Models of memory dysfunction? A comparison of the effects of scopolamine and lorazepam on memory, psychomotor performance and mood

An association between resting state EEG parameters and the severity of topiramate-related cognitive impairment

INTRODUCTION

Many commonly prescribed drugs cause cognitive deficits. We investigated whether parameters of the resting-state electroencephalogram (rsEEG) are related to the severity of cognitive impairments associated with administration of the antiseizure drug topiramate (TPM) and the benzodiazepine lorazepam (LZP).

METHODS

We conducted a double-blind, randomized, placebo-controlled crossover study. After a baseline visit, subjects completed three sessions at which they received either a single dose of TPM, LZP, or placebo. Four-hours after drug administration and at baseline, subjects completed a working memory (WM) task after their rsEEG was recorded. After quantifying drug-related behavioral (WM accuracy (ACC)/reaction time (RT)) and electrophysiological (alpha, theta, beta (1,2), gamma power) change for each subject, we constructed drug-specific mixed effects models of change for each WM and EEG measure. Regression models were constructed to characterize the relationship between baseline rsEEG measures and drug-related performance changes.

RESULTS

Linear mixed effects models showed theta power increases in response to TPM administration. The results of the regression models revealed a number of robust relationships between baseline rsEEG parameters and TPM-related, but not LZP-related, WM impairment.

CONCLUSIONS

We showed for the first time that parameters of the rsEEG are associated with the severity of TPM-related WM deficits; this suggests that rsEEG measures may have novel clinical applications in the future.

Memory impairment following intentional self-poisoning with benzodiazepines: Should we pay more attention to attention?

STUDY HYPOTHESIS

In cases where patients attempt suicide through intentional self-poisoning, they often ingest drugs such as benzodiazepines that alter the central nervous system and memory. This is problematic, given that experts recommend the recovery of a patient's cognitive capacity before any psychiatric assessment is conducted. A previous pilot study by our group showed that cognitive tests focusing on attention are the most valuable when it comes to determining whether sufficient cognitive recovery has occurred to ensure that patients will remember the assessment after intentional self-poisoning with benzodiazepines. The main aim of our study was to determine cognitive predictors of the recall of the psychiatric assessment after a suicide attempt. The second aim was to determine the threshold for episodic memory.

METHODS

We recruited 97 patients admitted for intentional self-poisoning. At the time of the psychiatric assessments, we quantified plasma benzodiazepine levels and performed a cognitive assessment. We then used a linear regression model to identify the associations in a control and a benzodiazepine group between cognitive functions and episodic memory scores obtained 24 hours after psychiatric assessment.

RESULTS

Our model accounted for 28% and 37%, respectively, of the variance in memory in the control and benzodiazepine groups. The most significant correlations were found for the Wechsler Adult Intelligence Scale coding test in both groups. In the control group, tests such as visual and verbal memory were also associated with recall.

CONCLUSIONS

Benzodiazepines particularly affect memory by impairing what is remembered of attentional tests. These are, however, the most suitable cognitive tests for predicting recall of the memory assessment.

Patient emergency assessment following deliberate self-poisoning with benzodiazepines: Can cognitive markers predict recall of the psychiatric interview? A pilot study

STUDY HYPOTHESIS

In cases of deliberate self-poisoning (DSP), patients often ingest benzodiazepines (BZDs), known to alter memory. Experts recommend recovery of the patient's cognitive capacity before psychiatric assessment. Unfortunately, there is no validated tool in common practice to assess whether sufficient cognitive recovery has occurred after DSP with BZDs to ensure patient memory of the assessment.

OBJECTIVE

The aim of the study was to identify cognitive functions and markers which predict preserved memory of the mental health care plan proposed at the emergency department after DSP.

METHODS

We recruited patients admitted for DSP with BZDs and control patients. At the time of the psychiatric assessment, we performed cognitive tests and we studied the relationship between these tests and the scores of a memory test performed 24 h after.

RESULTS

In comparison with the control group, we found memory impairment in the BZD group. We found significant impairment on the Trail Making Test A (TMT A) in the BZD group in comparison with the control group, while TMT A and Wechsler Adult Intelligence Scale (WAIS) Coding test scores were significantly correlated with memory scores.

CONCLUSIONS

Attentional functions tested by WAIS Coding test and TMT A were correlated with memory score. It could be profitable to assess it in clinical practice prior to a psychiatric interview.

A Distress Protocol for Respiratory Emergencies in Terminally Ill Patients With Lung Cancer or Chronic Obstructive Pulmonary Disease

A combination of opioid, midazolam, and scopolamine (that we call "distress protocol" [DP]) is used to induce transient sedation when emergencies occur in palliative care. We wished to describe the prescription and administration of DP in terminally ill patients with either lung cancer or chronic obstructive pulmonary disease (COPD). In a retrospective study, 96 of 100 patients with cancer and 85 of 100 patients with COPD had a DP prescribed. Thirty patients with cancer and 29 with COPD received at least 1 DP. All patients receiving a DP for an appropriate indication were sedated within 30 minutes. There was no difference in survival from DP administration among patients who received it and those who did not.

Blockade of muscarinic receptors impairs the retrieval of well-trained memory

Acetylcholine (ACh) is known to play an important role in memory functions, and its deficit has been proposed to cause the cognitive decline associated with advanced age and Alzheimer's disease (the cholinergic hypothesis). Although many studies have tested the cholinergic hypothesis for recently acquired memory, only a few have investigated the role of ACh in the retrieval process of well-trained cognitive memory, which describes the memory established from repetition and daily routine. To examine this point, we trained rats to perform a two-alternative forced-choice visual detection task. Each trial was started by having the rats pull upward a central-lever, which triggered the presentation of a visual stimulus to the right or left side of the display monitor, and then pulling upward a stimulus-relevant choice-lever located on both sides. Rats learned the task within 10 days, and the task training was continued for a month. Task performance was measured with or without systemic administration of a muscarinic ACh receptor (mAChR) antagonist, scopolamine (SCOP), prior to the test. After 30 min of SCOP administration, rats stopped manipulating any lever even though they explored the lever and surrounding environment, suggesting a loss of the task-related associative memory. Three hours later, rats were recovered to complete the trial, but the rats selected the levers irrespective of the visual stimulus, suggesting they remembered a series of lever-manipulations in association with a reward, but not association between the reward and visual stimulation. Furthermore, an m1-AChR, but not nicotinic AChR antagonist caused a similar deficit in the task execution. SCOP neither interfered with locomotor activity nor drinking behavior, while it influenced anxiety. These results suggest that the activation of mAChRs at basal ACh levels is essential for the recall of well-trained cognitive memory.

Acute effects of donepezil in healthy young adults underline the fractionation of executive functioning

The cholinergic system is involved in the modulation of both bottom-up and top-down attentional control. Top-down attention engages multiple executive control processes, but few studies have investigated whether all or selective elements of executive functions are modulated by the cholinergic system. To investigate the acute effects of the pro-cholinergic donepezil in young, healthy volunteers on distinct components of executive functions we conducted a double-blind, placebo-controlled, independent-groups design study including 42 young healthy male participants who were randomly assigned to one of three oral treatments: glucose (placebo), donepezil 5 mg or donepezil 7.5 mg. The test battery included measures of different executive components (shifting, updating, inhibition, dual-task performance, planning, access to long-term memory), tasks that evaluated arousal/vigilance/visuomotor performance, as well as functioning of working memory subsidiary systems. Donepezil improved sustained attention, reaction times, dual-task performance and the executive component of digit span. The positive effects in these executive tasks did not correlate with arousal/visuomotor/vigilance measures. Among the various executive domains investigated donepezil selectively increased dual-task performance in a manner that could not be ascribed to improvement in arousal/vigilance/visuomotor performance nor working memory slave systems. Other executive tasks that rely heavily on visuospatial processing may also be modulated by the cholinergic system.

