SEIZURE-INDUCED SYNTHESIS OF FIBRONECTIN IS RAPID AND AGE-DEPENDENT -IMPLICATIONS FOR LONG-TERM POTENTIATION AND SPROUTING

Extracellular matrix proteins are induced by activity in adult brain b ut the time course of these responses, and hence the possibility of th eir involvement in use-dependent synaptic plasticity, is not known. To evaluate this issue, the influence of seizures on fibronectin express ion was evaluated in the adult and developing hippocampus. In adult ra ts, kainic acid-induced seizures increased fibronectin mRNA and immuno reactivity (ir) by about 1 h after the first behavioral seizure. In si tu hybridization analysis indicated that fibronectin mRNA was increase d in broadly distributed glial cells as well as within discrete neuron al populations that normally express this transcript. Western blots de monstrated that increased fibronectin-ir was evident in both soluble a nd non-soluble fractions at the same time point. Immunocytochemical co localization confirmed that fibronectin-ir was indeed elevated in broa dly distributed glial fibrillary acidic protein-ir astroglia. Seizures had no detectable effect on fibronectin-ir in the hippocampus of nine day old rats. Together with previous results, the above findings sugg est that intense physiological activity triggers a 'matrix response' ( i.e., release proteases, activate integrins, secrete matrix proteins) that is sufficiently rapid to participate in the consolidation of long -term potentiation (LTP). The absence of such reactions in the immatur e hippocampus is in accord with the hypothesis that matrix proteins ge nerated by mature astroglia impose temporal and spatial limitations on axonal remodeling. (C) 1998 Elsevier Science B.V. All rights reserved .