Involvement of complexin II in synaptic plasticity in the CA1 region of the hippocampus: the use of complexin II-lacking mice.

An electrophysiological study was performed with mice lacking complexin II, a presynaptic protein. The long-term potentiation (LTP) by high-frequency stimulation, recorded in the hippocampal CA1 area, was decreased in complexin II-lacking mice (CPXII KO mice). The overall postsynaptic currents elicited by low frequency stimulation on the Schaffer collateral/commissural fibers in the hippocampal CA1 pyramidal cells were not different between wild-type and mutant mice. Excitatory postsynaptic currents (EPSCs) recorded in the presence of 50 microM bicuculline and inhibitory postsynaptic currents (IPSCs) recorded in the presence of 50 microM AP-5 (DL-2-amino-5-phosphonopentanoic acid) + 30 microM CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) were also identical between wild-types and mutants. Furthermore, the EPSCs following repetitive stimulation (10 Hz) in CPXII KO mice did not show any difference with wild-types. These findings suggest that complexin II does not play a crucial role in ordinary neural transmission, short-term synaptic plasticity or synaptic transmission during high-frequency repetitive stimulation. Therefore, the protein is thought to be involved in the LTP process following tetanic stimulation, including the induction and/or maintenance of the LTP.