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Investigation of the facilitation of the nociceptive withdrawal reflex evoked by repeated transcutaneous electrical stimulations as a measure of temporal summation in conscious horses

Claudia SpadavecchiaAnesthesiology Section, Department of Clinical Veterinary Sciences, University of Berne, Langassstrasse 124, 3012 Berne, Switzerland.

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Ole K. AndersenLaboratory for Experimental Pain Research, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark.

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 PhD
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Lars Arendt-NielsenLaboratory for Experimental Pain Research, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark.

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Luciano SpadavecchiaInstitute of Biophysics, National Research Council, Via De Marini 6, 16149 Genova, Italy.

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Marcus DoherrDepartment of Clinical Vetersinary Sciences, Division of Clinical Research, University of Berne, Langassstrasse 124, 3012 Berne, Switzerland.

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Urs SchatzmannAnesthesiology Section, Department of Clinical Veterinary Sciences, University of Berne, Langassstrasse 124, 3012 Berne, Switzerland.

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Abstract

Objective—To investigate whether facilitation of the nociceptive withdrawal reflex (NWR) can be evoked and quantified as a measure of temporal summation from the distal aspect of the left forelimb and hind limb in standing nonsedated horses via repeated stimulations of various subthreshold intensities and frequencies.

Animals—10 adult horses.

Procedure—Surface electromyographic activity evoked by stimulation of the digital palmar and plantar nerves was recorded from the common digital extensor and cranial tibial muscles. For each horse, the NWR threshold intensity to a single stimulus was determined for the forelimb and hind limb. Repeated stimulations were performed at subthreshold intensities and at frequencies of 2, 5, and 10 Hz. The reflex amplitude was quantified, and the behavioral responses accompanying the stimulations were scored.

Results—Repeated stimulations at subthreshold intensities were able to summate and facilitate the NWR in conscious horses. The reflex facilitation was significantly related to the intensity of the repeated stimuli, whereas no effect of stimulation frequency was found. Reaction scores increased significantly for increasing stimulation intensities.

Conclusions and Clinical Relevance—Temporal summation obtained by repeated stimulations of subthreshold intensity appears to represent a new tool for investigating nociceptive pathophysiologic processes in horses; this experimental model may be useful to examine the mode of action and efficacy of analgesic and anesthetic interventions and possibly to assess sensory dysfunction in clinical settings. (Am J Vet Res 2004;65:901–908)

Abstract

Objective—To investigate whether facilitation of the nociceptive withdrawal reflex (NWR) can be evoked and quantified as a measure of temporal summation from the distal aspect of the left forelimb and hind limb in standing nonsedated horses via repeated stimulations of various subthreshold intensities and frequencies.

Animals—10 adult horses.

Procedure—Surface electromyographic activity evoked by stimulation of the digital palmar and plantar nerves was recorded from the common digital extensor and cranial tibial muscles. For each horse, the NWR threshold intensity to a single stimulus was determined for the forelimb and hind limb. Repeated stimulations were performed at subthreshold intensities and at frequencies of 2, 5, and 10 Hz. The reflex amplitude was quantified, and the behavioral responses accompanying the stimulations were scored.

Results—Repeated stimulations at subthreshold intensities were able to summate and facilitate the NWR in conscious horses. The reflex facilitation was significantly related to the intensity of the repeated stimuli, whereas no effect of stimulation frequency was found. Reaction scores increased significantly for increasing stimulation intensities.

Conclusions and Clinical Relevance—Temporal summation obtained by repeated stimulations of subthreshold intensity appears to represent a new tool for investigating nociceptive pathophysiologic processes in horses; this experimental model may be useful to examine the mode of action and efficacy of analgesic and anesthetic interventions and possibly to assess sensory dysfunction in clinical settings. (Am J Vet Res 2004;65:901–908)