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Abstract
Spinal somatosensory evoked potentials (SEP) were recorded in 58 normal mice (C3H
strain) divided into 4 groups according to age (3-, 6-, 9- and 12 weeks). Monopolar
recordings of spinal SEP were made by subdermal needle electrodes from 3 vertebral
levels, ‘low-lumbar’, ‘high-lumbar’ and ‘mid-thoracic’, by stimulating the tibial
nerve bilaterally at the ankle. Three negative peaks, NI, NII and NIII, presumably
due to conduction through muscle afferents, cutaneous afferents (in the dorsal root
or dorsal white column) and spinocerebellar tract, respectively, were recorded at
the high-lumbar level in the 12-week-old mouse. Besides the NI and NII peaks, a small
ventral root potential was also occasionally recorded at the low-lumbar level. At
the mid-thoracic level, only NI and NIII were recordable. At both the high-lumbar
and mid-thoracic levels, the negative peaks were superimposed over long duration ‘summation
potentials’ of opposite polarities. Well-defined standing potentials were also recorded
at these two levels. The standing potentials could be the ‘entry point potential’
due to the entry of S1 root into the spinal cord at the T13 vertebral level. The summation
potential presumably is due to a fixed generator located between the T7 and T12 vertebral
levels resulting from intense synaptic activity at this level. In 3- and 6-week-old
mice, the entry point potential was recorded in the low-lumbar SEP also, possibly
due to less axial growth of the vertebral column at this stage of development. The
summation potential and NIII peak were reduced in size in these young mice, possibly
due to less developed collaterals and synaptic activity. The somatosensory conduction
velocity, measured between the low-lumbar and mid-thoracic recording sites, showed
a highly significant increase during the 3–6 and 6–9 week periods, suggesting that
a significant amount of myelination occurs in proprioceptive fibres postnatally in
mice.
Keywords
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Article info
Publication history
Accepted:
October 20,
1993
Received:
August 3,
1993
Identification
Copyright
© 1994 Elsevier Science B.V. All rights reserved. Published by Elsevier Inc.
