Neurotransmitter: From 3 Different Sources
A chemical released from a nerve ending that transmits impulses from one neuron (nerve cell) to another neuron, or to a muscle cell. When a nerve impulse reaches a nerve ending, neurotransmitters are released from synaptic vesicles and cross a tiny gap (synapse) to reach the target cell. Here, they cause channels in the target cell to open, letting through charged particles that stimulate an impulse in the cell. Alternatively, neurotransmitters may inhibit nerve impulses.
Scores of different chemicals fulfil this function in different parts of the nervous system. Many neurotransmitters act as both neurotransmitters and hormones, being released into the bloodstream to act on distant target cells.
One of the most important neurotransmitters is acetylcholine, which causes skeletal muscles to contract when it is released by neurons connected to the muscles. Acetylcholine is also released by neurons that control the sweat glands and the heartbeat, and transmits messages between neurons in the brain and spinal cord.
Another chemical, noradrenaline (norepinephrine), aids the nervous control of heartbeat, blood flow, and the body’s response to stress. Dopamine plays an important role in parts of the brain that control movement. Serotonin is one of the main neurotransmitters found in parts of the brain concerned with conscious processes.
Another group of neurotransmitters is called the neuropeptides.
This group includes the endorphins, which are used by the brain to control sensitivity to pain.
A chemical substance which transmits the action of a NERVE to a cell (see CELLS). It is released from nerve-endings and transmits the impulse across synapses (see SYNAPSE) to other nerves. In the central nervous system the substances acting as neurotransmitters include ACETYLCHOLINE, NORADRENALINE, DOPAMINE and SEROTONIN. The main transmitter in the peripheral system is acetylcholine, while for the sympathetic system it is noradrenaline. In recent years a new group of neurotransmitters called neuropeptides has been identi?ed, comprising large protein molecules. One of the best-known is that of endorphins, which the brain uses to control pain. (See also NEURON(E); NERVOUS SYSTEM; PAIN.)
n. a chemical substance released from nerve endings to transmit impulses across *synapses to other nerves and across the minute gaps between the nerves and the muscles or glands that they supply. Outside the central nervous system the chief neurotransmitter is *acetylcholine; *noradrenaline is released by nerve endings of the sympathetic system. In the central nervous system, as well as acetylcholine and noradrenaline, *dopamine, *serotonin, *gamma-aminobutyric acid, the amino acid glutamate, and several other substances act as transmitters.
The term applied to the anatomical relation of one NEURON(E) (nerve cell) with another which is e?ected at various points by contact of their branching processes. The two neurons do not come directly into contact, but the release of a chemical NEUROTRANSMITTER by one neuronal AXON is followed by this chemical travelling across the synapse and ?ring o? the signal along another nerve. A signal can be sent across a synapse in one direction only, from presynaptic or postsynaptic membranes. Synapses are divided into excitatory and inhibitory types. When a neurotransmitter travels across an excitatory synapse it usually provokes the receptor neuron into initiating an electrical impulse. Inhibitory synapses cool down the excitation of the adjacent neurons. Drugs that in?uence the NERVOUS SYSTEM usually do so by affecting the release or modi?cation of the neurotransmitters passing across the synapse.... synapse
Substances produced in the body from the dietary AMINO ACIDS, PHENYLALANINE and TYROSINE. They include ADRENALINE, NORADRENALINE and DOPAMINE which have varying functions, usually as NEUROTRANSMITTERS, in the sympathetic and central nervous systems (see under NERVOUS SYSTEM). Their chemical structure is based on a benzene ring with hydroxyl and amine side-chains.... catecholamines
A description of nerve ?bres that release ACETYLCHOLINE as a NEUROTRANSMITTER.... cholinergic
An ENZYME that helps to break down the neurotransmitter compound ACETYLCHOLINE.... cholinesterase
A gland that secretes its products through a duct to the surface of the body or of an organ. The sweat glands in the skin and the salivary glands in the mouth are examples. The secretion is set o? by a hormone (see HORMONES) or a NEUROTRANSMITTER.... exocrine gland
Better known by its trade name Prozac®, this drug – one of the SELECTIVE SEROTONINREUPTAKE INHIBITORS (SSRIS) – has been widely used, especially in North America, for the treatment of depression and anxiety (see MENTAL ILLNESS). Though causing fewer side-effects than TRICYCLIC ANTIDEPRESSANT DRUGS (the ?rst such drugs widely used), SSRI drugs should be prescribed with care and should not be stopped abruptly. Unlike benzodiazepine tranquillisers such as Valium®, ?uoxetine is not addictive, but there have been rare reports of it allegedly provoking people to acts of violence. The drug acts by modifying the activities of neurotransmitters, notably DOPAMINE and SEROTONIN in the brain, thus prolonging the effects of these chemical messengers.... fluoxetine
A type of neurotransmitter (a chemical that transmits messages between nerve cells or between nerve and muscle cells). Acetylcholine is the neurotransmitter found at all nervemuscle junctions and at many other sites in the nervous system. The actions of acetylcholine are called cholinergic actions, and these can be blocked by anticholinergic drugs.... acetylcholine
The inner part of the adrenals, derived embryonically from spinal nerve precursors, they secrete epinephrine, norepinephrine and dopamine; used locally as neurotransmitters, sensitive receptors can be mobilized totally by the adrenal medullas.... adrenal medulla
A pharmacological e?ect where the action of ACETYLCHOLINE, a chemical neurotransmitter released at the junctions (synapses) of parasympathetic and ganglionic nerves, is inhibited. The junctions between nerves and skeletal muscles have nicotinic receptors. A wide range of drugs with antimuscarinic effects are in use for various disorders including PSYCHOSIS, BRONCHOSPASM, disorders of the eye (see EYE, DISORDERS OF), PARKINSONISM, and problems of the GASTROINTESTINAL TRACT and URINARY TRACT. (See also ANTISPASMODICS.)... antimuscarine
Nutritional Profile
Energy value (calories per serving): Moderate
Protein: Low
Fat: Low
Saturated fat: Low Cholesterol: None Carbohydrates: High Fiber: Moderate Sodium: Low
Major vitamin contribution: B vitamins, vitamin C
Major mineral contribution: Potassium, magnesium
About the Nutrients in This Food
A banana begins life with more starch than sugar, but as the fruit ripens its starches turn to sugar, which is why ripe bananas taste so much better than unripe ones.* The color of a banana’s skin is a fair guide to its starch/ sugar ratio. When the skin is yellow-green, 40 percent of its carbohydrates are starch; when the skin is fully yellow and the banana is ripe, only 8 per- cent of the carbohydrates are still starch. The rest (91 percent) have broken down into sugars—glucose, fructose, sucrose, the most plentiful sugar in the fruit. Its high sugar content makes the banana, in its self-contained packet, a handy energy source.
