Dendritic calcium spikes induce bi-directional synaptic plasticity in the lateral amygdala

Postsynaptic induction of long-term potentiation (LTP) at cortical and thalamic afferent synapses onto lateral amygdala (LA) projection neurons not only involves NMDA receptor activation, but also depends on L-type voltage-dependent calcium channels (L-VDCCs). Here we show, using whole cell recordings and two-photon Ca2+ imaging, that L-VDCCs contribute to the induction of dendritic Ca2+ spikes in LA projection neurons. Dendritic Ca2+ spikes can be induced in the absence of sodium spikes by supra-threshold somatic depolarization or by pairing sub-threshold depolarization with synaptic stimulation. Moreover, synaptic induction of Ca2+ spikes is facilitated by R-VDCCs in a pathway-specific manner. Once induced, dendritic Ca2+ spikes propagate into large parts of the dendritic tree. We show that pairing synaptic stimulation with single dendritic Ca2+ spikes can induce bi-directional plasticity, the sign of which might be determined by the anatomical location of active synaptic inputs relative to the spike initiation zone. These data suggest an important role for dendritic Ca2+ spikes in dendritic integration and provide a mechanism by which local synaptic activity may influence global dendritic integration in LA projection neurons.