Diurnal variation in ornithine decarboxylase activity of different brain regions of the rat.

The activity of ornithine decarboxylase (ODC) was studied in the brain of Sprague-Dawley male rats weighing 200-250 g. In this study, animals were maintained at a temperature of 21 +/- 1 degree C and a 12:12 h light--dark cycle for a minimum of 3 weeks prior to any experimentation. Animals were sacrificed at 06.00 h and 18.00 h and the brain cerebral cortex, hypothalamus, amygdala, hippocampus, midbrain, pons, medulla oblongata and cerebellum were isolated and assayed for ODC activity. The data show significant diurnal variations (P less than 0.05) in hypothalamus, midbrain, medulla oblongata and cerebellum, with peak values during the active phase of the animal. Other brain parts studied did not show any significant diurnal variations.