Caffeine's influence on object recognition and working-memory in prepubertal mice and its modulation by gender

The GluN2C/D-specific positive allosteric modulator CIQ rescues delay-induced working memory deficits in mice

Working memory is of short duration and is, therefore, particularly sensitive to time delays. Moreover, NMDA receptors are significantly involved in working memory. In the present study, we tested whether a commonly used measure of working memory, spontaneous alternation in the Y-maze, is sensitive to time delays and, if so, whether impairments due to time-delay can be rescued by treatment with CIQ, a positive allosteric modulator of the GluN2C/D subunits of NMDA receptor. Our results indicate that the effects of time delay do depend on the performance of the individual mice under basal condition. Those mice that performed well under basal conditions showed impaired spontaneous alternations when tested with a 45-s delay. Treatment with CIQ resulted in an improvement of spontaneous alternations, regardless of delay, sex, or basal performance. On the one hand, our study shows that repeated measures of individual behavior can better control the effects of confounding factors such as time delays. On the other hand, our study also highlights the potential of GluN2C/D-specific positive allosteric modulators in the treatment of human disorders associated with working memory deficits, such as schizophrenia.

Caffeine facilitates extinction of auditory fear conditioning in rats

Caffeine is the most widely consumed psychostimulant drug which could affect learning and memory acting through central adenosine receptors. Although caffeine has been suggested to impair the acquisition and the expression of auditory fear conditioning, its effect on the extinction has not been elucidated. To address this issue, in the present study, we investigated whether caffeine affects the extinction of conditioned fear in an auditory fear conditioning paradigm. During conditioning, rats received pairings of auditory cues (conditioned stimulus, CS) and foot shocks (unconditioned stimulus). On the next day, the rats were intraperitoneally administrated saline or caffeine (5 or 10 mg/kg) and then subjected to the extinction training, in which CSs were repeatedly presented without the foot shocks. Twenty-four hours later, the rats were re-exposed to the presentations of CSs (retrieval test). We found an acute caffeine administration dose-dependently decreased freezing rates during the presentations of CS in the extinction training. Furthermore, caffeine-treated animals showed lower conditioned freezing responses in the retrieval test. These findings suggest that caffeine facilitates the extinction of conditioned fear.

Cognitive and hippocampal synaptic profiles in monosodium glutamate-induced obese mice

Obesity is a growing worldwide public health issue and is associated with a range of comorbidities, including cognitive deficits. The present study investigated synaptic changes in the hippocampus during the development of obesity. The treatment of newborn mice with monosodium-L-glutamate (MSG, 2 mg/g) induced obesity and recognition memory deficits in the novel object recognition (NOR) test at 16-17 weeks, but not at 8-9 weeks. Hippocampal synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), and excitatory synaptic transmission at Schaffer collateral-CA1 (SC-CA1) synapses were compared between MSG-treated mice and age-matched control mice. LTP and fiber volley amplitudes were enhanced in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. Furthermore, the strength of paired-pulse facilitation (PPF) changed in MSG-treated mice at 16-17 weeks, but not at 8-9 weeks. These results suggest that enhanced LTP in the SC-CA1 synapses of MSG-induced obese mice involves presynaptic rather than postsynaptic mechanisms.

Neuroprotective and Neurodegenerative Aspects of Coffee and Its Active Ingredients in View of Scientific Literature

Coffee and its components have several neuroprotective properties that lower the risk of cognitive decline and other neurodegenerative diseases. This study reviews the mechanisms by which coffee and its respective compounds affect the brain and its pathologies. Many epidemiological studies in this literature review have shown coffee to reduce the risk of developing dementia, stroke, and Alzheimer's disease. It may also have a positive impact on the disease course of amyotrophic lateral sclerosis, Parkinson's disease, and depression. The optimal benefits achieved from coffee in these pathologies rely on higher daily doses. Most of its effects are attributed to caffeine by the antagonism of adenosine receptors in the central nervous system; however, other coffee constituents like chlorogenic acids have also shown much promise in therapeutic value. Existing research considers coffee to have great potential, but additional studies are still needed to clarify the mechanisms and actual causal relationships in certain neuropathologies.

Prenatal nicotine exposure in mice induces sex-dependent anxiety-like behavior, cognitive deficits, hyperactivity, and changes in the expression of glutamate receptor associated-genes in the prefrontal cortex

In rodents, prenatal nicotine exposure (PNE) has been associated with increased risk for development of cognitive and emotional disturbances, but the findings are somewhat conflicting. Lack of behavioral alterations following PNE could be due to the variety of methods available for nicotine delivery, exposure time and species used, with inbred strains being mostly employed. Such differences suggest the need to investigate the behavioral phenotype in each PNE model available if we are to find models with enhanced translational value. In this study, we assessed sex-dependent effects of PNE on ADHD-related behaviors and on the levels of mRNA coding for glutamate receptor subunits within the prefrontal cortex in the outbred NMRI mice exposed to nicotine via maternal drinking water during gestation. Cotinine levels were assessed in newborn pups. Behaviors related to anxiety, compulsivity, working memory, and locomotion were evaluated in both sexes of young adult offspring using the elevated zero maze, marble burying, spontaneous alternation behavior, and locomotor activity tests. Expression of mRNA coding for different glutamate receptors subunits within the prefrontal cortex (PFC) was measured using RT-qPCR. Cotinine levels in the serum of newborns confirmed fetal nicotine exposure. Both male and female offspring showed ADHD-like behaviors, such as deficit in the SAB test and hyperactivity. In addition, PNE male mice displayed anxiety- and compulsive-like behaviors, effects that were absent in female offspring. Finally, PNE reduced the mRNA expression of GluN1-, GluN2B-, and mGluR2-related genes within the PFC of male offspring, whereas it reduced the expression of mRNA coding for GluA2 subunit in female mice. PNE in NMRI mice induced sex-dependent behavioral changes, which parallels clinical findings following maternal cigarette smoke exposure. Alterations detected in PFC mRNA glutamate receptor proteins could contribute to the abnormal behavioral responses observed, but other signaling pathways or brain regions are likely involved in the behavioral susceptibility of PNE individuals.

