KAINIC ACID ACTIVATES TRANSIENT EXPRESSION OF TENASCIN-C IN THE ADULT-RAT HIPPOCAMPUS

Kainic acid-induced limbic seizures enhance expression of tenascin-C ( TN) in the hippocampus of adult rats, TN mRNA was detectable by in sit u hybridization in many granule cells in the dentate gyrus 4.5 hr afte r kainic acid injection but not in saline-injected animals (controls) or in animals killed 2 or 24 hr after injection, Thirty days after kai nic acid injection, TN mRNA was detectable only in pyramidal cells of CA3 and CA1. At the protein level, TN was detectable by immunocytochem istry in control animals in the strata oriens and lacunosum moleculare of CA1, in the molecular layer, and within a narrow area at the inner surface of the granule cell layer in the dentate gyrus. Twenty-four h ours after kainic acid injection, TN immunoreactivity was enhanced in these areas and throughout the granule cell layer, Thirty days after k ainic acid injection, TN immunoreactivity was downregulated in these a reas, while it was prominent in the stratum oriens and in clusters of immunoreactivity in the stratum lucidum of CA3, Western blot analysis of the hippocampus showed a peak of TN expression 24 hr after kainic a cid injection, These observations show that TN expression is upregulat ed in predominantly neuronal cells already by 4.5 hr after kainic acid injection, coincident with activation of granule cells and sprouting of axon terminals, whereas the remaining TN expression 30 days after i njection relates to pyramidal cells in CA1 and CA3, coincident with an astroglial response, as marked by a strong expression of glial fibril lary acidic protein. (C) 1996 Wiley-Liss, Inc.