Selective D3 receptor antagonism modulates neural response during negative emotional processing in substance dependence

Introduction

Negative affective states contribute to the chronic-relapsing nature of addiction. Mesolimbic dopamine D3 receptors are well placed to modulate emotion and are dysregulated in substance dependence. Selective antagonists might restore dopaminergic hypofunction, thus representing a potential treatment target. We investigated the effects of selective D3 antagonist, GSK598809, on the neural response to negative emotional processing in substance dependent individuals and healthy controls.

Methodology

Functional MRI BOLD response was assessed during an evocative image task, 2 h following acute administration of GSK598809 (60 mg) or placebo in a multi-site, double-blind, pseudo-randomised, cross-over design. Abstinent drug dependent individuals (DD, n = 36) comprising alcohol-only (AO, n = 19) and cocaine-alcohol polydrug (PD, n = 17) groups, and matched controls (n = 32) were presented with aversive and neutral images in a block design (contrast of interest: aversive > neutral). Whole-brain mixed-effects and a priori ROI analyses tested for group and drug effects, with identical models exploring subgroup effects.

Results

No group differences in task-related BOLD signal were identified between DD and controls. However, subgroup analysis revealed greater amygdala/insular BOLD signal in PD compared with AO groups. Following drug administration, GSK598809 increased BOLD response across HC and DD groups in thalamus, caudate, putamen, and pallidum, and reduced BOLD response in insular and opercular cortices relative to placebo. Multivariate analyses in a priori ROIs revealed differential effects of D3 antagonism according to subgroup in substantia nigra; GSK598809 increased BOLD response in AO and decreased response in PD groups.

Conclusion

Acute GSK598809 modulates the BOLD response to aversive image processing, providing evidence that D3 antagonism may impact emotional regulation. Enhanced BOLD response within D3-rich mesolimbic regions is consistent with its pharmacology and with attenuation of substance-related hypodopaminergic function. However, the lack of group differences in task-related BOLD response and the non-specific effect of GSK598809 between groups makes it difficult to ascertain whether D3 antagonism is likely to be normalising or restorative in our abstinent populations. The suggestion of differential D3 modulation between AO and PD subgroups is intriguing, raising the possibility of divergent treatment responses. Further study is needed to determine whether D3 antagonism should be recommended as a treatment target in substance dependence.

FORWARDS-1: an adaptive, single-blind, placebo-controlled ascending dose study of acute baclofen on safety parameters in opioid dependence during methadone-maintenance treatment-a pharmacokinetic-pharmacodynamic study

Background

Treatment of opiate addiction with opiate substitution treatment (e.g. methadone) is beneficial. However, some individuals desire or would benefit from abstinence but there are limited options to attenuate problems with opiate withdrawal. Preclinical and preliminary clinical evidence suggests that the GABA-B agonist, baclofen, has the desired properties to facilitate opiate detoxification and prevent relapse. This study aims to understand whether there are any safety issues in administering baclofen to opioid-dependent individuals receiving methadone.

Methods

Opiate-dependent individuals (DSM-5 severe opioid use disorder) maintained on methadone will be recruited from addiction services in northwest London (NHS and third sector providers). Participants will be medically healthy with no severe chronic obstructive pulmonary disease or type 2 respiratory failure, no current dependence on other substances (excluding nicotine), no current severe DSM-5 psychiatric disorders, and no contraindications for baclofen or 4800 IU vitamin D (placebo). Eligible participants will be randomised in a 3:1 ratio to receive baclofen or placebo in an adaptive, single-blind, ascending dose design. A Bayesian dose-escalation model will inform the baclofen dose (10, 30, 60, or 90 mg) based on the incidence of ‘dose-limiting toxicity’ (DLT) events and participant-specific methadone dose. A range of respiratory, cardiovascular, and sedative measures including the National Early Warning Score (NEWS2) and Glasgow Coma Scale will determine DLT. On the experimental day, participants will consume their usual daily dose of methadone followed by an acute dose of baclofen or placebo (vitamin D3) ~ 1 h later. Measures including oxygen saturation, transcutaneous CO₂, respiratory rate, QTc interval, subjective effects (sedation, drug liking, craving), plasma levels (baclofen, methadone), and adverse events will be obtained using validated questionnaires and examinations periodically for 5 h after dosing.

