Zinc modulation of serotonin uptake in the adult rat corpus callosum

Antidepressants partially inhibit the uptake of 5-hydroxytryptamine (5-HT; serotonin) in the rat corpus callosum (CC), a white matter commissure involved in interhemispheric brain communication. It is also known that zinc modulates many proteins, including neurotransmitter transporters. We examined the effects of zinc on the uptake of 5-HT into slices of the adult rat CC, in the absence or presence of some antidepressants. Zinc increased 5-HT uptake in a concentration-dependent manner when the CC slices were incubated in a solution buffered with sodium bicarbonate; however, zinc exerted no effect on 5-HT transport when HEPES was the buffer. Potentiation of 5-HT uptake by zinc was maximal with 1 microM (45% over the control uptake). Moreover, 1 microM zinc potentiated 5-HT uptake in the cingulate cortex by 58% and in the Raphe nucleus by 65%. The antidepressants fluoxetine and imipramine inhibited 5-HT uptake in the CC by approximately 50%, whereas 6-nitroquipazine, a potent 5-HT uptake blocker, inhibited uptake by only 23%. Interestingly, inhibition of 5-HT uptake by all three substances, fluoxetine, imipramine, and 6-nitroquipazine, was counteracted by the presence of 1 microM zinc. Free zinc may thus contribute to modulation of extracellular levels of 5-HT and its removal. These actions should be considered in the treatment of mental depression with antidepressants.     

Membrane currents elicited by angiotensin II in astrocytes from the rat corpus callosum

The corpus callosum (CC) is the main white matter tract in the brain. It consists primarily of axons and glial cells. In the present work, membrane currents generated by angiotensin II (Ang II) in cultured astrocytes from the CC of newborn and 3-week-old rats were studied using the whole-cell voltage-clamp technique. After 4 days of culture, approximately 90% of cells were positive to glial fibrillary acidic protein (GFAP), indicating their astrocyte lineage. Ang II elicited inward currents in approximately 20% of cells and outward currents in approximately 4% of cells from the CC for newborn or 3-week-old rats. The main effect of Ang II on astrocytes from the newborn rat CC was a reduction of membrane conductance, by blocking of delayed rectifier K(+) currents in 96% of cells. However, no common action of Ang II was observed in cells from 3-week-old rat CC because the responses were quite variable, suggesting the participation of other ion currents. The partial agonist of AT(2) receptors, CGP-42112A, exerted effects on Ang II responses, whereas the AT(1) antagonist ZD7155 did not, suggesting that Ang II responses in CC astrocytes are predominantly mediated by activation of AT(2) receptors. This study is the first to show electrical responses generated by AT(2) receptors in glial cells from the rat central nervous system, and may help gain a better understanding of the functions of Ang II receptors in astrocytes from the rat CC in particular and of glial cells in general. (c) 2005 Wiley-Liss, Inc.     

A review of serotonin toxicity data: implications for the mechanisms of antidepressant drug action.

Data now exist from which an accurate definition for serotonin toxicity (ST), or serotonin syndrome, has been developed; this has also lead to precise, validated decision rules for diagnosis. The spectrum concept formulates ST as a continuum of serotonergic effects, mediated by the degree of elevation of intrasynaptic serotonin. This progresses from side effects through to toxicity; the concept emphasizes that it is a form of poisoning, not an idiosyncratic reaction. Observations of the degree of ST precipitated by overdoses of different classes of drugs can elucidate mechanisms and potency of drug actions. There is now sufficient pharmacological data on some drugs to enable a prediction of which ones will be at risk of precipitating ST, either by themselves or in combinations with other drugs. This indicates that some antidepressant drugs, presently thought to have serotonergic effects in animals, do not exhibit such effects in humans. Mirtazapine is unable to precipitate serotonin toxicity in overdose or to cause serotonin toxicity when mixed with monoamine oxidase inhibitors, and moclobemide is unable to precipitate serotonin toxicity in overdose. Tricyclic antidepressants (other than clomipramine and imipramine) do not precipitate serotonin toxicity and might not elevate serotonin or have a dual action, as has been assumed.     

