Kindling induced by pentylenetetrazole in rats is not directly associated with changes in the expression of NMDA or benzodiazepine receptors

Downregulatory effect of miR-342-3p on epileptogenesis in the PTZ-kindling model

BACKGROUND

Epileptogenesis is a process that results in neurons firing abnormally, causing seizures. Increasing evidence has shown that miRNAs expressed in the epileptic hippocampus are involved in epileptogenesis. We demonstrated the expression changes of miRNAs that may be effective in epileptogenesis in silico analysis in the kindling model created with Pentylenetetrazole (PTZ). Thus, we aimed to identify the target genes responsible for epileptogenesis.

METHODS AND RESULTS

Fifteen male Wistar-albino rats (200-230 g) were randomly divided into two groups control (n = 6) and PTZ (n = 9). The control group received 0.5 ml saline, and the PTZ group (35 mg/kg i.p.) intraperitoneally (i.p.) (11 times, every other day) to induce tonic-clonic seizures. Seizures were observed and scored 30 min after PTZ injection. After the last dose of PTZ (75 mg/kg) administration, the hippocampus tissues of the rats were removed by anesthesia. Analysis of miRNAs was performed with the Affymetrix gene chip miRNA sequence (728 miRNA) and confirmed by the Real-Time Polymerase Chain Reaction (Real-Time PCR) method (29 miRNAs). We evaluated the expression change of the target gene of miRNA, whose expression change was detected using in silico analysis, by q-RT PCR. Eight miRNAs with changes in expression were detected. Of these miRNAs, miR-342-p was downregulated in the PTZ group and was statistically significant (p < 0.005). Ultimately, we determined that the target gene of miR-342-p is a metabotropic glutamate receptor 2 (GRM2) and that GRM2 expression is upregulated.

CONCLUSIONS

Downregulation of miR-342-3p in the PTZ kindling model may result in the upregulation of GRM2.

The Effect of Coenzyme Q10 on Liver Injury Induced by Valproic Acid and Its Antiepileptic Activity in Rats

Valproic acid (VPA) has toxic metabolites that can elevate oxidative stress markers, and the hepatotoxicity of VPA has been reported. Coenzyme Q10 (CoQ10) is one of the most widely used antioxidants. The effect of CoQ10 on epileptogenesis and VPA hepatotoxicity were examined. Rats were randomly divided into five groups: the control group received 0.5% methylcellulose by oral gavages daily and saline by intraperitoneal injection three times weekly. The PTZ group received 1% methylcellulose by gavages daily and 30 mg/kg PTZ by intraperitoneal injection three times weekly. The valproic acid group received 500 mg/kg valproic acid by gavage and 30 mg/kg PTZ, as above. The CoQ10 group received 200 mg/kg CoQ10 by gavages daily and 30 mg/kg PTZ, as above. The Valproic acid + CoQ10 group received valproic acid and CoQ10, as above. Results: CoQ10 exhibited anticonvulsant activity and potentiated the anticonvulsant effect of VPA. CoQ10 combined with VPA induced a more significant reduction in oxidative stress and improved the histopathological changes in the brain and liver compared to VPA treatment. In addition, CoQ10 reduced the level of toxic VPA metabolites. These findings suggest that the co-administration of CoQ10 with VPA in epilepsy might have therapeutic potential by increasing antiepileptic activity and reducing the hepatotoxicity of VPA.

The potential antiepileptic activity of astaxanthin in epileptic rats treated with valproic acid

Objectives

Epilepsy is a neurological disease characterized by sudden, abnormal, and hyper- discharges in the central nervous system (CNS). Valproic acid (VPA) is commonly used as a broad-spectrum antiepileptic therapeutic. However, in many cases, patients develop resistance to VPA treatment due to overwhelming oxidative stress, which in turn might be a major catalyst for disease progression. Therefore, antioxidants can potentially become therapeutic agents by counteracting reactive oxygen species (ROS)-mediated damage. The present study is aimed to evaluate the potential antiepileptic effect of astaxanthin (ASTA) in pentylenetetrazol (PTZ) induced epileptic model rats that are chronically treated with VPA for 8 weeks.

Method

Fifty-male Wistar rats were randomly divided into five groups: Non-PTZ group, PTZ, PTZ/VPA, PTZ/ASTA, and PTZ/VPA/ASTA treated groups.

