Abstracts

Rationale: Ageing is associated with a failure in hippocampal synaptic plasticity and a normal decline in memory functions. In epileptic patients, age-related synaptic changes can influence the behavioral expression of seizures. In the audiogenic model of epilepsy, we have observed that repetitive audiogenic seizures in adult rats (audiogenic kindling, AK) promote a progressive change in seizure behavior from tonic-clonic generalized convulsions of brainstem origin to head and forelimb myoclonus, rearing and falling, typical of limbic behaviors. Previous reports from our lab have also shown that the hippocampus is engaged during the limbic recruitment. Therefore, in the present study we analyzed the effects of an assumed dysfunction in hippocampal plasticity during ageing on seizure expression during AK. Methods: Sixteeen senescent and six adult Wistar audiogenic rats were subjected to AK protocol consisting of 28 sound stimuli, twice a day (120dB SPL). The sound was presented for 1 min or until the rat expressed a tonic-clonic convulsion. At each experiment, behaviors were scored according to seizure indexes (categorized mesencephalic index and Racine’s limbic index) in order to measure the behavioral progression. At stimuli 1,7,14, 21 and 28, all rats were video-taped for 1 min before, during and after sound presentation, in order to extract behavioral sequences and quantify their interactions by means of neuroethological analysis. Results: Our results show that senescent rats had a different seizure expression pattern during AK when compared to adult rats: (1) the expression of limbic seizures was much less pronounced in senescent than in adults; (2) grooming behavioral clusters appeared before, during and after sound presentation much more often in senescent than in adult rats. In the 21st and 28th stimuli, they seemed somehow to have replaced limbic behaviors, and (3) tonic-clonic behaviors were more persistent after sound presentation in senescent than in adult rats, in which they were replaced by limbic behaviors. Conclusions: In conclusion, our data suggest that age-related dysfunctions in hippocampal synaptic plasticity could affect seizure expression that occurs in the course of AK involving limbic recruitment. In addition, it supports previous observations showing that Wistar audiogenic rats have a faster ageing process, with serious neuronal abnormalities.Financial support: FAPESP, Cinapce-FAPESP, CNPq, PROEX-CAPES, FAEPA.