The paradigm of sine-wave electrical stimuli has been used for sensory neurological assessment in humans. In the present study, we applied the paradigm to the dog for the quantitative assessment of sensory function. Sine-wave electrical current stimuli at frequencies of 2000, 250, and 5Hz were delivered to bipolar electrodes attached to the skin surface of the hind paws. The stimulation intensity was gradually increased, and the minimum intensity required to elicit the lifting behavior in the stimulated paw was determined as current threshold (CT) for each of the three frequencies. Dogs consistently showed the lifting behavior at CTs without showing aversive behaviors such as vocalization and wriggling. The baseline CTs (mean+/-SEM, n=12) were 4430+/-110microA for CT2000, 2215+/-173microA for CT250, and 2305+/-152microA for CT5. The CTs immediately increased after bolus intravenous injection of fentanyl at 10microg/kg, although the significant increase disappeared within 1h. The time course for the CTs was parallel to that of plasma fentanyl concentration. In conclusion, the present study applied the paradigm of transcutaneous sine-wave electrical stimuli to the dog, and used the hind paw lifting as endpoint behavior. This paradigm is simple, non-invasive, useful in the assessment of sensory function, and can be adapted to investigate the pharmacokinetics/pharmacodynamics relation of drugs. Further studies are needed to give the conclusive interpretation of the endpoint behavior.
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