Ostracising caffeine from the pharmacological arsenal for attention-deficit hyperactivity disorder--was this a correct decision? A literature review

Role of adenosine A2A receptors in hot and cold cognition: Effects of single-dose istradefylline in healthy volunteers

The role of the adenosine neurochemical system in human cognition is under-studied, despite such receptors being distributed throughout the brain. The aim of this study was to shed light on the role of the adenosine A2A receptors in human cognition using single-dose istradefylline. Twenty healthy male participants, aged 19-49, received 20 mg istradefylline and placebo, in a randomized, double-blind, placebo-controlled cross-over design. Cognition was assessed using computerized cognitive tests, covering both cold (non-emotional) and hot (emotion-laden) domains. Cardiovascular data were recorded serially. Cognitive effects of istradefylline were explored using repeated measures analysis of variance and paired t-tests as appropriate. On the EMOTICOM battery, there was a significant effect of istradefylline versus placebo on the Social Information Preference task (t = 2.50, p = 0.02, d=-0.59), indicating that subjects on istradefylline interpreted social situations more positively. No other significant effects were observed on other cognitive tasks, nor in terms of cardiovascular measures (pulse and blood pressure). De-briefing indicated that blinding was successful, both for participants and the research team. Further exploration of the role of adenosine A2A receptors in emotional processing may be valuable, given that abnormalities in related cognitive functions are implicated in neuropsychiatric disorders. The role of adenosine systems in human cognition requires further clarification, including with different doses of istradefylline and over different schedules of administration.

Effects of Caffeine Consumption on Attention Deficit Hyperactivity Disorder (ADHD) Treatment: A Systematic Review of Animal Studies

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by a persistent pattern of inattention and/or hyperactivity-impulsivity. ADHD impairments arise from irregularities primarily in dopamine (DA) and norepinephrine (NE) circuits within the prefrontal cortex. Due to ADHD medication’s controversial side effects and high rates of diagnosis, alternative/complementary pharmacological therapeutic approaches for ADHD are needed. Although the number of publications that study the potential effects of caffeine consumption on ADHD treatment have been accumulating over the last years, and caffeine has recently been used in ADHD research in the context of animal models, an updated evidence-based systematic review on the effects of caffeine on ADHD-like symptoms in animal studies is lacking. To provide insight and value at the preclinical level, a systematic review based on PRISMA guidelines was performed for all publications available up to 1 September 2021. Caffeine treatment increases attention and improves learning, memory, and olfactory discrimination without altering blood pressure and body weight. These results are supported at the neuronal/molecular level. Nonetheless, the role of caffeine in modulating ADHD-like symptoms of hyperactivity and impulsivity is contradictory, raising discrepancies that require further clarification. Our results strengthen the hypothesis that the cognitive effects of caffeine found in animal models could be translated to human ADHD, particularly during adolescence.

Caffeine-related genes influence anxiety disorders in children and adults with ADHD

Attention-deficit/hyperactivity disorder (ADHD) and anxiety disorders (AD) frequently co-occur, increasing morbidity and challenging treatment. Caffeine is a central nervous system stimulant and acts in the brain through adenosine receptors, influencing attention, alertness, and anxiety. In the present study, we performed a gene-set analysis to verify if genes related to caffeine response are associated with anxiety disorders in 240 children and 406 adults with ADHD. We demonstrated an association between the gene-set with AD in children (P = 0.0054) and with the number of anxiety disorders in adults (P = 0.0197). In order to test if this effect is a result of anxiety in general or is related to AD comorbid with ADHD, we evaluated the association between caffeine gene-set with AD in an adult control sample. The gene-set was neither associated with the AD presence (P = 0.3008) nor with the number of AD (P = 0.5594) in this control sample. We also test this gene set with ADHD (n = 55,374) and AD (n = 18,186) GWAS summary statistics, and we did not observe significant results with ADHD (P = 0.5587) or AD (P = 0.3930). These findings suggest the caffeine-related genes play a role in the etiology of an anxiety disorder phenotype present in children and adults with ADHD.

