Abstract
Introduction:70% of people experience a traumatic event in their lifetime, but only a subset, around 10%, develop Post-Traumatic Stress Disorder (PTSD). Given the crucial roles of sleep in processing daily experience, I hypothesise that the processing of trauma during the first subsequent sleep bout is critical for predicting future outcomes. This thesis uses two experiments designed to test this hypothesis in a rat model of trauma. The first explores whether sleep pre- and post-trauma predicts the development of PTSD-like behaviours. The second investigates which features of sleep physiology predict vulnerability to, and outcomes of, trauma.
Methods:
In experiment 1, the sleep-wake behaviour of 12 Lewis rats (males and females) was recorded using passive infrared cameras for two consecutive weeks. After one week, rats were exposed to an inescapable predatory odour (PTE) (bobcat urine) for ten minutes and the elevated plus maze (EPM) and open field (OF) assessed long-term anxiety. In experiment 2, electrophysiological activity in networks associated with emotional memory processing was recorded in seven rats. Local field potentials were recorded from the basolateral amygdala (BLA), ventral hippocampus (vCA1), and prelimbic cortex (PrL) during novel context exposure and PTE.
Results:
PTE induced an unconditioned fear response evident a week later in the OF and during context re- exposure, but not on the EPM. PTE increased wakefulness and reduced non-REM sleep. Additionally, I observed changes in coordinated network oscillations, including decreased theta power in the limbic system, as well as reduced synchrony at theta frequencies in BLA networks during REM. Sleep and electrophysiology changes did not correlate with anxiety.
Discussion:
PTE affected fear-related behaviour, sleep, and neural network activity, with sustained anxiety and altered network functional connectivity observed post-exposure. Collectively, these experiments offer insights into potential mechanisms that contribute to the development and maintenance of PTSD, adding to our understanding of its aetiology and supporting the development of targeted interventions.
| Date of Award | 5 Feb 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Ross J Purple (Supervisor) & Matt W Jones (Supervisor) |