The effect of increased CSF pressure on interstitial fluid flow during ventriculocisternal perfusion in the cat

Cerebral haemodynamics in patients with glutaryl-coenzyme A dehydrogenase deficiency

In glutaric aciduria type 1, glutaryl-coenzyme A and its derivatives are produced from intracerebral lysine and entrapped at high concentrations within the brain, where they interfere with energy metabolism. Biochemical toxicity is thought to trigger stroke-like striatal degeneration in susceptible children under 2 years of age. Here, we explore vascular derangements that might also contribute to brain damage. We studied injured and non-injured Amish glutaric aciduria type 1 patients using magnetic resonance imaging (n = 26), transcranial Doppler ultrasound (n = 35) and perfusion computed tomography (n = 6). All glutaric aciduria type 1 patients had wide middle cerebral, internal carotid and basilar arteries. In non-injured patients, middle cerebral artery velocities were 18-26% below control values throughout late infancy and early childhood, whereas brain-injured children had an early velocity peak (18 months) and low values thereafter. Perfusion scans from six patients showed that tissue blood flow did not undergo a normal developmental surge. We observed four different perfusion patterns. (i) Three children (two non-injured) had low cerebral blood flow, prolonged mean transit time, elevated cerebral blood volume and high mean transit time/cerebral blood flow and cerebral blood volume/cerebral blood flow ratios. This pattern optimizes substrate extraction at any given flow rate but indicates low perfusion pressure and limited autoregulatory reserve. (ii) Ten hours after the onset of striatal necrosis in an 8-month-old infant, mean transit time and cerebral blood volume were low relative to cerebral blood flow, which varied markedly from region to region. This pattern indicates disturbed autoregulation, regional perfusion pressure gradients, or redistribution of flow from functional capillaries to non-exchanging vessels. (iii) In an infant with atrophic putaminal lesions, striatal flow was normal but mean transit time and cerebral blood volume were low, consistent with perfusion in excess of metabolic demand. (iv) Finally, a brain-injured adult with glutaric aciduria type 1 had regional perfusion values within the normal range, but the putamina, which normally have the highest regional perfusion, had cerebral blood flow values 24% below cortical grey matter. Although metabolic toxicity appears central to the pathophysiology of striatal necrosis, cerebrovascular changes probably also contribute to the process. These changes may be the primary cause of expanded cerebrospinal fluid volume in newborns, intracranial and retinal haemorrhages in infants and interstitial white matter oedema in children and adults. This pilot study suggests important new areas for clinical investigation.

Differences in cerebrospinal fluid dynamics do not affect the levels of biochemical markers in ventricular CSF from patients with aqueductal stenosis and idiopathic normal pressure hydrocephalus

To compare levels of biochemical markers in ventricular cerebrospinal fluid (vCSF) between patients with aqueductal stenosis (AS) and idiopathic normal pressure hydrocephalus (INPH) and relate these results to clinical outcome after surgery. Neurofilament light protein, tau protein, sulfatide, vasoactive intestinal peptide (VIP), neuropeptide PYY (NPY) and CSF/serum albumin ratio were measured in vCSF from 18 consecutive AS and 19 consecutive INPH patients. Clinical outcome was evaluated after surgery by standardized indices. The levels of markers were related to clinical outcome. No differences in any of the markers were found between AS and INPH patients. The concentration of sulfatide and albumin ratio correlated inversely with psychometric improvement, whilst VIP and NPY correlated inversely with improvement in alertness. The similar levels of biochemical markers in vCSF from AS and INPH patients indicate similarities in pathophysiology and turnover rate of vCSF despite differences in CSF dynamics. High albumin ratio and sulfatide concentrations in vCSF in hydrocephalus patients have negative implications for surgical outcome and might indicate concomitant cerebrovascular disorder.

Progressive changes in cortical water and electrolyte content at three stages of rat infantile hydrocephalus and the effect of shunt treatment

Infantile hydrocephalus causes injury to the developing brain and despite surgical treatment, neurological deficits persist. The H-Tx rat develops inherited hydrocephalus in late gestation. Rapid postnatal ventricular enlargement, results in severe hydrocephalus by 21 days after birth. This is accompanied by changes in cortical morphology and metabolite content that indicate possible changes in intracellular composition. This study has tested the hypothesis that tissue water and electrolyte content is altered in hydrocephalus. The objective was to gain further insight into the mechanisms leading to neuronal damage. Water and electrolyte content (Na+, Cl-, and K+) were measured in the cerebral cortex of control and hydrocephalic rats at 4, 11, and 21 days after birth, and at 21 days in rats that received alleviating shunt surgery at 4 or 11 days. At all ages, hydrocephalic tissue was significantly increased over control for cortical water, Na+, and Cl- content. Additionally, at the intermediate (11-day) and advanced (21-day) stages there were significant decreases in K+ content, consistent with previous observations of decreases in organic osmolytes and energy metabolites. This suggests that by 11 days there are intracellular changes, probably through impaired membrane homeostatic mechanisms. In shunt-treated rats, the extracellular constituents were almost normal, although a small increase over control values persisted. The decrease in intracellular K+ was not corrected in either group of shunt-treated rats. It is concluded that early hydrocephalus is characterized by extracellular edema that largely reverses with shunt treatment. Subsequently, as the hydrocephalus progresses, there is a breakdown of cell homeostasis and an irreversible loss of intracellular constituents.

