Alteration of the behavioral effects of nicotine by chronic caffeine exposure

The neuroprotective effect of exogen melatonin upon fetal hippocampus damage caused by high-dose caffeine administration in pregnant rats

OBJECTIVE

The aim of this study is to evaluate whether exogenous melatonin (MEL) mitigates the deleterious effects of high-dose caffeine (CAF) administration in pregnant rats upon the fetal hippocampus.

MATERIALS AND METHODS

A total of 32 adult Wistar albino female rats were divided into four groups after conception (n = 8). At 9-20 days of pregnancy, intraperitoneal (i.p.) MEL was administered at a dose of 10 mg/kg/day in the MEL group, while i.p. CAF was administered at a dose of 60 mg/kg/day in the CAF group. In the CAF plus MEL group, i.p. CAF and MEL were administered at a dose of 60 and 10 mg/kg/day, respectively, at the same period. Following extraction of the brains of the fetuses sacrificed on the 21st day of pregnancy, their hippocampal regions were analyzed by hematoxylin and eosin and Cresyl Echt Violet, anti-GFAP, and antisynaptophysin staining methods.

RESULTS

While there was a decrease in fetal and brain weights in the CAF group, it was found that the CAF plus MEL group had a closer weight average to that of the control group. Histologically, it was observed that the pyramidal cell layer consisted of 8-10 layers of cells due to the delay in migration in hippocampal neurons in the CAF group, while the MEL group showed similar characteristics with the control group. It was found that these findings decreased in the CAF plus MEL group.

CONCLUSION

It is concluded that high-dose CAF administration causes a delay in neurogenesis of the fetal hippocampus, and exogenous MEL is able to mitigate its deleterious effects.

The antioxidant and anti-inflammatory activities of caffeine effectively attenuate nonalcoholic steatohepatitis and thioacetamide-induced hepatic injury in male rats

The antioxidant effect of caffeine, associated with its ability to upregulate the nuclear factor-E2-related factor-2 (Nrf2)-signaling pathway, was explored as a possible mechanism for the attenuation of liver damage. Nonalcoholic steatohepatitis (NASH) was induced in rats by the administration of a high-fat, high-sucrose, high-cholesterol diet (HFSCD) for 15 weeks. Liver damage was induced in rats by intraperitoneal administration of thioacetamide (TAA) for six weeks. Caffeine was administered orally at a daily dose of 50 mg/kg body weight during the period of NASH induction to evaluate its ability to prevent disease development. Meanwhile, rats received TAA for three weeks, after which 50 mg/kg caffeine was administered daily for three weeks with TAA to evaluate its capacity to interfere with the progression of hepatic injury. HFSCD administration induced hepatic steatosis, decreased Nrf2 levels, increased oxidative stress, induced the activation of nuclear factor-κB (NF-κB), and elevated proinflammatory cytokine levels, leading to hepatic damage. TAA administration produced similar effects, excluding steatosis. Caffeine increased Nrf2 levels; attenuated oxidative stress markers, including malondialdehyde and 4-hydroxynonenal; restored normal, reduced glutathione levels; and reduced NF-κB activation, inflammatory cytokine levels, and damage. Our findings suggest that caffeine may be useful in the treatment of human liver diseases.

Possible role of caffeine in nicotine use onset among early adolescents: Evidence from the Young Mountaineer Health Study Cohort

BACKGROUND

Preventing nicotine use onset among children and youth is an important public health goal. One possible contributor that has received little empirical investigation is caffeine use. The goal of this study was to examine the possible contribution of caffeine to nicotine onset during early adolescence.

METHODS

We used data from the Young Mountaineer Health Study Cohort. Survey data were collected from 1,349 (response rate: 80.7%) 6th grade students (mean age at baseline 11.5 years) in 20 middle schools in West Virginia during the fall of 2020 and spring of 2021. We limited our analyses to students reporting never having used any form of nicotine at baseline. Logistic regression was employed in analyses.

RESULTS

Approximately 8% of participants reported having used nicotine at least once between baseline and the follow-up, and 4.7% reported solely using electronic nicotine delivery systems (ENDS) and no other forms of nicotine. In multivariable analyses, we controlled for many environmental, social, and behavioral variables known to influence nicotine use such as alcohol use, peer substance use, and perceived access to nicotine. We formulated our main independent variable, caffeine consumption, as continuous deciles. Any nicotine use, as well as ENDS use only at follow-up, were modeled as dependent variables. Caffeine was significantly associated with nicotine use in both models with ORs of 1.15 (1.04-1.27) and 1.13 (1.00-1.28).

CONCLUSIONS

Caffeine consumption among 6th grade non-nicotine users was associated with nicotine use at approximately 6-months follow-up.

Caffeine Inhibits NLRP3 Inflammasome Activation by Downregulating TLR4/MAPK/NF-κB Signaling Pathway in an Experimental NASH Model

Caffeine elicits protective effects against liver diseases, such as NASH; however, its mechanism of action involving the pyrin domain-containing-3 (NLRP3) inflammasome signaling pathway remains to be elucidated. This study aimed to evaluate the effect of caffeine on the NLRP3 inflammasome signaling pathway in a rat model of NASH. NASH was induced by feeding rats a high-fat, -sucrose, and -cholesterol diet (HFSCD) for 15 weeks along with a weekly low dose (400 mg/kg, i.p.) of CCl₄. Caffeine was administered at 50 mg/kg p.o. The effects of HFSCD+CCl₄ and caffeine on the liver were evaluated using biochemical, ultrastructural, histological, and molecular biological approaches. The HFSCD+CCl₄-treated rats showed fat accumulation in the liver, elevated levels of inflammatory mediators, NLRP3 inflammasome activation, antioxidant dysregulation, and liver fibrosis. Caffeine reduced necrosis, cholestasis, oxidative stress, and fibrosis. Caffeine exhibited anti-inflammatory effects by attenuating NLRP3 inflammasome activation. Moreover, caffeine prevented increases in toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) protein levels and mitigated the phosphorylation of mitogen-activated protein kinase (MAPK). Importantly, caffeine prevented the activation of hepatic stellate cells. This study is the first to report that caffeine ameliorates NASH by inhibiting NLRP3 inflammasome activation through the suppression of the TLR4/MAPK/NF-κB signaling pathway.

Daily mocha coffee intake and psycho-cognitive status in non-demented non-smokers subjects with subcortical ischaemic vascular disease

Coffee intake has been recently associated with better cognition and mood in mild vascular cognitive impairment (mVCI). As tobacco can reduce the caffeine half-life, we excluded smokers from the original sample. Hamilton Depression Rating Scale (HDRS), mini-mental state examination (MMSE), Stroop Colour-Word Interference Test (Stroop), activities of daily living (ADL0) and instrumental ADL were the outcome measures. Significant differences were observed in higher consumption groups (moderate intake for HDRS; high intake for MMSE and Stroop) compared to the other groups, as well as in age and education. With age, education and coffee used as independent predictors, and HDRS, Stroop and MMSE as dependent variables, a correlation was found between age and both MMSE and Stroop, as well as between education and MMSE and between HDRS and Stroop; coffee intake negatively correlated with HDRS and Stroop. Higher coffee consumption was associated with better psycho-cognitive status among non-smokers with mVCI.

