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Effects of leukocytes on brain metabolism in granulocytic brain edema.

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ORIGINAL ARTICLES
Effects of Leukocytes on Brain
Metabolism in Granulocytic Brain Edema
Robert A. Fishman, MD, Kurt Sligar, MD, and Randall B. Hake
An in vitro model has been used to study the effects of granulocytic leukocytes (WBC) on brain metabolism to
elucidate the mechanism of the encephalopathy and cerebral edema of purulent meningitis and brain abscess. Single
first rat cortical brain slices were incubated in normal medium or medium containing a membrane fraction of WBC
prepared from rat peritoneal exudate cells induced by intraperitoneal glycogen. Membrane fraction caused
“cytotoxic” brain edema with increased brain water, cellular swelling (decreased inulin space), increased intracellulac sodium, and loss of intracellular potassium. The brain also showed increased glucose oxidation and lactate
production associated with energy depletion demonstrated by decreases in phosphocreatine, adenosine triphosphate,
and energy charge potential. The low glucose and high lactate of purulent cerebrospinal fluid reflect these changes in
brain metabolism. The model of granulocytic brain edema was not affected by dexamethasone. The factors in WBC
responsible for these changes were membrane bound, absent from the cytosol, and heat labile. The concentrations
used are compatible with concentrations in pathological exudates. Toxic factors in pus alter the integrity of brain cell
membranes and thus contribute to the encephalopathy and brain edema associated with purulent meningitis and
brain abscess.
Fishman RA, Sligar K, Hake RB: Effects of leukocytes on brain metabolism in granulocytic brain edema.
Ann Neurol 2:89-94, 1977
The encephalopathy of purulent meningitis is characterized by coma, seizures, and brain edema; in
severe cases fatal herniation may occur [21]. Extensive
infiltration of the Ieptomeninges and perivascular
spaces with inflammatory cells and exudate are also
major pathological findings. T h e cerebrospinal fluid
changes include intracranial hypertension, polymorphonuclear pleocytosis, increased protein, reduced
glucose, and increased lactic acid concentrations [6,
2 11. The magnitude of these changes correlates generally with the severity of the meningitis. Brain
abscess is also associated with severe edema, which is
often responsible for cerebral herniation. The encephalopathy of purulent meningitis and brain abscess
has generally been thought to result from inflammation and edema, but the metabolic basis for the
changes in cerebral function and for brain edema is
obscure. Therefore an in vitro model has been devised
using single, first cortical brain slices in order to study
the direct effects of inflammatory granulocytic leukocytes (WBC) upon brain metabolism and edema formation in the absence of immunological or circulatory
factors derived from the host. The data reveal that a
crude membrane fraction of granulocytic leukocytes
induces changes in the cortex characteristic of
“cytotoxic” brain edema [8, 131 associated with increased glucose oxidation and lactate production, as
well as a fall in energy charge potential (ECP). This
experimental model of granulocytic brain edema is
not affected by dexamethasone.
Methods
Preparation of WBC Membrane Fraction
Sprague-Dawley male rats weighing 200 to 250 gm were
injected intraperitoneally with 30 ml of 0.lV glycogen
in saline; 16 hours later the peritoneal exudate cells were
harvested after the method of Cohn and Morse [ 5 ] .T h e rats
were killed with ether, and 60 to 7 0 ml of Krebs-Ringer
solution with heparin, 14 units per milliliter, was injected
intraperitoneally, followed by kneading of the stomach 100
times. T h e fluid containing peritoneal exudate cells was then
drained through a longitudinal incision in the peritoneum
into 50 ml centrihge tubes. The suspension was centrifuged
at 250g for 5 minutes at 4°C. The supernatant was discarded
and the WBC pellet collected in 10 ml of the heparinized
Krebs-Ringer buffer. Most of the studies used a crude
membrane fraction prepared from the pellets as follows:
The suspension was centrifuged again at 250:: for 5 minutes
at 4°C. T h e supernatant was discarded and the cells were
resuspended in 3 ml of cold 0.95‘;;6NaC1. Nine milliliters of
cold distilled water was added, and the suspension was agitated by vigorous pipetting for 45 seconds to lyse any contaminating red blood cells [?]. Three milliliters of 3.5%
NaCl was immediately added and the suspension was centrifuged again at 250 g for 5 minutes at 4°C. Following the
last centrifugation, the supernatant was discarded and the
Address reprint requests to Dr Fishman, Deparrment of Neurol-
From the Deparrmenr of Neurology, University of California, San
Francisco, School of Medicine, San Francisco, CA.
