Development of long-lasting potentiation effects in the dentate gyrus during pentylenetetrazol kindling

The Role of 5-HT1A Receptors and Neuronal Nitric Oxide Synthase in a Seizur Induced Kindling Model in Rats

BACKGROUND AND OBJECTIVE

Dentate gyrus (DG) has a high density of 5-HT1A receptors. It has neural nitric oxide synthase (nNOS), which is involved in neural excitability. The purpose of this study was to investigate the role of 5-HT1A receptors and nNOS of DG in perforant path kindling model of epilepsy.

MATERIAL AND METHODS

To achieve this purpose, a receptor antagonist (WAY100635, 0.1 mg/kg, intracerebroventricular, i.c.v) and neuronal nitric oxide synthase inhibitor (7-NI, 15 mg/kg, intraperitoneal, i.p.) were injected during kindling aquisition. Adult male Wistar rats (280 ± 20 g) were used in this study Animals were kindled through the daily administration of brief electrical stimulations (10 stimulations per day) to the perforant pathway. Field potential recordings were performed for 20 min in DG beforehand. Additionally, glial fibrillary acidic protein (GFAP) expression rate in the DG was determined using immunohistochemistry as a highly specific marker for glia.

RESULTS

WAY100635 (0.1 mg/kg) significantly attenuated the kindling threshold compared to the kindled + vehicle group (P < 0.001). The co-administration of WAY100635 with 7-NI, exerted a significant anticonvulsive effect. Furthermore, the slope of field Excitatory Post Synaptic Potentials (fEPSP) at the end of 10 days in the kindled + 7-NI + WAY100635 group was significantly lower than in the kindled + vehicle group (P < 0.001). Furthermore, immunohistochemistry showed that the density of GAFP⁺ cells in the kindled + 7-NI + WAY100635 group was significantly higher than in the kindled + vehicle group (P < 0.001).

CONCLUSION

Our data demonstrate that antagonists of 5-HT1A receptors have proconvulsive effects and that astrocyte cells are involved in this process, while nNOS has an inhibitory effect on neuronal excitability.

Electromagnetic field protects against cognitive and synaptic plasticity impairment induced by electrical kindling in rats

Kindling results in abnormal synaptic potentiation and significant impairment in learning and memory. Electromagnetic field (EMF) effects on learning and memory in kindled animals and its effects on hippocampal neural activity are largely unknown. In the current study, the effects of EMF on learning and memory, as well as hippocampal synaptic plasticity, in kindled rats were investigated. EMF (10 mT; 100 Hz) was applied to fully kindled animals one hour/day for a period of one week. The behavioral and electrophysiological studies were performed 24 h following the EMF application. The kindled rats showed spatial learning deficits during the training phase of the Morris water maze (MWM) test. Moreover, there were increments in escape latency and path length compared to the sham group. The kindled rats spent less time in the target-quadrant probe test, indicating spatial memory impairment. Applying EMF to the KEMF group (kindling + EMF) restored learning and memory, and decreased escape latency and path length significantly compared to the kindled group. EMF alone had no significant effects on the learning and memory parameters. Based on the open field (OF) test results, EMF alone in the EMF group, but not in the kindled or the KEMF groups, decreased the total traveled distance and increased the spent time in the peripheral zone, compared to the sham group. Based on electrophysiological results, applying EMF in the KEMF group returned the ability of synaptic potentiation to the hippocampal CA1 area and high-frequency stimulation induced long-term potentiation (LTP). Accordingly, EMF can be considered a potential therapy for seizure-induced deficits in learning and memory.

The role of dopamine D2-like receptors in a "depotentiation-like effect" of deep brain stimulation in kindled rats

