Caffeine potentiates the release of GABA mediated by NMDA receptor activation: Involvement of A1 adenosine receptors

Caffeine intake during lactation has a sex-dependent effect on the hippocampal excitatory/inhibitory balance and pups' behavior

During early life, disruptions in glutamatergic and GABAergic synapse development in the hippocampus may contribute to several neurodevelopmental disorders, including cognitive deficits and psychiatric disorders. Caffeine is the most consumed psychoactive drug in the world, and previous work from our group has shown that caffeine disrupts visual system connections at different stages of development. This work aimed to investigate the effects of caffeine consumption during lactation in the glutamatergic and GABAergic synaptic markers in the hippocampus and on the behavior of rat offspring. We found that maternal caffeine intake significantly reduced GluN1 subunits of the NMDA receptor, increased the GluA1/GluA2 ratio of AMPA receptor in the dorsal hippocampus, and decreased GAD content in female pups' ventral hippocampus. On the other hand, an increase in GluN1/GluN2b subunits, a decrease in GAD content in the dorsal hippocampus, and a reduction of the GluA1 content in the ventral hippocampus were observed in male pups. In addition, changes in the behavior of the offspring submitted to indirect caffeine consumption were also sex-dependent, with females developing anxiety-like behavior and males showing anxiety-like behavior and hyper-locomotion. These results highlight that maternal caffeine intake promotes changes in the hippocampal excitatory and inhibitory balance and offspring behavior in a sex-dependent manner, suggesting that the population should be alerted to reduced caffeine consumption by breastfeeding mothers.

Antagonistic interaction between caffeine and ketamine in zebrafish: Implications for aquatic toxicity

The coexistence of caffeine (CF) and ketamine (KET) in surface waters across Asia has been widely reported. Previous studies have implied that CF and KET may share a mechanism of action. However, the combined toxicity of these two chemicals on aquatic organisms remains unclear at environmental levels, and the underlying mechanisms are not well understood. Here we demonstrate that KET antagonizes the adverse effects of CF on zebrafish larvae by modulating the gamma-aminobutyric acid (GABA)ergic synapse pathway. Specifically, KET (10-250 ng L-1) ameliorates the locomotor hyperactivity and impaired circadian rhythms in zebrafish larvae induced by 2 mg L-1 of CF, showing a dose-dependent relationship. Additionally, the developmental abnormalities in zebrafish larvae exposed to CF are mitigated by KET, with an incidence rate reduced from 26.7% to 6.7%. The competition between CF and KET for binding sites on the GABA-A receptor (in situ and in silico) elucidates the antagonistic interactions between the two chemicals. Following a seven-day recovery period, the adverse outcomes of CF exposure persist in the fish, whereas the changes observed in the CF + KET groups are significantly alleviated, especially with KET at 10 ng L-1. Based on these results, it is imperative to further assess the environmental risks associated with CF and KET co-pollution. This pilot study underscores the utility of systems toxicology approaches in estimating the combined toxicity of environmental chemicals on aquatic organisms. Moreover, the nighttime behavioral functions of fish could serve as a sensitive biomarker for evaluating the toxicity of psychoactive substances.

Molecular targets of caffeine in the central nervous system

Caffeine is an alkaloid obtained from plants and is one of the most consumptive drug in the form of chocolate, coffee and beverages. The potential impact of caffeine within CNS can be easily understood by mechanism of action-antagonism of adenosine receptor, calcium influx, inhibits phosphodiesterases. Adenosine a neuromodulator for adenosine receptors, which are abundantly expressed within the central nervous system. Caffeine antagonized the adenosine receptor, hence stimulate expression of dopamine. It plays pivotal role in many metabolic pathways within the brain and nervous system, it reduced the amyloid-β-peptide (Aβ) accumulation, downregulation of tau protein phosphorylation, stimulate cholinergic neurons and inhibits the acetylcholinestrase (AChE). It also possess antioxidant and antiapoptotic activity. Caffeine act as nutraceutical product, improves mental health. It contains antioxidants, vitamins, minerals and dietary supplements, by reducing the risk factor of several neurodegenerations including Alzheimer's disease, migraine, gallstone, cancer, Huntington's disease and sclerosis. This act as a stimulant and have capability to increase the effectiveness of certain pain killer. Beside positive affects, over-consumption of caffeine leads to negative impact: change in sleep pattern, hallucinations, high blood pressure, mineral loss and even heartburn. This chapter highlights pros and cons of caffeine consumption.