Bananas are a high-fiber food with insoluble cellulose and lignin in the tiny seeds and soluble pectins in the flesh. They are also a good source of vitamin C and potassium.
One small (six-inch) banana or a half-cup of sliced banana has 2.6 g dietary fiber and 8.8 mg vitamin C (12 percent of the R DA for a woman,
10 percent of the R DA for a man), plus 363 mg potassium.
The Most Nutritious Way to Serve This Food
Fresh and ripe. Green bananas contain antinutrients, proteins that inhibit the actions of amylase, an enzyme that makes it possible for us to digest
* They are also more healt hful. Green bananas contain proteins t hat inhibit amy- lase, an enzyme t hat makes it possible for us to digest complex carbohydrates.
starch and other complex carbohydrates. Raw bananas are richer in potassium than cooked bananas; heating depletes potassium.
Buying This Food
Look for: Bananas that will be good when you plan to eat them. Bananas with brown specks on the skin are ripe enough to eat immediately. Bananas with creamy yellow skin will be ready in a day or two. Bananas with mostly yellow skin and a touch of green at either end can be ripened at home and used in two or three days.
Avoid: Overripe bananas whose skin has turned brown or split open. A grayish yellow skin means that the fruit has been damaged by cold storage. Bananas with soft spots under the skin may be rotten.
Storing This Food
Store bananas that aren’t fully ripe at room temperature for a day or two. Like avocados, bananas are picked green, shipped hard to protect them from damage en route and then sprayed with ethylene gas to ripen them quickly. Untreated bananas release ethylene natu- rally to ripen the fruit and turn its starches to sugar, but natural ripening takes time. Artificial ripening happens so quickly that there is no time for the starches to turn into sugar. The bananas look ripe but they may taste bland and starchy. A few days at room temperature will give the starches a chance to change into sugars.
Store ripe bananas in the refrigerator. The cold air will slow (but not stop) the natural enzyme action that ripens and eventually rots the fruit if you leave it at room temperature. Cold storage will darken the banana’s skin, since the chill damages cells in the peel and releases polyphenoloxidase, an enzyme that converts phenols in the banana peel to dark brown compounds, but the fruit inside will remain pale and tasty for several days.
Preparing This Food
Do not slice or peel bananas until you are ready to use them. When you cut into the fruit, you tear its cell walls, releasing polyphenoloxidase, an enzyme that hastens the oxidation of phenols in the banana, producing brown pigments that darken the fruit. (Chilling a banana produces the same reaction because the cold damages cells in the banana peel.) You can slow the browning (but not stop it completely) by dipping raw sliced or peeled bananas into a solution of lemon juice or vinegar and water or by mixing the slices with citrus fruits in a fruit salad. Overripe, discolored bananas can be used in baking, where the color doesn’t matter and their intense sweetness is an asset.
What Happens When You Cook This Food
When bananas are broiled or fried, they are cooked so quickly that there is very little change in color or texture. Even so, they will probably taste sweeter and have a more intense aroma than uncooked bananas. Heat liberates the volatile molecules that make the fruit taste and smell good.
How Other Kinds of Processing Affect This Food
Drying. Drying removes water and concentrates the nutrients and calories in bananas. Bananas may be treated with compounds such as sulfur dioxide to inhibit polyphenoloxi- dase and keep the bananas from browning as they dry. People who are sensitive to sulfites may suffer severe allergic reactions, including anaphylactic shock, if they eat these treated bananas.
Freezing. Fresh bananas freeze well but will brown if you try to thaw them at room tem- perature. To protect the creamy color, thaw frozen bananas in the refrigerator and use as quickly as possible.
Medical Uses and/or Benefits
Lower risk of stroke. Various nutrition studies have attested to the power of adequate potassium to keep blood pressure within safe levels. For example, in the 1990s, data from the long-running Harvard School of Public Health/Health Professionals Follow-Up Study of male doctors showed that a diet rich in high-potassium foods such as bananas, oranges, and plantain may reduce the risk of stroke. In the study, the men who ate the higher number of potassium-rich foods (an average of nine servings a day) had a risk of stroke 38 percent lower than that of men who consumed fewer than four servings a day. In 2008, a similar survey at the Queen’s Medical Center (Honolulu) showed a similar protective effect among men and women using diuretic drugs (medicines that increase urination and thus the loss of potassium).
Improved mood. Bananas and plantains are both rich in serotonin, dopamine, and other natural mood-elevating neurotransmitters—natural chemicals that facilitate the transmis- sion of impulses along nerve cells.
Potassium benefits. Because potassium is excreted in urine, potassium-rich foods are often recommended for people taking diuretics. In addition, a diet rich in potassium (from food) is associated with a lower risk of stroke. A 1998 Harvard School of Public Health analysis of data from the long-running Health Professionals Study shows 38 percent fewer strokes among men who ate nine servings of high potassium foods a day vs. those who ate less than four servings. Among men with high blood pressure, taking a daily 1,000 mg potas- sium supplement—about the amount of potassium in one banana—reduced the incidence of stroke by 60 percent.
Adverse Effects Associated with This Food
Digestive Problems. Unripe bananas contain proteins that inhibit the actions of amylase, an enzyme required to digest starch and other complex carbohydrates.
