Antinociceptive effects of three escalating dexmedetomidine and lignocaine constant rate infusions in conscious horses

Risberg, Åse I.; Spadavecchia, Claudia; Ranheim, Birgit; Krontveit, Randi; Haga, Henning Andreas

doi:10.1016/j.tvjl.2014.09.007

Cited by 23 publications

(31 citation statements)

References 57 publications

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“…The nociceptive component (NWR, often defined as RIII in humans) is the one deriving from activation of Ad fibers, with an afferent conduction velocity ranging from 4 to 36 m/s (Gasser and Erlanger 1927). For horses, on the basis of experiences collected in several experiments, the epochs 80 -250 ms or 40 -200 ms after stimulation seem the most suitable to recognize the NWR, depending on the specific experimental settings chosen (Spadavecchia et al 2002, Spadavecchia et al 2003, Risberg et al 2014. Later components, possibly deriving from activation of slow conducting nociceptive C fibers, are difficult to recognize as they are contaminated by supraspinal reactions.…”

Section: Quantifying and Defining The Nwrmentioning

confidence: 99%

“…To be considered an NWR, the reflex component in the epoch of interest has to be at least 3 times the background activity (EMG recorded before stimulus onset) (Spadavecchia et al 2002, Spadavecchia et al 2003 or to have a RMS amplitude of at least 30 µV (Risberg et al 2014). …”

Section: Quantifying and Defining The Nwrmentioning

confidence: 99%

“…The total stimulation time was set at 2 s, as in most human experiments, and the EMG response was recorded for 4 s: 500 ms prestimulation, 2000 ms during stimulation and 1500 ms poststimulation (Spadavecchia et al 2004). The experience collected over the last years indicates that the best method to quantify the NWR facilitation consists in the determination of the RMS amplitude of the reflex response within the 40 -200 ms window following each stimulus (Risberg et al 2014). Nevertheless preliminary trials revealed that once the summation effect is initiated, the individual NWR can be recognized only with difficulty because of the gross limb movement mostly accompanied by strong generalized increase in the EMG activity.…”

Section: Temporal Summation: Background and Experiences In Horsesmentioning

confidence: 99%

“…Stimulation intensities: 0.7, 0.8 and 0.9 times the individual NWR threshold intensity (× NWRt); following stimulations at 0.8 and 0.9 ×NWRt, electromyographic activity is present also after the end of stimulation: the horse lifted the limb many times. very useful to consistently define the NWR threshold (Risberg et al 2014). On the basis of experimental observations, a specific numerical scale was introduced.…”

Section: Behavioural Reactions To Electrical Stimulationsmentioning

confidence: 99%

“…Some horses lift the limb with delay, following the whole body reaction. Following stimulations of intensities at or above the threshold, a direct quick lifting of the stimulated limb can be observed (Risberg et al 2014). The scoring system applied in equine studies was adequate to describe the pattern of reactions and to detect changes related to differences in stimulus intensity (Spadavecchia et al 2003).…”

Section: Behavioural Reactions To Electrical Stimulationsmentioning

confidence: 99%

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The model of the Nociceptive Withdrawal Reflex in horses

Spadavecchia¹,

Rohrbach²,

Levionnois³

et al. 2016

PHK

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Summary: In equine pain research, the Nociceptive Withdrawal Reflex (NWR) model has been proposed as an alternative to classical thermal, mechanical and electrical models to investigate the physiology of nociception. This model does not only allow a more reliable definition of the nociceptive threshold through neurophysiological characterization of the elicited response , but also consents plotting a stimulus-response curve as well as the evaluation of temporal summation mechanisms. Aim of this report is to summarize the experience and results obtained using the NWR model in horses over the last 15 years, firstly with the purpose of describing its physiological characteristics and secondly with the aim of evaluating its pharmacological modulation through analgesic and anaesthetic compounds. The NWR can be elicited in horses through electrical transcutaneous stimulation of a peripheral sensory nerve and is recorded through electromyographic electrodes from the muscles involved in the withdrawal reaction. As the non-nociceptive fibres have lower threshold to electrical stimuli than the nociceptive one, it is impossible to differentiate between the two groups on the stimulus side. So, the only guidance to assess the quality of the stimulus and the recruitment of nociceptive afferents should rely on the characteristics of the electromyographic response, most of all on the timing of its various components. A reflex response can be considered to be a true NWR only if it appears within a time epoch compatible with the conduction velocity of the A fibers. Furthermore a clearly recognizable EMG burst in the epoch of interest has to be accompanied by a consistent aversive behavioural reaction, thus allowing the definition of a reliable NWR threshold. Responses to stimulation intensities below and above thresholds can be quantified to draw a stimulus response curve. Furthermore, through repeated stimulation at subthreshold intensities, it is possible to elicit the phenomenon of temporal summation, considered to be the early phase of the wind up phenomenon and of relevant interest to study central integrative mechanisms of pain processing. Alpha-2 agonists, opioids, systemic lidocaine, ketamine and inhalation anaesthetics have been investigated using the NWR model in horses. Drug-specific modulation of NWR threshold, stimulus-response curves and temporal summation are summarized for each tested compound.

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