Ultradian rhythm of pontomesencephalic opiate receptor: modification by chloramphenicol

Pontomesencephalic receptor binding was measured in rats at 4-h intervals throughout a 24-h day. Two hours prior to each interval the animals were treated with either saline, thiamphenicol, or chloramphenicol. The results showed the existence of an ultradian rhythm of receptor binding. Such rhythm was abolished by chloramphenicol, but not by thiamphenicol. These results suggest that the number of available binding sites changes during a 24-h day, and that such availability is modified by chloramphenicol.