Mediators of the nervous system. What is a mediator: definition, types and functions What is a mediator in biology

In this article, we will get acquainted with the answer to the question, what are mediators? The main attention will be paid to the definition of neurotransmitters that are in our brain and cause various emotional manifestations, behavioral reactions of the subject, etc. In particular, we will look at the definition of the term, species diversity and impact.

Introduction

What is a mediator?

Answering this question, it will be important to find out that this concept exists in different spheres of human activity. Mediators can be:

A neurotransmitter is a chemically active substance of a biological nature necessary for the transmission of nerve impulses between cells.
Mediator - a device for musical instruments, in particular, for the guitar.
The design template is called a mediator.
A mediator is a 3rd neutral person, an entity that mediates a conflict and/or dispute and tries to help resolve it.
In a computer, a mediator is the process of using and managing data storage work when performing a procedure to stop or start a particular service.
Allergy mediators of the circulating and secreted type are participants in the responses of the immune system. However, in addition to allergies, there are other manifestations of the effect of the mediator on the body.

Drugs of medicinal origin are also called a mediator, in particular, they are called "Benfluorex". Nerve transmitters carry out the function of transporting signals through special cells that form our CNS and PNS.

A neurotransmitter is...

Neurotransmitters are substances of biological origin. They are chemically active and act as intermediaries in the process of transferring electrochemical impulses from nerve cells through the synaptic spaces between neutrons to other similar cells, but located on different parts of the reflex arc path (the path of the nerve impulse). During the arrival of a nerve impulse at the presynaptic ending, the mediator is released into the synaptic target.

Learn more about the interaction mechanism

Molecules represented by mediators are able to react with certain types of receptor proteins that make up the cell membrane. This interaction leads to the initiation of a chain of reactions of a biochemical nature. There is a change in the intermembrane ion flow, which causes the depolarization of the membrane and the further occurrence of an action potential. For example, an unconditioned reflex, in which a person pulls his hand away from a hot object, is a process of activity of nerve cells and the transmission of an electrical impulse with its further analysis and solution of the “problem” in the form of a response signal, carried out during signal transmission between cells, as described above .

The mediators of the nervous system are one of the main systems of our body, which in the course of evolution allowed a person to achieve a similar level of organization.

Amino acids

All neurotransmitters are usually divided into three groups: peptides, monoamines and amino acid molecules. The brightest representatives of amino acids are:

GABA (gamma-aminobutyric acid) is the main CNS neurotransmitter responsible for the inhibitory functions of any mammal, including humans.
Glycine - has a dual amino acid action. Glycine receptors are located almost throughout the spinal cord and brain. By establishing a connection with the receptor, this substance causes "inhibition" of the effect on neurons. It also reduces the production of the "excitatory" series of amino acids from neuronal cells. Glycine affects the release of GABA, increasing the performance of this neurotransmitter. It also allows signal transduction from glutamates and aspartates, excitatory neurotransmitters. For the spinal cord, glycine acts as a mediator that inhibits the reactions of motor neurons.
Glutamic acid is an excitatory neurotransmitter, the most common neurotransmitter nervous system any vertebrate animal. Most of it is in the cerebellum and spinal cord.
One of the types of mediators is represented by molecules of aspartic acid (aspartate). They are responsible for the excitation of neurotransmitters located in the cerebral cortex.

The concept of catecholamines

Answering the question of what mediators are and what types they are, it will be important to mention catecholamines. Substances of this class are divided into such hormones as:

Adrenaline is an excitatory neurotransmitter. Its role in synaptic transmission is currently not fully understood. This also applies to bombesin, bradykinin, carnosine, neurotensin, somatostatin, cholecystokinin and VIP.
Norepinephrine is a wakefulness mediator. He is a participant in the process of rising reticular active system(net formation responsible for maintaining constant excitation in the brain of the head). This neurotransmitter is characteristic of the bluish spot located in the brain stem, as well as the end sections of the sympathetic nervous system. There are very few noradrenergic neurons in the CNS, however, they have a wide field of innervation.
Dopamine - chemical factor internal maintenance; is a significant component of the system responsible for encouraging the consciousness of the subject. Able to cause a feeling of pleasure at different levels (anticipation or specific satisfaction), which plays an important role in the processes of motivation and / or learning.

