Longitudinal changes of brain amino acid content occurring before, during and after epileptic activity

Neurochemical evidence based suggested therapy for safe management of epileptogenesis

Most of the clinically available antiepileptic drugs have only antiseizure effects and are reported unable to prevent epileptogenesis. In the past decade, several drugs underwent clinical trials for management of epileptogenesis, but none of the drugs tested was found effective. One of the major lacunas is availability of appropriate preclinical approaches to delineate mechanisms of epileptogenesis. Thus, the present study attempts to suggest a neurochemistry based approach for safe management of epileptogenesis. The altered neurochemical milieu in amygdala, cortex and hippocampus areas of the mice brain in naïve, kindled and kindling resistant animals has been delineated. The endogenous natural antiepileptogenic neurochemical defense mechanism observed in kindling resistant animals may uncover neurochemical mechanisms of epileptogenesis and in turn suggest us novel interventions for safe management of epileptogenesis. The kindling epileptogenesis was carried out in two month old male Swiss albino mice by administering subconvulsive pentylenetetrazole (35mg/kg; i.p.) at an interval of 48±2h for 42days. 2h after the last pentylenetetrazole injection, the animals were subjected to behavioral evaluations. Four hours after behavioral evaluation, all animals were euthanized and discrete parts of brain (amygdala, cortex and hippocampus) were harvested for neurochemical analysis. Results revealed that 60% of animals responded to kindling as observed with decreased seizure threshold, while the rest were found resistant. The kindled animals were found to be associated with anxiety, depression and cognitive impairment; while in kindling resistant animals no such behavioral deficits were observed. The neurochemical analysis revealed that in kindled animals altered glutamate-GABA neurotransmission, and decreased taurine, glycine, d-serine, monoamine levels with elevated indoleamine 2,3-dioxygenase activity were observed, which may be convicted for progression of kindling epileptogenesis. However, in kindling resistant animals elevated GABA, taurine, tryptophan, serotonin, glycine, and d-serine levels with decreased indoleamine 2,3-dioxygenase activity were observed as natural endogenous antiepileptogenic mechanisms, which may be foreseen as safe pharmacological targets for management of epileptogenesis.

Content and traffic of taurine in hippocampal reactive astrocytes

Taurine is one of the most abundant free amino acids in the mammalian central nervous system, where it is crucial to proper development. Moreover, taurine acts as a neuroprotectant in various diseases; in epilepsy, for example, it has the capacity to reduce or abolish seizures. In the present study, taurine levels has been determine in mice treated with Kainic Acid (KA) and results showed an increase of this amino acid in hippocampus but not in whole brain after 3 and 7 days of KA treatment. This increase occurs when gliosis was observed. Moreover, taurine transporter (TAUT) was found in astrocytes 3 and 7 days after KA treatment, together with an increase in cysteine sulfinic acid decarboxylase (csd) mRNA, that codifies for the rate-limiting enzyme of taurine synthesis, in the hippocampus at the same times after KA treatment. Glial cultures enriched in astrocytes were developed to demonstrate that these cells are responsible for changes in taurine levels after an injury to the brain. The cultures were treated with proinflammatory cytokines to reproduce gliosis. In this experimental model, an increase in the immunoreactivity of GFAP was observed, together with an increase in CSD and taurine levels. Moreover, an alteration in the taurine uptake-release kinetics was detected in glial cells treated with cytokine. All data obtained indicate that astrocytes could play a key role in taurine level changes induced by neuronal damage. More studies are, therefore, needed to clarify the role taurine has in relation to neuronal death and repair.

Prevention of epilepsy by taurine treatments in mice experimental model

An experimental model based on kainic acid (KA) injections replicates many phenomenological features of human temporal lobe epilepsy, the most common type of epilepsy in adults. Taurine, 2-aminoethanesulfonic acid, present in high concentrations in many invertebrate and vertebrate systems, is believed to serve several important biological functions. In addition, it is believed to have a neuroprotective role against several diseases. In the present study, an experimental mouse model based on taurine pretreatment prior to KA administration has been improved to study whether taurine has a neuroprotective effect against KA-induced behavior and cell damage. Under different treatments tested, taurine's most neuroprotective effects were observed with intraperitoneal taurine injection (150 mg/kg dosage) 12 hr before KA administration. Thus, a reduction in or total absence of seizures, together with a reduction in or even disappearance of cellular and molecular KA-derived effects, was detected in mice pretreated with taurine compared with those treated only with KA. Moreover, the use of tritiated taurine revealed taurine entry into the brain, suggesting possible changes in intracellular:extracellular taurine ratios and the triggering of pathways related to neuroprotective effects.

