Korean J Physiol Pharmacol.
1997 Dec;1(6):603-611.
Role of the vestibular and medullary reticular nuclei for the motor evoked potentials in rats
- Affiliations
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- 1Department of Physiology, Wonkwang University, School of Medicine, Iksan 570-749, South Korea .
Abstract
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The motor evoked potentials (MEPs) have been advocated as a method of
monitoring the integrity of spinal efferent pathways in various injury
models of the central nervous system. However, there were many disputes
about origin sites of MEPs generated by transcranial electrical
stimulation. The purpose of present study was to investigate the effect
of major extrapyramidal motor nuclei such as lateral vestibular nucleus
(VN) and medullary reticular nucleus (mRTN) on any components of the
MEPs in adult Sprague-Dawley rats. MEPs were evoked by electrical
stimulation of the right sensorimotor cortex through a stainless steel
screw with 0.5mm in diameter, and recorded epidurally at T9 - T10
spinal cord levels by using a pair of teflon-coated stainless steel
wire electrodes with 1mm exposed tip. In order to inject lidocaine and
make a lesion, insulated long dental needle with noninsulated tips were
placed stereotaxically in VN and mRTN. Lidocaine of 2~3 mul was
injected into either VN or mRTN. The normal MEPs were composed of
typical four reproducible waves; P1, P2, P3, P4. The first wave (P1)
was shown at a mean latency of 1.2 ms, corresponding to a conduction
velocity of 67.5 m/sec. The latencies of MEP were shortened and the
amplitudes were increased as stimulus intensity was increased. The
amplitudes of P1 and P2 were more decreased among 4 waves of MEPs after
lidocaine microinjection into mRTN. Especially, the amplitude of P1 was
decreased by 50% after lidocaine microinjection into bilateral mRTN. On
the other hand, lidocaine microinjection into VN reduced the amplitudes
of P3 and P4 than other MEP waves. However, the latencies of MEPs were
not changed by lidocaine microinjection into either VN or mRTN. These
results
suggest that the vestibular and reticular nuclei contribute to partially different role in generation of MEPs elicited by transcranial electrical stimulation.
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