Factors influencing the reinforcing and subjective effects of ephedrine in humans

Ephedrine and cocaine cause developmental neurotoxicity and abnormal behavior in zebrafish

Ephedrine (EPH) and cocaine (COC) are illegal stimulant drugs, and have been frequently detected in aquatic environments. EPH and COC have negative effects on the nervous system and cause abnormal behaviors in mammals and fish at high concentrations, but their mechanisms of neurotoxicity remain unclear in larvae fish at low concentrations. To address this issue, zebrafish embryos were exposed to EPH and COC for 14 days post-fertilization (dpf) at 10, 100, and 1000 ng L-1. The bioaccumulation, development, behavior, cell neurotransmitter levels and apoptosis were detected to investigate the developmental neurotoxicity (DNT) of EPH and COC. The results showed that EPH decreased heart rate, while COC increased heart rate. EPH caused cell apoptosis in the brain by AO staining. In addition, behavior analysis indicated that EPH and COC affected spontaneous movement, touch-response, swimming activity and anxiety-like behaviors. EPH and COC altered the levels of the neurotransmitters dopamine (DA) and γ-aminobutyric acid (GABA) with changes of the transcription of genes related to the DA and GABA pathways. These findings indicated that EPH and COC had noticeable DNT in the early stage of zebrafish at environmentally relevant concentrations.

Pre-competition mental energy and performance relationships among physically disabled table tennis players

Energy is essential to human daily functioning and performance. However, the association of mental energy with athletes' performance has rarely been examined. We attempted to examine the pre-competition mental energy-performance relationships by two studies. Study 1 administered Athletic Mental Energy Scale (AMES, Lu et al., 2018) to nine elite physically-disabled table tennis players one day before competition in 5 international tournaments. Then, we collected their subjective performance after each competition. In Study 2, we sampled 77 National-level physically-disabled table tennis players and examined the pre-competition mental energy-performance relationship as the procedure in Study 1. Results from Study 1 provided initial findings of how pre-competition mental energy is associated with performance and portrayed in elite physically-disabled table tennis players. Results from Study 2 further confirmed the pre-competition mental energy- performance relationships. We suggested future studies to examine the mental energy-performance relationships in physically-disabled and abled athletes and different sports.

In search of an ideal drug for safer treatment of obesity: The false promise of pseudoephedrine

Obesity is a major public health problem worldwide. Only relatively few treatment options are, at present, available for the management of obese patients. Furthermore, treatment of obesity is affected by the widespread misuse of drugs and food supplements. Ephedra sinica is an old medicinal herb, commonly used in the treatment of respiratory tract diseases. Ephedra species contain several alkaloids, including pseudoephedrine, notably endowed with indirect sympathomimetic pharmacodynamic properties. The anorexigenic effect of pseudoephedrine is attributable primarily to the inhibition of neurons located in the hypothalamic paraventricular nucleus (PVN), mediating satiety stimuli. Pseudoephedrine influences lipolysis and thermogenesis through interaction with β3 adrenergic receptors and reduces fat accumulation through down-regulation of transcription factors related to lipogenesis. However, its use is associated with adverse events that involve to a large extent the cardiovascular and the central nervous system. Adverse events of pseudoephedrine also affect the eye, the intestine, and the skin, and, of relevance, sudden cardiovascular death related to dietary supplements containing Ephedra alkaloids has also been reported. In light of the limited availability of clinical data on pseudoephedrine in obesity, along with its significantly unbalanced risk/benefit profile, as well as of the psychophysical susceptibility of obese patients, it appears reasonable to preclude the prescription of pseudoephedrine in obese patients of any order and degree.

Over a century since ephedrine discovery: an updated revisit to its pharmacological aspects, functionality and toxicity in comparison to its herbal extracts

Ephedrine, a sympathomimetic amine that exhibits several adrenaline actions, is a plant alkaloid that is a common ingredient in several cold, asthma and narcolepsy treatment preparations, and in obesity management and sport medicine. Its principal action mechanism relies on its direct adrenergic actions as well as indirect role that involves the release of epinephrine and norepinephrine, thus increasing the activity of epinephrine and norepinephrine at the postsynaptic α and β receptors. Nevertheless, its serious side effects, including stroke, heart attack, drug abuse and interactions, have never been comprehensively reviewed. We conducted a systematic review of data on ephedrine, including its occurrence in functional foods, pharmacological aspects, metabolism, pharmaco/toxicokinetics and clinical features. Furthermore, a review of ephedrine natural structural analogues with regards to their differential adrenergic receptor binding affinities, food interaction, and their impact on the pharmacokinetics and effects relative to ephedrine are presented for the first time, and in comparison to its action when present in herbs.

