The CDP is a stationary-evoked potential arising in dorsal horn interneurons after stimulation of peripheral nerves or nerve roots. Results of experiments involving intramedullary recordings,1 osmic acid-induced lesions,2,3 and spinal cord hemisection4 in decapitated and decerebrated cats support the conclusion that the CDP is a purely sensory phenomenon. The waveform consists of a large, slow negative deflection, which is preceded by an initial small triphasic wave and followed by a slow positive wave. The large negative potential that defines the waveform represents depolarization of dorsal horn interneurons,1,5 whereas the initial triphasic spike represents the incoming volley in the primary afferent axons.6,7 The potential is generated in the dorsal gray matter over 1 to 2 spinal cord segments, with the largest waveform generated in the spinal cord segments where the stimulated dorsal nerve roots penetrate the spinal cord.1,2
In addition to early basic experimental data, there are examples of CDPs for dogs and cats recorded as part of spinal-evoked potential studies8–10 in intact animals following tibial and ulnar nerve stimulation. Details of CDP latencies and magnitudes have been established for those nerves in dogs.11 Procedures have also been described for CDP measurement after caudal nerve stimulation,12 but there are no data on normal latencies and magnitudes or the reliability of those measures to our knowledge. The purposes of the study reported here were to determine whether CDPs could be reliably recorded following caudal nerve stimulation in anesthetized adult dogs, which intervertebral location resulted in the largest caudal nerve CDP amplitude, and what effect administration of atracurium besylate had on the latency, magnitude, and subjective form of the potential. The ultimate goal of this study was to develop an electrophysiological tool for functional assessment of lumbosacral compressive lesions of peripheral nerves and nerve roots that pass over the lumbosacral space within the spinal canal in dogs.
Cord dorsum potential
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1. Bernhard CG. The cord dorsum potentials in relation to peripheral source of afferent stimulation. Cold Spring Harbor Symp Quant Biol 1952; 17:221–232.
2. Lindblom UF, Ottosson JO. Localization of the structure generating the negative cord dorsum potential evoked by stimulation of low threshold cutaneous fibres. Acta Physiol Scand 1953; 29:180–190.
3. Bernhard CG, Lindblom UF, Ottosson JO. The longitudinal distribution of the negative cord dorsum potential following stimulation of low threshold cutaneous fibres. Acta Physiol Scand 1953; 29:171–179.
4. Bernhard CG, Widen L. On the origin of the negative and positive spinal cord potentials evoked by stimulation of low threshold cutaneous fibres. Acta Physiol Scand 1953; 29:42–54.
6. Gasser HS, Graham HT. Potentials produced in the spinal cord by stimulation of dorsal roots. Am J Physiol 1933; 103:303–320.
7. Bernhard CG. The spinal cord potentials in leads from the cord dorsum in relation to peripheral source of afferent stimulation. Acta Physiol Scand 1953; 29:1–29.
8. Steiss JE, Wright JC. Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs. Am J Vet Res 1990; 51:1427–1432.
9. Redding RW, Lee AH, Wilson SG. Spinal-evoked potentials and spinal conduction velocity of the cat: reference values. Am J Vet Res 1984; 45:2175–2177.
10. Poncelet L, Delauche A & Vinals C, et al. Effect of bilateral stimulation on spinal evoked potentials in dogs. Am J Vet Res 1992; 53:1305–1308.
11. Cuddon PA, DeLauche AJ, Hutchison JM. Assessment of dorsal nerve root and spinal cord dorsal horn function in clinically normal dogs by determination of cord dorsum potentials. Am J Vet Res 1999; 60:222–226.
13. Holliday TA, Weldon NE, Ealand BG. Percutaneous recordings of evoked spinal cord potentials in dogs. Am J Vet Res 1979; 40:326–333.
14. Sims MH, Selcer RR. Somatosensory-evoked and spinal cord-evoked potentials in response to pudendal and tibial nerve stimulation in cats. Am J Vet Res 1989; 50:542–545.
15. Ellaway PH, Rawlinson SR & Lewis HS, et al. Magnetic stimulation excites skeletal muscle via motor nerve axons in the cat. Muscle Nerve 1997; 20:1108–1114.
16. Meij BP, Suwankong N & van den Brom WE, et al. Tibial nerve somatosensory evoked potentials in dogs with degenerative lumboacral stenosis. Vet Surg 2006; 35:168–175.