Caffeine-mediated presynaptic long-term potentiation in hippocampal CA1 pyramidal neurons

Mixing energy drinks and alcohol during adolescence impairs brain function: A study of rat hippocampal plasticity

In the last decades, the consumption of energy drinks has risen dramatically, especially among young people, adolescents and athletes, driven by the constant search for ergogenic effects, such as the increase in physical and cognitive performance. In parallel, mixed consumption of energy drinks and ethanol, under a binge drinking modality, under a binge drinking modality, has similarly grown among adolescents. However, little is known whether the combined consumption of these drinks, during adolescence, may have long-term effects on central function, raising the question of the risks of this habit on brain maturation. Our study was designed to evaluate, by behavioral, electrophysiological and molecular approaches, the long-term effects on hippocampal plasticity of ethanol (EtOH), energy drinks (EDs), or alcohol mixed with energy drinks (AMED) in a rat model of binge-like drinking adolescent administration. The results show that AMED binge-like administration produces adaptive hippocampal changes at the molecular level, associated with electrophysiological and behavioral alterations, which develop during the adolescence and are still detectable in adult animals. Overall, the study indicates that binge-like drinking AMED adolescent exposure represents a habit that may affect permanently hippocampal plasticity.

The neurobiological mechanisms and therapeutic prospect of extracellular ATP in depression

BACKGROUND

Depression is a prevalent psychiatric disorder with high long-term morbidities, recurrences, and mortalities. Despite extensive research efforts spanning decades, the cellular and molecular mechanisms of depression remain largely unknown. What's more, about one third of patients do not have effective anti-depressant therapies, so there is an urgent need to uncover more mechanisms to guide the development of novel therapeutic strategies. Adenosine triphosphate (ATP) plays an important role in maintaining ion gradients essential for neuronal activities, as well as in the transport and release of neurotransmitters. Additionally, ATP could also participate in signaling pathways following the activation of postsynaptic receptors. By searching the website PubMed for articles about "ATP and depression" especially focusing on the role of extracellular ATP (eATP) in depression in the last 5 years, we found that numerous studies have implied that the insufficient ATP release from astrocytes could lead to depression and exogenous supply of eATP or endogenously stimulating the release of ATP from astrocytes could alleviate depression, highlighting the potential therapeutic role of eATP in alleviating depression.

AIM

Currently, there are few reviews discussing the relationship between eATP and depression. Therefore, the aim of our review is to conclude the role of eATP in depression, especially focusing on the evidence and mechanisms of eATP in alleviating depression.

CONCLUSION

We will provide insights into the prospects of leveraging eATP as a novel avenue for the treatment of depression.

Comprehensive Review of Nutraceuticals against Cognitive Decline Associated with Alzheimer's Disease

Nowadays, nutraceuticals are being incorporated into functional foods or used as supplements with nonpharmacological approaches in the prevention and management of several illnesses, including age-related conditions and chronic neurodegenerative diseases. Nutraceuticals are apt for preventing and treating such disorders because of their nontoxic, non-habit-forming, and efficient bioactivities for promoting neurological well-being due to their ability to influence cellular processes such as neurogenesis, synaptogenesis, synaptic transmission, neuro-inflammation, oxidative stress, cell death modulation, and neuronal survival. The capacity of nutraceuticals to modify all of these processes reveals the potential to develop food-based strategies to aid brain development and enhance brain function, prevent and ameliorate neurodegeneration, and possibly reverse the cognitive impairment observed in Alzheimer's disease, the most predominant form of dementia in the elderly. The current review summarizes the experimental evidence of the neuroprotective capacity of nutraceuticals against Alzheimer's disease, describing their mechanisms of action and the in vitro and in vivo models applied to evaluate their neuroprotective potential.

Presenilins regulate synaptic plasticity in the perforant pathways of the hippocampus

Mutations in the Presenilin genes (PSEN1 and PSEN2) are the major cause of familial Alzheimer's disease (AD), highlighting the importance of Presenilin (PS) in AD pathogenesis. Previous studies of PS function in the hippocampus demonstrated that loss of PS results in the impairment of short- and long-term synaptic plasticity and neurotransmitter release at hippocampal Schaffer collateral (SC) and mossy fiber (MF) synapses. Cortical input to the hippocampus through the lateral perforant pathway (LPP) and the medial perforant pathway (MPP) is critical for normal cognitive functions and is particularly vulnerable during aging and early stages of AD. Whether PS regulates synaptic function in the perforant pathways, however, remained unknown. In the current study, we investigate PS function in the LPP and MPP by performing whole-cell and field-potential electrophysiological recordings using acute hippocampal slices from postnatal forebrain-restricted excitatory neuron-specific PS conditional double knockout (cDKO) mice. We found that paired-pulse ratio (PPR) is reduced in the LPP and MPP of PS cDKO mice. Moreover, synaptic frequency facilitation or depression in the LPP or MPP, respectively, is impaired in PS cDKO mice. Notably, depletion of intracellular Ca2+ stores by inhibition of sarcoendoplasmic reticulum Ca2+ ATPase (SERCA) minics and occludes the effects of PS inactivation, as evidenced by decreases of the evoked excitatory postsynaptic currents (EPSCs) amplitude in the LPP and MPP of control neurons but no effect on the EPSC amplitude in PS cDKO neurons, suggesting that impaired intracellular calcium homeostasis in the absence of PS may contribute to the observed deficits in synaptic transmission. While spontaneous synaptic events, such as both the frequency and the amplitude of spontaneous or miniature EPSCs, are similar between PS cDKO and control neurons, long-term potentiation (LTP) is impaired in the LPP and MPP of PS cDKO mice, accompanied with reduction of evoked NMDA receptor-mediated responses. These findings show the importance of PS in the regulation of synaptic plasticity and intracellular calcium homeostasis in the hippocampal perforant pathways.

Short-Term Intake of Chlorogenic Acids Improves Psychomotor Speed and Motor Speed in Adults: A Randomized Crossover Trial

Chlorogenic acid (CGA), a polyphenolic compound found in various plants, has been reported to improve cognitive function. However, it remains unclear how long it takes for CGAs to exert their effects. Here, we evaluated the short-term effects of CGAs on cognitive function. We assessed the effects of 2-week CGA intake on cognitive function. The study was carried out as a randomized, double-blind, placebo-controlled, crossover trial. Twenty-six healthy Japanese participants (50–65 years of age) were randomly assigned to either the active beverage (CGAs: 270 mg) or the placebo beverage group daily for 2 weeks. After a 2-week washout period, the participants consumed the other beverages. We assessed cognitive function at baseline and following the first treatment period using the Japanese version of CNS Vital Signs. CGAs significantly improved the scores for psychomotor speed, motor speed, and right and left finger tapping compared to placebo. In addition, processing speed scores improved significantly from baseline only after CGA intake. In conclusion, CGAs were confirmed to improve cognitive function over a short period of two weeks.

Subcellular localization of hippocampal ryanodine receptor 2 and its role in neuronal excitability and memory

Ryanodine receptor 2 (RyR2) is abundantly expressed in the heart and brain. Mutations in RyR2 are associated with both cardiac arrhythmias and intellectual disability. While the mechanisms of RyR2-linked arrhythmias are well characterized, little is known about the mechanism underlying RyR2-associated intellectual disability. Here, we employed a mouse model expressing a green fluorescent protein (GFP)-tagged RyR2 and a specific GFP probe to determine the subcellular localization of RyR2 in hippocampus. GFP-RyR2 was predominantly detected in the soma and dendrites, but not the dendritic spines of CA1 pyramidal neurons or dentate gyrus granular neurons. GFP-RyR2 was also detected within the mossy fibers in the stratum lucidum of CA3, but not in the presynaptic terminals of CA1 neurons. An arrhythmogenic RyR2-R4496C^+/− mutation downregulated the A-type K⁺ current and increased membrane excitability, but had little effect on the afterhyperpolarization current or presynaptic facilitation of CA1 neurons. The RyR2-R4496C^+/− mutation also impaired hippocampal long-term potentiation, learning, and memory. These data reveal the precise subcellular distribution of hippocampal RyR2 and its important role in neuronal excitability, learning, and memory.