Silva H, P. de Carvalho R, Ventura ALM, Calaza KC, Silveira MS, Kubrusly RCC, de Melo Reis RA. The Healthy and Diseased Retina Seen through Neuron-Glia Interactions

The retina is the sensory tissue responsible for the first stages of visual processing, with a conserved anatomy and functional architecture among vertebrates. To date, retinal eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, glaucoma, and others, affect nearly 170 million people worldwide, resulting in vision loss and blindness. To tackle retinal disorders, the developing retina has been explored as a versatile model to study intercellular signaling, as it presents a broad neurochemical repertoire that has been approached in the last decades in terms of signaling and diseases. Retina, dissociated and arranged as typical cultures, as mixed or neuron- and glia-enriched, and/or organized as neurospheres and/or as organoids, are valuable to understand both neuronal and glial compartments, which have contributed to revealing roles and mechanisms between transmitter systems as well as antioxidants, trophic factors, and extracellular matrix proteins. Overall, contributions in understanding neurogenesis, tissue development, differentiation, connectivity, plasticity, and cell death are widely described. A complete access to the genome of several vertebrates, as well as the recent transcriptome at the single cell level at different stages of development, also anticipates future advances in providing cues to target blinding diseases or retinal dysfunctions.

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.

NMDA Receptor Activation and Ca2+/PKC Signaling in Nicotine-Induced GABA Transport Shift in Embryonic Chick Retina

Nicotinic receptors are present in the retina of different vertebrates, and in the chick retina, it is present during early development throughout to post-hatching. These receptors are activated by nicotine, an alkaloid with addictive and neurotransmitter release modulation properties, such as GABA signaling. Here we evaluated the mechanisms of nicotine signaling in the avian retina during the development of neuron-glia cells at a stage where synapses are peaking. Nicotine almost halved [³H]-GABA uptake, reducing it by 45% whilst increasing more than two-fold [³H]-GABA release in E12 embryonic chick retinas. Additionally, nicotine mediated a 33% increase in [³H]-D-aspartate release. MK-801 50 μM blocked 66% of nicotine-induced [³H]-GABA release and Gö 6983 100 nM prevented the nicotine-induced reduction in [³H]-GABA uptake by rescuing 40% of this neurotransmitter uptake, implicating NMDAR and PKC (respectively) in the nicotinic responses. In addition, NO-711 prevented [³H]-GABA uptake and release induced by nicotine. Furthermore, the relevance of calcium influx for PKC activation was evidenced through fura-2 imaging. We conclude that the shift of GABA transport mediated by nicotine promotes GABA release by inducing transporter reversal via nicotine-induced EAA release through EAATs, or by a direct effect of nicotine in activating nicotinic receptors permeable to calcium and promoting PKC pathway activation and shifting GAT-1 activity, both prompting calcium influx, and activation of the PKC pathway and shifting GAT-1 activity.

Caffeine Improves GABA Transport in the Striatum of Spontaneously Hypertensive Rats (SHR)

The spontaneously hypertensive rat (SHR) is an excellent animal model that mimics the behavioral and neurochemical phenotype of attention-deficit/hyperactivity disorder (ADHD). Here, we characterized the striatal GABA transport of SHR and investigated whether caffeine, a non-selective antagonist of adenosine receptors, could influence GABAergic circuitry. For this purpose, ex vivo striatal slices of SHR and Wistar (control strain) on the 35th postnatal day were dissected and incubated with [3H]-GABA to quantify the basal levels of uptake and release. SHR exhibited a reduced [3H]-GABA uptake and release, suggesting a defective striatal GABAergic transport system. GAT-1 appears to be the primary transporter for [3H]-GABA uptake in SHR striatum, as GAT-1 selective blocker, NO-711, completely abolished it. We also verified that acute exposure of striatal slices to caffeine improved [3H]-GABA uptake and release in SHR, whereas Wistar rats were not affected. GABA-uptake increase and cAMP accumulation promoted by caffeine was reverted by A1R activation with N6-cyclohexyl adenosine (CHA). As expected, the pharmacological blockade of cAMP-PKA signaling by H-89 also prevented caffeine-mediated [3H]-GABA uptake increment. Interestingly, a single caffeine exposure did not affect GAT-1 or A1R protein density in SHR, which was not different from Wistar protein levels, suggesting that the GAT-1-dependent transport in SHR has a defective functional activity rather than lower protein expression. The current data support that caffeine regulates GAT-1 function and improves striatal GABA transport via A1R-cAMP-PKA signaling, specifically in SHR. These results reinforce that caffeine may have therapeutic use in disorders where the GABA transport system is impaired.

