Visualizing dendritic characteristics of corticotropin-releasing hormone neurons at single-cell resolution in the whole mouse brain

Corticotropin-releasing hormone (CRH) is an important neuromodulator with wide distribution in the brain. Here, we screened the CRH-IRES-Cre;Ai32 mouse line to reveal the morphologies of individual CRH neurons throughout the mouse brain by using fluorescence micro-optical sectioning tomography (fMOST) system. Diverse dendritic morphologies and projection fibers were found in various brain regions. Reconstructions showed hypothalamic CRH neurons had the smallest somatic volumes and simplest dendritic branches, and CRH neurons in several regions shared a bipolar morphology. Further investigations in the medial prefrontal cortex unveiled somatic depth-dependent morphologies that exhibited three types of connections and CRH neurons in the anterior parvicellular area of hypothalamus had fewer and smaller Herring bodies whereas in the periventricular area had more and larger Herring bodies that were present within fibers projecting to the third ventricle. Our findings provide the most comprehensive intact morphologies of CRH neurons throughout the mouse brain that is currently available.