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1
The multimodal antidepressant vortioxetine causes analgesia in a
mouse model of chronic neuropathic pain
Anna Rita Zuena1*, Daniela Maftei1*, Giovanni Sebastiano Alemà1, Francesca Dal
Moro1, Roberta Lattanzi1, Paola Casolini1, Ferdinando Nicoletti1,2
1Department of Physiology and Pharmacology, Sapienza University of Rome, Italy
2IRCCS Neuromed, Pozzilli, Italy
* Co-first author
Corresponding author:
Ferdinando Nicoletti, Department of Physiology and Pharmacology, Sapienza University
of Rome; Piazzale A. Moro, 5, 00185, Rome, Italy.
Email: ferdinandonicoletti@hotmail.com
Molecular Pain
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This article can be cited as 10.1177/1744806918808987
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Abstract
Vortioxetine is a multimodal antidepressant that potently antagonizes 5-HT3 serotonin
receptors, inhibits the high affinity serotonin transporter, activates 5-HT1A and 5-HT1B
receptors, and antagonizes 5-HT1D and 5-HT7 receptors. 5-HT3 receptors largely
mediate the hyperalgesic activity of serotonin that occurs in response to nerve injury.
Activation of 5-HT3 receptors contributes to explain why selective serotonin reuptake
inhibitors, such as fluoxetine, are not indicated in the treatment of neuropathic pain. Here,
we studied the analgesic action of vortioxetine in the chronic constriction injury (CCI)
model of neuropathic pain in mice. Vortioxetine was injected once a day for 27 days at
doses (10 mg/kg, i.p.) that determine >90% 5-HT3 receptor occupancy in the CNS. The
action of vortioxetine was compared to the action of equal doses of the serotonin-
noradrenaline reuptake inhibitor, venlafaxine (one of the gold standard drugs in the
treatment of neuropathic pain), and fluoxetine. Vortioxetine caused a robust analgesia in
CCI mice, and its effect was identical to that produced by venlafaxine. In contrast,
fluoxetine was inactive in CCI mice. Vortioxetine enhanced mechanical pain thresholds
in CCI mice without changing motor activity, as assessed by the open field and horizontal
bar tests. None of the three antidepressants caused analgesia in the complete Freund’s
adjuvant (CFA) model of chronic inflammatory pain. These findings raise the attractive
possibility that vortioxetine can be effective in the treatment of neuropathic pain,
particularly in patients with comorbid depression and cognitive dysfunction.
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Key words: vortioxetine - neuropathic pain - inflammatory pain – fluoxetine –
venlafaxine.
Introduction
A large body of evidence suggests that serotoninergic pathways descending from the
rostral ventromedial medulla (RVM) to the spinal cord are involved in the top-down
inhibitory control of pain (reviewed in Ref. 1,2). However, the effect of serotonin on
pain modulation in the spinal cord can be either inhibitory or facilitatory depending on
the receptor subtypes which are preferentially activated. Pharmacological studies have
shown that serotonin-induced analgesia is mediated by 5HT7 receptors whereas
hyperalgesia is mediated by 5HT3 receptors 3-6. While inhibition of nociceptive
transmission by serotonin may prevail in conditions of acute pain, serotonin-induced
hyperalgesia contributes to the development of chronic pain after tissue or nerve injury
6-9. Accordingly, shRNA interference-induced knock-down of the serotonin
synthesizing-enzyme, type-2 tryptophan hydroxylase, in the RVM causes analgesia in the
spinal nerve ligation (SNL) model of neuropathic pain in rats 10. An elegant work shed
light into the epigenetic mechanism underlying the hyperalgesic activity of serotonin in
response to nerve injury. SNL in rats caused a down-regulation of the GABA-
synthesizing enzyme, glutamate decarboxylase-65 (GAD-65), in the raphe magnus as a
result of a reduced H3-histone acetylation at the gad65 gene promoter 11. Disinhibition
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of serotoninergic neurons might drive maladaptive changes in serotonin descending
pathways resulting into nociceptive sensitization and chronic pain. These findings
contribute to explain why pure serotoninergic drugs, e.g., selective serotonin reuptake
inhibitors (SSRIs), are ineffective in the treatment of neuropathic pain. In contrast, drugs
that also inhibit noradrenaline uptake, such as venlafaxine, duloxetine, and amitriptyline
show level A rating for efficacy in the treatment of neuropathic pain 12.
