Neuropeptides are small protein-like substances produced and released through regulated secretory routes. They were initially discovered in the brain and where described as being released from neuronal cells and acting on neuronal tissue targets affecting brain function. Nowadays, it is generally accepted that different neuropeptides are involved in a wide range of functions, and in many cases peptides secreted from cells other than neurons, function in the periphery as neuropeptides.
To date, the human genome is found to contain 90 genes encoding neuropeptide precursors and about 100 different peptides have been identified to be released by different populations of neurons and/or peripheral cells. Neuropeptides can be broadly classified as follows:
Hypothalamic releasing factors
Neuronal and endocrine peptides
GI and brain peptides
Gastrointestinal tract and pancreas peptides
Neurons only peptides
Neuropeptides modulate intercellular communication through binding on cell surface receptors. Generally, they act on metabotropic or G-protein-coupled receptors expressed by selective populations of target cells. In essence they act as specific signals between one population of cells and another.
A large number of studies focus on the relative expression of neuropeptides and/or their specific receptors during health and papthologic conditions. Lately, neuropeptide signaling and its involvement in disease pathophysiology is believed to be key for the resolution of corresponding manifestations, often viewed as an integral link between the challenges of our environment and the resilience of our coping. Synthesized and released from neuronal and various other secretory cells, they are the focus of many studies dealing with neurological, psychiatric, skin and inflammatory bowel diseases.
Neuropeptides in the central nervous system, serve as neuroregulators. Recent interest has focused on their role in degenerative neurological diseases. In example, in Alzheimer's Disease and in dementia associated with Parkinson's disease, a number of neuropeptides are reduced. In Huntington's disease, basal ganglia neurons in which neuropeptides somatostatin and neuropeptide Y are co-localized are selectively preserved. Improved understanding of neuropeptides in degenerative neurological illnesses will help define which neuronal populations are specifically vulnerable to the pathological processes, and this could lead to improved therapy.
Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. Both the enteric nervous system (ENS) and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides that are thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. Evidence suggest that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis.