Effects of pentobarbital on heterosegmentally activated dorsal root depolarization in the rat. Investigation by sucrose-gap technique in vivo.
Slow positive cord dorsum (P-) potentials activated by segmental stimulation are believed to reflect primary afferent depolarizations and have been shown to be augmented by barbiturates. However, there have been no data to confirm whether heterosegmentally activated P-potentials also represent primary afferent depolarizations and are similarly affected by barbiturates. We therefore tested whether heterosegmental P-potentials reflect primary afferent depolarizations and how these heterosegmental potentials are affected by barbiturates. Heterosegmentally activated dorsal root (DR) depolarizations (depolarizations evoked in DRs of lumbar segments in response to afferent volleys to cervical segments produced by electrical stimulation of the forepaw) and P-potentials were simultaneously recorded, adapting the sucrose-gap technique for recording DR depolarization in vivo in the rat. Forepaw (heterosegmental) stimulations produced a large depolarization in the DRs of L5-S1 as well as a slow P-potential in the lumbosacral enlargement. Transection of the spinal cord at the level of C1-C2 abolished both the P-potential and DR depolarization activated by heterosegmental stimulation as well as the second component of segmentally (hind-paw) activated P-potential. Bicuculline (100 micrograms/kg, intravenous) augmented the P-potential and DR depolarization produced by heterosegmental stimulation, but larger doses, 400-600 micrograms/kg, eventually suppressed these. However, the drug, in a dose-dependent manner, suppressed both the P-potential and DR depolarization produced by the segmental stimulation. Pentobarbital (10-40 mg/kg, intravenous) suppressed in a dose-dependent manner both the heterosegmental P-potential and heterosegmental DR depolarization and prolonged their peak latencies. By contrast, pentobarbital augmented and prolonged the segmental P-potential and segmental DR depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
Shimoji
K
K
Department of Anesthesiology, Niigata University School of Medicine, Japan.
Fujiwara
N
N
Denda
S
S
Tomita
M
M
Toyama
M
M
Fukuda
S
S
D000818:Animals; D005552:Forelimb / Q000294:innervation; D006614:Hindlimb / Q000294:innervation; D008297:Male; D010424:Pentobarbital / Q000494:pharmacology*; D051381:Rats; D013126:Spinal Nerve Roots / Q000187:drug effects* / Q000502:physiology
D010424:Pentobarbital