A biomarker panel predicts progression of Barrett's esophagus to esophageal adenocarcinoma.

Progression from Barrett's esophagus (BE) to esophageal adenocarcinoma (EAC) is uncommon but the consequences are serious. Predictors of progression are essential to optimize resource utilization. This study assessed the utility of a promising panel of biomarkers applicable to routine paraffin embedded biopsies (FFPE) to predict progression of BE to EAC in a large population-based, nested case-control study.We utilized the Amsterdam-based ReBus nested case-control cohort. BE patients who progressed to high-grade dysplasia (HGD)/EAC (n = 130) and BE patients who never progressed (n = 130) were matched on age, sex, length of the BE segment, and duration of endoscopic surveillance. All progressors had minimum 2 years of endoscopic surveillance without HGD/EAC to exclude prevalent neoplasia. We assessed abnormal DNA content, p53, Cyclin A, and Aspergillus oryzae lectin (AOL) in FFPE sections. We performed conditional logistic regression analysis to estimate odds ratio (OR) of progression based on biomarker status.Expert LGD (OR, 8.3; 95% CI, 1.7-41.0), AOL (3 vs. 0 epithelial compartments abnormal; OR, 3.6; 95% CI, 1.2-10.6) and p53 (OR, 2.3; 95% CI, 1.2-4.6) were independently associated with neoplastic progression. Cyclin A did not predict progression and DNA ploidy analysis by image cytometry was unsuccessful in the majority of cases, both were excluded from the multivariate analysis. The multivariable biomarker model had an area under the receiver operating characteristic curve of 0.73.Expert LGD, AOL, and p53 independently predict neoplastic progression in BE patients and are applicable to routine practice. These biomarkers can aid in selecting patients for endoscopic ablation or more intensive surveillance.

A visual analogue scale and a Likert scale are simple and responsive tools for assessing dysphagia in eosinophilic oesophagitis.

BACKGROUND: While symptom scores have been developed to evaluate dysphagia in eosinophilic oesophagitis (EoE), their complexity may limit clinical use. AIM: To evaluate a visual analogue scale (VAS) and a 10-point Likert scale (LS) for assessment of dysphagia severity before and after EoE treatment. METHODS: We conducted a prospective cohort study enrolling consecutive adults undergoing out-patient endoscopy. Incident cases of EoE were diagnosed per consensus guidelines. At diagnosis and after 8 weeks of treatment, symptoms were measured using the VAS, LS and the Mayo Dysphagia Questionnaire (MDQ). The percentage change in scores before and after treatment were compared overall, in treatment responders (<15 eos/hpf) and non-responders, and in patients without baseline dilation. RESULTS: In 51 EoE cases, the median VAS decreased from 3.6 at baseline to 1.4 post-treatment (71% decrease), the LS decreased from 6 to 2 (67%) and the MDQ decreased from 20 to 10 (49%). The VAS correlated with both the LS (R = 0.77; P < 0.0001) and MDQ (R = 0.46, P = 0.001). After stratification by histological response, the LS decreased 70% in responders vs. 13% in non-responders (P = 0.02). In patients who did not receive baseline dilation, both the VAS and LS decreased significantly more in the histological responders. CONCLUSIONS: Both the VAS and LS were responsive to successful treatment as measured by histologic improvement. Because the VAS and LS are simple to administer and are responsive to treatment, they can provide an efficient and objective method for assessing dysphagia severity in EoE in clinical practice.

Design and anticipated outcomes of the eMERGE-PGx project: a multicenter pilot for preemptive pharmacogenomics in electronic health record systems.

We describe here the design and initial implementation of the eMERGE-PGx project. eMERGE-PGx, a partnership of the Electronic Medical Records and Genomics Network and the Pharmacogenomics Research Network, has three objectives: (i) to deploy PGRNseq, a next-generation sequencing platform assessing sequence variation in 84 proposed pharmacogenes, in nearly 9,000 patients likely to be prescribed drugs of interest in a 1- to 3-year time frame across several clinical sites; (ii) to integrate well-established clinically validated pharmacogenetic genotypes into the electronic health record with associated clinical decision support and to assess process and clinical outcomes of implementation; and (iii) to develop a repository of pharmacogenetic variants of unknown significance linked to a repository of electronic health record-based clinical phenotype data for ongoing pharmacogenomics discovery. We describe site-specific project implementation and anticipated products, including genetic variant and phenotype data repositories, novel variant association studies, clinical decision support modules, clinical and process outcomes, approaches to managing incidental findings, and patient and clinician education methods.

