Anti-seizure effect and neuronal activity change in the genetic-epileptic model rat with acute and chronic vagus nerve stimulation.

BACKGROUND: VNS showed time-dependent anti-seizure effect. However, the precise mechanism of VNS in acute and chronic anti-seizure effect has not been fully elucidated. Noda epileptic rat (NER) is genetic epilepsy model rat which exhibits spontaneous generalized tonic-clonic seizure (GTC) approximately once per 30 h and frequent dialeptic seizure (DS). We performed acute and chronic VNS on NER to focus on the acute and chronic anti-epileptic effect and neuronal activity change by VNS. METHODS: We performed acute VNS (2 h) on 22 NERs (VNS, n = 11, control, n = 11), then subsequently administered chronic (4 weeks) VNS on 10 of 22 NERs (VNS n = 5, control n = 5). We evaluated the acute and chronic anti-seizure effects of VNS on GTC and DS by behavioral and electroencephalographical observation (2 h every week). We carried out double immunofluorescence for biomarkers of short-term (c-Fos) and long-term (ΔFosB) neuronal activation to map regions in the brain that were activated by acute (VNS n = 6, control n = 6) or chronic VNS (VNS n = 5, control n = 5). Furthermore, we performed chronic VNS (4 w) on 12 NERs (VNS n = 6, control n = 6) with long-term observation (8 h a day, 5d per week) to obtain an adequate number of GTCs to elucidate the time dependent anti-epileptic effect on GTC. RESULTS: Acute VNS treatment reduced GTC seizure frequency and total duration of the DS. Chronic VNS resulted in a time-dependent reduction of DS frequency and duration. However, chronic VNS did not show time-dependent reduction of GTC frequency. There were significant c-Fos expressions in the central medial nucleus (CM), mediodorsal thalamic nucleus (MDM), locus coeruleus (LC), and nucleus of solitary tract (NTS) after acute VNS. And there were significant ΔFosB expressions in the lateral septal nucleus (LSV), medial septal nucleus (MSV), MDM, and pontine reticular nucleus caudal (PnC) after chronic VNS. Any decrease in frequency of GTCs by chronic VNS could not be confirmed even with long-term observation. CONCLUSION: We confirmed acute VNS significantly reduced the frequency of GTC and duration of DS. Chronic VNS decreased the frequency and duration of DS in a time-dependent manner. The brainstem and midline thalamus were activated after acute and chronic VNS. The forebrain was activated only after chronic VNS.

The Mechanism of Anti-Epileptogenesis by Levetiracetam Treatment is Similar to the Spontaneous Recovery of Idiopathic Generalized Epilepsy during Adolescence.

OBJECTIVE: The anti-epileptogenic drug levetiracetam has anticonvulsant and anti-epileptogenesis effects. Synergy between cell death and inflammation can lead to increased levels of apoptosis inhibitory factors and brain-derived neurotrophic factor, aberrant neurogenesis and extended axon sprouting. Once hyperexcitation of the neural network occurs, spontaneous seizures or epileptogenesis develops. This study investigated whether the anti-epileptogenic effect of levetiracetam is due to its alternate apoptotic activity. METHODS: Adult male Noda epileptic rats were treated with levetiracetam or vehicle control for two weeks. mRNA quantification of Bax, Bcl-2 and GAPDH expression were performed from prefrontal cortex and hippocampus tissue samples. RESULTS: The levetiracetam-treated group showed a significant increase of Bax/Bcl-2 mRNA expression ratio in the prefrontal cortex than the control group, but no change in the Bax/Bcl-2 mRNA expression ratio in hippocampus. CONCLUSION: Idiopathic generalized epilepsy including childhood absence epilepsy develop at childhood and recover spontaneously during adolescence. The aberrant neural excitable network is pruned by a neural-maturing action. This study suggests the mechanism of acquired anti-epileptogenesis by levetiracetam treatment may be similar to spontaneous recovery of idiopathic generalized epilepsy during adolescence.

Identification of Candidate Genes for Generalized Tonic-Clonic Seizures in Noda Epileptic Rat.

