Adenosine A2A Receptors in the Rat Prelimbic Medial Prefrontal Cortex Control Delay-Based Cost-Benefit Decision Making

Adenosinergic system and nucleoside transporters in attention deficit hyperactivity disorder: Current findings

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder with high heterogeneity that can affect individuals of any age. It is characterized by three main symptoms: inattention, hyperactivity, and impulsivity. These neurobehavioral alterations and neurochemical and pharmacological findings are mainly attributed to unbalanced catecholaminergic signaling, especially involving dopaminergic pathways within prefrontal and striatal areas. Dopamine receptors and transporters are not solely implicated in this imbalance, as evidence indicates that the dopaminergic signaling is modulated by adenosine activity. To this extent, alterations in adenosinergic signaling are probably involved in ADHD. Here, we review the current knowledge about adenosine's role in the modulation of chemical, behavioral and cognitive parameters of ADHD, especially regarding dopaminergic signaling. Current literature usually links adenosine receptors signaling to the dopaminergic imbalance found in ADHD, but there is evidence that equilibrative nucleoside transporters (ENTs) could also be implicated as players in dopaminergic signaling alterations seen in ADHD, since their involvement in other neurobehavioral impairments.

Impact of Coffee Intake on Measures of Wellbeing in Mice

Coffee intake is increasingly recognized as a life-style factor associated with the preservation of health, but there is still a debate on the relative effects of caffeinated and decaffeinated coffee. We now tested how the regular drinking of caffeinated and decaffeinated coffee for 3 weeks impacted on the behavior of male and female adult mice. Males drinking caffeinated coffee displayed statistically significant lower weight gain, increased sensorimotor coordination, greater motivation in the splash test, more struggling in the forced swimming test, faster onset of nest building, more marble burying and greater sociability. Females drinking caffeinated coffee displayed statistically significant increased hierarchy fighting, greater self-care and motivation in the splash test and faster onset of nest building. A post-hoc two-way ANOVA revealed sex-differences in the effects of caffeinated coffee (p values for interaction between the effect of caffeinated coffee and sex) on the hierarchy in the tube test (p = 0.044; dominance), in the time socializing (p = 0.044) and in the latency to grooming (p = 0.048; selfcare), but not in the marble burying test (p = 0.089). Intake of decaffeinated coffee was devoid of effects in males and females. Since caffeine targets adenosine receptors, we verified that caffeinated but not decaffeinated coffee intake increased the density of adenosine A1 receptors (A1R) and increased A1R-mediated tonic inhibition of synaptic transmission in the dorsolateral striatum and ventral but not dorsal hippocampus, the effects being more evident in the ventral hippocampus of females and striatum of males. In contrast, caffeinated and decaffeinated coffee both ameliorated the antioxidant status in the frontal cortex. It is concluded that caffeinated coffee increases A1R-mediated inhibition in mood-related areas bolstering wellbeing of both males and females, with increased sociability in males and hierarchy struggling and self-care in females.

Adenosinergic Modulation of Layer 6 Microcircuitry in the Medial Prefrontal Cortex Is Specific to Presynaptic Cell Type

Adenosinergic modulation in the PFC is recognized for its involvement in various behavioral aspects including sleep homoeostasis, decision-making, spatial working memory and anxiety. While the principal cells of layer 6 (L6) exhibit a significant morphological diversity, the detailed cell-specific regulatory mechanisms of adenosine in L6 remain unexplored. Here, we quantitatively analyzed the morphological and electrophysiological parameters of L6 neurons in the rat medial prefrontal cortex (mPFC) using whole-cell recordings combined with morphological reconstructions. We were able to identify two different morphological categories of excitatory neurons in the mPFC of both juvenile and young adult rats with both sexes. These categories were characterized by a leading dendrite that was oriented either upright (toward the pial surface) or inverted (toward the white matter). These two excitatory neuron subtypes exhibited different electrophysiological and synaptic properties. Adenosine at a concentration of 30 µM indiscriminately suppressed connections with either an upright or an inverted presynaptic excitatory neuron. However, using lower concentrations of adenosine (10 µM) revealed that synapses originating from L6 upright neurons have a higher sensitivity to adenosine-induced inhibition of synaptic release. Adenosine receptor activation causes a reduction in the probability of presynaptic neurotransmitter release that could be abolished by specifically blocking A1 adenosine receptors (A1ARs) using 8-cyclopentyltheophylline (CPT). Our results demonstrate a differential expression level of A1ARs at presynaptic sites of two functionally and morphologically distinct subpopulations of L6 principal neurons, suggesting the intricate functional role of adenosine in neuronal signaling in the brain.

