In situ hybridization and RNA blot-hybridization techniques were used (i) to examine the regional distribution of mRNA for a putative kainate receptor in adult rat brain and ii) to test the possibility that seizures affect expression of the receptor gene. The highest densities of hybridization were distributed within hippocampal pyramidal and granule cells, medial habenula, Purkinje cells and the molecular layer of cerebellum, and olfactory bulb. Recurrent limbic seizures caused a massive, delayed, and reversible reduction in levels of the kainate receptor mRNA in dentate gyrus; lesser decreases were found in pyramidal cell fields of hippocampus and superficial cortex. These findings provide evidence that unusual patterns of physiological activity can alter genomic expression for a subclass of glutamate receptors in brain.