Self-Medication of ADHD Symptoms: Does Caffeine Have a Role?

OBJECTIVE

Stimulants are the most effective treatment for Attention Deficit/ Hyperactivity disorder (ADHD). In addition, studies have shown that nicotine dependence in patients with ADHD is probably best explained by self-medication. The question is whether this is also true for caffeine use and caffeine dependence. The aim of our study was, therefore, to examine the relationship of ADHD symptoms, caffeine consumption, caffeine use disorder (CUD) and well-being. We hypothesized that those who have more ADHD symptoms and regularly consume caffeine have higher psychological well-being than those who have more ADHD symptoms, but do not consume caffeine.

METHODS

A general population sample (N = 2,259, 70.5% male, mean age 34.0) filled out the 10-item Caffeine Use Disorder Questionnaire (CUDQ), the Adult ADHD Self-report Scale (ASRS) and the WHO-5 Well-Being Index (WHO-5) and were asked about their caffeine consumption habits in an online survey.

RESULTS

There were no associations between ADHD and coffee, tea, energy drink or cola consumption or daily caffeine consumption. However, the results of the path analysis showed that the level of ADHD symptoms was positively associated with the level of CUD (β = 0.350) and negatively with the WHO-5 (β = -0.259).

CONCLUSIONS

Caffeine consumption was not associated with ADHD symptom severity and thus not likely to represent self-medication. On the contrary, caffeine use disorder severity is associated with more ADHD symptoms and both caffeine use disorder and ADHD are associated with lower well-being.

Exploring the Role of Caffeine Use in Adult-ADHD Symptom Severity of US Army Soldiers

There is a growing trend of using energy drinks and caffeinated beverages to improve cognitive performance that is widespread and well-studied among children and teenagers with Attention Deficit Hyperactive Disorder (ADHD), but little is known about adult ADHD (A-ADHD). As a consequence, the use of highly caffeinated drinks and their impact on ADHD symptoms are poorly understood. This is especially true in populations where A-ADHD and the use of these beverages are largely represented, such as in military samples. From the All Army Study (AAS) of the Army Study to Assess Risk and Resilience in Service members (STARRS) data, 1,239 A-ADHD soldiers and 17,674 peers without any psychiatric comorbidity were selected. The two groups were compared on: (1) the presence of substance use disorder (SUD) diagnosis both over their lifetime and in the previous 30 days; (2) patterns of alcohol and caffeine use using chi-square analyses. Lastly, the relationship between substance use and severity of A-ADHD symptoms was assessed using Pearson’s correlations. Soldiers with a diagnosis of A-ADHD had a higher prevalence of SUD diagnosis compared to their peers without psychiatric comorbidity. They also tended to use more alcohol, caffeine pills, energy drinks, and other caffeinated drinks. Alcohol use was positively correlated with A-ADHD symptoms; on the contrary, energy drinks, caffeine pills and other caffeinated drinks showed negative correlations with some aspects of A-ADHD symptomatology. The use of caffeinated compounds appears to be increased among military soldiers with ADHD, and they may help reducing A-ADHD symptoms and improve cognitive performance. These results suggest a possible role for caffeine as a potential pharmacological tool in the treatment of adult ADHD.

Caffeine and adenosine A2A receptors rescue neuronal development in vitro of frontal cortical neurons in a rat model of attention deficit and hyperactivity disorder

