BDNF Val66Met, Aβ amyloid, and cognitive decline in preclinical Alzheimer's disease

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has previously been implicated in Alzheimer's disease (AD)-related cognitive impairment. We aimed to determine the relationship between BDNF Val66Met and beta-amyloid (Aβ) on cognitive decline, hippocampal atrophy, and Aβ accumulation over 36 months in 165 healthy adults enrolled in the Australian Imaging, Biomarkers and Lifestyle study. In healthy adults with high Aβ, Met carriers showed significant and moderate-to-large declines in episodic memory, executive function, and language, and greater hippocampal atrophy over 36 months, compared with Val/Val homozygotes. BDNF Val66Met was not found to be related to rates of change in cognition or hippocampal volume in healthy adults with low Aβ. BDNF Val66Met did not relate to the amount of Aβ or to the rate of Aβ accumulation in either group. High Aβ levels coupled with Met carriage may be useful prognostic markers of accelerated cognitive decline and hippocampal degeneration in individuals in the preclinical stage of AD.

Neural and behavioral effects of a novel mu opioid receptor antagonist in binge-eating obese people

BACKGROUND

Binge eating is associated with obesity and has been conceptualized as "food addiction." However, this view has received only inconsistent support in humans, and limited evidence relates key neurocircuitry to the disorder. Moreover, relatively few studies have used pharmacologic functional magnetic resonance imaging to probe the underlying basis of altered eating behaviors.

METHODS

In a double-blind, placebo-controlled, parallel group study, we explored the effects of a potent mu-opioid receptor antagonist, GSK1521498, in obese individuals with moderate binge eating. Subjects were tested during a baseline placebo run-in period and retested after 28-days of drug (n = 21) or placebo (n = 21) treatment. Using functional magnetic resonance imaging and behavioral measures, we determined the drug's effects on brain responses to food images and, separately, on motivation to expend energy to view comparable images.

RESULTS

Compared with placebo, GSK1521498 was associated with a significant reduction in pallidum/putamen responses to pictures of high-calorie food and a reduction in motivation to view images of high-calorie food. Intriguingly, although motivational responding was reduced, subjective liking for the same images actually increased following drug treatment.

CONCLUSIONS

Stimulus-specific putamen/pallidal responses in obese people with binge eating are sensitive to altered mu-opioid function. This neuromodulation was accompanied by reductions in motivational responding, as measured by grip force, although subjective liking responses to the same stimuli actually increased. As well as providing evidence for a link between the opioid system and food-related behavior in binge-eating obese individuals, these results support a dissociation across measures of motivation and liking associated with food-related stimuli in these individuals.

Speed of facial affect intensity recognition as an endophenotype of first-episode psychosis and associated limbic-cortical grey matter systems

BACKGROUND

Psychotic disorders are highly heritable such that the unaffected relatives of patients may manifest characteristics, or endophenotypes, that are more closely related to risk genes than the overt clinical condition. Facial affect processing is dependent on a distributed cortico-limbic network that is disrupted in psychosis. This study assessed facial affect processing and related brain structure as a candidate endophenotype of first-episode psychosis (FEP).

METHOD

Three samples comprising 30 FEP patients, 30 of their first-degree relatives and 31 unrelated healthy controls underwent assessment of facial affect processing and structural magnetic resonance imaging (sMRI) data. Multivariate analysis (partial least squares, PLS) was used to identify a grey matter (GM) system in which anatomical variation was associated with variation in facial affect processing speed.

RESULTS

The groups did not differ in their accuracy of facial affect intensity rating but differed significantly in speed of response, with controls responding faster than relatives, who responded faster than patients. Within the control group, variation in speed of affect processing was significantly associated with variation of GM density in amygdala, lateral temporal cortex, frontal cortex and cerebellum. However, this association between cortico-limbic GM density and speed of facial affect processing was absent in patients and their relatives.

CONCLUSIONS

Speed of facial affect processing presents as a candidate endophenotype of FEP. The normal association between speed of facial affect processing and cortico-limbic GM variation was disrupted in FEP patients and their relatives.

Effects of mu opioid receptor antagonism on cognition in obese binge-eating individuals

RATIONALE

Translational research implicates the mu opioid neurochemical system in hedonic processing, but its role in dissociable high-level cognitive functions is not well understood. Binge-eating represents a useful model of 'behavioural addiction' for exploring this issue.

OBJECTIVE

The aim of this study was to objectively assess the cognitive effects of a mu opioid receptor antagonist in obese individuals with binge-eating symptoms.

METHODS

Adults with moderate to severe binge-eating and body mass index ≥30 kg/m² received 4 weeks of treatment with a mu opioid receptor antagonist (GSK1521498) 2 or 5 mg per day, or placebo, in a double-blind randomised parallel design. Neuropsychological assessment was undertaken at baseline and endpoint to quantify processing bias for food stimuli (visual dot probe with 500- and 2,000-ms stimulus presentations and food Stroop tasks) and other distinct cognitive functions (N-back working memory, sustained attention, and power of attention tasks).

RESULTS

GSK1521498 5 mg/day significantly reduced attentional bias for food cues on the visual dot probe task versus placebo (p = 0.042), with no effects detected on other cognitive tasks (all p > 0.10). The effect on attentional bias was limited to the longer stimulus duration condition in the higher dose cohort alone.

CONCLUSIONS

These findings support a central role for mu opioid receptors in aspects of attentional processing of food cues but militate against the notion of major modulatory influences of mu opioid receptors in working memory and sustained attention. The findings have implications for novel therapeutic directions and suggest that the role of different opioid receptors in cognition merits further research.

