Changes in the concentration of amino acids in the hippocampus of pentylenetetrazole-kindled rats

Scorpion venom heat-resistant synthesized peptide ameliorates epileptic seizures and imparts neuroprotection in rats mediated by NMDA receptors

Finding new and effective natural products for designing antiepileptic drugs is highly important in the scientific community. The scorpion venom heat-resistant peptide (SVHRP) was purified from Buthus martensii Karsch scorpion venom, and subsequent analysis of the amino acid sequence facilitated the synthesis of a peptide known as scorpion venom heat-resistant synthesis peptide (SVHRSP) using a technique for peptide synthesis. Previous studies have demonstrated that the SVHRSP can inhibit neuroinflammation and provide neuroprotection. This study aimed to investigate the antiepileptic effect of SVHRSP on both acute and chronic kindling seizure models by inducing seizures in male rats through intraperitoneal administration of pentylenetetrazole (PTZ). Additionally, an N-methyl-D-aspartate (NMDA)-induced neuronal injury model was used to observe the anti-excitotoxic effect of SVHRSP in vitro. Our findings showed that treatment with SVHRSP effectively alleviated seizure severity, prolonged latency, and attenuated neuronal loss and glial cell activation. It also demonstrated the prevention of alterations in the expression levels of NMDA receptor subunits and phosphorylated p38 MAPK protein, as well as an improvement in spatial reference memory impairment during Morris water maze (MWM) testing in PTZ-kindled rats. In vitro experiments further revealed that SVHRSP was capable of attenuating neuronal action potential firing, inhibiting NMDA receptor currents and intracellular calcium overload, and reducing neuronal injury. These results suggest that the antiepileptic and neuroprotective effects of SVHRSP may be mediated through the regulation of NMDA receptor function and expression. This study provides new insight into therapeutic strategies for epilepsy.

Pentylenetetrazole: A review

Pentylenetetrazole (PTZ), a tetrazole derivative, is commonly used as a chemical agent to induce neurological disorders and replicate the characteristics of human epileptic seizures in animal models. This review offers a comprehensive analysis of the behavioral, neurophysiological, and neurochemical changes induced by PTZ. The epileptogenic and neurotoxic mechanisms of PTZ are associated with an imbalance between the GABAergic and glutamatergic systems. At doses exceeding 60 mg/kg, PTZ exerts its epileptic effects by non-competitively antagonizing GABAA receptors and activating NMDA receptors, resulting in an increased influx of cations such as Na+ and Ca2+. Additionally, PTZ promotes oxidative stress, microglial activation, and the synthesis of pro-inflammatory mediators, all of which are features characteristic of glutamatergic excitotoxicity. These mechanisms ultimately lead to epileptic seizures and neuronal cell death, which depend on the dosage and method of administration. The behavioral, electroencephalographic, and histological changes associated with PTZ further establish it as a valuable preclinical model for the study of epileptic seizures, owing to its simplicity, cost-effectiveness, and reproducibility.

The effect of valproate on the amino acids, monoamines, and kynurenic acid concentrations in brain structures involved in epileptogenesis in the pentylenetetrazol-kindled rats

BACKGROUND

The study aimed to assess the influence of a single valproate (VPA) administration on inhibitory and excitatory neurotransmitter concentrations in the brain structures involved in epileptogenesis in pentylenetetrazol (PTZ)-kindled rats.

METHODS

Adult, male Wistar rats were kindled by repeated intraperitoneal (ip) injections of PTZ at a subconvulsive dose (30 mg/kg, three times a week). Due to the different times required to kindle the rats (18-22 injections of PTZ), a booster dose of PTZ was administrated 7 days after the last rats were kindled. Then rats were divided into two groups: acute administration of VPA (400 mg/kg) or saline given ip. The concentration of amino acids, kynurenic acid (KYNA), monoamines, and their metabolites in the prefrontal cortex, hippocampus, amygdala, and striatum was assessed by high-pressure liquid chromatography (HPLC).

RESULTS

It was found that a single administration of VPA increased the gamma-aminobutyric acid (GABA), tryptophan (TRP), 5-hydroxyindoleacetic acid (5-HIAA), and KYNA concentrations and decreased aspartate (ASP) levels in PTZ-kindled rats in the prefrontal cortex, hippocampus, amygdala and striatum.

