Sleep-promoting
effects of endogenous
pyrogen (interleukin- 1)
JAMES M. KRUEGER,
SHELDON
M. WOLFF,
JAMES WALTER,
CHARLES
AND LOUIS CHEDID
A. DINARELLO,
Department
of Physiology and Biophysics, The Chicago Medical School,
North Chicago, Illinois 60064; Department of Medicine, Tufts University School of Medicine,
Boston, Massachusetts 02111; and Immunotherapie Experimentale, Institut Pasteur, Paris, France
slow-wavesleep;rabbits; fever; anisomycin; muramyl peptide
A SUBSTANCE, factor
S, that induces slow-wave sleep
(SWS) in several species of animals has been shown to
be a muramyl peptide (21). Some synthetic muramyl
peptides, which have been studied extensively as immunoadjuvants (8, 12), have also been shown to be somnogenie (22) and pyrogenic (9). They have the additional
capacity (like many bacterial agents) of inducing synthesis and release of endogenous pyrogens in vivo and in
vitro (9, 27). Thus, muramyl
peptide-treated
macrophages contain in their supernatants endogenous pyrogen (EP), which produces fever (8). It was, therefore, of
interest to determine whether such dialyzed macrophage
supernatants or a purified preparation of EP could induce SWS. We found that both preparations
induced
prolonged increases in rabbit SWS and that excess SWS
was observed even when the associated febrile response
was blocked with the antipyretic anisomycin.
MATERIALS AND METHODS
The muramyl peptide used in this study, NAc-Mur-LAla-D-Gln-OMe
or MDP(Gln)-OMe,
was designed and
synthesized by P. Lefrancier (23). All chemicals were
reagent grade. Needles, syringes, glassware, media, and
solutions were sterile and pyrogen free.
Preparation of macrophage supernates. Rabbit peritoneal exudate cells (PEC) and human mononuclear cells
(PBMC)
were prepared as previously described (8).
Briefly, PEC were induced by an intraperitoneal
injecR994
tion of sterile mineral oil (50 ml). Rabbits were killed
with an intravenous overdose of pentobarbital
sodium 72
h later; PEC were harvested from the peritoneal cavity
using 300 ml of heparinized (5 U/ml) pyrogen-free saline.
Cells were washed twice and resuspended in RPM1 1640
medium (Flow Labs, McLean, VA) supplemented
with
a combination
of penicillin
and streptomycin
and with
N- 2 - hydroxyethylpiperazine
-N ’ - 2 - ethanesulfonic
acid
(HEPES) buffer (0.01 M, pH 7.1-7.3). PEC density was
lo7 cells/ml. PBMC were obtained from blood collected
from healthy adult volunteers. The buffy coat was diluted
1:3 with minimal essential medium (MEM) 199 (Institut
Pasteur Productions, Paris, France) supplemented with
heparin (1:lOO; Liquemine,
Hoffman-LaRoche,
Basel,
Switzerland).
The method of Boyum (4) was used to
recover PBMC after centrifugation
on Ficoll-Triosil.
Mononuclear
cells were diluted at 5 x lo6 cells/ml in
RPM1 1640 medium supplemented with antibiotics and
HEPES as described for PEC.
Both PBMC and PEC were incubated for 24 h with
100 pg/ml of MDP (Gin)-OMe.
Cell suspensions were
then subjected to centrifugation (1,000 g), and supernates
were dialyzed overnight against phosphate-buffered
saline (PBS; 0.15 M, pH 7.4) to eliminate residual synthetic
glycopeptide, because it has a molecular weight of about
500. Control cells were incubated without the glycopeptide, and supernates were treated in the same fashion.
MDP( Gln) -0Me was used because previous studies
showed that although this analogue is not somnogenic
(22) or pyrogenic in- vivo, it is capable of activating
macrophages in vitro to produce lymphocyte-activating
factor (LAF) and endogenous pyrogen (Parant, Riveau,
Parant, and Chedid, unpublished observations).