Sulfite allergies. See How other kinds of processing affect this food.
Latex-fruit syndrome. Latex is a milky fluid obtained from the rubber tree and used to make medical and surgical products such as condoms and protective latex gloves, as well as rub- ber bands, balloons, and toys; elastic used in clothing; pacifiers and baby bottle-nipples; chewing gum; and various adhesives. Some of the proteins in latex are allergenic, known to cause reactions ranging from mild to potentially life-threatening. Some of the proteins found naturally in latex also occur naturally in foods from plants such as avocados, bananas, chestnuts, kiwi fruit, tomatoes, and food and diet sodas sweetened with aspartame. Persons sensitive to these foods are likely to be sensitive to latex as well. NOTE : The National Insti- tute of Health Sciences, in Japan, also lists the following foods as suspect: Almonds, apples, apricots, bamboo shoots, bell peppers, buckwheat, cantaloupe, carrots, celery, cherries, chestnuts, coconut, figs, grapefruit, lettuce, loquat, mangoes, mushrooms, mustard, nectar- ines, oranges, passion fruit, papaya, peaches, peanuts, peppermint, pineapples, potatoes, soybeans, strawberries, walnuts, and watermelon.
Food/Drug Interactions
Monoamine oxidase (MAO) inhibitors. Monoamine oxidase inhibitors are drugs used to treat depression. They inactivate naturally occurring enzymes in your body that metabolize tyra- mine, a substance found in many fermented or aged foods. Tyramine constricts blood vessels and increases blood pressure. If you eat a food containing tyramine while you are taking an M AO inhibitor, you cannot effectively eliminate the tyramine from your body. The result may be a hypertensive crisis. There have been some reports in the past of such reactions in people who have eaten rotten bananas or bananas stewed with the peel.
False-positive test for tumors. Carcinoid tumors—which may arise from tissues of the endo- crine system, the intestines, or the lungs—secrete serotonin, a natural chemical that makes blood vessels expand or contract. Because serotonin is excreted in urine, these tumors are diagnosed by measuring the levels of serotonin by-products in the urine. Bananas contain large amounts of serotonin; eating them in the three days before a test for an endocrine tumor might produce a false-positive result, suggesting that you have the tumor when in fact you don’t. (Other foods high in serotonin are avocados, eggplant, pineapple, plums, tomatoes, and walnuts.)... bananas
Nutritional Profile
Energy value (calories per serving): Moderate
Protein: Moderate Fat: Low to moderate Saturated fat: Low to high Cholesterol: Low to high Carbohydrates: High
Fiber: Moderate to high
Sodium: Moderate to high
Major vitamin contribution: B vitamins
Major mineral contribution: Calcium, iron, potassium
About the Nutrients in This Food
All commercially made yeast breads are approximately equal in nutri- tional value. Enriched white bread contains virtually the same amounts of proteins, fats, and carbohydrates as whole wheat bread, although it may contain only half the dietary fiber (see flour).
Bread is a high-carbohydrate food with lots of starch. The exact amount of fiber, fat, and cholesterol in the loaf varies with the recipe. Bread’s proteins, from grain, are low in the essential amino acid lysine. The most important carbohydrate in bread is starch; all breads contain some sugar. Depending on the recipe, the fats may be highly saturated (butter or hydrogenated vegetable fats) or primarily unsaturated (vegetable fat).
All bread is a good source of B vitamins (thiamin, riboflavin, niacin), and in 1998, the Food and Drug Administration ordered food manufactur- ers to add folates—which protect against birth defects of the spinal cord and against heart disease—to flour, rice, and other grain products. One year later, data from the Framingham Heart Study, which has followed heart health among residents of a Boston suburb for nearly half a cen- tury, showed a dramatic increase in blood levels of folic acid. Before the fortification of foods, 22 percent of the study participants had a folic acid deficiency; after, the number fell to 2 percent.
Bread is a moderately good source of calcium, magnesium, and phos- phorus. (Breads made with milk contain more calcium than breads made without milk.) Although bread is made from grains and grains contain phytic acid, a natural antinutrient that binds calcium ions into insoluble, indigestible compounds, the phytic acid is inactivated by enzyme action during leavening. Bread does not bind calcium.
All commercially made breads are moderately high in sodium; some contain more sugar than others. Grains are not usually considered a good source of iodine, but commer- cially made breads often pick up iodine from the iodophors and iodates used to clean the plants and machines in which they are made.
Homemade breads share the basic nutritional characteristics of commercially made breads, but you can vary the recipe to suit your own taste, lowering the salt, sugar, or fat and raising the fiber content, as you prefer.
The Most Nutritious Way to Serve This Food
As sandwiches, with cheese, milk, eggs, meat, fish, or poultry. These foods supply the essen- tial amino acid lysine to “complete” the proteins in grains.
With beans or peas. The proteins in grains are deficient in the essential amino acids lysine and isoleucine and rich in the essential amino acids tryptophan, methionine, and cystine. The proteins in legumes (beans and peas) are exactly the opposite.
Diets That May Restrict or Exclude This Food
Gluten-free diet (excludes breads made with wheat, oats, rye, buckwheat and barley flour) Lactose-free diet
Low-fiber diet (excludes coarse whole-grain breads) Low-sodium diet
Buying This Food
Look for: Fresh bread. Check the date on closed packages of commercial bread.
Storing This Food
Store bread at room temperature, in a tightly closed plastic bag (the best protection) or in a breadbox. How long bread stays fresh depends to a great extent on how much fat it contains. Bread made with some butter or other fat will keep for about three days at room tempera- ture. Bread made without fat (Italian bread, French bread) will dry out in just a few hours; for longer storage, wrap it in foil, put it inside a plastic bag, and freeze it. When you are ready to serve the French or Italian bread, you can remove it from the plastic bag and put the foil- wrapped loaf directly into the oven.
Throw away moldy bread. The molds that grow on bread may produce carcinogenic toxins.
Do not store fresh bread in the refrigerator; bread stales most quickly at temperatures just above freezing. The one exception: In warm, humid weather, refrigerating bread slows the growth of molds.
