Deactivation of L-type Ca Current by Inhibition Controls LTP at Excitatory Synapses in the Cerebellar Nuclei

SummaryLong-term potentiation (LTP) of mossy fiber EPSCs in the cerebellar nuclei is controlled by synaptic inhibition from Purkinje neurons. EPSCs are potentiated by a sequence of excitation, inhibition, and disinhibition, raising the question of how these stimuli interact to induce plasticity. Here, we find that synaptic excitation, inhibition, and disinhibition couple to different calcium-dependent signaling pathways. In LTP induction protocols, constitutively active calcineurin can replace synaptic excitation, and constitutively active α-CaMKII can replace calcium influx associated with resumption of spiking upon disinhibition. Additionally, nimodipine can replace hyperpolarization, indicating that inhibition of firing decreases Ca influx through L-type Ca channels, providing a necessary signal for LTP. Together, these data suggest that potentiation develops after a calcineurin priming signal combines with an α-CaMKII triggering signal if and only if L-type Ca current is reduced. Thus, hyperpolarization induced by synaptic inhibition actively controls excitatory synaptic plasticity in the cerebellar nuclei.

► Inhibition gates LTP in the cerebellar nuclei by closing L-type Ca channels ► L-type calcium current suppresses LTP induction in the cerebellar nuclei ► Synaptic excitation activates calcineurin, and spiking activates CaMKII ► Calcineurin, CaMKII, and inhibition combine to generate LTP