Undergraduate Honors Thesis


Effect of time of training and recall interval on behavior and neural activity under the trace conditioned fear paradigm Public Deposited

  • Circadian rhythms are endogenous 24-hour cycles that regulate behavioral and physiological processes. Disruptions to these rhythms can lead to a wide range of health deficits, including impairments in fear-based mental disorders. One form of fear conditioning that has been extensively studied is delayed fear conditioning. The neuroanatomy and neural connections have been mapped out, and circadian rhythms in behavior and mRNA expression have been reported by our lab and others. Here, we set out to explore time-of-day differences in behavior and underlying neurobiology in a related fear paradigm called trace fear conditioning. For our experiment, adult male rats were conditioned through multiple trials of exposure to a 15-second tone followed by a 10-second “trace” period that concluded with a foot shock and a 240-second intertrial interval. We analyzed freezing behavior and c-Fos and Per1 mRNA data to see whether it was the time of training (ZT4-inactive phase or ZT16-active phase), the time of testing (ZT4 or ZT16), or the recall interval (24 hours, 36 hours, or 48 hours) that produced any significant differences. Freezing data was collected from previous work done in the lab. We then imaged and analyzed the basolateral amygdala, basomedial amygdala, central amygdala, medial amygdala, and the whole amygdala for mRNA expression of c-Fos (a common marker for neural activity) and Per1 (a circadian gene that also acts as an immediate early gene). We found time-of-day differences in freezing behavior and c-Fos expression, indicating multiple interactions between time of training, time of testing, and the recall, but surprisingly no time-of-day differences in Per1 expression. Taken together, our findings suggest that rats are biased toward fear recall during the inactive phase, potentially through an innate and unlearned suppression of fear behavior during the active phase. Such work has the potential to aid in the development of treatment methods and more specific diagnoses of fear-based mental disorders.

Date Awarded
  • 2023-04-10
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Last Modified
  • 2023-04-21
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