Dopamine D₂ receptor modulation of human response inhibition and error awareness

Response inhibition, comprising action cancellation and action restraint, and error awareness are executive functions of considerable clinical relevance to neuropsychiatric disorders. Nevertheless, our understanding of their underlying catecholamine mechanisms, particularly regarding dopamine, is limited. Here, we used the dopamine D2 agonist cabergoline to study its ability to improve inhibitory control and modulate awareness of performance errors. A randomized, double-blind, placebo-controlled, crossover design with a single dose of cabergoline (1.25 mg) and placebo (dextrose) was employed in 25 healthy participants. They each performed the stop-signal task, a well-validated measure of action cancellation, and the Error Awareness Task, a go/no-go measure of action restraint and error awareness, under each drug condition. Cabergoline was able to selectively reduce stop-signal RT, compared with placebo, indicative of enhanced action cancellation (p < .05). This enhancement occurred without concomitant changes in overall response speed or RT variability and was not seen for errors of commission on the Error Awareness Task. Awareness of performance errors on the go/no-go task was, however, significantly improved by cabergoline compared with placebo (p < .05). Our results contribute to growing evidence for the dopaminergic control of distinct aspects of human executive ability, namely, action cancellation and error awareness. The findings may aid the development of new, or the repurposing of existing, pharmacotherapy that targets the cognitive dysfunction of psychiatric and neurological disorders. They also provide further evidence that specific cognitive paradigms have correspondingly specific neurochemical bases.

Dopamine transporter genotype predicts attentional asymmetry in healthy adults

A number of recent studies suggest that DNA variation in the dopamine transporter gene (DAT1) influences spatial attention asymmetry in clinical populations such as ADHD, but confirmation in non-clinical samples is required. Since non-spatial factors such as attentional load have been shown to influence spatial biases in clinical conditions, here we sought to determine whether any association between DAT1 genotype and spatial bias might be moderated by non-spatial attentional load. Healthy adults were asked to react to sudden onset peripheral targets while demand on non-spatial attention was manipulated via a central task. Participants were genotyped for a DAT1 variable number of tandem repeat (VNTR) polymorphism. The 10-repeat allele of this variant is a replicated susceptibility allele for ADHD and has been shown to associate with spatial bias. As expected, an overall leftward asymmetry/pseudoneglect was observed when the data were averaged across the entire sample. When data were stratified by DAT1 genotype, individuals lacking homozygosity for the 10-repeat DAT1 allele (non-10/10) showed a pronounced leftward bias that was significantly different from zero. In line with past reports from children with ADHD, this leftward bias was attenuated in individuals who were homozygous for the DAT1 10-repeat allele (10/10), suggestive of relatively weaker right hemisphere dominance for spatial attention. This effect of DAT1 genotype on spatial bias was not modulated by non-spatial attention load. These data confirm in healthy adult participants both the existence and the direction of the relationship previously reported between DAT1 genotype and spatial bias in children with ADHD. These data add to a growing body of evidence showing that spatial attentional asymmetry is a stable quantitative trait, with individual differences in this trait significantly predicted by common DNA variation in the DAT1 gene.

Attention to language: novel MEG paradigm for registering involuntary language processing in the brain

Previous research indicates that, under explicit instructions to listen to spoken stimuli or in speech-oriented behavioural tasks, the brain's responses to senseless pseudowords are larger than those to meaningful words; the reverse is true in non-attended conditions. These differential responses could be used as a tool to trace linguistic processes in the brain and their interaction with attention. However, as previous studies relied on explicit instructions to attend or ignore the stimuli, a technique for automatic attention modulation (i.e., not dependent on explicit instruction) would be more advantageous, especially when cooperation with instructions may not be guaranteed (e.g., neurological patients, children etc). Here we present a novel paradigm in which the stimulus context automatically draws attention to speech. In a non-attend passive auditory oddball sequence, rare words and pseudowords were presented among frequent non-speech tones of variable frequency and length. The low percentage of spoken stimuli guarantees an involuntary attention switch to them. The speech stimuli, in turn, could be disambiguated as words or pseudowords only in their end, at the last phoneme, after the attention switch would have already occurred. Our results confirmed that this paradigm can indeed be used to induce automatic shifts of attention to spoken input. At ~250ms after the stimulus onset, a P3a-like neuromagnetic deflection was registered to spoken (but not tone) stimuli indicating an involuntary attention shift. Later, after the word-pseudoword divergence point, we found a larger oddball response to pseudowords than words, best explained by neural processes of lexical search facilitated through increased attention. Furthermore, we demonstrate a breakdown of this orderly pattern of neurocognitive processes as a result of sleep deprivation. The new paradigm may thus be an efficient way to assess language comprehension processes and their dynamic interaction with those of attention allocation. It does it in an automatic and task-free fashion, indicating its potential benefit for assessing uncooperative clinical populations.

Abnormal prefrontal activity subserving attentional control of emotion in remitted depressed patients during a working memory task with emotional distracters

BACKGROUND

Patients with major depressive disorder (MDD) show deficits in processing of facial emotions that persist beyond recovery and cessation of treatment. Abnormalities in neural areas supporting attentional control and emotion processing in remitted depressed (rMDD) patients suggests that there may be enduring, trait-like abnormalities in key neural circuits at the interface of cognition and emotion, but this issue has not been studied systematically.

METHOD

Nineteen euthymic, medication-free rMDD patients (mean age 33.6 years; mean duration of illness 34 months) and 20 age- and gender-matched healthy controls (HC; mean age 35.8 years) performed the Emotional Face N-Back (EFNBACK) task, a working memory task with emotional distracter stimuli. We used blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to measure neural activity in the dorsolateral (DLPFC) and ventrolateral prefrontal cortex (VLPFC), orbitofrontal cortex (OFC), ventral striatum and amygdala, using a region of interest (ROI) approach in SPM2.

RESULTS

rMDD patients exhibited significantly greater activity relative to HC in the left DLPFC [Brodmann area (BA) 9/46] in response to negative emotional distracters during high working memory load. By contrast, rMDD patients exhibited significantly lower activity in the right DLPFC and left VLPFC compared to HC in response to positive emotional distracters during high working memory load. These effects occurred during accurate task performance.

CONCLUSIONS

Remitted depressed patients may continue to exhibit attentional biases toward negative emotional information, reflected by greater recruitment of prefrontal regions implicated in attentional control in the context of negative emotional information.

