Cannabidiol modulates excitatory-inhibitory ratio to counter hippocampal hyperactivity

Cannabidiol (CBD), a non-euphoric component of cannabis, reduces seizures in multiple forms of pediatric epilepsies, but the mechanism(s) of anti-seizure action remain unclear. In one leading model, CBD acts at glutamatergic axon terminals, blocking the pro-excitatory actions of an endogenous membrane phospholipid, lysophosphatidylinositol (LPI), at the G-protein-coupled receptor GPR55. However, the impact of LPI-GPR55 signaling at inhibitory synapses and in epileptogenesis remains underexplored. We found that LPI transiently increased hippocampal CA3-CA1 excitatory presynaptic release probability and evoked synaptic strength in WT mice, while attenuating inhibitory postsynaptic strength by decreasing GABAARγ2 and gephyrin puncta. LPI effects at excitatory and inhibitory synapses were eliminated by CBD pre-treatment and absent after GPR55 deletion. Acute pentylenetrazole-induced seizures elevated GPR55 and LPI levels, and chronic lithium-pilocarpine-induced epileptogenesis potentiated LPI's pro-excitatory effects. We propose that CBD exerts potential anti-seizure effects by blocking LPI's synaptic effects and dampening hyperexcitability.

Encephalitis patient-derived monoclonal GABAA receptor antibodies cause epileptic seizures

Autoantibodies targeting the GABAA receptor (GABAAR) hallmark an autoimmune encephalitis presenting with frequent seizures and psychomotor abnormalities. Their pathogenic role is still not well-defined, given the common overlap with further autoantibodies and the lack of patient-derived mAbs. Five GABAAR mAbs from cerebrospinal fluid cells bound to various epitopes involving the α1 and γ2 receptor subunits, with variable binding strength and partial competition. mAbs selectively reduced GABAergic currents in neuronal cultures without causing receptor internalization. Cerebroventricular infusion of GABAAR mAbs and Fab fragments into rodents induced a severe phenotype with seizures and increased mortality, reminiscent of encephalitis patients' symptoms. Our results demonstrate direct pathogenicity of autoantibodies on GABAARs independent of Fc-mediated effector functions and provide an animal model for GABAAR encephalitis. They further provide the scientific rationale for clinical treatments using antibody depletion and can serve as tools for the development of antibody-selective immunotherapies.

Kainate and AMPA receptors in epilepsy: Cell biology, signalling pathways and possible crosstalk

Epilepsy is caused when rhythmic neuronal network activity escapes normal control mechanisms, resulting in seizures. There is an extensive and growing body of evidence that the onset and maintenance of epilepsy involves alterations in the trafficking, synaptic surface expression and signalling of kainate and AMPA receptors (KARs and AMPARs). The KAR subunit GluK2 and AMPAR subunit GluA2 are key determinants of the properties of their respective assembled receptors. Both subunits are subject to extensive protein interactions, RNA editing and post-translational modifications. In this review we focus on the cell biology of GluK2-containing KARs and GluA2-containing AMPARs and outline how their regulation and dysregulation is implicated in, and affected by, seizure activity. Further, we discuss role of KARs in regulating AMPAR surface expression and plasticity, and the relevance of this to epilepsy. This article is part of the special issue on 'Glutamate Receptors - Kainate receptors'.

Evaluation of the effect of Cooled HaEmodialysis on Cognitive function in patients suffering with end-stage KidnEy Disease (E-CHECKED): feasibility randomised control trial protocol

BACKGROUND

Cognitive impairment is common in haemodialysis (HD) patients and is associated independently with depression and mortality. This association is poorly understood, and no intervention is proven to slow cognitive decline. There is evidence that cooler dialysis fluid (dialysate) may slow white matter changes in the brain, but no study has investigated the effect of cooler dialysate on cognition. This study addresses whether cooler dialysate can prevent the decline in cognition and improve quality of life (QOL) in HD patients.

METHODS

This is a multi-site prospective randomised, double-blinded feasibility trial.

SETTING

Four HD units in the UK.

PARTICIPANTS AND INTERVENTIONS

Ninety HD patients randomised (1:1) to standard care (dialysate temperature 36.5 °C) or intervention (dialysate temperature 35 °C) for 12 months.

PRIMARY OUTCOME MEASURE

Change in cognition using the Montreal Cognitive Assessment (MoCA).