A mouse model containing a GFP-tagged ryanodine receptor 2 (RyR2) has shed light on the precise subcellular localization of hippocampal RyR2 and mechanisms underlying neuronal excitability, learning, and memory.

Prolactin enhances hippocampal synaptic plasticity in female mice of reproductive age

Dynamic signaling between the endocrine system (ES) and the nervous system (NS) is essential for brain and body homeostasis. In particular, reciprocal interaction occurs during pregnancy and motherhood that may involve changes in some brain plasticity processes. Prolactin (PRL), a hormone with pleiotropic effects on the NS, promotes maternal behavior and has been linked to modifications in brain circuits during motherhood; however, it is unclear whether PRL may regulate synaptic plasticity. Therefore, the main aim of the present work was to determine the cellular and molecular mechanisms triggered by PRL that regulate synaptic plasticity in the hippocampus. By analyzing extracellular recordings in CA3‐CA1 synapses of hippocampal slices, we report that PRL modifies short and long‐term synaptic plasticity in female mice of reproductive age, but not in sexually immature females or adult males. This effect is carried out through mechanisms that include participation of GABA_A receptors and activation of the JAK2‐mediated signaling pathway. These findings show for the first time how PRL enhances the synaptic strength in hippocampal circuits and that this effect is sexually dimorphic, which would influence complex brain processes in physiological conditions like pregnancy and lactation.

Caffeine has a dual influence on NMDA receptor-mediated glutamatergic transmission at the hippocampus

Caffeine, a stimulant largely consumed around the world, is a non-selective adenosine receptor antagonist, and therefore caffeine actions at synapses usually, but not always, mirror those of adenosine. Importantly, different adenosine receptors with opposing regulatory actions co-exist at synapses. Through both inhibitory and excitatory high-affinity receptors (A₁R and A₂R, respectively), adenosine affects NMDA receptor (NMDAR) function at the hippocampus, but surprisingly, there is a lack of knowledge on the effects of caffeine upon this ionotropic glutamatergic receptor deeply involved in both positive (plasticity) and negative (excitotoxicity) synaptic actions. We thus aimed to elucidate the effects of caffeine upon NMDAR-mediated excitatory post-synaptic currents (NMDAR-EPSCs), and its implications upon neuronal Ca²⁺ homeostasis. We found that caffeine (30-200 μM) facilitates NMDAR-EPSCs on pyramidal CA1 neurons from Balbc/ByJ male mice, an action mimicked, as well as occluded, by 1,3-dipropyl-cyclopentylxantine (DPCPX, 50 nM), thus likely mediated by blockade of inhibitory A₁Rs. This action of caffeine cannot be attributed to a pre-synaptic facilitation of transmission because caffeine even increased paired-pulse facilitation of NMDA-EPSCs, indicative of an inhibition of neurotransmitter release. Adenosine A_2ARs are involved in this likely pre-synaptic action since the effect of caffeine was mimicked by the A_2AR antagonist, SCH58261 (50 nM). Furthermore, caffeine increased the frequency of Ca²⁺ transients in neuronal cell culture, an action mimicked by the A₁R antagonist, DPCPX, and prevented by NMDAR blockade with AP5 (50 μM). Altogether, these results show for the first time an influence of caffeine on NMDA receptor activity at the hippocampus, with impact in neuronal Ca²⁺ homeostasis.

Morphine selectively disinhibits glutamatergic input from mPFC onto dopamine neurons of VTA, inducing reward

Ventral tegmental area (VTA) dopamine (DA) neurons presynaptic glutamate release plays a very important role in the mechanism of morphine. Previously, a study from our lab found that morphine disinhibited glutamatergic input onto the VTA-DA neurons, which was an important mechanism for the morphine-induced increase in the VTA-DA neuron firing and related behaviors (Chen et al., 2015). However, what source of glutamatergic inputs is disinhibited by morphine remains to be elucidated. Using optogenetic strategy combined with whole-cell patch-clamp, qRT-PCR, immunofluorescence and chemical genetic approach combined with behavioral methods, our results show that: 1) morphine promotes glutamate release from glutamatergic terminals of medial prefrontal cortex (mPFC) neurons projecting to VTA-DA neurons but does not on those from glutamatergic terminals of the lateral hypothalamus (LH) neurons projecting to VTA-DA neurons; 2) different response of glutamatergic neurons projecting to VTA-DA neurons from the mPFC or the LH to morphine is related to the expression of GABA_B receptors at terminals of these neurons; 3) inhibition of projection neurons from the mPFC to the VTA significantly reduces morphine-induced locomotor activity increase and conditioned place preference but inhibition of projection neurons from the LH to the VTA does not. These results suggest that morphine selectively promotes glutamate release of the glutamatergic input from mPFC onto VTA-DA neurons by removing the inhibition of the GABA_B receptors in this glutamatergic input from mPFC.

The physiological effects of caffeine on synaptic transmission and plasticity in the mouse hippocampus selectively depend on adenosine A1 and A2A receptors

Caffeine is the most consumed psychoactive drug worldwide and its intake in moderate amounts prevents neurodegenerative disorders. However, the molecular targets of caffeine to modulate activity in brain circuits are ill-defined. By electrophysiologically recording synaptic transmission and plasticity in Schaffer fibers-CA1 pyramid synapses of mouse hippocampal slices, we characterized the impact of caffeine using a concentration reached in the brain parenchyma upon moderate caffeine consumption. Caffeine (50 µM) facilitated synaptic transmission by 40%, while decreasing paired-pulse facilitation, and also decreased by 35% the amplitude of long-term potentiation (LTP). Clearance of extracellular adenosine with adenosine deaminase (2 U/mL) blunted all the effects of caffeine on synaptic transmission and plasticity. The A₁R antagonist DPCPX (100 nM) only eliminated caffeine-induced facilitation of synaptic transmission while not affecting caffeine-induced depression of LTP; conversely, the genetic (using A_2AR knockout mice) or the pharmacological blockade (with SCH58261, 50 nM) of A_2AR eliminated the effect of caffeine on LTP while not affecting caffeine-induced facilitation of synaptic transmission. Finally, blockade of GABA_A or of ryanodine receptors with bicuculline (10 μM) or dantrolene (10 μM), respectively, did not affect the ability of caffeine to alter synaptic transmission or plasticity. These results show that the effects of caffeine on synaptic transmission and plasticity in the hippocampus are selectively mediated by antagonizing adenosine receptors, where A₁R are responsible for the impact of caffeine on synaptic transmission and A_2AR regulate the impact of caffeine on LTP.

Intracellular Ca2+ Release and Synaptic Plasticity: A Tale of Many Stores

Ca2+ is an essential trigger for most forms of synaptic plasticity. Ca2+ signaling occurs not only by Ca2+ entry via plasma membrane channels but also via Ca2+ signals generated by intracellular organelles. These organelles, by dynamically regulating the spatial and temporal extent of Ca2+ elevations within neurons, play a pivotal role in determining the downstream consequences of neural signaling on synaptic function. Here, we review the role of three major intracellular stores: the endoplasmic reticulum, mitochondria, and acidic Ca2+ stores, such as lysosomes, in neuronal Ca2+ signaling and plasticity. We provide a comprehensive account of how Ca2+ release from these stores regulates short- and long-term plasticity at the pre- and postsynaptic terminals of central synapses.

