A selective serotonin reuptake inhibitor, citalopram, inhibits collagen-induced platelet aggregation and activation

Clinical depression is a significant risk factor for cardiovascular diseases and confers an increased risk of mortality. Increased platelet reactivity may predispose depressed patients to cardiovascular diseases. The antidepressants selective serotonin reuptake inhibitors (SSRIs) have been found to have cardioprotective effects probably via the attenuation of platelet activation independently in addition to treatment of depression itself. However, the characters of the inhibitory effect of SSRIs on platelets remain largely unknown. Here we show that an SSRI, citalopram, specifically inhibited collagen-induced platelet aggregation. Citalopram, however, revealed only little inhibitory effect on platelet aggregation induced by thrombin, U46619, and ionomycin, and failed to inhibit reversible platelet aggregation induced by adenosine diphosphate with fibrinogen. Collagen-induced of α_IIbβ₃ integrin activation in platelets under a static condition was not influenced by citalopram. Citalopram inhibited convulxin-induced platelet aggregation and α_IIbβ₃ integrin activation. In the experiments with fibrinogen-induced aggregation in elastase-treated platelets, citalopram inhibited only collagen-induced α_IIbβ₃ activation but not the binding activities between activated α_IIbβ₃ integrin and fibrinogen. Moreover, citalopram inhibited α-granule and dense granule secretion from platelets in response to collagen, as determined by a reduced expression of P-selectin and adenosine triphosphate release, respectively. In addition, collagen-induced thromboxane A₂ release in platelets was attenuated by citalopram pretreatment. These findings might specify the mechanisms of inhibitory effects of citalopram on collagen mediated platelet activation and aggregation, and further support the cardioprotective effect of SSRIs.     

Platelet serotonin reuptake inhibition and response to SSRIs in depressed adolescents

OBJECTIVE: The authors examined platelet serotonin reuptake inhibition and response to selective serotonin reuptake inhibitor (SSRI) treatment in depressed adolescents. METHOD: Twenty-three depressed adolescents participating in pharmacokinetic studies of SSRIs had platelet serotonin reuptake measured before and after 14-28 days of treatment. The Clinical Global Impression (CGI) improvement rating was determined on the basis of all clinical information and was performed blind to the platelet data. RESULTS: Improvement in depressive symptoms as rated with the CGI improvement subscale was significantly associated with the percentage change in platelet serotonin reuptake inhibition from pre- to posttreatment. Improvement in depression was also associated with absolute decrease in platelet serotonin reuptake when adjusted for the magnitude of baseline reuptake. CONCLUSIONS: Platelet serotonin reuptake inhibition may be an appropriate surrogate biological marker for the pharmacodynamic activity of SSRIs in depressed adolescents.     

Platelet MAO deamination of serotonin in depressed patients. Changes after imipramine treatment and clinical correlations

Monoamine oxidase (MAO) in blood platelets has been used as a model to study MAO in the central nervous system, where disorders in serotonergic systems are thought to occur in depression. Inconsistent changes in platelet MAO of depressed patients have been reported when several substrates other than serotonin (5-HT) have been used. To correlate changes in platelet MAO activity with the enzyme activity in central serotonergic systems, the platelet MAO activity of depressed patients (first unmedicated and then after 3 weeks and 2 months of imipramine treatment) and normal controls was measured using 5-HT as substrate. The results showed that there is a steady, measurable platelet MAO activity with that substrate. This activity was significantly higher in unmedicated depressed patients than in controls, and it decreased progressively with imipramine treatment, reaching a normal level when the patients were clinically recovered from depression after 2 months of therapy.     

Reduction of blood platelet serotonin levels in manic and depressed patients.