When You Are Ready to Serve This Food
Use a serrated knife to cut bread easily.
What Happens When You Cook This Food
Toasting is a chemical process that caramelizes sugars and amino acids (proteins) on the surface of the bread, turning the bread a golden brown. This chemical reaction, known both as the browning reaction and the Maillard reaction (after the French chemist who first identified it), alters the structure of the surface sugars, starches, and amino acids. The sugars become indigestible food fiber; the amino acids break into smaller fragments that are no longer nutritionally useful. Thus toast has more fiber and less protein than plain bread. How- ever, the role of heat-generated fibers in the human diet is poorly understood. Some experts consider them inert and harmless; others believe they may be hazardous.
How Other Kinds of Processing Affect This Food
Freezing. Frozen bread releases moisture that collects inside the paper, foil, or plastic bag in which it is wrapped. If you unwrap the bread before defrosting it, the moisture will be lost and the bread will be dry. Always defrost bread in its wrappings so that it can reabsorb the moisture that keeps it tasting fresh.
Drying. Since molds require moisture, the less moisture a food contains, the less likely it is support mold growth. That is why bread crumbs and Melba toast, which are relatively mois- ture-free, keep better than fresh bread. Both can be ground fine and used as a toasty-flavored thickener in place of flour or cornstarch.
Medical Uses and/or Benefits
A lower risk of some kinds of cancer. In 1998, scientists at Wayne State University in Detroit conducted a meta-analysis of data from more than 30 well-designed animal studies mea- suring the anti-cancer effects of wheat bran, the part of grain with highest amount of the insoluble dietary fibers cellulose and lignin. They found a 32 percent reduction in the risk of colon cancer among animals fed wheat bran; now they plan to conduct a similar meta- analysis of human studies. Breads made with whole grain wheat are a good source of wheat bran. NOTE : The amount of fiber per serving listed on a food package label shows the total amount of fiber (insoluble and soluble).
Early in 1999, however, new data from the long-running Nurses Health Study at Brigham Women’s Hospital/Harvard University School of Public Health showed that women who ate a high-fiber diet had a risk of colon cancer similar to that of women who ate a low fiber diet. Because this study contradicts literally hundreds of others conducted over the past 30 years, researchers are awaiting confirming evidence before changing dietary recommendations.
Calming effect. Mood is affected by naturally occurring chemicals called neurotransmitters that facilitate transmission of impulses between brain cells. The amino acid tryptophan amino acid is the most important constituent of serotonin, a “calming” neurotransmitter. Foods such as bread, which are high in complex carbohydrates, help move tryptophan into your brain, increasing the availability of serotonin.
Adverse Effects Associated with This Food
Allergic reactions and/or gastric distress. Bread contains several ingredients that may trigger allergic reactions, aggravate digestive problems, or upset a specific diet, among them gluten (prohibited on gluten-free diets); milk (prohibited on a lactose- and galactose-free diet or for people who are sensitive to milk proteins); sugar (prohibited on a sucrose-free diet); salt (controlled on a sodium-restricted diet); and fats (restricted or prohibited on a controlled-fat, low-cholesterol diet).... bread
An amino acid (see AMINO ACIDS) which, along with aspartate, is a major excitatory chemical neurotransmitter – method of communication between neurones (see NEURON(E)) – in the central nervous system. The two amino acids are found in the cortex and cerebellum of the BRAIN and in the SPINAL CORD.... glutamate
Genmaicha Tea is a savoury Japanese traditional green tea, having a light yellow colour and a sweet nutty flavour resulting from the combination with roasted brown rice. Originally drunk by poor Japanese people who were unable to purchase a sufficient amount of tea leaves and used it as a filler, Genmaicha Tea is now a beverage consumed by everyone.
The legend says that a slave accidentally dropped rice in his samurai master’s tea while it was brewing and he was consequently beheaded. But the master was delighted with the result and named the tea Genmaicha in the honour of the departed worker.
Genmaicha Tea brewing
In order to brew Genmaicha Tea, it is recommended to use water heated at an 80 to 85 degrees Celsius temperature. The steeping time should not exceed five minutes and is generally resumed at three minutes, but it is often believed that one minute of brewing suffices. Genmaicha Tea can be served both hot and cold without minimizing its unique roasted aroma.
Genmaicha Tea Health Benefits
Genmaicha Tea provides a wide variety of health benefitsdue to its antioxidant properties, which are completely retained despite the amount of brown rice it contains, which is relatively low. These antioxidants improve the immune system function, lower the risk of cardiovascular disease and prevent cell damage caused by free radicals. Genmaicha Tea has also been proven to improve joint and bone strength and is therefore beneficial and effective for people who suffer from arthritis or rheumatism.
Furthermore, Genmaicha Tea is also recommended for people who suffer from diabetes because it considerably increases the activity of insulin and reduces the glucose level in the organism.
This particular tea is also extremely effective in the weight loss process - studies show that the consumption of Genmaicha Tea accelerates the burning of fats. It is recommended to drink two or three cups of tea daily.
When to drink Genmaicha Tea
Genmaicha Tea can be used as a replacement for coffee, but it is best when consumed in the afternoon because it maintains the energy level up, it keeps you alert and relaxed at the same time due to its content of theanine, an amino acid which affects the brain’s neurotransmitters and thus promotes concentration.
Genmaicha Tea side effects
The possible side effects ofGenmaicha Tea consumption include those related to caffeine intake, such as nausea, stomach upset, nervousness or insomnia.
