Effects of a novel method of acute tryptophan depletion on plasma tryptophan and cognitive performance in healthy volunteers

Facial expressions of pain: the role of the serotonergic system

RATIONALE

Although interest in the neurobiology of facial communication of pain has increased over the last decades, little is known about which neurotransmitter systems might be involved in regulating facial expressions of pain.

OBJECTIVES

We aim to investigate whether the serotonergic system (5-HT), which has been implicated in various aspects of pain processing as well as in behavioral response inhibition, might play a role in facial expressions of pain. Using acute tryptophan depletion (ATD) to manipulate 5-HT function, we examined its effects on facial and subjective pain responses.

METHODS

In a double-blind, placebo-controlled within-subject design, 27 participants received either an ATD or a control drink in two separate sessions. Approximately 5-h post-oral consumption, we assessed pain thresholds (heat, pressure) as well as facial and subjective responses to phasic heat pain. Moreover, situational pain catastrophizing and mood were assessed as affective state indicators.

RESULTS

ATD neither influenced pain thresholds nor self-report ratings, nor catastrophizing or mood. Only facial responses were significantly affected by ATD. ATD led to a decrease in pain-indicative as well as in pain-non-indicative facial responses to painful heat, compared to the control condition.

CONCLUSIONS

Decrease in brain 5-HT synthesis via ATD significantly reduced facial responses to phasic heat pain; possibly due to (i) diminished disposition to display social behavior or due to (ii) decreased facilitation of excitatory inputs to the facial motor neuron.

The role of serotonin in declarative memory: A systematic review of animal and human research

The serotonergic system is involved in diverse cognitive functions including memory. Of particular importance to daily life are declarative memories that contain information about personal experiences, general facts, and events. Several psychiatric or neurological diseases, such as depression, attention-deficit-hyperactivity disorder (ADHD), and dementia, show alterations in serotonergic signalling and attendant memory disorders. Nevertheless, understanding serotonergic neurotransmission and its influence on memory remained a challenge until today. In this systematic review, we summarize recent psychopharmacological studies in animals and humans from a psychological memory perspective, in consideration of task-specific requirements. This approach has the advantage that comparisons between serotonin (5-HT)-related neurochemical mechanisms and manipulations are each addressing specific mnemonic circuits. We conclude that applications of the same 5-HT-related treatments can differentially affect unrelated tasks of declarative memories. Moreover, the analysis of specific mnemonic phases (e.g., encoding vs. consolidation) reveals opposing impacts of increased or decreased 5-HT tones, with low 5-HT supporting spatial encoding but impairing the consolidation of objects and verbal memories. Promising targets for protein synthesis-dependent consolidation enhancements include 5-HT₄ receptor agonists and 5-HT₆ receptor antagonists, with the latter being of special interest for the treatment of age-related decline. Further implications are pointed out as base for the development of novel therapeutic targets for memory impairment of neuropsychiatric disorders.

Functional consequences of acute tryptophan depletion on raphe nuclei connectivity and network organization in healthy women

Previous research on central nervous serotonin (5-HT) function provided evidence for a substantial involvement of 5-HT in the regulation of brain circuitries associated with cognitive and affective processing. The underlying neural networks comprise core subcortical/cortical regions such as amygdala and medial prefrontal cortex, which are assumed to be modulated amongst others by 5-HT. Beside the use of antidepressants, acute tryptophan depletion (ATD) is a widely accepted technique to manipulate of 5-HT synthesis and its respective metabolites in humans by means of a dietary and non-pharmacological tool. We used a double-blind, randomized, cross-over design with two experimental challenge conditions, i.e. ATD and tryptophan (TRP) supplementation (TRYP+) serving as a control. The aim was to perturb 5-HT synthesis and to detect its impact on brain functional connectivity (FC) of the upper serotonergic raphe nuclei, the amygdala and the ventromedial prefrontal cortex as well as on network organization using resting state fMRI. 30 healthy adult female participants (age: M ​= ​24.5 ​± ​4.4 ​yrs) were included in the final analysis. ATD resulted in a 90% decrease of TRP in the serum relative to baseline. Compared to TRYP ​+ ​for the ATD condition a significantly lower FC of the raphe nucleus to the frontopolar cortex was detected, as well as greater functional coupling between the right amygdala and the ventromedial prefrontal cortex. FC of the raphe nucleus correlated significantly with the magnitude of TRP changes for both challenge conditions (ATD & TRYP+). Network-based statistical analysis using time series from 260 independent anatomical ROIs revealed significantly greater FC after ATD compared to TRYP+ in several brain regions being part of the default-mode (DMN) and the executive-control networks (ECN), but also of salience or visual networks. Finally, we observed an impact of ATD on the rich-club organization in terms of decreased rich-club coefficients compared to TRYP+. In summary we could confirm previous findings that the putative decrease in brain 5-HT synthesis via ATD significantly alters FC of the raphe nuclei as well as of specific subcortical/cortical regions involved in affective, but also in cognitive processes. Moreover, an ATD-effect on the so-called rich-club organization of some nodes with the high degree was demonstrated. This may indicate effects of brain 5-HT on the integration of information flow from several brain networks.

Dissociable Effects of Tryptophan Supplementation on Negative Feedback Sensitivity and Reversal Learning

Serotonin has been shown to modulate probabilistic reversal learning (PRL) and negative feedback sensitivity (NFS) in both animal and human studies. Whilst these two measures are tightly coupled, some studies have suggested that these may be mediated by independent mechanisms; the former, representing perseveration and cognitive flexibility, and the latter measuring the ability to maintain a response set (win-stay) at the expense of lose-shift behavior when occasional misleading feedback has been presented. Here, we tested this hypothesis in 44 healthy participants who were administered tryptophan (22 placebo, 22 tryptophan), a precursor to serotonin. We found a dissociable effect of tryptophan supplementation on PRL/NFS. Specifically, tryptophan administration increased NFS compared to the placebo group but had no effect on PRL. We discuss these findings in relation to dosages and with a particular focus on the acute tryptophan depletion (ATD) procedures.

Tryptophan supplementation and serotonin function: genetic variations in behavioural effects

The neurotransmitter serotonin has a role in affective disorders such as depression and anxiety, as well as sleep, cognitive function and appetite. This review examines the evidence that serotonin-related genotypes may moderate the behavioural effects of supplementation with the serotonin precursor amino acidl-tryptophan (TRP), on which synthesis of serotonin (or 5-hydroxytryptamine; 5-HT) depends. However, 95 % of serotonin is synthesised and used in the periphery, and TRP is also metabolised via non-5-HT routes such as the kynurenine pathway. Moreover, understanding of genotypes involved in regulation of serotonin raises questions over the generalisability of TRP effects on behaviour across individuals with varied serotonergic genotypes. To date, only differences between variants of the 5-HT transporter-linked promoter region (5-HTTLPR) have been investigated in relation to behavioural effects of TRP supplementation. Effects of 5-HTTLPR genotypes are usually compared between the alleles that are either high (L/L′) or low (S/S′) expressing of mRNA for the 5-HT transporter receptor. Yet, another key genetic variable is sex: in women, the S/S′ genotype predicts sensitivity to improved mood and reduced cortisol by TRP supplementation, during stressful challenges, whereas the L/L′ genotype protects against stress-induced mood deterioration. In men, the L/L′ genotype may confer risk of stress-induced increases in negative affect; there are insufficient data to assess effects on male S/S′ genotypes. However, better-powered studies to detect sex by genotype by stress by TRP interactions, as well as consideration of more genotypes, are needed before strong conclusions and recommendations for behavioural effects of TRP treatment can be reached.

