RTN neuron projections to the ponto-medullary respiratory network are highly collateralized. A, Experimental approach to retrogradely label RTN^Nmb neurons using a Cre-reporter mouse. B, Location and distribution of AAV_rg-Cre injections. C, Group data percent of RTN^Nmb neurons that innervate the PreBötC, LPB, cVRG, and NTS. D, Same data as in C, except segregated according to the presence or absence of Galanin transcript (Gal). E, Image of retrograde-labeled RTN^Nmb neurons after injections in the cVRG. RTN^Nmb neurons that were Gal- were less commonly labeled that RTN^Nmb neurons that were Gal⁺, and that Gal⁺ often expressed low levels of Nmb. Scale bar, 100 µm. F, Distribution of retrograde-labeled RTN^Nmb neuron from a representative case from each targeted region.