Caenorhabditis elegans provides an efficient drug screening platform for GNAO1-related disorders and highlights the potential role of caffeine in controlling dyskinesia

Dominant GNAO1 mutations cause an emerging group of childhood-onset neurological disorders characterized by developmental delay, intellectual disability, movement disorders, drug-resistant seizures and neurological deterioration. GNAO1 encodes the α-subunit of an inhibitory GTP/GDP-binding protein regulating ion channel activity and neurotransmitter release. The pathogenic mechanisms underlying GNAO1-related disorders remain largely elusive and there are no effective therapies. Here, we assessed the functional impact of two disease-causing variants associated with distinct clinical features, c.139A > G (p.S47G) and c.662C > A (p.A221D), using Caenorhabditis elegans as a model organism. The c.139A > G change was introduced into the orthologous position of the C. elegans gene via CRISPR/Cas9, whereas a knock-in strain carrying the p.A221D variant was already available. Like null mutants, homozygous knock-in animals showed increased egg laying and were hypersensitive to aldicarb, an inhibitor of acetylcholinesterase, suggesting excessive neurotransmitter release by different classes of motor neurons. Automated analysis of C. elegans locomotion indicated that goa-1 mutants move faster than control animals, with more frequent body bends and a higher reversal rate and display uncoordinated locomotion. Phenotypic profiling of heterozygous animals revealed a strong hypomorphic effect of both variants, with a partial dominant-negative activity for the p.A221D allele. Finally, caffeine was shown to rescue aberrant motor function in C. elegans harboring the goa-1 variants; this effect is mainly exerted through adenosine receptor antagonism. Overall, our findings establish a suitable platform for drug discovery, which may assist in accelerating the development of new therapies for this devastating condition, and highlight the potential role of caffeine in controlling GNAO1-related dyskinesia.

Confounding effects of caffeine on neuroplasticity induced by transcranial alternating current stimulation and paired associative stimulation

OBJECTIVE

We examined the effects of caffeine, time of day, and alertness fluctuation on plasticity effects after transcranial alternating current stimulation (tACS) or 25 ms paired associative stimulation (PAS25) in caffeine-naïve and caffeine-adapted subjects.

METHODS

In two randomised, double-blinded, cross-over or placebo-controlled (caffeine) studies, we measured sixty subjects in eight sessions (n = 30, Male: Female = 1:1 in each study).

RESULTS

We found caffeine increased motor cortex excitability in caffeine naïve subjects. The aftereffects in caffeine naïve subjects were enhanced and prolonged when combined with PAS 25. Caffeine also increased alertness and the motor evoked potentials (MEPs) were reduced under light deprivation in caffeine consumers both with and without caffeine. In caffeine consumers, the time of day had no effect on tACS-induced plasticity.

CONCLUSIONS

We conclude that caffeine should be avoided or controlled as confounding factor for brain stimulation protocols. It is also important to keep the brightness constant in all sessions and study groups should not be mixed with caffeine-naïve and caffeine consuming participants.

SIGNIFICANCE

Caffeine is one of the confounding factors in the plasticity induction studies and it induces different excitability effects in caffeine-naïve and caffeine-adapted subjects. This study was registered in the ClinicalTrials.gov with these registration IDs: 1) NCT03720665 https://clinicaltrials.gov/ct2/results?cond=NCT03720665&term=&cntry=&state=&city=&dist= 2) NCT04011670 https://clinicaltrials.gov/ct2/results?cond=&term=NCT04011670&cntry=&state=&city=&dist=.

GABA-enriched teas as neuro-nutraceuticals

Teas enriched in GABA are consumed for their beneficial effects on blood pressure, stress and anxiety. These effects may involve actions of GABA on the central and peripheral nervous systems. The anaerobic procedures for the production of GABA-enriched teas increase GABA levels by 10-20 times. They also significantly alter the levels of other constituents that may interact with the actions of GABA. These include epigallocatechin gallate, caffeine and theanine. The possible interactions of these active constituents make the understanding of the effects of GABA-enriched teas complex. More data is needed to establish where and how GABA is acting following consumption of GABA-enriched teas. While there is considerable evidence that such GABA is acting on GABA receptors in the periphery, there is rather less evidence that is acting directly in the brain. Certainly, there is more to the action of GABA-enriched teas than GABA itself.