We reasoned that activation of 5-HT3 receptors could overcome a potential analgesic
activity of serotonin in neuropathic pain. This gave us the impetus to examine the action
of vortioxetine in a preclinical model of neuropathic pain. Vortioxetine is a new
multimodal antidepressant drug, which inhibits the high affinity serotonin transporter,
and also interacts with different types of serotonin receptors. In particular, vortioxetine
behaves as a full agonist of 5-HT1A receptors, a partial agonist of 5-HT1B receptors, and
an antagonist of 5-HT1B, 5-HT3, and 5-HT7 receptors. Vortioxetine displays the highest
affinity and CNS receptor occupancy for 5-HT3 receptors, and is nearly as potent as the
prototypical 5-HT3 receptor antagonist, ondansetron, in inhibiting the 5-HT3-dependent
Bezold-Jarisch reflex 13-15. Owing to these characteristics, vortioxetine is clinically
effective in improving cognitive dysfunction associated with unipolar depression (see
Discussion and References therein). We hypothesized that vortioxetine could be
beneficial in neuropathic pain by enhancing serotoninergic transmission and potently
inhibiting 5-HT3 receptors at the same time. We tested this hypothesis by comparatively
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evaluating the effect of a chronic treatment with vortioxetine, the serotonin-noradrenaline
reuptake inhibitor (SNRI), venlafaxine, and the SSRI, fluoxetine, in mouse models of
chronic inflammatory and neuropathic pain.
Materials and Methods
Animals
The experiments were carried out in two months old male CD1 mice (Charles River,
Italy). Animals were housed 3-4 per cage in a controlled-temperature room (21–23°C,
humidity 40–50%) maintained on a 12-h light/dark cycle (light on 07:00 am); food
(Standard Diet Charles River 4RF21, Italy) and water were available ad libitum. All
efforts were made to minimize the number of animals used and to alleviate their
discomfort. All experimental procedures were performed in conformity with the
European Union Directive (2010/63/EU) on the protection of animals used for scientific
purpose and were approved by the Italian Ministry of Health (DDL 26/2014 and previous
legislation; protocol number n° 882/2017-PR).
Drugs
Vortioxetine was provided by H. Lundback A/S (Denmark). Fluoxetine and venlafaxine
were purchased from LKT Laboratories Inc (Minnesota, USA). All drugs were dissolved
in 5% of 2-hydroxypropyl-β-cyclodextrin and administered intraperitoneally (i.p.) at the
dose of 10 mg/kg (50 µl/10 gr b.w.). Control animals received the vehicle alone (50 µl/10
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g, b.w.). The fixed dose of 10 mg/kg for the three drugs was selected on the basis of
previous studies using fluoxetine and/or venlafaxine in models of neuropathic pain [16-
20]. No studies with vortioxetine in pain models had been performed before. The dose
of 10 mg/kg of vortioxetine is used in most of the studies on cognitive function and
depressive-like behavior [21-24].
Induction of chronic inflammatory pain
Tissue inflammation was induced by a single sub-cutaneous (s.c.) injection of 20 µl of
Complete Freund’s Adjuvant (CFA, Sigma–Aldrich; 1 mg/ml) in the dorsal surface of the
right hind paw. Control mice (n = 7) were injected s.c. with saline in the right hind paw.
Three hours after CFA injection, mice were treated once a day (always at 2.00 p.m.) for
12 days with vortioxetine (n = 8), fluoxetine (n = 9), venlafaxine (n = 8) or their vehicle
(n = 7). Tactile allodynia was assessed before the injection of CFA (day 0) to determine
baseline thresholds and then 1, 3, 5, 7, 10 and 12 days after CFA (and drug) injections.
Induction of chronic neuropathic pain
Mononeuropathy was induced by the chronic constriction injury (CCI) of the sciatic nerve
in mice 25 anesthetized by i.p. injection of tiletamine-zolazepam + xylazine (30 mg/kg
+ 10 mg/kg). The sciatic nerve was exposed and three loose ligatures with 4–0 silk suture
thread were made around the nerve with a 1.0–1.5 mm interval between each of them. In
sham-operated mice, an identical dissection was performed on the same side, except that
the sciatic nerve was not tied. Fourteen days after CCI (day 0) mice were daily injected
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with vortioxetine (n = 10), fluoxetine (n = 9), venlafaxine (n = 9) or vehicle (n = 8) for
28 days. All treatments were performed at 2.00 p.m. Tactile allodynia was measured prior
to CCI to determine baseline thresholds, in the morning (10.00 a.m.) of the starting day
of drug treatments, and then at days 1, 3, 5, 7, 12, 14, 16, 21 and 27 of antidepressant
treatments.
Assessment of tactile allodynia
Tactile allodynia was assessed in the hind paws using calibrated von Frey filaments (2
Biological Instruments, Italy) and the up-down method previously described by Chaplan
26. Animals were placed in individual Plexiglas boxes on a raised metal mesh surface
and allowed to acclimatize for 30 min before the test. Testing was initiated with a
medium-sized filament, which was applied for 7 s to the plantar area (plantar territory of
the sural nerve) until the filament bent slightly. If the mouse withdrew or lifted the paw,
the response was considered positive and a one size smaller filament was tried.
Conversely, if no response was observed, a one size larger filament was tried. The
protocol was repeated until five changes in behavior had been observed. The 50% paw
withdrawal threshold (PWT) was determined according to the following equation: Xf +
kD, where Xf is the value of the last von Frey filament used, k is the Dixon value for the
positive/negative pattern, and D is the logarithmic difference between stimuli 27. Tests
were performed in the morning, before drug injections, thus reflecting the analgesic action
of the previous treatment day.
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Assessment of locomotor activity and catalepsy
Locomotor activity was assessed in an open field apparatus in all mice used for the study
of neuropathic pain (sham-operated mice and CCI mice treated with vehicle, fluoxetine,
vortioxetine, and venlafaxine) at day 18 after the onset of drug treatments (between day
16 and 21 of pain assessment). The open field apparatus was a Plexiglas squared arena
(40 x 40 cm) with grey walls (40 cm high) and an open roof, located in a sound-attenuated
and dimly-illuminated room. Animals were individually placed in the center of the arena
and allowed to explore for 10 minutes. The arena was cleaned with 50% ethanol solution
before each test. The frequency of line crossing was used to assess total general motor
activity. For this purpose, the floor was divided in 9 virtual quadrants of equal size. A line
crossing was considered when the animal entered another virtual quadrant with all four
paws. Behavioral data were acquired and analyzed using an automated video-tracking
system (Any-Maze, Stoelting, USA).
Catalepsy was assessed in the same mice at day 19 after the onset of treatments by the
horizontal bar test, in which the fore paws of mice were placed on a 15 cm long bar placed
at 4.5 cm above the surface level. The center of the bar was marked to assure identica l
placement of the mice during the test [28]. The time in which the fore paws remained in
the horizontal bar was recorded by an observer who was unaware of the treatments with
a cut-off time of 60 sec. If a mouse did not stay in the position after four attempts, the
cataleptic response time was registered as zero seconds.
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Statistical analysis
Statistical analysis of the paw withdrawal threshold (PWT) was performed by two-way
ANOVA for repeated measures followed by Bonferroni post-hoc comparisons, where
appropriate. Statistical significance was set at p<0.05.
Results
No analgesic effect of the selected antidepressants in the CFA model of chronic
inflammatory pain
A significant reduction of tactile withdrawal thresholds was observed in the ipsilateral
hind paw one day after unilateral CFA injection. In CFA mice chronically treated with
vehicle, tactile allodynia remained unaltered in the first 5 days and then gradually
decreased until the last day of pain assessment (12 days following CFA injection). None
of the selected antidepressants, including vortioxetine, caused changes on tactile
sensitivity in the hind paw ipsilateral to CFA injection (Fig. 1A). No changes in paw
withdrawal were found in the contralateral hind paw regardless of drug treatments (Fig.
1B).
Chronic treatment with vortioxetine caused analgesia in the CCI model of neuropathic
pain
Unilateral CCI of the sciatic nerve caused the expected reduction in mechanical pain
thresholds after 14 days with respect to basal thresholds and to thresholds detected in
sham-operated mice. Daily treatments with fluoxetine, venlafaxine, vortioxetine (all at 10
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mg/kg, i.p.) or their vehicle started at day 14 after CCI immediately after pain assessment
(indicated as time 0 in Fig. 2A,B). In CCI mice treated with vehicle, the reduction of
tactile pain thresholds in the ipsilateral hind paw remained unchanged for the whole
duration of the treatment (27 days, corresponding to 41 days after CCI) (Fig. 2A).
