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Observation on phrenic discharges induced by bicuculline or picrotoxin in spinal rabbits

Tu Yijun, Sun Qixun, Sun Shen, Wu Hongbin, Xiao Jun

Department of Physiology, Shanglong Medical University. Shanghai, China

Abstract

The respiratory activity of spinal cord-transectcd animals was reinvestigated
on 71 rabbits. Under light urethane anesthesia and paralyses by gallamine, the
spinal cord was transected at either C_(1) or C_(2) level, and phrenic discharges were monitored in 43 rabbits. After cordotomy, tonic phrenic discharges were observed in 25 of the 43 spinal rabbits. No spontaneous rhythmic phrenic activities appeared in any of the animal. Respiratory-like, long lasting phrenic bursts (lasting longer than 0.25s) or convulsive-like, short lasting phrenic bursts (lasting shorter than 0.1s on the average) were induced by adminstration of bicuculline(BCL,20 #mu#g/10 #mu#1-40#mu#g/ 20#mu#l, intrasubarachnoid space, i.s.s.) in 24 spinal rabbits or picrotoxin (PIC, 20
#mu#g/20#mu#l, i.s.s. or 3-5mg/kg i.v.) in 13 spinal rabbits. According to the pattern of the recruitment and de-recruitment of the phrenic discharges, the long lasting phrenic bursts may be divided into three types: Type Ⅰ, average frequency 23.5±2.3 cycles/min (BCL), incidence 58.5%(BCL) or 67.7% (PIC);Type Ⅱ，average frequency 33.8±4.7 cycles/min (BCL), incidence 39.3%(BCL) or 32.3% (PIC);Type Ⅲ,average frequency 21.3±2.8 cycles/min (BCL), incidence 2.2% (BCL) or 3.3% (PIC). The duration of the evoked phrenic discharges was 60.0±18.9 min (BCL) or 42.0±0.8 min (PIC).The type Ⅰ and type Ⅱ showed respiratorylike discharges, accounting for more than 97.8% of the incidence of the long lasting phrenic bursts. It is suggested that the endogeneous GABA system in spinal cord might exert a tonic inhibitory action on the spinal “respiration” activity.

Key words: Spinal rabbit;Spinal “respiration”;GABA;Bicuculline;Picrotoxin

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Citing This Article：

Tu Yijun, Sun Qixun, Sun Shen, Wu Hongbin, Xiao Jun. Observation on phrenic discharges induced by bicuculline or picrotoxin in spinal rabbits. Acta Physiol Sin 1990; 42 (3): (in Chinese with English abstract).