Neurotransmitters

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Neurotransmitters

• M.Prasad Naidu
• MSc Medical Biochemistry,
• Ph.D.Research Scholar

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• Neurotransmitters is a chemical substance or
  chemical messenger (within brain) that is
  secreted by neurons and that allow communication
  between nerve cells to produce physiological
  response such as muscle contraction.
• Neurotransmitters are chemical substances
  secreted by neurons and they convey messages from
  one neuron to a target cell.
• At the target cells, the neurotransmitters may
  alter ion flow (depolarise or hyperpolarise), or
  they may alter the cellular metabolism.
• The transmitter substances carry out the actual
  passage of a signal across a synapse.

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• Neurotransmitters are the principal signal
  molecules that mediate their actions via
  receptors that can function as ion channels.
• The neuron
• The neuron is the structural and functional unit
  of the nervous system.
• Neurons function by the production, propagation
  and transfer of nerve impulses.
• The functional components of a neuron consists of
  
• - the cell body (perikaryon) having the
  nucleus (karyon) and those organelles that
  maintain the cell.
• - the processes extending from the cell body
  which consists of axon and dendrites.

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• Synapses
• A Synapse is a site of functional contact between
  neurons that facilitate transmission of impulses
  from one (presynaptic) neuron to another
  (postsynaptic) neuron or effector (target) cells
  such as muscle and gland cells.
• Synapse is a site of neuron-to-neuron or
  neuron-to-effector cell communication.
• A typical Synapse contains presynaptic bouton or
  knob, synaptic cleft and postsynaptic membrane.

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• Classification of neurotransmitters
• Class Amine
• Examples are epinephrine, norepinephrine,
  dopamine and serotonin (5-hydroxytryptamine).
• Class Amino acid and amino acid derivatives
• Examples are glutamate, aspartate, glycine,
  histamine and GABA.
• Class Purines
• Examples are adenosine, ATP.
• Class Gas
• Examples are nitric oxide
• Class Miscellaneous

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• Examples are acetylcholine
• Acetyl choline
• Acetylcholine
• The first chemical neurotransmitter identified
  was acetylcholine.
• Synthesis and storage
• Release and action
• Reuptake and degradation
• Acetylcholine receptors muscarinic and
  nicotinic acetylcholine receptors.
• Cholinergic agonists are nicotine, muscarine and
  a-latrotoxin.

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• Cholinergic antagonists are atropine (and
  related compound scopolamine), botulinus toxin,
  a-bungarotoxin and d-tubocurarine (muscle
  relaxant).

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• Catecholamines
• The principal catecholamines are norepinephrine
  (noradrenaline), epinephrine (adrenaline) and
  dopamine.
• Synthesis
• Storage
• Release
• Receptors and action
• Reuptake and degradation
• Functions of catecholamines

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• Serotonin
• Serotonin also called 5-hydroxytryptamine (5-HT).
  
• Storage and release
• Reuptake and degradation
• Functions

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• GABA (Gamma Aminobutyric Acid)
• Synthesis
• Receptors and action
• Reuptake and degradation
• Functions of GABA

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• Histamine
• Synthesis and receptors
• Functions
• Degradation

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• Glycine
• Glycine is the inhibitory neurotransmitter in the
  spinal cord.
• Receptors and action
• Reuptake and degradation
• Functions of glycine

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• Glutamate
• Glutamate is the excitatory amino acid
  neurotransmitter in the brain.
• Receptors and action
• Reuptake and degradation
• Functions

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• Nitric oxide (NO)
• Nitric oxide also has been identified as a
  neurotransmitter.
• Synthesis
• Degradation
• Functions

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• Clinical importance
• Acetylcholine agonists with acetylcholinesterase
  inhibitors have significant medical application
  in the treatment of disorders such as
• - glaucoma by increasing the tone of the
  muscles of accomodation of the eye.
• -myasthenia gravis
• -in terminating the effects of neuromuscular
  blocking agents such as atropine.

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• Myasthenia gravis auto antibodies form to
  nicotinic type acetylcholine receptors which
  destroy some receptors and compete with
  acetylcholine to bind to the surviving receptors.
  
• Treatment may include administration of
  acetylcholine esterase inhibitors (e.g.,
  pyridostigmine, neostigmine) to prolong activity
  of acetylcholine at motor end plates.
• Alzheimers disease tacrine used in treatment
  of alzheimers disease is a long-acting
  cholinesterase inhibitor.

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• Catecholamines
• ß blockers, such as atenolol, are used to treat
  hypertension and chest pain (angina) in ischaemic
  heart disease because they antagonise the
  stimulatory effects of catecholamines on the
  heart.
• ß2 receptor agonists such as salbutamol which
  stimulates ß receptor of lungs, are used to
  produce bronchial dilation in asthma without
  stimulating ß1 receptor in the heart.
• D2 receptors (of dopamine) antagonist such as
  phenothiazines and haloperidol are used as a
  antipsychotic drugs.

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• Parkinsons disease
• Treatment may involve administration of
• Drugs such as deprenyl that inhibit the
  degradation of dopamine and other biogenic amines
  by monoamine oxidase type B
• L-dopa that can cross the blood-brain barrier
  and serve as a substrate for dopamine
  biosynthesis in striatal cells.

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• GABA
• The anxiolytic drugs like diazepam and
  barbiturate, sleep inducing and an anticonvulsant
  drug used in the treatment of epilepsy, exert
  their soothing effects by potentiating the
  binding of GABA to GABA-A receptors.

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• Serotonin
• Depression
• Treatment may include administration of tricyclic
  anti-depressants that inhibit uptake of both
  noradrenaline and adrenaline into brain cells, or
  other antidepressants such as fluoxetine (prozac)
  that preferentially inhibit serotonin uptake
  inhibitors of monoamine oxidase A that convert
  serotonin to an inactive aldehyde may also be
  used.

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• Histamine
• H1 receptors antagonists such as
  diphenhydramine are used in the treatment of
  allergic responses and for asymptomatic treatment
  of upper respiratory disorders.
• H2 receptors antahonists such as ranitidine or
  cimtidine are used in the treatment of peptic
  ulcers.
• H2 receptor inhibitors have no effect on
  allergy.

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Thank you