CONCLUSIONS

Our results indicate that a single administration of VPA in the PTZ-kindled rats restored proper balance between excitatory (decreasing the level of ASP) and inhibitory neurotransmission (increased concentration GABA, KYNA) and affecting serotoninergic neurotransmission in the prefrontal cortex, hippocampus, amygdala, and striatum.

Increased Hippocampal Afterdischarge Threshold in Ketogenic Diet is Accompanied by Enhanced Kynurenine Pathway Activity

The efficacy of a ketogenic diet (KD) in controlling seizure has been shown in many experimental and clinical studies, however, its mechanism of action still needs further clarification. The major goal of the present study was to investigate the influence of the commercially available KD and caloric restriction (CR) on the hippocampal afterdischarge (AD) threshold in rats, and concomitant biochemical changes, specifically concerning the kynurenine pathway, in plasma and the hippocampus. As expected, the rats on the KD showed higher AD threshold accompanied by increased plasma β-hydroxybutyrate level compared to the control group and the CR rats. This group presented also lowered tryptophan and elevated kynurenic acid levels in plasma with similar changes in the hippocampus. Moreover, the KD rats showed decreased levels of branched chain amino acids (BCAA) and aromatic amino acids (AAA) in plasma and the hippocampus. No regular biochemical changes were observed in the CR group. Our results are analogous to those detected after single administrations of fatty acids and valproic acid in our previous studies, specifically to an increase in the kynurenine pathway activity and changes in peripheral and central BCAA and AAA levels. This suggests that the anticonvulsant effect of the KD may be at least partially associated with those observed biochemical alternations.

Alterations in mRNA and Protein Expression of Glutamate Receptor Subunits Following Pentylenetetrazole-induced Acute Seizures in Young Rats

Acute seizures can severely affect brain function and development. However, the underlying pathophysiological mechanisms are still poorly understood. Disturbances of the glutamatergic system are considered one of the critical mechanisms of neurological abnormalities. In the present study, we analyzed changes in the expression of NMDA and AMPA receptor subunits in the different brain regions (dorsal hippocampus, amygdala, and the medial prefrontal, temporal, and entorhinal cortex) using a pentylenetetrazole (PTZ) model of seizures in 3-week-old rats. A distinctive feature of this model is that the administration of PTZ causes severe acute seizures, which are not followed by the development of spontaneous recurrent seizures later on. Subunit expression was analyzed using qRT-PCR and Western blotting during the first week after seizures. The most pronounced alterations of mRNA and protein levels were observed in the dorsal hippocampus. We found decreased expression of the GluA2 mRNA 7 days after seizures (PSE7), as well as reduced GluN2a protein levels on PSE7. Significant alterations in the expression of different receptor subunits in the mRNA but not protein levels were observed in the entorhinal cortex and amygdala. In contrast, in the medial prefrontal and temporal cortex, we found almost no changes in the expression of the studied genes. The identified changes deepen our understanding of post-seizure disturbances in the developing brain and confirm that although various brain structures are involved in seizures, the hippocampus is the most vulnerable.

Neurobiology, Functions, and Relevance of Excitatory Amino Acid Transporters (EAATs) to Treatment of Refractory Epilepsy

