Double-blind Within-subject Crossover Design Research Articles

Preliminary evidence for an association between intake of high-fat high-sugar diet, variations in peripheral dopamine precursor availability and dopamine-dependent cognition in humans.

Obesity is associated with alterations in dopaminergic transmission and cognitive function. Rodent studies suggest that diets rich in saturated fat and refined sugars (HFS), as opposed to diets diets low in saturated fat and refined sugars (LFS), change the dopamine system independent of excessive body weight. However, the impact of HFS on the human brain has not been investigated. Here, we compared the effect of dietary dopamine depletion on dopamine-dependent cognitive task performance between two groups differing in habitual intake of dietary fat and sugar. Specifically, we used a double-blind within-subject cross-over design to compare the effect of acute phenylalanine/tyrosine depletion on a reinforcement learning and a working memory task, in two groups that are on opposite ends of the spectrum of self-reported HFS intake (low vs high intake: LFS vs HFS group). We tested 31 healthy young women matched for body mass index (mostly normal weight to overweight) and IQ. Depletion of peripheral precursors of dopamine reduced the working memory specific performance on the operation span task in the LFS, but not in the HFS group (P=0.016). Learning from positive- and negative-reinforcement (probabilistic selection task) was increased in both diet groups after dopamine depletion (P=0.049). As a secondary exploratory research question, we measured peripheral dopamine precursor availability (pDAP) at baseline as an estimate for central dopamine levels. The HFS group had a significantly higher pDAP at baseline compared to the LFS group (P=0.025). Our data provide the first evidence indicating that the intake of HFS is associated with changes in dopamine precursor availability, which is suggestive of changes in central dopamine levels in humans. The observed associations are present in a sample of normal to overweight participants (ie, in the absence of obesity), suggesting that the consumption of a HFS might already be associated with altered behaviours. Alternatively, the effects of HFS diet and obesity might be independent.

Acute inflammation and psychomotor slowing: Experimental assessment using lipopolysaccharide administration in healthy humans

Data from clinical and cross-sectional studies suggest that inflammation contributes to psychomotor slowing and attentional deficits found in depressive disorder. However, experimental evidence is still lacking. The aim of this study was to clarify the effect of inflammation on psychomotor slowing using an experimental and acute model of inflammation, in which twenty-two healthy volunteers received an intravenous injection of lipopolysaccharide (LPS, dose: 0.8 ​ng/kg body weight) and of placebo, in a randomized order following a double-blind within-subject crossover design. A reaction time test and a go/no-go test were conducted 3 ​h after the LPS/placebo injection and interleukin (IL)-6 and tumor necrosis factor (TNF)-α concentrations were assessed. No effect of experimental inflammation on reaction times or errors for either test was found. However, inflammation was related to worse self-rated performance and lower effort put in the tasks. Exploratory analyses indicated that reaction time fluctuated more over time during acute inflammation. These data indicate that acute inflammation has only modest effects on psychomotor speed and attention in healthy subjects objectively, but alters the subjective evaluation of test performance. Increased variability in reaction time might be the first objective sign of altered psychomotor ability and would merit further investigation.

Dissociable Effects of Subthalamic Stimulation in Obsessive Compulsive Disorder on Risky Reward and Loss Prospects

Our daily decisions involve an element of risk, a behavioral process that is potentially modifiable. Here we assess the role of the associative-limbic subthalamic nucleus (STN) in obsessive compulsive disorder (OCD) testing on and off deep-brain stimulation (DBS) on anticipatory risk taking to obtain rewards and avoid losses. We assessed 12 OCD STN DBS in a randomized double-blind within-subject cross-over design. STN DBS decreased risk taking to rewards (p = 0.02) and greater risk taking to rewards was positively correlated with OCD severity (p = 0.01) and disease duration (p = 0.01). STN DBS was also associated with impaired subjective discrimination of loss magnitude (p < 0.05), an effect mediated by acute DBS rather than chronic DBS. We highlight a role for the STN in mediating dissociable valence prospects on risk seeking. STN stimulation decreases risk taking to rewards and impairs discrimination of loss magnitude. These findings may have implications for behavioral symptoms related to STN DBS and the potential for STN DBS for the treatment of psychiatric disorders.

Anodal tDCS over the Primary Motor Cortex Facilitates Long-Term Memory Formation Reflecting Use-Dependent Plasticity.

