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The Journal of Neuroscience, August 15, 1998, 18(16):6599-6607
Interleukin-1 Induces Slow-Wave Sleep at the Prostaglandin
D2-Sensitive Sleep-Promoting Zone in the Rat Brain
Akira
Terao1, 2,
Hitoshi
Matsumura1, 3, and
Masayuki
Saito2
1 Department of Molecular Behavioral Biology, Osaka
Bioscience Institute, Suita City, Osaka 565-0874, Japan,
2 Laboratory of Biochemistry, Department of Biomedical
Sciences, Graduate School of Veterinary Medicine, Hokkaido University,
Sapporo 060-0818, Japan, and 3 Department of
Neuropsychiatry, Osaka Medical College, Takatsuki City, Osaka 569-8686, Japan
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ABSTRACT |
To determine the site of action of the sleep-promoting effect of
interleukin-1 (IL-1), we continuously infused (between 11 P.M. and 5 A.M.) murine recombinant IL-1 into seven different locations in the
ventricular and subarachnoid systems of the brain in freely moving
rats. When IL-1 was infused at 10 ng/6 hr into the subarachnoid space
underlying the ventral surface of the rostral basal forebrain, which
previously was defined as the "prostaglandin (PG)
D2-sensitive sleep-promoting zone" (PGD2-SZ),
the total amount of slow-wave sleep (SWS) increased by 110.7 min (IL-1
was 208.1 ± 14.3 min vs control at 97.4 ± 9.3 min;
n = 8; p < 0.01 by paired Student's t test) from the baseline control level
obtained under continuous infusion of saline vehicle. The hourly SWS
during the infusion period reached the level of daytime SWS, the
physiological maximum, whereas paradoxical sleep (PS) was decreased
transiently. This site of action for the SWS promotion was dissociated
from the site in the third ventricle sensitive to the IL-1-mediated PS
suppression, fever, and anorexia. The SWS increase caused by IL-1
infusion into the PGD2-SZ was blocked completely by
coadministered diclofenac, a nonselective cyclooxygenase (COX)
inhibitor. Pretreatment of rats with NS-398 or piroxicam (3 mg/kg of
body weight, i.p.), which are said, respectively, to possess high and
relative specificity for the COX-2 enzyme, also blocked the
SWS-promoting effect of IL-1. We present a hypothesis that IL-1 induces
SWS, at least in part, via COX-2-mediated PG production in the
PGD2-SZ.
Key words:
interleukin-1; prostaglandin D2; slow-wave sleep; subarachnoid space; ventral surface of the rostral
basal forebrain; COX-2
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INTRODUCTION |
A variety of studies has
demonstrated the important role of interleukin-1 (IL-1) in the
sleep-wake phenomena under both physiological and pathological
conditions: (1) administration of IL-1 induced excess sleep, especially
slow-wave sleep (SWS), in rabbits, rats, cats, and monkeys (Krueger et
al., 1984 ) (for review, see Borbély and Tobler, 1989 ;
Krueger and Majde, 1994 ); (2) inhibition of endogenous IL-1 by an IL-1
receptor antagonist (Opp and Krueger, 1991 ) and by anti-IL-1 antibodies
(Opp and Krueger, 1994 ) inhibited the occurrence of spontaneous sleep
in rabbits; (3) anti-IL-1 antibodies suppressed the sleep rebound
subsequent to sleep deprivation (Opp and Krueger, 1994 ); and (4)
production of IL-1 varied along with sleep-wake behavior and increased
during sleep deprivation in various mammalian species, including humans
(Lue et al., 1988 ; Moldofsky et al., 1989 ). The site of action of IL-1
with respect to this SWS-enhancing effect was investigated by Walter
and colleagues (1989) , but they failed to define any parenchymal site
in the basal forebrain or in the brainstem. Instead, they noticed that the injection of IL-1 into the aqueduct of Sylvius led to an excess of
SWS.
On the other hand, a prostaglandin (PG) D2-sensitive
sleep-promoting zone (PGD2-SZ) was demarcated in the rat
within the ventral surface of the rostral basal forebrain, where
PGD2 applied into the subarachnoid space of the zone during
the night increased the SWS of this nocturnal animal up to the daytime
level, the physiological maximum (Matsumura et al., 1994 ). The level of
PGD2 in the CSF of rats exhibited a significant
alteration between its high during the daytime, i.e., the rest phase of
the animal, and its low during the night, the behaviorally active phase
(Pandey et al., 1995 ). The CSF level of PGD2 in rats
increased during sleep deprivation and tended to become higher along
with increasing propensity toward sleep and deepening of sleep under a
nonsleep-deprived normal condition (Ram et al., 1997 ).