ogy, University of California, San Francisco, School of Medicine,
Accepted for publication Feb 18, 1977.
San Francisco, CA 94143.
89
white cells were resuspended in 10 ml of heparinized
Krebs-Ringer buffer. White cells prepared in this way were
shown to be functionally preserved. A 0.1 ml aliquot was
added to 9.9 ml of Turk's solution (crystal violet in 393
aqueous acetic acid), and the cells were counted using a
hemocytometer. About 929; of the cells were viable after 1
hour, evidenced by trypan blue dye exclusion, and
phagocytosis was demonstrated by sudden increase in oxygen consumption following incubation with opsonized
zymosan, using an oxygen electrode [ l l ] .
The suspension was then centrifuged again at 250 g for 5
minutes at 4°C. After the supernatant was removed, the
white cells were resuspended in unheparinized KrebsRinger buffer so that there were 3.0 X 10' cells per mil!iliter. This suspension was homogenized with a Teflon pestle
rotating at 2,300 rpm for 8 minutes at 0°C. The homogenate was centrifuged at 17,000 g for 20 minutes at 4°C. The
supernatant was used as the cytosol fraction. T h e crude
membrane pellet was resuspended in unheparinized
Krebs-Ringer solution to obtain 3 x 10' cell equivalents per
milliliter; 0.5 ml of this suspension was added to 4.5 ml of
the buffer to make the incubation medium for one experimental cortical slice. The final concentration of white cell
equivalents used in most studies was 3 x lo7 per milliliter,
equivalent to 10 mg of protein per 5 ml bath, or 2 mg of
protein per milliliter. The studies utilized this crude white
cell preparation, termed membrane fraction. Red blood cell
(RBC) membrane preparations (red cell ghosts) were prepared by the method of Marchesi and Palade [ 1 7 ] and suspended in Krebs-Ringer buffer at a concentration of lo9
RBC per milliliter.
Preparation of Brain Cortical SliceJ
Male Sprague-Dawley rats weighing 80 to 200 gm were
decapitated and the brains rapidly removed and placed on
ice. Single first cortical slices with intact pia arachnoid, 40 to
50 mg in weight and 0.35 m m in thickness, were prepared as
described by Harvey and Mcllwain [lo]. Each single slice
was incubated in 5 ml of Krebs-Ringer solution at 37°C with
100% oxygen. Experimental slices were incubated in 5 ml of
medium containing 3 x l o i white cell equivalents per milliliter. Protein was determined o n homogenates of the membrane fraction by the method of Lowry et a1 [16].
Normal medium contained: NaC1, 140 mEq/L; KCI, 3.6
mEq/L; CaCI,, 3.0 mEq/L; KH,PO,, 1.4 mEq/L; MgSO,, 1.4
mEq/L; glucose, 10 mM; and Hepes buffer (Sigma Chemical
Co, St Louis, MO), 15 mM. The p H was 7.4.
Lactate concentration in the medium was measured enzymatically [ 7 ] .Tissue water content was obtained by desiccation at 105°C for 16 hours. Brain swelling was measured
as:
% Final water content initial water content
% Initial water content
Extracellular space was estimated with '"C-inulin (New
England Nuclear Co, Boston, MA) that was repurified by
column chromatography prior to use [41. Inulin was included in the incubation medium at the beginning of the
experiment, and the concentration in tissue was measured
after 70 minutes of incubation. The tissue was solubilized in
90 Annals of Neurology Vol 2
No 2
August 1977
Soluene-100 (Packard Instrument Co, Downer's Grove, IL)
prior to counting in a liquid scintillation spectrometer.