Study on the effects of combined tea drinking and mental activity after dinner on smokers in China

INTRODUCTION

Cigarette and tobacco use is a leading cause of chronic obstructive pulmonary disease, lung cancer, and other malignant tumors. In China, people prefer to engage in mental activities (gambling, overtime work, playing video games, or other mental activities) on the weekends or during spare time, especially in the evening before they prepare for bed. In China, smokers frequently consume tea while smoking. The relationship between smokers who consume tea, engage in mental activities after dinner, or both (drinking tea and engaging in cognitive activities after dinner together), and daily cigarette smoking or nicotine addiction must be clarified.

METHODS

A total of 438 smokers were included in the study. Age, gender, body mass index (BMI), smoking habits, Fagerström test for nicotine dependence scores, and behaviors, were recorded. The study excluded smokers with a Fagerström score <1 or with a mental disorder diagnosis. The smokers were divided into four groups based on their behaviors: those who did not drink tea, did not engage in mental activities after dinner, those who drank tea only, those who engaged in mental activities only, and those who engaged in both.

RESULTS

Only drinking tea or doing mental activities after dinner cannot increase cigarettes per day (22.20 ± 10.143 vs 23.49 ± 11.966, p=0.362; 22.20 ± 10.143 vs 22.66 ± 1.192, p=0.750) or FTND scores [6.0 (4.0; 7.0) vs 6.0 (4.0; 7.75), p=0.941; 6.0 (4.0; 7.0) vs 6.0 (4.25; 7.75), p=0.980]. People who drink tea and engage in mental activities after dinner smoke more (22.20 ± 10.143 vs 30.75 ± 17.264, p<0.0001) and have higher nicotine dependence levels [6.0 (4.0; 7.0) vs 7.0 (5.0; 8.0), p=0.015].

CONCLUSIONS

The consumption of tea or a mental activity after dinner is not associated with daily smoking or nicotine dependence. There is an association between the combined behaviors (tea drinking and mental activity after dinner) and the daily consumption of cigarettes, and the degree of nicotine dependence.

Prevalence of caffeine consumers, daily caffeine consumption, and factors associated with caffeine use among active duty United States military personnel

Background

Although representative data on caffeine intake in Americans are available, these data do not include US service members (SMs). The few previous investigations in military personnel largely involve convenience samples. This cross-sectional study examined prevalence of caffeine consumers, daily caffeine consumption, and factors associated with caffeine use among United States active duty military service members (SMs).

Methods

A stratified random sample of SMs were asked to complete an on-line questionnaire on their personal characteristics and consumption of caffeinated products (exclusive of dietary supplements). Eighteen percent (n = 26,680) of successfully contacted SMs (n = 146,365) completed the questionnaire.

Results

Overall, 87% reported consuming caffeinated products ≥1 time/week. Mean ± standard error per-capita consumption (all participants) was 218 ± 2 and 167 ± 3 mg/day for men and women, respectively. Caffeine consumers ingested 243 ± 2 mg/day (251 ± 2 mg/day men, 195 ± 3 mg/day women). On a body-weight basis, men and women consumed respectively similar caffeine amounts (2.93 vs 2.85 mg/day/kg; p = 0.12). Among individual caffeinated products, coffee had the highest use (68%), followed by sodas (42%), teas (29%), energy drinks (29%) and gums/candy/medications (4%). In multivariable logistic regression, characteristics independently associated with caffeine use (≥1 time/week) included female gender, older age, white race/ethnicity, higher body mass index, tobacco use or former use, greater alcohol intake, and higher enlisted or officer rank.

Conclusion

Compared to National Health and Nutrition Examination Survey data, daily caffeine consumption (mg/day) by SMs was higher, perhaps reflecting higher mental and physical occupational demands on SMs.

More than Addiction—The Nucleus Accumbens Contribution to Development of Mental Disorders and Neurodegenerative Diseases

Stress and negative emotions evoked by social relationships and working conditions, frequently accompanied by the consumption of addictive substances, and metabolic and/or genetic predispositions, negatively affect brain function. One of the affected structures is nucleus accumbens (NAc). Although its function is commonly known to be associated with brain reword responses and addiction, a growing body of evidence also suggests its role in some mental disorders, such as depression and schizophrenia, as well as neurodegenerative diseases, such as Alzheimer’s, Huntington’s, and Parkinson’s. This may result from disintegration of the extensive connections based on numerous neurotransmitter systems, as well as impairment of some neuroplasticity mechanisms in the NAc. The consequences of NAc lesions are both morphological and functional. They include changes in the NAc’s volume, cell number, modifications of the neuronal dendritic tree and dendritic spines, and changes in the number of synapses. Alterations in the synaptic plasticity affect the efficiency of synaptic transmission. Modification of the number and structure of the receptors affects signaling pathways, the content of neuromodulators (e.g., BDNF) and transcription factors (e.g., pCREB, DeltaFosB, NFκB), and gene expression. Interestingly, changes in the NAc often have a different character and intensity compared to the changes observed in the other parts of the basal ganglia, in particular the dorsal striatum. In this review, we highlight the role of the NAc in various pathological processes in the context of its structural and functional damage, impaired connections with the other brain areas cooperating within functional systems, and progression of the pathological processes.

Caffeine is negatively associated with depression in patients aged 20 and older

INTRODUCTION

Previous studies have observed the association between caffeine intake and depression, but few have considered the potential threshold effect of this issue. Therefore, the study aimed to examine the association between caffeine consumption and depression in patients aged 20 years or older using curve fitting analysis.

METHODS

The population was 3,263 patients from the 2017 to 2018 National Health and Nutrition Examination Survey (NHANES) with reliable answers to questions of caffeine intake and depression. Participants' depression levels were assessed using the 9-item Patient Health Questionnaire (PHQ-9) depression scale and the caffeine consumption were investigated in a private room of NHANES. The confounding variables of this study included level of education, monthly sleepiness, age, marital status, race, cigarette smoking, sex and recreational activities.

RESULTS

In linear regression analysis, patients with a higher PHQ-9 score tend to have less caffeine intake. A similar conclusion was drawn in logistic regression model using PHQ-9 ≥ 10 as a cut-off score for depression. But when caffeine intake exceeded 90 mg, there was no significant association between caffeine intake and depression based on the curve fitting analysis.

DISCUSSION

These results suggest that people can consume some caffeine to reduce depression. But further study is needed to examine the precise causal relationship between these factors.

Do nicotine dependence influencing and non-influencing behaviors have an association with high nicotine dependence in smokers?

INTRODUCTION

Nicotine dependence (ND) is a maladaptive pattern of tobacco smoking with withdrawal symptoms similar to other drug addictive disorders. It is very common in clinical practice that smokers always have different degrees of nicotine dependence with the same amount of tobacco consumption. Behaviors may influence daily cigarette consumption or smoking status. Hence it is critical to ascertain the association between concurrent behaviors and high nicotine dependence among smokers.

METHODS

A total of 343 patients who attended a clinic for smoking cessation were recruited, and the information on concurrent behaviors were recorded. Factors associated and not associated with nicotine dependence were recorded. Nicotine dependence was determined by Fagerström test for nicotine dependence (FTND).

RESULTS

High ND patients (FTND >5) showed significant behaviors distribution compared with mild and moderate ND patients (FTND ≤5). There is no single behavior that was significantly different between high ND and mild and moderate ND smokers. However, the combined effects of nicotine dependence influencing behaviors of caffeine drinking and mental activities after dinner have an association with high ND (OR=1.939; 95% CI: 1.154–3.258, p=0.012). In addition, the combined effects of inadequate sleep time (<8 hours), caffeine drinking and mental activities after dinner significantly distinguished patients of high ND from those of low ND (OR=2.208; 95% CI: 1.032–4.737, p=0.042).

