Decrease In Synaptic Transmission Research Articles

Inhibition of astroglial hemichannels prevents synaptic transmission decline during spreading depression

BackgroundSpreading depression (SD) is an intriguing phenomenon characterized by massive slow brain depolarizations that affect neurons and glial cells. This phenomenon is repetitive and produces a metabolic overload that increases secondary damage. However, the mechanisms associated with the initiation and propagation of SD are unknown. Multiple lines of evidence indicate that persistent and uncontrolled opening of hemichannels could participate in the pathogenesis and progression of several neurological disorders including acute brain injuries. Here, we explored the contribution of astroglial hemichannels composed of connexin-43 (Cx43) or pannexin-1 (Panx1) to SD evoked by high-K+ stimulation in brain slices.ResultsFocal high-K+ stimulation rapidly evoked a wave of SD linked to increased activity of the Cx43 and Panx1 hemichannels in the brain cortex, as measured by light transmittance and dye uptake analysis, respectively. The activation of these channels occurs mainly in astrocytes but also in neurons. More importantly, the inhibition of both the Cx43 and Panx1 hemichannels completely prevented high K+-induced SD in the brain cortex. Electrophysiological recordings also revealed that Cx43 and Panx1 hemichannels critically contribute to the SD-induced decrease in synaptic transmission in the brain cortex and hippocampus.ConclusionsTargeting Cx43 and Panx1 hemichannels could serve as a new therapeutic strategy to prevent the initiation and propagation of SD in several acute brain injuries.

Homeostatic Regulation of Motoneuron Properties in Development.

Homeostatic plasticity represents a set of compensatory mechanisms that are engaged following a perturbation to some feature of neuronal or network function. Homeostatic mechanisms are most robustly expressed during development, a period that is replete with various perturbations such as increased cell size and the addition/removal of synaptic connections. In this review we look at numerous studies that have advanced our understanding of homeostatic plasticity by taking advantage of the accessibility of developing motoneurons. We discuss the homeostatic regulation of embryonic movements in the living chick embryo and describe the spinal compensatory mechanisms that act to recover these movements (homeostatic intrinsic plasticity) or stabilize synaptic strength (synaptic scaling). We describe the expression and triggering mechanisms of these forms of homeostatic plasticity and thereby gain an understanding of their roles in the motor system. We then illustrate how these findings can be extended to studies of developing motoneurons in other systems including the rodents, zebrafish, and fly. Furthermore, studies in developing drosophila have been critical in identifying some of the molecular signaling cascades and expression mechanisms that underlie homeostatic intrinsic membrane excitability. This powerful model organism has also been used to study a presynaptic form of homeostatic plasticity where increases or decreases in synaptic transmission are associated with compensatory changes in probability of release at the neuromuscular junction. Further, we describe studies that demonstrate homeostatic adjustments of ion channel expression following perturbations to other kinds of ion channels. Finally, we discuss work in xenopus that shows a homeostatic regulation of neurotransmitter phenotype in developing motoneurons following activity perturbations. Together, this work illustrates the importance of developing motoneurons in elucidating the mechanisms and roles of homeostatic plasticity.

Sevoflurane Impairs Short-Term Memory by Affecting PSD-95 and AMPA Receptor in the Hippocampus of a Mouse Model.

