Synaptic-level organization of long-range cholinergic circuits in the basal forebrain

The basal forebrain cholinergic neurons with extensive long-range projections are critical for cortical plasticity, attention, and learning. Their mesoscopic, target area-specific wiring diagram plays a pivotal role in information transfer and pathology of neurodegenerative diseases. Here, using the fluorescence micro-optical sectioning tomography (fMOST) system, the brain-wide presynaptic puncta were comprehensively mapped and reconstructed at the mesoscopic scale. We revealed the precise connectivity and extensive laminar distribution of basal forebrain medial septum and diagonal band nucleus (MS/NDB) projections to downstream brain regions. Specifically, we observed complementary laminar innervation between cholinergic and PV+ neurons in the hippocampal dentate gyrus. Furthermore, two projection pathways to the amygdala with distinct presynaptic puncta distributions were identified, while the inhomogeneity of multiple-dimensional puncta distribution in axons and the heterogeneity of axonal and synaptic projections were explored. This study provides a comprehensive, brain-wide mapping of the presynaptic terminal connections of long-range cholinergic circuits. Whole-brain distribution of presynaptic terminals of basal forebrain cholinergic neurons was acquired via fMOST imaging, revealing their heterogeneous organizational patterns.