Nonphotic phase shifting in the old and the cold

Area of Science:

• Chronobiology
• Gerontology
• Animal Behavior

Background:

• Aging is associated with decreased physiological responses to stimuli.
• Circadian rhythm phase shifting is crucial for maintaining biological timing.
• Nonphotic stimuli, such as activity and arousal, influence circadian rhythms.

Purpose of the Study:

• To investigate the impact of aging on nonphotic circadian rhythm phase shifting in hamsters.
• To determine if reduced activity or arousal in older hamsters underlies impaired phase shifting.
• To explore methods for enhancing nonphotic inputs to improve phase advances in aging animals.

Main Methods:

• Comparing activity levels and phase shifts in young versus old hamsters under various conditions.
• Utilizing novel running wheels and triazolam injections to manipulate activity and arousal.
• Introducing social stimuli (estrous females) and environmental changes (cold temperatures) to modulate running behavior.

Main Results:

• Old hamsters exhibited lower activity levels compared to young hamsters in novel environments or with triazolam.
• Phase advances were achieved in older hamsters by increasing nonphotic stimuli, such as social presence or combined stimuli.
• Increased running in cold temperatures did not consistently induce phase shifts, suggesting motivation is key, not just activity.

Conclusions:

• The nonphotic phase-shifting mechanism itself appears largely intact in aging hamsters.
• Impaired phase shifting in older animals is likely due to insufficient strength of nonphotic inputs.
• Motivational context, rather than mere physical activity, is critical for effective nonphotic phase shifts in aging.