Objective To explore the effects of sevoflurane on the latency and error times of the passive avoidance and levels of PSD-95 and AMPA receptors in the hippocampus. We evaluated the effects of sevoflurane on short-term memory in adult mice and explored the possible mechanism. Methods 144 Kunming mice (2-3 months, 30-35 g) were randomly divided into two groups A (n = 64) and B (n = 80) and received the dark-avoidance (DA) and step-down avoidance (SA) tests, respectively. The groups DA and SA were further divided into control (inhaled 40% O2 2 h) and sevoflurane (3.3% sevoflurane and 40% O2 2 h) subgroups. Before inhalation intervention, all mice were trained to be familiar with the Morris water maze (MWM). According to the test points of behavioral indicators, 8 mice were randomly selected from each subgroup at point 12 h (T1), 24 h (T2), 48 h (T3), and 72 h (T4) after inhalation intervention. The step-through latency and error times were measured in 5 min. After the behavioral test, the mice were killed and the tissues of the hippocampus were taken for hematoxylin and eosin (H&E) staining. The expression level of PSD-95 and AMPA receptors in the hippocampus was detected by immunohistochemistry and Western Blot. The changes of synaptic transmission were measured via electrophysiology analysis of hippocampal slices. Results The mice in the control subgroups found the platform in a shorter pathway than those in the sevoflurane subgroups during an MWM test. The step-through latency of T1 and T2 in the sevoflurane subgroup was shorter than baseline time, and the error times were increased in 5 min and higher than baseline time when compared with the control subgroup (P < 0.05) in the A and B groups. Compared with the control subgroup, the expression level of PSD-95 and AMPA receptors in the hippocampus was decreased at T1 and T2 in the sevoflurane subgroup (P < 0.05). The nerve cells were partially swelling. Electrophysiology analysis showed that the levels of PSD-95 and AMPA receptor expression were associated with synaptic transmission. Conclusion Sevoflurane impaired short-term memory in adult mice by inhibiting the expression of PSD-95 and AMPA receptors in the hippocampus, which led to the decrease in synaptic transmission.

The development of synaptic transmission is time-locked to early social behaviors in rats

The development of functional synapses is a sequential process preserved across many brain areas. Here, we show that glutamatergic postsynaptic currents anticipated GABAergic currents in Layer II/III of the rat neocortex, in contrast to the pattern described for other brain areas. The frequencies of both glutamatergic and GABAergic currents increased abruptly at the beginning of the second postnatal week, supported by a serotonin upsurge. Integrative behaviors arose on postnatal day (P)9, while most motor and sensory behaviors, which are fundamental for pup survival, were already in place at approximately P7. A reduction in serotonin reuptake accelerated the development of functional synapses and integrative huddling behavior, while sparing motor and sensory function development. A decrease in synaptic transmission in Layer II/III induced by a chemogenetic approach only inhibited huddling. Thus, precise developmental sequences mediate early, socially directed behaviors for which neurotransmission and its modulation in supragranular cortical layers play key roles.

Acute hypoxic exposure and prolyl-hydroxylase inhibition improves synaptic transmission recovery time from a subsequent hypoxic insult in rat hippocampus

In the CNS short episodes of acute hypoxia can result in a decrease in synaptic transmission which may be fully reversible upon re-oxygenation. Stabilization of hypoxia-inducible factor (HIF) by inhibition of prolyl hydroxylase domain (PHD) enzymes has been shown to regulate the cellular response to hypoxia and confer neuroprotection both in vivo and in vitro. Hypoxic preconditioning has become a novel therapeutic target to induce neuroprotection during hypoxic insults. However, there is little understanding of the effects of repeated hypoxic insults or pharmacological PHD inhibition on synaptic signaling. In this study we have assessed the effects of hypoxic exposure and PHD inhibition on synaptic transmission in the rat CA1 hippocampus. Field excitatory postsynaptic potentials (fEPSPs) were elicited by stimulation of the Schaffer collateral pathway. 30 min hypoxia (gas mixture 95% N2/5% CO2) resulted in a significant and fully reversible decrease in fEPSP slope associated with decreases in partial pressures of tissue oxygen. 15–30 min of hypoxia was sufficient to induce stabilization of HIF in hippocampal slices. Exposure to a second hypoxic insult after 60 min resulted in a similar depression of fEPSP slope but with a significantly greater rate of recovery of the fEPSP. Prior single treatment of slices with the PHD inhibitor, dimethyloxalylglycine (DMOG) also resulted in a significantly greater rate of recovery of fEPSP post hypoxia. These results suggest that hypoxia and ‘pseudohypoxia’ preconditioning may improve the rate of recovery of hippocampal neurons to a subsequent acute hypoxia.