Impact of Sleep Disorder as a Risk Factor for Dementia in Men and Women

Sleep is an essential physiological process, especially for proper brain function through the formation of new pathways and processing information and cognition. Therefore, when sleep is insufficient, this can result in pathophysiologic conditions. Sleep deficiency is a risk factor for various conditions, including dementia, diabetes, and obesity. Recent studies have shown that there are differences in the prevalence of sleep disorders between genders. Insomnia, the most common type of sleep disorder, has been reported to have a higher incidence in females than in males. However, sex/gender differences in other sleep disorder subtypes are not thoroughly understood. Currently, increasing evidence suggests that gender issues should be considered important when prescribing medicine. Therefore, an investigation of the gender-dependent differences in sleep disorders is required. In this review, we first describe sex/gender differences not only in the prevalence of sleep disorders by category but in the efficacy of sleep medications. In addition, we summarize sex/gender differences in the impact of sleep disorders on incident dementia. This may help understand gender-dependent pathogenesis of sleep disorders and develop therapeutic strategies in men and women.

A translational pharmacology approach to understanding the predictive value of abuse potential assessments

Within the drug development industry the assessment of abuse potential for novel molecules involves the generation and review of data from multiple sources, ranging from in-vitro binding and functional assays through to in-vivo nonclinical models in mammals, as well as collection of information from studies in humans. This breadth of data aligns with current expectations from regulatory agencies in both the USA and Europe. To date, there have been a limited number of reviews on the predictive value of individual models within this sequence, but there has been no systematic review on how each of these models contributes to our overall understanding of abuse potential risk. To address this, we analyzed data from 100 small molecules to compare the predictive validity for drug scheduling status of a number of models that typically contribute to the abuse potential assessment package. These models range from the assessment of in-vitro binding and functional profiles at receptors or transporters typically associated with abuse through in-vivo models including locomotor activity, drug discrimination, and self-administration in rodents. Data from subjective report assessments in humans following acute dosing of compounds were also included. The predictive value of each model was then evaluated relative to the scheduling status of each drug in the USA. In recognition of the fact that drug scheduling can be influenced by factors other than the pharmacology of the drug, we also evaluated the predictive value of each assay for the outcome of the human subjective effects assessment. This approach provides an objective and statistical assessment of the predictive value of many of the models typically applied within the pharmaceutical industry to evaluate abuse potential risk. In addition, the impact of combining information from multiple models was examined. This analysis adds to our understanding of the predictive value of each model, allows us to critically evaluate the benefits and limitations of each model, and provides a method for identifying opportunities for improving our assessment and prediction of abuse liability risk in the future.

Human sex differences in d-amphetamine self-administration

Women and men may respond differently to the effects of stimulants such as amphetamine and cocaine.

AIM

In order to assess potential sex differences in the reinforcing effects of d-amphetamine, a retrospective-analysis was conducted on data collected from three studies that employed similar d-amphetamine self-administration procedures and used identical subject-rated drug-effect measures.

METHODS

Data from 10 women and 15 men were included in the analysis. In all studies, participants sampled placebo, low (8-10 mg) or high (16-20 mg) dose oral d-amphetamine. Following sampling sessions, participants worked for capsules containing one eighth of the previously sampled dose on a modified progressive-ratio schedule of reinforcement. We hypothesized that women and men would be differentially sensitive to the reinforcing effects of d-amphetamine. A two-way mixed-model analysis of variance (sex and dose) and planned comparisons were used in the statistical analyses.

RESULTS

The low dose of d-amphetamine functioned as a reinforcer in women, but not men, whereas the high dose of d-amphetamine functioned as a reinforcer in men, but not women. Men self-administered significantly more capsules under the high dose condition than women.

CONCLUSION

The results of this study suggest that men are more sensitive to the reinforcing effects of a high dose of d-amphetamine than women. Future research is needed that determines prospectively the reinforcing effects of weight-adjusted doses of d-amphetamine in women and men while controlling for menstrual cycle phase.

Over-the-counter stimulant, depressant, and nootropic use by veterinary students

US veterinary students are subject to significant stress throughout their veterinary education. In this article, the authors characterize the use of over-the-counter (OTC) medications and relate their use to stress in a veterinary student population. Of the students sampled, 35% were OTC medication users; 33% of these were regular OTC medication users. Forty-three percent of students were energy drink (ED) users; 45% of these were regular ED users. OTC medication users had significantly higher stress scores than non-OTC medication users, and ED users had significantly higher anxiety scores than non-ED users. The most common reasons for use given by OTC medication users were to help with studying and to fall asleep at night. Depression scores were significantly higher for juniors and sophomores than for freshmen. Depression, stress, and anxiety scores were all lower in the Colorado State University students when compared with the University of Georgia students. OTC medication and ED veterinary student users had distinct characteristics that differed from those of nonusers. Users suffered from more stress and anxiety and had more difficulties with sleep, which may have affected their overall health and academic performance. Educating veterinary students about the consequences of using OTC medication and ED and providing counseling support may be of benefit to veterinary students' psychological well-being.

