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Electrically induced blink reflex in horses
  1. S. Añor, DVM1,
  2. J. M. Espadaler, MD, PhD2,
  3. L. Monreal, DVM, PhD1 and
  4. I. G. Mayhew, BVSc, PhD, FRCVS3
  1. 1 Internal Medicine Unit, Department of Pathology and Animal Production, School of Veterinary Medicine, Autonomous University of Barcelona, 08193 Bellaterra (Barcelona), Spain
  2. 2 Neurophysiology Unit, Hospital del Mar de Barcelona, Passeig Maritim 25-29, 08003 Barcelona, Spain
  3. 3 Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG

Abstract

The electrically induced blink reflex was studied electromyographically in 21 healthy adult, detomidine-sedated horses. Using surface electrodes, the supraorbital nerve was electrically stimulated at the supraorbital foramen. The responses were recorded from the ipsilateral and contralateral orbicularis oculi muscles with concentric needle electrodes inserted in the lateral aspect of the ventral eyelids. Ipsilateral and contralateral recordings were made on successive stimulations of the same side of the face, maintaining a constant stimulus intensity. The electromyographically recorded responses consisted of an early R1 response in the orbicularis oculi muscle ipsilateral to the side of stimulation, a bilateral late response (ipsilateral R2 and contralateral Rc) and a third, R3 response, in the ipsilateral orbicularis oculi muscle. All the responses were polyphasic muscle potentials of variable duration and peak to peak amplitudes. The reflex latency of the R1 response was, as in man, fairly stable. The R2 response showed greater variability both within and between individual horses. The RC response was recorded in only 13 of the 21 horses and showed a slightly longer latency than the corresponding R2. The R3 response, which is significantly related to pain sensation in man, appeared in 19 horses and showed the greatest variability in latency.

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