Abstract
Naturally occurring canine osteoarthritis represents a welfare issue for affected dogs (Canis familiaris), but is also considered very similar to human osteoarthritis and has therefore been proposed as a model of disease in humans. Central sensitisation is recognized in human osteoarthritis sufferers but identification in dogs is challenging. Electromyographic measurement of responses to nociceptive stimulation represents a potential means of investigating alterations in central nociceptive processing, and has been evaluated in conscious experimental dogs, but is likely to be aversive. Development of a suitable anaesthetic protocol in experimental dogs, which facilitated electrophysiological nociceptive withdrawal reflex assessment, may increase the acceptability of using the technique in owned dogs with naturally occurring osteoarthritis. Seven purpose bred male hound dogs underwent electromyographic recording sessions in each of three states: acepromazine sedation, alfaxalone sedation, and alfaxalone anaesthesia. Electromyographic responses to escalating mechanical and electrical, and repeated electrical, stimuli were recorded. Subsequently the integral of both early and late rectified responses was calculated. Natural logarithms of the integral values were analysed within and between the three states using multi level modeling. Alfaxalone increased nociceptive thresholds and decreased the magnitude of recorded responses, but characteristics of increasing responses with increasing stimulus magnitude were preserved. Behavioural signs of anxiety were noted in two out of seven dogs during recordings in the acepromazine sedated state. There were few significant differences in response magnitude or nociceptive threshold between the two alfaxalone states. Following acepromazine premedication, induction of anaesthesia with 1–2 mg kg-1 alfaxalone, followed by a continuous rate infusion in the range 0.075–0.1 mg kg-1 min-1 produced suitable conditions to enable assessment of spinal nociceptive processing in dogs, without subjecting them to potentially aversive experiences. This methodology may be appropriate for obtaining electrophysiological nociceptive withdrawal reflex data in client-owned dogs with naturally occurring osteoarthritis.
Highlights
Osteoarthritis (OA) has been estimated to affect 20% of adult dogs (Canis familiaris), and the resulting pain presents a significant welfare challenge in the management of older animals [1]
We have demonstrated that it is possible to record robust and repeatable EMGs in response to mechanical and electrical nociceptive stimuli in dogs administered alfaxalone
Alfaxalone anaesthesia decreased the magnitude of EMGs recorded in response to mechanical stimuli, and both alfaxalone treatments decreased the magnitude of EMGs in response to electrical stimuli, compared to EMGs recorded in dogs sedated with acepromazine only
Summary
Osteoarthritis (OA) has been estimated to affect 20% of adult dogs (Canis familiaris), and the resulting pain presents a significant welfare challenge in the management of older animals [1]. Canine OA shares developmental, pathological and clinical features with human OA [2]. Client owned dogs are likely to be exposed to similar environmental conditions [3], and potentially lifestyle factors [4], as human OA sufferers. Occurring canine OA has been proposed as a model for further investigation of, and trial of therapeutics for the human condition, with the potential to impact both animal and human welfare [5]. If this model is to be optimized, all relevant outcome measures and measures of the pain state need to be developed and validated, including measures of central sensitisation
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