Serotonergic stimulation and nonphotic phase-shifting in hamsters

Area of Science:

• Chronobiology
• Neuroscience
• Circadian Rhythms

Background:

• Nonphotic stimuli, like activity, alter circadian clocks.
• Serotonergic (5-HT) pathways projecting to the suprachiasmatic nucleus (SCN) are implicated in nonphotic clock resetting.
• The precise role of 5-HT in mediating activity-induced phase shifts remains unclear.

Purpose of the Study:

• To investigate the contribution of locomotor activity to phase shifts induced by the 5-HT1A and 5-HT7 receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT).
• To determine if 5-HT receptor agonists directly affect circadian clock resetting independent of their motor effects.

Main Methods:

• Hamsters received 8-OH-DPAT at circadian time 8 to assess phase advances.
• Locomotion was prevented in a subset of animals after 8-OH-DPAT administration.
• The effects of varying 8-OH-DPAT doses on activity levels and phase shifts were examined.
• Quipazine, a non-specific 5-HT agonist, was administered during the subjective day.

Main Results:

• Preventing locomotion did not abolish the phase shifts induced by 8-OH-DPAT.
• Higher doses of 8-OH-DPAT reduced activity but did not alter the amplitude of phase shifts.
• Quipazine did not induce phase shifts in hamsters, contrasting with findings in rats.

Conclusions:

• The phase-shifting effects of 8-OH-DPAT in hamsters are not solely mediated by increased locomotor activity.
• Serotonin likely plays a direct role in the nonphotic resetting of the circadian clock in hamsters.
• Species-specific differences exist in the response of circadian rhythms to non-specific 5-HT agonists like quipazine.