Neuroscience 155 (2008) 1227–1236
Reg-2 EXPRESSION IN DORSAL ROOT GANGLION NEURONS AFTER
ADJUVANT-INDUCED MONOARTHRITIS
S. AVERILL,a* J. J. INGLIS,b,f V. R. KING,a
S. W. N. THOMPSON,c W. B. J. CAFFERTY,d
P. J. SHORTLAND,a S. P. HUNT,e B. L. KIDDb
AND J. V. PRIESTLEYa
Small- and medium-sized dorsal root ganglion (DRG) cells
comprise two neurochemically distinct subpopulations, defined according to their expression of neuropeptides and
response to neurotrophic factors (Snider and McMahon,
1998; Priestley et al., 2002). Cells in the first population are
commonly referred to as “peptidergic” because they constitutively express neuropeptides such as calcitonin generelated peptide (CGRP) and substance P. They also express the nerve growth factor (NGF) tyrosine kinase (trk)
receptor trkA, and respond to NGF (Verge et al., 1995;
Bennett et al., 1998). Cells in the second population mainly
do not express neuropeptides but express receptors for
the glial cell line– derived neurotrophic factor (GDNF) family, and respond to GDNF (Bennett et al., 1998; Wang et
al., 2003; Averill et al., 2004). They are often referred to as
“non-peptidergic” or as “IB4-positive” or simply “IB4 cells,”
these latter terms referring to the fact that they bind the
lectin Griffonia simplicifolia IB4. In both the peptidergic and
IB4-positive populations the majority of cells are likely to be
nociceptors (Michael and Priestley, 1999) and the role of
the peptidergic population, especially in inflammatory pain,
is reasonably well understood. Thus many peptidergic
cells express the vanilloid receptor TRPV1 and respond to
inflammatory factors such as NGF, bradykinin, eicosanoids and cytokines (Woolf and Costigan, 1999; Kidd
and Urban, 2001; Hensellek et al., 2007). Inflammation
leads to both sensitization and upregulation of TRPV1,
together with upregulation of substance P and CGRP.
These neuropeptides are released peripherally to cause
vasodilation and extravasation, and are released centrally
to contribute to sensitization in the spinal cord.
In contrast to the peptidergic group, little is known
about the function of the IB4-positive group. However
some recent studies indicate that there may be circumstances in which these neurons are regulated by tissuederived factors. Inflammation causes a GDNF-dependent
increase in TRPV1 expression in IB4 cells (Amaya et al.,
2004; Breese et al., 2005) and GDNF sensitizes TRPV1
(Malin et al., 2006). In addition to GDNF receptors, IB4positive neurons express receptors for members of the
interleukin-6 (IL-6) family of neuropoietic cytokines such as
IL-6 and ciliary neurotrophic factor (CNTF) (Shuto et al.,
2001), leukemia inhibitory factor (LIF) (Thompson et al.,
1997; Gardiner et al., 2002) and oncostatin M (Tamura et
al., 2003). The role of these cytokines in regulating DRG
neurons is still poorly understood but there is good evidence, for example, that LIF contributes to the dramatic
upregulation in galanin expression that occurs following
axotomy (Sun and Zigmond, 1996; Corness et al., 1996;
Thompson et al., 1998). In addition we have shown that
a
Neuroscience Centre, Institute of Cell and Molecular Science, Bart’s
& The London School of Medicine & Dentistry, 4 Newark Street,
Whitechapel, London E1 2AT, UK
b
Bone and Joint Unit, Bart’s & The London School of Medicine &
Dentistry, Queen Mary University of London, London, EC1M 6BQ, UK
c
School of Biological Sciences, University of Plymouth, PL4 8AA, UK
d
Department of Neurology, Yale University School of Medicine, New
Haven, CT 06520-8018, USA
e
Department of Anatomy and Developmental Biology, University College, London, WC1E 6BT, UK
f
Kennedy Institute of Rheumatology, Imperial College, London, W6
8LH, UK
Abstract—Reg-2 is a secreted protein that is expressed de
novo in motoneurons, sympathetic neurons, and dorsal root
ganglion (DRG) neurons after nerve injury and which can act
as a Schwann cell mitogen. We now show that Reg-2 is also
upregulated by DRG neurons in inflammation with a very
unusual expression pattern. In a rat model of monoarthritis,
Reg-2 immunoreactivity was detected in DRG neurons at 1
day, peaked at 3 days (in 11.6% of DRG neurons), and was
still present at 10 days (in 5%). Expression was almost exclusively in the population of DRG neurons that expresses
the purinoceptor P2X3 and binding sites for the lectin Griffonia simplicifolia IB4, and which is known to respond to glial
cell line– derived neurotrophic factor (GDNF). Immunoreactivity was present in DRG cell bodies and central terminals in
the dorsal horn of the spinal cord. In contrast, very little
expression was seen in the nerve growth factor (NGF) responsive and substance P expressing population. However
intrathecal delivery of GDNF did not induce Reg-2 expression, but leukemia inhibitory factor (LIF) had a dramatic effect, inducing Reg-2 immunoreactivity in 39% of DRG neurons and 62% of P2X3 cells.
