Neuroactive peptides
From Drug Rehab Wiki
Neuroactive peptides, usually called neuropeptides, are kinds of molecules found in brain and nerve tissue. They are made of up chains of amino acids manufactured, stored and released by nerve cells. Research into neuropeptides is only recent, and yet the amount of information being accumulated about this topic is staggering. As one researcher put it, what we know about neuropeptides is vastly different than what we knew six months ago, and vastly different than what we will know six months from now.
So far scientists have identified about 150 neuropeptides, but there are probably many more. These chemicals play a part in pain management, memory, aging, appetite, acclimation, and behavior itself, and scientists are only beginning to understand the roles of neuropeptides in human behavior and consciousness. Neuropeptides could be at the basis of any future understanding of consciousness, and some scientists believe that by controlling these chemicals, you could be able to control consciousness itself.
Neuropeptides were discovered in 1975 by John Hughes and Hans Kosterlitz, two Scottish scientists researching drug addiction. They were looking for a natural chemical similar to an opioid painkiller that the human body produced on its own and releases to ease pain. Hughes and Kosterlitz were able to isolate a substance they named "enkephalin," which blocks convulsions in the brain in the same way morphine does. Hughes and Kosterlitz discovered that enkephalin consisted of two amino-acid chains known as peptides, that work only if they are linked up in a specific way. It turned out that most neuropeptides are short chains of amino acids, but the order in which the molecules appear is vital to their functioning. One researcher explained that they are like cars in a certain order on a train, and unless they are in the right order, the train cannot move.
By 1980, "endorphin" had become a buzz word not only in science, but among the general population. Endorphins or natural painkillers were at the bottom of every pleasurable experience from "runner's high" to eating ice cream. The problem was that amino-acid-chain neuropeptides were much more complicated than just the simple concept of endorphins. There are over a hundred kinds of neuropeptides involved not only in pleasure, but mood, energy level, pain thresholds, body weight, problem-solving, memory, immune function, and more.
Neuropeptides are like neurotransmitters in that they are chemicals involved in the transmission of nerve impulses. A nerve cell or neuron is made up of a sphere with fibers. One long fiber is called the axon, and it carries nerve impulses away from the cell. Each cell also has many long, branch-like fibers called dendrites that carry messages toward the cell. Neuropeptides and neurotransmitters are produced in the cell bodies of nerve cells and stored in little sacs called vesicles.
When a nerve impulse travels through the body, it has to go from one nerve cell to another and there are little gaps between the cells. Although nerve impulses are electrical charges, getting across the gap between cells is achieved chemically, not electrically. Nerve cells stay in a resting state until their membranes open to receive a positive charge of electricity. This signals the cell to open up its vesicles, and release chemicals that flow across the gap to the dendrites of the next cell. Neurotransmitters excite neurons, but neuropeptides play a more diverse role, because when they are released, they must be received by cells that can accommodate their shapes exactly. It is something like a lock-and-key mechanism. A receptor cell is basically a space in a dendrite with a precise shape like a lock that can receive only a certain kind of neuropeptide like a key.
Neuropeptides therefore are able to carry very specific messages. For example, enkephalin, the neuropeptide that Hughes and Kosterlitz discovered, works with the neurotransmitter, serotonin, to relieve pain.
How neuropeptides function within an individual has to do with hereditary factors. So far scientists have isolated about 90 genes involved with neuropeptides and their function. Neuropeptides are found in plants and all species of the animal kingdom.
After the discovery of the first neuropeptides, scientists tried to find out if certain drugs could plug into the receptor "locks" the way neuropeptides do. One such drug, naloxone, is now used to treat drug addiction. Naloxone is a narcotic antagonist, or a drug that counteracts the effects of opioid drugs. It takes the place of opioid drugs like morphine by plugging into the receptor cells, thus blocking morphine from doing that.
Research about neuropeptides is continuing at a rapid rate to find more such drugs. For example, leptin, insulin, and ghrelin are hormones produced in the body involved in appetite control. With help from a neuropeptide called cholecystokinin, these hormones send signals to the brain when the person should stop eating. Studies are showing that if you do not feed a laboratory animal for some time and then administer cholecystokinin, the animal will not eat even though it needs food. Once scientists better understand how this mechanism works, they could be able to develop cures for obesity.
Other studies concern serotonin, dopamine, and acetylcholine. Studies of identical twins indicate that about half of anxiety disorders have a hereditary element, and increased anxiety may be due to shortages of certain proteins related to the reuptake of serotonin, the neurotransmitter that works with enkephalin. Other studies are showing a link between the body's natural painkillers and emotional illness. Dopamine receptors have been linked to risk-taking and thrill-seeking behaviors. Another neuropeptide can increase memory and learning up to 20% in laboratory studies.
Neuropeptides have caught the public's imagination. They are now advertised as miracle cures in skin creams and nutritional supplements.
