Serotonin, noradrenaline and cognitive function: a preliminary investigation of the acute pharmacodynamic effects of a serotonin versus a serotonin and noradrenaline reuptake inhibitor

Effect of vortioxetine versus venlafaxine on cognitive functions in adults with major depressive disorder: A randomized-controlled trial

Background

Vortioxetine and venlafaxine are antidepressants which have shown established efficacy to treat major depressive disorder (MDD). There are no studies that compared them for their efficacy in cognitive symptoms of depression. The study aimed to compare the effect of vortioxetine and venlafaxine on the change in cognitive scores in adults with MDD.

Methods

The present study was an open-label, active-controlled parallel design randomized clinical trial. After randomization, baseline clinical evaluations by Montgomery-Asberg Depression Rating Scale (MADRS) and Social and Occupational Functioning Assessment Scale (SOFAS) were done and coding (subset of WAIS-IV), WCST, TMT, Stroop test, PGI memory were used to assess cognition in 100 unmedicated MDD patients. They were reassessed after eight weeks of monotherapy with vortioxetine or venlafaxine.

Results

Primary cognitive measure (coding score) was found to be significantly higher (Mean Difference = 0.680; 95% CI:.202 to 1.158; P = 0.006) in vortioxetine in comparison with venlafaxine. Stroop test scores (word score, color score, color-word score) were also found to be significantly higher with vortioxetine. In other cognitive measures (WCST scores: total trials, total errors score, total perseverative responses score, total perseverative errors scores; TMT-A and B scores), a significant decrease in scores with vortioxetine in comparison with venlafaxine were observed. A significant decrease in MADRS and increase in SOFAS scores were observed with vortioxetine in comparison with venlafaxine. Both the drugs alleviated the symptoms of depression but vortioxetine was better tolerated.

Conclusion

Our study findings suggest that improvement in cognitive scores is significantly higher with vortioxetine than venlafaxine over the eight weeks of monotherapy.

Clinical Trial registration number

CTRI/2020/07/026819 (Registered with Clinical Trials Registry- India).

The Correlation Between Mid-Brain Serotonin Transporter Availability and Intelligence Quotient in Healthy Volunteers

Purpose:

This study was performed to investigate the association between the mid-brain serotonin transporter (SERT) availability and intelligence quotient (IQ).

Methods:

One hundred and thirteen healthy participants, including 52 male and 61 female subjects, were recruited. We used SPECT with [123I]ADAM images to determine the SERT availability in the mid-brain, and measured the subjects’ IQ using the WAIS-R.

Results:

We found a significant positive correlation between the mid-brain SERT availability and the IQ of the participants. Even when controlling for age and sex, the significant association still existed.

Conclusion:

This result implied that the higher the SERT binding in the mid-brain, the better the IQ in healthy participants.

Three weeks of SSRI administration enhances the visual perceptual threshold - a randomized placebo-controlled study

RATIONALE

The serotonergic system has been repeatedly linked to visual attention in general, but the effects of selective serotonin reuptake inhibitor (SSRI) on specific components of visual attention remain unknown. Changes in distinct perceptual and cognitive processes are not readily evident in most attention paradigms.

OBJECTIVE

In this study, we isolate basic components of visual attention to investigate potential effects of longer-term SSRI administration on non-emotional aspects of visual attention in healthy males.

METHODS

In a randomized double-blind placebo-controlled design, 32 young healthy males were tested on multiple attentional parameters, before and after a 3-week SSRI intervention with fluoxetine (40 mg daily) or placebo. Data were modeled with a computational theory of visual attention to derive independent estimates of five distinct components of visual attention.

RESULTS

The SSRI intervention selectively and significantly lowered the threshold for conscious visual perception. Specifically, we demonstrate that this improvement does not stem from a general increase in the speed of visual processing, as previously suggested, but specifically from a change in the perceptual threshold.

CONCLUSIONS

The study provides a novel description of the attentional dynamics affected by SSRI, while supporting previous findings on attentional effects of SSRI. Furthermore, it accentuates the utility of employing accuracy-based measures of attentional performance when conducting psychopharmacological research.

The role of serotonin in cognitive function: evidence from recent studies and implications for understanding depression

BACKGROUND

Symptoms of cognitive impairment such as poor concentration, memory loss and difficulty with decision making are prevalent in patients with depression, but currently are not specific targets for treatment. However, patients can continue to demonstrate cognitive impairments even when apparently clinically recovered. Drugs that potentiate serotonin (5-HT) function, such as selective serotonin reuptake inhibitors (SSRIs), are the mainstay of treatment for depression. Nevertheless, our understanding of the effects of SSRIs and other conventional antidepressant therapy on cognitive function in healthy humans and depressed patients remains limited.

OBJECTIVE

The purpose of this article is to provide a concise overview for clinicians on the impact of pharmacological manipulation of 5-HT on cognitive function in healthy humans with additional reference to animal models where human data are lacking, particularly regarding specific 5-HT receptor subtype modulation.