Effects of tryptophan depletion on selective serotonin reuptake inhibitor-remitted patients with obsessive compulsive disorder

BACKGROUND

Serotonergic antidepressants are first-line medication therapies for obsessive-compulsive disorder, however it is not known if synaptic serotonin availability is important for selective serotonin reuptake inhibitor efficacy. The present study tested the hypothesis that temporary reduction in central serotonin transmission, through acute tryptophan depletion, would result in an increase in anxiety in selective serotonin reuptake inhibitor-remitted obsessive-compulsive disorder patients.

METHODS

Eight patients (four males) with obsessive-compulsive disorder who showed sustained clinical improvement with selective serotonin reuptake inhibitor treatment underwent acute tryptophan depletion in a randomized, double-blind, placebo-controlled, within-subjects design, over two days one week apart. Five hours after consumption of the depleting/sham drink the participants performed a personalized obsessive-compulsive disorder symptom exposure task. Psychological responses were measured using the Spielberger State Anxiety Inventory, Yale-Brown Obsessive Compulsive Scale and Visual Analogue Scales.

RESULTS

Free plasma tryptophan to large neutral amino acid ratio decreased by 93% on the depletion day and decreased by 1% on the sham day, as anticipated. Psychological rating scores as measured by Visual Analogue Scale showed a significant decrease in perceived control and increase in interfering thoughts at the time of provocation on the depletion day but not on the sham day. A measure of convergent validity, namely Visual Analogue Scale Similar to past, was significantly higher at the time of provocation on both the depletion and sham days. Both the depletion and time of provocation scores for Visual Analogue Scale Anxiety, Spielberger State Anxiety Inventory, Yale-Brown Obsessive Compulsive Scale and blood pressure were not significant.

CONCLUSIONS

Acute tryptophan depletion caused a significant decrease in perceived control and increase in interfering thoughts at the time of provocation. Acute tryptophan depletion had no effect on the Spielberger State Anxiety Inventory or Visual Analogue Scale Anxiety measures, which suggests that the mechanism of action of selective serotonin reuptake inhibitors may be different to that seen in panic, social anxiety and post-traumatic stress disorder. Successful selective serotonin reuptake inhibitor treatment of obsessive-compulsive disorder may involve the ability of serotonin to switch habitual responding to goal-directed behaviour.

Prevalence and concentrations of drugs in older suspected drugged drivers

OBJECTIVE

Older drivers are somewhat more likely to be involved in car crashes than middle-aged drivers but less likely to be involved than younger drivers. This study aimed to assess the extent of drug use in older suspected drunk and drugged drivers, with respect to which drugs were detected and at which concentrations.

METHODS

Blood samples from older suspected drunk and drugged drivers taken between February 1, 2012, and May 22, 2013, were identified from the database at the Norwegian Institute of Public Health and were retrospectively analyzed for a broad repertoire of drugs relevant for impairment. The prevalence of different drugs among the suspected drunk and drugged drivers was studied. Regarding drug concentrations, the findings in older drivers (>65 years) were compared to a reference group of apprehended drivers aged 20-40 years.

RESULTS

Four hundred and ten older suspected drunk and drugged drivers were included. Any drug (including ethanol) was detected in 92% of blood samples, and ethanol was detected in 81%. Benzodiazepines were found in 15% of the older drivers and z-hypnotics (zopiclone or zolpidem) were detected in 13%. The most frequent single legal drugs found in blood samples taken from older impaired drivers were zopiclone (9.8%) and diazepam (9.3%). Regarding drug combinations, older drivers used a mean number of 1.4 drugs, and 20% of ethanol-positive cases showed at least one other drug. High drug concentrations of clonazepam and diazepam were more frequently seen in the younger group.

CONCLUSIONS

This study showed that drugs were detected in the vast majority of older drivers suspected for drunk or drugged driving. Ethanol was the most frequent drug detected, followed by zopiclone and diazepam. Older drivers combine drugs to a lesser degree than younger drivers, but their combination of ethanol and other drugs represents a considerable traffic risk. Lower concentrations of benzodiazepines are seen in older compared to younger drivers.

Effects of biperiden and acute tryptophan depletion and their combination on verbal word memory and EEG

BACKGROUND

Research on the neurobiological foundations of memory has shown that multiple neurotransmitters play an important role in memory processing. To study the interaction between neurotransmitters such as acetylcholine and serotonin, pharmacological models can be used. In this study, we tested the effects of the muscarinic M1 antagonist biperiden, acute tryptophan depletion (ATD), and the interaction between the two on episodic memory using the verbal learning task.

METHODS

The study was conducted according to a double-blind, placebo-controlled, four-way crossover design. Seventeen participants received biperiden (2.0 mg), ATD (SolugelP), a combination of both, or a placebo in counterbalanced order with a wash out of at least 7 days. A verbal learning task was performed while recording electroencephalography. The task consisted of an immediate and delayed recall as well as a recognition part.

RESULTS

Results revealed decreased scores on the delayed recall after biperiden and ATD separately but no significant interaction between the two. However, the event-related potential components P3b, N400, and P600 did show an interaction during encoding.

CONCLUSION

These results indicate that both BIP and ATD impair episodic memory. However, an interaction between the serotonergic and cholinergic system on memory performance is not supported.

Intake of tryptophan-enriched whey protein acutely enhances recall of positive loaded words in patients with multiple sclerosis

BACKGROUND & AIMS

Multiple sclerosis (MS) has physiological and/or immunological characteristics that diminish serotonin metabolism, a neurotransmitter associated with affective and cognitive functions. The aim was examine the acute and dose-dependent effects of a dietary tryptophan (TRP) enrichment on affective and cognitive functions in MS patients. We hypothesized that increased dietary availability of the amino acid TRP enhances serotonin concentrations and improves neuropsychological functions.

METHODS

In a double-blind, placebo-controlled, crossover study, MS patients with (n = 15) and without (n = 17) depressed mood ingested a whey protein mixture with 4 different amounts of TRP. Mood states, total plasma TRP and plasma TRP/ΣLNAA ratio were measured during each test session and cognitive tasks were conducted three hours after dietary intake.

RESULTS

A fast, transient and dose-dependent increase of total plasma TRP and TRP/ΣLNAA ratio was found. Ratings of negative mood decreased over time, independent of the TRP dose. Relative to whey-only, immediate word recall and delayed recognition improved after ingestion of the lowest added TRP dose and was mainly due to better recollection for positive loaded words. Executive functions were not affected by a difference in TRP availability.

CONCLUSIONS

A moderate addition of TRP to whey protein enhances memory processes without improving the mood state in MS. ccmo-registration number is NL32316.096.10.

