 |
 Previous Article | Next Article 
The Journal of Neuroscience, April 1, 1999, 19(7):2799-2806
Interleukin-1 in Immune Cells of the Abdominal Vagus Nerve:
a Link between the Immune and Nervous Systems?
Lisa E.
Goehler1,
Ron
P. A.
Gaykema1,
Kien T.
Nguyen1,
Jacqueline E.
Lee2,
Fred J. H.
Tilders3,
Steven F.
Maier1, and
Linda R.
Watkins1
Departments of 1 Psychology, and
2 Molecular, Cellular, and Developmental Biology,
University of Colorado, Boulder, Colorado 80309, and
3 Research Institute Neuroscience, Department of
Pharmacology, Vrije Universiteit, Amsterdam, The Netherlands
 |
ABSTRACT |
Intraperitoneal administration of the cytokine
interleukin-1 (IL-1) induces brain-mediated sickness symptoms
that can be blocked by subdiaphragmatic vagotomy. Intraperitoneal
IL-1 also induces expression of the activation marker c-fos in vagal
primary afferent neurons, suggesting that IL-1 is a key component of vagally mediated immune-to-brain communication. The cellular sources of
IL-1 activating the vagus are unknown, but may reside in either blood or in the vagus nerve itself. We assayed IL-1 protein after intraperitoneal endotoxin [lipopolysaccharide (LPS)] injection in
abdominal vagus nerve, using both an ELISA and
immunohistochemistry, and in blood plasma using ELISA. IL-1 levels
in abdominal vagus nerve increased by 45 min after LPS administration
and were robust by 60 min. Plasma IL-1 levels increased by 60 min,
whereas little IL-1 was detected in cervical vagus or sciatic nerve.
IL-1-immunoreactivity (IR) was expressed in dendritic cells and
macrophages within connective tissues associated with the abdominal
vagus by 45 min after intraperitoneal LPS injection. By 60 min, some
immune cells located within the nerve and vagal paraganglia also
expressed IL-1-IR. Thus, intraperitoneal LPS induced IL-1 protein
within the vagus in a time-frame consistent with signaling of immune
activation. These results suggest a novel mechanism by which IL-1
may serve as a molecular link between the immune system and vagus
nerve, and thus the CNS.
Key words:
dendritic cells; macrophages; rat; ELISA; immunohistochemistry; endotoxin; cytokines; vagus
| |
INTRODUCTION |
Macrophages, dendritic cells, and
other immune cells detect pathogens such as bacteria or viruses and
respond by releasing proinflammatory mediators, such as the cytokine
interleukin-1 (IL-1). IL-1 acts both to coordinate the
peripheral immune response and to signal the CNS (Dunn, 1993 ; Maier et
al., 1993). Such pathogen-induced IL-1 release activates the CNS to
orchestrate a cascade of endocrine, autonomic, and behavioral processes
collectively termed the acute phase response. This response functions
broadly to render physiological conditions of the host inhospitable to
the pathogen. The precise mechanisms by which IL-1 signals the CNS
are unknown, but possibilities include direct detection of immune
mediators by barrier cells of the brain (e.g., circumventricular organs
and endothelial cells) (Van Dam et al., 1992; Saper and Breder, 1994;
Ericsson et al., 1997) or by activation of primary afferent neurons of
the vagus nerve (Watkins et al., 1995b).
Subdiaphragmatic vagotomy inhibits a variety of acute phase responses
resulting from intraperitoneal administration of either IL-1 or
lipopolysaccharide (LPS; bacterial endotoxin, which induces the
expression of IL-1) (Watkins et al., 1994, 1995a; Bret-Dibat et al., 1995; Gaykema et al., 1995; Hansen and Krueger, 1997). In
addition, the neuronal activation marker c-fos is expressed in primary
afferent neurons of the vagus after intraperitoneal administration of
either LPS (Gaykema et al., 1998) or IL-1 (Goehler et al., 1998).
Furthermore, sensory structures associated with the abdominal vagus
(vagal paraganglia) express binding sites for IL-1 ligands (Goehler et
al., 1997). These lines of evidence support the idea that vagal
afferents are in fact activated by immune-related stimuli, notably
IL-1, and relay this information to the brain.
Vagal signaling of immune activation must occur fairly rapidly, because
the induction of centrally mediated acute phase responses such as fever
and hyperalgesia occurs within 90 min (Watkins et al., 1994,
1995a) and the vagal afferent neurotransmitter glutamate (Schaffar et al., 1997) is released in vagal afferent terminal fields
within 60 min of intraperitoneal LPS administration (Mascarucci et al.,
1998). If IL-1 is a constituent of a vagal signaling pathway, it
must be induced within this time frame, in either blood or perivagal
immune cells. Accordingly, we determined the time course of IL-1
protein expression in plasma and vagus nerve after intraperitoneal LPS
administration. To determine whether LPS induction of IL-1 is
specific to the abdominal vagus rather than a general feature of
peripheral nerves, we compared IL-1 expression in the abdominal
vagus with that in the cervical vagus and sciatic nerves. IL-1
protein levels were assessed across tissues and time points using an
ELISA. The cell types (e.g., perivagal immune cells) expressing IL-1
were determined using immunohistochemistry.
| |
MATERIALS AND METHODS |
Quantitative assessment of IL-1 with ELISA
Subjects and tissue collection. Adult male Sprague
Dawley viral-free rats (Harlan Sprague Dawley, Indianapolis, IN;
350-400 gm) were used. The subjects were maintained on a 12 hr
light/dark cycle (lights on 7:00 A.M.-7:00 P.M.) with standard
laboratory chow and water available ad libitum. Temperature
in the colony room was maintained at 23°C. All procedures were in
accordance with protocols approved by the University of Colorado
Institutional Animal Care and Use Committee.
