Download 5-7_Co-existanceNeurotransmitters_SimonT

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Co-existence of amine and/or peptide transmitters in the vast majority of neurons.
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Communication of information between neurons is accomplished by movement of chemicals across
a small gap called the synapse. Chemicals, called neurotransmitters, are released from one neuron at
the presynaptic nerve terminal. Neurotransmitters then cross the synapse where they may be
accepted by the next neuron at a specialized site called a receptor. The action that follows activation
of a receptor site may be either depolarization (an excitatory postsynaptic potential) or
hyperpolarization (an inhibitory postsynaptic potential). A depolarization makes it MORE likely that
an action potential will fire; a hyperpolarization makes it LESS likely that an action potential will fire.
And for this type of communications Neurons uses amine or peptide transmitters.
Peptide:
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Neuropeptides are small protein-like molecules (peptides) used by neurons to communicate with
each other. They are neuronal signaling molecules that influence the activity of the brain and the
body in specific ways. Different neuropeptides are involved in a wide range of brain functions,
including analgesia, reward, food intake, metabolism, reproduction, social behaviors, learning and
memory.
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Neuropeptides modulate neuronal communication by acting on cell surface receptors. Many
neuropeptides are co-released with other small-molecule neurotransmitters. The human genome
contains about 90 genes that encode precursors of neuropeptides. At present about 100 different
peptides are known to be released by different populations of neurons in the mammalian brain.[2]
Neurons use many different chemical signals to communicate information, including
neurotransmitters, peptides, and gasotransmitters. Peptides are unique among these cell-cell
signaling molecules in several respects. One major difference is that peptides are not recycled back
into the cell once secreted, unlike many conventional neurotransmitters (glutamate, dopamine,
serotonin). Another difference is that after secretion, peptides are modified by extracellular
peptidases; in some cases, these extracellular cleavages inactivate the biological activity, but in other
cases the extracellular cleavages increase the affinity of a peptide for a particular receptor while
decreasing its affinity for another receptor. These extracellular processing events add to the
complexity of neuropeptides as cell-cell signaling molecules.
Generally, peptides act at metabotropic or G-protein-coupled receptors expressed by selective
populations of neurons. In essence they act as specific signals between one population of neurons
and another. Neurotransmitters generally affect the excitability of other neurons, by depolarising
them or by hyperpolarising them. Peptides have much more diverse effects; amongst other things,
they can affect gene expression, local blood flow, synaptogenesis, and glial cell morphology. Peptides
tend to have prolonged actions, and some have striking effects on behaviour.
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Amine:
A catecholamine is a monoamine, an organic compound that has a catechol (benzene with two
hydroxyl side groups at carbons) and a side-chain amine.
The three catecholamine neurotransmitters:
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Norepinephrine (noradrenaline)
a neurotransmitter involved in sleep and wakefulness, attention, and feeding behavior, as
well as a stress hormone released by the adrenal glands that regulates the sympathetic
nervous system.
The general function of norepinephrine is to mobilize the brain and body for action.
Norepinephrine release is lowest during sleep, rises during wakefulness, and reaches much
higher levels during situations of stress or danger, in the so-called fight-or-flight response. In
the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances
formation and retrieval of memory, and focuses attention; it also increases restlessness and
anxiety. In the rest of the body, norepinephrine increases heart rate and blood pressure,
triggers the release of glucose from energy stores, increases blood flow to skeletal muscle,
reduces blood flow to the gastrointestinal system, and inhibits voiding of the bladder and
gastrointestinal motility.
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Epinephrine (adrenaline)
an adrenal stress hormone, as well as a neurotransmitter present at lower levels in the
brain.
Epinephrine, also known as adrenalin or adrenaline, is primarily a medication and a
hormone. As a medication it is used for a number of conditions including anaphylaxis, cardiac
arrest, and superficial bleeding. Inhaled epinephrine may be used to improve the symptoms
of croup. It may also be used for asthma when other treatments are not effective. It is given
intravenously, by injection into a muscle, by inhalation, or by injection just under the skin.
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Dopamine
a neurotransmitter involved in motivation, reward, addiction, behavioral reinforcement, and
coordination of bodily movement.
In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons
(nerve cells) to send signals to other nerve cells. The brain includes several distinct dopamine
pathways, one of which plays a major role in reward-motivated behavior. Most types of
reward increase the level of dopamine in the brain, and many addictive drugs increase
dopamine neuronal activity. Other brain dopamine pathways are involved in motor control
and in controlling the release of various hormones. These pathways and cell groups form a
dopamine system which is neuromodulatory.
Outside the central nervous system, dopamine functions in several parts of the peripheral
nervous system as a local chemical messenger. In blood vessels, it inhibits norepinephrine
release and acts as a vasodilator (at normal concentrations); in the kidneys, it increases
sodium excretion and urine output; in the pancreas, it reduces insulin production; in the
digestive system, it reduces gastrointestinal motility and protects intestinal mucosa; and in
the immune system, it reduces the activity of lymphocytes. With the exception of the blood
vessels, dopamine in each of these peripheral systems is synthesized locally and exerts its
effects near the cells that release it.
Resources used:
https://en.wikipedia.org/wiki/Catecholamine
https://en.wikipedia.org/wiki/Biogenic_amine
https://www.ncbi.nlm.nih.gov/pubmed/21922398
https://en.wikipedia.org/wiki/Neurotransmitter
https://en.wikipedia.org/wiki/Neuropeptide
https://en.wikipedia.org/wiki/Peptide
http://thebrain.mcgill.ca/flash/i/i_01/i_01_m/i_01_m_ana/i_01_m_ana.html#2
https://faculty.washington.edu/chudler/chnt1.html