Serotonin in the developing stomatogastric system of the lobster,Homarus americanus

We studied the development of the serotonergic modulation of the stomatogastric nervous system of the lobster, Homarus americanus. Although the stomatogastric ganglion (STG) is present early in embryonic development, serotonin immunoreactivity is not visible in the STG until the second larval stage. However, incubation of the STG with exogenous serotonin showed that a serotonin transporter is present in embryonic and early larval stages. Serotonin uptake was blocked by paroxetine and 0% Na⁺ saline. The presence of a serotonin transporter in the embryonic STG suggests that hormonally liberated serotonin could be taken up by the STG, and potentially released as a “borrowed transmitter”. Consistent with a potential hormonal role, serotonin is found in the pericardial organs, a major neurosecretory structure, by midembryonic development. The rhythmic motor patterns produced by embryonic and larval STGs were decreased in frequency by serotonin. Lateral Pyloric (LP) neuron‐evoked excitatory junctional potentials (EJPs) in the embryos and the first larval stage (LI) were larger, slower, and more variable than those in the adult. The amplitude of adult LP neuron‐evoked EJPs was increased more than twofold in serotonin, but in embryos and LI preparations this effect was negligible. In embryos and LI preparations, serotonin increased the occurrence of muscle fiber action potentials and altered the EJP wave‐form. These data demonstrate that serotonin receptors are present in the stomatogastric nervous system early in development, and suggest that the role of serotonin changes from modulation of muscle fiber excitability early in development to enhancement of neurally evoked EJPs in the adult. © 2002 Wiley Periodicals, Inc. J Neurobiol 54: 380–392, 2003     

Decrease of Serotonin Transporters in Blood Platelets after Epileptic Seizures

Serotonin transporter (SERT) was studied by [³H]-paroxetine binding in blood platelets from controls and epileptic patients with generalized convulsive seizures. The average K_D and B_Max were not different in the two cases. However, a significant decrease was found in the serotonin transporter density in the platelet membranes from patients having undergone an epileptic seizure less than 4 days before. This circumstance may indicate a homeostatic reaction to the epileptic attack.     

Effectiveness of paroxetine in the treatment of acute major depression in adults: a systematic re-examination of published and unpublished data from randomized trials

Background

Concern has been raised about the efficacy of antidepressant therapy for major depression in adults. We undertook a systematic review of published and unpublished clinical trial data to determine the effectiveness and acceptability of paroxetine.

Methods

We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Register, the Cochrane Central Register of Controlled Trials, the GlaxoSmithKline Clinical Trial Register, MEDLINE and EMBASE up to December 2006. Published and unpublished randomized trials comparing paroxetine with placebo in adults with major depression were eligible for inclusion. We selected the proportion of patients who left a study early for any reason as the primary outcome measure because it represents a hard measure of treatment effectiveness and acceptability.

Results

We included in our review 29 published and 11 unpublished clinical trials, with a total of 3704 patients who received paroxetine and 2687 who received with placebo. There was no difference between paroxetine and placebo in terms of the proportion of patients who left the study early for any reason (random effect relative risk [RR] 0.99, 99% confidence interval [CI] 0.88–1.11). Paroxetine was more effective than placebo, with fewer patients who did not experience improvement in symptoms of at least 50% (random effect RR 0.83, 99% CI 0.77–0.90). Significantly more patients in the paroxetine group than in the placebo group left their respective studies because of side effects (random effect RR 1.77, 95% CI 1.44–2.18) or experienced suicidal tendencies (odds ratio 2.55, 95% CI 1.17–5.54).