Various monoamines

Another point that is important when getting acquainted with the answer to the question of what mediators are, will be the description of monoamines.

Typical monoamines are histamine and serotonin. We have already defined histamine above, but it is worth adding that its various lipophilic antagonists may have sedative properties. This is due to their ability to block histamine receptors.

About serotonin

Serotonin is a CNS neurotransmitter. Neurons of serotonergic action gather in groups in the region of the brainstem, namely, in the pons varolii and raphe nuclei. The brain has downward projections that descend further into the spinal cord. The neurons of the nuclei are responsible for supplying ascending projections to the limbic system, the cerebellum, the basal ganglia, and the cortex. The dorsal and medial neurons of the raphe nuclei include axons that differ in the final target of innervation, as well as sensitivity to certain substances. An example of such compounds is methamphetamine.

There are many other types of mediators. For example, acetylcholine, adenosine triphosphoric acid, anandamides, vasoactive intestinal peptides (VIP), tryptamines, taurine, and endocannabionoids. Separately, it is worth mentioning the NAAG neurotransmitter - N-acetylaspartyl humate.

Impact

The functions of mediators depend on the characteristics of their chemical structure. They act as primary messengers, along with hormones. However, the process of their release and the arrangement of the mechanism of action in the chemical synapse has a number of extremely important differences that distinguish them from hormones.

The mediator system in the presynaptic cell vesicle, which has a neurotransmitter, is able to release it at a local level into an extremely small synaptic cleft. The "released" molecule diffuses and binds to a number of receptors located on the surface of postsynaptic membranes. Diffusion is a slow process, but the presence of such short distances, separating the post- and presynaptic space (from 0.1 microns and less) allows this signal transmission to occur in a short period of time. This allows you to quickly establish signals between the neurons themselves and muscle tissues. The lack of certain neurotransmitters causes depression in various forms.

Inflammation

Inflammatory mediators are another type of mediators that are involved in the inflammation process. The phenomenon of immunity is a general biological "incident". Its most striking manifestation is observed at the stage of "local reaction". This is the initial phase of the phenomenon. Alteration (a process similar to necrosis, but differing from it in the absence of cell death) causes the onset of many biochemical processes that contribute to the involvement of inflammatory mediators. Under their influence, there is a structural transformation of the tissue and its metabolic processes. This allows inflammatory reactions to develop. These mediators are of two types: cellular and plasma. The last mediators work on the principle of a cascade device, activating each other.

MEDIATORS of the nervous system(lat. mediator mediator; synonym: neurotransmitters, synaptic transmitters) - chemical transmitters of a nerve impulse from the nerve ending to the cells of peripheral organs or to nerve cells. Most often, low molecular weight (150-300 daltons) substances that perform other functions in the human and animal body act as Medtators. Mediators include acetylcholine (see), various catecholamines (see), in particular norepinephrine (see), some amino acids (see), peptides (see) and other biologically active substances. Mediators' research has yielded important practical results for the clinic. It turned out that in a number of diseases of the nervous system, some types of poisoning, the formation of M., the mechanism of their action and decay are disturbed. Knowledge of chem. M.'s transformations in the norm and in pathology made it possible to recommend and introduce new methods of drug treatment.

The hypothesis of the existence of substances mediating nerve influences arose at the beginning of the 20th century. Initially, it was based on the experience of pharmacology (imitation of sympathetic nerve influences by some exogenous substances, and parasympathetic - by others) and applied only to peripheral neuroeffector compounds. Elliott (Th. R. Elliott, 1904) called adrenaline a substance that could mediate the action of sympathetic nerves on effector organs. Experimental existence of OD. autonomic nerves proved in 1921 aust. pharmacologist O. Levi, who established that the heart perfusate after irritation of the vagus nerve is capable of exerting a vaga-like effect. On this basis, M. was originally called the humoral factors of nervous excitation. Subsequently, this name was abandoned, since it became clear that M.'s entry into the blood is a side and optional consequence of the process of synaptic transmission.

