Induction of somatostatin by kainic acid in pyramidal and granule cells of the rat hippocampus.

Seizures were induced in rats by systemic administration of kainic acid and, 1.5-12 h after, expression of preprosomatostatin and c-fos mRNAs in 9 hippocampal areas and in the cerebral perirhinal cortex was investigated using in situ hybridization histochemistry. Immunohistochemistry was also performed to study somatostatin peptide. In the control animals preprosomatostatin mRNA was expressed in some cells in the dentate hilus, the stratum oriens and the stratum radiatum of Ammon's horn, the subiculum and the cortex. Starting 3 h after kainic acid administration preprosomatostatin mRNA was expressed in a subpopulation of granule and pyramidal cells which did not normally express it. Preprosomatostatin mRNA-positive cells were markedly increased in the subiculum. Immunohistochemical examination confirmed that preprosomatostatin mRNA in granule and pyramidal cells was translated into peptide. In contrast, c-fos mRNA was induced in most hippocampal and cortical neurons starting 1.5 h after the kainic acid injection. When diazepam was injected to suppress the generalized seizures, preprosomatostatin mRNA was still expressed in pyramidal and subicular cells but not in granule cells.