Caffeine consumption disrupts hippocampal long-term potentiation in freely behaving rats

Caffeine, one of the most commonly consumed psychoactive substances in the world, has long been known to alter neurological functions, such as alertness, attention, and memory. Despite caffeine's popularity, systematic investigations of its effects on synaptic plasticity in the brain are still lacking. Here we used a freely behaving rodent model of long-term potentiation (LTP), a frequently studied form of synaptic plasticity, to assess the effects of caffeine consumption on hippocampal plasticity. LTP, which is a persistent increase in the strength of synaptic connections between neurons, is a cellular mechanism widely considered to underlie the processes of learning and memory. A group of 10-week-old Sprague-Dawley rats were administered caffeine (1 g/L) in their drinking water 3 weeks prior to collection of electrophysiological data. Another group of age-matched animals received tap water and served as controls. Stimulating and recording electrodes were chronically implanted in the perforant pathway (PP) and dentate gyrus (DG) region of the hippocampus, respectively, to permit stable electrophysiological recordings of synaptic transmission at this synapse. Population spike amplitude (PSA) measures of LTP induction and duration were acquired in vivo while animals were freely behaving using a well-established electrophysiological recording protocol. Results indicate caffeine-treated rats (n = 9) had a significantly (P < 0.05) reduced level of LTP induction compared with controls (n = 10). More studies are needed to identify the exact mechanism through which caffeine alters LTP induction in this freely behaving model of synaptic plasticity.

Effect of Chlorogenic Acids on Cognitive Function: A Randomized, Double-Blind, Placebo-Controlled Trial

(1) Background: Chlorogenic acids (CGAs) have been attracting interest of late, owing to their health benefits. Here, we performed a randomized, double-blind, placebo-controlled trial to investigate whether CGAs improved cognitive function in humans. (2) Methods: Thirty-eight healthy participants were assigned to either the CGA group, which was given CGA-added beverage daily for 16 weeks, or the placebo group. Cognitive functions were assessed using the Japanese version of the CNS Vital Signs (Cognitrax). (3) Results: The CGA group showed significant increase in the Cognitrax domain scores for motor speed, psychomotor speed, and executive function compared with the placebo group, as well as an improvement in the shifting attention test scores. In blood analysis, the CGA group showed increased levels of apolipoprotein A1 and transthyretin, both of which are putative biomarkers for early-stage cognitive decline. (4) Conclusions: These results suggest that CGAs may improve some cognitive functions, which would help in the efficient performance of complex tasks.

Effect of Chlorogenic Acid Intake on Cognitive Function in the Elderly: A Pilot Study

Objective

To evaluate the effect of chlorogenic acids (CGAs) intake on cognitive function.

Methods

In this pilot study, the Cogstate and CNS Vital Signs test batteries were used to evaluate cognitive function in 8 healthy elderly men and women complaining of subjective memory loss after a 6-month intake of a test beverage containing 330 mg of CGAs just before bedtime.

Results

After a 6-month CGA intake period, significant improvement was observed in the One Back Test of the Cogstate, the Shifting Attention Test, and Finger Tapping Test as well as in the composite memory, verbal memory, complex attention, cognitive flexibility, executive function, and motor speed domains of the CNS Vital Signs test battery.

Conclusion

A 6-month intake of CGAs may improve attentional, executive, and memory functions in the elderly with complaints of subjective memory loss.

Caffeine Controls Glutamatergic Synaptic Transmission and Pyramidal Neuron Excitability in Human Neocortex

Caffeine is the most widely used psychoactive drug, bolstering attention and normalizing mood and cognition, all functions involving cerebral cortical circuits. Whereas studies in rodents showed that caffeine acts through the antagonism of inhibitory A₁ adenosine receptors (A₁R), neither the role of A₁R nor the impact of caffeine on human cortical neurons is known. We here provide the first characterization of the impact of realistic concentrations of caffeine experienced by moderate coffee drinkers (50 μM) on excitability of pyramidal neurons and excitatory synaptic transmission in the human temporal cortex. Moderate concentrations of caffeine disinhibited several of the inhibitory A₁R-mediated effects of adenosine, similar to previous observations in the rodent brain. Thus, caffeine restored the adenosine-induced decrease of both intrinsic membrane excitability and excitatory synaptic transmission in the human pyramidal neurons through antagonism of post-synaptic A₁R. Indeed, the A₁R-mediated effects of endogenous adenosine were more efficient to inhibit synaptic transmission than neuronal excitability. This was associated with a distinct affinity of caffeine for synaptic versus extra-synaptic human cortical A₁R, probably resulting from a different molecular organization of A₁R in human cortical synapses. These findings constitute the first neurophysiological description of the impact of caffeine on pyramidal neuron excitability and excitatory synaptic transmission in the human temporal cortex, providing adequate ground for the effects of caffeine on cognition in humans.

Caffeine-mediated BDNF release regulates long-term synaptic plasticity through activation of IRS2 signaling

Caffeine has cognitive‐enhancing properties with effects on learning and memory, concentration, arousal and mood. These effects imply changes at circuital and synaptic level, but the mechanism by which caffeine modifies synaptic plasticity remains elusive. Here we report that caffeine, at concentrations representing moderate to high levels of consumption in humans, induces an NMDA receptor‐independent form of LTP (_CAFLTP) in the CA1 region of the hippocampus by promoting calcium‐dependent secretion of BDNF, which subsequently activates TrkB‐mediated signaling required for the expression of _CAFLTP. Our data include the novel observation that insulin receptor substrate 2 (IRS2) is phosphorylated during induction of _CAFLTP, a process that requires cytosolic free Ca²⁺. Consistent with the involvement of IRS2 signals in caffeine‐mediated synaptic plasticity, phosphorylation of Akt (Ser473) in response to LTP induction is defective in Irs2^−/− mice, demonstrating that these plasticity changes are associated with downstream targets of the phosphoinositide 3‐kinase (PI3K) pathway. These findings indicate that TrkB‐IRS2 signals are essential for activation of PI3K during the induction of LTP by caffeine.

Dexamethasone and levetiracetam reduce hetero-cellular gap-junctional coupling between F98 glioma cells and glial cells in vitro

Gap junctions (GJs) in astrocytes and glioma cells are important channels for cell-to-cell communication that contribute to homo- and heterocellular coupling. According to recent studies, heterocellular gap-junctional communication (H-GJC) between glioma cells and their surrounding environment enhances glioma progression. Therefore, we developed a new in vitro model to examine H-GJC between glioma cells, astrocytes and microglia. Consequently, F98 rat glioma cells were double-labeled with GJ-impermeable (CM-DiI) and GJ-permeable dye (calcein AM) and were seeded on unlabeled astrocyte-microglia co-cultures. Dual whole cell voltage clamp recordings were carried out on selected cell pairs to characterize the functional properties of H-GJC in vitro. The expression of four types of connexins (Cxs), including Cx32, Cx36, Cx43 and Cx45, and microglial phenotypes were analyzed by immunocytochemistry. The H-GJC between glioma cells and astrocytes/microglia increased after a longer incubation period with a higher number of glioma cells. We provided evidence for the direct GJ coupling of microglia and glioma cells under native in vitro conditions. In addition, we exploited this model to evaluate H-GJC after incubation with levetiracetam (LEV) and/or dexamethasone (DEX). Previous in vitro studies suggest that LEV and DEX are frequently used to control seizure and edema in glioma. Our findings showed that LEV and/or DEX decrease the number of heterocellular coupled cells significantly. In conclusion, our newly developed model demonstrated H-GJC between glioma cells and both astrocytes and microglia. The reduced H-GJC by LEV and DEX suggests a potential effect of both drugs on glioma progression.

