Regional differences in postweaning growth by choroid plexuses as affected by dietary salt deficiencies

Different inflammatory reactions to vitamin D3 among the lateral, third and fourth ventricular choroid plexuses of the rat

The four choroid plexuses in the brain ventricles are not identical, but differences among them have rarely been studied. The present work concerns the inflammatory and hemorrhagic choroid plexitis produced in Lewis rats by a single gavage of cholecalciferol (vitamin D(3)) or related steroids with vitamin D activity. Plexitis was very severe in the fourth ventricular plexus, somewhat less severe in the lateral ventricular plexuses, and almost absent in the third ventricular plexus. These findings were compared to the scanty data from the literature on differences among the plexuses.

Choroid plexus structure and function in young rats on a high-potassium diet

Rats, 20 days old, were fed a diet containing 20% KCl for 10 days. At 30 days these rats had lower body, brain and choroid plexus weights than matched controls and plasma [K+] was increased to 7.5 mM compared to 4.1 mM for controls. Cerebrospinal fluid (CSF) [K+] and bulk fluid secretion were not changed by the high K+ diet but there was a mild metabolic acidosis. The fourth ventricle choroid plexus was prepared for transmission electron microscopy and the structure of the epithelium analysed by quantitative stereology. The high K+ rats had a large increase in the mitochondrial volume fraction of the epithelium due to a 36% increase in individual mitochondrial volume. The high-K+ rats also had a decrease in the apical surface density of the epithelium due to a 41% decrease in the height of the microvilli. It is concluded that the increase in mitochondrial volume may provide the additional energy required for the increased transport of K+ out of the CSF in hyperkalaemia. The reduction in height of the microvilli could be a means for maintaining a normal CSF bulk secretion rate despite the increase in K+ transport required to maintain normal CSF [K+] in hyperkalaemia.

Third ventricle choroid plexus function and its response to acute perturbations in plasma chemistry

The homeostatic role of the third ventricle choroid plexus (3VCP) in the maintenance of CSF electrolytes was investigated by quantifying alterations in CP epithelial ion concentrations induced by chemical perturbations of plasma in adult Sprague-Dawley rats. Significant regional differences (third vs fourth (4VCP) and lateral ventricle CP (LVCP] were found in epithelial content of Na+ and K+, with respect to baseline levels as well as alterations caused by 5-60 min of systemic metabolic acidosis. 3VCP, which comprises ca. 10% of total choroidal tissue, has a water content, extracellular fluid volume and vascularity comparable to 4VCP and LVCP; yet 3VCP is characterized by relatively high and low values for cellular [Na+] (68 mM) and [K+] (118 mM). Compared to time-matched controls, acute metabolic acidosis (i.p. NH4Cl) effected a response, i.e. increases [K+] and decreases [Na+], in 3VCP that was less than in 4VCP, and substantially smaller than in LVCP. The onset and duration of induced electrolyte changes were qualitatively similar among the 3 plexus regions. Although systemic acidosis severely altered CP electrolyte concentrations, it did not compromise CSF homeostasis of [K+] and [Na+]. The function of 3VCP is discussed in terms of secretory capacity, embryological origin, and innervation. Overall, the findings indicate that transport/permeability phenomena which mediate transmembrane distribution of Na+ and K+ in 3VCP differ quantitatively from other regions of the blood-CSF barrier.