Peptide Neurotransmitters and Hormones


Neuropeptides are structurally diverse class of chemical messengers that play important roles in the coordination of many physiological and behavioural events. Neuropeptides are derived from the cleavage of the larger precursor proteins at the dibasic amino acid sites by prohormone convertases. They are synthesised in the cell body, packaged in the large dense core vesicles and released in a neuronal activity‐dependent manner. The neuropeptides may function as blood‐borne hormones, or as mediators/transmitters affecting neuronal activity in the nervous system. In the target cells, neuropeptides activate the complementary G protein‐coupled receptors and elicit responses that are specific to these cells. The released peptide is subsequently inactivated by the actions of several nonspecific extracellular peptidases.

Key Concepts:

  • Neuropeptides are structurally diverse class of chemical messengers produced by nerve cells to coordinate many physiological and behavioural processes.

  • The major neuroendocrine centre in the brain is the pituitary gland.

  • Neuropeptides are derived from the cleavage of the larger precursor proteins by specific endoproteases that are co‐packaged in the dense core secretory granules.

  • Receptors for neuropeptides belong mainly to the family of G protein‐coupled receptor.

Keywords: peptides; biosynthesis; function; degradation; endocrine/neuronal communication

Figure 1.

Schematic diagram of the biosynthesis of peptide transmitter/hormone and its effects on the target cell. The mRNA encoding the peptide precursor is transcribed in the nucleus, and translated at the rough (ER) into a biological inactive precursor protein. The precursor protein is transported to the Golgi apparatus (Golgi) and packaged into the dense core (SG) for further proteolytic processing and storage. Exocytosis of secretory granule releases the biological active peptides. When the peptide binds to its receptor (GPCR) in the target cell, it dissociates the Gα from Gβ and Gγ, and activates the corresponding downstream effector proteins. These events are depicted by the blue arrows. The peptide–receptor interaction also initiates desensitisation through receptor endocytosis. The receptor could recycle back to the plasma membrane for another round of receptor activation. These events are depicted by the yellow arrows.

Figure 2.

Structural organisation of proopiomelanocortin and its tissue‐specific processing in the pituitary gland. In the pituitary anterior lobe corticotrophs, PC1/3 is the predominant convertase and its action results in the release of intact ACTH and small amounts of β‐endorphin (β‐END), in addition to a number of other peptides. In the pituitary intermediate lobe, both PC2 and PC1/3 are expressed, resulting in the further processing of ACTH to α‐melanophore‐stimulating hormone with increased production of β‐END. R, Arg; K, Lys; sp, signal peptide; JP, joining peptide; LPH, lipotropic hormone; CLIP, corticotropin‐like intermediate lobe protein. Adapted from Zhou et al. .



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Li, Ka Wan(Dec 2012) Peptide Neurotransmitters and Hormones. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000063.pub2]