Chronic caffeine alters the density of adenosine, adrenergic, cholinergic, GABA, and serotonin receptors and calcium channels in mouse brain

Using caffeine as a chemical means to induce flow states

Flow is an intrinsically rewarding state characterised by positive affect and total task absorption. Because cognitive and physical performance are optimal in flow, chemical means to facilitate this state are appealing. Caffeine, a non-selective adenosine receptor antagonist, has been emphasized as a potential flow-inducer. Thus, we review the psychological and biological effects of caffeine that, conceptually, enhance flow. Caffeine may facilitate flow through various effects, including: i) upregulation of dopamine D1/D2 receptor affinity in reward-associated brain areas, leading to greater energetic arousal and 'wanting'; ii) protection of dopaminergic neurons; iii) increases in norepinephrine release and alertness, which offset sleep-deprivation and hypoarousal; iv) heightening of parasympathetic high frequency heart rate variability, resulting in improved cortical stress appraisal, v) modification of striatal endocannabinoid-CB1 receptor-signalling, leading to enhanced stress tolerance; and vi) changes in brain network activity in favour of executive function and flow. We also discuss the application of caffeine to treat attention deficit hyperactivity disorder and caveats. We hope to inspire studies assessing the use of caffeine to induce flow.

Somatostatin and the pathophysiology of Alzheimer's disease

Among the central features of Alzheimer's disease (AD) progression are altered levels of the neuropeptide somatostatin (SST), and the colocalisation of SST-positive interneurons (SST-INs) with amyloid-β plaques, leading to cell death. In this theoretical review, I propose a molecular model for the pathogenesis of AD based on SST-IN hypofunction and hyperactivity. Namely, hypofunctional and hyperactive SST-INs struggle to control hyperactivity in medial regions in early stages, leading to axonal Aβ production through excessive presynaptic GABAB inhibition, GABAB1a/APP complex downregulation and internalisation. Concomitantly, excessive SST-14 release accumulates near SST-INs in the form of amyloids, which bind to Aβ to form toxic mixed oligomers. This leads to differential SST-IN death through excitotoxicity, further disinhibition, SST deficits, and increased Aβ release, fibrillation and plaque formation. Aβ plaques, hyperactive networks and SST-IN distributions thereby tightly overlap in the brain. Conversely, chronic stimulation of postsynaptic SST2/4 on gulutamatergic neurons by hyperactive SST-INs promotes intense Mitogen-Activated Protein Kinase (MAPK) p38 activity, leading to somatodendritic p-tau staining and apoptosis/neurodegeneration - in agreement with a near complete overlap between p38 and neurofibrillary tangles. This model is suitable to explain some of the principal risk factors and markers of AD progression, including mitochondrial dysfunction, APOE4 genotype, sex-dependent vulnerability, overactive glial cells, dystrophic neurites, synaptic/spine losses, inter alia. Finally, the model can also shed light on qualitative aspects of AD neuropsychology, especially within the domains of spatial and declarative (episodic, semantic) memory, under an overlying pattern of contextual indiscrimination, ensemble instability, interference and generalisation.

A Mechanistic Review on Therapeutic Potential of Medicinal Plants and their Pharmacologically Active Molecules for Targeting Metabolic Syndrome

Metabolic syndrome (MetS) therapy with phytochemicals is an emerging field of study with therapeutic potential. Obesity, insulin resistance, high blood pressure, and abnormal lipid profiles are all components of metabolic syndrome, which is a major public health concern across the world. New research highlights the promise of phytochemicals found in foods, including fruits, vegetables, herbs, and spices, as a sustainable and innovative method of treating this illness. Anti-inflammatory, antioxidant, and insulin-sensitizing qualities are just a few of the many positive impacts shown by bioactive substances. Collectively, they alleviate the hallmark symptoms of metabolic syndrome by modulating critical metabolic pathways, boosting insulin sensitivity, decreasing oxidative stress, and calming chronic low-grade inflammation. In addition, phytochemicals provide a multimodal strategy by targeting not only adipose tissue but also the liver, skeletal muscle, and vascular endothelium, all of which have a role in the pathogenesis of MetS. Increasing evidence suggests that these natural chemicals may be useful in controlling metabolic syndrome as a complementary treatment to standard medication or lifestyle changes. This review article emphasizes the therapeutic potential of phytochemicals, illuminating their varied modes of action and their ability to alleviate the interconnected causes of metabolic syndrome. Phytochemical-based interventions show promise as a novel and sustainable approach to combating the rising global burden of metabolic syndrome, with the ultimate goal of bettering public health and quality of life.

Current therapeutic targets and multifaceted physiological impacts of caffeine

Caffeine, which shares consubstantial structural similarity with purine adenosine, has been demonstrated as a nonselective adenosine receptor antagonist for eliciting most of the biological functions at physiologically relevant dosages. Accumulating evidence supports caffeine's beneficial effects against different disorders, such as total cardiovascular diseases and type 2 diabetes. Conversely, paradoxical effects are also linked to caffeine ingestion in humans including hypertension-hypotension and tachycardia-bradycardia. These observations suggest the association of caffeine action with its ingested concentration and/or concurrent interaction with preferential molecular targets to direct explicit events in the human body. Thus, a coherent analysis of the functional targets of caffeine, relevant to normal physiology, and disease pathophysiology, is required to understand the pharmacology of caffeine. This review provides a broad overview of the experimentally validated targets of caffeine, particularly those of therapeutic interest, and the impacts of caffeine on organ-specific physiology and pathophysiology. Overall, the available empirical and epidemiological evidence supports the dose-dependent functional activities of caffeine and advocates for further studies to get insights into the caffeine-induced changes under specific conditions, such as asthma, DNA repair, and cancer, in view of its therapeutic applications.

Adjusting the brakes to adjust neuronal activity: Adenosinergic modulation of GABAergic transmission

About 50 years elapsed from the publication of the first full paper on the neuromodulatory action of adenosine at a 'simple' synapse model, the neuromuscular junction (Ginsborg and Hirst, 1972). In that study adenosine was used as a tool to increase cyclic AMP and for the great surprise, it decreased rather than increased neurotransmitter release, and for a further surprise, its action was prevented by theophylline, at the time only known as inhibitor of phosphodiesterases. These intriguing observations opened the curiosity for immediate studies relating the action of adenine nucleotides, known to be released together with neurotransmitters, to that of adenosine (Ribeiro and Walker, 1973, 1975). Our understanding on the ways adenosine uses to modulate synapses, circuits, and brain activity, vastly expanded since then. However, except for A_2A receptors, whose actions upon GABAergic neurons of the striatum are well known, most of the attention given to the neuromodulatory action of adenosine has been focusing upon excitatory synapses. Evidence is growing that GABAergic transmission is also a target for adenosinergic neuromodulation through A₁ and A_2A receptors. Some o these actions have specific time windows during brain development, and others are selective for specific GABAergic neurons. Both tonic and phasic GABAergic transmission can be affected, and either neurons or astrocytes can be targeted. In some cases, those effects result from a concerted action with other neuromodulators. Implications of these actions in the control of neuronal function/dysfunction will be the focus of this review.