The Effects of Ginseng, Ephedrine, and Caffeine on Cognitive Performance, Mood and Energy

A variety of claims regarding the purported energy-enhancing properties of nutritional supplements and food constituents have recently been made. It appears that the supplements most frequently associated with such assertions are ginseng, ephedrine, and caffeine. Claims of increased energy are difficult to evaluate objectively because their meaning is not usually defined or specified. Often it is not clear whether the claims refer to physical or mental energy or both. Furthermore, an agreed upon scientific definition of either physical or mental energy enhancement does not exist. In spite of obvious differences in what the term physical energy, as opposed to mental energy implies, there is no clear scientific consensus on whether there is a difference between the two types of energy. Because the substances in question have been anecdotally associated with improvements in both physical and mental performance, their effects on both functions will be discussed, but with an emphasis placed on cognitive function and mood. Of the three substances discussed, caffeine's effects on cognitive and physical function, mood, and energy are best understood. It is clear that this food/drug enhances these functions when administered in moderate doses. Ephedrine may also enhance certain physical and mental functions related to "energy," but the evidence that ginseng has such properties is exceedingly weak.

Allergy: a risk factor for suicide?

The rates of depression, anxiety, and sleep disturbance (suicide risk factors) are greater in patients with allergic rhinitis than in the general population. The rate of allergy is also greater in patients with depression. Preliminary data suggest that patients with a history of allergy may have an increased rate of suicide. Clinicians should actively inquire to diagnose allergy in patients with depression and depression in patients with allergy. Spring peaks of suicide are highly replicated, but their origin is poorly understood. Preliminary epidemiologic data suggest that seasonal spring peaks in aeroallergens are associated with seasonal spring peaks in suicide. Our research in Brown Norway rats demonstrates that sensitization and exposure to aeroallergens induces anxiety-like and aggressive behaviors as well as allergy-related helper T-cell type 2 (Th2) cytokine gene expression in the prefrontal cortex. Thus, it is possible that sensitization and exposure to aeroallergens, which peak in spring, may be conducive to seasonal exacerbation of suicide risk factors such as anxiety, depression, hostility/aggression, and sleep disturbance. Connecting allergy with suicide and suicide risk factors adds to previous neurologic literature connecting allergy with migraines and seizure disorders. Our recent report of Th2 (allergy-mediating) cytokine expression in the orbitofrontal cortex of suicide victims should lead to future studies to test the hypothesis that mediators of allergic inflammation in the nasal cavities may result in Th2 cytokine expression in the brain, influencing affect and behavioral modulation. Certain medications used to treat allergy can exacerbate suicide risk factors, potentially worsening suicide risk and even triggering suicide. Systemic (but not topical) corticosteroids have been associated with manic and depressive episodes and mixed mood states. Recently, the US Food and Drug Administration started investigating the possibility that montelukast may trigger suicide. Although this association requires further exploration and confirmation, clinicians should err on the side of caution, inquiring about past suicide attempts; hopelessness; reasons for living; and suicidal ideation, intent, or plan; and referring the patient to a mental health professional for evaluation if appropriate.

Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users

RATIONALE

Caffeine produces mild psychostimulant effects that are thought to underlie its widespread use. However, the direct effects of caffeine are difficult to evaluate in regular users of caffeine because of tolerance and withdrawal. Indeed, some researchers hypothesize that the psychostimulant effects of caffeine are due largely to the reversal of withdrawal and question whether there are direct effects of caffeine consumption upon mood, alertness, or mental performance in nondependent individuals.

OBJECTIVE

This study investigated the physiological, subjective, and behavioral effects of 0, 50, 150, and 450 mg caffeine in 102 light, nondependent caffeine users.

METHODS

Using a within-subjects design, subjects participated in four experimental sessions, in which they received each of the four drug conditions in random order under double blind conditions. Participants completed subjective effects questionnaires and vital signs were measured before and at repeated time points after drug administration. Forty minutes after the capsules were ingested, subjects completed behavioral tasks that included tests of sustained attention, short-term memory, psychomotor performance, and behavioral inhibition.

RESULTS

Caffeine significantly increased blood pressure, and produced feelings of arousal, positive mood, and high. Caffeine increased the number of hits and decreased reaction times in a vigilance task, but impaired performance on a memory task.