Discussion

Study outcomes will determine what dose of baclofen is safe to prescribe to those receiving methadone, to inform a subsequent proof-of-concept trial of the efficacy baclofen to facilitate opiate detoxification. To proceed, the minimum acceptable dose is 30 mg of baclofen in patients receiving ≤ 60 mg/day methadone based on the clinical experience of baclofen’s use in alcoholism and guidelines for the management of opiate dependence.

Trial registration

Clinicaltrials.gov NCT05161351. Registered on 16 December 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06821-9.

Alterations in white matter microstructure in alcohol and alcohol‐polydrug dependence: Associations with lifetime alcohol and nicotine exposure

Evidence suggests that alcohol dependence (AD) is associated with microstructural deficits in white matter, but the relationship with lifetime alcohol exposure and the impact of polydrug dependence is not well understood. Using diffusion tensor magnetic resonance (MR) imaging, we examined white matter microstructure in relation to alcohol and polydrug dependence using data from the Imperial College Cambridge Manchester (ICCAM) platform study. Tract‐based spatial statistics were used to examine fractional anisotropy (FA) in a cohort of abstinent AD participants, most of whom had a lifetime history of dependence to nicotine. A further subgroup also had a lifetime history of dependence to cocaine and/or opiates. Individuals with AD had lower FA throughout the corpus callosum, and negative associations with alcohol and nicotine exposure were found. A group‐by‐age interaction effect was found showing greater reductions with age in the alcohol‐dependent group within corpus callosum, overlapping with the group difference. We found no evidence of recovery with abstinence. A comparison of alcohol‐only‐ and alcohol‐polydrug‐dependent groups found no differences in FA. Overall, our findings show that AD is associated with lower FA and suggest that these alterations are primarily driven by lifetime alcohol consumption and cigarette smoking, showing no relationship with exposure to other substances such as cocaine, opiates or cannabis. Reductions in FA across the adult lifespan are more pronounced in AD and offer further support for the notion of accelerated ageing in relation to alcohol dependence. These findings highlight there may be lasting structural differences in white matter in alcohol dependence, despite continued abstinence.

A dose-finding design for dual-agent trials with patient-specific doses for one agent with application to an opiate detoxification trial

There is a growing interest in early phase dose-finding clinical trials studying combinations of several treatments. While the majority of dose finding designs for such setting were proposed for oncology trials, the corresponding designs are also essential in other therapeutic areas. Furthermore, there is increased recognition of recommending the patient-specific doses/combinations, rather than a single target one that would be recommended to all patients in later phases regardless of their characteristics. In this paper, we propose a dose-finding design for a dual-agent combination trial motivated by an opiate detoxification trial. The distinguishing feature of the trial is that the (continuous) dose of one compound is defined externally by the clinicians and is individual for every patient. The objective of the trial is to define the dosing function that for each patient would recommend the optimal dosage of the second compound. Via a simulation study, we have found that the proposed design results in high accuracy of individual dose recommendation and is robust to the model misspecification and assumptions on the distribution of externally defined doses.

Disturbances across whole brain networks during reward anticipation in an abstinent addiction population

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Analytical methods can capture key features of whole brain networks in addiction.

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We compared reward network connectivity in addiction (ADD) and control (CON) groups.

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The ADD group showed disruptions in global network connectivity.

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Global network measures may be more sensitive than traditional voxel-wise analyses.

The prevalent spatial distribution of abnormalities reported in cognitive fMRI studies in addiction suggests there are extensive disruptions across whole brain networks. Studies using resting state have reported disruptions in network connectivity in addiction, but these studies have not revealed characteristics of network functioning during critical psychological processes that are disrupted in addiction populations. Analytic methods that can capture key features of whole brain networks during psychological processes may be more sensitive in revealing additional and widespread neural disturbances in addiction, that are the provisions for relapse risk, and targets for medication development. The current study compared a substance addiction (ADD; n = 83) group in extended abstinence with a control (CON; n = 68) group on functional MRI (voxel-wise activation) and global network (connectivity) measures related to reward anticipation on a monetary incentive delay task. In the absence of group differences on MID performance, the ADD group showed reduced activation predominantly across temporal and visual regions, but not across the striatum. The ADD group also showed disruptions in global network connectivity (lower clustering coefficient and higher characteristic path length), and significantly less connectivity across a sub-network comprising frontal, temporal, limbic and striatal nodes. These results show that an addiction group in extended abstinence exhibit localised disruptions in brain activation, but more extensive disturbances in functional connectivity across whole brain networks. We propose that measures of global network functioning may be more sensitive in highlighting latent and more widespread neural disruptions during critical psychological processes in addiction and other psychiatric disorders.