Fast reconfiguration of high-frequency brain networks in response to surprising changes in auditory input

How do human brain networks react to dynamic changes in the sensory environment? We measured rapid changes in brain network organization in response to brief, discrete, salient auditory stimuli. We estimated network topology and distance parameters in the immediate central response period, <1 s following auditory presentation of standard tones interspersed with occasional deviant tones in a mismatch-negativity (MMN) paradigm, using magnetoencephalography (MEG) to measure synchronization of high-frequency (gamma band; 33-64 Hz) oscillations in healthy volunteers. We found that global small-world parameters of the networks were conserved between the standard and deviant stimuli. However, surprising or unexpected auditory changes were associated with local changes in clustering of connections between temporal and frontal cortical areas and with increased interlobar, long-distance synchronization during the 120- to 250-ms epoch (coinciding with the MMN-evoked response). Network analysis of human MEG data can resolve fast local topological reconfiguration and more long-range synchronization of high-frequency networks as a systems-level representation of the brain's immediate response to salient stimuli in the dynamically changing sensory environment.

Effects of donepezil on cognitive performance after sleep deprivation

OBJECTIVES

To identify tasks that were sensitive to a temporary decline in cognitive performance after sleep deprivation and to investigate the ability of the acetylcholinesterase inhibitor donepezil to reverse any sleep deprivation-induced impairment.

METHODS

Thirty healthy volunteers were administered either a 5-mg daily dose of donepezil or placebo for 14-17 days, in a double-blind parallel group design, then underwent either 24 h sleep deprivation or a normal night of sleep in non-blinded crossover, and were subsequently tested on a battery of cognitive tasks designed to measure different components of memory and executive function.

RESULTS

Sleep deprivation selectively impaired performance on several memory tasks whilst also impairing non-memory function on these tasks. Performance on other tasks was spared. Despite partially reversing the decline in subjective alertness associated with sleep deprivation, treatment with donepezil failed to significantly reverse the decline in cognitive performance on any of the tasks.

CONCLUSIONS

The results demonstrate the sensitivity of certain tests, particularly those that measure memory function, to cognitive impairment after sleep deprivation. The inability of donepezil to reverse this performance decline suggests that the sleep deprivation model of cognitive impairment may not be suitable for detecting pro-cognitive effects of cholinergic augmentation.

Interaction of estrogen with central serotonergic mechanisms in human sensory processing: loudness dependence of the auditory evoked potential and mismatch negativity

Estrogen may be involved in schizophrenia by inhibiting serotonin-1A (5-HT(1A)) receptor function. We examined the effects of estrogen pre-treatment on modulation of loudness dependence of the auditory evoked potential (LDAEP) and mismatch negativity by the 5-HT(1A) receptor partial agonist, buspirone. Using a double-blind, placebo-controlled, repeated-measures design in healthy female volunteers, we observed that buspirone treatment significantly increased LDAEP slope. Estrogen increased LDAEP slope on its own, and a further LDAEP increase by buspirone was not seen after estrogen pre-treatment. Similar results were observed for mismatch negativity, where buspirone caused a small increase of latency, although not amplitude, after placebo but not estrogen pre-treatment, which enhanced mismatch negativity latency on its own. These results are in line with our previous findings on prepulse inhibition showing an inhibitory effect of estrogen on the action of buspirone. Taken together, these data suggest that estrogen may inhibit 5-HT(1A) receptor-mediated disruptions of auditory processing.

High-dose glycine impairs the prepulse inhibition measure of sensorimotor gating in humans

An impaired capacity to filter or 'gate' sensory information is a core deficit in cognitive function associated with schizophrenia. These deficits have been linked in part to N-methyl-d-aspartate (NMDA) receptor dysfunction. An association between high levels of glycine, a positive allosteric modulator of the NMDA receptor, and sensorimotor gating impairments (i.e. prepulse inhibition (PPI) deficit) have been reported in animal models of schizophrenia as well as patients with schizophrenia. This study examined the acute effects of modulating the glycine site of the NMDA receptor (with high-dose glycine) on sensory gating as measured by PPI. Sixteen healthy male subjects (final sample size of 12) participated in a double-blind, placebo-controlled, crossover design in which each subject was tested under two acute treatment conditions separated by at least a 5-day washout period; placebo and 0.8 g/kg glycine. PPI was recorded 45 min post treatment using electromyography of the eye-blink response. Relative to placebo, high-dose glycine significantly impaired sensorimotor gating as demonstrated by a decrease in PPI (t(11) = -2.983, p < 0.05). Administration of a high dose of glycine is associated with impairments in PPI supporting earlier observations in animals and patients with schizophrenia. This result, when taken together with findings in patients, suggests that high synaptic levels of glycine may have some clinically relevant detrimental effects and suggests a potential dissociation of clinical symptomatology and sensory information processing as a function of NMDA receptor modulation in schizophrenia.

Chronic modulation of serotonergic neurotransmission with sertraline attenuates the loudness dependence of the auditory evoked potential in healthy participants

RATIONALE

The loudness dependence of the auditory evoked potential (LDAEP) has been reported to be an effective non-invasive measure of central serotonergic neurotransmission. However, acute manipulations of the serotonergic system in humans and animals have yielded inconsistent findings.

OBJECTIVES

In this study, we examined the chronic effect of serotonergic manipulation using the selective serotonin reuptake inhibitor, sertraline, on the LDAEP. In addition, we examined the influence of 5-HTTLPR genotype and individual differences in plasma drug concentrations on the LDAEP.

METHODS

The study utilised a double-blind, placebo-controlled, between-group design in which 40 (24 female) healthy adults (M age = 22.0 years, SE = 0.7) were tested following placebo or sertraline for an average of 24 days. The LDAEP was assessed 6 h post-final dose, and changes in the slope of amplitude of the N1/P2 across intensities (60, 70, 80, 90, 100 dB) were examined at Cz.

RESULTS

The sertraline group had a significantly smaller LDAEP than the placebo group [F(1,38) = 5.97, p = 0.02]. Drug plasma levels did not correlate with the LDAEP in the sertraline group, and there was no influence of 5-HTTLPR genotype.

CONCLUSIONS

We show for the first time that chronically modulating serotonin neurotransmission alters the LDAEP in healthy adults, consistent with extant literature indicating a moderating role of serotonin on this neurophysiological biomarker. The findings from this study together with previous studies suggest that the LDAEP may be a more sensitive marker of long-term or chronic rather than acute changes in the serotonin system.