Results

PTZ/VPA treated group showed a neuroprotective effect with improvement in antioxidant levels, behavioral test, and histopathological changes induced by PTZ. VPA also exhibited an anti-inflammatory effect as its treatment resulted in the reduction of tumor necrosis factor-α (TNF-α). ASTA exhibited an anticonvulsant effect and enhanced anti-inflammatory effect as compared to VPA. During the combined therapy, ASTA potentiated the antiepileptic effect of the VPA by reducing the oxidative stress and TNF-α as well as increased the glutathione (GSH) levels. Also, there were substantial improvements in the behavioral and histopathological changes in the VPA/ASTA treated group as compared to the VPA treated group.

Conclusion

ASTA could have an antiepileptic and anti-inflammatory effect by reducing ROS generation. Therefore, co-administration of both the therapeutics (VPA/ASTA) has a synergistic effect in treating epilepsy and could potentially minimize recurrence and/or exacerbation of seizures.

Effects of ferulic acid on oxidative stress, heat shock protein 70, connexin 43, and monoamines in the hippocampus of pentylenetetrazole-kindled rats

The present study investigated the effects of ferulic acid (FA) on pentylenetetrazole (PTZ)-induced seizures, oxidative stress markers (malondialdehyde (MDA), catalase, and reduced glutathione (GSH)), connexin (Cx) 43, heat shock protein 70 (Hsp 70), and monoamines (serotonin (5-HT) and norepinephrine (NE)) levels in a rat model of PTZ-induced kindling. Sixty Sprague Dawley rats were divided into 5 equal groups: (a) normal group; (b) FA group: normal rats received FA at a dose of 40 mg/kg daily; (c) PTZ group: normal rats received PTZ at a dose of 50 mg/kg i.p. on alternate days for 15 days; (d) FA-before group: treatment was the same as for the PTZ group, except rats received FA; and (e) FA-after group: rats received FA from sixth dose of PTZ. PTZ caused a significant increase in MDA, Cx43, and Hsp70 along with a significant decrease in GSH, 5-HT, and NE levels and CAT activity in the hippocampus (p < 0.05). Pre- and post-treatment with FA caused significant improvement in behavioral parameters, MDA, CAT, GSH, 5-HT, NE, Cx43 expression, and Hsp70 expression in the hippocampal region (p < 0.05). We conclude that FA has neuroprotective effects in PTZ-induced epilepsy, which might be due to attenuation of oxidative stress and Cx43 expression and upregulation of neuroprotective Hsp70 and neurotransmitters (5-HT and NE).

Effects of intravenous human umbilical cord blood mesenchymal stem cell therapy versus gabapentin in pentylenetetrazole-induced chronic epilepsy in rats

AIM

The identification and application of stem cells to treat central nervous system disorders represent a dramatic evolution and expansion into the realms of neurorestoration and neuroregeneration. The aim of this study was to assess the possible ameliorative effect of mesenchymal stem cells (MSCs) in comparison to gabapentin on pentylenetetrazole (PTZ)-induced epileptogenesis and its consequences.

METHODS

Thirty-two rats were divided into 4 equal groups; group I: saline-injected group, group II: PTZ group, which received 13 intraperitoneal (i.p.) injections of PTZ (30 mg/kg) 3 times/week, groups III and IV: groups received PTZ and were treated with i.p. gabapentin (200 mg/kg) 60 min before each PTZ injection (group III) or a single intravenous injection of 10(6) MSCs/rat at day 22 (group IV).

RESULTS

Treatment with either gabapentin or MSCs demonstrated a significant improvement in the PTZ-induced epileptogenesis and its severe consequences, i.e. oxidative stress damage, motor and cognitive impairments. Moreover, they enhanced the GABA neurotransmitter levels. Meanwhile, MSC administration to chronic epileptic rats afforded more ameliorative effects on PTZ-induced epileptogenesis and its severe consequences in comparison to gabapentin.

CONCLUSION

These data indicate that MSCs were superior to gabapentin in ameliorating PTZ-induced epileptogenesis and verified the potential use of MSCs in seizure control, motor and cognitive impairments, oxidative stress, and the impairing GABA level in experimentally induced epilepsy.

Assessment of seizure susceptibility in pilocarpine epileptic and nonepileptic Wistar rats and of seizure reinduction with pentylenetetrazole and electroshock models

PURPOSE

Pentylenetetrazole (PTZ) and maximal electroshock (MES) models are often used to induce seizures in nonepileptic control animals or naive animals. Despite being widely used to screen antiepileptic drugs (AEDs), both models have so far failed to detect potentially useful AEDs for treating drug-resistant epilepsies. Here we investigated whether the acute induction of MES and PTZ seizures in epileptic rats might yield a distinct screening profile for AEDs.

METHODS

Status epilepticus (SE) was induced in adult male Wistar rats by intraperitoneal pilocarpine injection (Pilo, 320 mg/kg, i.p.). One month later, controls or naive animals (Cont) that did not develop SE postpilocarpine (N-Epi) and pilocarpine-epileptic rats (Epi) received one of the following: phenobarbital (PB, 40 mg/kg), phenytoin (PHT, 50 mg/kg), or valproic acid (VPA, 400 mg/kg). Thirty min later the animals were challenged with either subcutaneous MES or PTZ (50 mg/kg, s.c.).

RESULTS

VPA, PB, and PHT were able to prevent MES in all groups tested (Cont, N-Epi, and Epi groups), whereas for the PTZ model, only the Cont group (naive animals) had seizure control with the same AEDs. In addition, Epi and N-Epi groups when challenged with PTZ exhibited a higher incidence of severe seizures (scores IV-IX) and SE (p < 0.05, Fisher's exact test).

CONCLUSIONS

Our findings suggest that the induction of acute seizures with PTZ, but not with MES, in animals pretreated with pilocarpine (regardless of SE induction) might constitute an effective and valuable method to screen AEDs and to study mechanisms involved in pharmacoresistant temporal lobe epilepsy (TLE).

Pentylenetetrazol kindling in rats: Is neurodegeneration associated with manifestations of convulsive activity?

Structural changes in neurons and measures of oxidative stress were studied in the hippocampus of rats tolerant (ST) and sensitive (SS) to developing clonic-tonic seizures in conditions of pentylenetetrazol kindling. Sequences of 11 injections of pentylenetetrazol significantly decreased the number of normal neurons in hippocampal field CA1 in SS rats, this effect being seen in both hippocampal field CA1 and the dentate fascia in ST rats. Decreases in the numbers of normal neurons were accompanied by increases in the numbers of damaged cells in field CA4 in rats of both groups. After 21 injections, decreases in the numbers of normal neurons were seen in field CA1 in both SS and ST rats, while the numbers of damaged neurons were significantly greater than control only in ST rats in fields CA1 and CA4. The glutathione level was significantly lower in the hippocampus in both groups of rats than in controls. Thus, rats " tolerant" to developing convulsions show signs of oxidative stress and neurodegenerative changes in the hippocampus. This suggests that oxidative neuron damage leading to neurodegeneration in the pentylenetetrazol kindling model is not directly associated with convulsive activity.

Chronic intermittent ethanol exposure enhances NMDA-receptor-mediated synaptic responses and NMDA receptor expression in hippocampal CA1 region

In previous studies, we found that chronic intermittent ethanol (CIE) treatment-a model of ethanol consumption in which animals are exposed to and withdrawn from intoxicating levels of ethanol on a daily basis-produces neuroadaptive changes in hippocampal area CA1 excitatory synaptic transmission and plasticity. Synaptic responses mediated by N-methyl-D-aspartate (NMDA) receptors are known to be sensitive to ethanol and could play an important role in the neuroadaptive changes induced by CIE treatment. To address this issue, we compared electrophysiological recordings of pharmacologically isolated NMDA-receptor-mediated field excitatory postsynaptic potentials (fEPSPs) in the CA1 region of hippocampal slices prepared from control rats and rats exposed to 2 weeks of CIE treatment administered by vapor inhalation. We found that fEPSPs induced by NMDA receptor activation were unaltered in slices prepared shortly after cessation of CIE treatment (i.e., < or = 1 day of withdrawal from CIE). However, following 7 days of withdrawal from CIE treatment, NMDA-receptor-mediated fEPSPs were augmented relative to age-matched controls. Western blot analysis of NMDA receptor subunit expression showed that, at 7 days of withdrawal, the level of protein for NR2A and NR2B subunits was elevated in the CA1 region of hippocampal slices from CIE-treated animals compared with slices from age-matched controls. These results are consistent with an involvement of NMDA-receptor-mediated synaptic responses in the neuroadaptive effects of CIE on hippocampal physiology and suggest that such changes may contribute to ethanol-induced changes in processes dependent on NMDA-receptor-mediated synaptic responses such as learning and memory, neural development, hyperexcitability and seizures, and neurotoxicity.

