Homeostatic Plasticity of Subcellular Neuronal Structures: From Inputs to Outputs

Neurons in the brain are highly plastic, allowing an organism to learn and adapt to its environment. However, this ongoing plasticity is also inherently unstable, potentially leading to aberrant levels of circuit activity. Homeostatic forms of plasticity are thought to provide a means of controlling neuronal activity by avoiding extremes and allowing network stability. Recent work has shown that many of these homeostatic modifications change the structure of subcellular neuronal compartments, ranging from changes to synaptic inputs at both excitatory and inhibitory compartments to modulation of neuronal output through changes at the axon initial segment (AIS) and presynaptic terminals. Here we review these different forms of structural plasticity in neurons and the effects they may have on network function.

TrendsStructural plasticity in response to chronic changes in activity occurs at synaptic inputs at the level of both excitatory and inhibitory compartments. Although opposite in direction, they act to normalise the overall activity of the network in a homeostatic manner.The output of neurons is also influenced by important structural modifications. The axon initial segment, where action potentials are initiated, undergoes changes in either length or position to fine-tune neuronal excitability.Presynaptic terminals, which provide the final stage in neuronal output through the release of neurotransmitter, also show structural alterations that match their postsynaptic partners.Overall, there appear to be multiple forms of plasticity that occur during chronic changes in activity, which together serve to stabilise network function.