Munc13-1 couples DAG and Ca ²⁺ signaling to dynamic vesicle priming, synaptic short-term plasticity, and posttetanic potentiation

Synaptic strength and plasticity are fine-tuned by neuromodulation and use-dependent second-messenger signaling. Presynaptic diacylglycerol (DAG), Ca 2+ , and Ca 2+ -calmodulin signaling converge on the essential synaptic vesicle (SV) priming protein Munc13-1 via its regulatory C 1 , C 2 B, and CaM-binding domains. Using brainstem-specific heterozygous mice expressing a DAG-binding-deficient Munc13-1 variant (Munc13-1 H567K ), we compared synaptic transmission in situ at glutamatergic calyx of Held synapses carrying either a single Munc13-1 H567K or a single Munc13-1 wt allele. Munc13-1 H567K/− synapses show enhanced initial strength but impaired steady-state release and slower recovery from depression. These deficits result from an increased initial abundance of fully primed SVs and a loss of activity-dependent acceleration of SV priming. Posttetanic potentiation (PTP) is strongly reduced in Munc13-1 H567K/− synapses and either increased or attenuated by C 2 B mutations that enhance or weaken Ca 2+ -phospholipid binding. Our data identify Munc13-1 as a target of presynaptic TrkB–phospholipase C–γ signaling and demonstrate that C 1 and C 2 B domain-dependent regulation of Munc13-1 determines synaptic strength and shapes short-term plasticity and PTP.