(A) HTR6 (labeled by CF633, green in merged panel) is highly enriched in CA1 neuronal primary cilia (ADCY3, magenta in the merged panel: 20 μm MIP).
(B) Magnified images from (A). 5-HTR6s are not evenly distributed along the length of cilia and can be enriched at areas with low ADCY3 labeling (arrow).
(C) Left panel: cilia (magenta) co-labeled with serotonergic axons (green). 20-μm maximum intensity projection (MIP). Middle panel: cilia in the left panel color coded by the shortest distance to a serotonergic axon. Right panel: cilia from left panel color coded with the shortest distance to a serotonergic axon-associated synaptophysin punctum.
(D) Floxed synaptophysin-EGFP driven by Tph2-Cre showed ADCY3-labeled cilia (magenta in the merged panel) in contact with serotonergic presynaptic terminals (amplified by anti-GFP and Alexa 488, green in the merged panel).
(E) 5-HTR6 (green in the merged panel) are enriched on the cilia at the axonal contact sites (SERT, cyan in the merged panel). Two cilia are in contact with a single serotonergic axonal varicosity. ADCY3 (magenta in the merged panel) can extend beyond the contact site that has few 5-HTR6 (arrow).
(A), (B), and (E) are deconvolved confocal images with photon counting detection (Leica). (C) and (D) are Airyscan images (Zeiss). Data from 3- to 4-month-old male C57BL/6J mice.