Objective: In our previous papers we demonstrated that changes in blood and cerebrospinal fluid (CSF) osmolarity have a strong influence on CSF pressure and volume, which is in accordance with a new proposed hypothesis of CSF physiology. Thus, acute changes in CSF volume should be reflected in the CSF concentration of different central nervous system (CNS) metabolites.
Methods: In anesthetized cats (n = 4) we measured the outflow volume of CSF by cisternal free drainage at a negative CSF pressure (-10 cmH2O) before and after the intraperitoneal (i.p.) application of a hypo-osmolar substance (distilled water). In samples of CSF collected at different time intervals (30 min) we measured the concentration of homovanillic acid (HVA).
Results: In spite of fact that constant CSF outflow volume was obtained after a 30-min period in our model, the concentration of HVA gradually increased over time and became stable after 90 min. After the i.p. application of distilled water the outflow CSF volume increased significantly, whereas the concentration of HVA significantly decreased over 30 min.
Conclusions: The results observed suggest that alterations in serum osmolarity change the CSF volume and concentrations of neurotransmitter metabolites because of the osmotic arrival of water from CNS blood capillaries in all CSF compartments.
Keywords: Blood osmolarity; Cat; Central nervous system; Cerebrospinal fluid; Cerebrospinal fluid hydrodynamics; Cerebrospinal fluid volume; Homovanillic acid; Monoamine neurotransmitter metabolites.