However, Genmaicha Tea brings numerous benefits for the metabolism of tea drinkers, contributing to a balanced lifestyle and enhancing the energy levels.... genmaicha tea
The poisonous principle found in some toadstools (see FUNGUS POISONING). It is a cholinergic substance with pharmacological properties resembling those of ACETYLCHOLINE, a chemical neurotransmitter released at the junctions (synapses) of parasympathetic nerves and at the junctions where nerves enter muscles.... muscarine
Also known as the growth-hormone-releaseinhibiting factor, this is a hormone secreted by the HYPOTHALAMUS and some non-nervous tissues (including the gastrointestinal tract and pancreas). It stops the pituitary-releasing somatotrophin – GROWTH HORMONE. Somatostatin and growth-hormone-releasing hormone are controlled by complicated neural mechanisms linked to exercise, sleep patterns, stress, NEUROTRANSMITTERS and blood GLUCOSE.... somatostatin
A drug used in the treatment of MIGRAINE attacks. Given by subcutaneous injection, it provides quick relief of pain, acting on the same receptors as 5-hydroxytryptamine – a neurotransmitter and vasoconstrictor agent. It may also be taken orally, but sumatriptan should not be used within 24 hours of treatment with ERGOTAMINE, the standard antimigraine treatment.... sumatriptan
In simple terms, this is the genetic recipe for making a human being. GENOME is a combination of the words gene and chromosome, and a genome is de?ned as all the genetic material – known as deoxyribonucleic acid, or DNA – in a cell. Most genes encode sequences of AMINO ACIDS, the constituents of proteins, thus initiating and controlling the replication of an organism. The identi?cation and characterisation of the human genetic puzzle have been a key bioscience research target. The Human Genome Project was launched in 1990 (and completed in 2003) to produce a full sequence of the three million base pairs that make up the human genome.
Carried out as two separate exercises – one by a privately funded American team; another by an international joint venture between tax-funded American laboratories, a charitably funded British one and several other smaller research teams from around the world – the ?rst results were announced on 26 June 2000. In February 2001 the privately funded American group, known as Celera Genomics, announced that it had identi?ed 26,558 genes. At the same time the Human Genome Project consortium reported that it had identi?ed 31,000. Allowing for margins of error, this gives a ?gure much lower than the 100,000 or more human genes previously forecast by scientists. Interestingly, genes were found to make up only 3 per cent of the human genome. The remaining 97 per cent of the genome comprises non-coding DNA which, though not involved in producing the protein-initiating genetic activity, does have signi?cant roles in the structure, function and evolution of the genome.
One surprise from the Project so far is that the genetic di?erences between humans and other species seem much smaller than previously expected. For example, the Celera team found that people have only 300 genes that mice do not have; yet, the common ancestor of mice and men probably lived 100 million years or more in the past. Mice and humans, however, have around twice as many genes as the humble fruit ?y.
Cells die out when they become redundant during embryonic development: genes also die out during evolution, according to evidence from the Genome Project – a ?nding that supports the constant evolutionary changes apparent in living things; the Darwinian concept of survival of the ?ttest.
Apart from expanding our scienti?c knowledge, the new information – and promise of much more as the Genome Project continues – should enhance and expand the use of genetic engineering in the prevention and cure of disease. Studies are in progress on the gene for a receptor protein in the brain which will shed light on how the important neurotransmitter SEROTONIN in the brain works, and this, for example, should help the development of better drugs for the treatment of DEPRESSION. Another gene has been found that is relevant to the development of ASTHMA and yet another that is involved in the production of amyloid, a complex protein which is deposited in excessive amounts in both DOWN’S (DOWN) SYNDROME and ALZHEIMER’S DISEASE.... human genome
An alkaloid which is the principal addictive agent in TOBACCO. The small amount of nicotine in a single cigarette is su?cient to stimulate mental and bodily activities. In larger quantities it acts as a depressant or narcotic – habitual smokers may ?nd its e?ect sedating. Nicotine works by stimulating the production of a chemical called DOPAMINE, a neurotransmitter or chemical messenger between nerve cells. Nicotine mimics the action of a neurotransmitter called ACETYLCHOLINE. Nerve cells that produce dopamine have acetylcholine-receptor molecules on their surfaces; when these ‘nicotine-like’ receptors are occupied by acetylcholine molecules, a cell is prompted to produce dopamine. So nicotine itself can arti?cially stimulate dopamine production. Dopamine is part of the neuronal circuitry that plays a part in the body’s perception of pleasure, which is why smoking is enjoyed by many people.... nicotine
A naturally occurring chemical that performs a wide range of biological roles. It is involved in the laying down of memories in the BRAIN; in killing viruses, bacteria and cancer cells; and in helping to control blood pressure. NO, comprising a nitrogen atom attached to an oxygen one, is one of the smallest of biologically active compounds as well as having such diverse functions. The chemical is a muscle relaxant and is important in maintaining the heart and circulation in good condition. NO is also the toxic agent released by macrophages (see MACROPHAGE) to kill invading germs and spreading cancer cells. It acts as an essential NEUROTRANSMITTER and protects nerve cells against stress. Researchers are studying how it might be used to treat diseases, for example by using it as an inhaled gas in certain respiratory conditions.... nitric oxide (no)
The abbreviation for gammaaminobutyric acid, a neurotransmitter. GABA controls the flow of nerve impulses by blocking the release of other neurotransmitters (e.g. noradrenaline and dopamine) that stimulate nerve activity. GABA activity is increased by benzodiazepine drugs and anticonvulsants. ... gaba
Commonly called sweat, it is an excretion from the SKIN, produced by microscopic sweat-glands, of which there are around 2·5 million, scattered over the surface. There are two di?erent types of sweat-glands, known as eccrine and apocrine. Insensible (that is unnoticed) perspiration takes place constantly by evaporation from the openings of the sweat-glands, well over a litre a day being produced. Sensible perspiration (that is, obvious) – to which the term ‘sweat’ is usually con?ned – occurs with physical exertion and raised body temperature: up to 3 litres an hour may be produced for short periods. Normal sweating maintains the body within its customary temperature range and ensures that the skin is kept adequately hydrated – for example, properly hydrated skin of the palm helps the e?ectiveness of a person’s normal grip.
The chief object of perspiration is to maintain an even body temperature by regulating the heat lost from the body surface. Sweating is therefore increased by internally produced heat, such as muscular activity, or external heat. It is controlled by two types of nerves: vasomotor, which regulate the local blood ?ow, and secretory (part of the sympathetic nervous system) which directly in?uence secretion.