Rats were injected intraperitoneally with LPS (0111:B4; 100 µg/kg;
Sigma, St. Louis, MO; lot L4391). At either 30, 45, or 60 min after
injection, the animals (n = 8 per group) were
anesthetized with sodium pentobarbital (60 mg/kg, i.p.), the thoracic
cavity was opened, and a sterile sample of cardiac blood was collected endotoxin-free in heparinized vials containing 17.55 mg EDTA (Becton Dickinson, Franklin Lakes, NJ) and immediately placed on ice until plasma could be collected. The animals were then quickly perfused transcardially with saline. The ventral abdominal vagus nerve including
the hepatic branch, a 1-1.5 cm section of the cervical vagus just
distal to the carotid bifurcation, and a 2 cm section of the proximal
sciatic nerve distal to the pelvis and proximal to the knee, were
dissected out and immediately frozen on dry ice. Nerves and plasma were
collected from additional rats in an identical manner 30 (n = 4) or 60 min (n = 5) after
equivolume vehicle (pyrogen-free physiological saline, 1 ml/kg). All
nerve samples were stored at  70°C before sonication. Blood samples were kept on ice and centrifuged at the end of collection at 4°C. Plasma was stored at 20°C until ELISA.
Tissue processing. Each nerve sample was added to 0.25-0.5
ml of Iscove's culture medium containing 5% fetal calf serum and a
cocktail enzyme inhibitor (in mM: 100 amino-n-caproic acid, 10 EDTA, 5 benzamidine HCl, and 0.2 phenylmethyl sulfonyl fluoride). Total protein was mechanically
dissociated from tissues using an ultrasonic cell disrupter (Heat
Systems, Farmingdale, NY; model MS-50). Sonication consisted of 10 sec
of cell disruption at the setting 10. Sonicated samples were
centrifuged at 10,000 × g, at 4°C, for 10 min.
Supernatants were removed and stored at 4°C until assayed.
Bradford protein assays. Bradford protein assays were
performed to determine total protein concentrations in nerve sonication samples. Total protein levels were measured using a version of the
Coomassie blue protein assay adapted from Bradford (1976), as
previously described (Nguyen et al., 1998). All data were expressed in
terms of micrograms of protein per 100 µl.
ELISA. The assays were performed using a commercially
available rat IL-1 ELISA kit (R & D systems, Minneapolis MN), as
previously described (Nguyen et al., 1998). This ELISA kit utilizes a
rabbit anti-rat IL-1 polyclonal antibody (Ab) that can recognize
both recombinant (r) as well as natural rat IL-1. The manufacturer did not observe significant cross-reactivity of this Ab to rHuman IL-1
receptor type I, IL-1 receptor type II, IL-1ra, rRat IL-1 , IL-2,
IL-4, interferon- , tumor necrosis factor-, rMouse IL-1, and
IL-1ra. The recovery rate of IL-1 with this assay is between 50 and
70% (our unpublished observations). The results were expressed as picograms of IL-1 per 100 µg of total protein.
Data analysis. The data were analyzed using ANOVA, followed
by post hoc t tests (Bonferroni-Dunn) for
differences between the groups.
Nerve-associated IL-1 immunoreactivity
Subjects and tissue collection. Animals (as above),
were injected with 100 µg/kg LPS. Either 30 (n = 8),
45 (n = 10), or 60 (n = 10) min after
injection they were anesthetized and perfused transcardially with
saline, as above. Additional groups of vehicle-treated animals were
perfused either 30 or 60 min after injection. The nerve tissues were
dissected in an identical manner as for the ELISA, as above, and
immersion-fixed in 4% paraformaldehyde/0.1 M phosphate
buffer (PB), pH 7.4, for 3-5 hr. They were cryoprotected overnight in
22% sucrose/PB, sectioned on a cryostat at 20 µm, and thaw-mounted
on electrically charged glass slides (Fisher Scientific, Houston, TX).
Antisera. The thaw-mounted cryostat sections of nerves were
processed for immunoreactivity (IR) using antisera directed against IL-1 [SILK6: mouse monoclonal IgG; the epitope is amino acid sequence 123-143 of the mature rat IL-1 (Schotanus et al., 1995) from Department of Pharmacology, Vrije Universiteit, Amsterdam, The
Netherlands]. In addition, consecutive sections were processed for the
following markers, to aid in identification of the cells expressing
IL--IR: tyrosine hydroxylase (TH; Incstar, Stillwater, MN), MHC
class II antigen (using OX-6, mouse monoclonal antibody; Biosource International, Camarillo, CA) and a macrophage marker (ED-1, mouse monoclonal IgG; Biosource International). TH is a marker for glomus cells in paraganglia (Berthoud et al., 1995) and was
used solely to confirm the relationship of IL-1-IR positive cells
with the vagus nerve and paraganglia. TH staining is not shown.
According to the manufacturer (Biosource International), OX-6 labels
the class II monomorphic antigen rat/mouse RT1B in dendritic cells and
some macrophages, whereas ED-1 recognizes a 90-100 kDa antigen present
in lysosomal membranes of macrophages and some dendritic cells.
Single-label immunohistochemistry. Sections were washed in
PBS and immersed in PBS containing 0.3% hydrogen peroxide and 0.1% sodium azide for 30 min to suppress endogenous peroxidase. Then the
slides were rinsed and incubated in 10% normal goat serum (NGS) in PBS
containing 0.5% Triton X-100 (PBS-T) for 1 hr. With intermittent
washes in PBS, the sections were sequentially incubated in avidin and
biotin (Vector AB blocking kit, both diluted 1:10 in PBS-T, each 1 hr;
Vector Laboratories, Burlingame, CA) to prevent staining of endogenous
biotin. Then the sections were incubated in primary mouse monoclonal
anti-rat/human IL-1 (SILK6, 1:100), mouse monoclonal OX-6 (1:100),
biotinylated mouse monoclonal ED-1 (1:300), or mouse monoclonal anti-TH
(1:1000) overnight at room temperature (RT). The next day the slides
were washed and incubated in secondary biotinylated goat anti-mouse IgG
antibody (1:100; Jackson ImmunoResearch, West Grove, PA) overnight at
RT, except those sections incubated in biotinylated ED-1. All
antibodies were diluted in PBS-T containing 0.1% sodium azide and 10%
NGS. Finally, sections were incubated in avidin-biotin complex
(Vector Elite kit, 1:100 in PBS-T, 2 hr; Vector Laboratories) and
rinsed in Tris HCl, pH 7.6. Peroxidase staining was performed using
3,3'-diaminobenzidine (Sigma) as a chromogen dissolved in Tris
HCl (50 mg/100 ml) using glucose oxidase (Sigma; type V-S, 0.02%) and
-D-glucose (0.1%) to generate hydrogen peroxide (Shu et
al., 1988). One series of sections was processed as above except that
the primary antibody was omitted from the incubation buffer (omission
controls). The slides were dried overnight, counterstained with cresyl
violet, and coverslipped before viewing with an Olympus Vanox II
bright-field microscope. Images were collected with a COHU CCD camera
coupled to an Apple PowerMac 7200 equipped with NIH Image software
(version 1.60) and stored on a Zip cartridge. The obtained micrographs were exported to and labeled using Adobe Photoshop. Except for small
adjustments of brightness and contrast, the images were not altered.