Fluoxetine treatment in CCI mice had no effect on tactile allodynia, and paw withdrawal
threshold values were indistinguishable from those detected in mice treated with vehicle
(Fig. 2A). In contrast, treatments with either venlafaxine or vortioxetine caused a robust
analgesia that was initially observed at day 7 and became substantial at day 12 of the
treatment (Fig. 2A). There was no difference between the analgesic effect of vortioxetine
and the effect of the venlafaxine (Fig. 2A). No changes in mechanical thresholds were
found in the hind paw contralateral to CCI regardless of drug treatments (Fig. 2B).
Vortioxetine and the other antidepressants had no effect on spontaneous locomotor
activity and did not induce catalepsy in sham-operated and CCI mice.
To exclude that changes in motor activity could influence the evaluation of pain
thresholds, we measured spontaneous locomotor activity in sham-operated mice, and in
CCI mice treated with vehicle, fluoxetine, venlafaxine, or vortioxetine. Mice were
evaluated in an open field apparatus at day 18 after the onset of drug treatments (pain
thresholds were measured at days 16 and 21). Measurements of total distance travelled
and number of line crossing showed that CCI itself (mice treated with vehicle) and drug
treatments did not change spontaneous locomotor activity, as compared to sham-operated
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mice (Fig. 3A,B). We also evaluated the ability of mice to remove their fore paws from a
horizontal bar (a test for the assessment of catalepsy) at day 19 after the onset of drug
treatments. All mice (sham-operated mice or CCI mice treated with vehicle, fluoxetine,
venlafaxine or vortioxetine) showed no cataleptic behavior, and immediately removed
both fore paws from the horizontal bar (not shown).
Discussion
Full functional recovery in patients affected by unipolar depression relies on the control
of residual symptoms and comorbid disorders. Cognitive dysfunction, which occurs in a
significant proportion of depressed patients, has a negative prognostic value and is
refractory to the majority of antidepressant medications. Depressed patients with
cognitive dysfunction, characterized by impairment in executive functions, speed of
processing, and working and episodic memory, often relapse in spite of continuous
medication, and this leads to a marked reduction in the quality of life 29-32. The
multimodal antidepressant, vortioxetine, has shown a remarkable efficacy in improving
cognitive dysfunction associated with unipolar depression 33-40. In a network
metanalysis of twelve clinical trials made uniform by the use of the digit-symbol
substitution test as a measure of cognitive function, vortioxetine has shown a large
superiority with respect to all other antidepressants drugs, such as SNRIs, SSRIs,
monoamine oxidase inhibitors, and tricyclic antidepressants 41. This unique property
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of vortioxetine largely depends on its ability to potently antagonize 5-HT3 receptors in
the prefrontal cortex and hippocampus, a mechanism that restrains the inhibitory activity
of selected populations of GABAergic interneurons on pyramidal cells 42,43. In spite
of this remarkable feature, vortioxetine is not yet considered as a first-choice drug in
patients with depression associated with comorbid neuropathic pain because the action of
vortioxetine on pain transmission is still unknown. In contrast, antidepressants that inhibit
both serotonin and noradrenaline reuptake, such as duloxetine, venlafaxine, amitriptyline,
are gold standard drugs in the treatment of neuropathic pain 12. Using an established
mouse model of neuropathic pain, we have shown here for the first time that vortioxetine
displays a strong analgesic activity, which is indistinguishable from the activity exhibited
by venlafaxine. To our knowledge, this is the first example of a pure serotoninergic drug
showing analgesic activity in a model of neuropathic pain. In contrast, chronic treatment
with the SSRI fluoxetine did not cause analgesia in the CCI model of neuropathic pain
(see 44 for similar data obtained in rats).
