Acute tryptophan depletion in healthy volunteers enhances punishment prediction but does not affect reward prediction.

Central serotonin (5-HT) has been implicated in emotional and behavioral control processes for many decades, but its precise contribution is not well understood. We used the acute tryptophan depletion procedure in young healthy volunteers to test the hypothesis that central 5-HT is critical for predicting punishment. An observational reversal-learning task was employed that provided separate measures of punishment and reward prediction. Under baseline, subjects made more prediction errors for punishment-associated stimuli than for reward-associated stimuli. This bias was abolished after central 5-HT depletion, which enhanced the ability to predict punishment while not affecting reward prediction. The selective potentiation of punishment prediction concurs with recent theorizing, suggesting that central 5-HT carries a prediction error for future punishment, but not for future reward (Daw et al, 2002). Furthermore, the finding highlights the importance of central 5-HT in resilience to adversity and may have implications for a variety of neuropsychiatric disorders including depression and anxiety.     

Effects of acute metabolic stress on striatal dopamine release in healthy volunteers.

Several lines of evidence indicate that a variety of metabolic stressors, including acute glucose deprivation are associated with dopamine release. Pharmacologic doses of the glucose analogue, 2-deoxyglucose (2DG) cause acute glucoprivation and are associated with enhanced dopamine turnover in preclinical studies. In this study, we utilized [11C]raclopride PET to examine 2DG-induced striatal dopamine release in healthy volunteers. Six healthy volunteers underwent PET scans involving assessment of 2DG-induced (40 mg/kg) decrements in striatal binding of the D(2)/D(3) receptor radioligand [11C]raclopride. Decreases in [11C]raclopride specific binding reflect 2DG-induced changes in synaptic dopamine. Specific binding significantly decreased following 2DG administration, reflecting enhanced synaptic dopamine concentrations (p =.02). The administration of 2DG is associated with significant striatal dopamine release in healthy volunteers. Implications of these data for investigations of the role of stress in psychiatric disorders are discussed.     

Lithium and 5-HT1A receptor sensitivity: a neuroendocrine study in healthy volunteers

The effect of lithium administration (800 mg daily for 7 days) on the neuroendocrine and temperature responses to the 5-HT_1A receptor agonist, gepirone, was studied in eight healthy male volunteers. Gepirone (20 mg orally) significantly increased plasma levels of prolactin, growth hormone, corticotropin and cortisol, and lowered oral temperature. None of these responses was significantly altered by lithium treatment. The results suggest that the ability of short-term lithium treatment to increase 5-HT-mediated neuroendocrine responses in humans is unlikely to be related to changes in the sensitivity of pre- or post-synaptic 5-HT_1A receptors.     

Dysfunction of ventral striatal reward prediction in schizophrenic patients treated with typical, not atypical, neuroleptics

Rational Clinical studies in patients with schizophrenia suggest that atypical neuroleptics are more effective than typical neuroleptics in reducing negative symptoms including apathy and anhedonia. Dysfunction of the dopaminergic reward system may contribute to negative symptoms in schizophrenia.Objective We used functional magnetic resonance imaging to assess the blood oxygen level dependency response in the ventral striatum of medicated schizophrenics and healthy control subjects during reward anticipation.Methods Twenty schizophrenics [ten medicated with typical (e.g., haloperidol) and ten with atypical (e.g., olanzapine and risperidone) neuroleptics] and ten age-matched healthy volunteers participated in an incentive monetary delay task in which visual cues predicted that a rapid response to a subsequent target stimulus would result either in monetary gain or no consequence.Results Healthy volunteers and schizophrenics treated with atypical neuroleptics showed ventral striatal activation in response to reward-indicating cues, but schizophrenics treated with typical neuroleptics did not. In patients treated with typical neuroleptics, decrease in activation of the left ventral striatum was correlated with the severity of negative symptoms.Conclusions Failure to activate the ventral striatum during reward anticipation was previously associated with the severity of negative symptoms in schizophrenia and was also found in schizophrenics treated with typical neuroleptics in this study. Significant blunting of ventral striatal activation was not observed in patients treated with atypical neuroleptics, which may reflect the improved efficacy of these drugs in treating negative symptoms.Georg Juckel and Florian Schlagenhauf contributed equally to this work.     