Interpretation

Among adults with moderate to severe major depression in the clinical trials we reviewed, paroxetine was not superior to placebo in terms of overall treatment effectiveness and acceptability. These results were not biased by selective inclusion of published studies.Although most treatment guidelines recommend one of the selective serotonin reuptake inhibitors in the pharmacologic treatment of moderate to severe depression in adults,^1,2 concerns have been raised in recent years about the efficacy of these drugs in alleviating symptoms of depression.^3,4First, in trials of antidepressants, the choice of the outcome of interest is often problematic. Whereas in other fields of medicine the definition of outcome measures may be relatively straightforward, efficacy in the treatment of depression may be an elusive concept, typically measured by rating scales. The use of rating scales as outcome measures has often been questioned by physicians, who seldom use them to define patients'' improvement under clinical circumstances.⁵ In addition, improvement in symptoms is typically documented as the difference between baseline and post-treatment scores. Although from a practical viewpoint this approach seems reasonable, in that it allows physicians to make a reasoned judgment in terms of proportions of patients (and not in terms of means and standard deviations), it may systematically magnify the effect of new drugs relative to placebo.³ As a consequence of this criticism, the field of mental health has seen a renewal of interest in “hard measures” of treatment effectiveness.^6–8 Hard measures include suicide attempts, treatment switching, hospital admissions, job loss or dropping out of the trial itself. Hard outcomes may also have a role in re-analyses of clinical trial data, where they may offer a “down-to-earth” evaluation of effectiveness and acceptability.A second concern is that the modest differences between active antidepressants and placebo, as calculated in systematic reviews of clinical trial data,^9–12 might be explained in part by the selective inclusion of specific subsets of studies, such as those submitted to regulatory authorities by drug companies, those that were eventually published or those supported by the manufacturers of selective serotonin reuptake inhibitors.¹³In the present systematic review, we used a hard measure to determine the effectiveness and acceptability of paroxetine, a commonly prescribed antidepressant belonging to the group of selective serotonin reuptake inhibitors. Paroxetine was chosen for 3 reasons: first, it is one of the most frequently prescribed antidepressant drugs both in primary and secondary care (as indicated by a search of the US National Center for Health Statistics database, www2.cdc.gov/drugs/); second, GlaxoSmithKline, the company that launched paroxetine, has recently adopted and implemented a disclosure policy to provide easy access to all published and unpublished data from clinical trials that it has sponsored; and third, the effectiveness and acceptability of paroxetine are particularly relevant in view of recent concerns about its safety profile, especially in terms of suicidal tendencies among pediatric and adult patients with major depression.^14–17     

Differences in serotonergic neurotransmission between rats displaying high or low anxiety/depression-like behaviour: effects of chronic paroxetine treatment

Disturbances in serotonergic neurotransmission have been suggested to be closely interlinked with hyperactivity of the hypothalamic-pituitary-adrenocortical (HPA) system, and are likely to be involved in the pathophysiology of anxiety disorders and major depression. We therefore investigated markers of serotonergic transmission and their modulation by chronic paroxetine in rats selectively bred for high (HAB) or low (LAB) anxiety-related behaviour, both under basal conditions and in response to emotional stress. Hippocampal serotonin 1 A (5-HT1A) receptor mRNA expression was reduced in HAB rats, whereas 5-HT concentrations in hippocampal microdialysates did not differ between HAB and LAB rats under basal conditions. In the hippocampus, overall expression of serotonin transporter binding sites was increased in HAB compared with LAB rats. Exposure to emotional stress failed to increase intrahippocampal 5-HT release in HAB rats whereas LAB rats displayed a physiological, albeit small rise. Chronic paroxetine treatment markedly increased the stress-induced rise in hippocampal 5-HT in HAB, but not LAB rats. This effect may be (at least in part) related to a greater down-regulation of hippocampal serotonin transporter binding sites by paroxetine in HABs compared with LABs, while 5-HT1A receptor expression remained unaffected in this brain area. The findings indicate reduced hippocampal serotonergic transmission in HAB rats as compared with LAB rats, which is evident both at the presynaptic (5-HT release) and the postsynaptic (5-HT1A receptor) level. Chronic paroxetine enhanced the presynaptic responsivity in HAB rats, but not LAB rats, pointing to a preferential efficacy of paroxetine in rats with enhanced anxiety/depression-related behaviour.     

