Differential induction of long term synaptic plasticity in inhibitory synapses of the hippocampus.

Long term synaptic plasticity has been more extensively studied in excitatory synapses, but it is also a property of inhibitory synapses. Many inhibitory synapses target hippocampal pyramidal neurons of the CA1 region. They originate from several interneuron classes that subdivide the surface area that they target on the pyramidal cell. Thus, many interneurons preferentially innervate the perisomatic area and axon hillock of the pyramidal cells while others preferentially target dendritic branches and spines. Methods to preferentially activate dendritic or somatic inhibitory synapses onto pyramidal neurons have been devised. By using these methods, the present work demonstrates that a stimulation pattern that induces long term potentiation (LTP) in excitatory synapses of the Schaffer collaterals is also capable of inducing distinct types of long term plastic changes in different classes of inhibitory synapses: Induction of long term depression (LTD) was seen in dendritic inhibitory synapses whereas LTP was observed in somatic inhibitory synapses. These findings suggest that inhibitory synapses arising from different interneuron classes may respond to the same stimulus according to their specific plastic potential enabling a spatial combinatorial pattern of inhibitory effects onto the pyramidal cell.