Kindling and status epilepticus models of epilepsy: rewiring the brain

This review focuses on the remodeling of brain circuitry associated with epilepsy, particularly in excitatory glutamate and inhibitory GABA systems, including alterations in synaptic efficacy, growth of new connections, and loss of existing connections. From recent studies on the kindling and status epilepticus models, which have been used most extensively to investigate temporal lobe epilepsy, it is now clear that the brain reorganizes itself in response to excess neural activation, such as seizure activity. The contributing factors to this reorganization include activation of glutamate receptors, second messengers, immediate early genes, transcription factors, neurotrophic factors, axon guidance molecules, protein synthesis, neurogenesis, and synaptogenesis. Some of the resulting changes may, in turn, contribute to the permanent alterations in seizure susceptibility. There is increasing evidence that neurogenesis and synaptogenesis can appear not only in the mossy fiber pathway in the hippocampus but also in other limbic structures. Neuronal loss, induced by prolonged seizure activity, may also contribute to circuit restructuring, particularly in the status epilepticus model. However, it is unlikely that any one structure, plastic system, neurotrophin, or downstream effector pathway is uniquely critical for epileptogenesis. The sensitivity of neural systems to the modulation of inhibition makes a disinhibition hypothesis compelling for both the triggering stage of the epileptic response and the long-term changes that promote the epileptic state. Loss of selective types of interneurons, alteration of GABA receptor configuration, and/or decrease in dendritic inhibition could contribute to the development of spontaneous seizures.

The effects of pentylenetetrazole-induced status epilepticus on behavior, emotional memory, and learning in rats

Status epilepticus (SE) can cause spatial learning, memory, and behavioral deficits; however, little information is available, especially regarding the effects of such seizures on emotional memory and learning functions. We investigated the effects of SE on emotional memory, learning, and behavior in mature rats over short and long periods. SE was induced in 50- to 60-day-old rats (P50-P60) using intraperitoneal injections of pentylenetetrazole (PTZ, n = 20); control rats received saline (n = 10). All animals were tested with elevated T-maze and open-field tests on the 1st, 7th, 14th, and 180th days after SE to evaluate emotional memory, learning, and behavior. The number of fecal boli increased, and one-way escape latency was long in a short period after SE. PTZ-induced SE causes transient memory deficits, which is related to unconditioned fear, but it did not cause any persistent abnormalities of behavior, emotional memory, and learning in mature rats.

Prolonged changes in Ca2+/calmodulin-dependent protein kinase II after a brief pentylenetetrazol seizure; potential role in kindling

This study evaluated the alteration of CaMKII autophosphorylation and distribution in rat brain following a single, brief pentylenetetrazol (PTZ) seizure and during PTZ kindling. Total CaMKII alpha subunit (alpha-CaMKII) and alpha-CaMKII phosphorylated at Thr(286) were detected by immunoblot. A large decrease in CaMKII Thr(286) phosphorylation, as well as CaMKII translocation from particulate to soluble fraction was observed in both cerebral cortex and hippocampus 0.5-4 h after the brief PTZ convulsion. These changes reverted to control values by 12 h. These long-lasting changes in CaMKII autophosphorylation and subcellular distribution after a brief seizure suggested that CaMKII could be involved in carrying forward the signal resulting from brief seizure activity, at least for a few hours, as would be required for kindling to occur. In PTZ kindled rats, convulsions produced changes in CaMKII Thr(286) phosphorylation and distribution in the same direction and of similar magnitude as after the acute convulsion, but lasting for a much longer time. In fact, reduced Thr(286) phosphorylation of alpha-CaMKII was observed up to 48 h, completely bridging the interval between PTZ injections. Similar, but intermediate changes were found in tissue from rats that were only partially kindled. These results implicate CaMKII as a molecular messenger in the acquisition of PTZ kindling.

Kindling status in sprague-dawley rats induced by pentylenetetrazole: involvement of a critical development period

Kindled seizures are widely used as a model for epileptogenesis. Although the achievement of kindling criterion is known to require time to develop, the precise developmental period has not been identified. We now report that optimal achievement of the kindling criterion in the Sprague-Dawley rat is associated with a critical inter-stimulus interval of 24 to 26 days. We show that highly efficient kindling can be achieved with only two subconvulsive doses of pentylenetetrazole so long as they are given 25 days apart. Using Northern blot hybridization we show that the increased seizure susceptibility at 25 days coincides with an increased expression of the plasticity-associated proteins, growth-associated protein-43 (GAP-43), microtubule-associated protein 1B (MAP1B), and tissue plasminogen activator (tPA) mRNAs in the hippocampus. By in situ hybridization and immunocytochemistry on tissue sections, we also show an increased expression for GAP-43 in the polymorphic layer of the dentate gyrus, mossy fibers, and pyramidal cells in the CA3 region of the hippocampus. The demonstration of a long, defined developmental interval for inducing the kindling criterion should enable a dissection of the cellular and genetic events underlying this phenomenon in the rat.