Journal of Neuroscience, Vol 6, 3430-3435, Copyright © 1986 by Society for Neuroscience
Induction of ornithine decarboxylase as a possible mediator of seizure- elicited changes in genomic expression in rat hippocampus
M Baudry, G Lynch and C Gall
Small electrolytic lesions placed in the hilus of the dentate gyrus have
been shown to induce behavioral seizures, an elevation in the concentration
of the opioid peptide enkephalin, and an increase in the transcription of
the gene coding for the peptide precursor of enkephalin. Since polyamines
and ornithine decarboxylase (ODC), the rate-limiting enzyme in their
synthesis, have been shown to play critical roles in the growth and
differentiation of several types of tissue, we tested for changes in ODC
activity at various times following the initiation of seizures. ODC
activity is significantly increased 3 hr after the lesions, reaches maximal
(50-fold) levels about 12 hr later, and returns to control values after 48
hr. The increase occurs in both hippocampi following unilateral
electrolytic lesions, is blocked by treatments that suppress limbic
seizures, and does not occur after lesions that fail to elicit seizures;
accordingly, we conclude that the increase in ODC activity results from
epileptiform activity rather than some other consequence of the hilar
lesion (e.g., deafferentation). The increase in ODC activity precedes the
increase in the amount of mRNA coding for the enkephalin prohormone, which,
in turn, precedes the increase in enkephalin levels. These results are
consistent with the hypothesis that the early induction of ODC following
the initiation of seizures leads to an alteration in genomic expression,
which, in turn, changes neuropeptide levels. Adult brains thus appear to
possess trophic responses of a type found in a variety of developing cell
types and organs, and the possibility exists that these are involved in the
control of seizure susceptibility.