Modeling the route of administration-based enhancement in the brain delivery of EAB 515, studied by microdialysis

EAB 515 (S-alpha-amino-5-phosphonomethyl[1,1'biphenyl]-3-propanoic acid) is an extremely hydrophilic N-methyl-D-aspartate antagonist. It shows marked CNS activity, in that it is a potent neuroprotector in models of cerebral ischemia, and also demonstrates social and non-social behavioral alteration following systemic administration in animals. Because of its high degree of ionization at physiologic pH, one would not expect appreciable brain uptake of EAB 515 across tight junctions of the blood-brain barrier. This is in contrast to its pharmacologic effect as well as brain/plasma ratios measured during systemic administration in rats. These observations lead us to investigate other transport pathways that might account for its brain uptake. Such mechanistic information is imperative in rational drug delivery and drug design strategies. Upon intracerebroventricular administration, the observed steady-state cortical extracellular fluid concentrations of EAB 515 were over 100-fold higher than those observed following intravenous administration, when normalized for the dosing rate. This increased distribution into the brain, based upon the route of administration, suggests the transport of drug directly between the cerebrospinal fluid and the brain extracellular space. The parameters of the model that adequately describes the data obtained from the two routes of administration in individual animals were estimated. The clinical significance of these results is in the use of intracerebroventricular administration for enhanced brain delivery of hydrophilic drugs that poorly cross the blood-brain barrier.

Surface topography of the cochlear nuclei in humans: two- and three-dimensional analysis

We used three-dimensional reconstruction to study the cochlear nuclear complex (CN) in postmortem adult brains. Resulting data show that the largest part of the CN surface, particularly the dorsal cochlear nucleus (DCN), is fully within the lateral recess of the fourth ventricle. The surface of another subdivision, the ventral cochlear nucleus (VCN), is also almost entirely within the recess, except for a narrow zone adjacent to the caudoventral border of the nucleus. The caudal portion of the exposed zone of the VCN is in the vicinity of the rootlets of the glossopharyngeal (IX) nerve, and the ventral portion is close to the terminal part of the vestibulocochlear (VIII) nerve. The border between the intraventricular part of the CN and the extraventricular portion and also the terminal part of the VIII nerve approximately coincides with the line of attachment of the inferior medullary velum of the fourth ventricle (tenia of the choroid plexus). In the narrow strip of this ventral most part of the tenia we did not observe big blood vessels or neurons. Accordingly this could be a reasonably safe surgical route to the intraventricular surface of the CN.

Sympathetic nervous control of cerebrospinal fluid production in experimental obstructive hydrocephalus

Hydrocephalus was induced in rabbits by cisternal injection of kaolin (0.5 ml of a 30 g/100 ml solution of hydrated aluminium silicate). The rate of bulk production of cerebrospinal fluid (CSF) was measured with a modified Pappenheimer [14C]inulin dilution technique in a ventriculoventricular perfusion system 3 days and 3 weeks after treatment. In the acute state of high-pressure hydrocephalus, CSF formation was reduced to almost one-half normal. Bilateral electrical stimulation of the cervical sympathetic nerves lowered the production rate by another 18%, with only an insignificant tendency to normalization after cessation of stimulation. In the chronic state of low-pressure hydrocephalus at 3 weeks after the kaolin injection, the rate of CSF formation was of the same magnitude as in animals studied after 3 days. However, sympathetic nerve stimulation now reduced the production rate by a further 39%, and prestimulation values were almost restored within 1 h after termination of stimulation. Thus, cranial sympathetic stimulation was very effective in reducing CSF formation in the chronic stage of low-pressure hydrocephalus. during acute high-pressure hydrocephalus, the sympathetic defence mechanisms were probably already recruited to such an extent that electrical activation of the sympathetic nerves was not able to further affect significantly the rate of CSF formation.

Pathophysiology of periventricular tissue changes with raised CSF pressure in cats

Intraventricular pressure (IVP) is increased in the early stages of acute hydrocephalus. Pressure falls, however, when compensatory routes for cerebrospinal fluid (CSF) absorption develop. In order to better understand the pathophysiology of acute hydrocephalus, the authors performed ventriculocisternal perfusions on adult cats with outflow pressures maintained at either -5, 20, or 40 cm H2O. Cerebral blood flow (CBF) was determined by the iodoantipyrine method. Penetration of an extracellular marker, horseradish peroxidase (HRP), was visualized histologically. Capillary transfer of radiolabeled molecules from CSF to blood was measured by steady-state tissue clearance. Increased IVP had several effects: 1) significant reduction in mean CBF in the periventricular white matter; 2) penetration of the HRP into deep white matter; and 3) prolongation of steady-state tissue clearance half-time for (14C)-ethylene glycol in the caudate nucleus. Reduced blood flow to periventricular white matter and impaired molecular clearance in the caudate nucleus may contribute to the clinical symptoms in acute hydrocephalus.