As outlined above, the serotonergic pathway descending from the lower brainstem to the
dorsal horns of the spinal cord becomes hyperalgesic under conditions of neuropathic
pain because of epigenetic processes developing in the raphe magnus and other
mechanisms (see Introduction and References therein). Serotonin-induced hyperalgesia
is mediated by activation of 5-HT3 receptors, which counteract the analgesic activity of
5-HT7 receptors (reviewed in Ref. 1). Vortioxetine acts as a multimodal serotonergic
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antidepressant, behaving as an inhibitor of the high affinity serotonin transporter, a full
agonist of 5-HT1A receptors, a partial agonist of 5-HT1B receptors, and an antagonist of
5-HT1D, -3, and -7 receptors (reviewed in Ref. 39). Measurements of target occupancy
in mice showed that 10 mg/kg of vortioxetine (the dose used in this study) nearly saturates
5-HT3 receptors and the serotonin transporter, but recruits only 20-30% of 5-HT7
receptors [45]. Thus, under conditions of serotonergic hyperactivity, as occurs in
neuropathic pain, vortioxetine will efficiently antagonize 5-HT3 receptors leaving the
vast majority of 5-HT7 receptors unoccupied and, therefore, available for activation by
serotonin. On the basis of these findings we could predict that SSRIs could be effective
as analgesic drugs in neuropathic pain if combined with a potent 5-HT3 receptor
antagonist. This interesting hypothesis warrants further investigation. We were surprised
to find that vortioxetine and venlafaxine were equally effective in causing analgesia in
the CCI model of neuropathic pain in spite of the different mechanism of action of the
two drugs. However, dose-response curves should be performed for a correct comparison
of the analgesic activities of vortioxetine and venlafaxine.
Because antidepressant drugs have intrinsic anti-inflammatory effects [46], we cannot
exclude that vortioxetine causes analgesia by restraining neuroinflammation associated
with neuropathic pain. Along this line, increasing evidence suggests that pain-associated
neuroinflammation is gender-dependent, with a greater involvement of microglia in
males, and T lymphocytes in females (reviewed by [47]. Sex steroids are known to affect
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neuroinflammation by modulating microglial responses to injuries [48-50]. Here, we
examined the analgesic activity of vortioxetine only in males to avoid heterogeneity
caused by the ovarian cycle. It will be interesting to extend the study to non-synchronized,
synchronized, and ovariectomized female mice (w/wo hormonal replacement therapy) to
gain insights into the influence of gender and sex steroids on the analgesic activity of
vortioxetine in models of neuropathic pain.
None of the antidepressants used in the present study caused analgesia in the CFA model
of chronic inflammatory pain. In a previous study, fluoxetine at the dose of 10 mg/kg was
found to enhance mechanical pain thresholds in CFA-injected rats [51]. To our
knowledge, fluoxetine has never been tested in the CFA model in mice, except in one
study in which fluoxetine had no effect on CFA-induced oedema but pain thresholds were
not determined [52]. High doses of venlafaxine (50 and 100 mg/kg) were reported to
enhance mechanical pain thresholds after intraplantar injection of carrageenan in rats
[53], but the drug has never been tested before in CFA mice. The lack of effects of
venlafaxine and vortioxetine on pain thresholds in CFA mice supports the hypothesis that
the molecular and trans-synaptic mechanisms underlying nociceptive sensitization in
inflammatory and neuropathic pain are different. We have shown recently that a 7-day
treatment with the antidepressant, amitriptyline, is effective in causing analgesia in the
CFA model of inflammatory pain in mice 54. Although amitriptyline shares with
venlafaxine the ability to inhibit both serotonin and noradrenaline reuptake, other
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mechanisms, such as inhibition of neurotransmitter receptors or voltage-sensitive sodium
channels, may contribute to the analgesic effect of amitriptyline and account for the
different actions of amitriptyline and venlafaxine in the CFA model of pain.
Our findings suggest that vortioxetine may enrich the therapeutic armamentarium in
patients affected by major depression associated with comorbid neuropathic pain. If
confirmed in clinical studies, the analgesic activity of vortioxetine will be particularly
helpful for patients with cognitive dysfunction, in which the drug shows a greater efficacy
with respect to all other classes of antidepressants. Another advantage is the good profile
of safety and tolerability of vortioxetine, which does not causes significant increases in
body weight and sexual dysfunction (as opposed to SSRIs) or cardiovascular adverse
effects (as opposed to SNRIs) 55-57. The analgesic effect of vortioxetine in the CCI
model paves the way for clinical studies in which vortioxetine should be compared to
gold standard antidepressants in the treatment of neuropathic pain.
Authors’ Note
The study was supported by an unrestricted grant from Lundbeck, Italy and by Lundbeck
Denmark for the pure ingredient.