Thus, both IL-1 and PGD2 possess sleep-promoting potency.
It may be noted generally that IL-1 and PGs share some biological effects such as induction of fever (Dinarello et al., 1983 ) and anorexia (Hellerstein et al., 1989 ), as well as activation of both the
sympathetic nervous system (Terao et al., 1995 ) and the hypothalamic-pituitary-adrenal system (Katsuura et al., 1988 ). However, little is known about the possible interactions between IL-1
and PGs, especially in terms of sleep regulation. Interestingly, neither the site of action for the SWS-promoting effect of IL-1 (Walter
et al., 1989 ) nor that for PGD2 (Matsumura et al., 1994 ) was demonstrated in the parenchymal region of the brain.
In this study we searched in freely moving rats for the site of action
for the SWS-promoting effect of IL-1 and found that IL-1 increased SWS
in the most pronounced manner when it was applied to the
PGD2-SZ. This site of action was dissociated from the
site(s) responsible for other effects of IL-1, such as suppression of paradoxical sleep (PS) and induction of fever and anorexia.
Furthermore, inhibitors of cyclooxygenase (COX), which is said to be
the rate-limiting enzyme for the synthesis of PGs, clearly were
demonstrated to block the SWS promotion caused by IL-1. We hypothesize
that IL-1 promotes SWS via activated synthesis of PGs in the
PGD2-SZ.
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MATERIALS AND METHODS |
Animals. One hundred and sixty-eight male rats of the
Sprague Dawley strain (Japan SLC, Hamamatsu City, Japan), weighing
between 300 and 380 gm (9-10 weeks old), were used. The animals were
housed before experimentation in a soundproof chamber at an ambient
temperature of 25°C and 60% relative humidity. The chamber was
maintained on a 12 hr light/12 hr dark cycle (lights on at 8 A.M.), and
standard laboratory rat chow and water were supplied ad
libitum. All animal use procedures were approved by the Animal
Care and Use Committee of Osaka Bioscience Institute.
Surgical operation. Under pentobarbital anesthesia (50 mg/kg
of body weight) each animal was chronically implanted with electrodes for recording the electroencephalogram and electromyogram as well as
with a thermistor probe for monitoring brain temperature, as described
previously (Matsumura et al., 1991 ). Seven locations were chosen for
placing the stainless steel cannulae (0.35 mm outer diameter) in the
ventricular and subarachnoid systems. Figure 1 illustrates the schematic sagittal and
coronal sections of the rat brain showing the infusion locations.
Locations of the tip of the respective infusion cannulae, based on the
stereotaxic coordinates adopted from the atlas of Paxinos and Watson
(1986) with bregma as the reference point, were as follows (shown as mm): location 1 (L1), in the subarachnoid space of the
PGD2-SZ [anteroposterior distance from bregma (A), 1.7;
lateral distance from the midline (L), 0.4; dorsoventral distance from
the horizontal plane passing through bregma on the surface of the skull
(D), 8.7; bilateral]; L2, in the third ventricle (3V), apposed to the medial preoptic area (A, 0.8; L, 0.0; D, 8.5; midline); L3, in the
lateral ventricle (A, 1.3; L, 1.8; D, 3.4; bilateral); L4, in the
subarachnoid space underlying the posterior hypothalamus (A, 4.3; L,
2.0; D, 9.4; bilateral); L5, in the 3V, near the aqueduct of Sylvius
(A, 5.3; L, 0.0; D, 5.9; midline); L6, between the aqueduct of
Sylvius and the fourth ventricle, apposed to the locus coeruleus (A,
8.8; L, 0.0; D, 6.2; midline); L7, in the cisterna magna (A, 15.7;
L, 0.0; D, 7.6; midline). For locations 1, 3, and 4 a pair of
cannulae was implanted bilaterally, whereas a single cannula was
directed to the respective midline position for locations 2, 5, 6, and
7. For implantation of a catheter into the cisterna magna, a burr hole
was made on the midline 5.0 mm posterior to the lambda (15.7 mm from
the bregma), and the catheter was inserted 7.0 mm deep toward the
cisterna magna, as described previously (Pandey et al., 1995 ).

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Figure 1.