Public and biobank participant attitudes toward genetic research participation and data sharing.

Research assessing attitudes toward consent processes for high-throughput genomic-wide technologies and widespread sharing of data is limited. In order to develop a better understanding of stakeholder views toward these issues, this cross-sectional study assessed public and biorepository participant attitudes toward research participation and sharing of genetic research data. Forty-nine individuals participated in 6 focus groups; 28 in 3 public focus groups and 21 in 3 NUgene biorepository participant focus groups. In the public focus groups, 75% of participants were women, 75% had some college education or more, 46% were African-American and 29% were Hispanic. In the NUgene focus groups, 67% of participants were women, 95% had some college education or more, and the majority (76%) of participants was Caucasian. Five major themes were identified in the focus group data: (a) a wide spectrum of understanding of genetic research; (b) pros and cons of participation in genetic research; (c) influence of credibility and trust of the research institution; (d) concerns about sharing genetic research data and need for transparency in the Policy for Sharing of Data in National Institutes of Health-Supported or Conducted Genome-Wide Association Studies; (e) a need for more information and education about genetic research. In order to increase public understanding and address potential concerns about genetic research, future efforts should be aimed at involving the public in genetic research policy development and in identifying or developing appropriate educational strategies to meet the public's needs.

Assessing the understanding of biobank participants.

Biobanks have been developed as a tool to better understand the genetic basis of disease by linking DNA samples to corresponding medical information. The broad scope of such projects presents a challenge to informed consent and participant understanding. To address this, 200 telephone interviews were conducted with participants in the NUgene Project, Northwestern University's biobank. Interviews included a modified version of the "quality of informed consent measure" (QuIC) and semi-structured questions which were analyzed thematically for 109 of the interviews. The QuIC, originally applied to cancer clinical trials, objectively assessed some of the components of informed consent for a biobank, and interview questions provided rich data to assist in interpreting participant understanding. The best understood domains included: the nature of the study, benefit to future patients, and the voluntary nature of participation. Lower knowledge scores included: potential risks and discomforts, experimental nature of the research, procedures in the event of study-related injury, and confidentiality issues. Qualitatively, confidentiality protections of the study were described as good by most (>50%). Although some cited concerns with employer (12%) or insurance discrimination (25%), most considered the risks to privacy low (25%) or none (approximately 60%). Only 10% of participants explicitly stated they had no expectation for personal benefit, and when asked whether they expected to be contacted with study results, respondents were split between having no expectation (39%), being hopeful for results (37%) and expecting to be contacted with results (12%). These findings are informative to those establishing and implementing biobanks, and to the IRBs reviewing such studies.

Agonist-induced serotonin 2A receptor desensitization in the rat frontal cortex and hypothalamus.

This study examined the time course and possible mechanisms of agonist-induced desensitization of 5-hydroxytryptamine serotonin 2A receptors in the rat frontal cortex and hypothalamic paraventricular nucleus after 1, 4, and 7 days of treatment with (-)-1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane HCl [(-)-DOI] (1 mg/kg i.p.), a selective 5-HT(2A/2C) receptor agonist. In the frontal cortex, 5-HT-mediated phospholipase C (PLC) enzyme activity decreased by 24 to 30% after 4 to 7 days of (-)-DOI treatment without any significant changes in the guanosine 5'-3-O-(thio)triphosphate-mediated PLC enzyme activity. Additionally, treatment with (-)-DOI did not significantly change the levels of G(alpha11), regulator of G protein signaling (RGS)4, or RGS7 proteins in the frontal cortex, whereas G(alphaq) protein levels in the frontal cortex decreased (47%) only after 7 daily (-)-DOI injections. The functional status of 5-HT(2A) receptors in the hypothalamic paraventricular nucleus was examined using 5-HT(2A) receptor-mediated increases in plasma hormone levels. Plasma adrenocorticotrophic hormone (ACTH) and oxytocin measurements showed that 5-HT(2A) receptor desensitization began after only 1 day of (-)-DOI treatment, and the desensitization continued to increase after 4 and 7 days of treatment (ACTH response decreased 64.2-67.7%; oxytocin response decreased 82.3-90.1%). There were no significant alterations in levels of G(alphaq) or G(alpha11) lamic paraventricular proteins in the hypothanucleus. In conclusion, these results suggest that chronically administered (-)-DOI induces desensitization of 5-HT(2A) receptors in vivo, via a reduction in the ability of 5-HT(2A) receptors to activate G proteins without consistently altering levels of G(alpha) proteins or RGS proteins.

