Submitted on May 23, 2006
Accepted on August 9, 2006
Spike-timing-dependent plasticity of inhibitory synapses in the entorhinal cortex
Julie S. Haas1*, Thomas Nowotny2, and Henry D.I. Abarbanel2
1 Insitute for Nonlinear Science, University of California, San Diego, La Jolla, California, United States
2 Institute for Nonlinear Science, University of California, San Diego, La Jolla, California, United States
* To whom correspondence should be addressed. E-mail: julie.haas{at}gmail.com.
Actions of inhibitory interneurons organize and modulate many neuronal processes, yet the mechanisms and consequences of plasticity of inhibitory synapses remains poorly understood. We report on spike-timing-dependent plasticity of inhibitory synapses in the entorhinal cortex. After pairing presynaptic stimulations at time tpre with evoked postsynaptic spikes at time tpost under pharmacological blockade of excitation we found, via whole-cell recordings, an asymmetrical timing rule for plasticity of the remaining inhibitory responses. Strength of response varied as a function of the time interval 
t = tpost - tpre : for t >0 inhibitory responses potentiated, peaking at a delay of 10 ms. For t <0 the synaptic coupling depressed, again with a maximal effect near 10 ms of delay. We also show that changes in synaptic strength depend on changes in intracellular calcium concentrations, and demonstrate that the calcium enters the postsynaptic cell through voltage-gated channels. Using network models, we demonstrate how this novel form of plasticity can sculpt network behavior efficiently and with remarkable flexibility.
