Abstract
A significant fraction of the total calciumcalmodulin-dependent protein kinase II (CaMKII) activity in neurons is associated with synaptic connections and is present in nerve terminals, thus suggesting a role for CaMKII in neurotransmitter release. To determine whether CaMKII regulates neurotransmitter release, we generated and analyzed knockout mice in which the dominant alpha-isoform of CaMKII was specifically deleted from the presynaptic side of the CA3-CA1 hippocampal synapse. Conditional CA3 alpha-CaMKII knockout mice exhibited an unchanged basal probability of neurotransmitter release at CA3-CA1 synapses but showed a significant enhancement in the activity-dependent increase in probability of release during repetitive presynaptic stimulation, as was shown with the analysis of unitary synaptic currents. These data indicate that alpha-CaMKII serves as a negative activity-dependent regulator of neurotransmitter release at hippocampal synapses and maintains synapses in an optimal range of release probabilities necessary for normal synaptic operation.