Estrogen desensitizes 5-HT(1A) receptors and reduces levels of G(z), G(i1) and G(i3) proteins in the hypothalamus.

The present study investigated whether estrogen would desensitize hypothalamic serotonin(1A) (5-HT(1A)) receptors by examining the neuroendocrine response to 8-OH-DPAT, a 5-HT(1A) agonist. Rats were ovariectomized, allowed to recover for 5 days, then given 2 daily injections of estradiol benzoate or vehicle (10 microg/day, s.c.). Twenty-four hours after the second injection, rats were challenged with a sub-maximal dose of 8-OH-DPAT (50 microg/kg, sc) or saline 15 min prior to sacrifice. 8-OH-DPAT produced a significant increase in plasma oxytocin, ACTH and corticosterone levels in ovariectomized rats. While estrogen treatment for 2 days did not alter basal hormone levels, it did significantly reduce the magnitude of oxytocin, ACTH and corticosterone responses to 8-OH-DPAT. The reduction in hormone responses was accompanied by a significant reduction in hypothalamic levels of G(z), G(i1) and G(i3) proteins (by 50%, 30% and 50%, respectively). These findings suggest that a reduction in these G proteins may contribute to the mechanisms underlying estrogen-induced desensitization of 5-HT(1A) receptors. The desensitization of 5-HT(1A) receptors has been suggested to underlie the therapeutic effects of antidepressant 5-HT uptake inhibitors (SSRIs). Thus, the present results suggest that estrogen or estrogen-like substances in combination with SSRIs may prove effective in developing novel therapeutic strategies for neuropsychiatric disorders in women.

5-HT3- and 5-HT2C-antagonist properties of cyamemazine: significance for its clinical anxiolytic activity.

RATIONALE: Cyamemazine is a neuroleptic compound which possesses anxiolytic properties in humans. On the other hand, 5-HT3- and 5-HT2C-receptors have been implicated in anxiety disorders and a previous binding study has shown that cyamemazine possesses high affinity for both serotonin receptor types. OBJECTIVE: The present study was undertaken to establish whether cyamemazine antagonizes 5-HT3- and/or 5-HT2C-mediated responses, and whether it compares with reference compounds. METHODS: Cyamemazine was tested for its ability to antagonize: (i) 5-HT3-dependent contraction of the isolated guinea-pig ileum and bradycardic responses in the rat and (ii) 5-HT2C-dependent phospholipase C (PLC) stimulation in rat brain membranes. RESULTS: In isolated guinea-pig ileum, cyamemazine potently and competitively antagonized 5-HT-dependent contractions (pA2 = 7.52 +/- 0.08; n = 5). In this test, cyamemazine was 5-7 times more potent (pIC50 = 6.75 +/- 0.13) than tropisetron (pIC50 = 6.02 +/- 0.04). In rats, cyamemazine i.v. antagonized 5-HT-dependent bradycardic responses with ID50% = 3.2 +/- 1.5 mg/kg (n = 4). Finally, in rat brain membranes cyamemazine antagonized 5-HT2C-dependent PLC stimulation with Ki = 424 nM (mianserin exhibits a Ki = 113 nM). CONCLUSIONS: Cyamemazine behaves as an antagonist at both 5-HT3- and 5-HT2C-receptors, which compares well with reference compounds. These 5-HT3- and 5-HT2C-antagonistic actions of cyamemazine can be involved, at least in part, in its beneficial therapeutic actions in anxiety disorders.

Regulation of cytokinesis.

At the end of mitosis, daughter cells are separated from each other by cytokinesis. This process involves equal partitioning and segregation of cytoplasm between the two cells. Despite years of study, the mechanism driving cytokinesis in animal cells is not fully understood. Actin and myosin are major components of the contractile ring, the structure at the equator between the dividing cells that provides the force necessary to constrict the cytoplasm. Despite this, there are also tantalizing results suggesting that cytokinesis can occur in the absence of myosin. It is unclear what the roles are of the few other contractile ring components identified to date. While it has been difficult to identify important proteins involved in cytokinesis, it has been even more challenging to pinpoint the regulatory mechanisms that govern this vital process. Cytokinesis must be precisely controlled both spatially and temporally; potential regulators of these parameters are just beginning to be identified. This review discusses the recent progress in our understanding of cytokinesis in animal cells and the mechanisms that may regulate it.

