KINDLING INDUCES TRANSIENT CHANGES IN NEURONAL EXPRESSION OF SOMATOSTATIN, NEUROPEPTIDE-Y, AND CALBINDIN IN ADULT-RAT HIPPOCAMPUS AND FASCIA-DENTATA

Fully hippocampus-kindled rats were examined 1 day and 1 month after t he last stimulation for changes in somatostatin (SS)-, neuropeptide Y (NPY)-, and calbindin (CaBP)-immunoreactivity (ir) and SS- and NPY-mRN A in situ hybridization (ISH). One day after the last stimulation, the re was marked, bilateral increase in SS- and NPY-ir in the outer part of the dentate molecular layer. The cell bodies of dentate hilar SS- a nd NPY-containing neurons, known to project to this area, also appeare d to display increased immunoreactivity as well as an increased ISH si gnal for SS and NPY mRNA. Bilateral de novo expression of NPY-ir in de ntate messy fiber projection to dentate hilus and CA3 was also evident , but we noted no corresponding NPY-mRNA signal in the parent cell bod ies, the dentate granule eels. After 1 month, the levels of NPY-ir and ISH signal appeared essentially normal. In contrast, the levels of SS apparently were decreased, although not yet normal. CaBP-ir was marke dly and selectively reduced in dentate granule cell bodies, dendrites, and messy fibers 1 day after the last stimulation, but after 1 month CaBP-ir appeared essentially normal. Because kindling, once establishe d, is a permanent phenomenon, the observed transient changes in SS, NP Y, and CaBP in specific hippocampal terminal fields and neuronal popul ations cannot be associated specifically with kindling. Rather, they r elate to the repeated high-frequency stimulations and may serve as pro tective measures against deleterious effects of such stimulations.