Potentiation of Schaffer-Collateral CA1 Synaptic Transmission by eEF2K and p38 MAPK Mediated Mechanisms

The elongation factor 2 kinase (eEF2K), likewise known as CaMKIII, has been demonstrated to be involved in antidepressant responses of NMDA receptor antagonists. Even so, it remains open whether direct inhibition of eEF2K without altering up-stream or other signaling pathways affects hippocampal synaptic transmission and neuronal network synchrony. Inhibition of eEF2K by the selective and potent eEF2K inhibitor A-484954 induced a fast pre-synaptically mediated enhancement of synaptic transmission and synchronization of neural network activity. The eEF2K-inhibition mediated potentiation of synaptic transmission of hippocampal CA1 neurons is most notably independent of protein synthesis and does not rely on protein kinase C, protein kinase A or mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase 1/2. Moreover, the strengthening of synaptic transmission in the response to the inhibition of eEF2K was strongly attenuated by the inhibition of p38 MAPK. In addition, we show the involvement of barium-sensitive and more specific the TWIK-related potassium-1 (TREK-1) channels in the eEF2K-inhibition mediated potentiation of synaptic transmission. These findings reveal a novel pathway of eEF2K mediated regulation of hippocampal synaptic transmission. Further research is required to study whether such compounds could be beneficial for the development of mood disorder treatments with a fast-acting antidepressant response.

Multiple Sclerosis Patient-Specific Primary Neurons Differentiated from Urinary Renal Epithelial Cells via Induced Pluripotent Stem Cells

As multiple sclerosis research progresses, it is pertinent to continue to develop suitable paradigms to allow for ever more sophisticated investigations. Animal models of multiple sclerosis, despite their continuing contributions to the field, may not be the most prudent for every experiment. Indeed, such may be either insufficient to reflect the functional impact of human genetic variations or unsuitable for drug screenings. Thus, we have established a cell- and patient-specific paradigm to provide an in vitro model within which to perform future genetic investigations. Renal proximal tubule epithelial cells were isolated from multiple sclerosis patients’ urine and transfected with pluripotency-inducing episomal factors. Subsequent induced pluripotent stem cells were formed into embryoid bodies selective for ectodermal lineage, resulting in neural tube-like rosettes and eventually neural progenitor cells. Differentiation of these precursors into primary neurons was achieved through a regimen of neurotrophic and other factors. These patient-specific primary neurons displayed typical morphology and functionality, also staining positive for mature neuronal markers. The development of such a non-invasive procedure devoid of permanent genetic manipulation during the course of differentiation, in the context of multiple sclerosis, provides an avenue for studies with a greater cell- and human-specific focus, specifically in the context of genetic contributions to neurodegeneration and drug discovery.

Multiple Sources of Ca2+ Contribute to Methylmercury-Induced Increased Frequency of Spontaneous Inhibitory Synaptic Responses in Cerebellar Slices of Rat

We previously showed that elevated intracellular Ca(2+) ([Ca(2+)]i) in the molecular layer and granule cells in cerebellar slices is responsible for the initial increases in frequency of spontaneous or miniature inhibitory postsynaptic currents (sIPSCs or mIPSCs) of Purkinje cells following methylmercury (MeHg) treatment. To identify the contribution of different Ca(2+) sources to MeHg-induced stimulation of spontaneous GABA release, we examined sIPSC or mIPSC frequency of Purkinje cells in acutely prepared cerebellar slices using whole-cell patch-clamp recording techniques under conditions of lowered [Ca(2+)]o, pretreatment with caffeine, cyclopiazonic acid (CPA), thapsigargin or ruthenium red (RR) to deplete ryanodine-sensitive and insensitive intracellular Ca(2+) stores or mitochondria, or a combination of lowering [Ca(2+)]o and increased BAPTA buffering. Lowering [Ca(2+)]o significantly reduced sIPSC or mIPSC frequency and amplitudes, but failed to completely prevent MeHg-induced increase in these events frequency. Caffeine, CPA, or thapisgargin also minimized MeHg-induced increase in sIPSC frequency, yet none of them completely blocked MeHg-induced increase in sIPSC frequency. Similarly, the mitochondrial Ca(2+) transport inhibitor RR, or a combination of lowering [Ca(2+)]o and BAPTA buffering reduced but did not prevent MeHg-induced changes in mIPSC frequency. Consistently, confocal Ca(2+) imaging under low [Ca(2+)]o conditions or in the presence of caffeine or CPA exhibited a marked reduction of MeHg-induced increases in [Ca(2+)]i in both molecular and granule layers. Thus, these results verify that a combination of extracellular Ca(2+) influx and Ca(2+) release from different intracellular Ca(2+) pools all contribute to MeHg-induced increase in [Ca(2+)]i and spontaneous GABA release, although extracellular Ca(2+) appears to be the primary contributor.

Reprint of "Caffeine protects against memory loss induced by high and non-anxiolytic dose of cannabidiol in adult zebrafish (Danio rerio)"

Cannabidiol (CBD) has been investigated in a wide spectrum of clinical approaches due to its psychopharmacological properties. CBD has low affinity for cannabinoid neuroreceptors and agonistic properties to 5-HT receptors. An interaction between cannabinoid and purinergic receptor systems has been proposed. The purpose of this study is to evaluate CBD properties on memory behavioral and locomotor parameters and the effects of pre-treatment of adenosine receptor blockers on CBD impacts on memory using adult zebrafish. CBD (0.1, 0.5, 5, and 10mg/kg) was tested in the avoidance inhibitory paradigm and anxiety task. We analyzed the effect of a long-term caffeine pre-treatment (~20mg/L - four months). Also, acute block of adenosine receptors was performed in co-administration with CBD exposure in the memory assessment. CBD promoted an inverted U-shaped dose-response curve in the anxiety task; in the memory assessment, CBD in the dose of 5mg/Kg promoted the strongest effects without interfering with social and aggressive behavior. Caffeine treatment was able to prevent CBD (5mg/kg) effects on memory when CBD was given after the training session. CBD effects on memory were partially prevented by co-treatment with a specific A2A adenosine receptor antagonist when given prior to or after the training session, while CBD effects after the training session were fully prevented by adenosine A1 receptor antagonist. These results indicated that zebrafish have responses to CBD anxiolytic properties that are comparable to other animal models, and high doses changed memory retention in a way dependent on adenosine.

Roles of Calcium Stores and Store-Operated Channels in Plasticity of Dendritic Spines

Calcium stores in the endoplasmic reticulum play important roles in a variety of mammalian cellular functions. However, the multitude of calcium-handling machineries in neurons, including voltage- and ligand-gated channels, calcium-binding proteins, pumps, and transporters, as well as the rapid mobility of calcium ions among different cellular compartments hampered the singling out of calcium stores as a pivotal player in synaptic plasticity. Despite these methodological obstacles, novel molecular and imaging tools afforded a rapid progress in deciphering the role of specific calcium stores in neuronal functions. In the present review, we will address several key issues related to the involvement of ryanodine receptors and the calcium entry channel Orai1 in dendritic spine development and plasticity as well as their derailing in neurodegenerative diseases.

Ryanodine-mediated conversion of STP to LTP is lacking in synaptopodin-deficient mice

In previous studies we and others have found that activation of ryanodine receptors (RyRs) facilitate expression of long-term potentiation (LTP) of reactivity to afferent stimulation in hippocampal slices, with a more pronounced action in the ventral hippocampus. We have also been able to link the involvement of synaptopodin (SP), an actin-binding protein, with neuronal plasticity via its interaction with RyRs. To test this link more directly, we have now compared the ability of ryanodine to convert short-term to LTP in hippocampal slices taken from normal and SP-knockout (SPKO) mice. Indeed, SPKO hippocampus expresses lower concentrations of RyRs and in slices of these mice ryanodine is unable to facilitate conversion of short-term to LTP. These observations link functionally SP with calcium stores.