Pharmacokinetic-pharmacodynamic relationships of central nervous system effects of scopolamine in healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• The cholinergic system is important for different central nervous system functions, including memory, learning and attention. Scopolamine, a centrally active muscarinic antagonist, has been used to model dementia and to demonstrate the pharmacological effects of cholinergic drugs, but for most effects the concentration-effect relationships are unknown.

WHAT THIS STUDY ADDS

• We determined the pharmacokinetic-pharmacodynamic relationships of scopolamine using a multidimensional central nervous system test battery in a large group of healthy volunteers. The results suggested there are various functional cholinergic systems with different pharmacological characteristics, which can be used to study the effects of drugs that directly or indirectly modify cholinergic systems. The design of such studies should take the different concentration-effect relationships into account. AIM(S) Although scopolamine is a frequently used memory impairment model, the relationships between exposure and corresponding central nervous system (CNS) effects are mostly unknown. The aim of our study was to characterize these using pharmacokinetic-pharmacodynamic (PK-PD) modelling.

METHODS

In two double-blind, placebo-controlled, four-way crossover studies, 0.5-mg scopolamine was administered i.v. to 90 healthy male subjects. PK and PD/safety measures were monitored pre-dose and up to 8.5 h after administration. PK-PD relationships were modelled using non-linear mixed-effect modelling.

RESULTS

Most PD responses following scopolamine administration in 85 subjects differed significantly from placebo. As PD measures lagged behind the plasma PK profile, PK-PD relationships were modelled using an effect compartment and arbitrarily categorized according to their equilibration half-lives (t(1/2) k(eo) ; hysteresis measure). t(1/2) k(eo) for heart rate was 17 min, saccadic eye movements and adaptive tracking 1-1.5 h, body sway, smooth pursuit, visual analogue scales alertness and psychedelic 2.5-3.5 h, pupil size, finger tapping and visual analogue scales feeling high more than 8 h.

CONCLUSIONS

Scopolamine affected different CNS functions in a concentration-dependent manner, which based on their distinct PK-PD characteristics seemed to reflect multiple distinct functional pathways of the cholinergic system. All PD effects showed considerable albeit variable delays compared with plasma concentrations. The t(1/2) k(eo) of the central effects was longer than of the peripheral effects on heart rate, which at least partly reflects the long CNS retention of scopolamine, but possibly also the triggering of independent secondary mechanisms. PK-PD analysis can optimize scopolamine administration regimens for future research and give insight into the physiology and pharmacology of human cholinergic systems.

Cognitive enhancement following acute losartan in normotensive young adults

RATIONALE

Losartan, an angiotensin II receptor antagonist (AIIA), is an antihypertensive that has previously been suggested to have cognitive-enhancing potential for older adults. The objective indices for such effects are equivocal, however, and if these drugs do offer dual advantages of hypertension control plus cognitive-enhancing potential, there exists a clear need to establish this directly.

OBJECTIVES

This work examines the potential of losartan administered as a single dose to healthy young adults to improve cognitive performance alone or to reverse scopolamine-induced cognitive decrements.

METHODS

In two placebo-controlled, double-blind studies, participants completed a cognitive test battery once before and once after drug absorption. In experiment 1, participants were randomly allocated to receive placebo, losartan 50 mg or losartan 100 mg. In experiment 2, participants were randomly allocated to one of four treatment groups: placebo/placebo, placebo/scopolamine, losartan/scopolamine and losartan/placebo (50 mg losartan p.o. and 1.2 mg scopolamine hydrochloride p.o.).

RESULTS

Losartan 50 mg improved performance on a task of prospective memory when administered alone and reversed the detrimental effects of scopolamine both in a standard lexical decision paradigm (p < 0.01) and when the task incorporated a prospective memory component (p < 0.008).

CONCLUSIONS

The findings highlight a cognitive-enhancing potential for losartan on compromised cognitive systems and emphasise the potential of AIIAs to produce benefits over and above hypertension control.

Cholinergic receptor subtypes and their role in cognition, emotion, and vigilance control: an overview of preclinical and clinical findings

RATIONALE

The cholinergic system has long been linked to cognitive processes. Two main classes of acetylcholine (ACh) receptors exist in the human brain, namely muscarinic and nicotinic receptors, of which several subtypes occur.

OBJECTIVES

This review seeks to provide an overview of previous findings on the influence of cholinergic receptor manipulations on cognition in animals and humans, with particular emphasis on the role of selected cholinergic receptor subtypes. Furthermore, the involvement of these receptor subtypes in the regulation of emotion and brain electrical activity as measured by electroencephalography (EEG) shall be addressed since these domains are considered to be important modulators of cognitive functioning.

RESULTS

In regard to cognition, the muscarinic receptor subtypes have been implicated mainly in memory functions, but have also been linked to attentional processes. The nicotinic α7 receptor subtype is involved in working memory, whereas the α4β2* subtype has been linked to tests of attention. Both muscarinic and nicotinic cholinergic mechanisms play a role in modulating brain electrical activity. Nicotinic receptors have been strongly associated with the modulation of depression and anxiety.

CONCLUSIONS

Cholinergic receptor manipulations have an effect on cognition, emotion, and brain electrical activity as measured by EEG. Changes in cognition can result from direct cholinergic receptor manipulation or from cholinergically induced changes in vigilance or affective state.

The effects of the glycine reuptake inhibitor R213129 on the central nervous system and on scopolamine-induced impairments in psychomotor and cognitive function in healthy subjects

In this study the effects of R213129, a selective glycine transporter 1 inhibitor, on central nervous system function were investigated in healthy males in the absence and presence of scopolamine. This was a double-blind, placebo-controlled, 4-period crossover ascending dose study evaluating the following endpoints: body sway, saccadic and smooth pursuit eye movements, pupillometry, electroencephalography, visual analogue scales for alertness, mood, calmness and psychedelic effects, adaptive tracking, finger tapping, Visual and Verbal Learning Task, Stroop test, hormone levels and pharmacokinetics. R213129 dose levels were selected based on exposure levels that blocked the GlyT1 sites >50% in preclinical experiments. Forty-three of the 45 included subjects completed the study. Scopolamine significantly affected almost every central nervous system parameter measured in this study. R213129 alone compared with placebo did not elicit pharmacodynamic changes. R213129 had some small effects on scopolamine-induced central nervous system impairments. Scopolamine-induced finger tapping impairment was further enhanced by 3 mg R213129 with 2.0 taps/10 seconds (95% CI -4.0, -0.1), electroencephalography alpha power was increased by 10 mg R213129 with respectively 12.9% (0.7, 26.6%), scopolamine-induced impairment of the Stroop test was partly reversed by 10 mg R213129 with 59 milliseconds (-110, -7). Scopolamine produced robust and consistent effects in psychomotor and cognitive function in healthy volunteers. The most logical reason for the lack of R213129 effects seems to be that the central nervous system concentrations were too low. The effects of higher doses in healthy volunteers and the clinical efficacy in patients remain to be established.

Dose effects of triazolam and alcohol on cognitive performance in healthy volunteers

Benzodiazepines and alcohol are widely used psychoactive substances that have performance-impairing effects. Research suggests that the impairment profiles for benzodiazepines and alcohol differ, although few cognitive psychopharmacological studies have directly compared these drugs. This double-blind, double-dummy, placebo-controlled, repeated measures study directly compared the acute dose effects of triazolam (0.125, 0.25 mg/70 kg) and alcohol (0.40, 0.80 g/kg) in 20 social drinkers. At doses that produced comparable psychomotor impairment, triazolam was more likely to impair several objective measures of cognitive performance (e.g., episodic memory, divided attention) and to slow performance across several measures. However, only alcohol impaired accuracy on the digit symbol substitution and semantic memory tasks. In addition to objective measures, both drugs impaired awareness of performance impairments (i.e., metacognition) such that participants overestimated impairment, and the magnitude of this effect was generally larger for alcohol. Only triazolam impaired other measures of metacognition (e.g., error detection on a choice reaction time task). Future research might examine the clinical implications of the performance impairments reported here given the widespread use of benzodiazepines and alcohol.