CONCLUSION

We confirm that acute doses of caffeine, at levels typically found in a cup of coffee, produce stimulant-like subjective effects and enhance performance in light, nondependent caffeine users. These findings support the idea that the drug has psychoactive effects even in the absence of withdrawal.

Toxicity and drug interactions associated with herbal products: ephedra and St. John's Wort

Health care providers are being increasingly confronted with the use of herbal medications by their patients. It is imperative that patients be questioned regarding herbal preparation use and that health care providers become familiar with these agents. Research into the active components and mechanisms of action of various herbals is ongoing [350]. Long-range studies need to be performed to follow patients for efficacy or toxicity in chronic use [351,352]. Adverse reactions to herbal remedies should be reported to the FDA MedWatch at http://www.fda.gov/medwatch. As withany therapeutic agent, risk of use must always be weighed against potential benefits.

Reinforcing effect of pseudoephedrine isomers and the mechanism of action

It has been proposed that ephedrine and its isomers may have abuse potential. When made available to rhesus monkeys (n = 4) for self-administration, +-pseudoephedrine functioned as a positive reinforcer in all monkeys, as did (-)-pseudoephedrine in two of three monkeys. Pseudoephedrine isomers were 10- to 33-fold less potent than cocaine. In in vitro binding in monkey brain tissue, both isomers had low affinity for dopamine and serotonin transporters by at least 200-fold relative to cocaine, but comparable affinity for norepinephrine transporters. +-Pseudoephedrine also blocked dopamine uptake in 293 hDAT cells with low potency relative to cocaine. When given in vivo +-pseudoephedrine significantly displaced radioligand binding to dopamine transporters with a potency comparable to that in self-administration. Therefore, pseudoephedrine isomers can function as reinforcers and the mechanism at dopamine transporters may underlie this effect. However, pseudoephedrine appears to be a weak reinforcer and may have relatively low abuse potential.

Discriminative stimulus effects of (-)-ephedrine in rats: analysis with catecholamine transporter and receptor ligands

A drug discrimination procedure was used to examine the neuropharmacology of (-)-ephedrine (5 mg/kg), a sympathomimetic amine found in a variety of dietary supplements. (-)-Ephedrine has caused concern because of its use as a precursor in the manufacture of street drugs (e.g. methamphetamine) and its potential for abuse and toxicity. In the present study, the catecholamine reuptake inhibitors mazindol and nomifensine, the norepinephrine (NE) reuptake inhibitor desipramine, and the dopamine D(2)-like (e.g. D(2), D(3) and D(4)) agonist quinpirole substituted for (-)-ephedrine (>/=80% (-)-ephedrine-lever responding). The NE reuptake inhibitor nisoxetine, the D(1)-like (e.g. D(1) and D(5)) agonists (+/-)-SKF 38393 and SKF 82958, and the mixed D(1)-/D(2)-like agonist apomorphine occasioned intermediate levels of responding (50-79% (-)-ephedrine-lever responding). The (-)-ephedrine cue was antagonized by the D(1)-like antagonist SCH 23390 and the alpha(1)-adrenoceptor antagonist prazosin as well as the D(2)-like antagonists (-)-eticlopride and haloperidol, although only at doses that disrupted responding in some rats. The discriminative stimulus effects of a small dose of (-)-ephedrine (1.25 mg/kg) were enhanced by the alpha(2)-adrenoceptor antagonist idazoxan and to a lesser extent by the beta-adrenoceptor antagonist (-)-propranolol. However, the alpha(2)-adrenoceptor agonist clonidine (0.04 mg/kg) did not attenuate the (-)-ephedrine stimulus. These results suggest that D(1)-, D(2)-like, and alpha(1)-adrenergic receptors mediate the discriminative stimulus effects of (-)-ephedrine. Substitution of desipramine for (-)-ephedrine and not for some other stimulants suggests that NE transmission is a prominent feature of the (-)-ephedrine discriminative stimulus, and that NE underlies therapeutic and abuse-related effects of (-)-ephedrine that diverge from those of other stimulants.

Alcohol choice and amphetamine effects in light and moderate drinkers

BACKGROUND

The results of previously published reports suggest that light and moderate drinkers respond differently to the effects of commonly abused sedatives (e.g., diazepam or ethanol). The purpose of this experiment was to determine whether light and moderate drinkers respond differentially to the effects of ethanol and d-amphetamine.