Epilepsy is one of the most prevalent and devastating neurological disorders characterized by episodes of unusual sensations, loss of awareness, and reoccurring seizures. The frequency and intensity of epileptic fits can vary to a great degree, with almost a third of all cases resistant to available therapies. At present, there is a major unmet need for effective and specific therapeutic intervention. Impairments of the exquisite balance between excitatory and inhibitory synaptic processes in the brain are considered key in the onset and pathophysiology of the disease. As the primary excitatory neurotransmitter in the central nervous system, glutamate has been implicated in the process, with the glutamatergic system holding center stage in the pathobiology as well as in developing disease-modifying therapies. Emerging data pinpoint impairments of glutamate clearance as one of the key causative factors in drug-resistant disease forms. Reinstatement of glutamate homeostasis using pharmacological and genetic modulation of glutamate clearance is therefore considered to be of major translational relevance. In this article, we review the neurobiological and clinical evidence suggesting complex aberrations in the activity and functions of excitatory amino acid transporters (EAATs) in epilepsy, with knock-on effects on glutamate homeostasis as a leading cause for the development of refractory forms. We consider the emerging data on pharmacological and genetic manipulations of EAATs, with reference to seizures and glutamate dyshomeostasis, and review their fundamental and translational relevance. We discuss the most recent advances in the EAATs research in human and animal models, along with numerous questions that remain open for debate and critical appraisal. Contrary to the widely held view on EAATs as a promising therapeutic target for management of refractory epilepsy as well as other neurological and psychiatric conditions related to glutamatergic hyperactivity and glutamate-induced cytotoxicity, we stress that the true relevance of EAAT2 as a target for medical intervention remains to be fully appreciated and verified. Despite decades of research, the emerging properties and functional characteristics of glutamate transporters and their relationship with neurophysiological and behavioral correlates of epilepsy challenge the current perception of this disease and fit unambiguously in neither EAATs functional deficit nor in reversal models. We stress the pressing need for new approaches and models for research and restoration of the physiological activity of glutamate transporters and synaptic transmission to achieve much needed therapeutic effects. The complex mechanism of EAATs regulation by multiple factors, including changes in the electrochemical environment and ionic gradients related to epileptic hyperactivity, impose major therapeutic challenges. As a final note, we consider the evolving views and present a cautious perspective on the key areas of future progress in the field towards better management and treatment of refractory disease forms.

Social deprivation substantially changes multi-structural neurotransmitter signature of social interaction: Glutamate concentration in amygdala and VTA as a key factor in social encounter-induced 50-kHz ultrasonic vocalization

Ultrasonic vocalizations are important for coordinating social behavior in rats. Examination of the neurochemical mechanisms that govern social behavior and ultrasonic vocalization emission is crucial for understanding the social impairments that occur in many neuropsychiatric disorders. To elucidate neurochemical changes in the brain structures related to social behavior and their mutual relationships, we conducted three-phase experiment. Neurochemicals were measured in the following behavioral situations: without social encounter, with short social encounter, with long social encounter in isolated and non-isolated rats. The aims of this study were to: (1) extract the most important neurotransmitters and their metabolites that are involved in social encounter-induced emission of 50 kHz calls; (2) to elucidate mutual relationships among the neurochemical changes in the selected, six brain structures, and analyze compound relationships by step analysis; (3) create a model of all-to-all neurotransmitter correlations; (4) find the neurochemical basis of 50-kHz USVs emission during social encounter. Our behavioral and neurochemical analysis indicated that social encounter was a triggering factor of the glutamatergic neurotransmission in the ventral tegmental area (VTA), hippocampus, and amygdala; serotonergic neurotransmission in the NAcc, CPu, and amygdala; the dopaminergic neurotransmission in the caudate putamen (CPu) and hippocampus; GABAergic neurotransmission in the hippocampus and VTA. Social encounter-induced 50-kHz USVs were bound up with changes in glutamate in amygdala and VTA, glycine in the amygdala, VTA, hippocampus, nucleus accumbens and CPu, and dopamine metabolites in VTA and CPu.

CE-MS metabolic profiling of volume-restricted plasma samples from an acute mouse model for epileptic seizures to discover potentially involved metabolomic features

Currently, a high variety of analytical techniques to perform metabolomics is available. One of these techniques is capillary electrophoresis coupled to mass spectrometry (CE-MS), which has emerged as a rather strong analytical technique for profiling polar and charged compounds. This work aims to discover with CE-MS potential metabolic consequences of evoked seizures in plasma by using a 6Hz acute corneal seizure mouse model. CE-MS is an appealing technique because of its capability to handle very small sample volumes, such as the 10 μL plasma samples obtained using capillary microsampling in this study. After liquid-liquid extraction, the samples were analyzed with CE-MS using low-pH separation conditions, followed by data analysis and biomarker identification. Both electrically induced seizures showed decreased values of methionine, lysine, glycine, phenylalanine, citrulline, 3-methyladenine and histidine in mice plasma. However, a second provoked seizure, 13 days later, showed a less pronounced decrease of the mean concentrations of these plasma metabolites, demonstrated by higher fold change ratios. Other obtained markers that can be related to seizure activities based on literature data, are isoleucine, serine, proline, tryptophan, alanine, arginine, valine and asparagine. Most amino acids showed relatively stable plasma concentrations between the basal levels (Time point 1) and after the 13-day wash-out period (Time point 3), which suggests its effectiveness. Overall, this work clearly demonstrated the possibility of profiling metabolite consequences related to seizure activities of an intrinsically low amount of body fluid using CE-MS. It would be useful to investigate and validate, in the future, the known and unknown metabolites in different animal models as well as in humans.