FINDINGS

The most consistent observation following manipulation of serotonin levels in humans is that low extracellular 5-HT levels are associated with impaired memory consolidation. Preclinical data show that agonism and antagonism at specific 5-HT receptors can exert effects in animal models of cognition.

CONCLUSIONS

Larger, consistently designed studies are needed to understand the roles of 5-HT in cognition in healthy and depressed individuals. Efforts to target specific 5-HT receptors to improve cognitive outcomes are warranted.

A systematic review of amnestic and non-amnestic mild cognitive impairment induced by anticholinergic, antihistamine, GABAergic and opioid drugs

BACKGROUND

Mild cognitive deficits are experienced by 18% of community-dwelling older adults, many of whom do not progress to dementia. The effect of commonly used medication on subtle impairments in cognitive function may be under-recognized.

OBJECTIVE

The aim of the review was to examine the evidence attributing amnestic or non-amnestic cognitive impairment to the use of medication with anticholinergic, antihistamine, GABAergic or opioid effects.

METHODS

MEDLINE and EMBASE were searched for randomized, double-blind, placebo-controlled trials of adults without underlying central nervous system disorders who underwent detailed neuropsychological testing prior to and after oral administration of drugs affecting cholinergic, histaminergic, GABAergic or opioid receptor pathways. Seventy-eight studies were identified, reporting 162 trials testing medication from the four targeted drug classes. Two investigators independently appraised study quality and extracted relevant data on the occurrence of amnestic, non-amnestic or combined cognitive deficits induced by each drug class. Only trials using validated neuropsychological tests were included. Quality of the evidence for each drug class was assessed based on consistency of results across trials and the presence of a dose-response gradient.

RESULTS

In studies of short-, intermediate- and long-acting benzodiazepine drugs (n = 68 trials), these drugs consistently induced both amnestic and non-amnestic cognitive impairments, with evidence of a dose-response relationship. H(1)-antihistamine agents (n = 12) and tricyclic antidepressants (n = 15) induced non-amnestic deficits in attention and information processing. Non-benzodiazepine derivatives (n = 29) also produced combined deficits, but less consistently than benzodiazepine drugs. The evidence was inconclusive for the type of cognitive impairment induced by different bladder relaxant antimuscarinics (n = 9) as well as for narcotic agents (n = 5) and antipsychotics (n = 5). Among healthy volunteers >60 years of age, low doses of commonly used medications such as lorazepam 0.5 mg, oxybutynin immediate release 5 mg and oxycodone 10 mg produced combined deficits.

CONCLUSION

Non-amnestic mild cognitive deficits are consistently induced by first-generation antihistamines and tricyclic antidepressants, while benzodiazepines provoke combined amnestic and non-amnestic impairments. Risk-benefit considerations should be discussed with patients in order to enable an informed choice about drug discontinuation or substitution to potentially reverse cognitive adverse effects.

Cognitive efficacy of quetiapine in early-onset first-episode psychosis: a 12-week open label trial

Twenty-three adolescents with psychotic disorders, aged from 13 to 18 years, participated in a 12-week open label trial (17 adolescents completed the study) in order to examine the impact of quetiapine on clinical status and cognitive functions (encompassing processing speed, attention, short-term memory, long-term memory and executive function). An improvement in Clinical Global Impression and Positive and Negative Symptom Scale (P's ≤ 0.001) was observed. In addition, after controlling for amelioration of symptoms, a significant improvement was observed on one executive function (P = 0.044; Trail Making Part B). The remaining cognitive abilities showed stability. In addition, we observed an interaction between quetiapine doses (>300 mg/day or <300 mg/day) and time, where lower doses showed more improvement in verbal short-term memory (P = 0.048), inhibition abilities (P = 0.038) and positive symptoms (P = 0.020). The neuropsychological functioning of adolescents with psychotic disorders remained mainly stable after 12 weeks of treatment with quetiapine. However, lower doses seemed to have a better impact on two components of cognition (inhibition abilities and verbal short-term memory) and on positive symptoms.

Neurochemical enhancement of conscious error awareness

How the brain monitors ongoing behavior for performance errors is a central question of cognitive neuroscience. Diminished awareness of performance errors limits the extent to which humans engage in corrective behavior and has been linked to loss of insight in a number of psychiatric syndromes (e.g., attention deficit hyperactivity disorder, drug addiction). These conditions share alterations in monoamine signaling that may influence the neural mechanisms underlying error processing, but our understanding of the neurochemical drivers of these processes is limited. We conducted a randomized, double-blind, placebo-controlled, cross-over design of the influence of methylphenidate, atomoxetine, and citalopram on error awareness in 27 healthy participants. The error awareness task, a go/no-go response inhibition paradigm, was administered to assess the influence of monoaminergic agents on performance errors during fMRI data acquisition. A single dose of methylphenidate, but not atomoxetine or citalopram, significantly improved the ability of healthy volunteers to consciously detect performance errors. Furthermore, this behavioral effect was associated with a strengthening of activation differences in the dorsal anterior cingulate cortex and inferior parietal lobe during the methylphenidate condition for errors made with versus without awareness. Our results have implications for the understanding of the neurochemical underpinnings of performance monitoring and for the pharmacological treatment of a range of disparate clinical conditions that are marked by poor awareness of errors.