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.

Adenosine receptors participate in anabolic-androgenic steroid-induced changes on risk assessment/anxiety-like behaviors in male and female rats

Anabolic-androgenic steroids (AAS) and caffeine can induce several behavioral alterations in humans and rodents. Administration of nandrolone decanoate is known to affect defensive responses to aversive stimuli, generally decreasing inhibitory control and increasing aggressivity but whether caffeine intake influences behavioral changes induced by AAS is unknown. The present study aimed to investigate behavioral effects of caffeine (a non-selective antagonist of adenosine receptors) alone or combined with nandrolone decanoate (one of the most commonly AAS abused) in female and male Lister Hooded rats. Our results indicated that chronic administration of nandrolone decanoate (10 mg/kg, i.m., once a week for 8 weeks) decreased risk assessment/anxiety-like behaviors (in the elevated plus maze test), regardless of sex. These effects were prevented by combined caffeine intake (0.1 g/L, p.o., ad libitum). Overall, the present study heralds a key role for caffeine intake in the modulation of nandrolone decanoate-induced behavioral changes in rats, suggesting adenosine receptors as candidate targets to manage impact of AAS on brain function and behavior.

Striatopallidal adenosine A2A receptor modulation of goal-directed behavior: Homeostatic control with cognitive flexibility

Dysfunction of goal-directed behaviors under stressful or pathological conditions results in impaired decision-making and loss of flexibility of thoughts and behaviors, which underlie behavioral deficits ranging from depression, obsessive-compulsive disorders and drug addiction. Tackling the neuromodulators fine-tuning this core behavioral element may facilitate the development of effective strategies to control these deficits present in multiple psychiatric disorders. The current investigation of goal-directed behaviors has concentrated on dopamine and glutamate signaling in the corticostriatal pathway. In accordance with the beneficial effects of caffeine intake on mood and cognitive dysfunction, we now propose that caffeine's main site of action - adenosine A2A receptors (A2AR) - represent a novel target to homeostatically control goal-directed behavior and cognitive flexibility. A2AR are abundantly expressed in striatopallidal neurons and colocalize and interact with dopamine D2, NMDA and metabotropic glutamate 5 receptors to integrate dopamine and glutamate signaling. Specifically, striatopallidal A2AR (i) exert an overall "break" control of a variety of cognitive processes, making A2AR antagonists a novel strategy for improving goal-directed behavior; (ii) confer homeostatic control of goal-directed behavior by acting at multiple sites with often opposite effects, to enhance cognitive flexibility; (iii) integrate dopamine and adenosine signaling through multimeric A2AR-D2R heterocomplexes allowing a temporally precise fine-tuning in response to local signaling changes. As the U.S. Food and Drug Administration recently approved the A2AR antagonist Nourianz® (istradefylline) to treat Parkinson's disease, striatal A2AR-mediated control of goal-directed behavior may offer a new and real opportunity for improving deficits of goal-directed behavior and enhance cognitive flexibility under various neuropsychiatric conditions. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Role of adenosine A2A receptors in the loss of consciousness induced by propofol anesthesia