Nicotinic antagonist effects on functional attention networks

Cholinergic neurotransmission has been implicated in memory and attention. We investigated the effect of the non-competitive nicotinic antagonist mecamylamine on three components of attention processes (i.e. alerting, orienting and executive control) in 12 healthy male subjects whilst performing the Attention Network Task (ANT) in a magnetic resonance imaging (MRI) scanner. Participants received 15 mg mecamylamine in a single blind and placebo- controlled randomized procedure 90 min prior to obtaining functional MRI data. Our results confirm previous reports of beneficial effects of cueing (alerting and orienting) and detrimental effects of conflict (executive control) on reaction times when performing the ANT. The functional MRI data confirmed distinct neural networks associated with each of the three attention components. Alerting was associated with increased left temporal lobe activation while orienting increased bilateral prefrontal, right precuneus and left caudate activation. Executive control activated anterior cingulate and precuneus. Mecamylamine slowed overall response time and down-regulated brain activation associated with orienting and to some extent brain activation associated with executive control when compared to placebo. These findings are consistent with nicotinic modulation of orienting attention by cueing and executive control when responding to conflicting information. The latter nicotine antagonist effect may be mediated via cholinergic modulation of dopamine neurotransmission in mesolimbic pathways.

The use of effect sizes to characterize the nature of cognitive change in psychopharmacological studies: an example with scopolamine

Drug induced cognitive change is generally investigated using small sample sizes. In terms of null hypothesis significance testing (NHST) this can render a meaningful change non-significant, as a result of insufficient power in the statistical model. NHST leads to 'all or none' thinking, where a non-significant result is interpreted as an absence of change. An effect size calculation indicates the magnitude of change which has occurred post-intervention, and therefore whether a significant result is meaningful. We used a scopolamine challenge to demonstrate the usefulness of effect sizes. The aim of the study was to determine how effect sizes could describe the cognitive changes that occur following administration of subcutaneous scopolamine (s.c. scopolamine). Twenty four healthy young males (M = 32.6, sd = 4.5 years) were administered placebo and 0.2 mg, 0.4 mg & 0.6 mg of s.c. scopolamine using a 4-way crossover design. Memory, learning, psychomotor function, attention and executive function were assessed. Scopolamine significantly impaired performance on all tasks in a dose and time related manner. These results demonstrate the functionality of change scores to draw comparisons between different times and doses. This methodology overcomes the limitations of comparisons between studies using different tasks, doses and time at which cognitive functions are measured.

Effects of lorazepam on deductive reasoning

RATIONALE

Benzodiazepines slow reasoning performance, but it is still unknown which phase of reasoning is affected and whether this effect is present for different types of relations between entities in reasoning problems.

OBJECTIVES

We investigated which phases of deductive reasoning are affected by lorazepam and whether this effect varies according to the type of relations in deductive reasoning problems.

METHODS

This was a double-blind, crossover design study of acute oral doses of lorazepam (2 mg) and placebo, using young healthy volunteers. We focused on response delay of three separable phases of deductive reasoning and matched working memory tasks (that involved only maintenance of information) the premise processing phase, the premise integration phase, and the validation phase, in which reasoners decide whether a conclusion logically follows from the premises (reasoning task) or is identical to one of the premises (maintenance task). Type of relations in the premises was also manipulated. We employed material that was difficult to envisage visually and visuospatially ("subiconic") and material easy to envisage visually or visuospatially.

RESULTS

Lorazepam slowed response as memory load increased, irrespective of type of relations. It also specifically slowed validation in reasoning problems with visual relations, an effect that disappeared after subtraction of maintenance scores, and increased validation time in problems with subiconic relations, which remained after this subtraction.

CONCLUSION

Acute lorazepam administration affected reasoning in two ways: it slowed processing nonspecifically when working memory demands increased and augmented validation time depending on the difficulty in generating and/or manipulating mental representations by the central executive.

Differential effects of scopolamine and lorazepam on working memory maintenance versus manipulation processes

Between-study comparisons of benzodiazepine and anticholinergic drugs on working memory suggest that anticholinergics may produce greater impairment in maintenance processes, whereas benzodiazepines may produce greater impairment in manipulation processes. This study directly compared acute effects ofthe benzodiazepine lorazepam (1.0 and 2.0 mg/70 kg, orally administered) and the anticholinergic scopolamine (0.25 and 0.50 mg/70 kg, subcutaneously administered) on working memory maintenance (storage and rehearsal) and manipulation processes in a placebo-controlled, double-dummy, double-blind, crossover design in 20 healthy volunteers. Using a modified Sternberg paradigm, storage, rehearsal, and manipulation processes were parametrically manipulated by varying memory load, delay between stimulus presentation and test, and number of operations performed on the letter strings, respectively, while controlling for drug effects on nonmemory processes. As predicted, the results suggested greater impairment in maintenance processes (rehearsal) with scopolamine than with lorazepam and greater impairment in manipulation processes with lorazepam than with scopolamine. In addition, the results suggested greater overall slowing of working memory processes with lorazepam.

Segregating two inhibitory circuits in human motor cortex at the level of GABAA receptor subtypes: a TMS study

OBJECTIVE

To investigate if different interneuronal circuits in human motor cortex mediate inhibition through different subtypes of the gamma-aminobutyric acid A receptor (GABAAR).

METHODS

Two distinct forms of motor cortical inhibition were measured in 10 healthy subjects by established transcranial magnetic stimulation (TMS) protocols: short interval intracortical inhibition (SICI) and short latency afferent inhibition (SAI). Their modification by a single oral dose of three different positive GABAAR modulators (20 mg of diazepam, 2.5 mg of lorazepam and 10 mg of zolpidem) with different affinity profiles at the various alpha-subunit bearing subtypes of the GABAAR (diazepam: non-selective, lorazepam: unknown, zolpidem: 10-fold higher affinity to alpha1- than alpha2- or alpha3-subunit bearing GABAARs, no affinity to alpha5-subunits) was tested in a randomized crossover design. In addition, the sedative drug effects were recorded by a visual analogue scale.

RESULTS

Diazepam and lorazepam increased SICI, whereas zolpidem did not change SICI. In contrast, diazepam had no effect on SAI, whereas lorazepam and zolpidem decreased SAI. The sedative effects were not different between drugs.

CONCLUSIONS

The dissociating patterns of drug modification of SICI versus SAI strongly suggest that different GABAAR subtypes are involved in SICI and SAI.

SIGNIFICANCE

We provide evidence, for the first time, for a dissociation of effects of diazepam and zolpidem on SAI and confirm the previously reported differential effect of zolpidem and of diazepam and lorazepam on SICI. The differential effects of the three benzodiazepines on SAI and SICI suggest that neuronal circuits in human motor cortex that mediate inhibition through different GABAAR subtypes can be segregated by TMS.

The role of sedation tests in identifying sedative drug effects in healthy volunteers and their power to dissociate sedative-related impairments from memory dysfunctions

The study investigated whether four specified drugs would show similar patterns on tests considered to measure sedation. In addition, their drug-effect patterns on sedation and memory performance were compared to determine whether the sedative effects could be differentiated from the memory effects. Two double-blind, placebo-controlled, crossover studies, each with 16 healthy volunteers, were performed, one testing lorazepam (2.5 mg) and mirtazapine (15 mg) and the other olanzapine (10 mg) and haloperidol (2.5 mg). Subjective sedation was assessed by means of visual analogue scales (VAS) and objective sedation using a simple-reaction-time (SRT) task and a choice-reaction-time (CRT) task, code substitution (symbol digit substitution test (SDST)) and the peak velocity of saccadic eye movements (SEM). A verbal memory test (VMT) was administered to evaluate memory capacity. Apart from haloperidol, all drugs proved to impair performance on all five sedation indices. Contrary to the VAS, the objective measures yielded different response profiles. Two types of drug-effect patterns emerged: one for greater impairments in response speed (SRT, SEM) and one for greater impairments in information processing (CRT, SDST). Lorazepam and olanzapine impeded memory performance, whereas mirtazapine did not. With the use of standardized scores it proved possible to differentiate between the size of the effects of the drugs on the sedation and memory tests. To accurately assess the level and nature of sedation and to differentiate sedation from memory impairments different types of sedation measures are required. Besides studying the subjective effects, it is recommended to also test psychomotor responses and information processing speed.