Sustained desensitization of hypothalamic 5-Hydroxytryptamine1A receptors after discontinuation of fluoxetine: inhibited neuroendocrine responses to 8-hydroxy-2-(Dipropylamino)Tetralin in the absence of changes in Gi/o/z proteins.

Long-term exposure to fluoxetine produces a desensitization of hypothalamic postsynaptic 5-hydroxytryptamine (5-HT)1A receptors, indicated by a substantial inhibition of the 5-HT1A receptor-mediated stimulation of oxytocin and adrenocorticotropic hormone (ACTH) secretion. The present study investigated the time course and mechanism of this desensitization after discontinuation of fluoxetine administration. Male rats were injected with saline or fluoxetine (10 mg/kg/day, i.p.) for 14 days and were challenged with a 5-HT1A agonist, [8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) 50 microg/kg, s.c.] 2, 4, 7, 14, 28, or 60 days post-treatment. In control animals, 8-OH-DPAT significantly increased (approximately 15-fold) plasma levels of oxytocin and ACTH. At 2 days post-treatment, oxytocin and ACTH responses to 8-OH-DPAT were reduced by 74% and 68%, respectively. During further withdrawal from fluoxetine, there was a gradual increase in the oxytocin response toward control levels. However, even 60 days after discontinuation of fluoxetine, the oxytocin response was still significantly reduced by 26% compared with controls. In contrast, the suppressed ACTH response to 8-OH-DPAT (a less-sensitive indicator of desensitization) gradually returned to control levels by day 14 of withdrawal from fluoxetine. Interestingly, the sustained reductions in the hormone responses occurred in the absence of reductions in Gz or Gi protein levels in the hypothalamus. Furthermore, this desensitization was sustained in the absence of detectable levels of fluoxetine and norfluoxetine in plasma and brain tissue. These findings suggest that the sustained desensitization of hypothalamic 5-HT1A receptor systems, observed during fluoxetine withdrawal, may be due to altered interactions among the protein components of the 5-HT1A receptor system, rather than their absolute levels.

Daily injections of fluoxetine induce dose-dependent desensitization of hypothalamic 5-HT1A receptors: reductions in neuroendocrine responses to 8-OH-DPAT and in levels of Gz and Gi proteins.

The present studies examined the dose-response relationship of fluoxetine-induced desensitization of hypothalamic postsynaptic 5-HT1A receptors, as measured from the reduced neuroendocrine responses to a 5-HT1A agonist. Because hypothalamic Gz proteins mediate the ACTH and oxytocin responses to 5-HT1A receptor activation, we also determined the effect of fluoxetine on the levels of Gz proteins in the hypothalamus. Rats were injected daily for 14 days with saline or with fluoxetine doses of 0.3, 1, 3, 5, 7. 5, or 10 mg/kg/day. Fluoxetine produced a dose-dependent reduction in the oxytocin, ACTH, and corticosterone responses to the 5-HT1A agonist 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT, 50 micrograms/kg, s.c.). The lowest fluoxetine dose that significantly, although incompletely, reduced the neuroendocrine responses to 8-OH-DPAT was 5 mg/kg/day. The 10 mg/kg/day dose of fluoxetine maximally inhibited all neuroendocrine responses to 8-OH-DPAT. Hypothalamic levels of Gz protein were reduced by both the 7.5 and 10 mg/kg/day doses of fluoxetine, whereas Gi1 protein levels were reduced only after the highest dose (10 mg/kg/day) of fluoxetine. Gi2, Gi3, and Go levels were not reduced by any fluoxetine dose. Cytosolic levels of Gi1 and Gz proteins were unaltered, indicating that reductions in Gz and Gi1 proteins are not caused by a redistribution of the proteins from the membrane into the cytosol. The results from the present study indicate that fluoxetine-induced desensitization of hypothalamic postsynaptic 5-HT1A receptor systems is dose-dependent and may be caused in part by reductions in the hypothalamic levels of Gz proteins.

Cell-type-specific rescue of myosin function during Dictyostelium development defines two distinct cell movements required for culmination.