Evaluating the role of serotonin on neuropsychological function after breast cancer using acute tryptophan depletion

Although cognitive dysfunction is a prevalent and disruptive problem for many breast cancer survivors (BCSs), little research has examined its etiology. One potential mechanism that remains to be explored is serotonin. Serotonin has been implicated in normal and dysfunctional cognitive processes, and serotonin levels are significantly affected by estrogen withdrawal, a common side effect of breast cancer treatment. However, no study has evaluated serotonin's role on cognitive dysfunction in BCSs. The purpose of this study was to examine the role of serotonin in cognitive dysfunction in survivors by lowering central serotonin concentrations via acute tryptophan depletion (ATD). Based on previous research in noncancer populations, we hypothesized that alterations in central serotonin levels would induce cognitive dysfunction in these women controlling for confounding characteristics such as fluctuating mood and glucose levels. Secondarily, we explored whether genetic variations in serotonin genes would partly explain ATD. Participants included 20 female BCSs, posttreatment for nonmetastatic breast cancer, who received ATD or control in a double-blind, crossover design. Cognitive performance was measured at the 5-hr tryptophan/serotonin nadir on each test day using standardized neuropsychological tests. Specific impairment was noted in episodic memory (delayed recall) and motor speed during ATD versus control. ATD did not alter new learning (immediate recall), working memory, verbal fluency, or information processing speed. Findings suggest that serotonin may play a critical role in memory consolidation and motor functioning in BCSs.

Differential effects of escitalopram on attention: a placebo-controlled, double-blind cross-over study

RATIONALE

The role of serotonin (5-HT) in attention is not fully understood yet.

OBJECTIVE

We aimed to investigate whether attention is modulated after treatment with escitalopram, a selective serotonin reuptake inhibitor (SSRI).

METHODS

We administered 10 mg of escitalopram to 20 healthy subjects in a placebo-controlled, double-blind cross-over design for 1 day or to another 20 participants for a period of 7 days. Attention was assessed at time of plasma peak escitalopram concentration using the computerised Attention Network Test (ANT), which is a combined flanker and cued reaction time task.

RESULTS

The results showed differential effects of serotonergic manipulation on attention depending on sequence of intake. For the acute treatment, we found significant differences between escitalopram and placebo for all warning conditions dependent of sequence of intake: participants receiving escitalopram as first treatment showed significant slower reaction times in all warning conditions as compared with placebo while participants receiving escitalopram as second treatment showed significant faster reaction times as compared with placebo. For the sub-chronic treatment, we found significant differences between escitalopram and placebo depending on sequence of intake, but only for the flanker condition: participants receiving escitalopram first had significant slower reaction times in incongruent trials with escitalopram as compared with placebo while participants starting with placebo had significant shorter reaction times in incongruent trials with escitalopram.

CONCLUSIONS

Thus, the results showed a differential effect of escitalopram in cognition, especially in attention, and are discussed with regard to an interaction between serotonin and familiarity with the attention test.

The bright side of being blue: depression as an adaptation for analyzing complex problems

Depression is the primary emotional condition for which help is sought. Depressed people often report persistent rumination, which involves analysis, and complex social problems in their lives. Analysis is often a useful approach for solving complex problems, but it requires slow, sustained processing, so disruption would interfere with problem solving. The analytical rumination hypothesis proposes that depression is an evolved response to complex problems, whose function is to minimize disruption and sustain analysis of those problems by (a) giving the triggering problem prioritized access to processing resources, (b) reducing the desire to engage in distracting activities (anhedonia), and (c) producing psychomotor changes that reduce exposure to distracting stimuli. As processing resources are limited, sustained analysis of the triggering problem reduces the ability to concentrate on other things. The hypothesis is supported by evidence from many levels-genes, neurotransmitters and their receptors, neurophysiology, neuroanatomy, neuroenergetics, pharmacology, cognition, behavior, and efficacy of treatments. In addition, the hypothesis provides explanations for puzzling findings in the depression literature, challenges the belief that serotonin transmission is low in depression, and has implications for treatment.

Cognitive toxicity of pharmacotherapeutic agents used in social anxiety disorder

OBJECTIVE

To compare cognitive impairment of medications used in social anxiety disorder (SAD).

METHODS

Data from peer-reviewed publications (1975-2007) of controlled, crossover design, pharmacodynamic studies on SAD medications in healthy volunteers were analysed. The number of objective psychometrics for each drug/dose level at all time points after dosing, and of instances of statistically significant impairment of cognitive function, enabled calculation of drug-induced cognitive impairment. The magnitude of impairment between drugs was compared using proportional impairment ratios (PIRs).