Naltrexone differentially modulates the neural correlates of motor impulse control in abstinent alcohol-dependent and polysubstance-dependent individuals

Identifying key neural substrates in addiction disorders for targeted drug development remains a major challenge for clinical neuroscience. One emerging target is the opioid system, where substance-dependent populations demonstrate prefrontal opioid dysregulation that predicts impulsivity and relapse. This may suggest that disturbances to the prefrontal opioid system could confer a risk for relapse in addiction due to weakened 'top-down' control over impulsive behaviour. Naltrexone is currently licensed for alcohol dependence and is also used clinically for impulse control disorders. Using a go/no-go (GNG) task, we examined the effects of acute naltrexone on the neural correlates of successful motor impulse control in abstinent alcoholics (AUD), abstinent polysubstance-dependent (poly-SUD) individuals and controls during a randomised double blind placebo controlled fMRI study. In the absence of any differences on GNG task performance, the AUD group showed a significantly greater BOLD response compared to the control group in lateral and medial prefrontal regions during both placebo and naltrexone treatments; effects that were positively correlated with alcohol abstinence. There was also a dissociation in the positive modulating effects of naltrexone in the orbitofrontal cortex (OFC) and anterior insula cortex (AIC) of the AUD and poly-SUD groups respectively. Self-reported trait impulsivity in the poly-SUD group also predicted the effect of naltrexone in the AIC. These results suggest that acute naltrexone differentially amplifies neural responses within two distinct regions of a salience network during successful motor impulse control in abstinent AUD and poly-SUD groups, which are predicted by trait impulsivity in the poly-SUD group.

Naltrexone ameliorates functional network abnormalities in alcohol-dependent individuals

Naltrexone, an opioid receptor antagonist, is commonly used as a relapse prevention medication in alcohol and opiate addiction, but its efficacy and the mechanisms underpinning its clinical usefulness are not well characterized. In the current study, we examined the effects of 50‐mg naltrexone compared with placebo on neural network changes associated with substance dependence in 21 alcohol and 36 poly‐drug‐dependent individuals compared with 36 healthy volunteers. Graph theoretic and network‐based statistical analysis of resting‐state functional magnetic resonance imaging (MRI) data revealed that alcohol‐dependent subjects had reduced functional connectivity of a dispersed network compared with both poly‐drug‐dependent and healthy subjects. Higher local efficiency was observed in both patient groups, indicating clustered and segregated network topology and information processing. Naltrexone normalized heightened local efficiency of the neural network in alcohol‐dependent individuals, to the same levels as healthy volunteers. Naltrexone failed to have an effect on the local efficiency in abstinent poly‐substance‐dependent individuals. Across groups, local efficiency was associated with substance, but no alcohol exposure implicating local efficiency as a potential premorbid risk factor in alcohol use disorders that can be ameliorated by naltrexone. These findings suggest one possible mechanism for the clinical effects of naltrexone, namely, the amelioration of disrupted network topology.

Using Baclofen to Explore GABA-B Receptor Function in Alcohol Dependence: Insights From Pharmacokinetic and Pharmacodynamic Measures

