Characteristics of burst-generating networks released by disinhibition in the spinal cord of neonatal rats

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  • Takahashi Shu
    Department of Physiology, Showa University School of Medicine Department of Orthopedic Surgery, Showa University Fujigaoka Hospital
  • Mikami Yoshihiro
    Department of Physiology, Showa University School of Medicine Department of Orthopedic Surgery, Showa University School of Medicine
  • Iizuka Makito
    Department of Physiology, Showa University School of Medicine
  • Izumizaki Masahiko
    Department of Physiology, Showa University School of Medicine

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Although （i） spinal cord disinhibition can cause spontaneous burst activities in the phrenic nerve and （ii） this propriospinal network can be harnessed to allow diaphragm function after a spinal cord injury, the characteristics of this network are unclear. To characterize this network, we cut the isolated spinal cord from neonatal rats aged 0-4 days into four blocks consisting of three spinal segments （C3-C5, T6-T8, L2-L4, and L6-S2）, and motor activities were recorded from C4, T7, L3, and S1 ventral roots （VRs）. Under control conditions, few spontaneous activities occurred in all VRs. When 10-µM strychnine （a broad antagonist of glycine and GABAA receptors） was applied, spontaneous burst activities were observed in all VRs, suggesting that a burst-generating network （BGN） exists in each segment. In spinal cord preparations from segments C3 to S2, local application of strychnine to the C3-C5 segments resulted in spontaneous bursts concurrently in not only the C4VR but in all other VRs. In spinal cord preparations, repetitive electrical stimulations to the phrenic afferent evoked burst activities in not only the phrenic nerve but also in other C4 and C5 spinal nerves under strychnine. In the C3-C5 block preparation, phrenic afferent stimulation failed to evoke burst activities in the phrenic motor nerve, whereas C4 spinal afferent stimulation evoked burst activities in not only the C4 and C5 spinal nerves but also in the phrenic motor nerve. Thus, it is difficult to specifically activate the BGN for the phrenic nerve in the neonatal rat spinal cord by local disinhibition of C3-C5 segments or by phrenic afferent stimulation.

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