Changes in inflammation have previously been observed
predominantly in the neuropeptide expressing, NGF responsive, DRG neurons. Our results show that changes also take
place in the IB4 population, possibly driven by members of
the LIF family of neuropoietic cytokines. In addition, the presence of Reg-2 in central axon terminals implicates Reg-2 as a
possible modulator of second order dorsal horn cells. © 2008
IBRO. Published by Elsevier Ltd. All rights reserved.
Key words: rat, DRG, Reg-2, inflammation, LIF.
*Corresponding author. Tel: ⫹44-020-7882-2284; fax: ⫹44-020-7882-2180.
E-mail address: s.a.averill@qmul.ac.uk (S. Averill).
Abbreviations: CFA, complete Freund’s adjuvant; CGRP, calcitonin
gene-related peptide; CNTF, ciliary neurotrophic factor; DAPI, 4,6diamidino-2-phenylindole; DRG, dorsal root ganglion; GDNF, glial cell
line– derived neurotrophic factor; IL-6, interleukin-6; LIF, leukemia inhibitory factor; NGF, nerve growth factor; TSA, tyramide signal amplification.
0306-4522/08 © 2008 IBRO. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.neuroscience.2008.06.049
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S. Averill et al. / Neuroscience 155 (2008) 1227–1236
Reg-2 is selectively upregulated in IB4 cells in the first few
days after axotomy (Averill et al., 2002). Reg-2 (also
known as PAPI, or peptide 23) is the rat homologue of
human hepatocarcinoma–intestine–pancreas/pancreaticassociated protein (HIP/PAP) which has various functions
(Lieu et al., 2006; Gironella et al., 2007) but which in
neurons has been shown to be a Schwann cell mitogen
and be regulated by members of the CNTF/LIF family
(Livesey et al., 1997; Nishimune et al., 2000). Cytokines
such as LIF increase markedly with inflammation (Zhu et
al., 2001), and may therefore contribute to changes in
DRG peptide expression. We have therefore used the
complete Freund’s adjuvant (CFA) model of mono-arthritis
to examine Reg-2 expression after inflammation. We show
that Reg-2 is selectively upregulated in IB4 cells, and that
Reg-2 expression in these cells can be induced by LIF
treatment.
EXPERIMENTAL PROCEDURES
Animal treatments
Thirty-two adult male Wistar rats (220 – 400 g body weight) were
processed for immunocytochemistry. Sixteen of these were
treated with an intraplantar injection of CFA into the right paw, 12
rats were injected with vehicle only (paraffin) and four rats were
left untreated. CFA was prepared as a 10 mg/ml suspension of
heat-attenuated Mycobacterium tuberculosis in paraffin oil. Inflammation was induced by a single intra-plantar injection (100 l) of
CFA into the right hind footpad of each animal. The rats survived
for a further 1, 3, 7 or 10 days (three or four per group) before
perfusion fixation. Footpad diameter, and mechanical (Von Frey)
and thermal hyperalgesia (Hargreaves test), were assessed in the
10 day group prior to, and at 1– 4 days and 7 days post-CFA
injection, using standard procedures (Kidd et al., 2003; Hargreaves et al., 1988). Statistical analysis of these parameters was
performed by one-way ANOVA with post hoc Bonferroni multiple
range testing and unpaired t-test or Mann-Whitney U test as
appropriate. Rats were perfused under pentobarbitone anesthesia
with a mixture of 2% paraformaldehyde, 1.36% L-lysine monohydrochloride and 0.213% sodium meta-periodate in 0.1 M phosphate buffer.