Preparation of purified human EP. Human plateletpheresis byproducts were separated on Ficoll-Hypaque
gradients (11), and the mononuclear cell layer was stimulated with heat-killed
Staphylococcus albus (bacteria:leukocyte
1O:l) in the presence of 1% fresh bovine
serum albumin. The mixture was allowed to settle onto
glass bottle surfaces for 1.5 h at 37°C followed by vigorous
shaking to remove nonadherent cells. The adherent monocytes were then incubated in serum-free MEM (Biological Associates, Walkerville,
MD). for 18 h. The supernate
was clarified by centrifugation
at 8,000 g and mixed with
Sepharose 4B-bound rabbit antihuman EP (11). After 2
h at room temperature,
the immunoabsorbent
was
0363-6119/84
$1.50
Copyright 0 1984 the American Physiological Society
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KRUEGER,JAMESM., JAMESWALTER,CHARLESA. DINARELLO, SHELDONM. WOLFF, AND LOUIS CHEDID. Sleep-promoting effects of endogenous pyrogen (inter&kin-l).
Am. J.
Physiol. 246 (Regulatory Integrative Comp. Physiol. 15): R994R999, l984.-When infused into the lateral cerebral ventricles
of rabbits, human endogenouspyrogen (EP) preparations induced dose-dependentincreasesin slow-wave sleep concomitant with increasing body temperature. Heating EP to 70°C
destroyed its sleep-promoting and pyrogenic activity. Anisomycin (an antipyretic) prevented EP from increasing body
temperature without affecting its sleep-promotingactivity. Intravenous injection of EP induced fever and transient increases
in slow-wavesleepbut failed to induce prolonged increasesin
slow-wavesleep. We conclude that the somnogenicactivity of
EP is not secondaryto its pyrogenic activity.
SLEEP-PROMOTING
EFFECTS
OF
ENDOGENOUS
PYROGEN
hour control recordings were obtained from rabbits at
the same time of day; these data provide each rabbit with
individual control values. Rectal temperatures were measured by a thermistor probe (Yellow Spring Instruments)
inserted 10 cm into the rectum. Temperatures
were determined immediately
after the infusion and 3 and 6 h
later. This procedure transiently
(5-10 min) disturbed
sleep. During control recordings, rectal temperatures
were also determined at 3-h intervals. After intravenous
injections of EP, rectal temperatures
were taken just
before the injection, l-2 h later, and 6 h later. The typical
monophasic fever induced by intravenous injection of
EP is maximum
at about 1 h after injection;
rectal
temperatures
are usually at control values 3 h after
injection (10).
EP samples (2-200 ~1) were diluted to 0.3 ml with
artificial CSF (in mM: 3 KCl, 1.15 CaC12, and 0.96 MgCl,)
in nonpyrogenic sterile saline (155 mM NaCl, Abbott).
Samples were infused over a 45-min period at a rate of
6.7 pl/min icv. In some cases anisomycin (700 pg/rabbit)
was also dissolved in either artificial CSF (control) or in
the EP-artificial
CSF solutions (experimental)
for intracerebroventricular
infusions. After receiving anisomycin,
rabbits were not used again for 2 mo. Cerebral ventricular
pressure was monitored to ensure that solutions were
infused into the ventricle (20). For systemic injections
the vehicle was pyrogen-free saline (Abbott). During and
after infusion, EEGs were recorded on Grass polygraphs
(model 7D). EEG leads were connected to the polygraph
via a rotary commutator
(BRS-Tech
Serv), which allowed unrestrained
movements of rabbits. The EEG
signal was also led through a band-pass filter (Buxco,
model 1802P), and the 0.5- to ~-HZ component was
rectified. The filtered rectified signal was recorded on
the polygraph simultaneously
with the EEG. The slowwave rectified signal was also integrated, and integrals
were printed on tape every minute. Body movements
were recorded from a water-filled tube attached to the
EEG cable and connected to a pressure transducer.