Selective serotonin reuptake inhibitors for unipolar depression: a systematic review of classic long-term randomized controlled trials

Background

Selective serotonin reuptake inhibitors are increasingly used in the long-term treatment of depression. Much of the supporting evidence about the effects of these drugs comes from discontinuation trials, a variant of randomized controlled trials whose design is problematic to interpret. We conducted a systematic review to examine the efficacy and acceptability of long-term therapy with selective serotonin reuptake inhibitors relative to placebo in the treatment of unipolar depression.

Methods

We identified placebo-controlled randomized trials with a treatment duration of at least 6 months by searching MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials to update a recently published systematic review. Efficacy was defined in terms of response to treatment (50% improvement in depression score relative to baseline) and remission (score of 7 or below on the Hamilton rating scale for depression). Key secondary outcomes included quality of life, return to work, need for additional treatment and self-harm. Overall acceptability was defined in terms of dropouts for any reason over a course of treatment.

Results

Of the 2693 records identified initially, we included 6 randomized controlled trials that met our eligibility criteria. These studies had a moderate risk of bias, had assigned a total of 1299 participants with depression to either treatment or placebo and had followed both groups for 6–8 months. We observed statistically significant improvements in response to treatment (odds ratio [OR] 1.66, 95% confidence interval [CI] 1.12–2.48), but not in remission (OR 1.46, 95% CI 0.92–2.32) or acceptability (OR 0.87, 95% CI 0.67–1.14). The effects appeared greater among patients without comorbidities.

Interpretation

There is a lack of classic randomized controlled trials of serotonin reuptake inhibitors lasting more than 1 year for the treatment of depression. The results of our systematic review support current recommendations for 6–8 months of antidepressant treatment following initial recovery but provide no guidance for longer treatment.Over the past decade, the use of selective serotonin reuptake inhibitors for the management of depression has increased dramatically, and preliminary evidence suggests that long-term use, for more than 1 or 2 years, accounts for much of this rise.^1–3 Clinical practice guidelines generally recommend a 6- to 9-month course following initial recovery after a first episode of depression and longer, sometimes indefinite, therapy after subsequent episodes, to prevent relapse.^4–10Long-term randomized controlled trials of antidepressants have typically used 1 of 2 possible designs, each answering different questions (Figure 1).¹¹ The most widely used design is called the “discontinuation trial,” a 2-phase study in which all participants are initially treated with an open (unblinded) course of drug therapy. Participants attaining a certain response during the open-treatment phase enter the second phase, during which they are randomly assigned to continue active drug treatment or to receive placebo.^12–14 Discontinuation trials are believed to minimize the number of participants with depression who must be exposed to placebo. This advantage comes at a cost, since the results apply only to patients with a response to the medication, not to those who experience spontaneous recovery; furthermore, withdrawal symptoms may lead to an overestimate of the true effect of the medication. When this design is used to test long-term therapy with selective serotonin reuptake inhibitors for the treatment of depression, the results are difficult to interpret with confidence because rates of spontaneous recovery in depression are potentially high and because withdrawal effects can mimic depression.^13–15Open in a separate windowFigure 1: Two designs of randomized controlled trials used to investigate long-term antidepressant therapy.The second type of randomized trial used to test long-term therapy with selective serotonin reuptake inhibitors is a 2-arm parallel randomized controlled trial, hereafter referred to as a classic randomized controlled trial (Figure 1).¹⁶ In this type of trial, participants with acute depression are assigned to receive either placebo or active drug, and all those achieving a certain response, either to the drug or to the placebo, are followed. The advantage of classic randomized controlled trials is that data from all participants contribute to our understanding of the drug''s real-world effectiveness. Their main drawback is that a greater number of acutely ill people may have to receive placebo than in a discontinuation trial.¹³ Most classic trials of antidepressants are short-term studies. Fergusson and colleagues,¹⁷ in a systematic review examining selective serotonin reuptake inhibitors and suicide, identified 702 classic trials involving a total of 18 413 participants, the majority of which (93%) lasted less than 6 months.A recent systematic review based mainly on studies with discontinuation designs showed that, in a subgroup of patients who experienced recovery while taking medications, long-term therapy with selective serotonin reuptake inhibitors reduced the chances of relapse by up to 70% for up to 36 months, relative to patients whose therapy was discontinued earlier.⁶ However, there has been no systematic review of classic randomized trials of long-term therapy with this drug class to determine the potential benefits in all patients with depression, including those with spontaneous recovery.We sought to examine the efficacy and acceptability of long-term therapy with selective serotonin reuptake inhibitors relative to placebo in the treatment of moderate to severe depression, including subgroups of patients with major chronic health conditions. We also examined a number of key indicators of the quality of evidence and its clinical importance.     