Evaluation of acute tryptophan depletion and sham depletion with a gelatin-based collagen peptide protein mixture

Acute Tryptophan Depletion (ATD) is a dietary method used to modulate central 5-HT to study the effects of temporarily reduced 5-HT synthesis. The aim of this study is to evaluate a novel method of ATD using a gelatin-based collagen peptide (CP) mixture. We administered CP-Trp or CP+Trp mixtures to 29 healthy volunteers; 13 from a randomized, double-blinded crossover study and sixteen from a randomized, double-blinded study run in our laboratory. Plasma amino acids, mood, side effects, cortisol concentrations, mean arterial blood pressure and heart rate were measured at multiple time-points. Repeated measures analysis of variance and Wilcoxon or Mann-Whitney U non-parametric tests were used to analyze the effects of intervention. Intake of the CP-Trp mixture efficiently reduced plasma Trp; however, the CP+Trp mixture induced a large significant increase in plasma Trp. No other significant effects of CP-Trp compared to CP+Trp were observed. The transient increase in plasma Trp after CP+Trp may impair comparison to the CP-Trp and we therefore recommend in future studies to use a smaller dose of Trp supplement to the CP mixture.

Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women

Common pharmacological treatments of mood disorders aim to modulate serotonergic neurotransmission and enhance serotonin levels in the brain. Brain serotonin levels are dependent on the availability of its food-derived precursor essential amino acid tryptophan (Trp). We tested the hypothesis that delivery of Trp via food may serve as an alternative treatment, and examined the effects of a Trp-rich, bioavailable dietary supplement from egg protein hydrolysate on cognitive and emotional functions, mood state, and sleep quality. In a randomised, placebo-controlled, parallel trial, fifty-nine mentally and physically healthy women aged 45-65 years received placebo (n 30) or the supplement (n 29) (both as 0.5 g twice per d) for 19 d. Emotional processing was significantly changed by supplementation, exhibiting a shift in bias away from negative stimuli. The results for the Affective Go/No-Go Task exhibited a slowing of responses to negative words, suggesting reduced attention to negative emotional stimuli. The results for the Facial Emotional Expression Rating Task also supported a shift away from attention to negative emotions and a bias towards happiness. An increase in arousal-like symptoms, labelled 'high energy', shorter reaction times and a slight benefit to sustained attention were observed in the treated subjects. Finally, when the supplement was taken 60-90 min before bedtime, a feeling of happiness before going to bed was consistently reported. In summary, daily consumption of a low-dose supplement containing bioavailable Trp may have beneficial effects on emotional and cognitive functions.

Association analysis of genes in serotonin pathway with attention and executive function in patients with bipolar affective disorder

BACKGROUND

The reason why it is difficult to identify susceptibility genes attributed to bipolar disorder (BPD) is the phenotypic heterogeneity. The use of endophenotypes has been advocated as one possible strategy to discovery cause variants of BPD.

METHODS

A total of 164 patients with BPD and 164 matched controls were employed in the present research. Fifty-two single nucleotide polymorphisms (SNPs) within the genes in serotonin pathway were selected for genotyping using the GoldenGate genotyping assay. All participants completed three neurocognitive tests including the tower of Hanoi (TOH), the Wisconsin card sorting test (WCST) and Trail making tests (TMTA and TMTB-M).

RESULTS

Patients with BPD demonstrated a wide range of deficits in mental activities of attention and speed of information processing, and executive function. Significant interactions between rs2760347 in 5HTR2A gene and diagnosis were found for the executive time of TOH, with β=11.82 and P=0.002 (adjusted P=0.03 after Bonferroni correction).

CONCLUSIONS

Cognitive impairments existing in BPD may be particularly notable in certain domains of attention and executive function, and 5HTR2A gene may be involved in modulating executive function of BP-I patients.

Ghrelin: a link between ageing, metabolism and neurodegenerative disorders

Along with the increase in life expectancy over the last century comes the increased risk for development of age-related disorders, including metabolic and neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's diseases. These chronic disorders share two main characteristics: 1) neuronal loss in motor, sensory or cognitive systems, leading to cognitive and motor decline; and 2) a strong correlation between metabolic changes and neurodegeneration. In order to treat them, a better understanding of their complexity is required: it is necessary to interpret the neuronal damage in light of the metabolic changes, and to find the disrupted link between the peripheral organs governing energy metabolism and the CNS. This review is an attempt to present ghrelin as part of molecular regulatory interface between energy metabolism, neuroendocrine and neurodegenerative processes. Ghrelin takes part in lipid and glucose metabolism, in higher brain functions such as sleep-wake state, learning and memory consolidation; it influences mitochondrial respiration and shows neuroprotective effect. All these make ghrelin an attractive target for development of biomarkers or therapeutics for prevention or treatment of disorders, in which cell protection and recruitment of new neurons or synapses are needed.

Cognitive impairment associated with carcinoid syndrome

OBJECTIVES

To evaluate the cognitive performance of patients with carcinoid syndrome (CS) compared with population norms and cancer patients with non-neuroendocrine (non-NET) liver metastases.

BACKGROUND

The release of serotonin into the systemic circulation from metastatic small bowel neuroendocrine tumors (SB NET) causes CS. Many patients with CS followed in a multidisciplinary NET clinic seemed to exhibit a unique cognitive impairment. Because serotonin is known to influence a range of cognitive function, the question arouse as to whether cognitive impairment is another manifestation of CS.

METHODS

Patients were recruited from the multidisciplinary NET and the hepatobilary cancer clinics at the cancer center. The CS group consisted of patients with proven SB NETs metastatic to liver; the cancer comparison group consisted of patients with liver metastases from non-NET cancer. All completed a self-reported cognitive questionnaire and a battery of 6 standardized neurocognitive tests. Both groups were compared to age/sex/educational-matched norms.

RESULTS

Thirty-six patients with CS and 20 with non-NET metastases were enrolled. Patients with CS reported greater cognitive dysfunction in all cognitive domains than both norms and the comparison cancer group. On cognitive testing, patients with CS demonstrated weakness in initiation, processing speed, visual memory, cognitive efficiency, and delayed verbal recall compared with norms. Although the patients with non-NET cancer also demonstrated some cognitive dysfunction compared with norms, the patients with CS did significantly worse on delayed recall (P = 0.03) and marginally slower on speeded mental flexibility (P = 0.097) compared with patients with non-NET cancer.

CONCLUSION

This study confirmed our clinical observation that patients with CS suffer from cognitive impairment that is different from the non-NET cancer group and population norms.

Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects

The acute tryptophan depletion (ATD) technique has been used extensively to study the effect of low serotonin in the human brain. This review assesses the validity of a number of published criticisms of the technique and a number of previously unpublished potential criticisms. The conclusion is that ATD can provide useful information when results are assessed in conjunction with results obtained using other techniques. The best-established conclusion is that low serotonin function after tryptophan depletion lowers mood in some people. However, this does not mean that other variables, altered after tryptophan depletion, are necessarily related to low serotonin. Each aspect of brain function has to be assessed separately. Furthermore, a negative tryptophan depletion study does not mean that low serotonin cannot influence the variable studied. This review suggests gaps in knowledge that need to be filled and guidelines for carrying out ATD studies.