Background: The role of GABA-B neurotransmission in addiction has recently received increased attention, with clinical trials indicating that baclofen, a GABA-B receptor agonist, may reduce alcohol consumption, craving and promote abstinence. However, the optimal dose to treat alcohol dependence is unclear with patients requesting and tolerating much higher doses of baclofen, compared with other clinical uses. We assessed the pharmacokinetics and pharmacodynamics (PK/PD) of baclofen to provide insight into GABA-B sensitivity in this patient group, relative to controls. Methods: Male healthy volunteers (controls, n = 12) and abstinent alcohol dependent individuals (AD, n = 8) received single oral doses of baclofen or placebo in a 3-way crossover design. Controls received placebo/10 mg/60 mg baclofen in a randomized, double-blind design, AD received placebo/60 mg/90 mg baclofen in a single-blind design. PK/PD measures were recorded at baseline and multiple time-points up to 6 h post-dosing, including plasma baclofen, plasma growth hormone (GH), Subjective High Assessment Scale (SHAS) and biphasic alcohol effects scale (BAES). Repeated measures ANOVA analysis explored "change from baseline" dose, time, group, and interaction effects, t-tests compared peak effects. Results: Dose-dependent effects of baclofen on PK and PD measures were observed in both control and AD groups. Whilst there were no significant group differences in any baclofen PK parameters (t _1/2, t _max , C _max , AUC), marked differences in PD effects were clearly evident. In controls, 60 mg baclofen significantly increased total SHAS and BAES scores, and significantly increased plasma GH levels compared with placebo, with peak effects at 60-120 min, in line with its PK profile. In AD, 60 mg baclofen had limited effects on these parameters; SHAS scores, BAES scores and plasma GH levels were significantly blunted compared with controls (significant group^*time interactions P = 0.0014, 0.0015 and P < 0.0001, respectively). Conclusions: Our study shows blunted sensitivity to baclofen in AD relative to controls, with no difference in PK suggesting a lower GABA-B receptor sensitivity. This may explain why higher baclofen doses are requested and tolerated in the treatment of alcohol dependence. Our data has implications for choice of dose in future clinical trials in AD and possibly other substances of dependence.

The Use of Baclofen as a Treatment for Alcohol Use Disorder: A Clinical Practice Perspective

Alcohol use disorder (AUD) is a brain disorder associated with high rates of mortality and morbidity worldwide. Baclofen, a selective gamma-aminobutyric acid-B (GABA-B) receptor agonist, has emerged as a promising drug for AUD. The use of this drug remains controversial, in part due to uncertainty regarding dosing and efficacy, alongside concerns about safety. To date there have been 15 randomized controlled trials (RCTs) investigating the use of baclofen in AUD; three using doses over 100 mg/day. Two additional RCTs have been completed but have not yet been published. Most trials used fixed dosing of 30-80 mg/day. The other approach involved titration until the desired clinical effect was achieved, or unwanted effects emerged. The maintenance dose varies widely from 30 to more than 300 mg/day. Baclofen may be particularly advantageous in those with liver disease, due to its limited hepatic metabolism and safe profile in this population. Patients should be informed that the use of baclofen for AUD is as an "off-label" prescription, that no optimal fixed dose has been established, and that existing clinical evidence on efficacy is inconsistent. Baclofen therapy requires careful medical monitoring due to safety considerations, particularly at higher doses and in those with comorbid physical and/or psychiatric conditions. Baclofen is mostly used in some European countries and Australia, and in particular, for patients who have not benefitted from the currently used and approved medications for AUD.

Acute naltrexone does not remediate fronto-striatal disturbances in alcoholic and alcoholic polysubstance-dependent populations during a monetary incentive delay task

There is a concerted research effort to investigate brain mechanisms underlying addiction processes that may predicate the development of new compounds for treating addiction. One target is the brain's opioid system, because of its role in the reinforcing effects of substances of abuse. Substance-dependent populations have increased numbers of the mu opioid receptor (MOR) in fronto-striatal regions that predict drug relapse, and demonstrate disturbances in these regions during the processing of non-drug rewards. Naltrexone is currently licensed for alcohol and opiate dependence, and may remediate such disturbances through the blockade of MORs in fronto-striatal reward circuitry. Therefore, we examined the potential acute modulating effects of naltrexone on the anticipation of, and instrumental responding for, non-drug rewards in long-term abstinent alcoholics, alcoholic poly substance-dependent individuals and controls using a monetary incentive delay (MID) task during a randomized double blind placebo controlled functional MRI study. We report that the alcoholic poly substance-dependent group exhibited slower and less accurate instrumental responding compared to alcoholics and controls that was less evident after acute naltrexone treatment. However, naltrexone treatment was unable to remediate disturbances within fronto-striatal regions during reward anticipation and 'missed' rewards in either substance-dependent group. While we have not been able to identify the underlying neural mechanisms for improvement observed with naltrexone in the alcoholic poly-substance dependent group, we can confirm that both substance-dependent groups exhibit substantial neural deficits during an MID task, despite being in long-term abstinence.