Counting efficiency was determined using an internal
standard. Inulin space (%) was calculated as follows:
DPM/gm brain final wet weight
x 100 = Inulin space(%)
DPMiml bath
The intracellular concentrations of sodium and potassium
were calculated as follows: Brain ion concentration in
mEq/kg final wet weight - inulin space x medium ion
concentration in mEq/L = intracellular ion concentration.
Sodium and potassium levels were measured by flame
photometry after desiccated tissue was extracted with 2 M
nitric acid. Glucose utilization was measured by adding
U-14C-glucoseto the medium and trapping all the ' T O 2in a
center well containing potassium hydroxide. Tissue creatine
phosphate and adenosine triphosphate, diphosphate, and
monophosphate (ATP, ADP, AMP) were measured by the
method of Lowry et a1 [151. ECP was calculated as follows
[21:
ECP =
ATP + 0.5 A D P
ATP + ADP + AMP
Paired cortical and experimental studies were done in each
group of experiments; the data were analyzed using the
t-test for paired samples. T h e data are presented plus or
minus standard error about the mean.
Results
Brain Swelling and Inzllin Space
Initially, studies were done to determine the time
course of brain swelling and lactate production of
cortical slices in control and experimental medium.
Brain swelling and lactate production were studied
after various periods of incubation: 15,30,60, and 90
minutes of incubation in normal or experimental
medium. There was a progressive increase in brain
swelling and lactate production in both control and
experimental medium over the times studied. Ninetyminute periods of incubation were used for most
studies because maximal changes were seen at this
time. Preliminary studies were also done to determine
the dose/response curve of brain swelling and lactate
production in response to various amounts of membrane fraction. Different concentrations of membrane
fraction were used: 0 , 2.5, 5.0, 10.0, and 20.0 mg of
protein per 5 ml bath, for a 90-minute period of
incubation. Changes were insignificant with 2.5 mg of
protein per 5 ml bath (equivalent t o 3.75 x lo7WBC
per 5 mi bath), but aprogressive increase in both brain
swelling and lactate production occurred with the
higher protein concentrations. The concentration of
white cell equivalents used for most studies was 1.5 x
lo8 WBC per 5 ml bath (10 rng protein per 5 ml bath)
because it gave satisfactory and reproducible increases
in tissue swelling and lactate production.
The data on brain swelling and inulin space are
Table I , Effects of Membrane Fraction on Brain Composition and Metabolism
Variable
575 Initial water
Control Brain
83.42 -+
84.77 t
1.6
42.0 &
18.8 -+
% Final water
$6 Swelling
% Inulin space
*
Lactate production
(pmol/gm/90 min)
Na- (mEqlkg final wet weight)
K+ (mEq/kg final wet weight)
Na' (rnEq/kg dry weight)
K+ (mEq/kg dry weight)
89.2
0.23
0.24
0.2
0.8
4.1
4.4
63.4 rt 4.2
558.4 2 27.3
396.9
24.6
9.45 k 0.71
2
*
''C-glucose oxidized ( pmolihr)
Values are expressed i standard error. NS
=
Brain Plus
Membrane Fraction
No. of
Pairs
P
0.29
0.32
0.2
1.1
8.2
19
19
19
20
12
NS
<0.001
92.9 2 8.0
50.6 f 8.3
618.4 ? 72.6
335.2 f 50.6
10.92
0.96
12
12
12
12
15
NS
83.59 f
85.77 &
2.7
35.8 ?
41.2 2
*
*
<0.001
<0.001
<0.001
<0.001
co.0 1
<0.01
co.01
not significant.
summarized in Table 1. The final water content after
90 minutes' incubation in normal medium was
84.77 2 0.2496, and the control swelling was 1.6%.