CONCLUSIONS

Interaction effects of mental activities after dinner and caffeine drinking have an association with high nicotine dependence. Sleep of less than 8 hours with behaviors of mental activities after dinner and caffeine drinking have the same effect.

The role of energy drink consumption in the intention to initiate marijuana use among adolescents

AIMS

The current study aims to examine whether energy drink consumption is associated with intentions to try marijuana among adolescents who have never tried marijuana, and whether the effects of energy drink consumption on the intention to try marijuana vary between adolescents who have previously tried alcohol or cigarettes and those who have not.

METHODS

This study employs a pooled cross-sectional design and uses a nationally representative sample of 8th (ages 13-14) and 10th (ages 15-16) grade adolescents from seven recent cohorts (2010-2016) of the Monitoring the Future (MTF) study. Logistic regression was employed to examine the association between energy drink consumption (none, light, moderate, heavy) and the odds of intending to initiate marijuana use in the next 12 months, controlling for sociodemographic factors and other health and social behaviors.

RESULTS

The results indicate that energy drink consumers are significantly more likely to intend to initiate marijuana use relative to non-consumers of energy drinks. Specifically, youth who heavily use energy drinks have significantly higher odds of having the intention to use marijuana in the near future than youth who consume energy drinks moderately or lightly. Additionally, evidence suggests that the relationship between energy drink consumption and the intention to use marijuana is moderated by use of other substances.

CONCLUSIONS

The current study suggests that energy drink consumption (particularly heavy consumption) may be one early precursor in the escalation of substance use. It may be beneficial to include energy drinks in drug education curriculums.

Lifelong exposure to caffeine increases anxiety-like behavior in adult mice exposed to tobacco smoke during adolescence

Caffeine and tobacco smoke are among the most frequently self-administered licit psychoactive drugs in the world. Both drugs affect anxiety levels, however, little is known on the impact of the dual exposure in the adolescent brain, the period during which smoking begins. Considering that anxiety is a relevant factor for smoking maintenance and relapse, we investigated the effects of lifelong exposure to caffeine on anxiety levels of Swiss mice exposed to tobacco smoke during adolescence. Caffeine was administrated during all prenatal and postnatal life (CAF, 0.1 g/l to drink). From postnatal day 30-45, animals were exposed to tobacco smoke (SMK, whole body exposure, 8 h/day) generated from research cigarettes type 3R4F (nicotine = 0.73 mg/per cigarette). Four groups were analyzed: (1) CAF + SMK exposure; (2) SMK exposure; (3) CAF exposure; (4) Control. Anxiety levels were assessed in the elevated plus maze at the end of smoke exposure (PN45), at short- (PN55) and long-term (PN75) withdrawal. Caffeine exposure reduced decision making time (time in center of maze) during adolescence (PN45 and PN55). In addition, caffeine increased anxiety-like behavior during long-term tobacco smoke withdrawal. The present study provides experimental evidence that caffeine and tobacco smoke during adolescence interact resulting in emotional dysregulation during tobacco smoke withdrawal. Particularly, increased anxiety-like behavior during long-term withdrawal in CAF + SMK animals demonstrates late-emergent effects. In this sense, our data suggest that lifelong caffeine exposure may be an important factor in tobacco relapse.

Nicotine-induced CREB and DeltaFosB activity is modified by caffeine in the brain reward system of the rat

Coffee and nicotine consumption are frequently combined, indicating possible intensifying effect of caffeine on smoking behavior, although neurobiological background of this phenomenon remains unknown. We aimed at determining the effect of caffeine and nicotine, applied separately or simultaneously, on activation of six structures of the brain reward system: nucleus accumbens (NAc), ventral tegmental area (VTA), amygdala (Amg), hippocampus (Hip), medial prefrontal cortex (mPfr) and dorsal striatum (CdP) in the adult male Wistar rats. Activation of two transcription factors, the phosphorylated form of cyclic AMP-response element binding protein (pCREB) and DeltaFosB (ΔFosB) was assessed by immunohistochemistry after multiple-dose five-days psychostimulants administration followed by 20min and 24h survival, respectively. Nicotine evoked the highest increase of pCREB-immunoreactivity (-ir) in NAc, while caffeine exerted the weakest effect in mPfr and CdP. Nicotine/caffeine co-administration resulted in decrease of pCREB-ir in NAc and increase in Amg, compared with the effect of each psychostimulant used separately. Nicotine was the strongest psychostimulant activating ΔFosB-ir in Amg, whereas caffeine - in Hip. Nicotine/caffeine-exerted effect upon ΔFosB-ir in Amg was weaker, whereas in mPfr stronger, than nicotine-evoked effect in these structures. In summary, pCREB and ΔFosB activation is dependent on the type of stimulus, brain structure and functional context. Activation of both transcription factors is responsible for caffeine's modifying effect upon nicotine-related behaviors and must be taken into account while quitting cigarette smoking.

Trajectories of energy drink consumption and subsequent drug use during young adulthood

BACKGROUND

Highly caffeinated energy drinks (EDs) are popular with adolescents and young adults, but longitudinal consumption patterns are poorly understood especially in relation to other substance use.

METHODS

ED and other substance use were assessed annually (modal ages 21-25) among a sample (n=1099) who were originally recruited as first-year college students (modal age 18). Trajectory groups were derived based on probability of past-year use during ages 21-24, and compared for possible differences in substance use outcomes at age 25, holding constant demographics, sensation-seeking, other caffeine consumption, and age 21 substance use.

RESULTS

From age 21-25, ED consumption declined in both annual prevalence [62.5%wt to 49.1%wt (wt=weighted)] and frequency of use among consumers (35.2-26.3 days/year). Yet individuals exhibiting a Persistent trajectory (51.4%) of consumption outnumbered those with Non-Use (20.6%), Intermediate (17.4%), or Desisting (10.6%) trajectories. Age 25 cocaine use, nonmedical use of prescription stimulants (NPS), and alcohol use disorder (AUD) risk were significantly associated with trajectory group membership, with Persistent and Intermediate groups exhibiting the highest risk for such outcomes, even accounting for prior substance use and other risk factors. Neither marijuana nor tobacco use were associated with group membership.

CONCLUSIONS

The typical pattern of ED consumption among this sample was sustained use throughout young adulthood. Such individuals appear to be at high risk for adverse substance use outcomes, and results suggest possible specificity regarding cocaine use and NPS, and AUD risk. More research is needed to understand the mechanisms underlying the connection between ED and substance use.

Adolescent intake of caffeinated energy drinks does not affect adult alcohol consumption in C57BL/6 and BALB/c mice

The rise in marketing and mass consumption of energy drink products by adolescents poses a largely unknown risk on adolescent development and drug reward. Yet, with increasing reports of acute health issues present in young adults who ingest large quantities of energy drinks alone or in combination with alcohol, the need to elucidate these potential risks is pressing. Energy drinks contain high levels of caffeine and sucrose; therefore, exposure to energy drinks may lead to changes in drug-related behaviors since caffeine and sucrose consumption activates similar brain pathways engaged by substances of abuse. With a recent study observing that adolescent caffeine consumption increased cocaine sensitivity, we sought to investigate how prolonged energy drink exposure in adolescence alters alcohol use and preference in adulthood. To do so, we utilized three different energy drink exposure paradigms and two strains of male mice (C57BL/6 and BALB/c) to monitor the effect of caffeine exposure via energy drinks in adolescence on adult alcohol intake. These paradigms included two models of volitional consumption of energy drinks or energy drink-like substances and one model of forced consumption of sucrose solutions with different caffeine concentrations. Following adolescent exposure to these solutions, alcohol intake was monitored in a limited-access, two-bottle choice between water and increasing concentrations of alcohol during adulthood. In none of the three models or two strains of mice did we observe that adolescent 'energy drink' consumption or exposure was correlated with changes in adult alcohol intake or preference. While our current preclinical results suggest that exposure to large amounts of caffeine does not alter future alcohol intake, differences in caffeine metabolism between mice and humans need to be considered before translating these results to humans.

