Nocturnal feeding in the mouse--opiate and pineal influences.

Mice displayed daily rhythms in their basal and morphine-induced food intake, consuming significantly greater amounts of food at night. Non-invasive inhibition of the activity of the pineal gland by either exposure to a bright pulse of light or treatment with the L-amino-acid decarboxylase inhibitor, benserazide, reduced the elevated night-time food intakes. These effects on feeding were most evident on the first night the activity of the pineal was reduced. On subsequent nights light pulses had a diminished effect on basal and morphine-induced food intake. These results suggest that although the enhanced nocturnal food intake of mice may be modulated by pineal and opioid sensitive mechanisms, pineal activity is not essential for the expression of opioid-mediated feeding.