The effects of ventricular fluid osmolality on the bulk flow of nascent fluid into the cerebral ventricles of anesthetized cats was measured during ventriculocisternal perfusion. This nascent fluid consists of both cerebrospinal fluid (CSF) and fluid which results from an osmotic gradient between ventricular fluid and the blood and/or brain. Perfusions were carried out with both mock CSF and with solutions containing either sucrose, urea, or NaCl. Differences between the normal bulk flow rate of nascent CSF and bulk flow rate measured during perfusion with anisotonic solutions were linearly related to corresponding differences in osmolality of the effluent fluid from the ventricles. The coefficients of somotic flow using sucrose (0.231 mul/min per mOsm) and NaCl (0.224) were similar, and greater than that using urea (0.156). During perfusion with sucrose when effluent osmolality increased by 200 mOsm (63% of normal), bulk flow rate of nascent fluid increased by 50 mul/min (200% of normal). Flow was undetectable when the effluent osmolality was 190 mOsm (decrease of 135 mOsm), although osmotically active particles continued to enter the ventricular system. Intravenous injection of acetazolamide reduced these coefficients to similar values of 0.0963 for NaCl, and 0.0955 for urea. In all experimental conditions no changes were found in cerebral water content. These results suggest that the increased bulk flow which occurs during perfusion with hypertonic solutions originates from the choroid plexus.

The effects of changes in serum osmolarity on the rate and osmolarity of bulk flow of fluid into the cerebral ventricles and on cortical white and grey matter water content were studied in cats. Bulk flow rates and osmolarities were measured during ventriculocisternal perfusion both before and after intravenous infusion of glucose solutions. Infusions of glucose in concentrations greater than 6% decreased fluid bulk flow rate and its osmolarity. Glucose in concentrations less than 6 percent increased fluid bulk flow rate and decreased its osmolarity. Bulk flow rate and serum osmolarity were found to be linearly related with a coefficient of osmotic flow of minus 0.835 mul/min per mOsm/l. At the extremes of induced serum osmolarities, (290 and 360 mOsm/l) bulk flow rate was either increased by 120 percent or completely inhibited. Effluent osmolarity also increased proportionately to serum osmolarity (0.338 mOsm/l per mOsm/l). When compared to controls, cortical grey and white matter water content increased by 1.9 percent and 2.9 percent, respectively, when the infused glucose concentration was 2.5 percent or less, and decreased by 1.8 percent and 2.9 percent when the concentration was 10 percent or more. The results of these experiments suggest that the increased bulk flow comes from the brain, rather then directly from the blood.

No abstract

✓ The effects of removal of the calvaria and excision of the dura on the development of hydrocephalus was studied in adult cats made hydrocephalic by an intracisternal injection of kaolin. In some animals, the calvaria was removed prior to the induction of experimental hydrocephalus, and in others when the hydrocephalus was compensated. In both groups of cats, the results were similar. Ventricular dilatation was massive, often leaving a cortical mantle less than 1 mm thick. A mean ventricular volume measured in 17 cats was 16.9 ml. Cerebrospinal fluid turnover measured during steady-state ventricular perfusion showed significant increases in formation and decreases in absorption of spinal fluid when compared to that in hydrocephalic cats with intact skulls.

Formation of cerebrospinal fluid (CSF)

CSF volume flow and sodium (Na+)-influx rates in normal and kaolin-induced hydrocephalic cats were measured during ventricular perfusion with anisotonic sucrose solutions. When ventricular fluid osmolality was 120 mOsm, CSF volume flow ceased for both groups of cats. As ventricular fluid osmolality was increased, the CSF volume flow rate of normal cats increased to 70 microliter per minute, and in hydrocephalic cats to 40 microliter per minute. In normal cats, for ventricular fluid osmolality between 50 and 350 mOsm, Na+-influx was constant and thought to occur by diffusion; while for higher osmolalities, Na+-influx increased. In hydrocephalic cats, Na+-influx increased over the entire range of ventricular osmolality but was less than in normal cats. Acetazolamide decreased the CSF volume flow in normal cats by 40 percent, but was ineffective in hydrocephalic cats. These results suggest that CSF secretion by the choroid plexus of cats with kaolin-induced hydrocephalus is impaired.