Tryptophan depletion alters the decision-making of healthy volunteers through altered processing of reward cues.

While accumulating evidence suggests that effective real-life decision-making depends upon the functioning of the orbitofrontal cortex, much less is known about the involvement of the monoamine neurotransmitter systems and, in particular, serotonin. In the present study, we explored the impact of depleting the serotonin precursor, tryptophan, on human decision-making. Eighteen healthy volunteers consumed an amino-acid drink containing tryptophan and 18 healthy volunteers consumed an amino-acid drink without tryptophan, before choosing between simultaneously presented gambles, differing in the magnitude of expected gains (ie reward), the magnitude of expected losses (ie punishment), and the probabilities with which these outcomes were delivered. Volunteers also chose between gambles probing identified non-nomative biases in human decision-making, namely, risk-aversion when choosing between gains and risk-seeking when choosing between losses. Tryptophan-depleted volunteers showed reduced discrimination between magnitudes of expected gains associated with different choices. There was little evidence that tryptophan depletion was associated with altered discrimination between the magnitudes of expected losses, or altered discrimination between the relative probabilities with which these positive or negative outcomes were delivered. Risk-averse and risk-seeking biases were also unchanged. These results suggest that serotonin mediates decision-making in healthy volunteers by modulating the processing of reward cues, perhaps represented within the orbitofrontal cortex. It is possible that such a change in the cognition mediating human choice is one mechanism associated with the onset and maintenance of anhedonia and lowered mood in psychiatric illness.     

Nicotine differentially modulates antisaccade performance in healthy male non-smoking volunteers stratified for low and high accuracy

Rationale  

Nicotinergic agents are currently examined as possible pro-cognitive drugs for a variety of clinical conditions marked by cognitive deficits, such as attention deficit hyperactivity disorder (ADHD) or schizophrenia. The response to acute nicotine is heterogeneous across subjects and samples; however, only a few reliable predictors of response have been identified.     

Weight of financial reward in the decision by medical students and experienced healthy volunteers to participate in clinical trials

Summary The aim of this survey was twofold: to assess the willingness of medical students to volunteer for clinical trials and to evaluate the weight of the financial reward and other general details as seen by healthy volunteers who had already participated in clinical trials. A specific questionnaire was given to each group to be answered anonymously. Among the medical students only 2.9% had already volunteered, 39.7% said that they would never participate, 24.7% would do it for scientific interest, 32.2% for scientific interest and financial reward, and 4.2% for the financial reward alone. In experienced volunteers, financial reward was the main reason to participate (90%) followed by curiosity (6.3%). The financial reward actually received was considered adequate compensation for the time and discomfort by most of the volunteers (83.7%). The information supplied by the research team and the arrangements made to treat any hazardous event were considered adequate (47.5%) or optimal (42.5%). Almost all the experienced volunteers (93.8%) answered positively when asked about participation in future studies. The results show that financial reward is a very important reason for healthy volunteers to participate in clinical trials.     

Modafinil augments brain activation associated with reward anticipation in the nucleus accumbens

Rationale

The nucleus accumbens (NAc) works as a key brain structure of the reward system, in which reward-related neural activity is well correlated with dopamine release from mesolimbic dopaminergic neurons.

Objectives

Since modafinil can modulate dopaminergic transmission through re-uptake inhibition of dopamine, we investigated whether modafinil affects the reward-related brain activity in the NAc in healthy subjects.

Methods

Twenty healthy participants underwent two series of functional magnetic resonance imaging while performing monetary incentive delay task in which they were cued to anticipate and respond to a rapidly presented target to gain or avoid losing varying amounts of money, under modafinil or placebo condition. Blood oxygenation-level dependent (BOLD) activation signals during gain and loss anticipations were analyzed in the NAc as an a priori region of interest as well as the whole brain.

Results

Modafinil significantly changed subjective feelings toward positive ones. The activation of BOLD signals was observed during gain anticipation under the placebo and modafinil conditions in the left and bilateral NAc, respectively. The modafinil condition showed significantly higher BOLD signal change at the highest gain (+¥500) cue compared to the placebo condition.

