Pharmacological and neuroethological study of the acute and chronic effects of lamotrigine in the genetic audiogenic seizure hamster (GASH:Sal).

The present study aimed to investigate the behavioral and anticonvulsant effects of lamotrigine (LTG) on the genetic audiogenic seizure hamster (GASH:Sal), an animal model of audiogenic seizure that is in the validation process. To evaluate the efficiency of acute and chronic treatments with LTG, GASH:Sals were treated with LTG either acutely via intraperitoneal injection (5-20mg/kg) or chronically via oral administration (20-25mg/kg/day). Their behavior was assessed via neuroethological analysis, and the anticonvulsant effect of LTG was evaluated based on the appearance and the severity of seizures. The results showed that acute administration of LTG exerts an anticonvulsant effect at the lowest dose tested (5mg/kg) and that chronic oral LTG treatment exerts an anticonvulsant effect at a dose of 20-25mg/kg/day. Furthermore, LTG treatment induced a low rate of secondary adverse effects. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Inhibition of long-term potentiation in the schaffer-CA1 pathway by repetitive high-intensity sound stimulation.

High-intensity sound can induce seizures in susceptible animals. After repeated acoustic stimuli changes in behavioural seizure repertoire and epileptic EEG activity might be seen in recruited limbic and forebrain structures, a phenomenon known as audiogenic kindling. It is postulated that audiogenic kindling can produce synaptic plasticity events leading to the spread of epileptogenic activity to the limbic system. In order to test this hypothesis, we investigated if long-term potentiation (LTP) of hippocampal Schaffer-CA1 synapses and spatial navigation memory are altered by a repeated high-intensity sound stimulation (HISS) protocol, consisting of one-minute 120 dB broadband noise applied twice a day for 10 days, in normal Wistar rats and in audiogenic seizure-prone rats (Wistar Audiogenic Rats - WARs). After HISS all WARs exhibited midbrain seizures and 50% of these animals developed limbic recruitment, while only 26% of Wistar rats presented midbrain seizures and none of them had limbic recruitment. In naïve animals, LTP in hippocampal CA1 neurons was induced by 50- or 100-Hz high-frequency stimulation of Schaffer fibres in slices from both Wistar and WAR animals similarly. Surprisingly, HISS suppressed LTP in CA1 neurons in slices from Wistar rats that did not present any seizure, and inhibited LTP in slices from Wistar rats with only midbrain seizures. However HISS had no effect on LTP in CA1 neurons from slices of WARs. Interestingly HISS did not alter spatial navigation and memory in both strains. These findings show that repeated high-intensity sound stimulation prevent LTP of Schaffer-CA1 synapses from Wistar rats, without affecting spatial memory. This effect was not seen in hippocampi from audiogenic seizure-prone WARs. In WARs the link between auditory stimulation and hippocampal LTP seems to be disrupted which could be relevant for the susceptibility to seizures in this strain.

Pharmacological and neuroethological studies of three antiepileptic drugs in the Genetic Audiogenic Seizure Hamster (GASH:Sal).

Epilepsy modeling is essential for understanding the basic mechanisms of the epileptic process. The Genetic Audiogenic Seizure Hamster (GASH:Sal) exhibits generalized tonic-clonic seizures of genetic origin in response to sound stimulation and is currently being validated as a reliable model of epilepsy. Here, we performed a pharmacological and neuroethological study using well-known and widely used antiepileptic drugs (AEDs), including phenobarbital (PB), valproic acid (VPA), and levetiracetam (LEV). The intraperitoneal administration of PB (5-20mg/kg) and VPA (100-300mg/kg) produced a dose-dependent decrease in GASH:Sal audiogenic seizure severity scores. The administration of LEV (30-100mg/kg) did not produce a clear effect. Phenobarbital showed a short plasmatic life and had a high antiepileptic effect starting at 10mg/kg that was accompanied by ataxia. Valproic acid acted only at high concentrations and was the AED with the most ataxic effects. Levetiracetam at all doses also produced sedation and ataxia side effects. We conclude that the GASH:Sal is a reliable genetic model of epilepsy suitable to evaluate AEDs.

Neuroanatomical and cellular substrates of hypergrooming induced by microinjection of oxytocin in central nucleus of amygdala, an experimental model of compulsive behavior.