The mechanism of propofol-anesthesia-induced loss of consciousness (LOC) remains largely unknown. We speculated that the adenosine A_2A receptor serves as a vital molecular target in regulating LOC states under propofol anesthesia. c-Fos staining helped observe the changes in the neuronal activity in the nucleus accumbens (NAc). Initially, the adenosine signals in the NAc were measured under propofol anesthesia using fiber photometry recordings. Then, behavior tests and electrophysiological recordings were used to verify the effect of systemic A_2A R agonist or antagonist treatment on propofol anesthesia. Next, the microinjection technique was used to clarify the role of the NAc A_2A R under propofol anesthesia. Fiber photometry recordings were applied to assess the effect of A_2A R agonist or antagonist systemic treatment on adenosine signal alterations in the NAc during propofol anesthesia. Then, as the GABAergic neurons are the main neurons in the NAc, we further measured the neuronal activity of GABAergic neurons. In our study, propofol anesthesia enhanced the neuronal activity in the NAc, and the adenosine signals were increased in the NAc. SCH58261 reduced the LOC time and sedative depth, while CGS21680 increased those via intraperitoneal injection. Additionally, CGS21680 increased the changes in delta, theta, alpha, beta, and low-gamma oscillations in the NAc. Moreover, microinjection of SCH58261 significantly shortened the LOC time, whereas microinjection of CGS21680 into the NAc significantly prolonged the LOC duration. The results illustrated that after A_2A R agonist administration, the level of extracellular adenosine signals in the NAc was decreased and the neuronal activity of GABAergic neurons was enhanced, whereas after A_2A R antagonist administration via intraperitoneal injection, the opposite occurred. This study reveals the vital role of the A_2A R in propofol-induced LOC and that the A_2A R could affect the maintenance of propofol anesthesia.

Epilepsy and Autism Spectrum Disorder (ASD): The Underlying Mechanisms and Therapy Targets Related to Adenosine

Epilepsy and autism spectrum disorder (ASD) are highly mutually comorbid, suggesting potential overlaps in genetic etiology, pathophysiology, and neurodevelopmental abnormalities. Adenosine, an endogenous anticonvulsant and neuroprotective neuromodulator of the brain, has been proved to affect the process of epilepsy and ASD. On the one hand, adenosine plays a crucial role in preventing the progression and development of epilepsy through adenosine receptordependent and -independent ways. On the other hand, adenosine signaling can not only regulate core symptoms but also improve comorbid disorders in ASD. Given the important role of adenosine in epilepsy and ASD, therapeutic strategies related to adenosine, including the ketogenic diet, neuromodulation therapy, and adenosine augmentation therapy, have been suggested for the arrangement of epilepsy and ASD. There are several proposals in this review. Firstly, it is necessary to further discuss the relationship between both diseases based on the comorbid symptoms and mechanisms of epilepsy and ASD. Secondly, it is important to explore the role of adenosine involved in epilepsy and ASD. Lastly, potential therapeutic value and clinical approaches of adenosine-related therapies in treating epilepsy and ASD need to be emphasized.

Accumbal adenosine A2A receptor inactivation biases for large and costly rewards in the effort- but not delay-based decision making

The cost-benefit decision-making (CBDM) is critical to normal human activity and a diminished willingness to expend effort to obtain rewards is a prevalent/noted characteristic of neuropsychiatric disorders such as schizophrenia, Parkinson's disease. Numerous studies have identified nucleus accumbens (NAc) as an important locus for CBDM control but their neuromodulatory and behavioral mechanisms remain largely under-explored. Adenosine A_2A receptors (A_2ARs), which are highly concentrated in the striatopallidal neurons, can integrate glutamate and dopamine signals for controlling effort-related choice behaviors. While the involvement of A_2ARs in effort-based decision making is well documented, the role of other decision variables (reward discrimination) in effort-based decision making and the role of A_2AR in delay-based decision making are less clear. In this study, we have developed a well-controlled CBDM behavioral paradigm to manipulate effort/cost and reward independently or in combination, allowing a dissection of four behavioral elements: effort-based CBDM (E-CBDM), delay-based CBDM (D-CBDM), reward discrimination (RD), effort discrimination (ED), and determined the effect of genetic knockdown (KD) of NAc A_2AR on the four behavioral elements. We found that A_2AR KD in NAc increased the choice for larger, more costly reward in the E-CBDM, but not D-CBDM. Furthermore, this high-effort/high-reward bias was attributable to the increased willingness to engage in effort but not the effect of discrimination of reward magnitude. Our findings substantiate an important role of the NAc A_2AR in control of E-CBDM and support that pharmacologically targeting NAc A_2ARs would be a useful strategy for treating the aberrant effort-based decision making in neuropsychiatric disorders.

The therapeutic potential of exercise and caffeine on attention-deficit/hyperactivity disorder in athletes

Attention-deficit/hyperactivity disorder (ADHD) is characterized by evident and persistent inattention, hyperactivity, impulsivity, and social difficulties and is the most common childhood neuropsychiatric disorder, and which may persist into adulthood. Seventy to 80% of children and adults with ADHD are treated with stimulant medication, with positive response rates occurring for both populations. Medicated ADHD individuals generally show sustained and improved attention, inhibition control, cognitive flexibility, on-task behavior, and cognitive performance. The ethics of ADHD medication use in athletics has been a debated topic in sport performance for a long time. Stimulants are banned from competition in accordance with World Anti-Doping Association and National Collegiate Athletic Association regulations, due to their ability to not only enhance cognitive performance but also exercise performance. Limited research has been conducted looking at the differences in exercise performance variables in unmedicated ADHD verses medicated ADHD. Not all ADHD athletes choose stimulant medication in their treatment plan due to personal, financial, or other reasons. Non-stimulant treatment options include non-stimulant medication and behavioral therapy. However, the use of caffeinated compounds and exercise has both independently been shown to be effective in the management of ADHD symptoms in human studies and animal models. This mini review will discuss the effect of exercise and caffeine on neurobehavioral, cognitive, and neurophysiological factors, and exercise performance in ADHD athletes, and whether exercise and caffeine should be considered in the treatment plan for an individual with ADHD.

Adenosine A2A Receptor Blockade Ameliorates Mania Like Symptoms in Rats: Signaling to PKC-α and Akt/GSK-3β/β-Catenin

Adenosinergic system dysfunction is implicated in the pathophysiology of multiple neuropsychiatric disorders including mania and bipolar diseases. The established synergistic interaction between A_2A and D₂ receptors in the prefrontal cortex could highlight the idea of A_2A receptor antagonism as a possible anti-manic strategy. Hence, the present study was performed to examine the effect of a selective adenosine A_2A receptor blocker (SCH58261) on methylphenidate-induced mania-like behavior while investigating the underlying mechanisms. Rats were injected with methylphenidate (5 mg/kg/day, i.p.) for 3 weeks with or without administration of either SCH58261 (0.01 mg/kg/day, i.p.) or lithium (150 mg/kg/day, i.p.) starting from day 9. In the diseased rats, adenosine A_2AR antagonism reduced locomotor hyperactivity and risk-taking behavior along with decreased dopamine and glutamate levels. Meanwhile, SCH58261 restored NMDA receptor function, suppressed PKC-α expression, down-regulated β-Arrestin-2, up-regulated pS473-Akt and pS9-GSK-3β. Further, SCH58261 promoted synaptic plasticity markers through increasing BDNF levels along with down-regulating GAP-43 and SNAP-25. The A_2A antagonist also reduced NF-κBp65 and TNF-α together with elevating IL-27 level giving an anti-inflammatory effect. In conclusion, suppression of PKC-α and modulation of Akt/GSK-3β/β-catenin axis through A_2AR inhibition, could introduce adenosine A_2AR as a possible therapeutic target for treatment of mania-like behavior. This notion is supported by the ability of the A_2AR antagonist (SCH58261) to produce comparable results to those observed with the standard anti-manic drug (Lithium).