Individual susceptibility or resistance to posttraumatic stress disorder-like behaviours

The aim of this study was to explore the neurobiological background of individual susceptibility and resistance to the development of posttraumatic stress disorder (PTSD)-like behaviours. Rats were divided into susceptible, PTSD(+), and resistant, PTSD(-), groups based on freezing duration during exposure to aversive context and the time spent in the central area in open field test one week after threefold stress experience (modified single prolonged stress). PTSD(-) rats showed increased concentrations of corticosterone in plasma and changes in GAD67 expression: decreased in the infralimbic cortex (IL) and increased in the lateral amygdala (LA), dentate gyrus (DG), and CA1 area of the hippocampus. Moreover, in this group, we found an increase in the number of CRF-positive nuclei in the parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN). The PTSD(+) group, compared to PTSD(-) rats, had decreased concentrations of corticosterone in plasma and reduced CRF expression in the pPVN, higher CRF expression in the CA1, increased expression of CRF-positive nuclei and GR receptors in the CA3 area of the hippocampus, and increased expression of GR receptors in the DG and the central amygdala (CeA). Biochemical analysis showed higher concentrations of noradrenaline, glutamic acid in the dorsal hippocampus and amygdala and lower levels of dopamine and its metabolites in the amygdala of the PTSD(+) group than in the PTSD(-) group. The study revealed different behavioural and biochemical profiles of PTSD(+) and PTSD(-) rats and suggested that individual differences in hypothalamic-pituitary-adrenal (HPA) axis activity may determine hippocampal- and amygdala-dependent memory and fear processing.

Inter-individual differences in serotonin and glutamate co-transmission reflect differentiation in context-induced conditioned 50-kHz USVs response after morphine withdrawal

A growing body of research provides compelling evidence that in rats 50-kHz USVs are a form of expression of positive emotions. Context-induced 50-kHz USVs emission is variable among rats, indicating individual differences in contextual response bound up with pharmacological reward. The aims of this study were to: extract the most important neurotransmitters related to context-induced conditioned 50-kHz USVs response; find biological basis of existing inter-individual differences in context-induced conditioned 50-kHz USVs response; create a model of all-to-all neurotransmitters correlations. The data collected here confirms that re-exposure to the context of morphine administration after the withdrawal period increases the level of 50-kHz USVs and this contextual response is associated with elevated serotonin concentrations in amygdala, hippocampus and mPFC and with increased Glu/Gln ratio in nucleus accumbens. The concentration of serotonin increases simultaneously in amygdala, nucleus accumbens and hippocampus. Moreover, 5-HT concentration in amygdala is bound up with glutamate level in this structure as well as in hippocampus. Furthermore, Glu/Gln ratio in nucleus accumbens has strong associations with Glu/Gln ratio simultaneously in VTA, amygdala, striatum and hippocampus. All-to-all-analysis indicate that concentration of glutamate in hippocampus is proportional to glutamate in VTA and GABA concentration in the hippocampus. We have also demonstrated that Glu/GABA ratio in VTA and amygdala was elevated after post withdrawal re-exposure to the pharmacological reward paired context. Presented analysis indicates a strong correlation between serotonergic and glutamatergic systems in context-induced conditioned response. The strength of this co-transmission correlates with the number of 50-kHz USVs emitted in response to morphine-paired context.

