THE INTERACTION OF VASOPRESSIN AND THE PHOTIC OSCILLATOR IN CIRCADIAN-RHYTHMS

Telemetered body temperature (BT), heart rate (HR), and activity (AC) data were collected in vasopressin-containing Long-Evans (LE) and vaso pressin-deficient Brattleboro (DI) rats. The rats were exposed to a 12 /12 h light/dark cycle under three conditions: 1) ad lib feeding throu ghout the 24-h cycle, 2) two scheduled-feeding periods during the diur nal component of the light/dark cycle, and 3) two scheduled-feeding pe riods during the nocturnal component of the light/dark cycle. With ad lib feeding, natural nocturnal cycles of BT, HR, and AC were maintaine d in both strains. Marked changes were observed under the condition of scheduled feeding during the diurnal component of the light/dark cycl e. In DI animals the influence of the photic oscillator was lost and B T, HR, and AC shifted from nocturnal to diurnal patterns. Circadian rh ythms in DI animals were now synchronized by the nonphotic zeitgeber o f scheduled food presentation. On the other hand, LE animals lost a we ll-defined circadian rhythmicity resulting from adherence to the photi c oscillator, while at the same time being influenced by the nonphotic oscillator. Under the condition of scheduled feeding during the noctu rnal component of the light/dark cycle, the circadian rhythms were sim ilar in DI and LE rats. Results show that vasopressin has a significan t interaction with the photic oscillator, which is obvious only when t he photic and nonphotic oscillators are uncoupled. In addition, the re sults demonstrate that the strength of the photic oscillator is decrea sed or that the effect of this oscillator is masked or lost in DI rats compared to LE rats.