SUMMARY The skull and dura were removed over one or both cerebral hemispheres of cats with experimental hydrocephalus, and the effects on ventricular volume and csf turnover were measured by ventricular perfusion. This procedure frequently resulted in bilateral massive ventriculomegaly when the calvarium was removed on both sides; when it was removed on one side, ventriculomegaly occurred only on that side. No differences in rates of csf formation and absorption between both groups of animals were noted; however, these rates may be significantly different from those noted in hydrocephalic cats with intact skulls. RÉSUMÉ Le rôle du crâne et de la duremère dans l'hydrocéphalie expérimentale du chat Le crâne et la duremère ont été supprimés sur l'un ou les deux hémisphèes cérébraux de chat présentant une hydrocéphalie expérimentale; les effets sur les volumes ventricu‐laires et la circulation du lcr furent mesurés par perfusion ventriculaire. Ce procédé a provoqué fréquemment une ventriculomégalie massive bilatérale en cas de résection de la boite crânienne des deux côtés; en cas de résection unilatérale, la ventriculomégalie ne se manifestait que du même côté. Entre les deux groupes, il n'a été noté aucune différence dans les taux d'absorption ou de formation de lcr, mais ces taux pouvaient être signi‐ficativement différents de ceux observés chez les chats hydrocéphales à crâne intact. ZUSAMMFASSUNG Die Bedeutung von Schädeldach und Dura bei experimentellem Hydrocephalus bei Katzen Bei Katzen mit experimentellem Hydrocephalus wurden das Schädeldach und die Dura entfernt, und durch ventriculäre Perfusion wurde der Einfluß auf das ventriculäre Volumen und die Liquorzirkulation gemessen. Bei Entfernung des Schädeldaches auf beiden Seiten resultierte dadurch häufig eine doppelseitige massive Ventrikelvergrößerung; wenn es nur auf einer Seite entfernt worden war, trat die Ventrikelvergrösserung nur auf der Seite auf. Zwischen den beiden Gruppen wurden keine Unterschiede bei der Liquorbildung und Liquorabsorption beobachtet, aber es ist möglich, daß dafür signifikante Unterschiede bei hydrocephalen Katzen mit intaktem Schädeldach bestehen. RESUMEN El papel del cráneo y fa dura en el hidrocéfalo experimental del gato Se extirpó la parte ósea del cráneo y la dura sobre uno o dos hemisferios cerebrales de gatos con hidrocefalia experimental y se midió por perfusión ventricular los efectos sobre el volumen ventricular y el ciclo del lcr. Este proceder daba lugar frecuentemente a una ventriculomegalia masiva bilateral cuando se extirpaba el hueso en ambos lados; si se extirpaba en un solo lado la ventriculomegalia ocurría sólo en este lado. No se observó ninguna diferencia en la velocidad de formación y absorción del lcr de ambos grupos, pero estas velocidades pueden ser significativamente diferentes de las observadas en gatos hidrocéfalicos con cráneo intacto.

The effects of changes in serum osmolality on the volume flow of fluid into the cerebral ventricles and on brain water content was examined in cats with kaolin-induced hydrocephalus. Slopes of the regression lines relating volume flow and serum osmolality for both normal and hydrocephalic cats are the same. The constant difference in flow rates between the two lines, 7 mul per minute, is probably due to impaired choroid plexuow rates between the two lines, 7 mul per minute, is probably due to impaired choroid plexus function of the hydrocephalic cats. The osmotic pressure gradient that causes the flow of fluid is therefore probably between blood and brain. Under these conditions changes in brain water content of hydrocephalic cats were smaller than in normals and can be related to the edema present in this disorder. Despite the inflammatory response to kaolin, the blood-brain barrier remains intact. From the calculated filtration coefficient, it can be inferred that the flow of water from serum through brain and into cerebrospinal fluid is limited by the resistance of fluid flow through the brain.