Double-label immunofluorescence. Sections were washed in PBS
and incubated in 10% NGS in PBS-T for 1 hr. The sections were then
incubated in a mixture of rabbit polyclonal antiserum against IL-1
(1:100; Endogen, Woburn, MA) and either mouse monoclonal anti-mouse
monoclonal OX-6 (1:100) or mouse monoclonal ED-1 (1:200) overnight at
RT. The antisera were diluted in PBS-T containing 0.1% sodium azide
and 10% NGS. The next day sections were rinsed and incubated in a
mixture of FITC-conjugated goat anti-mouse IgG (1:100; Jackson
ImmunoResearch) and Texas Red-conjugated goat anti-rabbit IgG (1:100;
Jackson ImmunoResearch) overnight at RT. The slides were then rinsed in
several changes of PBS, air-dried, and coverslipped in Vectashield
mounting medium (Vector Laboratories). Adjacent series of sections were
subjected to the same protocol with the omission of one of the two
primary antisera to verify the absence of cross-reactivity. Another
series of sections were incubated in the same mixture of primary
antisera, diluted in PBS-T and 10% normal donkey serum, and then
immersed in a different mixture of secondary antisera (purified for
minimal cross-reactivity), and with the fluorescent tags reversed:
Texas Red-conjugated donkey anti-mouse IgG, Fab2 fragment (1:100;
Jackson ImmunoResearch), and FITC-conjugated donkey anti-rabbit IgG
(1:100; Jackson ImmunoResearch). The sections were examined in a Nikon
epifluorescence microscope equipped with filters to excite either FITC
or Texas Red, or both.
| |
RESULTS |
ELISA analysis
IL-1 protein content of the abdominal vagus nerve increased
over time after intraperitoneal LPS (F(1,23) = 13.73; p < 0.001) (Fig.
1A) IL-1 levels were
very low (mean = 0.13 pg/100 µg protein) at 30 min, but were
elevated by 45 min (mean = 3.03 pg/100 µg protein;
p < 0.05). IL-1 levels were robust by 60 min
(mean = 12.69 pg/100 µg protein; p < 0.0001).
In the abdominal vagus nerves of saline-treated animals, IL-1 levels
remained very low (mean = 0.08 pg/100 µg protein) at both times
tested (Fig. 1A).
View larger version (17K):
[in this window]
[in a new window]
|
Figure 1.
Interleukin-1 content as assessed using ELISA
in abdominal vagus, cervical vagus, and proximal sciatic nerve tissues
(A) and blood plasma (B)
30, 45, and 60 min after intraperitoneal injection of 100 µg/kg LPS
or saline. Only the abdominal vagus shows the induction of IL-1 as
early as 45 min. IL-1 content in plasma is significantly elevated by
60 min. *p < 0.05; **p < 0.0002.
|
|
IL-1 levels in plasma increased over time after intraperitoneal LPS
(F(1,31) = 5.9; p < 0.02) as
shown in Figure 1B. IL-1 levels in plasma (Fig.
1B) remained low but detectable in saline- (mean = 3.7 pg/ml), and LPS-treated animals (means = 1.5-3.8 pg/ml) until 60 min after LPS injection, at which time plasma IL-1 content was significantly elevated (mean = 18.66 pg/ml) compared with saline controls (p < 0.0002).
In contrast, cervical vagus nerve and sciatic nerve IL-1 levels were
low or undetectable in both saline- and LPS-treated animals (Fig.
1A), and thus there were no significant effects of
LPS treatment over time (cervical vagus: F(1,23) = 0.53, NS; sciatic nerve: F(1,23) = 1.3, NS).
Patterns of immune marker immunoreactivity in nerves
Histological differences between the tissues
The ventral abdominal vagus, and especially the hepatic branch, is
characterized by abundant connective tissue, through which run several
small blood vessels and lymph ducts (L. Goehler, unpublished observations) (Prechtl and Powley, 1987). This connective tissue also
contains large aggregates of lymphoid/myeloid-like cells of varying
morphology [nerve-associated lymphoid/myeloid cells (NALC)]. In
contrast, connective tissue associated with the cervical vagus is
somewhat more limited, and around the sciatic nerve it is restricted to
a thin layer around the nerve sheath.
Expression of IL-1 immunoreactivity
The results from the immunohistochemical studies mirror those from
the ELISA analysis. IL-1-IR was not observed in saline-treated rats
at any time point. Whereas IL-1-IR was induced in a time-dependent manner in the abdominal vagus, very little IL-1-IR was induced in
cells associated with either the cervical region of the vagus or the
sciatic nerve. A summary of immunohistochemical observations is shown
in Table 1.
View this table:
[in this window]
[in a new window]
|
Table 1.
Summary of immunohistochemical observations of IL-1,
OX-6, and Ed-1 immunoreactivity in nerves after intraperitoneal LPS
treatment
|
|
IL-1-IR became evident in cells throughout the abdominal vagus,
including the hepatic branch, by 45 min after LPS injection. Cells
expressing IL-1 at this time point were scattered throughout the
connective tissue, but appeared more numerous along the connective tissue edges (Fig. 2A)
and within the NALC. The level of expression of IL-1-IR was somewhat
variable at this time point; some animals expressed limited IL-1-IR,
whereas others exhibited robust induction of IL-1.
View larger version (152K):
[in this window]
[in a new window]
|
Figure 2.
LPS-induced IL-1-IR in tissue associated with
the abdominal vagus nerve. A, Cells in perivagal NALC
expressing IL-1-IR (dark cytoplasmic staining
indicated with arrows) 45 min after intraperitoneal LPS
administration. B-D, IL-1-IR
dendritiform cells in connective tissue adjacent to the abdominal vagus
nerve 60 min after LPS. B shows a high magnification of
an IL-1-IR dendritiform cell. E, F,
Darkly stained IL-1-positive cells in perivagal NALC
(E, F, arrow), most of
which are round in shape. Some dendritiform IL-1-IR cells are
present between nerve fibers at edge of vagus nerve (F,
arrowheads). Scale bars: A, 25 µm;
B, 10 µm; C, 50 µm; D,
25 µm; E, 50 µm; F, 50 µm.