Caffeine exposure ameliorates acute ischemic cell death in avian developing retina

In infants, the main cause of blindness is retinopathy of prematurity that stems in a hypoxic-ischemic condition. Caffeine is a psychoactive compound that at low to moderate concentrations, selectively inhibits adenosine A1 and A2A receptors. Caffeine exerts beneficial effects in central nervous system of adult animal models and humans, whereas it seems to have malefic effect on the developing tissue. We observed that 48-h exposure (during synaptogenesis) to a moderate dose of caffeine (30 mg/kg of egg) activated pro-survival signaling pathways, including ERK, CREB, and Akt phosphorylation, alongside BDNF production, and reduced retinal cell death promoted by oxygen glucose deprivation in the chick retina. Blockade of TrkB receptors and inhibition of CREB prevented caffeine protection effect. Similar signaling pathways were described in previously reported data concerning chemical preconditioning mechanism triggered by NMDA receptors activation, with low concentrations of agonist. In agreement to these data, caffeine increased NMDA receptor activity. Caffeine decreased the levels of the chloride co-transporter KCC2 and delayed the developmental shift on GABAA receptor response from depolarizing to hyperpolarizing. These results suggest that the caffeine-induced delaying in depolarizing effect of GABA could be facilitating NMDA receptor activity. DPCPX, an A1 adenosine receptor antagonist, but not A2A receptor inhibitor, mimicked the effect of caffeine, suggesting that the effect of caffeine occurs through A1 receptor blockade. In summary, an in vivo caffeine exposure could increase the resistance of the retina to ischemia-induced cell death, by triggering survival pathways involving CREB phosphorylation and BDNF production/TrkB activation.

Keep an eye on adenosine: Its role in retinal inflammation

Adenosine is an endogenous purine nucleoside ubiquitously distributed throughout the body that interacts with G protein-coupled receptors, classified in four subtypes: A₁R, A_2AR, A_2BR and A₃R. Among the plethora of functions of adenosine, it has been increasingly recognized as a key mediator of the immune response. Neuroinflammation is a feature of chronic neurodegenerative diseases and contributes to the pathophysiology of several retinal degenerative diseases. Animal models of retinal diseases are helping to elucidate the regulatory roles of adenosine receptors in the development and progression of those diseases. Mounting evidence demonstrates that the adenosinergic system is altered in the retina during pathological conditions, compromising retinal physiology. This review focuses on the roles played by adenosine and the elements of the adenosinergic system (receptors, enzymes, transporters) in the neuroinflammatory processes occurring in the retina. An improved understanding of the molecular and cellular mechanisms of the signalling pathways mediated by adenosine underlying the onset and progression of retinal diseases will pave the way towards the identification of new therapeutic approaches.

Caffeine induces neurobehavioral effects through modulating neurotransmitters

Evidence demonstrates that chronic caffeine exposure, primarily through consumption of coffee or tea, leads to increased alertness and anxiety. Preclinical and clinical studies showed that caffeine induced beneficial effects on mood and cognition. Other studies using molecular techniques have reported that caffeine exhibited neuroprotective effects in animal models by protecting dopaminergic neurons. Moreover, caffeine interacts with dopaminergic system, which leads to improvements in neurobehavioral measures in animal models of depression or attention deficit hyperactivity disorder (ADHD). Glutamatergic receptors have been found to be involved on the neurobiological effects of caffeine. Additionally, caffeine has been found to suppress the inhibitory (GABAergic) activity and modulate GABA receptors. Studies have also found that modulating these neurotransmitters leads to neurobehavioral effects. The linkage between the modulatory role of caffeine on neurotransmitters and neurobehavioral effects has not been fully discussed. The purpose of this review is to discuss in detail the role of neurotransmitters in the effects of caffeine on neurobehavioral disorders.

