Analyzing global utilization and missed opportunities in debt-for-nature swaps with generative AI

We deploy a prompt-augmented GPT-4 model to distill comprehensive datasets on the global application of debt-for-nature swaps (DNS), a pivotal financial tool for environmental conservation. Our analysis includes 195 nations and identifies 21 countries that have not yet used DNS before as prime candidates for DNS. A significant proportion demonstrates consistent commitments to conservation finance (0.86 accuracy as compared to historical swaps records). Conversely, 35 countries previously active in DNS before 2010 have since been identified as unsuitable. Notably, Argentina, grappling with soaring inflation and a substantial sovereign debt crisis, and Poland, which has achieved economic stability and gained access to alternative EU conservation funds, exemplify the shifting suitability landscape. The study's outcomes illuminate the fragility of DNS as a conservation strategy amid economic and political volatility.

Data-driven discovery of molecular photoswitches with multioutput Gaussian processes

Photoswitchable molecules display two or more isomeric forms that may be accessed using light. Separating the electronic absorption bands of these isomers is key to selectively addressing a specific isomer and achieving high photostationary states whilst overall red-shifting the absorption bands serves to limit material damage due to UV-exposure and increases penetration depth in photopharmacological applications. Engineering these properties into a system through synthetic design however, remains a challenge. Here, we present a data-driven discovery pipeline for molecular photoswitches underpinned by dataset curation and multitask learning with Gaussian processes. In the prediction of electronic transition wavelengths, we demonstrate that a multioutput Gaussian process (MOGP) trained using labels from four photoswitch transition wavelengths yields the strongest predictive performance relative to single-task models as well as operationally outperforming time-dependent density functional theory (TD-DFT) in terms of the wall-clock time for prediction. We validate our proposed approach experimentally by screening a library of commercially available photoswitchable molecules. Through this screen, we identified several motifs that displayed separated electronic absorption bands of their isomers, exhibited red-shifted absorptions, and are suited for information transfer and photopharmacological applications. Our curated dataset, code, as well as all models are made available at https://github.com/Ryan-Rhys/The-Photoswitch-Dataset.

Achieving robustness to aleatoric uncertainty with heteroscedastic Bayesian optimisation

Bayesian optimisation is a sample-efficient search methodology that holds great promise for accelerating drug and materials discovery programs. A frequently-overlooked modelling consideration in Bayesian optimisation strategies however, is the representation of heteroscedastic aleatoric uncertainty. In many practical applications it is desirable to identify inputs with low aleatoric noise, an example of which might be a material composition which displays robust properties in response to a noisy fabrication process. In this paper, we propose a heteroscedastic Bayesian optimisation scheme capable of representing and minimising aleatoric noise across the input space. Our scheme employs a heteroscedastic Gaussian process surrogate model in conjunction with two straightforward adaptations of existing acquisition functions. First, we extend the augmented expected improvement heuristic to the heteroscedastic setting and second, we introduce the aleatoric noise-penalised expected improvement (ANPEI) heuristic. Both methodologies are capable of penalising aleatoric noise in the suggestions. In particular, the ANPEI acquisition yields improved performance relative to homoscedastic Bayesian optimisation and random sampling on toy problems as well as on two real-world scientific datasets. Code is available at: https://github.com/Ryan-Rhys/Heteroscedastic-BO

Mapping Materials and Molecules

The visualization of data is indispensable in scientific research, from the early stages when human insight forms to the final step of communicating results. In computational physics, chemistry and materials science, it can be as simple as making a scatter plot or as straightforward as looking through the snapshots of atomic positions manually. However, as a result of the "big data" revolution, these conventional approaches are often inadequate. The widespread adoption of high-throughput computation for materials discovery and the associated community-wide repositories have given rise to data sets that contain an enormous number of compounds and atomic configurations. A typical data set contains thousands to millions of atomic structures, along with a diverse range of properties such as formation energies, band gaps, or bioactivities.It would thus be desirable to have a data-driven and automated framework for visualizing and analyzing such structural data sets. The key idea is to construct a low-dimensional representation of the data, which facilitates navigation, reveals underlying patterns, and helps to identify data points with unusual attributes. Such data-intensive maps, often employing machine learning methods, are appearing more and more frequently in the literature. However, to the wider community, it is not always transparent how these maps are made and how they should be interpreted. Furthermore, while these maps undoubtedly serve a decorative purpose in academic publications, it is not always apparent what extra information can be garnered from reading or making them.This Account attempts to answer such questions. We start with a concise summary of the theory of representing chemical environments, followed by the introduction of a simple yet practical conceptual approach for generating structure maps in a generic and automated manner. Such analysis and mapping is made nearly effortless by employing the newly developed software tool ASAP. To showcase the applicability to a wide variety of systems in chemistry and materials science, we provide several illustrative examples, including crystalline and amorphous materials, interfaces, and organic molecules. In these examples, the maps not only help to sift through large data sets but also reveal hidden patterns that could be easily missed using conventional analyses.The explosion in the amount of computed information in chemistry and materials science has made visualization into a science in itself. Not only have we benefited from exploiting these visualization methods in previous works, we also believe that the automated mapping of data sets will in turn stimulate further creativity and exploration, as well as ultimately feed back into future advances in the respective fields.

Constrained Bayesian optimization for automatic chemical design using variational autoencoders

Automatic Chemical Design is a framework for generating novel molecules with optimized properties. The original scheme, featuring Bayesian optimization over the latent space of a variational autoencoder, suffers from the pathology that it tends to produce invalid molecular structures. First, we demonstrate empirically that this pathology arises when the Bayesian optimization scheme queries latent space points far away from the data on which the variational autoencoder has been trained. Secondly, by reformulating the search procedure as a constrained Bayesian optimization problem, we show that the effects of this pathology can be mitigated, yielding marked improvements in the validity of the generated molecules. We posit that constrained Bayesian optimization is a good approach for solving this kind of training set mismatch in many generative tasks involving Bayesian optimization over the latent space of a variational autoencoder.

Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance

RATIONALE

Although psilocybin has been used for centuries for religious purposes, little is known scientifically about its acute and persisting effects.

OBJECTIVES

This double-blind study evaluated the acute and longer-term psychological effects of a high dose of psilocybin relative to a comparison compound administered under comfortable, supportive conditions.

MATERIALS AND METHODS

The participants were hallucinogen-naïve adults reporting regular participation in religious or spiritual activities. Two or three sessions were conducted at 2-month intervals. Thirty volunteers received orally administered psilocybin (30 mg/70 kg) and methylphenidate hydrochloride (40 mg/70 kg) in counterbalanced order. To obscure the study design, six additional volunteers received methylphenidate in the first two sessions and unblinded psilocybin in a third session. The 8-h sessions were conducted individually. Volunteers were encouraged to close their eyes and direct their attention inward. Study monitors rated volunteers' behavior during sessions. Volunteers completed questionnaires assessing drug effects and mystical experience immediately after and 2 months after sessions. Community observers rated changes in the volunteer's attitudes and behavior.

RESULTS

Psilocybin produced a range of acute perceptual changes, subjective experiences, and labile moods including anxiety. Psilocybin also increased measures of mystical experience. At 2 months, the volunteers rated the psilocybin experience as having substantial personal meaning and spiritual significance and attributed to the experience sustained positive changes in attitudes and behavior consistent with changes rated by community observers.

CONCLUSIONS

When administered under supportive conditions, psilocybin occasioned experiences similar to spontaneously occurring mystical experiences. The ability to occasion such experiences prospectively will allow rigorous scientific investigations of their causes and consequences.

An abuse liability comparison of flunitrazepam and triazolam in sedative drug abusers

The present double-blind, placebo-controlled study compared the acute effects of oral administration of the benzodiazepine hypnotics flunitrazepam (6 mg/70 kg) and triazolam (1 and 2 mg/70 kg) on measures relevant to abuse liability as well as on psychomotor performance and observer- and participant-rated measures of drug effects in nine sedative drug abusers. Analysis of participant-rated measures collected 24 h after drug administration (next-day; assessing the overall effects of the drug received 24 h earlier) indicated that flunitrazepam, but neither triazolam dose, produced significant increases relative to placebo in next-day ratings of drug liking, the amount of money the drug would be worth on the street, and the amount of money the participant would be willing to pay for the drug on the street. Importantly, these abuse liability differences between flunitrazepam and triazolam were present at a dose of flunitrazepam (6 mg/70 kg) that produced overall drug effects that were comparable to, or significantly less than, those of a high triazolam dose (2 mg/70 kg). Consistent with results of a previous study in our laboratory, these results suggest that flunitrazepam may have a greater abuse liability than triazolam, and that this abuse liability difference emerges on measures taken 24 h after drug administration but not on same-day measures.