An additional group of 13 rats was treated intrathecally with
various growth factors. Under pentobarbitone anesthesia (40 mg/
kg, i.p., with sterile precautions), a small laminectomy was performed between L6 and S1 vertebrae and the dura was cut. A
silastic tube of 0.6 mm outer diameter was introduced intrathecally
so that its tip lay at the level of the lumbar enlargement of the
spinal cord and the intrathecal tubing was attached to an Alzet
mini-osmotic pump (Alzet, Alza corp., Palo Alto, CA, USA; type
2002) delivering at a rate of 0.5 l/h. Animals received either a
control infusion (n⫽4, saline with rat serum albumin, 1 mg/ml) or
this vehicle plus recombinant human GDNF (n⫽4 at 12 g/day),
recombinant human NGF (n⫽3 at 12 g/day), or recombinant
human LIF (n⫽2 at 3.9 g/day). These doses were chosen because they have been shown to be effective in previous studies
(Averill et al., 2004; Bennett et al., 1998; Michael et al., 1997;
Cafferty et al., 2001). Fourteen days later, animals were perfused
with vascular rinse solution followed by 4% paraformaldehyde. All
animal procedures were carried out according to Home Office
regulations, conformed to international guidelines on the ethical
use of animals and animal numbers and suffering were kept to a
minimum.
Immunocytochemistry
Left and right L4 and L5 dorsal root ganglia and spinal cord were
dissected out, postfixed for 1.5–2 h and frozen after cryoprotection. Cryostat sections (8 m) were stained using single or dual
color immunofluorescence or indirect tyramide signal amplification
(TSA) fluorescence procedures. The Reg-2 polyclonal antibody
was raised in rabbit against whole recombinant protein and used
at 1:6000 for indirect immunofluorescence, and 1:200,000 with
TSA amplification. For double labeling this antibody was combined with one of the following: guinea-pig anti P2X3 (Neuromics,
USA, 1:250,000), anti substance P (Chemicon, CA, USA, 1:2000),
anti trkA (Upstate, VA, USA, 1:8000), anti RET (1:500, for details
see (Molliver et al., 1997) or Griffonia simplicifolia IB4 lectin
(5 g/ml biotinylated IB4, Sigma, UK). After incubation in FITC- or
TRITC-labeled secondary reagents, sections were washed briefly
in PBS and then mounted in PBS/glycerol (1:3) containing 2.5%
(w/v) 1,4 diazobicyclo (2,2,2) octane (DABCO, antifading agent).
In some cases sections were also counterstained with 100 g/ml
4,6-diamidino-2-phenylindole (DAPI, Sigma) to reveal cell nuclei.
Controls for double labeling included reversing the order of the
primary antisera, as well as omitting the first or second primary
antiserum. Photographs were taken using a Hamamatsu
C4742-95 digital camera and plates assembled using Adobe Photoshop.
Quantification
Quantification of the proportion of Reg-2 expressing DRG neurons was determined by counting the number of immunoreactive and non-immunoreactive cells with visible nuclei. In doublelabeled sections the percentage of Reg-2 cells expressing a
second marker was assessed by switching between DAPI,
FITC and TRITC filter blocks. At least 250 labeled DRG neurons were examined for each marker and were counted on
randomly chosen sections. Counts were compared using nonparametric statistical tests. Specifically, a Kruskal-Wallis analysis
of variance was used to determine if there was a difference among
groups for a measure of interest. Any significant difference found
(P⬍0.05) was further analyzed by making pairwise comparisons
using the Mann-Whitney U test. For cell size distributions and
quantification, images were captured at 40⫻ objective magnification. Cells of interest were outlined manually using a computer
mouse, and the size determined using Scion Image.
