The predominant neuronal glutamate transporter, EAAC1 (for excitatory amino acid carrier-1), is localized to the dendrites and somata of many neurons. Rare presynaptic localization is restricted to GABA terminals. Because glutamate is a precursor for GABA synthesis, we hypothesized that EAAC1 may play a role in regulating GABA synthesis and, thus, could cause epilepsy in rats when inactivated. Reduced expression of EAAC1 by antisense treatment led to behavioral abnormalities, including staring-freezing episodes and electrographic (EEG) seizures. Extracellular hippocampal and thalamocortical slice recordings showed excessive excitability in antisense-treated rats. Patch-clamp recordings of miniature IPSCs (mIPSCs) conducted in CA1 pyramidal neurons in slices from EAAC1 antisense-treated animals demonstrated a significant decrease in mIPSC amplitude, indicating decreased tonic inhibition. There was a 50% loss of hippocampal GABA levels associated with knockdown of EAAC1, and newly synthesized GABA from extracellular glutamate was significantly impaired by reduction of EAAC1 expression. EAAC1 may participate in normal GABA neurosynthesis and limbic hyperexcitability, whereas epilepsy can result from a disruption of the interaction between EAAC1 and GABA metabolism.

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1. The development of epileptiform discharges in response to tetanic stimulation of the Schaeffer collaterals was studied by using extracellular field potential recordings in CA1, CA3, dentate gyrus, and entorhinal cortex and intracellular recordings in CA1 neurons in rat hippocampal-parahippocampal slices, which were cut so as to maintain reciprocal connections between entorhinal cortex and hippocampus in vitro. 2. The first type of epileptiform discharge to develop was an immediate afterdischarge, which grew in duration and amplitude with repeated stimulation trains at 10-min intervals, until it plateaued after five to nine trains at 40-s duration, on average. This afterdischarge, when fully developed, consisted of an early, high frequency tonic component, followed by a later, lower frequency clonic component. Fully developed primary afterdischarges were all-or-none, in that they had a definite threshold, and varied little in amplitude or duration when activated by threshold or suprathreshold stimulation. The primary discharge could be recorded simultaneously throughout the hippocampal-parahippocampal slice, providing evidence for the intact reciprocal connections between hippocampus and entorhinal cortex. Intracellular recordings in CA1 neurons revealed that during the tonic phase of the afterdischarge, neurons were depolarized by 15-30 mV and gradually repolarized during the clonic component. 3. After full development of the primary afterdischarge, a delayed secondary epileptiform discharge began to appear after five to nine stimulation trains. This late discharge began 2-5 min after the stimulation train and progressed in amplitude and duration with repeated stimulation, in some cases to 2-3 h long self-sustained epileptiform discharges. Like the primary afterdischarge, the secondary discharge could be recorded simultaneously throughout the hippocampal-parahippocampal slice, and individual bursts comprising the secondary discharge occurred at earliest latency in the dentate gyrus, followed by activation in CA3, CA1, and finally in the entorhinal cortex. Intracellular recordings in CA1 neurons established that the secondary discharge occurred without an accompanying depolarization. Rather, it appeared as synaptic bursts developing in an escalating frequency barrage, initiated 2-5 min after the primary afterdischarge. 4. Lesioning studies were conducted to begin determining the site of origin of the secondary epileptiform discharge. After appearance of the secondary discharge, the mossy fibers were cut. This lesion abolished the secondary discharge but did not block the primary afterdischarge. Moving the stimulating electrodes from the Schaeffer collaterals to the mossy fibers proximal to the cut reestablished a truncated secondary discharge. In a second lesioning experiment, a cut was made through the subicular region of the hippocampal-parahippocampal slice before the onset of stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

