Neuropeptide Y Neuropeptides are small protein-like molecules (peptides) used by neurons to communicate with each other. They are neuronal signaling molecules that influence the activity of the brain in specific ways. Different neuropeptides are involved in a wide range of brain functions, including analgesia, reward, food intake, metabolism, reproduction, social behaviors, learning and memory. Neuropeptides are related to peptide hormones, and in some cases peptides that function in the periphery as hormones also have neuronal functions as neuropeptides. The distinction between neuropeptide and peptide hormone has to do with the cell types that release and respond to the molecule; neuropeptides are secreted from neuronal cells (primarily neurons but also glia for some peptides) and signal to neighboring cells (primarily neurons). In contrast, peptide hormones are secreted from neuroendocrine cells and travel through the blood to distant tissues where they evoke a response. Both neuropeptides and peptide hormones are synthesized by the same sets of enzymes, which include prohormone convertases and carboxypeptidases that selectively cleave the peptide precursor at specific processing sites to generate the bioactive peptides. [1] Neuropeptides modulate neuronal communication by acting on cell surface receptors. Many neuropeptides are co-released with other small-molecule neurotransmitters. The human genome contains about 90 genes that encode precursors of neuropeptides. At present about 100 different peptides are known to be released by different populations of neurons in the mammalian brain.[2] Neurons use many different chemical signals to communicate information, including neurotransmitters, peptides, and gasotransmitters. Peptides are unique among these cell-cell signaling molecules in several respects. One major difference is that peptides are not recycled back into the cell once secreted, unlike many conventional neurotransmitters (glutamate, dopamine, serotonin). Another difference is that after secretion, peptides are modified by extracellular peptidases; in some cases, these extracellular cleavages inactivate the biological activity, but in other cases the extracellular cleavages increase the affinity of a peptide for a particular receptor while decreasing its affinity for another receptor. These extracellular processing events add to the complexity of neuropeptides as cell-cell signaling molecules. Many populations of neurons have distinctive biochemical phenotypes. For example, in one subpopulation of about 3000 neurons in the arcuate nucleus of the hypothalamus, three anorectic peptides are co-expressed: α-melanocyte-stimulating hormone (α-MSH), galanin-like peptide, and cocaine-and-amphetamine-regulated transcript (CART), and in another subpopulation two orexigenic peptides are co-expressed, neuropeptide Y and agouti-related peptide (AGRP). These are not the only peptides in the arcuate nucleus; β-endorphin, dynorphin, enkephalin, galanin, ghrelin, growth-hormone releasing hormone, neurotensin, neuromedin U, and somatostatin are also expressed in subpopulations of arcuate neurons. These peptides are all released centrally and act on other neurons at specific receptors. The neuropeptide Y neurons also make the classical inhibitory neurotransmitter GABA. Invertebrates also have many neuropeptides. CCAP has several functions including regulating heart rate, allatostatin and proctolin regulate food intake and growth, bursicon controls tanning of the cuticle and corazonin has a role in cuticle pigmentation and moulting. Peptide signals play a role in information processing that is different from that of conventional neurotransmitters, and many appear to be particularly associated with specific behaviours. For example, oxytocin and vasopressin have striking and specific effects on social behaviours, including maternal behaviour and pair bonding. FunctionEdit Generally, peptides act at metabotropic or G-protein-coupled receptors expressed by selective populations of neurons. In essence they act as specific signals between one population of neurons and another. Neurotransmitters generally affect the excitability of other neurons, by depolarising them or by hyperpolarising them. Peptides have much more diverse effects; amongst other things, they can affect gene expression, local blood flow, synaptogenesis, and glial cell morphology. Peptides tend to have prolonged actions, and some have striking effects on behaviour. Neurons very often make both a conventional neurotransmitter (such as glutamate, GABA or dopamine) and one or more neuropeptides. Peptides are generally packaged in large dense-core vesicles, and the co-existing neurotransmitters in small synaptic vesicles. The large dense-core vesicles are often found in all parts of a neuron, including the soma, dendrites, axonal swellings (vericosities) and nerve endings, whereas the small synaptic vesicles are mainly found in clusters at presynaptic locations.