Nanoscale Core–Rim Compartmentalization of Histamine and GABA within Individual Synaptic Vesicles

Classical synaptic transmission assumes that amino acid neurotransmitters and monoamines are stored in distinct vesicle populations. Here, we provide structural evidence for a dual-transmitter organization in which histamine and GABA are spatially partitioned into a core and rim within individual synaptic vesicles. Using an engineered glutaraldehyde–NaBH₄ immuno-electron microscopy platform, quantitative analysis of 2,195 vesicles revealed a previously unrecognized nanoscale architecture, with histamine-associated signal concentrated within the vesicular core (95.1%), while GABA is organized toward the peripheral rim. Light microscopy further demonstrated extensive histamine–GABA correspondence across central and peripheral tissues, including sympathetic ganglia and adrenal medulla. This intravesicular segregation challenges the conventional separation of amino acid and monoamine storage into distinct vesicle classes and reveals that chemically distinct transmitters can occupy organized domains within a single vesicular lumen. This architecture may provide a structural basis for the distinct physiological modes of GABAergic and histaminergic signaling, linking nanoscale vesicular organization to their established differences in temporal action.