METHODS

In the first phase of this experiment, volunteers (eight light drinkers and eight moderate drinkers) randomly sampled 0.5 g/kg of ethanol and placebo across two separate sessions. In the second phase, volunteers completed three sessions in which they chose either ethanol or placebo. In the third phase, volunteers received 0, 5, 10, and 15 mg of d-amphetamine. Each dose was tested twice. After drug administration in each phase, volunteers completed a battery of subject-rated, performance, and physiologic measures periodically for 5 hr.

RESULTS

Ethanol produced prototypical subject-rated effects (e.g., increased ratings on the Alcohol Sensation Scale), but it was chosen over placebo infrequently. Light and moderate drinkers did not differ in terms of the self-reported or reinforcing effects of ethanol. d-Amphetamine produced prototypical subject-rated stimulant-like effects (e.g., dose-dependent increases in ratings of High and Rush). Moderate drinkers reported significantly greater drug effects than light drinkers. Responses to ethanol reliably predicted subsequent responses to d-amphetamine on several measures.

CONCLUSIONS

The results of this experiment suggest that even moderate ethanol use may increase an individual's vulnerability to abuse drugs. Future studies should determine whether light and moderate drinkers respond differentially to other commonly abused drugs (e.g., opioids) and whether behavioral responses to ethanol also predict responses to these compounds.

Noradrenergic modulation of ephedrine-induced hypophagia

The hypophagic action of the sympathomimetic amine ephedrine (EPH) in the rat may reflect actions on central dopaminergic (DA) and noradrenergic (NE) systems. EPH indirectly facilitates DA and NE activity and acts as a partial agonist at alpha(1)-adrenergic receptors. Two approaches were used to assess the possible contribution of NE and DA pathways to EPH-induced hypophagia. In the first, regression analyses of published archival data were computed to characterize the relation between the hypophagic potency values of (-)-(EPH) and related sympathomimetic drugs, including (+)-amphetamine, aminorex, mazindol, and phentermine (data derived from Blosser JC et al., 1987) and the most potent action of these drugs on facilitating NE activity or DA activity in rat brain (data derived from Rothman RB et al., 2001). In the NE analyses, the ED(50) values for these drugs for the inhibition of eating in rats were significantly related (r = 0.91, P = 0.03) to the potency of each drug in facilitating NE activity (either release or inhibition of [(3)H]NE reuptake), whereas in the DA analyses the correlation between ED(50) values and DA activity for these drugs was also significant (r = 0.98, P = 0.003). The regression analyses are thus supportive of a role for NE or DA in the hypophagic capacity of EPH. Although an earlier study noted that administration of the putative DA antagonist pimozide in rats attenuated EPH hypophagia, pimozide exerts similar potency in antagonizing DA receptors and alpha(1)-adrenergic receptors. To clarify the role of alpha(1)-adrenoceptors in EPH-induced hypophagia, adult male rats were pretreated with the alpha(1)-adrenergic receptor antagonist prazosin (0.0.5 and 2 mg/kg) prior to the administration of (-)-EPH (0, 5, 10, or 20 mg/kg, IP). Prazosin pretreatment at 2.0 mg/kg significantly attenuated the hypophagia, but not the hypodipsia, induced by administration of 10 mg/kg and by 20 mg/kg (-)-EPH. Collectively, these results confirm a critical contribution of of alpha(1)-adrenoceptors to the hypophagic action of (-)-EPH in rats.

Informed decision-making on sympathomimetic use in sport and health

The International Olympic Committee, the World Anti-Doping Agency, and International Sport Federations have banned and restricted the use of many stimulants including prescription and over-the-counter medications and dietary supplements. In addition to elite athletes, people of all ages use stimulants in attempts to improve athletic performance, alter body composition, and increase levels of energy. Here we introduce a seven-stage model designed to facilitate informed decision-making by individuals taking or thinking of taking stimulants for sport, health, and/or appearance reasons. We review for amphetamines, over-the counter sympathomimetics, and caffeine their performance-enhancing and performance-degrading effects, health benefits and mechanisms of action, medical side effects, and legal, ethical, safety, and financial implications.

Analysis of the reinforcing and subjective effects of different doses of nitrous oxide using a free-choice procedure