Eccrine sweat is a faintly acid, watery ?uid containing less than 2 per cent of solids. The eccrine sweat-glands in humans are situated in greatest numbers on the soles of the feet and palms of the hands, and with a magnifying glass their minute openings or pores can be seen in rows occupying the summit of each ridge in the skin. Perspiration is most abundant in these regions, although it also occurs all over the body.
Apocrine sweat-glands These start functioning at puberty and are found in the armpits, the eyelids, around the anus in association with the external genitalia, and in the areola and nipple of the breast. (The glands that produce wax in the ear are modi?ed apocrine glands.) The ?ow of apocrine sweat is evoked by emotional stimuli such as fear, anger, or sexual excitement.
Abnormalities of perspiration Decreased sweating may occur in the early stages of fever, in diabetes, and in some forms of glomerulonephritis (see KIDNEYS, DISEASES OF). Some people are unable to sweat copiously, and are prone to HEAT STROKE. EXCESSIVE SWEATING, OR HYPERIDROSIS, may be caused by fever, hyperthyroidism (see THYROID GLAND, DISEASES OF), obesity, diabetes mellitus, or an anxiety state. O?ensive perspiration, or bromidrosis, commonly occurs on the hands and feet or in the armpits, and is due to bacterial decomposition of skin secretions. A few people, however, sweat over their whole body surface. For most of those affected, it is the palmar and/or axillary hyperhidrosis that is the major problem.
Conventional treatment is with an ANTICHOLINERGIC drug. This blocks the action of ACETYLCHOLINE (a neurotransmitter secreted by nerve-cell endings) which relaxes some involuntary muscles and tightens others, controlling the action of sweat-glands. But patients often stop treatment because they get an uncomfortably dry mouth. Aluminium chloride hexahydrate is a topical treatment, but this can cause skin irritation and soreness. Such antiperspirants may help patients with moderate hyperhidrosis, but those severely affected may need either surgery or injections of BOTULINUM TOXIN to destroy the relevant sympathetic nerves to the zones of excessive sweating.... perspiration
This group of drugs is one of three main types of drugs used to treat DEPRESSION, and was the ?rst to be introduced (in the 1950s). Tricyclic drugs work by blocking the re-uptake of the neurotransmitters SEROTONIN and NORADRENALINE (see NEUROTRANSMITTER), thus increasing the amount of the neurotransmitters at the nerve cell’s receptors. In people with depression, fewer neurotransmitters than normal are released, resulting in a slowing of neural activities. The drugs have a sedative e?ect, which can be useful for depressives with sleep problems, and an antimuscarinic action which can cause dry mouth and constipation (see ANTIMUSCARINE). Overdosage can produce COMA, ?ts (see SEIZURE) and irregular heart rhythm (ARRHYTHMIA). They are sometimes used for treating bed-wetting. (See also ANTIDEPRESSANT DRUGS.)... tricyclic antidepressant drugs
adj. 1. describing nerve fibres that release noradrenaline or adrenaline as a neurotransmitter. 2. describing receptors that are stimulated by noradrenaline or adrenaline. See adrenoceptor.... adrenergic
n. any substance that inhibits the action of *cholinesterase, the enzyme that is responsible for the breakdown of the neurotransmitter acetylcholine, and therefore allows acetylcholine to continue transmitting nerve impulses. Drugs with anticholinesterase activity include *neostigmine, *pyridostigmine, and *edrophonium; their uses include the diagnosis and treatment of *myasthenia gravis. See also parasympathomimetic.... anticholinesterase
cells that share the metabolic property of amine-precursor uptake and decarboxylation. They have a wide distribution, especially in the mucosa of the gastrointestinal tract and pancreas, and their function is to synthesize and release polypeptides that serve as regulator peptides and neurotransmitters. They are often known as the diffuse neuroendocrine system.... apud cells
n. a hormone secreted by the cells of the duodenum in response to the presence of partly digested food in the duodenum. It causes contraction of the gall bladder and expulsion of bile into the intestine and stimulates the production of digestive enzymes by the pancreas (see also pancreatic juice). In the brain cholecystokinin functions as a neurotransmitter, involved in the control of satiety.... cholecystokinin
A progressive condition in which nerve cells in the brain degenerate and the brain shrinks. Alzheimer’s disease is the most common cause of dementia. Onset is uncommon before the age of 60.
Early onset Alzheimer’s disease, in which symptoms develop before age 60, is inherited as a dominant disorder. Late onset Alzheimer’s disease is associated with a number of genes, including 3 that
are responsible for the production of the blood protein apolipoprotein E. These genes also result in the deposition of a protein called beta amyloid in the brain. Other chemical abnormalities may include deficiency of the neurotransmitter acetylcholine.
The features of Alzheimer’s disease vary, but there are 3 broad stages. At first, the person becomes increasingly forgetful, and problems with memory may cause anxiety and depression. In the 2nd stage, loss of memory, particularly for recent events, gradually becomes more severe, and there may be disorientation as to time or place. The person’s concentration and numerical ability decline, and there is noticeable dysphasia (inability to find the right word). Anxiety increases, mood changes are unpredictable, and personality changes may occur. Finally, confusion becomes profound. There may be symptoms of psychosis, such as hallucinations and delusions. Signs of nervous system disease, such as abnormal reflexes and faecal or urinary incontinence, begin to develop.
Alzheimer’s disease is usually diagnosed from the symptoms, but tests including blood tests and CT scanning or MRI of the brain may be needed to exclude treatable causes of dementia.
