Seizure-related regulation of GABAA receptors in spontaneously epileptic rats

Abstract

In this study, we analyzed the impact that spontaneous seizures might have on the plasma membrane expression, composition and function of GABAA receptors (GABAARs). For this, tissue of chronically epileptic rats was collected within 3 hours of seizure occurrence (≤3 hours group) or at least 24 hours after seizure occurrence (≥24 hours group). A retrospective analysis of seizure frequency revealed that selecting animals on the bases of seizure proximity also grouped animals in terms of overall seizure burden with a higher seizure burden observed in the ≤3 hours group. A biochemical analysis showed that although animals with more frequent/recent seizures (≤3 hours group) had similar levels of GABAAR at the plasma membrane they showed deficits in inhibitory neurotransmission. In contrast, tissue obtained from animals experiencing infrequent seizures (≥24 hours group) had increased plasma membrane levels of GABAAR and showed no deficit in inhibitory function. Together, our findings offer an initial insight into the molecular changes that might help to explain how alterations in GABAAR function can be associated with differential seizure burden. Our findings also suggest that increased plasma membrane levels of GABAAR might act as a compensatory mechanism to more effectively maintain inhibitory function, repress hyperexcitability and reduce seizure burden. This study is an initial step towards a fuller characterization of the molecular events that trigger alterations in GABAergic neurotransmission during chronic epilepsy.

GABAA currents are decreased by IL-1β in epileptogenic tissue of patients with temporal lobe epilepsy: implications for ictogenesis

“…It has been proposed since 1958 (Jung et al, 1958) that, seizures occur as a result of altered excitatory/inhibitory balance; therefore, an altered GABA A receptor (R) function may contribute to epileptogenesis (Scharfman and Brooks-Kayal, 2014;González et al, 2015). In line with this hypothesis, we have shown that GABA A -Rs in the epileptic brain, when repetitively activated, display a marked current desensitization known as rundown (Ragozzino et al, 2005;Palma et al, 2007), thereby contributing to the GABAergic impairment in epilepsy.…”

Regulation of the cell surface expression of chloride transporters during epileptogenesis

“…The methods described here are similar to those described elsewhere, for further details please refer to our previous reports [12, 13]. Samples were isolated from animals described in the above-mentioned studies and repurposed for the analysis of KCC2 and NKCC1 immunoreactivity.…”

“…Rats were injected intraperitoneally with scopolamine methyl nitrate (1 mg/kg) 30 minutes before administration of pilocarpine hydrochloride (385 mg/kg), as previously described [4, 12, 13, 27]. Diazepam (6 mg/kg; Hospira, Lake Forest, IL) was administered to stop seizure progression.…”

“…Rats were implanted with EEG electrodes as previously described [13]. Following recovery, rats were placed in a recording chamber equipped with flexible cables attached to a commutator (i.e., electric swivel) and recorded 24 hours/day using an automatic Pinnacle digital video-EEG system.…”

“…In previous independent studies, we analyzed the cell surface expression of GABA A R during the “latent” and “chronic” period of epilepsy and discovered deficits on the cell surface expression of GABA A R subunits [12, 13]. Here, the cell surface expression of KCC2 and NKCC1 was analyzed in tissue obtained during the epileptogenic period and in tissue obtained from chronically epileptic animals enduring both frequent and infrequent seizures.…”