Nerve endings in the choroid plexus of the fourth ventricle of the rat: electron microscopic study

Nerve fibers and nerve endings in the fourth ventricle choroid plexus of the adult rat were studied with the electron microscope. Nerve endings were found at two sites within the plexus: (1) on the smooth musculature of the blood vessels (i.e. vascular nerve endings), and (2) in the stroma between the choroidal epithelium and the fibrovascular core. Ultrastructurally all fibers were of the efferent type, and the majority were unmyelinated. No ganglion cell bodies were identified. Fibers ending in relation to the smooth muscle of the vessels presumably control the calibre of these vascular channels. Although the role of the stromal nerve endings is as yet unknown, these fibers may influence epithelial cell functions and thus indirectly regulate choroidal cerebrospinal fluid production.