SECONDARY OUTCOME MEASURES

Recruitment and attrition rates, reasons for non-recruitment, frequency of intradialytic hypotension, depressive symptom scores, patient and carers burden, a detailed computerised cognitive test and QOL assessments.

ANALYSIS

mixed method approach, utilising measurement of cognition, questionnaires, physiological measurements and semi-structured interviews.

DISCUSSION

The results of this feasibility trial will inform the design of a future adequately powered substantive trial investigating the effect of dialysate cooling on prevention and/or slowing in cognitive decline in patients undergoing haemodialysis using a computerised battery of neuro-cognitive tests. The main hypothesis that would be tested in this future trial is that patients treated with regular conventional haemodialysis will have a lesser decline in cognitive function and a better quality of life over 1 year by using cooler dialysis fluid at 35 °C, versus a standard dialysis fluid temperature of 36.5 °C. This also should reflect in improvements in their abilities for activities of daily living and therefore reduce carers' burden. If successful, the treatment could be universally applied at no extra cost.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03645733 . Registered retrospectively on 24 August 2018.

Changes in excitatory and inhibitory receptor expression and network activity during induction and establishment of epilepsy in the rat Reduced Intensity Status Epilepticus (RISE) model

The RISE model is an effective system to study the underlying molecular and cellular mechanisms involved in the initiation and maintenance of epilepsy in vivo. Here we profiled the expression of excitatory and inhibitory neurotransmitter receptor subunits and synaptic scaffolding proteins in the hippocampus and temporal lobe and compared these changes with alterations in network activity at specific timepoints during epileptogenesis. Significant changes occurred in all of the ionotropic glutamate receptor subunits tested during epilepsy induction and progression and the profile of these changes differed between the hippocampus and temporal lobe. Notably, AMPAR subunits were dramatically decreased during the latent phase of epilepsy induction, matched by a profound decrease in the network response to kainate application in the hippocampus. Moreover, decreases in the GABAAβ3 subunit are consistent with a loss of inhibitory input contributing to the perturbation of excitatory/inhibitory balance and seizure generation. These data highlight the synaptic reorganisation that mediates the relative hypoexcitability prior to the manifestation of seizures and subsequent hyperexcitability when spontaneous seizures develop. These patterns of changes give new insight into the mechanisms underpinning epilepsy and provide a platform for future investigations targeting particular receptor subunits to reduce or prevent seizures.

Reducing suffering in experimental autoimmune encephalomyelitis (EAE)

This report is based on discussions and submissions from an expert working group consisting of veterinarians, animal care staff and scientists with expert knowledge relevant to the field. It aims to facilitate the implementation of the Three Rs (replacement, reduction and refinement) in the use of animal models or procedures involving experimental autoimmune encephalomyelitis (EAE), an experimental model used in multiple sclerosis research. The emphasis is on refinement since this has the greatest potential for immediate implementation. Specific welfare issues are identified and discussed, and practical measures are proposed to reduce animal use and suffering. Some general issues for refinement are summarised to help achieve this, with more detail provided on a range of specific measures to reduce suffering.

NR2B-containing NMDA autoreceptors at synapses on entorhinal cortical neurons

We have previously shown that presynaptic N-methyl-D-aspartate receptors (NMDARs) can facilitate glutamate release onto principal neurons in the entorhinal cortex (EC). In the present study, we have investigated the subunit composition of these presynaptic NMDARs. We recorded miniature alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (mEPSCs), from visually identified neurons in layers II and V of the EC in vitro. In both layers, bath application of the NR2A/B subunit-selective agonist, homoquinolinic acid (HQA), resulted in a marked facilitation of mEPSC frequency. Blockade of presynaptic Ca(2+) entry through either NMDARs or voltage-gated Ca(2+) channels with Co(2+) prevented the effects of HQA, confirming that Ca(2+) entry to the terminal was required for facilitation. When the NR2B-selective antagonist, ifenprodil, was applied prior to HQA, the increase in mEPSC frequency was greatly reduced. In addition, we found that an NMDAR antagonist blocked frequency-dependent facilitation of evoked release and reduced mEPSC frequency in layer V. Thus we have demonstrated that NMDA autoreceptors in layer V of the EC bear the NR2B subunit, and that NMDARs are also present at terminals onto superficial neurons.