Mutant Dictyostelium cells lacking any of the component polypeptides of myosin II exhibit developmental defects. To define myosin's role in establishing Dictyostelium's developmental pattern, we have rescued myosin function in a myosin regulatory light chain null mutant (mlcR-) using cell-type-specific promoters. While mlcR- cells fail to progress beyond the mound stage, expression of RLC from the prestalk promoter, ecmA, produces culminants with normal stalks but with defects in spore cell localization. When GFP-marked prestalk and prespore cells expressing ecmA-RLC are mixed with wild-type cells, the mislocalization of prestalk cells, but not prespore cells, is rescued. Time-lapse video recording of ecmA-RLC cells showed that the posterior prespore zone failed to undergo a contraction important for the upward movement of prespore cells. Prespore cells marked with green fluorescent protein (GFP) failed to move toward the tip with the spiral motion typical of wild type. In contrast, expression of RLC in prespore cells using the psA promoter produced balloon-like structures reminiscent of sorocarps but lacking stalks. GFP-labeled prespore cells showed a spiral movement toward the top of the structures. Expression of RLC from the psA promoter restores the normal localization of psA-GFP cells, but not ecmA-GFP cells. These results define two distinct, myosin-dependent movements that are required for establishing a Dictyostelium fruiting body: stalk extension and active movement of the prespore zone that ensures proper placement of the spores atop the stalk. The approach used in these studies provides a direct means of testing the role of cell motility in distinct cell types during a morphogenetic program.

The serotonin 5-HT2C receptor is a prominent serotonin receptor in basal ganglia: evidence from functional studies on serotonin-mediated phosphoinositide hydrolysis.

Serotonin (5-hydroxytryptamine; 5-HT) 5-HT2A and 5-HT2C receptors belong to the class of phosphoinositide-specific phospholipase C (PLC)-linked receptors. Conditions were established for measuring 5-HT2A-linked and 5-HT2C-linked PLC activity in membranes prepared from previously frozen rat frontal cortex and caudate. In the presence of Ca2+ (300 nM) and GTPgammaS (1 microM), 5-HT increased PLC activity in caudate membranes. Pharmacological analysis using the selective 5-HT2A antagonist, spiperone, and the nonselective 5-HT(2A/2C) antagonist, mianserin, demonstrated that over half of the 5-HT-stimulated PLC activity was due to stimulation of 5-HT2C receptors as opposed to 5-HT2A receptors. Radioligand binding assays with [3H]RP 62203 and [3H]mesulergine were used to quantify 5-HT2A and 5-HT2C sites, respectively, in caudate. From these data, the Bmax for caudate 5-HT2A sites and 5-HT2C sites was 165.4 +/- 9.7 fmol/mg of protein and 49.7 +/- 3.3 fmol/mg of protein, respectively. In contrast to that in caudate, PLC activity in frontal cortex was stimulated by 5-HT in a manner that was inhibited by the 5-HT2A-selective antagonists, spiperone and ketanserin. Taken together, the results indicate that 5-HT2A- and 5-HT2C-linked PLC activity can be discerned in brain regions possessing both receptor subtypes using membranes prepared from previously frozen tissue. More importantly, significant 5-HT2C-mediated phosphoinositide hydrolysis was observed in caudate, despite the relatively low density of 5-HT2C sites. The significance of these observations with respect to the physiological function of 5-HT2C receptors is discussed.

Alterations in the postnatal development of striatal preprotachykinin but not preproenkephalin mRNA expression in the serotonin-depleted rat.

We examined the effects of diminished serotonin (5-hydroxytryptamine, 5-HT) levels on the postnatal development of striatal tachykinin and enkephalin neuropeptide systems. Neonatal rats received intracisternal injection of vehicle or the 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT; 100 micrograms) on postnatal day 2 followed by sacrifice 1-29 days later. Monoamine analysis by high-performance liquid chromatography with electrochemical detection revealed a drastic reduction of midbrain 5-HT levels, but not norepinephrine or dopamine, as early as 1 day and extending to 29 days following 5,7-DHT injection. Striatal preprotachykinin (PPT) mRNA levels were significantly increased 8 days following injection. However, PPT mRNA amounts failed to remain up-regulated, falling back to or below control levels during the second and third weeks following injection. By day 29, striatal PPT mRNA had normalized to control levels even though 5-HT amounts were still markedly reduced. Throughout the entire time course, striatal preproenkephalin mRNA levels did not significantly differ from control levels. These results suggest that striatal tachykinin, but not enkephalin, neurons may be transiently sensitive to lowered 5-HT neurotransmission during postnatal development.