Cognitive effort drives workspace configuration of human brain functional networks

Effortful cognitive performance is theoretically expected to depend on the formation of a global neuronal workspace. We tested specific predictions of workspace theory, using graph theoretical measures of network topology and physical distance of synchronization, in magnetoencephalographic data recorded from healthy adult volunteers (N = 13) during performance of a working memory task at several levels of difficulty. We found that greater cognitive effort caused emergence of a more globally efficient, less clustered, and less modular network configuration, with more long-distance synchronization between brain regions. This pattern of task-related workspace configuration was more salient in the β-band (16-32 Hz) and γ-band (32-63 Hz) networks, compared with both lower (α-band; 8-16 Hz) and higher (high γ-band; 63-125 Hz) frequency intervals. Workspace configuration of β-band networks was also greater in faster performing participants (with correct response latency less than the sample median) compared with slower performing participants. Processes of workspace formation and relaxation in relation to time-varying demands for cognitive effort could be visualized occurring in the course of task trials lasting <2 s. These experimental results provide support for workspace theory in terms of complex network metrics and directly demonstrate how cognitive effort breaks modularity to make human brain functional networks transiently adopt a more efficient but less economical configuration.

Opioid receptor modulation of hedonic taste preference and food intake: a single-dose safety, pharmacokinetic, and pharmacodynamic investigation with GSK1521498, a novel μ-opioid receptor inverse agonist

Endogenous opioids and µ-opioid receptors have been linked to hedonic and rewarding aspects of palatable food intake. The authors examined the safety, pharmacokinetic, and pharmacodynamic profile of GSK1521498, a µ-opioid receptor inverse agonist that is being investigated primarily for the treatment of overeating behavior in obesity. In healthy participants, GSK1521498 oral solution and capsule formulations were well tolerated up to a dose of 100 mg. After single doses (10-150 mg), the maximum concentration (C(max)) and area under the curve (AUC) in plasma increased in a dose-proportional manner. GSK1521498 selectively reduced sensory hedonic ratings of high-sugar and high-fat dairy products and caloric intake of high-fat/high-sucrose snack foods. These findings provide encouraging data in support of the development of GSK1521498 for the treatment of disorders of maladaptive ingestive behavior or compulsive consumption.

Methylphenidate but not atomoxetine or citalopram modulates inhibitory control and response time variability

BACKGROUND

Response inhibition is a prototypical executive function of considerable clinical relevance to psychiatry. Nevertheless, our understanding of its pharmacological modulation remains incomplete.

METHODS

We used a randomized, double-blind, placebo-controlled, crossover design to examine the effect of an acute dose of methylphenidate (MPH) (30 mg), atomoxetine (ATM) (60 mg), citalopram (CIT) (30 mg), and placebo (PLAC) (dextrose) on the stop signal inhibition task in 24 healthy, right-handed men 18-35 years of age. Participants performed the task under each of the four drug conditions across four consecutive sessions.

RESULTS

Methylphenidate led to a reduction in both response time variability and stop-signal reaction time (SSRT), indicating enhanced response inhibition compared with all other drug conditions. Crucially, the enhancement of response inhibition by MPH occurred without concomitant changes in overall response speed, arguing against a simple enhancement of processing speed. We found no significant differences between ATM and PLAC, CIT and PLAC, or ATM and CIT for either response time variability or SSRT.

CONCLUSIONS

An acute dose of MPH but not ATM or CIT was able to improve SSRT and reduce response time variability in nonclinical participants. Improvements in response inhibition and response variability might underlie the reported clinical benefits of MPH in disorders such as attention-deficit/hyperactivity disorder.

Evidence for sex differences in the loudness dependence of the auditory evoked potential in humans

OBJECTIVE

The loudness dependence of the auditory evoked potential (LDAEP) has been suggested as a marker of the serotonin system, although studies directly examining the relationship between acute changes in serotonin and the LDAEP have been inconsistent. Given the reported sex dichotomy in serotonin neurotransmission, this study examined if there are sex differences in the LDAEP.

METHODS

Data from 65 healthy participants from four independent studies were pooled, and their N1/P2 slopes were quantified.

RESULTS

Mean N1/P2 slopes for female participants were higher than those for male participants (p < 0.0001).

CONCLUSION

These findings suggest that the LDAEP is modulated by sex potentially because of differences in serotonergic neurotransmission, and these differences may account for some of the inconsistent findings linking serotonin function and LDAEP.

Amygdala reactivity to faces at varying intensities of threat in generalized social phobia: an event-related functional MRI study

Using functional magnetic resonance imaging, we measured amygdala reactivity to faces varying on threat intensity in patients with generalized social phobia (GSP) and healthy controls. GSP patients exhibited greater amygdala reactivity to threat faces at high and moderate intensities. More subtle displays of social threat are sufficient to evoke a fear-related neural response.

Augmenting serotonin neurotransmission with citalopram modulates emotional expression decoding but not structural encoding of moderate intensity sad facial emotional stimuli: an event-related potential (ERP) investigation

Antidepressants targeting the serotonergic system have been shown to modulate biases in emotional processing. The effects of serotonergic modulation on the temporal course of emotional processing (accruing within milliseconds) are unknown. Furthermore, it is unknown how serotonin affects different stages of facial emotional processing. The current study investigated the effects of acute serotonin augmentation on event-related potential (ERP) measures associated with 'structural encoding' (N170) and emotion 'expression decoding' (N250 and a late slow-wave positive potential [LPP]) of happy and sad facial stimuli, relative to neutral facial stimuli. The study was a double-blind, placebo-controlled, cross-over design, in which 14 healthy male participants completed a facial recognition task under two acute treatment conditions: 1) placebo (PLB) and 2) 20 mg citalopram (CIT). ERP recording were conducted while subjects viewed neutral, happy and sad facial stimuli. Findings indicated that under PLB, the N170 was not modulated by valence (happy or sad versus neutral), but the N250 and LPP were enhanced for processing happy (relative to neutral) faces. Citalopram had no effect on the N170, but it enhanced the LPP for processing sad (relative to neutral) faces. These findings suggest that serotonin enhancement has selective and temporal effects on emotional face processing, with evidence for modulating processes associated with 'expression decoding' but not 'structural encoding'. The enhanced cortical response to perception of moderately intense sad facial expressions following citalopram administration may relate to the cognitive processing of the social relevance or significance of such ambiguous stimuli.