Novel nutritional treatment for manic and psychotic disorders: a review of tryptophan and tyrosine depletion studies and the potential of protein-based formulations using glycomacropeptide

RATIONALE

Current amino acid (AA) mixtures used in acute tryptophan (Trp) and tyrosine (Tyr) plus phenylalanine (Phe) depletion and loading tests are unpalatable and lack specificity. Specificity is improved by reducing content of branched-chain amino acids (BCAA) and palatability to a certain extent by dose reduction.

OBJECTIVES

This study aims to identify a palatable naturally occurring alternative(s) to amino acids with the desired BCAA content for use in the above tests.

METHODS

A palatable alternative lacking in Trp, Tyr and Phe has been identified in the whey protein fraction caseino-glycomacropeptide (c-GMP). The absence of these three aromatic amino acids renders GMP suitable as a template for seven formulations for separate and combined depletion or loading and a placebo control. The absence of Phe and Tyr enables GMP to provide a unique nutritional therapy of manic and psychotic disorders by inhibition of cerebral dopamine synthesis and release and possibly also by enhancing glutamatergic function, in general, and in patients resistant to anti-psychotic medication, in particular.

RESULTS

Seven GMP-based formulations for the above tests are proposed, two of which can be used in the above nutritional therapy and a third formulation as a placebo control in clinical trials.

CONCLUSIONS

Development of these formulations should advance the above research and diagnostic tests, open new avenues for neuroscience research on monoamine function, and improve the therapy of bipolar and psychotic disorders and enhance the quality of life of sufferers.

No effect of acute tryptophan depletion on verbal declarative memory in young persons with ADHD

OBJECTIVE

Animal experiments and studies in adults have shown that the neurotransmitter serotonin (5-HT) plays an important role in learning and memory processes. However, data on this relationship in young persons are scarce, and neurodietary research in this age group is limited compared with the extensive literature on adults. Here, we aimed to explore the effects of a diminished central nervous 5-HT synthesis, which is achieved by acute tryptophan depletion (ATD) Moja-De , on memory function in young males with attention deficit hyperactivity disorder (ADHD).

METHOD

Twenty-two male patients with ADHD (ages 9-15 years, mean 10.95 ± 1.17 years) received ATD, thus diminishing central nervous 5-HT synthesis, and a tryptophan-balanced amino acid load (BAL) in a randomized, double-blind, within-subject, crossover design study. Approximately 1.7 h after administration of ATD/BAL, verbal declarative memory was assessed using the 'Auditory Verbal-Learning-Test' (AVLT).

RESULTS

There were no significant effects of ATD administration on verbal declarative memory function.

CONCLUSION

In this study, changes in 5-HT neurotransmission were not associated with specific aspects of verbal declarative memory in young persons with ADHD. Future studies with healthy control groups that address effects of covarying attentional processes are warranted.

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

OBJECTIVE

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).

METHOD

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.

RESULTS

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.

CONCLUSION

The present preliminary results are indicative of the contribution of serotonergic neurotransmission to attentional processes in adults with ADHD.

Association between TPH2 gene polymorphisms and attention deficit hyperactivity disorder in Korean children

Attention deficit hyperactivity disorder (ADHD) is a common disorder of the school-age population. ADHD is a familial disorder and genetic studies estimate heritability at 80%-90%. The aim of the present study was to investigate the association between the genetic type and alleles for the TPH2 gene in Korean children with ADHD. The sample consisted of 142 ADHD children and 139 control children. We diagnosed ADHD according to the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition). ADHD symptoms were evaluated with Conners' Parent Rating Scales and Dupaul Parent ADHD Rating Scales. Blood samples were taken from the 281 subjects, DNA was extracted from blood lymphocytes, and polymerase chain reaction was performed for TPH2 polymorphism. Alleles and genotype frequencies were compared using the chi-square test. We compared the allele and genotype frequencies of TPH2 gene polymorphism in the ADHD and control groups. This study showed that there was a significant correlation among the frequencies of the rs11179027 (odd ratio [OR]=2.12, 95% confidence interval [CI]=1.13-3.97, p=0.020) and rs1843809 (OR=0.48, 95% CI=0.24-0.97, p=0.040) of alleles of TPH2, but the final conclusions are not definite. Follow-up studies with larger patient or pure subgroups are expected. These results suggested that TPH2 might be related to ADHD symptoms.

Large neutral amino acids: dietary effects on brain neurochemistry and function

The ingestion of large neutral amino acids (LNAA), notably tryptophan, tyrosine and the branched-chain amino acids (BCAA), modifies tryptophan and tyrosine uptake into brain and their conversion to serotonin and catecholamines, respectively. The particular effect reflects the competitive nature of the transporter for LNAA at the blood-brain barrier. For example, raising blood tryptophan or tyrosine levels raises their uptake into brain, while raising blood BCAA levels lowers tryptophan and tyrosine uptake; serotonin and catecholamine synthesis in brain parallel the tryptophan and tyrosine changes. By changing blood LNAA levels, the ingestion of particular proteins causes surprisingly large variations in brain tryptophan uptake and serotonin synthesis, with minimal effects on tyrosine uptake and catecholamine synthesis. Such variations elicit predictable effects on mood, cognition and hormone secretion (prolactin, cortisol). The ingestion of mixtures of LNAA, particularly BCAA, lowers brain tryptophan uptake and serotonin synthesis. Though argued to improve physical performance by reducing serotonin function, such effects are generally considered modest at best. However, BCAA ingestion also lowers tyrosine uptake, and dopamine synthesis in brain. Increasing dopamine function in brain improves performance, suggesting that BCAA may fail to increase performance because dopamine is reduced. Conceivably, BCAA administered with tyrosine could prevent the decline in dopamine, while still eliciting a drop in serotonin. Such an LNAA mixture might thus prove an effective enhancer of physical performance. The thoughtful development and application of dietary proteins and LNAA mixtures may thus produce treatments with predictable and useful functional effects.

Does coffee enriched with chlorogenic acids improve mood and cognition after acute administration in healthy elderly? A pilot study

RATIONALE

Caffeine exerts positive effects on cognitive and behavioral processes, especially in sub-optimal conditions when arousal is low. Apart from caffeine, coffee contains other compounds including the phenolic compounds ferulic acid, caffeic acid, and the chlorogenic acids, which have purported antioxidant properties. The chlorogenic acids are the most abundant family of compounds found in coffee, yet their effects on cognition and mood have not been investigated.

OBJECTIVES

This study aims to ascertain whether a coffee rich in chlorogenic acid modulates brain function.

METHODS

The present pilot study examined the acute effects of decaffeinated coffee with regular chlorogenic acid content and decaffeinated coffee with high chlorogenic acid content on mood and cognitive processes, as measured by behavioral tasks and event-related potentials (ERPs). Performance and ERP responses to a battery of cognitive tasks were recorded at baseline and following the equivalent of three cups of coffee in a randomized, double-blind, crossover study of 39 healthy older participants.

RESULTS

Compared with the decaffeinated coffee with regular chlorogenic acid and placebo, caffeinated coffee showed a robust positive effect on higher-level mood and attention processes. To a lesser extent, the decaffeinated coffee high in chlorogenic acid also improved some mood and behavioral measures, relative to regular decaffeinated coffee.

