The hypothalamo-choroidal tract. I. Immunohistochemical demonstration of neurophysin pathways to telencephalic choroid plexuses and cerebrospinal fluid.

Neurosecretory pathways were examined in normal male rats by the use of the immunoperoxidase technique for the localization of neurophysin in Bouin-fixed, deparaffinized sections. Using this technique two projections of extrahypothalamic neuorosecretory fibers can be traced to the sites of origin of the choid plexuses of both horns of the lateral ventricles. Neurophysin-containing axons originating primarily from the paraventricular field course dorsolaterad to enter the choroid fissure of the dorsal horn. A caudally direced group of fibers course ventrolaterad to enter the ventral horn choroid fissures. The supraoptic nuclear field is the primary contributor to the latter group. Scattered neurosecretory neurons are found in association with both pathways, usually in contact with blood vessels supplying the choroid plexuses, or in the telencephalic subependymal stroma. Neurosecretory fibers and terminals occur within the choroid fissures and juxtaventricular neuropil. The neurosecretory terminals in the choroid fissures appear as Herring-body type neurohemal organs; in the neuropil they appear as punctate peri-neuronal desities suggestive of synaptic contacts. Thes morphologic findings are discussed in relation to reports indicating the presence of antidiuretic, vasopressin-like activity in cerebrospinal fluid and choroid plexus extraxts together with ultrastructural evidence supportive of vasopressin-mediated transchoroidal cerebrospinal fluid absorption. These results and those of others indicated the possible involvement of the neurosecretory system in the regulation of brain interstitial-ventricular cerebrospinal fluid dynamics.