Previous research suggests that anodal transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) modulates NMDA receptor dependent processes that mediate synaptic plasticity. Here we test this proposal by applying anodal versus sham tDCS while subjects practiced to flex the thumb as fast as possible (ballistic movements). Repetitive practice of this task has been shown to result in performance improvements that reflect use-dependent plasticity resulting from NMDA receptor mediated, long-term potentiation (LTP)-like processes. Using a double-blind within-subject cross-over design, subjects (n=14) participated either in an anodal or a sham tDCS session which were at least 3 months apart. Sham or anodal tDCS (1 mA) was applied for 20 min during motor practice and retention was tested 30 min, 24 hours and one week later. All subjects improved performance during each of the two sessions (p < 0.001) and learning gains were similar. Our main result is that long term retention performance (i.e. 1 week after practice) was significantly better when practice was performed with anodal tDCS than with sham tDCS (p < 0.001). This effect was large (Cohen’s d=1.01) and all but one subject followed the group trend. Our data strongly suggest that anodal tDCS facilitates long-term memory formation reflecting use-dependent plasticity. Our results support the notion that anodal tDCS facilitates synaptic plasticity mediated by an LTP-like mechanism, which is in accordance with previous research.

Studying the effects of dietary body weight-adjusted acute tryptophan depletion on punishment-related behavioral inhibition

BackgroundAlterations in serotonergic (5-HT) neurotransmission are thought to play a decisive role in affective disorders and impulse control.ObjectiveThis study aims to reproduce and extend previous findings on the effects of acute tryptophan depletion (ATD) and subsequently diminished central 5-HT synthesis in a reinforced categorization task using a refined body weight–adjusted depletion protocol.DesignTwenty-four young healthy adults (12 females, mean age [SD]=25.3 [2.1] years) were subjected to a double-blind within-subject crossover design. Each subject was administered both an ATD challenge and a balanced amino acid load (BAL) in two separate sessions in randomized order. Punishment-related behavioral inhibition was assessed using a forced choice go/no-go task that incorporated a variable payoff schedule.ResultsAdministration of ATD resulted in significant reductions in TRP measured in peripheral blood samples, indicating reductions of TRP influx across the blood–brain barrier and related brain 5-HT synthesis. Overall accuracy and response time performance were improved after ATD administration. The ability to adjust behavioral responses to aversive outcome magnitudes and behavioral adjustments following error contingent punishment remained intact after decreased brain 5-HT synthesis. A previously observed dissociation effect of ATD on punishment-induced inhibition was not observed.ConclusionsOur results suggest that neurodietary challenges with ATD Moja–De have no detrimental effects on task performance and punishment-related inhibition in healthy adults.

Stimulation of the mineralocorticoid receptor improves memory in young and elderly healthy individuals

Glucocorticoids play an important role in cognitive function and act on glucocorticoid receptors and mineralocorticoid receptors (MRs) in the brain. Previously, the blockade of the MR has been shown to impair visuospatial and working memory in healthy young men. Here, we investigated the effects of the MR agonist fludrocortisone on memory in young and elderly healthy individuals. Thirty-one young (mean age 25.4 ± 4.6 years) and 22 elderly (mean age 63.2 ± 8.2 years) healthy participants received the MR agonist fludrocortisone (0.4 mg) or placebo at least 3 days apart in a randomized, double-blind within-subject cross-over design. We measured verbal memory (auditory verbal learning test), nonverbal memory (Rey/Taylor complex figure test), and working memory (digit-span task). As expected, young participants performed significantly better than elderly individuals in visuospatial memory (effect of group: F = 42.7, p < 0.01), verbal memory (F = 33.1, p < 0.01), and working memory (digit-span backward: F = 4.5, p = 0.04). For visuospatial memory (F = 5.0, p = 0.03) and short-term and working memory (digit-span forward: F = 4.2, p = 0.05), we found a significant treatment effect indicating better memory performance after fludrocortisone compared with placebo across groups. In concert with the previous studies, our data suggest a role of the MR in memory function. A cognitive enhancing effect by MR stimulation warrants future studies.