The effect of caffeine on subsequent sleep: A systematic review and meta-analysis

The consumption of caffeine in response to insufficient sleep may impair the onset and maintenance of subsequent sleep. This systematic review and meta-analysis investigated the effect of caffeine on the characteristics of night-time sleep, with the intent to identify the time after which caffeine should not be consumed prior to bedtime. A systematic search of the literature was undertaken with 24 studies included in the analysis. Caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with an increase in sleep onset latency of 9 min and wake after sleep onset of 12 min. Duration (+6.1 min) and proportion (+1.7%) of light sleep (N1) increased with caffeine intake and the duration (-11.4 min) and proportion (-1.4%) of deep sleep (N3 and N4) decreased with caffeine intake. To avoid reductions in total sleep time, coffee (107 mg per 250 mL) should be consumed at least 8.8 h prior to bedtime and a standard serve of pre-workout supplement (217.5 mg) should be consumed at least 13.2 h prior to bedtime. The results of the present study provide evidence-based guidance for the appropriate consumption of caffeine to mitigate the deleterious effects on sleep.

Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives

For hundreds of years, mankind has been influencing its sleep and waking state through the adenosinergic system. For ~100 years now, systematic research has been performed, first started by testing the effects of different dosages of caffeine on sleep and waking behaviour. About 70 years ago, adenosine itself entered the picture as a possible ligand of the receptors where caffeine hooks on as an antagonist to reduce sleepiness. Since the scientific demonstration that this is indeed the case, progress has been fast. Today, adenosine is widely accepted as an endogenous sleep‐regulatory substance. In this review, we discuss the current state of the science in model organisms and humans on the working mechanisms of adenosine and caffeine on sleep. We critically investigate the evidence for a direct involvement in sleep homeostatic mechanisms and whether the effects of caffeine on sleep differ between acute intake and chronic consumption. In addition, we review the more recent evidence that adenosine levels may also influence the functioning of the circadian clock and address the question of whether sleep homeostasis and the circadian clock may interact through adenosinergic signalling. In the final section, we discuss the perspectives of possible clinical applications of the accumulated knowledge over the last century that may improve sleep‐related disorders. We conclude our review by highlighting some open questions that need to be answered, to better understand how adenosine and caffeine exactly regulate and influence sleep.

Neuromotor activity inhibition in zebrafish early-life stages after exposure to environmental relevant concentrations of caffeine

Caffeine (CAF), a neuroactive compound, has been found in surface waters at concentrations ranging from few nanograms up to micrograms and may induce adverse effects in aquatic vertebrates. Thus, the aim of this study was to evaluate the potential of CAF in affecting fish early-life stages in a wide concentration range, including occurring levels in surface waters. Specimens of zebrafish in early-life stages were exposed to CAF for 168 h and survival, developmental alterations, locomotor activity and acetylcholinesterase activity were evaluated. CAF induced mortality in embryos unable to hatch or in larvae after hatching (LC₅₀ - 168 h = 283.2 mg/L). Tail deformities were observed in organisms exposed to concentrations ≥ 40 mg/L, while edemas were found at concentrations of 100 mg/L. CAF also decreased the total swimming time and distance moved of exposed organisms (LOEC = 0.0006 mg/L). Locomotor inhibition may be associated with an acetylcholinesterase inhibition observed at concentration ≥ 0.0088 mg/L. Therefore, the hazard of CAF for fish populations deserves further attention since unexpected effects on neuro-behavioral parameters occurs at concentrations often detected in natural aquatic ecosystems.

Experimental study of pre- and postnatal caffeine exposure and its observable effects on selected neurotransmitters and behavioural attributes at puberty : Caffeine exposure and its observable effects on selected neurotranmitters and behaviour

Caffeine is globally consumed as a stimulant in beverages. It is also ingested in purified forms as power and tablets. Concerns have been raised about the potential consequences of intrauterine and early life caffeine exposure on brain health. This study modeled caffeine exposure during pregnancy and early postanal life until puberty, and the potential consequences. Caffeine powder was dissolved in distilled water. Thirty-two (n = 32) pregnant mice (Mus musculus) (dams) were divided into four groups- A, B, C and D. Group A animals served as a control, receiving placebo. Caffeine doses in mg/kg body weight were administered as follows: Group B, 10 mg/kg; Group C, 50 mg/kg; Group D, 120 mg/kg. Prenatal caffeine exposure [phase I] lasted throughout pregnancy. Half the number of offspring (pups) were sacrificed at birth; the rest were recruited into phase II and the experiment continued till day 35, marking puberty. Brain samples were processed following sacrifice. γ-aminobutyric acid (GABA), acetylcholine (ACh), and serotonin (5Ht) neurotransmitters were assayed in homogenates to evaluate functional neurochemistry. Anxiety and memory as neurobehavioural attributes were observed using the elevated plus and Barnes' mazes respectively. Continuous caffeine exposure produced positive effects on short and long-term memory parameters; the pattern interestingly was irregular and appeared more effective with the lowest experimental dose. Anxiety test results showed no attributable significant aberrations. Caffeine exposure persistently altered the neurochemistry of selected neurotransmitters including ACh and 5Ht, including when exposure lasted only during pregnancy. ACh significantly increased in group B^C+ to 0.3475μgg-¹ relative to control's 0.2508μgg-¹; pre-and continuous postnatal exposure in Group B increased 5Ht to 0.2203 μgg-¹ and 0.2213 μgg-¹ respectively relative to control's 0.1863 μgg-¹. From the current investigation, caffeine exposure in pregnancy had persistent effects on brain functional attributes including neurotransmitters activities, memory and anxiety. Caffeine in moderate doses affected memory positively but produced negative effects at the higher dosage including increased anxiety tendencies.

The Neuroprotective Effects of Moderate and Regular Caffeine Consumption in Alzheimer's Disease

The increasing numbers of elderly Alzheimer's disease (AD) patients because of a steady increase in the average lifespan and aging society attract great scientific concerns, while there were fewer effective treatments on AD progression due to unclear exact causes and pathogenesis of AD. Moderate (200-500 mg/d) and regular caffeine consumption from coffee and tea are considered to alleviate the risk of AD and have therapeutic potential. This paper reviewed epidemiological studies about the relationship of caffeine intake from coffee or/and tea with the risk of AD and summarized the caffeine-related AD therapies based on experimental models. And further well-designed and well-conducted studies are suggested to investigate the optimal dosages, frequencies, and durations of caffeine consumption to slow down AD progression and treat AD.

The impact of daily caffeine intake on nighttime sleep in young adult men

Acute caffeine intake can delay sleep initiation and reduce sleep intensity, particularly when consumed in the evening. However, it is not clear whether these sleep disturbances disappear when caffeine is continuously consumed during daytime, which is common for most coffee drinkers. To address this question, we investigated the sleep of twenty male young habitual caffeine consumers during a double-blind, randomized, crossover study including three 10-day conditions: caffeine (3 × 150 mg caffeine daily), withdrawal (3 × 150 mg caffeine for 8 days, then switch to placebo), and placebo (3 × placebo daily). After 9 days of continuous treatment, electroencephalographically (EEG)-derived sleep structure and intensity were recorded during a scheduled 8-h nighttime sleep episode starting 8 (caffeine condition) and 15 h (withdrawal condition) after the last caffeine intake. Upon scheduled wake-up time, subjective sleep quality and caffeine withdrawal symptoms were assessed. Unexpectedly, neither polysomnography-derived total sleep time, sleep latency, sleep architecture nor subjective sleep quality differed among placebo, caffeine, and withdrawal conditions. Nevertheless, EEG power density in the sigma frequencies (12-16 Hz) during non-rapid eye movement sleep was reduced in both caffeine and withdrawal conditions when compared to placebo. These results indicate that daily caffeine intake in the morning and afternoon hours does not strongly impair nighttime sleep structure nor subjective sleep quality in healthy good sleepers who regularly consume caffeine. The reduced EEG power density in the sigma range might represent early signs of overnight withdrawal from the continuous presence of the stimulant during the day.