RESULTS

Olanzapine, oxazepam, lorazepam and mianserin had twice the average cognitive toxicity of other treatments. Selective serotonin reuptake inhibitors (SSRIs) impaired cognition to a lesser extent than other pharmacological groupings. There was extensive intra-class variation: fluvoxamine (PIR = 0.08) possessed little detrimental cognitive activity, whereas sertraline (PIR = 5.33) caused impairment over five times the SSRI group average. Benzodiazepines caused noticeable cognitive impairment.

CONCLUSIONS

Substantial differences exist, both between and within therapeutic classes, in the behavioural toxicity of medications used for SAD.

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.

Plasma amitriptyline level after acute administration, and driving performance in healthy volunteers

AIMS

Amitriptyline triggers the impairment of cognitive and motor functions and has been confirmed to have harmful effects on driving performance. Although interindividual differences in plasma concentration may cause variations in driving performance, the relationship between plasma amitriptyline concentration and its effect on driving performance has not been completely elucidated. Thus, the aim of the present study was to assess the influence of individual pharmacokinetic differences on driving performance and cognitive functions.

METHODS

In this double-blinded study, 17 healthy male volunteers were given an acute, single, 25-mg dose of amitriptyline. The subjects were assigned three driving simulator tasks, three cognitive tasks, and the questionnaire of the Stanford Sleepiness Scale at the baseline and at 4 h after dosing. The plasma amitriptyline concentrations were measured on high-performance liquid chromatography.

RESULTS

A significant positive correlation was observed between the plasma amitriptyline concentration and road-tracking performance (r = 0.543, P < 0.05). There was no significant correlation between the plasma amitriptyline concentration and other driving performance, cognitive functions, and subjective somnolence.

CONCLUSIONS

Amitriptyline produces a concentration-related impairment on road-tracking performance. Therapeutic monitoring of amitriptyline would be useful for predicting the difficulties involved while driving.

The effects of acute treatment with paroxetine, amitriptyline, and placebo on driving performance and cognitive function in healthy Japanese subjects: a double-blind crossover trial

OBJECTIVE

To assess the effects of antidepressants on driving performance from a different methodological viewpoint in light of the recent traffic accidents.

METHODS

In this double-blinded, 3-way crossover trial, 17 healthy males received acute doses of 10 mg paroxetine, 25 mg amitriptyline, and placebo. The subjects were administered three driving tasks--road tracking, car following, and harsh braking--performed using a driving simulator and three cognitive tasks--Wisconsin Card Sorting Test, Continuous Performance Test, and N-back test at baseline and at 1 h and 4 h post-dosing. The Stanford Sleepiness Scale scores were also assessed.

RESULTS

At 4 h post-dosing, amitriptyline significantly impaired road-tracking and car-following performance, reduced driver vigilance, and caused subjective somnolence. Paroxetine impaired neither driving performance nor cognitive function.

CONCLUSIONS

Acute doses of amitriptyline significantly impaired driving performance in the context of driving on crowded urban roads at relatively low speeds. This setting is important with respect to skills necessary for daily driving and may be difficult to measure in actual driving tests. This simulator-based study replicated the results of previous studies and could be considered complementary to them. This method may enable easy and safe screening of the driving hazard potential of drugs.

Neurocognitive costs and benefits of psychotropic medications in older adults

Psychotropic medications are widely used in older adults and may cause neurocognitive deficits. Older adults are at increased risk of developing adverse effects because of age-related pharmacodynamic and pharmacokinetic changes. This article provides a comprehensive review of the undesirable, and at times beneficial, effects of psychotropic medications. The review covers a wide range of medications that impair executive function, memory, and attention, as well as a much smaller group of medications that lead to improved neurocognitive function. Some of the most commonly used psychotropic medications in older adults, namely, antidepressants, sedatives, and hypnotics, are among the drugs that most consistently lead to cognitive impairments. Medications with anticholinergic properties almost invariably lead to neurocognitive dysfunction, despite symptom improvement. The neurocognitive costs and benefits of psychiatric medications should be considered in the context of disease treatment in older adults.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

The effects of escitalopram on working memory and brain activity in healthy adults during performance of the n-back task

RATIONALE

Psychotropic medication affects cognition and brain function, making it a potential confounder in functional neuroimaging studies of psychiatric patients.

OBJECTIVE

To determine whether the sub-acute administration of an antidepressant (escitalopram) would induce differences in cognitive performance and associated brain function, which could be observed within the normal power of a functional imaging study.

MATERIALS AND METHODS

Healthy adults (N=10) received a short course of escitalopram (10 mg/day for 7 days). Participants performed a parametric working memory (WM) task during BOLD fMRI, both while medication-free and after medication. To control for order effects, the medication-free examination was completed by half the subjects before starting medication and by the other half at least one week after medication.

