorder (GAD) in a general population using standardized diagnostic methods.

AIM

To examine the prevalence, comorbidity and risk correlates of IBS and GAD in a general population.

METHODS

A random community-based telephone survey was conducted. The questionnaire covered symptoms of IBS, GAD, core depressive symptoms, help-seeking behaviour and functional impairment on the Sheehan Disability Scale.

RESULTS

A total of 2005 participants completed the interview. The current prevalence of IBS was 5.4% and the 12-month prevalence of GAD was 4%. GAD was five times more common among IBS respondents than non-IBS respondents (OR: 5.84, P < 0.001), whereas IBS was 4.7 times more common among GAD respondents than among non-GAD respondents (OR: 6.32, P < 0.001). Core depressive symptoms (OR: 6.25, P < 0.01) and education level (OR: 5.918, P = 0.021) were risk correlates of GAD among IBS respondents. Comorbid respondents were more impaired than respondents having either disorder alone, but were not more likely to seek professional help than IBS-only respondents.

CONCLUSION

Irritable Bowel Syndrome and GAD comorbidity was common and added to impairment in the community. The strong association between psychiatric morbidity and IBS observed in referral centres was not a consequence of increased help-seeking behaviour.

Altered coronary microvascular serotonin receptor expression after coronary artery bypass grafting with cardiopulmonary bypass

OBJECTIVE

We evaluated roles of serotonin 1B and 2A receptors, thromboxane synthase and receptor, and phospholipases A(2) and C in response to cardiopulmonary bypass.

METHODS

Patients' atrial tissues were harvested before and after cardiopulmonary bypass with cardioplegia (n = 13). Coronary microvessels were assessed for vasoactive response to serotonin with and without inhibitors of serotonin 1B and 2A receptors and phospholipases A(2) and C. Expressions of serotonin receptor messenger RNA were determined with reverse transcriptase polymerase chain reaction. Expressions of serotonin receptors and thromboxane A(2) receptor and synthase proteins were determined with immunoblotting and immunohistochemistry.

RESULTS

Microvessel exposure to serotonin elicited 7.3% +/- 2% relaxation before bypass, changing to contraction of -19.2% +/- 2% after bypass (P <.001). Additions of specific serotonin 1B receptor antagonist and inhibitor of phospholipase A(2) resulted in significantly decreased contraction, -8.6% +/- 1% (P < .001) and 2.8% +/- 3% (P = .001), respectively. Serotonin 1B receptor messenger RNA expression increased 1.82 +/- 0.34-fold after bypass (p = .044); serotonin 2A receptor messenger RNA expression did not change. Serotonin 1B but not 2A receptor protein expression increased after bypass by 1.35 +/- 0.7-fold (P = .0413). Thromboxane synthase and receptor expressions were unchanged after bypass. Serotonin 1B receptor increased mainly in arterial smooth muscle. There were no appreciable differences in arterial expressions of thromboxane synthase or receptor.

CONCLUSIONS

Serotonin-induced vascular dysfunction after cardiopulmonary bypass with cardioplegic arrest may be mediated by increased expression of serotonin 1B receptor and subsequent phospholipase A(2) activation in myocardial coronary smooth muscle.

Expression and function of 5-HT7 receptors in smooth muscle preparations from equine duodenum, ileum, and pelvic flexure

In horses, gastrointestinal (GI) disorders occur frequently and cause a considerable demand for efficient medication. 5-Hydroxytryptamine receptors (5-HT) have been reported to be involved in GI tract motility and thus, are potential targets for treating functional bowel disorders. Our studies extend current knowledge on the 5-HT(7) receptor in equine duodenum, ileum and pelvic flexure by studying its expression throughout the intestine and its role in modulating contractility in vitro by immunofluorescence and organ bath experiments, respectively. 5-HT(7) immunoreactivity was demonstrated in both smooth muscle layers, particularly in the circular one, and within the myenteric plexus. Interstitial cells of Cajal (ICC), identified by c-Kit labeling, show a staining pattern similar to that of 5-HT(7) immunoreactivity. The selective 5-HT(7) receptor antagonist SB-269970 increased the amplitude of contractions in spontaneous contracting specimens of the ileum and in electrical field-stimulated specimens of the pelvic flexure concentration-dependently. Our in vitro experiments suggest an involvement of the 5-HT(7) receptor subtype in contractility of equine intestine. While the 5-HT(7) receptor has been established to be constitutively active and inhibits smooth muscle contractility, our experiments demonstrate an increase in contractility by the 5-HT(7) receptor ligand SB-269970, suggesting it exerting inverse agonist properties.

Nonserotonergic projection neurons in the midbrain raphe nuclei contain the vesicular glutamate transporter VGLUT3

The brainstem raphe nuclei are typically assigned a role in serotonergic brain function. However, numerous studies have reported that a large proportion of raphe projection cells are nonserotonergic. The identity of these projection cells is unknown. Recent studies have reported that the vesicular glutamate transporter VGLUT3 is found in both serotonergic and nonserotonergic neurons in both the median raphe (MR) and dorsal raphe (DR) nuclei. We injected the retrograde tracer cholera toxin subunit B into either the dorsal hippocampus or the medial septum (MS) and used triple labeled immunofluorescence to determine if nonserotonergic raphe cells projecting to these structures contained VGLUT3. Consistent with previous studies, only about half of retrogradely labeled MR neurons projecting to the hippocampus contained serotonin, whereas a majority of the retrogradely labeled nonserotonergic cells contained VGLUT3. Similar patterns were observed for MR cells projecting to the MS. About half of retrogradely labeled nonserotonergic neurons in the DR contained VGLUT3. Additionally, a large number of retrogradely labeled cells in the caudal linear and interpeduncular nuclei projecting to the MS were found to contain VGLUT3. These data suggest the enigmatic nonserotonergic projection from the MR to forebrain regions may be glutamatergic. In addition, these results demonstrate a dissociation between glutamatergic and serotonergic MR afferent inputs to the MS and hippocampus suggesting divergent and/or complementary roles of these pathways in modulating cellular activity within the septohippocampal network.