The mechanisms involved in the anti-seizure effects of low-frequency stimulation (LFS) have not been completely determined. However, G_i-protein-coupled receptors, including D₂-like receptors, may have a role in mediating these effects. In the present study, the role of D₂-like receptors in LFS' anti-seizure action was investigated. Rats were kindled with semi-rapid (6 stimulations per day), electrical stimulation of the hippocampal CA1 area. In LFS-treated groups, subjects received four trials of LFS at 5 min, 6 h, 24 h, and 30 h following the last kindling stimulation. Each LFS set occurred at 5 min intervals, and consisted of 4 trains. Each train contained 200, 0/1 ms long, monophasic square wave pulses at 1 Hz. Haloperidol (D₂-like receptors antagonist, 2 µm) and/or bromocriptine (D₂-like receptors agonist 2 µg/µlit) were microinjected into the lateral ventricle immediately after the last kindling, before applying LFS. Obtained results showed that applying LFS in fully-kindled subjects led to a depotentiation-like decrease in kindling-induced potentiation and reduced the amplitude and rise slope of excitatory and inhibitory post-synaptic currents in whole-cell recordings from CA1 pyramidal neurons. In addition, LFS restored the kindling-induced, spatial learning and memory impairments in the Barnes maze test. A D₂-like receptor antagonist inhibited these effects of LFS, while a D₂-like receptor agonist mimicked these effects. In conclusion, a depotentiation-like mechanism may be involved in restoring LFS' effects on learning and memory, and synaptic plasticity. These effects depend on D₂-like receptors activity.

RNA Polymerase 1 Is Transiently Regulated by Seizures and Plays a Role in a Pharmacological Kindling Model of Epilepsy

Ribosome biogenesis, including the RNA polymerase 1 (Pol1)-mediated transcription of rRNA, is regulated by the pro-epileptogenic mTOR pathway. Therefore, hippocampal Pol1 activity was examined in mouse models of epilepsy including kainic acid- and pilocarpine-induced status epilepticus (SE) as well as a single seizure in response to pentylenetetrazole (PTZ). Elevated 47S pre-rRNA levels were present acutely after induction of SE suggesting activation of Pol1. Conversely, after a single seizure, 47S pre-rRNA was transiently downregulated with increased levels of unprocessed 18S rRNA precursors in the cornu Ammonis (CA) region. At least in the dentate gyrus (DG), the pilocarpine SE-mediated transient activation of Pol1 did not translate into long-term changes of pre-rRNA levels or total ribosome content. Unaltered hippocampal ribosome content was also found after a 20-day PTZ kindling paradigm with increasing pro-convulsive effects of low dose PTZ that was injected every other day. However, after selectively deleting the essential Pol1 co-activator, transcription initiation factor-1A (Tif1a/Rrn3) from excitatory neurons, PTZ kindling was impaired while DG total ribosome content was moderately reduced and no major neurodegeneration was observed throughout the hippocampus. Therefore, Pol1 activity of excitatory neurons is required for PTZ kindling. As seizures affect ribosome biogenesis without long-term effects on the total ribosome content, such a requirement may be associated with a need to produce specialized ribosomes that promote pro-epileptic plasticity.

Antiepileptic activity of total triterpenes isolated from Poria cocos is mediated by suppression of aspartic and glutamic acids in the brain

CONTEXT

Triterpenes from Poria cocos Wolf (Polyporaceae) have been used to treat various diseases in traditional Chinese medicine. However, the antiepileptic effects and mechanism are not fully understood.

OBJECTIVE

The objective of this study is to investigate the antiepileptic properties of total triterpenes (TTP) from the whole P. cocos.

MATERIALS AND METHODS

The ethanol extract TTP was identified by HPLC fingerprint analysis. Male ICR mice were gavaged (i.g.) with TTP (5, 20, 80 or 160 mg/kg) or reference drugs twice a day for 7 d. Antiepileptic activities of TTP were evaluated by maximal electroshock (MES)- and pentylenetetrazole (PTZ)-induced seizures in mice for 30 and 60 min, respectively. Locomotor activity and Rota-rod tests were performed for 60 min and 5 min, respectively. The levels of glutamic acid (Glu), aspartic acid (Asp), γ-aminobutyric acid (GABA) and glycine (Gly) in convulsive mice were estimated. The chronic epileptic model of Wistar rats was built to measure expressions of glutamate decarboxylase 65 (GAD65) and GABA_A in rat brain after TTP treatment.

RESULTS

The LC₅₀ of TTP (i.g.) was above 6 g/kg. TTP (5-160 mg/kg) protected mice against MES- and PTZ-induced convulsions at 65.0% and 62.5%, respectively, but have no effect on rota-rod treadmill; TTP (20-160 mg/kg) significantly reduced the locomotor activities, shortened the onset of pentobarbital sodium-induced sleep; TTP decreased Glu and Asp levels in convulsive mice, but increased the GAD65 and GABA_A expressions in chronic epileptic rats at doses usage.

