Daily hoarding opportunity entrains the pacemaker for hamster activity rhythms

Area of Science:

• Chronobiology
• Animal Behavior

Background:

• Circadian rhythms govern daily activity patterns in many species.
• The suprachiasmatic nuclei (SCN) is the primary pacemaker for circadian rhythms, typically entrained by light cues.
• Non-photic cues, such as feeding or social interactions, can also influence activity rhythms.

Purpose of the Study:

• To investigate the effects of a daily hoarding opportunity on the activity rhythms of Syrian hamsters.
• To determine if the SCN is essential for entrainment to this non-photic cue.
• To explore the potential existence of a separate oscillator system entrainable by non-photic stimuli.

Main Methods:

• Syrian hamsters were housed in continuous dim light with a daily 30-minute hoarding opportunity.
• Activity rhythms were monitored to assess entrainment to the hoarding time.
• Suprachiasmatic nuclei (SCN) ablations were performed in hamsters that showed stable entrainment.

Main Results:

• Six out of ten hamsters exhibited clear entrainment of activity rhythms to the hoarding opportunity.
• SCN lesions in two hamsters indicated the SCN's role in controlling the entrained rhythm.
• One hamster with a complete SCN lesion showed anticipatory activity, suggesting an unmasked oscillator.

Conclusions:

• Daily hoarding opportunities can entrain activity rhythms in Syrian hamsters, mediated by the SCN.
• SCN ablation can reveal a separate oscillator system responsive to non-photic cues.
• The hamster's non-photic entrainment system appears more tightly coupled to the SCN than in rats.