Phosphorylation and local presynaptic protein synthesis in calcium- and calcineurin-dependent induction of crayfish long-term facilitation

Long-term facilitation at the crayfish opener muscle is elicited by prolong ed high frequency stimulation, and arises from an increase in functional ac tive zones, resulting in increased transmitter release. LTF induction depen ds critically upon presynaptic calcium accumulation and calcineurin (PP2B) activity. The protein synthesis dependence of this synaptic strengthening w as investigated. LTF occurred without transcription, but the translation in hibitors cycloheximide and anisomycin, or local presynaptic injection of mR NA cap analog m(7)GpppG, impaired LTF expression. Both MAP kinase and phosp hatidylinositol 3-OH kinase (PI3K) activation are implicated in this rapamy cin-sensitive synaptic potentiation. This study defines an important role f or protein synthesis in the expression of activity-dependent plasticity, an d provides mechanistic insight for the induction of this process at presyna ptic sites.