Taurine supplementation to anti-seizure drugs as the promising approach to treat pharmacoresistant epilepsy: A pre-clinical study

Background Pharmacoresistance leads to severe, irreversible disabilities and premature death in ∼30% cases of epilepsy despite adequate and appropriate treatment with available anti-seizure drugs (ASDs) without any underlying cause. In light of the large body of evidence which suggests the anti-seizure action of taurine in experimental animals and its wide safety margins in human, supplementation of this inhibitory amino-sulfonic acid to available ASDs seems promising to treat pharmacoresistant epilepsy.

Methods We examined the anti-seizure effect of lamotrigine (15 mg/kg), levetiracetam (40 mg/kg), carbamazepine (40 mg/kg), phenytoin (35 mg/kg) & taurine (50, 100 & 200 mg/kg) in lamotrigine pre-treated pentylenetetrazole-kindled mice (LPK) which mimic core features of pharmacoresistant epilepsy, either alone ASDs or in combinations whereby three different doses of taurine were supplemented with tested ASDs.

Results Both, the ASDs and the taurine were failed to suppress generalized tonic-clonic seizures in LPK mice. However, taurine supplementation clearly restored the anti-seizure effect of tested ASDs. Further neurochemical studies revealed that higher levels of taurine in the hippocampus and cerebral cortex restored the imbalance between major excitatory neurotransmitters glutamate & its inhibitory counterpart GABA.

Conclusions These findings emphasize that supplementation of taurine with ASDs may be useful to treat pharmacoresistant epilepsy. Thus, further clinical validation is encouraged.

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.

Protective Effect of Resveratrol on the Brain in a Rat Model of Epilepsy

Accumulating evidence has suggested resveratrol as a promising drug candidate for the treatment of epilepsy. To validate this, we tested the protective effect of resveratrol on a kainic acid (KA)-induced epilepsy model in rats and investigated the underlying mechanism. We found that acute resveratrol application partially inhibited evoked epileptiform discharges in the hippocampal CA1 region. During acute, silent and chronic phases of epilepsy, the expression of hippocampal kainate glutamate receptor (GluK2) and the GABAA receptor alpha1 subunit (GABAAR-alpha1) was up-regulated and down-regulated, respectively. Resveratrol reversed these effects and induced an antiepileptic effect. Furthermore, in the chronic phase, resveratrol treatment inhibited the KA-induced increased glutamate/GABA ratio in the hippocampus. The antiepileptic effects of resveratrol may be partially attributed to the reduction of glutamate-induced excitotoxicity and the enhancement in GABAergic inhibition.

Stimulation of Anterior Thalamic Nuclei Protects Against Seizures and Neuronal Apoptosis in Hippocampal CA3 Region of Kainic Acid-induced Epileptic Rats

Background:

The antiepileptic effect of the anterior thalamic nuclei (ANT) stimulation has been demonstrated; however, its underlying mechanism remains unclear. The aim of this study was to investigate the effect of chronic ANT stimulation on hippocampal neuron loss and apoptosis.

Methods:

Sixty-four rats were divided into four groups: The control group, the kainic acid (KA) group, the sham-deep brain stimulation (DBS) group, and the DBS group. KA was used to induce epilepsy. Seizure count and latency to the first spontaneous seizures were calculated. Nissl staining was used to analyze hippocampal neuronal loss. Polymerase chain reaction and Western blotting were conducted to assess the expression of caspase-3 (Casp3), B-cell lymphoma-2 (Bcl2), and Bcl2-associated X protein (Bax) in the hippocampal CA3 region. One-way analysis of variance was used to determine the differences between the four groups.

Results:

The latency to the first spontaneous seizures in the DBS group was significantly longer than that in the KA group (27.50 ± 8.05 vs. 16.38 ± 7.25 days, P = 0.0005). The total seizure number in the DBS group was also significantly reduced (DBS vs. KA group: 11.75 ± 6.80 vs. 23.25 ± 7.72, P = 0.0002). Chronic ANT-DBS reduced neuronal loss in the hippocampal CA3 region (DBS vs. KA group: 23.58 ± 6.34 vs. 13.13 ± 4.00, P = 0.0012). After chronic DBS, the relative mRNA expression level of Casp3 was decreased (DBS vs. KA group: 1.18 ± 0.37 vs. 2.09 ± 0.46, P = 0.0003), and the relative mRNA expression level of Bcl2 was increased (DBS vs. KA group: 0.92 ± 0.21 vs. 0.48 ± 0.16, P = 0.0004). The protein expression levels of CASP3 (DBS vs. KA group: 1.25 ± 0.26 vs. 2.49 ± 0.38, P < 0.0001) and BAX (DBS vs. KA group: 1.57 ± 0.49 vs. 2.80 ± 0.63, P = 0.0012) both declined in the DBS group whereas the protein expression level of BCL2 (DBS vs. KA group: 0.78 ± 0.32 vs. 0.36 ± 0.17, P = 0.0086) increased in the DBS group.

