Ornithine decarboxylase is differentially induced by kainic acid during brain development in the rat.

The induction of brain ornithine decarboxylase (ODC) as a consequence of systemic kainic acid administration was studied in the hippocampus and the olfactory cortex-amygdala area of 10-day-old rat pups and 30-day-old young rats. In pups, ODC levels were moderately increased (plus 50-80%) 4 h after kainic acid administration, coming back quickly to control levels afterwards. In young rats, instead, ODC levels were dramatically increased by 17-25-fold, 16 h after kainic acid administration and decreased towards basal levels 48-72 h after injection. The present results suggest that the process of excitotoxic ODC induction can be split in two phases: a first phase characterized by moderate induction and essentially linked to the overstimulation of brain circuits and a second phase, during which a dramatic enzyme stimulation is accompanied by the appearance of neurodegenerative pathology.