Physical dependence in baboons chronically treated with low and high doses of diazepam

Physical dependence on diazepam was evaluated in male baboons chronically treated with either low or high doses of diazepam. Baboons received either a single oral daily administration of a low dose (0.5 mg/kg per day) of diazepam (n=4) or continuous intragastric infusion of a high dose (20 mg/kg per day) of diazepam (n=7). Development of physical dependence during chronic dosing with 0.5 mg/kg per day diazepam was assessed at 2 and 4 weeks and then monthly, during 1-h behavioral observations, following injections of the benzodiazepine competitive antagonist flumazenil. After 3-24 months of diazepam treatment, dosing was discontinued and physical dependence assessed via observation and responding for food pellets. In baboons that received 0.5 mg/kg per day diazepam, flumazenil precipitated a mild- to intermediate-intensity benzodiazepine withdrawal syndrome, which included decreases in the number of food pellets earned per day and increases in withdrawal postures, self-directed behaviors, aggressive behaviors and retching/vomiting. Three of four baboons showed signs of precipitated withdrawal after only 2 weeks of chronic low-dose treatment. Flumazenil continued to precipitate withdrawal signs, but with no systematic increase in severity, throughout the 6-10 months of 0.5 mg/kg diazepam administration. When 0.5 mg/kg per day diazepam dosing was discontinued, the number of food pellets earned per day decreased in two of the four baboons, but no systematic changes in behavioral signs were observed. In contrast, within 7-10 days of termination of 20 mg/kg per day diazepam dosing, withdrawal signs of intermediate intensity and a decrease in the number of food pellets earned per day occurred in all baboons. In the present study, physical dependence developed after 2 weeks of a chronic low dose of diazepam administration but did not increase further over long-term exposure to diazepam.

Cocaine-like subjective effects of nicotine are not blocked by the D1 selective antagonist ecopipam (SCH 39166)

The effects of ecopipam (a D(1) selective antagonist) or triazolam pretreatment on the subjective and physiological effects of intravenously administered nicotine were examined in 10 cigarette-smoking cocaine abusers. Under double-blind, randomized conditions, subjects received oral capsule pretreatment (0, 30 or 100 mg ecopipam, or 0.25 mg/70 kg triazolam), followed 120 min later by an intravenous injection of 2 mg/70 kg nicotine or saline. Subjective ratings, heart rate and blood pressure were assessed before and repeatedly after each intravenous injection. Compared to oral placebo pretreatment, both ecopipam and triazolam pretreatment produced significant elevations in subject-reported capsule effect and observer ratings of sleepiness/sedation. Nicotine increased ratings of 'drug effect', 'rush', 'high', 'stimulated', 'liking', 'good effects' and 'bad effects', and produced modest increases in heart rate and blood pressure. Following both intra-venous saline and nicotine injection, ecopipam tended to reduce heart rate and blood pressure. Although both ecopipam and triazolam lowered several subjective ratings following intravenous saline injection, neither ecopipam nor triazolam affected nicotine subjective effects. In contrast to Romach et al. (Arch Gen Psychiatry 56: 1101-1106, 1999), who showed that pretreatment with ecopipam blocked cocaine subjective effects, the current study found no attenuation of the subjective effects of nicotine, and thus, provides no support for the hypothesis that D(1) receptors mediate the cocaine-like subjective effects of nicotine.

Alcohol and triazolam: differential effects on memory, psychomotor performance and subjective ratings of effects

The effects of alcohol (0.80 g/kg) and the benzodiazepine hypnotic triazolam (0.25 mg/70 kg) were compared directly in a double-dummy, double-blind, placebo-controlled, repeated-measures design in 18 healthy volunteers. While alcohol (0.80 g/kg) and triazolam (0.25 mg/70 kg) produced comparable levels of psychomotor performance impairment, a dissociation was observed, such that the magnitude of memory impairment (measured by d', participants' sensitivity in discriminating between old and new words in the recognition memory paradigm) was greater with triazolam than with alcohol, whereas subjective ratings of the overall strength of drug effect were higher with alcohol than with triazolam. Participants also adopted a more conservative response bias in the recognition memory paradigm in the alcohol (0.80 g/kg) condition relative to both placebo and triazolam (0.25 mg/70 kg). In addition to characterizing the adverse effects of two widely used psychoactive substances, the present results may also contribute to the understanding of underlying neurochemical mechanisms.

Alcohol and false recognition: a dose-effect study

RATIONALE

The pattern of acute memory impairment produced by alcohol is similar to that produced by the benzodiazepines. However, in contrast to demonstrations that benzodiazepines decrease false recognition rates, results of a recent study suggest that a low dose of alcohol increases false recognition rates; false recognition refers to the phenomenon of mistakenly claiming that one has been exposed previously to a novel item.

OBJECTIVE

This study was designed to examine the acute dose-effects of alcohol on false recognition.

METHODS

Effects of alcohol (0.27 and 0.60 g/kg) on performance in the Deese/Roediger-McDermott false recognition paradigm were examined in a repeated measures placebo-controlled double-blind design in 18 healthy volunteers.

RESULTS

The 0.60 g/kg dose of alcohol significantly reduced true recognition rates (measured by hit rate) and induced a more conservative response bias (measured by C) relative to placebo; however, neither alcohol dose significantly impaired participants' sensitivity in discriminating between old and new words (d'). Neither alcohol dose affected false recognition rates.

CONCLUSIONS

Effects of alcohol on false recognition and on response bias may differ from those observed previously with benzodiazepines. A direct comparison at equivalent doses will be necessary to draw conclusions about qualitative differences between alcohol and benzodiazepines.

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

It is well documented that acute administration of the benzodiazepine hypnotic drug triazolam (Halcion) impairs episodic memory encoding. We examined the neuroanatomical substrates of this effect in healthy adult volunteers using a double-blind, within-subject design. Following oral capsule administration (0.25 mg/70 kg triazolam or placebo), regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) with 15O-H(2)O during the performance of semantic categorization, orthographic categorization, and visual fixation (resting) tasks. rCBF associated with episodic memory encoding was measured by the difference in rCBF during the orthographic categorization task relative to that during the semantic categorization task. Results in the placebo condition (n = 9) replicated those of previous nonpharmacological encoding studies (activation in the left prefrontal cortex, cerebellum, anterior cingulate cortex, temporal cortex, and occipital cortex). Relative to placebo, results in the triazolam condition (n = 6) revealed significantly impaired memory performance, and deactivation during encoding in a subset of areas shown previously to be associated with encoding (anterior cingulate cortex, cerebellum, and precuneus). Results are discussed in relation to triazolam's effects on mnemonic versus attentional processes.

Physiological, subjective and reinforcing effects of oral and intravenous cocaine in humans

RATIONALE

There is little comparative information on the qualitative similarity, relative potency and reinforcing effects of oral cocaine versus cocaine administered via other routes.

METHODS

The present study used a within-subject, double-blind, double-dummy design to compare the physiological, subjective and reinforcing effects of placebo and oral (62.5, 125, 250 mg/70 kg) and intravenous (IV) (12.5, 25, 50 mg/70 kg) cocaine in volunteers with histories of cocaine abuse.

RESULTS

Cocaine produced dose-dependent increases on heart rate and blood pressure, with effects lasting longer after oral than IV cocaine. Subjective ratings (e.g., "rush," "drug effect," "liking") were qualitatively similar and dose-dependently increased after oral and IV administration, and the duration of effects was similar under both routes. On a money versus drug choice measure of reinforcement, the monetary amounts at which participants chose drug over money increased as a function of cocaine dose under both routes of administration. At doses that produced comparable subjective, physiological, and reinforcing effects, oral cocaine was not identified as cocaine as frequently as IV cocaine. Across measures, the data suggested that IV cocaine was approximately 10 times more potent than oral cocaine.

CONCLUSIONS

Overall, the results of this study support qualitatively similar effects of oral and IV cocaine and suggest that oral cocaine may be an effective tool for studying cocaine's effects in human laboratory studies.