EEG records were visually scored to determine duration of SWS. Rabbit sleep is characterized by short SWS
episodes (l-10 min), which under control conditions
usually occupy 35-45% of the time during 1 h or more of
recording (20). The duration of an individual SWS episode was defined as that period of time during which
EEG slow waves (0.5-4 Hz) were not interrupted
for
more than 20 s by the high-frequency low-voltage EEG
that is characteristic of an awake animal. Visual assessment of the filtered rectified EEG recording facilitated
scoring; the large differences between amplitude of slow
waves of a sleeping vs. waking animal are easily distinguishable on the filtered rectified EEG recording. The
body movement record was used to distinguish movement artifact on the EEG. Slow-wave amplitudes (mean
rectified slow-wave voltages) averaged over 1 min. SWS
periods and waking periods were determined for each
rabbit using the printed integrals during control and
experimental conditions. Under control conditions these
values are stable for each animal within about 10% over
a period of weeks (20).
In some cases behavioral observations were made at
various times after administration
of EP samples. In
Downloaded from http://ajpregu.physiology.org/ by 10.220.33.5 on June 14, 2017
poured into a column and washed with 5 vol PBS (pH
3.0). EP was eluted with citric acid buffer (pH 3.0) and
collected into 1% lysine (final concn) and neutralized
with NaOH. This material was concentrated and chromatographed over Sephadex G-50, fine (170 x 5.0 cm,
4OC, 0.15 M NaCl, pH 5.9); the 15,000-dalton peak was
isolated (10) and concentrated
in autoclaved dialysis
tubing against dry polyethylene glycol (mol wt 6,000) at
4°C. The concentrated
material
was then dialyzed
against 4,000 vol PBS.
The material we prepared was shown to contain the
three isoelectric focusing points of EP (11). Rabbit pyrogen testing revealed 0.1 ml (intravenously)
to produce
a 1°C monophasic fever, typical of EP, and at dilutions
of 10"; this material doubled the phytohemagglutinin
response of murine thymocytes in the LAF assay (28).
Rabbit bioassay. Rabbits were used to assay EP samples
for several reasons. 1) Rabbits are frequently used in
experimental work on fever (3). 2) Rabbits develop fever
after administration
of human EP (8); we avoided, therefore, possible species specificity problems associated with
transfer of EP from one species to another (3). 3) In
rabbits, normal variations in the amount of time spent
in SWS from day to day are very small (SD t 7%) (21);
the small standard deviation reduces the number of
assays required to demonstrate the presence or absence
of sleep-promot .ing activity. 4) Rabbits (20), unlike rats
(20) and cats (16), adapt rapidly to experimental
cages,
thus an overnight acclimation period is sufficient to allow
for valid sleep measurements the next day. 5) We could
use the phen omenon of “supranorm .al” slow waves that
are observed after sleep deprivation (21 , 26) or administration of sleep-promoting
muramyl peptides (22) as an
objective criterion for identifying
active fractions. 6)
Intracerebral ventricular administration
of control solutions of artificial
cerebrospinal
fluid (CSF) does not
affect subsequent duration or patterns of sleep in rabbits
(20). 7) Rabbits spend less than 5% of their sleep time
in rapid-eye-movement
sleep (13); thus we simplified the
analysis by restricting it to SWS.
Male New Zealand White rabbits weighing 3-4 kg were
used. Under pentobarbital
sodium anesthesia (Nembutal,
Abbott; 15 -30 mg/kg body wt) stainless steel screws were
implanted over the frontal ., parietal, and occipital cortex.
Short electroencephalogram
(EEG) leads from a plug
(ITT-Cannon
#MIKO-l-7SH)
were soldered to these
screws. A cerebral ventricular
guide tube was also imPla nted 4 mm lateral and 1 mm posterior to the bregma
as previo usly described (20). Dental cement (DuzAll
acrylic) was then applied to insulate the leads and to
secure the guide tube and EEG plug to the skull. Following the operation each animal received 150,000 U of
procaine penicillin
G (Duracillin,
Lilly) and a topical
application of bacitracin (Lilly) around the incision. One
week was allowed for recovery.