Relation between coffee consumption and risk of seizure-related respiratory dysfunction in patients with drug-resistant focal epilepsy

OBJECTIVE

Caffeine is an antagonist of the adenosine pathway, which is involved in regulation of breathing. Extracellular concentrations of adenosine are increased in the immediate aftermath of a seizure. Seizure-related overstimulation of adenosine receptors might promote peri-ictal apnea. However, the relation between caffeine consumption and risk of seizure-related respiratory dysfunction in patients with drug-resistant focal epilepsy remains unknown.

METHODS

We performed a cross-sectional analysis of data collected in patients included in the SAVE study in Lyon's epilepsy monitoring unit at the Adult Epilepsy Department of the Lyon University Hospital between February 2016 and October 2018. The video-electroencephalographic recordings of 156 patients with drug-resistant focal epilepsy included in the study were reviewed to identify those with ≥1 focal seizure (FS), valid pulse oximetry (SpO₂ ) measurement, and information about usual coffee consumption. This latter was collected at inclusion using a standardized self-questionnaire and further classified into four groups: none, rare (≤3 cups/week), moderate (4 cups/week to 3 cups/day), and high (≥4 cups/day). Peri-ictal hypoxemia (PIH) was defined as SpO₂ < 90% for at least 5 s occurring during the ictal period, the post-ictal period, or both.

RESULTS

Ninety patients fulfilled inclusion criteria, and 323 seizures were analyzed. Both the level of usual coffee consumption (p = .033) and the level of antiepileptic drug withdrawal (p = .004) were independent risk factors for occurrence of PIH. In comparison with FS in patients with no coffee consumption, risk of PIH was four times lower in FS in patients with moderate consumption (odds ratio [OR] = .25, 95% confidence interval [CI] = .07-.91, p = .036) and six times lower in FS in patients with high coffee consumption (OR = .16, 95% CI = .04-.66, p = .011). However, when PIH occurred, its duration was longer in patients with moderate or high consumption than in those with no coffee consumption (p = .042).

SIGNIFICANCE

Coffee consumption may be a protective factor for seizure-related respiratory dysfunction, with a dose-dependent effect.

Exploring the Association between Urine Caffeine Metabolites and Urine Flow Rate: A Cross-Sectional Study

Examination of urine excretion of caffeine metabolites has been a simple but common way to determine the metabolism and effect of caffeine, but the relationship between urinary metabolites and urine flow rate is less discussed. To explore the association between urinary caffeine metabolite levels and urine flow rate, 1571 participants from the National Health and Nutrition Examination Survey (NHANES) 2011-2012 were enrolled in this study. We examined the association between urinary caffeine metabolites and urine flow rate with linear regression models. Separate models were constructed for males and females and for participants aged <60 and ≥60 years old. A positive association was found between concentrations of several urinary caffeine metabolites and urine flow rate. Three main metabolites, namely, paraxanthine, theobromine, and caffeine, showed significance across all subgroups. The number of caffeine metabolites that revealed flow-dependency was greater in males than in females and was also greater in the young than in the elderly. Nevertheless, the general weakness of NHANES data, a cross-sectional study, is that the collection is made at one single time point rather than a long-term study. In summary, urinary concentrations of several caffeine metabolites showed a positive relationship with the urine flow rate. The trend is more noticeable in males and in young subgroups.

Caffeine: An Overview of Its Beneficial Effects in Experimental Models and Clinical Trials of Parkinson's Disease

Parkinson’s Disease (PD) is a neurological disease characterized by the progressive degeneration of the nigrostriatal dopaminergic pathway with consequent loss of neurons in the substantia nigra pars compacta and dopamine depletion. The cytoplasmic inclusions of α-synuclein (α-Syn), known as Lewy bodies, are the cytologic hallmark of PD. The presence of α-Syn aggregates causes mitochondrial degeneration, responsible for the increase in oxidative stress and consequent neurodegeneration. PD is a progressive disease that shows a complicated pathogenesis. The current therapies are used to alleviate the symptoms of the disease without changing its clinical course. Recently, phytocompounds with neuroprotective effects and antioxidant properties such as caffeine have aroused the interest of researchers. The purpose of this review is to summarize the preclinical studies present in the literature and clinical trials recorded in ClinicalTrial.gov, aimed at illustrating the effects of caffeine used as a nutraceutical compound combined with the current PD therapies. Therefore, the preventive effects of caffeine in the neurodegeneration of dopaminergic neurons encourage the use of this alkaloid as a supplement to reduce the progress of the PD.

Caffeine-dependent changes of sleep-wake regulation: Evidence for adaptation after repeated intake

BACKGROUND

Circadian and sleep-homeostatic mechanisms regulate timing and quality of wakefulness. To enhance wakefulness, daily consumption of caffeine in the morning and afternoon is highly common. However, the effects of such a regular intake pattern on circadian sleep-wake regulation are unknown. Thus, we investigated if daily daytime caffeine intake and caffeine withdrawal affect circadian rhythms and wake-promotion in habitual consumers.

METHODS

Twenty male young volunteers participated in a randomised, double-blind, within-subject study with three conditions: i) caffeine (150 mg 3 x daily for 10 days), ii) placebo (3 x daily for 10 days) and iii) withdrawal (150 mg caffeine 3 x daily for eight days, followed by a switch to placebo for two days). Starting on day nine of treatment, salivary melatonin and cortisol, evening nap sleep as well as sleepiness and vigilance performance throughout day and night were quantified during 43 h in an in-laboratory, light and posture-controlled protocol.

RESULTS

Neither the time course of melatonin (i.e. onset, amplitude or area under the curve) nor the time course of cortisol was significantly affected by caffeine or withdrawal. During withdrawal, however, volunteers reported increased sleepiness, showed more attentional lapses as well as polysomnography-derived markers of elevated sleep propensity in the late evening compared to both the placebo and caffeine condition.

CONCLUSIONS

The typical pattern of caffeine intake with consumption in both the morning and afternoon hours may not necessarily result in a circadian phase shift in the evening nor lead to clear-cut benefits in alertness. The time-of-day independent effects of caffeine withdrawal on evening nap sleep, sleepiness and performance suggest an adaptation to the substance, presumably in the homeostatic aspect of sleep-wake regulation.

What Should We Do About Habitual Caffeine Use in Athletes?

Caffeine is a well-established ergogenic aid, demonstrated to enhance performance across a wide range of capacities through a variety of mechanisms. As such, it is frequently used by both athletes and non-athletes alike. As a result, caffeine ingestion is ubiquitous in modern society, with athletes typically being exposed to regular non-supplemental caffeine through a variety of sources. Previously, it has been suggested that regular caffeine use may lead to habituation and subsequently a reduction in the expected ergogenic effects, thereby blunting caffeine’s performance-enhancing impact during critical training and performance events. In order to mitigate this expected performance loss, some practitioners recommended a pre-competition withdrawal period to restore the optimal performance benefits of caffeine supplementation. However, at present the evidence base exploring both caffeine habituation and withdrawal strategies in athletes is surprisingly small. Accordingly, despite the prevalence of caffeine use within athletic populations, formulating evidence-led guidelines is difficult. Here, we review the available research regarding habitual caffeine use in athletes and seek to derive rational interpretations of what is currently known—and what else we need to know—regarding habitual caffeine use in athletes, and how athletes and performance staff may pragmatically approach these important, complex, and yet under-explored phenomena.