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This study evaluated hippocampal inhibitory function and the level of expression of y-aminobutyric acid type A (GABAA) receptor mRNA in an in vivo model of epilepsy. Chronic recurrent limbic seizures were induced in rats using injections of pilocarpine. Electrophysiological studies performed on hippocampal slices prepared from control and epileptic animals 1 to 2 months after pilocarpine injections demonstrated a significant hyperexcitability in the epileptic animals. Reduced levels of mRNA expression for the CY2 and a5 subunits of the GABAA receptors were evident in the CA1, CA2, and CA3 regions of the hippocampus of epileptic animals. No decrease in mRNA encoding al, 182, or y2 GABAA receptor subunits was observed. In addition, no change in the mRNA levels of a CaM kinase II was seen. Selective decreases in mRNA expression did not correlate with neuronal cell loss. The results indicate that selective, long-lasting reduction of GABAA subunit mRNA expression and increased excitability, possibly reflecting loss of GABAergic inhibition, occur in an in vivo model of partial complex epilepsy.-y-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter system in mammalian brain (1) and has been implicated in playing an important role in the induction and maintenance of epileptogenesis in several experimental models (2-6). In brain tissue from epileptic patients, decreased levels of GABA receptor-binding and of GABA-synthesizing enzymes have been documented (3). Furthermore, reduced benzodiazepine receptor binding in patients with temporal lobe epilepsy has been demonstrated in vivo by positronemission tomography (7). In animal models of epilepsy, changes in the level of GABA type A (GABAA) receptor binding have also been observed in specific hippocampal regions in kindled rats (8,9). Studies from our laboratories have shown a decrease in GABAA receptor binding in rat brain membranes (10) and a reduction in the physiological response to GABA in acutely isolated CAl hippocampal neurons (11) after the induction of epileptogenesis and persistent seizure discharge by pilocarpine injection. Thus, a considerable body of evidence indicates that decreased GABA receptor function and/or expression may play an important role in the induction and maintenance of epilepsy.Although GABA systems are altered in epilepsy, the specific molecular mechanisms mediating these changes have not been clearly elucidated (4,6). Long-term changes in gene expression produced by the induction of epileptogenesis have been suggested to play an important role in the persistent hyperexcitability observed in chronic epilepsy (12,13

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1. Combined hippocampal-parahippocampal slices were employed to study the development of complex epileptiform discharges after Schaeffer collateral stimulation in vitro. With repeated stimulation, slices generated several different types of epileptiform discharges, which were temporally linked to the preceding stimulus, and predictable in their progression. The first epileptiform discharge to be elicited by stimulation was a primary afterdischarge, which began immediately after the stimulation train and progressed with repeated stimulation until it had peaked in amplitude and duration by the third to fifth stimulus train. After development of the primary afterdischarge, a secondary afterdischarge began to appear, with a 2- to 5-min latency after the third to sixth stimulation train, and progressed in amplitude and duration with repeated stimulation, sometimes to durations > 30 min. 2. After development of the secondary afterdischarge, 65-70% of rostral slices triggered long-duration, spontaneous self-sustained activity. This activity consisted of repeated spontaneous 3- to 5-min duration ictallike discharges with a short interval (< 15 min between events), lasting for hours in many cases. These discharges were similar to activity seen in depth recordings of patients with complex partial status epilepticus. This cyclic spontaneous epileptiform activity was blocked by diazepam (100 nM to 1 microM), and potentiated by the N-methyl-D-aspartate (NMDA) antagonist 2-amino-5-phosphonovaleric acid (APV, 50 microM). Analysis of the temporal progression of epileptiform activity through multiple channel extracellular recordings demonstrated that both the interictal and ictal discharges evident during spontaneous recurrent ictal-like status epilepticus (SE) originated at a site distant from the stimulation locus, and then propagated to area CA1. 3. Intracellular recordings from CA3 neurons during spontaneous recurrent ictallike SE activity revealed the cellular correlates of this activity. Recurrent ictallike discharges were initiated at a cellular level by a large depolarization, accompanied by tonic action-potential firing. As the ictal event progressed, the neuron continued to depolarize, and a period of depolarization block ensued, which was terminated by the gradual repolarization of the neuron, with accompanying phasic burst firing. 4. A second variety of long-duration self-sustained activity was also seen in 5-10% of slices. This type of continuous sustained activity was initiated by an increase in duration of the secondary afterdischarge to 30-120 min duration with repeated stimulation. These sustained discharges were also increased in amplitude and frequency by APV (50 microM) and reduced or blocked by the benzodiazepines diazepam or clonazepam (1 microM). Sustained epileptiform discharges seen in vitro were similar to one form of seizure discharges seen in patients with SE in their frequency, duration, in their progression through a similar electrographic series of stages, and their sensitivity to benzodiazepines. 5...

Abstract:In recent years, Convolutional Neural Networks (ConvNets) have rapidly emerged as a widespread machine learning technique in a number of applications especially in the area of medical image classification and segmentation. In this paper, we propose a novel approach that uses ConvNet for classifying brain medical images into healthy and unhealthy brain images. The unhealthy images of brain tumors are categorized also into low grades and high grades. In particular, we use the modified version of the Alex Krizhevsky network (AlexNet) deep learning architecture on magnetic resonance images as a potential tumor classification technique. The classification is performed on the whole image where the labels in the training set are at the image level rather than the pixel level. The results showed a reasonable performance in characterizing the brain medical images with an accuracy of 91.16%.