Rabbits were brought to the experimental
cages for an
overnight acclimation
period before each experiment;
both the housing and experimental
rooms were temperature controlled (21 t 2°C) and on a 12-h light-12-h
dark cycle. Intracerebroventricular
infusions or intravenous injections were carried out between 8:00 and 10:00
A.M.
and were followed bY 6 or more h of recording. Six-
R995
R996
KRUEGER
particular we sought signs of abnormal autonomic function such as excess nasal and/or lacrimal secretion; these
responses are observed after large doses of sleep-promoting muramyl peptides (22). No behavioral abnormalities
were noted after EP administration
at the doses used.
ET AL.
80
RESULTS
Effects of human PBMC supernates. Infusion of 10 or
25 ~1 of solutions obtained from MDP(Gln)-OMe-treated
Effects of intravenous administration of rabbit PEC
supernates. Intravenous injection of PEC supernates re-
sulted in significant
rectal temperature
20
60
120
180
240
300
360
Time After Injection,
min.
FIG. 2. Time course of slow-wave sleep (SWS) responses following
intravenous injection of supernates obtained from rabbit peritoneal
exudate cells (PEC). Top solid line: effects of intravenous injection (1
ml/kg). Lower broken line: effects of intravenous injection of saline (1
ml/kg) in same animals (n = 4). Each point is mean t SE percent
SWS that occurred during 24-min period. Solutions were injected 2-5
min before time 0. After intravenous injection there appeared to be a
transient increase in SWS lasting about 96 min. This increase paralleled time course of febrile responses elicited by bolus intravenous
injection of endogenous pyrogen (10). After intracerebroventricular
infusion of PEC supernates, longer sleep responses (Fig. 3) and febrile
responses (6) were observed.
increases char1. Effects of rabbit PEC supernates on
rabbit S WS and rectal temperature
TABLE
Administration
--- 4
n
Dose,
Pm%
%SWS
Control
Exptl
Max Increase
in
Rectal Temp
IV
3
250
41 k 6
44 III 5
0.7 t 0.1*
Iv
4
500
41 t 2
42 I!I 1
0.7 t 0.2*
Iv
4
1,000
39 t 3
45 t 3
1.1 * 0.1*
Icv
4
17
42 t 4
59 If: 1*
1.1 Ik 0.3*
Values are means of: SE of 6-h recordings. PEC, peritoneal exudate
cells; SWS, slow-wave sleep; Iv, intravenous; Icv, intracerebroventricular. Rectal temperatures taken l-2 h after iv injection and 3 h after
icv infusion.
* Significantly different from control, P < 0.05. Each
rabbit was used as his own control; paired statistics were used.
38
20
IO
0
-10
4
I
I
I
I
I
I
IO
20
30
40
50
I
DOSE, pl
Effects of increasing doses of dialyzed macrophage supernates on rabbit slow-wave sleep (SWS) and rectal temperatures. Top
ordinate: rectal temperatures taken 3 h after infusion. At this time
febrile responses were greatest. Bottom ordinate: percent excess SWS
= (%SWS experimental) - (%SWS control). Percent SWS values for
each rabbit were determined during 1 or more 6-h control recordings.
Abscissa: microliters of each preparation intracerebroventricularly
infused. Top soLid lines: preparations obtained from MDP( Gln) -OMetreated human mononuclear cells. Bottom broken lines from control
macrophages. Each point represents mean t SE of 4 assays on 4
rabbits.
FIG.
1.
acteristically peaking 40-50 min following bolus injection
and returning to base-line levels after 3-4 h. Rabbits
were also observed to enter a short (40- to 60-min) period
of excess SWS, which coincided with the fever (Fig. 2).
Because these periods of excess sleep were of short duration, we were unable to demonstrate significant increases over the 6-h recording period using our routine
statistical methods of analysis. However, if we restrict
our analysis to the first 96 min, the period in which
febrile responses occur (lo), significant increases in SWS
were observed. During this period percent SWS values
were 50 t 5 (experimental)
and 34 t 2 (control) (P <
0.02). This preparation
was also infused intracerebroventricularly;
in this case 50 ~1 were sufficient to induce
prolonged increases in SWS and rectal temperatures
(Table 1).