Caffeine prevents neurodegeneration and behavioral alterations in a mice model of agitated depression

Longitudinal and some experimental studies have showed the potential of caffeine to counteract some depressive behaviors and synaptic dysfunctions. In this study, we investigated the potential of caffeine in preventing behavioral outcomes, neurodegeneration and synaptic proteins alterations in a mice model of agitated depression by bilateral olfactory bulbectomy (OB). For this purpose, bulbectomized mice received caffeine (0.3 g/L and 1.0 g/L, drinking water), during the active cycle, for seven weeks (two before the surgery and throughout five weeks after OB). Caffeine prevented OB-induced hyperactivity and recognition memory impairment and rescue self care and motivational behavior. In the frontal cortex, bulbectomized mice presented increase in the adenosine A₁ receptors (A₁R) and GFAP, while adenosine A_2A receptors (A_2AR) increased in the hippocampus and striatum and SNAP-25 was decreased in frontal cortex and striatum. Caffeine increased A₁R in the striatum of bulbectomized mice and in SHAM-water group caffeine increased A_2AR in the striatum and decreased SNAP-25 in the frontal cortex. Astrogliosis observed in the polymorphic layer of the dentate gyrus of OB mice was prevented by caffeine as well as the neurodegeneration in the striatum and piriform cortex. Based on these behavioral and neurochemical evidences, caffeine confirms its efficacy in preventing neurodegeneration associated with memory impairment and may be considered as a promising therapeutic tool in the prophylaxis and/or treatment of depression.

Effects of Preinjury and Postinjury Exposure to Caffeine in a Rat Model of Traumatic Brain Injury

Background: Lethal apnea is a significant cause of acute mortality following a severe traumatic brain injury (TBI). TBI is associated with a surge of adenosine, which also suppresses respiratory function in the brainstem. Methods and Materials: This study examined the acute and chronic effects of caffeine, an adenosine receptor antagonist, on acute mortality and morbidity after fluid percussion injury. Results: We demonstrate that, regardless of preinjury caffeine exposure, an acute bolus of caffeine given immediately following the injury dosedependently prevented lethal apnea and has no detrimental effects on motor performance following sublethal injuries. Finally, we demonstrate that chronic caffeine treatment after injury, but not caffeine withdrawal, impairs recovery of motor function. Conclusions: Preexposure of the injured brain to caffeine does not have a major impact on acute and delayed outcome parameters; more importantly, a single acute dose of caffeine after the injury can prevent lethal apnea regardless of chronic caffeine preexposure.

Safety of Short-Term Supplementation with Methylliberine (Dynamine®) Alone and in Combination with TeaCrine® in Young Adults

Methylliberine (Dynamine^®; DYM) and theacrine (Teacrine^®; TCR) are purine alkaloids purported to have similar neuro-energetic effects as caffeine. There are no published human safety data on DYM, and research on TCR is limited. The purpose of this study was to examine the effect of four weeks of DYM supplementation with and without TCR on cardiovascular function and blood biomarkers. One-hundred twenty-five men and women (mean age 23.0 yrs, height 169.7 cm, body mass 72.1 kg; n = 25/group) were randomly assigned to one of five groups: low-dose DYM (100 mg), high-dose DYM (150 mg), low-dose DYM with TCR (100 mg + 50 mg), high-dose DYM with TCR (150 mg + 25 mg) , and placebo. Regardless of group and sex, significant main effects for time were noted for heart rate, systolic blood pressure, and QTc (p < 0.001), high-density lipoproteins (p = 0.002), mean corpuscular hemoglobin (p = 0.018), basophils (p = 0.006), absolute eosinophils (p = 0.010), creatinine (p = 0.004), estimated glomerular filtration rate (p = 0.037), chloride (p = 0.030), carbon dioxide (p = 0.023), bilirubin (p = 0.027), and alanine aminotransferase (p = 0.043), among others. While small changes were found in some cardiovascular and blood biomarkers, no clinically significant changes occurred. This suggests that DYM alone or in combination with TCR consumed at the dosages used in this study does not appear to negatively affect markers of health over four weeks of continuous use.

Influence of continued ingestion of matcha on emotional behaviors after social stress in mice

Matcha has high contents of theanine, caffeine, and epigallocatechin gallate (EGCG). Among these, theanine reduces psychological and physiological stress responses, although this effect is disturbed by caffeine and EGCG. It was reported that the continued ingestion of high-quality matcha, whose molar ratio of caffeine and EGCG to theanine and arginine was kept at less than two, reduces stress responses. However, most matcha on the market has an inadequate ratio. Therefore, we investigated the influence of continued ingestion of matcha with a ratio of over two, on emotional behaviors after stress. Continued ingestion of matcha was suggested to reduce the anxiety-like behaviors induced by psychological and physiological stresses.

Sequential Changes in Brain Glutamate and Adenosine A1 Receptors May Explain Severity of Adolescent Alcohol Withdrawal after Consumption of High Levels of Alcohol

There is an excellent correlation between the age when alcohol consumption begins and the likelihood of lifelong problems with alcohol abuse. Alcohol use often begins in adolescence, a time marked by brain development and maturation of numerous brain systems. Rats are an important model, wherein the emergence of alcohol withdrawal symptoms serves as a gauge of dependency following chronic alcohol consumption. Previous work has shown that adolescent Long-Evans rats consume high levels of alcohol and develop a severe alcohol withdrawal syndrome when fed alcohol as part of a liquid diet. Acutely, alcohol inhibits two important excitatory receptors for glutamate (NMDA and AMPA) and may further decrease glutamate activity through modulatory adenosine receptors. The present study focuses on potential adaptive changes in expression of these receptors that may create a receptor imbalance during chronic alcohol consumption and lead to severe overexcitation of the adolescent brain during alcohol withdrawal. Levels of brain expression of NMDA, AMPA, and adenosine A1 and A2a receptors were determined by Western blotting after adolescent rats consumed an alcohol-containing liquid diet for 4, 11, or 18 days. Severity of alcohol withdrawal was also assessed at these time points. Levels increased for both AMPA and NMDA receptors, significant and approaching maximal by day 11. In contrast, A1 receptor density showed a slow decline reaching significance at 18 days. There were no changes in expression of adenosine A2a receptor. The most severe withdrawal symptoms appear to coincide with the later downregulation of adenosine A1 receptors coming on top of maximal upregulation of excitatory AMPA and NMDA glutamate receptors. Thus, loss of adenosine "brakes" on glutamate excitation may punctuate receptor imbalance in alcohol-consuming adolescents by allowing the upregulation of the excitatory receptors to have full impact during early alcohol withdrawal.