In the 20s. 20th century The M. of parasympathetic influences has been identified as acetylcholine. The role of adrenaline as a sympathetic M. in mammals in the 30s. has been revised. W. Cannon proposed to call the agents circulating in the blood and having a sympathomimetic effect, sympathins. The term "sympathy" meant a complex of M.'s own sympathetic nerves with some kind of factor. produced by the effector tissue. The sympathetic hypothesis turned out to be wrong. In 1946, Y. Euler identified the sympathetic M. of mammals as a compound close to adrenaline, norepinephrine.

The type of mediators of autonomic neuroeffector connections is not in all cases determined by their belonging to one or another department in c. n. With. In this regard, there was an assumption that it is specific for cellular, and not for anatomical units of the nervous system. G. Dale (1933) proposed to call the nerve fibers that secrete acetylcholine cholinergic, and the fibers that secrete adrenaline (actually norepinephrine) - adrenergic.

The content of the concept of "mediators" changed after A. F. Samoilov (1924) formulated a hypothesis about M.'s participation in the transmission of signals from neuron to neuron. He showed that the transition of excitation from the motor nerve to the skeletal muscle is a process qualitatively different from the conduction of excitation along the nerve or muscle: the transmission link is dominated by chemical components, and during the implementation - physical. Adhering to the generally accepted idea that the transmission mechanism is the same in the motor end plate and in the interneuronal synapse, A.F. Samoilov abandoned the hypothesis of the electrical nature of synaptic transmission. Experimental evidence of Samoilov's hypothesis about M.'s participation in signal transmission from neuron to neuron was obtained by A. V. Kibyakov in 1933.

A significant contribution to understanding the mechanisms of action of M. was also made by Soviet scientists A. G. Ginetsinsky, X. S. Koshtoyants, M. Ya. . in the USSR, work began on the use of M. for the treatment of nervous diseases.

M.'s participation in carrying out excitation is represented as follows. The place of M.'s application is the synapse (see). Its presynaptic link can be a neuron (see Nerve cell), or a receptor cell (eg, rods and cones of the retina, hair cells of the organs of hearing and balance). The presynaptic cell, apparently, is characterized by mediator specificity, i.e., the ability to synthesize, store, secrete and reutilize a strictly defined M. The cytoplasmic organelles in which M. are stored and through which they are released from the cell serve, according to the vesicular hypothesis of M. secretion. , special vesicles surrounded by a membrane. The section of the presynaptic cell specialized for secretion (in the neuron - the terminal parts of the axon, and sometimes dendrites) has a special external so-called. a secretory membrane, for a cut presence of potential-dependent calcium channels is characteristic. Secretion is caused by the incoming current of calcium ions, which occurs when the presynaptic cell is depolarized (i.e., when it is excited). The subtle mechanisms of action of calcium ions on synaptic vesicles have not yet been studied; apparently, secretion proceeds according to the type of exocytosis: the vesicle membrane is connected to the outer cell membrane so that an opening is formed, through which the contents of the vesicle enter the intercellular environment.

Having entered the synaptic cleft, M. diffuses to the postsynaptic cell and interacts with its specific receptors, as a result of which one or another change occurs in the state of the cell. This regulatory effect is most often based on a change in the ionic conductivity of the postsynaptic membrane.

The number of chem. compounds attributable to M., has a strong upward trend. Traditionally, the mediator function of a substance must be proved with maximum rigor. After proof for at least one case of synaptic transmission, this substance is considered true M. There are two criteria for assigning a substance - the so-called. candidate for mediators to actually synaptic transmitters (i.e., mediators): accumulation criterion - with fiziol. stimulation of the presynaptic structure, the “candidate” substance should be released from it in an amount proportional to the number of stimuli applied; the criterion for the identity of the action is that the influence of the “candidate” substance on the postsynaptic structure should be similar in its final effect and in molecular mechanisms to the action of a natural synaptic transmitter. Practical difficulties in establishing these two criteria encourage researchers to use additional, indirect criteria.