Hypodensity of platelet serotonin uptake sites in posttraumatic stress disorder: Associated clinical features

We have previously reported that binding to blood platelets of paroxetine, a selective serotonin (5-HT) reuptake inhibitor which binds to 5-HT uptake sites, is decreased in patients with posttraumatic stress disorder (PTSD). Specifically, we found a lower number of platelet ³H-paroxetine binding sites (B_max) and a lower dissociation constant (K_d) for ³H-paroxetine binding in combat veterans with PTSD compared to normal control subjects. In the current study we assessed the relationship of platelet ³H-paroxetine binding to clinical features in 41 Vietnam combat veterans with SCID-diagnosed PTSD. The results indicated that B_max of platelet ³H-paroxetine binding was negatively correlated with both state and trait anxiety, as well as with depressive and overall PTSD symptoms. However, there was no evidence that platelet ³H-paroxetine binding differed as a function of comorbid psychiatric diagnoses including major depression, other anxiety disorders and substance abuse in these patients.     

Synaptic and Extrasynaptic Secretion of Serotonin

Serotonin is a major modulator of behavior in vertebrates and invertebrates and deficiencies in the serotonergic system account for several behavioral disorders in humans.The small numbers of serotonergic central neurons of vertebrates and invertebrates produce their effects by use of two modes of secretion: from synaptic terminals, acting locally in hard wired circuits, and from extrasynaptic axonal and somatodendritic release sites in the absence of postsynaptic targets, producing paracrine effects.In this paper, we review the evidence of synaptic and extrasynaptic release of serotonin and the mechanisms underlying each secretion mode by combining evidence from vertebrates and invertebrates. Particular emphasis is given to somatic secretion of serotonin by central neurons.Most of the mechanisms of serotonin release have been elucidated in cultured synapses made by Retzius neurons from the central nervous system of the leech. Serotonin release from synaptic terminals occurs from clear and dense core vesicles at active zones upon depolarization. In general, synaptic serotonin release is similar to release of acetylcholine in the neuromuscular junction.The soma of Retzius neurons releases serotonin from clusters of dense core vesicles in the absence of active zones. This type of secretion is dependent of the stimulation frequency, on L-type calcium channel activation and on calcium-induced calcium release.The characteristics of somatic secretion of serotonin in Retzius neurons are similar to those of somatic secretion of dopamine and peptides by other neuron types. In general, somatic secretion by neurons is different from transmitter release from clear vesicles at synapses and similar to secretion by excitable endocrine cells.     

[3H]cocaine labels a binding site associated with the serotonin transporter in guinea pig brain: Allosteric modulation by paroxetine

