Innervation of ventricular and periventricular brain compartments

► Neurons that may release substances into the CSF were retrogradely labeled with intraventricular infusions of a tracer. ► The tracer diffused into periventricular regions and was retrogradely transported by numerous afferents. ► Labeled neurons were located in the telencephalon, diencephalon, midbrain, and brainstem. ► The data support the concept of volume transmission, whereby neuroactive substances diffuse to distant receptors.