Blood platelet serotonin levels were measured in unmedicated 12 manic and 74 depressive patients with 118 normal control subjects employed. Blood platelets were separated by multiple centrifugation in the medium of Na2-EDTA solution, and the loss of serotonin during collecting procedures was about 11%. The mean value of blood platelet serotonin levels in depressed patients was 594 +/- 288 ng/mg platelet protein (+/- S.D.), which was significantly lower than that for normal controls, 780 +/- 253 ng/mg protein (p less than 0.001). Age does not account for the reduction of serotonin levels both in depressed and in normal population. Unipolar and involutional depressed patients exhibited to have the most pronounced reduced levels of serotonin of various subtypes of depression, while bipolar depressed patients, neurotic and chronic characterological depressed patients as well as patients with first-episode depression had the values which were comparable with those in normal controls. Manic patients did not show enhancement but did reduction of serotonin levels, the mean being 580 +/- 152 ng/mg protein, which made a contrast with their clinical manifestations of exhilaration and hyperactivity. Changes in blood platelet serotonin levels were determined before, during and after administration of L-5-HTP with a maintenance dose of 300 mg daily in nine depressed patients. Serotonin levels in all subjects were lifted to normal levels during the L-5-HTP treatment, while clinical symptoms were not improved with the treatment. Reduction of blood platelet serotonin levels in depressed patients may be due to their psychobiological distinction, which involves abnormal biogenic amine metabolism in the brain.     

Platelet serotonin levels in pervasive developmental disorders and mental retardation: diagnostic group differences, within-group distribution, and behavioral correlates

OBJECTIVE: To investigate group differences, the within-group distributions, and the clinical correlates of platelet serotonin (5-HT) levels in pervasive developmental disorders (PDD). METHOD: Platelet 5-HT levels were measured in Dutch children and young adults, recruited from 2001 through 2003, with PDD (autism, Asperger's, and PDD-not otherwise specified [PDD-NOS]; n = 81) or with mental retardation (MR; n = 54) but without PDD, and in normal controls (n = 60). The distribution of platelet 5-HT levels was assessed using mixture-modeling analyses. Relationships between platelet 5-HT levels and a full range of demographic, clinical, and behavioral variables were examined. RESULTS: Group mean (+/- SD) platelet 5-HT levels (nmol/10 platelets) were significantly higher in the autistic (4.51 +/- 1.61, n = 33) and PDD-NOS (4.90 +/- 1.54, n = 43) groups compared to the MR (3.48 +/- 1.33, n = 54) or the normal control (3.58 +/- 1.08, n = 60) groups (F4,190 = 9.35, p <.001). Platelet 5-HT values in the combined PDD group showed a bimodal distribution, and an empirical cutpoint for hyperserotonemia was determined. None of the behavioral variables examined was significantly associated with platelet 5-HT levels. CONCLUSIONS: The platelet hyperserotonemia of autism was replicated in Dutch subjects. Platelet 5-HT levels were also increased in PDD-NOS, while no elevation was seen in MR. Platelet 5-HT levels appeared to be bimodally distributed in the PDD group, with an apparent hyperserotonemic subgroup.     

Physiological characteristics of platelet/circulatory serotonin: study on a large human population

The aim of this work was the study of platelet/circulatory serotonin (5-hydroxytryptamine, 5-HT), specifically alternative ways of its measurement and main physiological characteristics. The study was performed on a large human population (N=500) of blood donors of both sexes over the course of a longer time period (17 months). Owing to the heterogeneity in measurement of circulatory serotonin encountered in the literature, three ways of expression were comparatively studied: per unit number of platelets, per unit mass of platelet protein and per unit volume of whole blood. Results demonstrated unimodal distribution of individual frequencies of platelet/circulatory serotonin in the human population with the mean values of 579+/-169 ng 5-HT/10(9) platelets; 332+/-89.9 ng 5-HT/mg protein and 130+/-42.3 ng 5-HT/ml blood (mean+/-S.D.). A progressive decrease of serotonin level with age (18-65 years) was demonstrated, reaching statistical significance between the extreme age groups. No significant differences in the serotonin level between the sexes were observed. No seasonal oscillations in platelet/circulatory serotonin were found. Platelet serotonin demonstrated intra-individual stability over time. Finally, regarding the methodology of measurement, our results demonstrated a good correlation among the above-mentioned ways of expression of platelet/circulatory serotonin. This indicates the possibility of intercomparison of the literature reports expressing this physiological parameter either as 5-HT concentration in platelets or as 5-HT level in the circulation.     