Therapeutic drug monitoring of selective serotonin reuptake inhibitors influences clinical dosing strategies and reduces drug costs in depressed elderly patients

OBJECTIVE: This study was initiated in order to describe and evaluate the effects of a therapeutic drug monitoring (TDM) routine of selective serotonin reuptake inhibitors (SSRIs) on treatment strategies and drug costs in depressed elderly patients. METHOD: Blood samples were drawn from elderly depressed patients and analysed for steady-state trough serum concentrations of citalopram (n = 48), paroxetine (n = 48) or sertraline (n = 39). A global efficacy evaluation was made at baseline and after 6-9 months. Antidepressant drug costs before and after TDM were estimated. RESULTS: Eight samples were excluded due to technical problems or noncompliance. In 65 of the 127 (51.2%) remaining cases, the treatment strategy was changed according to the TDM outcome, in most a reduction of the prescribed dose. Bioanalytical TDM costs included the antidepressant drug costs after TDM were reduced by 10.2%. CONCLUSION: The results support the utility of TDM in the search for the individual minimum effective SSRI dose in the elderly.     

Buspirone potentiation of antidepressants in the treatment of PTSD

This article is a U.S. Government work and, as such, is in the public domain in the United States of America.     

Transitory uptake of serotonin in the developing sensory pathways of the common marmoset

Serotonin (5-HT) affects brain development during sensitive developmental periods. In rodents, transient sites of high affinity capture of 5-HT were demonstrated in the primary sensory neurons and in the sensory thalamocortical afferents. This uptake is required to adjust 5-HT receptor stimulation during the formation of sensory maps. To determine whether similar mechanisms exist in primates, we analyzed staged embryos and postnatal pups in the common marmoset (total gestation time, 142 days). Immunocytochemical analyses were performed using antisera to 5-HT, to the serotonin transporter (SERT), and to the vesicular monoamine transporter (VMAT2). 5-HT, SERT, and VMAT2 labeled the raphe neurons and their terminal network from embryonic day (E)70 to adulthood. In addition, from E70-130 VMAT2 and SERT were observed in all the sensory cranial nerves, the olfactory nerve, the gustatory, the trigeminal, the auditory fibers, in the retinal ganglion cells, and the optic tract up to the lateral geniculate nucleus and the superior colliculus. All the spinal sensory ganglia and their peripheral sensory branches were labeled. Accumulation of 5-HT was observed in all the sensory neurons expressing SERT and the corresponding axon tracts. Since these neurons were missing tryptophan hydroxylase (TPH), the synthesizing enzyme for 5-HT, they most likely accumulated 5-HT through the action of the amine transporters, as has been shown in rodents. No transient expression of 5-HT markers was detectable in the sensory thalamocortical axons at any of the ages examined. Thus, the existence of 5-HT uptake in nonserotoninergic neurons appears to be a conserved feature in primates, although the topographic extent of this transient expression is more restricted than that previously demonstrated in rodents.     

Self-poisonings with tricyclic antidepressants and selective serotonin reuptake inhibitors in Tehran,Iran

In a prospective hospital-based cohort study, we addressed the question of severity and outcome of antidepressant poisonings in patients who attended the Loghman-Hakim Hospital Poison Center, the only national center in Tehran dedicated for detoxification. The aim of the study was to find out if tricyclic antidepressant (TCA) intoxications require more therapeutic efforts than selective serotonin reuptake inhibitor (SSRI) intoxications. The study was applied over a 7-week period (28 March–20 May 2006). From 3578 intoxications, 334 patients with antidepressant or lithium self-poisoning were identified (9.3% of all poisoning cases; 233 females, 101 males; median age 24 years, min 13, max 70). Compared to SSRI single-substance intoxications (n=17), TCA single-substance intoxications (n=73) were associated with: (1) a significantly lower level of consciousness (P=0.005); (2) a significantly higher admission frequency (80.8 vs. 35.3%; P<0.001); and (3) a higher intubation frequency (13.7 vs. 0%; P=ns). SSRI multiple-substance intoxications were associated with a significantly lower level of consciousness than SSRI single-substance intoxications (P=0.042), while there was no significant difference between TCA multiple- and single-substance intoxications. This study suggests that an overdose with SSRIs results in a more favourable clinical outcome than an overdose with TCAs.     

