Post-traumatic stress disorder (PTSD) is a psychiatric condition caused by exposure to a traumatic event. Veterans are at especially high risk of PTSD. In Canada, in a survey conducted in 2016, 16% of Regular Force Veterans released during 1998-2015 reported having PTSD, which is at least two times higher than the estimated prevalence rate in the general population. Individuals with PTSD experience a range of debilitating symptoms, such as the intrusion of unwanted and distressing memories, persistent flashbacks, hypervigilance and nightmares. The neuropathophysiological mechanisms underlying symptoms of PTSD are not well understood, which remains a significant barrier to developing effective treatments. Hallmark PTSD symptoms such as hyperarousal and sleep disturbances may be related to dysregulation of noradrenaline (NA), a neurotransmitter produced in the locus coeruleus (LC) known to modulate cognition, arousal and sleep. This thesis examines the possible associations between dysregulation in rapid-eye-movement (REM) sleep and dysfunction in NA-containing neurons in the LC among veterans with PTSD. Twenty-two operationally deployed veterans with a history of PTSD were recruited through the Royal Ottawa Mental Health Centre in Ontario, Canada. A novel, non-invasive neuroimaging method, neuromelanin-sensitive magnetic resonance imaging (NM-MRI), was used to detect a by-product of NA called neuromelanin (NM) in the LC of each participant. Then a contrast-to-noise ratio (CNR) was calculated to obtain a marker of the NA function. The LC was segmented into three subdivisions to assess whether the association between NM and REM sleep may differ across regions of the LC. As hypothesized, we observed different associations between NM and REM sleep across regions of the LC. After controlling for antidepressant usage, there was (i) a moderate, negative, significant correlation between the percentage of REM sleep and rostral LCCNR, r(19) = -.476, p = .029, (ii) a weak positive non-significant correlation between the percentage of REM sleep and caudal LCCNR, r(19) = .33, p = .145, and (iii) no significant correlation between REM sleep percentage and LCCNR in the middle LC, r(19) = -.04, p = .876. This thesis is the first study to show that NM and REM sleep may be related in veterans with PTSD and that this relationship may vary across subdivisions of the LC. These results improve understanding of REM sleep among individuals with PTSD. The results may stimulate the investigation of novel pharmacotherapy focused on sleep disturbances in PTSD, the development of personalized treatments for PTSD, and the search for clinical biomarkers of PTSD based on brain function. The current study also made methodological contributions that may be applicable beyond the research on PTSD to the field of REM sleep and the NA system. Specifically, the current study showed the suitability of the NM-MRI method for examining the connections between NM and REM sleep, and it showed that segmenting the LC can lead to a more nuanced understanding of its role in the human body.