RESULTS

Escitalopram had no significant effect on WM accuracy or reaction time. Preliminary analysis of the imaging data revealed no significant (p(corrected)<0.05) differences in memory-load-dependent activation between conditions. However, small volume correction analysis of regions that were significant prior to correction for multiple comparisons highlighted between condition differences in regions likely to be susceptible to antidepressant effects (i.e. thalamus, anterior cingulate and inferior frontal gyrus).

CONCLUSIONS

These results suggest that the sub-acute administration of antidepressants in healthy controls does not affect cognitive or hemodynamic function in healthy adults to a magnitude greater than one standard deviation unit. Therefore, the confounding effect of antidepressants on signal intensity in imaging studies of medicated, depressed individuals may be limited.

Opposite effects of depression and antidepressants on processing speed and error rate

Depressions increase reaction times and antidepressant treatment decreases them. Is it possible to get information, how these two conditions affect the stimulus-response pathway? Therefore, auditory and visual, left-hand and right-hand, simple and choice reaction times were measured in 38 patients with depression and 30 healthy control subjects. From these data, the minimal reaction times and the error rates were calculated. In the first study, the reaction times and error rates of patients with depression were correlated with the antidepressant doses. In the second study, the differences between medicated, depressive patients and healthy control subjects were investigated. The result of the first study was that antidepressant doses correlated negatively with reaction times but positively with error rates. In the second study, the patients with depression showed increased reaction times but reduced error rates compared to healthy control subjects. The auditory tasks were more affected than the visual tasks and the minimal reaction times more than the median reaction times. Therefore, we concluded that depression and antidepressant treatment had opposite effects on reaction times and error rates. The findings in minimal reaction times and auditory tasks suggest a special involvement of early cortical auditory processing in depression and antidepressant treatment.

Differential effects of indoleamines on auditory choice reaction, selective attention, and pitch discrimination

The indoleamines serotonin and melatonin (MT) affected visual processing such as choice reaction. This study determined whether the indoleamines influence the processing of auditory stimuli. Serotonergic activity was increased using citalopram (CIT). We compared effects of single doses of 40 mg CIT, 1 mg MT, and placebo (randomized double-blind, cross-over design) in 18 healthy men. The applied tests assessed auditory choice reaction, selective attention, and serial discrimination using pitch variations as stimuli in each task. CIT reduced the performance in choice reaction and selective attention but not discrimination. MT tended to reduce selective attention and to improve discrimination. The findings suggest that indoleamines had different effects on distinct kinds of auditory processing. Serotonergic activation improved visual choice reaction, whereas the opposite effect was found in the auditory domain. We conclude that disorders and drugs affecting the indoleamines must be considered differentially in the auditory and the visual system.

Biomarkers for the effects of selective serotonin reuptake inhibitors (SSRIs) in healthy subjects

AIMS

Studies of novel centrally acting drugs in healthy volunteers are traditionally concerned with kinetics and tolerability, but useful information may also be obtained from biomarkers of clinical endpoints. This paper provides a systematic overview of CNS-tests used with SSRIs in healthy subjects. A useful biomarker should meet the following requirements: a consistent response across studies and drugs; a clear response of the biomarker to a therapeutic dose; a dose-response relationship; a plausible relationship between biomarker, pharmacology and pathogenesis.

METHODS

These criteria were applied to all individual tests found in studies of selective serotonin reuptake inhibitors (SSRIs), performed in healthy subjects since 1966, identified with a systematic MedLine search. Separate databases were created to evaluate the effects of single or multiple dose SSRI-studies, and for amitriptyline whenever the original report included this antidepressant as a positive control. Doses of the antidepressant were divided into high- and low-dose ranges, relative to a medium range of therapeutic doses. For each test, the drug effects were scored as statistically significant impairment/decrease (-), improvement/increase (+) or no change (=) relative to placebo.

RESULTS

56 single dose studies and 22 multiple dose studies were identified, investigating the effects of 13 different SSRIs on 171 variants of neuropsychological tests, which could be clustered into seven neuropsychological domains. Low single doses of SSRIs generally stimulated tests of attention and memory. High doses tended to impair visual/auditory and visuomotor systems and subjective performance, while showing an acceleration in motor function. The most pronounced effects were observed using tests that measure flicker discrimination (improvement at low doses: 75%, medium doses: 40%, high doses: 43% of studies); REM sleep (inconsistent decrease after medium doses, decrease in 83% of studies after high doses); and EEG recordings, predominantly in alpha (decrease in 60% and 43% of studies after low and medium doses, respectively) and in theta activity (increase in 43% and 33% of studies after medium and high doses, respectively). Amitriptyline generally impaired central nervous system (CNS) functions, which increased with doses. Multiple doses caused less pronounced effects on the reported tests. The most responsive tests to amitriptyline appeared to be EEG alpha and theta, and REM sleep duration.

CONCLUSIONS

SSRIs in healthy subjects appear to cause slight stimulating effects after low doses, which tend to diminish with dose. The most consistent effects were observed with flicker discrimination tests, EEG (alpha and beta bands), REM sleep duration, and subjective effects at higher doses. These effects are small compared with amitriptyline and other CNS-active drugs. Multiple dosing with SSRIs caused even fewer measurable differences from placebo, probably due to adaptive processes. SSRI-effects are best detected with a test battery that is sensitive to general CNS-stimulation, but such tests only comprise a very small portion of the close to 200 different methods that were found in current review.