Effects of naltrexone are influenced by childhood adversity during negative emotional processing in addiction recovery

Naltrexone is an opioid receptor antagonist used in the management of alcohol dependence. Although the endogenous opioid system has been implicated in emotion regulation, the effects of mu-opioid receptor blockade on brain systems underlying negative emotional processing are not clear in addiction. Individuals meeting criteria for alcohol dependence alone (n=18, alcohol) and in combination with cocaine and/or opioid dependence (n=21, alcohol/drugs) and healthy individuals without a history of alcohol or drug dependence (n=21) were recruited. Participants were alcohol and drug abstinent before entered into this double-blind, placebo-controlled, randomized, crossover study. Functional magnetic resonance imaging was used to investigate brain response while viewing aversive and neutral images relative to baseline on 50 mg of naltrexone and placebo. We found that naltrexone modulated task-related activation in the medial prefrontal cortex and functional connectivity between the anterior cingulate cortex and the hippocampus as a function of childhood adversity (for aversive versus neutral images) in all groups. Furthermore, there was a group-by-treatment-by-condition interaction in the right amygdala, which was mainly driven by a normalization of response for aversive relative to neutral images under naltrexone in the alcohol/drugs group. We conclude that early childhood adversity is one environmental factor that influences pharmacological response to naltrexone. Pharmacotherapy with naltrexone may also have some ameliorative effects on negative emotional processing in combined alcohol and drug dependence, possibly due to alterations in endogenous opioid transmission or the kappa-opioid receptor antagonist actions of naltrexone.

The ICCAM platform study: An experimental medicine platform for evaluating new drugs for relapse prevention in addiction. Part B: fMRI description

OBJECTIVES

We aimed to set up a robust multi-centre clinical fMRI and neuropsychological platform to investigate the neuropharmacology of brain processes relevant to addiction - reward, impulsivity and emotional reactivity. Here we provide an overview of the fMRI battery, carried out across three centres, characterizing neuronal response to the tasks, along with exploring inter-centre differences in healthy participants.

EXPERIMENTAL DESIGN

Three fMRI tasks were used: monetary incentive delay to probe reward sensitivity, go/no-go to probe impulsivity and an evocative images task to probe emotional reactivity. A coordinate-based activation likelihood estimation (ALE) meta-analysis was carried out for the reward and impulsivity tasks to help establish region of interest (ROI) placement. A group of healthy participants was recruited from across three centres (total n=43) to investigate inter-centre differences. Principle observations: The pattern of response observed for each of the three tasks was consistent with previous studies using similar paradigms. At the whole brain level, significant differences were not observed between centres for any task.

CONCLUSIONS

In developing this platform we successfully integrated neuroimaging data from three centres, adapted validated tasks and applied whole brain and ROI approaches to explore and demonstrate their consistency across centres.

The Imperial College Cambridge Manchester (ICCAM) platform study: An experimental medicine platform for evaluating new drugs for relapse prevention in addiction. Part A: Study description

Drug and alcohol dependence are global problems with substantial societal costs. There are few treatments for relapse prevention and therefore a pressing need for further study of brain mechanisms underpinning relapse circuitry. The Imperial College Cambridge Manchester (ICCAM) platform study is an experimental medicine approach to this problem: using functional magnetic resonance imaging (fMRI) techniques and selective pharmacological tools, it aims to explore the neuropharmacology of putative relapse pathways in cocaine, alcohol, opiate dependent, and healthy individuals to inform future drug development. Addiction studies typically involve small samples because of recruitment difficulties and attrition. We established the platform in three centres to assess the feasibility of a multisite approach to address these issues. Pharmacological modulation of reward, impulsivity and emotional reactivity were investigated in a monetary incentive delay task, an inhibitory control task, and an evocative images task, using selective antagonists for µ-opioid, dopamine D3 receptor (DRD3) and neurokinin 1 (NK1) receptors (naltrexone, GSK598809, vofopitant/aprepitant), in a placebo-controlled, randomised, crossover design. In two years, 609 scans were performed, with 155 individuals scanned at baseline. Attrition was low and the majority of individuals were sufficiently motivated to complete all five sessions (n=87). We describe herein the study design, main aims, recruitment numbers, sample characteristics, and explain the test hypotheses and anticipated study outputs.

