Norepinephrine and Epinephrine: Introduction


The catecholamines, norepinephrine and epinephrine (formerly named noradrenaline and adrenaline) are released from the adrenal gland and neurons in the brain. Norepinephrine is also released from the majority of postganglionic, sympathetic neurons in the peripheral (autonomic) nervous system. Conversion of the amino acid, tyrosine, to l‐3,4‐dihydroxyphenylalanine is the rate‐limiting step in the synthetic pathway for both these catecholamines. This process is regulated by several hormones and neurotransmitters, which act via intracellular messengers to help ensure that the rate of catecholamine synthesis matches the rate of their release. In the periphery, norepinephrine and epinephrine are essential for maintaining a stable internal body state (‘homoeostasis’). In the central nervous system, norepinephrine has an important role in the regulation of attention/vigilance/alarm and its synchronization with the autonomic nervous system, but little is known about the function of neuronal epinephrine.

Key Concepts

  • The distribution of norepinephrine and epinephrine in the periphery.
  • The distribution of norepinephrine and epinephrine in and brain.
  • Regulation of the biosynthesis of norepinephrine and epinephrine.
  • The role of norepinephrine and epinephrine in the periphery.
  • The role(s) of norepinephrine and epinephrine in the brain.

Keywords: arousal; attention; catecholamine; epinephrine; dopamine‐β‐hydroxylase; locus coeruleus; lateral tegmental nuclei; norepinephrine; phenylethanolamine‐N‐methyltransferase; tyrosine hydroxylase

Figure 1. The chemical structure of (a) norepinephrine and (b) epinephrine.
Figure 2. A schematic representation of the distribution of norepinephrine‐releasing neurons in the rat brain. The brainstem nuclei that contain neurons that release norepinephrine or epinephrine (C1–C3) are indicated, also. The main projections from the locus coeruleus (A6) form the dorsal bundle, dorsal longitudinal fasciculus and central tegmental tract. Some fibres of the dorsal bundle innervate the thalamus directly, whereas others, together with the central tegmental tract, join the medial forebrain bundle at the level of the caudal hypothalamus. This pathway then projects to many brain areas, including the amygdala nuclei, anterior thalamus, septum, olfactory areas and the neocortex. Fibres from the dorsal longitudinal fasciculus innervate the paraventricular nucleus and, possibly, the supraoptic nucleus in the hypothalamus. The medullary bundle, in which neurons from the locus coeruleus branch from the central tegmental tract, projects to the caudal medulla (not illustrated). Fibres from the central tegmental tract also descend to the spinal cord.
Figure 3. The distribution of the major neuronal projections from the locus coeruleus and lateral tegmental (norepinephrine) systems in the brain.
Figure 4. The synthetic pathway for norepinephrine (NE) and epinephrine (EPI) in neuron terminals and chromaffin cells. The amino acid, tyrosine, derived from the diet, is taken up into catecholamine‐secreting neurons, where it is converted into l‐DOPA in the neuronal cytoplasm. After conversion of l‐DOPA into dopamine, the latter is taken up into the storage vesicles, where it is converted into NE by the enzyme DβH. NE that leaks out of the vesicles is converted into EPI in the cytoplasm of neurons that contain the enzyme, PNMT. Vesicle stores of NE and EPI are maintained by active uptake via a protein transporter in the vesicle membrane.


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Further Reading

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Stanford, Susan Clare(Jul 2020) Norepinephrine and Epinephrine: Introduction. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000271.pub4]