α-Synuclein Selectively Impairs Motor Sequence Learning and Value Sensitivity: Reversal by the Adenosine A2A Receptor Antagonists

Parkinson's disease (PD) is characterized pathologically by alpha-synuclein (α-Syn) aggregates and clinically by the motor as well as cognitive deficits, including impairments in sequence learning and habit learning. Using intracerebral injection of WT and A53T mutant α-Syn fibrils, we investigate the behavioral mechanism of α-Syn for procedure-learning deficit in PD by critically determining the α-Syn-induced effects on model-based goal-directed behavior, model-free (probability-based) habit learning, and hierarchically organized sequence learning. 1) Contrary to the widely held view of habit-learning deficit in early PD, α-Syn aggregates in the dorsomedial striatum (DMS) and dorsolateral striatum (DLS) did not affect acquisition of habit learning, but selectively impaired goal-directed behavior with reduced value sensitivity. 2) α-Syn in the DLS (but not DMS) and SNc selectively impaired the sequence learning by affecting sequence initiation with the reduced first-step accuracy. 3) Adenosine A2A receptor (A2AR) antagonist KW6002 selectively improved sequence learning by preferentially improving sequence initiation and shift of sequence learning as well as behavioral reactivity. These findings established a casual role of α-Syn in the SN-DLS pathway in sequence-learning deficit and DMS α-Syn in goal-directed behavior deficit and suggest a novel therapeutic strategy to improve sequence-learning deficit in PD with enhanced sequence initiation by A2AR antagonists.

Use of knockout mice to explore CNS effects of adenosine

The initial exploration using pharmacological tools of the role of adenosine receptors in the brain, concluded that adenosine released as such acted on A₁R to inhibit excitability and glutamate release from principal neurons throughout the brain and that adenosine A_2A receptors (A_2AR) were striatal-'specific' receptors controlling dopamine D₂R. This indicted A₁R as potential controllers of neurodegeneration and A_2AR of psychiatric conditions. Global knockout of these two receptors questioned the key role of A₁R and instead identified extra-striatal A_2AR as robust controllers of neurodegeneration. Furthermore, transgenic lines with altered metabolic sources of adenosine revealed a coupling of ATP-derived adenosine to activate A_2AR and a role of A₁R as a hurdle to initiate neurodegeneration. Additionally, cell-selective knockout of A_2AR unveiled the different roles of A_2AR in different cell types (neurons/astrocytes) in different portions of the striatal circuits (dorsal versus lateral) and in different brain areas (hippocampus/striatum). Finally, a new transgenic mouse line with deletion of all adenosine receptors seems to indicate a major allostatic rather than homeostatic role of adenosine and may allow isolating P2R-mediated responses to unravel their role in the brain, a goal close to heart of Geoffrey Burnstock, to whom we affectionately dedicate this review.

Striatopallidal adenosine A2A receptors in the nucleus accumbens confer motivational control of goal-directed behavior

The ability to learn the reward-value and action-outcome contingencies in dynamic environment is critical for flexible adaptive behavior and development of effective pharmacological control of goal-directed behaviors represents an important challenge for improving the deficits in goal-directed behavior which may underlie seemingly disparate symptoms across psychiatric disorders. Adenosine A_2A receptor (A_2AR) is emerging as a novel neuromodulatory target for controlling goal-directed behavior for its unique neuromodulatory features: the ability to integrate dopamine and glutamate signaling, the "brake" constraint of various cognitive processes and the balanced control of goal-directed and habit actions. However, the contribution and circuit mechanisms of the striatopallidal A_2ARs in nucleus accumbens (NAc) to control of goal-directed behavior remain to be determined. Here, we employed newly developed opto-A_2AR and the focal A_2AR knockdown strategies to demonstrate the causal role of NAc A_2AR in control of goal-directed behavior. Furthermore, we dissected out multiple distinct behavioral mechanisms underlying which NAc A_2ARs control goal-directed behavior: (i) NAc A_2ARs preferentially control goal-directed behavior at the expense of habit formation. (ii) NAc A_2ARs modify the animals' sensitivity to the value of the reward without affecting the action-outcome contingency. (iii) A_2AR antagonist KW6002 promotes instrumental actions by invigorating motivation. (iv) NAc A_2ARs facilitate Pavlovian incentive value transferring to instrumental action. (v) NAc A_2ARs control goal-directed behavior probably not through NAc-VP pathway. These insights into the behavioral and circuit mechanisms for NAc A_2AR control of goal-directed behavior facilitate translational potential for A_2AR antagonists in reversal of deficits in goal-directed decision-making associated with multiple neuropsychiatric disorders.