We studied the characteristics of [³H]cocaine binding to membranes prepared from whole guinea pig brain. Cocaine binding was specific and saturable. A one-site binding model fit the data adequately: the Kd value of [³H]cocaine was 44 nM with a Bmax value of 280 fmol/mg protein. The rank order of potency for the [³H]cocaine binding site was paroxetine > clomipramine > (–)-cocaine > fluoxetine > mazindol > desipramine > GBR12909 > phencyclidine > benztropine > GBR12935 > (+)-cocaine. The IC50 values of these drugs for inhibition of [³H]cocaine binding were highly correlated with their IC50 values for inhibition of [³H]5-HT uptake into synaptosomes prepared from whole guinea pig brain. High affinity 5-HT uptake inhibitors produced dose-dependent wash-resistant (pseudoirreversible) inhibition of [³H]cocaine binding. The wash-resistant inhibition produced by paroxetine was due to an increase in the Kd of [³H]cocaine binding sites, and was accompanied by an increase in the dissociation rate, consistent with an allosteric mechanism. These studies suggest that, using membranes prepared from whole guinea pig brain, [³H]cocaine labels a binding site associated with serotonin transporter and that paroxetine and cocaine bind to different sites on the serotonin transporter.Abbreviations GBR12909 1-(2-{bis(4-fluorophenyl)methoxy}ethyl)-4-{3-phenylpropyl}piperazine - TCP 1-{1-(2-thienyl)cyclohexyl}piperidine - BTCP N-{1-(2-benzo(b)thiophenyl)cyclohexyl}piperidine - PCP 1-(1-phenylcyclohexyl)piperidine - GBR12935 (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine) - CMI clomipramine     

Solubilization and characterization of [3H]Imipramine and [3H]Paroxetine binding sites from calf striatum

The serotonin (5-HT) transporter from calf striatum cerebral membranes was solubilized with digitonin and characterized by gel exclusion chromatography. [³H]Imipramine and [³H]paroxetine were utilized as markers for labeling it.³H-imipramine labels a high- and a low-affinity site on striaturn membranes, whereas it binds to a single high-affinity site on the solubilized fraction. [³H]Paroxetine binds with the same affinity to a single site on both membranes and solubilized preparations. After gel exclusion chromatography of the solubilizate both [³H]imipramine and [³H]paroxetine bind on an identical fraction of 205 kDa molecular weight, with a similar maximum number of binding sites (Bmax). Our results suggest that both³H-imipramine and [³H]paroxetine bind to a common site on the 5-HT transporter.     

The Influence of 5-HTTLPR Genotype on the Association between the Plasma Concentration and Therapeutic Effect of Paroxetine in Patients with Major Depressive Disorder

Introduction

The efficacy of treatment with selective serotonin reuptake inhibitors in patients with major depressive disorder (MDD) can differ depending on the patient''s serotonin transporter-linked polymorphic region (5-HTTLPR) genotype, and the effects of varying plasma concentrations of drugs can also vary. We investigated the association between the paroxetine plasma concentration and clinical response in patients with different 5-HTTLPR genotypes.

Methods

Fifty-one patients were enrolled in this study. The Montgomery-Asberg Depression Rating Scale (MADRS) was used to evaluate patients at 0, 1, 2, 4, and 6 weeks. The patients'' paroxetine plasma concentrations at week 6 were measured using high-performance liquid chromatography. Additionally, their 5-HTTLPR polymorphisms (alleles S and L) were analyzed using a polymerase chain reaction with specific primers. We divided the participants into two groups based on their L haplotype: the SS group and the SL and LL group. We performed single and multiple regression analyses to investigate the associations between MADRS improvement and paroxetine plasma concentrations or other covariates for each group.

Results

There were no significant differences between the two groups with regard to demographic or clinical data. In the SS group, the paroxetine plasma concentration was significantly negatively correlated with improvement in MADRS at week 6. In the SL and LL group, the paroxetine plasma concentration was significantly positively correlated with improvement in MADRS at week 6 according to the results of the single regression analysis; however, it was not significantly correlated with improvement in MADRS at week 6 according to the results of the multiple regression analysis.

Conclusion

Among patients with MDD who do not respond to paroxetine, a lower plasma concentration or a lower oral dose of paroxetine might be more effective in those with the SS genotype, and a higher plasma concentration might be more effective in those with the SL or LL genotype.     

