Plain-language definitions grounded in the clinical and regulatory literature.
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Hormone
What it isNorepinephrine is a neurotransmitter and hormone released by the locus coeruleus and adrenal medulla. It drives arousal, vigilance, and the threat-response component of the stress reaction, and is centrally implicated in PTSD sleep disruption through its elevation during REM sleep.
Why it mattersElevated norepinephrine during sleep is the primary mechanism by which PTSD disrupts REM sleep and produces nightmares. Treatments like prazosin work by blocking norepinephrine receptors — directly targeting this pathway.
Think of it like thisNorepinephrine is the brain’s alarm system neurotransmitter: it sharpens attention and mobilizes threat response instantly, but when it fails to turn off at night, it keeps the brain in constant readiness that prevents restorative sleep.
Norepinephrine (3,4-dihydroxyphenethylamine) is a catecholamine neurotransmitter synthesized from dopamine by dopamine beta-hydroxylase. It acts on alpha-1, alpha-2, and beta-adrenergic receptors throughout the central and peripheral nervous systems. In the CNS, norepinephrine from the locus coeruleus modulates arousal, attention, and fear-learning circuits.
MechanismDuring normal sleep, locus coeruleus firing rate progressively decreases — reaching near-zero during slow-wave sleep. This nocturnal NE decline is necessary for REM fear extinction. In PTSD, chronic locus coeruleus sensitization maintains elevated NE during sleep, disrupting REM architecture and preventing the fear extinction that should defuse traumatic memories over time.
Scientific ConsensusNoradrenergic hyperactivity is one of the most consistently documented neurobiological findings in PTSD. The HPA-LC co-activation model establishes NE as central to both PTSD’s waking hypervigilance symptoms and its sleep manifestations (nightmares). Alpha-1 adrenergic blockade with prazosin reduces nightmare frequency by attenuating NE’s downstream receptor effects during sleep.
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