For each M. they try to find the most characteristics, making it possible to detect cellular systems with this M. Using various histochemical methods, in particular formaldehyde condensation, it was possible to map in detail the systems of monoaminergic brain neurons. However, direct histochem. localization is still possible only for a few M. A more promising and universal method is considered immunohistochemical, the identification of an enzyme involved in the synthesis of a given M. or another specific protein associated with a certain M. For this purpose, the ability of neurons to recycle their own M is also used. the neuron medium is injected with M. or its metabolic precursor with some (eg, radioactive) label and the subsequent distribution of the label is studied. The study of the morphology of the secretory vesicles of the presynaptic cell with the help of an electron microscope also helps to judge belonging to one or another known type of M..

Distribution of the neurons possessing the same M., and their functions are similar at systematically close organisms. This similarity can be traced within only one zool, type and is not observed when comparing different types (eg, vertebrates, arthropods and mollusks). However, organisms belonging to different zool types have the same mediator substances, i.e., a similar cellular composition of the nervous systems. This indicates the deep antiquity of mediator differences between neurons and the conservatism of the specific secretory chemistry of nerve cells.

A significant part of the known M. belongs to the group of biogenic amines (see), to-ruyu are decarboxylated derivatives of aromatic amino acids (the so-called arylethylamines). This group includes catecholamine M. The oldest (from an evolutionary point of view) of them is, apparently, dopamine, presented in a special category of neurons in most organisms that have a nervous system. The mediator function of dopamine has been proven in the giant interneuron of the pedal ganglion of some aquatic snails. In mammals, the systems of dopaminergic neurons are located mainly in the midbrain - the nigroneostriatal system (see Limbic system). In addition, neurons of this type are found in the hypothalamic region, in the retina. Assume that dopamine acts as M. interneurons of sympathetic ganglia (neuronal variant of chromaffin cells). Function of norepinephrine as M. is most studied in the neuroeffector terminations of sympathetic nerves. Groups of holes of adrenergic neurons are also found in the midbrain, cerebral pons, medulla oblongata and diencephalon. Adrenaline, which is a methylated derivative of norepinephrine, serves as the M. of sympathetic neurons in anurans. In the medulla oblongata of mammals, small groups of neurons synthesizing adrenaline have been found, but the question of the mediator function of adrenaline in them has not yet been studied enough.

The widespread biogenic amine serotonin (see) is a derivative of tryptophan. The mediator function of serotonin was first shown in shellfish. Serotonergic neurons of some nuclei of the brain stem innervate vast areas of c. n. With. mammals, including neocortex, hippocampus, hypothalamus, spinal cord. Serotonin-containing neurons are also found in the intestinal plexus in some vertebrates.

Acetylcholine is the only known ether mediator (choline acetic acid ester). The mediator function of acetylcholine has been studied in detail on some neuroeffector junctions and interneuronal synapses of the peripheral nervous system in vertebrates. Their peripheral secretory terminals originate from the following groups of cholinergic neurons: cells of the motor nuclei innervating skeletal muscles; spinal neurons innervating chromaffin tissue; preganglionic neurons innervating cells of intramural and extramural ganglia; a significant part of peripheral neurons, especially intramural ganglia. Cholinergic neurons have been found in many invertebrates, some of them are well studied (motor neurons of the stomatogastric system and some afferent neurons of crustaceans, interneurons of the central ganglia of mollusks, motor neurons of the somatic muscles of round and annelids, etc.). Interneurons of the brain and spinal cord have been studied much worse due to methodological difficulties in identifying cholinergic neurons. The data on the basis of which the identification of cholinergic neurons was based on histochemical detection of acetylcholinesterase should be considered largely erroneous.

Some M. are amino acids (see). In particular, glycine serves for some interneurons of the spinal cord and medulla oblongata. Glutamine to - that - M. excitatory, and gamma-aminobutyric to - that - inhibitory motoneurons of somatic muscles of arthropods; both of these M., apparently, are widely presented in a brain of mammals. "Candidates for mediators" are also aspartic acid, taurine and beta-alanine.

Histamine (a decarboxylation product of the amino acid histidine) is one of the "candidates for mediators". Methodological difficulties do not allow us to fully resolve the issue of its mediator role in the brain of vertebrates. Nevertheless, the discovery of large histaminergic neurons in the cerebral ganglia of some molluscs serves to some degree evidence of the mediator function of histamine. Two derivatives of tyrosine, tyramine and octopamine, are also considered as “candidates for mediators”.