The most important aspect of treatment for Alzheimer’s disease is the provision of suitable nursing and social care for sufferers and support for their relatives. Tranquillizer drugs can often improve difficult behaviour and help with sleep. Treatment with drugs such as donepezil and rivastigmine may slow the progress of the disease for a time, but side effects such as nausea and dizziness may occur.... alzheimer’s disease
n. an antidepressant drug that acts by prolonging the action of the neurotransmitter serotonin (5-hydroxytryptamine) in the brain (see SSRI). Side-effects may include dizziness, agitation, tremor, nausea, and diarrhoea.... citalopram
n. dihydroxyphenylalanine: a physiologically important compound that forms an intermediate stage in the synthesis of catecholamines (dopamine, adrenaline, and noradrenaline) from the essential amino acid tyrosine. It also plays a role itself in the functioning of certain parts of the brain. The laevorotatory form, *levodopa, is administered for the treatment of *parkinsonism, in which there is a deficiency of the neurotransmitter *dopamine in the brain.... dopa
A general term for a group of psychotic illnesses that are characterized by disturbances in thinking, emotional reaction, and behaviour.
Onset can be at any age but is most common in late adolescence and the early 20s, and may be triggered by stress. No causes have been identified, but many have been implicated. It is likely that inheritance plays a role. Disruption of the activity of some neurotransmitters in the brain is a possible mechanism. Brain imaging techniques have revealed abnormalities of structure and function in people with schizophrenia.
Schizophrenia may begin insidiously, with the individual becoming slowly more withdrawn and losing motivation. In other cases, the illness comes on more suddenly, often in response to external stress. The main symptoms are various forms of delusions such as those of persecution (which are typical of paranoid schizophrenia); hallucinations, which are usually auditory (hearing voices), but which may also be visual or tactile; and thought disorder, leading to impaired concentration and thought processes. Disordered thinking is often reflected in muddled and disjointed speech. Behaviour is eccentric, and selfneglect common. In a rare form of schizophrenia, catatonia may occur, in which rigid postures are adopted for prolonged periods, or there are outbursts of repeated movement.
Diagnosis of schizophrenia may take some time and, in some cases, it may be difficult to make a diagnosis at all.
Treatment is mainly with antipsychotic drugs, such as phenothiazine drugs, and new atypical antipsychotic drugs such as risperidone. In some cases, the drugs are given as monthly depot injections. Once the symptoms are controlled, community care, vocational opportunities, and family counselling can help to prevent a relapse.
Some people may make a complete recovery. However, the majority have relapses punctuated with partial or full recovery. A small proportion have a severe life-long disability.... schizophrenia
the theory that *schizophrenia is caused in part by abnormalities in the metabolism of *dopamine and can be treated in part by drugs that antagonize its action as a neurotransmitter.... dopamine hypothesis
n. the area of muscle cell membrane immediately beneath the motor nerve ending at a *neuromuscular junction. Special receptors in this area trigger muscular contraction when the nerve ending releases its *neurotransmitter.... end-plate
n. (in physiology) the coupling of the output of a process to the input. Feedback mechanisms are important in regulating many physiological processes; for example, the production of hormones and neurotransmitters. In negative feedback, a rise in the output of a substance will inhibit a further increase in its production, either directly or indirectly (see negative feedback loop). In positive feedback, a rise in the output of a substance is associated with an increase in the output of another substance, either directly or indirectly.... feedback
n. an *antidepressant drug that acts by prolonging the action of the neurotransmitter serotonin (5-hydroxytryptamine) in the brain (see SSRI). Side-effects may include sleepiness, agitation, tremor, vomiting, and diarrhoea.... fluvoxamine
any one of a class of drugs that block the action of acetylcholinesterase (see cholinesterase), an enzyme that quickly breaks down the neurotransmitter acetylcholine. This neurotransmitter is central to the functional interconnection between nerve cells in the outer layer (cortex) of the brain; the early impairment of cognitive function found in Alzheimer’s disease is associated with a reduction in acetylcholine levels. By inhibiting acetylcholine breakdown, acetylcholinesterase inhibitors have been found helpful in slowing down the rate of cognitive decline in mild to moderate dementia; they do not halt the progress of the disease. The group includes donepezil, galantamine, and rivastigmine... acetylcholinesterase inhibitor
(anticholinergic) adj. inhibiting the action of *acetylcholine, the neurotransmitter that conveys information in the parasympathetic nervous system. Antimuscarinic drugs block the effects of certain (muscarinic) receptors (hence their name). The actions of these drugs include relaxation of smooth muscle, decreased secretion of saliva, sweat, and digestive juices, and dilation of the pupil of the eye. *Atropine and similar drugs have these effects; they are used in the treatment of gut spasms (e.g. *propantheline) and of parkinsonism (e.g. *trihexyphenidyl) as bronchodilators (e.g. *ipratropium), and as *mydriatics. Characteristic side-effects include dry mouth, thirst, blurred vision, dry skin, increased heart rate, and difficulty in urination.... antimuscarinic
n. any one of a group of drugs used to treat severe mental disorders (psychoses), including schizophrenia and mania; some are administered in small doses to relieve anxiety and tic disorders or to treat impulsivity in *emotionally unstable personality disorder. Formerly called major tranquillizers, and later typical and atypical antipsychotics, they are now known as first- and second-generation antipsychotics. The first-generation (or typical) antipsychotics include the *phenothiazines (e.g. *chlorpromazine), *butyrophenones (e.g. *haloperidol), and thioxanthenes (e.g. *flupentixol). Side-effects of antipsychotic drugs can include *extrapyramidal effects, sedation, *antimuscarinic effects, weight gain, and *long QT syndrome. The second-generation (or atypical) antipsychotics are a group of more recently developed drugs that are in theory associated with fewer extrapyramidal effects than first-generation antipsychotics: they include *clozapine, *risperidone, amisulpride, aripiprazole, olanzapine, and quetiapine. Antipsychotics act on various neurotransmitter receptors in the brain, including dopamine, histamine, serotonin, and cholinergic receptors. Most of them block neurotransmitter activity, but some have partially agonistic effects. Recent evidence suggests that there are significant differences among the second-generation antipsychotics regarding their efficacy and side-effect profiles. Clozapine, amisulpride, and olanzapine were found to be the most effective antipsychotics. Clozapine, zotepine, and olanzapine caused the most weight gain; haloperidol, zotepine, and chlorpromazine caused the most extrapyramidal side-effects; sertindole, amisulpride, and ziprasidone caused the most QT-prolongation; and clozapine, zotepine, and chlorpromazine caused the most sedation.... antipsychotic