Conclusions:

This study demonstrated that chronic ANT stimulation could exert a neuroprotective effect on hippocampal neurons. This neuroprotective effect is likely to be mediated by the inhibition of apoptosis in the epileptic hippocampus.

Evidence in support of using a neurochemistry approach to identify therapy for both epilepsy and associated depression

The present study aimed to develop a neurochemistry-based single or adjuvant therapy approach for comprehensive management of epilepsy and associated depression employing pentylenetetrazole-kindled animals. Kindling was induced in two-month-old male Swiss albino mice by administering a subconvulsant pentylenetetrazole dose (35mg/kg, i.p.) at an interval of 48±2h. These kindled animals were treated with saline and sodium valproate (300mg/kg/day, i.p.) for 15days. Except for the naïve group, all other groups were challenged with pentylenetetrazole (35mg/kg, i.p.) on days 5, 10, and 15 to evaluate the seizure severity. Depression was evaluated in all experimental groups after normalization of locomotor activity, using tail suspension and forced swim test on days 1, 5, 10, and 15. Four hours after behavioral evaluations on day 15, all animals were euthanized to collect their serum and discrete brain parts. Corticosterone levels were estimated in all the experimental groups as a marker of a dysregulated hypothalamus pituitary adrenal axis. Neurochemical alterations (norepinephrine, dopamine, tryptophan, kynurenine, serotonin, glutamate, GABA, and total nitrate levels) were also estimated in the cortical and hippocampal areas of the mouse brain. Results revealed that saline-treated kindled animals were associated with significant depression and altered neurochemical milieu in comparison with naïve animals. Chronic valproate treatment in kindled animals significantly reduced seizure severity score bud did not ameliorate associated depression or completely restore altered biochemical and neurochemical milieu. Based on the observation of neurochemical changes in all the groups, we propose that restoration of altered neurochemical milieu, elevated indoleamine 2,3-dioxygenase enzyme activity, and corticosterone levels using pharmacological tools with/out valproic acid may be explored for management of both epilepsy and comorbid depression.

The role of IL-1β and glutamate in the effects of lipopolysaccharide on the hippocampal electrical kindling of seizures

In our study, we used rapid electrical hippocampal kindling and in vivo microdialysis methods to assess the involvement of inflammatory mediators: lipopolysaccharide (LPS) and proinflammatory interleukin-1β (IL-1β) in mechanisms of epileptogenesis. We observed, that both, LPS and IL-1β, administered into stimulated hippocampus, accelerated kindling process. LPS also increased the expression of IL-1β in stimulated hippocampus in kindled rats. In vivo acute LPS perfusion, via a microdialysis cannula implanted into the naïve rat's hippocampus, produced an increase in extracellular glutamate release. We suppose, that particularly IL-1β action and increased glutamate concentration may significantly contribute to LPS effects on kindling development.

κ-opioid receptor as a key mediator in the regulation of appetitive 50-kHz ultrasonic vocalizations

RATIONALE

Acute administration of high doses of morphine reduced 50-kHz ultrasonic vocalizations (USVs). Although morphine meets the classical criteria for inducing 50-kHz USVs (it causes place preference and induces dopamine release in nucleus accumbens), it also inhibits appetitive vocalizations.

OBJECTIVE

The aims of this study were to (i) study the pharmacological impact of κ-opioid (KOR) and μ-opioid receptor (MOR) ligands on the emission of 50-kHz USVs triggered by social interaction after long-term isolation and (ii) analyze the concentrations of the main neurotransmitters in reward-related structures (ventral tegmental area (VTA), nucleus accumbens (NAcc), and medial prefrontal cortex (mPFC)).