Cellular mechanisms of cobalt-induced hippocampal epileptiform discharges

PURPOSE

To explore the cellular mechanisms of cobalt-induced epileptiform discharges in mouse hippocampal slices.

METHODS

Hippocampal slices were prepared from adult mice and briefly exposed to a CoCl(2)-containing external solution. Population and single cell activities were examined via extracellular and whole-cell patch recordings.

RESULTS

Brief cobalt exposure induced spontaneous, ictal-like discharges originating from the CA3 area. These discharges were suppressed by anticonvulsants, gap junction blockers, or by raising extracellular Ca(2+), but their generation was not associated with overall hyperexcitability or impairment in GABAergic inhibition in the CA3 circuit. Electroencephalographic ictal discharges of similar waveforms were observed in behaving rats following intrahippocampal cobalt infusion.

DISCUSSION

Mechanisms involving activity-dependent facilitation of gap junctional communication may play a major role in cobalt-induced epileptiform discharges.

Alterations of taurine in the brain of chronic kainic acid epilepsy model

The aim of the study was to investigate the changes of taurine in the kainic acid (KA, 10 mg/kg, s.c.) chronic model of epilepsy, six months after KA application. The KA-rats used were divided into a group of animals showing weak behavioural response to KA (WDS, rare focal convulsion; rating scale <2 up to 3 h after KA injection) and a group of strong response to KA (WDS, seizures; rating >3 up to 3 h after KA injection). The brain regions investigated were caudate nucleus, substantia nigra, septum, hippocampus, amygdala/piriform cortex, and frontal, parietal, temporal and occipital cortices. KA-rats with rating <2 developed spontaneous WDS which occurred chronically and six months after KA injection increased taurine levels were found in the hippocampus (125.4% of control). KA-rats with rating >3 developed spontaneous recurrent seizures and six months after injection increased taurine levels were found in the caudate nucleus (162.5% of control) and hippocampus (126.6% of control), while reduced taurine levels were seen in the septum (78.2% of control). In summary, increased taurine levels in the hippocampus may involve processes for membrane stabilisation, thus favouring recovery after neuronal hyperactivity. The increased taurine levels in the caudate nucleus could be involved in the modulation of spontaneous recurrent seizure activity.

Disturbances of amino acids from temporal lobe synaptosomes in human complex partial epilepsy

We have studied the levels of neuroactive amino acids in synaptosomes (P2 fraction) isolated from brain tissue of ten patients with medically intractable epilepsy who were undergoing temporal lobectomy. First, lateral temporal tissue (nonfocal) was removed followed by medial temporal tissue (focal). A synaptosomal fraction (P2) was immediately prepared from each tissue and analyzed for free amino acid concentrations. Statistically significant reductions were seen in glutamine and GABA concentrations in focal tissue compared to nonfocal tissue. The ratio of excitatory amino acids (aspartate and glutamate) to inhibitory amino acids (taurine and GABA) was significantly higher in focal tissue compared to nonfocal. The glutamine/glutamate ratio was significantly reduced. These data support the hypothesis that alterations in the balance between excitatory and inhibitory amino acids may be involved in the expression of epilepsy.

Interictal and ictal activity in the rat cobalt/pilocarpine model of epilepsy decreased by local perfusion of diazepam