Seasonal variation of platelet serotonin uptake and 3H-imipramine binding in normal and depressed subjects

Density of 3H-imipramine binding sites and serotonin (5-HT) uptake in blood platelets were repeatedly recorded in normal controls (n = 9) and depressed patients (n = 7 for the imipramine binding assay and n = 4 for the serotonin uptake) over a 1-year period. The study demonstrated a striking seasonal variation of both parameters in both groups, with lower values in winter and spring than in summer and fall. No difference in the density of 3H-imipramine binding sites was found between the two populations throughout the year, but serotonin uptake was significantly decreased in depressed patients in May and September. These results underscore the importance of studying controls and patients at the same time of the year.     

Desensitization of 5-HT2A receptor function by chronic administration of selective serotonin reuptake inhibitors

We have previously shown that chronic treatment with selective serotonin reuptake inhibitors (SSRIs), fluvoxamine and paroxetine, attenuated m-chlorophenylpiperazine (mCPP)-induced hypolocomotion in rats. The effect of these SSRIs on the response to mCPP is thought to be caused by the desensitization of 5-HT2C receptor function. In the present study, we investigated whether chronic administration of SSRI could reduce another pharmacological response to mCPP in rats, i.e., the induction of the secretion of corticosterone. The mCPP-induced increase in the serum concentration of corticosterone was not blocked by the 5-HT2C antagonist SB242084, but was blocked by the 5-HT2A antagonist ketanserin. Chronic treatment with fluvoxamine and paroxetine attenuated the response to mCPP, while these SSRIs had no effects in control rats. These results suggest that the desensitization of 5-HT2A receptor function occurs in the same way as that of 5-HT2C receptor function through chronic treatment with either fluvoxamine or paroxetine as a consequence of prolonged exposure to elevated levels of serotonin. The hypersensitivity of 5-HT2A receptors is observed in depressed patients, and chronic treatment with many antidepressants such as tricyclic antidepressants have been reported to reduce 5-HT2A receptor density and/or efficacy. The desensitization of 5-HT2A receptor function might contribute to the therapeutic mechanism of action of these SSRIs, as seen with other classes of antidepressants.     

Reactivity of serotonin in whole blood: relationship with drug response in obsessive-compulsive disorder.

BACKGROUND: Obsessive-compulsive disorder responds almost only to potent serotonin reuptake inhibitors. Previous studies have suggested a relation between serotonergic function and clinical outcome in serotonin reuptake inhibitor treatment of obsessive-compulsive disorder. METHODS: In a randomized, double-blind trial, comparing clomipramine, paroxetine, and a placebo in obsessive-compulsive disorder, serotonin levels in whole blood (WB-5-HT) were measured at baseline, after 1 week, and after 4 weeks of treatment and related to clinical outcome in 36 patients. RESULTS: In patients treated with serotonin reuptake inhibitors there was a pronounced decrease of WB-5-HT, variable after 1 week and uniformly maximal after 4 weeks. The decrease of WB-5-HT after 1 week of serotonin reuptake inhibitor treatment correlated negatively with clinical outcome after 12 weeks (r = -.61, p =.0006); hence, patients with slower WB-5-HT reactivity eventually responded better to treatment. Baseline WB-5-HT, but not WB-5-HT reactivity, was related to season. Depression, autistic traits, and previous serotonin reuptake inhibitor treatment predicted nonresponse. CONCLUSIONS: A fast decrease of WB-5-HT was associated with poor clinical outcome. This may be related to faster serotonin efflux from platelets, which has previously been linked to autism. Further studies are necessary to identify the underlying mechanism and discern whether serotonin reuptake inhibitor-induced WB-5-HT decrease is clinically useful.     