METHODS

In an attempt to define the effects of opioid-receptor activation on the reward system, we used a social interaction test (after 21 days isolation). HPLC analysis was used to determine the monoamine and amino acid concentrations in reward-related structures.

RESULTS

U-50488 (10.0 mg/kg), morphine (5.0 and 1.0 mg/kg), and naltrexone (5.0 mg/kg) decreased, and nor-BNI (10.0 mg/kg) increased 50-kHz USVs. Acute pretreatment with nor-BNI or naltrexone reduced the 50-kHz suppression induced via morphine. The biochemical data showed several variations between groups regarding dopamine concentrations, serotonin, and their metabolites; these data may suggest that the levels of emitted ultrasound in the 50-kHz band are inversely proportional to the 5-hydroxyindoleacetic acid (5-HIAA)/3-methoxytyramine (3-MT) ratio in the VTA.

CONCLUSIONS

These results indicate an important role for KOR in the regulation of 50-kHz USV emissions and suggest that KOR activation may be a key mediator in the regulation of reward responses. Changes in the balance between serotonin and dopamine concentrations in the VTA may be a key predictor for 50-kHz USV emission.

Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability

RATIONALE

Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids.

OBJECTIVE

This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior.

CONCLUSION

The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.

Neuroprotective effects of electrical stimulation of the anterior nucleus of the thalamus for hippocampus neurons in intractable epilepsy

Epilepsy and Parkinson's disease (PD) are common neurological disorders. Both epilepsy and PD are potentially progressive disabling diseases that can be treated with the established therapy of deep brain stimulation (DBS). The difference in therapy is target selection and stimulation parameter modulation. The anterior nucleus of the thalamus (ANT) is chosen for intractable epilepsy and the subthalamic nucleus (STN) is chosen for PD. Long-term stable symptom control of STN-DBS can be seen in PD patients while the positive effect of ANT-DBS can be observed in epilepsy patients. Experimental data and clinical evidence have been reported that indicate the neuroprotective property of STN-DBS could be found in PD patients. Therefore, we hypothesize that the neuroprotective benefits of ANT-DBS may be present in epilepsy patients.

Stimulation of the anterior nucleus of the thalamus induces changes in amino acids in the hippocampi of epileptic rats

We investigated the changes in the levels of amino acids during high frequency stimulation (HFS) of the anterior nucleus of the thalamus (ANT) in epileptic rats, which had seizures induced by unilaterally stereotactic administration of kainic acid (KA). Thirty-six adult male Wistar rats were divided into three groups: the KA-stim group (KA rats received ipsilateral ANT stimulation), the KA-sham group (KA rats received sham stimulation) and the control group, which underwent stereotactic administration of saline and received ipsilateral ANT stimulation. Microdialysis probes were unilaterally lowered into the CA3 region of the hippocampus, but probes were implanted bilaterally in the KA-stim group. The concentrations of glutamate (Glu), taurine (Tau), aspartate (Asp) and γ-aminobutyric acid (GABA) in the dialysate samples were determined by high-performance liquid chromatography. The concentrations of Glu, Asp and Tau in the hippocampi of KA rats were significantly higher than that found in control rats; however, no difference in the concentrations of GABA were found. In the ipsilateral hippocampi (KA-injected) of rats in the KA-stim group, stimulation of the ANT caused decreases in concentrations of Glu and Asp, an increase in the concentration of GABA and no significant change in the concentration of Tau. Unilateral ANT stimulation did not influence the amino acids in the contralateral hippocampus. In control rats, extracellular Tau significantly increased during and after stimulation. This study demonstrated that unilateral ANT stimulation inhibited the hyperactivation of the excitatory process and promoted the inhibitory process in the ipsilateral hippocampus of KA rats.