DISCUSSION AND CONCLUSION

TTP extracted from P. cocos possessed potential antiepileptic properties and is a candidate for further antiepileptic drug development.

Comparison between standard protocol and a novel window protocol for induction of pentylenetetrazol kindled seizures in the rat

Experimental models of epilepsy, including pentylenetetrazol (PTZ) chemical kindling, are very important in studying the pathophysiology of epilepsy. The aim of the present study was to provide behavioral, electrophysiological and molecular evidences to confirm the similarities between standard and a modified protocol named window- (win-) PTZ kindling method. Standard PTZ kindling model was induced by injection of PTZ (37.5mg/kg) every other days. In win-PTZ kindling method, animals received 4 initial PTZ injections and the time of 3 last PTZ injections were determined according to the number of PTZ injections in standard PTZ kindling model. The behavioral signs of kindled seizures were observed for 20 min after each PTZ injection. Field potential recordings were done from the dentate gyrus granular cells following perforant path stimulation. In addition, the expression of γ2 subunit of GABAA receptor, NR2A subunit of NMDA receptor, adenosine A1 receptor, α-CaMKII and GAP-43 were evaluated in the hippocampus and dentate gyrus using RT-PCR technique. All the animals in win-PTZ kindling method group achieved fully kindled state after 3 last PTZ injections. There was no significant difference in population spike amplitude and expression of the mentioned genes during kindling acquisition between standard PTZ kindling model and win-PTZ kindling method. The similarities in electrophysiological and molecular parameters remained after 8 days post fully kindled state. Obtained data showed the similarities between this win-PTZ kindling method and standard PTZ kindling model. Thus, it may be suggested that not all PTZ injections are need for induction of PTZ induced fully kindled state.

A single pentylenetetrazole-induced clonic-tonic seizure episode is accompanied by a slowly developing cognitive decline in rats

According to different studies, between 5% and 10% of people suffer a single isolated seizure episode at some time in their life. However, little is known about the effects of a single seizure episode on cognitive function, and clinical investigations of this issue are not easy to perform. In this situation, animal models may be a reasonable choice. The aim of our study was to follow the time course of delayed effects of generalized clonic-tonic convulsions on learning and memory functions in rats. A clonic-tonic seizure episode was induced by a single i.p. injection of pentylenetetrazole (70 mg/kg). Different behavioral tests were performed between days 10 and 100 after the convulsant administration. A single seizure episode resulted in a gradual decline in short-term memory function as assessed by novel object recognition and social recognition tests. The seizure episode induced a quick increase in hippocampal cell proliferation; however, the excessive newly generated cells seemed to be eliminated by the time of obvious cognitive impairment. These observations are indicative of a slowly developing and long-lasting influence of a single seizure episode on cognitive function. A rather long time period between the seizure episode and the manifestations of cognitive decline provides a window for a possible therapeutic intervention, and an elaboration of such "post-conditioning" treatments may be a promising opportunity to prevent subsequent mental impairments in patients.

Effect of low frequency stimulation of perforant path on kindling rate and synaptic transmission in the dentate gyrus during kindling acquisition in rats

Low frequency stimulation (LFS) has an inhibitory effect on kindling acquisition. In the present study the effect of the perforant path LFS on induction of rapid perforant path kindled seizures and synaptic transmission in the dentate gyrus was investigated. Animals were kindled by perforant path stimulation in a rapid kindling manner (12 stimulations per day). In one group of animals LFS (0.1 ms pulse duration at 1 Hz, 200 pulses, and 50-150 microA) was applied to perforant path, immediately after termination of each rapid kindling stimulation. Application of LFS significantly retarded the kindling acquisition and increased the number of stimulations to achieved different kindled seizure stages. LFS also prevented an increment in the slope of field excitatory postsynaptic potentials and population spike amplitude during kindling. In addition, LFS significantly reduced the marked increase in early (10-50 ms intervals) and late (300-1000 ms intervals) paired-pulse depression induced by kindling. According to obtained results, it may be suggested that LFS of perforant path has a significant antiepileptogenic effect through inhibition of synaptic transmission in dentate gyrus. Meanwhile, LFS prevents an increase in the paired-pulse depression during kindling acquisition.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.