A novel herbal treatment reduces depressive-like behaviors and increases BDNF levels in the brain of stressed mice

Aims

Depression is a chronic, recurring and potentially life-threatening illness. Current treatments for depression are characterized by a low success rate and associated with a wide variety of side effects. The aim of the present study was to evaluate the behavioral and biological anti-depressant effects of a novel herbal treatment (NHT), as well as to assess its potential side effects, in comparison to treatment with the selective serotonin reuptake inhibitor escitalopram.

Main methods

Depressive-like behavior was evaluated using the forced swim test (FST) and the tail suspension test (TST). Sexual behavior was evaluated following treatment by measuring latency before first mount and number of total mounts. Brain derived neurotrophic factor (BDNF) levels were evaluated using enzyme-linked immunosorbent assay. Serotonin transporter (SERT) levels in the pre-frontal cortex (PFC) and hypothalamus were evaluated using high affinity binding assay.

Key findings

(1) The NHT reduced depressive-like behavior in the FST and TST; (2) BDNF levels in the PFC of mice treated both with the NHT and escitalopram were increased; (3) SERT levels in the hypothalamus were significantly higher in the NHT group, in comparison to escitalopram and the control groups, and significantly lower in the PFC of the NHT group in comparison to the escitalopram group; and (4) the NHT led to less sexual dysfunction, compared to treatment with escitalopram.

Significance

Our NHT has the potential of being highly efficacious in treating depression in humans, while causing minimal to no influence on sexual function.     

The Efficacy of Paroxetine and Placebo in Treating Anxiety and Depression: A Meta-Analysis of Change on the Hamilton Rating Scales

Background

Previous meta-analyses of published and unpublished trials indicate that antidepressants provide modest benefits compared to placebo in the treatment of depression; some have argued that these benefits are not clinically significant. However, these meta-analyses were based only on trials submitted for the initial FDA approval of the medication and were limited to those aimed at treating depression. Here, for the first time, we assess the efficacy of a selective serotonin reuptake inhibitor (SSRI) in the treatment of both anxiety and depression, using a complete data set of all published and unpublished trials sponsored by the manufacturer.

Methods and Findings

GlaxoSmithKline has been required to post the results for all sponsored clinical trials online, providing an opportunity to assess the efficacy of an SSRI (paroxetine) with a complete data set of all trials conducted. We examined the data from all placebo-controlled, double-blind trials of paroxetine that included change scores on the Hamilton Rating Scale for Anxiety (HRSA) and/or the Hamilton Rating Scale for Depression (HRSD). For the treatment of anxiety (k = 12), the efficacy difference between paroxetine and placebo was modest (d = 0.27), and independent of baseline severity of anxiety. Overall change in placebo-treated individuals replicated 79% of the magnitude of paroxetine response. Efficacy was superior for the treatment of panic disorder (d = 0.36) than for generalized anxiety disorder (d = 0.20). Published trials showed significantly larger drug-placebo differences than unpublished trials (d’s = 0.32 and 0.17, respectively). In depression trials (k = 27), the benefit of paroxetine over placebo was consistent with previous meta-analyses of antidepressant efficacy (d = 0.32).

Conclusions

The available empirical evidence indicates that paroxetine provides only a modest advantage over placebo in treatment of anxiety and depression. Treatment implications are discussed.     