RESULTS
Immunoreactivity for Reg-2 was only present in single
DRG neurons of occasional sections in normal lumbar
ganglia (Fig. 1). By 24 h after CFA injection, mean Reg-2
expression had increased and was present in 1.6% of
L4/L5 DRG neurons. Mean expression increased to
11.6% at 3 days, and then declined slightly at 7 and 10
days (Fig. 1, Table 1). At all time points studied, the
Reg-2 cells were small to medium in size (Fig. 2). Within
cell bodies, immunoreactivity appeared as prominent
punctate structures (Fig. 1E). In addition, immunoreactivity was present in a few axons, where it was localized
to small granules (Fig. 1E, F).
In order to identify the types of small- and mediumsized cells that upregulate Reg-2, immunostaining at the 3,
7 and 10 day time points was combined with a range of
markers for DRG subpopulations. Using IB4 and the purinoceptor P2X3 as markers for the IB4-positive population
(Bradbury et al., 1998), a very high degree of coexistence
with Reg-2 was observed (Fig. 3, Table 2). Thus at all time
S. Averill et al. / Neuroscience 155 (2008) 1227–1236
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Fig. 1. Low (A–D) and high (E, F) magnification micrographs showing Reg-2 immunoreactivity in L4 DRG. At all time points after induction of
inflammation, Reg-2 is expressed in small cells. Reg-2 immunoreactivity in ipsilateral (B–F) and naïve control (A) lumbar DRG at 3 days (B), 7 days
(C, E, F) and 10 days (D) after CFA inflammation. At high magnification, Reg-2 immunoreactivity can be seen in isolated axons (arrowhead) and within
punctuate structures (arrows) within cell bodies and axons. Scale bars⫽100 m (A–D); 20 m (E); 5 m (F).
points studied, greater than 93% of Reg-2 immunoreactive
cells were labeled for IB4 or P2X3. A similar result was
obtained when staining was carried out for Ret, the tyrosine kinase component of the GDNF receptor (Fig. 3,
Table 2). In contrast to Reg-2, the number of cells labeled for
IB4 and for P2X3 was either not changed (IB4, Ret) or only
slightly changed (P2X3) by the CFA treatment (Table 2).
To examine Reg-2 expression in the peptidergic population, staining was carried out for substance P and for
trkA. Coexistence between Reg-2 and these markers was
Table 1. Time course of Reg-2 expression after CFA inflammation
%
Naïve (n⫽3)
1 Day CFA (n⫽3)
3 Day CFA (n⫽3)
7 Day CFA (n⫽3)
10 Day CFA (n⫽3)
% Reg-2 ⫹ve cells
0⫾0
1.6⫾0.2
11.6⫾0.7*
8.2⫾1.8*
5⫾0.82*†
Reg-2 expression after CFA inflammation increases rapidly up to day 3 and then slowly declines.
* Indicates significantly different from 1 day.
†
Indicates significantly different from 3 day (P⬍0.05).
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S. Averill et al. / Neuroscience 155 (2008) 1227–1236
DISCUSSION
Fig. 2. Size distribution of Reg-2 immunoreactive sensory neurons in
L4/5 DRG following CFA inflammation. DRG neurons can be subdivided into three size ranges (small, 0 – 600 m2; medium, 600 –
1000 m2; large, 1000 –3200 m2) which approximate to the size
ranges of cells with C, A␦, and A␣/ conduction velocities. Note that at
all time points studied, Reg-2 expressing neurons are all predominantly small to medium sized.
much less extensive (Fig. 4, Table 3). For example, at the
various time points studied, less than 18% of Reg-2 cells
expressed substance P.
In addition to DRG cell bodies, CFA animals had Reg-2
immunoreactive terminals in the dorsal horn of the spinal
cord (Fig. 5). Staining, which was concentrated in lamina II
inner and confined to the ipsilateral termination zone of
sciatic afferents, was present at all survival times studied
but was most prominent in the 10 day CFA animals. Double labeling revealed that the Reg-2 immunoreactive terminals were not SP immunoreactive but were labeled for
P2X3.
