Noninvasive assessment of the facilitation of the nociceptive withdrawal reflex by repeated electrical stimulations in conscious dogs.
OBJECTIVE
To investigate the facilitation of the nociceptive withdrawal reflex (NWR) by repeated electrical stimuli and the associated behavioral response scores in conscious, nonmedicated dogs as a measure of temporal summation and analyze the influence of stimulus intensity and frequency on temporal summation responses.


METHODS
8 adult Beagles.


METHODS
Surface electromyographic responses evoked by transcutaneous constant-current electrical stimulation of ulnaris and digital plantar nerves were recorded from the deltoideus, cleidobrachialis, biceps femoris, and cranial tibial muscles. A repeated stimulus was given at 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 x I(t) (the individual NWR threshold intensity) at 2, 5, and 20 Hz. Threshold intensity and relative amplitude and latency of the reflex were analyzed for each stimulus configuration. Behavioral reactions were subjectively scored.


RESULTS
Repeated sub-I(t) stimuli summated and facilitated the NWR. To elicit temporal summation, significantly lower intensities were needed for the hind limb, compared with the forelimb. Stimulus frequency did not influence temporal summation, whereas increasing intensity resulted in significantly stronger electromyographic responses and nociception (determined via behavioral response scoring) among the dogs.


CONCLUSIONS
In dogs, it is possible to elicit nociceptive temporal summation that correlates with behavioral reactions. These data suggest that this experimental technique can be used to evaluate nociceptive system excitability and efficacy of analgesics in canids.
Department of Clinical Veterinary Medicine, Anaesthesiology Division, Vetsuisse Faculty, University of Berne, Länggassstrasse 124, CH-3001 Berne, Switzerland.
Alessandra
A
Bergadano
Ole K
OK
Andersen
Lars
L
Arendt-Nielsen
Claudia
C
Spadavecchia
D000818:Animals; D004285:Dogs / Q000502:physiology*; D004576:Electromyography / Q000009:adverse effects / Q000662:veterinary*; D005552:Forelimb / Q000294:innervation / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D010146:Pain; D012018:Reflex