Fast Homeostatic Plasticity of Inhibition via Activity-Dependent Vesicular Filling

Synaptic activity in the central nervous system undergoes rapid state-dependent changes, requiring constant adaptation of the homeostasis between excitation and inhibition. The underlying mechanisms are, however, largely unclear. Chronic changes in network activity result in enhanced production of the inhibitory transmitter GABA, indicating that presynaptic GABA content is a variable parameter for homeostatic plasticity. Here we tested whether such changes in inhibitory transmitter content do also occur at the fast time scale required to ensure inhibition-excitation-homeostasis in dynamic cortical networks. We found that intense stimulation of afferent fibers in the CA1 region of mouse hippocampal slices yielded a rapid and lasting increase in quantal size of miniature inhibitory postsynaptic currents. This potentiation was mediated by the uptake of GABA and glutamate into presynaptic endings of inhibitory interneurons (the latter serving as precursor for the synthesis of GABA). Thus, enhanced release of inhibitory and excitatory transmitters from active networks leads to enhanced presynaptic GABA content. Thereby, inhibitory efficacy follows local neuronal activity, constituting a negative feedback loop and providing a mechanism for rapid homeostatic scaling in cortical circuits

Glutamate Uptake Triggers Transporter-Mediated GABA Release from Astrocytes

Background: Glutamate (Glu) and c-aminobutyric acid (GABA) transporters play important roles in regulating neuronal activity. Glu is removed from the extracellular space dominantly by glial transporters. In contrast, GABA is mainly taken up by neurons. However, the glial GABA transporter subtypes share their localization with the Glu transporters and their expression is confined to the same subpopulation of astrocytes, raising the possibility of cooperation between Glu and GABA transport processes. Methodology/Principal Findings: Here we used diverse biological models both in vitro and in vivo to explore the interplay between these processes. We found that removal of Glu by astrocytic transporters triggers an elevation in the extracellular level of GABA. This coupling between excitatory and inhibitory signaling was found to be independent of Glu receptor-mediated depolarization, external presence of Ca2+ and glutamate decarboxylase activity. It was abolished in the presence of non-transportable blockers of glial Glu or GABA transporters, suggesting that the concerted action of these transporters underlies the process. Conclusions/Significance: Our results suggest that activation of Glu transporters results in GABA release through reversal of glial GABA transporters. This transporter-mediated interplay represents a direct link between inhibitory and excitatory neurotransmission and may function as a negative feedback combating intense excitation in pathological conditions such as epilepsy or ischemia

SEEG-RF for revealing and treating Geschwind syndrome's epileptic network: A case study

Stereotypic neural networks are repeatedly activated in drug-refractory epilepsies (DRE), reinforcing the expression of certain psycho-affective traits. Geschwind syndrome (GS) can serve as a model for such phenomena among patients with temporal lobe DRE. We describe stereo-electroencephalogram (SEEG) exploration in a 34-year-old male with DRE and GS, and his treatment by SEEG-radiofrequency (SEEG-RF) ablation. We hypothesized that this approach could reveal the underlying epileptic network and map eloquent faculties adjacent to SEEG-RF targets, which can be further used to disintegrate the epileptic network. The patient underwent a multi-modal pre-surgical evaluation consisting of video EEG (VEEG), EEG source localization, 18-fluorodexyglucose-PET/MRI, neuropsychological and psychiatric assessments. Pre-surgical multi-modal analyses suggested a T4-centered seizure onset zone. SEEG further localized the SOZ within the right amygdalo-hippocampal region and temporal neocortex, with the right parieto-temporal region as the propagation zone. SEEG-RF ablation under awake conditions and continuous EEG monitoring confirmed the abolishment of epileptic activity. Follow-up at 20 months showed seizure suppression (Engel 1A/ILEA 1) and a significantly improved and stable psycho-affective state. To the best of our knowledge this is the first description of the intracranial biomarkers of GS and its further treatment through SEEG-RF ablation within the scope of DRE

FIRDA, refractory epilepsy, and SEEG‐guided RF: A case report

Abstract Objectives We will demonstrate that FIRDA (frontal intermittent rhythmic delta activity)—otherwise related to systemic disorders and encephalopathy—has a role as an epileptic biomarker of deep‐seated midline SOZ. Its abolishment following SEEG‐guided radiofrequency of such SOZ correlates with clinical improvement suggesting its role as a noninvasive biomarker of otherwise inaccessible SOZs. Methods We report the case of AK who was admitted with “psychiatric and gastrointestinal complaints.” AK's complaints were further associated with FIRDA during VEEG. His previous refractoriness to AEDs, the clinico‐electroencephalographic correlation, MRI showing bilateral hippocampal atrophy (more to the left) and severe memory deficits, prompted us to suggest a left temporo‐mesial SOZ, for which SEEG was done. Dual SEEG and scalp electrodes were used primarily for diagnostic purposes but taking into account an option for a therapeutic action by RF ablation. Results The dual array demonstrated a clear association between left hippocampal high voltage spikes and HFOs on SEEG recordings with FIRDA on concomitant scalp EEG parallel to behavioral changes, as suspected in our preliminary hypothesis. A further RF ablation eliminated the epileptiform activity (Spikes, HFOs, and FIRDA) followed by clinical improvement. Significance This is the first report showing the clinical significance of FIRDA associated with behavioral changes as a marker for latent refractory mesial epilepsy. SEEG exploration has the potential to uncover deep sources, which are manifested as FIRDA on scalp EEG. These abnormalities and clinical symptoms can be eliminated by RF ablation