Investigation of preference for nightly triazolam versus placebo in moderate social alcohol drinkers

This study was designed to examine whether the widely prescribed benzodiazepine hypnotic triazolam has reinforcing effects in moderate social alcohol drinkers, without histories of drug abuse or insomnia, in the context of its use as a hypnotic. Eleven healthy adult volunteers who met criteria for 'good sleepers' participated in a 60-session double-blind choice study which was conducted on an outpatient basis with participants sleeping at home. Twenty three-session sampling/choice tests were conducted sequentially to provide 20 evaluations of the reinforcing effects of 0.25 mg/70 kg triazolam versus placebo, ingested orally 30 min before bedtime. Each three-session test consisted of two sampling sessions, in which participants received exposure to each of the two drug conditions in different colored capsules, followed by one choice session, in which participants were asked to choose one of the two colour-coded capsules for self-administration. Four participants exhibited a significant choice of triazolam, three, a significant choice of placebo (i.e. triazolam avoidance), and four, a random (i.e. non-significant) choice between triazolam and placebo. The reasons provided by participants were consistent with their choices and with the expected effects of triazolam versus placebo. Analyses of post-sleep questionnaires indicated that triazolam did not produce a clinically meaningful improvement in sleep. The finding that triazolam functioned as a reinforcer in participants without insomnia suggests that triazolam has reinforcing effects in some individuals for which hypnotic treatment is not clinically indicated, and that health care professionals must continue to assess the risk/benefit ratio of benzodiazepine hypnotic prescription.

Reinforcing effects of oral cocaine: contextual determinants

RATIONALE

Although the behavioral, subjective, and physiological effects of oral cocaine have been investigated, its reinforcing effects have not been demonstrated.

OBJECTIVE

The primary aims of this study were to examine the reinforcing effects of oral cocaine and determine whether such effects can be influenced by manipulating behavioral requirements following drug ingestion.

METHODS

Nine adult volunteers with histories of cocaine abuse were trained to discriminate between orally administered cocaine (100 mg/70 kg) and placebo capsules under double-blind conditions. Following acquisition of cocaine vs placebo discrimination (80% correct), the reinforcing effects of cocaine were determined using two different choice conditions (dependent and independent). Volunteers were first exposed to cocaine and placebo once each with a relaxation activity (sitting in a cushioned chair) and a vigilance activity (performing a computer task). Following exposure to each drug with each activity, volunteers began the dependent choice condition. Every 2 days volunteers chose which drug (cocaine or placebo) they ingested with the vigilance and relaxation activities. Volunteers could not choose the same drug with both activities. This procedure occurred 5 times over a 10-day period. The independent choice condition took place over 2 days. On one day, volunteers chose which drug (cocaine or placebo) they ingested with the relaxation activity and, on the other day (in counterbalanced order), which drug they ingested with the vigilance activity. Volunteers were allowed to select the same drug with both activities.

RESULTS

All volunteers successfully acquired the cocaine vs placebo discrimination. In the dependent choice condition, all volunteers significantly chose cocaine over placebo with the vigilance activity and chose placebo over cocaine with the relaxation activity. In the independent choice condition, volunteers significantly chose cocaine over placebo with the vigilance activity (i.e., cocaine functioned as a positive reinforcer in the vigilance context). Interestingly, the independent choice condition also showed that volunteers chose placebo over cocaine with the relaxation activity (i.e., cocaine functioned as a negative reinforcer because it was avoided relative to placebo).

CONCLUSION

The study shows that the behavioral requirements following drug ingestion can be a determinant of whether or not oral cocaine functions as a reinforcer in volunteers with histories of cocaine abuse.

Intravenous nicotine and caffeine: subjective and physiological effects in cocaine abusers

The subjective and physiological effects of intravenously administered caffeine and nicotine were compared in nine subjects with histories of using caffeine, tobacco, and cocaine. Subjects abstained from tobacco cigarette smoking for at least 8 h before each session. Dietary caffeine was eliminated throughout the study; however, to maintain consistency with the nicotine intake, subjects were administered caffeine (150 mg/70 kg b.i.d.) in capsules, with the last dose administered 15 to 18 h before each session. Under double-blind conditions, subjects received placebo, caffeine (100, 200, and 400 mg/70 kg), and nicotine (0.75, 1.5, and 3.0 mg/70 kg) in mixed order. Physiological and subjective data were collected before and repeatedly after drug or placebo administration. Compared with the highest dose of caffeine, the highest dose of nicotine produced greater subjective ratings on a number of scales. At doses that produced comparable ratings of drug effect (1.5 mg/70 kg of nicotine and 400 mg/70 kg of caffeine), both drugs produced similar increases in ratings of good effect, liking, high, stimulated, and bad effect. Nicotine showed a somewhat faster time to peak subjective effects than caffeine (2 versus 4 min). Subjective ratings that differentiated caffeine and nicotine were ratings of rush, blurry vision, and stimulant identification (elevated by nicotine) and ratings of unusual smell and/or taste (elevated by caffeine). Both caffeine and nicotine decreased skin temperature and increased diastolic blood pressure; however, caffeine decreased whereas nicotine increased heart rate. The study documents both striking similarities and some notable differences between caffeine and nicotine, which are among the most widely used mood-altering drugs.

Acute dose-effects of scopolamine on false recognition

RATIONALE

Recently, there has been increased research interest in the phenomenon of false recognition, in which participants claim to recognize words that had not been presented during an initial study phase but that are associatively related to presented words. Acute administration of the benzodiazepine hypnotic triazolam has been shown to decrease false recognition rates. However, no false recognition studies have examined the effects of scopolamine, an anticholinergic drug that might produce a different profile of memory-impairing effects than the benzodiazepines due to its distinct neurochemical profile.

OBJECTIVE

This study was designed to examine the acute dose-effects of scopolamine on false recognition.

METHODS

The effects of subcutaneously administered scopolamine (0.3 and 0.6 mg/70 kg) on performance in the Deese/Roediger-McDermott false recognition paradigm were examined in a repeated-measures placebo-controlled double-blind design in 18 healthy volunteers.

RESULTS

Scopolamine produced dose-related reductions in both true and false recognition rates, and induced a more conservative response bias relative to placebo for recollection-based ("remember") responses to studied words.

CONCLUSIONS

While scopolamine's effects on false recognition are similar to those observed previously with triazolam, its effects on response bias may differ from those of triazolam.

Zaleplon and triazolam physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The ability of the GABA(A)-receptor-subtype-selective hypnotic zaleplon to produce physical dependence was compared to the nonselective benzodiazepine triazolam. Progressively increasing doses of zaleplon and triazolam were given to baboons by intragastric infusion once each day, with doses increasing every 17 days. Next, the highest dose was given for 10-34 additional days by continuous infusion. Both drugs produced increases in food-maintained lever pressing, ataxia, and time to complete a fine motor task. Plasma levels increased dose-dependently; drug was detectable 24 h after higher doses. Flumazenil produced a mild or intermediate precipitated-withdrawal syndrome on day 14 of all dosing conditions. When drug delivery ended after 85-100 days, a benzodiazepine-type withdrawal syndrome occurred. Physical dependence potential of zaleplon and triazolam appear similar.

Acute effects of triazolam on false recognition

Neuropsychological, neuroimaging, and electrophysiological techniques have been applied to the study of false recognition; however, psychopharmacological techniques have not been applied. Benzodiazepine sedative/anxiolytic drugs produce memory deficits similar to those observed in organic amnesia and may be useful tools for studying normal and abnormal memory mechanisms. The present double-blind, placebo-controlled repeated measures study examined the acute effects of orally administered triazolam (Halcion; 0.125 and 0.25 mg/70 kg), a benzodiazepine hypnotic, on performance in the Deese (1959)/Roediger-McDermott (1995) false recognition paradigm in 24 healthy volunteers. Paralleling previous demonstrations in amnesic patients, triazolam produced significant dose-related reductions in false recognition rates to nonstudied words associatively related to studied words, suggesting that false recognition relies on normal memory mechanisms impaired in benzodiazepine-induced amnesia. The results also suggested that relative to placebo, triazolam reduced participants' reliance on memory for item-specific versus list-common semantic information and reduced participants' use of remember versus know responses.