CONCLUSIONS

Our pilot results suggest that non-caffeine compounds in coffee such as the chlorogenic acids may be capable of exerting some acute behavioral effects, thus warranting further investigation.

Reversal learning as a measure of impulsive and compulsive behavior in addictions

BACKGROUND

Our ability to measure the cognitive components of complex decision-making across species has greatly facilitated our understanding of its neurobiological mechanisms. One task in particular, reversal learning, has proven valuable in assessing the inhibitory processes that are central to executive control. Reversal learning measures the ability to actively suppress reward-related responding and to disengage from ongoing behavior, phenomena that are biologically and descriptively related to impulsivity and compulsivity. Consequently, reversal learning could index vulnerability for disorders characterized by impulsivity such as proclivity for initial substance abuse as well as the compulsive aspects of dependence.

OBJECTIVE

Though we describe common variants and similar tasks, we pay particular attention to discrimination reversal learning, its supporting neural circuitry, neuropharmacology and genetic determinants. We also review the utility of this task in measuring impulsivity and compulsivity in addictions.

METHODS

We restrict our review to instrumental, reward-related reversal learning studies as they are most germane to addiction.

CONCLUSION

The research reviewed here suggests that discrimination reversal learning may be used as a diagnostic tool for investigating the neural mechanisms that mediate impulsive and compulsive aspects of pathological reward-seeking and -taking behaviors. Two interrelated mechanisms are posited for the neuroadaptations in addiction that often translate to poor reversal learning: frontocorticostriatal circuitry dysregulation and poor dopamine (D2 receptor) modulation of this circuitry. These data suggest new approaches to targeting inhibitory control mechanisms in addictions.

Mechanism of acute tryptophan depletion: is it only serotonin?

The method of acute tryptophan depletion (ATD), which reduces the availability of the essential amino acid tryptophan (TRP), the dietary serotonin (5-hydroxytryptamine (5-HT)) precursor, has been applied in many experimental studies. ATD application leads to decreased availability of TRP in the brain and its synthesis into 5-HT. It is therefore assumed that a decrease in 5-HT release and subsequent blunted neurotransmission is the underlying mechanism for the behavioural effects of ATD. However, direct evidence that ATD decreases extracellular 5-HT concentrations is lacking. Furthermore, several studies provide support for alternative underlying mechanisms of ATD. This may question the utility of the method as a selective serotonergic challenge tool. As ATD is extensively used for investigating the role of 5-HT in cognitive functions and psychiatric disorders, the potential of alternative mechanisms and possible confounding factors should be taken into account. It is suggested that caution is required when interpreting ATD effects in terms of a selective serotonergic effect.

Escitalopram and enhancement of cognitive recovery following stroke

CONTEXT

Adjunctive restorative therapies administered during the first few months after stroke, the period with the greatest degree of spontaneous recovery, reduce the number of stroke patients with significant disability.

OBJECTIVE

To examine the effect of escitalopram on cognitive outcome. We hypothesized that patients who received escitalopram would show improved performance in neuropsychological tests assessing memory and executive functions than patients who received placebo or underwent Problem Solving Therapy.

DESIGN

Randomized trial.

SETTING

Stroke center.

PARTICIPANTS

One hundred twenty-nine patients were treated within 3 months following stroke. The 12-month trial included 3 arms: a double-blind placebo-controlled comparison of escitalopram (n = 43) with placebo (n = 45), and a nonblinded arm of Problem Solving Therapy (n = 41).

OUTCOME MEASURES

Change in scores from baseline to the end of treatment for the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and Trail-Making, Controlled Oral Word Association, Wechsler Adult Intelligence Scale-III Similarities, and Stroop tests.

RESULTS

We found a difference among the 3 treatment groups in change in RBANS total score (P < .01) and RBANS delayed memory score (P < .01). After adjusting for possible confounders, there was a significant effect of escitalopram treatment on the change in RBANS total score (P < .01, adjusted mean change in score: escitalopram group, 10.0; nonescitalopram group, 3.1) and the change in RBANS delayed memory score (P < .01, adjusted mean change in score: escitalopram group, 11.3; nonescitalopram group, 2.5). We did not observe treatment effects in other neuropsychological measures.

CONCLUSIONS

When compared with patients who received placebo or underwent Problem Solving Therapy, stroke patients who received escitalopram showed improvement in global cognitive functioning, specifically in verbal and visual memory functions. This beneficial effect of escitalopram was independent of its effect on depression. The utility of antidepressants in the process of poststroke recovery should be further investigated. Trial Registration clinicaltrials.gov Identifier: NCT00071643.

Differential effects of 5-HTTLPR genotypes on mood, memory, and attention bias following acute tryptophan depletion and stress exposure

RATIONALE

Polymorphisms of the serotonin transporter gene (5-HTTLPR) may be associated with increased vulnerability to acute tryptophan depletion (ATD) and depression vulnerability especially following stressful life events.

OBJECTIVE

The aim of the present study was to investigate the effects of ATD in subjects with different 5-HTTLPR profiles before and after stress exposure on affective and cognitive-attentional changes.

MATERIALS AND METHODS

Eighteen subjects with homozygotic short alleles (S'/S') and 17 subjects with homozygotic long alleles (L'/L') of the 5-HTTLPR participated in a double-blind, placebo-controlled, crossover design to measure the effects of ATD on mood, memory, and attention before and after acute stress exposure.

RESULTS

ATD lowered mood in all subjects independent of genotype. In S'/S' genotypes, mild acute stress increased depressive mood and in L'/L' genotypes increased feelings of vigor. Furthermore, S'/S' genotypes differed from L'/L' genotypes on measures of attention independent of treatment and memory following ATD.

CONCLUSIONS

Polymorphisms of the 5-HTTLPR differentially affect responses to mild stress and ATD, suggesting greater vulnerability of S'/S' carriers to serotonergic manipulations and supporting increased depression vulnerability.

Memory impairments in humans after acute tryptophan depletion using a novel gelatin-based protein drink

Acute tryptophan depletion (ATD) can be used to decrease serotonin levels in the brain. Traditionally, ATD has been established by administering amino acid (AA) mixtures and studies using this method showed that serotonin is involved in learning and memory processes. This study used a recently developed gelatin-based protein drink to examine whether it 1) is superior to the traditional AA method in controlling the tryptophan levels in the placebo condition, 2) impairs long-term memory and 3) differentially affects episodic and spatial memory. Sixteen healthy subjects participated in a double-blind, placebo-controlled study. Memory was assessed using a visual verbal learning test and an object relocation task (spatial memory). Tryptophan ratio significantly decreased after ATD and did not significantly increase in the placebo condition. Delayed recall in the verbal learning test and delayed relocation of objects to positions in the spatial task were impaired after ATD. Spatial short-term memory, however, improved. The current results indicate that the tryptophan levels were essentially neutral in the placebo condition compared with those in the traditional AA mixture. Our study provides further evidence that impairment in long-term episodic and elementary spatial memory after ATD is related to lowered tryptophan levels in plasma.

