Hyperthermic seizure induces persistent alteration in excitability of the dentate gyrus in immature rats

Febrile seizure (FS) is the most common type of seizure that occurs during early childhood. It has been proposed that atypical FS (prolonged, multiple, or lateralized) results in the development of recurrent complex partial seizures accompanied by Ammon's horn sclerosis or mesial temporal sclerosis, which is the most common of the intractable epilepsy. To elucidate the characteristics of epileptogenesis or acquired epilepsy following FS, we performed prospective long-term studies using hyperthermia-induced seizure model. Rat pups (postnatal 11 day old) were induced to hyperthermia (41-43 °C in core temperature) by exposure to a 175 W mercury vapor lamp. Six-nine weeks after hyperthermic seizure, the dentate gyrus showed impairments of paired-pulse inhibitions and excitability ratio. In addition, newly generated granule cells and synaptogenesis were observed in this region. Ten-twelve weeks after hyperthermic seizure, animals (~ 68%) showed electroencephalographic seizure activity with increased VGLUT-1 immunoreactivity in the dentate gyrus. Parvalbumin immunoreactivity was markedly reduced in the hilus. These findings indicate that in this model the epileptogenic changes in the dentate gyrus may be based on the persistent alterations in excitability via neurogenesis, synaptogenesis, and impaired GABA_B receptor-mediated inhibition.