The Effect of Systemic Lipopolysaccharide Treatment on Locomotor and Pain Behavior of Spinal Cord Injured Mice Open Access
Deng, Bowei (Spring 2022)
Published
Abstract
Importance: Approximately 296,000 persons currently live with a spinal cord injury (SCI) in the United States. Neuropathic pain, which can be expressed as an aggravated, sharp, stabbing pain around the level of SCI, is an important consequence of SCI. The mechanisms underlying neuropathic pain and other behavioral complications after SCI are poorly understood, although such an understanding is essential to discovering novel therapeutic interventions.
Objectives: This study examined the effect of systemic inflammation on chronic pain responses, hind-limb locomotor function, and inflammation-induced neuronal and cellular plasticity accompanying pain after SCI.
Methods: Liposaccharide (LPS) was intraperitoneally injected into mice to induce inflammation. A contusion SCI was created at the thoracic (T) 10 level with an Infinite Horizon impactor. The Basso Mouse Scale (BMS) was used to examine hind-limb locomotor function after SCI. Hind-paw mechanical hypersensitivity was assessed by the von Frey test, while the tail-flick test was used to measure thermal sensitivity. Respiratory rates (RR) were monitored at weekly time points, and the two-chamber conditioned place aversion (CPA) paradigm was used to assess affective pain in response to mechanical stimulation of the trunk. Spinal expression levels of pERK were measured at acute and chronic time points after LPS treatment.
Results: LPS pre-treatment in naïve mice produced mechanical and thermal hypersensitivity, and a short-lasting reduction in resting RRs. Although LPS had no effect on mechanical pain in SCI mice, it impaired the recovery of locomotor function at later time points. LPS had no effect on spinal pERK levels at the acute time point, although pERK2 was decreased at 35 days post-treatment.
Discussion and conclusion: The results suggest that whereas LPS-induced inflammation has a pain-producing effect in naïve subjects after SCI, this effect is diminished due to the more robust effect of SCI. Interestingly, the mechanisms underlying LPS-induced pain appear to be independent of pERK signaling in the spinal cord. Also, LPS impaired locomotion, while having no effect on pain after SCI, suggests that LPS pre-treatment differentially affects locomotor and pain systems after SCI. Additional studies are needed to fully elucidate the impact of LPS and systemic inflammation on pain behaviors after SCI.
Table of Contents
Table of Contents
1.0 Introduction………………………………………………………………………………….. 1
1.1 Overview: 1
1.2 Spinal Cord Injury: 1
1.3 Neuropathic Pain after SCI: 2
1.4 Systemic Inflammation after SCI: 4
1.5 Lipopolysaccharide: 5
2.0 Hypothesis……………………………………………………………………………………. 6
3.0 Methods…………………………………………………………………………………….… 7 3.1 Animals: 7
3.2 Spinal Cord Injury: 7
3.3 Administration of LPS: 9
3.4 Behavior Room Acclimation: 9
3.5 Basso Mouse Scale: 10
3.6 von Frey test: 10
3.7 Tail-Flick test: 11
3.8 Respiratory Rate: 12
3.9 Conditioned Place Aversion Paradigm: 14
3.10 Lumbar Spinal Cord Collection and Western Blot: 15
4.0 Blinding of Experiments and Statistical Analysis………………………………………….. 17
5.0 Experimental Design………………………………………………………………………... 19
6.0 Results……………...……………………………………………………………………….. 18
6.1 Results from Experiment 1
6.1.1 Basso Mouse Scale: 18
6.1.2 von Frey: 21
6.1.3 Respiratory Rate, weekly and 5DP: 23
6.1.4 Five-day Paradigm, Chamber Preference: 26
6.1.5 Five-day Paradigm, Chamber Transitions: 26
6.2 Results from Experiment 2
6.2.1 Tail-Flick Test: 29
6.3 Results from Experiment 3
6.3.1 Western Blot for Phosphor-ERK: 30
7.0 Discussion…………………………………………………………………………………... 31
8.0 References…………………………………………………………………………………... 37
List of Attachments
Apparatus 1: The Infinite Horizon impactor…………………………………………………….. 8
Apparatus 2: The von Frey Mesh………………………………………….…………………….. 11
Apparatus 3: The Tail-Flick Analgesia Meter………………..…………...…………………….. 12
Apparatus 4: Semi-Restraining Tube…………..……...………………………………………... 13
Apparatus 5: CPA Paradigm…………………………………………………………………….. 15
Figure 1: Line graph of BMS score for Saline/LPS treated naïve mice……..…………………... 20
Figure 2: Line graph of BMS score for Saline/LPS treated SCI mice………………………….. 20
Figure 3: Bar graph of von Frey withdrawal threshold for Saline/LPS treated naïve mice…….. 22
Figure 4: Bar graph of von Frey withdrawal threshold for Saline/LPS treated SCI mice……… 22
Figure 5: Line graph of weekly RR for Saline/LPS treated naïve mice………………….…….. 24
Figure 6: Line graph of weekly RR for Saline/LPS treated SCI mice…………………….……. 24
Figure 7: Line graph of RR during 5DP truncal stimulation……………….……………………. 25
Figure 8: Bar graph of 5DP Chamber Preferences………………………………………………. 27
Figure 9: Effect of LPS on 5DP Chamber Transitions……………………...…………………… 28
Figure 10: Bar graph of Tail Flick Test for Saline/LPS treated Naïve mice……………….…… 29
Figure 11: Spinal pERK Expression for Saline/LPS treated Naïve mice……………..….…….. 31
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