Cereblon Maintains Synaptic and Cognitive Function by Regulating BK Channel.

Mutations in the cereblon (CRBN) gene cause human intellectual disability, one of the most common cognitive disorders. However, the molecular mechanisms of CRBN-related intellectual disability remain poorly understood. We investigated the role of CRBN in synaptic function and animal behavior using male mouse and Drosophila models. Crbn knock-out (KO) mice showed normal brain and spine morphology as well as intact synaptic plasticity; however, they also exhibited decreases in synaptic transmission and presynaptic release probability exclusively in excitatory synapses. Presynaptic function was impaired not only by loss of CRBN expression, but also by expression of pathogenic CRBN mutants (human R419X mutant and Drosophila G552X mutant). We found that the BK channel blockers paxilline and iberiotoxin reversed this decrease in presynaptic release probability in Crbn KO mice. In addition, paxilline treatment also restored normal cognitive behavior in Crbn KO mice. These results strongly suggest that increased BK channel activity is the pathological mechanism of intellectual disability in CRBN mutations.SIGNIFICANCE STATEMENTCereblon (CRBN), a well known target of the immunomodulatory drug thalidomide, was originally identified as a gene that causes human intellectual disability when mutated. However, the molecular mechanisms of CRBN-related intellectual disability remain poorly understood. Based on the idea that synaptic abnormalities are the most common factor in cognitive dysfunction, we monitored the synaptic structure and function of Crbn knock-out (KO) animals to identify the molecular mechanisms of intellectual disability. Here, we found that Crbn KO animals showed cognitive deficits caused by enhanced BK channel activity and reduced presynaptic glutamate release. Our findings suggest a physiological pathomechanism of the intellectual disability-related gene CRBN and will contribute to the development of therapeutic strategies for CRBN-related intellectual disability.

Cortical Synaptic Transmission and Plasticity in Acute Liver Failure Are Decreased by Presynaptic Events

Neurological symptoms of acute liver failure (ALF) reflect decreased excitatory transmission, but the status of ALF-affected excitatory synapse has not been characterized in detail. We studied the effects of ALF in mouse on synaptic transmission and plasticity ex vivo and its relation to distribution of (i) synaptic vesicles (sv) and (ii) functional synaptic proteins within the synapse. ALF-competent neurological and biochemical changes were induced in mice with azoxymethane (AOM). Electrophysiological characteristics (long-term potentiation, whole-cell recording) as well as synapse ultrastructure were evaluated in the cerebral cortex. Also, sv were quantified in the presynaptic zone by electron microscopy. Finally, presynaptic proteins in the membrane-enriched (P2) and cytosolic (S2) fractions of cortical homogenates were quantitated by Western blot. Slices derived from symptomatic AOM mice presented a set of electrophysiological correlates of impaired transmitter release including decreased field potentials (FPs), increased paired-pulse facilitation (PPF), and decreased frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs/mEPSCs) accompanied by reduction of the spontaneous transmitter release-driving protein, vti1A. Additionally, an increased number of sv per synapse and a decrease of P2 content and/or P2/S2 ratio for sv-associated proteins, i.e. synaptophysin, synaptotagmin, and Munc18–1, were found, in spite of decreased content of the sv-docking protein, syntaxin-1. Slices from AOM-treated asymptomatic mice showed impaired long-term potentiation (LTP) and increased PPF but no changes in transmitter release or presynaptic protein composition. Our findings demonstrate that a decrease of synaptic transmission in symptomatic ALF is associated with inefficient recruitment of sv proteins and/or impaired sv trafficking to transmitter release sites.

L-DOPA Oppositely Regulates Synaptic Strength and Spine Morphology in D1 and D2 Striatal Projection Neurons in Dyskinesia.