Effects of purified human EP. Our results obtained by
macrophage supernates suggested that a nondialyzable
Downloaded from http://ajpregu.physiology.org/ by 10.220.33.5 on June 14, 2017
PBMC induced prolonged increases in SWS (Fig. 1).
Increases in rectal temperatures
above control values
were also observed after these infusions. Maximum
temperature increases were observed 3 h after the infusion;
6 h after infusion temperatures were still elevated above
control values. The excess SWS appeared normal despite
the development of fever in the sense that animals continued to sleep episodically, could easily be aroused, and
spontaneously awoke from time to time to eat, drink,
and groom. In contrast to these results, equal volumes of
supernates obtained from control macrophages failed to
induce significant
increases in either SWS or rectal
temperatures.
However, if the dose of this preparation
was increased to 50 ~1, slight increases in SWS and rectal
temperatures were observed.
SLEEP-PROMOTING
EFFECTS
OF ENDOGENOUS
PYROGEN
2. Effects of various dosesof purified
human endogenous pyrogen on S WS in rabbit
TABLE
% SWS
Dose,
Pl
n
Control
2
10
50
200
4
4
3
4
Postinfbsion,
o-3
38k4
38~15
35t4
35k2
h
Rectal
3-6
Temp,
C”
3 h postinfusion
Exptl
Control
Exptl
54tl*
67t3*
79t5*
70*7*
35t2
39t2
33*5
40t3
33t2
53t3*
66t4*
68t7*
Control
38.9tO. 1
38.8tO.l
39.4kO.2
39.2tO.l
Exptl
39.6rtO.2*
40.3&0.2*
41.3*0.1*
41.6&0.2*
Values are means t SE. SWS, slow-wave sleep.
* Significantly
different from corresponding control value; Student’s t test [df = 3 (or
2) for SWS and 6 (or 4) for temperature] exceeded P = 0.05 level.
temperatures during the first 6 h postinfusion; percent
SWS was 40 t 3 (control) and 40 t 2 (experimental)
(n
= 4/group). However, the day after anisomycin treatment there were large variations in duration of SWS
even though rectal temperatures
were normal. Other
long-term behavioral effects of anisomycin have been
reported (17).
Effects of EP on amplitude of EEG slow waves. Increases in amplitude of EEG slow waves during SWS are
observed during the deep sleep that follows sleep deprivation in rabbits (26), rats (l), and humans (2). Similar
increases are observed after administration
of factor S
(21) or other somnogenic muramyl peptides (22). In the
present study the amplitude of EEG slow waves during
SWS increased 27% above control values in those afebrile rabbits that received anisomycin plus 2 ~1 of purified
EP (Table 3). No significant
increases in slow-wave
amplitudes were observed in those control animals that
received only anisomycin. Significant increases in EEG
slow-wave voltages during SWS were also observed in
the febrile animals that received only purified EP. None
of these groups had significant changes in slow-wave
amplitudes during waking periods.
70 60-
53 &4%
p< .025
39_+3%
Effects of anisomycin on fever and sleep responses induced by purified EP. Cranston et al. (6) reported that
simultaneous
intracerebroventricular
infusion of anisomycin and EP blocked the expected febrile response.
Thus, to determine whether sleep responses persisted in
the absence of fever, we infused solutions containing
anisomycin and 2 ~1 of purified EP. Fever responses to
EP were completely blocked by anisomycin (Fig. 3), thus
confirming the observations of Cranston et al. However,
sleep responses elicited by EP were unaffected by the
anisomycin treatment. These results are similar to those
previously reported that showed that fever after intravenous administration
of MDP could be attenuated by
pretreatment
with an antipyretic without affecting the
capacity of MDP (Gin)-OMe to induce sleep (22). Anisomycin by itself did not affect duration of SWS or rectal
1
I
I
I
I
I
I
I
2
3
4
5
6
HOURS AFTER INFUSION
3. Effects of anisomycin on somnogenic and pyrogenic actions
of purified human endogenous pyrogen. Anisomycin (700 pg) was
simultaneously infused with 2 ~1 of purified EP preparation; 0.3 ml of
artificial cerebrospinal fluid was used as vehicle.?o> ordinate: change
in temperature = experimental - control. Average rectal temperatures
were not significantly different from control values obtained from same
rabbits. Bottom graph: M,
values obtained from rabbits after
infusion of anisomycin + endogenous pyrogen (EP); O---O, values
obtained from same rabbits during control recordings. Nos. to right are
%SWS values for entire 6-h recording period. Values shown are means
+ SE from 7 assays on 7 rabbits. Anisomycin completely blocked
pyrogenic actions of EP; sleep responses were slightly enhanced when
fever was blocked.
