Abstracts

Rationale: It has been reported that the two genetic absence models are resistant to secondary generalization during kindling. However, kindling from the mediodorsal (MD) thalamus suggests that this difference of resistance between rat strains depends on kindling sites. In this study we determined the stages of cortical recruitments between Sprague-Dawley (SD) and WAG/Rij rats during MD kindling.Methods: Adult male, 6 to 12-month-old WAG/Rij and nonepileptic SD rats were used. With streotaxic surgery, bipolar insulated stainless steel electrode (Plastic One) were implanted into the MD (-2.3mm AP, 1.0mm ML, 5.8mm DV, 10o angle) thalamus. Stainless steel screws were used as ground and cortical recording electrodes were placed bilaterally in the skull over frontal and parietal cortices. All of them were fixed to the skull with dental acrylic. After 7 days to recover from surgery, rats were kindled by fast kindling protocol, 6 stimuli per day, every other day until they achieved stable motor convulsions (at least three consecutive stage 4 or 5 seizures at Racine scale) or completed 30 stimulations. After discharge duration (ADD), behavioral seizure severity (BSS), cortical involvement were evaluated between groups. At the end of the experiment, all animals were decapitated and the brains placed in a formalin sucrose mixture. Location of the electrodes was confirmed histologically. All results are presented as means SEM. Comparisons were made between groups using t-test.Results: The mean number of stimulations to reach stage 4/5 were 5.4 1.4 and 8.2 1.1 for WAG/Rij and SD rats, respectively (p=0.1). Mean ADDs of three consecutive stage of stage 4/5 were 31.2 5.4 seconds in the WAG/Rij and 42.3 6.9 seconds in the SD groups (p=0.2). There were no statistical significant differences in kindling rates, ADDs as well as cortical recruitment patterns between groups.Conclusions: The resistance to kindling in WAG/Rij rats was not present with MD stimulation. These data suggests that the part of the seizure circuitry from the midline thalamus to the cortex act similar in WAG/Rij and SD rats.