Neural - Ventricular System Development

Introduction

The ventricular system develops from the single cavity formed from the hollow neural tube. This fluid-filled space is separated from the amnion following fusion of the neural tube and closure of neuropores. At different regions sites within the wall (floor of lateral ventricle and roof of the third and fourth ventricles) differentiate to form choroid plexus a modified vascular structure which will produce Cerebrospinal fluid (CSF)

In development and the space within the spinal cord (central canal) and the brain (ventricles) was derived from the same space within the neural tube. In the adult these 2 spaces remain connected containing the same CSF.

Early in development the cavity within the neural tube (which will form the ventricular space) is filled with amniotic fluid. As the brain and spinal cord grow, this fluid filled space makes up the majority of the nervous system (by volume). Upon closure of the neuropores and development of the embryonic vasculature, this fluid is then synthesized by the choroid plexus, a specialized vascular epithelium. In mammals, the choroid plexuses develop at four sites in the roof of the neural tube shortly after its closure, in the order forth (IV, lateral, and third (III) ventricles.

The choroid plexuses form one region of the blood-brain barrier that regulates the brain's internal environment.

Normal CSF contains high amounts of salts, sugars and lipids and low amounts of protein (0.3-0.7 microg/microL), though there appears to be 60+ proteins as identified by 2D gel. Presence of some protein in the CSF can be indicative of disruption of or incomplete blood/brain barrier.

Development Overview

Ventricles and Central Canal

Stage 11 - appearance of the optic ventricle. The neural groove/tube space is initially filled with amniotic fluid.

Stage 12 - closure of the caudal neuropore, onset of the ventricular system and separates the ependymal from the amniotic fluid

Stage 13 - cavity of the telencephalon medium is visible

Stage 14 - cerebral hemispheres and lateral ventricles begin, rhomboid fossa becomes apparent.

Stage 15 - medial and lateral ventricular eminences cause indentations in the lateral ventricle

Stage 16 - hypothalamic sulcus is evident

Stages 17-18 - interventricular foramina are becoming relatively smaller, and cellular accumulations indicate the future choroid villi of the fourth and lateral ventricles

Stage 18 - areae membranaceae rostralis and caudalis are visible in the roof of the fourth ventricle, and the paraphysis is appearing.

Stage 19 - choroid villi are visible in the fourth ventricle, and a mesencephalic evagination (blindsack) is visible

Stage 20 - choroid villi are visible in the lateral ventricle

Stage 21 - olfactory ventricle is visible

Stages 21-23 - lateral ventricle has become C-shaped (anterior and inferior horns visible). Recesses develop in the third ventricle (optic, infundibular, pineal).

Fetal Period - posterior horn of the lateral ventricle, choroid plexus of the third ventricle, suprapineal recess, interthalamic adhesion, aqueduct, and apertures in the roof of the fourth ventricle.

(Data from: O'Rahilly R, Müller F., 1990)

Choroid Plexus Development

Epithelium from the neural tube epithelium.

Mesenchyma from the meninges.

Enzymes required for CSF production are Na+/K+ ATPase and carbonic anhydrase.

Subarachnoid Space Development

Stage 14 (33 days) - initially as irregular spaces on the ventral surface of the spinal cord.

Stage 18 (44 days) - dura mater is formed and spaces surround the circumference of the spinal cord, which coalesce and contain many blood vessels.

(Data from: Patelska-Banaszewska M, Wozniak W., 2005)