Schematic sagittal and coronal drawings indicating
the seven locations (L1 through
L7) for infusing IL-1 into the ventricle and
subarachnoid space in the rat brain. Numerals indicate
the distance from bregma, the reference point, in the stereotaxic
coordinates. L1, In the subarachnoid space of the
PGD2-SZ; L2, in the 3V, apposed to the
medial preoptic area; L3, in the lateral ventricle;
L4, in the subarachnoid space underlying the posterior
hypothalamus; L5, in the 3V, near the aqueduct of
Sylvius; L6, between the aqueduct of Sylvius and the
fourth ventricle, apposed to the locus coeruleus; L7, in
the cisterna magna.
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Materials. Murine recombinant IL-1 (specific activity,
2.2 × 107 U/mg protein, based on the
IL-1 -dependent proliferation of D10 cells) was purchased from
Genzyme (Cambridge, MA). The manufacturer indicated a molecular weight
of 18 kDa and purity >98%, with an endotoxin contamination <0.013
ng/µg protein. IL-1 was diluted just before use at the desired
concentration in sterile physiological saline containing 0.01% bovine
serum albumin.
Diclofenac sodium (Sigma, St. Louis, MO) was dissolved in saline and
continuously and bilaterally infused at 46 µg (145 nmol) per 6 hr in
total (between 11 P.M. and 5 A.M.) into the PGD2-SZ, together with IL-1. Piroxicam (Sigma) and NS-398 (Cayman Chemicals, Ann
Arbor, MI) were dissolved separately in dimethyl sulfoxide (DMSO) and
further diluted in saline (1:1) before use. Either one (500 µl) was
injected intraperitoneally at 3 mg (~9 µmol) per kilogram of body
weight 3.2 hr before the commencement of the administration of
IL-1.
Experimental procedures. After surgery each rat was allowed
a minimum 9 d recovery period in an individual cage before being placed in our originally developed experimental cage (Matsumura et al.,
1995 ), which permitted multiple routes for infusion into, and
simultaneous multi-channel polygraph recordings from, a freely moving
animal (Osaka Microsystem, Osaka, Japan). A length of tubing, which had
been attached to each cannula implanted in rats, then was connected
with another tube coming from an infusion syringe; we commenced
continuous infusion of sterile physiological saline into the brain at a
speed of 0.2 µl/min. After an acclimation period of 3 d,
baseline recordings were taken in each animal for 24 hr, beginning at 8 P.M., which served as the control for the same animal. On the next
experimental day the infusion of saline was replaced by a test solution
during the period between 11 P.M. and 5 A.M. Sleep-wakefulness states,
brain temperature, and food intake were monitored for a period of 72 hr, which comprised baseline, experimental, and recovery days. When an
experiment was over, each rat was killed with an overdose of
pentobarbital sodium and injected through the implanted cannula(e) with
a microquantity of pontamine sky blue dye solution (0.5% w/v) to
verify the site of infusion. The excised brains were fixed in 10%
formalin solution, and the location of the track of each cannula was
ascertained histologically.
In the first series of experiments (n = 120) a solution
of IL-1 was infused into one of the seven locations described above. The total dose of IL-1 that was infused ranged from 0.1 to 100 ng/6 hr,
which corresponded to the IL-1 concentration of the test solution from
4.0 × 10 11 to 4.0 × 10 8 M for the bilateral infusion or
from 8.0 × 10 11 to 8.0 × 10 8 M for the midline single infusion.
In the second series of experiments (n = 48) the effect
of COX inhibitors (diclofenac, NS-398, and piroxicam) on the changes
produced by IL-1 was examined, where IL-1 was infused into the
subarachnoid space of the PGD2-SZ at 10 ng/6 hr.
Analysis of data. Duration of wakefulness, SWS, and PS was
measured on the generated polygraph recordings, based on the visual judgment by an expert of the sleep-wakefulness states. The minimal scoring interval was set at 0.25 min of recording time. All results were expressed as the mean ± SEM. Statistics were performed by the use of paired Student's t test or ANOVA,
depending on the experimental design. The Student-Neuman-Keuls
multiple comparison test was used as the post hoc.
Differences were considered to be significant at p < 0.05.
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RESULTS |
Effects of IL-1 at the seven locations in the brain
To determine the site of action of IL-1, we infused 10 ng of IL-1
continuously for 6 hr (between 11 P.M. and 5 A.M.) into seven different
locations of the rat brain (Fig. 1). Total amounts of SWS, PS, and food
intake plus the average brain temperature during the 6 hr period of
IL-1 infusion were compared with corresponding baseline values. The
deviations of the experimental values obtained by the IL-1 infusion
from corresponding baseline levels were calculated and averaged (Fig.