Neuropsychiatric adverse effects of centrally acting antiobesity drugs

INTRODUCTION

Central neurochemical systems including the monoamine, opioid, and cannabinoid systems have been promising targets for antiobesity drugs that modify behavioral components of obesity. In addition to modulating eating behavior, centrally acting antiobesity drugs are also likely to alter emotional behavior and cognitive function due to the high expression of receptors for the neurochemical systems targeted by these drugs within the fronto-striatal and limbic circuitry.

METHODS

This paper reviewed the neuropsychiatric adverse effects of past and current antiobesity drugs, with a central mechanism of action, linking the adverse effects to their underlying neural substrates and neurochemistry.

RESULTS

Antiobesity drugs were found to have varying neuropsychiatric adverse event profiles. Insomnia was the most common adverse effect with drugs targeting monoamine systems (sibutramine, bupropion and tesofensine). These drugs had some positive effects on mood and anxiety and may have added therapeutic benefits in obese patients with comorbid depression and anxiety symptoms. Sedation and tiredness were the most common adverse effects reported with drugs targeting the m-opioid receptors (i.e., naltrexone) and combination therapies targeting the opioid and monoamine systems (i.e., Contrave™). Cognitive impairments were most frequently associated with the antiepileptic drugs, topiramate and zonisamide, consistent with their sedative properties. Drugs targeting the cannabinoid system (rimonabant and taranabant) were consistently associated with symptoms of anxiety and depression, including reports of suicidal ideation. Similar adverse events have also been noted for the D₁/D₅ antagonist ecopipam.

CONCLUSION

These findings highlight the need to assess neuropsychiatric adverse events comprehensively using sensitive and validated methods early in the clinical development of candidate antiobesity drugs with a central mechanism of action.

The loudness dependence auditory evoked potential is insensitive to acute changes in serotonergic and noradrenergic neurotransmission

BACKGROUND

The loudness dependence of the auditory evoked potential (LDAEP) has been proposed as an electrophysiological marker for assessing serotonergic function in vivo in humans, although accumulating evidence suggests that it is insensitive to acute changes in serotonergic neurotransmission. Very little is known about the sensitivity of the LDAEP to other neurotransmitter systems including the noradrenergic system. The current study examined the effects of noradrenergic modulation as well as serotonergic modulation on the LDAEP.

METHODS

The study utilised a double-blind placebo-controlled design in which the LDAEP in 17 healthy males and females was tested following acute administration of each of citalopram (20 mg), reboxetine (4 mg) and placebo.

RESULTS

Neither citalopram nor reboxetine modulated the LDAEP relative to placebo treatment (p > 0.05).

CONCLUSION

These findings suggest that the LDAEP is insensitive to acute changes in serotonergic or noradrenergic neurotransmission and thus is a poor pharmacodynamic marker of these systems.

Amygdala-frontal connectivity during emotion regulation

Successful control of affect partly depends on the capacity to modulate negative emotional responses through the use of cognitive strategies (i.e., reappraisal). Recent studies suggest the involvement of frontal cortical regions in the modulation of amygdala reactivity and the mediation of effective emotion regulation. However, within-subject inter-regional connectivity between amygdala and prefrontal cortex in the context of affect regulation is unknown. Here, using psychophysiological interaction analyses of functional magnetic resonance imaging data, we show that activity in specific areas of the frontal cortex (dorsolateral, dorsal medial, anterior cingulate, orbital) covaries with amygdala activity and that this functional connectivity is dependent on the reappraisal task. Moreover, strength of amygdala coupling with orbitofrontal cortex and dorsal medial prefrontal cortex predicts the extent of attenuation of negative affect following reappraisal. These findings highlight the importance of functional connectivity within limbic-frontal circuitry during emotion regulation.

Acute dopamine and/or serotonin depletion does not modulate mismatch negativity (MMN) in healthy human participants

RATIONALE

Schizophrenia is commonly associated with impairments in pre-attentive change detection, as represented by reduced mismatch negativity (MMN). While the neurochemical basis of MMN has been linked to N-methyl-D: -aspartic acid (NMDA) receptor function, the roles of the dopaminergic and/or the serotonergic systems are not fully explored in humans.

OBJECTIVES

The aim of the present study was to investigate the effects of acutely depleting dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) alone or simultaneously by depleting their amino acid precursors on MMN in healthy participants.

METHODS

Sixteen healthy male subjects participated in a double-blind, placebo-controlled, cross-over design in which each subject's duration MMN was assessed under four acute treatment conditions separated by a 5-day washout period: balanced amino acid control (no depletion), tyrosine/phenylalanine depletion (to reduce DA neurotransmission), tryptophan depletion (to reduce 5-HT neurotransmission) and tryptophan/tyrosine/phenylalanine depletion (to reduce DA and 5-HT neurotransmission simultaneously).

RESULTS

Acute depletion of either DA and 5-HT alone or simultaneously had no effect on MMN.

CONCLUSIONS

These findings suggest that modulation of the dopaminergic and serotonergic systems acutely does not lead to changes in MMN.

Amygdala and insula response to emotional images in patients with generalized social anxiety disorder

BACKGROUND

Functional brain imaging studies have demonstrated amygdala and insula hyper-reactivity to probes of social threat in participants with generalized social anxiety disorder (gSAD). The amygdala and insula are known to serve broad functions in emotional processing, including integration of affective information. However, few studies have examined brain responses in socially anxious participants during general emotional processing. We examined brain response to emotionally evocative images in patients with gSAD and matched healthy controls.

METHODS

Eleven patients with gSAD who were not taking psychotropic medications and did not have psychiatric comorbidities and 11 matched healthy controls underwent functional magnetic resonance imaging while viewing blocks of emotionally salient (positive, negative, neutral) pictures.

RESULTS

Participants with gSAD exhibited enhanced bilateral amygdala and insula reactivity to negative (v. neutral) images compared with healthy controls who did not exhibit enhanced reactivity. Within the gSAD group, the extent of amygdala activation was correlated with social anxiety severity, whereas the extent of insula activation was correlated with trait anxiety.

