CSB332H1 Lecture Notes - Lecture 11: Dentate Gyrus, Schaffer Collateral, Synaptic Plasticity
14 May 2018
School
Department
Course
Professor
Stimulating - Perforant Fiber Pathway
Intracellular Recording – Dentate Gyrus
Stimulating – Schaffer Collateral Pathway
Intracellular Recording – CA1 pyramidal cell
Lecture 11(b): Altering Synapses I
LTP in the Hippocampus:
• The first cell circuit examined in the hippocampus was not CA1
neurons – the dentate gyrus was first looked at for synaptic
plasticity; looking at the perforant fiber pathway
o Form of homosynaptic LTP; involves just one synapse
Experiment:
• Stimulating electrode (purple) is stimulating the perforant
fiber pathway via tetanic stimuli; 15 action potentials per
second for the span of 10 seconds
o Over the 10 seconds, a ‘cloud’ of neurotransmitters will
settle on the neurons within the dentate gyrus
§ Dentate gyrus was later observed to examine the effects of the AP trains
ð Pathway was stimulated at each arrow (4 times; 150 AP over the span of 10 seconds); it was
observed that the response increased overtime which displays a long-term change as it lasted
in the form of hours: (red)
ð Control pathway is where no stimulation is occurring – if we have no increase in potentiation
or synaptic strength, we will not see an increase over time: (blue)
What would you expect to happen if we stimulate at the 6 hour point?
• Observing the trend, it would be expected to increase even more; however it does not
o There is a ceiling, set discrete amount of plasticity
Associative LTP:
• Two stimulating electrodes (purple) are stimulating the Schaffer-collateral commissural
pathway – each stimulating electrode is in a distinct group of presynaptic fibers
o Associated LTP is where we have repetitive activity to one synapse
§ LTP is associative; as long as two groups of synapses
are somewhat working together at roughly the same time –
both are going to get stronger
ð Repetitive activity to one synaptic input to a cell can influence whether
another input to the same cell is also potentiated by repetitive activity
Experiment:
• Stimulating electrode II leads to a post-tetanic potentiation for
a brief moment but then goes back to control levels
• Stimulating electrode I leads to a smaller post-tetanic potentiation
for a brief moment but then goes back to normal levels
o Both independently did not generate an LTP
ð If both stimuli were used at the same time we observe a massive
associative form of LTP
o Input from two different synapses coming into the same
neuron is what drives potentiation
Document Summary
Dentate gyrus was later observed to examine the effects of the ap trains. Pathway was stimulated at each arrow (4 times; 150 ap over the span of 10 seconds); it was observed that the response increased overtime which displays a long-term change as it lasted in the form of hours: (red) Control pathway is where no stimulation is occurring if we have no increase in potentiation or synaptic strength, we will not see an increase over time: (blue) What would you expect to happen if we stimulate at the 6 hour point: observing the trend, it would be expected to increase even more; however it does not, there is a ceiling, set discrete amount of plasticity. Associative ltp: two stimulating electrodes (purple) are stimulating the schaffer-collateral commissural pathway each stimulating electrode is in a distinct group of presynaptic fibers, associated ltp is where we have repetitive activity to one synapse.