Acute effects of breakfasts containing alpha-lactalbumin, or gelatin with or without added tryptophan, on hunger, 'satiety' hormones and amino acid profiles

Proteins are the most satiating macronutrients. Tryptophan (TRP) may contribute to the satiating effect, as it serves as a precursor for the anorexigenic neurotransmitter serotonin. To address the role of TRP in the satiating properties of dietary protein, we compared three different breakfasts, containing either alpha-lactalbumin (high in TRP), gelatin (low in TRP) or gelatin with added TRP (gelatin+TRP, high in TRP), on appetite. Twenty-four subjects (22-29 kg/m2; aged 19-37 years) received a subject-specific breakfast at t = 0 with 10, 55 and 35 % energy from protein, carbohydrate and fat respectively in a randomised, single-blind design. Hunger, glucagon-like peptide (GLP)-1, ghrelin, amino acid concentrations and energy intake during a subsequent lunch were determined. Suppression of hunger was stronger 240 min after the breakfast with alpha-lactalbumin compared with gelatin and gelatin+TRP. Total plasma amino acid concentrations were lower with alpha-lactalbumin compared with gelatin with or without TRP (from t = 180-240 min). TRP concentrations were higher after alpha-lactalbumin than after gelatin with or without TRP from t = 0-100 min, whereas from t = 100-240 min, TRP concentrations were lower after gelatin than after alpha-lactalbumin and gelatin+TRP. The plasma ratio of TRP to other large neutral amino acids (LNAA) was, only at t = 100 min, lower after gelatin+TRP than after the other breakfasts. Plasma amino acid responses, TRP concentrations and TRP:LNAA ratios were not correlated with hunger. GLP-1 and ghrelin concentrations were similar for all diets. Energy intake during a subsequent lunch was similar for all diets. Summarised, an alpha-lactalbumin breakfast suppresses hunger more than a gelatin or gelatin+TRP breakfast. This cannot be explained by (possible) differences found in TRP concentrations and TRP:LNAA ratios in the breakfasts and in plasma, as well as in circulating total amino acids, GLP-1 and ghrelin.

Phosphodiesterase 2 and 5 inhibition attenuates the object memory deficit induced by acute tryptophan depletion

The underlying mechanism of short-term memory improvement after inhibition of specific phosphodiesterases (PDEs) is still poorly understood. The present study aimed to reveal the ability of PDE5 and PDE2 inhibitors, that increase cyclic guanosine monophosphate (cGMP) and both cyclic adenosine monophosphate (cAMP) and cGMP, respectively, to reverse an object recognition deficit induced by acute tryptophan depletion. Acute tryptophan depletion is a pharmacological challenge tool to lower central serotonin (5-hydroxytryptamine; 5-HT) levels by depleting the availability of its dietary precursor tryptophan. Short-term object memory was tested in male Wistar rats by exposing them to the object recognition task. First, the effects of acute tryptophan depletion upon object recognition 2 h after administration of the nutritional mixture were established. Subsequently, acute tryptophan depletion was combined with the PDE5 inhibitor vardenafil (1, 3 and 10 mg/kg) or with the PDE2 inhibitor BAY 60-7550 (0.3, 1 and 3 mg/kg), 30 min prior to testing. Acute tryptophan depletion significantly lowered plasma tryptophan levels and impaired object recognition performance. Vardenafil (3 and 10 mg/kg) and BAY 60-7550 (3 mg/kg) were able to attenuate the acute tryptophan depletion induced object recognition impairment. Thus, both PDE5 and PDE2 inhibition improved short-term object recognition performance after an acute tryptophan depletion induced deficit. The underlying mechanisms, however, remain poorly understood and further studies are needed to determine whether the present findings can be explained by a direct effect of enhanced cAMP and cGMP levels upon 5-HT activity, or even other neurotransmitter systems, and possibly an interaction with synthesis of nitric oxide or effects upon cerebral blood flow function.

The effects of experimentally lowered serotonin function on emotional information processing and memory in remitted depressed patients

It has been well documented that acute tryptophan depletion (ATD) induces symptoms in remitted depressed patients treated with an SSRI. ATD also has effects on cognition, both in patients and in healthy samples. The exact nature of ATD-induced cognitive changes in depression remains unclear. It is also unclear whether cognitive effects can be induced through partial ('low-dose') depletion. The aim of this study is to investigate the differential effects of low-dose and high-dose ATD on emotional information processing and mood in remitted depressed patients. Eighteen remitted depressed patients received high-dose and low-dose ATD in a randomized, double-blind, within-subjects crossover design. Mood was assessed before and after administration of the depletion drink. Five hours after administration, patients conducted tests measuring neutral and emotional information processing. High-dose ATD increased depressive symptoms and induced a temporary depressive 'relapse' in half of the patients. High-dose ATD also decreased the recognition of fear and impaired learning and memory retrieval. The impaired learning occurred only in mood-responders. Low-dose ATD had no effects on mood but speeded the recognition of facial expressions of disgust. Accurate recognition of sad faces at baseline was associated with mood response to ATD. High-dose ATD leads to changes in memory and in the recognition of negative facial expressions in SSRI-treated remitted depressed patients. The effect of low-dose ATD on mood and cognition seems to be quite limited. Emotional information processing at baseline predicts mood-response to ATD.

Cognitive effects of acute tryptophan depletion in the healthy elderly

BACKGROUND

Studies investigating the cognitive effects of serotonin depletion, using the technique of acute tryptophan depletion (ATD) by dietary means, have generally suggested that ATD impairs delayed verbal recall and recognition. In two previous studies in the elderly, this result has not been replicated and ATD impaired working memory. These results may be susceptible to type II error but a similar testing schedule in the individual studies allows data to be pooled in a larger analysis.

METHODS

Data from two separate double-blind placebo-controlled studies of the effects of ATD on cognitive function in the elderly were combined. In one study, a low dose and in the other a high dose of amino acids was used. In a repeated measures analysis of variance, the effects of ATD and the interaction of this with the other factors (age, gender and dose) on cognitive measures was examined.

RESULTS

Data from 31 healthy subjects aged between 60 and 81 years were analysed. There were no main effects of ATD or consistent interactions between ATD and age, gender or dose. There were significant interactions between ATD, gender and dose. When tryptophan depleted, females having the higher dose drink had reduced scores on Digit span and immediate recall on the Rey Auditory Verbal Learning Test.

CONCLUSION

The enlarged data set did not confirm an overall effect of ATD on working memory or on delayed word recall but does suggest an effect of ATD on encoding or registration in the subgroup of females receiving a higher strength drink.

A functional variant of the tryptophan hydroxylase 2 gene impacts working memory: a genetic imaging study

Imaging studies have demonstrated that prefrontal and parietal regions are activated during working memory (WM) tasks. Recently some molecular genetic studies reported associations between a functional promoter polymorphism of the tryptophan hydroxylase 2 gene (TPH2), that regulates the synthesis of serotonin, and attention. In 49 healthy Caucasian subjects the role of the TPH2 -703 G/T polymorphism for WM was tested by means of an imaging genomics approach in an n-back task. fMRI data showed an increased activation for the 2-back as compared to the 0-back condition for a large network in prefrontal and parietal areas. Although behavioural data showed no performance differences between the genotype groups of the -703 G/T a significantly stronger activation of the TT genotype carriers in BA 6, BA 46, and BA 40 was visible in contrast to the GT and GG groups. Present findings in congruence with previous findings support the hypothesis that TT carriers compensate deficits in executive control functions by increased brain activity.