Dopamine depletion in Parkinson's disease (PD) produces dendritic spine loss in striatal medium spiny neurons (MSNs) and increases their excitability. However, the synaptic changes that occur in MSNs in PD, in particular those induced by chronic L-3,4-dihydroxyphenylalanine (L-DOPA) treatment, are still poorly understood. We exposed BAC-transgenic D1-tomato and D2-eGFP mice to PD and dyskinesia model paradigms, enabling cell type-specific assessment of changes in synaptic physiology and morphology. The distinct fluorescence markers allowed us to identify D1 and D2 MSNs for analysis using intracellular sharp electrode recordings, electron microscopy, and 3D reconstructions with single-cell Lucifer Yellow injections. Dopamine depletion induced spine pruning in both types of MSNs, affecting mushroom and thin spines equally. Dopamine depletion also increased firing rate in both D1- and D2-MSNs, but reduced evoked-EPSP amplitude selectively in D2-MSNs. L-DOPA treatment that produced dyskinesia differentially affected synaptic properties in D1- and D2-MSNs. In D1-MSNs, spine density remained reduced but the remaining spines were enlarged, with bigger heads and larger postsynaptic densities. These morphological changes were accompanied by facilitation of action potential firing triggered by synaptic inputs. In contrast, although L-DOPA restored the number of spines in D2-MSNs, it resulted in shortened postsynaptic densities. These changes in D2-MSNs correlated with a decrease in synaptic transmission. Our findings indicate that L-DOPA-induced dyskinesia is associated with abnormal spine morphology, modified synaptic transmission, and altered EPSP-spike coupling, with distinct effects in D1- and D2-MSNs.

Presynaptic inhibition upon CB1 or mGlu2/3 receptor activation requires ERK/MAPK phosphorylation of Munc18-1.

Presynaptic cannabinoid (CB1R) and metabotropic glutamate receptors (mGluR2/3) regulate synaptic strength by inhibiting secretion. Here, we reveal a presynaptic inhibitory pathway activated by extracellular signal-regulated kinase (ERK) that mediates CB1R- and mGluR2/3-induced secretion inhibition. This pathway is triggered by a variety of events, from foot shock-induced stress to intense neuronal activity, and induces phosphorylation of the presynaptic protein Munc18-1. Mimicking constitutive phosphorylation of Munc18-1 results in a drastic decrease in synaptic transmission. ERK-mediated phosphorylation of Munc18-1 ultimately leads to degradation by the ubiquitin-proteasome system. Conversely, preventing ERK-dependent Munc18-1 phosphorylation increases synaptic strength. CB1R- and mGluR2/3-induced synaptic inhibition and depolarization-induced suppression of excitation (DSE) are reduced upon ERK/MEK pathway inhibition and further reduced when ERK-dependent Munc18-1 phosphorylation is blocked. Thus, ERK-dependent Munc18-1 phosphorylation provides a major negative feedback loop to control synaptic strength upon activation of presynaptic receptors and during intense neuronal activity.

LTD expression is independent of glutamate receptor subtype.

Long-term depression (LTD) is a form of synaptic plasticity that plays a major role in the activity-dependent reshaping of synaptic transmission. LTD is expressed as a decrease in synaptic AMPA receptor number, though the exact mechanism remains controversial. Several lines of evidence have suggested necessary roles for both the GluA1 and GluA2 subunits, and specifically certain interactions with their cytoplasmic tails. However, it is unclear if either GluA1 or GluA2 are absolutely required for LTD. We tested this hypothesis using constitutive knock-outs and single-cell molecular replacement of AMPA receptor subunits in mouse hippocampus. We found that neither GluA1 or GluA2 are required for normal expression of LTD, and indeed a normal decrease in synaptic transmission was observed in cells in which all endogenous AMPA receptors have been replaced by kainate receptors. Thus, LTD does not require removal of specific AMPA receptor subunits, but likely involves a more general modification of the synapse and its ability to anchor a broad range of receptor proteins.

