Neurotransmitter and Related Topics

Dopamine

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Neuromodulatory molecule that plays several important roles in cells.

Dopamine processing in a synapse. After release dopamine can either be taken up again by the presynaptic terminal, or broken down by enzymes.
TH: tyrosine hydroxylase
DOPA: L-DOPA
DAT: dopamine transporter
DDC: DOPA decarboxylase
VMAT: vesicular monoamine transporter 2
MAO: Monoamine oxidase
COMT: Catechol-O-methyl transferase
HVA: Homovanillic acid

Major dopamine pathways. As part of the reward pathway, dopamine is manufactured in nerve cell bodies located within the ventral tegmental area (VTA) and is released in the nucleus accumbens and the prefrontal cortex. The motor functions of dopamine are linked to a separate pathway, with cell bodies in the substantia nigra that manufacture and release dopamine into the dorsal striatum.

Main circuits of the basal ganglia. The dopaminergic pathway from the substantia nigra pars compacta to the striatum is shown in light blue.

Illustration of dopaminergic reward structures

Dopamine HCl preparation, single dose vial for intravenous administration

Cocaine increases dopamine levels by blocking dopamine transporters (DAT), which transport dopamine back into a synaptic terminal after it has been emitted.

Methamphetamine hydrochloride also known as crystal meth

Dopamine can be found in the peel and fruit pulp of bananas.

In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons (nerve cells) to send signals to other nerve cells.

Neuron

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Electrically excitable cell that communicates with other cells via specialized connections called synapses.

Schematic of an anatomically accurate single pyramidal neuron, the primary excitatory neuron of cerebral cortex, with a synaptic connection from an incoming axon onto a dendritic spine.

Diagram of a typical myelinated vertebrate motor neuron

Golgi-stained neurons in human hippocampal tissue

Actin filaments in a mouse cortical neuron in culture

Image of pyramidal neurons in mouse cerebral cortex expressing green fluorescent protein. The red staining indicates GABAergic interneurons.

SMI32-stained pyramidal neurons in cerebral cortex

Different kinds of neurons:
1 Unipolar neuron
2 Bipolar neuron
3 Multipolar neuron
4 Pseudounipolar neuron

Synaptic vesicles containing neurotransmitters

A signal propagating down an axon to the cell body and dendrites of the next cell

An annotated diagram of the stages of an action potential propagating down an axon including the role of ion concentration and pump and channel proteins.

As long as the stimulus reaches the threshold, the full response would be given. Larger stimulus does not result in a larger response, vice versa.

Drawing by Camillo Golgi of a hippocampus stained using the silver nitrate method

Drawing of a Purkinje cell in the cerebellar cortex done by Santiago Ramón y Cajal, demonstrating the ability of Golgi's staining method to reveal fine detail

Drawing of neurons in the pigeon cerebellum, by Spanish neuroscientist Santiago Ramón y Cajal in 1899. (A) denotes Purkinje cells and (B) denotes granule cells, both of which are multipolar.

The axon terminal is found at the end of the axon farthest from the soma and contains synapses. Synaptic boutons are specialized structures where neurotransmitter chemicals are released to communicate with target neurons. In addition to synaptic boutons at the axon terminal, a neuron may have en passant boutons, which are located along the length of the axon.

Artistic interpretation of the major elements in chemical synaptic transmission. An electrochemical wave called an action potential travels along the axon of a neuron. When the action potential reaches the presynaptic terminal, it provokes the release of a synaptic vesicle, secreting its quanta of neurotransmitter molecules. The neurotransmitter binds to chemical receptor molecules located in the membrane of another neuron, the postsynaptic neuron, on the opposite side of the synaptic cleft.

Chemical synapse

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Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands.

Diagram of a chemical synaptic connection.

Release of neurotransmitter occurs at the end of axonal branches.

At a chemical synapse, one neuron releases neurotransmitter molecules into a small space (the synaptic cleft) that is adjacent to another neuron.

Acetylcholine

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Acetylcholine processing in a synapse. After release acetylcholine is broken down by the enzyme acetylcholinesterase.

Muscles contract when they receive signals from motor neurons. The neuromuscular junction is the site of the signal exchange. The steps of this process in vertebrates occur as follows: (1) The action potential reaches the axon terminal. (2) Calcium ions flow into the axon terminal. (3) Acetylcholine is released into the synaptic cleft. (4) Acetylcholine binds to postsynaptic receptors. (5) This binding causes ion channels to open and allows sodium ions to flow into the muscle cell. (6) The flow of sodium ions across the membrane into the muscle cell generates an action potential which induces muscle contraction. Labels: A: Motor neuron axon B: Axon terminal C: Synaptic cleft D: Muscle cell E: Part of a Myofibril

Components and connections of the parasympathetic nervous system.

Micrograph of the nucleus basalis (of Meynert), which produces acetylcholine in the CNS. LFB-HE stain.

Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter.

Norepinephrine

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Norepinephrine degradation. Metabolizing enzymes are shown in boxes.

Norepinephrine (labeled "noradrénaline" in this drawing) processing in a synapse. After release norepinephrine can either be taken up again by the presynaptic terminal, or broken down by enzymes.

Schema of the sympathetic nervous system, showing the sympathetic ganglia and the parts of the body to which they connect.

Brain areas containing noradrenergic neurons.

Chemical structure of octopamine, which serves as the homologue of norepinephrine in many invertebrate species

Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter.

Amino acid

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Amino acids are organic compounds that contain amino (\sNH3+) and carboxylic acid (\sCO2H) functional groups, along with a side chain (R group) specific to each amino acid.

The 21 proteinogenic α-amino acids found in eukaryotes, grouped according to their side chains' pKa values and charges carried at physiological pH (7.4)

Ionization and Brønsted character of N-terminal amino, C-terminal carboxylate, and side chains of amino acid residues

Composite of titration curves of twenty proteinogenic amino acids grouped by side chain category

Share of amino acid in various human diets and the resulting mix of amino acids in human blood serum. Glutamate and glutamine are the most frequent in food at over 10%, while alanine, glutamine, and glycine are the most common in blood.

The condensation of two amino acids to form a dipeptide. The two amino acid residues are linked through a peptide bond

Catabolism of proteinogenic amino acids. Amino acids can be classified according to the properties of their main degradation products:
* Glucogenic, with the products having the ability to form glucose by gluconeogenesis
* Ketogenic, with the products not having the ability to form glucose. These products may still be used for ketogenesis or lipid synthesis.
* Amino acids catabolized into both glucogenic and ketogenic products.

Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.

Glutamic acid

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An α-amino acid that is used by almost all living beings in the biosynthesis of proteins.

It is also the most abundant excitatory neurotransmitter in the vertebrate nervous system.

Serotonin

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Monoamine neurotransmitter.

Serotonin system, contrasted with the dopamine system

The pathway for the synthesis of serotonin from tryptophan.

Axons from the neurons of the raphe nuclei form a neurotransmitter system reaching almost every part of the central nervous system.

Monoamine neurotransmitter

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A phylogenetic tree showing how a number of monoamine receptors are related to each other.

Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH2-CH2-).

Synaptic vesicle

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Primary hippocampal neurons observed at 10 days in vitro by confocal microscopy. In both images neurons are stained with a somatodendritic marker, microtubule associated protein (red). In the right image, synaptic vesicles are stained in green (yellow where the green and red overlap). Scale bar = 25 μm.

In a neuron, synaptic vesicles (or neurotransmitter vesicles) store various neurotransmitters that are released at the synapse.

A report on Neurotransmitter

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