In the presence of membrane fraction an increase in
swelling was obtained; the final water content was
85.77% and the percentage swelling was increased to
2.7% (p < 0.001).The magnitude of swelling induced
by membrane fraction was compared to the swelling
induced by anoxia in a study in which first cortical
slices were incubated for 90 minutes in normal
medium in which 100% oxygen was replaced by
100% nitrogen. This resulted in 6.3 -+ 0.3% swelling (N = 7 ) .Thus, incubation of normal cortex with
membrane fraction, 1.5 x lo8 WBC per 5 ml bath,
resulted in over 40% of the tissue swelling obtained
with anoxia for the same period. The cytosol fraction
derived from the same population of white cells had
no effect o n brain swelling or lactate production in
nine paired studies. A preparation of RBC membranes (5 x lo9 RBC per milliliter), i.e., red cell
,ghosts, had no effect on cortical swelling or lactate
production in ten paired studies. Thus, membranebound factors in exudative WBC, not present in red
cell membranes, were responsible for brain swelling
and increased lactate production.
The inulin space was measured after 7 0 minutes of
incubation of first cortical slices with and without the
addition of membrane fraction. The control inulin
space was 42.0 k 0.8% and the experimental inulin
space was 35.8 -t 1.19; (p < 0.001, N = 20). This
reduction in inulin space indicates that the brain
edema induced by membrane fraction is associated
with cellular swelling and a decrease in extracellular
fluid volume, characteristic of cytotoxic brain edema.
but there was a significant increase in the sodium
content expressed per kilogram of dry weight. This
indicates that edematous brain cells gain both water
and sodium. The tissue potassium fell from 63.4 2 4.2
mEq per kilogram of final weight in the control study
to 50.6 +- 8.3 mEq per kilogram of final weight in the
experimental group, and a similar decline in potassium content was noted per kilogram of dry weight.
The intracellular sodium concentration (calculated
using the inulin space as a measure of extracellular
fluid volume) rose 40.8%, from 30.4 mEq per kilogram of final weight to 42.8. The calculated intracellularpotassiumfell20.4@, from 61.3 mEqper kilogram
of final weight to 48.8. These opposing changes in
tissue sodium and tissue potassium are characteristic
of both vasogenic and cytotoxic forms of brain edema
[8, 121. The failure to maintain intracellular potassium
and the increase in intracellular sodium correlate with
a decrease in creatine phosphate and ECP, also induced by membrane fraction.
Sodium and Potassium Content
The sodium and potassium content of normal cortex
and cortex incubated with membrane fraction was
measured (see Table 1). The sodium content, expressed per kilogram of final weight, was not affected,
Lactate Production
Lactate was measured in the 5 ml bath at the end of
the 90-minute period of incubation (see Table 1).
Lactate production was increased from 18.8 to 41.2
pmol of lactate per 70 minutes per gram of initial
weight (p < 0.001) in the presence of membrane
fraction. Neither the cytosol nor red cell ghosts, prepared as described above, had any effect on the rate of
lactate production. The potassium content of the
medium with membrane fraction was indistinguishable from the control medium at the end of the experiment, and was insufficient to alter the control rate of
lactate production. The potassium of the control
medium after 90 minutes of incubation was 5.8 mEq
per liter +- 0.1; in the experimental medium it was 5.7
mEq per liter 0.1. Initially the potassium content of
the medium was 5.0 mEq per liter; the minor increase
in potassium after 90 minutes' incubation was derived
from the brain slice.
Fishman, Sligar, and
Hake: Effects of Leukocytes in Granulocytic Brain Edema 91
*
Glucose Oxidation
The effects of membrane fraction on brain glucose
oxidation are summarized in Table 1. Glucose oxidation in the control slices was 9.45 k 0.71 p o l of
14C-glucose oxidized to 14COz/gm/hr;in the experimental slices it was 10.92 t 0.96 w o l of '%-glucose
oxidized to 14COs/gm/hr(p < 0.01, N = 15).
Effects of Membrane Fraction on Energy Metabolism
Table 2 summarizes the effects of membrane fraction
on phosphocreatine, AMP, ADP, ATP, and ECP.
