Graphs Built From Reported Results

Synapse — visual summary

A synapse converts an electrical signal in the presynaptic neuron to a chemical signal (neurotransmitter) that binds postsynaptic receptors, producing excitation or inhibition; presynaptic protein assemblies (e.g., Munc13/Munc18/SNAREs) dock and prime vesicles for Ca2+-triggered fusion, while postsynaptic receptor composition (AMPAR/GABAA) determines response type and strength Munc13 templating of SNAREs AMPAR assembly and Q/R editing

How a chemical synapse works — visuals first

This timeline is a qualitative schematic of the canonical steps: presynaptic AP → voltage-gated Ca2+ entry → Ca2+-sensing machinery triggers SNARE-mediated fusion → transmitter released → postsynaptic receptors (e.g., AMPA, NMDA, GABAA) transduce chemical signal into postsynaptic current (excitation or inhibition). Core molecular evidence below.

Structural/functional evidence: Munc13 oligomers template multiple SNAREpins and are required for efficient docking/priming and fast Ca2+-triggered release — cryoET + reconstitution + in vivo genetics supports this templating model and shows that disrupting Munc13 interfaces reduces SNARE assembly and release probability Munc13 templating evidence

The inhibitory concentrations (IC50) reported experimentally support that interfering with phosphoinositide metabolism and/or Ca2+ signaling reduces evoked transmitter release (neomycin IC50 ~0.5 mM for K+-evoked, ~0.65 mM for veratridine-evoked) — original measurements from rat brain slices and synaptosomes Neomycin inhibition of release

Postsynaptic response depends on receptor composition: AMPARs (fast depolarizing), NMDARs (voltage-dependent, Ca2+-permeable when GluR2 absent/edited state matters), and GABAA (fast Cl− mediated inhibition); AMPAR assembly and calcium permeability are strongly influenced by GluR2 Q/R editing which controls tetramerization and ER exit GluR2 Q/R editing controls AMPAR properties

Evidence strength & blindspots

• High-confidence molecular/structural data support Munc13 templating and SNARE assembly from cryoET + reconstitution + in vivo genetics, but in vitro simplifications and species differences remain possible confounders Munc13 evidence and limits.
• Postsynaptic receptor composition (AMPAR Q/R editing) strongly constrains Ca2+ permeability—biochemical evidence robust but physiological consequences depend on cell type and development AMPAR assembly evidence.
• Pharmacological perturbations (e.g., neomycin) show that blocking phosphoinositide/Ca2+ signaling reduces evoked transmitter release — data are ex vivo and concentration-dependent; extrapolate to intact circuits cautiously Neomycin ex vivo inhibition data.

Concise mechanistic chain (one line each)

1. AP opens presynaptic voltage-gated Ca2+ channels → local Ca2+ microdomain rises.
2. Ca2+ sensor (synaptotagmin) triggers SNARE-mediated membrane fusion at active zone; Munc13 organizes docking/priming and templates SNAREpins for speed/precision Munc13 role.
3. Transmitters diffuse across cleft (0.02–0.05 µm) and bind postsynaptic receptors → postsynaptic current/excitation or inhibition depending on receptor type (AMPAR/NMDAR vs GABAA) GABAA receptor dynamics review.

Selected sources used (inline above): Munc13 templating study (2025), AMPAR Q/R editing (2003), neomycin inhibition (1987), GABAA dynamics review (2008). See inline citation tags for full extracts.