Activation of presynaptic group III metabotropic glutamate receptors depresses spontaneous inhibition in layer V of the rat entorhinal cortex

Whole cell voltage clamp recording was used to investigate neurotransmitter release onto neurones in deep and superficial layers of rat entorhinal cortex in vitro. Activation of metabotropic glutamate receptors with the agonist (1S,3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid depressed spontaneous release of the inhibitory neurotransmitter GABA in layer V, but not in layer II. Depression of transmitter release did not persist in the presence of the sodium channel blocker tetrodotoxin. It seems likely that activation of presynaptic glutamate heteroreceptors inhibits action potential dependent release of neurotransmitter via a direct action at the presynaptic terminal. We confirmed that depression of inhibitory neurotransmission in layer V was mediated by group III metabotropic glutamate receptors using a specific group III antagonist, (RS)-cyclopropyl-4-phosphonophenylglycine. Application of the antagonist alone did not alter the frequency of spontaneous neurotransmitter release, suggesting that the metabotropic glutamate receptor is not tonically active. In layer V of the entorhinal cortex, activation of presynaptic metabotropic glutamate receptors enhances spontaneous glutamate release, and inhibits spontaneous release of GABA. These effects may combine to increase random action potential firing in this layer, thereby reducing its capacity for synchrony generation. Our results are consistent with an anticonvulsant action for group III metabotropic glutamate receptors in the entorhinal cortex.

Synaptically activated calcium responses in dendrites of hippocampal oriens-alveus interneurons

Activation of metabotropic glutamate receptors (mGluRs) by agonists increases intracellular calcium levels ([Ca(2+)](i)) in interneurons of stratum oriens/alveus (OA) of the hippocampus. We examined the mechanisms that contribute to dendritic Ca(2+) increases in these interneurons during agonist activation of mGluRs and during synaptically evoked burst discharges, using simultaneous whole cell recordings and confocal Ca(2+) imaging in rat hippocampal slices. First, we found that the group I/II mGluR agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD; 100 microM) increased dendritic [Ca(2+)](i) and depolarized OA interneurons. Dendritic Ca(2+) responses were correlated with membrane depolarizations, but Ca(2+) responses induced by ACPD were larger in amplitude than those elicited by equivalent somatic depolarization. Next, we used linescans to measure changes in dendritic [Ca(2+)](i) during synaptically evoked burst discharges and somatically elicited repetitive firing in disinhibited slices. Dendritic Ca(2+) signals and electrophysiological responses were stable over repeated trials. Peak Ca(2+) responses were linearly related to number and frequency of action potentials in burst discharges for both synaptic and somatic stimulation, but the slope of the relationship was steeper for responses evoked somatically. Synaptically evoked [Ca(2+)](i) rises and excitatory postsynaptic potentials were abolished by antagonists of ionotropic glutamate receptors. The group I/II mGluR antagonist S-alpha-methyl-4-carboxyphenylglycine (500 microM) produced a significant partial reduction of synaptically evoked dendritic Ca(2+) responses. The mGluR antagonist did not affect synaptically evoked burst discharges and did not reduce either Ca(2+) responses or burst discharges evoked somatically. Therefore ionotropic glutamate receptors appear necessary for synaptically evoked dendritic Ca(2+) responses, and group I/II mGluRs may contribute partially to these responses. Dendritic [Ca(2+)](i) rises mediated by both ionotropic and metabotropic glutamate receptors may be important for synaptic plasticity and the selective vulnerability to excitotoxicity of OA interneurons.

Differential actions of PKA and PKC in the regulation of glutamate release by group III mGluRs in the entorhinal cortex

