Spinal contribution to CSF pressure lowering effect of mannitol in cats.
OBJECTIVE
After application of hyperosmolar mannitol the cerebrospinal (CSF) pressure is usually lowered within 30 min but this effect cannot be explained either by changes in intracranial blood volume and flow or by changes in brain volume. We assume that this effect of mannitol my be consequence of CSF volume decrease primarily in the spinal CSF due to high compliance of the spinal dura.


METHODS
To explore such a possibility we planned to separate spinal and cerebral CSF. In chloralose anaesthetized cats dorsal laminectomy of C2 vertebrae was performed and a plastic semi ring was positioned extradurally separating cranial and spinal CSF. CSF pressures were recorded via cannulas positioned in lateral ventricle and lumbar subarachnoid space at L3 vertebrae, respectively.


RESULTS
After intravenous bolus of 20% mannitol (0.5 or 1.0 g/kg/ 3 min) in control animals without cervical stenosis, the fall of both ventricular and lumbar CSF pressures was equal over time. At 15 min after mannitol application in cats with cervical stenosis an slight increase of ventricular and a fall of lumbar CSF pressures were observed, while at 30 min a gradient of these pressures of 5.5 and 7 cm H2O at lower and higher dose of mannitol, respectively, were registered. However, after removal of cervical stenosis these gradients disappeared.


CONCLUSIONS
The observed changes of CSF pressures in spinal and intracranial space indicate that spinal subarachnoid space contributes a great deal to overall fall of CSF pressure and volume in the early period after mannitol application probably due to high compliance of the spinal dura.
Klarica
M
M
Department of Pharmacology and Croatian Institute for Brain Research, School of Medicine, Zagreb, Croatia. mklarica@hiim.hr
Varda
R
R
Vukić
M
M
Oresković
D
D
Rados
M
M
Bulat
M
M
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000503:physiopathology*; D002415:Cats; D015170:Cerebrospinal Fluid Pressure / Q000187:drug effects*; D008353:Mannitol / Q000008:administration & dosage*; D013116:Spinal Cord / Q000187:drug effects* / Q000503:physiopathology*; D013130:Spinal Stenosis / Q000134:cerebrospinal fluid / Q000188:drug therapy / Q000503:physiopathology*
D008353:Mannitol