LIMITATIONS

The small sample size may have limited our ability to detect group differences in other relevant brain regions and in behavioural measures.

CONCLUSION

In addition to prior findings of probes of social information processing, our findings suggest that the amygdala and insula responses are hyper-reactive to general emotional images with negative emotional content and that these brain regions may play divergent roles in their representation of different phenotypes.

Evidence for modulation of facial emotional processing bias during emotional expression decoding by serotonergic and noradrenergic antidepressants: an event-related potential (ERP) study

RATIONALE

Serotonergic (SSRI) and noradrenergic (NRI) antidepressants modulate biases in emotional processing such that perceptual bias is shifted away from negative and towards positive emotional material. However, the effects of serotonergic and noradrenergic modulation on the temporal course (occurring in milliseconds) of emotional processing, and in particular, the rapid physiological changes associated with the different stages of emotional processing, are unknown.

OBJECTIVE

The current study assessed the effects of acute serotonergic (i.e. with citalopram) and noradrenergic (i.e. with reboxetine) augmentation on event-related potential (ERP) measures associated with 'structural encoding' (N170) and emotion expression decoding (N250 and late positive potential [LPP]) for positive (happy) and negative (sad) facial stimuli relative to neutral facial stimuli.

MATERIALS AND METHODS

This study employed a double-blind, placebo-controlled, cross-over design in which 12 healthy male participants completed a facial expression recognition task tested under three acute conditions: (a) placebo, (b) citalopram (20 mg) and (c) reboxetine (4 mg).

RESULTS

Both citalopram and reboxetine had no effect on the N170 ERP component associated with structural encoding, but potentiated the N250 associated with happy (relative to neutral) emotional facial expression decoding. Both drugs had no valence effects on later ERP measures of emotion expression decoding (LPP).

CONCLUSIONS

Citalopram and reboxetine have selective effects on the temporal course of emotional processing with evidence to suggest specific effects on emotion expression decoding of positive (happy) emotional facial stimuli as evidenced by changes in the attention-modulated N250 but not structural encoding. These findings provide physiological evidence that antidepressants may shift perceptual biases in emotional processing away from negative and towards positive stimuli.

Examining the nootropic effects of a special extract of Bacopa monniera on human cognitive functioning: 90 day double-blind placebo-controlled randomized trial

While Ayurvedic medicine has touted the cognitive enhancing effects of Bacopa monniera for centuries, there is a need for double-blind placebo-controlled investigations. One hundred and seven healthy participants were recruited for this double-blind placebo-controlled independent group design investigation. Sixty-two participants completed the study with 80% treatment compliance. Neuropsychological testing using the Cognitive Drug Research cognitive assessment system was conducted at baseline and after 90 days of treatment with a special extract of Bacopa monniera (2 x 150 mg KeenMind) or placebo. The Bacopa monniera product significantly improved performance on the 'Working Memory' factor, more specifically spatial working memory accuracy. The number of false-positives recorded in the Rapid visual information processing task was also reduced for the Bacopa monniera group following the treatment period. The current study provides support for the two other published studies reporting cognitive enhancing effects in healthy humans after a 90 day administration of the Bacopa monniera extract. Further studies are required to ascertain the effective dosage range, the time required to attain therapeutic levels and the effects over a longer term of administration.

Galantamine-induced improvements in cognitive function are not related to alterations in alpha(4)beta (2) nicotinic receptors in early Alzheimer's disease as measured in vivo by 2-[18F]fluoro-A-85380 PET

INTRODUCTION

The nicotinic acetylcholine receptor (nAChR) system plays a regulatory role in a number of cognitive processes. Cholinesterase inhibitors (i.e., galantamine) that potentiate cholinergic neurotransmission improve cognitive function in Alzheimer's disease (AD); however, the relationship between these effects and associated changes in nAChRs are yet to be established in vivo.

MATERIALS AND METHODS

2-[18F]Fluoro-A-85380 (2-FA) binds to nAChRs and with positron emission tomography (PET) imaging provides a composite measure of receptor density and ligand affinity. This study aimed to: (1) quantify nAChRs in vivo in 15 drug-naïve patients with mild AD before and after chronic treatment with galantamine, using 2-FA and PET, and (2) examine the relationship between treatment-induced changes in nAChRs and improvements in cognitive function. Participants were nonsmokers and underwent extensive cognitive testing and a PET scan after injection of approximately 200 MBq of 2-FA on two occasions (before and after 12 weeks, galantamine treatment). A 3-day washout period preceded the second scan. Brain regional 2-FA binding was assessed through a simplified estimation of distribution volume (DV(S)).

RESULTS

Performance on global measures of cognition significantly improved following galantamine treatment (p < 0.05). This improvement extended to specific cognitive measures of language and verbal learning. No significant differences in nAChR DV(S) before and after galantamine treatment were found. The treatment-induced improvement in cognition was not correlated with regional or global nAChR DV(S), suggesting that changes in nAChRs may not be responsible for the improvements in cognition following galantamine in patients with mild AD.

Estradiol treatment and its interaction with the cholinergic system: effects on cognitive function in healthy young women

The steroid hormone estradiol has been shown to modulate cognitive function in both animals and humans, and although the exact mechanisms associated with these effects are unknown, interactions with the cholinergic system have been proposed. We examined the neurocognitive effects of short-term estradiol treatment and its interaction with the cholinergic system using the muscarinic receptor antagonist scopolamine in healthy young women. Thirty-four participants (Mean age+/-SD=22.4+/-4.4) completed baseline cognitive assessment and then received either 100 microg/day transdermal estradiol or transdermal placebo for 31 days. On days 28 and 31 of treatment, further cognitive assessment was performed pre- and 90 min post-scopolamine (0.4 mg) or placebo (saline) injection, under a randomized double-blind placebo-controlled design. Short-term estradiol treatment significantly enhanced spatial working memory with a trend for improvement in long-term verbal learning and memory. Overall, estradiol treatment did not protect against or attenuate the scopolamine-induced impairments in the cognitive domains assessed. Findings suggest that estrogen has minimal effects on cholinergic-mediated cognitive processes following short-term treatment. Effects of estradiol treatment may be dependent on age, dose of estradiol, integrity of cholinergic innervation and baseline endogenous estrogen levels, which may in part explain the inconsistent findings in the literature.