Changes of motor drive, cortical arousal and perceived exertion following prolonged cycling to exhaustion

The aims of this study were to (1) quantify any central fatigue that occurs following prolonged dynamic exercise, i.e. reduced muscle force caused by impaired motor drive from the central nervous system and (2) determine whether decreased cortical arousal, assessed using critical flicker fusion threshold (CFF), occurs and is related to impaired exercise performance. Fifteen healthy men cycled at 70% VO2peak until exhaustion. The peak force of maximum voluntary isometric contractions (MVC) of the quadriceps muscle group was reduced by 30% at exhaustion. The voluntary activation ratio determined using superimposed tetanic stimulation fell from 0.99 to 0.86 at exhaustion. The central fatigue (%) at exhaustion was 33+/-12% (+/- SD) (assessed via the tetanus interpolation technique) and 54+/-32% (assessed via the relative decline of MVC and peak tetanic force) of the total fatigue. The MVC only partially recovered and central fatigue persisted at 30 min post-exercise. CFF increased from 39.2+/-2.3 to 41.8+/-3.5 Hz at exhaustion, but did not correlate with central fatigue. Every subject reached the highest rating of perceived exertion (RPE) at exhaustion of 20 on the Borg scale. The time to exhaustion was related to how quickly the RPE increased and to the ability to sustain exercise at very high RPE. These data suggest that with prolonged cycling: (1) there is considerable and a persistent form of central fatigue, (2) there is an increased level of cortical arousal, and (3) exhaustion is linked to very high subjective RPE.

Pleiotropic effect of the TPH A779C polymorphism on nicotine dependence and personality

Recent studies from molecular genetics have suggested an association between the tryptophan hydroxylase 1 (TPH1) gene and nicotine addiction indicating a dysfunction of the serotonergic (5-HT) system in smoking behavior. In a sample of 252 healthy subjects, a significant association between variations observed in nicotine dependence and the heterozygous AC-genotype of the TPH A779C polymorphism could be demonstrated. Moreover, the heterozygous genotype was significantly associated with a personality trait of neurotic aggression (indirect hostility, negativism), as measured by the Buss-Durkee-Hostility-Inventory (BDHI). The positive heterosis effects with respect to nicotine addiction and personality support the idea that the TPH1 gene exerts pleiotropic effects.

Serotonin Reuptake Inhibitors in Auditory Processing Disorders in Elderly Patients: Preliminary Results

OBJECTIVE/HYPOTHESIS

One mechanism associated with degeneration in the elderly is the decrease of neurotransmitters. In the central auditory pathway serotonin, can be found from cochlear nucleus to the auditory cortex, and it constitutes one of the most important neuromodulatory circuits in hearing processing. The present study analyzed the action of citalopram, a selective inhibitor of serotonin reuptake, in aged patients with normal to moderate sensorineural hearing loss (HL) and low performance on auditory processing.

STUDY DESIGN/METHOD

Prospective, double-blind, randomized, placebo-controlled study. Thirty-eight selected patients were randomly divided into two groups. Nineteen patients made up group A and received placebo for 60 days. Nineteen patients of Group B received 20 mg per day of citalopram for 60 days. Hearing evaluation was performed initially and after 60 days and included pure-tone audiometry, speech discrimination test (SDT), emittanciometry (acoustic impedance audiometry), identification of synthetic sentences with an ipsilateral competitive message (SSI/ICM), tests of pitch-pattern sequences (PPS), and the staggered spondaic words test (SSW).

RESULTS

Comparisons of tests of auditory processing pre- and posttreatment in each group showed a statistical improvement in performance on all tests in group B after 2 months of therapy. Comparisons pre- and posttreatment between groups showed that patients who received citalopram presented statistically significantly better results in the SSI/ICM test (P < .0001) after treatment. The same comparison in results for the PPS test and the SSW test revealed a tendency (P = .09 and 0.058, respectively) toward better performance in the group receiving citalopram.

CONCLUSION

These preliminary results suggest that the use of citalopram can have a positive impact on auditory processes in elderly patients with low performance in auditory process.

Does antidepressant therapy improve cognition in elderly depressed patients?

OBJECTIVES

To analyze the effects of antidepressants on cognitive functioning in elderly depression.

METHODS

Data were pooled for elderly participants with major depression from two double-blind 12-week studies (n = 444) comparing sertraline to fluoxetine and to nortriptyline. A cognitive battery was performed pre-treatment and post-treatment that included the Shopping List Task (SLT), which quantifies short-term and long-term memory storage and retrieval, and the Digit Symbol Substitution Test (DSST), which measures visual tracking, motor performance, and coding.

