British Journal of Anaesthesia, Vol 76, Issue 2 258-265, Copyright © 1996 by The Board of Management and Trustees of the British Journal of Anaesthesia
S. Denda, K. Shimoji, M. Tomita, H. Baba, T. Yamakura, H. Masaki, H. Endoh and S. Fukuda
It has been suggested that heterosegmentally activated slow positive
potentials (HSP), recorded from the spinal cord of rat and humans, are
feedback inhibitory potentials. The present study was carried out to define
ascending and descending spinal tracts and the sites of central nuclei
involved in the production of these HSP, and the effects of ketamine on
these central nuclei. The spinal cords in ketamine- anaesthetized rats were
transected to determine the ascending and descending tracts involved in the
production of hindpaw (HP) and forepaw (FP) HSP, respectively. Lesions of
the brain at various levels were performed stereotactically during ketamine
anaesthesia. Dorsal one- third resection of the cord at the T8-9 level did
not affect HSP significantly, while contralateral lesion of the dorsal
two-thirds of the cord decreased FP-HSP but not HP-HSP during ketamine.
Bilateral transection of the ventral one-third of the cord abolished both
HSP. Ablation of the cerebral cortex, cerebellum, thalamus, midbrain and
pons did not affect HSP significantly. However, transection of the middle
medulla decreased, while transection of the most caudal part of the medulla
completely abolished both HSP. Ketamine decreased HSP even in the
medulla-spinal cord preparation and the segmental slow positive wave in
spinalized animals. In ketamine-anaesthetized rats, ascending and
descending spinal tracts involved in the production of HP-HSP and FP-HSP
are located bilaterally in the ventrolateral quadrant and in the
contralateral lateral funiculus and ventrolateral quadrant, respectively.
Principal central nuclei feeding back HSP might be situated diffusely in
the medulla down to the caudal part. Ketamine is suggested to suppress
these inhibitory feedback potentials predominantly at, and partly even
below, the level of the medulla.
LABORATORY INVESTIGATIONS
Central nuclei and spinal pathways in feedback inhibitory spinal cord potentials in ketamine-anaesthetized rats
Department of Anaesthesiology, Niigata University School of Medicine, 1-757 Asahi-machi, Niigata 951, Japan
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