Effects of amoxapine on serotonin uptake in human blood platelets of depressed patients and normal controls

The effect of amoxapine and imipramine on the serotonin (5-HT) uptake of blood platelets from depressed patients and normal controls was studied ex vivo or in vitro, respectively. Amoxapine was approximately one-tenth as potent as imipramine in inhibiting 5-HT uptake in blood platelets from normal controls in vitro. Both drugs inhibited 5-HT uptake in a competitive manner. However, ex vivo studies demonstrated that imipramine produced a mixed inhibition and amoxapine, a competitive inhibition of 5-HT uptake. There was no relationship between the change in the platelet affinity for 5-HT after treatment with amoxapine and clinical response to amoxapine.     

Relationship between mepacrine-labelled dense body number, platelet capacity to accumulate 14C-5-HT and platelet density in the Bernard-Soulier and Hermansky-Pudlak syndromes

We have used the mepacrine-labelling procedure to measure the dense body (serotonin storage organelle) content of the platelets of 2 hereditary disorders where abnormalities in dense body number were suspected. The platelets were incubated with mepacrine and examined by fluorescence microscopy. A mean number of 5.4 +/- 0.8 (SD) dense bodies per platelet was calculated from the data obtained using platelets isolated from 40 normal human subjects. In contrast the platelets of 2 patients with the Bernard-Soulier syndrome contained an average of 14 and 17 labelled granules. This increase was associated with a much greater capacity of the platelets to accumulate 14C-5-HT. The opposite result was obtained using the platelets from 2 patients with the Hermansky-Pudlak syndrome which contained few granules labelled by mepacrine and took up less 14C-5-HT than normal human platelets. Centrifugation of the patients' platelets on discontinuous sucrose gradients showed that the platelets of the 2 Bernard-Soulier patients were much denser than normal whereas a high proportion of low density platelets was observed in the Hermansky-Pudlak syndrome. These results further define the platelet abnormalities in the two syndromes and suggest that dense body number may be one of the factors governing platelet density.     

Characterization of rat platelet serotonin receptors with tryptamine agonists and the antagonists: ketanserin and SCH 23390.

Current literature suggests that the platelet 5-HT2 receptor, thought to be the only active platelet serotonin (5-HT) receptor, may be both heterogeneous and not the sole 5-HT receptor subtype on platelet membranes. The present studies used more selective tryptamine agonists, and the antagonists ketanserin and SCH 23390 to characterize rat platelet 5-HT receptors in vitro. The present studies also addressed anticoagulant effects (citrate versus heparin) on platelet 5-HT aggregation in the rat. 5-HT was less potent at enhancing ADP-induced aggregation in heparinized rat platelet rich plasma (PRP) as compared to citrated PRP. However, potency and maximum aggregation to ADP were greater in heparinized platelets. In citrated rat PRP, the selective tryptamine agonists, 5-carboxamidotryptamine (5-CT) and 2-CH3-5-HT, produced little change in the baseline ADP-induced aggregation and induced platelet shape change only in higher concentrations (greater than 1 microM). In contrast, alpha-CH3-5-HT-induced shape change and enhancement of ADP aggregation were superimposable with that of 5-HT itself suggesting 5-HT2 receptor activation. The antagonists, ketanserin and SCH 23390, inhibited 5-HT enhancement of ADP-induced aggregation with affinity constants consistent with the presence of 5-HT2 receptors as well. Studies with heparinized rat PRP did not unmask activity to 5-CT or 2-CH3-5-HT. Thus, although reports of multiple platelet 5-HT receptors exist, the only detectable, functional 5-HT receptor to enhance aggregation in rat platelets was probably of the 5-HT2 type.     

