Norepinephrine
Norepinephrine, also called noradrenaline, is a chemical messenger (neurotransmitter) in the brain. Most of the norepinephrine released in the brain comes from the locus coeruleus, a small nucleus in the brainstem linked to attention and arousal.
What it means in practice
Nerve cells release norepinephrine to pass signals to other cells [2]. In the brain, most of it is supplied by a very small nucleus on each side of the brainstem called the locus coeruleus [2]. That nucleus sends fibers into widespread brain regions, and researchers refer to the pair as the locus coeruleus-norepinephrine (LC-NE) system [1].
A 2019 review lists attention, arousal, emotion, cognition and the sleep-wake cycle among the brain functions in which the LC-NE system plays a role [1]. Historically, research linked the system to arousal [3]. A 2005 review of recordings and models in monkeys described two activity modes in locus coeruleus neurons, phasic and tonic, and proposed that they relate to staying with a task or looking for alternatives [3]. Brainstem neurons that use norepinephrine also take part in the body's stress response, together with the hormone chain that ends in cortisol release [4].
The body builds norepinephrine from the amino acid tyrosine, which is the precursor of the catecholamine neurotransmitters dopamine and norepinephrine [5].
Why it matters when reading nootropics research
Norepinephrine comes up often in research on L-tyrosine. Tyrosine is the raw material for norepinephrine and dopamine, and a 2015 systematic review framed the tyrosine findings it reviewed in terms of brain catecholamine levels, which tyrosine may restore when they are depleted [5]. That explanation is a mechanism. This proposed mechanism does not by itself establish an effect on attention, memory or mood in people.
Design matters too. The same review covered 15 tyrosine studies in healthy adults and found that all but one gave tyrosine in a single test session [5], so a paper may describe a short-term test, not regular use.
Some of the detail about the locus coeruleus on this page comes from animal work, such as the monkey recordings above [3]. When a page on this site reports a finding like that, it says it came from animals.
References
- Satoh A, Iijima KM. Roles of tau pathology in the locus coeruleus (LC) in age-associated pathophysiology and Alzheimer's disease pathogenesis: Potential strategies to protect the LC against aging. Brain Res. 2019.
- Schwarz LA, Luo L. Organization of the locus coeruleus-norepinephrine system. Curr Biol. 2015.
- Aston-Jones G, Cohen JD. An integrative theory of locus coeruleus-norepinephrine function: adaptive gain and optimal performance. Annu Rev Neurosci. 2005.
- Smith SM, Vale WW. The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress. Dialogues Clin Neurosci. 2006.
- Hase A, Jung SE, aan het Rot M. Behavioral and cognitive effects of tyrosine intake in healthy human adults. Pharmacol Biochem Behav. 2015.