The reinforcing and subjective effects of five doses of nitrous oxide (0, 10, 20, 30, 40% N(2)O in O(2)) were studied in 20 non-drug-abusers using a free-choice procedure. During each of five sessions, subjects sampled a dose of N(2)O and 100% O(2) (placebo) for 10 min each. Later they chose nine times, once every 5 min, among N(2)O (e.g. 'Agent A'), placebo (e.g. 'Agent B'), or a no-drug option. Mean preference ratios (N(2)O choices/[N(2)O choices+placebo choices]) and total N(2)O choice increased with increasing N(2)O dose. Individual preference ratios suggested that at least one active dose of N(2)O functioned as a reinforcer in 80% of subjects, and the doses that functioned as reinforcers varied across subjects. N(2)O choice was positively correlated with end-of-session and post-session ratings of N(2)O liking and of wanting to inhale N(2)O again, but not with ratings of those effects during sampling. Placebo was chosen significantly less than the no-drug option, even though both were 100% O(2). More robust reinforcing effects of N(2)O were observed in this subject population than in previous studies. Choice data emphasize the importance of examining a range of doses, and of examining those effects within-subject, when assessing reinforcing effects of drugs. Inclusion of the no-drug option eliminated the 'forced' choice of placebo, making preference ratios easier to interpret than in previous, forced-choice procedures. Reinforcing effects were more correlated with subjective effects assessed after the session than with subjective effects obtained while subjects were under the influence of the drug.

Reinforcing and discriminative-stimulus effects of ephedrine isomers in rhesus monkeys

Ephedrine is a sympathomimetic drug that is currently found in many over-the-counter preparations. This compound exists as four isomers which, in addition to a racemic mixture, were evaluated for their positive reinforcing effects and for their similarity to (+)-amphetamine as a discriminative stimulus. Rhesus monkeys (N=3) with intravenous cocaine (0.1 mg/kg/inj) or saline as a consequence for lever pressing were shown to self-administer all of the ephedrine compounds (range tested: 0.03-3.0 mg/kg/inj), with the exception of (-)-pseudoephedrine, when each drug/dose was substituted for cocaine or saline during test sessions. However, the (-)-pseudoephedrine isomer was evaluated within a limited dose range due to solubility limitations. Systematically increasing the number of responses required for an injection indicated that these isomers were not as effective as reinforcers as was cocaine. Rhesus monkeys (N=3) trained to discriminate intragastric 1.0 mg/kg (+)-amphetamine from saline were given substitution tests with the ephedrine isomers and the racemic mixture. When given intragastrically, at least one dose of all the ephedrine isomers substituted for the (+)-amphetamine discriminative stimulus in at least one of the subjects tested. However, (+)-amphetamine-like effects were not systematically related to dose. When the discriminative-stimulus effects of (-)-ephedrine were also compared with those of (+)-amphetamine across three different routes of administration, full, dose-related, (+)-amphetamine-like responding was observed with both the intramuscular and intravenous routes. Taken together, these results suggest that the ephedrines have psychomotor stimulant-like abuse potential, lower than that of cocaine. Parenteral administration may enhance psychomotor-stimulant-like effects.

Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide in healthy volunteers

Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide (N(2)O) was studied across five sessions. Twelve volunteers with no history of drug dependence sampled 30% N(2)O and 100% oxygen for 10 min each, then chose nine times, once every 5 min, among N(2)O (e.g. "Agent A"), oxygen (e.g. "Agent B"), or "drug-free air." Choice varied across subjects but was stable within subjects. Quantitative differences in subjective effects occurred within and across subjects. Some subjective effects were correlated with choice and/or differed between subjects who were consistent choosers of N(2)O versus those who were not. However, drug liking and euphoria, two face-valid measures of abuse liability, were unrelated to choice. Thus, the present study found individual differences (i.e. between-subject variability) in subjective and reinforcing effects of N(2)O and, in terms of within-subject variability, suggested that subjective effects fluctuate across sessions to a relatively greater extent than do reinforcing effects. The varying degrees of correlation between N(2)O choice and its subjective effects emphasize the need for obtaining multiple measures when characterizing abuse liability of this drug.

Amphetamine-type central nervous system stimulants release norepinephrine more potently than they release dopamine and serotonin

A large body of evidence supports the hypothesis that mesolimbic dopamine (DA) mediates, in animal models, the reinforcing effects of central nervous system stimulants such as cocaine and amphetamine. The role DA plays in mediating amphetamine-type subjective effects of stimulants in humans remains to be established. Both amphetamine and cocaine increase norepinephrine (NE) via stimulation of release and inhibition of reuptake, respectively. If increases in NE mediate amphetamine-type subjective effects of stimulants in humans, then one would predict that stimulant medications that produce amphetamine-type subjective effects in humans should share the ability to increase NE. To test this hypothesis, we determined, using in vitro methods, the neurochemical mechanism of action of amphetamine, 3,4-methylenedioxymethamphetamine (MDMA), (+)-methamphetamine, ephedrine, phentermine, and aminorex. As expected, their rank order of potency for DA release was similar to their rank order of potency in published self-administration studies. Interestingly, the results demonstrated that the most potent effect of these stimulants is to release NE. Importantly, the oral dose of these stimulants, which produce amphetamine-type subjective effects in humans, correlated with the their potency in releasing NE, not DA, and did not decrease plasma prolactin, an effect mediated by DA release. These results suggest that NE may contribute to the amphetamine-type subjective effects of stimulants in humans.