Decrease of neocortical paired-pulse depression in GAERS and possible implication of gap junctions

Thalamocortical slices are widely used to study thalamocortical relationships and absence epilepsy. However, it is still not known whether (1) intracortical synaptic transmission, in particular neocortical paired-pulse depression (PPD), is maintained in these slices and (2) whether PPD is altered in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS, a model of absence epilepsy for which cortico-thalamic loops are involved). Furthermore, while the involvement of gap junctions (GJ) in the mechanisms leading to epileptiform discharges has been intensively studied, little is known about their effect on intracortical transmission. We first studied intracortical connection efficacy and PPD in thalamocortical slices from GAERS and non-epileptic rats (NER). We then investigated the effects of GJ blockers (carbenoxolone and quinidine) on intracortical response following single or paired-pulse stimulations in coronal slices from Wistar rats. We show that the efficacy of intracortical connections is not impaired in GAERS. We also show that neocortical PPD is preserved in thalamocortical slices of NER, but that its efficacy is strongly decreased in GAERS. Moreover, a NMDA antagonist strongly reduced the PPD in NER but had no effect in GAERS. Cortical responses to white matter stimulation were not modified by quinidine or carbenoxolone in coronal slices of Wistar rats. PPD was recorded in these slices and was decreased by carbenoxolone but not by quinidine. We hypothesize that the decrease of PPD observed in GAERS might be due to a decrease in function of (1) NMDA receptors and/or (2) astrocytic GJ's.

Contribution of Ca2+ release channels to hippocampal synaptic plasticity and spatial memory: potential redox modulation

SIGNIFICANCE

Memory is an essential human cognitive function. Consequently, to unravel the cellular and molecular mechanisms responsible for the synaptic plasticity events underlying memory formation, storage and loss represents a major challenge of present-day neuroscience.

RECENT ADVANCES

This review article first describes the wide-ranging functions played by intracellular Ca2+ signals in the activity-dependent synaptic plasticity processes underlying hippocampal spatial memory, and next, it focuses on how the endoplasmic reticulum Ca2+ release channels, the ryanodine receptors, and the inositol 1,4,5-trisphosphate receptors contribute to these processes. We present a detailed examination of recent evidence supporting the key role played by Ca2+ release channels in synaptic plasticity, including structural plasticity, and the formation/consolidation of spatial memory in the hippocampus.

CRITICAL ISSUES

Changes in cellular oxidative state particularly affect the function of Ca2+ release channels and alter hippocampal synaptic plasticity and the associated memory processes. Emphasis is placed in this review on how defective Ca2+ release, presumably due to increased levels of reactive oxygen species, may cause the hippocampal functional defects that are associated to aging and Alzheimer's disease (AD).

FUTURE DIRECTIONS

Additional studies should examine the precise molecular mechanisms by which Ca2+ release channels contribute to hippocampal synaptic plasticity and spatial memory formation/consolidation. Future studies should test whether redox-modified Ca2+ release channels contribute toward generating the intracellular Ca2+ signals required for sustained synaptic plasticity and hippocampal spatial memory, and whether loss of redox balance and oxidative stress, by altering Ca2+ release channel function, presumably contribute to the abnormal memory processes that occur during aging and AD.

Endoplasmic reticulum calcium stores in dendritic spines

Despite decades of research, the role of calcium stores in dendritic spines structure, function and plasticity is still debated. The reasons for this may have to do with the multitude of overlapping calcium handling machineries in the neuron, including stores, voltage and ligand gated channels, pumps and transporters. Also, different cells in the brain are endowed with calcium stores that are activated by different receptor types, and their differential compartmentalization in dendrites, spines and presynaptic terminals complicates their analysis. In the present review we address several key issues, including the role of calcium stores in synaptic plasticity, their role during development, in stress and in neurodegenerative diseases. Apparently, there is increasing evidence for a crucial role of calcium stores, especially of the ryanodine species, in synaptic plasticity and neuronal survival.

Reversible neuronal and muscular toxicity of caffeine in developing vertebrates

This study utilizes zebrafish embryos to understand the cellular and molecular mechanisms of caffeine toxicity in developing vertebrate embryos. By using a high concentration of caffeine, we observed almost all the phenotypes that have been described in humans and/or in other animal models, including neural tube closure defect, jittery, touch insensitivity, and growth retardation as well as a drastic coiled body phenotype. Zebrafish embryos exposed to 5mM caffeine exhibited high frequent movement, 10 moves/min comparing with around 3 moves/min in control embryos, within half an hour post exposure (HPE). They later showed twitching, uncoordinated movement, and eventually severe body curvature by 6HPE. Exposure at later stages resulted in the same phenotypes but more posteriorly. Surprisingly, when caffeine was removed before 6HPE, the embryos were capable of recovering but still exhibited mild curvature and shorter bodies. Longer exposure caused irreversible body curvature and lethality. These results suggest that caffeine likely targets the neuro-muscular physiology in developing embryos. Immunohistochemistry revealed that the motorneurons in treated embryos developed shorter axons, abnormal branching, and excessive synaptic vesicles. Developing skeletal muscles also appeared smaller and lacked the well-defined boundaries seen in control embryos. Finally, caffeine increases the expression of genes involved in synaptic vesicle migration. In summary, our results provide molecular understanding of caffeine toxicity on developing vertebrate embryos.

Dendritic calcium nonlinearities switch the direction of synaptic plasticity in fast-spiking interneurons

Postsynaptic calcium (Ca2+) nonlinearities allow neuronal coincidence detection and site-specific plasticity. Whether such events exist in dendrites of interneurons and play a role in regulation of synaptic efficacy remains unknown. Here, we used a combination of whole-cell patch-clamp recordings and two-photon Ca2+ imaging to reveal Ca2+ nonlinearities associated with synaptic integration in dendrites of mouse hippocampal CA1 fast-spiking interneurons. Local stimulation of distal dendritic branches within stratum oriens/alveus elicited fast Ca2+ transients, which showed a steep sigmoidal relationship to stimulus intensity. Supralinear Ca2+ events required Ca2+ entry through AMPA receptors with a subsequent Ca2+ release from internal stores. To investigate the functional significance of supralinear Ca2+ signals, we examined activity-dependent fluctuations in transmission efficacy triggered by Ca2+ signals of different amplitudes at excitatory synapses of interneurons. Subthreshold theta-burst stimulation (TBS) produced small amplitude postsynaptic Ca2+ transients and triggered long-term potentiation. In contrast, the suprathreshold TBS, which was associated with the generation of supralinear Ca2+ events, triggered long-term depression. Blocking group I/II metabotropic glutamate receptors (mGluRs) during suprathreshold TBS resulted in a slight reduction of supralinear Ca2+ events and induction of short-term depression. In contrast, blocking internal stores and supralinear Ca2+ signals during suprathreshold TBS switched the direction of plasticity from depression back to potentiation. These data reveal a novel type of supralinear Ca2+ events at synapses lacking the GluA2 AMPA subtype of glutamate receptors and demonstrate a general mechanism by which Ca2+ -permeable AMPA receptors, together with internal stores and mGluRs, control the direction of plasticity at interneuron excitatory synapses.

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.