In vitro thromboxane synthesis of depleted blood platelets following renal transplantation

Renal transplant rejection is associated with platelet activation in vivo which may lead to partially alpha- and delta-granule-depleted platelets that continue to circulate. These "exhausted" platelets are hemostatically defective. To quantitate the extent of platelet granule depletion following kidney transplantation, we determined intraplatelet levels of beta-thromboglobulin (beta TG), platelet factor 4 (PF4), and serotonin (5-hydroxytryptamine, 5-HT) ex vivo in Triton X-100-treated platelet lysates. To explore biochemical alterations of partially depleted platelets, we studied platelet thromboxane A2 (TXA2) synthesis in citrated platelet-rich plasma (PRP) upon stimulation with thrombin or collagen in 45 recipients of renal allografts and 10 healthy volunteers. The patients were divided into subjects with acute and chronic allograft rejection (N = 15), those with compensated renal failure after kidney transplantation but without evidence of allograft rejection (N = 15), and those with functioning renal transplant (N = 15). The mean intraplatelet content of beta TG (38.6 +/- 4.2 micrograms/10(9) platelets), PF4 (11.8 +/- 1.8 micrograms/10(9) platelets), and 5-HT (274 +/- 31 ng/10(9) platelets) in patients with acute or chronic renal allograft rejection was significantly lower than in other recipients of kidney transplants or healthy volunteers (beta TG: 59.9 +/- 4.7 micrograms/10(9) platelets; PF4: 20.4 +/- 2.3 micrograms/10(9) platelets; 5-HT: 461 +/- 48 ng/10(9) platelets; p less than 0.005 in all cases).(ABSTRACT TRUNCATED AT 250 WORDS)     

Resolution of Sleepiness and Fatigue in Major Depressive Disorder: A Comparison of Bupropion and the Selective Serotonin Reuptake Inhibitors

BACKGROUND: The purpose of this study was to examine whether the treatment of major depressive disorder (MDD) with the norepinephrine-dopamine reuptake inhibitor (NDRI) bupropion results in a greater resolution of sleepiness and fatigue than with the selective serotonin reuptake inhibitors (SSRIs). METHODS: Six double-blind, randomized clinical trials comparing bupropion (n = 662) with an SSRI (n = 655) for the treatment of MDD were pooled. Hypersomnia scores were defined as the sum of scores of the Hamilton Depression Rating Scale (HDRS) items #22, 23, and 24. Fatigue scores were defined as the score of HDRS item #13. RESULTS: There was a greater improvement in hypersomnia scores among bupropion-treated than SSRI-treated (p < .0001) or placebo-treated patients (p = .0008). There was also a greater improvement in fatigue scores among bupropion-treated (p < .0001) and SSRI-treated (p = .0005) than placebo-treated patients as well as a greater improvement in fatigue scores among bupropion-treated than SSRI-treated patients (p = .0078). Fewer bupropion-remitters than SSRI-remitters experienced residual hypersomnia (20.5% vs. 32.1%; p = .0014) or residual fatigue (19.5% vs. 30.2%; p = .0020). CONCLUSION: Treatment of MDD with the NDRI bupropion resulted in a greater resolution of sleepiness and fatigue than SSRIs treatment. Although preliminary, these results warrant prospectively designed studies examining potential differences between bupropion and the SSRIs on these specific depressive symptoms.     

Sex differences in diencephalon serotonin transporter availability in major depression.