NALC, Nerve-associated lymphoid/myeloid cells;
VN, vagus nerve.
|
|
By 60 min after LPS injection, many more cells expressed IL-1-IR,
and the intensity of staining was much greater (Fig.
2B-F). Cells expressing IL-1-IR
appeared to consist primarily of cells of the dendritic or macrophage
phenotype. Cells with similar characteristics to those expressing MHC
class II-IR (Fig. 2B-D, and see below) expressed IL-1-IR within the connective tissue surrounding the nerve, as well as within the perineurium. Other cells expressing IL-1-IR included small cells with a distribution, size, and
morphology consistent with macrophages (Fig.
2E,F, and see below, ED-1-IR). Many
darkly stained cells could be seen among the NALC (Fig.
2E,F). At this time point, a
few cells expressing IL-1-IR extended within the nerve fibers (Fig.
2F), and some small cells with thin processes were
seen within many paraganglia (Fig.
3E). The dendritiform processes of these cells appeared similar to MHC-II-IR also seen in
paraganglia (Fig. 3D, and see below). Other IL-1-IR
appeared to envelope the unlabeled type I (glomus cells), and thus may represent type 2 cells (described by Morgan et al., 1976). Variability was minimal, as all LPS-treated animals expressed robust
IL-1-IR.
View larger version (158K):
[in this window]
[in a new window]
|
Figure 3.
A-C, MHC class
II-IR dendritiform cells (dark reaction product) within
the abdominal vagus nerve (A), cervical vagus
nerve (B), and proximal sciatic nerve
(C). Note the difference in density of
immunostained cells, which is highest in the abdominal vagus
(A) and lowest in the proximal sciatic nerve
(C). MHC class II-IR is present in both saline-
and LPS-treated rats. D, E, Immune cells
in abdominal vagal paraganglia constitutively expressing MHC class
II-IR (D) interspersed among vagus nerve fibers
and glomus cells in a paraganglion, and those with similar morphology
expressing LPS-induced IL-1-IR (E) surrounding
unlabeled glomus cells. F, ED-1-IR in cells of perivagal
NALC 60 min after LPS treatment, showing macrophage-like (round or
oval-shaped) morphology. Counterstaining with cresyl violet provides
light background staining in A-D. Scale
bars, 50 µm. NALC, Nerve-associated lymphoid/myeloid
cells; PG, paraganglion; VN, vagus
nerve.
|
|
Expression of MHC class II-IR (OX-6)
MHC class II-IR occurred in all three (abdominal vagus, cervical
vagus, and sciatic) nerves in saline-treated animals, as well in those
treated with LPS (Fig. 3A-C). MHC class II-IR
was particularly abundant in the abdominal vagus, where cells formed a
plexus extending along and between the vagus nerve fibers. They were dense within the connective tissue, as well as the nerve trunk, forming the appearance of a network. They occurred in the NALC as well, where they extended processes around and between the
other cells. Many MHC class II-IR cells were found along and within the
perineurium. Some MHC class II-IR cells extended across the surface of
the vagal paraganglia, where their processes penetrated between the
glomus cells (Fig. 3D). The cells expressing MHC class II-IR
were comparatively large (10-20 µm) dendritiform, and possessed highly variable cell bodies with irregular shapes (Figs. 3,
4A). Some of these
cells were nearly round, with one or two prominent dendrites, whereas
others were elongate or fusiform. All cells showed strong cytoplasmic
expression of MHC class II-IR. These characteristics suggest that most
of these cells were dendritic cells (Steinman, 1991; Banchereau and
Steinman, 1998). MHC class II-IR cells displayed a similar pattern in
the cervical vagus nerve and sciatic nerve, where their distributions
were much more sparse (Fig. 3B,C),
even in cervical vagus nerve samples that contained connective
tissue.
View larger version (53K):
[in this window]
[in a new window]
|
Figure 4.
Colocalization of immunofluoresence for IL-1
(A'-C'), MHC-II
(A, B), and ED-1
(C) in connective tissue surrounding the
abdominal vagus. A, B',
Arrows indicate cells showing strong immunofluorescence
for both MHC-II (A, B) and
IL-1 (A', B'). Subcellular
localization of the two antigens is not always overlapping.
Single arrowheads indicate strongly MHC class
II-positive cells that lack prominent labeling for IL-1.
Double arrowheads (A, A')
point to cells that show clear IL-1-IR but have weak or no MHC class
II-IR. C, C', Cells show strong dual
labeling for ED-1 (C, arrows) and IL-1
(C', arrows). Arrowheads
point to weak ED-1-positive cells that lack IL-1-IR. Scale bars, 25 mm.
|
|
Expression of ED-1-IR
ED-1-IR occurred in the sciatic, cervical vagus, and abdominal
vagus nerves at low levels in saline-treated animals and increased expression was induced by 60 min after LPS injection. However, ED-1-positive cells were far more numerous in the abundant connective tissue of the abdominal vagus. These cells were small (5-10 µm), with a slightly irregular shape (Fig. 3F). They were
located along the connective tissue edges, where they formed small and
large aggregates. ED-1-positive cells were also distributed among the NALC (Fig. 3F) where they appeared to be major
constituents. Some ED-1-IR occurred along the nerve perineurium,
especially at 45 and 60 min after LPS injection.
Double-label immunofluorescence
In sections of vagus nerve incubated with antisera against IL-1
and either MHC class II or ED-1, double-labeled cells were observed
(Fig. 4). Cells double positive for IL-1 and MHC class II were large
(>10 µm) and varied morphologically. Some cells were nearly round,
but with a distinctly irregularly shaped nucleus (Fig.
4A,A',B,B'),
whereas others were spindle-shaped with a dendritic appearance (Fig.
4B,B'). Cells double positive for
IL-1 and ED-1 occurred in clumps of smaller cells (6 µm diameter)
primarily in the connective tissue or NALC (Fig.