Caffeine as a model drug of dependence: recent developments in understanding caffeine withdrawal, the caffeine dependence syndrome, and caffeine negative reinforcement

Caffeine is an excellent model compound for understanding drugs of abuse/dependence. The results of self-administration and choice studies in humans clearly demonstrate the reinforcing effects of low and moderate doses of caffeine. Caffeine reinforcement has been demonstrated in about 45% of normal subjects with histories of moderate and heavy caffeine use. Recent studies provide compelling evidence that caffeine physical dependence potentiates the reinforcing effects of caffeine through the mechanism of withdrawal symptom avoidance. Tolerance to the subjective and sleep-disrupting effects of caffeine in humans has been demonstrated. Physical dependence as reflected in a withdrawal syndrome in humans has been repeatedly demonstrated in adults and recently demonstrated in children. Withdrawal severity is an increasing function of caffeine maintenance dose, with withdrawal occurring at doses as low as 100 mg per day. Increased cerebral blood flow may be the physiological mechanism for caffeine withdrawal headache. Case studies in adults and adolescents clearly demonstrate that some individuals meet DSM-IV diagnostic criteria for a substance dependence syndrome on caffeine, including feeling compelled to continue caffeine use despite desires and recommendations to the contrary. Survey data suggest that 9% to 30% percent of caffeine consumers may be caffeine dependent according to DSM-IV criteria.

Is caffeine a flavoring agent in cola soft drinks?

BACKGROUND

Concern has been expressed about the nutrition and health impact of high rates of soft drink consumption. Caffeine is an added ingredient in approximately 70% of soft drinks consumed in the United States. The soft drink manufacturers' justification to regulatory agencies and the public for adding caffeine to soft drinks is that caffeine is a flavoring agent.

OBJECTIVE

To examine the claim that caffeine plays an integral role in the flavor profile of soft drinks, by examining the effect of caffeine on the threshold for detection of flavor differences in cola beverages.

DESIGN

Double-blind crossover study starting November 1998 and ending July 1999.

SETTING

An academic research center.

PARTICIPANTS

Twenty-five adult regular consumers of cola soft drinks. Based on a screening session, all were able to detect a flavor difference between cola containing sugar and diet cola.

INTERVENTION

A sensitive version of a forced-choice flavor-detection procedure was used to evaluate the effects of a wide range of caffeine concentrations (range, 0.05-1.6 mg/mL) on the ability to detect flavor differences between caffeinated and caffeine-free cola beverages. Repeated tests permitted determination of significant detection at each concentration in individual subjects.

MAIN OUTCOME MEASURES

Percentage of subjects significantly detecting a flavor difference and mean percentage of trials correct at each caffeine concentration.

RESULTS

Detection of flavor differences increased as a function of caffeine concentration. At the 0.1-mg/mL concentration, which is the approximate concentration in the majority of cola soft drink products, 2 subjects (8%) significantly detected a flavor difference and the mean percentage correct (53%) was at chance levels.

CONCLUSIONS

The finding that only 8% of a group of regular cola soft drink consumers could detect the effect of the caffeine concentration found in most cola soft drinks is at variance with the claim made by soft drink manufacturers that caffeine is added to soft drinks because it plays an integral role in the flavor profile. It is valuable for the general public, the medical community, and regulatory agencies to recognize that the high rates of consumption of caffeinated soft drinks more likely reflect the mood-altering and physical dependence-producing effects of caffeine as a central nervous system-active drug than its subtle effects as a flavoring agent. Arch Fam Med. 2000;9:727-734

Caffeine withdrawal increases cerebral blood flow velocity and alters quantitative electroencephalography (EEG) activity

RATIONALE

Cessation of daily caffeine consumption produces a withdrawal syndrome comprised of subjective symptoms and functional impairment. Few controlled studies have examined the physiological effects of caffeine withdrawal.

OBJECTIVE

The present study examined the effect of caffeine withdrawal on cerebral blood flow velocity and quantitative EEG.

METHODS

Ten volunteers reporting moderate caffeine intake (mean 333 mg/day) participated in this double-blind study. Subjects completed several tests when maintaining their normal diet (baseline period) and during two 1-day periods during which they consumed caffeine-free diets and received capsules containing placebo (placebo test session) or caffeine (caffeine test session) in amounts equal to their baseline daily caffeine consumption. Blood flow velocity was determined for four arteries: right and left middle (MCA), and right and left anterior (ACA) cerebral arteries using pulsed transcranial Doppler sonography. EEG was recorded for 3 min from eight scalp sites while subjects sat, with eyes closed, in a sound-attenuated electronically shielded chamber. Subjective effects were assessed with questionnaires.

RESULTS

Results showed an effect of the placebo (21-h withdrawal) condition compared to the caffeine condition. Placebo significantly increased the mean velocity, systolic velocity and diastolic velocity (cm/s) in all four cerebral arteries. In the MCA, the pulsatility index was significantly decreased following placebo. Placebo significantly increased EEG theta power. Placebo also produces subjective effect changes, including increases in heavy feelings in arms and legs and decreases in ability to concentrate. The caffeine and baseline conditions produced similar results on both the physiological and subjective measures.

CONCLUSION

Cessation of daily caffeine consumption produced changes in cerebral blood flow velocity and quantitative EEG. These changes may be related to classic caffeine withdrawal symptoms of headache, drowsiness and decreased alertness.

A controlled study of flumazenil-precipitated withdrawal in chronic low-dose benzodiazepine users

RATIONALE

Preclinical studies of the benzodiazepine antagonist flumazenil (Romazicon) have contributed to the understanding of the physical dependence associated with chronic benzodiazepine use; when administered to animals chronically pretreated with benzodiazepines, flumazenil precipitates a withdrawal syndrome. However, few controlled clinical studies have been conducted.

OBJECTIVES

The objective was to characterize the effects of flumazenil in long-term users of therapeutic doses of benzodiazepines.

METHODS

The acute physiological, participant-rated, and observer-rated effects of intravenously administered flumazenil (1 mg/70 kg) and caffeine (300 mg/70 kg; active drug control) were evaluated in an experimental group of 13 long-term users (mean 4.6 years) of low therapeutic doses (mean 11.2 mg/day diazepam equivalent) relative to a matched group of 13 volunteers without prior exposure to benzodiazepines in a double-blind, placebo-controlled, mixed design.

RESULTS

Whereas the experimental group did not differ from the control group with respect to the effects of placebo, and both groups showed some changes in response to caffeine (e.g., increased blood pressure and anxiety scores), only the experimental group showed considerable changes in physiological measures, participant ratings (e.g., increased ratings of dizziness, blurred vision, heart pounding, feelings of unreality, pins and needles, nausea, sweatiness, noises louder than usual, jitteriness, things moving, sensitivity to touch), and observer ratings in response to flumazenil; in addition, four participants developed panic attacks.

CONCLUSIONS

This study clearly demonstrates that flumazenil can precipitate symptoms commonly associated with benzodiazepine withdrawal in chronic low-dose benzodiazepine users.

Comparison of the intravenous reinforcing effects of propofol and methohexital in baboons

Propofol is a widely used intravenous anesthetic that can directly activate and positively modulate the GABA(A)-receptor. Propofol is not currently regulated under the USA Controlled Substances Act. The present study evaluated the intravenous reinforcing effects of propofol compared to the intravenous barbiturate anesthetic methohexital in baboons using a procedure in which doses of the test drug were substituted for a standard cocaine dose. Drug or vehicle was available for self-injection during daily 5.5-h sessions under a fixed-ratio 120 or 160 schedule of reinforcement. A 40-min timeout after each injection limited the maximum of injections per session to eight. Food pellets were available continuously during the session under a fixed ratio 10 schedule of reinforcement. Self-injection of cocaine (0.001-0.32 mg/kg/injection) and vehicle was characterized first. Cocaine maintained self-injection in a dose-dependent manner, with peak injections maintained by 0.32 mg/kg. Vehicle and each dose of propofol (0.1-1.0 mg/kg/injection) and methohexital (0.01-1.0 mg/kg/injection) were substituted for 0.32 mg/kg cocaine for at least 10 sessions. Propofol and methohexital maintained self-injection greater than vehicle in all three baboons, and these effects were dose dependent. Methohexital maintained peak mean levels of self-injection that were >6 injections/day at doses of 0.56 and 1.0 mg/kg, and did not alter food intake systematically. Propofol maintained peak mean levels of self-injection at 1.0 mg/kg that ranged from 2.2 to >6 injections/day across the baboons. Food intake was increased slightly above vehicle levels by propofol self-injection in two baboons, and was decreased in the third baboon. These data indicate that propofol, like methohexital, can function as a positive reinforcer.