Sleep and its disorders in translational medicine

The study of sleep is a useful approach to studying the brain in psychiatric disorders and in investigating the effects of psychotropic drugs. Sleep physiology lends itself well to pharmacological and physiological manipulation, as it has the advantage of a functional output, the electroencephalograph, which is common to all mammals, and can be measured in freely moving (or naturally sleeping) animals under controlled laboratory conditions or in a naturalistic home environment. The complexity of sleep architecture varies between species but all share features which are comparable. In addition, sleep architecture is sensitive to changes in brain neurotransmitters such as serotonin, so cross-species sleep measurement can be combined with pharmacological manipulation to investigate the receptor mechanisms controlling sleep-wake regulation and sleep architecture in response to known and novel agents. Translational approaches such as these have improved our understanding of sleep circuitry and facilitated the development of new treatments for sleep disorders, particularly insomnia. This review provides examples of how research findings within the sleep field have been translated between animal models, healthy volunteers and patient populations with particular focus on the serotonergic system.

5-HT radioligands for human brain imaging with PET and SPECT

The serotonergic system plays a key modulatory role in the brain and is the target for many drug treatments for brain disorders either through reuptake blockade or via interactions at the 14 subtypes of 5-HT receptors. This review provides the history and current status of radioligands used for positron emission tomography (PET) and single photon emission computerized tomography (SPECT) imaging of human brain serotonin (5-HT) receptors, the 5-HT transporter (SERT), and 5-HT synthesis rate. Currently available radioligands for in vivo brain imaging of the 5-HT system in humans include antagonists for the 5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(4) receptors, and for SERT. Here we describe the evolution of these radioligands, along with the attempts made to develop radioligands for additional serotonergic targets. We describe the properties needed for a radioligand to become successful and the main caveats. The success of a PET or SPECT radioligand can ultimately be assessed by its frequency of use, its utility in humans, and the number of research sites using it relative to its invention date, and so these aspects are also covered. In conclusion, the development of PET and SPECT radioligands to image serotonergic targets is of high interest, and successful evaluation in humans is leading to invaluable insight into normal and abnormal brain function, emphasizing the need for continued development of both SPECT and PET radioligands for human brain imaging.

Characterisation of the effects of caffeine on sleep in the rat: a potential model of sleep disruption

Caffeine is known to disrupt sleep and its administration to human subjects has been used to model sleep disruption. We previously showed that its effects on sleep onset latency are comparable between rats and humans. This study evaluated the potential use of caffeine as a model of sleep disruption in the rat, by assessing its effects on sleep architecture and electroencephalogram (EEG) frequency spectrum, and using sleep-promoting drugs to reverse these effects. Rats were implanted with radiotelemetry devices for body temperature, EEG, electromyogram and locomotor activity. Following recovery, animals were dosed with caffeine (10 mg/kg) alone or in combination with zolpidem (10 mg/kg) or trazodone (20 mg/kg). Sleep was scored for the subsequent 12 h using automated analysis software. Caffeine dose-dependently disrupted sleep: it increased WAKE time, decreased NREM (non-REM) sleep time and NREM bout duration (but not bout number), and decreased delta activity in NREM sleep. It also dose-dependently increased locomotor activity and body temperature. When given alone, zolpidem suppressed REM whilst trazodone increased NREM sleep time at the expense of WAKE, increased NREM bout duration, increased delta activity in NREM sleep and reduced body temperature. In combination, zolpidem attenuated caffeine's effects on WAKE, whilst trazodone attenuated its effects on NREM sleep, NREM bout duration, delta activity, body temperature and locomotor activity. Caffeine administration produced many of the signs of insomnia that were improved by two of its most successful current treatments. This model may therefore be useful in the study of new drugs for the treatment of sleep disturbance.

