Calcium‐permeable AMPA receptors are expressed in a rodent model of status epilepticus

Abstract

Objective To characterize the plasticity of AMPA receptor (AMPAR)-mediated neurotransmission in the hippocampus during status epilepticus (SE). Methods SE was induced by pilocarpine and animals were studied after 10 min (refractory-SE) or 60 min (late-SE) of the first grade V seizures. AMPAR-mediated currents were recorded from CA1 pyramidal neurons and dentate granule cells (DGCs) by voltage-clamp technique. The surface expression of GluA2 subunit on hippocampal membranes was determined using a biotinylation assay. GluA2 internalization and changes in intracellular calcium ([Ca]i) levels were studied in hippocampal cultures using immunocytochemical and live-imaging techniques. AMPAR antagonist treatment of SE was evaluated by video and EEG. Results AMPAR-mediated currents recorded from CA1 neurons from refractory and late SE animals were inwardly-rectifying and philanthotoxin-sensitive; similar changes were observed in recordings obtained from DGCs from refractory SE animals. GluA2 subunit surface expression was reduced in the hippocampus during refractory and late SE. In cultured hippocampal pyramidal neurons, recurrent bursting diminished surface expression of the GluA2 subunit and enhanced its internalization rate. Recurrent bursting-induced increase in [Ca]i levels was reduced by selective inhibition of GluA2-lacking AMPARs. GYKI-52466 terminated diazepam-refractory SE. Interpretation During SE, there is rapid, ongoing plasticity of AMPARs with the expression of GluA2-lacking AMPARs. These receptors provide another source of Ca2+ entry into the principal neurons. Benzodiazepam-refractory SE can be terminated by AMPAR antagonism. The data identify AMPARs as potential therapeutic target for the treatment of SE.

Pathophysiology of status epilepticus

“…GluA2-lacking AMPA receptors are calcium permeable and may contribute to calcium accumulation, possibly leading to neuronal death [48]. These findings indicate a role for glutamate receptor antagonists in status epilepticus, and, in particular, NMDA receptor antagonists as a means of modifying the condition (possibly preventing drug resistance).…”

“…receptor and GABA(B) receptor expression is decreased, and AMPA receptors lose their GluA2 subunit [25,[47][48][49]. GluA2-lacking AMPA receptors are calcium permeable and may contribute to calcium accumulation, possibly leading to neuronal death [48].…”

“…Ca 2+ permeable AMPA receptors may also play a role [48]. During the development of status epilepticus and as a result of neuronal death, ATP is released into the extracellular fluid and can activate P2X receptors, which may also permit calcium entry into neurons and glia and may play a role in neuro-inflammation and neuronal death [63].…”

Receptor trafficking hypothesis revisited: Plasticity of AMPA receptors during established status epilepticus

“…Extending these findings, herein we hypothesize that AMPAR-mediated excitatory conductance is progressively enhanced during ESE. To test this hypothesis, SE was induced in lithium-pretreated adult male rats using pilocarpine, and the animals were studied either 10 min (early ESE) or 60 min (late ESE) after the onset of the first grade V behavioral seizure using a combination of electrophysiological and biochemical studies as described previously (Rajasekaran et al, 2012;Kozhemyakin et al, 2013).AMPAR-mediated excitatory postsynaptic currents (EPSCs) were recorded from CA1 pyramidal neurons (CA1-PNs) and dentate granule cells (DGCs) by voltageclamp technique. Analysis of recordings obtained from CA1-PNs revealed that the frequency of action-potential independent EPSCs (m-EPSCs) increased with increasing seizure duration (p < 0.0001, one-way analysis of variance [ANOVA]).…”

CaV3.2 calcium channels control NMDA receptor-mediated transmission: a new mechanism for absence epilepsy

“…TTA-P2 (10 mg/ kg; supplied by Dr. Victor Uebele at Merck), 0.05 mg/kg MK 801, and/or 20 mg/kg GYKI 52466 (cf. Rajasekaran et al 2012) were administered via i.p. injections prior to EEG and behavior recording.…”