Caffeine, a common active adulterant of cocaine, enhances the reinforcing effect of cocaine and its motivational value

RATIONALE

Caffeine is one of the psychoactive substances most widely used as an adulterant in illicit drugs, such as cocaine. Animal studies have demonstrated that caffeine is able to potentiate several cocaine actions, although the enhancement of the cocaine reinforcing property by caffeine is less reported, and the results depend on the paradigms and experimental protocols used.

OBJECTIVES

We examined the ability of caffeine to enhance the motivational and rewarding properties of cocaine using an intravenous self-administration paradigm in rats. Additionally, the role of caffeine as a primer cue during extinction was evaluated.

METHODS

In naïve rats, we assessed (1) the ability of the cocaine (0.250-0.125 mg/kg/infusion) and caffeine (0.125-0.0625 mg/kg/infusion) combination to maintain self-administration in fixed ratio (FR) and progressive ratio (PR) schedules of reinforcement compared with cocaine or caffeine alone and (2) the effect of caffeine (0.0625 mg/kg/infusion) in the maintenance of responding in the animals exposed to the combination of the drugs during cocaine extinction.

RESULTS

Cocaine combined with caffeine and cocaine alone was self-administered on FR and PR schedules of reinforcement. Interestingly, the breaking point determined for the cocaine + caffeine group was significantly higher than the cocaine group. Moreover, caffeine, that by itself did not maintain self-administration behavior in naïve rats, maintained drug-seeking behavior of rats previously exposed to combinations of cocaine + caffeine.

CONCLUSIONS

Caffeine enhances the reinforcing effects of cocaine and its motivational value. Our results highlight the role of active adulterants commonly used in cocaine-based illicit street drugs.

Effects of caffeine intake and smoking on neurocognition in schizophrenia

Although most studies support the beneficial effects of caffeine on neurocognition, its effects have never been assessed in psychiatric patients. In addition, results from studies in smokers are contradictory. Moreover, there are no data available about the neurocognitive effects of caffeine and tobacco together. We explored the concomitant effects of regular caffeine and tobacco intake on neurocognition in 52 schizophrenic patients and 61 healthy controls. Verbal fluency, processing speed, and working, visual and verbal memory were assessed. For each measurement, two tasks with two levels of complexity were administered. Our results showed that caffeine intake had beneficial effects on male schizophrenic patients only in complex tasks requiring deeper cognitive processing (semantic fluency, cognitive speed, working memory, and visual memory). Female patients and controls were unaffected. In contrast, smoking had a negative effect on male, but not on female, schizophrenic patients in semantic fluency. The effects of smoking in controls were inconsistent. In conclusion, our data showed, for the first time, beneficial effects of caffeine intake on neurocognition in male schizophrenic patients. These data suggest that further research of therapeutics based on caffeine is needed, as this could be beneficial for schizophrenic patients. In contrast, smoking appears to be detrimental.

Energy-drink consumption and its relationship with substance use and sensation seeking among 10th grade students in Istanbul

Aim of this study was to determine the prevalence and correlates of energy-drink (ED) consumption among 10th grade students in Istanbul/Turkey. Cross-sectional online self-report survey conducted in 45 schools from the 15 districts in Istanbul. The questionnaire included sections about demographic data, self-destructive behavior and use of substances including tobacco, alcohol and drugs. Also Psychological Screening Test for Adolescents (PSTA) was used. The analyses were conducted based on the 4957 subjects. Rate of those reported a ED consumption once within last year was 62.0% (n=3072), whereas rate of those reported ED consumption at least once in a month was 31.1%. There were consistent, statistically significant associations between genders, lifetime substance use (tobacco, alcohol and drug use), measures of sensation seeking, psychological problems (depression, anxiety, anger, impulsivity) and self-destructive behavior (self-harming behavior and suicidal thoughts) with ED consumption. In logistic regression models male gender, sensation seeking, life-time tobacco, alcohol and drug use predicted all frequencies of ED consumption. In addition to these predictors, anger and self-harming behavior also predicted ED consumption at least once in a month. There were no interactions between the associations of lifetime tobacco, alcohol and drug use with ED consumption. The findings suggest that the ED consumption of male students is related with three clusters of substances (tobacco, alcohol and drug) through sensation seeking and these relationships do not interact with each other.

Relations Among Caffeine Consumption, Smoking, Smoking Urge, and Subjective Smoking Reinforcement in Daily Life

Caffeine consumption and cigarette smoking tend to occur within the same individuals and at the same time. One potential explanation for this co-use is that caffeine consumption increases subjective smoking reinforcement. Electronic diaries were used to collect momentary reports of smoking, caffeine consumption, temptation/urge to smoke, and subjective smoking reinforcement in 74 prequit smokers. Momentary reports of caffeine consumption and smoking were associated, replicating previous findings. These results remained significant when contextual factors (time of day, weekday/weekend, presence of others, presence of others smoking, location, and past hour alcohol consumption) were covaried. Caffeine consumption was also associated with positive cigarette appraisals and reports of strong temptation/urge to smoke and urge reduction from the prior cigarette. Under the conditions of caffeine consumption versus at other times, smokers were significantly more likely to report their last cigarette as producing a rush/buzz, being pleasant, relaxing, and tasting good. The effects for temptation/urge to smoke and rush/buzz varied as a function of latency since smoking. Caffeine consumption increased reports of urge to smoke and rush/buzz only when smoking occurred more than 15 minutes prior to the diary entry. Findings suggest that caffeine consumption influences some aspects of smoking motivation or affects memorial processing of smoking reinforcement.

Allostatic load as a tool for monitoring physiological dysregulations and comorbidities in patients with severe mental illnesses

Severe mental illnesses like schizophrenia and bipolar disorder are disabling, chronic conditions that are often accompanied by medical comorbidities. In this theoretical article, we review the allostatic load model representing the "wear and tear" that chronic stress exacts on the brain and body. We propose an innovative way of monitoring physical and psychiatric comorbidities by integrating the allostatic load model into clinical practice. By interpreting peripheral biomarkers differently, medical professionals can calculate a simple, count-based, allostatic load index known to predict diverse stress-related pathologies. In addition to screening for comorbidities, allostatic load indices can be used to monitor the effects of pharmacological and psychosocial interventions. This framework can also be used to generate a dialogue between patient and practitioner to promote preventive and proactive approaches to health care.

Smoking among individuals with schizophrenia in Korea: gender differences

OBJECTIVE

This study examined gender differences in smoking and quitting among individuals diagnosed with schizophrenia in Korea. In addition, the study investigated differences in caffeine use by gender and smoking status.

METHOD

An anonymous self-report survey was conducted with psychiatric inpatients.