Presenilins regulate calcium homeostasis and presynaptic function via ryanodine receptors in hippocampal neurons

Presenilin (PS) plays a central role in the pathogenesis of Alzheimer's disease, and loss of PS causes progressive memory impairment and age-related neurodegeneration in the mouse cerebral cortex. In hippocampal neurons, PS is essential for neurotransmitter release, NMDA receptor-mediated responses, and long-term potentiation. PS is also involved in the regulation of calcium homeostasis, although the precise site of its action is less clear. Here we investigate the mechanism by which PS regulates synaptic function and calcium homeostasis using acute hippocampal slices from PS conditional knockout mice and primary cultured postnatal hippocampal neurons, in which PS is inducibly inactivated. Using two different calcium probes, Fura-2 and Mag-Fura-2, we found that inactivation of PS in primary hippocampal neurons does not affect calcium concentration in the endoplasmic reticulum. Rather, in the absence of PS, levels of ryanodine receptor (RyR) are reduced in the hippocampus, measured by Western analysis and radioligand binding assay, although the mRNA expression is unaffected. RyR-mediated function is also impaired, as indicated by reduced RyR agonist-induced calcium release from the ER and RyR-mediated synaptic responses in the absence of PS. Furthermore, knockdown of RyR expression in wild-type hippocampal neurons by two independent shRNAs to levels comparable with the RyR protein reduction in PS-deficient hippocampal neurons mimics the defects exhibited in calcium homeostasis and presynaptic function. Collectively, our findings show that PS regulates calcium homeostasis and synaptic function via RyR and suggest that disruption of intracellular calcium homeostasis may be an early pathogenic event leading to presynaptic dysfunction in Alzheimer's disease.

Dopamine release regulation by astrocytes during cerebral ischemia

Brain ischemia triggers excessive release of neurotransmitters that mediate neuronal damage following ischemic injury. The striatum is one of the areas most sensitive to ischemia. Release of dopamine (DA) from ischemic neurons is neurotoxic and directly contributes to the cell death in affected areas. Astrocytes are known to be critically involved in the physiopathology of cerebrovascular disease. However, their response to ischemia and their role in neuroprotection in striatum are not completely understood. In this study, we used an in vitro model to evaluate the mechanisms of ischemia-induced DA release, and to study whether astrocytes modulate the release of DA in response to short-term ischemic conditions. Using slices of adult mouse brain exposed to oxygen and glucose deprivation (OGD), we measured the OGD-evoked DA efflux using fast cyclic voltammetry and also assessed metabolic impairment by 2,3,5-triphenyltetrazolium chloride (TTC) and tissue viability by propidium iodide (PI) staining. Our data indicate that ischemia induces massive release of DA by dual mechanisms: one which operates via vesicular exocytosis and is action potential dependent and another involving reverse transport by the dopamine transporter (DAT). Simultaneous blockade of astrocyte glutamate transporters and DAT prevented the massive release of dopamine and reduced the brain tissue damage. The present results provide the first experimental evidence that astrocytes function as a key cellular element of ischemia-induced DA release in striatum, constituting a novel and promising therapeutic target in ischemia.

Normalization of Dyrk1A expression by AAV2/1-shDyrk1A attenuates hippocampal-dependent defects in the Ts65Dn mouse model of Down syndrome

The cognitive dysfunctions of Down Syndrome (DS) individuals are the most disabling alterations caused by the trisomy of human chromosome 21 (HSA21). In trisomic Ts65Dn mice, a genetic model for DS, the overexpression of HSA21 homologous genes has been associated with strong visuo-spatial cognitive alterations, ascribed to hippocampal dysfunction. In the present study, we evaluated whether the normalization of the expression levels of Dyrk1A (Dual specificity tyrosine-phosphorylation-regulated kinase 1A), a candidate gene for DS, might correct hippocampal defects in Ts65Dn mice. In the hippocampus of 2 month-old Ts65Dn mice, such normalization was achieved through the stereotaxical injection of adeno-associated viruses containing a short hairpin RNA against Dyrk1A (AAV2/1-shDyrk1A) and a luciferase reporter gene. The injected hippocampi were efficiently transduced, as shown by bioluminescence in vivo imaging, luciferase activity quantification and immunohistochemical analysis. At the molecular level, viral infusion allowed the normalization of the targeted Dyrk1A expression, as well as of the key players of the MAPK/CREB pathway. The electrophysiological recordings of hippocampal slices from Ts65Dn mice injected with AAV2/1-shDyrk1A displayed attenuation of the synaptic plasticity defects of trisomic mice. In contrast, contralateral hippocampal injection with an AAV2/1 control virus containing a scrambled sequence, showed neither the normalization of Dyrk1A levels nor changes of synaptic plasticity. In the Morris water maze task, although long-term consolidation of the task was not achieved, treated Ts65Dn mice displayed initially a normalized thigmotactic behavior, similar to euploid littermates, indicating the partial improvement in their hippocampal-dependent search strategy. Taken together, these results show Dyrk1A as a critical player in the pathophysiology of DS and define Dyrk1A as a therapeutic target in adult trisomic mice.

Direct association of the reticulon protein RTN1A with the ryanodine receptor 2 in neurons

RTN1A is a reticulon protein with predominant localization in the endoplasmic reticulum (ER). It was previously shown that RTN1A is expressed in neurons of the mammalian central nervous system but functional information remains sparse. To elucidate the neuronal function of RTN1A, we chose to focus our investigation on identifying possible novel binding partners specifically interacting with the unique N-terminus of RTN1A. Using a nonbiased approach involving GST pull-downs and MS analysis, we identified the intracellular calcium release channel ryanodine receptor 2 (RyR2) as a direct binding partner of RTN1A. The RyR2 binding site was localized to a highly conserved 150-amino acid residue region. RTN1A displays high preference for RyR2 binding in vitro and in vivo and both proteins colocalize in hippocampal neurons and Purkinje cells. Moreover, we demonstrate the precise subcellular localization of RTN1A in Purkinje cells and show that RTN1A inhibits RyR channels in [(3)H]ryanodine binding studies on brain synaptosomes. In a functional assay, RTN1A significantly reduced RyR2-mediated Ca(2+) oscillations. Thus, RTN1A and RyR2 might act as functional partners in the regulation of cytosolic Ca(2+) dynamics the in neurons.

Entorhinal theta-frequency input to the dentate gyrus trisynaptically evokes hippocampal CA1 LTP

There exists substantial evidence that some forms of explicit learning in mammals require long-term potentiation (LTP) at hippocampal CA3-CA1 synapses. While CA1 LTP has been well characterized at the monosynaptic level, it still remains unclear how the afferent systems to the hippocampus can initiate formation of this neuroplastic phenomenon. Using voltage-sensitive dye imaging (VSDI) in a mouse brain slice preparation, we show that evoked entorhinal cortical (EC) theta-frequency input to the dentate gyrus highly effectively generates waves of neuronal activity which propagate through the entire trisynaptic circuit of the hippocampus (“HTC-Waves”). This flow of activity, which we also demonstrate in vivo, critically depends on frequency facilitation of mossy fiber to CA3 synaptic transmission. The HTC-Waves are rapidly boosted by the cognitive enhancer caffeine (5 μM) and the stress hormone corticosterone (100 nM). They precisely follow the rhythm of the EC input, involve high-frequency firing (>100 Hz) of CA3 pyramidal neurons, and induce NMDA receptor-dependent CA1 LTP within a few seconds. Our study provides the first experimental evidence that synchronous theta-rhythmical spiking of EC stellate cells, as occurring during EC theta oscillations, has the capacity to drive induction of CA1 LTP via the hippocampal trisynaptic pathway. Moreover, we present data pointing to a basic filter mechanism of the hippocampus regarding EC inputs and describe a methodology to reveal alterations in the “input–output relationship” of the hippocampal trisynaptic circuit.