4C,C').
| |
DISCUSSION |
The results of this study demonstrate that IL-1 protein is
induced in the abdominal vagus nerve within 1 hr after intraperitoneal LPS administration, as assessed by ELISA and immunohistochemistry. The
cells expressing IL-1 immunoreactivity are primarily dendritic-type cells that are located along the nerve perineurium, connective tissue,
and NALC, and in macrophage-like cells located in clusters also within
the associated connective tissue and NALC. In addition, IL-1
immunoreactivity is also induced in cells located between vagal nerve
fibers and in paraganglia. These observations are consistent with the
idea that IL-1 is rapidly expressed by immune cells after detection
of pathogens and that these cells then signal the abdominal vagus by
releasing cytokines such as IL-1.
Rapid induction of perivagal IL-1 is consonant with findings from
other studies implicating IL-1 as a key mediator in immune signaling
from the peritoneum to the brain (Dunn, 1993; Maier et al., 1993).
Intraperitoneal injection of IL-1 activates vagal afferents (Goehler
et al., 1998) and initiates brain-mediated acute phase responses that
can be blocked by either pretreatment with systemic IL-1 receptor
antagonist or subdiaphragmatic vagotomy (Maier et al., 1993, Schotanus
et al., 1993; Watkins et al., 1994). Glutamate, a likely
neurotransmitter for a majority of vagal afferents (Schaffar et al.,
1997), is released in the nucleus of the solitary tract (the site of
termination for vagal primary afferent nerve fibers) after
intraperitoneal injection of either LPS or IL-1 (Mascarucci et al.,
1998). Taken together with our observation of rapid induction of
perivagal IL-1 after LPS treatment, these findings reinforce the
idea that a major pathway for the actions of IL-1 on the brain is
via the abdominal vagus nerve.
Site specificity of IL-1 expression in immune cells associated
with nerves
The abdominal vagus nerve was the only nerve tested in which
IL-1 was induced within 60 min after intraperitoneal LPS treatment. These observations indicate that rapid expression of intraperitoneal LPS-induced IL-1 is not a general feature of peripheral nerves.
Although IL-1 was not detected in either the cervical vagus or
proximal sciatic nerve after intraperitoneal LPS treatment, these
nerves do clearly contain small populations of resident immune cells,
as evidenced by the presence of MHC class II-positive cells observed
between the nerve fibers of both the cervical vagus and sciatic nerves.
ED-1-positive macrophage-like cells were also observed in connective
tissue associated with these nerves, the numbers of which appeared to
increase moderately after LPS treatment. This increase in ED-1
expression may represent migration of activated macrophages to this
tissue or may reflect the possibility that LPS in the systemic
circulation by 60 min after the intraperitoneal injection (our
unpublished observations) was sufficient to activate some of the
resident cells. The functions of these nerve-associated immune cells
are unclear, but some possibilities include initiation of immune
responses to injury or infection (Clatworthy et al., 1995; Banchereau
and Steinman, 1998) and/or they may serve trophic or regulatory
functions, as has been suggested for dendritic-type cells in endocrine
organs such as pituitary and gonads (Hoek et al., 1997).
The lack of IL-1 expression in the proximal sciatic and the cervical
vagus after LPS may relate to the fact that both these nerves consist
primarily of axons of nerve fibers that terminate a distance away and
may not normally be exposed to immune stimuli. In contrast, the
subdiaphragmatic vagus is located at the distal end of the nerve,
closer to terminal fields of vagal afferents, and thus in closer
proximity to likely sites of immune activation (e.g., by ingested or
translocated pathogens, as well as intraperitoneal LPS), than are the
other two nerve regions. It is also possible that immune cells in the
cervical region of the vagus and/or the sciatic nerve failed to express
IL-1 because they were not exposed to LPS. However, intraperitoneal
LPS at this dose or similar doses (Lenczowski et al., 1998; our
unpublished observations) can be measured in the general
circulation. The time points investigated in this experiment were
intentionally short, and it is possible that IL-1 may in fact be
induced in other nerves, but later than in the abdominal region of the
vagus nerve.
Source of IL-1 relevant to vagal afferents
In this study we show that intraperitoneal LPS induces significant
IL-1 immunoreactivity in plasma by 60 min. IL-1 in plasma may
therefore signal immune activation to vagal afferents. However, because
IL-1 is induced earlier (by 45 min) in perivagal immune cells, it
seems likely that additional sources of IL-1 relevant to the vagus
are located within the nerve or its associated tissues and are probably
dendritic cells and macrophages. These observations speak to a
continuing controversy regarding the source of IL-1 and other
cytokines that activate acute phase responses. In some studies, acute
phase responses are evident in the absence of detectable levels of
cytokines in the circulation (Kluger, 1991). Even when endotoxin or
cytokines are detected in plasma, their levels or timing do not always
correlate with acute phase activation after intraperitoneal
administration of immune stimuli (Kluger, 1991). These observations
have led to the suggestion that the relevant signals are not in the
circulation, but rather arise in the peritoneum or other discrete
tissue sites (Carlson, 1997). However, levels of IL-1 obtained from
peritoneal lavage also do not correlate with brain-mediated illness
responses (Lenczowski et al., 1998). The results from the present study
offer a potential explanation for these seemingly confusing
observations. Perivagal immune cells respond rapidly to intraperitoneal
LPS, and they are located near enough to the vagal afferents and/or
paraganglia that IL-1 may not need to enter either the general
circulation or the peritoneal fluid to exert its effects.
Immune cells in paraganglia
The constitutive presence of MHC class II-IR in cells within the
vagal paraganglia suggest that immune cells are normal residents of
these structures. In addition, IL-1 is induced in immune-like, nonglomus cells by 60 min after intraperitoneal LPS
administration. Glomus cells, many of which are innervated by vagal
afferents (Berthoud et al., 1995), can express binding sites for IL-1
ligands (Goehler et al., 1997). The codistribution of glomus-type cells potentially expressing binding sites for IL-1 with immune-type cells
capable of producing IL-1 provides a possible pathway by which
immune-derived IL-1, or other mediators, leads to vagal activation.