Linkage mapping of serotonin transporter protein gene SLC6A4 on chromosome 17

Abnormalities in monoamine metabolism, including serotonin metabolism, have been implicated in the pathophysiology of affective disorders, schizophrenia, suicide, and other psychiatric disorders. Serotonin transporter protein (SERT) allows neurons to retrieve serotonin that has been released into a synapse. SERT is a site of action for several drugs with CMS effects, including both therapeutic agents (e.g., antidepressants) and drugs of abuse (e.g., cocaine). This gene had previously been physically mapped to chromosome 17. We used a PCR product corresponding to the 3 untranslated region of the gene as a probe to identify restriction fragment length polymorphism (RFLP), which we then used to establish that the SLC6A4, genetic locus for SERT, is near 17q12 and probably flanked by D17S58 and D17S73 (a location consistent with observed crossovers). These data should be useful for linkage studies of neuropsychiatric disorders. (Joyce et al. 1993). Neurotransmitter reuptake sites (including also the norepinephrine transporter protein and the dopamine transporter protein) are logical candidate genes for susceptibility to psychiatric illness. We have previously (Gelernter et al. 1993) mapped the norepinephrine transporter protein to chromosome 16q21. We describe here linkage mapping of the serotonin transporter protein gene (gene symbol SLC6A4, for solute carrier family 6 (neurotransporter, serotonin), member 4), which was cloned in 1991 (Blakely et al. 1991; Hoffman et al. 1991) and previously assigned to chromosome 17, most likely to band 17q11.2, by in situ hybridization (Ramamoorthy et al. 1993). Our linkage results confirm the initial mapping of SLC6A4 and place it in the linkage map of proximal 17q.     

Thermostabilization of the Human Serotonin Transporter in an Antidepressant-Bound Conformation

Serotonin is a ubiquitous chemical transmitter with particularly important roles in the gastrointestinal, cardiovascular and central nervous systems. Modulation of serotonergic signaling occurs, in part, by uptake of the transmitter by the serotonin transporter (SERT). In the brain, SERT is the target for numerous antidepressants including tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs). Despite the importance of SERT in human physiology, biochemical, biophysical and high-resolution structural studies have been hampered due to the instability of SERT in detergent micelles. To identify a human SERT (hSERT) construct suitable for detailed biochemical and structural studies, we developed an efficient thermostability screening protocol and rapidly screened 219 mutations for thermostabilization of hSERT in complex with the SSRI paroxetine. We discovered three mutations—Y110A, I291A and T439S –that, when combined into a single construct, deemed TS3, yielded a hSERT variant with an apparent melting temperature (Tm) 19°C greater than that of the wild-type transporter, albeit with a loss of transport activity. Further investigation yielded a double mutant—I291A and T439S—defined as TS2, with a 12°C increase in Tm and retention of robust transport activity. Both TS2 and TS3 were more stable in short-chain detergents in comparison to the wild-type transporter. This thermostability screening protocol, as well as the specific hSERT variants, will prove useful in studies of other integral membrane receptors and transporters and in the investigation of structure and function relationships in hSERT.     

Serotonin and fluoxetine modulate bone cell function in vitro

Recent studies have proposed a role for serotonin and its transporter in regulation of bone cell function. In the present study, we examined the in vitro effects of serotonin and the serotonin transporter inhibitor fluoxetine "Prozac" on osteoblasts and osteoclasts. Human mononuclear cells were differentiated into osteoclasts in the presence of serotonin or fluoxetine. Both compounds affected the total number of differentiated osteoclasts as well as bone resorption in a bell-shaped manner. RT-PCR on the human osteoclasts demonstrated several serotonin receptors, the serotonin transporter, and the rate-limiting enzyme in serotonin synthesis, tryptophan hydroxylase 1 (Tph1). Tph1 expression was also found in murine osteoblasts and osteoclasts, indicating an ability to produce serotonin. In murine pre-osteoclasts (RAW264.7), serotonin as well as fluoxetine affected proliferation and NFkappaB activity in a biphasic manner. Proliferation of human mesenchymal stem cells (MSC) and primary osteoblasts (NHO), and 5-HT2A receptor expression was enhanced by serotonin. Fluoxetine stimulated proliferation of MSC and murine preosteoblasts (MC3T3-E1) in nM concentrations, microM concentrations were inhibitory. The effect of fluoxetine seemed direct, probably through 5-HT2 receptors. Serotonin-induced proliferation of MC3T3-E1 cells was inhibited by the PKC inhibitor (GF109203) and was also markedly reduced when antagonists of the serotonin receptors 5-HT2B/C or 5-HT2A/C were added. Serotonin increased osteoprotegerin (OPG) and decreased receptor activator of NF-kappaB ligand (RANKL) secretion from osteoblasts, suggesting a role in osteoblast-induced inhibition of osteoclast differentiation, whereas fluoxetine had the opposite effect. This study further describes possible mechanisms by which serotonin and the serotonin transporter can affect bone cell function.     

