The suppressive effect of electrical stimulation on nociceptive responses in the rat

School of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Republic of China.

BACKGROUND AND PURPOSE: The aim of this investigation was to study the effect of electrical stimulation on nociceptive responses within the lumbar levels of the rat spinal cord. METHODS: A single high-energy thermal pulse produced by a surgical laser stimulator (5 W, 30 milliseconds) was applied on the plantar surface of the hind paws of male Sprague-Dawley rats. The spinal cord field potential evoked by the laser pulse was used as an indicator of thermosensitive nociceptive responses. Low-intensity single stimulation, high-intensity single stimulation, low-intensity train stimulation, and high-intensity train stimulation were applied on the common peroneal nerve with protected cuff electrodes in different trials. RESULTS: Neither low-intensity nor high-intensity single stimulation suppressed field potentials. In contrast, low-intensity train stimulation elicited partial inhibition of field potentials. Furthermore, high-intensity train stimulation elicited biphasic inhibition at a wider range of intervals lasting for 20 seconds. CONCLUSION AND DISCUSSION: The results demonstrate that two modes of train electrical stimulation can produce two patterns of fast-onset (within milliseconds), short-duration (within 20 seconds) inhibition of field potentials in the spinal cord. These results provide evidence that noxious heat-related impulses are modulated by the presence of specific electrical stimulation. The clinical application of transcutaneous electrical nerve stimulation to block pain is supported.