LIM domain only 4 (LMO4) regulates calcium-induced calcium release and synaptic plasticity in the hippocampus

The LIM domain only 4 (LMO4) transcription cofactor activates gene expression in neurons and regulates key aspects of network formation, but the mechanisms are poorly understood. Here, we show that LMO4 positively regulates ryanodine receptor type 2 (RyR2) expression, thereby suggesting that LMO4 regulates calcium-induced calcium release (CICR) in central neurons. We found that CICR modulation of the afterhyperpolarization in CA3 neurons from mice carrying a forebrain-specific deletion of LMO4 (LMO4 KO) was severely compromised but could be restored by single-cell overexpression of LMO4. In line with these findings, two-photon calcium imaging experiments showed that the potentiation of RyR-mediated calcium release from internal stores by caffeine was absent in LMO4 KO neurons. The overall facilitatory effect of CICR on glutamate release induced during trains of action potentials was likewise defective in LMO4 KO, confirming that CICR machinery is severely compromised in these neurons. Moreover, the magnitude of CA3-CA1 long-term potentiation was reduced in LMO4 KO mice, a defect that appears to be secondary to an overall reduced glutamate release probability. These cellular phenotypes in LMO4 KO mice were accompanied with deficits in hippocampus-dependent spatial learning as determined by the Morris water maze test. Thus, our results establish LMO4 as a key regulator of CICR in central neurons, providing a mechanism for LMO4 to modulate a wide range of neuronal functions and behavior.

Selective facilitation of LTP in the ventral hippocampus by calcium stores

The effects of low concentrations of caffeine and ryanodine on field excitatory postsynaptic potentials (EPSPs) and long-term potentiation (LTP) were studied in CA1 region of slices of dorsal and ventral hippocampus (DH and VH, respectively). There was a striking difference between the two regions in the magnitude of effect of both drugs, as well as the ability to interact with a tetanic stimulation to produce LTP. Low concentration of caffeine (1 mM) produced a postsynaptic increase in the slope of population EPSPs in VH, and facilitated LTP in this region. Low concentration of ryanodine (0.2 μM) was able to convert short-term potentiation (STP) to LTP in VH only. These effects are postsynaptic and they reflect a higher concentration of ryanodine receptors (RyRs) in the VH compared to the DH.

Overexpression of Reelin prevents the manifestation of behavioral phenotypes related to schizophrenia and bipolar disorder

Despite the impact of schizophrenia and mood disorders, which in extreme cases can lead to death, recent decades have brought little progress in the development of new treatments. Recent studies have shown that Reelin, an extracellular protein that is critical for neuronal development, is reduced in schizophrenia and bipolar disorder patients. However, data on a causal or protective role of Reelin in psychiatric diseases is scarce. In order to study the direct influence of Reelin's levels on behavior, we subjected two mouse lines, in which Reelin levels are either reduced (Reelin heterozygous mice) or increased (Reelin overexpressing mice), to a battery of behavioral tests: open-field, black-white box, novelty-suppressed-feeding, forced-swim-test, chronic corticosterone treatment followed by forced-swim-test, cocaine sensitization and pre-pulse inhibition (PPI) deficits induced by N-methyl-D-aspartate (NMDA) antagonists. These tests were designed to model some aspects of psychiatric disorders such as schizophrenia, mood, and anxiety disorders. We found no differences between Reeler heterozygous mice and their wild-type littermates. However, Reelin overexpression in the mouse forebrain reduced the time spent floating in the forced-swim-test in mice subjected to chronic corticosterone treatment, reduced behavioral sensitization to cocaine, and reduced PPI deficits induced by a NMDA antagonist. In addition, we demonstrate that while stress increased NMDA NR2B-mediated synaptic transmission, known to be implicated in depression, Reelin overexpression significantly reduced it. Together, these results point to the Reelin signaling pathway as a relevant drug target for the treatment of a range of psychiatric disorders.

IRS-2 Deficiency impairs NMDA receptor-dependent long-term potentiation

The beneficial effects of insulin and insulin-like growth factor I on cognition have been documented in humans and animal models. Conversely, obesity, hyperinsulinemia, and diabetes increase the risk for neurodegenerative disorders including Alzheimer's disease (AD). However, the mechanisms by which insulin regulates synaptic plasticity are not well understood. Here, we report that complete disruption of insulin receptor substrate 2 (Irs2) in mice impairs long-term potentiation (LTP) of synaptic transmission in the hippocampus. Basal synaptic transmission and paired-pulse facilitation were similar between the 2 groups of mice. Induction of LTP by high-frequency conditioning tetanus did not activate postsynaptic N-methyl-D-aspartate (NMDA) receptors in hippocampus slices from Irs2(-/-) mice, although the expression of NR2A, NR2B, and PSD95 was equivalent to wild-type controls. Activation of Fyn, AKT, and MAPK in response to tetanus stimulation was defective in Irs2(-/-) mice. Interestingly, IRS2 was phosphorylated during induction of LTP in control mice, revealing a potential new component of the signaling machinery which modulates synaptic plasticity. Given that IRS2 expression is diminished in Type 2 diabetics as well as in AD patients, these data may reveal an explanation for the prevalence of cognitive decline in humans with metabolic disorders by providing a mechanistic link between insulin resistance and impaired synaptic transmission.

Unified patch clamp protocol for the characterization of Pannexin 1 channels in isolated cells and acute brain slices

In the central nervous system, Pannexin 1 (Panx1) channels are implicated in a variety of physiological and pathological conditions. One of the prerequisites to enlighten the role of Panx1 is the development and standardization of reliable methods. Here, we address the applicability of voltage clamp protocols to identify Panx1 channel mediated currents in neurons of acutely dissected brain slices. We improved an established protocol and report on a modified paradigm that robustly evokes Panx1 channel currents. Crucial advances are the use of physiologic ion gradient conditions and a preconditioning step of depolarizing membrane potential ramps of long duration. This new paradigm provides significant impact on membrane current generation at hypo- and depolarized holding potential steps post voltage ramp preconditioning in heterologous expression systems and primary hippocampal CA1 neurons of mouse brain slices in vitro. Finally, we demonstrate that under these conditions the analysis of tail currents elicited by repolarization of the cells from preconditioning holding potential depolarization permits an independent method to isolate Panx1 mediated channel activity. In summary, this study provides a comprehensive methodological improvement in the biophysical analysis of Panx1 channels with a particular focus on investigations under physiological conditions in complex tissues.

Sleep deprivation prevents stimulation-induced increases of levels of P-CREB and BDNF: protection by caffeine

It is well known that caffeine and sleep deprivation have opposing effects on learning and memory; therefore, this study was undertaken to determine the effects of chronic (4wks) caffeine treatment (0.3g/l in drinking water) on long-term memory deficit associated with 24h sleep deprivation. Animals were sleep deprived using the modified multiple platform method. The results showed that chronic caffeine treatment prevented the impairment of long-term memory as measured by performance in the radial arm water maze task and normalized L-LTP in area CA1 of the hippocampi of sleep-deprived anesthetized rats. Sleep deprivation prevents the high frequency stimulation-induced increases in the levels of phosphorylated-cAMP response element binding protein (P-CREB) and brain-derived neurotrophic factor (BDNF) seen during the expression of late phase long-term potentiation (L-LTP). However, chronic caffeine treatment prevented the effect of sleep-deprivation on the stimulated levels of P-CREB and BDNF. The results suggest that chronic caffeine treatment may protect the sleep-deprived brain probably by preserving the levels of P-CREB and BDNF.

