Lecture9 v8 - Chemical Synaptic Transmission II

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www.utexas.edu/neuroscience/Neurobiology/WesThompson Chemical Synaptic Transmission II
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Overview for lecture 9 1.Review criteria for a Neurotransmitter 2.Overview of Basics in Chemical Transmission 3.Discovery of the basis for the EPP – mEPP 4.Quantum hypothesis 5.Calcium Hypothesis 6.Synaptic Vesicle cycle Steps in Exocytosis Molecules involved in Exocytosis
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Time Course and Spatial Distribution of the EPP At the endplate the depolarization rose rapidly and declined slowly. As the recording electrode was moved away from the end plate, the EPP amplitude decreased and it’s time became longer. NT release is at the synapse!
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http://www.unmc.edu/Physiology/Mann/pix_13/ep_bath.gif   End plate: Point of contact between the Nerve and muscle. Evidence that the Postsynaptic response is mimmicked by application of the Neurotransmitter. Acetylcholine in microelectrode How does this work: Ach has a + charge Pass positive current through the electrode This is know as Ionophoresis
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http://www.unmc.edu/Physiology/Mann/pix_13/ep_bath.gif Curare Abolishes  EPP  Curare is a drug that  binds to AChR and  blocks The binding of  Acetylcholine
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Eserine (NEOSTIGMINE) Potentiates EPP Inhibits AChE EPP is larger and longer in duration
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NT Uptake and Termination of Signal More on Thursday . . . . Neurotransmitter is removed from the cleft by two mechanisms i) transmitter is destroyed by an enzyme such as acetylcholine esterase ii) transmitter is taken back up into the presynaptic cell and recycled e.g. - acetylcholine esterase, breaks down acetylcholine in cleft, choline is recycled back into the presynaptic terminal
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The amount of transmitter released depends on the degree of depolarization of the synaptic terminal.
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Bernard Katz leads the field with his students and colleagues: Hodgkin, Fatt, del Castillo, Miledi, Kuffler HOW IS AN EPP GENERATED? CLUE: 1. Spontaneous miniature end-plate potentials – small depolarizations which has the appearance of small end- plate potentials 2. Only occur at nerve terminal – like EPPs – must be a NT 3. They occur randomly with an average frequency of 1/sec 1951 “Quantal” nature of  synaptic transmission  discovered  1. Normal distribution with amplitudes of approximately 0.5mV 2. They were abolished by curare 3. Amplitude was increased with in the presence of anticholinesterases 4. Frequency was not effected by depolarization or hyperpolarization of the post synaptic membrane
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mEPP 1. Abolished with cutting the nerve 2. Abolished when treating the nerve-muscle preparation with botulinum toxin (BOTOX) 1951 “Quantal” nature of  synaptic transmission  discovered   What is the basis of a mEPP? Leakage of a single molecule of ACh?
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Lecture9 v8 - Chemical Synaptic Transmission II

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