Caffeine regulates GABA transport via A1R blockade and cAMP signaling

Caffeine is the most consumed psychostimulant drug in the world, acting as a non-selective antagonist of adenosine receptors A₁R and A_2AR, which are widely expressed in retinal layers. We have previously shown that caffeine, when administered acutely, acts on A₁R to potentiate the NMDA receptor-induced GABA release. Now we asked if long-term caffeine exposure also modifies GABA uptake in the avian retina and which mechanisms are involved in this process. Chicken embryos aged E11 were injected with a single dose of caffeine (30 mg/kg) in the air chamber. Retinas were dissected on E15 for ex vivo neurochemical assays. Our results showed that [³H]-GABA uptake was dependent on Na⁺ and blocked at 4 °C or by NO-711 and caffeine. This decrease was observed after 60 min of [³H]-GABA uptake assay at E15, which is accompanied by an increase in [³H]-GABA release. Caffeine increased the protein levels of A₁R without altering ADORA1 mRNA and was devoid of effects on A_2AR density or ADORA2A mRNA levels. The decrease of GABA uptake promoted by caffeine was reverted by A₁R activation with N6-cyclohexyl adenosine (CHA) but not by A_2AR activation with CGS 21680. Caffeine exposure increased cAMP levels and GAT-1 protein levels, which was evenly expressed between E11-E15. As expected, we observed an increase of GABA containing amacrine cells and processes in the IPL, also, cAMP pathway blockage by H-89 decreased caffeine mediated [³H]-GABA uptake. Our data support the idea that chronic injection of caffeine alters GABA transport via A₁R during retinal development and that the cAMP/PKA pathway plays an important role in the regulation of GAT-1 function.

Using caffeine on the patients as therapeutic option against treatment-resistant obsessive-compulsive disorder

Introduction

Obsessive-compulsive disorder (OCD) is one of the most common and debilitating diseases. Approximately 40-30% of these patients are resistant to treatment, which auxiliary drugs are used to treat these patients. One of these drugs is caffeine, which is capable of affecting adenosine receptors and interfering with its release and serotonin reuptake. Considering the limitations of previous studies in this area, including lack of control group, this double-blind study compared the effectiveness of caffeine in the management of patients with treatment-resistant OCD in comparison with placebo group.

Materials and Methods

62 patients who referred to the psychiatric clinic of Imam Hossein Hospital in Tehran from 2017 to 2018 were enrolled in the study. According to the psychiatrist's interview, patients with OCD were selected randomly in two groups including caffeine and placebo, after having met the criteria for inclusion and obtaining informed consent. Patients were followed for 8 weeks and compared in terms of the severity of OCD before and after intervention using YBOCS questionnaire.

Results

The two groups of treatment and control were similar in terms of study variables (gender, age, education, age, comorbidity). The mean Yale-Brown Obsessive Compulsive Scale (Y-BOCS) in the treatment and control groups before intervention were determined to be 27.16 and 25.4, respectively, which changed to 24 and 27.23 after medication intervention, which exhibited a decrease of about 3 points (12%) in the treatment group, and was statistically significant based on linear regression analysis (P = 0.009). Considering other variables, the effect of caffeine was still statistically significant in the two groups.

Conclusion

Based on the findings of our study, caffeine can reduce the severity of the symptoms of OCD and serve as an auxiliary treatment for OCD.

Microglial-driven changes in synaptic plasticity: A possible role in major depressive disorder

Recent data gathered from both in vitro and in vivo models of Major Depressive Disorder (MDD) have indicated that microglia play an active role in modifying some of the most important sources for neuronal plasticity, specifically long-term potentiation (LTP) and long-term depression (LTD). In addition, microglia have been implicated in neuro-immune interaction dysregulations, which are considered a core constituent of MDD pathology. While prior studies have investigated the diverse effects activated microglia can have in the context of depression, including regulation of inflammatory cytokine production and structural changes, recent evidence has revealed a more direct relationship between microglial activation and changes in synaptic function and plasticity, including LTP and LTD. Here we review these findings from animal models, as well as discuss how current preclinical evidence might shed light on novel therapeutic targets for patients with depressive disorder.

Purinergic signaling in the retina: From development to disease

Retinal injuries and diseases are major causes of human disability involving vision impairment by the progressive and permanent loss of retinal neurons. During development, assembly of this tissue entails a successive and overlapping, signal-regulated engagement of complex events that include proliferation of progenitors, neurogenesis, cell death, neurochemical differentiation and synaptogenesis. During retinal damage, several of these events are re-activated with both protective and detrimental consequences. Purines and pyrimidines, along with their metabolites are emerging as important molecules regulating both retinal development and the tissue's responses to damage. The present review provides an overview of the purinergic signaling in the developing and injured retina. Recent findings on the presence of vesicular and channel-mediated ATP release by retinal and retinal pigment epithelial cells, adenosine synthesis and release, expression of receptors and intracellular signaling pathways activated by purinergic signaling in retinal cells are reported. The pathways by which purinergic receptors modulate retinal cell proliferation, migration and death of retinal cells during development and injury are summarized. The contribution of nucleotides to the self-repair of the injured zebrafish retina is also discussed.