Cordycepin improves behavioral-LTP and dendritic structure in hippocampal CA1 area of rats

Cordycepin, an adenosine analog, has been reported to improve cognitive function, but which seems to be inconsistent with the reports showing that cordycepin inhibited long-term potentiation (LTP). Behavioral-LTP is usually used to study long-term synaptic plasticity induced by learning tasks in freely moving animals. In order to investigate simultaneously the effects of cordycepin on LTP and behavior in rats, we applied the model of behavioral-LTP induced by Y-maze learning task through recording population spikes in hippocampal CA1 region. Golgi staining and Sholl analysis were employed to assess the morphological structure of dendrites in pyramidal cells of hippocampal CA1 area, and western blotting was used to examine the level of adenosine A1 receptors and A2A receptors (A2AR). We found that cordycepin significantly improved behavioral-LTP magnitude, accompanied by increases in the total length of dendrites, the number of intersections and spine density but did not affect Y-maze learning task. Furthermore, cordycepin obviously reduced A2AR level without altering adenosine A1 receptors level; and the agonist of A2AR (CGS 21680) rather than antagonist (SCH 58261) could reverse the potentiation of behavioral-LTP induced by cordycepin. These results suggested that cordycepin improved behavioral-LTP and morphological structure of dendrite in hippocampal CA1 but did not contribute to the improvement of learning and memory. And cordycepin improved behavioral-LTP may be through reducing the level of A2AR in hippocampus. Collectively, the effects of cordycepin on cognitive function and LTP were complex and involved multiple mechanisms.

Accumbal Adenosine A2A Receptors Enhance Cognitive Flexibility by Facilitating Strategy Shifting

The deficits of cognitive flexibility (including attentional set-shifting and reversal learning) concomitant with dysfunction of the striatum are observed in several neuropsychiatric disorders. Rodent and human studies have identified the striatum [particularly the dorsomedial striatum (DMS) and nucleus accumbens (NAc)] as the critical locus for control of cognitive flexibility, but the effective neuromodulator and pharmacological control of cognitive flexibility remains to be determined. The adenosine A2A receptors (A2ARs) are highly enriched in the striatopallidal neurons where they integrate dopamine and glutamate signals to modulate several cognitive behaviors, but their contribution to cognitive flexibility control is unclear. In this study, by coupling an automated operant cognitive flexibility task with striatal subregional knockdown (KD) of the A2AR via the Cre-loxP strategy, we demonstrated that NAc A2AR KD improved cognitive flexibility with enhanced attentional set-shifting and reversal learning by decreasing regressive and perseverative errors, respectively. This facilitation was not attributed to mnemonic process or motor activity as NAc A2AR KD did not affect the visual discrimination, lever-pressing acquisition, and locomotor activity, but was associated with increased attention and motivation as evident by the progressive ratio test (PRT). In contrast to NAc A2ARs, DMS A2ARs KD neither affected visual discrimination nor improved set-shifting nor reversal learning, but promoted the effort-related motivation. Thus, NAc and DMS A2ARs exert dissociable controls of cognitive flexibility with NAc A2ARs KD selectively enhancing cognitive flexibility by facilitating strategy shifting with increased motivation/attention.

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.