Dendritic cells and macrophages as sentinels for the
nervous system
The presence of numerous dendritic cells in such close association
with vagal nerve fibers and paraganglia reinforces the idea that one
function of the vagus nerve is to signal immune activation in internal
tissues to the CNS. Steinman (1991) has described dendritic cells as
the "sentinels of the immune system". Dendritic cells are typically
distinguished by their highly irregular cell shape, numerous and often
extensive processes (dendrites), and high constitutive and cytoplasmic
expression of MHC class II molecules (Cella et al., 1997; Banchereau
and Steinman, 1998). They are specialized to detect pathogens, thus
they express pinocytic and phagocytic capability, as well as receptors
for a variety of pathogens (Cella et al., 1997). They are well situated
to serve as immune sentinels because they are distributed throughout
the body (Banchereau and Steinman, 1998). When dendritic cells detect pathogens, they migrate in lymph to the draining lymph nodes, where
they activate T-cells (Ni and O'Neill, 1997). In fact, dendritic cells
are the only cells capable of activating naive T-cells (Banchereau and
Steinman, 1998). Thus, dendritic cells are critical for the initiation
of primary immune responses. Their prominent location within and around
vagal nerve fibers and their expression of IL-1 after LPS
administration suggests that they may serve as immune sentinels for the
nervous system as well.
Macrophages, which also responded to intraperitoneal LPS by expressing
IL-1 are also well suited to act as immune-to-brain sentinels. In
addition to important clearance and primary defense functions (e.g.,
phagocytosis and release of peroxide and superoxide), macrophages help
orchestrate primary immune responses (Goerdt et al., 1996). Macrophages
express receptors for pathogen-associated molecules, such as LPS, and
are active phagocytes, thus able to respond to a wide variety of
pathogens (Goerdt et al., 1996). Their location within vagal nerve
connective tissue and induction of IL-1 after LPS injection suggests
that one function of IL-1 produced by these cells may be to signal
the vagus nerve.
Conclusions
Intraperitoneal LPS induces perivagal immune cells to rapidly
express IL-1 immunoreactivity. These results are consistent with a
model of immune-to-brain communication such that immune activation
within the peritoneal cavity stimulates dendritic cells and macrophages
to synthesize and release cytokines such as IL-1, which then
activate vagal afferents. Vagal afferents then, via their terminations
in the nucleus of the solitary tract, activate CNS-mediated illness
consequences. In this way, immune cells may signal the brain using a
paracrine action to stimulate neural, in addition to humoral,
immune-to-brain communication pathways. It may be that this neural
pathway is especially important as a rapid signaling pathway in the
early phases of host defense.
| |
FOOTNOTES |
Received Nov. 20, 1998; revised Jan. 19, 1999; accepted Jan. 21, 1999.
This work was supported by National Institutes of Health Grants
MH55283, MH01558, and MH00314 and internal funds of the Vrije Universiteit Amsterdam.
Correspondence should be addressed to Dr. Lisa E. Goehler, Department
of Psychology, Muenzinger Hall, Box 345, University of Colorado,
Boulder, CO 80309.
| |
REFERENCES |
-
Banchereau J,
Steinman RM
(1998)
Dendritic cells and the control of immunity.
Nature
392:425-252.
-
Berthoud H-R,
Kressel M,
Neuhuber WL
(1995)
Vagal afferent innervation of rat abdominal paraganglia as revealed by anterograde DiI-tracing and confocal microscopy.
Acta Anat
152:127-132[Medline].
-
Bradford MM
(1976)
A rapid and sensitive method for quantification of microgram quantities of protein utilizing the principle of protein-dye binding.
Anal Biochem
72:248-254[Web of Science][Medline].
-
Bret-Dibat JL,
Bluthé R-M,
Kent S,
Kelley K,
Dantzer R
(1995)
Lipopolysaccharide and interleukin-1 depress food-motivated behavior in mice by a vagal-mediated mechanism.
Brain Behav Immun
9:242-246[Web of Science][Medline].
-
Carlson DE
(1997)
Adrenocorticotropin correlates strongly with endotoxemia after intravenous but not after intraperitoneal inoculations of E. coli.
Shock
7:65-69[Web of Science][Medline].
-
Cella M,
Sallusto F,
Lanzavecchia A
(1997)
Origin, maturation and antigen presenting function of dendritic cells.
Curr Opin Immunol
9:10-16[Web of Science][Medline].
-
Clatworthy AL,
Illich PA,
Castro GA,
Walters ET
(1995)
Role of peri-axonal inflammation in the development of thermal hyperalgesia and guarding behavior in a rat model of neuropathic pain.
Neurosci Lett
184:5-8[Web of Science][Medline].
-
Dunn AJ
(1993)
Role of cytokines in infection-induced stress.
Ann NY Acad Sci
697:189-202[Web of Science][Medline].
-
Ericsson A,
Arias C,
Sawchenko PE
(1997)
Evidence for an intramedullary prostaglandin-dependent mechanism in the activation of stress-related neuroendocrine circuitry by intravenous interleukin-1.
J Neurosci
17:7166-7179[Abstract/Free Full Text].
-
Gaykema RPA,
Dijkstra I,
Tilders FJH
(1995)
Subdiaphragmatic vagotomy suppresses endotoxin-induced activation of the hypothalamic corticotrophin-releasing hormone neurons and ACTH secretion.
Endocrinology
136:4717-4720[Abstract].
-
Gaykema RPA,
Goehler LE,
Tilders FJH,
Bol JGJM,
McGorry M,
Fleshner M,
Maier SF,
Watkins LR
(1998)
Bacterial endotoxin induces Fos immunoreactivity in primary afferent neurons of the vagus nerve.
Neuroimmunomodulation
5:234-240[Web of Science][Medline].
-
Goehler LE,
Relton JK,
Dripps D,
Keichle R,
Tartaglia N,
Maier SF,
Watkins LR
(1997)
Vagal paraganglia bind biotinylated interleukin-1 receptor antagonist: a possible mechanism for immune-to-brain communication.
Brain Res Bull
43:357-364[Web of Science][Medline].
-
Goehler LE,
Gaykema RPA,
Hammack SE,
Maier SF,
Watkins LR
(1998)
Interleukin-1 induces c-Fos immunoreactivity in primary afferent neurons of the vagus nerve.
Brain Res
804:306-310[Web of Science][Medline].
-
Goerdt S,
Kodelja V,
Schmuth M,
Orfanos CE,
Sorg C
(1996)
The mononuclear phagocyte-dendritic cell dichotomy: myths, facts, and a revised concept.
Clin Exp Immunol
105:1-9[Web of Science][Medline].
-
Hansen MK,
Krueger JM
(1997)
Subdiaphragmatic vagotomy blocks the sleep- and fever-promoting effects of interleukin-1.