Zaleplon and triazolam in humans: acute behavioral effects and abuse potential

Zaleplon, a pyrazolopyrimidine that is under development as a hypnotic, produces its pharmacological effects at the benzodiazepine-recognition site on the GABA(A) benzodiazepine-receptor complex. Unlike most benzodiazepines, zaleplon binds selectively to the BZ1 (omega1) subtype of the benzodiazepine receptor. The present study compared the acute subject-rated effects, performance-impairing effects, and abuse potential of zaleplon and triazolam, a triazolobenzodiazepine hypnotic, in 14 healthy volunteers with histories of drug abuse. Zaleplon (25, 50, and 75 mg), triazolam (0.25, 0.5, and 0.75 mg) and placebo were administered orally in this double-blind, crossover study. Zaleplon and triazolam produced comparable dose-related effects on several subject-rated drug-effect questionnaires. Zaleplon and triazolam also produced comparable dose-dependent decrements on several performance tasks including balance, circular lights, digit-enter and recall, DSST, picture recall/recognition and repeated acquisition. Same-day and next-day subject-rated measures reflecting abuse potential (e.g., drug liking, good effects, and monetary street value) also suggest that zaleplon and triazolam were comparable. The only notable between-drug difference observed in the present study was that the time-action function of zaleplon differed from that of triazolam. The onset time, time to maximum drug effect, and duration of action were shorter with zaleplon than triazolam. Thus, despite its non-benzodiazepine structure and unique benzodiazepine-receptor binding profile, the behavioral pharmacological profile of zaleplon is similar to that of triazolam.

Evaluation of limited and unlimited food intake during withdrawal in triazolam-dependent baboons

Chronic administration of benzodiazepine (BZ) agonists in baboons typically increases food intake, in a dose-dependent manner, during drug administration and suppresses food intake after termination of drug dosing. To determine if suppressed food intake after termination of chronic BZ administration (i.e. withdrawal) was related to increased food consumption during drug administration, the effects of chronic triazolam (1.0 mg/kg/day, intragastrically, for 30-34 days) and subsequent triazolam withdrawal on food intake was studied under two conditions in each of four baboons: (1) when the number of pellets was unlimited; and (2) when the number of pellets was limited so that pellet intake could not increase above the mean number of pellets per day obtained during a preceding vehicle condition. Pellets were available during daily 20-h sessions under a fixed-ratio 10 schedule of reinforcement. All baboons completed both pellet conditions, and the order of exposure was counterbalanced across subjects. During the unlimited pellet condition, pellets per day were increased during triazolam administration and then were suppressed in a time-limited manner when triazolam was discontinued in all four baboons. When pellet intake was limited during triazolam administration, pellet intake after triazolam discontinuation was suppressed in three of four baboons, and the magnitude and duration of suppression was generally less than during the unlimited pellet condition. Other behavioral signs of withdrawal (e.g., tremor/jerk, vomit/retch) were observed in all four baboons under both pellet conditions. These data suggest that the hyperphagic effects of triazolam appear to contribute to the subsequent suppression of food intake during triazolam withdrawal. However, these hyperphagic effects do not account for the entire phenomenon of suppressed food intake during BZ withdrawal.

Drug discrimination analysis of partial agonists at the benzodiazepine site. I. Differential effects of U-78875 across training conditions in baboons and rats

The benzodiazepine receptor ligand U-78875 [3-(5-cyclopro pyl-1,2, 4-oxadiazol-3-yl)-5-(1-methylethyl)imidazol(1, 5-a)quinoxalin-4(5H)-o-ne] was studied in rats trained to discriminate i.p. 1.0 mg/kg lorazepam, 1.0 mg/kg diazepam, or 10 mg/kg pentobarbital, and baboons trained to discriminate oral 1.8 mg/kg lorazepam or 10 mg/kg pentobarbital. U-78875 doses were 0.01 to 10 mg/kg i.p. in rats and 0.32 to 56 mg/kg orally in baboons. U-78875 occasioned drug-appropriate responding in pentobarbital-trained (ED50 = 1.8 mg/kg) and diazepam-trained (ED50 = 0.056 mg/kg) rats, but it occurred in only one pentobarbital-trained baboon and not in the majority of lorazepam-trained baboons or rats. In baboons that generalized to U-78875, discriminative effects were antagonized by flumazenil. The interaction of U-78875 with pentobarbital, diazepam, and lorazepam revealed further differences in its behavioral effects. U-78875 potentiated the effects of pentobarbital, even in baboons that did not generalize to U-78875, but U-78875 had little effect in combination with diazepam. In lorazepam-trained animals that did not generalize to it, U-78875 antagonized lorazepam's effects, but U-78875 neither antagonized nor potentiated lorazepam in animals that did generalize to U-78875. Thus, although U-78875 generally functioned as a benzodiazepine agonist in pentobarbital- and diazepam-trained animals, its unique effects in lorazepam-trained animals appear to reflect its in vitro profile as a partial agonist.

Triazolam and zolpidem: effects on human memory and attentional processes

RATIONALE

The imidazopyridine hypnotic zolpidem may produce less memory and cognitive impairment than classic benzodiazepines, due to its relatively low binding affinity for the benzodiazepine receptor subtypes found in areas of the brain which are involved in learning and memory.

OBJECTIVES

The study was designed to compare the acute effects of single oral doses of zolpidem (5, 10, 20 mg/70 kg) and the benzodiazepine hypnotic triazolam (0.125, 0.25, and 0.5 mg/70 kg) on specific memory and attentional processes.

METHODS

Drug effects on memory for target (i.e., focal) information and contextual information (i.e., peripheral details surrounding a target stimulus presentation) were evaluated using a source monitoring paradigm, and drug effects on selective attention mechanisms were evaluated using a negative priming paradigm, in 18 healthy volunteers in a double-blind, placebo-controlled, crossover design.

RESULTS

Triazolam and zolpidem produced strikingly similar dose-related effects on memory for target information. Both triazolam and zolpidem impaired subjects' ability to remember whether a word stimulus had been presented to them on the computer screen or whether they had been asked to generate the stimulus based on an antonym cue (memory for the origin of a stimulus, which is one type of contextual information). The results suggested that triazolam, but not zolpidem, impaired memory for the screen location of picture stimuli (spatial contextual information). Although both triazolam and zolpidem increased overall reaction time in the negative priming task, only triazolam increased the magnitude of negative priming relative to placebo.

CONCLUSIONS

The observed differences between triazolam and zolpidem have implications for the cognitive and pharmacological mechanisms underlying drug-induced deficits in specific memory and attentional processes, as well for the cognitive and brain mechanisms underlying these processes.

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.

Caffeine withdrawal: a parametric analysis of caffeine dosing conditions

Although caffeine is the most widely used behaviorally active drug in the world, caffeine physical dependence has been only moderately well characterized in humans. Four double-blind experiments were conducted in independent groups of healthy participants to assess the conditions under which withdrawal symptoms occur upon cessation of low to moderate doses of caffeine. In experiment 1, there was no evidence that the range or magnitude of caffeine withdrawal symptoms differed when 300 mg of caffeine was consumed as a single dose in the morning versus 100 mg at three time points across the day. In experiment 2, both the range and severity of withdrawal increased as a function of caffeine maintenance dose (100, 300, and 600 mg/day), with even the lowest dose (100 mg) producing significant caffeine withdrawal. Experiment 3 showed that when individuals were maintained on 300 mg caffeine/day and tested with a range of lower doses (200, 100, 50, 25, and 0 mg/day), a substantial reduction in caffeine consumption (</=100 mg/day) was necessary for the manifestation of caffeine withdrawal. Experiment 4 manipulated duration of exposure to caffeine (1, 3, 7, or 14 days of 300 mg/day) and showed that caffeine withdrawal occurred after as little as 3 days of caffeine exposure, with a somewhat increased severity of withdrawal observed after 7 or 14 days of exposure. As a whole, this set of experiments provides the most complete parametric characterization of caffeine withdrawal to date and suggests that caffeine physical dependence can occur under more modest conditions (i.e., fewer doses per day, lower daily dose, shorter duration of exposure) than previously recognized.

Evaluation of the intravenous reinforcing effects of clonidine in baboons

Clonidine HCl is an antihypertensive that is also sometimes used to alleviate symptoms of withdrawal during narcotics detoxification. Recently, there have been reports abuse of clonidine by methadone patients and opioid abusers. The present study evaluated the intravenous self-administration of clonidine in four baboons. Self-injections were available 24 h/day under a fixed-ratio (FR 120 or 160) schedule of injection with a 3-h timeout after each injection. Doses of clonidine (0.0001-0.056 mg/kg per injection) or its vehicle (saline) were substituted for cocaine (0.32 mg/kg) for at least 15 days. Food pellets were available continuously under a concurrent FR 30 schedule of pellet delivery. Clonidine maintained self-injection greater than its saline vehicle in all four baboons. Although self-injection of clonidine increased as a function of dose within each baboon, there were differences between baboons in the range of doses of clonidine that maintained self-injection. Doses of 0.032 or 0.056 mg/kg maintained peak mean levels of clonidine self-injection which ranged from low (3.2 injections/day) to high (> 6 injections/day) across baboons. Levels of self-injection were similar to vehicle at 0.01 mg/kg clonidine in two of four baboons. However, in the other two baboons, very low doses of clonidine (0.0001-0.001 mg/kg) maintained low to moderate levels of self-injection. Acute administration of clonidine produced signs of sedation including lip droop, drooling and sitting with eyes closed. At high doses, some toxicity was apparent: Baboons were pale and not responsive. Food intake was generally increased in a dose dependent manner. The present study indicates that clonidine functions as a positive reinforcer.