RESULTS

Compared to males, females were less likely to be current smokers (P<.001) and more likely to be former smokers (P<.01). Females were also less likely to be daily caffeine users (P<.001). Having more years of education (P<.05) and higher nicotine dependence scores (P<.05) were associated with decreased odds of intending to quit smoking, whereas having more previous quit attempts (P<.01) was associated with increased odds. These findings were significant even after adjusting for gender. Smokers were more likely to be daily caffeine users (P<.001) than their non-smoking counterparts.

CONCLUSION

Nurses in Korea should play an active role in tobacco control for patients with schizophrenia by providing cessation counseling and educating the effect of caffeine use on cigarette consumption, while tailoring the service to gender differences found in this study.

Effects of caffeine on alcohol consumption and nicotine self-administration in rats

BACKGROUND

Caffeine, alcohol, and nicotine are 3 of the most widespread self-administered psychoactive substances, which are known to be extensively co-administered. However, little is known about the degree to which they may mutually potentiate each other's consumption.

METHODS

In the current set of studies, we examined in rats the effect of caffeine administration on alcohol drinking and intravenous (i.v.) self-administration of nicotine. In male alcohol-preferring (P) rats, caffeine (5, 10, and 20 mg/kg) or the saline vehicle was administered acutely either by subcutaneous (S.C.) injection or orally (PO) by gavage. In a chronic study, the effect of PO caffeine (5 and 20 mg/kg) on alcohol intake over a 10-day period was tested. In another experiment, the effect of acute PO administration of caffeine (20 mg/kg) or saline on saccharin intake (0.2% solution) was determined in P rats. Effects of 20 mg/kg caffeine on motor activity were also determined in P rats. Finally, the effects of acute PO caffeine administration on nicotine self-administration in Sprague-Dawley rats were also determined.

RESULTS

Both routes of administration of caffeine, S.C. and PO, caused a significant dose-related decrease in alcohol intake and preference during free access to alcohol and after 4-day deprivation of alcohol. However, the low dose of 5 mg/kg caffeine increased alcohol intake. Acute PO caffeine also reduced saccharin intake. Acute systemic administration of 20 mg/kg caffeine did not exert a significant effect on motor activity. In Sprague-Dawley rats trained to self-administer i.v. nicotine, acute PO administration of caffeine significantly increased self-administration of nicotine in a dose-related manner.

CONCLUSIONS

These results suggest that adenosine receptor systems may play a role in both alcohol and nicotine intake and deserve further study regarding these addictions.

Effects of caffeine on persistence and reinstatement of nicotine-seeking behavior in rats: interaction with nicotine-associated cues

RATIONALE

Caffeine and nicotine are the most commonly co-used psychostimulants. However, it is still unclear whether caffeine exposure enhances nicotine-seeking behavior.

OBJECTIVE

The present study examined the effects of caffeine on nicotine-seeking in rats trained to self-administer nicotine with and without presession administration of caffeine.

METHODS

Male Sprague-Dawley rats were trained to intravenously self-administer nicotine (0.03 mg/kg/infusion, freebase) on a fixed ratio 5 schedule of reinforcement and associate a stimulus cue with each nicotine administration. Five minutes before the sessions, the rats received an intraperitoneal administration of caffeine (5 mg/kg). Extinction tests were conducted under four conditions: presession caffeine administration, response-contingent presentation of nicotine cues, neither condition, or both conditions. Reinstatement tests were conducted after responding was extinguished by withholding presession caffeine, nicotine, and its cues. A separate group of rats trained without presession caffeine exposure was also subjected to the reinstatement tests.

RESULTS

In the rats trained with presession caffeine exposure, continued caffeine administration sustained nicotine-seeking responses and interacted with nicotine cues to significantly delay the extinction of nicotine-seeking behavior. Readministration of caffeine after extinction effectively reinstated nicotine-seeking behavior. In caffeine-naive rats, caffeine administration did not reinstate extinguished nicotine-seeking behavior but significantly potentiated the cue-induced reinstatement of nicotine-seeking.

CONCLUSION

These data demonstrate that caffeine administration sustained and reinstated nicotine-seeking behavior, possibly via its acquired discriminative-stimulus properties predictive of nicotine availability. These findings suggest that smokers who attempt to quit may benefit from stopping caffeine consumption.

Caffeine choice prospectively predicts positive subjective effects of caffeine and d-amphetamine

BACKGROUND

Individuals vary in their subjective and behavioral response to psychomotor stimulants and these differences may be associated with the likelihood of developing problematic use of these drugs. The present study sought to determine whether individual differences in caffeine choice prospectively predict subjective response to acute doses of caffeine and d-amphetamine.

METHODS

In Phase 1, Choosers and Nonchoosers of caffeine were identified using 10 independent choice trials in which subjects repeatedly chose between caffeine (200mg/70 kg) and placebo. Choosers were defined as those who chose caffeine over placebo on ≥7 of the 10 trials; Nonchoosers were those who chose placebo on ≥7 trials. In Phase 2, Choosers and Nonchoosers were compared in their subjective response to caffeine (100, 200, 400mg/70 kg) and d-amphetamine (5, 10, 20 mg/70 kg).

RESULTS

Of the 22 participants completing the study, 11 met criteria for being a caffeine Chooser and 8 were Nonchoosers. In Phase 1, Choosers reported higher ratings of positive (i.e., pleasant) and lower ratings of negative (i.e., unpleasant) effects of caffeine during the sampling sessions. In Phase 2, caffeine Choosers reported more positive subjective effects and fewer negative effects of caffeine and d-amphetamine, particularly at the highest doses examined.

CONCLUSIONS

Individual differences in caffeine reinforcement predicted subsequent subjective response to both d-amphetamine and caffeine. This observation may have clinical utility for identifying individuals who are vulnerable to the reinforcing effects of abused psychomotor stimulants.

Effects of smoking cues on caffeine urges in heavy smokers and caffeine consumers with and without schizophrenia

Cigarette smoking and caffeine use are established and problematic drug-use behaviors in people with schizophrenia. Associative links between drugs of abuse may occur but the relationship between caffeine use and cigarette smoking has received little attention in schizophrenia. In this cross-cue reactivity laboratory study, we examined the effects of neutral and smoking cues on craving for caffeinated beverages in participants with schizophrenia or schizoaffective disorder (SS; n=15) and non-psychiatric controls (CS; n=18) all of whom were heavy smokers and daily caffeine users. Participants were tested under non-abstinent and 5-hour abstinent conditions. SS tended to report greater daily levels of caffeine use than CS. Although this difference was not significant, that may be due to the small sample sizes as the size of this effect was large. Daily caffeine intake was significantly correlated with daily smoking rate in SS but not CS. A significant interaction between group and cue type after controlling for caffeine intake indicated that exposure to smoking cues increased urge for caffeinated beverages in SS but not CS. These results indicate support for associative connections between cigarette smoking cues and craving for caffeine in smokers with schizophrenia.

