Block 2: CNS neurotransmitters

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How do most CNS drugs act?: alter synaptic transmission
AND
modulate effects of neurotransmitters
How do a few CNS drugs act?: voltage-gated ion channels
Dale's hypothesis? Is it true?: Neurons use only one transmitter.

True for classical transmitters only.
Neuropeptides are co-transmitters in many cells.
3 criteria for "transmitter": 1. Presence- in presynaptic nerve terminals with its substrate and synthesizing enzyme
2. Release- release in response to depolarizing stimuli is CALCIUM dependent
3. Pharmacologic identity- effects of transmitter when applied experimentally must = effects of stimulating presynaptic pathway
Give 3 examples of small transmitters: ACh
Amines- DA, NE, Epi, Serotonin
Amino acids- glutamate, GABA, Glycine
Give 2 examples of peptide transmitters: opiods
NPY
Give 2 examples of transmitter gases: N2O
CO
How does an ionotropic receptor work: transmitter binds multimeric ligand-gated ion channel -->
increased permeability to one or more ions -->
either EPSP or IPSP
AMPA glutamate receptor: excitatory inotropic
kainate glutamate receptor: excitatory ionotropic
NMDA glutamate receptor: excitatory ionotropic
GABA receptor: inhibitory ionotropic
How do metabotropic receptors work: transmitter binds receptor bound to G-proteins -->
activates second messengers (IP3, DAG)
-->
modulate cellular physiology
Metabotropic glutamate receptor: metabotropic receptor
(if it were only that easy)
GABA-beta receptor: metabotropic receptor
alpha and beta adrenergic receptors: metabotropic receptors
Most excitatory synapses use...: glutamate
Glutamate transporters that take up glutamate are dependent on which ion?: Na
Where is glutamine made?: Nerve terminal mitochondria
Name three ligand gated ion channels/ionotropic receptors.: AMPA
kainate
NMDA
Other names for metabotropic glutamate receptors?: mGluR1-8 receptors
Which mGluR type(s) couples with G proteins and activates the IP3 system via PLC?: Type I
Which mGluR type(s) inhibit AMP synthesis by adenylyl cyclase?: Types II and III
Other than ligand binding, what else does the NMDA receptor need?: membrane depolarization
How does the NMDA receptor work?: increases intracellular Ca --> act as second messenger
Name five correlations to the NMDA receptor: 1. learning and memory
2. ischemic neuronal damage
3. epileptic seizures
4. PCP psychosis
5. ketamine anesthesia
What is the major inhibitory neurotransmitter in the CNS?: GABA
How is GABA made?: From glutamate using GAD (glutamic acid decarboxylase) (w/ PP(vit B6))
What is GABA release dependent on?: Ca
Where does GABA work?: presynaptic autoreceptors and postsynaptic receptors
Which GABA receptor(s) are ionotropic, increase chloride ion conductance?: GABA-A and GABA-C
Which GABA receptor(s) are metabotropic?: GABA-B
Active GABA uptake into presynaptic endings and glia is dependent on which ion?: Na
What does GABA-T do?: Turns GABA into glutamine in mitochondria
Which GABA receptor is both presynaptic and postsynaptic?: GABA-B
Which GABA receptor has multiple binding sites for neuroactive drugs?: GABA-A
Name 3 agonists for GABA-A receptors?: 1. Benzodiazepines- allosterically enhance GABA binding
2. Ethanol- enhances Cl channel opening
3. General anesthetics- bind hydrophobic site
Name 4 GABA-A antagonists; what can they cause?: 1. bicuculline
2. picrotoxin
3. pentylenetetrazol
4. penicillin

seizures
Describe how GABA-B presynaptic receptors work: G/Go --> block Ca channel --> dec presynaptic Ca --> inhibit transmitter release
Nama a GABA-B presynaptic receptor agonist: Baclofen- centrally acting muscle relaxant (spasmolytic)
Describe how GABA-B postsynaptic receptors work: G/Go --> open K channel --> hyperpolarizes neuron --> inhibits depolarization
What is 5-hydroxytryptamine, 5HT: Serotonin
How is serotonin made?: tryptophan --> 5-hydroxytryptophan --> 5-hydroxytraptamine
Which areas of the CNS are involved with serotonin?: Raphe nuclei send serotonergic projections to --> cerebral cortex, limbic system, and diencephalon
What is serotonin release dependent on? What increases the release?: Ca

fenfluramine
What types are most of the 15 different serotonin receptors?: pre and postsynaptic metabotropic (GPCRs)
What terminates action of serotonin? What can stop that?: active re-uptake into presynaptic terminals

SSRIs- fluoxetine, etc
What enzymatically degrades serotonin: MAO
How does LSD work?: inhibits firing of serotonin neurons --> reduces release of 5HT --> acts at presynaptic autoreceptors and modulates serotonin release
What is the excitatory neurotransmitter in the spinal cord?: ACh
Name two nicotinic receptor (ionotropic) agonists: ACh
nicotine
Name one nicotinic receptor (ionotropic) antagonist: curare
Name 2 muscarinic receptor (metabotropic) agonists: ACh
muscarine
Name 2 muscarinic receptor (metabotropic) antagonists: Atropine
Scopolamine
What may serve as a retrograde transmitter from postsynaptic to presynaptic cell?: NO
How is NO made?: Arginine --> NO + citrulline
via NO synthase
What activates NO synthase?: calcium-calmodulin
How can NO enhance transmitter release?: activates heme-containing gyanylyl cyclase
Where in the CNS is NO involved?: cerebellum
Name two correlations to CNS NO?: 1. learning and memory
2. ischemic neuronal damage

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