The presence of membrane fraction induced a 58%
fall in brain phosphocreatine and a 21% decline in
ATP concentration; ADP was unchanged, and there
was an increase in AMP level. These changes resulted
in a fall of ECP from 0.87 to 0.80 (p < 0.02).
Heat lability of Membrane Fraction
The effect of heating membrane fraction prior to
incubation with brain cortex was studied in terms of its
ability to induce swelling and increase lactate production. Heating the membrane fraction for 10minutes at
60°C prior to use reduced its ability to induce swelling, and heating at 100°C for 5 minutes inactivated
the membrane fraction-i.e., percentage swelling and
lactate production were the same in the paired control
and experimental studies (N = 6).
Failure of Dexamethasone To Affect
Granulocytic Edema
The possible protective effects of the glucocorticoid
dexamethasone on granulocytic brain edema were
studied with several dosage schedules (Table 3). Two
groups of studies were done in which dexamethasone
was added to the bath in dosages of 0.001 mg per
milliliter and 0.01 mg per milliliter. The steroid was
present for a 30-minute preincubation of the slice in
normal medium and for the 60-minute experimental
period. Brain swelling and lactate production were not
affected by either concentration of dexamethasone. In
a second series of experiments, rats were pretreated
with dexamethasone at dosages of 0.5 or 2.0 mg per
100 gm at 24 and 6 hours prior to decapitation and
preparation of first cortical slices. These slices were
then incubated with medium containing dexamethasone, 0.04 mg per milliliter. In this series of
animals (N = 20), neither the increase in cortical
swelling nor lactate production induced with membrane fraction was affected by steroid pretreatment.
Thus, dexamethasone could not be shown to influence
the in vitro model of cytotoxic granulocytic brain
edema.
Discussion
Despite advances in the treatment of acute bacterial
meningitis, relatively high mortality and morbidity
Table 2. Effects of Membrane Fraction on Brain Energy Metabolism"
Variable
Control Brain
Phosphocreatine (nmolimg)
ATP (nmollmg)
ADP (nmolimg)
AMP (nmoVmg)
Energy charge potential
2.12
0.12
1.04 +- 0.04
0.28 +- 0.02
0.05
0.01
0.87
0.01
*
Brain Plus
Membrane Fraction
No. of
Pairs
P
0.89 2 0.13
0.82 +- 0.06
12
12
12
10
10
<0.001
<0.001
NS
<0.003
c0.02
0.27
0.10
0.80
*
*
?
*
*
0.02
0.02
0.02
aDistribution of phosphonucleotides and creatine phosphate after 90 minutes' incubation in control brain and in brain incubated with
standard error.
membrane fraction, 1.5 x loBWBCi5 ml bath. Values are expressed
*
ATP
=
adenosine triphosphate; ADP = adenosine diphosphate; AMP = adenosine monophosphate; NS = not significant.
Table 3. Effects of Dexumetbusone on .Br& Swellina and Lactate Production"
Bath
(mdml)
0
0.001
0.04
Dexamethasone
In Vivo Dose
(mgi100 gm body weight)
% Swelling
0
3.3
3.0
2.0
4.0
0
Brain Plus Membrane Fraction
Lactate
(1.~mol/gm/60 m i d
2
0.2 (N
=
19)
2
0.4 (N
=
6)
0.4 (N
=
12)
*
51.0 +- 4.5 (N = 18)
41.8 2 3.7 (N = 6)
59.7
6.8 (N = 12)
"Slices were preincubated for 30 minutes in control buffer or in buffer containing dexamechasone prior to 60 minutes' incubation with
membrane fraction(l.5 x 10%WBCiS ml bath). Dexamethasone concentrations were the same in the preincubation and incubation periods
The in vivo dose of dexamethasone was given twice: at 24 hours and at 6 hours prior to preparation of the slice. Values are expressed %standard
error. Neither dosage of dexamethasone altered the swelling or lactate production induced by membrane fraction.
