Phase-shifting effect of triazolam on the hamster's circadian rhythm of activity is not mediated by a change in body temperature

Abstract

Treatment with the short-acting benzodiazepine, triazolam (Tz), 6 h before activity onset (CT 6) induces large phase advances in the circadian rhythm of locomotor activity in golden hamsters free-running in constant lighting conditions. These phase shifts are associated with acute increases in locomotor activity. The acute increases in activity appear to be necessary for induction of phase shifts in the activity rhythm by Tz, since suppression of this activity by restraining the animal blocks the phase shifts normally induced by Tz.Furthermore, other stimuli which induce an acute increase in locomotor activity phase shift the circadian clock in a similar manner as does Tz. Since increased locomotor activity is associated with a rise in body temperature in mammals, and changes in temperature have been associated with changes in circadian rhythms, this study was designed to determine whether the phase-shifting effect of Tz on the circadian clock could be mediated by the change in body temperature resulting from the induced acute increase in locomotor activity. Hamsters free-running in constant light (LL) were implanted with Mini-Mitter biotelemetry devices and either injected with Tz at CT 6, injected with Tz at CT 6 and restrained for the next 6 h, or restrained for 6 h beginning at CT 6. Treatment with Tz resulted in large phase advances in the activity rhythm, while the other two treatments did not induce phase advances. Mean body temperature increased over control levels for all 3 groups during most of the 6 h following the beginning of treatment, and there were no significant differences in body temperature changes between any pairs of groups. These results indicate that the phase shifts in the circadian rhythm of activity induced by Tz are not mediated by the resulting increase in body temperature, since: (1) restraint alone from CT 6 to CT 12 induces an increase in body temperature but does not induce phase shifts in the activity rhythm; and (2) restraint blocks Tz-induced phase shifts but not the increase in body temperature.