Pre- and post-synaptic dopamine imaging and its relation with frontostriatal cognitive function in Parkinson disease: PET studies with [11C]NNC 112 and [18F]FDOPA

Frontostriatal cognitive dysfunction is common in Parkinson disease (PD), but the explanation for its heterogeneous expressions remains unclear. This study examined the dopamine system within the frontostriatal circuitry with positron emission tomography (PET) to investigate pre- and post-synaptic dopamine function in relation to the executive processes in PD. Fifteen non-demented PD patients and 14 healthy controls underwent [(18)F]FDOPA (for dopamine synthesis) and [(11)C]NNC 112 (for D(1) receptors) PET scans and cognitive testing. Parametric images of [(18)F]FDOPA uptake (K(i)) and [(11)C]NNC 112 binding potential (BP(ND)) were calculated using reference tissue models. Group differences in K(i) and BP(ND) were assessed with both volume of interest and statistical parametric mapping, and were correlated with cognitive tests. Measurement of [(18)F]FDOPA uptake in cerebral cortex was questionable because of higher K(i) values in white than adjacent gray matter. These paradoxical results were likely to be caused by violations of the reference tissue model assumption rendering interpretation of cortical [(18)F]FDOPA uptake in PD difficult. We found no regional differences in D(1) receptor density between controls and PD, and no overall differences in frontostriatal performance. Although D(1) receptor density did not relate to frontostriatal cognition, K(i) decreases in the putamen predicted performance on the Wisconsin Card Sorting Test in PD only. These results suggest that striatal dopamine denervation may contribute to some frontostriatal cognitive impairment in moderate stage PD.

The loudness dependence of the auditory evoked potential (LDAEP) as an in vivo biomarker of central serotonergic function in humans: rationale, evaluation and review of findings

OBJECTIVES

The loudness dependence of the auditory evoked potential (LDAEP) has been proposed as a valid means of non-invasively assessing in vivo central serotonin (5-hydroxytryptamine, 5-HT) function in humans. The specificity and sensitivity of the LDAEP to changes in 5-HT neurotransmission have recently been explored directly in a number of pharmacological and genetic studies. Subsequently, this review was undertaken in an attempt to critically evaluate the potential role of the LDAEP as a marker of the central 5-HT function.

DESIGN

Findings from clinical, experimental animal and human studies examining the relationship between the LDAEP and the 5-HT system as well as other neurochemical systems including dopaminergic, glutamatergic and the cholinergic systems were reviewed.

RESULTS

The majority of evidence for an association between the LDAEP and 5-HT has come from animal studies. Indirect studies in clinical disorders of presumed serotonergic dysfunction have been circumstantial and inconsistent with more recent investigations utilising direct genetic association studies also providing conflicting reports. Pharmacological studies in humans provide overwhelming evidence that the LDAEP is insensitive to acute changes in 5-HT function, with additional evidence outlining sensitivity to other neurotransmitter systems including the glutamatergic system.

CONCLUSIONS

The available evidence suggests that the LDAEP lacks sensitivity and specificity to acute changes in serotonergic neurotransmission. Overall the findings do not provide strong support for its utility as a marker of central 5-HT function. However the LDAEP shows more promise as a potential predictor of antidepressant treatment response and this predictive ability may provide the basis for future research involving the LDAEP.

Differential effects of acute serotonin and dopamine depletion on prepulse inhibition and p50 suppression measures of sensorimotor and sensory gating in humans

Schizophrenia is associated with impairments of sensorimotor and sensory gating as measured by prepulse inhibition (PPI) of the acoustic startle response and P50 suppression of the auditory event-related potential respectively. While serotonin and dopamine play an important role in the pathophysiology and treatment of schizophrenia, their role in modulating PPI and P50 suppression in humans is yet to be fully clarified. To further explore the role of serotonin and dopamine in PPI and P50 suppression, we examined the effects of acute tryptophan depletion (to decrease serotonin) and acute tyrosine/phenylalanine depletion (to decrease dopamine) on PPI and P50 suppression in healthy human participants. In addition, we also examined for the first time, the effects of simultaneous serotonin and dopamine depletion (ie combined monoamine depletion) on PPI and P50 suppression. The study was a double-blind, placebo-controlled cross-over design in which 16 healthy male participants completed the PPI and P50 paradigms under four acute treatment conditions: (a) balanced/placebo control, (b) acute tryptophan depletion, (c) acute tyrosine/phenylalanine depletion, and (d) acute tyrosine/phenylalanine/tryptophan depletion (combined monoamine depletion). Selective depletion of dopamine had no significant effect on either PPI or P50 suppression, whereas selective serotonin depletion significantly disrupted PPI, but not P50 suppression. Finally, the simultaneous depletion of both serotonin and dopamine resulted in significant reduction of both PPI and P50 suppression. We suggest these results can be explained by theories relating to optimal levels of monoaminergic neurotransmission and synergistic interactions between serotonergic and dopaminergic systems for normal 'gating' function. These findings suggest that a dysfunction in both serotonin and dopamine neurotransmission may, in part, be responsible for the gating deficits observed in schizophrenia, and their normalization following administration of atypical antipsychotic drugs.

Effects of selective and combined serotonin and dopamine depletion on the loudness dependence of the auditory evoked potential (LDAEP) in humans

BACKGROUND

The loudness dependence of the auditory evoked potential (LDAEP) has been suggested as a possible in vivo measure of central serotonin function. However, more recent studies suggest that the LDAEP may be modulated by multiple neuromodulatory systems in addition to the serotonergic system. Accordingly we further examined the effects of selective serotonin, dopamine and simultaneous serotonin and dopamine depletion on the LDAEP in healthy subjects.

METHODS

The study employed a placebo-controlled, double-blind, cross over design. Fourteen subjects were tested under four acute treatment conditions: placebo (balanced amino acid drink), tryptophan (serotonin) depletion (ATD), tyrosine/phenylalanine (dopamine) depletion (ATPD) and combined tryptophan/tyrosine/phenylalanine (serotonin and dopamine) depletion (CMD). Testing was conducted 5.5 h post-depletion and changes in the amplitude of the N1/P2 at varying intensities (60, 70, 80, 90, 100 dB) were examined at C(Z).