Am J Physiol
273:R1246-R1253[Abstract/Free Full Text].
-
Hoek A,
Allaerts W,
Leenan PJN,
Schoemaker J,
Drexhage HA
(1997)
Dendritic cells and macrophages in the pituitary and gonads. Evidence for their role in the fine regulation of the reproductive endocrine response.
Eur J Endocrinol
136:8-24[Abstract/Free Full Text].
-
Kluger MJ
(1991)
Fever: the role of pyrogens and cryogens.
Physiol Rev
71:93-127[Abstract].
-
Lenczowski MJP,
Schmidt ED,
Van Dam A-M,
Gaykema RPA,
Tilders FJH
(1998)
Individual variation in hypothalamus-pituitary-adrenal responsiveness of rats to endotoxin and IL-1.
Ann NY Acad Sci
856:139-147[Web of Science][Medline].
-
Maier SF,
Wiertelak EP,
Martin D,
Watkins LR
(1993)
Interleukin-1 mediates the behavioral hyperalgesia produced by lithium chloride and endotoxin.
Brain Res
623:321-324[Web of Science][Medline].
-
Mascarucci P,
Perego C,
Terrazino S,
De Simoni MG
(1998)
Glutamic acid release in the nucleus tractus solitarius induced by peripheral endotoxin and interleukin-1.
Neuroscience
86:1285-1290[Web of Science][Medline].
-
Morgan M,
Pack RJ,
Howe A
(1976)
Structure of cells and nerve endings in abdominal vagal paraganglia of the rat.
Cell Tissue Res
169:467-484[Medline].
-
Nguyen KT,
Deak T,
Owens SM,
Kohno T,
Fleshner M,
Watkins LR,
Maier SF
(1998)
Exposure to acute stress induces brain interleukin-1 protein in the rat.
J Neurosci
18:2239-2246[Abstract/Free Full Text].
-
Ni K,
O'Neill HC
(1997)
The role of dendritic cells in T cell activation.
Immunol Cell Biol
75:223-230[Medline].
-
Prechtl JC,
Powley TL
(1987)
A light and electron microscopic examination of the vagal hepatic branch of the rat.
Anat Embryol
176:115-126[Medline].
-
Saper CB,
Breder CD
(1994)
The neurological basis of fever.
N Engl J Med
330:1880-1886[Free Full Text].
-
Schaffar N,
Rao H,
Kessler JP,
Jean A
(1997)
Immunohistochemical detection of glutamate in rat vagal sensory neurons.
Brain Res
778:302-308[Web of Science][Medline].
-
Schotanus K,
Tilders FJH,
Berkenbosch F
(1993)
Human recombinant interleukin-1 receptor antagonist prevents ACTH, but not interleukin-6 responses to bacterial endotoxin in rats.
Endocrinology
133:2461-2468[Abstract/Free Full Text].
-
Schotanus K,
Holtkamp GM,
Meloen RH,
Puijk WC,
Berkenbosch F,
Tilders FJH
(1995)
Domains of rat interleukin-1b involved in type I receptor binding.
Endocrinology
136:332-339[Abstract].
-
Shu S,
Ju G,
Fan L
(1988)
The glucose oxidase-DAB-nickel method in peroxidase histochemistry of the nervous system.
Neurosci Lett
85:169-171[Web of Science][Medline].
-
Steinman RM
(1991)
The dendritic cell system and its role in immunogenicity.
Annu Rev Immunol
9:271-296[Web of Science][Medline].
-
Van Dam A-M,
Brouns M,
Louisse S,
Berkenbosch F
(1992)
Appearance of interleukin-1 in macrophages and ramified microglia in the brain of endotoxin-treated rats: a pathway for the induction of non-specific symptoms of sickness?
Brain Res
588:291-296[Web of Science][Medline].
-
Watkins LR,
Weirtelak EP,
Goehler LE,
Smith KP,
Martin D,
Maier SF
(1994)
Characterization of cytokine induced hyperalgesia.
Brain Res
654:15-26[Web of Science][Medline].
-
Watkins LR,
Goehler LE,
Relton JK,
Tartaglia N,
Silbert L,
Martin D,
Maier SF
(1995a)
Blockade of interleukin-1 induced hyperthermia by subdiaphragmatic vagotomy: evidence for vagal mediation of immune-brain communication.
Neurosci Lett
183:17-31[Medline].
-
Watkins LR,
Maier SF,
Goehler LE
(1995b)
Cytokine-to-brain communication: a review and analysis of alternative mechanisms.
Life Sci
57:1011-1026[Web of Science][Medline].
Copyright © 1999 Society for Neuroscience 0270-6474/99/1972799-08$05.00/0
This article has been cited by other articles:
|
|
|
|
 
J. Sandkuhler
Models and Mechanisms of Hyperalgesia and Allodynia
Physiol Rev,
April 1, 2009;
89(2):
707 - 758.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. N. Dilger and R. W. Johnson
Aging, microglial cell priming, and the discordant central inflammatory response to signals from the peripheral immune system
J. Leukoc. Biol.,
October 1, 2008;
84(4):
932 - 939.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Fernandez, S. Gonzalez, S. Rey, P. P. Cortes, K. R. Maisey, E.-P. Reyes, C. Larrain, and P. Zapata
Lipopolysaccharide-induced carotid body inflammation in cats: functional manifestations, histopathology and involvement of tumour necrosis factor-{alpha}
Exp Physiol,
July 1, 2008;
93(7):
892 - 907.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. Calderon-Garciduenas, A. C. Solt, C. Henriquez-Roldan, R. Torres-Jardon, B. Nuse, L. Herritt, R. Villarreal-Calderon, N. Osnaya, I. Stone, R. Garcia, et al.
Long-term Air Pollution Exposure Is Associated with Neuroinflammation, an Altered Innate Immune Response, Disruption of the Blood-Brain Barrier, Ultrafine Particulate Deposition, and Accumulation of Amyloid {beta}-42 and {alpha}-Synuclein in Children and Young Adults
Toxicol Pathol,
February 1, 2008;
36(2):
289 - 310.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Kern and T. Ziemssen
Review: Brain immune communication psychoneuroimmunology of multiple sclerosis
Multiple Sclerosis,
January 1, 2008;
14(1):
6 - 21.