Recognising nicotine: the neurobiological basis of nicotine discrimination

Drug discrimination methodology makes possible the objective, quantitative study of the perception of psychoactive drug effects in either human or animal subjects. Investigations of the nicotine discriminative stimulus complex have contributed to our present understanding of nicotine psychopharmacology by defining the origin of its effects at specific subtypes of nicotinic receptor and the role of diverse neurotransmitter systems as mediating and modulating mechanisms. The evidence strongly supports central sites as the origins of the nicotine stimulus, and these are likely to be located in the mesocorticolimbic dopaminergic neurons; the medial prefrontal cortex is primarily involved, with the Nucleus accumbens and ventral tegmental area of secondary importance, while another element of the complex stimulus may arise in the dorsal hippocampus. Additionally, it appears that interactions of nicotine with the dopamine, serotonin, cannabinoid and probably glutamate systems all contribute to the final perceived stimulus. The resemblance between the nicotine discriminative stimulus and those of the psychomotor stimulant drugs amphetamine and cocaine contributes to defining the nature of the addictive properties of nicotine. It is particularly interesting that acute and chronic exposure to caffeine produce quantitative and qualitative changes in the characteristics of the nicotine stimulus. Interactions of nicotine with caffeine and cannabinoids strengthen proposals that the use of one substance serves as a "gateway" in sequential shifts of the target substance for drug-seeking behaviour, with profound implications for the human use of the substances concerned. Drug discrimination is also an important standard technique used in assessments of the abuse liability of novel psychoactive compounds, with relevance to attempts to develop novel nicotinic agonists for use as cognitive enhancers.

Caffeinated energy drinks--a growing problem

Since the introduction of Red Bull in Austria in 1987 and in the United States in 1997, the energy drink market has grown exponentially. Hundreds of different brands are now marketed, with caffeine content ranging from a modest 50 mg to an alarming 505 mg per can or bottle. Regulation of energy drinks, including content labeling and health warnings differs across countries, with some of the most lax regulatory requirements in the U.S. The absence of regulatory oversight has resulted in aggressive marketing of energy drinks, targeted primarily toward young males, for psychoactive, performance-enhancing and stimulant drug effects. There are increasing reports of caffeine intoxication from energy drinks, and it seems likely that problems with caffeine dependence and withdrawal will also increase. In children and adolescents who are not habitual caffeine users, vulnerability to caffeine intoxication may be markedly increased due to an absence of pharmacological tolerance. Genetic factors may also contribute to an individual's vulnerability to caffeine-related disorders including caffeine intoxication, dependence, and withdrawal. The combined use of caffeine and alcohol is increasing sharply, and studies suggest that such combined use may increase the rate of alcohol-related injury. Several studies suggest that energy drinks may serve as a gateway to other forms of drug dependence. Regulatory implications concerning labeling and advertising, and the clinical implications for children and adolescents are discussed.

The endocannabinoid system: a new molecular target for the treatment of tobacco addiction

Tobacco addiction is one of the leading preventable causes of mortality in the world and nicotine appears to be the main critical psychoactive component in establishing and maintaining tobacco dependence. Several lines of evidence suggest that the rewarding effects of nicotine, which underlie its abuse potential, can be modulated by manipulating the endocannabinoid system. For example, pharmacological blockade or genetic deletion of cannabinoid CB(1) receptors reduces or eliminates many behavioral and neurochemical effects of nicotine that are related to its addictive potential. This review will focus on the recently published literature about the role of the endocannabinoid system in nicotine addiction and on the endocannabinoid system as a novel molecular target for the discovery of medications for tobacco dependence.

The effects of caffeine on L-arginine metabolism in the brain of rats

In our study, the short-term effects of caffeine on L-arginine metabolism in the brains of rats were investigated. Caffeine was given orally at two different doses: 30 mg/kg and 100 mg/kg (a high non-toxic dose). Brain tissue arginase activity in rats from the caffeine-treated groups decreased significantly compared with the control group. Malondialdehyde (MDA) levels in the brain tissue and serum of animals in the caffeine groups also decreased significantly. Brain tissue and serum nitric oxide (NO) levels increased significantly after caffeine administration. Tumor necrosis factor-alpha (TNF-alpha) levels were also investigated in rat serum, but there was no statistically significant difference between the TNF-alpha levels of the caffeine-treated rats groups and the control rats. Our study indicates that brain arginase activity decreases after caffeine administration at doses of 30 mg/kg and 100 mg/kg. As a result, we can say that arginine induces production of NO in the organism.

Factors associated with smokeless tobacco cessation in an Appalachian population

Identifying factors associated with successful tobacco quit attempts may help in the development and targeting of effective cessation strategies. This paper aims to describe factors associated with smokeless tobacco (ST) cessation and compares the results to findings in the smoking cessation literature. Prospective data on 116 men aged 19 to 70 and participating in a ST cessation program were used to examine correlates of successful ST cessation at 1-year post-intervention. Controlling for age, level of education (p=0.002) and daily coffee consumption (p=0.005) had significant independent associations with successful cessation. No ST use variables were significant predictors of cessation success. In a multivariable logistic regression model three factors were significantly associated with cessation: education (p=0.010), coffee consumption (p=0.019), and age (p=0.029). Factors associated with successful ST cessation in this sample are consistent with predictors of smoking cessation reported in the literature. Based on its widespread use and the strength of its association with successful quitting, the role of caffeine consumption in ST cessation merits further study.

Caffeine's influence on nicotine's effects in nonsmokers

OBJECTIVE

To determine if nicotine's effects are influenced by caffeine in nonsmoking, moderate-caffeine consuming individuals (N=20).

METHODS

The first 3 sessions included one of 3 randomly ordered, double-blind caffeine doses (0, 75, or 150 mg, oral [po]) and 2 single-blind nicotine gum doses (2 and 4 mg) in ascending order. The fourth session (single blind) repeated the 0 mg caffeine condition.

RESULTS

Nicotine increased heart rate and subjective ratings indicative of aversive effects, and decreased reaction times. These effects were independent of caffeine dose and reliable across sessions.

CONCLUSIONS

In nonsmokers, nicotine effects are not influenced by moderate caffeine doses.

Personality traits associated with caffeine intake and smoking

OBJECTIVES

Some studies find a relationship between certain personality traits, as impulsivity or sensation seeking, and caffeine consumption, but these studies do not consider the potential confounding effect of smoking on caffeine intake, a co-occurrence that has been well demonstrated in epidemiological and clinical studies. The main objective of this cross-sectional study was to analyze the association of personality with caffeine intake controlling for the effects of smoking; a secondary objective was to explore the effect of caffeine intake on the previously known relationship between personality and smoking.

METHODS

A sample of 498 adults answered a self-questionnaire including socio-demographic variables, and items regarding consumption of tobacco and caffeine. Personality was measured by the Temperament and Character Inventory (TCI-125). We analyzed the association of personality traits with both caffeine intake and smoking, controlling the possible confounding effects of sex, age and each substance with the other one.

RESULTS

Logistic regression analyses showed that the temperamental dimension of novelty seeking was associated with heavy caffeine consumption (>200 mg/day) (adjusted OR=2.0; 95% CI: 1.1-3.9), controlling for the effect of smoking. Moreover, novelty seeking was associated with both smoking (adjusted OR=1.8; 95% CI: 1.1-2.9) and heavy smoking (>20 cigarettes/day) (adjusted OR=1.8; 95% CI: 1.0-3.7), after controlling for the effect of caffeine intake.

CONCLUSION

Our study offers an epidemiological evidence of the relationship of novelty seeking, considered to be associated with low basal dopaminergic activity, with both nicotine consumption and heavy caffeine intake, two substances that enhance dopaminergic neurotransmission.

