Regulation of synaptic scaling by action potential-independent miniature neurotransmission.

Synaptic scaling represents a homeostatic adjustment in synaptic strength that was first identified as a cell-wide mechanism to achieve firing rate homeostasis after perturbations to spiking activity levels. In this review, we consider a form of synaptic scaling that is triggered by changes in action potential-independent neurotransmitter release. This plasticity appears to be both triggered and expressed locally at the dendritic site of the synapse that experiences a perturbation. A discussion of different forms of scaling triggered by different perturbations is presented. We consider work from multiple groups supporting this form of scaling, which we call neurotransmission-based scaling. This class of homeostatic synaptic plasticity is compared in studies using hippocampal and cortical cultures, as well as in vivo work in the embryonic chick spinal cord. Despite differences in the tissues examined, there are clear similarities in neurotransmission-based scaling, which appear to be molecularly distinct from the originally described spike-based scaling.