In a previous study we showed that activation of a presynaptically located metabotropic glutamate receptor (mGluR) with pharmacological properties of mGluR4a causes a facilitation of glutamate release in layer V of the rat entorhinal cortex (EC) in vitro. In the present study we have begun to investigate the intracellular coupling linking the receptor to transmitter release. We recorded spontaneous alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory postsynaptic currents (EPSCs) in the whole cell configuration of the patch-clamp technique, from visually identified neurons in layer V. Bath application of the protein kinase A (PKA) activator, forskolin, resulted in a marked facilitation of EPSC frequency, similar to that seen with the mGluR4a specific agonist, ACPT-1. Preincubation of slices with the PKA inhibitor H-89 abolished the effect of ACPT-1, as did preincubation with the adenylate cyclase inhibitor, SQ22536. Activation of protein kinase C (PKC) using phorbol 12 myristate 13-acetate (PMA) did not affect sEPSC frequency; however, it did abolish the facilitatory effect of ACPT-1 on glutamate release. A robust enhancement of EPSC frequency was seen in response to bath application of the specific PKC inhibitor, GF 109203X. Both H-89 and the group III mGluR antagonist (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) abolished the effects of GF 109203X. These data suggest that in layer V of the EC, presynaptic group III mGluRs facilitate release via a positive coupling to adenylate cyclase and subsequent activation of PKA. We have also demonstrated that the PKC system tonically depresses transmitter release onto layer V cells of the EC and that an interaction between mGluR4a, PKA, and PKC may exist at these synapses.

Activation of presynaptic group III metabotropic receptors enhances glutamate release in rat entorhinal cortex

The role of group III metabotropic glutamate receptors (mGluRs) in modulating excitatory synaptic transmission was investigated in the rat entorhinal cortex (EC) in vitro. AMPA receptor-mediated excitatory postsynaptic currents (EPSCs) were recorded in the whole cell configuration of the patch-clamp technique from visually identified neurons in layers V and II. In layer V, bath application of the specific group III mGluR agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4, 500 microM) resulted in a marked facilitation of both spontaneous and activity-independent "miniature" (s/mEPSC) event frequency. The facilitatory effect of L-AP4 (100 microM) on sEPSC frequency prevailed in the presence of DL-2-amino-5-phosphonopentanoic acid (100 microM) but was abolished by the group III antagonist (RS)-cyclopropyl-4-phosphonophenylglycine (20 microM). These data confirmed that group III mGluRs, and not N-methyl-D-aspartate (NMDA) receptors were involved in the response to L-AP4. Bath application of the specific mGluR4a agonist (1S,3R,4S)-1-aminocyclopentane-1,2, 4-tricarboxylic acid (20 microM) also had a facilitatory effect on sEPSC frequency, suggesting involvement of mGluR4a. In layer II neurons, L-AP4 caused a reduction in sEPSC frequency but did not affect mEPSCs recorded in the presence of tetrodotoxin. These findings suggest that a group III mGluR with mGluR4a-like pharmacology is involved in modulating synaptic transmission in layer V cells of the EC. The effect on mEPSCs suggests that this receptor is located presynaptically and that its activation results in a direct facilitation of glutamate release. This novel facilitatory effect is specific to layer V and, to our knowledge, is the first report of a direct facilitatory action of group III mGluRs on synaptic transmission. In layer II, L-AP4 had an inhibitory effect on glutamate release similar to that reported in other brain regions.

Differential induction of long-lasting potentiation of inhibitory postsynaptic potentials by theta patterned stimulation versus 100-Hz tetanization in hippocampal pyramidal cells in vitro

Tetanization of Schaffer collaterals, which induces long-term potentiation of excitatory transmission in the hippocampus of the rat, also affects local inhibitory circuits. Mechanisms controlling plasticity of early and late components of inhibitory postsynaptic potentials in CA1 pyramidal cells were studied using intracellular recordings and Ca2+ imaging in rat hippocampal slices. High-frequency stimulation (100 Hz/s) of Schaffer collaterals resulted in no change in the mean amplitude of early or late inhibitory postsynaptic potentials 30 min post-tetanus. However, intracellular injection of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetate unmasked a significant increase in mean amplitude of both inhibitory postsynaptic potentials 30 min post-tetanus and the induction of this potentiation was blocked by the N-methyl-D-aspartate receptor antagonist(+/-)-2-amino-5-phosphopentanoic acid. In contrast to high-frequency tetanization, "theta-burst" stimulation in normal medium resulted in a significant potentiation of the mean amplitude of both early and late inhibitory postsynaptic potentials 30 min post-tetanus. This potentiation was blocked by the N-methyl-D-aspartate receptor antagonist. The more physiological tetanization pattern, which mimics the endogenous theta rhythm, therefore resulted in an N-methyl-D-aspartate-dependent increase in inhibition 30 min post-tetanus. Calcium imaging during whole-cell recordings from pyramidal cells revealed differences in the Ca2+ signal associated with high-frequency and theta-burst stimulations. During theta-burst stimulation of Schaffer collaterals, the mean time to peak of Ca2+ signals was significantly longer, and the mean peak amplitude and area under the Ca2+ response were larger than during high-frequency stimulation. These results indicate that tetanization induces long-lasting synaptic plasticity in hippocampal inhibitory circuits. This plasticity involves an interaction between a Ca2(+)-mediated postsynaptic depression and an N-methyl-D-aspartate-mediated potentiation of GABAA and GABAB inhibition, and these processes are differentially sensitive to tetanization parameters.

