NEUROTRANSMITTERS
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Neurotransmitter
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Description
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Subtype
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Function
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Amino Acid
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· In vast majority of fast-acting,
directed synapses in CNS
· Molecular building blocks of
proteins
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«
Glutamate
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Aspartate
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Glycine
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·
Common proteins we consume
·
Glutamate – most prevalent excitatory n.t.
in mammalian CNS
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Gamma-aminobutyric acid (GABA)
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·
Synthesized by simple modification of structure of glutamate
·
most prevalent inhibitory n.t.
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Monoamine
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· Small molecule n.t.
· Synthesized from 1 amino acid
· Slightly larger than amino acid n.t.
· More diffuse effects
· In small groups of neurons whose
cell bodies @ brainstem (highly branched axon w/ many varicosities)
· Varicosities where monoamine is
released
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«
Catecholamines:
§
Dopamine
§
Norepinephrine
§
Epinephrine
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·
Synthesized fr. amino acid tyrosine
à L-dopa à dopamine
·
Norepinephrine have extra enzyme à dopamine to norepinephrine
·
Epinephrine have have extra enzyme à norepinephrine to epinephrine
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«
Indolamines:
§
Serotonin (5 HT)
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·
Synthesized fr. amino acid tryptophan
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Soluble-Gas
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· Small molecule n.t.
· Do not act like n.t.
· Produced in neural cytoplasm
· Diffuse thru cell memberane into extracellular
fluid then to nearby cells
· Easily pass thru cell membranes bec. soluble lipids
· Once in other cells, stimulate
production of 2nd messenger
& immediately broken down
· Thus, exist for only a few seconds
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«
Nitric oxide
«
Carbon monoxide
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·
Nitric oxide = mediate retrograde
transmission (transmit signals from postsynaptic to presynaptic
neuron)
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Acetylecholine
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· Small molecule n.t.
· Unique
· Created by adding acetyle group to choline
molecule
· @ neuromuscular junction, @ many
synapses in autonomic NS, @ synapses in some CNS parts
· Broken down by enzyme acetylcholinesterase
· Cholinergic neurons
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PSYCHOACTIVE DRUGS: 4 EXAMPLES
- Effects
of drugs on synaptic transmission:
(SEE PAGE 100, FIGURE 4.17)
1.
Agonists =
facilitate effects of neurotransmitter
·
á synthesis of n.t.
molecules
·
á no. of n.t.m. by destroying
degrading enzymes
·
á release of n.t.m. fr. terminal buttons
·
bind to autoreceptors
& block inhibitory effect on n.t. release
·
bind to postsynaptic
receptors & either actives them or á effect on them of n.t.m.
·
blocks deactivation of n.t.m.
by blocking degradation or reuptake
2.
Antagonists = inhibit effects of neurotransmitter (some called receptor blockers bind to postsynaptic receptors w/c block usual
neurotransmitter)
·
block synthesis of n.t.m.
·
cause n.t.m. leak fr. vesicles & destroyed by degrading enzymes
·
block release of n.t.m.
fr. terminal buttons
·
activate autoreceptors
& inhibit n.t. relase
·
receptor blocker; bind
to postsynaptic receptors & block
effect of n.t.
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Psychoactive Drugs
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Description
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Cocaine
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· Potent catecholamine agonist
· Highly addictive
· á activity of dopamine & norepinephrine
by blocking reuptake
· if á levels in brain, dopamine & norepinephrine in synapse continue to activate
postsynaptic receptors
· euphoria, loss of appetite,
insomnia
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Benzodiazepines
- Chloradiazepoxine (Librium)
- Diazepam (Valium)
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· Anxiolytic effect (anxiety-reducing) –
serving as GABA agonists, binding to ionotropic
GABA receptor
· Sedative effect (sleep-inducing)
· Anticonvulsant effect
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Atropine
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· From extracts of plants
· Active ingredient belladonna (pupil-dilating effect that
enhance beauty in Greek times)
· Receptor blocker; agonist effect
· Binds to metabotropic
acetylcholine receptors (muscarinic
receptors) w/c block acetylcholine effect
· Disruptive effect of á doses on memory
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Curare
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· From extracts of certain class of
woody vines
· Used to kill by South American
Indians
· Receptor blocker @ cholinergic
synapses
· Bind to Nicotinic receptors (ionotropic
subtype) = block transmission at neuromuscular junctions = paralyze &
kill by blocking respiration
· Given during surgery to ensure
muscles do not contract during incision w/c necessitate respirator
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