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Open Access Research

Homeostatic regulation of spontaneous and evoked synaptic transmission in two steps

Richard C Gerkin123*, David W Nauen13, Fang Xu4 and Guo-Qiang Bi134*

Author Affiliations

1 Department of Neurobiology, University of Pittsburgh, 15213 Pittsburgh, PA, USA

2 School of Life Sciences, Arizona State University, 85287 Tempe, AZ, USA

3 Center for the Neural Basis of Cognition, Carnegie Mellon University, 15213 Pittsburgh, PA, USA

4 CAS Key Laboratory of Brain Function and Disease, and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China

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Molecular Brain 2013, 6:38  doi:10.1186/1756-6606-6-38

Published: 22 August 2013

Abstract

Background

During development both Hebbian and homeostatic mechanisms regulate synaptic efficacy, usually working in opposite directions in response to neuronal activity. Homeostatic plasticity has often been investigated by assaying changes in spontaneous synaptic transmission resulting from chronic circuit inactivation. However, effects of inactivation on evoked transmission have been less frequently reported. Importantly, contributions from the effects of circuit inactivation and reactivation on synaptic efficacy have not been individuated.

Results

Here we show for developing hippocampal neurons in primary culture that chronic inactivation with TTX results in increased mean amplitude of miniature synaptic currents (mEPSCs), but not evoked synaptic currents (eEPSCs). However, changes in quantal properties of transmission, partially reflected in mEPSCs, accurately predicted higher-order statistical properties of eEPSCs. The classical prediction of homeostasis – increased strength of evoked transmission – was realized after explicit circuit reactivation, in the form of cells’ pairwise connection probability. In contrast, distributions of eEPSC amplitudes for control and inactivated-then-reactivated groups matched throughout.

Conclusions

Homeostatic up-regulation of evoked synaptic transmission in developing hippocampal neurons in primary culture requires both the inactivation and reactivation stages, leading to a net increase in functional circuit connectivity.

Keywords:
Homeostasis; Metaplasticity; Quantal hypothesis