Norepinephrine

What is Norepinephrine?

Norepinephrine (NE), also known as noradrenaline, is a neurotransmitter involved in the regulation of attention, emotions, sleeping patterns, dreaming, and learning. As a hormone, it plays a vital role in the body's fight-or-flight response, affecting blood vessel constriction, heart function, and the release of stored energy. Its effects depend on receptor type and context; vasoconstriction can trigger reflex slowing of the heart. Disruptions in norepinephrine signaling have been associated with various mood disorders and neurological conditions, including depression, anxiety disorders, and attention deficit hyperactivity disorder (ADHD).

Where does norepinephrine come from?

Norepinephrine is released by sympathetic nerve endings and secreted as a hormone by the adrenal medulla. It also acts as a neurotransmitter in the central nervous system. Noradrenergic refers to signaling that involves norepinephrine.

Functions

• Attention and Alertness

  Norepinephrine activity helps regulate alertness and task engagement. Its effects depend on firing pattern, receptor and task; greater activity does not invariably improve attention.

• Stress Response

  As a critical component of the sympathetic nervous system, norepinephrine is involved in the body's stress response, also known as the fight-or-flight response. During periods of stress or danger, norepinephrine levels increase, contributing to changes in blood vessel constriction, blood pressure, and the release of stored energy as part of a broader stress response.

• Sleep and Wakefulness

  Norepinephrine contributes to the regulation of sleep-wake cycles. It is involved in promoting wakefulness and inhibiting REM sleep, the sleep stage associated with dreaming. Norepinephrine activity tends to be high during periods of wakefulness, particularly when attention and vigilance are required, and low during sleep.

Associated Disorders

• Depression

  Depression has been associated with dysfunctions in norepinephrine signaling. Depression cannot be diagnosed or adequately explained by assuming a simple norepinephrine deficiency. Certain types of antidepressants, known as norepinephrine reuptake inhibitors, work by increasing the levels of norepinephrine available to transmit signals in the brain.

• Anxiety Disorders

  Anxiety disorders have also been linked to abnormalities in norepinephrine function. Increased activity of the norepinephrine system, particularly during periods of stress, may contribute to symptoms of anxiety, such as heightened arousal and increased vigilance.

• Attention Deficit Hyperactivity Disorder

  Attention Deficit Hyperactivity Disorder (ADHD) has been associated with dysfunctions in several neurotransmitter systems, including the norepinephrine system. Some medications used to treat ADHD, such as atomoxetine, work by inhibiting the reuptake of norepinephrine, increasing its availability in the brain and improving symptoms of inattention and hyperactivity.

Interpreting its role

Norepinephrine participates in attention, stress, and sleep. More activity is not always better, and a person's symptoms cannot be read as a simple measure of this chemical.

Sources and evidence

• Gary Aston-Jones and Jonathan D. Cohen: Adaptive gain and the role of the locus coeruleus-norepinephrine system in optimal performance. A theory drawing substantially on animal research; not a simple human concentration-performance rule.
• Matthew D. Smith and Christopher V. Maani: Norepinephrine. Clinical infusion effects illustrate receptor mechanisms; they do not predict every endogenous stress response.