Effects of acute tryptophan depletion on affective processing in first-degree relatives of depressive patients and controls after exposure to uncontrollable stress

RATIONALE

Individuals with a family history of depression may be more likely to develop depression due to an innate vulnerability of their serotonergic system. However, even though serotonergic vulnerability may constitute a risk factor in the development of depression, it does not seem to be sufficient to cause a depressive episode. Based on previous data, it is suggested that stress may be a mediating factor.

OBJECTIVES

This study examined the role of serotonin (5-HT) in stress coping in individuals with or without a family history of depression.

MATERIALS AND METHODS

Nineteen healthy first-degree relatives of depressive patients (FH+) and 19 healthy controls without a family history of depression (FH-) were tested in a double-blind placebo-controlled design for affective processing under acute stress exposure, following acute tryptophan depletion (ATD) or placebo.

RESULTS

Significant negative effects were found of stress on affective processing in FH- and FH+. In addition, FH- responded slower to positive words after stress only following ATD, whereas FH+ responded marginally slower under stress already after placebo and before stress following ATD.

CONCLUSION

Acute stress exposure reduces positive affective bias; supporting the role of stress as an important predecessor in the development of depression. Furthermore, FH+ may be more susceptible than FH- to the negative effects of stress as well as to the negative effects of ATD. The results support the assumption that the 5-HT system is involved in stress resilience and may be more vulnerable in first-degree relatives of depression.

The effects of serotonin manipulations on emotional information processing and mood

BACKGROUND

Serotonin is implicated in both mood and cognition. It has recently been shown that antidepressant treatment has immediate effects on emotional information processing, which is much faster than any clinically significant effects. This review aims to investigate whether the effects on emotional information processing are reliable, and whether these effects are related to eventual clinical outcome. Treatment-efficiency may be greatly improved if early changes in emotional information processing are found to predict clinical outcome following antidepressant treatment.

METHODS

Review of studies investigating the short-term effects of serotonin manipulations (including medication) on the processing of emotional information, using PubMed and PsycInfo databases.

RESULTS

Twenty-five studies were identified. Serotonin manipulations were found to affect attentional bias, facial emotion recognition, emotional memory, dysfunctional attitudes and decision making. The sequential link between changes in emotional processing and mood remains to be further investigated.

LIMITATIONS

The number of studies on serotonin manipulations and emotional information processing in currently depressed subjects is small. No studies yet have directly tested the link between emotional information processing and clinical outcome during the course of antidepressant treatment.

CONCLUSIONS

Serotonin function is related to several aspects of emotional information processing, but it is unknown whether these changes predict or have any relationship with clinical outcome. Suggestions for future research are provided.

Selective verbal and spatial memory impairment after 5-HT1A and 5-HT2A receptor blockade in healthy volunteers pre-treated with an SSRI

Serotonergic neurotransmission has been implicated in memory impairment. It is unclear however if memory performance is mediated through general 5-HT availability, through specific 5-HT receptors or both. The aim of the present study was to assess the contribution of 5-HT reuptake inhibition and specific blockade of 5-HT(1A) and 5-HT(2A) receptors to memory impairment. The study was conducted according to a randomized, double-blind, placebo-controlled, four-way cross-over design including 16 healthy volunteers. The treatment consisted of oral administration of escitalopram 20 mg + placebo, escitalopram 20 mg + ketanserin 50 mg, escitalopram 20 mg + pindolol 10 mg and placebo on 4 separate days with a washout period of minimum 7 days. Different memory tasks were performed including verbal memory, spatial working memory and reversal learning. Escitalopram showed an impairing effect on immediate verbal recall which nearly reached statistical significance. No effects of escitalopram were found on other types of memory. In combination with pindolol, immediate verbal recall was significantly impaired. Escitalopram in combination with ketanserin impaired spatial working memory significantly. No effects were found on reversal learning. Selective impairment of immediate verbal recall after a 5-HT(1A) partial agonist and selective impairment of spatial working memory performance after 5-HT(2A) receptor antagonist, both in combination with a selective serotonergic reuptake inhibitor (escitalopram), suggests that 5-HT(1A) and 5-HT(2A) receptors are distinctly involved in verbal and spatial memory.

Impaired executive control is associated with a variation in the promoter region of the tryptophan hydroxylase 2 gene

Current models of attention describe attention not as a homogenous entity but as a set of neural networks whose measurement yields a set of three endophenotypes-alerting, orienting, and executive control. Previous findings revealed different neuroanatomical regions for these subsystems, and data from twin studies indicate differences in their heritability. The present study investigated the molecular genetic basis of attention in a sample of 100 healthy subjects. Attention performance was assessed with the attention network test that distinguishes alerting, orienting, and executive control (conflict) using a simple reaction time paradigm with different cues and congruent and incongruent flankers. Two gene loci on candidate genes for cognitive functioning, the functional catechol-O-methyltransferase (COMT) VAL158MET and the tryptophan hydroxylase 2 (TPH2) -703 G/T promoter polymorphism, were tested for possible associations with attention. COMT is involved in the catabolism of dopamine, and TPH is the rate-limiting enzyme for serotonin synthesis. Results showed no effect of the COMT polymorphism on attention performance. However, the TT genotype of TPH2 -03 G/T was significantly associated with more errors (a possible indicator of impaired impulse control; p = .001) and with decreased performance in executive control (p = .001). This single-nucleotide polymorphism on the TPH2 gene explained more than 10% of the variance in both indicators of attention stressing the role of the serotonergic system for cognitive functions.

Chronic reduction in dietary tryptophan leads to a selective impairment of contextual fear memory in mice

The depletion of systemic tryptophan is an important tool to study the effects of reduced 5-HT on cognition. Indeed, previous reports indicated that acute depletion of TRP leads to a memory impairment in human subjects and rodents. From the view of nutrition, it is important to investigate the effects of chronic limitation of L-tryptophan (TRP) on learning and memory formation. In this study, we examined the effects of chronic consumption of a low TRP diet on memory formation in mice. Specifically, we assessed the ability to form contextual fear, cued fear, conditioned taste aversion, and spatial memories in mice fed a TRP-limited diet for at least 1 month. TRP-limited mice showed impaired formation of contextual fear memory that is hippocampus-dependent. In contrast, these mice showed normal hippocampus-dependent spatial memory in the Morris water maze test, as well as in cued fear and conditioned taste aversion memories, which are amygdala-dependent memory processes. Thus, dietary TRP restriction appears to result in selective impairments in hippocampus-dependent contextual fear memory formation in mice.

Do serotonin1–7 receptors modulate short and long-term memory?