Membrane potential and intracellular Ca2+ oscillations activated by mGluRs in hippocampal stratum oriens/alveus interneurons

Metabotropic glutamate receptors (mGluRs) are expressed heterogeneously in hippocampal interneurons, and their signal transduction cascades remain largely unclear. We characterized an oscillatory response activated by the mGluR agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) in hippocampal interneurons of stratum oriens-alveus (OA) with simultaneous whole cell current-clamp recordings and intracellular Ca2+ imaging with confocal microscopy. 1S,3R-ACPD induced oscillatory membrane depolarizations and rises in intracellular Ca2+ that persisted in tetrodotoxin and were blocked by the antagonist of group I and II mGluRs (S)-alpha-methyl-4-carboxyphenylglycine. Membrane depolarizations and intracellular Ca2+ rises were blocked by extracellular Cd2+ and in Ca2+-free medium. mGluR responses therefore required Ca2+ influx via voltage-gated Ca2+ channels. 1S, 3R-ACPD responses were also antagonized by depleting intracellular stores with thapsigargin and ryanodine, indicating that Ca2+ release from intracellular stores was also necessary. These data suggest that oscillatory responses generated by group I/II mGluRs involve a coupling of Ca2+ entry through voltage-gated Ca2+ channels and Ca2+ release from internal stores. In contrast, 1S,3R-ACPD evoked only smaller depolarizations and intracellular Ca2+ rises, with no oscillations, in other hippocampal interneurons located in or near stratum lacunosum-moleculare. Thus mGluR-mediated oscillatory responses are specifically expressed in certain interneuron subtypes. This heterogeneous expression of glutamate and Ca2+ signaling pathways in specific interneurons may be relevant to their selective vulnerability to excitotoxicity.

Interneuron-specific Ca2+ responses linked to metabotropic and ionotropic glutamate receptors in rat hippocampal slices

Glutamate-mediated regulation of intracellular Ca2+ levels was examined in different populations of CA1 interneurons, using confocal microscopy and the Ca2+ indicator fluo 3-AM in rat hippocampal slices. Interneurons in basal [stratum oriens/alveus (OA)] and apical [strata radiatum and lacunosum-moleculare (R/LM)] dendritic layers responded heterogeneously to glutamate. In control medium, OA interneurons responded mostly with oscillatory Ca2+ responses, which consisted of a large Ca2+ transient and successive smaller elevations. R/LM interneurons responded mostly with biphasic responses, characterized by an initial large transient and a secondary prolonged elevation. Other interneurons in both R/LM and OA responded with transient elevations in Ca2+ levels. Ionotropic glutamate receptor antagonists (+/-)2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitro-quinoxaline-2,3-dione reduced peak Ca2+ responses in OA and R/LM cells, and blocked biphasic responses in R/LM interneurons. The metabotropic glutamate receptor antagonist (RS)-alpha-methyl-4-carboxyphenylglycine reduced peak Ca2+ responses only in OA interneurons, and prevented oscillatory responses. In low Ca2+ medium, peak responses were reduced in R/LM but not in OA interneurons, and oscillatory responses were absent. Combination of ionotropic and metabotropic receptor antagonists blocked all glutamate-evoked Ca2+ responses. Activation of different types of glutamate receptors may thus produce heterogeneous Ca2+ signals in subpopulations of CA1 interneurons. Ionotropic receptors may generate biphasic responses in interneurons in apical dendritic layers, whereas combined activation of metabotropic and ionotropic receptors may trigger oscillatory responses in interneurons of basal dendritic layers. These heterogeneous Ca2+ responses indicate that glutamate-mediated Ca2+ processes and second messenger systems differ in subpopulations of hippocampal interneurons and suggest possible postsynaptic functional specialization of interneurons.