As an aid to identifying a possible role for Reg-2, a
range of functional endpoints was examined in the CFA
treated animals. These included thermal and mechanical
thresholds, and footpad diameter. For all parameters studied, and in agreement with previous reports (e.g. Inglis et
al., 2005), changes were maximal by 1–3 days and were
then maintained up to the 10 day time point (data not
shown). The functional endpoints thus contrasted with the
Reg-2 expression, which did not peak until 3 days and then
declined steadily (Table 1).
In order to identify growth factors that might be responsible for the changes in Reg-2 upregulation with inflammation, expression was examined after treatment with various
growth factors. Animals treated with vehicle (Fig. 6A),
GDNF (Fig. 6B) or NGF showed Reg-2 expression in only
occasional cells and were similar to naïve controls. In
contrast, animals treated with rhLIF showed strong Reg-2
immunoreactivity in many small- to medium-sized DRG
neurons (Fig. 6C–H), in total comprising 39% of DRG
neurons. In LIF-treated animals, a high degree of coexistence between Reg-2 and IB4 or P2X3 was observed (Fig.
6C–H, Table 4), although not quite as high as after CFA
treatment (Table 2). For example, 71% of Reg-2 immunoreactive cells showed IB4 labeling in rhLIF-treated animals, compared with 98% in 3 day or 7 day CFA animals.
RhLIF treatment caused a small increase in P2X3 expression but no change in IB4 labeling (Table 4).
In this study we have shown that Reg-2 is upregulated in
DRG neurons and their central terminals after inflammation, that this upregulation occurs selectively in the IB4/
P2X3 population of neurons, and that the neuropoietic
cytokine LIF is a candidate regulator of this Reg-2 expression. Our results implicate for the first time Reg-2 and the
IB4 population of cells in the response of DRG neurons to
inflammation, and demonstrate some very novel aspects
of DRG plasticity.
Reg-2 is upregulated after nerve injury and axonally
transported toward the injury site (Averill et al., 2002; Livesey et al., 1997). Our demonstration that IB4/P2X3 cells
also upregulate Reg-2 after inflammation is unexpected
because molecules that are upregulated by DRG neurons
after inflammation are normally down-regulated after nerve
injury. This is the case, for example, with substance P,
CGRP and TRPV1 and is due to the fact that their expression is regulated by target-derived NGF (reviewed in
Woolf, 1996; Priestley et al., 2002). NGF levels increase
after inflammation (Donnerer et al., 1992) but fall after
axotomy (Raivich et al., 1991) and expression of regulated
molecules in DRG neurons changes in consequence. In
contrast molecules which are upregulated after nerve injury, such as c-jun, ATF3, and neuropeptide Y, do not
change following inflammation (Tsujino et al., 2000;
Wakisaka et al., 1992). GAP-43 and galanin are slight
exceptions in that they are upregulated after both axotomy
and inflammation. The upregulation of galanin, however, is
thought to be due to destruction of peripheral tissue, akin
to an axotomy (Calza et al., 2000) while the GAP-43 upregulation is short-lived (peaks at 48 h, see Leslie et al.,
1995). Reg-2 is therefore unique in being upregulated with
a similar time course, and in the same population of cells,
by both axotomy and inflammation. However there are
some differences in the two responses. After axotomy,
Reg-2 is seen initially (24 h) only in the IB4/P2X3 cells but
at longer time points (5–7 days) appears in medium- and
