Neurotransmitters Flashcards
What are neurotransmitters?
Neurotransmitters are endogenous chemicals released extracellularly by neurons. They are used to signal to other neurons, myocytes (muscle cells), endocrine cells, and other target cells under physiological conditions.
How are dopamine, noradrenaline, and adrenaline synthesized?
Dopamine, noradrenaline, and adrenaline share the same synthesis pathway. The synthesis process stops depending on the enzymes present in the neuron or cell. Noradrenaline is released by sympathetic nerve terminals, while adrenaline is secreted by chromaffin cells in the adrenal medulla.
How are neurotransmitters stored and released?
Neurotransmitters are stored in synaptic vesicles within the presynaptic neuron. When an action potential reaches the presynaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft through exocytosis. The neurotransmitters then bind to receptors on the postsynaptic cell, initiating a response.
What are adrenoceptors?
Adrenoceptors are receptors that respond to neurotransmitters such as noradrenaline (NA) and adrenaline (Adr). They are classified into two main types: α-adrenoceptors and β-adrenoceptors.
What are the subtypes of α-adrenoceptors?
The subtypes of α-adrenoceptors include α1 and α2. They can be found in both post-synaptic and pre-synaptic locations. α1-adrenoceptors are present in the blood vessels of organs and tissues (except skeletal muscle vessels).
What are the agonists and antagonists for α-adrenoceptors?
Agonists for α-adrenoceptors include noradrenaline (NA), adrenaline (Adr), and isoprenaline. An antagonist for α-adrenoceptors is phentolamine.
What are the subtypes of β-adrenoceptors?
The subtypes of β-adrenoceptors include β1, β2, and β3. β1-adrenoceptors are found in the myocardium (heart muscle), β2-adrenoceptors are found in bronchi, uterus, muscle, and coronary vessels, and β3-adrenoceptors are found in adipose tissue, bladder, and gallbladder.
What are the agonists and antagonists for β-adrenoceptors?
Agonists for β-adrenoceptors include isoprenaline, adrenaline (Adr), and noradrenaline (NA). An antagonist for β-adrenoceptors is propranolol.
Are β-adrenoceptors sensitive to up/down regulation?
Yes, β-adrenoceptors are sensitive to up/down regulation, meaning their expression and sensitivity can be altered based on various factors.
What are the second messenger systems associated with α1-adrenoceptors and α2-adrenoceptors?
The second messenger system associated with α1-adrenoceptors is Gαq coupled, which activates phospholipase C. This leads to an increase in IP3 (inositol triphosphate) and DAG (diacylglycerol) levels. The second messenger system associated with α2-adrenoceptors is Gαi coupled, which inhibits adenylyl cyclase. It also modulates Ca2+ and K+ channels.
What is the second messenger system associated with β1/β2/β3-adrenoceptors?
The second messenger system associated with β1/β2/β3-adrenoceptors is Gαs coupled, which activates adenylyl cyclase. This leads to an increase in cAMP (cyclic adenosine monophosphate) levels.
How does the final effect of adrenoceptor activation vary?
The final effect of adrenoceptor activation, such as dilation, contraction, and ion alterations, depends on the specific tissue or cells involved. The response will vary based on the expression and distribution of adrenoceptors in different tissues.
Where are α1-adrenoceptors located, and what effects do they mediate?
α1-adrenoceptors are located in blood vessels, gastrointestinal (GI) smooth muscle, and GI sphincteric muscle/bladder sphincter. They mediate smooth muscle contraction, leading to vasoconstriction in blood vessels, relaxation in GI smooth muscle, and contraction in GI sphincteric muscle and bladder sphincter.
Where are α2-adrenoceptors located, and what effects do they mediate?
α2-adrenoceptors are located on presynaptic sympathetic neurons. Activation of α2-adrenoceptors leads to decreased neurotransmitter release, providing a negative feedback mechanism.
Where are β1-adrenoceptors located, and what effects do they mediate?
β1-adrenoceptors are located in the heart. Activation of β1-adrenoceptors increases heart rate and the force of contraction, leading to increased cardiac output.
Where are β2-adrenoceptors located, and what effects do they mediate?
β2-adrenoceptors are located in bronchi and blood vessels. Activation of β2-adrenoceptors leads to bronchial dilation and relaxation of blood vessels.
Where are β3-adrenoceptors located, and what effects do they mediate?
β3-adrenoceptors are located in adipose tissue and the bladder. Activation of β3-adrenoceptors promotes lipolysis (breakdown of fat) in adipose tissue and relaxation of the bladder, preventing urination.
What is the main mechanism for regulating noradrenaline (NA) levels in the synaptic cleft?
The main mechanism for regulating NA levels in the synaptic cleft is reuptake via the plasma membrane noradrenaline transporter (NAT or NET). This transporter is located in the membrane of the presynaptic neuron and is responsible for removing NA from the synaptic cleft. The reuptake process limits the duration of NA action and allows for its recycling.
Besides neuronal cells, where else is NA taken up by?
In addition to neuronal cells, a minority of NA uptake occurs in non-neuronal cells.
What are the enzymes involved in the metabolism of endogenous and exogenous NA and Adr?
The metabolism of endogenous and exogenous NA and Adr involves two main enzymes: monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT). MAO has different isoforms, and both enzymes play a role in the breakdown of NA and Adr.
What are the steps involved in the synthesis, storage, release, and termination of NA action?
Synthesis in the cytosol.
Storage in vesicles.
Vesicle transport and fusion with the membrane.
Release into the synaptic cleft.
Diffusion across the synaptic cleft.
Action on post-synaptic cells via receptors.
Termination of the signal through metabolism by cholinesterase enzymes, specifically acetylcholinesterase (AChE) and butyrylcholinesterase (BuChe).
What are the subtypes of muscarinic receptors (mAChR)?
The subtypes of muscarinic receptors are M1, M2, M3, M4, and M5. They are metabotropic receptors, belonging to the G protein-coupled receptor (GPCR) family.
Where are muscarinic receptors (mAChR) located and what are their agonists and antagonists?
Muscarinic receptors are located postsynaptically in smooth muscle, cardiac muscle, and glands. Their agonists include acetylcholine (ACh) and muscarine, while their antagonist is atropine (belladonna).
What are the subtypes of nicotinic receptors (nAChR)?
Nicotinic receptors have multiple subtypes, but the main classification is ionotropic and pentameric cation channels.
Where are nicotinic receptors (nAChR) located and what are their agonists and antagonists?
Nicotinic receptors are found in autonomic ganglia, motor endplates, and the central nervous system (CNS). Their agonists include acetylcholine (ACh) and nicotine, while their antagonist is curare (tubocurarine).
What are the subtypes of muscarinic receptors (mAChR)?
The subtypes of muscarinic receptors are M1, M2, M3, M4, and M5. They are metabotropic receptors, belonging to the G protein-coupled receptor (GPCR) family.
Where are muscarinic receptors (mAChR) located and what are their agonists and antagonists?
Muscarinic receptors are located postsynaptically in smooth muscle, cardiac muscle, and glands. Their agonists include acetylcholine (ACh) and muscarine, while their antagonist is atropine (belladonna).
What are the subtypes of nicotinic receptors (nAChR)?
Nicotinic receptors have multiple subtypes, but the main classification is ionotropic and pentameric cation channels.
Where are nicotinic receptors (nAChR) located and what are their agonists and antagonists?
Nicotinic receptors are found in autonomic ganglia, motor endplates, and the central nervous system (CNS). Their agonists include acetylcholine (ACh) and nicotine, while their antagonist is curare (tubocurarine).