Effects on sleep stages and microarchitecture of caffeine and its combination with zolpidem or trazodone in healthy volunteers

Caffeine is the world's most popular stimulant and is known to disrupt sleep. Administration of caffeine can therefore be used in healthy volunteers to mimic the effects of insomnia and thus to test the hypnotic effects of medication. This study assessed the effects of caffeine on sleep architecture and electroencephalography (EEG) spectrum alone and in combination with two different sleep-promoting medications. Home polysomnography was performed in 12 healthy male volunteers in a double-blind study whereby subjects received placebo, caffeine (150 mg), caffeine plus zolpidem (10 mg) and caffeine plus trazodone (100 mg) at bedtime in a randomised crossover design. In addition to delaying sleep onset, caffeine decreased total sleep time (TST), sleep efficiency (SE) and stage 2 sleep without significantly altering wake after sleep onset or the number of awakenings. Zolpidem attenuated the caffeine-induced decrease in SE and increased spindle density in the caffeine plus zolpidem combination compared with placebo. Trazodone attenuated the decrease in SE and TST, and it also increased stage 3 sleep, decreased the number of awakenings and decreased the spindle density. No significant changes in rapid eye movement (REM) sleep were observed, neither was any significant alteration in slow wave activity nor other EEG spectral measures, although the direction of change was similar to that previously reported for caffeine and appeared to 'normalise' after trazodone. These data suggest that caffeine mimics some, but not all of the sleep disruption seen in insomnia and that its disruptive effects are differentially attenuated by the actions of sleep-promoting compounds with distinct mechanisms of action.

NAPSAQ-1: National Patient Sleep Assessment Questionnaire in depression

Objectives. Sleep disturbance is a common feature of depression. Symptoms often persist after treatment of the depressive episode, representing a risk factor for relapse. There is a lack of data regarding the nature of sleep disturbance in depression in the UK. Methods. We surveyed patients' views about their depressive symptoms and associated sleep difficulties. We received 513 responses via postal questionnaire. Results. A total of 97% reported sleep difficulties during depression: symptoms of insomnia were more frequently reported than hypersomnia. Ninety-nine percent of those with sleep problems also reported daytime symptoms including lack of concentration, exhaustion and lethargy, no energy and feeling sleepy; 40% admitted napping during the day; 59% indicated that poor sleep greatly affected their quality of life (QOL); 34% considered it to be "very distressing"; 69% of respondents were taking antidepressant medication at the time (44% said it improved their sleep, 56% said it had no effect or worsened their sleep); 69% had sought extra treatment for their sleep problems. Conclusions. Sleep disturbance in depression is a common and distressing problem that seems relatively unresolved by treatment. There is a need for more successful management in order to improve QOL in these patients and reduce a factor in depressive relapse.

A translational, caffeine-induced model of onset insomnia in rats and healthy volunteers

RATIONALE

Insomnia is a common and disabling complaint for which there is a need for improved treatments. Successful drug discovery relies on the use of appropriate animal models to assess likely outcome in the clinic.

OBJECTIVES

The purpose of this study was to develop a translational, caffeine-induced model of insomnia in rats and healthy volunteers. We used sleep onset latency (SOL) as a comparable sleep measure between the two species. The model was validated by two effective sleep-promoting agents with different pharmacology, zolpidem and trazodone, which have GABA-ergic and serotonergic mechanisms, respectively.

MATERIALS AND METHODS

In rats, radiotelemetry transmitters with electroencephalogram and electromyogram electrodes were implanted for sleep recording. Animals were administered with caffeine alone (10 mg/kg) or in combination with zolpidem (10 mg/kg) or trazodone (20 mg/kg), or vehicle, in crossover experiments. Home polysomnography was performed in 12 healthy male volunteers in a randomised, placebo-controlled, 4-week crossover study. Subjects received placebo, caffeine (150 mg) or caffeine in combination with zolpidem (10 mg) or trazodone (100 mg). Subjective sleep effects in volunteers were assessed using the Leeds Sleep Evaluation Questionnaire.

RESULTS

Caffeine caused a significant prolongation in objective SOL in rats and humans. This effect was sensitive to zolpidem and trazodone, both of which attenuated the caffeine-induced increase in SOL. Furthermore, both hypnotics restored the disruption in subjective measures of sleep onset caused by caffeine in volunteers.

CONCLUSIONS

This model therefore provides a promising paradigm in which we can study novel treatments for sleep disorders and an opportunity for direct comparison of results between rodents and humans.

