Neuropeptide
Neuropeptides are "peptides released by neurons as intercellular messengers. Many neuropeptides are also hormones released by non-neuronal cells."[1] In general, neuropeptides are synthesised as part of a much larger precursor molecule which is then cleaved enzymatically to yield various peptide fragments. In neurons, neuropeptides are generally packaged within large neurosecretory vesicles, that may be found in any region of the neuron - soma, dendrites, axons and nerve endings. The vesicle contents are released into the extracellular fluid when the vesicle membrane fuses with the neuronal plasma membrane in a prosess of calcium-dependent exocytosis. For example, vasopressin is made by magnocellular neurons in the supraoptic nucleus and paraventricular nucleus of the hypothalamus; it is a nine-amino acid fragment of a large (~30kD) precursor molecule which is packaged into large membrane-bound vesicles that are transported to all parts of the cell but especially to the neurosecretory nerve endings in the posterior pituitary gland. During transport, the precursor molecule is cleaved to yield a signal peptide, vasopressin, vasopressin-related neurophysin (neurophysin II), and a glycoprotein. The glycoprotein has no known function; neurophysin is important for the correct folding of the precursor hormone to allow it to be packaged in vesicles. Each vesicle contains about 85,000 molecules of vasopressin.
Types of neuropeptides
More than 100 different peptides have been shown to be expressed by different subpopulations of neurons in the CNS.
Gastrins
- Gastrin
- Cholecystokinin (CCK)
Neuropeptide Y
- Neuropeptide Y (NY)
- Pancreatic polypeptide (PP)
- Peptide YY (PYY)
- Adrenocorticotropic hormone, ACTH)
Opioids
Secretins
Somatostatins
Others
References
- ↑ Anonymous. Neuropeptides. National Library of Medicine. Retrieved on 2008-01-21.