Efficacy of mediodorsal thalamic nucleus stimulation in a rat model of cortical seizure.

OBJECTIVE: The mediodorsal thalamic nucleus (MD) has strong connectivity to the limbic systems and frontal lobe. The aim of this study was to determine whether the mediodorsal thalamic nucleus influences seizure induction by electrical stimulation in the rat frontal cortex. MATERIALS AND METHODS: Juvenile male rats (n=7) were used in the experiment. At postnatal day 28 (P28), stainless steel skull screws were inserted for stimulating cortices. Depth-stimulating electrodes were stereotaxically inserted into the MD of the bilateral thalamus. Electrical stimulation, which produces afterdischarges, was applied to the frontal cortices once/day for four consecutive days from postnatal day 38. Additional conditioning electrical stimulation to the bilateral MD was fixed at 0.1 mA, and the stimulus frequency was increased from 0 Hz, 1 Hz, and 5 Hz to 10 Hz. All seven rats were stimulated with those frequencies by rotation every other day. The data of animals with 0 Hz MD stimulation were defined as controls. Afterdischarge thresholds and durations were measured at each frequency. RESULTS: Seizures were accompanied by bilateral tonic-clonic convulsions and cortical spikes. Seizure behaviors were not different among the groups and there were no statistically significant differences in the cortical afterdischarge (AD) thresholds between animals with MD stimulations and controls in all frequencies. In the cortical AD durations, there were also no statistically significant differences between animals with MD stimulation and controls although the mean duration at 10-Hz stimulation was less than the control animals. CONCLUSION: These results indicated that thalamic MD stimulation might not suppress epileptic seizure induction. Further studies are needed to analyze other stimulus parameters, altered stimulus locations, and different test paradigms.