RESULTS

Older age, male gender, higher systolic blood pressure, and higher illness severity were associated with lower performance on specific cognitive measures at baseline. For the entire group, improved depression and a lower anticholinergic side effect (dry mouth and constipation) severity were associated with statistically significant improvement in the SLT and DSST. The correlations between improvements in depression and improvement in tested cognitive function were highest for sertraline followed by nortriptyline and then fluoxetine.

CONCLUSIONS

Acute improvement in depression is associated with cognitive improvement as measured by the SLT and DSST. Prospective studies are warranted to study the effects of potential differences among antidepressant therapies on long-term cognitive outcomes in geriatric depression.

The effects of acute tryptophan depletion on neuropsychological function

Serotonin (5-HT, 5-hydroxytryptamine) may have an important role in the maintenance of normal neuropsychological functioning. The method of acute tryptophan depletion (ATD) provides a pharmacological challenge by which central 5-HT levels can be temporarily decreased and effects on learning, memory and mood examined. Twenty healthy male volunteers were recruited to take part in this within-subject, double-blind, crossover study. Neuropsychological function was evaluated 4-6 h after ingestion of a control or 52 g tryptophan (TRP) depleting amino-acid drink. ATD significantly lowered levels of plasma total and free TRP (p < 0.001), but this did not affect mood or performance on tests of verbal and visuo-spatial learning and memory, attention or executive function. These results contradict previous findings; however, the degree of disruption of central 5-HT levels resulting from the use of the 52 g amino-acid protocol may be an important factor in explaining the lack of effect. By utilizing more specific probes of individual 5-HT receptor subtypes, future studies can fully explore the role of 5-HT in neuropsychological functioning and may elucidate the factors determining vulnerability to the effects of serotonergic dysfunction.

Effects of acute tryptophan depletion on executive function in healthy male volunteers

BACKGROUND

Neurocognitive impairment is frequently described in a number of psychiatric disorders and may be a direct consequence of serotonergic dysfunction. As impairments in executive functions are some of the most frequently described, the purpose of this study was to examine the performance of normal volunteers on a range of executive tasks following a transient reduction of central serotonin (5-HT) levels using the method of acute tryptophan depletion (ATD).

METHODS

Fifteen healthy male subjects participated in a within-subject, double-blind, counterbalanced crossover study. ATD was induced by ingestion of a 100 g amino-acid drink. Executive function was evaluated using the Wisconsin Card Sorting Test, Stroop, Verbal Fluency and Trail Making. Visual analogue scales were administered to assess mood.

RESULTS

Plasma free and total tryptophan concentrations were significantly reduced by the depleting drink (P < 0.001). ATD selectively improved motor speed/ attention on the Trails A test (P = 0.027), with no effect on subjective ratings of mood. Interaction effects between drink and the order of drink administration were observed on most neurocognitive tests.

CONCLUSIONS

The improvement in simple motor speed/ attention following ATD is in keeping with the ascribed role of 5-HT in the cortex, however performance on tests of executive function is not robustly altered. The presence of interaction effects on most tasks suggests that subtle changes may occur but are masked, possibly by simple learning effects, in the context of a crossover design. This has implications for the design of future studies, particularly those examining executive functions.

Treatment of memory disorders in epilepsy

Impaired memory is a common and often debilitating complaint in patients with epilepsy. Overlapping variables such as seizure control, attentional dysfunction, and mood disorders further complicate diagnosis and management. Direct therapy for memory deficits associated with epilepsy is rarely attempted. The varied pharmacological (AED selection, cholinesterase inhibitors, stimulants, antidepressants, and herbal supplements) and nonpharmacological approaches to cognitive remediation in epilepsy patients are reviewed.

Critical flicker frequency for quantification of low-grade hepatic encephalopathy

Subclinical hepatic encephalopathy (SHE) is currently diagnosed by psychometric tests or neurophysiologic techniques. In view of its sociomedical relevance, simple and reproducible tests for routine diagnosis are required. This study evaluates critical flicker-frequency thresholds for quantification of low-grade hepatic encephalopathy. A total of 115 patients (92 with cirrhosis, 23 controls) were analyzed for HE severity (mental state, computerized psychometric tests), and the threshold frequencies at which light pulses are perceived as fused (fusion frequency) or flickering light (critical flicker frequency [CFF]). CFF was a highly reproducible parameter with little age, day-time, and training dependency. CFFs in cirrhotic patients without HE (HE 0) were not different from those found in noncirrhotic controls. Significantly lower CFFs were found in cirrhotic patients with subclinical or manifest HE, and the various HE groups separated from each other at a high level of significance (P <.01). By using a CFF cut-off value of 39 Hz, a 100% separation of patients with manifest HE from noncirrhotic controls and HE 0 cirrhotic patients was obtained. SHE patients separated from HE 0 cirrhotic patients with high sensitivity (55%) and specificity (100%). The HE severity-dependent differences were found in both, alcoholic and posthepatitic cirrhosis. Statistically significant correlations (P <.01) were found between CFFs and individual psychometric tests. Aggravation of preexisting HE after transjugular intrahepatic portosystemic stent shunt (TIPS) implantation was accompanied by a corresponding decrease of CFF, whereas improvement of HE increased CFF. In conclusion, CFF is a sensitive, simple, and reliable parameter for quantification of low-grade HE severity in cirrhotic patients and may be useful for the detection and monitoring of SHE.