The Noda epileptic rat (NER) exhibits generalized tonic-clonic seizures (GTCS). A genetic linkage analysis identified two GTCS-associated loci, Ner1 on Chr 1 and Ner3 on Chr 5. The wild-type Ner1 and Ner3 alleles suppressed GTCS when combined in double-locus congenic lines, but not when present in single-locus congenic lines. Global expression analysis revealed that cholecystokinin B receptor (Cckbr) and suppressor of tumorigenicity 5 (St5), which map within Ner1, and PHD finger protein 24 (Phf24), which maps within Ner3, were significantly downregulated in NER. De novo BAC sequencing detected an insertion of an endogenous retrovirus sequence in intron 2 of the Phf24 gene in the NER genome, and PHF24 protein was almost absent in the NER brain. Phf24 encodes a Gαi-interacting protein involved in GABAB receptor signaling pathway. Based on these findings, we conclude that Cckbr, St5, and Phf24 are strong candidate genes for GTCS in NER.

The Mechanism of Anti-Epileptogenesis by Levetiracetam Treatment is Similar to the Spontaneous Recovery of Idiopathic Generalized Epilepsy during Adolescence

OBJECTIVE: The anti-epileptogenic drug levetiracetam has anticonvulsant and anti-epileptogenesis effects. Synergy between cell death and inflammation can lead to increased levels of apoptosis inhibitory factors and brain-derived neurotrophic factor, aberrant neurogenesis and extended axon sprouting. Once hyperexcitation of the neural network occurs, spontaneous seizures or epileptogenesis develops. This study investigated whether the anti-epileptogenic effect of levetiracetam is due to its alternate apoptotic activity. METHODS: Adult male Noda epileptic rats were treated with levetiracetam or vehicle control for two weeks. mRNA quantification of Bax, Bcl-2 and GAPDH expression were performed from prefrontal cortex and hippocampus tissue samples. RESULTS: The levetiracetam-treated group showed a significant increase of Bax/Bcl-2 mRNA expression ratio in the prefrontal cortex than the control group, but no change in the Bax/Bcl-2 mRNA expression ratio in hippocampus. CONCLUSION: Idiopathic generalized epilepsy including childhood absence epilepsy develop at childhood and recover spontaneously during adolescence. The aberrant neural excitable network is pruned by a neural-maturing action. This study suggests the mechanism of acquired anti-epileptogenesis by levetiracetam treatment may be similar to spontaneous recovery of idiopathic generalized epilepsy during adolescence.

Dual mechanisms diminishing tonic GABAA inhibition of dentate gyrus granule cells in Noda epileptic rats.

The Noda epileptic rat (NER), a Wistar colony mutant, spontaneously has tonic-clonic convulsions with paroxysmal discharges. In the present study, we measured phasic and tonic γ-aminobutyric acid A (GABAA) current (I tonic) in NER hippocampal dentate gyrus granule cells and compared the results with those of normal parent strain Wistar rats (WIS). I tonic, revealed by a bicuculline-induced outward shift in holding current, was significantly smaller in NER than in WIS (P < 0.01). The frequency of inhibitory postsynaptic currents (IPSCs) was also significantly lower in NER than in WIS (P < 0.05), without significant differences in the IPSC amplitude or decay time between WIS and NER. I tonic attenuation in NER was further confirmed in the presence of GABA transporter blockers, NO-711 and nipecotic acid, with no difference in neuronal GABA transporter expression between WIS and NER. I tonic responses to extrasynaptic GABAA receptor agonists (THIP and DS-2) were significantly reduced in NER compared with WIS (P < 0.05). Allopregnanolone caused less I tonic increase in NER than in WIS, while it prolonged the IPSC decay time to a similar rate in the two groups. Expression of the GABAA receptor δ-subunit was decreased in the dentate gyrus of NER relative to that of WIS. Taken together, our results showed that a combination of attenuated presynaptic GABA release and extrasynaptic GABAA receptor expression reduced I tonic amplitude and its sensitivity to neurosteroids, which likely diminishes the gating function of dentate gyrus granule cells and renders NER more susceptible to seizure propagation.