We investigated the efficacy of focal perfusion of diazepam (DZP) in reducing seizures produced by focal cobalt and systemic pilocarpine in the rat. Cobalt chloride crystals (3.5 mg/kg) were inserted stereotactically into the left hippocampus and recording electrodes affixed to the head of 23 rats. Focal spiking was evident within 5-7 days of implantation. Occasional ictal electrographic events were observed with cobalt alone, but consistent ictal events could be produced by intraperitoneal injection of pilocarpine hydrochloride (60 mg/kg) into the cobalt-treated animals. When rhythmical spiking was observed, the animals were treated either with DZP (0.25 mg in 50 microliters) or a vehicle (VEH) delivered into the left hippocampus. Blinded spike counts before and after injection showed spiking at 133.3 +/- 53.4% of baseline (mean +/- SD, n = 8) for the VEH-treated animals and 2.7 +/- 3.3% (n = 8) for the DZP-treated animals. Ictal events occurred in seven of the eight VEH-treated and two of the eight DZP-treated rats. Mean time to the first ictal event was 5.9 +/- 6.9 min for VEH-treated animals and 24 +/- 32.6 min for DZP-treated animals. DZP injected into the hippocampus contralateral to the cobalt did not reduce spiking. Systemic levels of DZP were unmeasurable in nine of ten tested animals. Focal perfusion of DZP therefore effectively reduced spiking in this cobalt chloride/pilocarpine model of focal and secondarily generalized epilepsy. This model, while involving GABAergic mechanisms, does not entirely depend upon GABAergic mechanisms. The findings therefore broaden the possibility of using focal DZP as a treatment for partial seizures.

Amino acid levels in cerebrospinal fluid of rats after administration of pentylenetetrazol

1. We studied the effect of pentylenetetrazol (PTZ)-induced myoclonic jerks and generalized clonic-tonic convulsions (GC) on the levels of neurotransmitter amino acids in the cisternal CSF of rats. 2. The levels of aspartate, glutamate, glycine, and taurine were elevated in the CSF during myoclonic jerks and more distinctly immediately after GC. 3. During the recovery period of postictal depression seen in EEG (5 min after GC), the CSF levels of transmitter amino acids were lower than in the control group. 4. PTZ-induced irritative activity in the EEG disappeared in 24 hr but the levels of amino acids remained abnormal. 5. Amino acid changes in the CSF following PTZ-induced convulsions might indicate that the release of amino acids into the extracellular space is increased before and during the propagation of PTZ-induced seizure and decreased during postictal depression.

Alterations in neurotransmitter amino acids in hippocampal kindled seizures

Rats were rapidly kindled with electrical stimuli to the hippocampus, and the concentrations of GABA and related amino acids were measured in several brain regions, both in the baseline kindled state and during active seizures. In the baseline kindled state, a consistent pattern was found throughout the hippocampus where GABA levels were depressed and glutamate and glutamine levels were elevated. During seizures GABA rose slightly while glutamate and glutamine increased to twice control values. These changes were seen to various degrees in other brain areas. Turnover in the GABA-glutamate-glutamine cycle was measured in kindled rats experiencing seizures and compared to control animals. During seizures there was an increased turnover of the excitatory compounds glutamate and aspartate relative to GABA. The data indicate that kindling produces a change of presynaptic GABA metabolism which results in diminished inhibition.

Na+-dependent transport of taurine by membrane vesicles of neuroblastoma x glioma hybrid cells

The transport of taurine into membrane vesicles prepared from neuroblastoma x glioma hybrid cells 108CC5 was studied. A great part of the taurine uptake by the membrane preparation is due to the transport into an osmotically sensitive space of membrane vesicles. Taurine uptake by membrane vesicles is an active transport driven by the concentration gradient of Na+ across the membrane (outside concentration greater than inside). The Km value of 36 microM for Na+-dependent taurine uptake indicates a high-affinity transport system. The rate of taurine transport by the membrane vesicles is enhanced by the K+ gradient (inside concentration greater than outside) and the K+ ionophore valinomycin. Taurine transport is inhibited by several structural analogs of taurine: hypotaurine, beta-alanine, and taurocyamine. All these results indicate that the taurine transport system of the membrane vesicles displays properties almost identical to those of intact neuroblastoma X glioma hybrid cells.