Apparently, neurons are widespread, in which the mediator function is performed by peptides built from a small number of amino acids (oligopeptides), in particular substance P (a peptide consisting of I amino acids), as well as endogenous opiates - endorphins, enkephalins (see Endogenous opiates ). Hypothalamic neurohormones of some secretory terminals of the corresponding axons perform M.'s function, acting on a nearby cellular target. Apparently, some peptides of the enteric (zhel.-kish.) group of hormones can serve as possible M.. ATP or its derivatives are the most likely "candidates for mediators" in some neuromuscular compounds went. - kish. tract of vertebrates.

Bibliography: Buck 3. M. Chemical transmission of a nerve impulse, per. from French, Moscow, 1977; Glebov R. N. and Kryzhanovsky G. N. Functional biochemistry of synapses, M., 1978; Zefirov L. N. and Rakhmankulova G. M. Mediators, Exchange, Physiological role and pharmacology, Kazan, 1975; Kibyakov A. V. On the humoral transfer of excitation from one neuron to another, Kazansk, honey. journal, "N" 5-6, p. 457, 1933; Samoilov A.F. On the transition of excitation from the motor nerve to the muscle, Sat. dedicated. 75th anniversary of I. P. Pavlov, ed. V. L. Omelyansky and L. A. Orbeli, p. 75, L., 1924; Gerschenf eld H. M. Chemical transmission in invertebrate central nervous systems and neuromuscular junctions, Physiol. Rev., v. 53, p. 1, 1973, bibliogr.; Krnjevi 6 K. Chemical nature of synaptic transmission in vertebrates, ibid., v. 54, p. 418, 1974; Loewi O. Uber hu-morale Ubertragbarkeit der Herznerven-wirkung, Pfliigers Arch. ges. Physiol., Bd 189, S. 239, 1921, Bd 193, S. 201, 1922; McLennan H. Synaptic transmission, Philadelphia, 1970.

D. A. Sakharov.

MEDIATORS MEDIATORS

(from lat. mediator - mediator), neurotransmitters, physiologically active substances, through which contact intercellular interactions are carried out in the nervous system; produced by nerve and receptor cells. M.'s molecules are released into the intercellular environment (synaptic cleft) by a section of the presynaptic surface membrane specialized for secretion. cells (source M.) and diffuse to the postsynaptic receptor membrane. cells; reaction between M. and a receptor serves as an initial link synaptic. transmission (see SYNAPSE). This process can be very fast (units of ms) and can be repeated at a high frequency, since synaptic. the gap is usually small (20-50 nm) and an effective mechanism for removing M. operates in it (enzymatic inactivation, reuptake by the presynaptic cell, etc.). The nervous and receptor cells producing M. are characterized by chemical. specificity, i.e., the ability to synthesize, accumulate and secrete a secret of a certain composition. M. concentrate in cytoplasmic. bubbles (so-called synaptic. vesicles), accumulations to-rykh are characteristic of presynaptic. sections of the neuron (terminal extensions of the axon, sometimes dendrites). They are removed from the cell by a mechanism called. exocytosis: the membrane of the vesicle connects to the superficial secretory membrane so that a hole is formed, through which the contents of the vesicle enter the intercellular environment. The intensity of the secretory process is regulated by Ca2+ ions. M. are ambivalent, that is, each of them is able to provide different, including opposite, synaptic. effects. The sign of the effect (excitation, inhibition), as well as its speed, is determined by Ch. arr. type of ion channels postsynaptic. membranes that open or close when M. interacts with the receptor. Acetylcholine, dopamine, norepinephrine, adrenaline, serotonin, histamine, octopamine, a number of neuropeptides (enkephalins, somatostatin, etc.), certain amino acids (glutamic, aspartic, glycine, gamma-aminobutyric, possibly taurine, etc.) belong to M. The number of the substances possessing mediator function increases in process of studying, hl. arr. due to physiologically active peptides of the nervous tissue - neuropeptides. In addition, cells specialized for the synthesis and secretion of substances similar to known peptide hormones (angiotensin, neurotensin, etc.) were found in the nervous tissue, for some of them a mediator function has already been shown. M.'s diversity is inherent in all organisms with a nervous system, while in animals belonging to different systematic. groups, similar sets of specific are observed. neurons. Obviously, mediator differences between neurons are an ancient, conservative feature of neuronal systems, essential for their functioning.

