REGULATION OF NEURONAL NITRIC-OXIDE SYNTHASE MESSENGER-RNA LEVELS IN RAT-BRAIN BY SEIZURE ACTIVITY

THE regulation of neuronal nitric oxide synthase (NOS) mRNA levels dur ing kindling epileptogenesis in the rat brain was investigated using i n situ hybridization. Following 40 rapidly recurring seizures evoked b y hippocampal stimulations, NOS mRNA expression decreased by 56% in th e dentate granule cell layer (maximum at 2 h) and increased by 420,105 and 1260% in the CA1 and CA3 pyramidal layers and piriform cortex, re spectively (maximum at 12-24 h). Gene expression had returned to contr ol levels after one week. The presumed alterations of nitric oxide pro duction, following the changes in NOS mRNA shown here, may modulate sy naptic function during kindling development, and could influence neuro nal vulnerability after epileptic insults.