Effects of the 5-HT1a receptor agonist 8-OH-DPAT and other non-photic stimuli on the circadian rhythm of wheel-running activity in hamsters under different constant conditions.

Our findings show that administration of the 5-HT1A receptor agonist 8-OH-DPAT (8-hydroxy-2-[di-n-propylamino] tetralin) was able to induce significant phase-advances 4 h before onset of hamster locomotor activity under constant darkness. All other non-photic treatments applied such as melatonin, dimethyl sulphoxide, Ringer, saline or enforced wheel-running failed to induce any significant phase-advances. Similar results were obtained in pinealectomized animals. In constant light (LL), all treatments produced phase-advances. These results show that: (1) LL seems to be an inappropriate constant condition to study the chronobiological effect of drugs or other non-photic stimuli; (2) the endogenous circadian pacemaker (SCN) can be affected specifically by 8-OH-DPAT.