FIG.
Downloaded from http://ajpregu.physiology.org/ by 10.220.33.5 on June 14, 2017
substance, produced by macrophages under conditions
known to elicit EP, induced excess SWS. To avoid possible nonspecific effects of the relatively crude supernate
samples we used purified EP for further studies. Four
doses of purified EP were tested (Table 2). At the lowest
dose (2 pl), excess SWS was observed only during the
first 3 postinfusion
h. When the dose was increased
greater excess SWS was observed and responses persisted throughout the 6-h recording period. In some cases
we recorded for 30 h after administration
of 200 ~1 EP.
Excess SWS was observed during the first 18 postinfusion h; no rebound in wakefulness was observed in subsequent hours. It is important
to mention that during
the first hour after infusion excess SWS was observed;
following intracerebroventricular
infusions of sleep-promoting muramyl peptides excess SWS was not evident
until the second postinfusion hour (22). The febrile responses induced by EP were also dose dependent. As
described above, the excess SWS appeared normal even
though animals were simultaneously
febrile.
Purified EP was obtained from macrophages treated
with heat-killed S. albus. Thus to control for the possibility of an inadvertant
copurification
of a heat-stable
biologically active bacterial product with EP, samples of
purified EP were heated (7O”C, 30 min) before intracerebroventricular
administration
of 10 ~1. EP is inactivated
by this treatment
(10, 28). Somnogenic and pyrogenic
actions of our purified EP samples were lost after heat
treatment; percent SWS values were 41 t 2 (control)
and 41 t 1 (experimental)
(n = 3/group) for the 6 h
postinfusion period.
R997
R998
KRUEGER
ET
AL.
circadian rhythms of core body temperature; duration of
sleep episodes was greatest when subjects entered sleep
during peak temperatures (7).
Em PV
Es, PV
Proposals concerning the role that EP may play in
Infusate
n
normal sleep and temperature regulation should take
Control
Exptl
Control
Exptl
into account the fact that normal sleep is usually accomAnisomycin
(7OOpg)
4
20t 2 22 + 3 80 k 12
87k8
panied by a regulated decrease rather than an increase
EP (2 ~1) + anisomy6
15 t 1
16 t 2
52 z!z 5
66 t 7*
in body temperature (18). If EP is involved in normal
tin (700 pg)
EP (200 ~1)
4 19 t 3
19 t 3
63 tll
81 t 17*
sleep, one might assume that it is delivered by very
precise mechanisms, perhaps in concert with other sleep
Values are means t SE. EP, endogenous
pyrogen;
EEG, electroencephalogram;
E, and E,, EEG slow-wave
voltage during awake periods
and temperature modulators, to those cells involved in
* Significantly
different
from
and slow-wave
sleep, respectively.
the induction of SWS. Thus in normal sleep the increases
control,
P < 0.05. Individual
E, and E, values differed
substantially
in body temperature that we observed after rapid delivery
from one rabbit to another;
paired statistics
were used.
