Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. A neuromodulator can be conceptualized as a neurotransmitter that is not reabsorbed by the pre-synaptic neuron or broken down into a metabolite. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second messenger signaling cascade that induces a broad, long-lasting signal. This modulation can last for hundreds of milliseconds to several minutes. Some of the effects of neuromodulators include: alter intrinsic firing activity, increase or decrease voltage-dependent currents, alter synaptic efficacy, increase bursting activity and reconfiguration of synaptic connectivity.

Major neuromodulators in the central nervous system include: dopamine, serotonin, acetylcholine, histamine, norepinephrine, nitric oxide, and several neuropeptides. Cannabinoids can also be powerful CNS neuromodulators.

Acetylcholine

Acetylcholinesterase (EC 3.1.1.7, e.g. from Torpedo californica, TcAChE) hydrolysizes the neurotransmitter acetylcholine , producing group. ACh directly binds (via its nucleophilic Oγ atom) within the catalytic triad of (ACh/TcAChE structure 2ace). The residues are also important in the ligand recognition. After this binding acetylcholinesterase ACh.

Acetylcholine Receptors

Nicotinic acetylcholine receptors

• Nicotinic Acetylcholine Receptors in general

The receptor is a transmembrane pentameric glycoprotein. It cylindrical in appearance by electron microscopy approximately 16nm in length and 8nm in diameter. The main ion channel is composed of a water pore that runs through the entire length of the protein. If viewed from the synaptic cleft, the protein will look like a pseudo-symmetrical rosette shown in the picture below composed of 10 different alpha and 4 different beta subunits.

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• Alpha-bungarotoxin is a nicotinic cholinergic antagonist that is found within the venom of Bungarus multicinctus, a South-asian snake.
• Binding site of AChR
• Acetylcholine Receptor and its Reaction to Cobra Venom

When cobra venom is introduced into the body is moves along the bloodstream to a diaphragm muscle. It works as a postsynaptic neurotoxin binding to the receptor as an extracellular ligand by interacting with OH group leaving the acetylcholine channel open which releases ions used in creating an action potential. There must be 5 molecules of cobra toxin (red) to block the receptor (blue) as each molecule binds with an individual alpha chain on the acetylcholine receptor. The 2nd image depicts an individual toxin binding with one chain on the receptor, both in the same color. . This representation shows each molecule of the .

Muscarinic acetylcholine receptors

M1, M3, M5 receptors are coupled with G_q proteins, while M2 and M4 receptors are coupled with G_i/o proteins. They belong to GPCRs Subfamily A18.

• Muscarinic acetylcholine receptor

Acetylcholinesterase

• Acetylcholinesterase: Treatment of Alzheimer's disease
  
• Torpedo californica acetylcholinesterase with bifunctional inhibitor
  
• Acetylcholinesterase: Substrate Traffic and Inhibition
  
• Acetylcholinesterase Inhibitor Pharmacokinetics
  
• Acetylcholinesterase inhibitors
  
• AChE inhibitors and substrates
  
• Human Acetylcholinesterase
  
• African Malaria Mosquito Acetylcholinesterase
  
• Acetylcholinesterase inhibited by nerve agent soman
  
• Acetylcholinesterase with DFP
  
• Acetylcholinesterase with OTMA
  
• Acetylcholinesterase with acetylcholine
  
• Acetylcholinesterase complexed with N-9-(1',2',3',4'-tetrahydroacridinyl)-1,8-diaminooctane
  
• Complex of TcAChE with an iminium galanthamine derivative
  
• Complex of TcAChE with bis-acting galanthamine derivative
  
• Cholinesterase
  
• Flexibility of aromatic residues in acetylcholinesterase
  
• Huperzine A Complexed with Acetylcholinesterase & Huperzine A Complexed with Acetylcholinesterase (Chinese)
  
