The model of the Nociceptive Withdrawal Reflex in horses

Spadavecchia, Claudia; Rohrbach, Helene; Levionnois, Olivier; Leandri, M (2016). The model of the Nociceptive Withdrawal Reflex in horses. Pferdeheilkunde, 32(5), pp. 416-427. Hippiatrika Verlagsgesellschaft 10.21836/PEM20160501

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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 Aδ 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.

Item Type:

Journal Article (Original Article)

Division/Institute:

05 Veterinary Medicine > Department of Clinical Veterinary Medicine (DKV)
05 Veterinary Medicine > Department of Clinical Veterinary Medicine (DKV) > DKV - Anaesthesiology

UniBE Contributor:

Spadavecchia, Claudia; Rohrbach, Helene and Levionnois, Olivier

Subjects:

600 Technology > 610 Medicine & health
600 Technology > 640 Home & family management

ISSN:

0177-7726

Publisher:

Hippiatrika Verlagsgesellschaft

Language:

English

Submitter:

Helene Rohrbach Rüegsegger

Date Deposited:

20 Jul 2017 17:24

Last Modified:

20 Jul 2017 17:24

Publisher DOI:

10.21836/PEM20160501

URI:

https://boris.unibe.ch/id/eprint/96115

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