Final answer:
Individuals with PTSD have abnormally low levels of cortisol, which is essential for stress regulation. Additionally, noradrenaline is a neurotransmitter significantly involved in stress response and mood disorders, highlighting the intricate biochemistry of mental health conditions.
Step-by-step explanation:
The question regarding the levels of certain substances in people with post-traumatic stress disorder (PTSD) touches upon a significant area of research within psychobiology and medicine. The correct answer to the question is e. cortisol. Individuals with PTSD have been shown to exhibit abnormally low levels of cortisol, a stress hormone responsible for regulating various bodily functions, which can be linked to their symptoms.
For people with other types of mood disorders, such as major depressive disorder (MDD), particularly in the melancholic subtype, there's evidence of abnormally high levels of cortisol. This goes hand in hand with the involvement of the HPA (hypothalamic-pituitary-adrenal) axis, and is associated with a state of hyperarousal and anxiety.
The neurotransmitter norepinephrine (also called noradrenaline), while not the direct answer to the question, also plays a role in stress response and mood regulation and is important in the context of depression and anxiety disorders.