[citation needed]Release of the large vesicles and the small vesicles is regulated differently. ExamplesEdit The following is a list of neuroactive peptides coexisting with other neurotransmitters. Transmitter names are shown in bold. Norepinephrine (noradrenaline). In neurons of the A2 cell group in the nucleus of the solitary tract), norepinephrine co-exists with: Galanin Enkephalin Neuropeptide Y GABA Somatostatin (in the hippocampus) Cholecystokinin Neuropeptide Y (in the arcuate nucleus) Acetylcholine VIP Substance P Dopamine Cholecystokinin Neurotensin Epinephrine (adrenaline) Neuropeptide Y Neurotensin Serotonin (5-HT) Substance P TRH Enkephalin Some neurons make several different peptides. For instance, Vasopressin co-exists with dynorphin and galanin in magnocellular neurons of the supraoptic nucleus and paraventricular nucleus, and with CRF (in parvocellular neurons of the paraventricular nucleus) Oxytocin in the supraoptic nucleus co-exists with enkephalin, dynorphin, cocaine-and amphetamine regulated transcript (CART) and cholecystokinin. Diabetes linkEdit A 2006 discovery might have important implications for treatment of diabetes,.[3][4] Researchers at the Toronto Hospital for Sick Children injected capsaicin into NOD mice (Non-obese diabetic mice, a strain that is genetically predisposed to develop the equivalent of Type 1 diabetes) to kill the pancreatic sensory nerves. This treatment reduced the development of diabetes in these mice by 80%, suggesting a link between neuropeptides and the development of Type 1 diabetes. When the researchers injected the pancreas of the diabetic mice with substance P, they were cured of the diabetes for as long as 4 months. Also, insulin resistance (characteristic of type 2 diabetes) was reduced. These research results are in the process of being confirmed, and their applicability in humans will have to be established in the future. Any treatment that could result from this research is probably years away. Depression linkEdit There are studies investigating the relation of neuropeptides and CNS disorders including depression. References External links See also Read in another language Wikipedia ® MobileDesktop Content is available under CC BY-SA 3.0 unless otherwise noted. Terms of UsePrivacy Douglas Gauld added 2 new photos. 11 mins · Edited · Peptides: A tetrapeptide (example Val-Gly-Ser-Ala) with green marked amino end (L-Valine) and blue marked carboxyl end (L-Alanine). Peptides (from Gr. πεπτός, digested, derived from πέσσειν, to digest) are naturally occurring biological molecules. They are short chains of amino acid monomers linked by peptide (amide) bonds. The covalent chemical bonds are formed when the carboxyl group of one amino acid reacts with the amino group of another. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligo- and polysaccharides, etc. Peptides are distinguished from proteins on the basis of size, and as an arbitrary benchmark can be understood to contain approximately 50 or fewer amino acids.[1] Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule (DNA, RNA, etc.), or to complex macromolecular assemblies. Finally, while aspects of the techniques that apply to peptides versus polypeptides and proteins differ (i.e., in the specifics of electrophoresis, chromatography, etc.), the size boundaries that distinguish peptides from polypeptides and proteins are not absolute: long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides. Amino acids that have been incorporated into peptides are termed residues due to the release of either a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both, as a water molecule is released during formation of each amide bond.[2] All peptides except cyclic peptides have an N-terminal and C-terminal residue at the end of the peptide (as shown for the tetrapeptide in the image). Peptide classesEdit Peptides are divided into several classes, depending on how they are produced: Milk peptides Two naturally occurring milk peptides are formed from the milk protein casein when digestive enzymes break this down; they can also arise from the proteinases formed by lactobacilli during the fermentation of milk.[3] Ribosomal peptides Ribosomal peptides are synthesized by translation of mRNA. They are often subjected to proteolysis to generate the mature form. These function, typically in higher organisms, as hormones and signaling molecules. Some organisms produce peptides as antibiotics, such as microcins.