Coffee drinking enhances the analgesic effect of cigarette smoking

Nicotine (from cigarette smoke) and caffeine (from coffee) have analgesic effects in humans and experimental animals. We investigated the combined effects of coffee drinking and cigarette smoking on pain experience in a group of moderate nicotine-dependent, coffee drinking, young smokers. Pain threshold and pain tolerance were measured during cold pressor test following the habitual nocturnal deprivation of smoking and coffee drinking. Smoking increased pain threshold and pain tolerance in both men and women. Coffee drinking, at a dose that had no independent effect, doubled the increase in pain threshold induced by smoking. The effect could not be explained by a cumulative raise in blood pressure. Our data suggest that caffeine enhances the analgesic effect of nicotine.

Survey of caffeine levels in retail beverages in Portugal

The caffeine content of 85 retail beverage samples purchased from local supermarkets between 1995 and 2004 was determined. The potential intake of caffeine through the consumption of these beverages (but excluding coffee) was estimated for students of the University of Coimbra, Portugal. The caffeine content of the beverages ranged from 47.5 to 282.5 mg l(-1) for teas, from 20.1 to 47.2 mg l(-1) for tea extracts samples, and from 80.7 to 168.7 mg l(-1) for cola soft drinks. Caffeine was not completely absent from caffeine-free colas, and energy drinks had a far greater caffeine content than regular drinks, ranging from 21 to 2175 mg l(-1). Soft drinks were consumed by 72% of the individuals, although 14% of the survey participants did not drink any of the different types of the beverages studied. Contrary to expectations for this age group, no consumptions of energy drinks was reported. Daily caffeine intake was estimated to range from 4.7 to 200 mg day(-1), but with only 5% reporting a daily intake around 200 mg caffeine. Cola-type beverages were an important dietary source of caffeine for the population studied. Statistical differences in the caffeine intake between the male and female populations were found, with p = 0.014, being higher for the male population. Of the beverages studied, cola-type drinks showed statistical differences for the male population, p = 0.03, and tea showed statistical differences for female population p = 0.013, respectively.

Investigating the pharmacological and nonpharmacological factors that modulate drug reinforcement

Drug use is driven by principles of reinforcement and is sensitive to influences in the environmental context in which it occurs. Although a wide range of factors has been shown to directly influence the reinforcing effects of commonly abused drugs, 2 general types include pharmacological and nonpharmacological factors. Both can assert a powerful impact on a drug's reinforcing effects and, therefore, the degree to which a particular drug comes to be used and abused. This invited review seeks to briefly describe some of the current psychopharmacology research on the interactions between these factors and drug abuse. Several pharmacological influences on drug use will be discussed, including the interactions between psychomotor stimulants and recent advances in the development of pharmacotherapies for opioid abuse. With regard to nonpharmacological factors, there is a large body of research demonstrating that nondrug reinforcers can exert a powerful influence on the reinforcing effects of commonly abused drugs. More specifically, identifying alternative nondrug sources of reinforcement can, if made available contingent on drug abstinence, produce robust decreases in drug self-administration. Presented here is a very brief review of some recent scientific efforts to develop and extend behavioral interventions targeting drug use across a wide range of clinical populations. In summary, understanding the interactions among the variables present in the context of drug use is critical to understanding risk factors for substance use disorders as well as developing efficacious treatments for drug dependence.

Increased caffeine and nicotine consumption in community-dwelling patients with schizophrenia

INTRODUCTION

It is known that people with schizophrenia make poor dietary choices and smoke at alarmingly high rates. There is also anecdotal evidence that they may ingest large amounts of caffeine. However, while smoking habits in this population have been examined, no recent study has quantified caffeine consumption taking into account various dietary caffeine sources unrelated to coffee including convenience foods such as candy bars, chocolate or soft drinks, and compared results to US population data.

METHODS

We employed 24-h diet recalls to assess dietary habits in a sample of outpatients suffering from schizophrenia or schizoaffective disorder. Caloric intake and caffeine consumption were quantified and the relationship to various sociodemographic variables including body mass index (BMI) and dietary quality was examined.

RESULTS

146 patients were recruited. Mean BMI in the sample was 32.7+/-7.9. Patients ingested 3,057+/-1,132 cal on average. Patients smoked at higher rates (59.6% vs. 23.4%, p< or =0.001), higher numbers of cigarettes/day (24+/-14.4 vs. 13.5+/-11.3, t=8.549, p<0.001) and ingested more caffeine (471.6+/-584.6 mg vs. 254.2+/-384.9 mg, t=6.664, p<0.001) than US population comparisons. Caffeine consumption was correlated to the number of cigarettes smoked daily (r=0.299, p< or =0.001), but not to BMI (r=0.134, p=0.107) or dietary parameters such as caloric intake (r=0.105, p=0.207).

CONCLUSION

Community-dwelling schizophrenia patients consume significantly more caffeine and nicotine than US population comparisons. Clinicians should be aware that while a significant proportion of patients are overweight and have poor dietary quality - which merits lifestyle counseling on its own - there is a lack of correlation between those factors and smoking and caffeine intake. Thus, lifestyle modification counseling in all patients should address smoking and caffeine intake concurrently.

Fewer but heavier caffeine consumers in schizophrenia: a case-control study

According to the literature, there is an association between schizophrenia and caffeine consumption, but it is not clear whether schizophrenia is associated with either higher prevalence of daily caffeine intake or the amount consumed. In this study we compared our previously published schizophrenia patients (n=250) with a control sample (n=290) after controlling for demographic variables and tobacco and alcohol consumption. Current caffeine intake was less frequent in schizophrenia patients (59%, 147/250) than in controls (70%, 204/290). In the multivariate analyses, caffeine intake was less frequent at an older age and in schizophrenia patients, and more frequent in smokers and alcohol users. Among caffeine consumers, heavy caffeine intake (> or =200 mg/day) was significantly associated with schizophrenia (64%, 94/147 in schizophrenia versus 36%, 73/204 in controls), as well as older age and smoking. Daily amount of caffeine intake and smoked cigarettes correlated significantly in the schizophrenia group but not in the control group; the correlation of caffeine intake with nicotine dependence was low and non-significant in both groups. The association between current smoking and heavy caffeine intake may be partly explained by a pharmacokinetic effect: tobacco smoke compounds induce caffeine metabolism by the cytochrome P450 1A2. Although schizophrenia by itself may be associated with heavy caffeine intake in caffeine users, part of this association was explained by the association between schizophrenia and smoking. The relationship between caffeine and alcohol intake appeared to be more complex; alcohol and caffeine use were significantly associated, but within caffeine users alcohol was associated with less frequent heavy caffeine consumption among smokers. In future studies, the measurement of plasma caffeine levels will help both to better define heavy caffeine intake and to control for smoking pharmacokinetic effects.

Nicotine antagonizes caffeine- but not pentylenetetrazole-induced anxiogenic effect in mice

RATIONALE

Nicotine and caffeine are widely consumed licit psychoactive drugs worldwide. Epidemiological studies showed that they were generally used concurrently. Although some studies in experimental animals indicate clear pharmacological interactions between them, no studies have shown a specific interaction on anxiety responses.

OBJECTIVES

The present study investigates the effects of nicotine on anxiety induced by caffeine and another anxiogenic drug, pentylenetetrazole, in mice. The elevated plus-maze (EPM) test was used to evaluate the effects of drugs on anxiety.

METHODS

Adult male Swiss Webster mice (25-32 g) were given nicotine (0.05-0.25 mg/kg s.c.) or saline 10 min before caffeine (70 mg/kg i.p.) or pentylenetetrazole (15 and 30 mg/kg i.p.) injections. After 15 min, mice were evaluated for their open- and closed-arm time and entries on the EPM for a 10-min session. Locomotor activity was recorded for individual groups by using the same treatment protocol with the EPM test.