BACKGROUND: Major depression is more prevalent in women than men. The present study evaluated if previous findings that demonstrated decreased 5-hydroxytryptamine (5-HT) transporter availability in depressed patients would be confirmed in a larger sample and also evaluated sex differences. METHODS: Depressed (n = 32) and healthy subjects (n = 32), including 16 pairs of women and men, participated in an iodine-123-2 beta-carbomethoxy-3beta-(4-iodophenyltropane) ([(123)I]beta-CIT) single photon emission computed tomography (SPECT) and a magnetic resonance imaging (MRI) scan. Participants were administered [(123)I]beta-CIT (225.7 +/- 3.7 MBq) and imaged 23.0 +/- 1.6 hours later. Statistical analyses included analysis of variance and a regression analysis of the main and interactive effects of age, sex, and depression. RESULTS: Overall, depressed patients demonstrated 12% lower diencephalon and no change in striatal or brainstem [(123)I]beta-CIT uptake. Significant age by sex, sex by depression, and age by sex by depression interactions were noted due to 22% lower diencephalon [(123)I]beta-CIT uptake in depressed women compared with less than a 1% decrease in depressed men. CONCLUSIONS: As observed previously, diencephalon 5-HT transporter availability is decreased in depressed patients. However, the decrease appears to be sex-specific and age-dependent. These findings suggest that serotonergic mechanisms mediating depressed mood differ between men and women in an age-dependent manner and may explain why young women respond better to treatment with selective serotonin reuptake inhibitor (SSRI) antidepressants.     

Maternal sertraline treatment and serotonin transport in breast-feeding mother-infant pairs

OBJECTIVE: Pharmacological treatment of postpartum depression is frequently complicated by the mother's desire to breast-feed. Although breast milk levels of several selective serotonin reuptake inhibitors (SSRIs) have been reported to be relatively low, a critical question is whether SSRI exposure during nursing results in clinically significant blockade of serotonin (5-HT) reuptake in infants. This study determined the degree of transporter blockade in infants exposed to sertraline through maternal breast milk. METHOD: The extent of maternal and infant transporter blockade was assessed by measurement of platelet levels of 5-HT in 14 breast-feeding mother-infant pairs before and after 6-16 weeks of maternal treatment with sertraline for major depression with postpartum onset. Plasma sertraline and desmethylsertraline levels were obtained in 13 of these mothers and 11 of their infants. RESULTS: Marked declines in platelet 5-HT levels of 70%-96% were observed in mothers after sertraline treatment, 25-200 mg/day. In contrast, infants showed little or no change in platelet 5-HT levels after exposure through breast-feeding. Mean levels of maternal plasma sertraline and its major metabolite, desmethylsertraline, were 30.7 ng/ml and 45.3 ng/ml, respectively. Drug and drug metabolite concentrations in the infants were at or below the lower limit of quantitation. CONCLUSIONS: The data indicate that while mothers receiving clinical doses of sertraline experience substantial blockade of the platelet 5-HT transporter, platelet 5-HT uptake in nursing infants of treated mothers is unaltered. The observations suggest that mothers taking sertraline can breast-feed without appreciably affecting peripheral or central 5-HT transport in their infants.     

Effects of chronic antidepressant treatments on serotonin transporter function, density, and mRNA level.

To investigate functional changes in the brain serotonin transporter (SERT) after chronic antidepressant treatment, several techniques were used to assess SERT activity, density, or its mRNA content. Rats were treated by osmotic minipump for 21 d with the selective serotonin reuptake inhibitors (SSRIs) paroxetine or sertraline, the selective norepinephrine reuptake inhibitor desipramine (DMI), or the monoamine oxidase inhibitor phenelzine. High-speed in vivo electrochemical recordings were used to assess the ability of the SSRI fluvoxamine to modulate the clearance of locally applied serotonin in the CA3 region of hippocampus in drug- or vehicle-treated rats. Fluvoxamine decreased the clearance of serotonin in rats treated with vehicle, DMI, or phenelzine but had no effect on the clearance of serotonin in SSRI-treated rats. SERT density in the CA3 region of the hippocampus of the same rats, assessed by quantitative autoradiography with tritiated cyanoimipramine ([(3)H]CN-IMI), was decreased by 80-90% in SSRI-treated rats but not in those treated with phenelzine or DMI. The serotonin content of the hippocampus was unaffected by paroxetine or sertraline treatment, ruling out neurotoxicity as a possible explanation for the SSRI-induced decrease in SERT binding and alteration in 5-HT clearance. Levels of mRNA for the SERT in the raphe nucleus were also unaltered by chronic paroxetine treatment. Based on these results, it appears that the SERT is downregulated by chronic administration of SSRIs but not other types of antidepressants; furthermore, the downregulation is not caused by decreases in SERT gene expression.     

