Effects of electrical stimulation of the sciatic nerve on background electromyography and static stretch reflex activity of the trunk muscles in rats: possible implications of neuronal mechanisms in the development of sciatic scoliosis.
METHODS
The effects of electrical stimulation of the sciatic nerve on background electromyographic and static stretch reflex activity of the trunk muscles were studied.


OBJECTIVE
To verify the hypotheses that sciatic scoliosis is induced reflexively by radiculopathic pain, and that scoliosis might be maintained by prolonged asymmetric alteration of the trunk muscle tonus caused by central sensitization of the spinal neurons that constitute the postural reflex pathways.


BACKGROUND
Sciatic scoliosis usually occurs with convexity to the side of the herniated disc. The neuronal mechanism of sciatic scoliosis has not been well clarified. Recently, prolonged alteration of motor function in the hindlimbs of animals caused by central sensitization has been reported.


METHODS
In spinalized rats (transection of the spinal cord), the sciatic nerve was stimulated electrically as a conditioning stimulus. Muscle stretch elicited by bending of the lumbar spine was applied as a test stimulus. Background and stretch reflex activities of the bilateral oblique abdominal, psoas, and quadratus lumborum muscles were recorded. Rats in which MK-801, an N-methyl-d-aspartate antagonist, was preadministered also were used.


RESULTS
The conditioning stimulus enhanced background electromyographic activity in bilateral oblique abdominal, contralateral psoas, and quadratus lumborum muscles. Furthermore, the conditioning stimulus induced prolonged facilitation and depression of stretch reflex activity of the contralateral psoas and quadratus lumborum, and ipsilateral psoas and quadratus lumborum muscles, respectively. Preadministration of MK-801 reduced these excitatory and inhibitory effects.


CONCLUSIONS
It was found that the pattern of electromyographic activity of the trunk muscles evoked by sciatic nerve stimulation coincided with the typical direction of sciatic scoliosis in patients with lumbar disc herniation. It was supposed that the prolonged asymmetric alteration of the trunk muscle tonus was caused by central sensitization, and that central sensitization of spinal neurons may underlie the neuronal mechanism of sciatic scoliosis.
Hirayama
J
J
Physiology, School of Medicine, Chiba University, Chiba, Japan. j-hiraya@bk9.so-net.ne.jp
Takahashi
Y
Y
Nakajima
Y
Y
Takahashi
K
K
Yamagata
M
M
Moriya
H
H
D000818:Animals; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation; D004576:Electromyography; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009412:Nerve Fibers / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D020671:Posterior Horn Cells / Q000502:physiology; D011843:Radiculopathy / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism; D012026:Reflex, Stretch / Q000187:drug effects / Q000502:physiology*; D012584:Sciatic Nerve / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology*; D012585:Sciatica / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D012600:Scoliosis / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate