Norepinephrine (NE), also known as noradrenaline, is a neurotransmitter and a hormone. As a neurotransmitter, it is a chemical messenger that helps transmit nerve signals across nerve endings to another nerve cell, muscle cell, or gland cell. As a hormone, it is released into the bloodstream by the adrenal glands in response to stress.

Where is norepinephrine found in the brain?

Norepinephrine is found in many different areas of the brain, including the:

• Locus coeruleus (LC): The LC is a small nucleus in the brainstem that is considered to be the main source of norepinephrine in the brain.
• Prefrontal cortex (PFC): The PFC is involved in higher-order cognitive functions such as attention, planning, and decision-making.
• Hippocampus: The hippocampus is involved in memory and learning.
• Amygdala: The amygdala is involved in processing emotions, such as fear and anxiety.

Neuronal pathway and receptor(s)

Norepinephrine is released from neurons in the LC and travels to other parts of the brain through a network of axons. It binds to two types of receptors: alpha and beta receptors.

• Alpha receptors: Alpha receptors are found on blood vessels, smooth muscles, and the heart. When norepinephrine binds to alpha receptors, it causes blood vessels to constrict, smooth muscles to relax, and the heart rate to increase.
• Beta receptors: Beta receptors are found on the heart, lungs, and liver. When norepinephrine binds to beta receptors, it causes the heart rate to increase, breathing to become more rapid, and blood sugar levels to rise.

How does an excess or deficiency in norepinephrine contribute to psychiatric illness?

An excess or deficiency in norepinephrine can contribute to a number of psychiatric disorders, including:

• Depression: Low levels of norepinephrine are thought to play a role in depression.
• Anxiety: High levels of norepinephrine can contribute to anxiety disorders, such as panic disorder and social anxiety disorder.
• Post-traumatic stress disorder (PTSD): People with PTSD often have high levels of norepinephrine in response to stressors.
• Attention deficit hyperactivity disorder (ADHD): People with ADHD may have lower levels of norepinephrine in certain areas of the brain.
• Substance abuse disorders: Norepinephrine plays a role in the rewarding effects of drugs of abuse.

Specific psychiatric disorders affected by norepinephrine

• Depression
• Anxiety disorders (panic disorder, social anxiety disorder, generalized anxiety disorder)
• Post-traumatic stress disorder (PTSD)
• Attention deficit hyperactivity disorder (ADHD)
• Substance abuse disorders

How do medications that target norepinephrine levels work?

A number of medications that target norepinephrine levels are used to treat psychiatric disorders. These medications include:

• Antidepressants: Antidepressants, such as serotonin-norepinephrine reuptake inhibitors (SNRIs) and tricyclic antidepressants (TCAs), work by increasing the levels of norepinephrine in the brain.
• Anxiolytics: Anxiolytics, such as benzodiazepines, work by calming the central nervous system and reducing the release of norepinephrine.
• Stimulants: Stimulants, such as methylphenidate (Ritalin) and amphetamine/dextroamphetamine (Adderall), work by increasing the levels of norepinephrine and dopamine in the brain.

Conclusion

Norepinephrine is a neurotransmitter and hormone that plays an important role in many different functions, including mood, attention, and stress response. An imbalance in norepinephrine levels can contribute to a number of psychiatric disorders. Medications that target norepinephrine levels are commonly used to treat these disorders.