Urokinase-type Plasminogen Activator-induced Mouse Back Pain Model

Summary

Methods for simple, rapid induction of a back pain model in mice are provided here using an intraligament injection of urinary plasminogen activator.

Abstract

A model of persisting lower back pain can be induced in mice with the simple methodology described herein. Step-by-step methods for simple, rapid induction of a persisting back pain model in mice are provided here using an injection of urokinase-type plasminogen activator (urokinase), a serine protease present in humans and other animals. The methodology for induction of persisting lower back pain in mice involves a simple injection of urokinase along the ligamentous insertion region of the lumbar spine. The urokinase inflammatory agent activates plasminogen to plasmin. Typically, the model can be induced within 10 min and hypersensitivity persists for at least 8 weeks.

Hypersensitivity, gait disturbance, and other standard anxiety- and depression-like measures can be tested in the persisting model. Back pain is the most prevalent type of pain. To improve awareness of back pain, the International Association for the Study of Pain (IASP) named 2021 the "Global Year about Back Pain" and 2022 the "Global Year for Translating Pain Knowledge to Practice." One limitation of the therapeutic advancement of pain therapeutics is the lack of suitable models for testing persistent and chronic pain. The features of this model are suitable for testing potential therapeutics aimed at the reduction of back pain and its ancillary characteristics, contributing to IASP's naming 2022 as the Global Year for Translating Pain Knowledge to Practice.

Introduction

Low back pain is one of the most common causes of disability with 1 in 5 people suffering worldwide¹. In spite of these efforts, few reliable animal models of back pain are popularly used in animal research in the pain field, especially in mice. Previous models have almost exclusively made use of rats for the induction of chronic back pain (CBP) such as those induced by injection of urinary plasminogen activator (uPA) into the lumbar facet joint^2,3, injection of nerve growth factor (NGF) into trunk musculature⁴, or monosodium iodoacetate (MIA)^5<....

Protocol

All animal procedures described are in compliance with the NIH Guide for the Care and Use of Laboratory Animals. Studies were approved by the local Institutional Care and Use Committee (IACUC #23-201364-HSC) of the University of New Mexico Health Sciences Center. All studies comply with policies under the auspices of an OLAW Assurance of Compliance (A3002-01) on the use of animals in research, as described in Part III. II. Assurances and Certifications. Animals are housed in the Animal Resources Center (ARC) housing facility maintained by the laboratory staff and Division of Laboratory and Animal Resources (DLAR) staff. The method of euthanasia (100 µL of 59 mg/m....

Discussion

This model of chronic back pain is simple to induce, and hypersensitivity established within 1 week can last for up to (and possibly beyond) 8 weeks. This allows for accurate study of the chronic pain state as opposed to other acute models that only last for a week or two. While we show the model in mice, the uPA-induced CBP model can also be established in rats². An advantage of the model is that the prolonged time course provokes the development of anxiety- and depression-like behaviors, which a.......

Materials

Name	Company	Catalog Number	Comments
Animals and Consumables
70% ethanol	Local Source
BALB/c mice	Envigo		20-25 g
Cotton balls	Fisher Scientific	19-090-702
Cotton-tipped applicators	Fisher Scientific	19-062-616
Isoflurane inhalant anesthetic	MedVet	RXISO-250
Labeling tape	Fisher Scientific	NGFP7002
Nitrile exam gloves	Fisher Scientific
Oxygen tank	Local Source
Surgical drape, Steri-Drape Utility Sheet, Absorbent Prevention	VWR	76246-788	cut into 15 x 15 cm pieces
Tygon tubing with 3 mm inner diameter	Grainger	22XH87
Equipment
#11 carbon steel scalpel blades	VWR	21909-612
Anesthesia induction chamber	Summit Medical Equipment Company	AS-01-0530-LG
Autoclave	Local Unit
Biology Dumont #5 forceps	Fine Science Tools	11252-30
Glass bead sterilizer Germinator 500	VWR	102095-946
IITC Life Sciences Series 8 Model PE34 Hot/Cold Plate Analgesia Meter	IITC	PE34
Integra Miltex cotton & dressing pliers	Safco Dental Supply	66-317
OPTIKA CL31 double arm LED illuminator	New York Microscope Company	OPCL-31
Plantar Test System with InfraRed Emitter, i. e. Hargreaves Apparatus	Ugo Basile	37370-001 and 37370-002
Scalpel Handle No. 3	VWR	25607-947
Small animal heating pad	Valley Vet Supply	47375
Student Vannas spring scissors, straight blade	Fine Science Tools	91500-09
Table top animal research portable anesthesia workstation “PAM”	Patterson Scientific	AS-01-0007
Von Frey Filaments	Ugo Basile	37450-275