2).

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Figure 2.
Changes in SWS, PS, brain temperature, and food
intake from respective baseline levels caused by the 6 hr (from 11 P.M.
to 5 A.M.) infusion of IL-1. The difference between the experimental
level by the IL-1 infusion and the baseline level (control) under the
infusion of saline vehicle was calculated for each rat; each
column indicates the mean ± SEM of the differences
obtained in this manner in a group of rats (n = 8 each) ascribed to the experiment for one of the seven locations.
*p < 0.05, **p < 0.01 by
paired Student's t test, compared between the IL-1
experiment and vehicle baseline. §p < 0.05, §§p < 0.01 compared among the
changes for the seven locations by Student-Newman-Keuls test
following one-way ANOVA, wherein the mark above L1 in
the panel for SWS and that above L2 in the panel for
brain temperature ( Brain temp.) indicate the
significant differences over the changes for the other six
locations.
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Regardless of the site of infusion, the total amounts of SWS that
appeared during the IL-1 infusion period were increased significantly
over their corresponding baseline levels. However, the magnitude of
these SWS increments differed greatly, in a site-dependent manner. When
IL-1 was infused into L1, an extraordinary increase in SWS by 110.7 min
(IL-1 was 208.1 ± 14.3 min vs control at 97.4 ± 9.3 min;
n = 8; p < 0.01 by paired Student's
t test) was attained. In contrast, infusion into any of the
other six locations produced only mildly increasing responses
(24.1-61.9 min). Thus, the increment attained at L1 was significantly
larger than the increments at the other six locations
(p < 0.01 by Student-Neuman-Keuls multiple comparison test following one-way ANOVA; F = 6.460;
p = 0.0001).
Infusion of IL-1 into L2 caused a significant decrease in the total
amount of PS (IL-1 was 7.0 ± 2.1 min vs control at 19.6 ± 1.8 min; n = 8; p < 0.01 by paired
Student's t test), whereas infusion into the other
locations resulted in marginal changes.
Infusion of IL-1 also caused fever and anorexia at all seven locations
that were examined. Fever was induced most severely at L2 among the
seven locations (p < 0.01 by
Student-Neuman-Keuls multiple comparison test following one-way
ANOVA; F = 11.345; p = 0.0001). The
degree of anorexia caused by the infusion of IL-1 into L2 was also
significantly more severe than that seen under infusion into L1 or L7
(p < 0.05 by Student-Neuman-Keuls multiple
comparison test following one-way ANOVA; F = 11.345; p = 0.0167).
Comparisons of the effects between L1 and L2
Because SWS was promoted most effectively by IL-1 at L1, whereas
L2 was the site for the most severe fever and anorexia, dose-dependent (Fig. 3) and time-dependent (Fig.
4) responses were examined further at
these two locations.

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Figure 3.
Changes in SWS, PS, brain temperature, and food
intake caused by the 6 hr infusion of IL-1 at different doses from
respective baseline (control) levels. See Figure 2 for the method of
calculation. Each datum point represents the mean ± SEM of eight rats. , Results by IL-1 infused into L2; ,
results by IL-1 infused into L1. *p < 0.05, **p < 0.01 by paired Student's t
test, compared between the IL-1 experiment and the baseline under
saline infusion. §§p < 0.01 by
repeated two-way ANOVA between L1 and L2.
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Figure 4.
The 24 hr profiles of SWS, PS, brain temperature,
and food intake in rats that received IL-1 into L1 and
L2. , Baseline; , experimental day; each
datum point represents the mean ± SEM of eight
values. IL-1 was infused into each rat between 11 P.M. and 5 A.M.
(indicated by the shaded area) on the experimental day
at 10 ng/6 hr. *p < 0.05, **p < 0.01 by paired Student's t test, compared between
the experimental datum point and the corresponding baseline
point.
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Dose-related responses
Infusion of IL-1 into L1 and L2 caused similar dose-dependent
increases in SWS, with respective maximum levels at 10 ng/6 hr of
infusion (Fig. 3). However, the magnitude of the overall responses was
significantly larger at L1 when compared with that at L2
(F = 13.932; p = 0.0004 by repeated
two-way ANOVA). Furthermore, at a rate of 0.1 ng/6 hr the infusion of
IL-1 into L1 increased SWS from the baseline by 15.1 min with
statistical significance (p < 0.05 by paired
Student's t test), whereas infusion into L2 caused no
significant change.