RESULTS

Greater than 80% plasma precursor depletion was achieved across all conditions. Despite significant depletion of monoamine precursors, ATD, (p = 0.318), ATPD (p = 0.061) and CMD (p = 0.104) had no effects on the LDAEP (60-100 dB).

CONCLUSION

Acute serotonin and dopamine depletion did not modulate the LDAEP. This finding adds support to growing evidence that the LDAEP is insensitive to acute changes in serotonin and dopamine neurotransmission.

An examination of acute changes in serotonergic neurotransmission using the loudness dependence measure of auditory cortex evoked activity: effects of citalopram, escitalopram and sertraline

OBJECTIVE

The underlying effect of serotonergic neurotransmission has been implicated in several psychiatric disorders. The inability to routinely and non-invasively determine the integrity of the serotonergic system in vivo has limited our understanding of disorders with a putative serotonergic abnormality. The loudness dependence of the auditory evoked potential (LDAEP) has been proposed as a reliable measure of central serotonin function in humans. While animal studies suggest that the LDAEP is sensitive to changes in central serotonin neurotransmission, evidence in humans has been indirect and inconsistent. The aim of this study was to assess the sensitivity of the LDAEP to acute augmentation in central serotonergic neurotransmission in humans.

METHODS

The study used a double-blind, placebo-controlled cross-over design, in which healthy subjects were tested under four acute treatment conditions, with pharmacologically equivalent single doses of placebo, escitalopram (10 mg), citalopram (20 mg) and sertraline (50 mg) to examine the direct effect of acute enhancement of synaptic serotonin on the LDAEP. Furthermore, the outcome of the serotonergic modulatory effects on the LDAEP was also examined using two methods (dipole source analysis (DSA) vs. scalp analysis).

RESULTS

Escitalopram, citalopram and sertraline had no effects on the LDAEP and were independent of the analysis method used.

CONCLUSION

These findings question the sensitivity of the LDAEP to acute changes in serotonin neurotransmission and its validity as a reliable measure of central serotonin function in humans.

The cognitive effects of modulating the glycine site of the NMDA receptor with high-dose glycine in healthy controls

N-methyl-D-aspartate (NMDA) receptors play an important role in learning and memory. Targeting the glycine modulatory site of the NMDA receptor has been suggested as a therapeutic strategy to improve cognition, although findings have not been convincing. We used the Cognitive Drug Research computerised assessment system to examine the effects of high-dose glycine on a number of cognitive processes in healthy young subjects. The study was a randomised placebo controlled repeated measures design in which each subject received acute placebo or glycine (0.8 g/kg) orally, with treatment conditions separated by a 5-day washout period. No significant effects of glycine were found on measures of working memory, declarative memory, attention or perceptual processing. These findings, together with those of previous studies, cast doubt over the ability of acute high-dose glycine to improve cognitive function in healthy subjects and suggest that the optimum dose of glycine for improving cognition may vary between different populations, possibly due to differences in endogenous glycine levels and the functional status of NMDA receptors.

Tyrosine depletion alters cortical and limbic blood flow but does not modulate spatial working memory performance or task-related blood flow in humans

Dopamine appears critical in regulating spatial working memory (SWM) within the PFC of non-human primates; however findings in humans are less clear. Recent studies of the effects of global depletion of dopamine via acute tyrosine/phenylalanine depletion (TPD) on SWM task performance have yielded inconsistent results, which may be partly related to task differences. These previous studies do not address whether TPD can directly impair PFC functioning. The current study investigated the effects of TPD on (1) regional cerebral blood flow (rCBF) during a SWM n-back task using H(2) (15)O Positron Emission Tomography (PET), and (2) behavioural performance on three different SWM tasks. Ten healthy males were scanned twice: once following a placebo (balanced) amino acid mixture and once following an equivalent mixture deficient in tyrosine/phenylalanine (TPD condition). Participants completed two additional delayed-response tasks to examine whether differences in response demands influenced TPD effects on performance. TPD resulted in widespread increases in rCBF, with maximum increases in the region of the parahippocampal gyrus bilaterally, left inferior frontal gyrus, and the putamen. TPD related rCBF reductions were observed in the medial frontal gyrus bilaterally, right inferior temporal gyrus and the pons. Despite widespread changes in blood flow following TPD, no specific effects on SWM neural networks or task performance were observed. The use of three different SWM tasks suggests that task differences are unlikely to account for the lack of effects observed. These findings question the capacity of TPD to consistently modulate dopamine function and SWM neural networks in humans.

High-dose glycine inhibits the loudness dependence of the auditory evoked potential (LDAEP) in healthy humans

RATIONALE

The loudness dependence of the auditory evoked Potential (LDAEP) has been suggested to be a putative marker of central serotonin function, with reported abnormalities in clinical disorders presumed to reflect serotonin dysfunction. Despite considerable research, very little is known about the LDAEP's sensitivity to other neurotransmitter systems.

OBJECTIVES

Given the role of N-methyl-D-aspartate (NMDA) receptors in modulating pyramidal cell activity in cortico-cortico and thalamo-cortical loops, we examined the effect of targeting the glycine modulatory site of the NMDA receptor with high-dose glycine on the LDAEP in healthy subjects.

MATERIALS AND METHODS

The study was a double-blind, placebo-controlled repeated-measures design in which 14 healthy participants were tested under two acute treatment conditions, placebo and oral glycine (0.8 g/kg). Changes in the amplitude of the N1/P2 at varying intensities (60, 70, 80, 90, 100 dB) were examined at C(Z).

RESULTS

Compared to placebo, high-dose glycine induced a weaker LDAEP (a pronounced decrease in the slope of the N1/P2 with increasing tone loudness; p < 0.02).

CONCLUSION

While the exact mechanism responsible for the effects of glycine on the LDAEP are not known, the findings suggest an inhibitory effect in the cortex, possibly via activation of NMDA receptors on GABA interneurons or inhibitory glycine receptors. The findings add to the growing literature exhibiting modulation of the LDAEP by multiple neurochemical systems in addition to the serotonergic system.