The impact of acute tryptophan depletion on attentional performance in adult patients with ADHD

To date, the impact of the neurotransmitter serotonin (5-HT) on different neuropsychological functions in adults with attention deficit hyperactivity disorder (ADHD) is underinvestigated. We aimed to examine the effects of acute tryptophan depletion (ATD) and the resulting reduction in central nervous 5-HT synthesis on target/non-target discrimination ability and sustained attention in adults with ADHD using an AX-Continuous Performance Test (AX-CPT). Twenty male patients with ADHD (age: M = 30.25 SD = 9.37) and twenty male healthy controls (age: M = 27.90 SD = 6.01) received ATD on one day and a tryptophan-balanced control condition (BAL) on another day in a double-blind within-subject crossover design. A continuous performance test (AX-CPT) with three conditions (AX, AY, and BX) was administered on both days under depleted and sham-depleted conditions. In patients omissions increased after ATD when compared with BAL. Patient's reaction time decreased after ATD when compared with BAL, which was contrasted by opposite effects in controls. Patients showed fewer correct responses (AX condition) and showed a higher rate of errors (condition AXE ) independent of ATD or BAL intake. The present preliminary results are indicative of the contribution of serotonergic neurotransmission to attentional processes in adults with ADHD.

Effects of tryptophan depletion on reactive aggression and aggressive decision‐making in young people with ADHD

The neurotransmitter serotonin (5-HT) has been linked to the underlying biological processes related to aggressive behaviour. However, only a few studies on this subject involving young people have been published so far. We aimed to investigate the effects of acute tryptophan depletion (ATD) on reactive aggression and decision-time for aggressive responses in a sample of young people with Attention deficit hyperactivity disorder (n = 20), a population at risk for aggressive behaviour. The study design was a double-blind within-subject crossover design. Aggression was assessed using a Point subtraction aggression game (PSAG) with high (HP) and low provocation (LP) trials 2.5 h after the intake of ATD and a tryptophan-balanced control condition. A chi-square comparison was used to identify the effect of ATD on increased aggression after LP. Boys were more likely to respond with an increased aggressive response after HP under ATD as represented by an increased relative risk and odds ratios. Girls had a higher relative risk than boys of an increased point subtraction under ATD after LP. No significant gender differences in decision-time were detected. An effect of ATD on increased aggression was found in the whole sample after LP. Research involving larger samples is needed to confirm the present preliminary findings.

Acute tryptophan depletion in accordance with body weight: influx of amino acids across the blood–brain barrier

Acute tryptophan depletion (ATD) is a method of reducing central nervous serotonin (5-HT) synthesis in humans by administering an amino acid (AA) beverage lacking in tryptophan (TRP), the physiological precursor of 5-HT. However, to date, the use of conventional ATD protocols in children and adolescents was limited due to frequently observed side effects (e.g., vomiting and nausea). This study investigated the effects of diminished central nervous system 5-HT synthesis on plasma concentrations of relevant AAs and TRP influx into the brain in 24 healthy young adults using the ATD procedure Moja-De, a test protocol that has been used in preliminary research in youths. Twenty-four healthy participants received ATD and a TRP-balanced amino acid load (BAL) using a randomized double-blind within-subject crossover design. Plasma concentrations of the relevant AAs that compete with TRP on the same transport system were assessed at baseline and 90, 180, and 240 min after ATD/BAL intake. TRP influx across the blood–brain barrier was calculated using Michaelis–Menten kinetics with a correction for multiple substrate competition, indicating a significant decrease in TRP influx into the central nervous system under Moja-De. ATD Moja-De decreased TRP influx into the brain and central nervous system 5-HT synthesis safely and effectively and was well tolerated, allowing it to be used in children and adolescents. Future research into other secondary, compensatory effects induced by ATD in patients with neuropsychiatric disorders and healthy populations is needed. ATD Moja-De allows this type of research with a focus on a developmental viewpoint.Electronic supplementary materialThe online version of this article (doi:10.1007/s00702-012-0793-z) contains supplementary material, which is available to authorized users.

Diminished central nervous 5‐HT neurotransmission and mood self‐ratings in children and adolescents with ADHD: no clear effect of rapid tryptophan depletion

Research on 5-HT-functioning in adult patients and healthy subjects using rapid tryptophan depletion (RTD) has indicated weak but stable effects on mood ratings. Altered mood in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) can confound the differential diagnosis between severe ADHD and mood disorders such as pediatric bipolar disorder. The present study investigated the effects of RTD induced lowered central nervous 5-HT-levels on mood self-ratings in children with ADHD. Seventeen boys with ADHD participated in the study in a double-blind within-subject crossover-design. They were administered RTD within an amino acid drink lacking tryptophan, thus lowering central nervous 5-HT-synthesis. On another day they received a placebo. Self-rated mood was assessed on both days at baseline conditions and at three different post-drink time-points. RTD had no clear effect on mood within the whole sample. Low scorers on venturesomeness were more strongly affected by RTD in terms of feelings of inactivity and negative feelings compared to high venture patients. Our data did not show a significant effect of RTD on mood self-ratings. However, the findings must be considered as preliminary and require further replication, in particular as they could be due to sampling bias.