Oxytocin (OT) is a neurosecretory nonapeptide synthesized in hypothalamic cells that project to the neurohypophysis as well as to widely distributed sites in the central nervous system. Central OT microinjections induce a variety of cognitive, sexual, reproductive, grooming and affiliative behaviors in animals. Obsessive-compulsive disorder (OCD) includes a range of cognitive and behavioral symptoms that bear some relationship with OT. Here, we study the neuroanatomical and cellular substrates of the hypergrooming induced by administration of OT in the central nucleus of amygdala (CeA). In this context, this hypergrooming is considered as a model of compulsive behavior. Our data suggest a link between the CeA and the hypothalamic grooming area (HGA). The HGA includes parts of the paraventricular nucleus and the dorsal hypothalamic area. Our data on colocalization of OT (immunohistochemistry for peptide), OT receptor (binding assay) and its retrogradely labeled cells after Fluoro-Gold injection in the CeA suggest that CeA and connections are important substrates of the circuit underlying this OT-dependent compulsive behavioral pattern.

Neuroethology application for the study of human temporal lobe epilepsy: from basic to applied sciences.

The aim of this investigation was to apply neuroethology to the study of human temporal lobe epilepsy (TLE). For this purpose, 42 seizures in 7 patients recorded during video/EEG monitoring (1997-1998) were analyzed by means of a behavioral glossary containing all behaviors. Video recordings were reobserved, and all patients' behaviors were annotated second-by-second. Data were analyzed using Ethomatic software and displayed as flowcharts including frequency, mean duration, and sequential statistic interaction of behavioral items (chi2 > or = 10.827, P<0.001). Flowcharts of (1) a group of seizures from a single patient, (2) the sum of four seizures per patient of two patients with right and five patients with left TLE, and (3) the comparison of left versus right TLE are shown. Well-established data in the literature were confirmed, such as aura (especially epigastric), contralateral lateralization value of dystonia and version, consciousness and language alterations in ictal and postictal periods, mostly with respect to dominant hemisphere involvement, among others. Less well established data such as awakening seizures in TLE patients, lateralization value of facial wiping (ipsilateral to the focus), statistically significant associations between behavioral pairs (dyads), and new behavioral sequences in TLE were also observed. We suggest that neuroethology also has great potential in the study of human epilepsy semiology. This work had an important role in method standardization for human epilepsy, setting the basis for the development of future clinical studies including correlation with other diagnostic methods (EEG, magnetic resonance, and SPECT). The next step will be the comparative study of seizures of patients with left and right TLE, with a greater number of patients, and the development of a digital video library.

Quantitative study of the response to genetic selection of the Wistar audiogenic rat strain (WAR).

To study the relationship between genetics and epilepsy, Wistar rats susceptible to audiogenic seizure were selected from the main breeding stock of the Ribeirão Preto School of Medicine at the University of São Paulo, Brazil, and inbred. The criteria for selection were the highest seizure severity index (SI) and shortest latencies of the first running fit (LI). Because behavioral response to sound stimulation (120 dB) at 70 to 78 days of age was very stable, SI and LI were evaluated within this age range. Analysis of 9450 observations in 1575 animals from the 3rd to 17th generations demonstrated significant effects of generation, parity, and litter on SI and of generation and litter on LI. The SI and LI averages were, respectively, 37.13 and 22.82 s in the 3rd generation and 83.06 and 7.84 in the 17th generation. Heritabilities of both characters were estimated, by maximum likelihood, as 0.37 +/- 0.066 and 0.44 +/- 0.059, respectively. Because a significant regression related individual breeding values for both SI and LI to generation number, we concluded that genetic selection has a positive impact on the traits analyzed. Therefore, the Wistar audiogenic rat (WAR) strain appears, as per the 17th to 20th generations of genetic selection to be an audiogenic rat strain suitable for epilepsy studies.

Anticonvulsant and proconvulsant roles of nitric oxide in experimental epilepsy models

The effect of acute (120 mg/kg) and chronic (25 mg/kg, twice a day, for 4 days) intraperitonial injection of the nitric oxide (NO) synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NOARG) was evaluated on seizure induction by sound drugs such as pilocarpine and pentylenetetrazole (PTZ) and by stimulation of audiogenic seizure-resistant (R) and audiogenic seizure-susceptible (S) rats. Seizures were elicited by a subconvulsant dose of pilocarpine (100 mg/kg) only after NOS inhibition. NOS inhibition also simultaneously potentiated the severity of PTZ-induced limbic seizures (60 mg/kg) and protected against PTZ-induced tonic seizures (80 mg/kg). The audiogenic seizure susceptibility of S or R rats did not change after similar treatments. In conclusion, proconvulsant effects of NOS inhibition are suggested to occur in the pilocarpine model and in the limbic componentes of PTZ-induced seizures, while an anticonvulsant role is suggested for the tonic seizures induced by higher doses of PTZ, revealing inhibitor-specific interations with convulsant dose and also confirming the hypothesis that the effects of NOS inhibitors vary with the model of seizure.