Evidence from invertebrates to human studies indicates that serotonin (5-hydroxytryptamine; 5-HT) system modulates short- (STM) and long-term memory (LTM). This work is primarily focused on analyzing the contribution of 5-HT, cholinergic and glutamatergic receptors as well as protein synthesis to STM and LTM of an autoshaping learning task. It was observed that the inhibition of hippocampal protein synthesis or new mRNA did not produce a significant effect on autoshaping STM performance but it did impair LTM. Both non-contingent protein inhibition and 5-HT depletion showed no effects. It was basically the non-selective 5-HT receptor antagonist cyproheptadine, which facilitated STM. However, the blockade of glutamatergic and cholinergic transmission impaired STM. In contrast, the selective 5-HT(1B) receptor antagonist SB-224289 facilitated both STM and LTM. Selective receptor antagonists for the 5-HT(1A) (WAY100635), 5-HT(1D) (GR127935), 5-HT(2A) (MDL100907), 5-HT(2C/2B) (SB-200646), 5-HT(3) (ondansetron) or 5-HT(4) (GR125487), 5-HT(6) (Ro 04-6790, SB-399885 and SB-35713) or 5-HT(7) (SB-269970) did not impact STM. Nevertheless, WAY100635, MDL100907, SB-200646, GR125487, Ro 04-6790, SB-399885 or SB-357134 facilitated LTM. Notably, some of these changes shown to be independent of food-intake. Concomitantly, these data indicate that '5-HT tone via 5-HT(1B) receptors' might function in a serial manner from STM to LTM, whereas working in parallel using 5-HT(1A), 5-HT(2A), 5-HT(2B/2C), 5-HT(4), or 5-HT(6) receptors.

Effects of acute tryptophan depletion on mood and facial emotion perception related brain activation and performance in healthy women with and without a family history of depression

The present study examined the effects of acute tryptophan (Trp) depletion (ATD), a well-recognized method to lower central serotonin (5-HT) metabolism, on brain activation during a facial emotion perception task. Brain activation was measured using fMRI, and healthy female volunteers with a positive family history of unipolar depression (FH+) were compared to healthy female volunteers without such a history (FH-). Participants viewed two morphed faces and were instructed to choose between the faces based either on the intensity of the emotional expression (direct task) or the gender of the face (incidental task). In the FH+ group, depletion led to the expected lowering of mood, which partly determined the effect of depletion on performance and brain activation. A stronger mood lowering effect was associated with less accurate performance on faces expressing a negative emotion in the incidental task and a stronger right amygdala response to fearful faces in comparison to happy faces. These results were explained in terms of a mood-induced bias leading to a stronger impact of the expressed negative emotion which subsequently leads to more interference in the incidental task and a stronger amygdala response. It was concluded that the effects of ATD on mood, performance, and brain activation in a facial emotion perception task depend on family history of depression. Performance and brain activation partly depend on the effect of ATD on mood.

MDMA use and neurocognition: a meta-analytic review

RATIONALE

To determine the association between MDMA misuse and neurocognition using meta-analysis.

OBJECTIVE

Separate analyses were conducted based on two sets of inclusion/exclusion criteria. A relatively stringent set required that the subjects be matched on important moderator variables, whereas the other did not. The study participants' performance in the following neurocognitive domains was reviewed: attention/concentration, verbal and nonverbal learning and memory, psychomotor speed and executive systems functioning.

RESULTS

In the 11 studies meeting the relatively stringent inclusion/exclusion criteria for this review, MDMA use was associated with neurocognitive deficits in each domain. Similarly, in the 23 studies meeting the relatively lenient inclusion/exclusion criteria for this review, MDMA use was associated with neurocognitive deficits in each domain. Small to medium effect sizes were generally observed. A comparison of the effect sizes across the two sets of analyses did not reveal significant differences.

CONCLUSIONS

The findings from this review reveal that MDMA use is associated with neurocognitive deficits. The implications of these findings are discussed.

Acute tryptophan depletion reduces activation in the right hippocampus during encoding in an episodic memory task

Acute tryptophan depletion (ATD), a well-recognized method to lower central serotonin levels, was used to examine the effects of lower central serotonin levels on memory function in healthy males. Functional Magnetic Resonance Imaging (fMRI) was used to examine changes in brain activation during the encoding and the retrieval phase of a visual verbal episodic memory task. ATD led to more positively rated words in the encoding phase and to poorer recognition of these positively rated words in the retrieval phase. Furthermore, encoding was accompanied by enhanced brain activation in occipital, middle and superior frontal, anterior and posterior cingulate and striatal areas. Retrieval attempt was accompanied by enhanced activation in the cuneus, inferior occipital gyrus and inferior and middle frontal areas. Retrieval success was accompanied by activation in an extensive network including frontal, parietal, temporal, cingulate, striatal and cerebellar areas. In the encoding phase ATD attenuated activation in the right hippocampus and ATD did not affect brain activity in the retrieval phase. These results show that serotonin is important in long term memory processes, and that serotonin acts on the encoding phase and not on the retrieval phase.

Identification of first candidate genes for creativity: a pilot study

Studies from behavioral genetics have demonstrated the high heritability of intelligence. However, the endeavor to detect the genes forming the molecular basis of intelligence has been rather unsuccessful until now. Pharmacological studies have demonstrated the influence of the dopaminergic (DA) and the serotonergic (5-HT) system on subcomponents of cognitive functioning, and first studies from molecular genetics have demonstrated that genes related to the DA metabolism are associated with mental abilities. However, candidate genes for creativity have not been identified so far. Therefore, the influence of the catechol-O-methyltransferase (locus: COMT VAL158MET) gene and the dopamine D2 receptor gene (locus: DRD2 TAQ IA) on creativity was tested in addition to a serotonergic gene, TPH1 (locus: TPH-A779C), in a sample of N = 92 healthy Caucasian subjects while controlling for intelligence. Results showed that the DRD2 gene and the TPH gene were both associated with total creativity, explaining 9% of the variance, while COMT was not related to creativity at all. With respect to the subcomponents, the A1+ allele of DRD2 was related to higher verbal creativity as compared to the A1- allele, and carriers of the A allele of TPH1 showed significantly higher scores in figural and in numeric creativity, indicating that the two gene loci discriminate between higher cortical functions according to the organization of cognitive functions in the respective hemispheres.

Transmission disequilibrium of polymorphic variants in the tryptophan hydroxylase-2 gene in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is the most common behavioral disorder in childhood with substantial heritability. Pharmacological and molecular genetic studies as well as characterization of animal models have implicated serotonergic dysfunction in the pathophysiology of ADHD. Here, we investigated the effect of polymorphic variants in the gene of the tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme of serotonin (5-HT) synthesis in the brain, in children and adolescents with ADHD. We analyzed three single nucleotide polymorphisms (SNPs) in and downstream of the transcriptional control region of the TPH2 gene in 103 families with 225 affected children. Allelic association in families with more than one affected child was assessed using the pedigree disequilibrium test. Preferential transmissions were detected for the two SNPs in TPH2's regulatory region (rs4570625, P=0.049; rs11178997, P=0.034), but not for the third SNP in intron 2 (rs4565946, P=0.3517). Haplotype analysis revealed a strong trend of association between the regulatory region SNPs (rs4570625, rs11178997) and ADHD (P=0.064). Our results link potentially functional TPH2 variations to the pathophysiology of ADHD, and further support the relevance of 5-HT in disorders related to altered motor activity and cognitive processes.