Concurrent validity of different functional and neuroproteomic pain assessment methods in the rat osteoarthritis monosodium iodoacetate (MIA) model

Abstract

BackgroundLack of validity in osteoarthritis pain models and assessment methods is suspected. Our goal was to 1) assess the repeatability and reproducibility of measurement and the influence of environment, and acclimatization, to different pain assessment outcomes in normal rats, and 2) test the concurrent validity of the most reliable methods in relation to the expression of different spinal neuropeptides in a chemical model of osteoarthritic pain.MethodsRepeatability and inter-rater reliability of reflexive nociceptive mechanical thresholds, spontaneous static weight-bearing, treadmill, rotarod, and operant place escape/avoidance paradigm (PEAP) were assessed by the intraclass correlation coefficient (ICC). The most reliable acclimatization protocol was determined by comparing coefficients of variation. In a pilot comparative study, the sensitivity and responsiveness to treatment of the most reliable methods were tested in the monosodium iodoacetate (MIA) model over 21 days. Two MIA (2 mg) groups (including one lidocaine treatment group) and one sham group (0.9 % saline) received an intra-articular (50 μL) injection.ResultsNo effect of environment (observer, inverted circadian cycle, or exercise) was observed; all tested methods except mechanical sensitivity (ICC <0.3), offered good repeatability (ICC ≥0.7). The most reliable acclimatization protocol included five assessments over two weeks. MIA-related osteoarthritic change in pain was demonstrated with static weight-bearing, punctate tactile allodynia evaluation, treadmill exercise and operant PEAP, the latter being the most responsive to analgesic intra-articular lidocaine. Substance P and calcitonin gene-related peptide were higher in MIA groups compared to naive (adjusted P (adj-P) = 0.016) or sham-treated (adj-P = 0.029) rats. Repeated post-MIA lidocaine injection resulted in 34 times lower downregulation for spinal substance P compared to MIA alone (adj-P = 0.029), with a concomitant increase of 17 % in time spent on the PEAP dark side (indicative of increased comfort).ConclusionThis study of normal rats and rats with pain established the most reliable and sensitive pain assessment methods and an optimized acclimatization protocol. Operant PEAP testing was more responsive to lidocaine analgesia than other tests used, while neuropeptide spinal concentration is an objective quantification method attractive to support and validate different centralized pain functional assessment methods.

Sensitivity of functional targeted neuropeptide evaluation in testing pregabalin analgesic efficacy in a rat model of osteoarthritis pain

“…Our finding correlates with earlier reports, where MIA‐placebo rats displayed a persistent decrease in the ipsilateral PWT to stimulation with von Frey filament. An important advance in operant behaviours is that these approaches may allow the detection and mechanistic investigation of spontaneous neuropathic or ongoing inflammatory/nociceptive (ie, non‐evoked) pain that is otherwise difficult to assess in nonverbal animals .…”

“…An important advance in operant behaviours is that these approaches may allow the detection and mechanistic investigation of spontaneous neuropathic or ongoing inflammatory/nociceptive (ie, non‐evoked) pain that is otherwise difficult to assess in nonverbal animals . Whereas in a previous experiment using MIA model of OA in rat, PEAP presented attractive metric properties, it is uncertain why we did not reproduce similar alteration in the time spent in the dark side for the MIA‐placebo group. However, there was a trend in deterioration for the MIA‐placebo group, and the PEAP test was sensitive to detect an effect of analgesic medications: the PGB or carprofen‐, and morphine‐treated rats respectively, attenuated and deteriorated the PEAP behaviour.…”

“…In our experiments, behavioural outcomes included the PWT sensory‐reflexive method, assessing potential tactile allodynia, and the PEAP operant test, reflecting affective and cognitive dimensions of pain. All both methods had demonstrated interesting metric properties to detect IA lidocaine‐induced analgesia in the rat MIA model …”

“…The subsequent release of excitatory neurotransmitters, glutamate and neuropeptides such as pronociceptive substance P (SP) and calcitonin gene‐related peptide (CGRP), from the central terminals of sensitized nociceptive fibers leads, in part, to phosphorylation of the N ‐methyl‐D‐aspartate receptor and an increase in intracellular calcium ion, which finally is translated to long lasting transcriptional and post‐translational changes . Indeed, in an OA rat model, higher levels of neuropeptides, such SP and CGRP have been found in the spinal cord …”

“…The chemical monosodium iodoacetate (MIA)‐induced joint degeneration in rats is one of the most used animal models to screen analgesic drugs to alleviate OA pain . Having established a high‐level sensitivity method for quantifying spinal neuropeptides, our group recently tested their reliability and validity as pain outcome in MIA‐induced OA: spinal nociceptive neuropeptides demonstrated face (high responsiveness to OA induction), construct (high specificity with lower concentration in naïve and sham rats), and criterion‐related validity (high sensitivity to detect analgesic response to punctual intra‐articular (IA) lidocaine administrations); their time‐response was also determined, demonstrating also repeatability and test‐retest reliability, as well as reproducibility in different chemical or surgical OA models in rats . At the same time, functional pain assessment methods were tested and validated, either spontaneous (static and dynamic weight‐bearing alteration), sensory‐reflexive (tactile and mechanical withdrawal threshold), or operant (requiring pain integration) testing .…”