Candidate autism gene screen identifies critical role for cell-adhesion molecule CASPR2 in dendritic arborization and spine development

Mutations in the contactin-associated protein 2 (CNTNAP2) gene encoding CASPR2, a neurexin-related cell-adhesion molecule, predispose to autism, but the function of CASPR2 in neural circuit assembly remains largely unknown. In a knockdown survey of autism candidate genes, we found that CASPR2 is required for normal development of neural networks. RNAi-mediated knockdown of CASPR2 produced a cell-autonomous decrease in dendritic arborization and spine development in pyramidal neurons, leading to a global decline in excitatory and inhibitory synapse numbers and a decrease in synaptic transmission without a detectable change in the properties of these synapses. Our data suggest that in addition to the previously described role of CASPR2 in mature neurons, where CASPR2 organizes nodal microdomains of myelinated axons, CASPR2 performs an earlier organizational function in developing neurons that is essential for neural circuit assembly and operates coincident with the time of autism spectrum disorder (ASD) pathogenesis.

Threshold-Independent Meta-Analysis of Alzheimer`s Disease Transcriptomes shows Progressive Changes in Hippocampal Functions, Epigenetics and microRNA Regulation

End-stage Alzheimer's disease (AD) involves drastic modifications in neuronal molecular and cellular processes, but little is known about the dynamics of these modifications during disease initiation and progression. Here, we report meta-analysis of 100 publicly available Microarray datasets using threshold-independent analysis. We found that different patients react to AD progression by variable single transcript alterations which however lead to similar changes in functional gene groups. Stratification by patients' cognitive deterioration pre`sented hippocampal-specific mRNA alterations which involved progressively changed gene categories and indicate changes in epigenetic state and microRNA profiles. In addition, datasets from laser-captured neurofibrillary tangles-free hippocampal neurons and transcript classification by cell types identified many of these changes in neurons. Intriguingly, we discovered that early-onset decline in alternative splicing, protein folding and transport transcripts occur concurrently with decreases in synaptic transmission, whereas at later stages these changes progressed into enhanced oxidative stress and inflammation. Our findings open new venues for identifying novel targets for intervention with AD progression.

Acute knockdown of AMPA receptors reveals a trans-synaptic signal for presynaptic maturation

Newly formed glutamatergic synapses often lack postsynaptic AMPA-type glutamate receptors (AMPARs). Aside from 'unsilencing' the postsynaptic site, however, the significance of postsynaptic AMPAR insertion during synapse maturation remains unclear. To investigate the role of AMPAR in synapse maturation, we used RNA interference (RNAi) to knockdown AMPARs in cultured hippocampal neurons. Surprisingly, loss of postsynaptic AMPARs increased the occurrence of presynaptically inactive synapses without changing the release probability of the remaining active synapses. Additionally, heterologous synapses formed between axons and AMPAR-expressing HEK cells develop significantly fewer inactive presynaptic terminals. The extracellular domain of the AMPAR subunit GluA2 was sufficient to reproduce this effect at heterologous synapses. Indeed, the retrograde signalling by AMPARs is independent of their channel function as RNAi-resistant AMPARs restore synaptic transmission in neurons lacking AMPARs despite chronic receptor antagonist treatment. Our findings suggest that postsynaptic AMPARs perform an organizational function at synapses that exceeds their standard role as ionotropic receptors by conveying a retrograde trans-synaptic signal that increases the transmission efficacy at a synapse.

A study of long-term potentiation in transgenic mice over-expressing mutant forms of both amyloid precursor protein and presenilin-1

Synaptic transmission and long-term potentiation (LTP) in the CA1 region of hippocampal slices have been studied during ageing of a double transgenic mouse strain relevant to early-onset familial Alzheimer's disease (AD). This strain, which over-expresses both the 695 amino acid isoform of human amyloid precursor protein (APP) with K670N and M671L mutations and presenilin 1 with the A246E mutation, has accelerated amyloidosis and plaque formation. There was a decrease in synaptic transmission in both wildtype and transgenic mice between 2 and 9 months of age. However, preparing slices from 14 month old animals in kynurenic acid (1 mM) counteracted this age-related deficit. Basal transmission and paired-pulse facilitation was similar between the two groups at all ages (2, 6, 9 and 14 months) tested. Similarly, at all ages LTP, induced either by theta burst stimulation or by multiple tetani, was normal. These data show that a prolonged, substantially elevated level of Aβ are not sufficient to cause deficits in the induction or expression of LTP in the CA1 hippocampal region.