Caffeine: Well-known as psychotropic substance, but little as immunomodulator

To date, numerable reviews are found in the literature prominent to the effect of caffeine on the immune system, with the latest review published in 2006. Database screening reveals around three thousand articles that have been published during the last decade. Interestingly, less than hundred articles involved humans and rodents as tested models, out of which 20% is of interest to this paper excluding studies done on the nervous and cardiac systems, and in pregnant and cancer cases. In this review, information pertaining to the experimental setup of various studies, namely, the tested model, the study type (in vivo or in vitro), and caffeine dose is covered to discern the behaviour of major cellular and molecular immune components in light of caffeine exposure. Although it is hard to extrapolate results done in rodents to humans and to relay conclusions from in vitro to in vivo studies, most of the collected data favor the suppressive effects of caffeine on the proliferation of stimulated lymphocytes. Macrophages and natural killer cells also exhibited a reduced activity in the presence of high caffeine doses compared to increased activity at low doses. Immunosuppression is also supported by reduced levels of major anti-inflammatory cytokines, IL-2, IL-6, TNF-α. Moreover, certain innate and adaptive immune receptors, such as TLR1, TLR2, TLR4, and MHC class I-related chain B (MICB) molecules, exhibited decreased expression levels. Thus, we support the use of caffeine to alleviate various inflammatory conditions and autoimmune diseases.

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.

Age-Related Decrease in Male Extra-Striatal Adenosine A1 Receptors Measured 11C-MPDX PET

Adenosine A₁ receptors (A₁Rs) are widely distributed throughout the entire human brain, while adenosine A_2A receptors (A_2ARs) are present in dopamine-rich areas of the brain, such as the basal ganglia. A past study using autoradiography reported a reduced binding ability of A₁R in the striatum of old rats. We developed positron emission tomography (PET) ligands for mapping the adenosine receptors and we successfully visualized the A₁Rs using 8-dicyclopropylmethyl-1-¹¹C-methyl-3-propylxanthine (¹¹C-MPDX). We previously reported that the density of A₁Rs decreased with age in the human striatum, although we could not observe an age-related change in A_2ARs. The aim of this study was to investigate the age-related change of the density of A₁Rs in the thalamus and cerebral cortices of healthy participants using ¹¹C-MPDX PET. We recruited eight young (22.0 ± 1.7 years) and nine elderly healthy male volunteers (65.7 ± 8.0 years). A dynamic series of decay-corrected PET scans was performed for 60 min starting with the injection of ¹¹C-MPDX. We placed the circular regions of interest of 10 mm in diameter in ¹¹C-MPDX PET images. The values for the binding potential (BP_ND) of ¹¹C-MPDX in the thalamus, and frontal, temporal, occipital, and parietal cortices were calculated using a graphical analysis, wherein the reference region was the cerebellum. BP_ND of ¹¹C-MPDX was significantly lower in elderly participants than young participants in the thalamus, and frontal, temporal, occipital, and parietal cortices. In the human brain, we could observe the age-related decrease in the distribution of A₁Rs.

Acute doses of caffeine shift nervous system cell expression profiles toward promotion of neuronal projection growth

Caffeine is a widely consumed psychoactive substance, but little is known about the effects of caffeine stimulation on global gene expression changes in neurons. Here, we conducted gene expression profiling of human neuroepithelial stem cell-derived neurons, stimulated with normal consumption levels of caffeine (3 μM and 10 μM), over a period of 9 h. We found dosage-dependent activation of immediate early genes after 1 h. Neuronal projection development processes were up-regulated and negative regulation of axon extension processes were down-regulated at 3 h. In addition, genes involved in extracellular matrix organization, response for wound healing, and regulation of immune system processes were down-regulated by caffeine at 3 h. This study identified novel genes within the neuronal projection guidance pathways that respond to acute caffeine stimulation and suggests potential mechanisms for the effects of caffeine on neuronal cells.

