Figure 4. Broad output divergence of LC-NE neurons revealed by projection-based viral-genetic labeling.

a, In this strategy, neurons in region B projecting to the C region where CAV-Cre is delivered are labeled, including their collaterals to other output regions (e.g., blue neurons to C₂). b, In this strategy, only Cre+ neurons in region B projecting to the C region where CAV-FLEx^loxP-Flp is delivered are labeled. c, Schematic for data in (d). In this example, CAV was injected in the OB and TC was injected in the LC. TC+ LC-NE axons were imaged in the designated brain regions. All TC+ axons were co-stained with anti-norepinephrine transporter (NET; inset), confirming their NE identity. d, Average normalized fraction of TC+ LC-NE axons in each brain region when CAV was injected into four output sites, or Cre-dependent TC was injected directly into the LC of Dbh-Cre mice (color code on top right). LC: n=4 (Dbh-Cre); Hi: n=4 (Dbh-Cre); AC: n=4 (2 wt, 2 Dbh-Cre); OB: n=5 (3 wt, 2 Dbh-Cre); Me: n=4 (Dbh-Cre). LC-NE neurons labeled in each condition were: 855±102 (LC, n=4); 235±35 (Hi, n=4); 80±31 (OB, n=5); 114±31 (AC, n=4); 202±63 (Me, n=4). e, Comparison of the fraction of TC+ axons at CAV injection sites between projection-based and direct LC labeling methods. Unpaired two-tail t-tests. *, p<0.05. Error bars, s.e.m. Scale, 10 μm. Abbreviations: AC, auditory cortex; CC, cingulate cortex; Cb, cerebellum; Hi, hippocampus; Hy, hypothalamus; LC, locus coeruleus; Me, medulla; OB, olfactory bulb; SC, somatosensory cortex.