Reduced serotonergic functioning changes heart rate in ADHD

Reduced mean heart rate (HR) was shown to be a biophysiological marker for aggression, which in turn was proven to be related to changed serotonergic neurotransmission. A total of 16 ADHD-diagnosed boys were subjected to rapid tryptophan depletion (RTD) and a placebo in a double-blind within-subject crossover-design. Mean HR was assessed under RTD/placebo. Low impulsive patients behaving aggressively under RTD showed a lowered HR under RTD versus placebo. Diminished 5-HT functioning was associated with lowered HR and aggressive behaviour.

Varenicline Improves Mood and Cognition During Smoking Abstinence

Neuronal nicotinic acetylcholine receptors (nAChRs) are a key target in medication development for various neuropsychiatric disorders, including nicotine dependence. Varenicline, a partial agonist at the alpha4beta2 nAChRs, is a new, efficacious medication for nicotine dependence. Its effects on the affective and cognitive dimensions of nicotine withdrawal have yet to be well characterized. Sixty-seven treatment-seeking smokers were administered varenicline (x 21 days) and placebo (x 21 days) in a double-blind within-subject crossover design. Following medication run-up (Days 1-10), there was a 3-day mandatory smoking abstinence phase (Days 11-13) during which subjective symptoms and cognitive performance were assessed. Participants were reexposed to a scheduled smoking lapse (Day 14) and followed for days to lapse (Days 15-21) in each medication period. In the varenicline period, compared with placebo, withdrawal symptoms (p = .04), smoking urges (p < .001), and negative affect (p = .01) during manditory abstinence were significantly lower, and levels of positive affect (p = .046), sustained attention (p = .018), and working memory (p = .001) were significantly greater. Varenicline also significantly reduced subjective rewarding effects of the scheduled smoking lapse (e.g., satisfaction, relief, liking; p = .003). Medication effects on days to lapse following the scheduled smoking lapse were dependent on treatment order (p = .001); among participants who received placebo in the first period, varenicline increased days of abstinence in the follow-up period. These data identify novel affective and cognitive effects of varenicline and may have implications for medication development for other neuropsychiatric conditions.

Diminished 5‐HT functioning in CBCL pediatric bipolar disorder‐profiled ADHD patients versus normal ADHD: susceptibility to rapid tryptophan depletion influences reaction time performance

There is a current debate on characterizing children with pediatric bipolar disorder (PBD) through a profile within the child behaviour checklist (CBCL), and on the involvement of the 5-HT system in the underlying neurobiological processes of PBD. The aim of the present paper was to investigate reaction time performance in patients with CBCL-PBD and to discriminate ADHD from ADHD with CBCL-PBD with respect to diminished 5-HT functioning and reaction time. Twenty-two patients with ADHD received the rapid tryptophan depletion test (RTD) thus lowering the central-nervous 5-HT synthesis rate within a placebo-controlled double-blind within-subject crossover design. Reaction time was assessed using a competitive reaction time game with low and high provocation after both depletion and placebo intake. The study sample was divided into high and low scorers according to their CBCL-PBD scores. Comparing those six patients with the highest and clinically significant CBCL-PBD scores versus those six patients with the lowest, patients with a high CBCL-PBD score showed a slower reaction time under RTD compared to patients with low CBCL-PBD scores after high provocation. CBCL-'aggression' discriminated between the two groups. The results suggest alterations in 5-HT functioning in CBCL-PBD-spectrum patients, and 'aggression' as a potential moderator variable to ADHD.