.(Source: "Biological Encyclopedic Dictionary." Chief editor M. S. Gilyarov; Editorial board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected . - M .: Sov. Encyclopedia, 1986.)

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Picks (lat. mediator mediator: a synonym for neurotransmitters)

biologically active substances secreted by nerve endings and causing the transmission of nerve impulses in synapses. The most various substances. In total, there are about 30 types of mediators, but only seven of them (, norepinephrine, serotonin, gamma-aminobutyric acid, and glutamic acid) are usually referred to as "classical" mediators.

M.'s participation in transfer of a nervous impulse is represented as follows. The section of the presynaptic cell specialized for the secretion of M. has a special outer so-called secretory membrane, which, when the presynaptic cell is excited, forms a membrane vesicle containing M. The contents of the vesicle then pours into the synaptic cleft, diffuses to the postsynaptic membrane, where it interacts with its specific receptors. When studying the action of M. on peripheral organs and ts.n.s. identified different types receptors to the same mediator (m-, n-cholinergic receptors, α-, β-adrenergic receptors, etc.). Their separation is based on the features of biochemical reactions occurring in the system -. For example, in m-receptors it is muscarine-like (they are not sensitive to poison), in n-receptors it is nicotine-like (sensitive to curare poison). The interaction of mediators with α-receptors causes an excitatory effect (constriction of blood vessels, uterus, etc.): with β-receptors - inhibitory effects (vasodilation, relaxation of the bronchi). However, α - and β-receptors located in different organs may respond differently to. Depending on the nature of the interaction of α- and β-receptors with various M., these receptors are respectively divided into α 1 -, α 2 -, β 1 - and β 2 -adrenergic receptors.

The main part of the "classical" mediators refers to biogenic amines. The phylogenetically oldest of these is dopamine. In mammals and humans, dopaminergic neurons are concentrated predominantly in the midbrain nigrostriatal system (see Limbic system) , as well as in the hypothalamus and retinal neurons. It is believed that dopamine is a mediator of interneurons of sympathetic ganglia (see Autonomic nervous system) . Assume the existence of two types of dopamine receptors - D 1 and D 2. The effect of dopamine on is due to its ability to release norepinephrine from presynaptic cell membranes; specific action (through dopamine receptors) is accompanied by a decrease in renal vascular resistance, an increase in blood flow and glomerular filtration.

Along with direct excitation or inhibition of the target cell, mediators in some cases act on, strengthening and reducing other mediators from it. It was considered to be that separate secretes only one M. (Dale's principle). However ability of the same cells to synthesize M. of different types is found. Most often, the following combinations of secretions by the same cell are noted: classical mediators and neuropeptides (serotonin + substance P, serotonin + thyrotropin, norepinephrine + somatostatin, norepinephrine + enkephalin, norepinephrine + pancreatic, dopamine +, acetylcholine + vasoactive intestinal polypeptide).

The principles of pharmacotherapy of the pathochemical stage of allergic reactions are based on the suppression of the synthesis of mediators, the processes of their release from cells, and the inhibition of the effect on effector organs (see Antiallergic drugs) .

Bibliography: Ado A.D. General, M., 1978; Gushchin I. S. Immediate cells, M., 1976: , ed. W. Paul, . from English, vol. 1, p. 437. M., 1987; Lieberman F.L. and Crawford G.W. patients with allergies, trans. from English, p. 103. M., 1986; Medunitsyn N.V. Hypersensitivity of the delayed type, p. 41, M., 1983; Brain, trans. from English, ed. P.V. Simonova, p. 148, M., 1984; Pytsky V.I., Adrianov N.V. and Artomasova A.V. Allergic diseases, p. 29. M., 1984; man, ed. R. Schmidt and G. Thevs, trans. from English, vol. 1, p. 99, M., 1985; Yalkut S . I. and Kotova S.A. Cyclic nucleotides and features of homeostasis in allergy, p. 47, Kyiv, 1987.

1. Small medical encyclopedia. - M.: Medical Encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic dictionary of medical terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what "Mediators" are in other dictionaries:

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