(NA) An alternative name, which originated in the United States, is NOREPINEPHRINE: the names noradrenaline and norepinephrine refer to exactly the same chemical. It is also known as ARTERENOL. Noradrenaline and ADRENALINE were named this way in the United Kingdom, because they were first synthesized there from tissue taken from the ADRENAL GLAND; the terms epinephrine and norepinephrine were used in the United States because they was first synthesized from tissue taken from the KIDNEY (from Greek, nephros: kidney).
Noradrenaline is one of the NEUROTRANSMITTERS; neurons that contain noradrenaline are said to be NORADRENERGIC. It is a CATECHOLAMINE neurotransmitter and therefore a member of the even larger family of MONOAMINE neurotransmitters. The full chemical name for noradrenaline is 3,4-DIHYDROXYPHENYLETHANOLAMINE. Noradrenaline, like DOPAMINE, is synthesized from the amino acid LTYROSINE. The enzyme TYROSINE HYDROXYLASE catalyses the conversion of tyrosine to LDOPA (L-3,4-dihydroxyphenylalanine). LDOPA is then converted by AROMATIC LAMINO ACID DECARBOXYLASE to dopamine. In dopaminergic neurons, this is as far as the conversion goes, dopamine being transported and packaged for use as a neurotransmitter. However, further conversion of dopamine produces noradrenaline. The presence of the enzyme DOPAMINE BETA-HYDROXYLASE, involved in the conversion of dopamine to noradrenaline, is the principal way to discriminate noradrenaline- from dopamine-containing neurons. In other neurons a further conversion can occur: the enzyme PHENYLETHANOLAMINE-N-METHYLTRANSFERASE is involved in the production of adrenaline from noradrenaline. There are multiple receptors for noradrenaline (see ADRENOCEPTORS). The synaptic action of noradrenaline is terminated in two ways: destruction by enzymes or by REUPTAKE, for which there are specific noradrenaline transporters. As with dopamine catabolism, enzymatic destruction can be achieved by either of two enzymes: MONOAMINE OXIDASE (MAO) or CATECHOL-O-METHYLTRANSFERASE (COMT).
In the CENTRAL NERVOUS SYSTEM, noradrenaline neurons have their cell bodies in the PONS and MEDULLA, but axons ascend to innervate an exceptionally large proportion of the central nervous system. There are three principal groups of noradrenaline neurons: the LOCUS COERULEUS complex; the lateral tegmental noradrenaline neurons; and the dorsal medullary noradrenaline neurons. (An older terminology discussed these in terms of the DORSAL NORADRENERGIC BUNDLE [from the locus coeruleus] and the VENTRAL NORADRENERGIC BUNDLE [including the lateral tegmental and dorsal medullary neurons]). These neurons were first characterized using HISTOFLUORESCENCE techniques and were catalogued using the CLASSIFICATION OF DAHLSTRÖM & FUXE. The functions of noradrenaline neurons are many and varied, as one would expect for neurons that project so widely through the central nervous system. In biological psychology, the neurons of the locus coeruleus have been associated with ATTENTION, MEMORY and with the regulation of SLEEP, while the pontine and medullary neurons have been associated with a variety of AUTONOMIC processes, including the control of FEEDING. Noradrenaline neurons en masse are though to be an essential component of the ASCENDING RETICULAR ACTIVATING SYSTEM. In the PERIPHERAL NERVOUS SYSTEM, noradrenaline is the neurotransmitter for the postganglionic sympathetic neurons (see AUTONOMIC NERVOUS SYSTEM). In addition, the CHROMAFFIN CELLS of the ADRENAL GLAND secreted both noradrenaline and adrenaline. The action of noradrenaline released from here is more like that of a hormone rather than a neurotransmitter, in that it diffuses around the body in the blood, binding to any appropriate receptors contacted (see FIGHT-OR-FLIGHT; STRESS).
Reference
Feldman R., Meyer J.S. & Quenzer L.F. (1997) Principles of Neuropsychopharmacology, Sinauer Associates: Sunderland MA.
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