Deoxyelephantopin ameliorates lipopolysaccharides (LPS)-induced memory impairments in rats: Evidence for its anti-neuroinflammatory properties

AIM

Neuroinflammation is a critical pathogenic mechanism of most neurodegenerative disorders especially, Alzheimer's disease (AD). Lipopolysaccharides (LPS) are known to induce neuroinflammation which is evident from significant upsurge of pro-inflammatory mediators in in vitro BV-2 microglial cells and in vivo animal models. In present study, we investigated anti-neuroinflammatory properties of deoxyelephantopin (DET) isolated from Elephantopus scaber in LPS-induced neuroinflammatory rat model.

MATERIALS AND METHODS

In this study, DET (0.625. 1.25 and 2.5 mg/kg, i.p.) was administered in rats for 21 days and those animals were challenged with single injection of LPS (250 μg/kg, i.p.) for 7 days. Cognitive and behavioral assessment was carried out for 7 days followed by molecular assessment on brain hippocampus. Statistical significance was analyzed with one-way analysis of variance followed by Dunnett's test to compare the treatment groups with the control group.

KEY FINDINGS

DET ameliorated LPS-induced neuroinflammation by suppressing major pro-inflammatory mediators such as iNOS and COX-2. Furthermore, DET enhanced the anti-inflammatory cytokines and concomitantly suppressed the pro-inflammatory cytokines and chemokine production. DET treatment also reversed LPS-induced behavioral and memory deficits and attenuated LPS-induced elevation of the expression of AD markers. DET improved synaptic-functionality via enhancing the activity of pre- and post-synaptic markers, like PSD-95 and SYP. DET also prevented LPS-induced apoptotic neurodegeneration via inhibition of PARP-1, caspase-3 and cleaved caspase-3.

SIGNIFICANCE

Overall, our studies suggest DET can prevent neuroinflammation-associated memory impairment and neurodegeneration and it could be developed as a therapeutic agent for the treatment of neuroinflammation-mediated and neurodegenerative disorders, such as AD.

Effects of acute caffeine on anxiety-related behavior in rats chronically exposed to the drug, with some evidence of possible withdrawal-reversal

For 20days male and female PVG/c hooded rats were provided with caffeinated (approximately 50mg/kg/day) or unadulterated drinking water, and then their anxiety-related behavior was observed in an open field and elevated plus maze. Their choices of a brightness change were also observed in a Y maze to assess any caffeine effects on spatial memory. 24h later, all rats were tested again following an intraperitoneal injection of 50mg/kg acute caffeine, or vehicle. Earlier chronic caffeine decreased ambulation, walking, rearing, center occupancy and increased immobility in the open field thereby suggesting increased anxiety. However, occupancy of the plus-maze open arms and the Y-maze novel arm were increased by caffeine for male rats, but decreased for females probably because of sex differences in control levels of the response rather than to drug effects on anxiety and memory respectively. Following caffeine withdrawal, acute caffeine had the opposite effect to chronic treatment namely, increased open-field ambulation, walking, center occupancy and decreased immobility and defecation for caffeine-naïve rats that were suggestive of decreased anxiety. Similar but more consistent effects (plus decreased emergence latencies from a darkened start box into the open field) also typified the caffeine-experienced rats which in this case may have been accentuated by caffeine withdrawal-reversal. There was no evidence of either chronic or acute caffeine affecting spatial memory measured in the Y maze. There were also examples of lower overall activity and higher anxiety in male rats, than in females, and some sex-dependent caffeine effects.

Caffeine and sleep-deprivation mediated changes in open-field behaviours, stress response and antioxidant status in mice

OBJECTIVES

Effects of daily caffeine consumption on open-field behaviours, serum corticosterone and brain antioxidant levels were investigated after six hours of total sleep-deprivation in prepubertal mice. We tested the hypothesis that daily caffeine consumption may significantly alter behaviour, stress and antioxidative response of prepubertal mice to an acute episode of total sleep-deprivation.

METHODS

Prepubertal Swiss mice of both sexes were assigned to two main groups of 120 each (subdivided into 6 groups of 10 each, based on sex), and administered vehicle or graded oral doses of caffeine (10, 20, 40, 80 and 120 mg/kg/day) for 14 days. On day 14, a main group was subjected to 6 h of total sleep-deprivation by 'gentle-handling'. Open-field behaviours were then assessed in both groups, after which animals were euthanized, and levels of corticosterone, superoxide dismutase and glutathione peroxidase assayed.

RESULTS

Horizontal locomotion, rearing and grooming increased significantly, compared to control, with sleep-deprived (SD) mice showing stronger caffeine-driven responses at higher doses; and SD female mice showing sustained response to caffeine, compared to respective males. Plasma corticosterone increased with increasing doses of caffeine in both non sleep-deprived (NSD) and SD mice; although SD mice had higher corticosterone levels. Sleep-deprivation and/or higher doses of caffeine were associated with derangements in brain antioxidant levels.

CONCLUSION

Repeated caffeine consumption and/or acute sleep-deprivation led to significant changes in pattern of open-field behaviour and stress/antioxidant response in mice. Responses seen in the study are probably due to modulatory effects of caffeine on the total body response to stressful stimuli.