Dose-response relationship of selective serotonin reuptake inhibitors treatment-emergent hypomania in depressive disorders

Objective: The notion that antidepressant treatment‐associated hypomania or mania being pharmacologically induced has been challenged. To determine whether selective serotonin reuptake inhibitors (SSRI) induced hypomania is secondary to medication effects, we examined the dose–response relationship of SSRI‐induced hypomania in two patients with depressive disorder. Method: Case study. Result: Hypomanic symptoms emerged during treatment with sertraline at the dose of 300 mg per day in a 45‐year‐old male with major depression. Paroxetine treatment at the dose of 80 mg per day induced hypomania in a 37‐year‐old female with dysthymia and trichitillomania. These patients have no family or personal history of bipolar disorder. Hypomania resolved when sertraline was decreased to 200 mg per day and paroxetine to 40 mg per day. No hypomanic switch was observed during 18–24 months follow‐up. Conclusion: In the absence of risk factors for manic switch, SSRI‐induced hypomania may be dose‐dependent medication effects.     

Effects of fenfluramine and antidepressants on protein kinase C activity in rat cortical synaptoneurosomes

Fenfluramine releases serotonin (5-HT) via the 5-HT transporter (SERT). Previous work has shown that amphetamine increases particulate protein kinase C (PKC) activity in striatal synaptoneurosomes. The increased PKC activity is linked to the outward transport of dopamine, and when release is diminished, the inward transport of amphetamine inhibits PKC instead. Since there is homology among monoamine transporters, this study was undertaken to determine if D-fenfluramine has similar effects on PKC. The role of 5-HT receptors and endogenous 5-HT were also examined. Naive rats and rats pretreated with p-chlorophenylalanine (PCPA), a 5-HT synthesis inhibitor, were sacrificed. Cortical synaptoneurosomes were prepared and incubated with fenfluramine. PKC activity was determined by thiophosphorylation of endogenous substrates. It was found that 5-HT, D/L-fenfluramine, and D-fenfluramine increased PKC activity in a time- and dose-dependent manner. The 5-HT-mediated increase in PKC activity was attenuated by pretreatment with the 5-HT(2) antagonist ketanserin, but not with the SERT inhibitor fluoxetine. The D-fenfluramine-induced increase in PKC activity was completely prevented, however, by pretreatment with SERT inhibitors and partially with ketanserin. It was also attenuated by pretreatment with PCPA, resulting in a dose-dependent inhibition of PKC instead. Thus, when 5-HT release was diminished the uptake of D-fenfluramine inhibited PKC. Similar effects have been observed with amphetamine. Unlike D-fenfluramine, the D/L-fenfluramine-induced increase in PKC activity was partially resistant to PCPA pretreatment but was attenuated with bupropion, a dopamine transporter (DAT) inhibitor. SERT inhibitors (sertraline, paroxetine, citalopram, and fluoxetine) also increased PKC activity. Nefazodone and bupropion increased PKC activity, but mirtazapine was relatively inactive. The SERT inhibitor-induced increase in PKC was unaffected by pretreatment with PCPA but was inhibited by calcium. Similar effects on PKC activity have been observed with DAT inhibitors. These results, showing that D-fenfluramine altered PKC activity similar to D-amphetamine, suggest that the topographic homology between DAT and SERT may extend to their effects on PKC activity.     

Treatment of severe depression with the selective serotonin reuptake inhibitors

The selective serotonin reuptake inhibitors (SSRIs) are recognized as effective as and better tolerated than older antidepressant therapies and have become the drugs of choice in the treatment of mild to moderate depression. However, there is a clinical impression that the SSRIs are less effective than older therapies in the severely depressed patient. A limited number of trials have attempted to address this issue. This review assesses 16 controlled studies of SSRIs in severe depression. The findings from a majority of studies found the SSRIs to be superior to placebo and as effective as but better tolerated than the tricyclic antidepressants (TCAs) in severely depressed patients. Although future studies are needed to corroborate and elaborate on these data, studies still support the use of SSRIs in this patient population. Depression and Anxiety 4:182–189, 1996/1997. © 1997 Wiley-Liss, Inc.     