A preliminary investigation on the acute pharmacodynamic effects of hypericum on cognitive and psychomotor performance

Research has indicated that the herb St John's Wort (Hypericum perforatum) has comparable efficacy to conventional antidepressants in the treatment of depression. Although clinical studies have demonstrated that hypericum has a superior side-effect profile compared to standard antidepressants, no study has directly compared the cognitive and psychomotor effects of hypericum with those of other antidepressants. The aim of the current study was to examine the acute effects of hypericum on cognitive and psychomotor function, and to compare its effects with those of amitriptyline. Thirteen healthy volunteers received an acute dose of placebo, amitriptyline (25 mg, positive control) or hypericum (900 mg or 1800 mg) in a double-blind, placebo-controlled design. Cognitive and psychomotor tests and subjective measures of sedation were administered before and 1, 2 and 4 hours after drug administration. Amitriptyline impaired performance on a battery of psychological tests, which included critical flicker fusion (CFF), choice reaction time (CRT), digit symbol substitution test (DSST), profile of mood states (POMS) and the line analogue rating scale (LARS), while hypericum had neutral effects on performance in these tests. However, hypericum induced a dose-related impairment on DSST. Current findings suggest that clinical doses of hypericum do not impair attention, sensorimotor function or information processing.

Venlafaxine extended-release: a review of its use in the management of major depression

Venlafaxine inhibits presynaptic reuptake of serotonin (5-hydroxytryptamine; 5-HT) and noradrenaline (norepinephrine). Venlafaxine extended-release (XR) has been investigated in patients with major depression and in patients with major depression with associated anxiety in randomised, double-blind, multicentre trials. A therapeutic response in patients with major depression was evident at week 2 of treatment with venlafaxine XR 75 to 225 mg/day in a placebo-controlled trial. By week 4, the drug was significantly more effective than placebo at reducing both the Hamilton Rating Scale for Depression (HAM-D) and Montgomery-Asberg Depression Rating Scale (MADRS) total scores. Furthermore, cumulative relapse rates were lower among recipients of venlafaxine XR 75 to 225 mg/day than placebo recipients after 3 and 6 months in another trial. Venlafaxine XR 75 to 150 mg/day was significantly more effective than venlafaxine immediate-release (IR) 75 to 150 mg/day or placebo during a 12-week study. Reductions from baseline in all 4 efficacy parameters (HAM-D, MADRS, HAM-D depressed mood item and the Clinical Global Impression Severity of Illness scale) were significantly higher among patients treated with venlafaxine XR than venlafaxine IR or placebo at week 12 (using an intent-to-treat, last observation carried forward analysis). Venlafaxine XR 75 to 225 mg/day was compared with fluoxetine 20 to 60 mg/day in patients with major depression in 2 randomised, double-blind, placebo-controlled, multicentre studies. Remission rates were significantly in favour of venlafaxine XR recipients in one study: 37, 22 and 18% of patients treated with venlafaxine XR, fluoxetine or placebo, respectively, achieved full remission (HAM-D total score < or = 7 at end-point). In the other trial, venlafaxine XR and fluoxetine had comparable efficacy in reducing HAM-D and Hamilton Rating Scale for Anxiety (HAM-A) total scores compared with placebo. However, the HAM-A response rate was significantly higher with venlafaxine XR than with fluoxetine at week 12. In a comparative study involving paroxetine, reductions from baseline in HAM-D and MADRS total scores in patients given venlafaxine XR 75 mg/day or paroxetine 20 mg/day for 12 weeks were significant, but no significant differences between treatment groups were evident. Discontinuation rates because of unsatisfactory clinical response were similar among patients treated with venlafaxine XR, fluoxetine or paroxetine. Adverse events pertaining to the digestive (nausea, dry mouth), nervous (dizziness, somnolence, insomnia) and urogenital (abnormal ejaculation) systems as well as sweating were the most frequently reported adverse events during 8 to 12 weeks of treatment in 3 randomised, double-blind, multicentre trials. Comparative studies with fluoxetine and paroxetine demonstrated a similar adverse event profile to venlafaxine XR.

CONCLUSION

Venlafaxine XR has shown efficacy in the treatment of major depression and was at least as effective as fluoxetine or paroxetine and more effective than venlafaxine IR. Furthermore, it is effective at reducing symptoms of anxiety in depressed patients. The incidence of adverse events in recipients of venlafaxine XR is similar to that in patients receiving treatment with well established selective serotonin reuptake inhibitors. As an effective and well tolerated antidepressant, venlafaxine XR should be considered as a first-line pharmacological treatment in patients with major depression.