Glutamic acid as a putative transmitter of the interhemispheric corticocortical connections in the rat

The effect of hemidecortication on the endogenous levels of amino acids in medial, sulcal, and dorsal frontal cortex as well as in parietal, temporal, and occipital cortex of the rat was investigated. Under aseptic conditions, the right cerebral cortex was aspirated by suction. Then, 21 days later, the content of glutamic acid, aspartic acid, gamma-aminobutyric acid, glycine, serine, threonine, and alanine was analyzed in six areas of the intact contralateral cortex using GLC. The results demonstrated a specific decrease in the endogenous levels of glutamic acid in both parietal and temporal cortex after hemidecortication of the contralateral side. This finding suggests that glutamic acid may serve as a neurotransmitter for some of the interhemispheric corticoparietal and corticotemporal fibers. In a follow-up experiment, the effect of a frontal lesion on the endogenous levels of the same amino acids in the striatum was also examined. In this case, the glutamic acid content exhibited a decrease of 31% relative to the control value. This observation confirms the earlier finding of a glutamate-containing pathway from the frontal cortex to the striatum.

The epileptogenic action of 6-aminomethyl-3-methyl,1-4H-1,2,6-benzothiadiazine-1,1-diazide hydrochloride (TAG): non-specific versus specific antitaurine pathogenesis

Cortical superfusion with 6-aminomethyl-3-methyl, 1-4H-1,2,6-benzothiadiazine-1,1-diazide hydrocholoride (TAG) at a concentration which selectively blocks taurine (Tau) action fails to modify electroencephalographic (EEG) activity, cortical neuronal firing and caudate-induced inhibition of cortical neuronal activity. Higher concentrations of TAG increase neuronal firing rate and eventually induce EEG interictal spikes that can be suppressed by topical gamma-aminobutyric acid (GABA), but not by glycine or beta-alanine. Topical Tau consistently enhances the epileptiform activity. It is concluded that specific blockade of Tau does not affect any of the physiological function under observation and that the epileptogenic effect of TAG is due to its GABA antagonistic action.

Reduced plasma haptoglobin and urinary taurine in familial seizures identified through the multisib strategy

The multisib (MS) sampling strategy was used for detecting possible genetic influences on a complex and heterogeneous disorder. The MS strategy increases the likelihood of selecting pedigrees for single genetic factors and allows the efficient analysis of data. The collection of complete pedigrees will procure additional data, but at a large marginal expense. The MS ascertainment procedure was applied to seizure disorders by examination of taurine excretion levels and by conducting two-dimensional gel electrophoresis of plasma proteins. Reduced taurine excretion (proposed to be genetically controlled) was found to associate with seizures, particularly in those individuals with a generalized spike and wave (GSW) EEg, or in families with a GSW-seizure history. Examination of two-dimensional gels showed hypohaptoglobinemia in several seizure patients [Panter et al, 1984]. The frequency of hypohaptoglobinemia is greatly increased in familial seizure cases, and may also be genetically controlled. Thus the MS strategy has proven successful in identifying kindreds in which specific physiological alterations may contribute toward the complex phenotype of seizures.

Altered amino acid levels in multiply affected sibships with seizures

Evidence of genetic factors in seizure disorders by examination of plasma amino acid concentrations in multiply affected sibships was investigated. The strategy of multiply affected sibship ascertainment was used to reduce heterogeneity as one of several potential sources of variation in quantitative amino acid levels. Our results do not support previously reported increases in plasma taurine, aspartic acid, or glutamic acid in seizure patients. However, we do find that multiply affected sibships have significantly elevated plasma concentrations of arginine and asparagine, and significantly decreased ornithine. These amino acid concentrations may be under quantitative genetic control. Within-sibship comparisons indicate that seizure patients have increased glutamine and decreased lysine and phenylalanine, possibly secondary to the seizures. We also find that anticonvulsant use complicates statistical analyses. Further studies to more clearly delineate the genetics of plasma amino acid concentrations (or other quantitative metabolic measures) and their role in seizure disorders are required and will benefit from the use of a homogeneous sampling strategy.

Altered time course of changes in the hippocampal concentration of excitatory and inhibitory amino acids during kainate-induced epilepsy

The temporal sequence of electrophysiological and biochemical correlates of epilepsy induced by systemic injection of kainic acid (15 mg/kg i.p.) was investigated in male rats. A significant decrease in the hippocampal concentration of glutamate and aspartate was observed 20 min after the injection. These decreases preceded both electrographic and behavioral manifestations of epilepsy, thus suggesting a causal relationship between acidic amino acid changes and the genesis of kainate-induced hyperactivity. About 30-45 min after kainate injection, a decrease in glutamate, aspartate, glycine and taurine and no change in GABA concentration were observed. Bioelectrical activity, recorded in the regio inferior (CA3) of the hippocampus or in the fascia dentata revealed the presence of high frequency bursts separated by a long-lasting depression of discharge. About 55-75 min after the injection, the number of spikes in each burst increased and the duration and frequency of interictal pauses decreased. This stage was characterized by a decrease in glutamate and aspartate, restoration to normal of glutamine, glycine and taurine and a decrease in GABA.

