Photoperiod, food restriction and memory for objects and places in mice

Area of Science:

• Chronobiology
• Neuroscience
• Animal Behavior

Background:

• The suprachiasmatic nucleus (SCN) regulates circadian rhythms, influenced by photoperiod, affecting physiology and behavior.
• While C57BL/6 mice lack seasonal functions, they exhibit photoperiodic modulation of SCN output, with potential downstream effects on cognition.
• Previous research indicated long days may enhance memory in these mice, and restricted feeding can block photoperiod encoding in SCN output.

Purpose of the Study:

• To investigate if restricted feeding blocks the effect of long days on memory in C57BL/6 mice.
• To assess the impact of photoperiod and restricted feeding on object and spatial working memory.

Main Methods:

• Mice were entrained to long (18h:6h) or short (6h:18h) light-dark cycles.
• Object preference (NOP) and spatial alternation (SA) memory tests were conducted with food ad libitum and during restricted feeding.
• Free-running period (τ) was measured in constant darkness to assess photoperiod encoding.

Main Results:

• Photoperiod influenced τ as expected but did not alter NOP or SA performance.
• Restricted feeding improved NOP performance in both photoperiods, diminishing time-of-day effects.
• No photoperiod-dependent memory benefits were observed up to 18-hour days.

Conclusions:

• Restricted feeding enhances cognitive function, specifically object memory, independent of photoperiod.
• Photoperiod does not appear to confer memory benefits in C57BL/6 mice at daylengths up to 18 hours.
• The study highlights the cognitive benefits of restricted feeding and questions the direct role of photoperiod on memory in this model.