Monosynaptic rabies tracing maps region-specific inputs to excitatory SUB cells in young WT mice. Representative fluorescent coronal section images from the WT young group. A, Dorsal SUB injection site. Rabies virus-infected neurons are labeled by DsRed, and AAV-infected neurons are labeled by EGFP. B, Enlarged view of the SUB injection site, including white arrows to represent starter neurons. Starter neurons are labeled both red (RV) and green (AAV) fluorescent proteins. C–R, Major presynaptic input regions of the SUB mapped by rabies virus-mediated retrograde monosynaptic tracing. The input regions include the SUB (A,B), anterior CA1 (C,D), posterior CA1 (E,F), CA2 and CA3 (G), MS-DB (H), thalamus (I), RSC (J), postSUB (K), Vis cortex (L), Aud cortex (M), SS cortex (N), Tea and Ect and Prh (O,P), and EC (Q,R). (D), (F), (P), and (R) are enlarged views of the white boxes in (C), (E), (O), and (Q), respectively. All slices are counterstained by DAPI in blue. Scale bars labeled for each panel represent 200 μm.