Subjective and physiological effects of intravenous nicotine and cocaine in cigarette smoking cocaine abusers

The subjective and physiological effects of intravenously administered cocaine and nicotine were compared in 10 cigarette-smoking cocaine abusers. Subjects abstained from smoking at least 8 h before each session. Under double blind conditions, subjects received placebo, cocaine (10, 20, and 40 mg/70 mg), or nicotine (0.75, 1.5, 3.0 mg/70 kg) in mixed order. Physiological and subjective data were collected before and repeatedly after each intravenous drug administration. Subjects also completed a drug versus money multiple-choice procedure in which they chose between that day's drug and 44 monetary values. Both drugs increased blood pressure and heart rate and decreased skin temperature. Nicotine showed a more rapid onset of subjective effects than cocaine. Overall, although both cocaine and nicotine increased subjective ratings of "drug effect", "rush", "good effects", "liking", "high", and "stimulated", only nicotine increased ratings of "bad effects" and "jittery". Although the highest nicotine dose produced greater effects than the highest cocaine dose on most subjective measures, the highest cocaine dose produced somewhat greater ratings of drug liking. At doses that produced comparable ratings of drug effect (40 mg/70 kg cocaine versus 1.5 mg/70 kg nicotine), cocaine produced significantly greater good effects, whereas nicotine produced greater bad effects. All three cocaine doses and the intermediate and high nicotine doses were frequently categorized as producing effects similar to those of cocaine or amphetamine. The drug versus money measure showed that the highest cocaine dose was worth twice as much as the highest nicotine dose. Thus, intravenous cocaine and nicotine can be differentiated by their subjective and reinforcing effects.

Flunitrazepam and triazolam: a comparison of behavioral effects and abuse liability

The performance, observer-rated, and participant-rated effects of orally administered placebo, and two benzodiazepines, flunitrazepam (2, 4 and 8 mg/70 kg) and triazolam (0.25, 0.5 and 1 mg/70 kg), were compared in 14 sedative drug abusers using a double-blind crossover design. Both flunitrazepam and triazolam produced dose-related decrements in memory and psychomotor/cognitive performance, and increases in many participant- and observer-rated measures. Effects of flunitrazepam had an earlier onset and a longer duration than those of triazolam. Although there was evidence that the flunitrazepam doses selected for study were somewhat higher overall relative to the selected triazolam doses, analysis of the participant-rated measures collected 24 h after drug administration (next-day) suggests that flunitrazepam may have a greater abuse liability than triazolam when abuse liability is assessed 24 h after drug administration. The highest flunitrazepam dose produced effects that were significantly greater than those of the highest triazolam dose on next-day ratings of good effects, take again, and worth; all tested flunitrazepam doses produced effects greater than any triazolam dose on next-day ratings of liking and take again. The highest flunitrazepam dose, but no triazolam dose, significantly increased the maximum dollar value at which participants chose drug over money in a Drug versus Money Choice Procedure.

Zolpidem is differentiated from triazolam in humans using a three-response drug discrimination procedure

The discriminative stimulus effects of the imidazopyridine hypnotic zolpidem and the classic benzodiazepine hypnotic triazolam were examined in seven healthy volunteers using a three-response drug discrimination procedure and a within-subject design. During an initial sampling phase, the training drug conditions (placebo, 20 mg/70 kg zolpidem, and 0.5 mg/70 kg triazolam) were identified to subjects by letter codes before oral drug administration. During a subsequent training phase, subjects earned money for correct drug identifications made 3.75 h after drug administration. Five out of seven subjects acquired the three-response discrimination. Analyses of standardized and unstructured self-report questionnaires revealed that zolpidem and triazolam produced different profiles of effects; zolpidem was associated with a number of negative somatic symptoms including nausea, blurred vision, visual images/hallucinations, and heavy limbs, whereas triazolam was associated with greater sedative effects. These results demonstrate a distinct profile of discriminative stimulus and subjective effects for zolpidem, relative to triazolam, which is consistent with its somewhat distinct pharmacological profile, and provide evidence for the sensitivity of the three-response drug discrimination procedure for detecting between-drug differences.

Physical dependence increases the relative reinforcing effects of caffeine versus placebo

Using a within-subject cross-over design, this study examined the role of physical dependence in caffeine reinforcement by experimentally manipulating physical dependence. Each subject was exposed to two chronic drug phases (300 mg/70 kg/day caffeine and placebo) for 9-12 days, with order of phases counterbalanced across subjects. On 2 separate days immediately following each of the chronic drug exposures, subjects received acute doses of either caffeine (300 mg/70 kg) or placebo in counterbalanced order. The reinforcing effects of these drugs were then determined by using a multiple-choice procedure in which subjects made a series of discrete choices between receiving varying amounts of money or receiving the drug again, and a choice between the two drugs. To ensure that subjects completed the form carefully, following exposure to both of the acute drug administrations, one of the subject's previous choices from the multiple-choice form was randomly selected and the consequence of that choice was implemented. When subjects were maintained on chronic caffeine, they were willing to forfeit significantly more money and showed significant increases in typical withdrawal symptoms (e.g. fatigue, mood disturbance) after receiving placebo as compared to the other three conditions. When subjects were maintained on chronic caffeine, they also chose to receive caffeine over placebo twice as often than when they were maintained on chronic placebo. These findings provide the strongest evidence to date indicating that caffeine physical dependence increases the relative reinforcing effects of caffeine versus placebo.

Buspirone is differentiated from diazepam in humans using a three-response drug discrimination procedure

The discriminative stimulus effects of buspirone and diazepam were examined in 12 healthy volunteers using a three-response drug discrimination procedure and a within-subject design. During an initial sampling phase, the training drug conditions (placebo, 15 mg/70 kg buspirone, and 10 mg/70 kg diazepam) were identified to subjects by letter codes before oral drug administration. During a subsequent training phase, subjects earned money for correct drug identifications made two hours after drug administration. Ten out of 12 subjects acquired the three-response discrimination. When lower doses of buspirone (3.75 and 7.5 mg/70 kg) and diazepam (2.5 and 5.0 mg/70 kg) were tested in a subsequent generalization testing phase, both buspirone and diazepam produced dose-related increases in appropriate drug identifications, without significant cross-generalization. Analyses of standardized and unstructured self report questionnaires revealed that buspirone and diazepam produced different profiles of effects, and that buspirone was associated with a number of "negative" subject-rated effects including tension, nausea, and dizziness. These results demonstrate a distinct profile of discriminative stimulus and subjective effects for buspirone relative to diazepam which is consistent with its distinct pharmacological profile, and provide evidence for the sensitivity of the three-response drug discrimination procedure.

Zolpidem self-injection with concurrent physical dependence under conditions of long-term continuous availability in baboons

Intravenous zolpidem self-injection, and the concurrent development of physical dependence under conditions of continuous drug availability, was characterized in three baboons. Previously, under similar conditions, 1.0 mg/kg midazolam maintained low, but stable, daily rates of self-injection (e.g. less than 20 injections/day) over 30 or more days and resulted in the development of physical dependence in baboons. In the current experiments, saline and zolpidem (1.0 mg/kg) were available for self-injection under a fixed-ratio (FR-30) schedule of lever-pull responses with a 5 min time-out after each injection. Saline maintained only low levels of responding (i.e. less than five injections per day). Zolpidem maintained an orderly spaced within-day pattern of injections and daily rates of self-injection were higher than saline (i.e. 10 or more injections per day). Daily rates of zolpidem self-injection were relatively stable in two baboons, and increased over time in the third baboon. Substitution of saline for zolpidem produced a rapid decrease in responding that remained low (i.e. less than five injections per day) in all three baboons. Chronic self-injection of zolpidem produced an increase in responding maintained by food pellet delivery and an increase in body weights. Administration of flumazenil (0.1-1.0 mg/kg, i.v.) after at least 35 days of zolpidem self-injection produced postures and behavioral signs typical of a classic flumazenil-precipitated benzodiazepine withdrawal syndrome. Substitution of saline after chronic zolpidem self-injection produced a time-limited spontaneous withdrawal syndrome. Behavioral signs and postures were similar to those observed during flumazenil-precipitated withdrawal and were most prominent during the first 8 days after zolpidem was discontinued. Therefore, like midazolam, zolpidem maintained self-injection and physical dependence developed under conditions of long-term continuous availability.

