Pseudotyped rabies virus tracing reveals the monosynaptic projection from SuM to PV⁺ neurons in CA3. A, Experimental procedure and timeline. B, Top left, Sample confocal image represents the viral injection site in dorsal CA3 from a PV-Cre mouse. Top right, Expanded view represents a starter cell (mCherry⁺/GFP⁺) that is also immunopositive for PV staining (arrowhead). Bottom, Expanded views of the starter cell. C, Sample confocal images represent mCherry⁺ cells observed in SuM (top). Two mCherry⁺ cells in SuM shown in the expanded views (bottom). D, Sample confocal image represents the viral injection site in dorsal CA3 from a SOM-Cre mouse. E, No mCherry⁺ cells detected in SuM (repeated in 4 SOM-Cre mice).