[4] Since they are translated, the amino acid residues involved are restricted to those utilized by the ribosome. However, these peptides frequently have posttranslational modifications, such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation and disulfide formation. In general, they are linear, although lariat structures have been observed.[5] More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom.[6] Nonribosomal peptides Nonribosomal peptides are assembled by enzymes that are specific to each peptide, rather than by the ribosome. The most common non-ribosomal peptide is glutathione, which is a component of the antioxidant defenses of most aerobic organisms.[7] Other nonribosomal peptides are most common in unicellular organisms, plants, and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases.[8] These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product.[9] These peptides are often cyclic and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for building fatty acids and polyketides, hybrid compounds are often found. The presence of oxazoles or thiazoles often indicates that the compound was synthesized in this fashion.[10] Peptones See also Tryptone Peptones are derived from animal milk or meat digested by proteolysis.[11] In addition to containing small peptides, the resulting spray-dried material [clarification needed] includes fats, metals, salts, vitamins and many other biological compounds. Peptones are used in nutrient media for growing bacteria and fungi.[12] Peptide fragments Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein.[13] Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples that have been degraded by natural effects.[14][15] Peptide synthesisEdit Main article: Peptide synthesis Table of amino acids Solid-phase peptide synthesis on a rink amide resin using Fmoc-α-amine-protected amino acid Peptides in Molecular BiologyEdit Peptides received prominence in molecular biology for several reasons. The first is that peptides allow the creation of peptide antibodies in animals without the need to purify the protein of interest.[16] This involves synthesizing antigenic peptides of sections of the protein of interest. These will then be used to make antibodies in a rabbit or mouse against the protein. Another reason is that peptides have become instrumental in mass spectrometry, allowing the identification of proteins of interest based on peptide masses and sequence. In this case the peptides are most often generated by in-gel digestion after electrophoretic separation of the proteins. Peptides have recently been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to see where protein-peptide interactions occur- see the page on Protein tags. Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases.[17] For example, one of the most promising application is through peptides that target LHRH.[18] These particular peptides act as an agonist, meaning that they bind to a cell in a way that regulates LHRH receptors. The process of inhibiting the cell receptors suggests that peptides could be beneficial in treating prostate cancer. However, additional investigations and experiments are required before the cancer-fighting attributes, exhibited by peptides, can be considered definitive.[19] Well-known peptide familiesEdit The peptide families in this section are ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as longer propeptides or proproteins and truncated prior to exiting the cell. They are released into the bloodstream where they perform their signaling functions. Tachykinin peptides Main article: Tachykinin peptides Substance P Kassinin Neurokinin A Eledoisin Neurokinin B Vasoactive intestinal peptides Main article: Secretin family VIP (Vasoactive Intestinal Peptide; PHM27) PACAP Pituitary Adenylate Cyclase Activating Peptide Peptide PHI 27 (Peptide Histidine Isoleucine 27) GHRH 1-24 (Growth Hormone Releasing Hormone 1-24) Glucagon Secretin Pancreatic polypeptide-related peptides NPY (NeuroPeptide Y) PYY (Peptide YY) APP (Avian Pancreatic Polypeptide) PPY Pancreatic PolYpeptide Opioid peptides Main article: Opioid peptide Proopiomelanocortin (POMC) peptides Enkephalin pentapeptides Prodynorphin peptides Calcitonin peptides Calcitonin Amylin AGG01 Other peptides B-type Natriuretic Peptide (BNP) - produced in myocardium & useful in medical diagnosis Lactotripeptides - Lactotripeptides might reduce blood pressure,[20][21][22] although the evidence is mixed.[23] Notes on terminology Doping in sports See also References Read in another language Wikipedia ® MobileDesktop Content is available under CC BY-SA 3.0 unless otherwise noted. 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