large-sized (IB4 negative) cells (Averill et al., 2002). In
contrast, Reg-2 expression after inflammation was confined to IB4/P2X3 cells at all time points studied (3–10
days). In addition Reg-2 after axotomy is not transported
centrally and does not appear in the dorsal horn (Averill et
al., 2002), whereas Reg-2 immunoreactivity after inflammation does appear in the dorsal horn, presumably due to
axonal transport into central terminals. It is therefore likely
that Reg-2 in inflammation has a quite different role to that
in nerve injury, where it is thought to promote regeneration
(Livesey et al., 1997). For example, the axonal transport
into central terminals raises the possibility that Reg-2 is
released in the dorsal horn to modulate glial or neuronal
function in the spinal cord. If this does occur, the lack of
correlation that we observed between Reg-2 expression
and either thermal or mechanical hyperalgesia would suggest that Reg-2 plays some other function than simply
contributing to nociceptive transmission. Previous studies
in mice in which the Reg2 gene has been knocked out
have shown that pancreatic inflammation was more exten-
S. Averill et al. / Neuroscience 155 (2008) 1227–1236
1231
Fig. 3. After CFA inflammation, Reg-2 is expressed selectively in the IB4-binding population of DRG neurons. (A, B) Low magnification micrograph
showing Reg-2 and IB4 double labeling in an L5 DRG, 3 days after CFA treatment. The majority of Reg-2 immunoreactive cells are double-labeled
(arrows). (C–H) High magnification micrographs showing Reg-2 and either IB4 (C, D), P2X3 (E, F) or Ret (G, H) double labeling at either 3 days (C, D)
or 7 days (E–H) after CFA treatment. In each pair of micrographs, many Reg-2 positive cells are positive for the second marker (arrows). The
arrowheads in C and E show rare Reg-2 immunoreactive cell that are not IB4 or P2X3 labeled. Scale bars⫽50 m (A, B); 50 m (C–H).
sive and apoptosis more severe than in wild type mice
(Gironella et al., 2007). Similarly in liver, Reg2 knockout
mice have revealed that Reg2 is a critical mitogenic and
anti-apoptotic factor (Lieu et al., 2006). If Reg2 had a
similar role in the dorsal horn, it might protect neurons from
excitotoxic damage and perhaps restrict activation of nonneuronal cells such as microglia which are thought to
contribute to chronic pain states (Marchand et al., 2005).
These possibilities deserve further investigation.
Another unexpected aspect of our results is the identity
of the cells that upregulate Reg-2 following inflammation.
To date, most changes that take place in DRG neurons
following inflammation have been reported to occur in the
trkA/neuropeptide population of DRG neurons and are
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S. Averill et al. / Neuroscience 155 (2008) 1227–1236
Table 2. IB4-positive cells express Reg-2 after CFA inflammation
%
%
%
%
%
%
%
IB4 ⫹ve DRG neurons
Reg-2 cells also IB4 ⫹ve
P2X3 ⫹ve DRG neurons
of Reg-2 cells also P2X3 ⫹ve
RET ⫹ve DRG neurons
Reg-2 cells also Ret ⫹ve
Naïve (n⫽3)
3 Day CFA (n⫽3)
7 Day CFA (n⫽3)
10 Day CFA (n⫽3)
48.3⫾2.3
NA
32.7⫾0.8
NA
66.4⫾3.3
NA
49.5⫾1.9
98.2⫾0.2
38.0⫾0.9*†
96.5⫾1.8
73⫾2.7
100⫾0
49.9⫾3.5
98.3⫾1.7
44.6⫾1.0*
97.1⫾1.1
74.6⫾4.7
100⫾0
48.3⫾3.8
94.2⫾1.3
37.4⫾2.8†
93.2⫾1.4
72.4⫾2.7
100⫾0
Reg-2 expression after CFA inflammation occurs predominantly in the IB4-binding population of DRG neurons. Thus at all CFA time points studied,
the vast majority of Reg-2 expressing cells show labeling for IB4, P2X3 or Ret.
* Indicates significantly different from naive.