Developmental changes in presynaptic Ca(2 +) clearance kinetics and synaptic plasticity in mouse Schaffer collateral terminals

Presynaptic Ca(2+) influx pathways, cytoplasmic Ca(2+) buffering proteins and Ca(2+) extrusion processes undergo considerable change during the first postnatal month in rodent neurons. These changes may be critical in establishing short-term plasticity at maturing presynaptic terminals where neurotransmitter release is directly dependent on the dynamics of cytoplasmic residual Ca(2+) ([Ca(2+)](res)). In particular, the robust paired-pulse facilitation characteristic of adult neurons is almost entirely lacking in newborns. To examine developmental changes in processes controlling [Ca(2+)](res), we measured the timecourse of [Ca(2+)](res) decay in presynaptic terminals of Schaffer collateral to CA1 synapses in acute hippocampal slices following single and paired orthodromic stimuli in the stratum radiatum. Developmental changes were observed in both the rise time and slow exponential decay components of the response to single stimuli such that this decay was larger and faster in the adult. Furthermore, we observed a greater caffeine-sensitive basal Ca(2+) store, which was differentially affected when active uptake into the endoplasmic reticulum was blocked, in the presynaptic fields of the Schaffer collateral to CA1 terminals of P6 and younger mice when compared to adults. These transitions in [Ca(2+)](res) dynamics occurred gradually over the first weeks of postnatal life and correlated with changes in short-term plasticity.

The potential of caffeine for functional modification from cortical synapses to neuron networks in the brain

Structure and function of the brain are use-dependent variables based on "synapse plasticity". Since synapses are driven by chemical transmitters, synaptic functions are liable to be modified by extrinsic chemicals displaying affinities for synaptic receptors or modulators. Caffeine is a widely used chemical substance that can invade synapses, and has several biochemical and metabolic actions on synaptic activities. This review focuses on the actions of caffeine on changes in structure and function in the region of the hippocampal formation and neocortex, which exhibit high synapse plasticity. At the synapse level, various synaptic receptors and channel activities are modulated by caffeine via mobilization of intracellular calcium, inhibition of phosphodiesterase, antagonism of adenosine receptors and GABA receptors. These actions of caffeine enable neurons to induce plastic changes in the properties of synaptic activities, such as synaptic transmission efficiency and morphology. At the network level, caffeine has the ability to activate cortical neural oscillators that deliver repetitive N-methyl-D-aspartate receptor-dependent signals to surrounding areas, causing strengthening of long-range inter-cortical communications. Caffeine might thus allow reorganization of cortical network functions via synaptic mobilizations.

The Spine Apparatus, Synaptopodin, and Dendritic Spine Plasticity

The spine apparatus (SA) is an essential component of mature dendritic spines of cortical and hippocampal neurons, yet its functions are still enigmatic. Synaptopodin (SP), an actin-binding protein, colocalizes with the SA. Hippocampal neurons in SP-knockout mice lack SA, and they express lower LTP. SP probably plays a role in synaptic plasticity, but only recently it is being linked mechanistically to synaptic functions. These authors and others have studied endogenous and transfected SP in dendritic spines of cultured hippocampal neurons. They found that spines containing SP generate twice as large responses to flash photolysis of caged glutamate than SP-negative ones. An N-methyl-d-aspartate receptor—mediated chemical LTP caused accumulation of GFP-GluR1 in spine heads of control but not of shRNA transfected, SP-deficient neurons. SP is linked to calcium stores, because their pharmacological blockade eliminated SP-related enhancement of glutamate responses. Furthermore, release of calcium from stores produces an SP-dependent delivery of GluR1 into spines. Thus, SP plays a crucial role in the calcium store-associated ability of neurons to undergo long-term plasticity.

Contributions of SERCA pump and ryanodine-sensitive stores to presynaptic residual Ca2+

The presynaptic Ca2+ signal, which triggers vesicle release, disperses to a broadly distributed residual [Ca2+] ([Ca2+](res)) that plays an important role in synaptic plasticity. We have previously reported a slowing in the decay timecourse of [Ca2+](res) during the second of paired pulses. In this study, we investigated the contributions of organelle and plasma membrane Ca2+ flux pathways to the reduction of effectiveness of [Ca2+](res) clearance during short-term plasticity in Schaffer collateral terminals in the CA1 field of the hippocampus. We show that the slowed decay timecourse is mainly the result of a transport-dependent Ca2+ clearance process; that presynaptic caffeine-sensitive Ca2+ stores are not functionally loaded in the unstimulated terminal, but that these stores can effectively take up Ca2+ even during high frequency trains of stimuli; and that a rate limiting step of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) kinetics following the first pulse is responsible for a large portion of the observed slowing of [Ca2+](res) clearance during the second pulse. We were able to accurately fit our [Ca2+](res) data with a kinetic model based on these observations and this model predicted a reduction in availability of unbound SERCA during paired pulses, but no saturation of Ca2+ buffer in the endoplasmic reticulum.

Ryanodine receptors contribute to the induction of nociceptive input-evoked long-term potentiation in the rat spinal cord slice

Background

Our previous study demonstrated that nitric oxide (NO) contributes to long-term potentiation (LTP) of C-fiber-evoked field potentials by tetanic stimulation of the sciatic nerve in the spinal cord in vivo. Ryanodine receptor (RyR) is a downstream target for NO. The present study further explored the role of RyR in synaptic plasticity of the spinal pain pathway.

Results

By means of field potential recordings in the adult male rat in vivo, we showed that RyR antagonist reduced LTP of C-fiber-evoked responses in the spinal dorsal horn by tetanic stimulation of the sciatic nerve. Using spinal cord slice preparations and field potential recordings from superficial dorsal horn, high frequency stimulation of Lissauer's tract (LT) stably induced LTP of field excitatory postsynaptic potentials (fEPSPs). Perfusion of RyR antagonists blocked the induction of LT stimulation-evoked spinal LTP, while Ins(1,4,5)P3 receptor (IP₃R) antagonist had no significant effect on LTP induction. Moreover, activation of RyRs by caffeine without high frequency stimulation induced a long-term potentiation in the presence of bicuculline methiodide and strychnine. Further, in patch-clamp recordings from superficial dorsal horn neurons, activation of RyRs resulted in a large increase in the frequency of miniature EPSCs (mEPSCs). Immunohistochemical study showed that RyRs were expressed in the dorsal root ganglion (DRG) neurons. Likewise, calcium imaging in small DRG neurons illustrated that activation of RyRs elevated [Ca²⁺]_i in small DRG neurons.

Conclusions

These data indicate that activation of presynaptic RyRs play a crucial role in the induction of LTP in the spinal pain pathway, probably through enhancement of transmitter release.

Application of caffeine reveals input frequency-dependent determination of signal-traveling routes between primary and secondary visual cortices in rats

Upon entering the neocortex, neural signals are required to select which neocortical circuits to propagate through. The present study focused attention on use-dependent selection of signal-traveling routes. Rat brain slices including primary visual cortex (Oc1) and the medial part of the secondary visual cortex (Oc2M) were prepared. Electrical stimulation was delivered to white matter in Oc1 and spatiotemporal aspects of traveling signals were observed using optical recording methods under caffeine application. With an interstimulus interval (ISI) of 4-8s, signals traveled horizontally along deep layers from Oc1 to Oc2M, climbed within Oc2M, then returned along layer II/III from Oc2M to Oc1. Conversely, with an ISI of 40-64s, signals climbed within Oc1 and traveled horizontally along layer II/III from Oc1 to Oc2M in parallel with signals traveling along deep layers. Pharmacological experiments with antagonists for ionotropic glutamate receptors revealed that signal-traveling routes under higher-frequency stimulation were N-methyl-d-aspartate (NMDA) receptor activity-dependent, while those at the lower-frequency were non-NMDA receptor activity-dependent. These results suggest that neural circuits between Oc1 and Oc2M possess an input frequency-dependent gating system, in which signal-traveling routes might be affected by the relative balance of receptor activities between NMDA and non-NMDA receptors.