Lecture 11

3 Pages
Unlock Document

Cell and Systems Biology
Melanie Woodin

CSB332H1S L11; Feb. 15, 2012  Key w synaptic plasticity: Synaptic Plasticity o Change in synapse strength persists after activity (ex. train of Read Ch. 16 APs) that induced plasticity  Changes in presynaptic &/or postsynaptic [Ca2+]i underlie most Plasticity is the capacity of the nervous system to change forms of synaptic plasticity  Today talking about short-term o  ex. phosphorylates AMPA recs  Synaptic plasticity = the capacity to alter the strength of synaptic  Mechanisms often classified as presynaptic or postsynaptic transmission  Long-term potentiation = most-studied form of synaptic plasticity o Modifying connections o Short-term (ms - mins, don’t normally require prot synthesis) or long-term (hrs, need prots to maintain long-term, GABA) o Can be due to Presynaptic &/or Postsynaptic changes  Most short-term due to Presynaptic  Most long-term need Postsynaptic (need retrograde signalling)  Always changes on both sides of synapse o = a change in synaptic efficacy or strength  Efficiency of transmission  Hebbian (Activity-dependent) o Talking about most o Plasticity induced by pattern of electrical activity (act pot firing) o Hebb = name of famous Canadian neuropsychologist  or Heterosynaptic (Activity-independent) o chemical LTP, using some kind of ligand, without changing pattern of act pot firing How can we test for synaptic plasticity?  Mostly looking at neuromuscular junction  To test strength of synapse: o Stimulating electrode placed in presynaptic cell or bundle of axons & Recording electrode placed in postsynaptic cell or muscle  Stimulation of presynaptic cell  firing of a presynaptic AP & release of neurotransmitter  Binding of neurotransmitter postsynaptically  opens ion channels (ionotropic or metabotropic)  synaptic pot – recorded postsynaptically  Amplitude of synaptic pot recorded postsynaptically is a measure of  Short-term  Looking at amplitudes in postsynaptic muscle strength of synapse  Can induce two types of plasticity at same synapse o Using test pulse/stimulation first  Mech is Ca o First use low freq (Hz) to stimulate 1 act pot (don’t usually activate synapse or induce plasticity on own)  In general, most synapses are more likely to either be facilitated or  1 Hz = 1 stimulation per second (1 act pot) depressed o Test for 10min to make sure have steady baseline  Stimulate 4 times  produces 4 end-plate pots of dif sizes o  increase = facilitation  Initial baseline-recording period o Wait a couple ms  stimulation  second end-plate pot = larger o Once confident in baseline, induce plasticity (Induction Protocol) than initially was, but not as large as biggest  Then test synapse again like in baseline test, see if changed Artificially regulating level of extracellular Ca strength (amplitude changes), compare to baseline o Short term mechs are dependent on amt of Ca, so trying to  See if change persists after induction exaggerate to illustrate pt  Bathed tissue in lower level of extracellular Ca o  mech underlying facilitation partially due to amt of Ca in presynaptic synaptic terminal  Time for chelation & for levels to rise again  Ca levels normally build  more neurotransmitter released  So 3ms later, end-plate pot larger  But 1 sec later, response gone o At NMJ, firing 1 act pot can often cause a postsynaptic act pot,  Stimulating electrode in bundle of presynaptic axons in hippocampus but want to measure underlying end-plate pots  end-plate pots smaller  Recording electrode on dendrites in CA1 region  Effect outlasts initial induction stimulus but lasts shortly for only a Synaptic Plasticity second  Arrival of indiv APs presynaptically don’t usually activate synapse  B: bath synapse in high level of Ca  Trains of APs are more common o Also puts curare in bath (antagonist of Ach)  lowers synaptic response  Such ongoing activity can have significant effects of strength of o Mech depends on amt of Ca synapse o  depression  Changes in synapse strength = changes in synaptic efficacy  When activity (trains or patterns of APs) cause change in synaptic o Release a lot of quanta but subsequent atc pots are smaller efficacy:  Ca comes in, nearly all vesicles released so that less available to be released at 2 act pot o Activity-dependent synaptic plasticity  Rapidly depleted synaptic vesicles o If were to stimulate again, would see end-plate pot at 300ms o Hard to measure underlying amplitude of end-plate pots, want would still be smaller (outlasts stimulus), but back to normal to weaken by hyperpolarizing membrane pot so at more after 1 sec (enough time to move vesicles from reserve pool to negative value further from threshold  more unlikely to reach terminal) for act pot o Ca levels usually constant in cerebrospinal fluid o Stimulate synapse  record wave form w two parts  Depends on microdomains & other factors regulating  Initial peak than secondary peak neurotransmitter release  Initial peak doesn’t change in amplitude  C: combine A & B  Indicates there is an electrical synapse, not chemical; o Get some elements of fac & depr occurring together also know since see response immediately o Get fac but then 3 & 4 are same  Secondary wave form = end-plate pot o At 300ms, test synapse, response much smaller so synapse has o Test strength of synapse (control) undergone a depression o Induction protocol  then see if plasticity occurs  So need to test synapse after the Induction Protocol and  T=0 compare to initial test  Don’t care what it looks like during induction o 15s after, test strength  huge end-plate pot that leads to act pot; so know there has been huge increase in synapse strength; end-plate pot was 1mV before o Wait 1min, test again  see huge end-plate pot but not enough to reach threshold o By 10min, returns close to baseline but still larger, so know isn’t long-term form of
More Less

Related notes for CSB332H1

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.