A number of biological factors have been linked to PTSD symptoms. It has been claimed that they make people with PTSD hyper-responsive to stressful stimuli, especially stimuli that are reminiscent of the trauma.

Chronic Stress Reaction

Chronically enhanced secretion of adrenaline and noradrenaline in patients of PTSD are consistent with a chronic stress reaction. In keeping with the enhanced secretion of these stress hormones, patients show enhanced startle response and higher baseline heart rates and blood pressure.

Hypothalamic-pituitary-adrenal axis abnormalities

Patients with PTSD have abnormally low levels of cortisol. On administration of low dose dexamethasone, patients exhibit hypersuppresion of cortisol, the pattern of findings suggesting enhanced negative feedback in the Hypothalamic-  pituitary- adrenal axis and that it is set to produce large response to further stresors.

Neuroendocrinological abnormalities

Several neurotransmitter systems seem to be dysregulated in PTSD

• Sensitization of the noradrenergic system - in particular downreglation of the alpha 2 adrenergic receptors causing increased levels of noradrenaline and enhanced locus coeruleus activity, explaining in part symptoms of autonomic hyperarousal and re-experiencing (through the effects of beta adrenergic receptors in the amygdalae and cortical structures)
• Sensitization of the serotonergic system - serotonin controls the function of septohippocampal behavioral inhibition system, sensitization would lead to activation of the same by mild everyday stressors, explaining in parts symptoms of hyperarousal
• Endogenous opiates have been suspected to mediate the symptoms of emotional numbing and amnesia
• Veterans with PTSD have been found to have enhanced levels of corticotrophin releasing factor (CRF) in the cerebrospinal fluid, this might be the reason behind enhanced plasma adrenaline and noradrenaline concentration and the consequent anxiety and fear related behavior

Thyroid function

Some studies have detected increased levels of thyroid hormones in PTSD patients, the levels correlating with the severity of hyperarousal symptoms.

Neuroimaging

• Magnetic Resonance Imaging have shown a reduced hippocampal volume in war veterans and women with a history of childhood sexual abuse. Disturbances of hippocampal function may lead to enhanced reactivity to stimulation and deficits in autobiographical memory.
• Dysfunction of the amygdalae is often considered as the key to delay in the extinction of fear responses to reminders of the traumatic event.
• Positron emission tomography has depicted reduced blood flow in the middle temporal cortex, which is supposed to play a role in the extiction of fear through inhibition of amygdala function.

Genetic Factors

• Higher concordance of PTSD among monozygotic than dizygotic twins.
• Higher prevalence of psychiatric disorders among family members.

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