• Acetylcholinesterase complexed with Tacrine, the 1st anti Alzheimer's drug
  
• UMass Chem 423 Student Projects 2011-1: Acetylcholinesterase bound by Tacrine
• Torpedo Californica Acetylcholinesterase in complex with an (R)-Tacrine-(10)-Hupyridone inhibitor
  
• Torpedo Californica Acetylcholinesterase in complex with an (S)-Tacrine-(10)-Hupyridone inhibitor
  
• Torpedo californica acetylcholinesterase with alkylene-linked tacrine dimer (5 carbon linker)
  
• Torpedo californica acetylcholinesterase with alkylene-linked tacrine dimer (7 carbon linker)
  
• Torpedo californica acetylcholinesterase with bifunctional inhibitor
  
• Tetramerization domain of acetylcholinesterase
  
• African Malaria Mosquito Acetylcholinesterase
• Group:SMART:Acetylcholinesterase:A Story of Substrate Traffic and Inhibition by Green Mamba Snake Toxin
  
• Treatments:AChE Inhibitor References
  

Adrenaline (Epinephrine)/Noradrenaline (Norepinephrine)

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• Phenylethanolamine N-methyltransferase (Noradrenaline N-Methyltransferase) catalyzes the conversion of norepinephrine (noradrenaline) to epinephrine (adrenaline). This is the last step in the conversion of tyrosine to adrenaline^[1].

Adrenergic receptors in general

The adrenergic receptors are metabolic G protein-coupled receptors. They are the targets of catecholamines. The binding of an agonist to them causes a sympathetic response.

• The α-2 adrenergic receptor (A2AR) inhibits insulin or glucagons release.
  
• The β-1 adrenergic receptor (B1AR) increases cardiac output and secretion of rennin and ghrelin.^[2]
  
• The β-2 adrenergic receptor (B2AR) triggers many relaxation reactions.

β1 adrenergic receptor

• 3D structures in Adrenergic receptor.
• Beta-1 Adrenergic receptor
• G_s: adenylate cyclase activated, cAMP up.

• β1-adrenergic agonists:
  • Dobutamine, see Beta-1 Adrenergic receptor, 2y00, 2y01, 6h7l.
  • Isoprenaline, see Beta-1 Adrenergic receptor, 2y03.
  • Noradrenaline
  • Carmoterol, see 2y02.
  • Salbutamol (Albuterol in USA), 2y04.
• Beta blockers:
  • Metoprolol
  • Atenolol
  • Bisoprolol
  • Propranolol
  • Timolol
  • Nebivolol
  • Vortioxetine

β2 adrenergic receptor

• The human β2 adrenergic receptor bound to a G-protein (3sn6) is featured in a scene above, and additional structures are on the Adrenergic receptor page.
• Article Beta-2 Adrenergic Receptor by Wayne Decatur, David Canner, Dotan Shaniv, Joel L. Sussman, Michal Harel
• Article Beta-2 adrenergic receptor by Joel L. Sussman, Tala Curry, Michal Harel, Jaime Prilusky
• Group:SMART:A Physical Model of the beta-Adrenergic Receptor
• G_s: adenylate cyclase activated, cAMP up. For G_s see Beta2 adrenergic receptor-Gs protein complex updated.

β2-adrenergic agonists:

• • Salbutamol (Albuterol in USA)
  • Bitolterol mesylate
  • Formoterol
  • Isoprenaline
  • Levalbuterol
  • Metaproterenol
  • Salmeterol
  • Terbutaline
  • Ritodrine
• Beta blockers:
  • Butoxamine
  • Timolol
  • Propranolol
  • ICI-118,551
  • Paroxetine

Beta-adrenergic receptor kinase

Monoamine oxidases (MAO)

Monoamine oxidases (MAO) (EC 1.4.3.4) are a family of enzymes that catalyze the oxidation of monoamines including adrenaline, noradrenaline, serotonin and dopamine.

Monoamine oxidase

Monoamine oxidase b