Effect of chronic administration of duloxetine on serotonin and norepinephrine transporter binding sites in rat brain.

BACKGROUND: Chronic treatment of rats with certain selective serotonin or norepinephrine reuptake inhibitors produces significant decreases, respectively, in serotonin and norepinephrine transporter binding sites in brain. Duloxetine may be a dual serotonin/norepinephrine reuptake inhibitor, as it is only a slightly more potent inhibitor of serotonin than norepinephrine uptake in vitro. Consequently, we hypothesized that chronic duloxetine treatment, at doses producing serum levels within its therapeutic range, would affect both monoamine transporters dose-dependently, with a higher dose causing greater reductions of binding sites for both transporters. METHODS: Rats were treated with either 4 or 8 mg/kg/d of duloxetine, paroxetine, desipramine, or vehicle via subcutaneous osmotic minipumps for 21 days. Binding sites for serotonin and norepinephrine transporters were measured in amygdala and hippocampus using quantitative autoradiography. RESULTS: Both doses of duloxetine and paroxetine produced equivalent and significant decreases in [3H] cyanoimipramine binding to serotonin transporters, but only desipramine treatment significantly reduced [3H] nisoxetine binding to norepinephrine transporters. CONCLUSIONS: At doses producing rat serum concentrations in the range achieved in patients at recommended daily doses of the drug, duloxetine behaves in vivo more as a selective serotonin reuptake inhibitor than a dual reuptake inhibitor in its capacity to selectively reduce serotonin transporter density.     

Dexamethasone suppression test identifies a subset of elderly depressed patients with reduced platelet serotonin transport and resistance to imipramine inhibition of transport

Dysregulation of the hypothalamus-pituitary-adrenal axis (HPA) is more common in elderly patients with depression than in younger depressed patients, and glucocorticoids are known to influence serotonergic function. Elderly depressed patients are also reportedly more resistant to therapeutic effects of antidepressants. In the current study, we measured platelet serotonin transporter binding sites and transport function in young and elderly depressed patients and determined the relationship to HPA status as assessed with the dexamethasone suppression test (DST). The density and affinity of transporter molecules showed no differences between young and elderly depressed patients, regardless of DST results. Nevertheless, transporter function showed a substantial interaction of aging with DST: elderly DST suppressors showed a deficit in [³H]serotonin uptake capabilities and resistance to imipramine inhibition of uptake. No such defects were seen in the young depressed cohort, regardless of DST status, nor in elderly depressed DST non-suppressors. These results are consistent with the view that depression in the elderly exhibits basic biological differences from depression in earlier life, and that such distinctions may account in part for therapeutic ineffectiveness of antidepressants in specific subgroups, associated with the presence or absence of appropriate HPA regulation. Depression and Anxiety 6:19–25, 1997. © 1997 Wiley-Liss, Inc.     

Organic cation transporter capable of transporting serotonin is up-regulated in serotonin transporter-deficient mice

The serotonin (5HT) transporter (5HTT) regulates serotonergic neurotransmission by mediating the reuptake of 5HT from the synaptic cleft. Although lacking the high affinity and selectivity of the 5HTT, the brain expresses a large number of other transporters, including the polyspecific organic cation transporters (OCTs). OCT1 and OCT3, members of the potential-sensitive organic cation transporter gene family, physiologically transport a wide spectrum of organic cations. In addition, both transporters mediate low-affinity 5HT transport and, therefore, may participate in the clearance of excessive 5HT. Because concentrations of extracellular 5HT are increased in the brain of 5HTT-deficient mice, they are a model for investigating the role of OCTs in 5HT system homeostasis. Here, we analyzed OCT1 and OCT3 gene expression in the brain of 5HTT knockout mice by semiquantitative competitive polymerase chain reaction and in situ hybridization. We demonstrate that, in 5HTT-deficient mice, OCT3 mRNA concentrations were significantly increased in the hippocampus, but not in other brain regions, including cortex, striatum, cerebellum, and brainstem. In contrast, no difference in OCT1 expression was detected between 5HTT knockout and control mice. Up-regulation of OCT3 expression and enhanced low-affinity 5HT uptake may limit the adverse effects of elevated extracellular 5HT and may play a critical role in maintaining 5HT-dependent functions of the hippocampus in the absence of 5HTT.     

