Spines or Shaft: How inhibitory synapse location matters
Today I want to talk about the synaptic postion on the dendritic tree. Specifically I want to focus on a review article by Dr. Boivin and Dr. Nedivi called Functional implications of inhibitory synapse placement on signal processing in pyramidal neuron dendrites. Here they propose inhibitory synapse can perform three different functions depending on where they are placed on the dendritic tree.
There can be inhibition on the spines of dendritic trees. Dendritic Spines are little protrusions of cell membrane along the dendritic tree. these regions usually are electrically compact and somewhat isolated from the main dendritic shaft. When Excitatory synapses connect to dendritic spines it allows dendritic spikes to stay relatively localized in the dendritic spine. Of course some of the voltage will leak out into the shaft. If many spines fire dendritic spikes, then the shaft might as well.
It shouldn't come as a surprise that if inhibition is within a spine, then its effect stays within the spine. It does not diffuse outward from the spine. However if the inhibition is on the shaft of the dendritic tree, then all nearby spines feel its influence. Thus inhibition on dendritic shafts have further reach.
However inhibition role is more powerful than that. If the inhibition is closer to the soma it can block action potential backpropagation. This is when the Soma fires an action potential and it backpropagates into the dendritic tree. This is how the synapses become aware if presynaptic activity caused the soma to fire. This allows the neuron to correlate inputs and output, and has huge consequences for Hebbian learning. Well timed inhibition can block these back propagating action potentials, preventing the synapses from knowing if the soma fired or not.
Thus knowing the precise location of inhibition on the dendritic tree is important, as different locations have different effects.
Author: Alex White
Source: https://www.sciencedirect.com/science/article/abs/pii/S0959438817302830
There can be inhibition on the spines of dendritic trees. Dendritic Spines are little protrusions of cell membrane along the dendritic tree. these regions usually are electrically compact and somewhat isolated from the main dendritic shaft. When Excitatory synapses connect to dendritic spines it allows dendritic spikes to stay relatively localized in the dendritic spine. Of course some of the voltage will leak out into the shaft. If many spines fire dendritic spikes, then the shaft might as well.
It shouldn't come as a surprise that if inhibition is within a spine, then its effect stays within the spine. It does not diffuse outward from the spine. However if the inhibition is on the shaft of the dendritic tree, then all nearby spines feel its influence. Thus inhibition on dendritic shafts have further reach.
However inhibition role is more powerful than that. If the inhibition is closer to the soma it can block action potential backpropagation. This is when the Soma fires an action potential and it backpropagates into the dendritic tree. This is how the synapses become aware if presynaptic activity caused the soma to fire. This allows the neuron to correlate inputs and output, and has huge consequences for Hebbian learning. Well timed inhibition can block these back propagating action potentials, preventing the synapses from knowing if the soma fired or not.
Thus knowing the precise location of inhibition on the dendritic tree is important, as different locations have different effects.
Author: Alex White
Source: https://www.sciencedirect.com/science/article/abs/pii/S0959438817302830
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