The effects of electrical hippocampal kindling of seizures on amino acids and kynurenic acid concentrations in brain structures

Our study demonstrated that the development of seizures during the electrically induced kindling of seizures is associated with significant changes in the concentration of kynurenic acid (KYNA) and its precursor, tryptophan (TRP). The primary finding of our study was an increase in KYNA levels and the KYNA/TRP ratio (a theoretical index of activity of the kynurenine pathway) in the amygdala and hippocampus of kindled animals. We also found decreases in the concentration of tryptophan in the hippocampus and prefrontal cortex. Changes in the concentration of KYNA and TRP in the amygdala were accompanied by a significant decrease in γ-Aminobutryic Acid (GABA) levels and an increase in the glutamate/GABA ratio. Moreover, we found a significant negative correlation between the local concentrations of KYNA and glutamate in the amygdala of kindled rats. However, there were no changes in the local concentrations of the following amino acids: glutamate, aspartate, glutamine, glycine, taurine and alanine. In conclusion, these new results suggest a modulatory influence of KYNA on the process of epileptogenesis, characterized by a negative relationship between the KYNA and glutamate systems in the amygdala.

An early decrease in cell proliferation after pentylenetetrazole-induced seizures

There are increasing data on the influence of seizures on neurogenesis in the adult brain. However, data on cell proliferation and differentiation during the early stages of kindling are scarce. We have used pentylenetetrazole (PTZ)-induced kindling to investigate the temporal profile of cytogenesis in the germinative zones of adult rat brain. For comparison, we also used a single PTZ-induced generalized tonic-clonic seizure. During kindling development, the density of 5-bromo-2'-deoxyuridine-positive cells demonstrated similar changes in all germinative zones: a dramatic decrease after the first subthreshold PTZ injection, and a gradual increase to the control level following repeated PTZ administration. On the contrary, a single PTZ-induced generalized tonic-clonic seizure was followed by an increase in the number of proliferating cells in both the dentate gyrus and the subventricular zone. These results may indicate the existence of global mechanisms affecting cellular proliferation in adult brain during seizures. Different temporal profiles of neuronal damage and proliferation changes suggest that neurodegeneration is unlikely to be a global proliferation-regulating factor. The data may contribute to better understanding of the initial phase of kindling development and epileptogenesis.

Doxycycline protects against pilocarpine-induced convulsions in rats, through its antioxidant effect and modulation of brain amino acids

This work evaluated doxycycline (2nd generation tetracycline) protection against pilocarpine-induced convulsions in rats. The animals were treated with doxycycline (Dox: 10 to100 mg/kg, i.p., 7days), 30min before the pilocarpine injection (P: 300mg/kg, i.p.) and observed for cholinergic signs, latencies to the first convulsion and death. Amino acid concentrations, lipid peroxidation and nitrite levels in temporal cortices were determined as well as the radical scavenging activity. Doxycycline increased latencies to the first convulsion and death as compared to the untreated P300 group. It also decreased glutamate and aspartate, increased GABA, blocked nitrite formation, reduced TBARS contents and showed a radical scavenging activity. Finally, doxycycline decreased the number of degenerating neurons (evaluated by fluoro-jade staining) and increased the number of viable neurons (assessed by cresyl violet staining) as compared do the P300 group. The antioxidant effect associated with decreased levels of excitatory and increased levels of inhibitory amino acids could explain the neuroprotective effect of doxycycline.

Mapping of c-Fos expression in the rat brain during the evolution of pentylenetetrazol-kindled seizures

c-Fos protein immunocytochemistry was used to map the brain structures recruited during the evolution of seizures that follows repeated administration of a subconvulsive dose (35mg/kg, ip) of pentylenetetrazol in rats. c-Fos appeared earliest in nucleus accumbens shell, piriform cortex, prefrontal cortex, and striatum (stages 1 and 2 of kindling in comparison to control, saline-treated animals). At the third stage of kindling, central amygdala nuclei, entorhinal cortex, and lateral septal nuclei had enhanced concentrations of c-Fos. At the fourth stage of kindling, c-Fos expression was increased in basolateral amygdala and CA1 area of the hippocampus. Finally, c-Fos labeling was enhanced in the dentate gyrus of the hippocampus only when tonic-clonic convulsions were fully developed. The most potent changes in c-Fos were observed in dentate gyrus, piriform cortex, CA1, lateral septal nuclei, basolateral amygdala, central amygdala nuclei, and prefrontal cortex. Piriform cortex, entorhinal cortex, prefrontal cortex, lateral septal nuclei, and CA3 area of the hippocampus appeared to be the brain structures selectively involved in the process of chemically induced kindling of seizures.