Symptomatic treatment of Alzheimer’s disease: identification of biomarkers to aid translation from bench to bedside

In the absence of robust pharmacodynamic markers, the potential success of novel therapeutic agents for the symptomatic relief of Alzheimer’s disease is largely unknown until the drugs enter relatively large studies, assessing clinical outcome over a 6-month period. In order to increase the efficiency of future clinical development there is, therefore, a need to identify pharmacodynamic markers of drug response, pharmacodynamic models that allow early prediction of efficacy and markers to aid the stratification of the patient population. Using literature available from cholinesterase inhibitors, memantine and Ginkgo biloba, this review focuses on the identification of potential pharmacodynamic markers/models and highlights the utility of these end points throughout the drug discovery process, from preclinical to clinical development.

Functional evaluation of cerebral cortex in dementia with Lewy bodies

Neurochemical investigations have demonstrated central cholinergic dysfunction in patients with dementia with Lewy bodies (DLB). Central cholinergic circuits of the human brain can be tested non-invasively by coupling peripheral nerve stimulation with transcranial magnetic stimulation of the contralateral motor cortex. This test, named short latency afferent inhibition has been shown in healthy subjects to be sensitive to the blockage of muscarinic acetylcholine receptors and it is impaired in patients with Alzheimer disease (AD), a cholinergic form of dementia, while it is normal in non-cholinergic forms of dementia such as fronto-temporal dementia. We evaluated short latency afferent inhibition in a group of patients with DLB and compared the data with that from a group of AD patients and a control group of age-matched healthy individuals. Short latency afferent inhibition was significantly reduced in DLB and AD patients. The findings suggest that this method can be used as a non-invasive test for the assessment of cholinergic pathways in patients with dementia and may represent a useful additional tool for discriminating between cholinergic and non-cholinergic forms of dementia.

Pharmacological models in healthy volunteers: their use in the clinical development of psychotropic drugs

Animal models of diseases are widely used in the preclinical phase of drug development. They have a place in early human clinical psychopharmacology as well, in order to get early clues that contribute to establish the proof of concept (POC) already in healthy volunteers (HV). Different types of models are available (pharmacological or non-pharmacological provocation, models based on age-related characteristics). This review is focused on pharmacological models in HV, with the aim to identify the main issues raised by their use in pharmaceutical trials. The available models unevenly fulfil the requirements of face validity, sufficient response rate, test-retest consistence and responsiveness to reference drugs. Most of them have been developed in the purpose of pathophysiology studies, using rating instruments validated for clinical practice. Substantial progress could be made by adapting models to the specific requirements of pharmaceutical trials, including wider use of biomarkers. Characteristics that make models, as well as biomarkers, suitabLe for use in drug development are proposed. Despite obvious limitations, human models can significantly enhance the way phase I studies contribute to establish the POC, provided they are integrated into adapted phase I development plans. Their use as industrial tools for drug evaluation requires specific, dedicated development.

Altered benzodiazepine receptor sensitivity in alcoholism: a study with fMRI and acute lorazepam challenge

Previous studies suggested altered sensitivity of the GABA/benzodiazepine receptor system in alcoholic patients. Expanding on these findings, the present functional magnetic resonance imaging (fMRI) study aimed to assess whether a differential modulation of cognitive brain activation by an acute GABAergic drug challenge could be detected in patients with alcoholism. Eight detoxified male patients meeting DSM-IV criteria for alcohol dependence and nine healthy male control subjects were studied with fMRI while performing a 2-back working memory task. The fMRI scans were performed 1 h after intravenous administration of saline and again 1 h after 0.03 mg/kg lorazepam I.V. After saline, a task x group interaction effect with higher task activation in alcoholic patients in the left cerebellum and the right prefrontal cortex emerged. Additionally, a differential task x drug x group interaction was identified in the right cerebellum with more pronounced reduction in cognitive activation after lorazepam in the patient group. A significant correlation between lorazepam sensitivity and duration of alcohol dependence was detected. The present findings are in line with previous studies suggesting disrupted prefrontal-cerebellar activation with potential compensatory hyperactivation of the compromised brain networks in alcoholism. Moreover, the results suggest enhanced responsivity to an acute GABAergic challenge in the right cerebellum with disease-related disruption of cerebellar functional integrity.

Diazepam impairs temporal dynamics of visual attention

The effect of benzodiazepines on attention has been the object of few investigations. Studies using the spatial cueing paradigm (Posner's paradigm) have reported inconsistent results, which are likely due to methodological and/or dose differences but suggest impaired disengagement of attention from the cue to the target. The authors investigated the effect of a benzodiazepine (diazepam) on attentional shifting in the temporal domain. The attentional blink effect refers to difficulties in detecting a target if it follows the identification of a previous target occurring within a temporal window of 200-400 ms. The authors assessed whether the duration of the attentional blink was affected by diazepam. Streams of 15 real-world scenes displaying a road were presented for 50 ms each. A city name (target) appeared at Serial Positions 2, 3, or 4 of each stream. A vehicle (probe) appeared at different intervals following the city name. In a dual-task condition, participants were asked to report the city name and whether a vehicle was present. In a control condition, participants had to report only the presence of a vehicle and ignore the city name. Thirty-six healthy volunteers were assigned to 3 groups (placebo, diazepam 0.1 mg/kg, or 0.3 mg/kg). Diazepam increased both the magnitude and duration of the attentional blink effect. Participants treated with a high dose of diazepam needed more than 600 ms to detect a vehicle following identification of the name. Results suggest that diazepam at a therapeutic dosage affects attentional shifting in the temporal domain and impairs dual-task performance.

Dose effects of triazolam on brain activity during episodic memory encoding: a PET study

RATIONALE

Although it is well established that acute benzodiazepine administration impairs episodic memory encoding, little is known about the neuroanatomical substrates of this effect.

OBJECTIVE

The objective was to examine the acute dose effects of the benzodiazepine hypnotic triazolam on brain activity during episodic memory encoding.

METHODS

After oral capsule administration (placebo, 0.1, 0.2, and 0.4 mg/70 kg triazolam), regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) with 15O-H2O during performance of semantic categorization and orthographic categorization tasks in a double-blind, within-subject design in 12 healthy volunteers. The rCBF associated with episodic memory encoding was measured by subtracting the rCBF during orthographic categorization from that during semantic categorization and by examining correlations between brain activity during encoding and subsequent recognition memory performance.

RESULTS

Results in the placebo condition replicated those of nonpharmacological encoding studies, including activation in left ventrolateral prefrontal cortex. Correlations between brain activity and subsequent memory performance additionally showed medial temporal activation. Triazolam produced dose-related impairment in memory performance and dose-related deactivation in encoding-associated areas including right prefrontal cortex, left parahippocampal gyrus, and left anterior cingulate cortex.

CONCLUSIONS

Results are consistent with behavioral evidence that benzodiazepines impair prefrontal control processes as well as contextual memory and episodic binding processes thought to be controlled by the medial temporal lobe. In addition to elucidating the brain mechanisms underlying these benzodiazepine-induced behavioral deficits, results of this study also help validate hypotheses generated in nonpharmacological neuroimaging studies regarding the processes controlled by these brain regions.