Sex differences in nicotine effects and self-administration: review of human and animal evidence

Although both the human and animal literatures are notable for the general lack of attention paid to possible sex differences in drug self-administration behavior, evidence is accumulating to suggest that males and females may differ in factors that maintain tobacco smoking or nicotine self-administration. Self-administration of nicotine per se may be less robust in women, and women are less sensitive than men to some effects of nicotine that may be reinforcing. Compared to men, smoking behavior of women may be influenced more by non-nicotine stimuli associated with smoking, suggesting greater conditioned reinforcement of smoking in women. Moreover, nicotine replacement, the current standard treatment for smoking cessation, is sometimes less effective in women, further suggesting the need for greater consideration of non-nicotine factors that may maintain women's smoking. Very recent research on rats also indicates sex differences in nicotine self-administration. However, these differences are complex and suggest that nicotine-seeking behavior is composed of several components, including hedonic, incentive-motivational, and conditioning effects; males and females may differ in one or more of these components. Menstrual or estrous cycle phase effects on the maintenance of nicotine self-administration are not particularly apparent in humans or animals, although cycle phase may influence other stages of dependence (e.g., withdrawal symptoms during cessation). Future research should evaluate further the consistency of results across human and non-human species, identify the conditions and procedures under which sex differences are observed, and elucidate the specific components of reinforcement that may differ between males and females. Studies also should examine the possible generalizability of these sex differences to other drugs of abuse. Identification of specific factors responsible for these sex differences may lead to improved interventions for smoking cessation and other substance abuse in women.

An examination of isomeric phenylpropanolamines in (-)ephedrine-trained rats

A total of eight isomeric phenylpropanolamines are possible when the terminal amine is either an N-monomethylamine or a primary amine: (-)ephedrine, (+)ephedrine, (+)pseudoephedrine, (-)pseudoephedrine, (-)norephedrine, (+)norephedrine, (+)cathine, and (-)cathine. Few previous studies have examined the individual optical isomers of these phenylpropanolamines and, with the exception of one report on locomotor effects, no comparative behavioral data have been published on this series of agents. Using rats trained to discriminate 4 mg/kg of (-)ephedrine (i.p.) from saline vehicle using standard operant conditioning with a VI 15-s schedule of reinforcement, all eight agents were examined in tests of stimulus generalization. The (-)ephedrine stimulus (ED50 = 0.90 mg/kg) generalized to (+)ephedrine (ED50 = 2.64 mg/kg), (+)pseudoephedrine (ED50 = 6.58 mg/kg), (-)norephedrine (ED50 = 1.86 mg/kg), (+)norephedrine (ED50 = 5.75 mg/kg), and (+)cathine (ED50 = 4.87 mg/kg). The (-)ephedrine stimulus failed to generalize to either (-)pseudoephedrine or (-)cathine; the latter agents produced a maximum of 29 and 31% (-)ephedrine-appropriate responding, respectively. Thus, (a) six of the eight phenylpropanolamines produced ephedrine-like stimulus effects, (b) (-)ephedrine was the most potent of the examined agents, and (c) where stimulus generalization occurred, ED50 values spanned less than a tenfold range.

Discriminative effects of compound drug stimuli: a focus on attention

Discrimination research has increasingly used compound stimuli emerging from drugs acting through multiple neurotransmitter systems or from injections of drug mixtures that approximate "street-wise" drug-taking behaviors. Accompanying this trend has been an interest in the role of cognitive factors in drug discrimination learning. Accounts of multidimensional drug stimuli have focused mainly on specific neuronal mechanisms, and have largely ignored the contribution of stimulus information to the perception of internal events or to the selection processes, heretofore called attention mechanisms, which may underlie the observer's idiosyncratic response to drug administration. It is argued here that research in drug discrimination may benefit from a more detailed consideration of the processes by which an observer interacts with the emergent stimulus properties of drug administration. Therapeutic intervention initiatives may critically depend on knowing the interactions between the specific attributes of the drug experience that capture the attention of the individual and that may later acquire stimulus control over complex drug-taking behaviors.

