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


METHODS
10 adult horses.


METHODS
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
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.
Anesthesiology Section, Department of Clinical Veterinary Sciences, University of Berne, Langassstrasse 124, 3012 Berne, Switzerland.
Claudia
C
Spadavecchia
Ole K
OK
Andersen
Lars
L
Arendt-Nielsen
Luciano
L
Spadavecchia
Marcus
M
Doherr
Urs
U
Schatzmann
D000704:Analysis of Variance; D000818:Animals; D004558:Electric Stimulation; D004576:Electromyography / Q000662:veterinary; D005071:Evoked Potentials / Q000502:physiology; D005552:Forelimb / Q000502:physiology; D006614:Hindlimb / Q000502:physiology; D006736:Horses / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology; D010146:Pain / Q000503:physiopathology / Q000662:veterinary*; D017288:Pain Threshold / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012018:Reflex / Q000502:physiology*