†
Indicates significantly different from 7 day (P⬍0.05). NA⫽not applicable.
thought to be regulated by NGF. This is the case for
peptides such as substance P and CGRP (Woolf et al.,
1994), the neurotrophin brain-derived neurotrophic factor
(Cho et al., 1997), receptors such as TRPV1 (Ji et al.,
2002), the NaV1.8 Na channel (Kerr et al., 2001), the
transcription factor oct-2 (Ensor et al., 1996), and GAP-43
(Leslie et al., 1995). Although cytokines are thought to play
an important role in inflammation (Marchand et al., 2005),
many of their effects on DRG neurons appear to be indirect
and mediated by NGF (Woolf et al., 1997). It is clear that
many IB4 neurons are nociceptors (Gerke and Plenderleith, 2001) but their exact role is unclear, and studies that
have compared the responses properties of IB4-positive
and IB4-negative neurons have identified only minor dif-
Fig. 4. After CFA inflammation, Reg-2 is only expressed in a small proportion of the peptidergic population of DRG neurons. (A, B) Low magnification
micrograph showing Reg-2 and substance P (SP) double labeling in an L5 DRG 3 days after CFA treatment. A few Reg-2 immunoreactive cells are
SP immunoreactive (arrows) but the majority are not (arrowheads). (C–F) High magnification micrographs showing Reg-2 and SP (C, D) or trkA (E, F)
double labeling 3 days after CFA treatment. In each pair of micrographs, some Reg-2 immunoreactive cells are positive for the second marker (arrows)
but many are not (arrowheads). Scale bars⫽100 m (A, B); 50 m (C–F).
S. Averill et al. / Neuroscience 155 (2008) 1227–1236
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Table 3. Neuropeptide cells show low Reg-2 expression after CFA inflammation
%
%
%
%
%
SP ⫹ve DRG neurons
of Reg-2 cells also SP ⫹ve
trkA ⫹ve DRG neurons
of Reg-2 cells also trkA ⫹ve
Naïve (n⫽3)
3 Day CFA (n⫽3)
7 Day CFA (n⫽3)
10 Day CFA (n⫽3)
21.3⫾0.8
NA
42.8⫾2.8
NA
18.3⫾1.0
9.5⫾0.8*
44.7⫾1.3
26.4⫾9.6
19.2⫾1.2
7.5⫾1.3*
44.3⫾3.0
22.3⫾2.4
19.4⫾1.5
17.6⫾2.3
42.2⫾2.8
16.1⫾3.7
Reg-2 expression after CFA inflammation shows low coexistence with substance P (SP) and trkA, markers for the peptidergic DRG subpopulation.
Thus at all CFA time points studied, less than 26% of Reg-2 expressing cells show labeling for SP or trkA.
NA, not applicable.
* Indicates significantly different from 10 day (P⬍0.05).
ferences (Stucky and Lewin, 1999; Petruska et al., 2000;
Dirajlal et al., 2003; Liu et al., 2004; Breese et al., 2005).
Recently, however, a role for IB4 cells in inflammation has
been proposed based on data showing that TRPV1 expression increases in IB4-positive cells (Amaya et al.,
2004; Breese et al., 2005) as well as in IB4-negative (trkA
immunoreactive) cells (Amaya et al., 2004) during inflammation. Our study supports such a role, and in addition is
the first to demonstrate a molecule (Reg-2) that is upregulated selectively in IB4 neurons in response to inflamma-
tion. Our results also support the hypothesis that IB4 cells
form a parallel pathway to the peptidergic/NGF-regulated
one (Hunt et al., 1992) with distinctive properties and mode
of regulation (see below).
Although previous studies have shown that Reg-2 can
be regulated by members of the CNTF/LIF family (Livesey
et al., 1997; Nishimune et al., 2000), the very selective
expression of Reg-2 in IB4/P2X3 cells implicates GDNF as
a regulator. IB4/P2X3 cells show selective expression of
GDNF receptors and many proteins expressed by IB4/
Fig. 5. Three days after CFA inflammation, Reg-2 immunoreactive terminals are visible in the ipsilateral dorsal horn of the spinal cord (B) but not on
the contralateral side (A). Terminals are concentrated in the medial substantia gelatinosa (asterisk in B), corresponding to the sciatic innervation
territory. Double labeling with P2X3 (C–E) reveals that the Reg-2 terminals are in lamina II inner, in register with the P2X3 terminals (7 day CFA). High
magnification confocal analysis (F, G) reveals individual Reg-2/P2X3 double-labeled terminals (arrows). In the dorsal roots/tract of Lissauer (H) Reg-2
immunoreactivity is visible in individual axons (arrows, 10 day CFA). Scale bars⫽100 m (A, B); 50 m (C–E, H); 20 m (F, G).