Behavioral choice by presynaptic inhibition of tactile sensory terminals

When presented with multiple stimuli, animals generally choose to respond only to one input. The neuronal mechanisms determining such behavioral choices are poorly understood. We found that the medicinal leech had greatly diminished responses to moderate mechanosensory input as it fed. Feeding dominated other responses by suppressing transmitter release from mechanosensory neurons onto all of their neuronal targets. The effects of feeding on synaptic transmission could be mimicked by serotonin. Furthermore, the serotonin antagonist mianserin blocked feeding-induced decreases in synaptic transmission. These results indicate that feeding predominates behaviors by using serotonin at an early stage of sensory processing, namely on presynaptic terminals of mechanosensory neurons.

Susceptibility to induction of long-term depression is associated with impaired memory in aged Fischer 344 rats

The current study employed aged and young male Fischer 344 rats to examine the relationship between long-term depression (LTD), age, and memory. Memory performance was measured on two tasks that are sensitive to hippocampal function; inhibitory avoidance and spatial discrimination on the Morris water maze. The slope of the extracellular excitatory postsynaptic field potential was recorded from CA3–CA1 synapses in hippocampal slices. Low frequency stimulation (LFS) induced a modest LTD only in aged animals under standard recording conditions. The decrease in synaptic transmission examined only in aged animals correlated with memory scores on the spatial task and LTD was not observed in aged animals with the highest memory scores. LTD induction was facilitated by increasing the Ca 2+/Mg 2+ ratio of the recording medium or employing a paired-pulse stimulation paradigm. Age differences disappeared when LFS was delivered under conditions of elevated Ca 2+/Mg 2+ in the recording medium. Using multiple induction episodes under conditions which facilitate LTD-induction, no age-related difference was observed in the maximum level of LTD. The results indicate that the increased susceptibility to LTD induction is associated with impaired memory and results from a shift in the induction process. The possible relationship between LTD and memory function is discussed.

Investigating the safety factor at an invertebrate neuromuscular junction

Fidelity of synaptic transmission is essential at the neuromuscular junction (NMJ). To ensure that transmission does not fail, vertebrate motoneurons often release more neurotransmitter than is required for muscle contraction. This safety factor allows some loss of synaptic function without failure of muscle contraction. It is not known whether a similar mechanism operates at the invertebrate neuromuscular junction. In our study of the Drosophila NMJ, we find that glutamate receptor mutants can exhibit a substantial decrease in synaptic function while maintaining muscle contraction. The persistence of neuromuscular function in these mutants is not explained by synaptic facilitation, temporal summation of high frequency stimuli, or a hyperpolarizing shift in the activation range of muscle calcium channels. Instead, the attenuated synaptic response is sufficient to drive muscle contraction. Quantitative analysis of the decrease in synaptic transmission in these mutants implies that at the wild-type NMJ there is an approximately five- to ninefold excess in released transmitter. Hence, the presence of a synaptic safety factor is a conserved feature of neuromuscular organization in both invertebrates and vertebrates.

Norepinephrine Modulates Glutamatergic Transmission in the Bed Nucleus of the Stria Terminalis

