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Post-traumatic stress disorder (PTSD) is associated with lowered levels of a neurotransmitter in a brain region that plays a role in panic and stress, researchers reported.

In a cohort study, positron emission tomography also linked the availability of the molecule, norepinephrine transporter or NET, to one of the five facets of the syndrome, according to, of NYU School of Medicine in New York City, and colleagues.

One possible implication of the finding is that medications aimed at norepinephrine or the norepinephrine transporter might be useful as PTSD therapies,

, the researchers noted, and weakens neuronal signaling by promoting rapid clearance of which plays a central role in the fight-or-flight response.

Data from animal experiments have suggested that chronic stress is associated with a reduction in the availability of NET in the, a small region in the pons where concentrations of the molecule are highest, Neumeister and colleagues noted.

But it hasn't been clear if those findings have any bearing in PTSD, they added. To help fill the gap, they recruited 56 participants for a positron emission tomography study, including 18 healthy controls, 22 people with PTSD, and 16 people who had suffered trauma, but had not developed PTSD.

One objective of the study, which used a radioactively labeled compound to reveal norepinephrine transporter levels, was to see if there was an association with PTSD, compared with healthy and non-PTSD trauma controls.

The other objective was to see if norepinephrine transporter levels in the PTSD participants were associated with anxiety arousal, one of the five symptom clusters (including re-experiencing, avoidance, numbing, and dysphoric arousal) in PTSD.

Analysis showed that NET levels in the PTSD participants was 41% lower than in the healthy controls, they reported, which was statistically significant (P=0.003). The differences between the health controls and the non-PTSD trauma group and between the two trauma groups -- 31% and 15%, respectively -- did not reach significance.

The presence or absence of major depressive disorder or alcohol abuse or dependence did not affect NET levels, nor did the type of trauma, numbers of traumas, or age at onset, Neumeister and colleagues reported.

Among the PTSD participants, the investigators reported, NET availability in the locus coeruleus was independently and positively associated with the severity of anxious arousal symptoms, such as hypervigilance, but not with re-experiencing, avoidance, numbing, or dysphoric arousal symptoms.

Treatments for PTSD have included exposure and cognitive therapy, but the study "addresses a concern that there has been limited progress in the development of truly innovative novel neurobiology-based treatment models," the researchers concluded.

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