ACTIVATION OF SOMATOSTATIN-SYNTHESIZING NEURONS IN THE HIPPOCAMPAL-FORMATION THROUGH KINDLING-INDUCED SEIZURES

The present study was designed to determine if and to what extent soma tostatin (SST) synthesizing neurons of the hippocampal formation are a ctivated during seizures, elicited through kindling of the perforant p athway. Tissue was used and analyzed from animals which had experience d a single afterdischarge, or a stage 3 or stage 5 seizure. The protei n expression of the oncogene c-fos in activated, depolarizing neurons was utilized to identify seizure-activated SST-synthesizing neurons. C ombined immunocytochemical and in situ hybridization methods were used to identify these double-labeled, Fos protein, and SST mRNA-containin g neurons. The results were quantified and compared across seizure sta ges. The resulting data demonstrate that at every stage of seizure dev elopment, a majority of SST-synthesizing neurons is activated, but tha t these activated SST mRNA-containing neurons represent only a minorit y of all seizure-activated, Fos-expressing neurons in the hippocampal formation. The data further reveal a numerical hierarchy in which the majority of double-labeled neurons is present in the hilus of the dent ate, followed by the stratum oriens of CA1. It is concluded that SST-s ynthesizing neurons represent an integral component of the kindling ac tivated neuronal network and, since the SST synthesizing neurons repre sent the minority of all seizure-activated neurons in the hippocampal formation, that this neuronal network is likely to be of considerable neurochemical complexity. (C) 1995 Wiley-Liss, Inc.