The infusion of IL-1 into L1 apparently increased PS at 0.1-1 ng/6 hr
but decreased it at 10-100 ng/6 hr, with statistical significance at
100 ng/6 hr (p < 0.01 by paired Student's
t test). On the other hand, PS was dose-dependently
suppressed at 0.1 ng/6 hr and above when IL-1 was infused into L2.
These profiles of PS for L1 and L2 differed significantly from each
other (F = 4.342; p = 0.0409 by
repeated two-way ANOVA).
Infusion of IL-1 also raised the brain temperature at 0.1 ng/6 hr and
above, regardless of the site of infusion at L1 or L2. However, site L2
appeared to be more sensitive than L1 in raising the temperature
(F = 14.704; p = 0.0003 by repeated
two-way ANOVA).
Significant decreases in food intake were observed under the infusion
of IL-1 into both L1 and L2 at 1 ng/6 hr and above. However, the
dose-dependent decrease for L2 was significantly more severe than that
for L1 (F = 10.733; p = 0.0017 by
repeated two-way ANOVA).
The 24 hr profiles
In the time-dependent profiles of SWS (Fig. 4) the amount of SWS
during the first hour of the IL-1 infusion was not increased greatly
from the corresponding baseline levels in either L1 or L2 profile;
i.e., the duration of latency before the increase in SWS was not
greatly different between the two locations. However, from the second
hour of IL-1 infusion the hourly mean SWS reached its maximum level in
the profile for L1, whereas the maximum level was attained only at the
last hour of the infusion in the profile for L2. It is notable that,
when IL-1 was infused into L1, the hourly SWS level increased to a
level comparable to that of daytime SWS, which is the physiological
maximum.
Incidentally and interestingly, the rebound decrease in SWS appeared to
be more severe in the profile for L2 during the light period after the
IL-1 infusion, in contrast to the marginal rebound in the profile for
L1, in which significant rebound was observed transiently only between
9 and 10 A.M. Thus, in the profile for L2 in comparison with that for
L1, the smaller increase in SWS by IL-1 was followed by a larger
decreasing rebound.
With regard to PS, brain temperature, and food intake (Fig. 4), their
responses were more outstanding in the profiles for L2 than in those
for L1 from the viewpoints of latency before the onset of marked
responses and the magnitude of the responses. In these profiles no
rebound phenomena were noticeable, at least within the time duration
shown in Figure 4.
Analyses of SWS episodes
The state of SWS is composed of episodes, with each duration
varying from several seconds up to several minutes. The duration of all
SWS episodes was measured, and the values were averaged on an hourly
basis (Fig. 5L1-A,L2-A). Under
the IL-1 infusion into L1 (Fig. 5L1-A) the average episode
duration for the second hour of the infusion period was prolonged
significantly when compared with the corresponding average value
calculated from the baseline-day recording (mean duration of SWS
episodes for IL-1 experiment was 2.21 ± 0.17 min vs baseline at
1.48 ± 0.20 min; n = 8; p < 0.01 by paired Student's t test). A histogram comprising the
numbers of SWS episodes with lengths within respective ranges is shown for this hour (Fig. 5L1-B). It indicates that the numbers of
episodes were increased irrespective of their length. It is notable
that the number of SWS episodes with a duration >3 min or even the number of those episodes >6 min was increased greatly by IL-1 and that
the number of SWS episodes of shorter duration also was increased. In
contrast, the infusion of IL-1 into L2 shortened the average duration
of SWS episodes during the fourth and fifth hour after the commencement
of IL-1 infusion (Fig. 5L2-A). The histogram for the SWS
episodes during the fourth hour (mean duration of SWS episodes for IL-1
experiment was 0.96 ± 0.08 min vs baseline at 1.29 ± 0.11 min; n = 8; p < 0.01 by paired
Student's t test) indicates that the numbers of episodes
<2 min were increased but that episodes with longer duration were
suppressed mainly by the infusion of IL-1 into L2 (Fig.
5L2-B).

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Figure 5.
Changes in the hourly mean of SWS episode duration
caused by the IL-1 infusion. L1-A, The 24 hr profiles of
the hourly mean of the SWS episode duration on the baseline day ( )
and on the experimental day ( ), which were obtained for rats that
received IL-1 infusion into L1; L1-B, Histogram
indicating the changes in the number of SWS episodes of various length
ranges, which was for the SWS episodes that appeared between 12 and 1 A.M. on the baseline day (open column) and on the
experimental day (open + closed column)
in L1-A. L2-A, The 24 hr profiles of the
hourly mean of the SWS episode duration in rats that received the IL-1
infusion into L2; L2-B, Histogram for the SWS episodes
that appeared between 2 and 3 A.M. in L2-A. SWS episode
duration is expressed as the mean ± SEM of eight rats. IL-1
was infused between 11 P.M. and 5 A.M. (indicated by the shaded
area) at 10 ng/6 hr through implanted cannulae.
