Altered hippocampal expression of neuropeptide Y, somatostatin, and glutamate decarboxylase in Ihara's epileptic rats and spontaneously epileptic rats

By in situ hybridization and immunocytochemistry, expression of neuropeptid e Y (NPY), somatostatin and glutamate decarboxylase 65 (GAD65) was studied in the hippocampus of two different epileptic mutant rats, Ihara's epilepti c rat (IER) and the spontaneously epileptic rat (SER). GAD65 mRNA expressio n was enhanced in interneurons of the hippocampus in young IER, that had no t yet developed generalized seizures. In older IER and older SER that both showed spontaneous seizures, marked increases of NPV mRNA in hippocampal gr anule cells and interneurons were found, as well as elevated GAD65 mRNA lev els in interneurons. NPY immunoreactivity was enhanced in hilar interneuron s and the dentate gyrus of older IER. In addition, some older IER stained h eavily for NPY in mossy fibers. These findings suggest that up-regulation o f NPY and GAD65 synthesis may be important in epileptogenesis. (C) 2000 Els evier Science Ireland Ltd. All rights reserved.