"Broad spectrum" antidepressants: is more better for the treatment of depression?

The majority of antidepressants in current use selectively inhibit the reuptake of serotonin and/or norepinephrine. "Broad spectrum" antidepressants are compounds that inhibit the reuptake of norepinephrine, serotonin and dopamine, the three biogenic amines most closely linked to depression. The pharmacological profile of one such compound has recently been described (European Journal of Pharmacology, 461 (2003) 99). DOV 21,947, an azabicyclo[3.1.0]hexane, potently inhibits norepinephrine, serotonin and dopamine reuptake by the corresponding human transporter proteins. DOV 21,947 is orally active in the forced swim and tail suspension tests, preclinical procedures that are highly predictive of antidepressant action in patients. A closely related compound, DOV 216,303 is safe and well-tolerated in Phase I studies. The plasma concentrations of DOV 216,303 following both single and multiple doses appear sufficient to inhibit norepinephrine, serotonin, and dopamine reuptake. Based on the pivotal role proposed for dopamine in depression, it has been hypothesized that a broad spectrum antidepressant will produce a more rapid onset and/or higher efficacy than agents inhibiting the reuptake of serotonin and/or norepinephrine.     

Metabolism and Pharmacokinetics of Selective Serotonin Reuptake Inhibitors

1. Five drugs with the predominant pharmacologic effect of inhibiting the neuronal reuptake of serotonin are available worldwide for clinical use. This class of psychoactive drugs, known as selective serotonin reuptake inhibitors (SSRIs), is comprised of fluoxetine, sertraline, paroxetine, fluvoxamine, and citalopram.2. The SSRIs appear to share similar pharmacodynamic properties which translate to efficacy in the treatment of depression and anxiety syndromes. The drugs are differentiated by their pharmacokinetic properties with regard to stereochemistry, metabolism, inhibition of cytochrome enzymes, and participation in drug–drug interactions. Studies focusing on the relationship of plasma drug concentration to therapeutic and adverse effects have not confirmed the value of plasma concentration monitoring.3. This review summarizes the metabolism and relevant pharmacokinetic properties of the SSRIs.     

Serotonin in the developing stomatogastric system of the lobster,Homarus americanus

We studied the development of the serotonergic modulation of the stomatogastric nervous system of the lobster, Homarus americanus. Although the stomatogastric ganglion (STG) is present early in embryonic development, serotonin immunoreactivity is not visible in the STG until the second larval stage. However, incubation of the STG with exogenous serotonin showed that a serotonin transporter is present in embryonic and early larval stages. Serotonin uptake was blocked by paroxetine and 0% Na(+) saline. The presence of a serotonin transporter in the embryonic STG suggests that hormonally liberated serotonin could be taken up by the STG, and potentially released as a "borrowed transmitter". Consistent with a potential hormonal role, serotonin is found in the pericardial organs, a major neurosecretory structure, by midembryonic development. The rhythmic motor patterns produced by embryonic and larval STGs were decreased in frequency by serotonin. Lateral Pyloric (LP) neuron-evoked excitatory junctional potentials (EJPs) in the embryos and the first larval stage (LI) were larger, slower, and more variable than those in the adult. The amplitude of adult LP neuron-evoked EJPs was increased more than twofold in serotonin, but in embryos and LI preparations this effect was negligible. In embryos and LI preparations, serotonin increased the occurrence of muscle fiber action potentials and altered the EJP wave-form. These data demonstrate that serotonin receptors are present in the stomatogastric nervous system early in development, and suggest that the role of serotonin changes from modulation of muscle fiber excitability early in development to enhancement of neurally evoked EJPs in the adult.