Preprotachykinin and preproenkephalin mRNA expression within striatal subregions in response to altered serotonin transmission.

The effects of lowered serotonin (5-hydroxytryptamine; 5-HT) neurotransmission on preprotachykinin (PPT) and preproenkephalin (PPE) mRNA levels were examined in subregions of the striatum. Adult male rats were treated systemically with para-chlorophenylalanine (pCPA; 350 mg/kg single i.p. injection) which reduced forebrain 5-HT amounts to approximately 20% of saline-injected controls at 24 and 48 h. As measured by Northern analysis, PPT and PPE mRNA levels were elevated 50% and 160% respectively in the anterior ventromedial striatum (region included nucleus accumbens). PPT mRNA levels were raised 90% in posterior striatum (at the level of the globus pallidus) by 48 h post-pCPA injection. To determine if increased PPT and PPE mRNA levels represented a transient response to brief 5-HT inhibition, additional experiments were performed to provide continual suppression of 5-HT within the striatum. First, rats received daily intraperitoneal injections of saline or the 5-HT1A receptor agonist, 8-OH-DPAT (1 mg/kg), for 7 days to reduce 5-HT release from raphestriatal terminals. In a parallel experiment, the serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT, 5 micrograms), was stereotaxically injected into the striatum as a means to permanently remove 5-HT terminals. Although levels of each mRNA species were differentially sensitive to 5,7-DHT or 8-OH-DPAT, PPT and PPE mRNAs were lowered between 30-55% within the anterior dorsolateral and ventromedial striatum. Although these results support previous studies suggesting an overall positive regulatory role of serotonin on striatal tachykinin biosynthesis, PPT and PPE gene regulation in certain striatal subregions may by differentially sensitive to lowered 5-HT neurotransmission. This suggestion is supported by observations that acute systemic stimulation of 5-HT2A/C receptors with DOI (7 mg/kg single i.p. injection) raised PPT and PPE mRNA levels within anterior dorsolateral (30-60%) and posterior (100-200%) striata, but not within the anterior ventromedial striatum.

Effect of corticosterone on serotonin and catecholamine receptors and uptake sites in rat frontal cortex.

The effects of corticosterone (1 mg/kg per day for 7 days) on serotonin 5-HT1A, 5-HT2A, 5-HT uptake sites, and alpha 2-adrenergic receptor sites were measured. Corticosterone treatment significantly decreased the number of 5-HT1A receptor sites (Bmax = 108 +/- 8.20 fmol/mg protein and 152.31 +/- 13.36 fmol/mg protein in corticosterone- and vehicle-treated rats, respectively). No significant differences were found in other measures. It is possible that corticosteroids exert some of their behavioral effects via regulation of 5-HT1A sites in frontal cortex.

Role of essential sulfhydryl groups in drug interactions at the neuronal 5-HT transporter. Differences between amphetamines and 5-HT uptake inhibitors.

The sulfhydryl-selective alkylating agent, N-ethylmaleimide (NEM), has been used as a tool to discern whether different binding domains exist on the neuronal serotonin (5-HT) transporter for 5-HT and 5-HT uptake inhibitors (Reith, M. E. A., Allen, D. L., Sershen, H., and Lajtha, A. (1984) J. Neurochem. 43, 249-255; Graham, D., Esnaud, H., Habert, E., and Langer, S. Z. (1989) Biochem. Pharmacol. 38, 3819-3826). However, relatively high concentrations of NEM and long incubation times have been required for inactivation of the transporter-binding site which raises the possibility that NEM is reacting with other nucleophilic groups (Smyth, D. G., Blumenfeld, O. O., and Konigsberg, W. (1964) Biochem. J. 91, 589-595). In the present work, the reactivity and essential nature of sulfhydryl groups associated with substrate/inhibitor binding to the neuronal 5-HT transporter was assessed. [3H]Paroxetine, a potent and selective 5-HT uptake inhibitor, was used to label the 5-HT transporter. The effects of a relatively wide range of sulfhydryl reagents on [3H]paroxetine binding in digitoninsolubilized preparations of rat brain neuronal membranes and the relative abilities of different classes of drugs to protect against NEM-induced inactivation of [3H]paroxetine binding were studied. It was observed that digitonin-solubilized preparations were more sensitive than membrane preparations to the inactivating effects of NEM. The pKa of the reactive group was estimated to be 6.17, in the range expected for a reactive sulfhydryl. Sulfhydryls essential to ligand binding reacted preferentially with hydrophobic compounds (p-hydroxymercuribenzoate = dithiobisnitrobenzoate > methyl methanethiosulfonate > N-phenylmaleimide > N-ethylmaleimide) and were unreactive toward hydrophilic reagents such as iodoacetate and iodoacetamide. 5-HT, 5-HT uptake inhibitors and cocaine protected the digitonin-solubilized transporter from NEM-induced inactivation while the amphetamine-related releasing agents p-chloroamphetamine and fenfluramine were ineffective. The observation that the binding of some, but not all, ligands requires reduced sulfhydryl groups, suggests that differential mechanisms and/or different binding domains do exist for agents which interact at the neuronal 5-HT transporter.