*p < 0.05, **p < 0.01 by
paired Student's t test.
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Incidentally, it is also notable that the average duration of SWS
episodes was shortened markedly during the light period that followed
the IL-1 infusion. This shortening of SWS episodes appeared to be
longer lasting in the profile for L2 (Fig. 5L2-A) than in
that for L1 (Fig. 5L1-A). It is likely that the rebound decreases in SWS in Figure 4 were caused, at least in part, by the
shortening of SWS episodes.
Effect of COX inhibitors on the SWS promotion
Coadministration of the nonselective COX inhibitor diclofenac (46 µg/6 hr) with IL-1 (10 ng/6 hr) to L1 resulted in the disappearance of the SWS-promoting effect of IL-1 (Figs.
6A vs
4L1) as well as in that of its effects on brain
temperature and food intake (data not shown). The rebound decrease in
SWS during the light period that followed the IL-1 infusion (Fig.
4L1) was not visible, either, after this
coadministration. Neither the elongation of the average SWS episode
during the second hour of the IL-1 infusion period nor the shortening
of SWS episodes during the rebound phase after the IL-1 infusion (Fig.
5L1-A) became visible (Fig. 6B). Thus,
those changes in SWS and SWS episodes produced by IL-1 infusion completely disappeared by the addition of diclofenac.

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Figure 6.
Effect of COX inhibitors on the SWS-promoting
effect of IL-1 in L1. Shown are the 24 hr profiles of the hourly amount
of SWS (A) and those of the hourly mean of the
SWS episode duration (B) in rats that received
the coinfusion into L1 of IL-1 (10 ng/6 hr) and diclofenac sodium (46 µg/6 hr) between 11 P.M. and 5 A.M. (indicated by the shaded
area). , Baseline day; , experimental day.
C, Piroxicam (3 mg/kg), NS-398 (3 mg/kg), or vehicle
(for the column marked IL-1) was injected
intraperitoneally at 500 µl, 3.2 hr before the commencement of the
continuous infusion of IL-1 (or saline vehicle) into L1 between 11 P.M.
and 5 A.M. at 10 ng/6 hr. Each datum column represents
the mean ± SEM of eight rats. **p < 0.01 by
paired Student's t test between the experimental result
(filled column) and the corresponding control
result (open column).
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The SWS-promoting effect of IL-1 (Fig. 6C) as well as its
effects on brain temperature and food intake (data not shown) also were
blocked by NS-398 and by piroxicam, which are said, respectively, to
possess high and relative specificity for the COX-2 enzyme (Futaki et
al., 1994 ; Engelhardt et al., 1996 ; Riendeau et al., 1997 ). They were
injected intraperitoneally at 3 mg/kg of body weight 3.2 hr before the
commencement of continuous infusion of IL-1. These COX inhibitors had
been dissolved in 500 µl of vehicle composed of saline and DMSO at
50:50% (v/v), and the intraperitoneal injection of this vehicle alone
exhibited no effect on SWS or on PS, brain temperature, and food intake
(data not shown). The intraperitoneal injection of NS-398 or piroxicam
did not affect SWS by itself, whereas the combination of the
intraperitoneal injection of vehicle and the continuous infusion of
IL-1 into L1 produced a significant increase in SWS, by 89.1 min, from
the baseline level.
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DISCUSSION |
Site of action
Among the seven locations that were examined, L1 appeared to be
the most effective in promoting SWS (see Fig. 2), a region that
previously was reported by our group to be the site of action for the
SWS-promoting effect of PGD2 (Matsumura et al., 1994 ). At
other locations IL-1 also increased SWS, but the magnitude of those
increments was much smaller than that produced by IL-1 infusion into
L1. Walter and colleagues (1989) searched for the site of action of
IL-1 in rabbits but failed to find any specific location in the brain
parenchyma. These findings may suggest that IL-1 acts on some
tissues/cells existing within or adjacent to the subarachnoid space
underlying the rostral basal forebrain to promote SWS.
In contrast to the SWS response, other parameters were found to be
affected most markedly by the infusion of IL-1 into L2 among those
sites that were examined (see Fig. 2). The PS response varied according
to the site of infusion from L1 through L7, but a statistically
significant change from the baseline was attained only at L2. Thus, it
is likely that IL-1 inhibited PS by acting at the region adjacent to
the 3V.