Sedation and memory: studies with a histamine H-1 receptor antagonist

The influence of sedation on the effect of an H-1 receptor antagonist on various cognitive functions, including memory, were evaluated. Diphenhydramine (50, 75 and 100 mg) and lorazepam (0.5 and 1.5 mg) were given on single occasions to 12 healthy volunteers (six males, six females) aged 20-33 (mean 23.4) years. Subjective assessments of sedation, sleep latencies, digit symbol substitution, choice reaction time, sustained attention and memory recall were studied 1.0 h before and 0.5, 2.0 and 3.5 h after drug ingestion. The study was double blind, placebo controlled and with a crossover design. With all doses of diphenhydramine there was subjective sedation, reduced sleep latencies and impairments in performance on the digit symbol substitution, choice reaction time and sustained attention tasks. No effects were observed with 0.5 mg lorazepam. With 1.5 mg lorazepam there was subjective sedation, fewer digit symbol substitutions, slowed choice reaction time, impaired attention and memory, but no effect on sleep latencies. Contrast analysis of data measured at all time points showed that although there was no difference in the effect of diphenhydramine (100 mg) and lorazepam (1.5 mg) on those tasks without a memory component, response times were slower with lorazepam on those tasks with a memory component. However, both 100 mg diphenhydramine and 1.5 mg lorazepam impaired prompted recall measured at 2 h post-ingestion only. It is considered that impaired memory is not necessarily associated with sedation, and that impairment of memory with drugs that lead to sedation may be effected through neuronal systems independent of those that affect arousal.

Gender differences in response to lorazepam in a human drug discrimination study

Gender differences in the discriminative stimulus properties of drugs of abuse have sometimes been reported, although we have previously found no differences in subjective or discriminative responses in human subjects acquiring an alcohol discrimination. The aim of the present work was to determine if there were gender differences in the effects of lorazepam, a benzodiazepine-receptor agonist which substituted for the alcohol stimulus in trained social drinkers. Volunteers who had already acquired an alcohol (0.2g/kg) placebo discrimination were administered (double-blind) either placebo (nine females, nine males) or lorazepam 2mg (six females, six males). They then sampled a series of five drinks and rated each one for likeness to the training stimulus (the generalization response). In addition they completed rating scales for subjective effects and the Digit Symbol Substitution Test (DSST). Lorazepam substituted for the alcohol stimulus equally in both sexes and increased associated scores for lightheadedness. Females however, showed a much greater DSST performance impairment following lorazepam, compared with males. This effect was independent of body weight differences and sedation. These results are discussed in the light of current knowledge of gender differences in response to drugs of abuse and suggest that the stimulus and cognitive effects of benzodiazepine-receptor agonists are modulated by different brain mechanisms.

Cognitive effects of modafinil in student volunteers may depend on IQ

The results of two previous studies on the effects of modafinil, a selective wakefulness-promoting agent, in healthy university students were combined in a retrospective analysis. This allowed determination of whether the effects of modafinil were dependent on IQ and whether the larger sample size (n=89) would reveal more cognitive benefits. A battery of cognitive tests was completed 2-3 h after dosing. In the whole sample, modafinil (200 mg) significantly reduced the number of missed targets in a test of sustained attention (RVIP). However, interestingly, several interactions between modafinil and IQ emerged. Modafinil (100 and 200 mg) significantly improved target sensitivity in the RVIP test, but only in the group of 'lower' IQ (mean+/-sem=106+/-0.6), not in the 'higher' IQ group (mean+/-sem=115.5+/-0.5). Furthermore, there were significant modafinil x IQ interactions in two further tests. Modafinil significantly reduced speed of responding in a colour naming of dots, and in clock drawing, but only in the 'lower' IQ group. Thus, the cognitive benefits of modafinil seem particularly marked in tests of vigilance and speed, in which sleepiness would be an important factor. Furthermore, the results indicate that high IQ may limit detection of modafinil's positive effects.

Modulation of memory and visuospatial processes by biperiden and rivastigmine in elderly healthy subjects

RATIONALE

The central cholinergic system is implicated in cognitive functioning. The dysfunction of this system is expressed in many diseases like Alzheimer's disease, dementia of Lewy body, Parkinson's disease and vascular dementia. In recent animal studies, it was found that selective cholinergic modulation affects visuospatial processes even more than memory function.

OBJECTIVE

In the current study, we tried to replicate those findings. In order to investigate the acute effects of cholinergic drugs on memory and visuospatial functions, a selective anticholinergic drug, biperiden, was compared to a selective acetylcholinesterase-inhibiting drug, rivastigmine, in healthy elderly subjects.

METHODS

A double-blind, placebo-controlled, randomised, cross-over study was performed in 16 healthy, elderly volunteers (eight men, eight women; mean age 66.1, SD 4.46 years). All subjects received biperiden (2 mg), rivastigmine (3 mg) and placebo with an interval of 7 days between them. Testing took place 1 h after drug intake (which was around Tmax for both drugs). Subjects were presented with tests for episodic memory (wordlist and picture memory), working memory tasks (N-back, symbol recall) and motor learning (maze task, pursuit rotor). Visuospatial abilities were assessed by tests with high visual scanning components (tangled lines and Symbol Digit Substitution Test).

RESULTS

Episodic memory was impaired by biperiden. Rivastigmine impaired recognition parts of the episodic memory performance. Working memory was non-significantly impaired by biperiden and not affected by rivastigmine. Motor learning as well as visuospatial processes were impaired by biperiden and improved by rivastigmine.

CONCLUSIONS

These results implicate acetylcholine as a modulator not only of memory but also of visuospatial abilities.

Dissociated effects of diazepam and lorazepam on short-latency afferent inhibition

Peripheral nerve inputs have an inhibitory effect on motor cortex excitability at short intervals (short-latency afferent inhibition, SAI). This can be tested by coupling electrical stimulation of peripheral nerve with transcranial magnetic stimulation (TMS) of the motor cortex. SAI is reduced by the anticholinergic drug scopolamine, and in patients with Alzheimer's disease. Therefore, it is possible that SAI is a marker of central cholinergic activity important for memory function. The benzodiazepine lorazepam also reduces SAI. Since benzodiazepines impair memory formation, but do not do so uniformly, with a maximum amnesic effect after lorazepam but less or no effect after diazepam, we were interested in testing in this non-behavioural study to what extent the effects of lorazepam and diazepam on circuits involved in SAI could be dissociated. In addition, and for control, we tested the effects of lorazepam and diazepam on short-interval intracortical inhibition (SICI), a motor cortical inhibition mediated through the GABA(A) receptor. Lorazepam markedly reduced SAI, whereas diazepam slightly increased it. In contrast, both benzodiazepines uniformly increased SICI. Our findings demonstrate opposite effects of lorazepam and diazepam on SAI, an inhibition modulated by central cholinergic activity, but the same effects on SICI, a marker of neurotransmission through the GABA(A) receptor. This dissociation suggests, for the first time, that TMS measures of cortical inhibition provide the opportunity to segregate differences of benzodiazepine action in human central nervous system circuits.

Does modafinil enhance cognitive performance in young volunteers who are not sleep-deprived?

In a double-blind, parallel groups study, 60 healthy student volunteers (29 men and 31 women, aged 19-22 years) were randomly allocated to receive placebo, 100 or 200 mg modafinil. Two hours later, in the early evening, they completed an extensive cognitive battery. The 3 groups did not differ in self-ratings of sleepiness or tiredness before the testing session, and there were no treatment-associated changes in these or in mood ratings during the tests. Modafinil was without effect in several tests of reaction time and attention, but the 200-mg group was faster at simple color naming of dots and performed better than placebo in the Rapid Visual Information Processing test of sustained attention. Modafinil was without effect on spatial working memory, but the 100-mg group performed better in the backward part of the digit span test. Modafinil was without effect on verbal short-term memory (story recall), but 100 mg improved digit span forward, and both doses improved pattern recognition, although this was accompanied by a slowing of response latency in the 200-mg group. There were no significant effects of modafinil compared with placebo in tests of long-term memory, executive function, visuospatial and constructional ability, or category fluency. These results suggest that the benefits of modafinil are not clearly dose-related, and those from 100 mg are limited to the span of immediate verbal recall and short-term visual recognition memory, which is insufficient for it to be considered as a cognitive enhancer in non-sleep-deprived individuals.