Zolpidem physical dependence assessed across increasing doses under a once-daily dosing regimen in baboons

The current study examined behavioral effects and possible development of physical dependence after once-daily doses of zolpidem (0, 1.0, 3.2, 10.0, 32.0 mg/kg intragastrically [i.g.]) in three baboons. Each dose was administered for 17 days and then the dose was increased; the 32.0 mg/kg dose was administered for 27 days. Baboons had access to food pellets for 20 hr/day beginning 15 min after dosing. Each day, baboons were presented with a fine motor task. Observation sessions were conducted 1 hr after dosing on days 1, 10, 12 and 14 of each dose condition and after termination of drug dosing. On days 10 and 14 of each dose condition, vehicle and flumazenil (5 mg/kg i.m.) were administered, respectively. Zolpidem increased the number of pellets obtained by two of three baboons. Vomit and/or retch and grimace (signs believed to be indicative of abdominal discomfort) were observed in one or two baboons during all zolpidem dose conditions (1.0-32.0 mg/kg). Time to complete the fine motor task increased dose-dependently in all three baboons, and incoordination was observed during the task in two baboons at 10.0 and 32.0 mg/kg. Analysis of blood plasma showed that measurable levels of zolpidem were present 24 hr after dosing in all drug conditions. The signs of flumazenil-precipitated withdrawal were summarized on a 9-point scale. Scores ranged from 1 to 5 in the 1.0 mg/kg condition, from 2 to 5 in the 3.2 and 10.0 mg/kg conditions and from 4 to 6 in the 32.0 mg/kg condition. Signs that were considered intermediate in severity were observed. Specifically, tremor, jerk and/or rigidly braced posture was observed in one baboon at 1.0 mg/kg, two baboons at the next two doses and all three baboons at 32.0 mg/kg. Vomit and/or retch also occurred in two baboons at dose conditions above 1.0 mg/kg. Discontinuation of zolpidem dosing after 78 to 79 days resulted in mild withdrawal signs (e.g., number of pellets obtained were lower and number of 1-min intervals increased in which eyes were closed, or in which lying down, head lower than torso posture and/or withdrawn posture were observed) on the first day in two baboons. The peak withdrawal scores were 4 or 5 on days 5 to 10; two baboons vomited and/or retched and all three baboons showed tremor, jerk and/or rigidly braced posture. Thus, zolpidem produced physical dependence under once-daily dosing conditions, and the severity of the withdrawal syndrome can be characterized as intermediate.

Stable low-rate midazolam self-injection with concurrent physical dependence under conditions of long-term continuous availability in baboons

The current research was undertaken to characterize intravenous midazolam self-injection and the concurrent development of physical dependence under conditions of continuous drug availability. Baboons (n=6) i.v. self-injected midazolam under conditions of continuous availability under a fixed-ratio 30 schedule of lever-pull responses with a 5-min time-out after each injection. Midazolam (1.0 mg/kg) maintained an orderly spaced within-day pattern of injections and low, but stable, daily rates of self-injection over 30 or more days (e.g. <20 injections/day). Sequential substitution of saline and then midazolam produced rapid extinction and then reinstatement of responding at the same stable rate. In subsequent manipulations, a range of lower doses of midazolam (0.0156-0.25 mg/kg) were also shown to reinstate self-injection responding after extinction on saline; however, both chronic and acute dose manipulations indicated that dose-regulation was poor. Chronic self-injection of the high dose (1.0 mg/kg) but not lower doses produced a suppression in responding maintained by food pellet delivery. Chronic self-injection of 1.0 and 0.25 mg/kg midazolam produced physical dependence as reflected in classic benzodiazepine spontaneous and flumazenil-precipitated withdrawal syndromes, including tremor, vomiting and, in one instance, seizure. The stable, low-rate self-injection of midazolam, with concurrent development of physical dependence, demonstrated in the present study may provide a useful model system for investigating factors which contribute to long-term inappropriate use of benzodiazepines by physically dependent patients.

Benzodiazepine self-administration in humans and laboratory animals--implications for problems of long-term use and abuse

Drug reinforcement may represent the primary behavioral-pharmacological mechanism underlying two types of problematic use of benzodiazepines--recreational abuse by polydrug abusers and inappropriate chronic use by patients. High dose polydrug abuse for the purpose of getting high is readily recognized as a significant social problem. Inappropriate chronic benzodiazepine use is more subtle but relatively common: for anxiolytics, 36% of past-year users (3% of the adult population in the US) report using these drugs for 4 consecutive months or longer. The risks of such long-term use are much better documented than the benefits. This paper provides a current review of various problems that have been identified with the long-term use and the recreational abuse of benzodiazepines, including memory impairment, risk of accidents, falls and hip fractures in the elderly, a withdrawal syndrome, brain damage, overuse in the elderly, overuse by chronic pain patients, overuse by alcoholics and recreational abuse among alcoholics and polydrug abusers. A comprehensive review of the literature on benzodiazepine reinforcing effects in humans and laboratory animals is also provided. Drug self-administration studies in humans and laboratory animals provide models of both types of problematic benzodiazepine use. Recreational abuse of benzodiazepines has been modeled in human research with polydrug abusers and in laboratory animal studies, which show that the reinforcing effect of benzodiazepines is intermediate relative to other sedative compounds and is increased in subjects with histories of previous sedative drug self-administration. The problem of inappropriate long-term use of benzodiazepines by people without histories of drug abuse has been partially modeled in human studies showing that benzodiazepines function as reinforcers in subjects with anxiety, insomnia, and histories of moderate alcohol consumption, and in preclinical studies showing stable, low-rate benzodiazepine self-injection with concurrent physical dependence under conditions of continuous availability. Both human and animal research suggests that the drug history and current behavioral context may be important in the establishment of benzodiazepines as reinforcers. Limited human and animal research provides little support for the common belief that physical dependence enhances benzodiazepine reinforcement.

Triazolam and zolpidem: a comparison of their psychomotor, cognitive, and subjective effects in healthy volunteers

The psychomotor/cognitive performance, subject-rated, and observer-rated effects of single oral doses of the benzodiazepine hypnotic triazolam (0.125, 0.25, and 0.5 mg/70 kg) and the imidazopyridine hypnotic zolpidem (5, 10, and 20 mg/70 kg) were compared in 11 volunteers, in a double-blind, placebo-controlled, crossover design. Triazolam and zolpidem produced similar dose-related decrements on several performance measures, and similar dose-related increases on most observer-rated and several subject-rated measures. The drugs differed in the time course of their effects on these measures; the effects of zolpidem typically peaked 30 min earlier (1-1.5 h postdrug) than the effects of triazolam (1.5-2 h postdrug). Triazolam and zolpidem produced a different profile of effects on other performance measures which could not be attributed to time course differences. Triazolam produced significantly more impairment than zolpidem in time estimation. Triazolam, but not zolpidem, produced significant impairment on a short-term memory task. Zolpidem produced significantly more impairment than triazolam on several novel measures of performance on a computerized trail-making test. The observed differences between triazolam and zolpidem may be related to zolpidem's reported binding selectivity for the omega 1 receptor subtype.

Ethanol and pentobarbital: comparison of behavioral and subjective effects in sedative drug abusers

The behavioral and subjective effects of acute oral doses of placebo, ethanol (0.5, 1.0, and 2.0 g/kg), and pentobarbital (150, 300, 600, and 750 mg/70 kg) were compared in 8 male volunteers with histories of sedative drug abuse using a double-blind, double-dummy, cross-over design. Ethanol and pentobarbital produced similar dose-related decrements in psychomotor and cognitive performance and exhibited a similar profile of effects on staff- and participant-rated measures. There was some evidence indicating that, at the highest dose, pentobarbital was perceived by participants as being more sedating than ethanol and that pentobarbital has a greater abuse liability than ethanol. In conjunction with the results of previous human laboratory studies comparing the effects of different types of sedative-hypnotic drugs, these results support a mostly barbiturate-like rather than benzodiazepine-like profile of effects for ethanol.