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Fig. 6. After LIF treatment, Reg-2 is expressed in many DRG neurons and these are predominantly of the IB4-binding type. (A, B) Low magnification
micrographs showing Reg-2 immunoreactivity after 2 weeks’ intrathecal vehicle (A) or GDNF (B) treatment. Only one or two Reg-2 immunoreactive
cells are visible (arrows). (C–F) Low magnification micrographs showing Reg-2 and P2X3 (C, D) or IB4 (E, F) double labeling after 2 weeks’ intrathecal
LIF treatment. Many double-labeled cells are visible (arrows). (G, H) High magnification micrographs showing Reg-2 and IB4 double labeling after LIF
treatment. Many of the Reg-2 immunoreactive cells are also positive for IB4 (arrows), but some single-labeled Reg-2 cells are also present
(arrowheads). Scale bars⫽100 m (A–F); 50 m (G, H).
S. Averill et al. / Neuroscience 155 (2008) 1227–1236
Table 4. LIF treatment induces Reg-2 expression
%
%
%
%
%
%
%
%
Reg-2 ⫹ve DRG neurons
IB4⫹ DRG neurons
P2X3 ⫹ve DRG neurons
Reg-2 cells also IB4 ⫹ve
of IB4 cells also Reg-2 ⫹ve
of Reg-2 cells also P2X3 ⫹ve
of P2X3 cells also Reg-2 ⫹ve
Naïve (n⫽3)
2 Week rhLIF
(n⫽2)
0⫾0
48.3⫾2.3
32.7⫾0.8
NA
NA
NA
NA
38.5
47.5
40.7
71.4
50.2
58.1
62.3
Reg-2 expression after LIF treatment occurs predominantly in IB4and P2X3-labeled cells, markers for the IB4-binding population of DRG
neurons.
NA, not applicable.
P2X3 cells are positively regulated by GDNF family members, including P2X3, TMP, somatostatin, TRPV1, and IB4
binding (Bennett et al., 1998; Bradbury et al., 1998; Amaya
et al., 2004). In addition the injury-induced transcription
factor, ATF3, is negatively regulated in IB4/P2X3 cells by
GDNF (Averill et al., 2004). We did not determine whether
GDNF can block the inflammation-induced upregulation of
Reg-2, but we have shown that exogenous GDNF does not
induce Reg-2 expression in naïve rats. In contrast, exogenous LIF upregulated Reg-2 in IB4⫹ cells. It was outside
the scope of this study to establish whether endogenous
cytokines of the CNTF/LIF family are responsible for the
Reg-2 upregulation after inflammation, but our results suggest that this might be the case. LIF is upregulated in
inflammatory states (Sugiura et al., 2000; Zhu et al., 2001)
and interestingly appears to have both pro- and anti-inflammatory roles (Thompson et al., 1996; Banner et al.,
1998; Sugiura et al., 2000; Zhu et al., 2001; Kerr and
Patterson, 2004). However the pattern of Reg-2 expression in response to intrathecal LIF was not as selective for
IB4⫹ cells as that seen with inflammation. Thus Reg-2 was
upregulated in both IB4⫹ and IB4⫺ cells, consistent with
the fact that some cells in both populations express LIF
receptors (Thompson et al., 1997; Gardiner et al., 2002). It
is therefore not clear what restricts the Reg-2 upregulation
to IB4⫹ cells following inflammation, although possibilities
include the presence of other receptors that modify the
response, or differences between IB4⫹ and IB4⫺ cells in
intracellular signaling pathways. These possibilities are
worth further investigation.
Acknowledgments—We gratefully acknowledge support from the
Wellcome Trust. We also wish to thank Genentech Inc. and Amgen Inc. for the gift of NGF and GDNF, Dr. Q. Yan for the Ret
antiserum, and Dr. J. Heath (Birmingham) for LIF.
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(Accepted 10 June 2008)
(Available online 1 July 2008)