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Noor et al. Neuroimmunol Neuroinflammation 2019;6:10 I http://dx.doi.org/10.20517/2347-8659.2019.18 Page 11 of 32

threshold for statistical significance for all sets of multiple comparisons was set a priori to α = 0.05. All data
are presented as the mean ± Standard Error of the Mean.

RESULTS
Male and female mice with CCI of the sciatic nerve using either 4-0 or 5-0 chromic gut suture
material develop allodynia with similar onset, duration and spontaneous recovery
The mouse CCI model has been performed using a range of suture types and sizes [4,47,70,71] . Here, we
examined the profile of allodynia using chromic gut suture material of two thickness characteristics (4-0
vs. 5-0), whereby the 4-0 suture material is thicker than the 5-0 suture material. Assessment for hindpaw
light mechanical touch responses at BL revealed no difference between male or female mice (ipsilateral:
F = 0.78, P = 0.576; contralateral: F = 2.37, P = 0.063) [Figure 1A and B].
5,30
5,30
Compared to mice that underwent sham manipulations, mice that underwent CCI surgery developed
bilateral allodynia, which replicated similar experiments reported previously [47,51,72-75] . All mice with either 4-0
or 5-0 CCI reached maximal bilateral allodynia by Day 8 (ipsilateral) or Day 10 (contralateral) post-surgery,
with main effects of time (ipsilateral: F 2.4,74.7 = 207.56, P < 0.001; contralateral: F 2.7,81.5 = 212.64, P < 0.001) and
surgery (ipsilateral: F = 141.3, P < 0.001; contralateral: F = 420.18, P < 0.001), and an interaction between
2,30
2,30
time and surgery (ipsilateral: F 4.9,74.7 = 53.99, P < 0.001; contralateral: F 5.4,81.5 = 56.28, P < 0.001). Compared to
sham-treated mice, stable bilateral hindpaw sensitivity (allodynia) persisted in CCI-treated mice ipsilaterally
(Day 8-27) and contralaterally (Day 10-19), as supported by a main effect of surgery (ipsilateral: F = 591.25,
2,30
P < 0.001; contralateral: F = 352.59, P < 0.001). A gradual and spontaneous return to levels similar to BL
2,30
was observed bilaterally with complete reversal occurring by Day 56, as supported by a main effect of time
(ipsilateral: Day 27-56 post-surgery: F 3.5,105.0 = 113.37, P < 0.001; contralateral: Day 19-56 post-surgery: F 4.3,131.6 =
91.55, P < 0.001) and surgery (ipsilateral: F = 151.37, P < 0.001; contralateral: F = 192.63, P < 0.001), and
2,30
2,30
the interaction between time and surgery (ipsilateral: F 7.0,105.0 = 27.86, P < 0.001; contralateral: F 8.7,131.6 = 21.52,
P < 0.001) [Figure 1A and B]. While hindpaw responses between males and females were similar during
most of the timecourse following surgery, differences during the initial phase of allodynia were observed.
Statistical differences in the onset of allodynia were revealed between males and females, as supported by a
main effect of sex (ipsilateral: BL-Day 10 post-surgery: F = 13.05, P = 0.001; contralateral: BL-Day 10 post-
1,30
surgery: F = 9.03, P = 0.005), and between 4-0 and 5-0 chromic gut suture. That is, in comparison with
1,30
other groups, males with 4-0 chromic gut suture material (thicker than 5-0) developed robust allodynia
by Day 3 post-surgery, while females with 5-0 chromic gut suture material did not develop clear maximal
allodynia until Day 8 post-surgery.

Reversal from allodynia prior to full reabsorption of the chromic gut suture material was observed in
virtually all of the mice treated with CCI, regardless of the chromic gut suture thickness. Representative
photographs of each treatment condition (with suture removed) are presented [Figure 1C-H]. Unpublished
reports that examined reabsorption of 4-0 chromic gut from the SCN at Day 72 post-surgery in a rat model
of CCI revealed variable degrees of reabsorption, and often observed a complete absence of chromic gut
[75]
material, despite the presence of allodynia . This further supports a published report that by Day 60
[46]
and 120 post-CCI in rats, the connective tissue capsule has been resorbed . The current report sought to
conduct gross morphological examination of the SCN in the mouse model of 4-0 and 5-0 chromic gut CCI
following resolution of allodynia.

The data suggest that, while SCNs from sham-operated mice appear translucent with little discoloration
[Figure 1C and D], the nerves treated with 4-0 chromic gut suture were found to possess a sciatic sheath/
capsule surrounding the sutures, which was similar between male and female mice [Figure 1E and F].
However, SCNs from mice treated with a 5-0 chromic gut CCI revealed visibly less remaining suture