ADAM is an effective tool for in vivo study of serotonergic function: validation in rat models

ADAM, 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine, is a recently described SPECT tracer for exploration of the serotonin transporter. We evaluated its potential to detect abnormalities in serotonergic function in the rat using 1) a model of serotonergic neuron lesion induced with 5,7-dihydroxytryptamine (5,7-DHT), and 2) experimental induction of acute decrease in endogenous brain serotonin levels. Cerebral biodistribution studies of [125I]ADAM were performed in normal conditions, in 5,7-DHT-lesioned rats, and after acute serotonin depletion obtained with p-chlorophenylalanine (pCPA). Around 50% reduction in accumulation of ADAM was observed in the hypothalamus and hippocampus 3 weeks after lesion of serotonergic neurons, whereas a more modest decrease of 15-30% occurred in the thalamus, frontal cortex, and striatum. This demonstrated the ability of the tracer to detect serotonergic neuron loss in vivo. After inducing acute 5-HT depletion with pCPA, we observed an increase in in vivo [125I]ADAM binding in all brain areas studied. The higher in vivo binding of [125I]ADAM in pCPA-treated rats than in controls was mainly due to an increase in specific binding to the SERT, as demonstrated by greatly reduced binding in the presence of a saturating dose of paroxetine. This may indicate in vivo competition between ADAM and 5-HT for binding to the SERT. The present findings thus demonstrate that ADAM is a specific SERT radioligand which can be used for in vivo study of central serotonin systems, and supports its use as a tracer for SPECT studies in human disorders involving dysfunction of serotonergic neurotransmission.     

Selective serotonin reuptake inhibitor exposure during early pregnancy and the risk of birth defects

Gentile S. Selective serotonin reuptake inhibitor exposure during early pregnancy and the risk of birth defects. Objective: To assess the methodological value of studies that signaled one or more selective serotonin reuptake inhibitors (SSRIs) as teratogenic agents. Method: Medical literature, published in English (1980–November 2010), was searched using MEDLINE/PubMed, TOXNET, EMBASE, and The Cochrane Library to identify all articles, reporting primary data that suggested any increased rate of congenital malformations following prenatal exposure to SSRIs as a group or single SSRI agents. Results: Reviewed studies showed some severe methodological limitations, such as data coming from retrospective studies and incomplete information available with reference to timing of exposure and dosages. Further, data continue to be extrapolated from automated databases that do not declare whether the women reported actually used the prescribed medication. Further, it should be noted the distinct lack of research analysis available with reference to the potential impact of non‐iatrogenic confounders on pregnancy. Conclusion: In light of such considerations, the hypothesized teratogenicity of SSRIs remains undemonstrated. Hence, further, well‐designed research is needed to differentiate definitively the detrimental impact of depression on pregnancy outcomes from potential iatrogenic events.     

Repeated isoflurane in adult male mice leads to acute and persistent motor decrements with long-term modifications in corpus callosum microstructural integrity

Isoflurane is a commonly used inhalational anesthetic, clinically and in animal experimental studies. Although it has been reported as safe, recent findings suggest that despite widespread use, isoflurane-induced inhalational anesthesia can lead to various pathophysiological and cognitive alterations. Therefore, we aimed to investigate the long-term behavioral and white matter consequences of repeated isoflurane exposure. Twenty 3-month-old C57BL/6J male mice received one exposure of isoflurane for 40 min or 2 exposures to isoflurane separated by 3 days. Behavioral paradigms (open field, balance beam, foot fault, rotarod, elevated zero maze, tail suspension, water maze, and social recognition tests) were administered at 1, 3, 5, 7, and 90 days post exposure. Animals exposed to repeated isoflurane showed significant motor deficits on the balance beam and increased anxiety-like behavior. Animals exposed to single isoflurane showed impaired performance on the foot fault test. Diffusion tensor imaging showed that repeated isoflurane exposure led to long-term disruption of water diffusivity in corpus callosum (CC) white matter. Furthermore, 2-D structure-tensor analysis from stained brain sections showed differences in the microstructural organization of CC white matter in mice with single versus repeated isoflurane exposures. These results suggest that behavioral deficits observed up to 90 days after repeated isoflurane exposure resulted from, at least in part, altered CC white matter microstructural integrity.     