Caffeine induces sustained apoptosis of human gastric cancer cells by activating the caspase‑9/caspase‑3 signalling pathway

Caffeine is one of the most widely consumed substances found in beverages, and has demonstrated anticancer effects in several types of cancer. The present study aimed to examine the anticancer effects of caffeine on gastric cancer (GC) cells (MGC‑803 and SGC‑7901) in vitro, and to determine whether the apoptosis‑related caspase‑9/-3 pathway is associated with these effects. The sustained antiproliferative effects of caffeine on gastric cancer were also investigated. GC cell viability and proliferation were evaluated using cell counting and colony forming assays, following treatment with various concentrations of caffeine. Flow cytometry was performed to assess cell cycle dynamics and apoptosis. Western blot analysis was conducted to detect the activity of the caspase‑9/-3 pathway. The results indicated that caffeine treatment significantly suppressed GC cell growth and viability and induced apoptosis by activating the caspase‑9/-3 pathway. Furthermore, the anticancer effects of caffeine appeared to be sustained, as the caspase‑9/-3 pathway remained active following caffeine withdrawal. In conclusion, caffeine may function as a sustained anticancer agent by activating the caspase‑9/-3 pathway, which indicates that it may be useful as a therapeutic candidate in gastric cancer.

Caffeine-Induced Suppression of GABAergic Inhibition and Calcium-Independent Metaplasticity

GABAergic inhibition plays a critical role in the regulation of neuron excitability; thus, it is subject to modulations by many factors. Recent evidence suggests the elevation of intracellular calcium ([Ca²⁺]_i) and calcium-dependent signaling molecules underlie the modulations. Caffeine induces a release of calcium from intracellular stores. We tested whether caffeine modulated GABAergic transmission by increasing [Ca²⁺]_i. A brief local puff-application of caffeine to hippocampal CA1 pyramidal cells transiently suppressed GABAergic inhibitory postsynaptic currents (IPSCs) by 73.2 ± 6.98%. Time course of suppression and the subsequent recovery of IPSCs resembled DSI (depolarization-induced suppression of inhibition), mediated by endogenous cannabinoids that require a [Ca²⁺]_i rise. However, unlike DSI, caffeine-induced suppression of IPSCs (CSI) persisted in the absence of a [Ca²⁺]_i rise. Intracellular applications of BAPTA and ryanodine (which blocks caffeine-induced calcium release from intracellular stores) failed to prevent the generation of CSI. Surprisingly, ruthenium red, an inhibitor of multiple calcium permeable/release channels including those of stores, induced metaplasticity by amplifying the magnitude of CSI independently of calcium. This metaplasticity was accompanied with the generation of a large inward current. Although ionic basis of this inward current is undetermined, the present result demonstrates that caffeine has a robust Ca²⁺-independent inhibitory action on GABAergic inhibition and causes metaplasticity by opening plasma membrane channels.

The effect of GABA transporter 1 (GAT1) inhibitor, tiagabine, on scopolamine-induced memory impairments in mice

BACKGROUND

GABAergic neurotransmission is involved in long-term potentiation, a neurophysiological basis for learning and memory. On the other hand, GABA-enhancing drugs may impair memory and learning in humans and animals. The present study aims at investigating the effect of GAT1 inhibitor tiagabine on memory and learning.

METHODS

Albino Swiss (CD-1) and C57BL/6J mice were used in the passive avoidance (PA), Morris water maze (MWM) and radial arm water maze (RAWM) tasks. Scopolamine (1mg/kg ip) was applied to induce cognitive deficits.

RESULTS

In the retention trial of PA scopolamine reduced step-through latency as compared to vehicle-treated mice, and pretreatment with tiagabine did not have any influence on this effect. In MWM the results obtained for vehicle-treated mice, scopolamine-treated group and combined scopolamine+tiagabine-treated mice revealed variable learning abilities in these groups. Tiagabine did not impair learning in the acquisition trial. In RAWM on day 1 scopolamine-treated group made nearly two-fold more errors than vehicle-treated mice and mice that received combined scopolamine and tiagabine. Learning abilities in the latter group were similar to those of vehicle-treated mice in the corresponding trial block on day 1, except for the last trial block, during which tiagabine+scopolamine-injected mice made more errors than control mice and the scopolamine-treated group. In all groups a complete reversal of memory deficits was observed in the last trial block of day 2.

CONCLUSIONS

The lack of negative influence of tiagabine on cognitive functions in animals with scopolamine-induced memory impairments may be relevant for patients treated with this drug.