Effect of tetrahydrobiopterin on serotonin synthesis, release, and metabolism in superfused hippocampal slices.

The effects of 6R-5,6,7,8-tetrahydro-L-biopterin (6R-BH4), the in vivo cofactor for tryptophan hydroxylase, on the synthesis, release, and metabolism of serotonin were studied in superfused slices from rat hippocampus. 6R-BH4 did not alter the spontaneous release of [3H]serotonin but it did significantly increase release when slices were depolarized with 30 mM KCl. Under the same incubation conditions, 6R-BH4 altered neither the synthesis (basal or tryptophan-stimulated) nor the metabolism of serotonin in hippocampal slices. The synthetic pteridine 6-methyl-5,6,7,8-tetrahydropterin also augmented release under depolarizing conditions whereas biopterin, the oxidized form of 6R-BH4, did not. The 6S isomer of BH4, which is relatively inactive as a cofactor for tryptophan hydroxylase, was equipotent with 6R-BH4 in stimulating serotonin release. 6R-BH4 did not inhibit serotonin uptake nor did it function as a serotonin autoreceptor antagonist to increase release. A direct serotonin releasing effect of 6R-BH4, like that produced by p-chloroamphetamine, could also be ruled out. At suboptimal concentrations of extracellular calcium, the KCl-induced release of 3H was significantly reduced, yet the increase in release caused by BH4 remained the same in magnitude. It is concluded that 6R-BH4 increases the depolarization-induced release of serotonin through an interaction with the release mechanism itself, possibly by enhancing calcium influx or by increasing the sensitivity of the release mechanism to calcium. The effects of 6R-BH4 on serotonin release are independent from its function as the cofactor for tryptophan hydroxylase.

Inhibition of tryptophan hydroxylase by benserazide and other catechols.

Tryptophan hydroxylase (L-tryptophan, tetrahydropteridine:oxygen oxidoreductase [5-hydroxylating]; EC 1.14.16.4; TPH), the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin, was inhibited directly by benserazide, an inhibitor of aromatic-L-amino-acid decarboxylase (3,4-dihydroxy-L-phenylalanine carboxy-lyase; EC 4.1.1.28; AAAD). Benserazide was a competitive inhibitor for the pterin cofactor tetrahydrobiopterin and an uncompetitive inhibitor for the substrate tryptophan. NSD 1015, another decarboxylase inhibitor, did not directly inhibit TPH. Other compounds with catechol moieties in their structures such as 3,4-dihydroxyphenylalanine (DOPA), dopamine, apomorphine, and SKF 38393 were also found to be potent inhibitors of TPH. These results indicate that drugs or neurotransmitters with catechol structures directly inhibit the activity of TPH and add to a growing body of evidence indicating that endogenous dopamine can exert untoward effects on serotonin neurons, including inhibition of TPH. Furthermore, the use of decarboxylase inhibitors to cause the accumulation of 5-hydroxytryptophan as an in vivo measure of TPH activity could be problematic, particularly when drugs with catechol structures or dopamine-releasing compounds are also administered.

Cocaine and serotonin neurochemistry.

The neurochemical interactions between cocaine and the serotonin (5-HT) neuronal system are the subject of this Commentary. Attempts to understand the mechanisms through which the euphoric and rewarding properties of cocaine are mediated have focused on the brain dopamine system, with particular emphasis on the dopamine uptake site. However, increasing amounts of research have led to the realization that cocaine also exerts a powerful influence over the serotonin neuronal system. These data are briefly discussed from the standpoint of how cocaine alters the functional or synaptic activity of serotonin. Recent evidence also indicates that the reinforcing properties of cocaine can be reduced by treatments which interact directly or indirectly with the serotonin neuronal system.