Although some studies have supported the effects of caffeine for treatment of Attention deficit and hyperactivity disorder (ADHD), there were no evidences about its effects at the neuronal level. In this study, we sought to find morphological alterations during in vitro development of frontal cortical neurons from Spontaneoulsy hypertensive rats (SHR, an ADHD rat model) and Wistar-Kyoto rats (WKY, control strain). Further, we investigated the effects of caffeine and adenosine A₁ and A_2A receptors (A₁R and A_2AR) signaling. Cultured cortical neurons from WKY and SHR were analyzed by immunostaining of microtubule-associated protein 2 (MAP-2) and tau protein after treatment with either caffeine, or A₁R and A_2AR agonists or antagonists. Besides, the involvement of PI3K and not PKA signaling was also assessed. Neurons from ADHD model displayed less neurite branching, shorter maximal neurite length and decreased axonal outgrowth. While caffeine recovered neurite branching and elongation from ADHD neurons via both PKA and PI3K signaling, A_2AR agonist (CGS 21680) promoted more neurite branching via PKA signaling. The selective A_2AR antagonist (SCH 58261) was efficient in recovering axonal outgrowth from ADHD neurons through PI3K and not PKA signaling. For the first time, frontal cortical neurons were isolated from ADHD model and they presented disturbances in the differentiation and outgrowth. By showing that caffeine and A_2AR may act at neuronal level rescuing ADHD neurons outgrowth, our findings strengthen the potential of caffeine and A_2AR receptors as an adjuvant for ADHD treatment.

Caffeine and cannabinoid receptors modulate impulsive behavior in an animal model of attentional deficit and hyperactivity disorder

Attention deficit and hyperactivity disorder (ADHD) is characterized by impaired levels of hyperactivity, impulsivity, and inattention. Adenosine and endocannabinoid systems tightly interact in the modulation of dopamine signaling, involved in the neurobiology of ADHD. In this study, we evaluated the modulating effects of the cannabinoid and adenosine systems in a tolerance to delay of reward task using the most widely used animal model of ADHD. Spontaneous Hypertensive Rats (SHR) and Wistar-Kyoto rats were treated chronically or acutely with caffeine, a non-selective adenosine receptor antagonist, or acutely with a cannabinoid agonist (WIN55212-2, WIN) or antagonist (AM251). Subsequently, animals were tested in the tolerance to delay of reward task, in which they had to choose between a small, but immediate, or a large, but delayed, reward. Treatment with WIN decreased, whereas treatment with AM251 increased the choices of the large reward, selectively in SHR rats, indicating a CB₁ receptor-mediated increase in impulsive behavior. An acute pre-treatment with caffeine blocked WIN effects. Conversely, a chronic treatment with caffeine increased the impulsive phenotype and potentiated the WIN effects. The results indicate that both cannabinoid and adenosine receptors modulate impulsive behavior in SHR: the antagonism of cannabinoid receptors might be effective in reducing impulsive symptoms present in ADHD; in addition, caffeine showed the opposite effects on impulsive behavior depending on the length of treatment. These observations are of particular importance to consider when therapeutic manipulation of CB1 receptors is applied to ADHD patients who consume coffee.

New Developments on the Adenosine Mechanisms of the Central Effects of Caffeine and Their Implications for Neuropsychiatric Disorders

Recent studies on interactions between striatal adenosine and dopamine and one of its main targets, the adenosine A_2A receptor–dopamine D₂ receptor (A2AR–D2R) heteromer, have provided a better understanding of the mechanisms involved in the psychostimulant effects of caffeine and have brought forward new data on the mechanisms of operation of classical orthosteric ligands within G protein-coupled receptor heteromers. The striatal A2AR–D2R heteromer has a tetrameric structure and forms part of a signaling complex that includes a Gs and a Gi protein and the effector adenyl cyclase (subtype AC5). Another target of caffeine, the adenosine A₁ receptor–dopamine D₁ receptor (A1R–D1R) heteromer, seems to have a very similar structure. Initially suggested to be localized in the striatum, the A1R–D1R heteromer has now been identified in the spinal motoneuron and shown to mediate the spinally generated caffeine-induced locomotion. In this study, we review the recently discovered properties of A2AR–D2R and A1R–D1R heteromers. Our studies demonstrate that these complexes are a necessary condition to sustain the canonical antagonistic interaction between a Gs-coupled receptor (A2AR or D1R) and a Gi-coupled receptor (D2R or A1R) at the adenylyl cyclase level, which constitutes a new concept in the field of G protein-coupled receptor physiology and pharmacology. A2AR antagonists targeting the striatal A2AR–D2R heteromer are already being considered as therapeutic agents in Parkinson's disease. In this study, we review the preclinical evidence that indicates that caffeine and A2AR antagonists could be used to treat the motivational symptoms of depression and attention-deficit/hyperactivity disorder, while A1R antagonists selectively targeting the spinal A1R–D1R heteromer could be used in the recovery of spinal cord injury.

