Glutamate and ?-aminobutyric acid content and release of synaptosomes from temporal lobe epilepsy patients

Abstract

During surgical intervention in medically refractory temporal lobe epilepsy (TLE) patients, diagnosed with either mesial temporal lobe sclerosis (MTS)- or tumor (T)-associated TLE, biopsies were taken from the anterior temporal neocortex and the hippocampal region. Synaptosomes, isolated from these biopsies were used to study intrasynaptosomal Ca(2+) levels ([Ca(2+)](i)), and glutamate and gamma-aminobutyric acid (GABA) contents and release. All synaptosomal preparations demonstrated a basal [Ca(2+)](i) of about 200 nM, except neocortical synaptosomes from MTS-associated TLE patients (420 nM). K(+)-induced depolarization resulted in a robust increase of the basal [Ca(2+)](i) in all preparations. Neocortical synaptosomes from TLE patients contained 22.9 +/- 3.0 nmol glutamate and 4.6 +/- 0.5 nmol GABA per milligram synaptosomal protein, whereas rat cortical synaptosomes contained twice as much glutamate and four times as much GABA. Hippocampal synaptosomes from MTS-associated TLE patients, unlike those from T-associated TLE patients, contained about 70% less glutamate and 55% less GABA than neocortical synaptosomes. Expressed as percentage of total synaptosomal content, synaptosomes from MTS-associated TLE patients exhibited an increased basal and a reduced K(+)-induced glutamate and GABA release compared to rat cortical synaptosomes. In MTS-associated TLE patients, only GABA release from neocortical synaptosomes was partially Ca(2+)-dependent. Control experiments in rat synaptosomes demonstrated that at least part of the reduction in K(+)-induced release can be ascribed to resection-induced hypoxia in biopsies. Thus, synaptosomes from MTS-associated TLE patients exhibit a significant K(+)-induced increase in [Ca(2+)](i), but the consequent release of glutamate and GABA is severely impaired. Our data show that at least part of the differences in glutamate and GABA content and release between human biopsy material and fresh rat tissue is due to the resection time.

Alterations of intracerebral γ‐aminobutyric acid (GABA) levels by titration with levetiracetam in patients with focal epilepsies

“…Therefore, we cannot exclude that findings might be different in regions of epileptic cortex. Nevertheless, Hoogland et al, (2000) found the GABA content in synaptosomes from neocortical projection areas to be reduced to the same extent in patients with temporal lobe epilepsy (TLE) with and without tumor. In agreement with a study measuring effects of vigabatrin on brain GABA (Mueller et al, 2003) the presence of structural abnormality or its type does not seem to influence the occipital GABA levels found at baseline or in response to LEV.…”

Relationship between fluid-attenuated inversion-recovery (FLAIR) signal intensity and inflammatory mediator's levels in the hippocampus of patients with temporal lobe epilepsy and mesial temporal sclerosis

“…A deficiency in glutamine synthesis in astrocytes, found by several authors 22 , can also explain the high levels of glutamate in extracellular space, suggesting increased release of this amino acid. Working with synaptosomes from hippocampus of patients with TLE and MTS, was found 23 increased basal release of glutamate and GABA, data that could support our findings. Thus, the decreased concentration found in sclerotic hippocampus could be associated to increased release of this neurotransmitter, as already reported by several authors.…”

Two-Photon Imaging to Unravel the Pathomechanisms Associated with Epileptic Seizures: A Review

“…Two-photon uncaging produces excited states exactly as UV excitation does while also overcoming major limitations when probing biological tissue, such as spatial resolution, tissue penetration, and toxicity [73]. Two-photon uncaging is of special interest in epilepsy research, as imbalances between excitatory (glutamatergic) and inhibitory (GABAergic) neurotransmission have been implicated in the pathogenesis of the disorder [27,28,74]. Uncaging is used in four of the studies included in this review.…”

“…When probing molecular environments wherein intensity-based measurements alone are often insufficient, fluorescence lifetime-based measurements may be capable of yielding additional data [26]. Finally, the development of a wide range of fluorescent markers has made it possible to study various aspects of the pathophysiology of epilepsy, such as neurotransmitter levels [27,28], metabolism [28,29], pathological neuronal activity [27], and hypersynchronous network firing [30].…”