RESULTS

Nicotine (0.05-0.25 mg/kg) itself did not produce any significant effect in the EPM test, whereas caffeine (70 mg/kg) and pentylenetetrazole (30 mg/kg) produced an anxiogenic effect, apparent with decreases in open-arm time and entry. Nicotine (0.25 mg/kg) pretreatment blocked the caffeine- but not pentylenetetrazole-induced anxiety. Administration of each drug and their combinations did not produce any effect on locomotor activity.

CONCLUSIONS

Our results suggest that the antagonistic effect of nicotine on caffeine-induced anxiety is specific to caffeine, instead of a non-specific anxiolytic effect. Thus, it may extend the current findings on the interaction between nicotine and caffeine.

Caffeine and amphetamine produce cross-sensitization to nicotine-induced locomotor activity in mice

Sensitization development is linked to the addictive potential of the drugs. The same mechanisms might play a role in sensitization development to the different addictive drugs. The aim of the study was to investigate the development of cross-sensitization to caffeine and amphetamine in nicotine-induced locomotor sensitization in mice. Caffeine (2.5-20 mg/kg), amphetamine (1-16 mg/kg) or saline were injected to Swiss-Webster mice and locomotor activity was recorded for 30 min. Nicotine (0.5-2 mg/kg) or saline were injected to mice and locomotor activity was recorded for 30 min. Process was applied for 19 days, every other day (10 sessions). Caffeine (5 mg/kg), amphetamine (4 mg/kg) or saline were challenged to the different groups of nicotine-sensitized mice 2 days later on the last nicotine injection, and locomotor activity was recorded. Repetitive injections of nicotine (0.5-2 mg) produced locomotor sensitization in mice. After caffeine and amphetamine challenge injections, locomotor activity of the nicotine-sensitized mice was found to be significantly higher than saline-pretreated mice. Saline challenge did not produce any significant effect in nicotine- or saline-pretreated mice. Our results suggest that a cross-sensitization developed to both caffeine and amphetamine in nicotine-sensitized mice. In conclusion, similar central mechanisms may be responsible for the development of addiction to these substances.

Caffeine and the dopaminergic system

Caffeine is the most widely consumed psychostimulant substance, being self-administered throughout a wide range of conditions and present in numerous dietary products. Due to its widespread use and low abuse potential, caffeine is considered an atypical drug of abuse. The main mechanism of action of caffeine occurs via the blockade of adenosine A1 and A2A receptors. Adenosine is a modulator of CNS neurotransmission and its modulation of dopamine transmission through A2A receptors has been implicated in the effects of caffeine. This review provides an updated summary of the results reported in the literature concerning the behavioural pharmacology of caffeine and the neurochemical mechanisms underlying the psychostimulant effects elicited by caffeine. The review focuses on the effects of caffeine mediated by adenosine A2A receptors and on the influence that pre-exposure to caffeine may exert on the effects of classical drugs of abuse.

Stimulus properties of nicotine, amphetamine, and chlordiazepoxide as positive features in a pavlovian appetitive discrimination task in rats

Recent experiments from our laboratory have demonstrated that drug states can signal when environmental cues will be followed by rewarding outcomes (ie Pavlovian conditioning). However, little is known about the generality of this approach and whether it can be used for studying the pharmacological properties of drug states. Accordingly, the present experiments tested the pharmacological specificity of nicotine (0.4 mg/kg), amphetamine (1 mg/kg), and chlordiazepoxide (CDP, 5 mg/kg) in this Pavlovian drug discrimination procedure. Following drug administration, presentation of a conditional stimulus (CS) was followed by brief access to sucrose. When saline was administered, the same CS was presented but sucrose was withheld. In substitution tests, rats in each condition received varying doses of all training drugs and caffeine. Anticipatory food seeking developed during the CS on drug sessions but not on saline sessions for all drug features (ie drug state-specific conditional response (CR)). In generalization tests, this CR decreased as a function of decreases in the training dose. Median effective doses (ED50s) were calculated for nicotine (0.054 mg/kg), amphetamine (0.26 mg/kg), and CDP (2.48 mg/kg). No compound tested substituted for the CDP training drug. Partial substitution was evident between nicotine and amphetamine; CDP did not substitute for either of these drug features. Caffeine fully substituted for nicotine (ED50 = 15.45 mg/kg) and amphetamine (ED50 = 3.70 mg/kg), but not for CDP. These results are consistent with the hypothesis that drug states can occasion appetitive Pavlovian CRs in a pharmacologically specific manner.

Transdermal nicotine maintenance attenuates the subjective and reinforcing effects of intravenous nicotine, but not cocaine or caffeine, in cigarette-smoking stimulant abusers

The effects of transdermal nicotine maintenance on the subjective, reinforcing, and cardiovascular effects of intravenously administered cocaine, caffeine, and nicotine were examined using double-blind procedures in nine volunteers with histories of using tobacco, caffeine, and cocaine. Each participant was exposed to two chronic drug maintenance phases (21 mg/day nicotine transdermal patch and placebo transdermal patch). Within each drug phase, the participant received intravenous injections of placebo, cocaine (15 and 30 mg/70 kg), caffeine (200 and 400 mg/70 kg), and nicotine (1.0 and 2.0 mg/70 kg) in mixed order across days. Subjective and cardiovascular data were collected before and repeatedly after drug or placebo injection. Reinforcing effects were also assessed after each injection with a Drug vs Money Multiple-Choice Form. Intravenous cocaine produced robust dose-related increases in subjective and reinforcing effects; these effects were not altered by nicotine maintenance. Intravenous caffeine produced elevations on several subjective ratings; nicotine maintenance did not affect these ratings. Under the placebo maintenance condition, intravenous nicotine produced robust dose-related subjective effects, with maximal increases similar to the high dose of cocaine; nicotine maintenance significantly decreased the subjective and reinforcing effects of intravenous nicotine. The results of the present study demonstrate that chronic nicotine maintenance produces tolerance to the effects of intravenous nicotine, but does not affect the subjective or reinforcing effects of cocaine or caffeine.

Effects of caffeine on human health

Caffeine is probably the most frequently ingested pharmacologically active substance in the world. It is found in common beverages (coffee, tea, soft drinks), in products containing cocoa or chocolate, and in medications. Because of its wide consumption at different levels by most segments of the population, the public and the scientific community have expressed interest in the potential for caffeine to produce adverse effects on human health. The possibility that caffeine ingestion adversely affects human health was investigated based on reviews of (primarily) published human studies obtained through a comprehensive literature search. Based on the data reviewed, it is concluded that for the healthy adult population, moderate daily caffeine intake at a dose level up to 400 mg day(-1) (equivalent to 6 mg kg(-1) body weight day(-1) in a 65-kg person) is not associated with adverse effects such as general toxicity, cardiovascular effects, effects on bone status and calcium balance (with consumption of adequate calcium), changes in adult behaviour, increased incidence of cancer and effects on male fertility. The data also show that reproductive-aged women and children are 'at risk' subgroups who may require specific advice on moderating their caffeine intake. Based on available evidence, it is suggested that reproductive-aged women should consume </=300 mg caffeine per day (equivalent to 4.6 mg kg(-1) bw day(-1) for a 65-kg person) while children should consume </=2.5 mg kg(-1) bw day(-1).