92 Annals of Neurology Vol 2 No 2
August 1977
rates persist. Seizures, focal cerebral signs, and brain
edema occur acutely and are associated with high
mortality. Major neurological sequelae include mental retardation, seizures, deafness, and hemiparesis [6,
2 11. There is considerable uncertainty regarding the
pathogenesis of both the acute and chronic changes in
cerebral function. Four major mechanisms have been
suggested [ 191: (1) occlusion of meningeal vessels, (2)
direct interference with cerebral metabolism by invading organisms and their toxins, ( 3 ) inhibition of
essential enzyme reactions, and (4) diffuse cerebral
edema. The role of meningeal vasculitis is difficult to
assess. Adams, Kubik, and Bonner [ 11, in an analysis
of 14 patients with Hemophilzls injzlenzae meningitis
who died 14 hours to 76 days after the infection,
found only 4 patients with demonstrable thrombophlebitis, although each of the 14 patients showed
cortical necrosis with reactive microgliosis and astrocytosis. Similarly, only 5 of 30 fatal cases of meningitis examined by Swartz and Dodge [6, 211 showed
unequivocal thrombosis of small cortical tissue. Often
no bacteria were found, cultures were negative, and
the pathological changes were viewed as “a noninfectious encephalopathy” of uncertain cause. There are
only fragmentary data available regarding brain metabolism in meningitis. Although the low CSF glucose
and increase in CSF lactate characteristic of purulent
meningitis have suggested increased glycolysis in
brain adjacent to the CSF [18, 201, no data are available showing whether the higher lactate reflects a
specific increase in cerebral glucose utilization o r
whether it might be due to a reduction in cortical
blood flow and cortical hypoxia. The present study
establishes that factors derived from leukocytes increase brain glucose utilization and lactate production
as well as inducing cytotoxic brain edema in the
absence of hypoxia.
The effects of granulocytes (WBC) on cerebral
metabolism have not been studied previously, although it has long been recognized that WBC in an
acute inflammatory exudate can be injurious to tissues, in addition to serving a beneficial role through
phagocytosis of microorganisms or immune reactants
[ 1 4 ] The
.
present experiments used an in vitro model
t o study the direct effects of WBC upon brain metabolism. A single first cortical slice with the pia
arachnoid membrane intact was used. T h e 50 mg slice,
0.35 mm thick, allows adequate oxygenation of the
center of the slice. The tissue is entirely cortical, i.e.,
white matter is not included. (Analogous studies are in
progress using first pontine slices as a preparation of
white matter.) There are clear advantages and limitations to the in vitro study. The technique allows analysis of brain metabolism with precise control of the
extracellular fluid milieu. T h e disadvantages of brain
slices have been well discussed in the literature [lo,
121. Despite great precision in handling single first
cortical slices in a standardized and gentle manner,
“normal” control slices swell rapidly after contact with
physiological medium, with an increase in tissue
water, decrease in extracellular (inulin) space, increase in tissue sodium, decrease in tissue potassium,
and depression of ATP content and ECP. Thus, control slices are mildly edematous. However, partial
return of each of these changes toward normal occurs
within 30 minutes of incubation in optimal medium,
which results in partial restoration toward normal in
vivo values [ l o , 121.
The present studies have demonstrated that a crude
membrane fraction derived from peritoneal exudate
cells induces cytotoxic edema, with cellular swelling,
elevated tissue water and intracellular sodium content, and loss of intracellular potassium. T h e brain also
showed increased glucose utilization and lactate production associated with energy depletion. The
peritoneal exudate cells used were chiefly of the
granulocytic series; 92% were viable in terms of exclusion of trypan blue when harvested, and they demonstrated a burst of oxygen consumption following
incubation with opsonized zymosan. The factors in
t h e WBC were clearly in the crude membrane fraction, were heat labile, and were absent from cytosol.