Differential Behavioral and Biochemical Responses to Caffeine in Male and Female Rats from a Validated Model of Attention Deficit and Hyperactivity Disorder

Epidemiological studies suggest sex differences in attention deficit and hyperactivity disorder (ADHD) symptomatology. The potential benefits of caffeine have been reported in the management of ADHD, but its effects were not properly addressed with respect to sex differences. The present study examined the effects of caffeine (0.3 g/L) administered since childhood in the behavior and brain-derived neurotrophic factor (BDNF) and its related proteins in both sexes of a rat model of ADHD (spontaneously hypertensive rats-SHR). Hyperlocomotion, recognition, and spatial memory disturbances were observed in adolescent SHR rats from both sexes. However, females showed lack of habituation and worsened spatial memory. Although caffeine was effective against recognition memory impairment in both sexes, spatial memory was recovered only in female SHR rats. Besides, female SHR rats showed exacerbated hyperlocomotion after caffeine treatment. SHR rats from both sexes presented increases in the BDNF, truncated and phospho-TrkB receptors and also phospho-CREB levels in the hippocampus. Caffeine normalized BDNF in males and truncated TrkB receptor at both sexes. These findings provide insight into the potential of caffeine against fully cognitive impairment displayed by females in the ADHD model. Besides, our data revealed that caffeine intake since childhood attenuated behavioral alterations in the ADHD model associated with changes in BDNF and TrkB receptors in the hippocampus.

Caffeine's influence on gambling behavior and other types of impulsivity

BACKGROUND

Young adulthood is a developmental period frequently associated with occurrence of impulsive behaviors including gambling. It is estimated that 73% of children and 87% of adults in the United States regularly use caffeine. Questions remain, however, concerning the role of caffeine in the development and maintenance of impulsive behaviors such as gambling.

METHODS

Sixty-one young adults with at least some degree of disordered gambling were recruited from two Mid-Western university communities in the United States using media advertisements. Caffeine intake over the preceding month was quantified using the Caffeine Use Questionnaire. Clinician rating scales, questionnaires, and cognitive tests germane to impulsivity were completed. Relationships between caffeine intake and demographic, gambling symptom, and neurocognitive measures were evaluated using the statistical technique of partial least squares (PLS).

RESULTS

Average weekly caffeine intake in the gamblers was 1218.5mg (a figure higher than previously reported in the general population). PLS yielded an optimal model with one latent factor, which explained 14.8% of variation in demographic/clinical/cognitive measures and 32.3% of variation in caffeine intake. In this model, higher caffeine intake was significantly associated with earlier age at first gambling, higher personality-related impulsiveness, more nicotine consumption, older age, and more impulsive decision-making.

CONCLUSIONS

These data suggest a particularly strong relationship between caffeine intake, earlier age of first gambling, and certain types of impulsivity in gamblers. Providing education about healthy caffeine use may be especially valuable in gamblers. Future work should explore whether the relationship between caffeine use and gambling is due to a common predisposing factor (impulsive tendencies) or, rather, constitutes a form of self-medication in gamblers (or a means of sustaining gambling habits for longer).

Purinergic system in psychiatric diseases

Psychiatric disorders are debilitating diseases, affecting >80 million people worldwide. There are no causal cures for psychiatric disorders and available therapies only treat the symptoms. The etiology of psychiatric disorders is unknown, although it has been speculated to be a combination of environmental, stress and genetic factors. One of the neurotransmitter systems implicated in the biology of psychiatric disorders is the purinergic system. In this review, we performed a comprehensive search of the literature about the role and function of the purinergic system in the development and predisposition to psychiatric disorders, with a focus on depression, schizophrenia, bipolar disorder, autism, anxiety and attention deficit/hyperactivity disorder. We also describe how therapeutics used for psychiatric disorders act on the purinergic system.