The clinical toxicology of caffeine: A review and case study

Caffeine is a widely recognized psychostimulant compound with a long history of consumption by humans. While it has received a significant amount of attention there is still much to be learned with respect to its toxicology in humans, especially in cases of overdose. A review of the history of consumption and the clinical toxicology of caffeine including clinical features, pharmacokinetics, toxicokinetics, a thorough examination of mechanism of action and management/treatment strategies are undertaken. While higher (i.e., several grams) quantities of caffeine are known to cause toxicity and potentially lethality, cases of mainly younger individuals who have experienced severe side effects and death despite consuming doses not otherwise known to cause such harm is troubling and deserves further study. An attempted case reconstruction is performed in an effort to shed light on this issue with a focus on the pharmacokinetics and pharmacodynamics of caffeine.

Receptor Regulation in Taste: Can Diet Influence How We Perceive Foods?

Taste buds are the dedicated sensory end organs of taste, comprising a complex and evolving profile of signaling elements. The sensation and ultimate perception of taste depends on the expression of a diverse array of receptors and channels that sense their respective tastes. Receptor regulation is a recognized and well-studied phenomenon in many systems, observed in opioid addiction, insulin resistance and caffeine tolerance. Results from human sensory studies suggest that receptor sensitivity or expression level may decrease after chronic exposure to respective tastants through diet. We review data supporting the theory that taste receptors may become downregulated with exposure to a specific tastant, along with presenting data from a small pilot study, showing the impact of long-term tastant exposure on taste receptor expression in mice. Mice treated with monosodium salt monohydrate (MSG), saccharin and NaCl (typically appetitive tastes) all displayed a significant decrease in mRNA expression for respective umami, sweet and salty receptors/sensory channels. Reduced sensitivity to appetitive tastes may promote overconsumption of foods high in such stimuli.

J-difference-edited MRS measures of γ-aminobutyric acid before and after acute caffeine administration

PURPOSE

The aim of this study was to investigate potential effects of acute caffeine intake on J-difference-edited MRS measures of the primary inhibitory neurotransmitter γ-aminobutyric acid (GABA).

METHODS

J-difference-edited Mescher-Garwood PRESS (MEGA-PRESS) and conventional PRESS data were acquired at 3T from voxels in the anterior cingulate and occipital area of the brain in 15 healthy subjects, before and after oral intake of a 200-mg caffeine dose. MEGA-PRESS data were analyzed with the MATLAB-based Gannet tool to estimate GABA+ macromolecule (GABA+) levels, while PRESS data were analyzed with LCModel to estimate levels of glutamate, glutamate+glutamine, N-acetylaspartate, and myo-inositol. All metabolites were quantified with respect to the internal reference compounds creatine and tissue water, and compared between the pre- and post-caffeine intake condition.

RESULTS

For both MRS voxels, mean GABA+ estimates did not differ before and after caffeine intake. Slightly lower estimates of myo-inositol were observed after caffeine intake in both voxels. N-acetylaspartate, glutamate, and glutamate+glutamine did not show significant differences between conditions.

CONCLUSION

Mean GABA+ estimates from J-difference-edited MRS in two different brain regions are not altered by acute oral administration of caffeine. These findings may increase subject recruitment efficiency for MRS studies.

Sucrose or sucrose and caffeine differentially impact memory and anxiety-like behaviours, and alter hippocampal parvalbumin and doublecortin

Caffeinated sugar-sweetened "energy" drinks are a subset of soft drinks that are popular among young people worldwide. High sucrose diets impair cognition and alter aspects of emotional behaviour in rats, however, little is known about sucrose combined with caffeine. Rats were allocated to 2 h/day 10% sucrose (Suc), 10% sucrose plus 0.04% caffeine (CafSuc) or control (water) conditions. The addition of caffeine to sucrose appeared to increase the rewarding aspect of sucrose, as the CafSuc group consumed more solution than the Suc group. After 14 days of intermittent Suc or CafSuc access, anxiety was assessed in the elevated plus maze (EPM) prior to their daily solution access, whereby CafSuc and Suc rats spent more time in the closed arms, indicative of increased anxiety. Following daily solution access, CafSuc, but not Suc, rats showed reduced anxiety-like behaviour in the open-field. Control and CafSuc rats displayed intact place and long-term object memory, while Suc showed impaired memory performance. Sucrose reduced parvalbumin immunoreactivity in the hippocampus, but no differences were observed between Control and CafSuc conditions. Parvalbumin reactivity in the basolateral amygdala did not differ between conditions. Reduced doublecortin immunoreactivity in the dentate gyrus relative to controls was seen in the CafSuc, but not Suc, treatment conditions. These findings indicate that the addition of caffeine to sucrose attenuated cognitive deficits. However, the addition of caffeine to sucrose evoked anxiety-like responses under certain testing conditions, suggesting that frequent consumption of caffeinated energy drinks may promote emotional alterations and brain changes compared to standard soft drinks.

Two combined amino acids promote sleep activity in caffeine-induced sleepless model systems

BACKGROUND/OBJECTIVES

The aim of this study was to evaluate the biological and sleep-promoting effects of combined γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP) using caffeine-induced sleepless fruit flies, ICR mice, and Sprague-Dawley rats.

MATERIALS/METHODS

Video-tracking analysis was applied to investigate behavioral changes of Drosophila melanogaster. Pentobarbital-induced sleep test and electroencephalogram (EEG) patterns were used for analysis of sleep latency, duration, and quantity and quality of sleep in vertebrate models.

RESULTS

Administration of combined GABA/5-HTP could significantly reverse the caffeine induced total distance of flies (P < 0.001). Also, individually administered and combined GABA/5-HTP significantly increased the total sleeping time in the caffeine-induced sleepless ICR mice (P < 0.001). In the caffeine-induced sleepless SD-rats, combined GABA/5-HTP showed significant differences in sleep quality between individual amino acid administrations (P < 0.05).

CONCLUSIONS

Taken together, we identified inhibitory effects of combined GABA/5-HTP in locomotor activity, sleep quantity and quality in caffeine-induced sleepless models, indicating that combined GABA/5-HTP may be effective in patients with insomnia by providing sufficient sleep.

Coffee extract and caffeine enhance the heat shock response and promote proteostasis in an HSF-1-dependent manner in Caenorhabditis elegans

As the population ages, there is a critical need to uncover strategies to combat diseases of aging. Studies in the soil-dwelling nematode Caenorhabditis elegans have demonstrated the protective effects of coffee extract and caffeine in promoting the induction of conserved longevity pathways including the insulin-like signaling pathway and the oxidative stress response. We were interested in determining the effects of coffee and caffeine treatment on the regulation of the heat shock response. The heat shock response is a highly conserved cellular response that functions as a cytoprotective mechanism during stress, mediated by the heat shock transcription factor HSF-1. In the worm, HSF-1 not only promotes protection against stress but is also essential for development and longevity. Induction of the heat shock response has been suggested to be beneficial for diseases of protein conformation by preventing protein misfolding and aggregation, and as such has been proposed as a therapeutic target for age-associated neurodegenerative disorders. In this study, we demonstrate that coffee is a potent, dose-dependent, inducer of the heat shock response. Treatment with a moderate dose of pure caffeine was also able to induce the heat shock response, indicating caffeine as an important component within coffee for producing this response. The effects that we observe with both coffee and pure caffeine on the heat shock response are both dependent on HSF-1. In a C. elegans Huntington's disease model, worms treated with caffeine were protected from polyglutamine aggregates and toxicity, an effect that was also HSF-1-dependent. In conclusion, these results demonstrate caffeinated coffee, and pure caffeine, as protective substances that promote proteostasis through induction of the heat shock response.

