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 neuropeptide Y (NPY), somatostatin and glutamate decarboxylase 65 (GAD65) was studied in the hippocampus of two different epileptic mutant rats, Ihara's epileptic rat (IER) and the spontaneously epileptic rat (SER). GAD65 mRNA expression was enhanced in interneurons of the hippocampus in young IER, that had not yet developed generalized seizures. In older IER and older SER that both showed spontaneous seizures, marked increases of NPY mRNA in hippocampal granule cells and interneurons were found, as well as elevated GAD65 mRNA levels in interneurons. NPY immunoreactivity was enhanced in hilar interneurons and the dentate gyrus of older IER. In addition, some older IER stained heavily for NPY in mossy fibers. These findings suggest that up-regulation of NPY and GAD65 synthesis may be important in epileptogenesis.