Alterations in Serotonin Receptors and Transporter Immunoreactivities in the Hippocampus in the Rat Unilateral Hypoxic-induced Epilepsy Model

Unilateral hypoxic-ischemia results in the frequent occurrence of interictal spikes, and occasionally sustained ictal discharges accompanied by a reduction in paired-pulse inhibition within the non-lesioned dentate gyrus. To elucidate the roles of serotonin (5-hydroxytryptamine [5-HT]) in an epileptogenic insult, we investigated the changes in 5-HT receptors and serotonin transporter (5-HTT) immunoreactivities within the lesioned and contralateral hippocampus following unilateral hypoxic-ischemia. During epileptogenic periods following hypoxic-ischemia, both 5-HT_1A and 5HT_1B receptor immunoreactivities were decreased within the lesioned and the non-lesioned hippocampus. However, 5-HTT immunoreactivity was transiently increased within the hippocampus bilaterally. These findings indicate that alteration of the 5-HT system results in a “diaschisis” pattern, and may contribute to neuronal death and the development of emotional disorders in epileptic patients accompanied by psychological stress.