Effects of CRF1 receptor antagonists and benzodiazepines in the Morris water maze and delayed non-matching to position tests

RATIONALE

Benzodiazepines continue to be widely used for the treatment of anxiety, but it is well known that benzodiazepines have undesirable side effects, including sedation, ataxia, cognitive deficits and the risk of addiction and abuse. CRF(1) receptor antagonists are being developed as potential novel anxiolytics, but while CRF(1) receptor antagonists seem to have a better side-effect profile than benzodiazepines with respect to sedation and ataxia, the effects of CRF(1) receptor antagonists on cognitive function have not been well characterized. It is somewhat surprising that the potential cognitive effects of CRF(1) receptor antagonists have not been more fully characterized since there is some evidence to suggest that these compounds may impair cognitive function.

OBJECTIVE

The Morris water maze and the delayed non-matching to position test are sensitive tests of a range of cognitive functions, including spatial learning, attention and short-term memory, so the objective of the present experiments was to assess the effects of benzodiazepines and CRF(1) receptor antagonists in these tests.

RESULTS

The benzodiazepines chlordiazepoxide and alprazolam disrupted performance in the Morris water maze and delayed non-matching to position at doses close to their therapeutic, anxiolytic doses. In contrast, the CRF(1) receptor antagonists DMP-904 and DMP-696 produced little or no impairment in the Morris water maze or delayed non-matching to position test even at doses 10-fold higher than were necessary to produce anxiolytic effects.

CONCLUSIONS

The results of the present experiments suggest that, with respect to their effects on cognitive functions, CRF(1) receptor antagonists seem to have a wider therapeutic index than benzodiazepines.

Isoflavones and cognitive function in older women: the SOy and Postmenopausal Health In Aging (SOPHIA) Study

OBJECTIVE

This study examines the effects of a dietary supplement of isoflavones on cognitive function in postmenopausal women.

DESIGN

Participants for this 6-month, double-blind, randomized, placebo-controlled clinical trial were women who were in good health, were postmenopausal at least 2 years, and were not using estrogen replacement therapy. Between July 24, 2000, and October 31, 2000, 56 women aged 55 to 74 years were randomized; 2 in the placebo group and 1 in the active treatment group did not complete the 6-month evaluation, and none withdrew because of adverse effects. Women randomized to active treatment (n = 27) took two pills per day, each containing 55 mg of soy-extracted isoflavones (110 mg total isoflavones per day; Healthy Woman: Soy Menopause Supplement, Personal Products Company, McNeil-PPC Inc., Skillman, NJ, USA). Women assigned to placebo (n = 26) took two identical-appearing pills per day containing inert ingredients. Cognitive function tests administered at baseline and follow-up included the following: Trails A and B, category fluency, and logical memory and recall (a paragraph recall test assessing immediate and delayed verbal memory).

RESULTS

At baseline, all women were cognitively intact; there were no significant differences by treatment assignment in age, education, depressed mood, or cognitive function (all P values > 0.10). Compliance was 98% and 97%, respectively, in the placebo and treatment groups; all women took at least 85% of their pills. The women in the treatment group did consistently better, both as compared with their own baseline scores and as compared with the placebo group responses at 6 months. Comparisons of percentage change in cognitive function between baseline and follow-up showed greater improvement in category fluency for women on active treatment as compared with the case of those on placebo (P = 0.02) and showed (nonsignificantly) greater improvement on the two other tests of verbal memory and Trails B.

CONCLUSION

These results suggest that isoflavone supplementation has a favorable effect on cognitive function, particularly verbal memory, in postmenopausal women.

Human models as tools in the development of psychotropic drugs

Despite the growing means devoted to research and development (R α D) and refinements in the preclinical stages, the efficiency of central nervous system (CMS) drug development is disappointing. Many drugs reach patient studies with an erroneous therapeutic indication andlor in incorrect doses. Apart from the first clinical studies, which are conducted in healthy volunteers and focus only on safety, iolerability, and pharmacokinetics, drug development mostly relies on patient studies. Psychiatric disorders are characterized by heterogeneity and a high rate of comorbidity. It is becoming increasingly difficult to recruit patients for clinical trials and there are many confounding factors in this population, for example, those related to treatments. In order to keep patient exposure and financial expenditure to a minimum, it is important to avoid ill-designed and inconclusive studies. This risk could be minimized by gathering pharmacodynamic data earlier in development and considering that the goal of a phase 1 plan is to reach patient studies with clear ideas about the compound's pharmacodynamic profile, its efficacy in the putative indication (proof of concept), and pharmacokinetic/pharmacodynamic relationships, in addition to safety, tolerability, and pharmacokinetics. Human models in healthy volunteers may be useful tools for this purpose, but their use necessitates a global adaptation of the phase scheme, favoring pharmacodynamic assessments without neglecting safety. We are engaged in an R α D program aimed to adapt existing models and develop new paradigms suitable for early proof of concept substantiation.

The effects of single-dose lorazepam on memory and behavioural learning

To assess the influence of lorazepam on memory and behavioural learning, a non-clinical sample of undergraduate psychology students (n = 24), received lorazepam (2.5 mg) or placebo orally. Pre-drug and post-drug neuropsychological assessment comprised the Rey auditory verbal learning test, verbal fluency test, digit span and word stem completion. Relative to placebo, lorazepam induced a marked deficit in delayed free-recall, perceptual priming, and written word fluency, with preservation of digit span. Behavioural learning was assessed on a computer-aided vicarious exposure treatment for obsessive-compulsive disorder, administered post-drug, and repeated 1 week later, drug free. Compared to placebo, lorazepam treated participants enacted 51% less exposure activity on the behavioural learning task post-drug. Whilst both groups enacted increased exposure at the drug-free session, exposure activity was 49% less in the lorazepam group, indicating a carryover effect of the impaired learning under drug 1 week before. There were no significant differences between lorazepam and placebo on indices of overall activity on the program. These results suggest lorazepam-induced impairment in the ability to learn behavioural strategies, possibly due to impaired acquisition of information into long-term episodic memory. These findings suggest caution in the co-prescribing of benzodiazepines in people undergoing behavioural therapies in clinical populations.

Cholinergic modulation of experience-dependent plasticity in human auditory cortex

The factors that influence experience-dependent plasticity in the human brain are unknown. We used event-related functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to measure cholinergic modulation of experience-dependent plasticity in human auditory cortex. In a differential aversive conditioning paradigm, subjects were presented with high (1600 Hz) and low tones (400 Hz), one of which was conditioned by pairing with an electrical shock. Prior to presentation, subjects were given either a placebo or an anticholinergic drug (0.4 mg iv scopolamine). Experience-dependent plasticity, expressed as a conditioning-specific enhanced BOLD response, was evident in auditory cortex in the placebo group, but not with scopolamine. This study provides in vivo evidence that experience-dependent plasticity, evident in hemodynamic changes in human auditory cortex, is modulated by acetylcholine.

Pharmacological modulation of behavioral and neuronal correlates of repetition priming

In this experiment we address the pharmacological modulation of repetition priming, a basic form of learning, using event-related functional magnetic resonance imaging. We measured brain activity in a word-stem completion paradigm in which, before study, volunteers were given either placebo, lorazepam (2 mg orally), or scopolamine (0.4 mg, i.v.). Relative to placebo, both drugs attenuated the behavioral expression of priming. Repetition was associated with a decreased neuronal response in left extrastriate, left middle frontal, and left inferior frontal cortices in the placebo group. Both drugs abolished these "repetition suppression" effects. By showing a concurrence of behavioral and neuronal modulations, the results suggest that GABAergic and cholinergic systems influence the neuronal plasticity necessary for repetition priming.

