Pain
Thermal Pain
Hot-Plate Test
Tail Flick Test
The hot plate and tail flick assays model acute thermal pain. Pain sensitivity is measured on a hot plate or in response to a radiant heat beam focused on the mouse tail. Latency to the first pain response is recorded as a measure of thermal pain sensitivity.
Chemically-Induced Pain
Formalin Test
The formalin test is a model for chemically-induced pain. In the formalin assay, the duration of pain behavior is measured in 5-min segments and divided into an early (acute) phase and late (tonic) phase following footpad injection of formalin. The difference in footpad swelling in response to formalin injection is also assessed as a measure of inflammation.
Carrageenan-Induced Inflammatory Pain
Carrageenan-induced inflammation is a model for acute inflammatory pain. Carrageenan is injected into the hind paw and the latency or threshold to nociceptive behavior in response to thermal and/or mechanical stimuli respectively, are measured for the treated and untreated hind paws. The difference between the injected and non-injected hind paws is a measure of thermal hyperalgesia whereas a difference in 50% mechanical threshold is a measure of mechanical allodynia. Hindpaw swelling is also measured to assess the severity of inflammation.
Mechanical Pain
von Frey Fiber Test
The von Frey plantar test is a measure for acute mechanical pain sensitivity. An automated von Frey plantar stimulator or von Frey fibers are used to measure the mechanical pain threshold (in grams).
Neuropathic Pain Models
Chronic Constrictive Injury (CCI) Model
Partial sciatic Nerve Ligation (PNL) Model
Tibial Nerve Transection (TNT) Model
Spinal Nerve Ligation (SNL) Model
Neuropathic pain is a condition resulting from nerve injury or inflammation. The pain may persist for years even though the damaged tissues may have appeared to heal. Various experimental paradigms have been developed to mimic this human condition. The CCI, PNL, TNT and SNL models are recognized as stable and consistent models for neuropathic pain. To induce CCI, loose ligatures are tied around the proximal part of the sciatic nerve. PNL is induced by ltight ligation of ½ of the sciatic nerve trunk. TNT is induced by ligation and transaction of the tibial nerve, one of the htree major terminal branches of the sciatic nerve. To perform an SNL, the L5 spinal nerve is ligated and transected.The procedures are undertaken on one side of the animal and the contra-lateral side serves as an internal control. Enhanced pain responses to thermal and/or mechanical stimulation are assessed by the Hargreaves’ test and/or the von Frey fiber assay. In the Hargreaves’ test, a radiant heat beam is projected on the plantar skin of each hind paw. The latency to paw withdrawal is recorded as a measure of the thermal pain threshold. Mechanical allodynia is determined by determining the 50% mechanical threshold with von Frey fibers using Dixon’s up-and-down method.Arthritic Pain
Pain is a major symptom of arthritis and an indicator of lost joint function. Pain sensitivity is determined after induction of Collagen Induced Arthritis when paw swelling reaches its peak. Arthritis-induced thermal hyperalgesia and mechanical allodynia are determined using the Hargreaves’ (radiant heat) assay and von Frey fiber test, respectively.
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