In vitro and in vivo effect of BU99006 (5-isothiocyanato-2-benzofuranyl-2-imidazoline) on I2 binding in relation to MAO: Evidence for two distinct I2 binding sites

BU99006 is an irreversible I(2) ligand which selectively inactivates I(2) binding sites, making it an ideal tool with which to study I(2) site mechanism. We sought to determine the effects of BU99006 on I(2) binding in relation to monoamine oxidase (MAO), and the time course of these effects. In vitro, rat brain membranes that were pre-treated with 10 microM BU99006 showed no change in MAO activity, despite suffering a significant reduction in [(3)H]2BFI binding (52.5+/-19.6 to 8.5+/-3.8 fmol mg(-1), 84%). Furthermore, reversible I(2) ligands 2BFI and BU224 were able to inhibit MAO, whether treated with BU99006 or not. In vivo, a 5 mg kg(-1) i.v. dose of BU99006 in rats rapidly reduced [(3)H]2BFI binding with similar magnitude (85%, maximal reduction after 20 min), without effect on either MAO activity or the specific binding of selective MAO-A and MAO-B radioligands. Moreover, following this irreversible treatment, recovery of central [(3)H]2BFI binding occurred with a rapid half-life of 4.3 h in rat brain (2.0 h in mouse), which is not consistent with a site on MAO. These data indicate that the high affinity site which is occupied by [(3)H]2BFI and irreversibly binds BU99006, is not the same as that which causes inhibition of MAO, and may point to the existence of another I(2) binding site.

Antidepressants and REM sleep in Wistar–Kyoto and Sprague–Dawley rats

Compared to other rat strains, the Wistar-Kyoto rats show increased amount of REM sleep, one of the characteristic sleep changes observed in depressed patients. The aims of this study were firstly to validate a simple sleep stage discriminator and then compare the effect of antidepressants on suppression of rapid eye movement (REM) sleep in Wistar-Kyoto rats and an outbred rat strain (Sprague-Dawley). Rats were implanted with telemetry transmitters with electroencephalogram/electromyogram electrodes. Following recovery, the animals were orally dosed at light onset with either desipramine (20 mg/kg), fluoxetine (10 mg/kg), citalopram (10 or 40 mg/kg) or vehicle in a cross-over design. Every 12-s epoch was automatically scored as WAKE, NREM or REM sleep. Results confirm that Wistar-Kyoto rats show increased amount of REM sleep and decreased REM latency compared with Sprague-Dawley rats. All antidepressants significantly suppressed REM sleep in Sprague-Dawley rats, but only the high dose of citalopram suppressed REM sleep in Wistar-Kyoto rats. These findings suggest that the enhanced REM activity in Wistar-Kyoto rats is less sensitive to the effect of antidepressants and therefore does not provide any additional predictive validity for assessing antidepressant efficacy.

In Vivo Estimation of Imidazoline2 Binding Site Turnover

Turnover of imidazoline(2) (I(2)) binding sites in the mouse and rat brain has been measured following an acute intravenous dose of BU99006. This ligand selectively and irreversibly knocks out I(2) sites, as defined by [(3)H]2BFI binding. Recovery was measured using radioligand binding and autoradiography to determine global and regional changes in I(2) density. The density of I(2) sites in brain recovered from BU99006 treatment with a half-life of 2.1 hours in mice and 4.3 hours in rats. Monoamine oxidase (MAO) activity and MAO binding density were unaltered in the brains of BU99006-treated animals. These data suggest that the I(2) site that reacts with BU99006 recovers rapidly and is independent of MAO.

Relationship Between Imidazoline2 Sites and Monoamine Oxidase

I(2) site-selective compounds are known to interact with and inhibit monoamine oxidase (MAO), but it remains unclear as to whether this interaction occurs through an allosteric or competitive interaction. This study used the new selective, irreversible I(2) ligand BU99006, to clarify the relationship between MAO and the I(2) binding sites (I(2)-BS). Results demonstrate that irreversible binding of BU99006 to rat brain membranes does not inhibit the enzyme or interfere with its interaction with other imidazoline enzyme inhibitors. This finding suggests that the I(2) sites that react with BU99006 are not those implicated in MAO inhibition and points to the existence of at least two distinct I(2) binding proteins.