Neurotransmitters
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Amino Acid Neurotransmitter
• found in majority of fast-acting “directed”
synapses in CNS
• molecular building blocks of protein
• Glutamate
– most prevalent excitatory
neurotransmitter
– common in proteins that we eat
• GABA (gamma-aminobutyric acid)
– most prevalent inhibitory neurotransmitter
– synthesized by simple change to
glutamate
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Acetylcholine
• Primary neurotransmitter secreted by efferent axons
of the PNS
• Major concentrations of ACh in the CNS include:
– dorsolateral pons (role in REM sleep)
– basal forebrain (role in learning)
– medial septum (role in memory)
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Acetylcholine Synthesis
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Non-directed synapses
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3
Catecholamine Order of Synthesis
Tyrosine
tyrosine hydroxylase
L-dopa
DOPA decarboxylase
Dopamine
dopamine ß-hydroxylase
Norepinephrine
Epinephrine
phenylethanolamine-Nmethyl transferase
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Serotonin Synthesis
Tryptophan
Tryptophan hydroxylase
5-hydroxytryptophan
(5-HTP)
5-HTP decarboxylase
5-hydroxytryptamine
(5-HT or Serotonin)
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4
Monoamine Oxidase (MAO)
Two forms: MAO-A and MAO-B
• MAO-A generally metabolizes
norepinephrine, epinephrine, dopamine,
and serotonin
• MAO-B mainly metabolizes dopamine
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Synaptic Events (mechanisms)
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Example of Agonists
• Cocaine
– blocks reuptake of dopamine
– agonist for dopamine
• Nicotine
– stimulates postsynaptic receptors
– agonist for acetylcholine
• L-Dopa
– is precursor molecule for dopamine
– increases synthesis of dopamine
– agonist for dopamine
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Example of Antagonists
• Botulinum toxin
– inhibits release of acetylcholine
– antagonist for acetylcholine
• Curare
– blocks postsynaptic receptors
– antagonist for acetylcholine
• Atropine
– blocks postsynaptic receptors
– antagonist for acetylcholine
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