Serotonin and kindling development.

The inhibitory effect of serotonin on the kindling model of epilepsy was investigated in the adult rat. Specific neurotoxins such as 5-6 or 5-7 dihydroxytryptamine were used to destroy serotoninergic neurons before kindling sessions, and an immunocytochemical control revealed, at the end of the experiments, the location and the extent of the lesions. The destruction of serotoninergic terminals in the epileptic focus (olfactory bulb or amygdala) facilitated the initial development of kindling obtained by stimulations of these structures. Lesions of pontis, centralis and dorsalis nuclei of the raphe enhanced the rate of olfactory bulb kindling. Finally, we transplanted foetal raphe cells into the olfactory bulb of adult rats before olfactory bulb kindling. The presence of viable grafts, controlled by immunocytochemistry, was associated with an increase of afterdischarge threshold in the olfactory bulb. All these results confirm the inhibitory function of serotonin on kindling development and demonstrate that serotoninergic neurons exert an important control both on local excitability and on the progressive establishment of kindling phenomena.