Investigating the role of the food-entrainable oscillator and the effect of light manipulations on hippocampal-dependent and hippocampal-independent tasks

Circadian rhythms are responsible for physiological processes necessary for survival. The presence of certain external cues (e.g., light, food) are necessary to maintain rhythmicity in the suprachiasmatic nucleus. However, disruption of circadian rhythms occurs through irregular patterns in external cues (e.g., shift work). Circadian disruption impairs hippocampal-dependent memory. Two experiments were conducted that explored the influence of circadian disruption (i.e., light manipulations) on performance of hippocampal-dependent and -independent tasks. Additionally, food access was restricted to assess any benefit of consistent feeding schedules in performance on these tasks. Experiment 1 used a modified 30-day light manipulation and had rats on either single or multiple meal schedules. The results of Experiment 1 found an impairment in acquisition of the hippocampal-dependent Morris Water Maze task in the groups exposed to the light manipulation, but no effect of meal schedule. There were no differences between groups in performance of the hippocampal-independent tasks (i.e., Elevated-Plus Maze, and Stimulus-Response Task). Experiment 2 used a previously validated light manipulation, with the addition of rats placed on either a single of multiple meal regimen. The results of Experiment 2 found no differences between groups in retention of the Morris Water Maze task. Overall, the light manipulation in Experiment 1 resulted in an impairment in the acquisition phase of the Morris Water Maze task, but the impairment was not present in the probes or other phases of the task. Experiment 2 was incomplete due to COVID-19; It is expected that with the addition of a second cohort an effect of meal will be observed in retention of the Morris Water Maze Task