The neuroprotective effects of caffeine in neurodegenerative diseases

Caffeine is the most widely used psychostimulant in Western countries, with antioxidant, anti-inflammatory and anti-apoptotic properties. In Alzheimer's disease (AD), caffeine is beneficial in both men and women, in humans and animals. Similar effects of caffeine were observed in men with Parkinson's disease (PD); however, the effect of caffeine in female PD patients is controversial due to caffeine's competition with estrogen for the estrogen-metabolizing enzyme, CYP1A2. Studies conducted in animal models of amyotrophic lateral sclerosis (ALS) showed protective effects of A_2A R antagonism. A study found caffeine to be associated with earlier age of onset of Huntington's disease (HD) at intakes >190 mg/d, but studies in animal models have found equivocal results. Caffeine is protective in AD and PD at dosages equivalent to 3-5 mg/kg. However, further research is needed to investigate the effects of caffeine on PD in women. As well, the effects of caffeine in ALS, HD and Machado-Joseph disease need to be further investigated. Caffeine's most salient mechanisms of action relevant to neurodegenerative diseases need to be further explored.

Caffeine and Cannabis Effects on Vital Neurotransmitters and Enzymes in the Brain Tissue of Juvenile Experimental Rats

BACKGROUND

Caffeine and cannabis are globally consumed and abused psychoactive substances. While caffeine is legally used in various forms, including in tea and coffee as beverages, it is also consumed in soda and energy drinks as additives. Cannabis, on the other hand, is considered illegal in most countries; albeit, it is being consumed globally particularly by adolescents.

PURPOSE

The adolescent stage marks a critical stage of brain development and maturation. Influences of agents on the brain at this stage may affect neuronal structural and functional attributes. To this end, the current experiment considered the effects of cannabis and caffeine on selected key neurotransmitters and enzymes in the brain tissues after regimented caffeine and cannabis treatment for 21 days.

METHODS

A total of 72 juvenile Wistar rats that were approximately 40 days old were divided into 6 groups A-F. The group A served as the control. Other groups were administered various dosages of caffeine or cannabis in distilled water, using oral gavages as follows: group B animals received 100 mg/kg body weight of caffeine, group C animals received 50 mg/kg body weight of caffeine, group D animals received 500 mg/kg body weight of cannabis, group E animals received 200 mg/kg body weight of cannabis, and group F received a low dose of cannabis (200 mg/kg body weight) plus a low dose of caffeine (50 mg/kg body weight). The animals were killed by cervical dislocation 24 h after the last administration. The brain tissues were excised and homogenized. The enzymes cytochrome C oxidase and glucose-6-phosphate dehydrogenase were assayed to observe tissue energy metabolism while the neurotransmitters gamma-amino butyric acid (GABA), glutamate, and dopamine were assayed to observe the effects of the psychoactive substances on their activities relative to mental activities.

RESULTS

GABA, glutamate, and dopamine were generally higher in the treated groups of animals. The levels of G-6-PDH were higher in all treated animals' brains. Caffeine produced quite more significant effects relative to cannabis and the combination of both increased the level of G-6-PDH significantly.

CONCLUSION

Results showed that caffeine and cannabis influenced the activities of the enzymes and neurotransmitters in the brain. Both stimulants altered brain chemistry relative to the tested enzymes and neurotransmitters.

Safety issues of compounds acting on adenosinergic signalling

OBJECTIVES

Much research has been performed on the field of identifying the roles of adenosine and adenosinergic signalling, but a relatively low number of marketing authorizations have been granted for adenosine receptor (AdR) ligands. In part, this could be related to their safety issues; therefore, our aim was to examine the toxicological and adverse effects data of different compounds acting on adenosinergic signalling, including different AdR ligands and compounds resembling the structure of adenosine. We also wanted to present recent pharmaceutical developments of experimental compounds that showed promising results in clinical trial setting.

KEY FINDINGS

Safety issues of compounds modulating adenosinergic signalling were investigated, and different mechanisms were presented. Structurally different classes of compounds act on AdRs, the most important being adenosine, adenosine derivatives and other non-nucleoside compounds. Many of them are either not selective enough or are targeting other targets of adenosinergic signalling such as metabolizing enzymes that regulate adenosine levels. Many other targets are also involved that are not part of adenosinergic signalling system such as GABA receptors, different channels, enzymes and others. Some synthetic AdR ligands even showed to be genotoxic.

SUMMARY

Current review presents safety data of adenosine, adenosine derivatives and other non-nucleoside compounds that modulate adenosinergic signalling. We have presented different mechanisms that participate to an adverse effect or toxic outcome. A separate section also deals with possible organ-specific toxic effects on different in-vitro and in-vivo models.

Behavioral profile assessment in offspring of Swiss mice treated during pregnancy and lactation with caffeine

The association between caffeine consumption and various psychiatric manifestations has long been observed. The objective was to assess the behavioral profile in offspring of Swiss mice treated during pregnancy and lactation with caffeine. For this purpose, two groups (n = 6 each and BW ~ 35 g) of female mice were treated during pregnancy and lactation by: tap water and caffeine solution at a concentration of 0.3 mg/mL through oral route. The offspring obtained, by completing 70 days of life, was underwent a behavioral battery test. Statistical analysis was performed by student t test and the different significance adopted was p < 0.05. According to our results, it was not found any significant differences in tail suspension and forced swimming tests. In anxiety related responses however, the mice of caffeine group had greater number of fecal pellets (178 %, p = 0.001) in the open field test, higher number of attempts (51 %, p = 0.03) in light-dark box and decreased percentage of entries in open arms (41 %, p = 0.01) in elevated plus maze test. Moreover, in the marble burying test, there was a significant decrease in the number of buried marbles compared with controls (110 %, p = 0,002). In the meantime, in the von Frey test, it was observed an exacerbation of mechanical allodynia both in basal conditions and after the carrageenan administration (p < 0.001). Furthermore, caffeine treatment during pregnancy and lactation causes long-term behavioral changes in the mice offspring that manifest later in life.

Modulatory effects of caffeine on oxidative stress and anxiety-like behavior in ovariectomized rats

Menopause is accompanied by enhanced oxidative stress and behavioral changes, effects attenuated by antioxidants. The aim of this study was to evaluate the effects of caffeine on behavior and oxidative stress in an experimental model of menopause. Female rats were divided into the following groups: sham-operated (CON), sham-operated and caffeine-treated (CAF), ovariectomized (OVX), ovariectomized and caffeine-treated (OVX+CAF). Caffeine (6 mg/kg) and vehicle were administered for 21 days (subchronic) and 42 days (chronic), using 2 experimental subsets. Behavioral tests and oxidative stress parameters in the blood, whole brain, and hippocampus were assessed. The subchronic administration of caffeine decreased the lipid peroxidation and improved the antioxidant defense in the blood and brain. The GSH/GGSG ratio in the brain was improved by chronic administration, with reduced activities of antioxidant enzymes and enhanced nitric oxide and malondialdehyde levels. In particular, the lipid peroxidation in the hippocampus decreased in both experiments. The rats became hyperactive after 21 days of treatment, but no effect was observed after chronic administration. In both experimental subsets, caffeine had anxiolytic effects as tested in elevated plus maze. The administration of low doses of caffeine, for a short period of time, may be a new therapeutic approach to modulating the oxidative stress and anxiety in menopause.

Acute effects of energy drinks in medical students

PURPOSE

To determine the acute effects of a variety of recognized energy drinks on medical students, based on the hypothesis that these beverages may affect negatively cardiovascular parameters, stress levels and working memory.