Serotonergic functioning and trait‐impulsivity in attention‐deficit/hyperactivity‐disordered boys (ADHD): influence of rapid tryptophan depletion

The present study investigated the effects of rapid tryptophan depletion (RTD) and the ensuing reduction of central nervous levels of serotonin (5-HT) on reactive aggression with respect to personality factors comprising aspects of trait-impulsivity and -aggression in boys with attention-deficit/hyperactivity-disorder (ADHD). Twenty-two male adolescent patients with ADHD received the RTD test on one day, and, on another day a tryptophan balanced placebo in a double-blind within-subject crossover design. Impulsive personality factors and trait-impulsivity were assessed in advance of the study. Aggression was provoked using a competitive reaction time game 270 min after RTD/placebo intake. RTD had a significant effect on increased aggressive behaviour with which low-grade impulsive patients responded. High-grade impulsive patients were not affected by RTD or even responded with increased aggressive behaviour while receiving placebo treatment. The present study supports the hypothesis that 5-HT functioning in ADHD patients influences reactive aggression depending on aspects of trait-impulsivity. Future studies are necessary in order to detect the specific influence of ADHD as regards the relevance to 5-HT-induced changed aggressive responding.

Effect of acute hypoxia on plasma leptin concentrations in men

Rationale: Leptin, a hormone secreted by the adipose tissue, is tightly involved in the endocrine control of energy expenditure and body weight regulation. Previous studies emphasize a relationship between hypoxia and leptin, but are contradicting. The aim of this study was to investigate the effects of brief hypoxia on leptin concentrations in healthy men. Methods: In a double-blind within-subject crossover design, we examined 14 healthy young men with age between 20 and 25 years and body mass index of < 25 kg/m2. Hypoxic versus normoxic conditions were induced by decreasing oxygen saturation to 75% (vs. 96% in the control condition) under the condition of an euglycaemic clamp. Plasma leptin concentrations were determined at baseline, after 3 h of euglycaemic clamp, during hypoxia and the following 2.5 h thereafter. Results: T-test comparisons revealed no significant differences between the conditions at baseline (p=0.446). Also, at the euglycaemic equilibrium after 3h, plasma leptin concentrations were comparable (p>0.137). During hypoxia (p>0.195) as well as 2.5 h after hypoxia (p=0.476) plasma leptin concentrations remained equal in both conditions. There were no statistical differences between hypoxic and normoxic conditions in ANOVA (p=0.269). AUC comparison remained non-significant (p=0.180). Overall, leptin increases significantly in hypoxia (p<0.001) and normoxia (p=0.001) during the course of 6 h. Conclusions: Our results show an increase of plasma leptin concentrations after 6 h of clamping most likely reflecting the known diurnal variation of the hormone. We found no significant changes in leptin concentrations during and after brief hypoxia under euglycaemic clamp conditions. Leptin levels, therefore, seem to be unaffected by short hypoxic episodes of moderate degree.

Effects of cholecystokinin and calcitonin on evoked brain potentials and satiety in man

Central nervous effects of the peptides cholecystokinin (CCK) and calcitonin (CT) were tested in an attention task for their effects on Auditory Event Related Potentials (AERPs) and for their effects on satiety and activation as measured in self-rating scales. Thirteen healthy subjects received either 3 IDU/kg body weight CCK 1–33, 0.1 IU/kg bodyweight CT and placebo according to a double-blind within-subject cross-over design. Subjects had fasted for at least 16 hr prior to the experiment. CCK induced the feeling of satiety after stimulation with the preparation of a meal. The peptides prevented an attenuation of the N2-component of the AERP after the preparation of a meal, indicating that the subjects were less distracted by the food cues. The results suggest that the central nervous effects of CCK and CT may constitute an aspect of satiated behavior.

The Failure of Antimotion Sickness Medication to Improve Reading in Developmental Dyslexia

Although there have been no randomized clinical trials of the efficacy of antimotion sickness medication treatment of developmental dyslexia, some children are treated in this way. We have performed two evaluations of such treatments. In Experiment 1, 12 children participated in a double-blind within-subject crossover design to test the acute (2-day) administration of four preparations: 10 mg methylphenidate, 12.5 mg meclizine, both methylphenidate and meclizine, or placebo. Improvements obtained with each drug were scattered across measures of reading fluency, balance and coordination, and eye movements, suggesting that a chronic trial would be justified. In Experiment 2, six children from Experiment 1 received 12.5 mg meclizine b.i.d. for 3 months and placebo for 3 months in a double-blind within-subject crossover design. Meclizine had no effect on reading, but it significantly improved ocular motor stability during steady fixation. This study thus failed to support the hypothesis that meclizine is of benefit in developmental dyslexia.