Use of epidurally derived evoked potentials for quantification of caudal nociception in ponies.
OBJECTIVE
To determine whether epidurally derived evoked potentials (EPs) can be used to reliably assess nociception and antinociception in ponies.


METHODS
7 ponies.


METHODS
EPs and electromyograms (EMGs) from the quadriceps femoris muscles were recorded simultaneously, following electrical stimulation applied to the distal portion of the hind limb. The effect of increasing stimulus intensity, conduction velocities of the stimulated nerves, effect of epidurally applied methadone, and effect of systemically administered propofol were evaluated.


RESULTS
In the EP and EMG waveforms, 2 distinct complexes, the EP N25 and P50 and the EMG P27 and N62, respectively, were identified. On the basis of their latency and calculated conduction velocities, the EP P50 and EMG N62 were considered to be related to nociception (AD-mediated). All complexes increased significantly in amplitude with increasing stimulus intensity and decreased significantly following epidural administration of methadone or systemic administration of propofol.


CONCLUSIONS
Although the experimental setup allowed successful discrimination between tactile- and nociceptive-associated responses, the identified EPs, considered to reflect activity in the spinal cord, could not be definitively differentiated from activity in the lumbosacral epaxial musculature. Further research is required to refine measurement techniques to allow for discrimination between these 2 signals. Similar to other species, neurophysiologic variables such as EPs could potentially become a useful additional tool in quantifying nociception in equidae.
van Loon
Johannes P A M
JP
Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, 3508 TD Utrecht, The Netherlands.
Stienen
Peter J
PJ
Doornenbal
Arie
A
Hellebrekers
Ludo J
LJ
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D004576:Electromyography / Q000662:veterinary; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006614:Hindlimb / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology; D007268:Injections, Epidural; D008161:Lumbosacral Region / Q000502:physiology; D008297:Male; D008691:Methadone / Q000008:administration & dosage / Q000494:pharmacology; D010146:Pain / Q000662:veterinary*; D010147:Pain Measurement / Q000662:veterinary*; D015742:Propofol / Q000008:administration & dosage / Q000494:pharmacology
D000701:Analgesics, Opioid; D006993:Hypnotics and Sedatives; D008691:Methadone; D015742:Propofol