The bed nucleus of the stria terminalis (BNST) and its adrenergic input are key components in stress-induced reinstatement and maintenance of drug use. Intra-BNST injections of either beta-adrenergic receptor (beta-AR) antagonists or alpha2-adrenergic receptor (alpha2-AR) agonists can inhibit footshock-induced reinstatement and maintenance of cocaine- and morphine-seeking. Using electrophysiological recording methods in an in vitro slice preparation from C57/Bl6j adult male mouse BNST, we have examined the effects of adrenergic receptor activation on excitatory synaptic transmission in the lateral dorsal supracommissural BNST (dBNST) and subcommissural BNST (vBNST). Alpha2-AR activation via UK-14,304 (10 microM) results in a decrease in excitatory transmission in both dBNST and vBNST, an effect predominantly dependent upon the alpha2A-AR subtype. Beta-AR activation via isoproterenol (1 microM) results in an increase in excitatory transmission in dBNST, but not in vBNST. Consistent with the work with receptor subtype specific agonists, application of the endogenous ligand norepinephrine (NE, 100 microM) elicits two distinct effects on glutamatergic transmission. In dBNST, NE elicits an increase in transmission (62% of dBNST NE experiments) or a decrease in transmission (38% of dBNST NE experiments). In vBNST, NE elicits a decrease in transmission in 100% of the experiments. In dBNST, the NE-induced increase in synaptic transmission is blocked by beta1/beta2- and beta2-, but not beta1-specific antagonists. In addition, this increase is also reduced by the alpha2-AR antagonist yohimbine and is absent in the alpha2A-AR knockout mouse. In vBNST, the NE-induced decrease in synaptic transmission is markedly reduced in the alpha2A-AR knockout mouse. Further experiments demonstrate that the actions of NE on glutamatergic transmission can be correlated with beta-AR function.

Decrease in Synaptic Transmission Can Reverse the Propagation Direction of Epileptiform Activity in Hippocampus In Vivo

Most types of epileptiform activity with synaptic transmission have been shown to propagate from the CA3 to CA1 region in hippocampus. However, nonsynaptic epileptiform activity induced in vitro is known to propagate slowly from the caudal end of CA1 toward CA2/CA3. Understanding the propagation modes of epileptiform activity, and their causality is important to revealing the underlying mechanisms of epilepsy and developing new treatments. In this paper, the effect of the synaptic transmission suppression on the propagation of epilepsy in vivo was investigated by using multiple-channel recording probes in CA1. Nonsynaptic epileptiform activity was induced by calcium chelator EGTA with varied concentrations of potassium. For comparison, disinhibition synaptic epileptiform activity was induced by picrotoxin (PTX) with or without partial suppression of excitatory synaptic transmission. The propagation velocity was calculated by measuring the time delay between two electrodes separated by a known distance. The results show that in vivo nonsynaptic epileptiform activity propagates with a direction and velocity comparable to those observed in in vitro preparations. The direction of propagation for nonsynaptic activity is reversed from the PTX-induced synaptic activity. A reversal in propagation direction and change in velocity were also observed dynamically during the process of synaptic transmission suppression. Even a partial suppression of synaptic transmission was sufficient to significantly change the propagation direction and velocity of epileptiform activity. These results suggest the possibility that the measurement of propagation can provide important information about the synaptic mechanism underlying epileptic activity.

Adenosine promotes neuronal recovery from reactive oxygen species induced lesion in rat hippocampal slices

Reactive oxygen species (ROS) are believed to be involved in the pathogenesis of several neurological disorders. We now tested whether the endogenous neuroprotective substance, adenosine, attenuates the cell damage induced by ROS. In rat hippocampal slices, the xanthine oxidase (40 mU/ml) plus xanthine (1 mM) (X/XO) system produced a 27.8±7.3% ( n=3) increase in ROS, measured by fluorimetry with 2′,7′-dichlorodihydrofluorescein, a 246.9±18.4% ( n=6) increase in the release of tritiated adenosine, and a decrease in synaptic transmission that fully recovered after washout. In the presence of the adenosine A 1 receptor selective antagonist, 1,3-dipropyl-8-cyclopentylxanthine (100 nM), X/XO induced a similar inhibition, however synaptic transmission only recovered to 70.7±5.8% of control ( n=5). The blockade of A 2A receptors was devoid of effect ( n=4). Adenosine is released by ROS-generating systems, and attenuates the deleterious cellular consequences of ROS through A 1 receptor activation.