Considerations for ADHD in the child with epilepsy and the child with migraine

INTRODUCTION

Attention Deficit Hyperactivity Disorder (ADHD) is a common comorbid condition in children with epilepsy and migraine. Treatment of ADHD in children with epilepsy or migraine is essential but clinicians may overlook symptoms of ADHD and avoid appropriate use of medications that may reduce symptoms of ADHD without compromising treatment of epilepsy or migraine. Areas covered: PubMed was searched for articles on ADHD and epilepsy or migraine. Key papers were reviewed for additional articles. Areas of interest were: epidemiology, etiological factors, and treatment with emphasis on therapy. Expert commentary: Stimulant medication, especially methylphenidate, appears to be safe and effective in the treatment of ADHD in children with epilepsy or migraine. Unfortunately, data is limited with very few controlled trials of methylphenidate and very limited information on the use of amphetamines or non-stimulant drugs.

Treatment of GABA from Fermented Rice Germ Ameliorates Caffeine-Induced Sleep Disturbance in Mice

γ-Aminobutyric acid (GABA), a major inhibitory neurotransmitter in the mammalian central nervous system, is involved in sleep physiology. Caffeine is widely used psychoactive substance known to induce wakefulness and insomnia to its consumers. This study was performed to examine whether GABA extracts from fermented rice germ ameliorates caffeine-induced sleep disturbance in mice, without affecting spontaneous locomotor activity and motor coordination. Indeed, caffeine (10 mg/kg, i.p.) delayed sleep onset and reduced sleep duration of mice. Conversely, rice germ ferment extracts-GABA treatment (10, 30, or 100 mg/kg, p.o.), especially at 100 mg/kg, normalized the sleep disturbance induced by caffeine. In locomotor tests, rice germ ferment extracts-GABA slightly but not significantly reduced the caffeine-induced increase in locomotor activity without affecting motor coordination. Additionally, rice germ ferment extracts-GABA per se did not affect the spontaneous locomotor activity and motor coordination of mice. In conclusion, rice germ ferment extracts-GABA supplementation can counter the sleep disturbance induced by caffeine, without affecting the general locomotor activities of mice.

Impact of ADHD symptoms on clinical and cognitive aspects of problem gambling

BACKGROUND

Problem gambling is common across cultures, and has been conceptualized in terms of impulsivity. While elevated rates of attention deficit hyperactivity disorder (ADHD) have been observed in problem gamblers, the relationship between these two conditions, and other dissociable forms of impulsivity, has received little research attention.

METHODS

N=126 non-treatment seeking young adults with problem gambling were recruited from the community, and were grouped according to the presence or absence of probable current ADHD. Clinical and cognitive measures pertaining to impulsivity were collected via detailed psychiatric assessment, questionnaires, and computerized neuropsychological tests. These variables were compared between groups.

RESULTS

Probable current ADHD was identified in 21.4% of the sample, and was associated with earlier age at onset of gambling behaviors, higher Barratt impulsivity scores (all three subscales), greater caffeine intake, worse response inhibition (Stop-Signal Test), and impaired decision-making (greater proportion of points gambled, Cambridge Gamble Test). Problem gamblers with and without ADHD did not differ on demographic characteristics or the rate of other psychiatric disorders, depression scores, nicotine and alcohol consumption, and body mass index. No significant group differences were found for general response speed, working memory, or executive planning.

CONCLUSIONS

ADHD is common in young adults with dysfunctional gambling behaviors and is associated with elevated questionnaire and cognitive based measures of impulsivity, along with heightened caffeine use. Future work should study the causal nature between these factors and the treatment implications of these findings.