In the present study a standard number of white cells
was used (1.5 x 10* WBC per 5 ml bath), which
provided satisfactory responses. The concentration of
3 x 107WBCper milliliter, although an arbitrary one,
is compatible with concentrations in pathological
exudates seen in abscess cavities and in the perivascular and subarachnoid spaces in purulent meningitis.
There have been many studies of the subcellular
components of leukocytes from glycogen-induced
peritoneal exudates [3, 141. A great number of
lysozomal enzymes and other membrane-bound enzymes are included in the crude membrane fraction
used in these studies. These enzymes include phospholipases, proteases, peptidases, peroxidases (including myeloperoxidase and glutathione peroxidase), esterases, and complex cationic proteins
with multiple binding affinities [ 3 , 141. The manner in
which the membrane fraction alters cell metabolism is not certain, and the mechanism involved requires further study. T h e effects described here include: (1)increase in cell membrane permeability with
loss of potassium and gain in sodium and water content, resulting in cytotoxic edema; (2) increased
glycolysis and lactate production; and (3) reduction in
energy charge potential. All these changes could be
induced if the “first” event was a change in brain cell
membrane integrity o r permeability, allowing greater
entry of sodium ions, but elucidation of such a membrane defect requires further study.
Three types of cerebral edema have been de-
Fishman, Sligw, and Hake: Effects of Leukocytes in Granulocytic Brain Edema 93
scribed: vasogenic, cytotoxic, and interstitial (hydrocephalic) brain edema [S, 131. Both vasogenic
edema and interstitial brain edema are characterized
by increased extracellular fluid space, unlike cytotoxic
brain edema, in which cellular swelling and decreased
extracellular fluid space are seen. The occurrence of
vasogenic and interstitial edema in purulent meningitis has previously been established. Prockop and
Fishman [20] showed a general increase in permeability of the blood-CSF barrier in experimental
pneumococcal meningitis in dogs to 3-0-methy1 glucose, mannitol, and albumin; such permeability
changes are characteristic of vasogenic edema. These
authors further showed a defect of absorption of albumin and sugars from cisternal fluid to blood, which
also supports the presence of interstitial (hydrocephalic) cerebral edema in purulent meningitis.
The present studies indicate that granulocytic factors
also induce cytotoxic brain edema. Thus, the three
types of brain edema may coexist in purulent meningitis. In the present studies we used single first cortical
slices. These are composed of gray matter only, as
reflected in their high initial water content and as
confirmed by histological analysis. Preliminary studies
have indicated similar responses of single first pontine
slices, which are composed of white matter (Fishman
RA: unpublished observations, 1777).
The effects of dexamethasone on the model were
studied by adding the steroid to the bath and by obtaining cortex from rats pretreated with the drug in
vivo. In no case could any inhibition of granulocytic
brain edema, in terms of reduction in swelling or
lactate production, be shown. This observation is
compatible with the hypothesis that steroids are protective only in vasogenic edema and not in cytotoxic
edema-i.e., their antiedema effects are chiefly o n
capillary endothelial cell membranes and not on
neuronal or glial membranes. In vivo, the encephalopathy of purulent meningitis has features of
vasogenic, cytotoxic, and interstitial (hydrocephalic)
edema, and steroids might be protective in treating
the vasogenic or interstitial components.
These studies have shown that pus is toxic to the
brain. Further studies are in progress to define better
the factors in WBC membrane fraction responsible
for the brain edema and changes in brain metabolism.
Attention must be focused on the mechanism of the
changes in membrane permeability and excitability
that characterize the encephalopathy in order to improve the morbidity and mortality of granulocytic
brain edema.
Supported by Grant NS07336 from t h e National Institutes of
Health and by the Luck Stern and Mildred K. Perez Research
Funds.
Mr ,James Spigel and Ms Yee Ping Wong provided technical assisEIhCe.
94 Annals of Neurology
Vol 2
No 2
August 1977
Presented in part at the April, 2774, meeting of the American
Academy of Neurology, San Francisco, CA, and at the June, 1975,
meeting of the American Neurological Association, New York,
NY.
~~
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