Acute participant-rated and behavioral effects of alprazolam and buspirone, alone and in combination with ethanol, in normal volunteers

The acute behavioral effects of buspirone (15 and 30 mg/70 kg), alprazolam (0.75 and 1.5 mg/70 kg), and placebo, alone and in combination with ethanol (0-0.6 g/kg), were tested in 13 volunteers. Ethanol alone produced only a few significant behavioral effects. Alprazolam and buspirone produced comparable dose-related increases in participant ratings of sedation, but only alprazolam impaired performance. The buspirone-ethanol and alprazolam-ethanol combinations produced robust sedative-like participant-related drug effects that were similar in magnitude, but, in general, only the alprazolam-ethanol combinations impaired performance. These findings suggest that the participant-rated effects of therapeutic doses of buspirone in combination with moderate doses of ethanol are similar to those of therapeutic doses of alprazolam in combination with ethanol, but the performance-impairing effects of buspirone are distinguishable from those of alprazolam, alone and in combination with ethanol.

Selectivity in the generalization profile in baboons trained to discriminate lorazepam: benzodiazepines, barbiturates and other sedative/anxiolytics

The discriminative stimulus effects of benzodiazepines often have been indistinguishable from those of barbiturates or other sedative/anxiolytics. However, baboons and rats trained to discriminate lorazepam did not reliably generalize to pentobarbital in previous studies, although animals comparably trained to discriminate pentobarbital reliably generalized to lorazepam. The present study investigated the generalization profile for a variety of anxiolytic, sedative and other drugs in baboons trained to discriminate oral lorazepam (1.8 mg/kg). Triazolam, alprazolam, diazepam, midazolam, bromazepam, temazepam and nordiazepam occasioned >80% of total responses on the lorazepam-paired lever, in that order of potency, 60 min after oral dosing; chlordiazepoxide did so in three of five baboons. However, barbiturates (amobarbital, hexobarbital, methohexital, pentobarbital, phenobarbital, secobarbital) and methypryIon occasioned lorazepam-appropriate responding in only one or two baboons. Testing barbiturates at different pretreatment times (amobarbital, hexobarbital, pentobarbital or secobarbital) or by an i.m. route of administration (methohexital, pentobarbital) did not produce an increase in generalization. Neither other classic sedatives/anxiolytics (chloral hydrate, clomethiazole, ethanol, methaqualone, meprobamate, triclofos), nor anticonvulsants (phenytoin, valproic acid), nor drugs from other pharmacological classes shared discriminative-stimulus effects with lorazepam. These results, together with those from previous studies in which lorazepam or another benzodiazepine served as the training stimulus, indicate that lorazepam training results in a more selective generalization profile with respect to sedative/anxiolytic drugs than does training with other benzodiazepines.

The role of dopamine in the behavioral effects of caffeine in animals and humans

Dopamine has been proposed to mediate some of the behavioral effects of caffeine. This review discusses cellular mechanisms of action that could explain the role of dopamine in the behavioral effects of caffeine and summarizes the results of behavioral studies in both animals and humans that provide evidence for a role of dopamine in these effects. Caffeine is a competitive antagonist at adenosine receptors and produces a range of central and physiological effects that are opposite those of adenosine. Recently, caffeine has been shown to enhance dopaminergic activity, presumably by competitive antagonism at adenosine receptors that are colocalized and interact functionally with dopamine receptors. Thus, caffeine, as a competitive antagonist at adenosine receptors, may produce its behavioral effects by removing the negative modulatory effects of adenosine from dopamine receptors, thus stimulating dopaminergic activity. Consistent with this interpretation, preclinical behavioral studies show that caffeine produces behavioral effects similar to classic dopaminergically mediated stimulants such as cocaine and amphetamine, including increased locomotor activity, increased turning behavior in 6-hydroxydopamine-lesioned animals, stimulant-like discriminative stimulus effects, and self-administration. Furthermore, caffeine potentiates the effects of dopamine-mediated drugs on these same behaviors, and some of caffeine's effects on these behaviors can be blocked by dopamine receptor antagonists. Although more limited in scope, human studies also show that caffeine produces subjective, discriminative stimulus and reinforcing effects that have some similarities to those produced by cocaine and amphetamine.

Caffeine reinforcement: the role of withdrawal

This study examined caffeine's acute and withdrawal effects in moderate caffeine consumers (mean = 379 mg/day caffeine) to compare the relative contributions each might have to caffeine reinforcement. Subjects were caffeine restricted on the night before each of three sessions, which generally occurred at weekly intervals; these restrictions lasted until the session was completed approximately 19 h later. During the first two sessions, subjects received either placebo or caffeine (each subject's average daily intake). These two conditions occurred using a double-blind, quasi-random, crossover design. At the end of each session subjects completed the POMS, a caffeine withdrawal questionnaire, and a Multiple-Choice Form on which subjects made a series of discrete choices between receiving the drug again or receiving varying amounts of money. This form also included negative money amounts to assess how much subjects would forfeit to avoid placebo (e.g., withdrawal symptoms after placebo). During the third session, one of the previous choices was randomly selected and the consequence of that choice was implemented. Placebo increased self-reported feelings of "worn out," "headache," and "flu-like feelings," and decreased "alert," "upset stomach," "helpful," and "well-being" relative to caffeine. On the Multiple-Choice Forms, subjects chose to receive caffeine rather than an average of $0.38 and to forfeit $2.51 to avoid receiving placebo again. "Headache" was significantly correlated with amount of money forfeited to avoid placebo. These results suggest that, under these conditions, choice of caffeine is more potently controlled by avoiding withdrawal than it is by the positive effects of caffeine.

Human drug discrimination and multiple chemical sensitivity: caffeine exposure as an experimental model

Multiple chemical sensitivity is a controversial diagnosis. Rigorous, controlled, laboratory-based research can reduce this controversy and lead to potential clinical confirmatory tests. The literature on human caffeine discrimination provides a rigorous methodology that can address reports that patients who suffer multiple chemical sensitivity (MCS) are sensitive to usually well-tolerated chemical doses; the studies require patients to discriminate caffeine from placebo under double-blind conditions. Several issues relevant to the conduct of caffeine discrimination studies using MCS patients as subjects are addressed; these issues include study design, determination of safe and tolerable training doses, and discrimination training. Such research will benefit patients and clinicians dealing with a diagnosis of MCS.

Acute participant-rated and behavioral effects of alprazolam and buspirone, alone and in combination with ethanol, in normal volunteers

The acute behavioral effects of buspirone (15 and 30 mg/70 kg), alprazolam (0.75 and 1.5 mg/70 kg), and placebo, alone and in combination with ethanol (0-0.6 g/kg), were tested in 13 volunteers. Ethanol alone produced only a few significant behavioral effects. Alprazolam and buspirone produced comparable dose-related increases in participant ratings of sedation, but only alprazolam impaired performance. The buspirone-ethanol and alprazolam-ethanol combinations produced robust sedative-like participant-related drug effects that were similar in magnitude, but, in general, only the alprazolam-ethanol combinations impaired performance. These findings suggest that the participant-rated effects of therapeutic doses of buspirone in combination with moderate doses of ethanol are similar to those of therapeutic doses of alprazolam in combination with ethanol, but the performance-impairing effects of buspirone are distinguishable from those of alprazolam, alone and in combination with ethanol.

Mecamylamine does not precipitate withdrawal in cigarette smokers

Mecamylamine is an antihypertensive that acts via nicotinic antagonism and has been suggested as an aid in smoking cessation. Nicotine dependent patients may not accept mecamylamine if it precipitates withdrawal, as it does in nicotine dependent rats. This study examined mecamylamine's effects using procedures designed to measure precipitated withdrawal symptoms in humans. Ten cigarette smokers (mean of 37.5 cigarettes/day) and ten non tobacco-using subjects participated in three 6-h sessions. After a 2-h baseline period in which smokers smoked one cigarette every 30 min, oral mecamylamine (0, 10, or 20 mg randomly ordered across sessions) was administered (double-blind). No smoking was allowed for the remainder of the session. Mecamylamine reduced blood pressure and increased heart rate relative to placebo in both the smokers and the non-tobacco users. No reliable direct subjective effects of mecamylamine were observed. Smokers' subjective reports of cigarette craving and tobacco withdrawal increased, and DSST performance was disrupted over the last 4 h of each session. Effects were independent of dose (placebo versus active). These results suggest that up to 20 mg mecamylamine will not precipitate nicotine withdrawal and that this medication would be acceptable for use in smoking cessation.