METHODS

Eighty young healthy medical students were included in the study. 62.5 % of the participants were male, and the age mean was 21.45 years. Each person was evaluated via measurement of systolic and diastolic blood pressure, electrocardiogram (ECG), heart rate, oxygen saturation, breath rate, temperature, STAI score (to assess anxiety state), salivary cortisol and N-back task score (to determine cognitive enhancement). These evaluations were performed before and following the intake of either carbonated water or one of three energy drinks containing caffeine in similar concentrations and an undetermined energy blend; A contained less sugar and no taurine.

RESULTS

Thirty-minute SBP increased significantly in the A and C groups. The B group exhibited a diminution of the percentage of the 1-h SBP increase, an increase of 1-h DBP and QTc shortening. HR showed an increase in the percent change in the A and C groups. Cortisol salivary levels increased in the B group. The STAI test score decreased in the C group. The percent change in N-back scores increased in the A group.

CONCLUSIONS

The data reinforce the need for further research on the acute and chronic effects of energy drinks to determine the actual risks and benefits. Consumers need to be more informed about the safety of these energy drinks, especially the young student population.

Caffeine exposure alters adenosine system and neurochemical markers during retinal development

Evidence points to beneficial properties of caffeine in the adult central nervous system, but teratogenic effects have also been reported. Caffeine exerts most of its effects by antagonizing adenosine receptors, especially A1 and A2A subtypes. In this study, we evaluated the role of caffeine on the expression of components of the adenosinergic system in the developing avian retina and the impact of caffeine exposure upon specific markers for classical neurotransmitter systems. Caffeine exposure (5-30 mg/kg by in ovo injection) to 14-day-old chick embryos increased the expression of A1 receptors and concomitantly decreased A2A adenosine receptors expression after 48 h. Accordingly, caffeine (30 mg/kg) increased [(3) H]-8-cyclopentyl-1,3-dipropylxanthine (A1 antagonist) binding and reduced [(3) H]-ZM241385 (A2A antagonist) binding. The caffeine time-response curve demonstrated a reduction in A1 receptors 6 h after injection, but an increase after 18 and 24 h. In contrast, caffeine exposure increased the expression of A2A receptors from 18 and 24 h. Kinetic assays of [(3) H]-S-(4-nitrobenzyl)-6-thioinosine binding to the equilibrative adenosine transporter ENT1 revealed an increase in Bmax with no changes in Kd , an effect accompanied by an increase in adenosine uptake. Immunohistochemical analysis showed a decrease in retinal content of tyrosine hydroxylase, calbindin and choline acetyltransferase, but not Brn3a, after 48 h of caffeine injection. Furthermore, retinas exposed to caffeine had increased levels of phosphorylated extracellular signal-regulated kinase and cAMP-response element binding protein. Overall, we show an in vivo regulation of the adenosine system, extracellular signal-regulated kinase and cAMP-response element binding protein function and protein expression of specific neurotransmitter systems by caffeine in the developing retina. The beneficial or maleficent effects of caffeine have been demonstrated by the work of different studies. It is known that during animal development, caffeine can exert harmful effects, impairing the correct formation of CNS structures. In this study, we demonstrated cellular and tissue effects of caffeine's administration on developing chick embryo retinas. Those effects include modulation of adenosine receptors (A1 , A2 ) content, increasing in cAMP response element-binding protein (pCREB) and extracellular signal-regulated kinase phosphorylation (pERK), augment of adenosine equilibrative transporter content/activity, and a reduction of some specific cell subpopulations. ENT1, Equilibrative nucleoside transporter 1.

Sleep-promoting effects of a GABA/5-HTP mixture: Behavioral changes and neuromodulation in an invertebrate model

AIMS

This study was to investigate the sleep promoting effects of combined γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP), by examining neuronal processes governing mRNA level alterations, as well as assessing neuromodulator concentrations, in a fruit fly model.

MAIN METHODS

Behavioral assays were applied to investigate subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep of two amino acids and GABA/5-HTP mixture with caffeine treated flies. Also, real-time PCR and HPLC analysis were applied to analyze the signaling pathway.

KEY FINDINGS

Subjective nighttime activity and sleep patterns of individual flies significantly decreased with 1% GABA treatment in conjunction with 0.1% 5-HTP treatment (p<0.001). Furthermore, GABA/5-HTP mixture resulted in significant differences between groups related to sleep patterns (40%, p<0.017) and significantly induced subjective nighttime sleep in the awake model (p<0.003). These results related to transcript levels of the GABAB receptor (GABAB-R1) and serotonin receptor (5-HT1A), compared to the control group. In addition, GABA/5-HTP mixture significantly increased GABA levels 1h and 12h following treatment (2.1 fold and 1.2 fold higher than the control, respectively) and also increased 5-HTP levels (0 h: 1.01 μg/protein, 12h: 3.45 μg/protein).

SIGNIFICANCE

In this regard, we successfully demonstrated that using a GABA/5-HTP mixture modulates subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep to a greater extent than single administration of each amino acid, and that this modulation occurs via GABAergic and serotonergic signaling.

Caffeine: Friend or Foe?

The debate on the safety of and regulatory approaches for caffeine continues among various stakeholders and regulatory authorities. This decision-making process comes with significant challenges, particularly when considering the complexities of the available scientific data, making the formulation of clear science-based regulatory guidance more difficult. To allow for discussions of a number of key issues, the North American Branch of the International Life Sciences Institute (ILSI) convened a panel of subject matter experts for a caffeine-focused session entitled "Caffeine: Friend or Foe?," which was held during the 2015 ILSI Annual Meeting. The panelists' expertise covered topics ranging from the natural occurrence of caffeine in plants and interindividual metabolism of caffeine in humans to specific behavioral, reproductive, and cardiovascular effects related to caffeine consumption. Each presentation highlighted the potential risks, benefits, and challenges that inform whether caffeine exposure warrants concern. This paper aims to summarize the key topics discussed during the session.

Effects of caffeine on locomotor activity in streptozotocin-induced diabetic rats

Diabetes mellitus modifies the expression of adenosine receptors in the brain. Caffeine acts as an antagonist of A1 and A2A adenosine receptors and was shown to have a dose-dependent biphasic effect on locomotion in mice. The present study investigated the link between diabetes and locomotor activity in an animal model of streptozotocin-induced diabetes, and the effects of a low-medium dose of caffeine in this relation. The locomotor activity was investigated by using Open Field Test at 6 weeks after diabetes induction and after 2 more weeks of chronic caffeine administration. Diabetes decreased locomotor activity (total distance moved and mobility time). Chronic caffeine exposure impaired the locomotor activity in control rats, but not in diabetic rats. Our data suggested that the medium doses of caffeine might block the A2A receptors, shown to have an increased density in the brain of diabetic rats, and improve or at least maintain the locomotor activity, offering a neuroprotective support in diabetic rats. Abbreviations: STZ = streptozotocin, OFT = Open Field Test.