Conclusions

The present study showed that modafinil affects reward processing in the NAc in healthy subjects through enhancing more positive anticipation, and it may provide a basis for the use of this drug for treating anhedonia observed in psychiatric disorders.     

DRD2 Taq1A polymorphism modulates prolactin secretion induced by atypical antipsychotics in healthy volunteers

Hyperprolactinemia mediated by antagonism of dopaminergic neurotransmission in the pituitary gland is a common adverse effect of antipsychotics. Recent studies have suggested that polymorphisms of dopamine receptors can affect the therapeutic response to antipsychotics. Thus, our aim was to evaluate whether 2 such polymorphisms (DRD2 Taq1A and DRD3 Ser9Gly) modulate prolactin release in healthy volunteers (n = 119) receiving a single dose of quetiapine (25 mg, n = 26), olanzapine (5 mg, n = 57), or risperidone (1 mg, n = 36). The increases in maximum concentration and in area under the curve were calculated from plasma prolactin levels after subtraction of pretreatment levels. Multiple regression analyses revealed that prolactin increases in maximum concentration and in area under the curve depended on drug (quetiapine < olanzapine < risperidone; P < 0.001), sex (women > men; P < 0.001), and Taq1A polymorphism (A1? > A2/A2; P < 0.05). Analysis of the individual drugs revealed that prolactin secretion was modulated by sex and Taq1A polymorphism in olanzapine and risperidone (P < 0.05); however, these factors were not linked to prolactin secretion in quetiapine.     

Phenytoin binding in healthy volunteers

The pharmacologic effect of phenytoin is directly related to the unbound concentration in the serum, which previously has been reported in the literature to be approximately 10%. The results of 13 out of 14 20-35 year-old healthy male volunteers studied indicate that less than 10% unbound phenytoin is present in the majority of subjects taking two different doses of phenytoin.     

Cyclosporine kinetics in healthy volunteers

The pharmacokinetics of cyclosporine was studied in five healthy male volunteers following intravenous administration. The subjects received 2.1 mg/kg of cyclosporine as a two-hour intravenous infusion. Blood samples were collected over the subsequent 48 hours. Cyclosporine was extracted from whole blood and analyzed by high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). Following the intravenous infusion of cyclosporine, the drug exhibited multicompartmental behavior. The harmonic mean distribution half-life based on HPLC data was 0.45 hours, and the harmonic mean terminal disposition half-life was 6.2 hours. The clearance of cyclosporine based on HPLC cyclosporine concentrations was 3.9 mL/min/kg, and the volume of distribution at steady state of cyclosporine was 1.23 L/kg. Cyclosporine has a shorter half-life, lower clearance, and smaller Vss in healthy persons as compared to patient populations. The differences observed in the pharmacokinetics of cyclosporine in healthy persons as compared to patient populations may be due to differences in hematocrit, lipoprotein profiles, and/or concurrent drug therapy between the groups. Cyclosporine concentrations determined by RIA were consistently higher than those determined by HPLC, resulting in a significantly higher area under the blood concentration versus time curve and lower clearance rate for cyclosporine. We conclude that: (1) kinetic parameter estimates for cyclosporine are different in healthy individuals as compared with organ-transplant recipients, and (2) the kinetic parameters for cyclosporine are different, depending on the assay technique used.     

The D2 antagonist sulpiride modulates the neural processing of both rewarding and aversive stimuli in healthy volunteers

Rationale  

Animal studies indicate that dopamine pathways in the ventral striatum code for the motivational salience of both rewarding and aversive stimuli, but evidence for this mechanism in humans is less established. We have developed a functional magnetic resonance imaging (fMRI) model which permits examination of the neural processing of both rewarding and aversive stimuli.     