Sensitization of anorexia and locomotion induced by chronic administration of ephedrine in rats

Repeated daily administration of the sympathomimetic agent ephedrine (EPH) leads to an augmentation (sensitization) of locomotor activity in rats. The present experiments examined the impact of repeated administration of the (-)- and (+)-EPH enantiomers on feeding in rats to assess whether the anorexic activity of EPH exhibits tolerance or sensitization during chronic exposure and whether the time course of these effects follows that observed in studies of locomotion. Adult male rats were injected once daily for 12 days with either vehicle or 5, 10 or 20 mg/kg (-)-EPH or with 10 or 20 mg/kg (+)-EPH. Horizontal locomotion and diet consumption were assessed for 60 min in an activity chamber. Suppression of feeding and the induction of locomotion were augmented over the first four days of administration of either 10 mg/kg or 20 mg/kg of the (-)-EPH enantiomer. In contrast, repeated administration of 20 mg/kg (+)-EPH resulted in augmentation of appetite suppression but not locomotion. These results confirm and extend the phenomenon of locomotor and feeding sensitization for ephedrine, but suggest that these effects may differ for the two enantiomers of ephedrine.

Over-the-counter stimulants: abuse and addiction

A widely held belief is that amphetamine-like stimulants have abuse potential, but addiction to these drugs is seldom mentioned. We describe seven patients who fulfilled criteria for amphetamine-like abuse or dependence, based on the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders. This case series lends clinical support to the research findings that amphetamine-like drugs are reinforcing and therefore can be addictive. The use of standardized criteria to classify excessive over-the-counter stimulant use as abuse or dependence distinguishes these case reports from others in the medical literature. Public concern about the misuse of this class of drugs is discussed. We propose that clinicians use standardized criteria to diagnose accurately abuse of or dependence on over-the-counter stimulants for a better understanding of the extent of this problem.

Discriminative stimulus effects of cocaine in female versus male rats

Eight female and 8 male rats were trained to discriminate 5.6 mg/kg i.p. cocaine from saline on 2-lever, food-reinforced drug discrimination procedure. Female rats acquired the cocaine discrimination in approximately the same number of sessions that males did (43 +/- 7 vs. 51 +/- 9 sessions, respectively), and the ED50 for cocaine discrimination was nearly equivalent in female and male rats (2.46 +/- 0.41 vs. 2.32 +/- 0.49 mg/kg, respectively). The time course for cocaine discrimination was similar in female and male rats, except the offset of cocaine's effects occurred significantly earlier in females than in males. D-Amphetamine dose-dependently substituted for cocaine in all 7 males and 6 of 7 females tested, with no significant sex difference in the ED50 values for D-amphetamine substitution. None of the three opioid agonists tested, morphine (mu), U69,593 (kappa) or BW373U86 (delta), fully substituted for cocaine in rats of either sex. The dopamine antagonist fluphenazine blocked the discriminative stimulus effects of cocaine to approximately the same extent in both sexes. Further drug discrimination training with a higher dose of cocaine, 10 mg/kg, did not significantly alter the ED50 for cocaine discrimination, and there was still no significant sex difference in ED50 values (3.50 +/- 0.39 vs. 2.36 +/- 0.41 mg/kg in females vs. males, respectively). In these same rats, however, cocaine (1-10 mg/kg) produced significantly greater locomotor activation in females than in males on a test of spontaneous locomotor activity. Thus, these results suggest that there are few sex differences in discriminative stimulus effects of cocaine, even at doses that produce significantly different locomotor responses in female versus male rats.

Evaluation of the cocaine-like discriminative stimulus effects and reinforcing effects of modafinil

Modafinil [(diphenyl-methyl)sulphinyl-2-acetamide] is a novel psychostimulant drug which is effective in the treatment of narcolepsy and idiopathic hypersomnia. It also has neuroprotective effects in animal models of striatal neuropathology. Although the cellular mechanisms of action of modafinil are poorly understood, it has been shown to have a profile of pharmacological effects that differs considerably from that of amphetamine-like stimulants. There is some evidence that modafinil has central alpha 1-adrenergic agonist effects. In the present study modafinil was evaluated for cocaine-like discriminative stimulus effects in rats and for reinforcing effects in rhesus monkeys maintained on intravenous cocaine self-administration. Modafinil, l-ephedrine and d-amphetamine all produced dose dependent increases in cocaine-lever responding, with maximal levels of 67%, 82% and 100%, respectively. Modafinil produced full substitution in four out of the six rats tested while the highest levels of substitution were associated with substantial response rate decreasing effects. Little evidence was obtained that the discriminative stimulus effects of modafinil were produced by alpha 1-adrenergic activation, based upon results of tests performed in combination with prazosin. In the self-administration procedure, modafinil and l-ephedrine functioned as reinforcers in rhesus monkeys. The reinforcing and discriminative stimulus effects of modafinil-required very high doses: modafinil was over 200 times less potent than d-amphetamine and was also less potent than l-ephedrine. These results show that modafinil has some cocaine-like discriminative stimulus effects and, like other abused stimulants, can serve as a reinforcer at high doses.