Anxiolytic effects of aniracetam in three different mouse models of anxiety and the underlying mechanism

The anxiolytic effects of aniracetam have not been proven in animals despite its clinical usefulness for post-stroke anxiety. This study, therefore, aimed to characterize the anxiolytic effects of aniracetam in different anxiety models using mice and to examine the mode of action. In a social interaction test in which all classes (serotonergic, cholinergic and dopaminergic) of compounds were effective, aniracetam (10-100 mg/kg) increased total social interaction scores (time and frequency), and the increase in the total social interaction time mainly reflected an increase in trunk sniffing and following. The anxiolytic effects were completely blocked by haloperidol and nearly completely by mecamylamine or ketanserin, suggesting an involvement of nicotinic acetylcholine, 5-HT2A and dopamine D2 receptors in the anxiolytic mechanism. Aniracetam also showed anti-anxiety effects in two other anxiety models (elevated plus-maze and conditioned fear stress tests), whereas diazepam as a positive control was anxiolytic only in the elevated plus-maze and social interaction tests. The anxiolytic effects of aniracetam in each model were mimicked by different metabolites (i.e., p-anisic acid in the elevated plus-maze test) or specific combinations of metabolites. These results indicate that aniracetam possesses a wide range of anxiolytic properties, which may be mediated by an interaction between cholinergic, dopaminergic and serotonergic systems. Thus, our findings suggest the potential usefulness of aniracetam against various types of anxiety-related disorders and social failure/impairments.

Are lorazepam-induced deficits in attention similar to those resulting from aging?

The purpose of this experiment was to compare, in three tasks of attention, the impairment caused by lorazepam (1 and 2.5 mg) administered to young volunteers with the impairment that results from aging. Performance on digit cancellation (DC), digit-symbol substitution (DSS), and Paced Auditory Serial Addition Task (PASAT) was significantly impaired by lorazepam (2.5 mg) and was significantly worse in the middle-aged group (mean +/- SEM, aged 58.9+/-0.8 years) compared with the younger, IQ-matched group (20.7+/-0.2 years). However, there were interesting differences in the extent of impairments among the three tests. In the DC test, lorazepam (2.5 mg) produced a significantly greater impairment than was seen in either the middle-aged men or middle-aged women. However, in the DSS test, the middle-aged women were significantly more impaired than either the middle-aged men or the young volunteers tested after lorazepam (2.5 mg). In the PASAT, both the lorazepam (2.5 mg) group and the middle-aged women were more impaired than the middle-aged men. These results raise the important possibility of gender differences in age-related decline of attentional processes.

Anxiogenic effects of nicotine in the dorsal hippocampus are mediated by 5-HT1A and not by muscarinic M1 receptors

After direct administration into the dorsal hippocampus nicotine decreased the time spent in social interaction, without changing locomotor activity, indicating an anxiogenic effect. The possibility that post-synaptic M1 muscarinic receptors mediated this effect was examined by determining whether dorsal hippocampal administration of a specific M1 receptor agonist (McN-A-343) had anxiogenic effects, and whether the anxiogenic effect of nicotine could be reversed by co-administration of the M1 receptor antagonist, pirenzepine. McN-A-343 (0.3, 1.6, 3.2, 15.8 nmol) was without effect on social interaction, and pirenzepine (0.7 and 2.4 nmol) injection into the dorsal hippocampus failed to reverse the decrease in social interaction caused by nicotine (6.3 nmol) injection into this area. However, the decrease in social interaction after nicotine (50 nmol) was completely reversed by the specific 5-HT1A receptor antagonist, WAY 100635 (0.4 nmol) after co-administration of both drugs into the dorsal hippocampus. Thus, the anxiogenic effect of nicotine in this brain region seems to be mediated by 5-HT1A, but not M1, receptors. In contrast to the effect of nicotine in naive animals, those retested after a second injection of 50 nmol did not show a significant anxiogenic effect. The theoretical implications of this are discussed and from a practical point of view this suggests caution in the retesting of animals after central injections.

The Effect of Cholinergic Receptor Blockade by Scopolamine on Memory Performance and the Auditory P3

Abstract Previous research has suggested a possible link between the effects of scopolamine-induced muscarinic cholinergic receptor blockade on memory and its effect on auditory P3 amplitude and latency. A potential problem with this hypothesis is that, although scopolamine has been reported to increase P3 latency in both visual and auditory modalities, amplitude reductions have been reported only in the case of auditory P3 at Cz. In the present study, subjects were injected intravenously with 5.7 μg/kg of scopolamine or saline in a double blind design. A significant reduction in verbal recognition memory performance was observed. This memory impairment was shown to be largely specific to the encoding of verbal material. The drug effect was of equal magnitude when words of either high or low word frequency were used. Auditory P3 was recorded from frontal central and parietal sites along the midline and over left and right hemispheres. In contrast to a number of earlier reports using a similar drug dose, only limited evidence was found of either latency increase or amplitude reduction of the auditory P3. Importantly, two potentially confounding drug-related ERP modulations were observed prior to and during the latency range of the P3. The first was a widespread increase in N2 amplitude and latency preceding the P3. The second was that ERPs became relatively more negative at frontal and central sites in the 200-450 ms latency range in both target and non-target conditions. Whether this effect is the result of an increase in negativity or a reduction in P3a amplitude remains to be determined. Interestingly, ERPs to target stimuli became significantly less positive at frontal sites in the drug condition in the latency range 400-900 ms. This is consistent with recent reports highlighting the importance of frontal regions in normal memory function. Previously hypothesized links between cholinergic receptor block ade, effects on P3 latency and amplitude, and drug-induced memory impairments are discussed in the light of these findings.

Single dose pharmacodynamics of thioridazine and remoxipride in healthy younger and older volunteers

Phenothiazines are widely used in older patients, but little experimental work has been carried out in this age group. Two groups of healthy volunteers, a younger group (Y: six males and six females, aged 20-42 years) and an older group (O: six males and eight females, aged 65-77 years) took part in a randomized double-blind three-period crossover study in which they received by mouth single doses of thioridazine (Y: 50 mg; O: 25 mg) remoxipride (Y: 100 mg; O: 50 mg) or placebo. Measures of central nervous system (CNS) and haemodynamic function were carried out before drug administration and at 1.5-h intervals up to 9 h post-dose, and blood samples were collected over a 24-h period. No significant differences in dose-corrected pharmacokinetic variables were found between the two groups. There was evidence of marked CNS depressant effects of thioridazine from both objective and subjective measures. The effects for remoxipride were similar, though generally less marked. After allowance was made for dose, there was little indication of any difference in degree of CNS depression between the two age groups. Haemodynamic measures showed orthostatic reductions in blood pressure with thioridazine which were particularly marked in the older group, who also showed lower compensatory increases in pulse rate. These results indicate potential problems with orthostatic hypotension with thioridazine in older patients. CNS depression may also be a problem, especially in patients with compromised cholinergic function.

