The effects of congenital absence of visual input on daily rhythms of feeding behavior and tissue ornithine decarboxylase activity were examined in hereditary blind rats. Food intake of normal and hereditary microphthalmic rats was determined every 3 h over 48 h under a 12 h-12 h light-dark cycle. Normal rats took their daily food mainly during the dark period, with two clear peaks in the evening and morning, but hereditary microphthalmic rats ate continuously, suggesting that the feeding rhythm of the hereditary microphthalmic rats is not entrained by the light-dark cycle due to a lack of their optic nerve. The hepatic and renal ornithine decarboxylase activities in normal rats showed a circadian rhythm with a peak at 2000 hours in the dark period as reported previously. In hereditary blind rats, however, the hepatic and renal enzyme activities were found not to undergo any remarkable diurnal change through the light-dark period. These results mean that the feeding rhythm and hepatic and renal ornithine decarboxylase activity rhythm in hereditary blind rats disappeared.
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