Milnacipran: a comparative analysis of human monoamine uptake and transporter binding affinity.

BACKGROUND: Though selective serotonin reuptake inhibitors have revolutionized the field of psychiatry with demonstrated efficacy in affective and anxiety disorders with minimal side effects, norepinephrine-serotonin reuptake inhibitors may provide efficacy similar to tricyclic antidepressants without the adverse side effects associated with tricyclic antidepressants. METHODS: The affinity and selectivity of milnacipran, duloxetine, venlafaxine, citalopram, amitriptyline, and nortriptyline were determined for the human serotonin, norepinephrine, and dopamine transporters. RESULTS: Both milnacipran and duloxetine were potent inhibitors of serotonin and norepinephrine uptake. Unlike duloxetine and venlafaxine, milnacipran appears serotonin transporter selective in binding (ratio = 2.61) and norepinephrine transporter selective in uptake (ratio =.45). CONCLUSIONS: Milnacipran's binding and uptake inhibition profile more closely resembles that of the tricyclic antidepressants than that of duloxetine. Whether these differences observed in vitro manifest themselves in vivo is not clear.     

Decreased densities of dopamine and serotonin transporters and of vesicular monoamine transporter 2 in severely kainic acid lesioned subregions of the striatum

Summary. Fifteen days after a striatal kainic acid (KA) injection, we have examined presynaptic modifications of dopamine and serotonin terminals in the striatum through (i) autoradiographic labeling of dopamine, serotonin and vesicular monoamine transporters respectively with ³H-mazindol, ³H-citalopram and ³H-dihydrotetrabenazine, and (ii) determination of the contents in dopamine, serotonin and their metabolites. Acetylcholinesterase histochemical labeling enabled the definition of severely and moderately KA-lesioned subregions within the striatum. A significant decrease of the three transporters labeling density was observed only in the severely lesioned subregions. The strong decrease in serotonin transporter labeling revealed here has not been described until now. Besides, the striatal contents of homovanillic acid (dopamine metabolite) and 5-hydroxyindolacetic acid (serotonin metabolite) were significantly increased in the lesioned striatum. The whole data evidence an incomplete sparing of dopamine and serotonin terminals in the striatum 15 days after a KA injection, especially in the areas where the degeneration of postsynaptic neurons was the most extensive. Received May 31, 2000; accepted October 23, 2000     

Citalopram — Pharmacological profile of a specific serotonin uptake inhibitor with antidepressant activity

1. Citalopram (Lu 10-171), a new bicyclic phthalane derivative, is an extremely potent inhibitor of neuronal serotonin (5-HT) uptake but has no effect on the uptake of noradrenaline (NA) and dopamine (DA). 2. Citalopram has no antagonistic activity towards DA, NA, 5-HT, histamine, gamma aminobutyric acid (GABA), acetylcholine, and morphine receptors. In this way it clearly deviates from many old and new antidepressant drugs which have antagonistic effects towards some of these transmitters. 3. In contrast to many tricyclic antidepressants citalopram is devoid of cardiotoxic effects, even when animals are exposed to concentrations far above the therapeutic level. 4. In man citalopram is metabolized to compounds which are also potent 5-HT-uptake inhibitors without effect of NA uptake and which are found in lower concentrations than citalopram itself. 5. In account of its extreme specificity as a 5-HT-uptake inhibitor citalopram should be considered as an experimental tool of the utmost importance. In preliminary clinical experiments citalopram has shown a clear antidepressant effect. This property together with the absence of troublesome anticholinergic adverse effects and cardiotoxic effects also make citalopram a most promising antidepressant drug.