The influence of olfactory stimulation on the development of limbic seizures in rats Wistar

Abstract

The Temporal Lobe Epilepsy (TLE) is the most common epileptic syndrome in the population. One of the experimental models used to study epilepsy is the electrical kindling of the amygdala, characterized by low intensity electrical stimulation (Santos, 2011) which promotes the progressive development of behavioral and electroencephalographic seizures (EEGráfica) (Ebert and Löscher, 1995; Foresti, 2008). The amygdala is one of the most sensitive brain area to electrical kindling (Goddard et al., 1969) and according to Löscher and Ebert (2000), the piriform cortex plays an important role, because it amplifies and propagates seizure activity to other limbic areas such as hippocampus, entorhinal cortex and adjacent cortices. In conventional kindling, electrical stimulation of the amygdala is performed twice daily for two weeks (Ebert and Löscher, 1995). A quick and effective alternative to conventional electrical flashover is the fast electrical stimulation, with 20 electrical stimuli for 2 days. On day 3 an additional stimulus is applied (Ebert and Löscher, 1995; Foresti, 2008; Foresti et al., 2008). In conventional kindling olfactory stimulation, e.g. toluene removed the crises in most animals with the same electrical stimulus 20% higher than necessary to trigger a seizure (Ebert and Löscher, 2000). In the model of audiogenic stimulation in rats of the Wistar Audiogenic Rat (WAR) strain, olfactory stimulation with toluene also decreased the severity of behavioral seizures (Bertti et al., 2011; Bertti et al., 2010). In humans, the blocking of epileptic seizures by the presence of an odor has also been previously described (Efron, 1956). The objective of this study is to evaluate the influence of the presentation of an olfactory stimulus in the model of rapid electrical amygdala kindling. For this purpose, male Wistar rats will be subjected to unilateral stereotactic surgery for implantation of stimulation electrodes in the basal amygdala and of recording eletrodes in the amygdala, hippocampus and piriform cortex. Later, after a recovering period animals should be subjected to rapid electrical kindling model proposed by Foresti et al. (2008), according to the group to which they belong. After 24 hours of the 20 electrical stimulation, the animals will then be submitted by 15 seconds to olfactory stimulation with toluene (C7H8) - 92.14 PM - Merck Chemical Industry Rio de Janeiro, Brazil) or 0.9% saline, prior the presence or absence of 21 electrical stimulus. EEG and behavioral data of 1, 20 and 21 stimuli will be recorded. Behavioral analysis will be performed by the statistical program ETHOMATIC (Garcia-Cairasco et al., 1992) and the data will be plotted in the form of flowcharts. The EEG recordings will also be evaluated to identify the presence or absence of epileptiform discharges in the amygdala, hippocampus and piriform cortex. Also, the brain tissue will be used for histochemical analyzes to evaluate neurodegeneration (Fluoro-Jade C), and also Nissl staining to verify the electrode placement. Moreover, it will be performed an immunohistochemistry for Fos assess cell activation. All analyzes will be made in the following areas: hippocampus, the basolateral amygdala and piriform cortex.