How do changes in meal predictability and timing affect hippocampal dependent tasks?

Huggard, Summer Gaskill (2022) How do changes in meal predictability and timing affect hippocampal dependent tasks? Masters thesis, Memorial University of Newfoundland.

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Abstract

Light is the most prominent zeitgeber for circadian rhythms, but other stimuli such as food are also robust entrainers. Manipulations of the Light-Dark cycle impair hippocampal-dependent memory in rodents; however, little is known about the effects of meal timing on this type of memory. The purpose of these experiments was to determine the effect of manipulating meal timing and predictability on the Morris Water Maze (MWM) task. Rats received their food either in one meal at the same time of day (1M), multiple meals at random and unpredictable times (MM), or of their own choosing (ad libitum). Rats were trained on the MWM to find a hidden platform before their memory retention was tested using no-platform probes. In Study 1 (i.e., Standard Lighting), it was predicted that the 1M group would show better memory retention than the MM group. The 1M performed as expected by showing high memory retention; however, the MM group did not show a memory deficit likely due to issues with nocturnality. Thus, Study 2 was a replication of Study 1 that utilized a reverse lighting schedule such that meals and testing were administered during the dark cycle. The 1M and MM group continued to perform above chance, indicating that light was a robust entrainment tool that masked any potential effects of meal manipulation. Finally, Study 3 implemented a constant darkness manipulation to eliminate the influence of light. It was expected that rats with a disrupted lighting and feeding schedule (i.e., the DD-MM group) would show a memory deficit on the retention probes. This was confirmed, thus indicating that there is an additive effect of light and food as zeitgebers on hippocampal-dependent memory. Taken together, these studies provide evidence that light is the most prominent entrainment tool and, when available, the influence of lighting information will mask that of other zeitgebers. Studies of this nature will help elucidate the impact of disrupting zeitgebers not controlled by the suprachiasmatic nucleus.

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