NEITHER TRIAZOLAM NOR ACTIVITY PHASE ADVANCE CIRCADIAN LOCOMOTOR-ACTIVITY IN SCN-LESIONED HAMSTERS BEARING FETAL SCN TRANSPLANTS

Both triazolam (Tz) and exercise can phase advance free-running locomotor activity rhythms in intact hamsters. Furthermore, Tz increases activity at the time of injection, and this appears to be the mechanism whereby Tz produces phase shifts. This study tested the phase-shifting effect of Tz in SCN-lesioned (SCN-X) hamsters that had regained circadian rhythms of locomotor activity after transplantation of fetal SCN into the third ventricle. The results indicate that in both groups, increases in locomotor activity are seen at the time of Tz injection, and most intact animals, but no grafted animals show a phase advance in response to Tz administration. Given that hamsters bearing SCN grafts have limited neural connections between the host brain and transplanted SCN tissue, the results suggest that a site outside the SCN, with afferents to these nuclei, mediates the phase-shifting effect of Tz and of exercise.