THE ROLE OF VASOPRESSIN IN MODULATING CIRCADIAN-RHYTHM RESPONSES TO PHASE-SHIFTS

Telemetered body temperature CBT), heart rate (HR), and motor activity (AC) data were collected in vasopressin-containing, Long-Evans (LE) a nd vasopressin-deficient, Brattleboro (DI) rats. In Experiment 1, the rats were initially exposed to a 12 h/12 h light/dark cycle under ad-l ibitum feeding and were then subjected to either a phase-advance or ph ase-delay shift of 6 h. After the phase-advance shift, neither strain adapted; however, after the phase-delay shift, both strains adapted ra pidly. In Experiment 2, the animals were subjected to either a nocturn al or a diurnal restricted-feeding paradigm and were then exposed to e ither a phase-advance or phase-delay shift with synchronized feeding. In the nocturnal restricted-feeding paradigms, both strains rapidly ad apted to both shifts. Concerning diurnal restricted-feeding, DI animal s readily entrained to the presentation of food in both shifts; wherea s, LE animals exhibited a confused rhythmicity. In Experiment 3, anima ls were subjected to a phase-advance shift, while the time of feeding was held constant. Following the shift, LE animals responded to the on set of the dark at the new time; yet, were still influenced by the pre sentation of food. The DI animals maintained the preshift circadian pa ttern and continued to be dominated by the presentation of food. These experiments indicate that circadian rhythms of LE animals are dominat ed by the light entrainable oscillator (LEO) in ad-libitum feeding and by both the LEO and food entrainable oscillator (FEO) in restricted-f eeding. On the other hand, the circadian rhythms of DI animals are dom inated by the FEO unless food is provided ad-libitum. The demonstrated role of vasopressin in synchronizing circadian rhythms to the LEO may be of significance in understanding human circadian rhythm disturbanc es, such as jet lag. (C) 1998 Elsevier Science Inc.