The pyrogenic and anorectic effects of IL-1 also were outstanding when
IL-1 was infused into L2. The anorectic effect was concordant with
those previous results that were demonstrated with continuous infusion
of IL-1 into the 3V (Plata-Salamán, 1994 ; Plata-Salamán et
al., 1996 ). In addition, latency before the onset of fever and anorexia
that followed IL-1 infusion into L2 was much shorter than that after
infusion into L1 (see Fig. 4). IL-1 generally is considered as a
biological mediator of fever (Dinarello et al., 1983 ) and anorexia
(Hellerstein et al., 1989 ; Plata-Salamán, 1994 ;
Plata-Salamán et al., 1996 ), and emphasis has been placed on the
predominant roles of the hypothalamus in these phenomena (Sellami et
al., 1995 ). We infer that the 3V side, rather than the subarachnoid
side, of the organum vasculosum of the lamina terminalis (OVLT) plays
crucial roles in these effects of IL-1.
Effect of IL-1 on SWS episodes
During the increase in SWS that was caused by IL-1 infusion into
L1, the number of SWS episodes increased regardless of the length range
of the episodes (see Fig. 5L1-B); i.e., both long and short
episodes increased in number. This feature was strikingly different
from the feature observed in the SWS increase brought about by IL-1
infusion into L2 (see Fig. 5L2-B), wherein episodes with
short duration increased but those with long duration were suppressed.
Because IL-1 activates both the hypothalamic-pituitary-adrenal system
(Sapolsky et al., 1987 ) and the sympathetic nervous system (Terao et
al., 1994 ), the shortening of SWS episodes caused especially by IL-1
infusion into L2 might be correlated with the activation of these two
systems. Even with the infusion into L1, the activation of these two
systems may not have been negligible because of diffusion toward the L2
region. This might explain why the elongation of SWS episodes, which is
a characteristic of physiological daytime sleep, occurred only during
the second hour of the IL-1 infusion period and not thereafter at L1
(see Fig. 5L1-A).
Involvement of COX in the effects of IL-1
It is postulated that COX in the brain plays a critical role in
the central actions of IL-1 such as fever (Dinarello et al., 1983 ) and
anorexia (Hellerstein et al., 1989 ) induction and is critically
involved in the sympathetic nervous system (Terao et al., 1995 ) and
hypothalamic-pituitary-adrenal system (Katsuura et al., 1988 ). On the
other hand, COX-mediated promotion of sleep has been doubtful until now
(Krueger et al., 1982 ).
In the current study, however, not only IL-1-induced fever and anorexia
(data not shown) but also SWS promotion were all blocked completely by
COX inhibitors (see Fig. 6). The blocking of the SWS-promoting effect
of IL-1 by the COX inhibitor also became manifest from the finding
that, not only during the IL-1 infusion but also during the expected
rebound phase after IL-1 infusion, IL-1-induced changes in the length
of SWS episodes were abolished by the addition of diclofenac (see Figs.
6B vs 5L1-A).
We infer that in the study of Krueger and colleagues (1982) , the
antipyretic drug may not have been fully supplied to the ventral
surface, sleep-promoting zone of the rostral basal forebrain defined as
the site of action of PGD2 and IL-1. We believe that the
current results have provided solid evidence for the crucial role of
COX in the SWS-promoting effect of IL-1.
Diclofenac is a general inhibitor of COX regardless of subtypes of the
enzyme, i.e., COX-1 and COX-2, whereas inhibitors NS-398 and piroxicam,
respectively, are said to possess high and relative specificity for the
COX-2 (Futaki et al., 1994 ; Engelhardt et al., 1996 ; Riendeau et al.,
1997 ). Because these COX-2 inhibitors themselves were sufficient to
block completely the promotion of SWS by IL-1 (see Fig. 6C),
it is likely that COX-2 rather than COX-1 plays the major role in this
promotion of SWS. COX-2 generally is thought to be an inducible enzyme;
however, it also was observed to be expressed in the CNS of the rat
even under the normal, nonstimulated condition (Yamagata et al., 1993 ;
Breder et al., 1995 ; Cao et al., 1996 ). Therefore, it remains to be
clarified whether the promotion of SWS produced by the sequence of IL-1
and COX-2 action is exclusively pathological or even active under the
physiological condition.