Alterations in the content of amino acid neurotransmitters before the onset and during the course of methoxypyridoxine-induced seizures in individual rabbit brain regions

In rabbits, generalized seizures were induced by methoxypyridoxine, and changes in amino acid concentrations of 15 brain regions were investigated before seizure onset and during the course of sustained epileptiform activity. As previously reported, gamma-aminobutyric acid (GABA) concentration decreased preictally in most regions. At the same time, taurine level was elevated in the hypothalamus, thalamus, hippocampus, caudatum, and frontal cortex. After 90 min of seizures, it was significantly decreased in the hypothalamus, periaqueductal grey, substantia nigra, frontal cortex, and cerebellum. Glycine content was reduced preictally only in the substantia nigra; after seizure onset its concentration rose in all brain areas. Glutamate content in the frontal cortex decreased before seizure onset; after 1.5 h of seizures, its concentration in cerebellum, caudatum, and hippocampus was reduced. Aspartate level was decreased in most areas after sustained seizures; in putamen, however, it was elevated. In contrast, glutamine content increased preictally in the superior colliculus and in all brain areas by approximately 200% after 90 min of seizures. Alanine and valine content also rose markedly in most brain areas after prolonged seizures, and threonine showed the same tendency. The single brain regions were observed to respond to methoxypyridoxine in highly individualistic ways. For example, the glycine content of the substantia nigra, which is believed to utilize this amino acid as a neurotransmitter, decreased preictally. The potential importance of the superior colliculus in seizure induction is considered in view of the early rise in glutamine level. The antagonistic preictal behavior of taurine and GABA is discussed with respect to synthesis, uptake from the blood, and antiepileptic properties.

Focal seizures disrupt protein synthesis in seizure pathways: an autoradiographic study using [1-14C]leucine

We have used a new autoradiographic technique developed by Smith et al.22,33 for visualizing rates of incorporation of [1-14C]leucine into protein in brain. Focal seizures caused by topical convulsants resulted in a marked decrease in autoradiographic density. This was primarily confined to the seizure focus, especially marked in pyramidal cell layers, and to subcortical seizure pathways. There were no distinct changes in cortico-cortical pathways beyond the seizure focus. Pure orthodromic pathways through basal ganglia showed an 18% inhibition of leucine incorporation in caudate nucleus and substantia nigra, pars compacta (P less than 0.05). By contrast, thalamic nuclei connected both ortho- and antidromically to the focus showed a 30-63% inhibition (P less than 0.01). The topographic pattern and intensity of the thalamic changes were related to the site, size and intensity of the seizure focus. As seizures became severe there was a more generalized depression of metabolism beyond seizure pathways, especially in the ipsilateral hemisphere. The results suggest that seizures block incorporation of leucine into protein either by an increase oxidation of the precursor, and/or an inhibition of protein synthesis per se. The effect is most severe in neurons undergoing epileptic burst discharge in the focus and in thalamic neuronal beds connected reciprocally with the focus.

Effect of epileptogenic agents on the incorporation of 3H-glycine into proteins in the cat's cerebral cortex

Filter paper strips soaked in 3H-glycine solution were applied to acoustic cortex of cats, anaesthetized with Nembutal and pretreated with epileptogenic agents (Metrazol, G-penicillin, and 3-amino-pyridine) and cycloheximide. The untreated contralateral hemisphere served as control. After 1 h incubation, both cortical samples were excised simultaneously and fixed in Bouin solution for autoradiography. Incorporation was blocked by cycloheximide. There was no glycine incorporation on the penicillin-treated side, while pyramidal cells were intensively labelled in layers II-V of the mirror focus. 3-Aminopyridine produced the same result. Metrazol as convulsant proved to be far weaker than the previous two. The intensity of incorporation was significantly more intensive in the mirror focus than in the primary one. Penicillin and 3-aminopyridine, while provoking cortical seizures, seem to inhibit glycine incorporation into a neuron-specific, function-dependent protein contained by the labelled cells in the autoradiogram.

