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The locus coeruleus is quite small in absolute terms—in primates, it is estimated to contain around 15,000 neurons, less than one-millionth of the neurons in the brain—but it sends projections to every major part of the brain and also to the spinal cord. These noradrenergic cell groups were first mapped in 1964 by Annica Dahlström and Kjell Fuxe, who assigned them labels starting with the letter "A" (for "aminergic"). Thus cannabinoids can inhibit both the noradrenergic and purinergic components of sympathetic neurotransmission.
Surviving Sepsis Campaign recommended norepinephrine as first line agent in treating septic shock which is unresponsive to fluid resuscitation, supplemented by vasopressin and epinephrine. Norepinephrine is also produced by Merkel cells which are part of the somatosensory system. Norepinephrine released by the locus coeruleus affects brain function in several ways. Noradrenergic cell group A1 is located in the caudal ventrolateral part of the medulla, and plays a role in the control of body fluid metabolism.
A number of important medical problems involve dysfunction of the norepinephrine system in the brain or body. However, the usefulness of beta blockers is limited by a range of serious side effects, including slowing of heart rate, a drop in blood pressure, asthma, and reactive hypoglycemia. Noradrenergic cell group A2 is located in a brainstem area called the solitary nucleus; these cells have been implicated in a variety of responses, including control of food intake and responses to stress. Sympathetic activation of the adrenal glands causes the part called the adrenal medulla to release norepinephrine (as well as epinephrine) into the bloodstream, from which, functioning as a hormone, it gains further access to a wide variety of tissues. Like many other biologically active substances, norepinephrine exerts its effects by binding to and activating receptors located on the surface of cells. Many important psychiatric drugs exert strong effects on noradrenaline systems in the brain, resulting in effects that may be helpful or harmful. Alpha blockers, which counter the effects of noradrenaline on alpha-adrenergic receptors, are occasionally used to treat hypertension and psychiatric conditions.
A large number of important drugs exert their effects by interacting with norepinephrine systems in the brain or body. Alpha-2 receptors usually have inhibitory effects, but many are located pre-synaptically (i.e., on the surface of the cells that release norepinephrine), so the net effect of alpha-2 activation is often a decrease in the amount of norepinephrine released. Outside the brain, norepinephrine is used as a neurotransmitter by sympathetic ganglia located near the spinal cord or in the abdomen, as well as Merkel cells located in the skin. The neurotransmitter that transmits your brain’s nervous system message of what to do is norepinephrine (noradrenaline). As a medication, norepinephrine is used to increase and maintain blood pressure in limited, short-term serious health situations. Both epinephrine and norepinephrine can affect your heart, blood sugar levels, and blood vessels.
Norepinephrine is transported back into the cytosol of the presynaptic neuron (uptake 1) or a nearby non-neuronal cell (uptake 2). Norepinephrine-mediated signal transduction and ultimate cellular function depend on which type of receptor (α-adrenergic or β-adrenergic receptor) it binds. Noradrenergic neurons are projected bilaterally from this nucleus to several brain areas, including the cerebral cortex, limbic system, and spinal cord. Vesicular monoamine transporter (VMAT) protein is responsible for transporting norepinephrine into synaptic vesicles. After synthesis, norepinephrine is stored in the synaptic vesicles. Both of these catecholamines bind to adrenergic receptors and participate in the fight-or-flight response. Structurally, norepinephrine is quite similar to epinephrine, another catecholamine, except that a methyl group in epinephrine is replaced by a hydrogen atom in norepinephrine.
People with depression may be treated with a class of medications called serotonin and norepinephrine reuptake inhibitors (SNRIs). ADHD medications target norepinephrine and dopamine, both of which affect your attention and concentration, according to KidsHealth. Epinephrine, also known as adrenaline, plays an important role in your body’s fight-or-flight response. As a hormone, epinephrine is made from norepinephrine inside of your adrenal gland. Epinephrine is part of your sympathetic nervous system, which is part of your body’s emergency response system to danger — the "fight-or-flight" response. Epinephrine, also called adrenaline, is both a hormone and a neurotransmitter.

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