Microbubble-induced serotonin secretion in human platelets

The effect of nitrogen (N2) microbubbles on platelets resembles that of common platelet agonists with respect to aggregation (Thorsen T et al., Undersea Biomed Res 1986; 13: 289-303). In the present study we examined the effect of microbubbles on platelet secretion of preloaded 14C-serotonin. We demonstrate that stirring of platelet-rich plasma with N2-microbubbles causes a loss of single platelets that is associated with secretion. However, secretion did not increase above baseline values until after 20 min of microbubble exposure, when platelet aggregation had reached 40%. After that time the secretion rate increased. There was no correlation between secreted serotonin and the degree of platelet aggregation. Although no 14C-serotonin secretion occurred in presence of acetylsalicyclic acid (ASA), microbubble-induced platelet aggregation was only marginally reduced. Epinephrine alone caused significant platelet aggregation but no 14C-serotonin secretion and it enhanced N2-microbubble-induced platelet aggregation and secretion; ASA completely prevented secretion under these circumstances but failed to abolish the enhancement of aggregation compared with microbubbles alone. Earlier studies have shown that platelets adhere to the bubble surfaces (Thorsen T et al., Undersea Biomed Res 1987; 14: 45-59). The results in the present study indicate that non-adhering platelets in the bulk phase are not activated by means of autocrine stimulation through dense granule material.     

Peripheral and central neurochemical effects of the selective serotonin reuptake inhibitors (SSRIs) in humans and nonhuman primates: assessing bioeffect and mechanisms of action

It is clear that selective serotonin reuptake inhibitors (SSRIs) act powerfully to inhibit serotonin (5-hydroxytryptamine, 5-HT) uptake centrally and peripherally. However, there are a number of critical unanswered questions concerning the effects of the drugs in adults and children. The influence of age and duration of treatment on the extent of uptake inhibition and on the enhancement of central serotonergic functioning are unclear. In addition, the relationship of these factors and effects to the therapeutic and adverse effects of the SSRIs remain to be clarified. The general clinical utility of platelet 5-HT measurement is reviewed and studies assessing central and peripheral uptake blockade in infants and children and non-human primates are discussed. Recent investigations of central neurochemical effects of the SSRIs in primates assessed through measurement of 5-HT and related compounds in cisternal cerebrospinal fluid (CSF) of the rhesus monkey are presented. In summary, the studies described have found that: human fetal exposure to SSRIs has substantial effects on 5-HT transport in utero; exposure to SSRIs through breastmilk of mothers treated for postpartum depression usually has negligible effects on 5-HT uptake; prescribed SSRIs appear to exert similar effects on 5-HT transporter blockade in children and adults; and rapid and sustained increases are seen in monkey cisternal CSF levels of 5-HT upon initiation of SSRI administration. The implications of the observations in terms of behavioral effects, clinical practice, and underlying mechanisms of action of the SSRIs are discussed.     

Differential effects of the 5-HT2 receptor antagonist on the anti-immobility effects of noradrenaline and serotonin reuptake inhibitors in the forced swimming test

The effects of the 5-HT(2) receptor antagonist, LY 53857 on the effects of noradrenaline and serotonin reuptake inhibitors were investigated using the forced swimming test. LY 53857 enhanced anti-immobility effects of clomipramine and maprotiline, which can inhibit reuptake of noradrenaline. However, LY 53857 did not affect the immobility time of mice treated with the selective serotonin reuptake inhibitors (SSRIs) fluoxetine and fluvoxamine. These results suggest that antagonism of the 5-HT(2) receptor leads to potentiation of the antidepressant effects of noradrenaline reuptake inhibitors but not SSRIs and that LY 53857 may modify the activity of noradrenergic neurons.