Meal-engendered circadian-ensuing activity in rats.

Area of Science:

• Chronobiology
• Behavioral Neuroscience
• Circadian Rhythms

Background:

• Large meals provided at intervals longer than 24 hours can induce enhanced activity patterns.
• This phenomenon, termed meal-induced circadian ensuing activity (meal CEA), is not fully explained by current models of food-anticipatory activity.

Purpose of the Study:

• To characterize the process responsible for meal-induced circadian ensuing activity (meal CEA).
• To investigate the influence of feeding schedules, age, and suprachiasmatic nucleus (SCN) integrity on meal CEA.

Main Methods:

• Female Sprague-Dawley rats (young, middle-aged, SCN-lesioned) were housed with running wheels and pellet dispensers.
• Rats received two 1-hour meals every 31 or 34 hours, with alternating short and long fasting periods.
• Activity patterns were monitored in response to feeding schedules and subsequent meal delays or cessation.

Main Results:

• Young intact rats exhibited enhanced activity approximately 24 hours after the meal series began.
• Meal CEA showed sensitivity to daily meal delays, age (attenuated in middle-aged rats), and was present in SCN-lesioned rats.
• A single meal at a novel time could reset this SCN-independent oscillating process, which continued after the feeding schedule ended.

Conclusions:

• Meal CEA is a distinct circadian activity pattern influenced by food availability, independent of the SCN.
• The process is highly sensitive to shifts in meal timing, suggesting a mechanism for resetting circadian processes.
• Feeding schedules with intervals greater than 24 hours are effective for studying food-related resetting of circadian activity.