Response of seizure-induced newborn neurons in the dentate gyrus of adult rats to second episode of seizures

In this study we examined the unknown issue of whether seizure-induced newbom hippocampal neurons in freely moving adult rats are able to respond to pathophysiological stimuli in the same way as their neighboring neurons do. Three days after pentylenetrazol (PTZ)-induced generalized seizures, rats received 5-bromodeoxyuridine (BrdU) injections to label dividing cells, followed 4 weeks later by the second PTZ injection to induce second episode of generalized seizures. We observed that the first episode of PTZ-induced seizures resulted in a significant increase in the number of newborn neurons in the adult hippocampal dentate gyrus. In comparison with vehicle-injected control rats that exhibited no Fos immunoreactivity and mild glutamic acid decarboxylase 67 (GAD67) expression in the dentate granule cells, rats killed 2-6 h following the second PTZ injection showed intensive Fos and GAD67 expression in virtually all granule cells with or without BrdU double-labeling. These findings provide important evidence indicating that seizure-induced newborn neurons in freely moving adult rats are able to respond to pathophysiological stimuli in the same way as neighboring neurons do. (C) 2004 Elsevier B.V. All rights reserved.