Developmental changes in the serotonergic system in El mouse brain

El mice manifest epileptiform seizures which are gradually elicited by tossing stimulation once a week from 5 to 10 weeks of ages. It was reported that brain monoamines, especially serotonin (5-HT), are important factors in seizure susceptivity. In this study, we observed changes in brain 5-HT and its metabolite, 5-hydroxyindolacetic acid (5-HIAA), and its metabolic enzymes, tryptophan hydroxylase (Trp-OHase) and monoamine oxidase-A (MAO-A) , during growth with and without tossing stimulation. In non-stimulated El mice, the 5-HT level was lower at 6 and 7 weeks than that in other ages, and the 5-HIAA level was generally lower in older mice. In stimulated El mice, the 5-HT level was higher after the first stimulation, lower at 8 weeks, and then higher again at 10 weeks. However, 5-HIAA levels were generally higher in older mice. The Trp-OHase activity was higher at 8 and 10 weeks, and the MAO-A activity was higher at 8 weeks compared to that of non-stimulated El mice. These findings suggest that a disordered release and metabolism of 5-HT influences the development of the epileptiform seizures induced by tossing stimulation.

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