Inhibitory respiratory responses to progesterone and allopregnanolone in newborn rats chronically treated with caffeine

KEY POINTS

In premature newborns, recurrent apnoea is systematically treated with caffeine to prevent long-term neurocognitive disorders, but a substantial percentage of apnoea persists particularly in neonates born before 28 weeks of gestation. Progesterone has been proposed as a respiratory stimulant potentially suitable for the treatment of newborn apnoea persistent to caffeine. Accordingly we asked whether acute progesterone administration reduces apnoea frequency in newborn rats treated with caffeine. Surprisingly our results show that in newborn rats treated with caffeine, administration of progesterone inhibits breathing and increases apnoea frequency. Additional experiments showed an enhanced GABAergic inhibitory drive on breathing after caffeine treatment, and that progesterone is converted to allopregnanolone (an allosteric modulator of GABAA receptors) to inhibit breathing. We conclude that combining progesterone and chronic caffeine is not an option in preterm neonates, unless the effects of allopregnanolone can be counteracted.

ABSTRACT

Caffeine is the main treatment for apnoea in preterm neonates, but its interactions with other respiratory stimulants like progesterone are unknown. We tested the hypothesis that the addition of progesterone to caffeine treatments further stimulates ventilation. Newborn rats were treated with water (control) or caffeine (15 mg kg(-1)) by daily gavage between postnatal day (P)3 and P12. At P4 and P12, we measured apnoea frequency, ventilatory responses and metabolic parameters under both normoxia and hypoxia (12% O2, 20 min) following an acute administration of either saline or progesterone (4 mg kg(-1); i.p.). Progesterone injection increased the serum levels of both progesterone and its neuroactive metabolite allopregnanolone. Progesterone had no effect on ventilation in control rats under normoxia. Progesterone depressed ventilation in P12 caffeine-treated rats under normoxia and hypoxia and increased apnoea frequency in both P4 and P12 rats. Because allopregnanolone is an allosteric modulator of GABAA receptors and caffeine may enhance GABAergic inhibition in newborns, we studied the effects of the GABAA receptor antagonist bicuculline at 0, 1, 2 and 3 mg kg(-1) doses and allopregnanolone (10 mg kg(-1) dose) in P12 rats. In caffeine-treated rats, bicuculline enhanced ventilation, while allopregnanolone decreased ventilation and increased total apnoea time. Progesterone had no effect on ventilation and apnoea frequency in caffeine-treated rats injected with finasteride, which blocks the conversion of progesterone to allopregnanolone. We conclude that combining progesterone and chronic caffeine therapy is not an option for the treatment of persistent apnoea in preterm neonates, unless the effects of allopregnanolone can be counteracted.

Lipoic acid and pentoxifylline mitigate nandrolone decanoate-induced neurobehavioral perturbations in rats via re-balance of brain neurotransmitters, up-regulation of Nrf2/HO-1 pathway, and down-regulation of TNFR1 expression

Behavioral perturbations associated with nandrolone decanoate abuse by athletes and adolescents may be attributed to oxidative stress and inflammation. However, the underlying mechanisms are not yet fully explored. On the other hand, the natural antioxidant lipoic acid can pass the blood brain barrier and enhance Nrf2/HO-1 (nuclear factor erythroid-2 related factor 2/heme oxygenase-1) pathway. In addition, the phosphodiesterase-IV inhibitor xanthine derivative pentoxifylline has a remarkable inhibitory effect on tumor necrosis factor-alpha (TNF-α). Therefore, this study aimed at investigation of the possible protective effects of lipoic acid and/or pentoxifylline against nandrolone-induced neurobehavioral alterations in rats. Accordingly, male albino rats were randomly distributed into seven groups and treated with either vehicle, nandrolone (15mg/kg, every third day, s.c.), lipoic acid (100mg/kg/day, p.o.), pentoxifylline (200mg/kg/day, i.p.), or nandrolone with lipoic acid and/or pentoxifylline. Rats were challenged in the open field, rewarded T-maze, Morris water maze, and resident-intruder aggression behavioral tests. The present findings showed that nandrolone induced hyperlocomotion, anxiety, memory impairment, and aggression in rats. These behavioral abnormalities were accompanied by several biochemical changes, including altered levels of brain monoamines, GABA, and acetylcholine, enhanced levels of malondialdehyde and TNF-α, elevated activity of acetylcholinesterase, and up-regulated expression of TNF-α receptor-1 (TNFR1). In addition, inhibited catalase activity, down-regulated Nrf2/HO-1 pathway, and suppressed acetylcholine receptor expression were observed. Lipoic acid and pentoxifylline combination significantly mitigated all the previously mentioned deleterious effects mainly via up-regulation of Nrf2/HO-1 pathway, inhibition of TNF-α and down-regulation of TNFR1 expression. In conclusion, the biochemical and histopathological findings of this study revealed the protective mechanisms of lipoic acid and pentoxifylline against nandrolone-induced behavioral changes and neurotoxicity in rats.

Involvement of the central melanocortin system in the effects of caffeine on anxiety-like behavior in mice

AIMS

To investigate the role of the melanocortin (MC) system in the framework of the central nucleus of the amygdala (CeA) in the differential effects of the adenosine receptor blocker caffeine on anxiety-like behavior, using the social interaction (SI) test.

MAIN METHODS

Caffeine was injected intraperitoneally, alone or in combination with alpha-melanocyte stimulating hormone (α-MSH), the MC4 receptor agonist RO27-3225 or the antagonist HS014 via the intra-CeA route. The effects of chronic (21 days) caffeine, given alone or concurrently with α-MSH, or RO27-3225, were investigated. The effects of withdrawal of these treatments on SI time were also evaluated. Furthermore, the acute effects of HS014 were investigated in different sets of caffeine-withdrawn mice.

KEY FINDINGS

Acute injection of caffeine, RO27-3225, or α-MSH produced anxiety-like behavior. Prior treatment with α-MSH, or RO27-3225 potentiated the caffeine-induced anxiety-like behavior. Subchronic treatment with HS014 increased the SI time, which was attenuated by caffeine. Chronic administration of caffeine resulted in tolerance to caffeine's anxiogenic effect, while abrupt discontinuation of the treatment produced peak anxiety-like behavior at 72 h post-withdrawal. Concurrent administration of α-MSH, or RO27-3225 with chronic caffeine delayed the development of tolerance and prevented withdrawal-induced anxiety-like behavior. Moreover, acute treatment with HS014 at 72 h post-withdrawal attenuated the anxiety-like behavior.

SIGNIFICANCE

α-MSH, possibly via MC4 receptor in the neuroanatomical framework of the CeA, may contribute to the acute, chronic and withdrawal actions of caffeine associated with anxiety-like behavior in the neuroanatomical framework of the CeA.

The Janus face of caffeine

Caffeine is certainly the psychostimulant substance most consumed worldwide. Over the past years, chronic consumption of caffeine has been associated with prevention of cognitive decline associated to aging and mnemonic deficits of brain disorders. While its preventive effects have been reported extensively, the cognitive enhancer properties of caffeine are relatively under debate. Surprisingly, there are scarce detailed ontogenetic studies focusing on neurochemical parameters related to the effects of caffeine during prenatal and earlier postnatal periods. Furthermore, despite the large number of epidemiological studies, it remains unclear how safe is caffeine consumption during pregnancy and brain development. Thus, the purpose of this article is to review what is currently known about the actions of caffeine intake on neurobehavioral and adenosinergic system during brain development. We also reviewed other neurochemical systems affected by caffeine, but not only during brain development. Besides, some recent epidemiological studies were also outlined with the control of "pregnancy signal" as confounding variable. The idea is to tease out how studies on the impact of caffeine consumption during brain development deserve more attention and further investigation.