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Authors’ contribution
A.R.Z. performed pain experiments and contributed to write the manuscript; D.M.,
F.D.M. and R.L. performed pain experiments; S.A. performed experiments on motor
behaviour; P.C. and F.N. planned research and wrote the manuscript.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research,
authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or
publication of this article.
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Fig. 1 - Chronic treatment with fluoxetine, venlafaxine, and vortioxetine did not
cause analgesia in the CFA mouse model of inflammatory pain.
Mice were injected with CFA in the right hind paw. Control mice received an equal
volume of saline in the hind paw. In CFA mice, systemic treatments with fluoxetine (10
mg/kg), venlafaxine (10 mg/kg), or vortioxetine (10 mg/kg) started three hours after CFA
injection. All drugs were injected i.p. once a day for 12 days. Tactile pain thresholds were
assessed at days 1, 3, 5, 7, 10 and 12 after CFA injection. Pain threshold measured in the
ipsilateral hind paw are shown in (A), where values are means + S.E.M. of 7-9 mice per
group. In order to assess the inflammatory effect of CFA injection we first compared each
of the CFA-injected groups with the group of sham-operated mice treated with vehicle.
Two-way ANOVA for repeated measures (treatment x days) indicated that all CFA-
injected groups were statistically different from sham (CFA/vehicle vs. sham/vehicle:
F1,98= 79.76, p<0.05; CFA/fluoxetine vs. sham/vehicle: F1,103= 16.36, p<0.05;
CFA/venlafaxine vs. sham/vehicle: F1,97= 12.39, p<0.05; CFA/vortioxetine vs
sham/vehicle F1,97= 11.99, p<0.05). Then we assessed the treatment effect comparing all
CFA-injected groups without the group of sham-operated mice treated with vehicle. Two-
way ANOVA for repeated measure indicated a significant effect of the day (F3,199= 98.29,
p<0.05) but no effect of antidepressant treatment (F3,199= 1.33, p= 0.3). Pain threshold in
the contralateral hind paw are shown in (B).
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Molecular Pain
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Fig. 2 – Analgesic effects of vortioxetine and venlafaxine in the CCI model of
neuropathic pain.
Mice were subjected to CCI of the right sciatic nerve and treated, after 14 days, with
either fluoxetine (10 mg/kg), venlafaxine (10 mg/kg), vortioxetine (10 mg/kg), or their
vehicle. Treatments were performed i.p. once a day for 27 days (i.e., up to 41 days after
CCI). Tactile pain thresholds in the ipsilateral hind paw are shown in (A) where values
are means + S.E.M. of 8-10 mice per group. In order to assess the induction of neuropathic
pain after CCI we first compared all CCI groups with the group of sham-operated mice
treated with vehicle. Two-way ANOVA for repeated measures (treatment x days)
indicated that each of the CCI groups was statistically different from the group sham-
operated mice treated with vehicle (CFA/vehicle vs. sham/vehicle: F1,180= 255.25,
p<0.05; CFA/fluoxetine vs. sham/vehicle: F1,180= 264.59, p<0.05; CFA/venlafaxine vs.
sham/vehicle: F1,180= 98.16, p<0.05; CFA/vortioxetine vs. sham/vehicle: F1,190= 156.51,
p<0.05). Then, we assessed the treatment effect comparing all CCI groups without the
group of sham-operated mice. Two-way ANOVA for repeated measure indicated a
significant effect of the day (F3,370= 18.17, p<0.05), a significant effect of the treatment
(F3,370= 23.97, p<0.05) and an interaction between the two factors (F3,370= 10.61, p<0.05).
Values obtained in CCI mice treated with vortioxetine or venlafaxine were significantly
different with respect to values obtained in CCI mice treated with vehicle or fluoxetine
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from day 12 of treatment (*p<0.05, Bonferroni’s post-hoc test). Mechanical pain
thresholds in the contralateral hind paw are shown in (B).
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Fig. 3 – Antidepressant treatment did not cause changes in spontaneous locomotor
activity in mice subjected to CCI of the sciatic nerve.
Spontaneous locomotor activity was assessed in mice subjected to CCI of the right sciatic
nerve treated with antidepressants or their vehicle (see legend of Fig. 2), and in sham-
operated mice at day 32 after surgery (day 18 of treatments in CCI mice). Distance
travelled (in meters) (A) and numbers of line crossing (B) were determined in an open
field apparatus (10 min of total observation). Values are means + S.E.M. of 8-10 mice
per group.
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