Amlodipine pharmacokinetics in healthy volunteers

In the present study we investigated the pharmacokinetics and comparative bioavailability of three oral doses of amlodipine in 12 healthy male volunteers. A randomized, open-label, three period crossover study design was employed. Each subject received, on three separate occasions a single oral dose of 2.5, 5 and 10 mg amlodipine. Standing diastolic blood pressure was reduced by 1.1, 4.8 and 8 mmHg six hours after 2.5, 5 and 10 mg amlodipine, respectively. There were no significant changes in pulse rate, nor on the EKG. The curves for the mean plasma concentrations versus time for the three doses showed parallel time-courses. Highly significant positive correlations were observed between dose and AUC (0-72 hrs) and between dose and Cmax. However, dose corrected AUC and Cmax were 10-20% lower with 2.5 mg, than with 5 and 10 mg. Peak levels were achieved 5.6 to 6.4 hours postdose. Half lives were 31.2, 33 and 36.8 hours for 2.5, 5 and 10 mg respectively. Headache was the most common side effect, and was more frequently observed with the highest dose. In summary, linear relationships were found between the dose and the plasma levels of amlodipine. Decreases in standing diastolic blood pressure were also dose related. Because of its long half-life and gradual absorption, amlodipine should be effective in lowering blood pressure given once daily and the incidence of side effects due to rapid absorption should be minimized.     

Neural responses to reward anticipation and feedback in adult and adolescent cannabis users and controls

Chronic use of drugs may alter the brain’s reward system, though the extant literature concerning long-term cannabis use and neural correlates of reward processing has shown mixed results. Adolescents may be more vulnerable to the adverse effects of cannabis than adults; however, this has not been investigated for reward processing. As part of the ‘CannTeen’ study, in the largest functional magnetic resonance imaging study of reward processing and cannabis use to date, we investigated reward anticipation and feedback in 125 adult (26–29 years) and adolescent (16–17 years) cannabis users (1–7 days/week cannabis use) and gender- and age-matched controls, using the Monetary Incentive Delay task. Blood-oxygen-level-dependent responses were examined using region of interest (ROI) analyses in the bilateral ventral striatum for reward anticipation and right ventral striatum and left ventromedial prefrontal cortex for feedback, and exploratory whole-brain analyses. Results showed no User-Group or User-Group × Age-Group effects during reward anticipation or feedback in pre-defined ROIs. These null findings were supported by post hoc Bayesian analyses. However, in the whole-brain analysis, cannabis users had greater feedback activity in the prefrontal and inferior parietal cortex compared to controls. In conclusion, cannabis users and controls had similar neural responses during reward anticipation and in hypothesised reward-related regions during reward feedback. The whole-brain analysis revealed tentative evidence of greater fronto-parietal activity in cannabis users during feedback. Adolescents showed no increased vulnerability compared with adults. Overall, reward anticipation and feedback processing appear spared in adolescent and adult cannabis users, but future longitudinal studies are needed to corroborate this.Subject terms: Human behaviour, Cognitive neuroscience, Reward     

Atropine and verapamil interactions in healthy volunteers

Summary The calcium antagonist falipamil, a chemical congener of verapamil, has anticholinergic properties. It was decided to study the interaction of verapamil with the anticholinergic drugs, atropine and pirenzepine, using healthy male volunteers.After atropine alone a significant tachycardia developed at 2 min and remained significant up to 90 min. Verapamil pretreatment followed by atropine administration resulted in a significantly greater tachycardia. Pirenzepine alone caused a bradycardic response which was accentuated after verapamil pretreatment.It is postulated that short term verapamil administration is accompanied by reflex activation of the sympathetic nervous system which does not manifest with a tachycardia owing to combined influence of verapamil and vagus on the sino-atrial node. Reduction of vagal tone with atropine treatment results in sympathetic overriding of the sino-atrial suppression, thus causing an additive tachycardia. The clinical use of atropine for prolonged verapamil-induced atrio-ventricular conduction is supported by these results.     