of exogenous EP would not be encountered. It is possible
that EP can, under certain physiological conditions, inDISCUSSION
duce excess SWS. Cannon and Kluger (5) reported that
The results presented here clearly demonstrate that
increases in EP-like activity accompany an increase in
febrile and sleep responses elicited by EP can be sepa- circulating leukocytes in postexercise marathon contestants. Shapiro et al. (29) reported large increases in SWS
rated from each other. After intracerebroventricular
administration of EP, fever was blocked by anisomycin
during postmarathon nights. Subsequently, Horne and
but excess SWS was not. It is possible that sleep re- Staff (19) showed that passive heating, which increased
sponses were due to a separate macrophage product
body temperature, also resulted in increased duration of
copurified with EP, which may independently induce SWS. This could suggest that increases in SWS following
SWS. Traditionally the product(s) of activated macro- exercise result from increases in body temperature rather
phages have been named in accordance with their biolog- than EP; however, EP levels were not measured in this
ical activities, i.e., endogenous pyrogen for the production
study. It is also possible that the subjective feelings of
of fever and lymphocyte-activating
factor for enhance- sleepinessthat often accompany infectious diseasecould
ment of lymphocyte responses to mitogens and antigens. be due to EP elicited by the infectious agent.
The preparations used in the present experiments conThe onset of excess SWS following intracerebroventained both EP and LAF activity. There is evidence that
tricular EP administration (Fig. 3) is faster than that
those biological activities may be due to a single sub- following infusion of sleep-promoting muramyl peptides
stance, or closely related family of substances, and are (22). This could suggest that muramyl peptides exert
often referred to as interleukin-1 (8, 24). Other studies, their effects on SWS through a step involving production
however, have shown that EP and LAF activities are not
of EP or another monokine. An alternative possibility is
secreted together from macrophages activated by certain
that muramyl peptides and monokines independently
analogues of MDP(Gln)-OMe
(8); thus the possibility of affect those neurons involved in the generation of SWS.
a separate somnogenic macrophage product remains.
Evidence for this hypothesis stems from the experiments
of Riveau et al. (27), who were unable to detect EP after
Regardless of the number of macrophage products
involved, what is clear from the present studies is that
central administration
of very large amounts of
those conditions we used to stimulate macrophages elic- MDP(Gln-OMe).
However, if small amounts of EP were
ited both EP and sleep-promoting activity. That these generated in or near the specific neurons involved in the
activities may be intimately related is no t surp rising
induction of sleep and/or fever, it could go undetected
because many relationships between sleep and temperaby current methods of analysis. There is evidence that
ture regulation have been described. For example, many
astrocytes and C6 glioma cells can produce an interleudrugs or neurotransmitters can induce perturbations in kin-l-like substance (14). We also consider the possibility that EP may contain a muramyl peptide component,
both temperature regulation and sleep but the effects
depend on dose, route of administration, and species because its structure remains unknown.
(25). Under some circumstances increases in body temWe thank Drs. J. R. Pappenheimer
and M. L. Karnovsky
for their
perature are associated with increases in sleep and/or
counsel and Dr. C. McCormack
for reviewing
this manuscript.
EEG synchronization (15,30-32). Local changes in brain
This study was supported
in part by Office
of Naval
Research
temperature may also affect sleep; in kangaroo rats in- Contracts
N00014-82-K-0393,
NIH-BRSG-RR5366,
and NIH-AIcreases in SWS or rapid-eye-movement sleep can be 15614.
elicited by local warming of the hypothalamus (18). In
humans deprived of environmental timing cues, the timReceived
1 August 1983; accepted in final form 13 January
1984.
ing and architecture of sleep can be correlated with
3. Effects of human EP on rabbit
EEG slow-wave voltages
TABLE
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A. A., AND H. U. NEWHAUS.
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effects
on sleep and EEG in the rat. J. Cornp. Physiol. 133: 71-87, 1979.
2. BORBELY, A. A., F. BAUMANN,
D. BRANDEIS,
I. STRAUCH, AND D.
LEHMANN.
Sleep-deprivation:
effect on sleep stages and EEG
power density in man. Electroencephalogr.
Clin. Neurophysiol.
51:
483-493,198l.
3. BORSOOK,
D., H. LABURN,
AND D. MITCHELL.
The febrile
responses in rabbits
and rats to leucocyte
pyrogens
of different
species. J. Physiol. London
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