[Calcium dependent forms of synaptic plasticity in cerebellar Purkinje cells]

Elevation of intracellular calcium concentration ([Ca(2+)](i)) induces several forms of long-term synaptic plasticity in cerebellar Purkinje cells (PCs). These include (1) long-term depression (LTD) at parallel fiber (PF) to PC synapses, (2) LTD at climbing fiber (CF) to PC synapses, (3) long-term potentiation (LTP) at synapses from inhibitory interneurons (rebound potentiation). The current knowledge about calcium dependency for these forms of synaptic plasticity is described in this chapter. (1) Induction of PF-LTD is dependent on elevation of [Ca(2+)](i), that derives from two distinct sources. One is through voltage-dependent calcium channel (VDCC). A CF stimulation leads to elevation of [Ca(2+)](i) due to activation of VDCCs. The other is from the internal calcium store. PFs stimulation activates metabotropic glutamate receptor subtype 1 (mGluR1). It leads to production of inositol-1,4,5-triphosphate (IP(3)) and diacylglycerol (DG) which cause calcium release from internal stores and activation of protein kinase C, respectively. The conjunctive activation of PF and CF inputs is necessary for PF-LTD. (2) LTD at CF to PC synapses (CF-LTD) is induced by the mechanisms similar to those involved in PF-LTD. CF-LTD requires elevation of [Ca(2+)](i) and activation of the mGluR1 to PKC cascade. (3) Rebound potentiation is induced by transient elevation of [Ca(2+)](i) due to activation of VDCCs or IP3-mediated calcium release from internal stores. Elevation of [Ca(2+)](i) activates calcium/ calmodulin-dependent protein kinase II and leads to persistent up-regulation of postsynaptic GABAA receptor function. At the three types of synapses described above, elevation of [Ca(2+)](i) also causes short-term depression of neurotransmitter release from presynaptic terminals. Recent studies demonstrate that transient elevation of [Ca(2+)](i) produces endocannabinoids in PCs that act retrogradely onto presynaptic terminals and suppress neurotransmitter release.