Glutamate and dopamine receptors contribute to the lateral spread of epileptiform discharges in rat neocortical slices

Interictal spikes during spatial working memory carry helpful or distracting representations of space and have opposing impacts on performance

In temporal lobe epilepsy, interictal spikes (IS) - hypersynchronous bursts of network activity - occur at high rates in between seizures. We sought to understand the influence of IS on working memory by recording hippocampal local field potentials from epileptic mice while they performed a delayed alternation task. We found that IS disrupted performance when they were spatially non-restricted and occurred during running. In contrast, when IS were clustered at reward locations, animals performed well. A machine learning decoding approach revealed that IS at reward sites were larger than IS elsewhere on the maze, and could be classified as occurring at specific reward locations - suggesting they carry informative content for the memory task. Finally, a spiking model revealed that spatially clustered IS preserved hippocampal replay, while spatially dispersed IS disrupted replay by causing over-generalization. Together, these results show that IS can have opposing outcomes on memory.

Embelin ameliorates cognitive dysfunction and progression of kindling in pentylenetetrazol-induced kindling in mice by attenuating brain inflammation

OBJECTIVE

This study was conducted to evaluate the effect of embelin (EMB) on various epileptic models and related brain inflammation.

METHODS

Male Swiss albino mice were administered EMB (5, 10, and 20 mg/kg/p.o.) in acute and chronic study for 7 days and 35 days, respectively. Acute study included increasing current electroshock (ICES) and pentylenetetrazol (PTZ)-induced seizure test. Step-down latency (SDL) and forced swim test (FST) were performed to evaluate cognitive functions and depression-like behavior, respectively. Chronic study included PTZ-induced kindling. Levels of inflammatory biomarkers, namely interleukin-1 beta (IL-1β), interleukin-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), were estimated in the hippocampus and cortex of the kindled brains by ELISA technique. Further, neurotransmitters (NTs), namely gamma aminobutyric acid (GABA), glutamate, and dopamine, were estimated by using validated liquid chromatography-mass spectrometry (LC-MS) method followed by ultra-high-performance liquid chromatography (UHPLC).

RESULTS

Embelin (EMB) treatment increased the seizure threshold to hind limb extension (HLE) in the ICES test and decreased the seizure scores in the kindling experiment. Significantly low levels of IL-1β, IL-1Ra, IL-6, and TNF-α were observed in the hippocampus of PTZ + EMB (10 and 20 mg/kg)-treated groups compared with PTZ+ vehicle-treated group. Significantly lower levels of IL-1Ra, IL-6, and TNF-α compared with PTZ+ vehicle-treated group were observed in the cortex of PTZ + EMB (10 and 20 mg/kg)-treated groups, while IL-1β levels were found to be significantly lower only in the cortex of PTZ + EMB (20 mg/kg)-treated group. Increased levels of dopamine and GABA and decreased levels of glutamate in both hippocampus and cortex were observed in EMB + PTZ-treated groups compared with vehicle + PTZ-treated group. Latency of step down was found to be increased and immobility time in FST was decreased in EMB + PTZ groups compared with vehicle + PTZ group.

CONCLUSION

Embelin suppressed epileptogenesis in the kindled mice via neurochemical modulation of neurotransmitters and inhibiting the inflammatory pathway. Further, EMB was also observed to be protecting the kindled animals from cognition and depression-like behavior.

Propagation of cortical spreading depression into the hippocampus: The role of the entorhinal cortex

Propagation of cortical spreading depression (CSD) to the subcortical structures could be the underlying mechanism of some neurological deficits in migraine with aura. The entorhinal cortex (EC) as a gray matter bridge between the neocortex and subcortical regions plays an important role in this propagation. In vitro combined neocortex-hippocampus brain slices were used to study the propagation pattern of CSD between the neocortex and the hippocampus. The effects of different compounds as well as tetanic electrical stimulations in the EC on propagation of CSD to the hippocampus were investigated. Repetitive induction of CSD by KCl injection in the somatosensory cortex enhanced the probability of CSD entrance to the hippocampus via EC. Local application of AMPA receptor blocker CNQX and cannabinoid receptor agonist WIN 55212-2 in EC facilitated the propagation of CSD to the hippocampus, whereas application of NMDA receptor blocker APV and GABA_A receptor blocker bicuculline in this region reduced the probability of CSD penetration to the hippocampus. Application of tetanic stimulation in EC also facilitated the propagation of CSD entrance to the hippocampus. Our data suggest the importance of synaptic plasticity of EC in filtering the propagation of CSD into subcortical structures and possibly the occurrence of concomitant neurological deficits. Synapse 68:574-584, 2014. © 2014 Wiley Periodicals, Inc.

Spatiotemporal dynamics of high-K+-induced epileptiform discharges in hippocampal slice and the effects of valproate

The epileptic seizure is a dynamic process involving a rapid transition from normal activity to a state of hypersynchronous neuronal discharges. Here we investigated the network properties of epileptiform discharges in hippocampal slices in the presence of high K(+) concentration (8.5 mmol/L) in the bath, and the effects of the anti-epileptic drug valproate (VPA) on epileptiform discharges, using a microelectrode array. We demonstrated that epileptiform discharges were predominantly initiated from the stratum pyramidale layer of CA3a-b and propagated bi-directionally to CA1 and CA3c. Disconnection of CA3 from CA1 abolished the discharges in CA1 without disrupting the initiation of discharges in CA3. Further pharmacological experiments showed that VPA at a clinically relevant concentration (100 μmol/L) suppressed the propagation speed but not the rate or duration of high-K(+)-induced discharges. Our findings suggest that pacemakers exist in the CA3a-b region for the generation of epileptiform discharges in the hippocampus. VPA reduces the conduction of such discharges in the network by reducing the propagation speed.

The effects of tetanic stimulation on plasticity of remote synapses in the hippocampus-perirhinal cortex-amygdala network

In the temporal lobe, multiple synaptic pathways reciprocally link different structures. These multiple pathways play an important role in the integrity of the function of the temporal lobe and malfunction in this network has been suggested to underlie some neurological disorders such as epilepsy. To test whether the induction of long-term potentiation (LTP) in one temporal lobe structure would modulate functional synaptic plasticity in other structures of this network, tetanic stimulation was applied to the white matter of the perirhinal cortex, Schaffer collaterals of the hippocampus, or the external capsule in combined rat amygdala-hippocampus-cortex slices. This tetanic stimulation was accompanied by enhancement of the evoked field potential slope in the third layer of perirhinal cortex, hippocampal CA1 area, and the lateral amygdala. Induction of LTP in each of these structures was concomitant with increased evoked field potentials in the neighboring structures. Surgical disconnection of anatomical pathways between these structures inhibited this concomitant enhancement of the evoked field potential slope. Both NMDA and AMPA glutamate sub-receptors were involved in changes of synaptic plasticity elicited by induction of LTP in the neighboring structures. The present data indicate a reciprocal control among the perirhinal cortex, the amygdala, and the hippocampus plasticity. This could be important for the formation and retention of the medial temporal lobe-dependent memory and may play a role in the involvement of all different regions of the temporal lobe in pathological conditions such as epilepsy that affect this brain structure.