There was a time lag between the commencement of IL-1 infusion and the
onset of the increase in SWS, which was calculated to be ~55 min. In
a previous study of our group (Matsumura et al., 1994 ) the time lag
between the commencement of infusion of PGD2 and the onset
of the SWS increase was assessed to be 35 min. The infusion of IL-1 in
the present study and that of PGD2 in our previous study
were both made into the same site, i.e., L1. Expression of mRNA of
COX-2 was shown to be induced by intraperitoneal injection of IL-1 by
use of an in situ hybridization technique (Cao et al.,
1996 ). These findings lead us to postulate the following: (1) IL-1
induced the synthesis of COX-2, which subsequently catalyzed the
formation of PGH2 from arachidonate, resulting in the
formation of PGD2 and other PGs and in the promotion of
SWS; and/or (2) IL-1 increased the availability of arachidonate, which
facilitated the production of PGH2 from arachidonate,
resulting in the formation of PGD2 and other PGs to promote
SWS.
Role of PGs in the promotion of SWS
At this moment there is no report on whether PGD2
production is augmented by an IL-1 challenge in vivo, but
the PGE2 level reportedly rose in response to intravenous
injection of IL-1 in some brain areas, including the OVLT (Komaki et
al., 1992 ). In cultured rat astrocytes IL-1 stimulated the production
of PGE2 (Katsuura et al., 1989 ) and PGD2
(Yamamoto et al., 1988 ). Because PGD synthase is abundant in
leptomeninges and CSF (Urade et al., 1993 ; Watanabe et al., 1994 ), it
is highly probable that PGD2 is synthesized actively in the
ventral surface zone of the rostral basal forebrain after the induction
of COX-2 and/or the increased availability of arachidonates, both of
which might be caused by IL-1.
It was shown previously that PGE2 possessed a
wakefulness-promoting potency in rats and monkeys, which was brought
about by its action in the diencephalon (Matsumura et al., 1988 ; Onoe
et al., 1992 ; Gerozissis et al., 1995 ). However, the same
PGE2 promoted SWS when it was infused into the subarachnoid
space of the PGD2-SZ (Ram et al., 1997 ). In this zone
PGF2 also promoted SWS in the same study. Thus, these
three PGs were all SWS-promoting in the zone; therefore, it is
plausible without any contradiction that hyperproduction of
PGH2 is an important step in the promotion of SWS triggered
by the infusion of IL-1 into this zone of the rostral basal
forebrain.
Type 1 IL-1 receptor (Ericsson et al., 1995 ), COX-2 (Cao et al., 1996 ),
PGD synthase (Urade et al., 1993 ), and PGD receptor (Oida et al., 1997 )
were all shown to be expressed predominantly in the leptomeninges as
well as, in some cases, in blood vessels and other tissues/cells. These
findings support the idea that the leptomeninges and CSF in the
PGD2-SZ of the rostral basal forebrain play critical roles
in the mediation of SWS promotion. Because CSF levels of IL-1 activity
vary in phase with sleep-wake cycles (Lue et al., 1988 ) and because
the expression of mRNA of IL-1 exhibited a diurnal variation (Taishi et
al., 1997 ), a sequence of events including IL-1 and PGs may be
responsible, at least in part, for physiological sleep-wakefulness
phenomena as well as for certain kinds of pathological processes.
 |
FOOTNOTES |
Received Jan. 16, 1998; revised June 1, 1998; accepted June 4, 1998.
This work was supported in part by funding from the program
Grants-in-Aid for Scientific Research of the Ministry of Education, Science, and Culture of Japan and from the Special Coordination Funds
for Promoting Science and Technology of the Science and Technology
Agency of the Japanese Government, as well as by Grant 8A-6 from the
program Research Grants for Nervous and Mental Disorders of the
Ministry of Health and Welfare and by a grant from the Naito
Foundation. A.T. was supported by a fellowship of the Japan Society for
Promotion of Science. We are grateful to Drs. Kiyoshi Matsumura, Chunyu
Cao, Shinsuke Satoh, Yoshihiro Urade, and Osamu Hayaishi (Osaka
Bioscience Institute) for valuable discussions and Dr. Larry D. Frye
for critical reading of this manuscript. We also thank Tomoko Nakajima,
Keiko Kasahara-Orita, Nobuko Konishi, and Miyako Matsumura for their
excellent technical assistance.
Correspondence should be addressed to Dr. Hitoshi Matsumura, Department
of Neuropsychiatry, Osaka Medical College, 2-7 Daigakumachi, Takatsuki
City, Osaka 569-8686, Japan.
 |
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