Studies on gamma-aminobutyric acid transport in cobalt experimental epilepsy in the rat

Crude brain homogenates and cerebral tissue slices from rats with cobalt metal implanted in right and left cerebral cortices were used to examine high- and low-affinity GABA transport. High-affinity GABA transport was maximally reduced to 34% of controls 7 days after cobalt implantation, a time that coincides with peak seizure activity in this model. Kinetic analysis of high-affinity GABA transport, using brain homogenates, revealed a significant change in Vmax 7 days after cobalt implantation. (Vmax = 446.4 +/- 26.2 pmol/mg prot./min, cobalt, versus 787.8 +/- 67.3, control). An analysis of the low-affinity system revealed no depression of Km or Vmax parameters. Administration of valproic acid at a concentration as high as 1 mM in vitro or a dose of 300 mg/kg in vivo had no effect on high- or low-affinity GABA transport. The results obtained from cobalt-treated rats provide additional evidence for an involvement of GABA in experimental epilepsy.

Neurotransmitter, receptor and biochemical changes in monkey cortical epileptic foci

Epileptic and normal Macaca mulatta monkey cortex was investigated using ligand binding techniques. Subpial injections of aluminum hydroxide gel into the left sensorimotor cortex produced stable seizure frequencies over a two year period and resulted in specific biochemical and receptor abnormalities. Pair matched CSF samples comparing epileptic and non-epileptic hemispheres showed a significant decreased GABA concentration over the epileptic side. The epileptic cortex demonstrated markedly reduced GABA receptor binding and diminished tissue GABA concentration and GAD activity. Two patterns of receptor loss were observed: nonspecific local cellular drop out involving multiple neurotransmitter receptors; and distal receptor loss which was specific for the neurotransmitter intervention pattern of the cortex. GABAergic receptor loss was more marked than receptor losses for the other neurotransmitter and was more widespread. Scatchard plot analysis demonstrated that the diminished GABAergic receptors within the focus were due to receptor loss and not affinity changes. Spearman rank correlations showed a significant correlation only between the degree of GABAergic receptor loss or decrease in GAD activity and the seizure frequency. Epilepsy appears to be a multifactoral disorder with multiple neuroreceptor abnormalities, the most notable of which are the destruction of GABAergic neurons and GABA receptors.

The action of glycine on rat epileptic foci

The action of glycine (Gly) intravenously injected on rat epileptic foci induced by strychnine or penicillin topically applied, was compared with that of GABA. Gly (450 mg/kg i.v.) produced a complete block of the spiking activity. The inhibitory action of GABA (80 mg/kg), in terms of threshold and duration, was stronger than the action of Gly. The same inhibitory effect was also observed if these amino acids were applied topically or intracisternally. These results are consistent with the possibility that Gly has a role in the rat cortical inhibition.

Effect of amino-oxyacetic acid (AOAA) on focal penicillin seizures

The biochemical and behavioral effects of the anticonvulsant amino-oxyacetic acid (AOAA) have been studied in a model of focal penicillin seizures in rats. At 20 mg/Kg AOAA treatment results in a progressive 11 fold increase in GABA levels in cortex over three hours. There is a decrease in aspartate, ketoglutarate, alanine and glutamine, and an initial decrease followed by an increase in pyruvate and glutamate. These results reflect a functional inhibition of several B-6 dependent aminotransferase enzymes. When rats are pretreated 30 min before the onset of focal penicillin seizures there is a 60% reduction in the number of discharges and a 34% reduction in seizure duration. Pretreatment beyond 75 min results in progressively less anticonvulsant effect, such that seizures eventually become more severe than control. There is an increase in the number and duration of discharges, seizure spikes become complex, and tonic-clonic events develop. Penicillin seizures do not cause a change in levels of GABA, but result in a decrease in glutamate within the focus. AOAA pretreatment initially prevents this decrease in glutamate but later accentuates it. The biochemical effects of AOAA are complex, but biphasic anticonvulsant properties coincide in time with a change in the balance of excitatory and inhibitory amino acids in the seizure focus.