(GABA) an amino acid found in the central nervous system, predominantly in the brain, where it acts as an inhibitory *neurotransmitter.... gamma-aminobutyric acid
(glutamate) see amino acid; neurotransmitter.... glutamic acid
n. a *neurohormone or a *neurotransmitter.... neurohumour
(myoneural junction) the meeting point of a nerve fibre and the muscle fibre that it supplies. Between the enlarged end of the nerve fibre (motor end-plate) and the membrane of the muscle is a gap across which a *neurotransmitter must diffuse from the nerve to trigger contraction of the muscle.... neuromuscular junction
a receptor on synapses that binds the *neurotransmitter glutamate and also binds its *agonist NMDA (N-methyl-D-aspartate). This receptor is involved in learning, memory, mood, and cognition; its overactivity is associated with chronic pain. NMDA-receptor antibodies are associated with an *encephalitis preceded by psychiatric symptoms, often in patients with ovarian malignancy (teratoma). NMDA-receptor antagonists (e.g. *amantadine, *memantine hydrochloride, *riluzole) are used in the treatment of (among other conditions) epilepsy, Alzheimer’s disease, and chronic pain syndromes.... nmda receptor
a condition characterized by inappropriate and sometimes severe anxiety, without adequate cause, that lasts for at least six months. It affects about 2% of the population, women twice as often as men, and often develops in early adult life. It can, however, start at any age. There is a hereditary tendency to develop the disorder and about 25% of immediate relatives of sufferers are also affected. The disorder is thought to be caused by a disturbance of the functions of neurotransmitters, such as adrenaline or GABA, in the frontal lobes or the *limbic system of the brain. Symptoms affect all parts of the body. Palpitations, sweating, tremor, and dry mouth are core symptoms; additional symptoms include giddiness, *bruxism, restlessness, fatigability, breathlessness, lightheadedness, headaches, pins and needles, chest pain, fear of imminent death or losing control, diarrhoea, flushing, dysphagia, cramps, and muscle ache. Treatment includes *cognitive behavioural therapy and medication (*SSRIs or *SNRIs).... generalized anxiety disorder
a chronic disease marked by abnormal fatigability and weakness of selected muscles, which is relieved by rest. The degree of fatigue is so extreme that these muscles are temporarily paralysed. The muscles initially affected are those around the eyes, mouth, and throat, resulting in drooping of the upper eyelids (*ptosis), double vision, *dysarthria, and *dysphagia. Myasthenia gravis is an *autoimmune disease in which acetylcholine-receptor autoantibodies bind to cholinergic receptors on muscle cells, which impairs the ability of the neurotransmitter acetylcholine to induce muscular contraction. Treatment with *anticholinesterase drugs and surgical removal of the thymus in younger patients (under the age of 45 years) lessen the severity of the symptoms. Steroid therapy, intravenous immunoglobulin treatment, and plasma exchange may be used to treat the more severely affected patients.... myasthenia gravis
(norepinephrine) n. a hormone, closely related to *adrenaline and with similar actions, secreted by the medulla of the *adrenal gland and also released as a *neurotransmitter by sympathetic nerve endings. Among its many actions are constriction of small blood vessels leading to an increase in blood pressure, increased blood flow through the coronary arteries and a slowing of the heart rate, increase in the rate and depth of breathing, and relaxation of the smooth muscle in intestinal walls.... noradrenaline
n. a drug used to control severe nausea and vomiting, especially when it results from chemotherapy and radiotherapy. Ondansetron works by opposing the action of the neurotransmitter *serotonin (5-hydroxytryptamine) at 5HT3 receptors. Side-effects include constipation, headache, and flushing. Related drugs with similar actions and effects include granisetron and palonosetron.... ondansetron
adj. opposing the effects of the *parasympathetic nervous system. *Antimuscarinic drugs have this effect by preventing acetylcholine from acting as a neurotransmitter.... parasympatholytic
n. an antidepressant drug that acts by prolonging the action of the neurotransmitter serotonin (5-hydroxytryptamine) in the brain (see SSRI). It is taken by mouth for the treatment of depression, obsessive–compulsive disorder, panic disorder, post-traumatic stress disorder, and some other anxiety disorders; side-effects may include nausea, indigestion, abdominal pain, diarrhoea, and rash. Because of its short half-life paroxetine is often associated with *discontinuation syndrome upon stopping.... paroxetine
n. an *antidepressant drug that acts by inhibiting reabsorption of the neurotransmitter *noradrenaline, thus prolonging its action in the brain. Side-effects include dry mouth, constipation, insomnia, and dizziness.... reboxetine
n. an antidepressant drug that acts by prolonging the action of the neurotransmitter serotonin (5-hydroxytryptamine) in the brain (see SSRI). It is taken for the treatment of depression, obsessive–compulsive disorder, and panic disorder; side-effects may include dizziness, agitation, tremor, nausea, diarrhoea, and drowsiness.... sertraline
n. an amino acid that is a constituent of the *bile salt taurocholate and also functions as a *neurotransmitter in the central nervous system.... taurine
(vasoactive intestinal peptide) a peptide hormone and neurotransmitter found widely throughout the central nervous system and the gastrointestinal tract. It has numerous actions, including vasodilatation of blood vessels in the gut, reduction of acid secretion by the stomach, and enhanced secretion of electrolytes into the small bowel.... vip
n. 1. a cell or group of cells specialized to detect changes in the environment and trigger impulses in the sensory nervous system. All sensory nerve endings act as receptors, whether they simply detect touch, as in the skin, or chemical substances, as in the nose and tongue, or sound or light, as in the ear and eye. See exteroceptor; interoceptor; mechanoreceptor; proprioceptor. 2. a specialized area of a cell membrane, consisting of a specially adapted protein, that can bind with a specific hormone (e.g. *oestrogen receptors), neurotransmitter (e.g. *adrenoceptors), drug, or other chemical, thereby initiating a change within the cell.... receptor
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