Increased somatostatin and enkephalin-like immunoreactivity in the rat hippocampus following hippocampal kindling.

As neuropeptides may play a role in the electrical kindling model of epileptogenesis, hippocampal somatostatin, Met-enkephalin and cholecystokinin were studied by immunocytochemistry in rats 24 h following full hippocampal kindling (three stage 5 seizures). As control animals we used sham-kindled rats, unoperated rats and rats subjected to a single electroshock-induced seizure. In addition, the distribution of septohippocampal, cholinergic fibers and hippocampal mossy fibers were studied by histochemistry. The important finding was that after kindling there was, as compared to unoperated control, (1) a marked increase of somatostatin immunoreactivity in cell bodies in the dentate hilus and their presumed projections area in the outer parts of the dentate molecular layer, and (2) a marked increase of Met-enkephalin immunoreactivity in hippocampal mossy fiber terminals. We found no evidence of aberrant sprouting of mossy fiber collaterals in the fascia dentata.