[Abstract]
[PDF]
|
|
|
|
|
|
|
C. Y. Liu, M. H. Mueller, D. Grundy, and M. E. Kreis
Vagal modulation of intestinal afferent sensitivity to systemic LPS in the rat
Am J Physiol Gastrointest Liver Physiol,
May 1, 2007;
292(5):
G1213 - G1220.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. M. Huston, M. Ochani, M. Rosas-Ballina, H. Liao, K. Ochani, V. A. Pavlov, M. Gallowitsch-Puerta, M. Ashok, C. J. Czura, B. Foxwell, et al.
Splenectomy inactivates the cholinergic antiinflammatory pathway during lethal endotoxemia and polymicrobial sepsis
J. Exp. Med.,
July 10, 2006;
203(7):
1623 - 1628.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. S. C. Fabricio, G. Tringali, G. Pozzoli, M. C. Melo, J. A. Vercesi, G. E. P. Souza, and P. Navarra
Interleukin-1 mediates endothelin-1-induced fever and prostaglandin production in the preoptic area of rats
Am J Physiol Regulatory Integrative Comp Physiol,
June 1, 2006;
290(6):
R1515 - R1523.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Nickerson, G. F. Elphick, J. Campisi, B. N. Greenwood, and M. Fleshner
Physical activity alters the brain Hsp72 and IL-1{beta} responses to peripheral E. coli challenge
Am J Physiol Regulatory Integrative Comp Physiol,
December 1, 2005;
289(6):
R1665 - R1674.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. R. Johnson, J. C. O'Connor, R. Dantzer, and G. G. Freund
Inhibition of vagally mediated immune-to-brain signaling by vanadyl sulfate speeds recovery from sickness
PNAS,
October 18, 2005;
102(42):
15184 - 15189.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Moriez, C. Salvador-Cartier, V. Theodorou, J. Fioramonti, H. Eutamene, and L. Bueno
Myosin Light Chain Kinase Is Involved in Lipopolysaccharide-Induced Disruption of Colonic Epithelial Barrier and Bacterial Translocation in Rats
Am. J. Pathol.,
October 1, 2005;
167(4):
1071 - 1079.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P Gourmelon, C Marquette, D Agay, J Mathieu, and D Clarencon
Involvement of the central nervous system in radiation-induced multi-organ dysfunction and/or failure
Br. J. Radiol.,
January 1, 2005;
Supplement_27(1):
62 - 68.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Campisi,, M. K. Hansen,, K. A. O'Connor,, J. C. Biedenkapp,, L. R. Watkins,, S. F. Maier,, and M. Fleshner
Circulating cytokines and endotoxin are not necessary for the activation of the sickness or corticosterone response produced by peripheral E. coli challenge
J Appl Physiol,
November 1, 2003;
95(5):
1873 - 1882.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. R. Ziegler and J. P. Herman
Neurocircuitry of Stress Integration: Anatomical Pathways Regulating the Hypothalamo-Pituitary-Adrenocortical Axis of the Rat
Integr. Comp. Biol.,
July 1, 2002;
42(3):
541 - 551.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Gatti, J. Beck, G. Fantuzzi, T. Bartfai, and C. A. Dinarello
Effect of interleukin-18 on mouse core body temperature
Am J Physiol Regulatory Integrative Comp Physiol,
March 1, 2002;
282(3):
R702 - R709.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Hosoi, Y. Okuma, A. Ono, and Y. Nomura
Subdiaphragmatic vagotomy fails to inhibit intravenous leptin-induced IL-1beta expression in the hypothalamus
Am J Physiol Regulatory Integrative Comp Physiol,
February 1, 2002;
282(2):
R627 - R631.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. S. Emch, G. E. Hermann, and R. C. Rogers
TNF-alpha -induced c-Fos generation in the nucleus of the solitary tract is blocked by NBQX and MK-801
Am J Physiol Regulatory Integrative Comp Physiol,
November 1, 2001;
281(5):
R1394 - R1400.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. S. Munford and J. Pugin
The crucial role of systemic responses in the innate (non-adaptive) host defense
Innate Immunity,
August 1, 2001;
7(4):
327 - 332.
[Abstract]
[PDF]
|
|
|
|
|
|
|
S. B. Oh, P. B. Tran, S. E. Gillard, R. W. Hurley, D. L. Hammond, and R. J. Miller
Chemokines and Glycoprotein120 Produce Pain Hypersensitivity by Directly Exciting Primary Nociceptive Neurons
J. Neurosci.,
July 15, 2001;
21(14):
5027 - 5035.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. K. Hansen, K. A. O'Connor, L. E. Goehler, L. R. Watkins, and S. F. Maier
The contribution of the vagus nerve in interleukin-1{beta}-induced fever is dependent on dose
Am J Physiol Regulatory Integrative Comp Physiol,
April 1, 2001;
280(4):
R929 - R934.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. E. Hermann, G. S. Emch, C. A. Tovar, and R. C. Rogers
c-Fos generation in the dorsal vagal complex after systemic endotoxin is not dependent on the vagus nerve
Am J Physiol Regulatory Integrative Comp Physiol,
January 1, 2001;
280(1):
R289 - R299.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Hosoi, Y. Okuma, and Y. Nomura
Electrical stimulation of afferent vagus nerve induces IL-1beta expression in the brain and activates HPA axis
Am J Physiol Regulatory Integrative Comp Physiol,
July 1, 2000;
279(1):
R141 - R147.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. K. Hansen, K. T. Nguyen, M. Fleshner, L. E. Goehler, R. P. A. Gaykema, S. F. Maier, and L. R. Watkins
Effects of vagotomy on serum endotoxin, cytokines, and corticosterone after intraperitoneal lipopolysaccharide
Am J Physiol Regulatory Integrative Comp Physiol,
February 1, 2000;
278(2):
R331 - R336.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Li, E. Sehic, Y. Wang, A. L. Ungar, and C. M. Blatteis
Relation between complement and the febrile response of guinea pigs to systemic endotoxin
Am J Physiol Regulatory Integrative Comp Physiol,
December 1, 1999;
277(6):
R1635 - R1645.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. R. Watkins and S. F. Maier
Implications of immune-to-brain communication for sickness and pain
PNAS,
July 6, 1999;
96(14):
7710 - 7713.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
TOP
ABSTRACT
INTRODUCTION
