Adrenaline and Noradrenaline: Introduction

Abstract

Adrenaline and noradrenaline belong to a family of molecules known as ‘catecholamines’. They are both released from the adrenal gland and neurons in the central nervous system. Noradrenaline 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 pathway for synthesis of both of these catecholamines. This biosynthetic pathway is regulated by several hormones and neurotransmitters, which act through intracellular messengers and help to ensure that the rate of catecholamine synthesis matches the rate of their release. Adrenaline and noradrenaline have important roles in mediating peripheral autonomic function and the maintenance of a stable internal body state (‘homoeostasis’). In the brain, their distribution and functional interactions underlie their strong influence on arousal state (attention/vigilance/alarm) and its integration with the autonomic system.

Key Concepts:

  • Adrenaline and noradrenaline are members of the catecholamine family of neurotransmitters and hormones.

  • In the brain, the cell bodies of noradrenergic and adrenergic neurons are clustered in the brainstem and are the source of an extensive network of diffuse projections to nearly all other brain regions and the spinal cord.

  • The rate of synthesis of adrenaline and noradrenaline is highly regulated and ensures that their intracellular store is maintained under normal physiological conditions.

  • In the periphery, release of noradrenaline and adrenaline from postganglionic sympathetic neurons and the adrenal medulla mediate sympathoadrenal (autonomic) responses in the target organs.

  • In the brain, adrenaline and noradrenaline contribute to the integration of autonomic, cognitive and emotional arousal.

Keywords: adrenaline; adrenal medulla; arousal; catecholamine; dopamine‐β‐hydroxylase; lateral tegmental nuclei; locus coeruleus; noradrenaline; sympathetic nervous system

Figure 1.

The chemical structure of (a) noradrenaline and (b) adrenaline.

Figure 2.

A schematic representation of the distribution of noradrenaline‐releasing neurons in the rat brain. The brainstem nuclei that contain neurones the release for neurons that release noradrenaline or adrenaline (C1‐C3) are indicated, also. The main projections from the locus coeruleus (A6) are the (noradrenergic) 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 neuronal projections from the locus coeruleus and lateral tegmental (noradrenaline) systems in the brain.

Figure 4.

The synthetic pathway for noradrenaline (NA) and adrenaline in neuron terminals and chromaffin cells. 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 NA by the enzyme DβH. NA that leaks out of the vesicles is converted into adrenaline in the cytoplasm of neurons that contain PNMT. Vesicle stores of NA and adrenaline are maintained by active uptake via a protein transporter in the vesicle membrane.

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Further Reading

Brading A (1999) The Autonomic Nervous System and its Effectors. Oxford: Blackwell Science.

Fillenz M (1990) Noradrenergic Neurons. Cambridge, UK: Cambridge University Press.

Iversen L, Iversen S, Bloom Fe et al. (2009) Introduction to Neuropsychopharmacology. Oxford: Oxford University Press. ISBN‐10: 0195380533 | ISBN‐13: 978‐0195380538.

Steckler T, Klain NH and Reul JMHM (2005) Handbook of Stress and the Brain. Amsterdam: Elsevier. ISBN: 0‐444‐51822‐3.

Trendlenburg U and Weiner N (eds) (2012) Catecholamines II (Handbook of Experimental Pharmacology) Vol. 90/II, ISBN‐10: 3642735533 | ISBN‐13: 978‐3642735530. Heidleberg: Springer.

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Stanford, S Clare(Apr 2013) Adrenaline and Noradrenaline: Introduction. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000271.pub3]