Effects of butorphanol on the withdrawal reflex using threshold, suprathreshold and repeated subthreshold electrical stimuli in conscious horses.
OBJECTIVE
To assess the effects of a single intravenous dose of butorphanol (0.1 mg kg(-1)) on the nociceptive withdrawal reflex (NWR) using threshold, suprathreshold and repeated subthreshold electrical stimuli in conscious horses.


METHODS
'Unblinded', prospective experimental study.


METHODS
Ten adult horses, five geldings and five mares, mean body mass 517 kg (range 487-569 kg).


METHODS
The NWR was elicited using single transcutaneous electrical stimulation of the palmar digital nerve. Repeated stimulations were applied to evoke temporal summation. Surface electromyography was performed to record and quantify the responses of the common digital extensor muscle to stimulation and behavioural reactions were scored. Before butorphanol administration and at fixed time points up to 2 hours after injection, baseline threshold intensities for NWR and temporal summation were defined and single suprathreshold stimulations applied. Friedman repeated-measures analysis of variance on ranks and Wilcoxon signed-rank test were used with the Student-Newman-Keul's method applied post-hoc. The level of significance (alpha) was set at 0.05.


RESULTS
Butorphanol did not modify either the thresholds for NWR and temporal summation or the reaction scores, but the difference between suprathreshold and threshold reflex amplitudes was reduced when single stimulation was applied. Upon repeated stimulation after butorphanol administration, a significant decrease in the relative amplitude was calculated for both the 30-80 and the 80-200 millisecond intervals after each stimulus, and for the whole post-stimulation interval in the right thoracic limb. In the left thoracic limb a decrease in the relative amplitude was found only in the 30-80 millisecond epoch.


CONCLUSIONS
Butorphanol at 0.1 mg kg(-1) has no direct action on spinal Adelta nociceptive activity but may have some supraspinal effects that reduce the gain of the nociceptive system.


CONCLUSIONS
Butorphanol has minimal effect on sharp immediate Adelta-mediated pain but may alter spinal processing and decrease the delayed sensations of pain.
Spadavecchia
Claudia
C
Anesthesiology Section, Department of Clinical Veterinary Sciences, Vetsuisse Faculty, University of Berne, Berne, Switzerland. claudia.spadavecchia@veths.no
Arendt-Nielsen
Lars
L
Spadavecchia
Luciano
L
Mosing
Martina
M
Auer
Ulricke
U
van den Hoven
Renè
R
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002077:Butorphanol / Q000494:pharmacology*; D003243:Consciousness; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D005552:Forelimb / Q000502:physiology; D006736:Horses / Q000502:physiology*; D008297:Male; D010146:Pain / Q000662:veterinary; D017288:Pain Threshold / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects*
D000701:Analgesics, Opioid; D002077:Butorphanol