High versus low reactivity to a novel environment: behavioural, pharmacological and neurochemical assessments

Based on their rearing response to a novel open field, male Wistar rats were divided into two sub-groups with either high or low behavioural activity (high rearings, versus low rearings). These sub-groups were repeatedly exposed to the same open field and tested for behavioural habituation. Since we previously found neurochemical evidence for different cholinergic reactivities in such high rearing and low rearing rats, their behavioural responses to the muscarinic antagonist scopolamine (0.5 mg/kg) were also investigated in the open field. Additionally, they were exposed to the elevated plus-maze to test for possible differences in measures of anxiety. After behavioural testing, tissue concentrations of biogenic amines were determined in the ventral striatum (nucleus accumbens, olfactory tubercle), frontal cortex, striatum, hippocampus and amygdala. The results show that the higher rearing responses of high rearing rats in the novel open field were paralleled by higher locomotor activity. These behavioural differences between groups decreased with repeated open field exposure, an effect which was largely due to between-session habituation in high rearing rats. Thereby, high rearing rats approached the lower levels of low rearing rats, in which locomotor activity and rearings did not habituate between testing. Nevertheless, habituation was also observed in low rearing rats, especially in the measure of thigmotactic scanning, since the levels of scanning declined both between and within test sessions. The anticholinergic challenge with scopolamine induced a general pattern of behavioural activation. Furthermore, scopolamine partly reinstated the behavioural differences between high and low rearing rats that had been observed in the novel open field, since high rearing rats showed more rearing behaviour than low rearing rats under scopolamine. In contrast to the open field, there were no significant differences between high and low rearing rats in the plus-maze. The neurochemical analysis revealed, among others, higher dopamine levels in the ventral striatum of high rearing rats together with lower serotonin levels in the medial frontal cortex. The current findings thus indicate that high and low rearing rats not only differ in their behavioural response to a novel environment, but also in their patterns of behavioural habituation, and with respect to behaviour induced by an anti-cholinergic challenge. These differential behavioural profiles of high and low rearing animals are discussed with respect to the role of dopaminergic mechanisms in the forebrain, and the potential impact of cholinergic mechanisms.

Selective effects of zolpidem on human memory functions

Zolpidem is an imidazopyridine hypnotic with preferential binding affinity for the omega1-benzodiazepine (BZD) receptor. The present double-blind, placebo-controlled study evaluated the effects of orally administered zolpidem (15mg/70kg) on specific memory functions in 16 healthy volunteers using a battery of word and picture memory tasks. Relative to placebo, zolpidem significantly impaired memory for material presented after drug administration when memory was assessed directly by referring subjects back to the prior study episode (explicit memory: recall and recognition) but not when memory was assessed indirectly by evaluating subjects' ability to identify degraded versions of studied stimuli (implicit memory: fragment completion). Zolpidem did not impair explicit memory for material presented before drug administration or memory for previously acquired knowledge (semantic memory: categorization). There was evidence suggesting that zolpidem enhanced explicit and implicit memory for material presented before drug administration and that zolpidem produced a specific deficit in the acquisition of contextual information about material presented after drug administration. Despite zolpidem's unique pharmacological profile, the observed selectivity of zolpidem's memory-impairing effects for particular functions appears qualitatively similar to the selectivity observed with classic BZDs in previous studies.

Alertness and memory after sleep deprivation and diazepam intake

Benzodiazepines (BZDs) give rise to memory impairments. It has been questioned whether or not these impairments are related to the drug's sedative, alertness-reducing effects. Therefore, in this study, alertness was reduced in healthy subjects both pharmacologically (15 mg diazepam) and non-pharmacologically (24-h sleep deprivation, SD) in order to assess whether these manipulations both gave rise to memory impairments. Twelve subjects were tested using a repeated measures cross-over design. Drug administration was placebo-controlled and double-blind. A subjective alertness reduction was established after diazepam intake and even more after SD. Additionally, performance-disruptive effects were found on psychomotor tasks after both SD and liazepam intake. However, only diazepam, and not SD, impaired delayed recall of a word list and recall of paired associates. Thus a reduction in alertness, i.e. sedation, cannot fully account for BZD-induced memory impairments.

The neurosteroid pregnenolone sulfate reduces learning deficits induced by scopolamine and has promnestic effects in mice performing an appetitive learning task

The effects of the neurosteroid pregnenolone sulfate (PS) on learning as well as on scopolamine-induced learning deficits were studied in Swiss mice using an appetitively reinforced Go-No Go visual discrimination task. Subcutaneous (SC) administration of scopolamine (0.3-3 mg/kg) after the first session of training dose-dependently impairs learning during the following sessions in this task. Moreover, intracerebroventricular (ICV) administration of PS (0.01-10 nmol) dose-dependently blocks learning deficits induced by scopolamine (3 mg/kg), with the most potent effects at the dose of 0.5 nmol PS. In addition to antagonizing the amnestic effects of scopolamine, PS (0.5 nmol ICV) has a memory-enhancing effect, when administered alone after the first training session. Scopolamine (3 mg/kg SC) also produced substantial deficits on retrieval performance in the Go-No Go visual discrimination task, and caused motor disturbances, when administered 15 min before testing. PS (0.5 nmol ICV) also reduced scopolamine-induced deficits on retrieval but had no effect on scopolamine-induced motor impairments in the traction reflex test. Such a rapid effect of PS on memory processes may be mediated via NMDA and/or GABAA receptors.

Age-related decline in central cholinergic function demonstrated with scopolamine

Scopolamine hydrobromide was administered intravenously to 23 normal subjects (40-89 years) in doses of 0.1 mg, 0.25 mg, and 0.5 mg, in a double-blind. Placebo-controlled, random-order fashion. The effects of scopolamine, as compared to placebo, were assessed using a comprehensive cognitive test battery, as well as behavioral and physiological measures. Scopolamine produced the expected dose-dependent impairments in most of the cognitive functions assessed. Behavioral and physiological measures were also affected, but only minimally. More importantly, there was a significant overall correlation between age and scopolamine-impaired performances on psychomotor speed, short-term recall, visual tracking speed, visuo-motor coordination, and sequencing ability. There was, however, some inter-individual variability in this phenomenon. The results provide further evidence that cholinergically mediated cognitive functions show an increased sensitivity to scopolamine with age, albeit with heterogeneity that bears further investigation.

The effects of a benzodiazepine receptor antagonist beta-carboline ZK-93426 on scopolamine-induced impairment on attention, memory and psychomotor skills

The effects of a single dose of scopolamine alone and in combination with ZK 93426 (a beta-carboline antagonist at the GABAA/BZ receptor complex with weak inverse agonist activity) were tested in two studies. In one study (study 1) the emphasis of enquiry was on different stages of information processing measured by a psychometric battery; in the second study (study 2) performance at different stages of memory and psychomotor abilities was tested and electroencephalogram recordings and video-tracking were also performed. Each study consisted of two parts, part I in which scopolamine (0.5 mg; 1 ml) or placebo were administered subcutaneously, and part II in which scopolamine (0.5 mg; 1 ml) was administered subcutaneously followed by an intravenous injection of ZK 93426 (0.04 mg; 0.04 ml/kg) or placebo. Thirty-six volunteers, who were randomly allocated to receive one of the two treatments (n = 18 per treatment), participated in each part. In study 1 attention was measured by a continuous attention task and a rapid information processing task, vigilance was measured by a visual vigilance task, and working memory and reasoning were evaluated by a logical reasoning task. A visual memory task was also included to measure acquisition and retention. In study 2 acquisition and short term storage and retrieval were measured by a word lists-Buschke restricted reminding procedure, and retention was tested by delayed recall and recognition. Psychomotor performance was assessed by measuring tapping speed (related to gross motoric abilities) and a pegboard task (related to fine motoric abilities). A task to measure working memory, the Pauli test, was also included. In study 1 scopolamine significantly impaired performance in the attentional and vigilance tasks (P < 0.05), but there was no effect in the logical reasoning task main measurements of time and accuracy. In study 2, scopolamine also impaired performance in the psychomotor tasks (P < 0.05) and the Pauli test. ZK 93426 partially antagonised most of the effects of scopolamine on memory and attention, suggesting that an interaction between the GABA-ergic and cholinergic systems is reflected in measurements of both attention and memory. In general a dissociation was found in the effects of scopolamine on memory, i.e. scopolamine impaired performance during all acquisition measurements but left retention unaffected.