Disposition of loratadine in healthy volunteers

The absorption, metabolism and excretion of carbon-14-labeled loratadine (LOR, SCH 29851, Claritin®) administered orally to healthy male volunteers were evaluated. Following a single oral 10-mg dose of [¹⁴C]LOR (～102?µCi), concentrations of LOR and desloratadine (DL; a pharmacologically active descarboethoxy metabolite of LOR) were determined in plasma. Metabolites in plasma, urine and feces were characterized using a liquid chromatography-mass spectrometry system (LC-MS) connected in line with a flow scintillation analyzer (FSA). Maximum plasma LOR and DL concentrations were achieved at 1.5?h and 1.6?h, respectively; thus, LOR was rapidly absorbed but also rapidly metabolized as indicated by these similar t_max values. Metabolite profiles of plasma showed that LOR was extensively metabolized via descarboethoxylation, oxidation and glucuronidation. Major circulating metabolites included 3-hydroxy-desloratadine glucuonide (3-OH-DL-Glu), dihydroxy-DL-glucuronides, and several metabolites resulting from descarboethoxylation and oxidation of the piperidine ring. LOR was completely metabolized by 6?h post-dose. LOR-derived radiocarbon was excreted almost equally in the urine (41%) and feces (43%). About 13% of the dose was eliminated in the urine as 3-OH-DL-Glu. DL accounted for less than 2% of the dose recovered in the urine and only trace amounts of LOR were detected. 3-OH-DL was the major fecal metabolite (～17% of the dose). The combined amount of 5- and 6-hydroxy-DL contributed to an additional 10.7% of the dose in feces. Approximately 5.4% and 2.7% of the dose were excreted in the feces as unchanged drug and DL, respectively.     

艾司西酞普兰在健康人体的药动学

目的:评价健康中国人口服艾司西酞普兰片后的药动学。方法:20名健康受试者男女各半,分别进行艾司西酞普兰片低(5mg)、中(10mg)、高(20mg)3种剂量水平的单剂量药动学试验,并对中间剂量进行多次给药及稳态试验。采用高效液相色谱-串联质谱(HPLC-MS/MS)法测定血浆艾司西酞普兰浓度,用DAS软件进行数据处理。结果:单剂量口服5、10和20 mg艾司西酞普兰后,主要药动学参数AUC_(0～144)分别为(219±s 49),(367±60)和(689±174)μg·h·L~(-1);AUC_(0～∞)分别为(242±64),(414±79)和(745±207)μg·h·L~(-1);c_(max)分别为(5.5±1.0),(8.8±1.3)和(21±6)μg·L~(-1);t_(max)分别为(4±3),(6±3)和(3.0±1.5)h;t_(1/2)分别为(40±11),(48±10)和(37±6)h;MRT分别为(56±13),(63±11)和(51±7)h。多剂量口服10 mg艾司西酞普兰受试制剂后,艾司西酞普兰的主要药动学参数AUC_(0～144)为(914±202)μg·h·L~(-1);AUC_(0～∞)为(993±214)μg·h·L~(-1);AUC_(ss)为(364±78)μg·h·L~(-1);c_(max)~(ss)为(26±4)μg·L~(-1);c(min)~(ss)为(12.4±1.1)μg·L~(-1);c_(av)~(ss)为(15±3)μg·L~(-1);DF为0.87±0.22;t_(max)为(2.6±1.7)h;t_(1/2)为(40±7)h。结论:艾司西酞普兰的体内过程符合二房室开放模型,在研究剂量范围(5～20 mg)内c_(max)和AUC的增加与剂量呈正相关,t_(max)、t_(1/2)和MRT基本不受剂量变化的影响,具线性药动学行为。     

Pharmacokinetics of pinazepam in healthy volunteers

The kinetics of pinazepam were studied in six healthy male volunteers aged between 26 and 31 years. The drug was administered in a single oral dose (10 mg). The concentrations of the parent compound and metabolites were measured in the plasma and urine by gas-chromatographic analysis. Plasma levels of pinazepam were fitted to a two-compartment open model with first order absorption rate using a three-exponential equation. Absorption rate constant and peak plasma levels of pinazepam were 1.36 +/- 0.15 h-1 and 36.8 +/- 5.1 ng/ml respectively. Plasma decay of the drug consisted of an initial rapid elimination phase (alpha = 0.46 +/- 0.06 h-1) followed by a slow one (beta = 0.046 +/- 0.004 h-1). N-desmethyldiazepam was the only metabolite detected in the plasma. Its plasma concentrations were higher than those of the parent compound shortly after administration. Urine was collected for 72 h after dosing. Those specimens contained unconjugate pinazepam and N-desmethyldiazepam and glucuronated oxazepam and 3-OH-pinazepam. Only 0.016% of the pinazepam administered was recovered as unchanged compound in the urine.